Vasoactive Intestinal Polypeptide: Inactivation in Liver and Potentiation in Lung of Anesthetized Dogs

Abstract

Summary The role of the liver and the lung in the inactivation or potentiation of the biological activity of the vasoactive intestinal polypeptide (VIP) was examined in five anesthetized dogs. Infusions of the peptide were made into the right ventricle, the left ventricle, and the portal vein. Each animal received 4 doses, ranging from 0.29 to 2.23 μg/kg. Systemic arterial blood pressure, tidal volume, breathing frequency, and minute ventilation were continually monitored. The biological effects of the peptide were measured in terms of (a) the fall in arterial blood pressure; and (b) respiratory stimulation. Infusions of the peptide into the portal vein produced either no effect or significantly weaker effects (P < 0.01) than infusions into the right ventricle. The latter infusions were moderately more potent (P < 0.05) than infusions into the left ventricle. VIP thus appears to be effectively inactivated during passage through the liver. The apparent increase in biological potency of the peptide during its passage through the lung may be attributable to the release of additional vasodilator substances, or to further activation of the peptide. We are grateful to Mr. Wallace T. Ford, Jr., and Mr. Richard Schmitt for valuable technical assistance.