Neuropeptide control of rat gastric mucosal blood flow. Increase by calcitonin gene-related peptide and vasoactive intestinal polypeptide, but not substance P and neurokinin A

Abstract

Submucosal blood vessels of the mammalian stomach are densely innervated by neurons containing calcitonin gene-related peptide (CGRP), substance P, neurokinin A, and vasoactive intestinal polypeptide (VIP). Because all these peptides are vasodilators in certain vascular beds, we tested the hypothesis that rat α-CGRP, rat VIP, substance P, and neurokinin A are candidate mediators of noncholinergic vasodilator neurons in the gastric mucosa and submucosa. The experiments were performed on urethane-anesthetized Sprague-Dawley rats. Gastric mucosal blood flow (GMBF) was measured by the hydrogen gas clearance technique, and the peptides were infused close arterially to the stomach via a catheter inserted retrogradely in the splenic artery. Basal GMBF was in the range of 35-50 ml/min/100 g. Infusion of rat α-CGRP (15 and 75 pmol/min) significantly increased GMBF in a dose-dependent manner, whereas mean arterial blood pressure was significantly lowered only by the higher dose of CGRP. Substance P (125 and 625 pmol/min) and neurokinin A (50 and 250 pmol/min) failed to alter GMBF, although the higher dose of each peptide led to a significant decrease in mean arterial blood pressure. Infusion of rat VIP (25 pmol/min) failed to affect GMBF and mean arterial blood pressure, whereas a fivefold higher dose of VIP (125 pmol/min) led to a significant rise of GMBF and to significant hypotension. These findings indicate that substance P and neurokinin A are unlikely to be of physiological significance for the regulation of GMBF. CGRP and VIP, however, can be considered as candidate mediators of submucosal nerve endings involved in the neural control of GMBF. By taking account of the origins of these nerve endings, CGRP would transmit sensory nerve-induced vasodilatation, while VIP would mediate vasodilatation induced by the enteric nervous system.