Abstract
Possible reciprocal interactions among vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and adenosine were investigated in anesthetized rats. Changes in arterial blood pressure were taken as a parameter to evaluate the interactions. The i.v. bolus injections of VIP (0.3 or 1 μg kg −1), CGRP (0.1 or 0.3 μg kg −1) and adenosine (1–100 μg kg −1), like acetylcholine (0.1 μg kg −1), produced reductions of blood pressure, accompanied by slight changes (less than 5% except for 100 μg kg −1 adenosine) in heart rate (HR). The vasodepressor responses to VIP and CGRP were significantly augmented by i.v. infusion of adenosine (3 μg kg −1 min −1). The vasodepressor responses to adenosine and CGRP by VIP (0.03 μg kg −1 min −1), and those to adenosine and VIP by CGRP (1 ng kg −1 min −1) were also enhanced. The response to acetylcholine remained unchanged before and during i.v. infusion of either VIP, CGRP or adenosine. The i.v. infusion of cromakalim (0.1 μg kg −1 min −1) also augmented the responses to VIP, CGRP and adenosine, but not to acetylcholine, whereas a single bolus i.v. injection of glibenclamide (20 mg kg −1) significantly attenuated each one of them. The present results suggest that endogenous vasodilators, such as VIP, CGRP and adenosine, reciprocally interact in the body, at least partly through ATP-sensitive K + channels.
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