Interaction of U-50,488H and noradrenergic systems on isolated right atria

1. The present study examined the effect of U-50,488H on auricular rate on isolated right atria of the rat. 2. The negative chronotropic action induced by the kappa-agonist (U-50,488H) was potentiated by propranolol (10(-8) or 5 x 10(-8) M) or yohimbine (5 x 10(-7) or 10(-6) M) and in reserpinized rats (5 mg/kg i.p. 24 h before the experiments). 3. These results suggest that catecholaminergic mechanisms are involved in the cardiac depressant effect induced by U-50,488H.