INVOLVEMENT OF CATECHOLAMINES IN THE EFFECT OF U-50,488H ON ISOLATED LEFT ATRIA OF THE RAT

1. The present study examined the effect of U-50,488H on auricular con traction of isolated left atria of the rat. 2. The negative inotropic action induced by the kappa-agonist was antagonized in the presence of propranolol (10(-8) or 5 x 10(-8) M), yohimbine (5 x 10(-7) or 10(-6) M) or in reserpinized rats (5 mg/kg i.p. 24 hr before the experiments ). 3. These results suggest that catecholaminergic mechanisms are invo lved in the cardiac depressant effect induced by U-50,488H.