To determine the hemodynamic effects of
isomazole, an
imidazopyridine, we administered
isomazole (10 and 20 micrograms/kg/min) to 10 awake dogs with right-sided
congestive heart failure produced by pulmonary artery constriction and tricuspid valve avulsion.
Isomazole increased cardiac output, heart rate, right ventricular and left ventricular (LV) dP/dt, LVdP/dt/P and decreased aortic pressure and total peripheral vascular resistance. Simultaneously, blood flow increased to myocardium, quadriceps muscle, brain and splanchnic beds, whereas vascular resistance decreased. Furthermore,
isomazole increased LV oxygen consumption and decreased transcoronary arteriovenous
oxygen difference. Similar administration of
normal saline had no effects.
Angiotensin II was infused to restore mean aortic pressure to base-line values during
isomazole infusion; however, despite the return of aortic pressure to base-line values, cardiac output, LVdP/dt and LVdP/dt/P remained elevated. The systemic and regional hemodynamic effects of
isomazole were unaffected by pretreatment with
propranolol and
mecamylamine. Thus,
isomazole exerted positive inotropic, chronotropic and
vasodilator effects in
congestive heart failure dogs. The inotropic effect of
isomazole was independent of the decrease in aortic pressure, and the hemodynamic effects of
isomazole were not mediated via the autonomic nervous system. Furthermore, the decrease in transcoronary arteriovenous
oxygen difference suggests that
isomazole exerted an active coronary
vasodilator action which may improve myocardial
oxygen demand/supply ratio.