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Am J Physiol Regul Integr Comp Physiol 279: R1321-R1329, 2000;
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Vol. 279, Issue 4, R1321-R1329, October 2000

Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Albert Moraska1, Terrence Deak2, Robert L. Spencer2, David Roth1, and Monika Fleshner1

1 Departments of Kinesiology and Applied Physiology and 2 Psychology, University of Colorado, Boulder, Colorado 80309


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Exercise training produces a vast array of physiological adaptations, ranging from changes in metabolism to muscle mitochondrial biogenesis. Researchers studying the physiological effects of exercise often use animal models that employ forced exercise regimens that include aversive motivation, which could activate the stress response. This study examined the effect of forced treadmill running (8 wk) on several physiological systems that are sensitive to training and stress. Forced treadmill running produced both positive and negative physiological adaptations. Indicative of positive training adaptations, exercised male Sprague-Dawley rats had a decrease in body weight gain and an increase in muscle citrate synthase activity compared with sedentary controls. In contrast, treadmill running also resulted in the potentially negative adaptations of adrenal hypertrophy, thymic involution, decreased serum corticosteroid binding globulin, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM. Such alterations in neuroendocrine tissues and immune responses are commonly associated with chronic stress. Thus treadmill running produces both positive training adaptations and potentially negative adaptations that are indicative of chronic stress. Researchers employing forced activity need to be aware that this type of exercise procedure also produces physiological adaptations indicative of chronic stress and that these changes could potentially impact other measures of interest.

immune function; exercise; corticosteroid binding globulin; immunoglobulin; keyhole limpet hemocyanin


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

FORCED TREADMILL RUNNING is a common method of training used by researchers investigating physiological adaptations produced by exercise (2, 33, 45, 58, 61). Some benefits of this specific mode of training include the repeatability of training volume and consistency of changes that occur in muscle (skeletal and cardiac) as a result of training. This type of training, however, forces the animals to run according to the experimenters demands, that is, the experimenter chooses the time, duration, and intensity of the running that could chronically activate the stress response. Thus it is possible that stress-induced physiological changes could interact with and confound other physiological adaptations produced by exercise. This study therefore examined the effect of forced treadmill running on several measures indicative of training adaptations and of chronic stress.

Repeated bouts of exercise produces many physiological adaptations that allow an organism to perform greater amounts of work with improved efficacy. These changes are often referred to as training adaptations (4). Many of these training adaptations reported in the literature occur after 8 wk of gradually increasing treadmill training (40-43, 45, 55, 61). Two reported changes that are hallmarks of training are increased metabolic rate or energy expenditure and increased muscle mitochondrial biogenesis. A gross measure of increased metabolic rate or energy expenditure is a reduction in body weight. A commonly reported measure of improved muscle mitochondrial biogenesis is increased citrate synthase activity. Citrate synthase is an important rate-limiting enzyme in the energy-producing mitochondrial citric acid cycle or tricarboxylic acid cycle. An increase in this enzyme is believed to facilitate muscle energy output via oxidative metabolism.

In 1936 Seyle (53) first reported that chronic exposure to a wide variety of noxious agents or stressors produced a triad of common pathophysiological changes. Specifically, Seyle noted that with exposure to chronic stress, animals experienced adrenal hypertrophy, thymic involution, and gastrointestinal ulceration (54). More recently it has been recognized that the physiological systems affected by the stress response include nervous, endocrine, and immune, and that the nature of the responses of these systems is stressor dependent (32, 46). Importantly, in contrast to chronic stimulation, acute activation of the stress response is an adaptive physiological response that facilitates the fight-flight response and potentially survival after bodily injury (9, 22, 38, 39). Thus the initial fundamental observations of Seyle remain valid and continued to be refined.

Chronic exposure to psychological and/or physical stress can also result in maladaptive consequences of the stress response, such as suppression of many aspects of the immune response and an increased incidence of disease (29, 31, 49). Psychological challenges that are capable of activation of the stress response often share several common features, including "loss of control" and exposure to aversive events (37). In addition to the physical stress of exercise, forced treadmill running would seem likely to also produce chronic mental stress because the animals are both forced to run (loss of control) and often are aversively motivated (footshock, physical prodding, loud sounds, air and water spray). The demands of running at the intensity levels commonly used [i.e., 70-90% maximal O2 consumption (Vo2 max)] are known to produce short-term neural and endocrine responses indicative of physical stress or challenge (4, 48). In addition, Yancey and Overton (60) and Dunn et al. (11) found significant increases in mean arterial pressure, heart rate, and mesenteric blood flow at the outset of forced treadmill, but not voluntary free wheel, running. Elevations in peripheral blood pressure and heart rate are indicative of activation of the stress response (38). Psychological factors associated with physical activity also may contribute to the stress of activity that is measured in exercise and immune studies (25). Some investigators have specifically avoided forced exercise programs to study the effects of physical activity on specific immunity because of the stress associated with this type of activity (6). Indeed, 6 wk of treadmill exercise in mice resulted in decreased spleen weight and immune performance as measured by mitogen-stimulated splenocyte proliferation (26). Therefore, it is unlikely that the isolated effects of exercise are being measured in studies using a forced treadmill running activity program. Rather, the combined effects of psychological and physical stress are influencing the physiological measures that are then reported.

