The effects of acute and repeated treatment with salbutamol, a beta-adrenoceptor agonist, on clonidine-induced hypoactivity in rats.

A dose-dependent decrease in exploratory activity of naive rats was observed after 5-20 mg/kg i.p. of salbutamol. This effect was antagonized by the pretreatment with propranolol and yohimbine. Furthermore, in a single dose of mg/kg salbutamol increased clonidine-induced hypoactivity. By contrast to acute effects, repetitive administration of salbutamol (5 mg/kg twice daily for 10 days) failed to change exploratory activity of rats and abolished the clonidine-induced hypoactivity. The results demonstrate differences in the acute and chronic effects of salbutamol on behaviour which may indicate changes in the sensitivity of adrenergic pre- as well as postsynaptic alpha-adrenoceptors. Tentatively, the results could be explained by development of alpha2-adrenoceptor subsensitivity and the involvement of beta-adrenoceptors in the regulation of their activity.