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-MSH suppresses LPS fever via central melanocortin
receptors independently of its suppression of corticosterone and
IL-6 release
1 Division of Endocrinology, Diabetes, Metabolism and Molecular Medicine, Department of Medicine and the Tupper Research Institute, Tufts University School of Medicine and New England Medical Center Hospitals, Boston, Massachusetts 02111; and 2 Department of Chemistry, University of Arizona, Tucson, Arizona 85721
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ABSTRACT |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Systemically
administered 
-melanocyte-stimulating hormone (-MSH) inhibits
endotoxin (lipopolysaccharide; LPS)- or interleukin (IL)-1-induced
fever and adrenocortical activation, but the sites of these actions and
the mechanisms involved are unknown. The aims of this study were,
first, to determine whether melanocortin receptors (MCR) located within
the central nervous system mediate the suppressive effects of
peripherally administered -MSH on LPS-induced fever and activation
of the pituitary-adrenal axis and, second, to determine whether
systemic -MSH suppresses the LPS-induced rise in plasma IL-6 levels,
potentially contributing to its antipyretic effect. Male rats received
Escherichia coli LPS (25 µg/kg ip).
Core body temperatures (Tb) were
determined hourly by radiotelemetry (0-8 h), and blood was
withdrawn via venous catheters for plasma hormone immunoassays
(0-2 h) and IL-6 bioassay (0-8 h). -MSH (100 µg/kg ip)
completely prevented the onset of LPS-induced fever during the first
3-4 h after LPS and suppressed fever throughout the next 4 h but
did not affect Tb in afebrile rats
treated with intraperitoneal saline rather than LPS. Intraperitoneal
-MSH also suppressed the LPS-induced rise in plasma IL-6, ACTH, and
corticosterone (CS) levels. Intracerebroventricular injection of
SHU-9119, a potent melanocortin-4 receptor (MC4-R)/MC3-R antagonist,
completely blocked the antipyretic effect of intraperitoneal -MSH
during the first 4 h after LPS but had no effect on -MSH-induced suppression of LPS-stimulated plasma IL-6 and CS levels. Taken together, the results indicate that the antipyretic effect of peripherally administered -MSH during the early phase of fever is
mediated by MCR within the brain. In contrast, the inhibition of
LPS-induced increases in plasma CS and IL-6 levels by intraperitoneal -MSH appears to be mediated by a different mechanism(s), and these
effects do not contribute to its antipyretic action.
lipopolysaccharide; adrenocorticotropic hormone; interleukin-6; rat; SHU-9119; -melanocyte-stimulating hormone
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INTRODUCTION |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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IN VERTEBRATES, BACTERIAL infection activates an array
of stereotypical adaptive responses, including fever and increased adrenal glucocorticoid secretion, that are believed to be mediated in
large part by host-derived proinflammatory cytokines (5, 13). Exogenous
melanocortins [-melanocyte-stimulating hormone (-MSH)- and
ACTH-related peptides] have been widely observed to suppress
these responses. Administration of -MSH either centrally or
peripherally, at doses that do not affect body temperatures (Tb) of afebrile animals,
inhibits fevers induced by endotoxin, interleukin (IL)-1, IL-6, or
tumor necrosis factor- (3). Similarly, exogenous -MSH suppresses
lipopolysaccharide (LPS)- or IL-1-induced adrenocortical activation
(17, 20).
The mechanisms involved in these effects and the precise sites of
action of -MSH are unknown, but certain evidence points to a role of
melanocortin receptors (MCR) within the brain in mediating the
antipyretic action of -MSH. Melanocortins have greater antipyretic
potency when administered centrally than peripherally (30), and
intraparenchymal administration of melanocortins in preoptic and septal
central nervous system (CNS) sites suppresses fever in animal models
(2, 6). In addition, MCR proteins and mRNA encoding the MCR subtypes
MC3-R and MC4-R are present in animals and humans in a number of
hypothalamic and other brain regions believed to be involved in fever
and regulation of the hypothalamic-pituitary-adrenal (HPA) axis (15,
18, 22, 25). We recently showed that the antipyretic effect of
centrally administered -MSH in rats is mediated by central MCR,
because it was prevented by blockade of central MCR using
intracerebroventricular injection of an MC4-R/MC3-R antagonist
(9)
[Ac-Nle4,c-[Asp5,DNal(2')7,Lys10]-MSH(4-10)-NH2;
SHU-9119 (8)]. Furthermore, SHU-9119 given
intracerebroventricularly, but not intravenously, exacerbated Escherichia coli LPS-induced fever,
indicating that endogenous melanocortin peptides act via central MCR
during LPS-induced fever to exert an antipyretic effect (9).