The following study therefore examined the effect of an 8-wk treadmill training regimen. The training regimen consisted of a gradually accelerating program that attained running for 60 min/day, 5 days/wk up to a velocity of 29.2 m/min at a 10% grade by the end of the study. The training program used involved running at intensities commonly reported in the literature (40-42). This training regimen has been reported previously to produce positive training adaptations such as reduced body weight gain, increased soleus muscle citrate synthase activity, and increased stress protein expression in myocardium (4, 40-43, 45, 55, 61). The treadmill training program in this study is expected to produce a reduction in body weight gain and an increase in muscle citrate synthase activity.

In addition, the following stress-sensitive measures were also taken: 1) thymus and adrenal weight, 2) serum corticosteroid binding globulin (CBG) levels, 3) antigen-specific immunoglobulin production, 4) lymphocyte proliferation, and 5) mitogen-stimulated lymphocyte nitric oxide (NO) production. Thymus and adrenal weight measures were taken because adrenal hypertrophy and thymic involution are part of Seyle's triad of common pathophysiological changes produced by chronic stress. Serum CBG was measured because previous research has documented that chronic, and some types of acute, stressor exposure reduces serum levels of this corticosterone carrier protein (8, 19, 56). Corticosterone was not measured in this study because stress-free blood sampling at the time of death was not possible. Antigen-specific immunoglobulin production and lymphocyte proliferation were measured because both measures of immune function are sensitive to suppression by stress (16, 21, 35, 38, 49). Splenic NO levels were measured because increases in leukocyte NO after psychological and/or physical acute or chronic stress have been reported previously (7, 14, 22, 34). If treadmill running chronically activates stress responsive systems, then treadmill training also would be expected to produce adrenal hypertrophy, thymic involution, decreased serum CBG, suppressed lymphocyte proliferation and antibody production, and increased nitrite production.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Animals

Male Sprague-Dawley rats (320-350 g, 8 wk old) were purchased from Harlan Sprague Dawley (Indianapolis, IN). Rats were housed in a controlled temperature room (22°C) with a 12:12-h light-dark cycle (0600-1800 lights on) and access to laboratory rat chow (LabChow) and water ad libitum. To reduce the stress associated with shipping and acclimatization to the moderate altitude of Boulder, Colorado (elevation 5,400 feet), rats were individually housed in standard Plexiglas cages for 14 days before onset of any running activity. Care and use of the animals were in accordance with protocols approved by the University of Colorado Institutional Animal Care and Use Committee.

Procedures

Exercise training. Rats were either treadmill trained (n = 10) or remained sedentary (n = 8). Treadmill-trained rats were housed in clear plastic cages (43 × 21.6 × 20.3 cm) and followed a standard exercise training protocol shown to induce cardiovascular fitness in rats (41). The 8-wk exercise training protocol consisted of running on a motorized treadmill up a 10% grade five times per week with an incremental increase in treadmill velocity (17.4-29.2 m/min) and run duration (10-60 min) to accommodate increased fitness. The highest level of activity (29.2 m/min for 60 min) included two 5-min warm-up periods at 21.5 and 25.5 m/min, and the final 5 min consisted of a warm down at 21.5 m/min. Increases in velocity and/or duration were performed when the rats could maintain the current exercise intensity for 5 consecutive days. A shock grid at the back of the treadmill provided a mild but aversive footshock (1.6 mA) if the pace of the rat slowed below treadmill rate. Very few shocks were administered during a training session and occurred within the first week of training. In fact, Dunn et al. (11, 12) reported that treadmill-trained rats with no footshock have changes in central nervous system noradrenergic metabolism that are indicative of chronic stress (12). This training protocol resulted in a training intensity of 75% Vo2 max (41). The sedentary rats were handled identically to the treadmill-trained rats. At the same time of day, the sedentary rats were placed on a stationary treadmill, with the shock grid turned off, 5 days per week for the duration of the treadmill training session. Mean average distances run have been presented in part elsewhere (43).

Body weight. All rats were housed individually, and body weight was determined to the nearest gram on an Ohaus triple-beam balance at weekly intervals. Body weight data have been presented in part elsewhere (43).

Death. After 8 wk, both exercised and control rats were killed by decapitation. Exercise training ceased 18 h before death for treadmill-trained rats. Trunk blood was collected for CBG measurement. Serum was separated by centrifugation and stored at -20°C. The soleus muscle was dissected and flash frozen in liquid nitrogen. The spleen and mesenteric lymph nodes (MLN) were aseptically dissected and placed in cold medium (Iscoves, supplemented with 1.0% penicillin-streptomycin, GIBCO). Thymus and adrenal glands were excised, rinsed, blotted dry, and weighed. Right hindleg tibia length was measured to the nearest millimeter using a micrometer. Tibia length measurement allowed for standardization of thymus and adrenal weight to an internal variable that would not be altered by exercise training.

Citrate synthase activity. Citrate synthase activity in soleus muscle samples was measured according to Srere (57) and measured at 30°C. These data have been presented in part elsewhere (43).

CBG assay. Serum CBG concentration from trunk blood obtained on death was assessed using a competitive binding assay adapted by Westphal (59). Serum samples initially were diluted 1:200 in buffer [10 mM Trizma base, 1.0 mM EDTA, 10% glycerol (vol/vol), and 1.0 mM dithiothreitol, pH 8.0], then mixed with [3H]corticosterone (15 nM) or unlabeled corticosterone (10 mM) at a final dilution of 1:600. Samples were incubated overnight at 4°C. Bound and unbound steroids were separated using activated charcoal (performed in duplicate). The bound fraction was mixed with scintillation cocktail and counted with a liquid scintillation counter (TriCarb 1600TR; Packard, Meriden, CT).

