Satoko Arakawa

The Involvement of Dopamine in the Regulation of Steroidogenesis in Rat Ovarian Cells

To investigate a role for dopamine (DA) in steroidogenesis in the rat ovary, ovarian cells of pregnant-mare-serum gonadotropin (PMSG)-treated rats were incubated with DA agonists, antagonists, adrenergic drugs and beta-blocker for 1 h. DA, norepinephrine (NE) and isoproterenol (Iso) increased the level of progesterone (P4) and cAMP in the conditioned medium. D1 agonists (SKF38393, SKF82526J, CY208-243) increased P4 secretion, while the D2 agonist, bromocriptine, showed no significant effect on P4 secretion. The effect of NE or Iso was inhibited by the beta-blocker propranolol (Pro), but was not suppressed by the D2 antagonist, domperidone. The effects of D1 agonists were suppressed by bulbocapnine (Bul), while neither Pro nor the D2 antagonist, domperidone, affected the levels of P4. The D1 receptor was demonstrated in the PMSG-treated rat ovary, and its Bmax was 1.33 fmol/mg tissue and the Kd was 0.357 nM. These results suggest that DA has a direct stimulatory effect on P4 secretion in PMSG-treated rat ovarian cells through they D1 receptor. The observed action may indicate a physiological role for DA in the regulation of ovarian functions in rats.

Effects of Gonadotropin-Releasing Hormone Agonist on Steroidogenesis in the Rat Ovary

To assess the regulatory roles of gonadotropin-releasing hormone (GnRH) in ovarian function, the kinetics of the ovarian GnRH receptor and the effects of the GnRH superagonist buserelin on steroidogenesis in ovarian cell culture were examined. Scatchard analysis of buserelin-binding to crude ovarian cell membrane revealed a specific high-affinity GnRH receptor. Buserelin together with follicle-stimulating hormone stimulated estradiol (E2) production in immature follicles in hypophysectomized and DES-treated rats. On the other hand, applied to developing follicles of rats treated with pregnant-mare-serum gonadotropin buserelin suppressed E2 production to terminate follicle maturation and simultaneously stimulated progesterone (P4) production to induce luteinization. With ovarian cells luteinized by human chorionic gonadotropin in vitro, buserelin suppressed production of both P4 and E2, leading to luteolysis. Buserelin affected steroid production by modulating activities of key enzymes in steroid synthesis. These findings indicate that buserelin action depended on the gonadotropin priming of ovarian cells, and suggest the possible involvement of GnRH in the regulation of steroidogenesis throughout the ovulatory cycle.

Luteolytic effect of the antiprogestin and antiglucocorticoid agent RU486 in rats.

Ovarian cells of pregnant rats were cultured with synthetic progestins (R5020, R2323), dexamethasone and RU486. Progesterone and 20 alpha-hydroxy-pregn-4-en-3-one (20 alpha-dihydroprogesterone) in the medium were measured by specific radioimmunoassay. Both R5020 and R2323 increased concentrations of these intrinsic progestins. RU486 decreased concentrations of progesterone, however, the addition of R5020 or R2323 counteracted this action. Immature hypophysectomized rats treated with pregnant mare serum gonadotropin (PMS) and human chorionic gonadotropin (hCG) were administered with RU486; the serum levels of progesterone and 20 alpha-dihydroprogesterone tended to decrease. R5020 and R2323 inhibited the effect of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), whereas RU486 did not. Inhibition of the cholesterol side chain cleavage enzyme (CSCC) by RU486 was more marked than that by R5020 or R2323. These results show that RU486 decreases progesterone synthesis in cultured ovarian cells. A part of the mechanism may involve an inhibition of CSCC.

Dopamineはラット卵巣の3β-HSD活性の亢進により, progesterone生成を増加させる

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 beta -hydroxysteroid dehydrogenase (3 beta -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 beta -HSD activity were inhibited by Bul. DA showed no effect on 17 alpha-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 beta -HSD activity of the PMSG-treated rat ovary which regulated P synthesis.