Abstract

Five adrenergic blocking drugs, each representing a different chemical class, have been examined for their effectiveness in inhibiting the increases in cardiac contractile force produced by levarterenol, epinephrine and isoproterenol in dogs with intact circulatory systems. Phentolamine and Dibenzyline completely blocked the cardiac actions of the amines, whereas large doses of piperoxan and azapetine blocked the effects by 50 to 75 per cent. Hydergine, even in very large doses, produced only 15 to 30 per cent blockade. With each blocking drug, the dose required to inhibit the cardiac responses of the amines was larger than that required to reverse the pressor response toepinephrine. None of the blocking drugs had any demonstrable influence upon the increases in contractile force produced by ouabain.