(Hypertension. 1996;27:684-687.)
© 1996 American Heart Association, Inc.
Articles |
Mechanisms of Action of Atrial Natriuretic Factor and C-Type Natriuretic Peptide
From the Hypertension and Vascular Research Division, Department of Internal Medicine and Heart and Vascular Institute, Henry Ford Hospital, Detroit, Mich.
Correspondence to Janki Amin, MD, Hypertension and Vascular Research Division, Henry Ford Hospital, 2799 W Grand Blvd, Detroit, MI 48202.
 |
Abstract |
|---|
 Top Abstract IntroductionMethods Results Discussion References |
|---|
Abstract After secretion by the heart, atrial natriuretic factor (ANF) circulates in plasma, whereas C-type natriuretic peptide (CNP), which is found in abundance in the endothelium, may regulate vascular tone in a paracrine manner. However, there is little information on the effect of CNP on renal microvessels. We hypothesized that CNP dilates the afferent arteriole via the nitric oxide pathway, whereas ANF acts directly on vascular smooth muscle cells. When we perfused rat kidneys with minimal essential medium and bovine serum albumin at 100 mm Hg and examined the juxtamedullary afferent arterioles, neither CNP nor ANF was found to have any effect. When the peptides were added to arterioles preconstricted with norepinephrine, CNP and ANF dilated them in a similar fashion; diameters increased by 25±4% (n=7) and 29±6% (n=6) at 10-7 mol/L, respectively (P<.008). Pretreatment with 10-4 mol/L N-nitro-L-arginine methyl ester (L-NAME) or 5x10-6 mol/L indomethacin blocked CNP-induced dilation; dilation by ANF was unaffected by indomethacin (52±25%, n=5) and potentiated by L-NAME (73±14%, n=5). Thus, CNP dilates the afferent arterioles via the prostaglandin/nitric oxide pathway, whereas ANF dilates them directly. This difference may be important in controlling glomerular hemodynamics.
Key Words: nitric oxide • prostaglandins • renal hemodynamics
|
Introduction |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
Natriuretic peptides are important regulators of cardiovascular homeostasis through their actions on the vasculature, adrenal glands, kidneys, and brain.1 2 Although structurally similar, these peptides are encoded by separate genes and differ in their tissue distribution, receptor affinities, and biological actions.1 2 ANF and BNP are secreted largely by the heart and originally were considered circulating hormones. CNP was initially isolated from the porcine brain3 and was described as a neuromodulator because of its abundance in the central nervous system.4 5 In contrast to ANF or BNP, CNP is either undetectable5 or found at low levels6 7 in plasma; therefore, its peripheral actions are likely to be autocrine or paracrine in nature.
In the kidney, mRNA coding for CNP has been detected in the glomerulus, vasa recta bundle, and arcuate artery,8 whereas mRNA for its receptor is widely distributed, with relatively large amounts localized to the above structures as well as to distal nephron segments. Although CNP may have a role in the regulation of renal function, there is little information regarding its direct action on the renal microcirculation. In the present study, we compared the actions of CNP and ANF in the juxtamedullary Af-Art and determined whether NO or PGs might be involved.
|
Methods |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
We used the in vitro perfused juxtamedullary nephron preparation originally developed by Casellas and Navar.9 10 Male Sprague-Dawley rats weighing 350 to 400 g were anesthetized with pentobarbital sodium (40 mg/kg IP) and given an intravenous injection of heparin (300 U). The right renal artery was cannulated via the superior mesenteric artery and immediately perfused with ice-cold MEM (pH 7.4) containing 50 g/L BSA (Intergen). While still being perfused via the cannula, the kidney was removed and sectioned longitudinally, leaving the papilla intact in the dorsal two thirds. With the use of a stereomicroscope (model SZH; Olympus), small incisions were made in the lateral fornices, and the papilla was reflected back to expose the underlying pelvic cavity. The pelvic mucosa and the adipose and connective tissues overlying the inner cortical surface were removed, exposing the main branches of the renal artery, tubules, glomeruli, and related microvasculature of the juxtamedullary nephrons. Tight ligatures were placed around the distal ends of the large arteries so that the perfusate flowed only into the juxtamedullary nephrons arising from the proximal segments of the arterioles. The perfusate was administered with the use of 60-mL syringes, with driving force provided by a tank containing 95% O2/5% CO2. A small cannula positioned in the tip of a double-barreled perfusion cannula was connected to a DPM-II Universal pressure meter (Bio-Tek), allowing continuous measurement of renal perfusion pressure. Pressure was maintained at 100 mm Hg by adjusting an air regulator positioned between the tank and the syringes. The inner cortical surface of the kidney was continuously superfused with warmed MEM (37°C) containing 10 g/L BSA.
