Alpha-human atrial natriuretic peptide is a coronary vasodilator in the Langendorff-perfused guinea pig heart

Hypoxic coronary vasodilatation and cGMP overproduction are blocked by a nitric oxide synthase inhibitor, but not by a guanylyl cyclase ANF receptor antagonist

Myocardial hypoxia is known to be accompanied by the release of atrial natriuretic factor (ANF), a peptide which dilates the coronary vessels by stimulating particulate guanylyl cyclase. We have assessed whether ANF plays a paracrine role in hypoxic coronary vasodilatation, a reaction which we had previously found to be associated with increased cyclic GMP production. Compound HS 142-1 (100 micrograms/ml), a specific antagonist of the guanylyl cyclase ANF receptor, inhibited by 50-70% the coronary-vasodilating effects of human ANF (1-10 micrograms) administered to isolated guinea pig hearts, but affected neither hypoxic coronary vasodilation nor cyclic GMP overflow. In contrast, the nitric oxide synthase inhibitor N omega-methyl-L-arginine (300 microM) reduced hypoxic coronary vasodilatation and cyclic GMP overproduction by approximately 70% and 50-60%, respectively. Thus, unlike nitric oxide, ANF appears not to play a paracrine role in hypoxic coronary vasodilatation.

Effects of alpha-human atrial natriuretic peptide in guinea-pig isolated heart

The aim of the present investigation has been to ascertain whether or not atrial natriuretic peptides (ANP) can exert a direct effect on myocardial contractility. Alpha-human ANP (alpha-hANP) concentrations ranging from 1 pM to 50 nM have been used to perfuse guinea-pig isolated hearts in a non-recirculating Langendorff apparatus. A dual concentration-related effect has been induced by alpha-hANP on myocardial function. A maximal increase of +LV dP/dtmax (+56%; P < 0.001) has been observed when guinea-pig hearts were perfused with 100 pM alpha-hANP, whereas a 25% decrease (P < 0.01) occurred with 50 nM alpha-hANP. Similar effects have also been induced by alpha-hANP on the coronary flow rate (CFR). A significant CFR increase (maximal at 10 pM alpha-hANP) was induced by picomolar concentrations of alpha-hANP, whereas a progressive decrease, which was maximal (-28%; P < 0.01) at 50 nM alpha-hANP, was observed with nanomolar concentrations of the peptide. No effects have been observed on heart rate. These results suggest that ANP has direct effects on both vascular and myocardial muscle cells. Coronary vasoconstriction induced by nanomolar concentrations of ANP can contribute to the cardiodepression, whereas ANP in picomolar concentrations can induce a coronary vasodilation which is not coupled with the enhanced myocardial contractility. The latter is the likely expression of a direct effect of the peptide on myocardial function.

Renal, hormonal, and hemodynamic effects of low-dose infusion of atrial natriuretic factor in acute myocardial infarction

The effects of low-dose infusion of atrial natriuretic factor (ANF; 3 pmol/kg/min; i.e., 10 ng/kg/min) were investigated in a single-blind, random-order, placebo-controlled study of 12 patients with uncomplicated acute myocardial infarction (MI). Compared with the placebo, ANF induced an increase in urine volume (p less than 0.05), sodium excretion (p less than 0.05), and chloride excretion (p less than 0.05). Urinary potassium and creatinine clearance were unchanged. The maximal response of urinary sodium excretion rate after ANF infusion was positively correlated with the basal sodium excretion rate (r = 0.579; p less than 0.05) and inversely correlated with basal plasma renin activity (r = -0.623; p less than 0.05). Furthermore, the plasma aldosterone concentration (PAC) after infusion of ANF was significantly decreased compared with the basal level. The maximal change in PAC was closely correlated with the basal PAC (r = -0.857; p less than 0.01). However, no significant effect on hemodynamic variables was detected with infusion of ANF. Although additional studies are needed to assess the clinical efficacy of ANF infusion in acute MI, our observations suggest that low-dose infusion of the peptide is potentially valuable, as either sole or adjunctive therapy, for the management of water-sodium retention in acute MI.

Sustained dilatation of large coronary artery by alpha-human atrial natriuretic peptide in conscious dogs: a comparison with nitroglycerin

The effects of alpha-human atrial natriuretic peptide (alpha-hANP) on the coronary circulation were compared with those of nitroglycerin in 16 conscious dogs chronically instrumented with a pair of miniature sonomicrometers and an electromagnetic flow probe placed on the left circumflex coronary artery. alpha-hANP (1 and 10 micrograms) and nitroglycerin (0.1, 1 and 10 micrograms) were administered intracoronarily via a cannula implanted in the proximal left circumflex coronary artery. Both alpha-hANP and nitroglycerin dose dependently increased the coronary diameter and coronary blood flow. Although alpha-hANP (10 micrograms) and nitroglycerin (1 microgram) dilated the large coronary artery to almost the same extent (92 +/- 10 vs. 98 +/- 8 microns), the time course of the dilating action differed; the peak dilatation occurred at 5.6 +/- 0.8 and 0.9 +/- 0.07 min (P less than 0.01), and full recovery occurred at 31.5 +/- 3.8 and 5.5 +/- 1.3 min (P less than 0.01) after alpha-hANP and nitroglycerin, respectively. Topical application of alpha-hANP (50 micrograms) to the epicardial coronary artery of three anesthetized open-chest dogs did not affect the coronary diameter and coronary blood flow, while nitroglycerin (50 micrograms) increased both variables. Thus, intracoronary alpha-hANP dilates the large coronary artery more gradually and more sustainedly than nitroglycerin does.