Effects of vasoactive intestinal polypeptide (VIP) on renal function and plasma renin activity in the conscious rabbit.

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Abstract
Conscious rabbits received either vasoactive intestinal polypeptide (VIP) at a dose of 1, 10 or 25 pmol kg-1 min-1 or vehicle alone (control) through an ear vein for 2 h. Experimental design followed a randomized Latin square arrangement. VIP led to a decrease in effective renal plasma flow and glomerular filtration rate (P < 0.01) during infusion of the middle and high doses. Mean arterial blood pressure rose slightly (P < 0.05) and filtration fraction increased (P < 0.01) during infusion of the middle dose. The high dose produced a rise in heart rate, a fall in plasma Na, K and phosphate concentrations and a rise in plasma solids (P < 0.01). In spite of the renal hemodynamic effects and changes in plasma composition during infusion of the high dose, fractional excretion of Na, K and Cl doubled (P < 0.05), suggesting a direct action of VIP on renal tubular function. Plasma renin activity increased between 2- and 3-fold (P < 0.01). The mechanism of the renin response is uncertain. These results, together with the reported presence of VIP-like material in the renal cortex, may indicate a role for VIP in the regulation of renal function, including renin release.