INHIBITORY EFFECTS OF PUTATIVE DOPAMINE D-3 RECEPTOR AGONISTS, 7-OH-DPAT AND QUINPIROLE, ON PROLACTIN SECRETION IN RATS

The present experiments were performed to investigate effects of opyla mino)-7-hydroxy-1,2,3,4-tetrahydronaphthalene (7-OH-DPAT) or quinpirol e (LY 171555), putative dopamine (DA) D-3 receptor agonists, on serum prolactin levels in male rats. Basal prolactin levels were reduced dos e-dependently by SC administration of 7-OH DPAT or quinpirole at respe ctive doses of 10-100 mu g/kg and 25-250 mu g/kg. Daily treatment with estradiol, 35 mu g/kg/day for 3 days, increased serum prolactin level s to fourfold higher levels than those of nonprimed rats. Intraperiton eal injection of alpha-methyl-p-tyrosine (alpha-MT), 300 mg/kg, also i ncreased serum prolactin levels. 7-OH-DPAT or quinpirole at a dose of 50 mu g/kg caused a marked reduction in serum prolactin levels in both the estradiol- and alpha-MT-induced hyperprolactinemia. The 7-OH-DPAT - and quinpirole-induced decreases in serum prolactin levels were anta gonized by the administration of the DA D-2 receptor antagonist, spipe rone, at 0.5 mg/kg. The results indicate that 7-OH-DPAT and quinpirole decrease prolactin levels in rats by stimulation of the D-2 receptor.