| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Institut für Vegetative Physiologie und Pathophysiologie, Universität Hamburg, D-20246 Hamburg, Germany
IN THE
1980S A REVOLUTION took place in cardiovascular
physiology unnoticed by many researchers working in the field. At that time, the rat and the dog were the prime animal models to study integrative mechanisms involved in cardiovascular regulation. The
notorious but true saying that cells do not have a blood pressure implies that in vivo experiments will always be critical in the process
of discovering new principles of circulatory control. Studies in rats
and dogs have helped to unravel many basic principles of cardiovascular
physiology, such as autoregulation of blood flow (11, 28),
reflex control of blood pressure (3), or blood volume
regulation through signals originating from the heart (2),
to name just a few. Nevertheless, the lack of techniques to directly
link the activity of specific genes to physiological functions Today, more than 3,000 different knockout mice have been
constructed. Many of these mutations affect cardiovascular function, and some of them have helped to solve long-standing open questions in
cardiovascular regulation. For example, it has been known for long that
the tubuloglomerular feedback (TGF) is a key mechanism of
autoregulation of renal blood flow and glomerular filtration and is
intimately involved in blood volume homeostasis. In the kidney, the
proximal part of the distal tubule gets in close contact with the
afferent arteriole to form the juxtaglomerular apparatus. Within this
region, the TGF communicates changes in proximal tubular flow rate to
afferent arteriolar smooth muscle and renin-secreting cells, causing a
decrease in vascular tone and an increase in renin secretion rate if
tubular flow rate falls and vice versa. Twenty years ago it was
postulated that changes in local adenosine concentrations contribute to
the signaling mechanism underlying the TGF response; however,
participation of adenosine has remained controversial. Now two
independent groups of investigators reported that mice carrying a
targeted deletion of the A1-adenosine receptor, which is
expressed at a high level in the juxtaglomerular apparatus, completely
lack a TGF response (5, 34). These studies clearly demonstrate that adenosine, the major agonist of
A1-adenosine receptors, plays an essential role in the
signaling cascade mediating the TGF. Future studies will have to show
whether this role is that of a mediator or a modulator (25,
29).
This example illustrates the major strength of the genetic approach
compared with the more classical pharmacological and correlative approaches. Although the latter are inherently indirect,
pharmacological studies often suffer from uncertain pharmacokinetics
and a lack of specificity. Accordingly, the observation of a sevenfold
higher salt intake after an overnight fluid restriction in mice
carrying a targeted deletion of the oxytocin gene constitutes strong
direct evidence for the concept derived from infusion studies of
agonists and antagonists that sodium appetite is negatively regulated
by central oxytocin (1). The finding that mice lacking
tumor necrosis factor- In accordance with its increasing importance in cardiovascular
research, the basic physiology of the murine circulatory system has
been intensively studied recently. Most relevant techniques and
experimental protocols to assess cardiovascular function have now been
adapted to the small size of the mouse. These include chronic
measurements of blood pressure (6, 14, 21, 23) and cardiac
output (16), the analysis of the different components of
the baroreceptor reflex (22), and renal function and
balance studies (21). Many aspects of the murine
cardiovascular system Nevertheless, there are also important peculiarities specific to the
mouse. For example, studies using autonomic blocking agents indicate
that mice generate a high resting cardiac sympathetic tone (14,
17). Mice have a relatively labile blood pressure and are
extremely sensitive to stressful conditions such as anesthesia (21) and changes in ambient temperature (37).
Sympathetic neurotransmitter release is also enhanced by stressful
housing conditions, such as social deprivation and exposure to novel
odors (9). A negative energy balance can cause severe
hypotension and bradycardia in mice, possibly resulting in
torporlike states (37). The development of hypotension is
accelerated if mice are housed at an ambient temperature of 23°C,
which is the normal room temperature in most laboratories. Dietary
preferences (31) as well as metabolic responses to leptin
(13) differ between strains and can confound
cardiovascular measurements. The metabolism of melatonin is also strain
dependent (18), which may impact on circadian
cardiovascular rhythms. These factors need to be considered when
designing experiments in mice.
