Evidence for dopaminergic regulation of prolactin and a luteotropic complex in the ferret

The role of dopaminergic agents in prolactin (Prl) release and the luteotrophic role of Prl and luteinizing hormone (LH) were investigated in pseudopregnant female ferrets. A single injection of the dopamine antagonist pimozide (0.63 mg/kg) resulted in a tenfold elevation of plasma Prl in anestrous females. Subcutaneous injection of pimozide on alternate days from Day 2 through Day 16 of pseudopregnancy elevated both Prl and progesterone levels. Daily treatment with the dopamine agonist 2 alpha-bromoergocryptine (bromocriptine, 4 mg/kg), from Day 2 through Day 16 of pseudopregnancy lowered levels of both plasma Prl and progesterone. Neither pimozide nor bromocriptine had a direct effect on progesterone secretion by luteal cells in vitro. Daily intraperitoneal administration of a monoclonal antibody against gonadotropin-releasing hormone from Day 2 through Day 10 of pseudopregnancy lowered both plasma LH and progesterone, but had no effect on plasma Prl concentrations. Daily administration of equine antisera against bovine LH or 100 IU of human chorionic gonadotrophin to pseudopregnant ferrets lowered progesterone levels. It is concluded that Prl release is influenced by dopaminergic compounds, and both Prl and LH are required for luteal maintenance in the ferret.