Despite this evidence that -MSH can act within the CNS to modulate
fever, it is not clear whether systemic -MSH may exert its
antipyretic or HPA axis-inhibitory effects by acting on target sites
within the CNS, because the ability of blood-borne -MSH to traverse
the blood-brain barrier (BBB) is very limited (28). Therefore, one
objective of the present study was to determine whether MCR located
within the CNS mediate the suppressive effects of peripherally
administered -MSH on LPS-induced fever and HPA responses.
Although the postreceptor effectors involved in mediating the
antipyretic action of -MSH are unknown, one potential mechanism for
modulation of fever is via altered cytokine production. Therefore, our
second objective was to determine whether systemically administered -MSH suppresses the LPS-induced rise in blood levels of the
endogenous pyrogenic cytokine IL-6 (13, 14), potentially
contributing to -MSH-induced suppression of LPS-induced fever and
adrenocortical responses.
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MATERIALS AND METHODS |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Drugs
LPS (E. coli serotype 055:B5, no. L-4055, Sigma Chemical) was dissolved in sterile pyrogen-free 0.9% saline solution (saline). SHU-9119 was synthesized by Dr. Wei Yuan using methods previously reported (8). It was dissolved in saline containing 0.1% low-endotoxin BSA (Sigma, A-3675) at a concentration of 1 mg/ml and stored at
70°C. Immediately before each
experiment, a stock aliquot of SHU-9119 was further diluted with saline
to a final concentration of 50 ng/µl. Stock aliquots of synthetic
-MSH (Peninsula Laboratories, Belmont, CA) were diluted in saline
immediately before use. Recombinant human IL-6 (specific activity,
107 U/mg protein) was purchased
from Collaborative Research (Bedford, MA).
Animals and Surgical Procedures
Adult male Sprague-Dawley rats (Taconic Farms or Harlan Sprague Dawley) initially weighing 270-300 g were used. Before surgery the rats were housed three per cage in a temperature (22 ± 1°C)- and light (12:12-h dark-light cycle, lights on at 0600)-controlled room, with standard rat chow and water available ad libitum. All procedures described were approved by the Animal Research Committee of Tufts University Medical School and New England Medical Center. Each rat was anesthetized with pentobarbital sodium (50 mg/kg ip) and implanted intraperitoneally with a miniature radio transmitter for telemetric measurements of Tb (Mini-Mitter, Sunriver, OR). For experiments involving intracerebroventricular injections, rats were then implanted with a permanent 22-gauge stainless steel intracerebroventricular cannula (Plastics One, Roanoke, VA) in the right lateral ventricle, as described in detail previously (9). After surgery, the animals were kept in individual plastic cages and maintained in a separate room with temperature controlled at 25 ± 1°C, a near-thermoneutral ambient temperature for rats, by means of a convection heater with remote thermostat. Correct placement of intracerebroventricular cannulas was verified postmortem by injecting 10 µl of 0.4% trypan blue at the termination of the experiment. Only rats exhibiting staining throughout the ventricles were included in the analysis. For experiments involving blood sampling for hormone measurements, each rat was implanted with an indwelling jugular catheter under pentobarbital sodium anesthesia 2 days before the experiment. Intrajugular catheters consisted of a 5.5-in. length of silicone tubing (Silastic; Dow Corning, Midland, MI), exteriorized at the nape of the neck, filled with sterile heparinized saline solution, and sealed.Animal Handling
To minimize the influence of nonspecific manipulative stress during experiments, each rat was conditioned by gentle handling daily for 5 consecutive days preceding the experiment. For rats bearing intracerebroventricular cannulas, the handling included a simulated intracerebroventricular injection performed by removing the dummy cannula and connecting the injection device.Intracerebroventricular Infusion
For intracerebroventricular injections, the dummy cannula was removed and replaced with a 28-gauge internal cannula connected by a flexible connector tubing (C313CS, Plastic One) to a 100-µl Hamilton syringe driven by a microinfusion pump (Bee Syringe Pump MF-9090; Bioanalytical Systems, West Lafayette, IN), allowing each rat to move about freely in its home cage during infusion. Intracerebroventricular injectates were infused in a volume of 4 µl at a rate of 2 µl/min. After intracerebroventricular infusion, the internal cannula was left in place for 2 min to prevent backflow of injectate through the guide cannula.Tb Measurements
Tb was measured hourly using a model RTA-500 receiver and a model SM-2372 frequency counter (Mini-Mitter). Emitted frequencies were converted to Tb by interpolating from the calibration curves of individual transmitters, and the transmitters were calibrated before and after each experiment according to the manufacturer's instructions.Experimental Protocols
Rats were randomly assigned to treatment groups, and each rat was used only once. Drugs for intraperitoneal injection (200-µl injection volume) or intracerebroventricular infusion were dissolved in saline. For each parameter tested, the total number of rats studied in each treatment group is indicated in the corresponding figure (Figs. 1-4). On the day of the experiment, immediately after baseline Tb data and blood samples were taken, rats were injected intraperitoneally with LPS or saline as indicated. To control for the influence of circadian rhythm on Tb and hormone levels, this intraperitoneal LPS or saline injection was performed between 0900 and 1000 in all experiments.Dose-response for antipyretic action of
intraperitoneal -MSH. Thirty minutes after LPS, rats
were injected intraperitoneally with saline or with -MSH at the
indicated dose (25-100 µg/kg). Tb values were determined hourly
for 8 h after LPS treatment by briefly placing each rat's home
cage on the receiver to record the emitted frequency (Fig.
