Dopaminergic and alpha 1-adrenergic properties of B-HT920 revealed in morphine-dependent rats.

B-HT920 is known to be a selective alpha 2-adrenoceptor agonist, and has been used in a study on morphine-withdrawal in rats. In accordance with other alpha 2-agonists B-HT920 was found to potentiate "jumping" and to reduce "body shakes." However, B-HT920 did not suppress body weight loss. Furthermore, it induced strong salivation and prevented ptosis (described for the alpha 1-adrenergic agonist ST-587). Rearing and locomotor activity appeared to be enhanced, an effect shared by dopamine-agonist lisurid. The effects of B-HT920 have been specified using the alpha-adrenergic antagonists yohimbine and prazosin and the dopamine antagonist haloperidol. Yohimbine could not antagonize any of the actions of B-HT920. However the increase in rearing and locomotion was blocked by haloperidol. The induction of salivation was prevented by prazosin. Pretreatment with prazosin showed a decrease in the loss of body weight caused by B-HT920, while pretreatment with yohimbine showed that B-HT920 induced an increased loss in body weight. These data suggest that B-HT920 under certain conditions exerts dopamine-agonistic actions in stimulating locomotor activity and alpha 1-adrenergic actions in inducing salivation and enhanced loss of body weight.