Inotropic effects of calcitonin gene-related peptide, vasoactive intestinal polypeptide and somatostatin on the human right atrium in vitro.

Inotropic responses to calcitonin gene-related peptide (alpha-CGRP), substance P, neurokinin A, capsaicin, neuropeptide Y, vasoactive intestinal polypeptide (VIP) and somatostatin (Som, 14 and 28 were analysed using the isolated, electrically driven auricle of the human right atrium. alpha-CGRP and VIP stimulated atrial contractility concentration dependently. alpha-CGRP was about 10-fold more potent than noradrenaline (NA) as an inotropic agent. Phentolamine plus metoprolol decreased the atrial response to NA significantly while the alpha-CGRP effect remained unchanged. Som did not influence the basal contractility of the atria, which, however, was inhibited by acetylcholine (ACh). ACh, Som 14 and Som 28 inhibited the NA-induced stimulation of atrial contractility, whereby Som 28 was more potent than Som 14. The inhibitory effects of ACh were completely blocked by atropine which did not influence the response to Som. Capsaicin, substance P, neurokinin A, neuropeptide Y (NPY) and the NPY fragments 1-19 and 26-36 did not induce any changes in contractility of the electrically driven human atrium. The present results suggest that some of the recently discovered neuropeptides (alpha-CGRP, VIP and Som) could be of importance in the regulation of cardiac contractility in man.