Insurmountable antagonism of ouabain-induced coronary constriction by prazosin

A linear dose-response curve was produced by the addition of ouabain (10(-8)-10(-6) M) to the media bathing segments of porcine right coronary arteries. A concentration of 10(-6) M ouabain produced constriction equal to 47% of that resulting from exposure to 35 mM KCl. The ouabain dose-response curve was competitively displaced one order of magnitude by the previous addition of verapamil (2.2 X 10(-8) M), and non-competitively by the prior exposure to prazosin (6.5 X 10(-7)-6.5 X 10(-13) M). The inhibitory effect of prazosin appears to be unrelated to its alpha 1-adrenergic blocking action.