Effect of LH on steroidogenesis by hamster follicles isolated at defined stages of development

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.