INOTROPIC EFFECTS OF OUABAIN ON RABBIT LEFT ATRIA IN PRESENCE OF BETA-ADRENERGIC BLOCKING DRUGS.

Summary The positive inotropic effects of ouabain on electrically driven rabbit left atrial preparations was studied in the presence of 3 drugs known to be potent and specific beta-adrenergic receptor antagonists (pronethalol, propranolol and MJ-1999). Ouabain alone (6.9 × 10-7 M) produced a highly significant increase in contraction force compared to untreated controls. Pronethalol (3.76 × 10-6 M) and propranolol (1.35 × 10-6 M) were found to produce significant decreases in contraction force. The methanesulfonanilide substituted isopropylphenylethylamine (MJ-1999) had no significant effects on contraction force in a concentration of 1.3 × 10-5 M. Administering ouabain after pretreatment with and in the presence of either pronethalol, propranolol, or MJ-1999 failed to modify significantly the normal positive inotropic effect of the glycoside. Therefore, no evidence was found to indicate that beta-adrenergic receptor blockade could prevent the positive inotropic effect of ouabain on isolated rabbit left atria.