Microdialysis study of bromocriptine and its metabolites in rat pituitary and striatum

Bromocriptine, a D-2 receptor agonist, was administered intravenously (1 mg /kg) to anesthetized rats. Microdialysis probes were implanted in the pitui tary and the striatum, known sites of D-2 agonist action. Bromocriptine and its metabolites were monitored in plasma and tissue dialysates for 4 h. Dr ug analyses were performed using two different enzyme immunoassays specific for untransformed bromocriptine or a pool of parent drug plus hydroxylated metabolites. The metabolites/parent drug ratio for areas under the curve w as 5.5 in plasma and 1 in the pituitary. No metabolites could be detected i n the striatum. Bromocriptine penetration was at least 10-fold greater in t he pituitary than in the striatum. The kinetics of bromocriptine in the pit uitary and striatum did not parallel those in plasma, indicating that the p rolonged action of bromocriptine reported by other authors may be due to sl ow dissociation from receptors.