Oestradiol synthesis by granulosa cells from immature rats treated with pregnant mare's serum gonadotrophin

Granulosa cells harvested from follicles in hypophysectomized or intact immature rats treated with 20 IU of pregnant mare's serum gonadotrophin (PMS) produced immunoreactive oestradiol (E2) when incubated in Krebs Ringer bicarbonate buffer containing an NADPH generating system; inclusion of steroid substrates in the medium increased the rate of synthesis. Further, tritiated E2 was synthesized when labelled progesterone was used as substrate. Granulosa cells removed from pre-ovulatory follicles on the morning of prooestrus in adult females also produced E2 in vitro. Although E2 synthesis was apparent by cells from immature hypophysectomized rats within 12 h of PMS treatment, it inceased greatly with longer in vivo exposure to the gonadotrophin. Production was linear with the number of cells incubated and with time, at least through the first 30 min; the production rate decreased slightly with longer incubations. Exposure of the cells in vivo to hCG or ovine LH, before incubation, destroyed most of their ability to synthesize E2 even if progesterone or pregnenolone was added to the medium, but conversion of testosterone to E2 was reduced by only about 50%. Inhibitors of steroid synthesis, i.e. 4-OH-androstenedione, SU-10603, cyanoketone, or aminoglutethimide, greatly reduced the amount of E2 synthesized by the cells. The results indicate that granulosa cells exposed in vivo to gonadotrophins can synthesize E2 without the addition of androgenic substrate provided that cofactors are supplied. This finding has important implications for the current 'two cell' theory for oestrogen production by the ovary. A deficiency in steroidogenic enzymes within the granulosa cell appears to be an inadequate basis for the theory. However, the total synthesis of E2 in vivo by granulosa cells has not been shown.