Abstract
The cardiovascular beta-adrenergic receptor blocking activities of YB-2 and its optical isomers were investigated in isolated guinea pig atria and anesthetized dogs, and compared with that of propranolol. In isolated guinea pig atria, the positive inotropic and chronotropic responses to isoproterenol were competitively antagonized by these agents, and the order of beta-adrenergic blockade was as follows: 1YB-2>dl-YB-2 ?? propranolol>d-YB-2. In anesthetized dogs, the effects of isoproterenol and cardiac sympathetic nerve stimulations on diastolic blood pressure, heart rate and dLVP/dt were competitively antagonized by the beta-adrenergic blocking agents. The blockade appears to be specific for beta-adrenergic receptors. In these experiments, cardioselectise blocking activity was not observed with any agent employed. 1-YB-2 was 1.7-2 times more potent than dl-YB-2 and 50-100 times more potent than d-YB-2 in antagonism against the cardiovascular responses to isoproterenol and nerve stimulations. dl-YB-2 was 1.2-1.7 times more potent than propranolol. The results coincided with those in isolated guinea pig atria. In conclusion, YB-2 and its optical isomers appear to have a similar potency ratio for the blockade of cardiac beta-adrenergic receptor stimulations as is the case with propranolol.
