Abstract
The in vitro chronotropic and inotropic effects of vasoactive intestinal peptide (VIP) and of isoproterenol, two agents known to stimulate cardiac adenylate cyclase were compared on the heart from Cynomolgus monkey using the spontaneously beating right atrium, the electrically stimulated left atrium, and the electrically-stimulated ventricular papillary muscle. VIP increased concentration-dependently the rate of beating of the right atrium as well as the contractility of both atria but its efficiency was lower than that of D,L-isoproterenol. VIP also stimulated concentration-dependently, and this time as efficiently as D,L-isoproterenol, the contractility of papillary muscle. These VIP effects were unaltered by the neuronal blocker tetrodotoxin. In addition, the moderate inhibition exerted by the beta-adrenergic blocker D,L-propranolol on VIP effects argued against the implication of beta-adrenergic receptors in VIP effects. These results indicate that VIP exerts a direct stimulatory influence on the rate and contractility of Cynomolgus monkey heart.
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