Lymphocyte proliferation. Cells from the spleen and MLN were dissociated from the tissues using a sterile modified glass tissue homogenizer. Cell enumeration was achieved using a Coulter counter. Spleen and MLN were washed in dissection medium and resuspended in Iscoves culture medium supplemented with 10% heat-inactivated fetal bovine serum, 1% penstrep, 1% L-glutamine, and 5.5 × 10-5 M 2-mercaptoethanol (GIBCO). Cell concentrations were adjusted to 1.25, 2.5, 5.0, and 10.0 × 106/ ml. Cells (100 µl/well) were plated in triplicate in a 96-well round-bottom microtiter plate (Corning). Proliferation was stimulated by addition of 100 µl culture medium containing either concanavalin A (ConA, 5.0 µg/ml) or keyhole limpet hemocyanin (KLH, 250 µg/ml). Cells were incubated for 46 h (37°C, 5% CO2). The degree of proliferation was determined using Cell Titer 96 Aqueous One Solution Cell Proliferation Assay according to the manufacturers instructions (Promega). Briefly, 20 µl of a tetrazolium compound [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl-2H-tetrazolium)] containing an electron coupling agent (phenazine ethosulfate) were added to each well and were bioreduced into formazine by NADH obtained from metabolically active cells. Plates were incubated (37°C, 5% CO2) for an additional 2 h in the dark and read on an enzyme-linked immunosorbent assay (ELISA) reader (490 nm, Dynatech). Total incubation time in the presence of antigen-mitogen was 48 h. This technique has been demonstrated to yield similar results as [3H]thymidine incorporation assays (50). Samples were run in triplicate, and the average of the responses was analyzed.

NO assessment. Individual spleens and MLN were dissociated using a modified glass tissue homogenizer. Cell enumeration was achieved using Coulter Counter particle counter. Dissociated cells were washed in dissection medium and resuspended in ice-cold sterile culture medium (Iscoves, 10% fetal bovine serum, 1% penstrep, 1% L-glutamine). Cell concentration was adjusted to 20.0 × 106 cells/ml for each spleen or MLN. A 1.0-ml cell suspension was plated into a 24-well plate (Corning). To optimize NO measurement, cells were incubated for 48 h (37°C, 5% CO2) with ConA (5.0 µg/ml) or KLH (250.0 µg/ml) stimulation. Culture supernatants were collected, centrifuged to remove cells, and stored at -20°C until nitrite assays were performed.

NO production was determined by measuring nitrite levels in culture supernatants. Nitrite is a stable nitrogen intermediate formed from the degradation of NO in an aerobic environment. Nitrite was measured using the Greiss reagent assay. The Greiss reagent consisted of a 1:1 (vol/vol) solution of 1% sulfanilamide (Sigma Chemical) in a 4.25% phosphoric acid solution (Mallinckrodt) and 0.1% N-(1-naphthyl)ethylenediamine dichloride (Sigma Chemical) in distilled deionized water. A standard curve was generated with a starting concentration of 2.5 mM sodium nitrite (Sigma Chemical) in culture medium. Standards (100 µl) were serially diluted 1:2, ten times, to obtain a standard curve. All standards were added to 96-well flat-bottom plates (Immulon 4, Dynatech Laboratories) in duplicate. Sample culture supernatants (100 µl) were also run in duplicate. Greiss reagent (100 µl) was added to each well and allowed to incubate at room temperature for 10 min. Absorbances were read at 540-nm wavelength using a microplate reader (MRX microplate reader, Dynatech Laboratories). Samples were compared with a standard curve containing serial dilutions of sodium nitrite.

Anti-KLH immunoglobulin. All rats were immunized with a 0.5-ml intraperitoneal injection containing 200 µg of KLH in sterile saline on days 0 and 49 of exercise training, stimulating a primary and secondary response, respectively. KLH is a benign, antigenic protein that will stimulate an antigen-specific immune responses without making the animal sick (15, 20, 21, 38).

Tail vein blood samples were quickly collected (within 2 min of touching the cage) by gently wrapping the rat in a small towel and lightly restraining it with a Velcro strapping apparatus. The tail was exposed, a small nick was made with a scalpel (No. 15 blade), and the blood sample (300 µl) was quickly milked from the tail vein. Serum levels of anti-KLH IgM and IgG were determined using an ELISA. The details of the ELISA procedures (using alkaline phosphatase, p-nitrophenyl phosphate disodium) have been presented previously (17, 18).

The primary anti-KLH IgM and IgG response was measured on days 7, 14, 21, 28, and 35 after KLH immunization. The secondary anti-KLH IgM and IgG response was measured on day 56, 1 wk after the second KLH challenge. Each anti-KLH IgM and anti-KLH IgG sample was calculated as a proportion of its plate positive, which is very nearly equal to 1.0 absorption unit. This is a standard transformation for data reported using ELISA (10). A negative control (serum from rats not challenged with KLH) was tested on each plate. Little nonspecific binding was found (OD < 0.1-0.2). Primary antibody data were presented for samples assayed at the 1:400 dilution for IgM and the 1:6,000 dilution for IgG. Because a secondary or memory antibody response is much greater than the primary response, samples were assayed at the 1:3,200 for IgM and 1:32,000 for IgG. These dilutions were chosen so that samples fall within the linear range of the plate reader. Observed differences were consistent across dilutions.

