Perrella, Mark A.

The pulmonary and renal vasculatures, in contrast to the systemic vasculature, constrict during hypoxia. The endothelium has been implicated in mediating these vascular responses to acute hypoxia via the production of endothelium-derived vasoactive factors. The present study, performed in anesthetized dogs, was designed to investigate the role of endothelium-derived relaxing factor (EDRF) to attenuate the vasoconstrictor response of the pulmonary and renal circulations during acute hypoxia. In response to hypoxia, pulmonary (2.2 +/- 0.3 to 4.5 +/- 0.6 mmHg.l-1.min) and renal (0.60 +/- 0.07 to 0.90 +/- 0.14 mmHg.ml-1.min) vascular resistances increased. Inhibition of endogenous EDRF with NG-monomethyl-L-arginine resulted in similar increases in pulmonary (3.0 +/- 0.1 to 4.8 +/- 0.4 mmHg.l-1.min) and renal (0.67 +/- 0.07 to 0.90 +/- 0.09 mmHg.ml-1.min) vascular resistances as in hypoxia. However, in the presence of both hypoxia and EDRF inhibition, an exaggerated pulmonary vascular response was observed (2.2 +/- 0.2 to 7.4 +/- 0.9 mmHg.l-1.min), in contrast to the renal vascular response to EDRF inhibition during hypoxia (0.61 +/- 0.05 to 0.95 +/- 0.10 mmHg.ml-1.min), which was not different from hypoxia or EDRF inhibition individually. The endothelium-derived contracting factor endothelin, which modestly increased during hypoxia (11.7 +/- 1.9 to 15.6 +/- 2.4 pg/ml), may also contribute to this vasoconstrictive response to hypoxia. This study suggests in the intact animal that EDRF serves to oppose the pulmonary vasoconstrictor response to hypoxia and further characterizes the role of endothelium-derived factors in the regulation of vascular function during hypoxia.

The endothelium has emerged as an important modulator of vascular tone by producing both vasodilating and vasoconstricting substances. In vitro studies have demonstrated that endothelial cells produce endothelium-derived relaxing factor (EDRF), which promotes vasodilation via the stimulation of intracellular guanosine 3',5'-cyclic monophosphate (cGMP). However, the role of EDRF in the basal regulation of cardiopulmonary and renal function is not well defined. The present study was therefore designed to assess the function of EDRF by studying two groups of normal anesthetized dogs, of which one received a competitive inhibitor to EDRF generation, NG-monomethyl-L-arginine (L-NMMA; 50 micrograms.kg-1.min-1 iv), and the other received a vehicle. The L-NMMA infusion produced no significant increase in mean arterial pressure but marked increases in systemic, pulmonary, and renal vascular resistances compared with the vehicle group. Although renal blood flow decreased with L-NMMA, no changes were observed in glomerular filtration rate or sodium excretion. Associated with the cardiopulmonary and renal responses with L-NMMA was a modest increase in plasma endothelin (7.9 +/- 1.3 to 10.2 +/- 1.8 pg/ml, P less than 0.05), an endothelium-derived vasoconstrictor. No alteration was observed in plasma or urinary cGMP with EDRF inhibition. These cardiopulmonary and renal responses with L-NMMA may be attributed not only to EDRF inhibition but to an imbalance between endothelium-derived relaxing and contracting factors.

Systemic inhibition of nitric oxide synthesis with NG-monomethyl-L-arginine (L-NMMA) increases renal perfusion pressure (RPP) and urinary sodium excretion. Increased RPP has been proposed as one of the mechanisms for the natriuresis caused by intravenous infusion of L-NMMA. We tested the hypothesis that increases in renal interstitial hydrostatic pressure (RIHP) are required for the natriuresis of L-NMMA infusion. Experiments were performed in four groups of Sprague-Dawley rats in which partial aortic clamping and/or bilateral renal decapsulation was performed to control RPP and RIHP. Infusion of L-NMMA (15 mg/kg bolus + 500 micrograms.kg-1 x min-1 continuous infusion) increased RPP (delta+ 14 +/- 1 mmHg), RIHP (delta+ 3.6 +/- 0.7 mmHg), and fractional excretion of sodium (FENa; delta 2.4 +/- 0.6%, P < 0.005). When RPP was prevented from increasing by controlling RPP with an adjustable clamp around the suprarenal aorta, RIHP and FENa did not significantly change. When only RIHP was held constant by bilateral renal decapsulation, FENa was not significantly increased (delta+ 0.68 +/- 0.36%, not significant), despite a significant rise in RPP (delta+ 18 +/- 2 mmHg, P < 0.001). Control of both RPP and RIHP prevented the increase in FENa. Thus, when renal interstitial pressure was controlled, the infusion of L-NMMA did not result in an increase in FENa. These results demonstrate that an increase in RIHP is a necessary component in the natriuresis due to systemic infusion of L-NMMA.

