Efferent Function of Capsaicin-Sensitive Nerves and Neurogenic Vasodilation in Rat Mesenteric Circulation

Abstract

Sequential or double immunostaining studies revealed the coexistence of substance P and CGRP in perivascular nerve fibers in mesenteric arteries (Uddman et al., 1986) and veins (Warthon et al., 1986). The potential role of capsaicin-sensitive primary afferents in the physiological regulation of dog intestinal blood flow was first suggested by Rozsa et al. (1984, 1985). Later on, it was shown that intraluminal capsaicin administration in isolated perfused rat mesenteric bed elicits remarkable vasodilation which is unaffected by cholinergic or adrenergic blockade, hexamethonium and tetrodotoxin (Manzini and Perretti, 1988). This relaxation was markedly reduced or even abolished after “in vivo” or “in vitro” capsaicin pretreatment suggesting desensitization, a typical feature of a certain subset of primary sensory nerves (Maggi and Meli, 1988). Kawasaki et al. (1988) have presented functional evidence that in mesenteric resistance vessels calcitonin gene-related peptide (CGRP) released from capsaicin-sensitive nonadrenergic-noncholinergic (NANC) fibers may act as a potent endogenous vasodilator.