Statistical Analysis

Repeated measures analysis of variances (ANOVAs) were used to analyze total distances run, body weight, anti-KLH immunoglobulin and proliferation data. Data for citrate synthase activity, thymus weight, adrenal weight, and CBG levels were analyzed using a two-group ANOVA. Nitrite production was analyzed by a 2 (treadmill vs. sedentary) × 2 (ConA vs. KLH) factorial ANOVA. Post hoc pairwise comparisons were performed using Fishers protected least-significant difference test. A statistical difference was accepted at P < 0.05. All data are reported as the means ± SE.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Running Activity

Weekly total running distance is presented in Fig. 1A. Because of the regimented treadmill training program, average weekly running distances were the same for all rats and continued to increase until week 7, at which point training was not increased over the final week.


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  		Fig. 1.   A: total weekly running distance of treadmill exercised rats. Running activity was performed 5 days/week on an inclined, motorized treadmill. Intensity and duration of activity were increased to accommodate fitness as described in MATERIALS AND METHODS. B: animal body weight was determined at weekly intervals, before running activity, using an Ohaus triple-beam balance.

Body Weight

The effect of treadmill running on body weight is depicted in Fig. 1B. Both sedentary and treadmill-trained rats gained weight over the 8 wk of the study (P <=  0.0001); however, treadmill runners gained overall statistically less weight than their matched sedentary controls (P <=  0.05). This decrease in body weight due to running was greatest during the final weeks of the study (P <=  0.0001).

Soleus Muscle Citrate Synthase Activity

Figure 2 clearly depicts an increase in citrate synthase activity in soleus muscle after 8 wk of treadmill running (P <=  0.05).


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  		Fig. 2.   The activity of the oxidative enzyme citrate synthase was determined from soleus muscle of both sedentary and treadmill exercised rats after week 8 of the experiment.

Thymus Gland Weight

Figure 3A presents thymus weight corrected for body weight. Clearly, 8 wk of treadmill training produced a large reduction in thymus weight (P <=  0.001). Treadmill rats had a 42% reduction in normalized thymus weight compared with sedentary controls. The results for thymus weight were the same when corrected for tibia length (data not shown).


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  		Fig. 3.   Thymus (A) and adrenal (B) glands were excised at the time of death (week 8 of the experiment). Wet tissue weight was adjusted for individual body weight.

Adrenal Gland Weight

Figure 3B presents adrenal gland weight corrected for body weight. Treadmill training produced a large increase in adrenal weight (P <=  0.001). The results for adrenal weight were the same when corrected for tibia length (data not shown).

CBG

Figure 4 presents the effect of treadmill running on CBG, the carrier protein for the stress hormone corticosterone. Eight weeks of treadmill running decreased serum CBG (P <=  0.005).


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  		Fig. 4.   Corticosteroid binding globulin (CBG) was determined from serum taken at time of death (week 8) using a competitive binding assay.

Lymphocyte Proliferation

Proliferation of mesenteric lymph node cells is shown in Fig. 5, A and B. Treadmill running suppressed both the ConA- (P = 0.08) and KLH- (P <=  0.005) stimulated proliferative response compared with sedentary controls. Although the suppression of ConA-stimulated proliferation was only trending to be statistically reliable, the suppression of KLH-specific proliferation was clearly suppressed. Treadmill running did not produce a reliable suppression of either ConA- or KLH-stimulated proliferation of splenocytes (Fig. 6, A-B).


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  		Fig. 5.   Mesenteric lymphocyte proliferation was determined by measuring the cellular metabolic product NADH after 48 h in culture. Cells (1.25, 2.5, 5.0, or 10.0 × 105/well) were taken from rats after 8 wk of activity (treadmill) or a comparable duration of inactivity (sedentary) and cultured with concanavalin A (ConA, 5.0 µg/ml, A) or keyhole limpet hemocyanin (KLH, 250 µg/ml, B).



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  		Fig. 6.   Splenocyte proliferation was determined by measuring the cellular metabolic product NADH after 48 h in culture. Cells (1.25, 2.5, 5.0, or 10.0 × 105/well) were taken from rats after 8 wk of activity (treadmill) or a comparable duration of inactivity (sedentary) and cultured with ConA (5.0 µg/ml, A) or KLH (250 µg/ml, B).

NO Production

Nitrite concentrations were measured in supernatants of MLN cells and splenocytes (20.0 × 106 cells/ml) after 48 h of stimulation with either ConA or KLH (Fig. 7, A-B). Treadmill running did not affect nitrite production in the absence of in vitro antigen stimulation for either MLN or spleen (unstimulated). As shown in Fig. 7A, MLN ConA- or KLH-stimulated production of nitrite also was not affected by treadmill training. In contrast, splenocytes (Fig. 7B) stimulated with either ConA or KLH from treadmill-trained rats produced higher levels of nitrite compared with sedentary controls (P <=  0.05).


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  		Fig. 7.   Nitrite production was measured in culture supernatant using the Greiss reagent assay. Tissues were taken after 8 wk of activity (treadmill) or a comparable duration of inactivity (sedentary), adjusted to 20.0 × 106 cells/ml for either mesenteric lymphocyte (A) or spleen (B) and cultured for 48 h with ConA (5 µg/ml), KLH (250 µg/ml), or without stimulation.