It is very likely that targeted deletions will be introduced into most
of the mouse's ~30,000 genes within the next few years. Keeping in
mind the murine peculiarities listed above, the combination of mouse
genetics and physiology seems to have a bright future. There are,
however, several caveats. Most importantly, the vast majority of
targeted deletions inactivate the target gene in each cell from
conception onward. Such a lifelong deletion of gene function cannot
only severely alter developmental processes, but might also disturb the
normal homeostatic balance, causing secondary and/or compensatory up-
and downregulation at the level of the genome as well as the level of
the organism. Thus more subtle genetic constructs will be required,
such as conditional targeted deletions and combinations of gene
inactivations with the introduction of transgenes that restrict the
expression of a specific gene to a limited area (e.g., in the central
nervous system) or time (e.g., during development) (10,
20). Furthermore, although gene targeting is a very efficient
way to investigate the function of a certain gene, it is considerably
less powerful to uncover the genetic pathways underlying a given
physiological process, particularly if the biology of this process is
only poorly understood. In this latter situation, mutagenesis screens
are much more likely to yield new insights. Such screens, however,
require huge numbers of animals to be generated, housed, and
phenotyped. Even though mutagenesis screens are already performed in
mice, they can be realized much easier in the zebrafish (4,
26). And, finally, despite all the similarities between mice,
rat, and humans, we will always need research that translates the
results obtained in mice to the human physiology and pathophysiology
(12).
ARTICLE
TOP
ARTICLE
REFERENCES
which
was then possible already in cellular systemsremained a major
drawback. Thus the development of experimental procedures to induce
mutations in single genes and the eventual successful generation of
mice carrying a targeted mutation in 1989 (7, 19) marked
the beginning of a new era area also in cardiovascular physiology.
(TNF-) display threefold elevated renal
renin mRNA levels under control conditions as well as after salt
depletion provides the first in vivo evidence for a possible
physiological function of TNF- as a negative regulator of renin
synthesis (35). Studies in TNF- 
/ mice also
indicate that a strong increase in the local production of TNF-
initiates intimal hyperplasia after vascular injury (38).
Further examples for important advances in our understanding of
cardiovascular regulation obtained by the use of gene-targeted mice are
the discovery of a major role of the K+ channel 
-subunit
KCNE1 in K+ and renal fluid homeostasis (36),
the unmasking of an enhanced central response to dehydration in
angiotensin AT1A / mice (24), the
identification of multiple physiological functions of
2-adrenergic receptors (27),and
the demonstration that the vagal effects on atrial rate are independent
from M3-muscarinic receptor signaling (33).
anatomic and physiologicalare identical to
larger mammals. Nearly all values of cardiovascular parameters obtained
in mice are well within the range predicted by allometric scaling
equations from rats and humans (15). The baroreceptor
reflex (22) and the regulation of fluid and electrolyte
homeostasis by the renin-angiotensin system (8), two of
the major blood pressure regulating systems (30, 32), seem
to function in a very similar fashion as in larger mammals.
| |
FOOTNOTES |
|---|
Address for reprint requests and other correspondence: H. Ehmke, Institut für Vegetative Physiologie und Pathophysiologie, Universität Hamburg, Martinistrasse 52, D-20246 Hamburg, Germany (E-mail: ehmke{at}uke.uni-hamburg.de).
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.
10.1152/ajpregu.00531.2002
| |
REFERENCES |
|---|
|
TOP
ARTICLE
REFERENCES
|
|---|
1.
Amico, JA,
Morris M,
and
Vollmer RR.
Mice deficient in oxytocin manifest increased saline consumption following overnight fluid deprivation.
Am J Physiol Regul Integr Comp Physiol
281:
R1368-R1373,
2001
2.
Andersen, JL,
Sandgaard NCF,
and
Bie P.
Volume expansion during acute angiotensin II receptor (AT1) blockade and NOS inhibition in conscious dogs.
Am J Physiol Regul Integr Comp Physiol
282:
R1140-R1148,
2002
3.
Baldridge, BR,
Burgess DE,
Zimmerman EE,
Carroll JJ,
Sprinkle AG,
Speakman RO,
Li SG,
Brown DR,
Taylor RF,
Dworkin S,
and
Randall DC.
Heart rate-arterial blood pressure relationship in conscious rat before vs. after spinal cord transection.
Am J Physiol Regul Integr Comp Physiol
283:
R748-R756,
2002
4.
Briggs, JP.
The zebrafish: a new model organism for integrative physiology.
Am J Physiol Regul Integr Comp Physiol
282:
R3-R9,
2002
5.