The perfusion chamber containing the prepared kidney was mounted on the movable stage of a Nikon microscope (Optiphot-2) equipped with water-immersion objectives (x4, x10, x20, and x40). The tissue was transilluminated, and the focused image was transferred via a high-resolution Newvicon camera (model NC-70m; Dage-MTI) and displayed on a video monitor (model PVM-1343MD; Sony) while simultaneously recording the video signal (model SLV-R5UC; Sony). An image-analysis system (Fryer) was used to measure luminal diameter.
Experimental Protocols
After the 20-minute equilibration
period, the Af-Art image was
recorded and the luminal perfusate was replaced with MEM
containing either CNP or ANF (Peninsula Laboratories) in concentrations
increasing from 10-12 to
10-7 mol/L. The Af-Art was observed for
10 minutes at each concentration.
Vessels perfused in vitro with a
synthetic solution have little
intrinsic tone, making it difficult to observe vasodilator responses.
Therefore, to examine the vasodilator action of CNP or ANF,
norepinephrine was added to the luminal perfusate
to decrease the diameter by 
30% to 40%. Then either CNP or ANF
(10-12 to
10-7 mol/L) was added, and
dose-response curves were obtained in the presence of
norepinephrine. Luminal diameter is reportedly reduced by
20% when juxtamedullary Af-Arts are perfused with
blood.11
After the equilibration period, L-NAME (Sigma Chemical Co), a compound that inhibits synthesis of NO, was added to the arterial perfusate at 10-4 mol/L and continued until the end of the experiment. Ten minutes later, we examined the effect of either CNP or ANF as described above.
Indomethacin (Sigma), a cyclooxygenase inhibitor, was dissolved in 0.02 mol/L Trizma base solution at a concentration of 5x10-3 mol/L. Indomethacin was added to the dissection solution at a final concentration of 5x10-6 mol/L from the beginning. In addition, indomethacin was added to the bath and arteriolar perfusate from the equilibration period to the end of the experiment and the effect of either CNP or ANF examined as described above.
Statistical Analysis
Values are expressed as mean±SEM,
and all statistical
analyses were carried out with absolute values. Student's
paired t test was used to examine whether the diameter at a
given concentration was different from the controls. ANCOVA was
used to examine whether dose-response curves differed between
groups, and a two-sample t test was used to examine
whether the change in diameter at a given concentration differed
between groups. A value of P<.008 was considered
significant using Bonferroni's adjustment for multiple
comparisons.
|
Results |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
Response to CNP or ANF in Nonpreconstricted Af-Arts
Luminal diameter was 17.8±2 µm (n=4) and 18.4±1.3 µm (n=4) before the addition of CNP and ANF, respectively. It remained unchanged during the application of CNP or ANF (17.1±2.3 µm at 10-7 mol/L CNP and 18.4±1.3 µm at 10-7 mol/L ANF).
Response to CNP or ANF in
Norepinephrine-Preconstricted Af-Arts
Fig 1
depicts the
effects of CNP and ANF on Af-Art
luminal diameter. Basal diameter in the CNP group was 20.1±1.3 µm
(n=7), which was reduced to 13.8±1.3 µm by
norepinephrine. Subsequent infusion of CNP at
10-12,
10-11,
10-10,
10-9,
10-8, and
10-7 mol/L dilated Af-Arts in a
dose-dependent manner; diameter increased from 13.8±1.3 µm to
15.1±1.2, 15.3±1.4, 15.3±1.2, 16.0±0.9,
16.7±0.9, and 17.0±1.1
µm, respectively.
|
In the ANF group, basal Af-Art diameter was 18.5±1.5 µm (n=6), which was reduced to 11.2±1.4 µm by norepinephrine. Subsequent infusion of ANF at 10-12, 10-11, 10-10, 10-9, 10-8, and 10-7 mol/L dilated Af-Arts in a similar dose-dependent fashion, increasing from 11.2±1.4 µm to 12.5±1.7, 12.6±1.3, 13.3±1.5, 14.6±1.5, 15.0±1.9, and 14.5±1.7 µm, respectively. There was no significant difference in vasodilator response between CNP and ANF (P>.05).