Anti-KLH IgM and IgG

Weekly serum levels of the primary KLH-specific immunoglobulin response is shown in Fig. 8, A-B. Treadmill running reduced the amount of anti-KLH IgM (Fig. 8A, P <=  0.05), but not anti-KLH IgG (Fig. 8B, P = 0.2). Interestingly, the secondary anti-KLH IgM (Fig. 9, P <=  0.01) but not secondary anti-KLH IgG (Fig. 9) response was also reduced in treadmill trained rats.


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  		Fig. 8.   The primary KLH-specific immunoglobulin response was measured at weekly intervals in serum of rats that were immunized with KLH (200 µg/rat) at the onset (day 0) of the experiment. Blood samples were then taken at weekly intervals for 35 days and assayed for anti-KLH IgM (A) or anti-KLH IgG (B) using an anti-KLH enzyme-linked immunosorbent assay (ELISA). Each sample was calculated to a proportion of its plate-positive control (anti-KLH-positive control serum).



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  		Fig. 9.   The secondary keyhole limpet (KLH)-specific immunoglobulin response was determined in serum on day 56, 1 wk after the second KLH immunization (200 µg/rat). The primary KLH immunization occurred on day 0. Anti-KLH IgM or anti-KLH IgG was determined by an anti-KLH ELISA. Each sample was calculated to a proportion of its plate-positive control (anti-KLH-positive control serum).


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Running exercise is a frequently used training modality for rats, and treadmill running has the propensity to induce both psychological and physical stress. The purpose of this paper was to characterize effect of treadmill running on several training responsive and stress responsive physiological adaptations. The treadmill training protocol used in this study involves a gradual increase in running intensity and is commonly used in the literature. The results of this experiment were that treadmill running produced both positive or adaptive and potentially negative or maladaptive physiological changes. The positive adaptations reported here were reductions in body weight gain and increases in soleus citrate synthase activity. The potentially negative physiological adaptations exhibited were adrenal hypertrophy, thymic involution, decreased serum CBG, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM.

The mechanisms and specific benefits of reductions in body weight gain and increases in muscle citrate synthase activity after training have been discussed elsewhere and are beyond the scope of this paper. There is evidence, however, that both changes result in benefits to the organism (4).

Classically stress-induced changes in adrenal and thymus weight occur because of long-term stimulation of the hypothalamic-pituitary-adrenal axis (54). In brief, repeated daily stressor exposure, through central nervous system inputs to the hypothalamus, stimulates hypothalamic corticotropin-releasing hormone, which stimulates pituitary to release adrenocorticotropin hormone (ACTH) into the peripheral circulation. ACTH stimulates adrenal production of corticosterone. Chronic stimulation of the adrenal gland by ACTH will result in proliferation of adrenal cortical cells and hence adrenal hypertrophy. Thymic involution is due to chronically elevated corticosterone (1, 27). Thymocytes are sensitive to corticosterone-induced apoptosis (5, 28). Thus chronically high-circulating corticosterone kills thymocytes and results in thymic involution.

Clearly short-term activation of the hypothalamic-pituitary-adrenal response is important for facilitating energy utilization during the stress response (44). However, chronically elevated glucocorticoids have been reported previously to result in negative consequences to the organism health (52, 56), including eventual adrenal exhaustion and a reduction in developing T cells (thymic involution). It should be noted, however, that others have proposed that an enlarged adrenal gland or the "sports adrenal" may be a positive training adaptation (4).

The mechanism(s) for stress-induced decreased serum CBG, elevated leukocyte nitrite concentration, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM are not as clear. It has been proposed that both the elevation in NO and the reduction in CBG are indicative of stress-induced activation of the acute phase response (8, 22, 38). The acute phase response is a systemic response to pathogenic challenge and is characterized by a shift in liver protein metabolism and a facilitation of the inflammatory response (3). CBG is a "negative reactant" and is expected to decrease during the acute phase response, whereas leukocyte release of NO facilitates the inflammatory response (13). Thus a decrease in CBG and an increase in NO could be reflective of stimulation of the acute phase response. The functional consequences of an increase in antigen-mitogen-stimulated NO remains unknown. It is possible that the potentiated NO response could improve bactericidal killing by inflammatory cells (13). In contrast, it also is possible that the potentiated NO response could be detrimental to the organism by damaging normal cells (13, 22). In fact, it has been proposed that an increase in leukocyte NO could be a mechanism for stress-induced suppression in lymphocyte proliferation and anti-KLH antibody responses (7, 14, 22, 34). Although the precise mechanisms of these changes remain unknown, it is clear that they are associated with activation of the stress response (7, 9, 14, 19, 22, 34, 56). Therefore, the presence of these changes after 8 wk of treadmill running supports the conclusion that treadmill running chronically activates stress-responsive systems.

Are reduced serum CBG, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM adaptive or maladaptive to the organism? As stated previously, a short-term reduction in CBG and elevation in NO is characteristic of activation of the acute phase response. In addition there is evidence that acute stressor activation of these responses is an adaptive response for the organism (8, 9, 22, 38). CBG is a carrier protein for corticosterone and serves to provide a reservoir of biologically inactive hormone that can be quickly made active. A short-term reduction in CBG can aid site-specific regulation of inflammatory responses (24). However, a long-term reduction in circulating CBG could lead to a chronic elevation in biologically free corticosterone that can become detrimental to health (52, 56). Clearly, reduced CBG after treadmill running was biologically relevant to the animal because it experienced a nearly 50% reduction in thymus size. Reductions in lymphocyte proliferation and generation of antigen-specific immune responses also are potentially maladaptive consequences to exposure to this training regimen. Importantly, the suppression in lymphocyte proliferation and the secondary anti-KLH IgM response occurred at the end of 8 wk of treadmill training. Studies that have reported the effect of acute stress on lymphocyte proliferation and anti-KLH IgM production demonstrate that stressor exposure is no longer immunosuppressive if the KLH is administered (23) or the cells are removed (unpublished observation) within 2-7 days of stressor termination. This suggests that the immunosuppressive effect of treadmill running is not due to the initial novelty of the experience and that the effect is not habituating with repeated treadmill running. These findings may reflect a maladaptive adaptation as reductions in cellular proliferation and antibody production can increase disease susceptibility (30, 49).

