Abstract
Bromocriptine is a selective agonist for dopamine D2-receptors and is used in the treatment of Parkinson's disease. In this study, we performed pharmacokinetic and pharmacodynamic (PK/PD) analyses of the antiparkinsonian effect of bromocriptine and evaluated drug-induced contralateral rotations in rats in which unilateral striatal lesions had been generated by microinjection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle. The plasma concentration (Cp) and D2 receptor occupancy (Phi(D2)) were quantitated by HPLC and with an in vivo back-titration method using [(3)H]-raclopride, respectively. Bromocriptine induced contralateral rotations (E(rot)) in a dose-dependent manner following intraperitoneal administration in an animal model of Parkinson's disease. The Cp of bromocriptine peaked at 15-30 min after the administration and decreased time-dependently, whereas the Phi(D2) of bromocriptine increased gradually for 180 min after administration. The relationship between Cp and E(rot) exhibited an anticlockwise hysteresis, whereas the relationship between Phi(D2) and E(rot) showed a linear correlation. These results suggest that in vivo Phi(D2) is a good pharmacological indicator of the effect of a D2 agonist.
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