Little is known about the dopamine system in the ovary. The present study has been undertaken to investigate the effect of dopamine (DA) on the ovarian steroidogenic enzymes of pregnant mare serum gonadotropin (PMSG)-treated immature rats.
Ovarian cells from PMSG-treated rats were cultured for 1-5 hours with or without DA, D₁ agonists or bulbocapnine (Bul)(D₁ antagonist). Progesterone (P) and estradiol (E₂) in the media were assayed by specific RIAs. The enzyme activities were assayed by adding radioactive substrates in the media before incubation.
DA and D₁ agonists increased P in the media which was caused by the increment of 3 β-hydroxysteroid dehydrogenase (3 β-HSD) activity because cholesterol side chain cleavage enzyme (CSCC) activity showed no significant change. The stimulating effects of DA and DA agonists on P and 3 β-HSD activity were inhibited by Bul. DA showed no effect on 17 α-hydroxylase activity. DA decreased 17, 20 lyase activity, but this decrement was probably a non specific effect. DA alone did not affect the E₂ level in the media and aromatase activity.
The present results suggest that DA mainly stimulated 3 β-HSD activity of the PMSG-treated rat ovary which regulated P synthesis.