VASOACTIVE-INTESTINAL-PEPTIDE REGULATES ANGIOTENSIN-II CATABOLISM IN THE RABBIT

Although vasoactive intestinal peptide (VIP) is natriuretic it stimulates renin and aldosterone secretion. Therefore, to effect a natriuresis, VIP may need to modulate the sodium conserving actions of the renin angiotensin system (RAS) by another means. One possibility is that it alters the rate of disappearance from the circulation of one or more components of the RAS. We sought to determine whether VIP regulates the rate of catabolism of angiotensin II (Ang II). Steady state metabolic clearance studies of Ang II were undertaken with and without simultaneous VIP infusion. These studies were performed in rabbits on low, normal and high sodium diets, as dietary sodium has been shown to affect the metabolism of both VIP and Ang II. The effects of VIP on plasma Ang II concentration and secretion were also studied. VIP decreased Ang II catabolism in rabbits on low (P < 0.05) and normal sodium diets (P < 0.05). Plasma levels of Ang II increased significantly in response to VIP in rabbits on these diets (low, P < 0.04; normal, P < 0.05). In contrast, in rabbits on a high sodium diet VIP increased the rate of catabolism of Ang II (P < 0.001). Thus we conclude that the effect of VIP on sodium excretion may be modulated by its effects on Ang II metabolism. The decrease in Ang II catabolism seen in rabbits on low and normal sodium diets may prevent or ameliorate any natriuresis while the more rapid degradation of Ang II which occurs in dietary sodium excess map enhance the natriuretic effect of VIP.