Selective regional effect of various neuroactive drugs on bromocriptine concentration in the brain of rats

Bromocriptine (2-Br-alpha-ergocryptine), a partial ergoline derivative, is a dopamine agonist which has been used successfully in the treatment of hyperprolactinemia, acromegaly and Parkinson's disease. The main targets for the action of the drug are the hypothalamic, hypophyseal pathway and the striatum. These regions contain different populations of neurons which interact with each other in a complex way. In order to check the mechanism of these interactions in rats, we administered different neuroactive drugs together with bromocriptine. After a single intraperitoneal injection, bromocriptine concentration in the striatum was 13.1 +/- 2.9 ng/mg protein, and in the hypothalamus 13.9 +/- 0.8 ng/mg protein. The largest increase in the bromocriptine content in the striatum was found after the concomitant administration of naloxone, an opiate receptor blocker (21.2 +/- 2.5 ng/mg protein). The largest increase of the bromocriptine content in the hypothalamus was found after the concomitant injection of methysergide, a serotonin receptor blocker (27.8 +/- 2.6 ng/mg protein). Amantadine, diazepam and haloperidol caused the largest decrease in the two regions. The mechanism of interaction and therapeutic implication of these findings are discussed.