1).
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Effects of intraperitoneal -MSH and central MCR
blockade on LPS fever and IL-6 responses. Thirty
minutes after LPS or saline treatment, rats received
intracerebroventricular infusion of SHU-9119 or saline, followed
immediately by intraperitoneal injection of saline or -MSH (100 µg/kg) (Figs. 2 and 3).
Blood samples (0.7 ml) were collected 2, 4, 6, and 8 h after the
injection of intraperitoneal LPS or saline for the measurement of
plasma IL-6 levels. To prevent loss of blood volume, immediately after
each blood collection, 0.7 ml of sterile saline was infused via the
intravenous catheter. No correction was applied for the minor dilution
of total blood volume by the infused saline. Blood samples were placed
in ice-chilled sterile test tubes containing Trasylol (500 kallikrein
inhibitory units) and EDTA (1 mg). After centrifugation at 2,000 rpm
for 10 min at 4°C, the plasma was aliquoted and kept at
20°C until assayed.
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Effects of intraperitoneal -MSH and central MCR
blockade on LPS-induced ACTH and corticosterone
secretion. In this experiment series, rats were
prepared and experiments were performed exactly as described above for
the studies of Figs. 2 and 3, except as follows: intraperitoneal
implantation of radio transmitters and Tb determinations were omitted,
and blood samples were collected immediately before and 30, 60, and 120 min after intraperitoneal administration of LPS or saline (Fig.
4).
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ACTH and Corticosterone Assays
Plasma ACTH levels were determined using a two-site immunoradiometric assay kit (Nichols Institute Diagnostics, San Juan Capistrano, CA) according to the manufacturer's instructions. Samples were assayed in duplicate. The assay limit of detection was 5 pg/ml. The assay is highly specific for ACTH and does not cross-react with-MSH,
-MSH, -lipotropin or -endorphin. Plasma corticosterone (CS)
levels were determined as described earlier (9). Briefly, samples were
diluted to 1:100 in assay buffer (0.1 M PBS containing 0.1% gelatin
and 0.04% sodium azide, pH 7.4) and heat denatured (70°C for 30 min). Samples were assayed in duplicate. The diluted plasma samples or
CS reference standard (Sigma) was incubated overnight at 4°C with
125I-CS and rabbit anti-CS serum
(ICN Pharmaceuticals, Costa Mesa, CA), and bound tracer was separated
from unbound using a sheep anti-rabbit second antibody method on the
following day. The inter- and intra-assay coefficients of variation
were 9.2 and 10.3%, respectively.
