Effect of RMI 81968, a combined alpha- and beta-adrenergic receptor blocking agent, on histamine-induced...

The interaction of propranolol and RMI 81968 on histamine-induced bronchoconstriction was studied in the anesthetized dog using the respiratory overflow technique of Konzett and Rössler. Propranolol, 3 and 10 mumol/kg i.v., enhanced histamine-induced bronchoconstriction. In contrast, RMI 81968, at 10 or 30 mumol/kg i.v., had no effect in this test. It is believed that the alpha-receptor blocking component of RMI 81968 prevents the bronchoconstriction induced by beta-adrenergic receptor blockade. The results of this study suggest that RMI 81968 is less likely than propranolol to produce bronchoconstriction in asthmatic patients.