A comparative study of the effects of OPC-1085 and propranolol on isolated guinea pig atrium

Effects of a newly synthesized beta-blocker, 5-(3-tert-butylamino-2-hydroxy) propoxy-3,4-dihydrocarbostyril (OPC-1085) were compared with those of propranolol. OPC-1085 had a potency about 3 times greater than that of propranolol in blocking the positive inotropic and chronotropic effects of isoprenaline on the isolated guinea pig atrium. At a concentration of over 3 X 10(-5) M OPC-1085 produced negative inotropic and chronotropic effects. However, these effects were about 10 times weaker than those of propranolol. Suppressing effects on the rate of rise and on the maximum driving frequency of action potentials were also more than 10 times less than those of propranolol. There was almost no change in the action potential of vagus nerve after a 10 min treatment with OPC-1085 (10(-5) M), while the action potential was reduced to 60-70% with propranolol (10(-5) M).