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 pituitary and the striatum, known sites of D-2 agonist action. Bromocriptine and its metabolites were monitored in plasma and tissue dialysates for 4 h. Drug 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 was 5.5 in plasma and 1 in the pituitary. No metabolites could be detected in the striatum. Bromocriptine penetration was at least 10-fold greater in the pituitary than in the striatum. The kinetics of bromocriptine in the pituitary and striatum did not parallel those in plasma, indicating that the prolonged action of bromocriptine reported by other authors may be due to slow dissociation from receptors.