Pretreatment With L-NAME
L-NAME decreased basal diameter
significantly (from 18.9±0.8 to
16.6±0.9 µm), and it was reduced further to 11.7±1.9 µm
with
norepinephrine (n=5). As shown in Fig 2A, the
addition of CNP failed to induce dilation in the presence of L-NAME.
Fig 3 shows a comparison of CNP-induced changes in diameter
from the preconstricted level in the presence and absence of L-NAME.
Although CNP increased diameter by 3.2±0.3 µm at
10-7 mol/L in the absence of L-NAME,
this vasodilator response was completely blocked by L-NAME.
|
|
In the ANF
group, L-NAME decreased basal diameter from 21.0±2.4 to
16.7±1.1 µm (n=5), and it was reduced further to
11.9±1.2 µm by
norepinephrine. Fig 2B
shows ANF action in the absence and
presence of L-NAME. In marked contrast to the action of CNP, the
vasodilator action of ANF was not inhibited by L-NAME but rather was
augmented at high concentrations. As shown in Fig 4, the
increase in diameter induced by ANF at
10-7 mol/L was 3.2±0.6 µm without
L-NAME and 8.4±1.7 µm with L-NAME.
|
Pretreatment With Indomethacin
The diameter of the
indomethacin-treated
Af-Arts in the CNP group was 18.4±1.0 µm, which was reduced to
13.6±1.4 µm by norepinephrine (n=5). As with L-NAME,
indomethacin completely blocked the vasodilator action
of CNP (Fig 3).
In the ANF group, the diameter of the
indomethacin-treated Af-Arts was 19.8±1.8
µm, which was reduced further to 13.5±2.1 µm by
norepinephrine (n=5). In contrast to CNP, ANF still dilated
Af-Arts even in the presence of indomethacin,
increasing by 5.2±1.5 µm in diameter at
10-7 mol/L (Fig 4). The change in
diameter with and without indomethacin did not differ
for any dose of ANF.
|
Discussion |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
There are at least three receptors for natriuretic peptides.1 Two of them—GC-A and GC-B—contain intracellular guanylyl cyclase moieties. These receptors have different affinities for natriuretic peptides; GC-A specifically binds ANF and BNP, whereas GC-B binds CNP. The best understood peripheral CNP system is that found in the vasculature, where endothelial cells synthesize CNP7 12 and GC-B receptors are believed to be localized predominantly to vascular smooth muscle cells.
In the kidney, immunoreactivity and mRNA for CNP as well as GC-B receptor mRNA5 8 have been detected in the vasculature, including the arcuate artery, glomeruli, and vasa recta. However, little information is available regarding the action of CNP on the renal microcirculation. Our results clearly demonstrate that CNP and ANF have similar vasodilator actions on the juxtamedullary Af-Art; however, the mechanism involved appears to differ. Although CNP-induced dilation appears to require intact synthesis of NO and PG, ANF-induced dilation may be due to direct action on the vascular smooth muscle cells of the Af-Art. Such differences are inconsistent with the notion that the mechanisms of action of ANF and CNP are both mediated by elevation of intracellular cGMP. However, recent studies indicate that at least in some tissues, CNP can exert its action without elevating cGMP and is therefore independent of GC-B receptors.13
Despite the potent hypotensive action of CNP, intravenous or intrarenal infusion has been shown to cause little change in renal hemodynamics in anesthetized dogs14 and conscious sheep.15 The reason for the discrepancy between our findings and those of other investigators may be related to species differences, the presence or absence of factors such as changes in hemodynamics and neurohormones, or both. In addition, it is possible that unlike juxtamedullary nephrons, which represent only a small proportion of the total, Af-Arts of superficial nephrons may not dilate in response to CNP. Because the juxtamedullary nephron has an important role in the mechanism of urine concentration and therefore sodium homeostasis, selective dilation of the juxtamedullary Af-Art may help explain the natriuretic and diuretic actions of CNP in the absence of changes in total renal blood flow and glomerular filtration rate.