Brown, R,
Ollerstam A,
Johansson B,
Skøtt O,
Gebre-Medhin S,
Fredholm B,
and
Persson AEG
Abolished tubuloglomerular feedback and increased plasma renin in adenosine A1 receptor-deficient mice.
Am J Physiol Regul Integr Comp Physiol
281:
R1362-R1367,
2001
6.
Butz, GM,
and
Davisson RL.
Long-term telemetric measurement of cardiovascular parameters in awake mice: a physiological genomics tool.
Physiol Genomics
5:
89-97,
2001
7.
Capecchi, MR.
Altering the genome by homologous recombination.
Science
244:
1288-1292,
1989
8.
Cholewa, BC,
and
Mattson DL.
Role of the renin-angiotensin system during alterations of sodium intake in conscious mice.
Am J Physiol Regul Integr Comp Physiol
281:
R987-R993,
2001
9.
D'Arbe, M,
Einstein R,
and
Lavidis NA.
Stressful animal housing conditions and their potential effect on sympathetic neurotransmission in mice.
Am J Physiol Regul Integr Comp Physiol
282:
R1422-R1428,
2002
10.
Dono, R,
Faulhaber J,
Galli A,
Zuniga A,
Volk T,
Texido G,
Zeller R,
and
Ehmke H.
FGF2 signaling is required for the development of neuronal circuits regulating blood pressure.
Circ Res
90:
E5-E10,
2002
11.
Feng, MG,
Dukacz SAW,
and
Kline RL.
Selective effect of tempol on renal medullary hemodynamics in spontaneously hypertensive rats.
Am J Physiol Regul Integr Comp Physiol
281:
R1420-R1425,
2001
12.
Hall, JE.
The promise of translational physiology.
Am J Physiol Regul Integr Comp Physiol
282:
R1259-R1260,
2002
13.
Harris, RBS,
Mitchell TD,
Yan X,
Simpson JS,
and
Redmann SM, Jr.
Metabolic responses to leptin in obese db/db mice are strain dependent.
Am J Physiol Regul Integr Comp Physiol
281:
R115-R132,
2001
14.
Janssen, BJA,
Leenders PJA,
and
Smits JFM
Short-term and long-term blood pressure and heart rate variability in the mouse.
Am J Physiol Regul Integr Comp Physiol
278:
R215-R225,
2000
15.
Janssen, BJA,
and
Smits JFM
Autonomic control of blood pressure in mice: basic physiology and effects of genetic modification.
Am J Physiol Regul Integr Comp Physiol
282:
R1545-R1556,
2002
16.
Janssen, B,
Debets J,
Leenders P,
and
Smits J.
Chronic measurement of cardiac output in conscious mice.
Am J Physiol Regul Integr Comp Physiol
282:
R928-R935,
2002
17.
Just, A,
Faulhaber J,
and
Ehmke H.
Autonomic cardiovascular control in conscious mice.
Am J Physiol Regul Integr Comp Physiol
279:
R2214-R2221,
2000
18.
Kennaway, DJ,
Voultsios A,
Varcoe TJ,
and
Moyer RW.
Melatonin in mice: rhythms, response to light, adrenergic stimulation, and metabolism.
Am J Physiol Regul Integr Comp Physiol
282:
R358-R365,
2002
19.
Koller, BH,
Hagemann LJ,
Doetschman T,
Hagaman JR,
Huang S,
Williams PJ,
First NL,
Maeda N,
and
Smithies O.
Germ-line transmission of a planned alteration made in a hypoxanthine phosphoribosyltransferase gene by homologous recombination in embryonic stem cells.
Proc Natl Acad Sci USA
86:
8927-8931,
1989
20.
Lazartigues, E,
Dunlay SM,
Loihl AK,
Sinnayah P,
Lang JA,
Espelund JJ,
Sigmund CD,
and
Davisson RL.
Brain-selective overexpression of angiotensin (AT1) receptors causes enhanced cardiovascular sensitivity in transgenic mice.
Circ Res
90:
617-624,
2002
21.
Lorenz, JN.
A practical guide to evaluating cardiovascular, renal, and pulmonary function in mice.
Am J Physiol Regul Integr Comp Physiol
282:
R1565-R1582,
2002
22.
Ma, X,
Abboud FM,
and
Chapleau MW.
