[Heart and circulatory effects of quinidine stereoisomers]

Quinidine sulfate shows dose-related activity. On the cardio-vascular system of anaesthetized cats. It reduces heart rate, prolongs QRS and QT of the ECG, lowers peripheral blood pressure and depresses slightly myocardial contractility. Quinidine hydrochloride lowers blood pressure but alters the ECG only in very high doses. Epiquinidine has no blood pressure lowering activity. According to the Easson and Stedman hypothesis this may be the result of stereoselectivity of alpha-adrenergic receptors. Only very high doses of the epimer produce a transient decrease of blood pressure. The ECG-waves are, however, markedly altered. QT is prolonged only with epiquinine-epiquinidine-sulfate. The salts of epiquinidine tested are much better water-soluble than those of quinidine.