Plasma IL-6 Assay
Plasma IL-6 levels were determined by bioassay using the IL-6-dependent B9 hybridoma cell line as described previously (10). Briefly, B9 cells were plated in 96-well flat-bottom tissue culture plates (Costar, Cambridge, MA) at a density of 7,000 cells per well in 200 µl RPMI 1640 media (Life Technologies, Gaithersburg, MD) containing 10% fetal bovine serum (Hyclone Laboratories, Lorang, UT) and 1% antibiotic-antimycotic (Life Technologies). The cells were incubated for 72 h in the presence of serial dilutions of samples, each assayed in duplicate, and the cells were pulsed with 10 ml of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) during the last 4 h of incubation. At the end of the incubation, conversion of MTT to formazan was determined colorimetrically as an index of B9 cell proliferation. Samples were read at 570 nm using a Bio-Rad model 3550 microplate reader, and the data were analyzed using microplate manager software (Bio-Rad Laboratories, Hercules, CA). IL-6 activity in the diluted plasma samples was interpolated from a reference standard curve based on recombinant human IL-6 (concentration range 0.028 to 1,666 pg/ml), run in the same assay and expressed in nanograms per milliliter. The inter- and intra-assay variations were 8 and 12%, respectively.Statistics
All data are presented as group means ± SE. Tb and plasma hormone data were first analyzed by two-way ANOVA for repeated measures. In experiments producing significant main effects, the data for each time point were then analyzed by one-way ANOVA, and significance of differences between treatment groups was determined by t-tests corrected for multiple comparisons by the method of Scheffé (19). Values of P < 0.05 were considered significant.| |
RESULTS |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Potency and Time Course of Intraperitoneal -MSH-Induced
Suppression of LPS Fever
-MSH in the rat was first
determined. As shown in Fig. 1, LPS (25 µg/kg ip) produced a gradual
rise in Tb, which reached maximal
levels at 6-7 h after injection. -MSH (100 µg/kg ip) injected
30 min after LPS administration produced a marked suppression of
LPS-induced fever beginning at its onset and continuing throughout the
8-h observation period, whereas -MSH at doses of 50 µg/kg (Fig. 1)
and 25 µg/kg (data not shown) were ineffective. In contrast, -MSH
(100 µg/kg) had no effect on Tb
in afebrile rats as compared with saline-injected controls (data not
shown).
Effect of Central MCR Blockade on Antipyretic Action of
Intraperitoneal -MSH
-MSH, SHU-9119 (200 ng) was injected intracerebroventricularly 30 min after intraperitoneal LPS in -MSH-treated and -untreated rats. Intracerebroventricular SHU-9119 completely prevented the antipyretic effect of intraperitoneal -MSH
during the first 4 h after LPS treatment (Fig. 2). During the period
4-8 h after LPS, Tb values in
-MSH-treated rats began to rise in parallel with, but still remained
lower than, those in rats receiving LPS but not -MSH (Fig. 2).
SHU-9119 treatment had no effect on the sustained antipyretic effect of
-MSH during this latter period. In control rats receiving
intraperitoneal saline rather than LPS, effects of comparable treatment
with intraperitoneal -MSH and intracerebroventricular SHU-9119 on
Tb were negligible (Fig. 2).
Effect of -MSH and of Central MCR Blockade on
LPS-Induced Plasma IL-6 Elevation
-MSH treatment on LPS-induced plasma
IL-6 levels were determined in the presence and absence of
intracerebroventricular SHU-9119 injection. Plasma IL-6 levels increased markedly after LPS treatment, attaining maximal values 2 h
after LPS and remaining elevated for several hours (Fig. 3). Treatment
of rats with intraperitoneal -MSH (100 µg/kg, 30 min after LPS)
significantly reduced the LPS-induced elevation in plasma IL-6 levels
(Fig. 3). In contrast to its blockade of the antipyretic effect of
intraperitoneal -MSH presented in Fig. 2, intracerebroventricular
administration of SHU-9119 was completely without effect on
-MSH-induced suppression of plasma IL-6 levels in response to LPS
(Fig. 3). The combined administration of intraperitoneal -MSH and
intracerebroventricular SHU-9119 had no significant effect on plasma
IL-6 levels in control rats receiving intraperitoneal saline rather
than LPS (Fig. 3).
Effect of Intraperitoneal -MSH and of Central MCR
Blockade on Pituitary-Adrenal Response to LPS
-MSH (100 µg/kg
ip) significantly inhibited the LPS-induced rise in both ACTH and CS
levels (Fig. 4). Intracerebroventricular administration of the -MSH
antagonist SHU-9119 reversed the -MSH-induced suppression of ACTH
levels evident at 120 min after LPS treatment (Fig.
4A) but had no effect on -MSH
suppression of LPS-induced plasma CS responses (Fig.
4B). In control rats receiving
intraperitoneal saline rather than LPS, followed by intraperitoneal
-MSH and intracerebroventricular SHU-9119, plasma ACTH and CS levels
were significantly lower than in LPS-treated rats, exhibiting little change from baseline levels (Fig. 4).