Previous studies have demonstrated that the biological actions of atrial natriuretic factor (ANF) are mediated via increases in its intracellular second messenger guanosine 3',5'-cyclic monophosphate (cGMP). Because cGMP egresses rapidly from target cells after ANF binding to particulate guanylate cyclase-linked receptors, extracellular cGMP may be a useful biological marker for the action of ANF in vivo under pathophysiological conditions. The present studies tested the hypothesis that the avid sodium retention and renal ANF resistance characteristic of chronic congestive heart failure (CHF) are associated with attenuated renal cGMP responses to ANF. We assessed the natriuretic and cGMP responses to endogenous and exogenous ANF during the evolution of CHF produced by 6 days of rapid ventricular pacing in conscious dogs (n = 6). Simultaneous measurement of plasma and urinary cGMP concentrations allowed determination of the net renal generation of cGMP, an indicator of the renal contribution to total urinary cGMP excretion. In early CHF, increased sodium excretion and renal cGMP production were observed in association with increases in plasma ANF. Exogenous ANF administration (10 micrograms/kg iv) before CHF also produced parallel increases in sodium excretion and renal cGMP production. In more advanced CHF produced by 6 days of pacing, we observed avid sodium retention in association with reversal of earlier increases in renal cGMP production despite progressive increases in circulating ANF. Natriuretic and renal cGMP responses to exogenous ANF were similarly attenuated in chronic CHF. These studies suggest that 1) renal cGMP production is a useful biological marker for the renal natriuretic action of ANF; 2) endogenous ANF contributes to the maintenance of sodium excretion in early CHF via increases in renal cGMP production; and 3) the avid sodium retention and renal ANF resistance in advanced CHF are, in part, linked to attenuated renal cGMP responses to endogenous and exogenous ANF.

Atrial natriuretic factor (ANF) is a circulating 28-amino acid peptide that functions in the regulation of sodium homeostasis and vascular tone. ANF metabolism occurs via degradation by neutral endopeptidase 24.11 and binding to the ANF clearance receptor (ANFR-C). The present study was performed on anesthetized dogs, normal (control) and with experimental congestive heart failure (CHF), and was designed to investigate the ability of an ANF ligand specific for ANFR-C [C-ANF-(4-23)] to increase plasma ANF and also to evaluate the influence of ANFR-C on regional pulmonary and renal ANF clearances. C-ANF-(4-23) increased plasma ANF in controls (51 +/- 15 to 123 +/- 39 pg/ml; P < 0.05) and further increased plasma ANF in CHF dogs (242 +/- 30 to 327 +/- 34; P < 0.05), demonstrating that ANFR-C plays a significant role in the overall metabolism and clearance of ANF, even with chronically elevated ANF. Infusion of C-ANF-(4-23) produced a marked decrease in ANF pulmonary clearance (PCLANF) in controls (1,018 +/- 405 to -286 +/- 383 ml/min; P < 0.05); however, PCLANF was not altered by the ANF ligand in CHF dogs [-137 +/- 174 to -106 +/- 226 ml/min; not significant (NS)], suggesting an occupancy of ANFR-C or a downregulation of this receptor with chronically elevated plasma ANF. ANF renal clearance (RCLANF) was not altered in either group by C-ANF-(4-23) infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Congestive heart failure (CHF) is a pathophysiological condition associated with increased plasma levels of atrial natriuretic factor (ANF), a peptide hormone of cardiac origin that participates in the homeostatic control of intravascular volume and vascular tone. Atrial myocytes serve as the principal source of ANF under physiological conditions, although recent studies have demonstrated that ventricular myocardium may also synthesize ANF in models of CHF associated with ventricular hypertrophy. The current study was designed to investigate the roles of atrial and ventricular myocardium to synthesize, store, and release ANF during the evolution of tachycardia-induced CHF in the dog. The present study demonstrates a persistent elevation of plasma ANF during the evolution of CHF. In acute CHF (3 h), plasma ANF increased independent of cardiac ANF synthesis. In chronic CHF (15 and 30 days), plasma ANF is maintained by an increase in atrial synthesis and release of the peptide, without recruitment of ventricular ANF synthesis. The present study demonstrates that in acute CHF the increase in plasma ANF is regulated by release of stored peptide, and in chronic CHF the persistent elevation of plasma ANF is maintained by an increase in atrial synthesis of ANF.

BACKGROUND Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) are a family of structurally related peptides that participate in the integrated control of renal and cardiovascular function. Previous studies suggest a functional role for these hormonal peptides in cardiorenal regulation in congestive heart failure (CHF). METHODS AND RESULTS The present studies were performed in normal subjects (n = 6) and in patients with mild (New York Heart Association [NYHA] class I to II, n = 20) and severe (NYHA class III to IV, n = 20) CHF by use of radioimmunoassay and immunohistochemical staining (IHCS). Plasma ANP was significantly increased in both mild and severe CHF compared with normal subjects. In contrast, plasma BNP was only moderately increased in the severe CHF group, and plasma CNP concentration was unchanged in CHF compared with normal subjects. Atrial tissue concentrations of the natriuretic peptides did not parallel circulating concentrations. ANP predominated in normal atrial tissue, but BNP predominated in CHF. In ventricular tissue, IHCS staining was present for all three peptides in normal ventricular myocardium and was markedly enhanced in CHF. CONCLUSIONS These studies support a differential regulation of ANP, BNP, and CNP circulating concentrations and tissue activity in human CHF.

Recent studies demonstrate that endothelin, a potent endogenous vasoconstrictor peptide, circulates in plasma of normal animals and humans. However, the role of this peptide in pathophysiological states remains unclear. The present study was designed to test the hypothesis that circulating endothelin concentrations are increased in experimental congestive heart failure (CHF), a pathophysiological state characterized by activation of vasoconstrictor mechanisms. In anesthetized dogs with CHF produced by 8 days of rapid ventricular pacing (n = 28), circulating plasma endothelin was increased compared with values for normal controls (n = 28; 20.4 +/- 1.4 versus 9.7 +/- 0.9 pg/ml, respectively; p less than 0.0001). A plasma endothelin level of more than 14.0 was a sensitive and specific indicator of significant CHF. Moreover, within the group with experimental CHF, right atrial pressure and pulmonary capillary wedge pressure correlated independently with circulating endothelin levels. Based on recent studies demonstrating the physiological actions of twofold increases in circulating endothelin, as observed in the present study, a possible role for endothelin in the pathophysiology of CHF is advanced.