The D1 agonist SKF 38393 inhibits the antiparkinsonian activity of the D2 agonist LY 171555 in the MPTP-treated marmoset.

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to common marmosets induced persistent motor deficits. Administration of the D1 agonist SKF 38393 (2.5-20 mg/kg, i.p.) caused a dose-dependent increase of this akinesia. Administration of the D2 agonist LY 171555 (0.3 mg/kg, i.p.) reversed the motor deficits induced by MPTP treatment. Pretreatment of animals with SKF 38393 (2.5-20 mg/kg, i.p.) caused dose-dependent inhibition of the anti-parkinsonian action of LY 171555 (0.3 mg/kg i.p.). In primates SKF 38393 does not reverse motor deficits induced by MPTP and inhibits the actions of a D2-agonist.