The current study cannot address which particular components of treadmill exercise are responsible for producing the changes in stress-responsive systems. In addition to the previously discussed psychological (loss of control and aversive motivation) and physical (pushed to attain 75% Vo2 max) stressors, rats trained on the treadmill are often forced to run during their light phase. Rats are normally most active during their dark phase (51). This difference in time of day of activity could lead to disruptions in biological rhythms that have been reported to activate stress-responsive systems (36). Although the current study cannot discern the source of the stress (e.g., exercise intensity, aversive motivation, fear, loss of control, disruption of biological rhythms, etc.), the results support the conclusion that the treadmill protocol tested in this study and commonly used by many researchers produces physiological adaptations that are indicative of chronic stress. Therefore, it is important to be aware of the potential negative impact that chronic activation of the stress response, due to forced treadmill running, can have on physiological measures of interest.

Chronic activation of the stress response may not occur as a consequence of all treadmill training protocols and could be dependent on exercise intensities, gender, time of training, or rat strains. In a recent paper by Palmer et al. (47), e.g., female Sprague-Dawley rats that were trained on a treadmill for 20 wk with a very gradual increase in running speed and duration, did not experience adrenal hypertrophy. In some circumstances, therefore, the stress-evoking effects of treadmill training can be minimized.


    FOOTNOTES

Address for reprint requests and other correspondence: M. Fleshner, Dept. of Kinesiology and Applied Physiology, Campus Box 354, Univ. of Colorado-Boulder, Boulder, Colorado 80309-0354 (E-mail: fleshner{at}spot.colorado.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 8 October 1999; accepted in final form 3 April 2000.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Akana, S, Cascia C, Shinsako J, and Dallman M. Corticosterone: narrow range required for normal body and thymus weight and ACTH. Am J Physiol Regulatory Integrative Comp Physiol 249: R527-R532, 1985[Abstract/Free Full Text].

2.   Apple, FS, and Billadello JJ. Expression of creatine kinase M and B mRNAs in treadmill trained rat skeletal muscle. Life Sci 55: 585-592, 1994[ISI][Medline].

3.   Bauman, H, and Gauldie J. The acute phase response. Immunol Today 15: 74-81, 1994[ISI][Medline].

4.   Brooks, GA, Fahey TD, and White TP. Exercise Physiology: Human Bioenergetics and Its Applications. Mountain View, CA: Mayfield Publishing, 1995.

5.   Cohen, JJ. Glucorticoid-induced apoptosis in the thymus. Immunology 4: 363-369, 1992.

6.   Coleman, KJ, and Rager DR. Effects of voluntary exercise on immune function in rats. Physiol Behav 54: 771-774, 1993[Medline].

7.   Coussons-Read, ME, Maslonek KA, Fecho K, Perez L, and Lysle DT. Evidence for the involvement of macrophage-derived nitric oxide in the modulation of immune status by a conditioned aversive stimulus. J Neuroimmunol 50: 51-58, 1994[ISI][Medline].

8.   Deak, T, Meriwether JL, Fleshner M, Spencer RL, Abouhamze A, Moldawer LL, Grahn RE, Watkins LR, and Maier SF. Evidence that brief stress may induce the acute phase response in rats. Am J Physiol Regulatory Integrative Comp Physiol 273: R1998-R2004, 1997.

9.   Deak, T, Nguyen KT, Fleshner M, Watkins LR, and Maier SF. Acute stress may facilitate recovery from a subcutaneous bacterial challenge. Neuroimmunomodulation 6: 344-354, 1999[ISI][Medline].

10.   DeSavigny, D, and Voller A. The communication of quantitative ELISA results. In: Immunoenzymatic Techniques, edited by Malvano R.. Boston, MA: Nijhoff, 1980, p. 116-132.

11.   Dunn, A, Reigle T, Youngstedt S, Armstrong R, and Dishman R. Brain norepinephrine and metabolites after treadmill training and wheel running in rats. Med Sci Sports Exerc 28: 204-209, 1996[ISI][Medline].

12.   Dunn, AL, Reigle TG, Youngstedt SD, Armstrong RB, and Dishman RK. Brain norepinephrine and metabolites after treadmill training and wheel running in rats. Med Sci Sports Exerc 28: 204-209, 1996.

13.   Fang, FC. Prospectives series: host/pathogen interaction. Mechanisms of nitric oxide-related antimicrobial activity. J Clin Invest 99: 2818-2825, 1997[ISI][Medline].

14.   Fecho, K, Maslonek DA, Coussons-Read ME, Dykstra LA, and Lysle DT. Macrophage-derived nitric oxide is involved in the depressed conconavalin A responsiveness of splenic lymphocytes from rats administered morphine in vivo. J Immunol 152: 5845-5852, 1994[Abstract].

