Effects of atriopeptin III on renal function, regional blood flows and left ventricular function in conscious dogs in presence or absence of hypovolaemia

Abstract. The effects of atriopeptin III (AP III) on the left ventricular and renal functions were studied in thirteen chronically instrumented conscious dogs and compared to those of the solvent (saline). In the normovolaemic state, an AP III infusion (1 μg kg^‐1 min^‐1 i.v.) had no effects on heart rate, on mean arterial or left ventricular pressure, on (dP/dt) Max (2989±119 vs. 3007±155 mmHg s^‐1; NS) or on the relaxation rate. The left ventricular endocardial and epicardial coronary blood flows (radioactive microspheres) and the renal flow in the outer cortex (707–683 ml (min^‐1 100 g^‐1); NS) or in the inner cortex (563–570; NS) were also insignificantly affected by AP III infusion. However, AP III increased urinary flow from 24±6 to 36±7 ml h^‐1 (P<0·025) and the Na⁺ and Cl^‐ excretions by 92 and 98%, respectively, (P<0·025 and P<0·05 vs. saline group) without altering significantly K⁺, urea and creatinine eliminations. In the moderately hypovolaemic state (mean reduction in renal flow: outer cortex ‐15%; P<0·05, inner cortex ‐5%; NS), AP III infusion at two doses (1 and 3 μg kg^‐1 min^‐1) still had no effects on arterial pressure and on the indexes of left ventricular inotropic state and relaxation but in this setting, the diuretic effect of AP III became variable. Five dogs markedly increased their excretion of water, Na⁺ and Cl^‐ whereas no change was noted in the seven remaining dogs. Regional renal blood flows and urinary output before infusion were similar in the responders and non‐responders but the mean arterial pressure (81±2 vs. 73±3 mmHg; P<0·01) was lower in the non‐responders. It is concluded that AP III has no effect on left ventricular contractility or on the coronary vasculature; at small doses, its diuretic effects appear independent of a renal vasodilation and are rapidly blunted in the presence of hypotension.