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DISCUSSION |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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The first major finding of these studies is that the antipyretic action
of peripherally administered -MSH is mediated by activation of MCR
located within the CNS. Central MCR blockade, induced by
intracerebroventricular administration of the MC4-R/MC3-R antagonist
SHU-9119, completely prevented the antipyretic effect of
intraperitoneal -MSH for at least 3.5 h. The ability of
intracerebroventricular SHU-9119 to block the antipyretic effect of
intraperitoneal -MSH is not attributable to any potential
nonspecific hyperthermic effects, nor to peripheral actions, of the
antagonist, because we showed previously that the same dose of SHU-9119
had no effect on Tb when
administered intracerebroventricularly in afebrile rats and had no
effect on LPS fever when injected intravenously (9). Taken together,
these findings indicate that the major and earliest component of the
antipyretic effect of peripherally administered -MSH is mediated by
central MCR.
It has long been recognized that peripherally administered
melanocortins can affect various aspects of CNS function (3, 4, 16).
However, because the ability of circulating -MSH to cross the BBB is
very limited (28), previously it has been unclear whether -MSH in
systemic blood exerts these effects by acting directly on target sites
within the CNS. The present results support the hypothesis that -MSH
administered peripherally does gain biologically effective access to
central MCR, because central MCR blockade inhibited the antipyretic
action of intraperitoneal -MSH. Furthermore, intraperitoneal -MSH
(100 µg/kg) inhibited fever in a manner that was remarkably similar,
in qualitative and temporal respects, to that observed after its
intracerebroventricular injection (300 ng) in rats receiving an
identical LPS challenge in our previous study (9). Together, these
observations suggest that the BBB does not interfere qualitatively with
the ability of -MSH injected intraperitoneally to activate central
MCR.
Theoretically, there are several routes by which systemic -MSH may
gain access to central MCR. For example, -MSH could cross the BBB
directly to activate MCR expressed within the CNS parenchyma, but the
very low permeability of the BBB to -MSH (28) does not overtly favor
this hypothesis. One subset of central MCR that is perhaps more likely
to contribute to the antipyretic effect of systemic -MSH is that
expressed in certain circumventricular organs (CVOs), which lack a
tight BBB. MCR proteins are present in CVOs, including the median
eminence (22, 23, 27) and several centrally projecting CVOs (J. Tatro
and M. Entwistle, unpublished data). They are present at a low level in
another CVO, the organum vasculosum of the lamina terminalis (OVLT),
and at a much higher density in the adjacent ventromedial preoptic nucleus (VMPO) (24; Tatro and Entwistle, unpublished data). Extensive evidence supports a critical role of the OVLT and the VMPO in transducing LPS- and cytokine-induced pyrogenic signals leading to the
increase in hypothalamic Tb set
point of fever (5). Hence it is possible that blood-borne -MSH could
suppress LPS-induced fever by acting on MCR within the OVLT.
Alternatively, because the VMPO receives a dense network of
-MSH-containing neuron projections (24), -MSH acting within the
OVLT could generate local signals that cause the release of -MSH
from nerve terminals in the neighboring VMPO, thence activating MCR
within the VMPO to suppress the febrile response. Therefore, MCR
located within the OVLT and its immediate vicinity may play a role in
mediating the antipyretic action of blood-borne -MSH. Similarly, the
SFO contains neurons projecting centrally to key autonomic regulatory
sites (21), and the median eminence is a potential target of
pluripotent neuroendocrine modulation by blood-borne -MSH; hence MCR
within these CVOs could also potentially be involved in the antipyretic
and neuroendocrine actions of systemic -MSH. Discriminating between
the potential roles of MCR localized in CVOs and those requiring
trans-BBB transport for effective access by blood-borne melanocortins
is a complex problem that will require further study.
The second major issue addressed in this study was the potential role
of altered IL-6 secretion in mediating the antipyretic action of
-MSH. Because IL-6 is an endogenous pyrogen (13, 14) believed to
participate in mediating LPS-induced fever (11, 12), we tested whether
systemically administered -MSH suppresses LPS-induced IL-6
production. Indeed, -MSH markedly attenuated LPS-induced elevation
of plasma IL-6 levels. However, data from the same experiment also
ruled out any significant contribution of the -MSH-induced
suppression of plasma IL-6 responses to the observed antipyretic
effect, because intracerebroventricular administration of the MCR
antagonist SHU-9119 blocked the antipyretic effect of -MSH but had
no effect on its suppression of LPS-induced plasma IL-6 responses.
