MYOCARDIAL ELECTROPHYSIOLOGICAL EFFECTS OF VASOACTIVE-INTESTINAL-PEPTIDE IN DOGS

Vasoactive intestinal peptide (VIP) is a potent inotrope and coronary vasodilator. To test whether VIP also exerts regional myocardial electrophysiological (EP) effects, dose-response and time-course effects of intracoronary injections (10(-10)-10(-4) M) were obtained in 4 intact hearts and 12 in situ normoperfused right ventricular flap preparations in chloralose-anesthetized dogs. Under constant rate, activation (A), recovery (R), and A-R interval (ARI) maps were constructed from multiplexed unipolar surface electrograms recorded simultaneously from 32 sites. Effects were compared with those of isoproterenol (Iso) and forskolin (For). The main finding with all agonists was the uniform shortening of ARIs in a dose-response fashion with a maximum of 30 +/- 4 ms or 20% from control. Although the maximal EP changes were similar for all agonists, they occurred at different molecular concentrations (10(-6) Iso, 10(-5) VIP, and 10(-4) For). Also, whereas the duration of EP effect did not exceed 5 min for Iso and For, it was markedly sustained for VIP, outlasting its contractile but paralleling its vasodilatory effect. The physiological endoepicardial differences in ARI and the recovery sequence were preserved for all agonists. Thus VIP, in addition to coronary vasodilation and myocardial inotropy, exerts a strong balanced global myocardial EP effect, similar to, but more sustained than, the adrenergic effect. The difference in duration of inotropic and EP effects may point to different mediating mechanisms.