Influence of stenopril on the isometric myogram and the action potential of isolated myocardium of warm-blooded animals.

The effect of the original Bulgarian drug Stenopril (1-phenyl-2/1-phenylpropyl-/3/-amino/propane hydrochloride) on the papillary muscle of guinea-pig right ventricle was studied in vitro. The isometric myogram and the transmembrane cellular activity were recorded. At low Stenopril concentrations (1-5 x 10(-6)M) three effects were observed: weak positive inotropic effect, phasic response (initial increase and subsequent decrease of the amplitude of the contractions) and weak negative inotropic effect. Concentrations of 10(-5) and 10(-4)M inhibit the contractile activity of the myocardium. The changes in the action potentials at the low concentrations are small. At the higher concentrations the Stenopril-negative inotropy is accompanied by lowering of the plateau and extension of the potential at the expense of the late repolarization, as well as decrease of the repolarization velocity. In a number of experiments the excitability decreased until the appearance of local responses. Isoprenaline (10(-6)M) completely restores the Stenopril-inhibited electrical and contractile activity of the drug. It is assumed that Stenopril influences the inward calcium current, similar to the calcium antagonists, and that it also inactivates the Na-permeability of the membrane.