Intraovarian localization of luteinizing hormone/human chorionic gonadotropin stimulation of testosterone and estradiol synthesis in the pregnant rat.

The objective of this investigation was to determine whether LH acts directly on luteal cells to stimulate testosterone and estradiol synthesis or whether it stimulates follicular and/or interstitial production of androgen and thus provides androgen substrate for luteal cell production of estradiol. Pregnant rats were injected with 1.5 IU human CG (hCG) twice daily sc between days 12 and 14. On day 14, blood was obtained from both the jugular and ovarian vein. Corpora lutea (CL), follicles, and interstitium were isolated and incubated at 37 C for 4 h. Estradiol, testosterone, and progesterone levels were measured in the peripheral circulation, ovarian vein plasma, tissues, and medium. After hCG treatment, no ovulation occurred, rats remained pregnant, and progesterone levels in the serum and in the ovarian vein plasma remained unchanged. In contrast, estradiol and testosterone levels in the ovarian vein increased from 0.7 +/- 0.1 and 0.6 +/- 3.4 ng/ml, respectively, in vehicle-treated rats to 12.5 +/- 3.5 and 4.8 +/- 1.4 ng/ml in hCG-treated animals. In vivo treatment with hCG dramatically increased the in vitro capacity of luteal cells to synthesize de novo both testosterone and estradiol but had no stimulatory effect on progesterone synthesis. Testosterone synthesis by CL increased from 21 +/- 4 to 255 +/- 114 pg/CL whereas estradiol synthesis rose from 30 +/- 7 to 4481 +/- 641 pg/CL. hCG also increased follicular synthesis of both estradiol and testosterone. The interstitium responded to the hCG challenge with a 50-fold increase in testosterone synthesis but with no change in estradiol production. To determine whether hCG rapidly stimulates ovarian production of testosterone, both in vivo and in vitro approaches were used. In the in vitro experiments, CL follicles, or interstitium obtained from day 14 pregnant rats were incubated with or without 3 IU hCG. In the in vivo experiments, day 14 pregnant rats were injected with 3 IU hCG iv and were bled from the jugular and ovarian veins 0.5 and 2 h later. No increase in testosterone and estradiol production was observed after a short challenge with hCG. In summary, this study demonstrates that in the pregnant rat a sustained increase in serum hCG activity stimulates ovarian secretion of both testosterone and estradiol. We conclude that LH can act to induce the synthesis and/or activation of enzyme(s) involved in the conversion of progesterone to androgen in luteal tissue. The results also demonstrate that LH stimulates the synthesis of androgens but not of estradiol in interstitial tissue and confirms the finding that LH stimulates follicular production of both testosterone and estradiol.