Comparative partial agonist activity of -adrenoceptor antagonists.

Inotropic dose-response curves were constructed for a series of beta-adrenoceptor antagonists, based on the inotropic responses of isolated dog trabecular muscles stimulated to contract at a regular rate. Propranolol exerted only a negative inotropic effect but K01366, LB46, oxprenolol and practolol all evoked a positive inotropic response, whether or not catecholamine-depleted muscles were used. The order of potency for this positive inotropic activity was K01366>LB46>oxprenolol>practolol. The duration of the positive inotropic response to the antagonists was more prolonged than that due to isoprenaline. Propranolol significantly reduced the positive inotropic response to K01366, LB46, oxprenolol and practolol.