Prolactin inhibition of luteinizing hormone-stimulated androgen synthesis in ovarian interstitial cells cultured in defined medium: mechanism of action.
The mechanism by which PRL acts on ovarian interstitial cells to inhibit androgen synthesis was examined using primary cultures of ovarian cells from hypophysectomized immature rats grown in serum-free medium. In the presence of LH, the cultured interstitial cells showed a 200-fold increase in androgen production, of which androsterone was the principal metabolite. The addition of highly purified PRL (100 ng/ml) markedly inhibited (98%) the LH-stimulated androsterone accumulation. The ED50 of PRL action was calculated to be 1.3 +/- 0.4 ng/ml. The inhibition of androsterone production by PRL was rapid (t 1/2 = 75 min), not readily reversible, and could be evoked at any time during the culture period. The effects of PRL on LH-stimulated androgen production were not due to changes in [125I]iodo-hCG binding. LH-stimulated adenylate cyclase, cell number, or cell viability. As with LH, prostaglandin E2, cholera toxin, or 8-bromo cAMP also caused marked increases in androsterone synthesis, and these effects were blocked (98-99%) by PRL. Studies on the metabolism of steroid hormones revealed that PRL decreased LH-stimulated androsterone and 5 alpha-androstane-3 alpha, 17 beta-diol accumulation by 99%, androstenedione by 94%, testosterone by 90%, dehydroepiandrosterone by more than 80%, pregnenolone and 17 alpha-hydroxyprogesterone by 80%, 17 alpha-hydroxypregnenolone by 84%, and progesterone by 71%. Binding experiments demonstrated the presence of a single class of high affinity (Kd = 2.42 x 10(10) M), low capacity (2.37 fmol/10(6) cells) [125I]iodo-PRL-binding sites in the interstitial cells, suggesting that such receptors mediate the inhibitory action of PRL. It is inferred from these results that PRL antagonizes the stimulatory effects of LH on ovarian androgen biosynthesis by inhibiting a step distal to cAMP formation and before or at the cholesterol side-chain cleavage step.
D000728:Androgens / Q000096:biosynthesis*; D000818:Animals; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000378:metabolism; D003470:Culture Media; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D007986:Luteinizing Hormone / Q000037:antagonists & inhibitors*; D010053:Ovary / Q000166:cytology* / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
D000728:Androgens; D006063:Chorionic Gonadotropin; D003470:Culture Media; D011388:Prolactin; D007986:Luteinizing Hormone; D000242:Cyclic AMP