Dopamine receptor affinities in vitro and stereotypic activities in vivo of cabergoline in rats.

Abstract

An ergot alkaloid derivative, cabergoline, and its metabolites were investigated for their affinities for dopamine D1 and D2 receptors in rat striatum in vitro in comparison with those of bromocriptine and pergolide. The affinity for D1 receptors was in the following order: pergolide > des-dimethylaminopropyl cabergoline (FCE21904) > cabergoline > or = bromocriptine > or = des-methyl cabergoline (FCE27395) > or = des-ethylcarbamoyl cabergoline (FCE21590). From the effects of GTP on these affinities for the D1 receptor, cabergoline, some of its metabolites, and pergolide were characterized as agonists in contrast to bromocriptine which was classified as an antagonist. The affinity for D2 receptors was ranked as follows: pergolide > or = cabergoline > or = FCE27395 > or = FCE21904 > bromocriptine > FCE21590 > carboxylic acid-type derivative of cabergoline (FCE21589). The affinity of each compound for the D2 receptor was much higher than that for the D1 receptor. The selectivity of cabergoline for D2 receptor was higher than those of bromocriptine and pergolide. Furthermore, these ergot alkaloids were investigated for eliciting stereotypy after subcutaneous administration to normal rats. Pergolide potently induced stereotypy at doses of 0.5 and 1.0 mg/kg, cabergoline slightly induced it only at a high dose of 2.0 mg/kg, whereas bromocriptine did not induce it at any of the doses tested, 10-40 mg/kg. These results suggest that pharmacological properties of cabergoline for the D1 and D2 receptors differ from those of bromocriptine and pergolide.