Central beta- and alpha-adrenolytic activities of adimolol

The central adrenergic blocking activity of adimolol (ADL) was studied in rats and mice in the tests which can differentiate beta-, alpha 1-, and alpha 2-adrenolytic effects. Clenbuterol- and salbutamol-induced sedation in rats (open field test) and clenbuterol-induced hyperthermia (at high ambient temperature) were antagonized by low doses of ADL (0.1-1.0 mg/kg ip). ADL (10 mg/kg ip) attenuated the clonidine-induced aggression in mice, and its higher doses (20 and 40 mg/kg ip) depressed the hind limb flexor reflex of the spinal rat and counteracted the stimulatory action of clonidine. ADL at doses from 2.5 to 40 mg/kg ip affected neither the clonidine-induced sedation in rats and mice (locomotor activity, open field test), nor the hyperthermia (at high temperature). The hypothermia (at a room temperature of 21 degrees C) induced by clonidine was partially antagonized. The Ki values for ADL displacement of 3H-dihydroalprenolol and 3H-prazosin binding in the rat cerebral cortex were 1.2 nM and 951 nM respectively. These results indicate that ADL is a potent antagonist of central beta-adrenoceptors and has a weaker alpha 1-adrenolytic action. The central alpha 2-antagonistic effect is either very weak or absent.