Analysis of afferent, central and efferent components of the baroreceptor reflex in mice.
Am J Physiol Regul Integr Comp Physiol
283:
R1033-R1040,
2002
23.
Mattson, DL.
Long-term measurement of arterial blood pressure in conscious mice.
Am J Physiol Regul Integr Comp Physiol
274:
R564-R570,
1998
24.
Morris, M,
Means S,
Oliverio MI,
and
Coffman TM.
Enhanced central response to dehydration in mice lacking angiotensin AT1a receptors.
Am J Physiol Regul Integr Comp Physiol
280:
R1177-R1184,
2001
25.
Nishiyama, A,
and
Navar LG.
ATP mediates tubuloglomerular feedback.
Am J Physiol Regul Integr Comp Physiol
283:
R273-R275,
2002
26.
Patton, EE,
and
Zon LI.
The art and design of genetic screens: zebrafish.
Nat Rev Genet
2:
956-966,
2001[Web of Science][Medline].
27.
Philipp, M,
Brede M,
and
Hein L.
Physiological significance of 2-adrenergic receptor subtype diversity: one receptor is not enough.
Am J Physiol Regul Integr Comp Physiol
283:
R287-R295,
2002
28.
Sandgaard, NCF,
Andersen JL,
Holstein-Rathlou NN,
and
Bie P.
Aortic blood flow subtraction: an alternative method for measuring total renal blood flow in conscious dogs.
Am J Physiol Regul Integr Comp Physiol
282:
R1528-R1535,
2002
29.
Schnermann, J.
Adenosine mediates tubuloglomerular responses.
Am J Physiol Regul Integr Comp Physiol
283:
R276-R277,
2002
30.
Skøtt, O.
Renin.
Am J Physiol Regul Integr Comp Physiol
282:
R937-R939,
2002
31.
Smith, BK,
Volaufova J,
and
West DB.
Increased flavor preference and lick activity for sucrose and corn oil in SWR/J vs. AKR/J mice.
Am J Physiol Regul Integr Comp Physiol
281:
R596-R606,
2001
32.
Stauss, HM.
Baroreceptor reflex function.
Am J Physiol Regul Integr Comp Physiol
283:
R284-R286,
2002
33.
Stengel, PW,
Yamada M,
Wess J,
and
Cohen ML.
M3-receptor knockout mice: muscarinic receptor function in atria, stomach fundus, urinary bladder, and trachea.
Am J Physiol Regul Integr Comp Physiol
282:
R1443-R1449,
2002
34.
Sun, D,
Samuelson LC,
Yang T,
Huang Y,
Paliege A,
Saunders T,
Briggs J,
and
Schnermann J.
Mediation of tubuloglomerular feedback by adenosine: evidence from mice lacking adenosine 1 receptors.
Proc Natl Acad Sci USA
98:
9983-9988,
2001
35.
Todorov, V,
Muller M,
Schweda F,
and
Kurtz A.
Tumor necrosis factor- inhibits renin gene expression.
Am J Physiol Regul Integr Comp Physiol
283:
R1046-R1051,
2002
36.
Warth, R,
and
Barhanin J.
The multifaceted phenotype of the knockout mouse for the KCNE1 potassium channel gene.
Am J Physiol Regul Integr Comp Physiol
282:
R639-R648,
2002
37.
Williams, TD,
Chambers JB,
Henderson RP,
Rashotte ME,
and
Overton JM.
Cardiovascular responses to caloric restriction and thermoneutrality in C57BL/6J mice.
Am J Physiol Regul Integr Comp Physiol
282:
R1459-R1467,
2002
38.
Zimmerman, MA,
Selzman CH,
Reznikov LL,
Miller SA,
Raeburn CD,
Emmick J,
Meng X,
and
Harken AH.
Lack of TNF- attenuates intimal hyperplasia after mouse carotid artery injury.
Am J Physiol Regul Integr Comp Physiol
283:
R505-R512,
2002
This article has been cited by other articles:
|
|
 |
|
  M. E. Reichelt, L. Willems, J. G. Molina, C.-X. Sun, J. C. Noble, K. J. Ashton, J. Schnermann, M. R. Blackburn, and J. P. Headrick Genetic Deletion of the A1 Adenosine Receptor Limits Myocardial Ischemic Tolerance Circ. Res., February 18, 2005; 96(3): 363 - 367. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