Consistent with its systemic hypotensive effect, CNP has been shown to relax strips obtained from the aorta and saphenous arteries and veins.16 Although renal veins dilated in response to CNP, renal arteries were unresponsive. Furthermore, removal of the endothelium either had no effect (in arteries) or potentiated the vasodilator response (in veins). In contrast, we observed that CNP dilated juxtamedullary Af-Arts and that this dilation was completely blocked by either L-NAME or indomethacin. Such blockade is not due to the inability of Af-Arts to dilate because ANF-induced dilation was not impaired. Although the reason for the discrepancy between our study and others is not clear, it may be due to differences in the species and vascular segments that were studied. It may also be related to differences in the preparation used; in our experiments, the Af-Art endothelium was exposed to luminal flow, which is a potent stimulus of NO and PG synthesis, and thus there might be some interaction between CNP and flow, as seen with angiotensin II.17
We observed that the vasodilator action of CNP on the juxtamedullary Af-Art can be blocked by either L-NAME or indomethacin. If CNP acts through both NO and PGs, then blockade of one system would at best blunt (not abolish) the response because the other system would compensate. Lahera et al18 19 reported that in anesthetized dogs, the renal vasodilator action of acetylcholine or bradykinin was not affected by blocking the synthesis of either NO or PGs alone. Thus, our results indicate that there are significant interactions between NO and PGs in mediating CNP action. Although the mechanism remains speculative, there are several previous studies (including ours) that indicate an interaction between NO and PGs (particularly PGI2) at various intracellular levels.20 21 22 23 24
The vasodilator action of ANF in the present study is consistent with that reported in a number of previous studies that examined the effects of ANF on the renal microvasculature.25 In marked contrast to the complete blockade of CNP-induced dilation, neither L-NAME nor indomethacin blocked ANF-induced dilation. Although the lack of effect of indomethacin is consistent with previous studies that involved isolated rat Af-Arts,26 the potentiation of ANF-induced dilation with L-NAME (although significant only at high ANF concentrations) is surprising. It may be that both ANF and NO exert dilator action via a common mechanism; thus, inhibition of endogenous NO (and therefore the mechanism involved) would enhance the response to activation of the same mechanism by ANF. For example, Moncada et al27 reported that supersensitivity to nitrovasodilators develops after inhibition of endogenous NO synthesis.
In conclusion, we have provided evidence that CNP and ANF dilate juxtamedullary Af-Arts via discrete mechanisms. Although CNP appears to act via NO and PGs, ANF-induced dilation may be due to its direct action on vascular smooth muscle cells. Such differences may be important under certain physiological and pathological conditions.
|
Selected Abbreviations and Acronyms |
|---|
|
|
Acknowledgments |
|---|
This study was supported by National Institutes of Health grants HL-46518 and HL-28982.
|
References |
|---|
|
TopAbstractIntroductionMethods Results Discussion References |
|---|
1. Jamison RL, Canaan-Kuhl S, Pratt R. The natriuretic peptides and their receptors. Am J Kidney Dis. 1992;20:519-530. [Medline] [Order article via Infotrieve]
2. Rosenzweig A, Seidman CE. Atrial natriuretic factor and related peptide hormones. Annu Rev Biochem. 1991;60:229-255. [Medline] [Order article via Infotrieve]
3. Sudoh T, Minamino N, Kangawa K, Matsuo H. C-type natriuretic peptide (CNP): a new member of the natriuretic peptide family identified in porcine brain. Biochem Biophys Res Commun. 1990;168:863-870. [Medline] [Order article via Infotrieve]
4. Kojima M, Minamino N, Kangawa K, Matsuo H. Cloning and sequence analysis of a cDNA encoding a precursor for rat C-type natriuretic peptide (CNP). FEBS Lett. 1990;276:209-213. [Medline] [Order article via Infotrieve]
5.
