AJP - Heart and Circulatory Physiology, Vol 259, Issue 5 1559-H1565, Copyright © 1990 by American Physiological Society
Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs
A. C. Kralios, F. L. Anderson and F. A. Kralios
Cardiology Section, Salt Lake City Veterans Administration Medical Center 84148.
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.
