In vitro follicular and luteal steroidogenesis in the pregnant hamster with preliminary studies in the rat.

Serum levels of progesterone (P4), 17 alpha-hydroxyprogesterone (17-OHP), androstenedione (delta) and estradiol (E2) reached their zenith on Day 14 of hamster pregnancy but were not associated with increases in serum pituitary gonadotropins or placental lactogen (Day 1 = day of sperm in vaginal smear). Steroid levels declined drastically on Day 16-the day of delivery. When follicles from proestrous hamsters (0900 h) were incubated for 1 h, E2 was accumulated in the medium at about twice the levels produced by follicles from pregnant animals except on Day 8 of gestation, when the values were about the same as for proestrus and on Days 12 and 16 when E2 was usually undetectable. Addition of 100 ng luteinizing hormone (LH) for 1 h showed that the proestrous follicle was considerably more active in E2 production than any of the follicles of pregnancy, with maximal stimulation in the latter group observed on Day 8 and minimal responsiveness on Day 16. An inverse relationship existed between the patterns of follicular production of P4 and 17-OHP versus delta and E2. Thus, during the baseline incubation, the proestrous follicle accumulated much less P4 than E2 in comparison to the situation during pregnancy. When stimulated by LH, maximal follicular production of P4 was on Day 16 of pregnancy when conversion to E2 and delta was minimal. Although the pathway from C21 to C18 steroids was "open" at all times for the hamster follicle during pregnancy, the rate at which P4 was converted to E2 varied at different stages of gestation. Corpora lutea (CL) from pregnant hamsters were incubated for 1 h to determine the amount of steroids accumulated in the medium. The CL were capable of producing steroids from P4 through E2 except on Day 16 when the levels for all steroids were very low. When 10 ng delta or testosterone were added as substrate, luteal E2 accumulation was greatly increased with peak conversion on Days 12 and 14 of pregnancy. Luteal and follicular function were compared for rats and hamsters on Day 8 of pregnancy. The CL of both species produced E2 per CL, to the same extent in the absence or presence of testosterone. The rat follicle in the baseline incubation accumulated 8X as much P4 and one-fifth as much E2 as the hamster. When stimulated by LH, the rat follicle did not increase the accumulation of E2 or delta over baseline levels but there was a striking increase in P4 (8 ng/follicle). Possible reasons for altered steroidogenesis during pregnancy are discussed.