Furthermore, the same data also indicate that the suppression of plasma
IL-6 responses to LPS caused by intraperitoneal -MSH is not mediated
by central MCR, at least not by the same MCR population that mediates
its antipyretic effect.
The present results also provide some insight into the mechanism(s) by
which intraperitoneal -MSH suppresses LPS-induced CS secretion.
Intraperitoneal -MSH given at an antipyretic dose suppressed the
LPS-induced rise in plasma ACTH and CS levels, consistent with previous
findings by others (17, 20). Intracerebroventricular SHU-9119 treatment
reversed the -MSH-induced suppression of ACTH levels observed 2 h
after LPS, suggesting that -MSH acts at least in part via central
MCR to suppress LPS-induced ACTH release. However, despite its partial
restorative effect on ACTH secretion, central MCR blockade by
intracerebroventricular SHU-9119, at a dose that completely blocked the
first 3-4 h of the antipyretic action of intraperitoneal -MSH,
had no effect whatsoever on -MSH-induced inhibition of
LPS-stimulated CS secretion. Therefore, additional mechanisms besides
modulation of ACTH secretion may be involved in the inhibition of
LPS-stimulated adrenal CS release by intraperitoneal -MSH, such as
direct actions of -MSH at the adrenal cortical level. In this
connection, an -MSH-responsive MCR subtype known as MC5-R is
expressed within the rat adrenal cortex (7, 26), but whether this
receptor is involved in the regulation of glucocorticoid secretion is
not yet known. In sum, these results suggest that systemic -MSH
suppresses LPS-induced ACTH release by acting at the central
and/or adrenal cortical levels.
Our direct measurements of stress hormone levels also permit an
assessment of the potential impact of nonspecific stress as a
confounding or contributing factor in these studies. Basal
(time zero) CS and ACTH levels in all
groups were low, and in the non-LPS-treated rats only small increases
in CS and ACTH occurred. These findings clearly indicate that the rats
were relatively unstressed by their surgical implants and the
experimental procedures, probably owing to extensive preconditioning of
the rats to the procedures. Furthermore, in our previous study,
treatment with intracerebroventricular SHU-9119 alone (9) had no
significant effects on basal or LPS-stimulated ACTH or CS levels,
indicating that intracerebroventricular treatment with SHU-9119 per se
did not exert nonspecific effects on HPA responses. Taken together,
these results suggest that nonspecific stress did not contribute
significantly to the observed antipyretic and HPA-modulating effects of
exogenous -MSH.
The specific brain MCR subtype(s) that mediate the antipyretic effects
of -MSH in rats cannot be determined from this study, because
SHU-9119 has similar antagonist potencies on the rat MC3-R and rat
MC4-R (9). Nevertheless, it is likely that one or both of these MCR
subtypes contribute to the antipyretic central action of peripherally
injected -MSH, because the mRNAs encoding rat MC3-R and MC4-R are
distributed among ventral forebrain structures involved in
thermoregulation (15, 18) and are the predominant MCR mRNA subtypes
known to be expressed in rat brain (24). In contrast, mRNA encoding the
other principal MCR subtype reportedly expressed in the rat brain,
MC5-R, is of very low abundance, as it is not detectable by sensitive
RNase protection assay or in situ hybridization, but only by the
ultrasensitive polymerase chain reaction (1, 7). A very restricted
presence of MC1-R in a few cells in the midbrain has also been reported
(29). However, SHU-9119 is a full agonist of the MC5-R and MC1-R
subtypes (8), whereas it blocked the antipyretic effect of -MSH
administered either intraperitoneally (present study) or
intracerebroventricularly (9). Therefore, considered together with the
low abundance and/or restricted distribution of the putative
CNS-associated MC5-R and MC1-R, the data appear to rule out any role of
these MCR subtypes in mediating the antipyretic action of -MSH.
In summary, the present study demonstrates that, in the rat,
peripherally administered -MSH inhibits LPS-induced fever and suppresses LPS-induced plasma IL-6 and CS responses via different mechanisms. The antipyretic effect of -MSH is mediated by central MCR, whereas -MSH-induced suppression of IL-6 and CS responses to
LPS are not mediated centrally, or if so must involve a different central MCR population, and the effects of -MSH on IL-6 and CS levels do not contribute to its antipyretic action. These findings carry further significance beyond their direct implications concerning fever and HPA regulation, because they suggest that metabolic or other
CNS-associated effects of systemic -MSH (4, 16) may be mediated by
MCR located within the brain.
