EFFECT OF OXYPHENAMONE, A NEW INODILATOR, ON ISOLATED CARDIAC MUSCLES AND ARTERIES

The cardiotonic and vasodilating effects of oxyphenamone were studied in preparations of rat Langendorff′s heart, isolated cardiac muscles of guinea pigs and isolated arteries of dogs. In the preparations of rat Langendorff′s heart, infusion of oxyphenamone at 0.1 and 1.0 μmol·L^-1 increased myocardial contractility and coronary blood flow moderately and decreased heart rate slightly. Oxyphenamone (1～100 μmol·L^-1) increased the contractile force of papillary muscle (PM) and left atrium(LA) of guinea pigs dosedependently. The positive inotropic effect of oxyphenamone (the ED₅₀ was found to be 18.35 μmol·L^-1 in PM and 9.17 μmol·L^-1 in LA) was close to that of milrinone, an inhibitor of phosphodiesterase(the ED₅₀ was shown to be 6.23 μmol·L^-1 in PM and 4.59 μmol·L^-1 in LA). The difference between these two agents is that oxyphenamone decreased the spontaneous pulse rate of right atrium, while milrinone increased it. The vasoconstrictions of dog coronary, basilar and mesenteric arteries induced by KCl, 5-HT and CaCl² were antagonized non-competitively by oxyphenamone at 1 and 50 μmol·L^-1, suggesting that oxyphenamone has a relaxant effect on vascular smooth muscles.