Is the natriuretic effect of atrial natriuretic factor in conscious rats mediated by renal vasodilatation?

Atrial natriuretic factors (ANF) have both vasorelaxant and natriuretic properties. It has been suggested that their effects on sodium excretion depend on renal vasodilatation. We studied the haemodynamic (ultrasound Doppler flow probes) effects of synthetic atriopeptin II at natriuretic doses in conscious rats. Intravenous injections of atriopeptin II induced a marked, dose-dependent increase in sodium excretion. This was accompanied by a slight reduction in blood pressure (BP) and a transient decrease in renal, mesenteric and aortic blood flow. In contrast, a selective renal vasodilator, CGP 22,979, induced a moderate increase in sodium excretion concomitantly with a rise in renal blood flow. Blood pressure and the other regional flows remained unchanged. These findings suggest that the natriuretic effect of CGP 22,979 is closely related to an increased renal blood flow. Conversely, the natriuresis induced by atriopeptin II is not accompanied by selective renal vasodilatation and appears to be due either to a tubular action or to changes in intrarenal haemodynamics.