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ACKNOWLEDGEMENTS |
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We would like to thank Dr. Wei Yuan for preparing SHU-9119.
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FOOTNOTES |
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This work was supported by National Institutes of Health Grants MH-44694 (to J. B. Tatro) and DK-17420 (to V. J. Hruby).
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. §1734 solely to indicate this fact.
Address for reprint requests: J. B. Tatro, Division of Endocrinology, Diabetes, Metabolism and Molecular Medicine, Box 268, New England Medical Center, 750 Washington St., Boston, MA 02111.
Received 12 January 1998; accepted in final form 20 April 1998.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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1.
Alvaro, J. D.,
J. B. Tatro,
J. M. Quillan,
M. Fogliano,
M. Eisenhard,
M. R. Lerner,
E. J. Nestler,
and
R. S. Duman.
Morphine down-regulates melanocortin-4 receptor expression in brain regions that mediate opiate addiction.
Mol. Pharmacol.
50:
583-591,
1996[Abstract].
2.
Bock, M.,
J. Roth,
M. J. Kluger,
and
E. Zeisberger.
Antipyresis caused by stimulation of vasopressinergic neurons and intraseptal or systemic infusions of 
-MSH.
Am. J. Physiol.
266 (Regulatory Integrative Comp. Physiol. 35):
R614-R621,
1994
3.
Catania, A.,
and
J. M. Lipton.
-Melanocyte stimulating hormone in the modulation of host reactions.
Endocr. Rev.
14:
564-576,
1993[Medline].
4.
DeWied, D.,
and
J. Jolles.
Neuropeptides derived from pro-opiocortin: behavioral, physiological and neurochemical effects.
Physiol. Rev.
62:
976-1059,
1982
5.
Elmquist, J.,
T. Scammell,
and
C. Saper.
Mechanisms of CNS response to systemic immune challenge: the febrile response.
Trends Neurosci.
20:
565-570,
1997[Medline].
6.
Feng, J. D.,
T. Dao,
and
J. M. Lipton.
Effects of preoptic microinjections of alpha-MSH on fever and normal temperature control in rabbits.
Brain Res.
18:
473-477,
1987.
7.
Griffon, N.,
V. Mignon,
P. Facchinetti,
J. Diaz,
J. Schwartz,
and
P. Sokoloff.
Molecular cloning and characterization of the rat fifth melancortin receptor.
Biochem. Biophys. Res. Commun.
200:
1007-1014,
1994[Medline].
8.
Hruby, V. J.,
D. Lu,
S. D. Sharma,
A. L. Castrucci,
R. A. Kesterson,
F. A. Al-Obeidi,
M. E. Hadley,
and
R. D. Cone.
Cyclic lactam -melanotropin analogues of Ac-Nle4-cyclo[Asp5, D-Phe7, Lys10]--melanocyte-stimulating hormone-(4
10)-NH2 with bulky aromatic amino acids at position 7 show high antagonist potency and selectivity at specific melanocortin receptors.
J. Med. Chem.
38:
3454-3461,
1995[Medline].
9.
Huang, Q.-H.,
M. L. Entwistle,
J. D. Alvaro,
R. S. Duman,
V. J. Hruby,
and
J. B. Tatro.
Antipyretic role of endogenous melanocortins mediated by central melanocortin receptors during endotoxin-induced fever.
J. Neurosci.
17:
3343-3351,
1997
10.
Huang, Q.-H.,
A. Takaki,
and
A. Arimura.
Central noradrenergic system modulates plasma interleukin-6 production by peripheral interleukin-1.
Am. J. Physiol.
273 (Regulatory Integrative Comp. Physiol. 42):
R731-R738,
1997
11.
Klir, J. J.,
J. L. McClellan,
and
M. J. Kluger.
Interleukin-1 causes the increase in anterior hypothalamic interleukin-6 during LPS-induced fever in rats.
Am. J. Physiol.
266 (Regulatory Integrative Comp. Physiol. 35):
R1845-R1848,
1994
12.
Klir, J. J.,
J. Roth,
Z. Szelenyi,
J. L. McClellan,
and
M. J. Kluger.
Role of hypothalamic interleukin-6 and tumor necrosis factor-alpha in LPS fever in rat.
Am. J. Physiol.
265 (Regulatory Integrative Comp. Physiol. 34):
R512-R517,
1993.
13.
Kluger, M. J.
Fever: role of pyrogens and cryogens.
Physiol. Rev.
71:
93-127,
1991[Abstract].