Komatsu Y, Nakao K, Suga S, Ogawa Y, Mudoyama M, Arai
H, Shirakami G, Hosoda K, Nakagawa O, Hama N, Kishimoto I, Imura
H. C-type natriuretic peptide (CNP) in rats and
humans. Endocrinology. 1991;129:1104-1106.
6.
Clavell AL, Stingo AJ, Wei C, Heublein DM, Burnett JC
Jr. C-type natriuretic peptide: a selective
cardiovascular peptide. Am J Physiol. 1993;264:R290-R295.
7.
Stingo AJ, Clavell AL, Heublein DM, Wei C, Burnett JC
Jr. Presence of C-type natriuretic peptide in cultured
human endothelial cells and plasma. Am J
Physiol. 1992;263:H1318-H1321.
8.
Yoshio T, Tomita K, Nonoguchi H, Yang T, Marumo
F. PCR localization of C-type natriuretic peptide
and B-type receptor mRNAs in rat nephron segments. Am J
Physiol. 1994;267:F215-F222.
9.
Casellas D, Navar LG. In vitro perfusion of
juxtamedullary nephrons in rats. Am J Physiol. 1984;246:F349-F358.
10.
Inscho EW, Carmines PK, Navar LG. Juxtamedullary
afferent arteriolar responses to P1 and P2
purinergic stimulation. Hypertension. 1991;17:1033-1037.
11.
Imig JD, Gebremedhin D, Harder DR, Roman RJ.
Modulation of vascular tone in renal microcirculation by erythrocytes:
role of EDRF. Am J Physiol. 1993;264:H190-H195.
12. Suga S, Nakao K, Ito H, Komatsu Y, Ogawa Y, Hama N, Imura H. Endothelial production of C-type natriuretic peptide and its marked augmentation by transforming growth factor-ß: possible existence of `vascular natriuretic peptide system.' J Clin Invest. 1992;90:1145-1149.
13.
Trachte GJ, Drewett JG. C-type
natriuretic peptide neuromodulates independently of
guanylyl cyclase activation. Hypertension. 1994;23:38-43.
14.
Stingo AJ, Clavell AL, Aarhus LL, Burnett JC Jr.
Cardiovascular and renal actions of C-type
natriuretic peptide. Am J Physiol. 1992;262:H308-H312.
15.
Charles CJ, Espiner EA, Richards MA, Nicholls GM,
Yandle TG. Biological actions and pharmacokinetics of C-type
natriuretic peptide in conscious sheep. Am J
Physiol. 1995;268:R201-R207.
16.
Wei C, Aarhus LL, Miller VM, Burnett JC Jr. Action of
C-type natriuretic peptide in isolated canine arteries and
veins. Am J Physiol. 1993;264:H71-H73.
17. Juncos LA, Arima S, Garvin J, Carretero OA, Ito S. Flow modulation of myogenic response and angiotensin II (Ang II) action in isolated microperfused rabbit afferent arterioles (Af-Arts). J Hypertens. 1994;12(suppl 3):S6. Abstract.
18.
Lahera V, Salom MG, Fiksen-Olsen MJ, Raij L, Romero
CJ. Effects of
NG-monomethyl-L-arginine
and L-arginine on acetylcholine renal response.
Hypertension. 1990;15:659-663.
19. Lahera V, Salom MG, Fiksen-Olsen MJ, Romero CJ. Mediatory role of endothelium-derived nitric oxide in renal vasodilatory and excretory effects of bradykinin. Am J Hypertens. 1991;4:260-262. [Medline] [Order article via Infotrieve]
20. Arima S, Ren Y, Juncos LA, Carretero OA, Ito S. Glomerular prostaglandins modulate vascular reactivity of the downstream efferent arterioles. Kidney Int. 1994;45:650-658. [Medline] [Order article via Infotrieve]
21. Shimokawa H, Flavahan NA, Lorenz RR, Vanhoutte PM. Prostacyclin releases endothelium-derived relaxing factor and potentiates its action in coronary arteries of the pig. Br J Pharmacol. 1988;95:1197-1203. [Medline] [Order article via Infotrieve]
22. Whorton AR, Collawn JB, Montgomery ME, Young SL, Kent RS. Arachidonic acid metabolism in cultured aortic endothelial cells: effect of cAMP and 3-isobutyl-1-methylxanthine. Biochem Pharmacol. 1985;34:119-123. [Medline] [Order article via Infotrieve]
23.
