| Abstract: | Multiple follicular growth was stimulated in groups of immature female hamsters by the administration of PMSG. The ovaries were removed 72-78 or 96-102 h later. The animals at 96-102 h were subdivided according to whether the concentration of plasma progesterone was within the range of the concentrations found at the previous period (0.45-13.18 nmol/l; Group I) or above (Group II). Thecal and granulosa cells from batches of isolated follicles (591-740 micron) were cultured together in the presence or absence of LH and the products of steroidogenesis were measured in the culture fluid. The results showed that there was a significant increase in the production of progesterone and 17 alpha-hydroxyprogesterone in follicles from Groups I and II at 96-102 h. In the presence of LH there was a significant increase in the yield of progesterone and 17 alpha-hydroxyprogesterone over the control values at all time periods. There were, however, reductions in the yields of 17 alpha-hydroxyprogesterone and androstenedione in the presence of LH at 96-102 h compared with 72-78 h and in Group II compared with Group I, although the concentrations of 17 alpha-hydroxyprogesterone were approximately 40-fold those of androstenedione. In addition, the production of oestradiol decreased significantly in follicles from both groups at 96-102 h and was reduced further in the presence of LH. It is concluded that the major rate-limiting step of steroidogenesis in hamster follicles undergoing the oestrogen-progestagen shift involves the side-chain cleavage of 17 alpha-hydroxyprogesterone. |