14.
LeMay, L. G.
Role of interleukin 6 in fever in rats.
Am. J. Physiol.
258 (Regulatory Integrative Comp. Physiol. 27):
R798-R803,
1990
15.
Mountjoy, K. G.,
M. T. Mortrud,
M. J. Low,
R. B. Simerly,
and
R. D. Cone.
Localization of the melanocortin-4 receptor (MC4-R) in neuroendocrine and autonomic control circuits in the brain.
Mol. Endocrinol.
8:
1298-1308,
1994[Abstract].
16.
O'Donohue, T. L.,
and
D. M. Dorsa.
The opiomelanotropinergic neuronal and endocrine systems.
Peptides
3:
353-395,
1982[Medline].
17.
Rivier, C.,
R. Chizzonite,
and
W. Vale.
In the mouse, the activation of the hypothalamic-pituitary-adrenal axis by a lipopolysaccharide (endotoxin) is mediated through interleukin-1.
Endocrinology
125:
2800-2805,
1989[Abstract].
18.
Roselli-Rehfuss, L.,
K. G. Mountjoy,
L. S. Robbins,
M. T. Mortrud,
M. J. Low,
J. B. Tatro,
M. L. Entwistle,
R. B. Simerly,
and
R. D. Cone.
Identification of a receptor for POMC peptides in the medial basal hypothalamus and limbic system.
Proc. Natl. Acad. Sci. USA
90:
8856-8860,
1993
19.
Scheffé, H.
The Analysis of Variance. New York: Wiley, 1959.
20.
Shalts, E.,
Y.-J. Feng,
M. Ferin,
and
S. L. Wardlaw.
-Melanocyte-stimulating hormone antagonizes the neuroendocrine effects of corticotropin-releasing factor and interleukin-1- in the primate.
Endocrinology
131:
132-138,
1992[Abstract].
21.
Swanson, L. W.,
and
R. W. Lind.
Neural projections subserving the initiation of a specific motivated behavior in the rat; new projections from the subfornical organ.
Brain Res.
379:
399-403,
1986[Medline].
22.
Tatro, J. B.
Melanotropin receptors in the brain are differentially distributed and recognize both corticotropin and -melanocyte stimulating hormone.
Brain Res.
536:
124-132,
1990[Medline].
23.
Tatro, J. B.
Brain receptors for central and peripheral melanotropins.
Ann. NY Acad. Sci.
680:
621-625,
1993[Medline].
24.
Tatro, J. B. Melanocortin receptor expression and
function in the nervous system. In: The Melanocortin
Receptors, edited by R. D. Cone. Totowa, NJ:
Humana. In press.
25.
Tatro, J. B.,
and
M. L. Entwistle.
Distribution of melanocortin receptors in the lower brainstem of the rat.
Ann. NY Acad. Sci.
739:
311-314,
1994[Medline].
26.
Van der Kraan, M., R. A. H. Adan, M. E. Entwistle, W. H. Gispen, J. P. H. Burbach, and
J. B. Tatro. Expression of melanocortin 5 receptor in
secretory epithelia supports a functional role in exocrine and
endocrine glands. Endocrinology.
139:2348-2355.
27.
Van Houten, M.,
M. N. Khan,
R. J. Walsh,
G. B. Baquiran,
L. P. Renaud,
C. Bourque,
S. Sgro,
S. Gauthier,
M. Chretien,
and
B. I. Posner.
NH2-terminal specificity and axonal localization of adrenocorticotropin binding sites in rat median eminince.
Proc. Natl. Acad. Sci. USA
82:
1271-1275,
1985
28.
Wilson, J. F.
Low permeability of the blood-brain barrier to nanomolar concentrations of immunoreactive alpha-melanotropin.
Psychopharmacology (Berl.)
96:
262-266,
1988[Medline].
29.
Xia, Y.,
J. E. S. Wikberg,
and
V. Chhajlani.
Expression of melanocortin 1 receptor in periaqueductal gray matter.
Neuroreport
6:
2193-2196,
1995[Medline].
30.
Zimmer, J. A.,
and
J. M. Lipton.
Central and peripheral injections of ACTH-(124) reduce fever in adrenalectomized rabbits.
Peptides
2:
413-417,
1981[Medline].
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3 h. * P < 0.05 vs. LPS/Sal/Sal and LPS/
P < 0.05 vs.
LPS/
0.0001) and for
interaction (P = 0.003).
* P < 0.05 vs. all other
groups.