15.   Fleshner, M. Exercise and neuroendocrine regulation of antibody production: the protective effect of physical activity on stress-induced suppression of the specific antibody response. Int J Sports Med 21, Suppl1: S14-S19, 2000.

16.   Fleshner, M, Bellgrau D, Laudenslager ML, Watkins LR, and Maier SF. Stress-induced changes in the mixed lymphocyte reaction is dependent on macrophages but not on shifts in phenotypes. J Neuroimmunol 56: 45-52, 1995[ISI][Medline].

17.   Fleshner, M, Brennan FX, Watkins LR, and Maier SF. RU486 blocks the suppressive effect of stress on the in vivo anti-KLH immunoglobulin response. Am J Physiol Regulatory Integrative Comp Physiol 271: R1344-R1352, 1996[Abstract/Free Full Text].

18.   Fleshner, M, Brohm M, Watkins LR, Laudenslager ML, and Maier SF. Modulation of the in vivo antibody response by benzodiazepine-inverse agonist (DMCM) given centrally or peripherally. Physiol Behav 54: 1149-1154, 1993[Medline].

19.   Fleshner, M, Deak T, Spencer RL, Laudenslauger ML, Watkins LR, and Maier SF. A long term increase in basal levels of corticosterone and a decrease in corticosteroid-binding globulin after acute stressor exposure. Endocrinology 136: 5336-5342, 1995[Abstract].

20.   Fleshner, M, Hermann J, Lockwood LL, Watkins LR, Laudenslager ML, and Maier SF. Stressed rats fail to expand the CD45RC+CD4+ (Th1-like) T cell subset in response to KLH: possible involvement of IFN-gamma. Brain Behav Immun 9: 101-112, 1995[ISI][Medline].

21.   Fleshner, M, Laudenslager ML, Simons L, and Maier SF. Reduced serum antibodies associated with social defeat in rats. Physiol Behav 45: 1183-1187, 1989[Medline].

22.   Fleshner, M, Nguyen KT, Cotter CS, Watkins LR, and Maier SF. Acute stressor exposure both potentiates innate immunity and suppresses acquired immunity. Am J Physiol Regulatory Integrative Comp Physiol 275: R870-R878, 1998[Abstract/Free Full Text].

23.   Fleshner, M, Watkins LR, Bellgrau D, Laudenslager ML, and Maier SF. Specific changes in lymphocyte subpopulations: a potential mechanism for stress-induced immunosuppression. J Neuroimmunol 41: 131-142, 1992[ISI][Medline].

24.   Hammond, G. Molecular properties of corticosteroid binding globulin and the sex-steroid binding proteins. Endocr Rev 11: 65-79, 1990[ISI][Medline].

25.   Hoffman-Goetz, L, and Pederson BK. Exercise and the immune system: a model of the stress response. Immunol Today 15: 382-387, 1994[ISI][Medline].

26.   Hoffman-Goetz, L, Keir R, Thorne R, Houston ME, and Young C. Chronic exercise stress in mice depresses splenic T lymphocyte mitogenesis in vitro. Clin Exp Immunol 66: 551-557, 1986[ISI][Medline].

27.   Hori, T, Fukada M, Suzuki H, Yano S, and Ono T. SART stress effects on lymphocytes in the thymus and spleen of normal, adrenalectomized, and sympathectomized mice. Clin Immunol Immunopathol 68: 243-255, 1993[ISI][Medline].

28.   Jeon, SH, Kang MG, Kim YH, Jin YH, Lee C, Hee-Yong C, Kwon H, Park SD, and Seong RH. A new mouse gene, SRG3, related to the WEI3 of Saccharomyces cerevisiae, is required for apoptosis induced by glucocorticoids in a thymoma cell line. J Exp Med 185: 1827-1836, 1997[Abstract/Free Full Text].

29.   Kiecolt-Glaser, JK, Dura JR, Speicher CE, Trask OJ, and Glaser R. Spousal caregivers of demetia victims: longitudinal changes in immunity and health. Psychosom Med 53: 345-362, 1991[Abstract/Free Full Text].

30.   Kusnecov, AV, Grota LJ, Schmidt SG, Bonneau RH, Sheridan JF, Glaser R, and Moynihan JA. Decreased herpes simplex viral immunity and enhanced pathogenesis following stressor administration in mice. J Neuroimmunol 38: 129-138, 1992[ISI][Medline].

31.   Laudenslager, ML, and Fleshner M. Stress and immunity: of mice, monkeys, models, and mechanisms. In: The Handbook of Human Stress and Immunity, edited by Glaser R, and Kiecolt-Glaser J.. New York: Academic Press, 1994, p. 161-181.

32.   Levy, A, Gauer E, Ben-Nathan D, and de Kloet ER. New Frontiers in Stress Research: Modulation of Brain Function. Canada: Harwood Academic, 1998.

33.   Locke, M, Noble EG, Tanguary RM, and Feild MR. Activation of heat-shock transcription factor in rat heart after heat shock and exercise. Am J Physiol Cell Physiol 268: C1387-C1394, 1995[Abstract/Free Full Text].

34.   Lysle, DT, Fecho K, Maslonek KA, and Dykstra LA. Evidence for the involvement of macrophage-derived nitric oxide in the immunomodulatory effect of morphine and aversive Pavolovian conditioning. Adv Exp Med Biol 373: 141-147, 1995[Medline].

35.   Lysle, DT, Lyte M, Fowler H, and Rabin BS. Shock-induced modulation of lymphocyte reactivity: suppression, habituation, and recovery. Life Sci 41: 1805-1814, 1987[ISI][Medline].

