Natriuresis during atrial distension and a concurrent decline in plasma atriopeptin

In the conscious dog, left atrial distension elicits a composite response that modulates both cardiovascular and renal function. The response to atrial distension may be mediated by the combined effects of neural reflexes and the release of atriopeptin. To assess the relative contributions of atrial reflex mechanisms and circulating atriopeptin to the renal response elicited by atrial distension, alpha-human atrial natriuretic peptide (alpha-hANP) was infused into conscious dogs at 50 ng.kg-1.min-1 for 60 min. Then the infusion was stopped abruptly, and left atrial pressure was increased 8 mmHg by inflating a balloon positioned above the mitral valve. Plasma atriopeptin decreased during the 40-min period of atrial distension, but urine flow and sodium excretion increased during this time. In another series of experiments, volume expansion was substituted for atrial distension. Saline (24 ml/kg) was infused intravenously for 5 min immediately after the 60-min period of alpha-hANP infusion. Urine flow and sodium excretion increased after administration of saline even though plasma atriopeptin decreased substantially during the same time period. These results provide evidence that circulating levels of atriopeptin do not play a dominant role in influencing sodium excretion either during atrial distension or in response to saline infusion.