Salvemini D, Misko TP, Masferrer JL, Seibert K, Currie
MG, Needleman P. Nitric oxide activates
cyclooxygenase enzymes. Proc Natl
Acad Sci U S A. 1993;90:7240-7244.
24. Graier WF, Groschner K, Schmidt K, Kukovetz WR. Increases in endothelial cyclic AMP levels amplify agonist-induced formation of endothelium-derived relaxing factor (EDRF). Biochem J. 1992;288:345-349.
25.
Veldkamp PJ, Carmines PK, Inscho EW, Navar LG.
Direct evaluation of the microvascular action of ANP in juxtamedullary
nephrons. Am J Physiol. 1988;254:F440-F444.
26.
Lanese DM, Yuan BH, Falk SA, Conger JD. Effects
of atriopeptine III on isolated rat afferent and efferent
arterioles. Am J Physiol. 1991;261:F1102-F1109.
27.
Moncada S, Rees DD, Schulz R, Palmer MJ.
Development and mechanism of a specific supersensitivity to
nitrovasodilators after inhibition of vascular nitric oxide
synthesis in vivo. Proc Natl Acad Sci
U S A. 1991;88:2166-2170.
This article has been cited by other articles:
 |
|
 |
|
  A. Simon, E. O. Harrington, G. X. Liu, G. Koren, and G. Choudhary Mechanism of C-type natriuretic peptide-induced endothelial cell hyperpolarization Am J Physiol Lung Cell Mol Physiol, February 1, 2009; 296(2): L248 - L256. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Jankowska, B. Burczynska, T. Duda, J. B. Warchol, and R. K. Sharma Calcium-Modulated Rod Outer Segment Membrane Guanylate Cyclase Type 1 Transduction Machinery in the Testes J Androl, January 1, 2007; 28(1): 50 - 58. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. S. Andrew and S. Kaufman Guanylyl cyclase mediates ANP-induced vasoconstriction of murine splenic vessels Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2003; 284(6): R1567 - R1571. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. J.M Best, J. C Burnett Jr., S. H Wilson, D. R Holmes Jr., and A. Lerman Dendroaspis natriuretic peptide relaxes isolated human arteries and veins Cardiovasc Res, August 1, 2002; 55(2): 375 - 384. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Brunner and G. Wolkart Relaxant effect of C-type natriuretic peptide involves endothelium and nitric oxide-cGMP system in rat coronary microvasculature Cardiovasc Res, August 15, 2001; 51(3): 577 - 584. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. W. Wennberg, V. M. Miller, T. Rabelink, and J. C. Burnett Jr. Further attenuation of endothelium-dependent relaxation imparted by natriuretic peptide receptor antagonism Am J Physiol Heart Circ Physiol, October 1, 1999; 277(4): H1618 - H1621. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. L. Woods and M. J. M. Jones Atrial, B-type, and C-type natriuretic peptides cause mesenteric vasoconstriction in conscious dogs Am J Physiol Regulatory Integrative Comp Physiol, May 1, 1999; 276(5): R1443 - R1452. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Zellner, A. A. Protter, E. Ko, M. R. Pothireddy, T. DeMarco, S. J. Hutchison, T. M. Chou, K. Chatterjee, and K. Sudhir Coronary vasodilator effects of BNP: mechanisms of action in coronary conductance and resistance arteries Am J Physiol Heart Circ Physiol, March 1, 1999; 276(3): H1049 - H1057. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Beaulieu, R. Cardinal, P. Page, F. Francoeur, J. Tremblay, and C. Lambert Positive chronotropic and inotropic effects of C-type natriuretic peptide in dogs Am J Physiol Heart Circ Physiol, October 1, 1997; 273(4): H1933 - H1940. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||