36.   Maestroni, G, Conti A, and Poerpaoli W. Role of the pineal gland in immunity. Circadian synthesis and release of melatonin modulates the immunosuppressive effect of corticosterone. J Neuroimmunol 13: 19-30, 1986[ISI][Medline].

37.   Maier, SF. Learned helplessness and animal models of depression. Prog Neuropsychopharmacol Biol Psychiatry 8: 435-446, 1984[Medline].

38.   Maier, SF, Fleshner M, and Watkins LR. Neural, endocrine, and immune mechanisms of stress-induced immunomodulation. In: New Frontiers in Stress Research: Modulation of Brain Function. Canada: Harwood Academic, 1998, p. 117-126.

39.   Maier, SF, Watkins LR, and Fleshner M. Psychoneuroimmunology: the interface between brain, behavior, and immunity. Am Psychol 49: 1004-1017, 1994[Medline].

40.   Mazzeo, RS. Catecholamine responses to acute and chronic exercise. Med Sci Sports Exerc 23: 839-845, 1991[ISI][Medline].

41.   Mazzeo, RS, Brooks GA, and Horvath SM. Effects of age on metabolic response to endurance training in rats. J Appl Physiol 57: 1369-1374, 1984[Abstract/Free Full Text].

42.   Mazzeo, RS, and Grantham PA. Norepinephrine turnover in various tissues at rest and during exercise: evidence for a training effect. Metabolism 38: 479-483, 1989[ISI][Medline].

43.   Noble, EG, Moraska A, Mazzeo RS, Roth DA, Olsson MC, and Fleshner M. Differential expression of stress proteins in rat myocardium following free wheel or treadmill run training. J Appl Physiol 86: 1696-1701, 1999[Abstract/Free Full Text].

44.   Norris, DO. Vertebrate Endocrinology. Philadelphia, PA: Lea & Febiger, 1985.

45.   Ong, JM, Simsolo RB, Saghizadeh M, Goers JW, and Kem PA. Effects of exercise training and feeding on lipoprotein lipase gene expression in adipose tissue, heart, and skeletal muscle of the rat. Metabolism 44: 1565-1605, 1995.

46.   Pacak, K, Palkovits M, Yadid G, Kvetnansky R, Kopin IJ, and Goldstein DS. Heterogeneous neurochemical responses to different stressors: a test of Selyes's doctrine of nonspecificity. Am J Physiol Regulatory Integrative Comp Physiol 275: R1247-R1255, 1998[Abstract/Free Full Text].

47.   Palmer, BM, Lynch JM, Snyder SM, and Moore RL. Effects of chronic run training on Na+-dependent Ca2+ efflux from rat left ventricular myocytes. J Appl Physiol 86: 584-591, 1999[Abstract/Free Full Text].

48.   Pederson, BK, Bruunsgaard H, Klokker M, MacLean HB, Rohde T, Ullum H, and Zacho M. Exercise-induced immunomodulation-possible roles of neuroendocrine and metabolic factors. Int J Sports Med 18: 52-57, 1997.

49.   Plotnikoff, N, Murgo A, Faith R, and Wybran J. Stress and Immunity. Boca Raton, FL: CRC, 1991.

50.   Riss, T, and Moravec R. Comparison of MTT, XTT, and a novel tetrazolium compound MTS for in vitro proliferation and chemosensitivity assays (Abstract). Mol Biol Cell 3: 184a, 1992.

51.   Roebuck, BD, McCaffrey J, and Baumgartner K. Protective effects of voluntary exercise during the postinitiation phase of pancreatic carcinogenesis in the rat. Cancer Res 50: 6811-6816, 1990[Abstract/Free Full Text].

52.   Sapolsky, RM. Neuroendocrinology of the Stress Response. Cambridge, MA: MIT, 1992.

53.   Seyle, H. A syndrome produced by diverse nocuous agents. Nature 138: 32, 1936.

54.   Seyle, H. The Stress of Life. New York: McGraw-Hill, 1976.

55.   Somani, SM, and Rybak LP. Comparative effects of exercise training on transcription of antioxidant enzyme and the activity in old rat heart. Indian J Physiol Pharmacol 40: 205-212, 1996[Medline].

56.   Spencer, RL, Miller AH, Moday H, McEwen BS, Blanchard RJ, Blanchard DC, and Sakai RR. Chronic social stress produces reductions in available splenic type II corticosteroid receptor binding and plasma corticosteroid binding globulin levels. Psychoneuroendocrinology 21: 95-109, 1996[ISI][Medline].

57.   Srere, PA. Citrate synthase. Methods Enzymol 13: 3-8, 1969.

58.   Tokuda, S, Kai M, Kawahara S, and Otsuji S. Changes in carbonic anhydrase activity in rat skeletal muscles due to aerobic treadmill exercise. J Sports Med Phys Fitness 27: 380-383, 1987[ISI][Medline].

59.   Westphal, U. Steroid-protein interactions. Monog Endocrinol 4: 1-567, 1971.

60.   Yancey, S, and Overton M. Cardiovascular responses to voluntary and treadmill exercise in rats. J Appl Physiol 75: 1334-1340, 1993[Abstract/Free Full Text].

61.   Zhou, Q, and Dohm GL. Treadmill running increases phosphatidylinostol 3-kinase activity in rat skeletal muscle. Biochem Biophys Res Commun 236: 647-650, 1997[ISI][Medline].

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