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 myo cardial contractility. Alpha-human ANP (alpha-hANP) concentrations ran ging from 1 pM to 50 nM have been used to perfuse guinea-pig isolated hearts in a non-recirculating Langendorff apparatus. A dual concentrat ion-related effect has been induced by alpha-hANP on myocardial functi on. A maximal increase of +LV dP/dt(max) (+56%; P < 0.001) has been ob served when guinea-pig hearts were perfused with 100 pM alpha-hANP, wh ereas a 25% decrease (P < 0.01) occurred with 50 nM alpha-hANP. Simila r effects have also been induced by alpha-hANP on the coronary flow ra te (CFR). A significant CFR increase (maximal at 40 pM alpha-hANP) was induced by picomolar concentrations of alpha-hANP, whereas a progress ive 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 d irect effects on both vascular and myocardial muscle cells. Coronary v asoconstriction induced by nanomolar concentrations of ANP can contrib ute to the cardiodepression, whereas ANP in picomolar concentrations c an induce a coronary vasodilation which is not coupled with the enhanc ed myocardial contractility. The latter is the likely expression of a direct effect of the peptide on myocardial function.