In Vivo and in Vitro Ovarian Steroidogenesis in the Long Term Hypophysectomized Rat*

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Abstract
Ovarian steroidogenesis in the hypophysectomized rat was studied using immature female rats pretreated with 5 IU PMS at 30 days of age and hypophysectomized between 0900–1000 h on either day 32 (before ovulation; group without corpora lutea) or day 33 (the day of ovulation; group with corpora lutea). Serum levels of progesterone (P) and estradiol-17β (E2) in the group with corpora lutea were consistently low, but detectable, from day 5–40 after hypophysectomy, whereas serum 20α-dihydroprogesterone (20α-OHP) and testosterone (T) remained relatively high. However, serum P, 20α-OHP, T, and E2 in the animals without corpora lutea were significantly less on days 5–20, suggesting that these hormones were primarily secreted from corpora lutea but not nonluteal ovarian tissues. The steroidogenic capacity of the corpora lutea and nonluteal ovary at different times after hypophysectomy was assessed by incubation for 2 h in Krebs-Ringer bicarbonate. Five to 40 days after hypophysectomy, the corpora lutea in vitro produced large amounts of 20α-OHP and T and small amounts of P, but on days 5 and 10, they produced only negligible amounts of E2. Transplantation of the puituitary to the kidney capsule in the hypophysectomized rat on the day of ovulation resulted in significant increases in serum P and T and luteal P, 20α-OHP, T, and E2. Twice daily injections of PRL (500 μg/day) from days 7–9 after hypophysectomy significantly reduced on day 10 serum P, 20α-OHP, and T and luteal P, 20α-OHP, T, and E2. A single ip injection of 5 μg LH on day 10 after hypophysectomy in the animals with corpora lutea resulted 3 h later in significant increases in serum P, whereas significant increases in serum P and 20α-OHP were noted in the group lacking corpora lutea. The in vitro luteal production rates of P and 20α-OHP were also increased after the ip administration of LH. Small amounts of P, 20α-OHP, and T were produced on days 5–40 by the nonluteal ovary from the group with corpora lutea, whereas in the other group the nonluteal ovary produced consistently lesser amounts of these hormones. The injection of LH also increased 3 h later the nonluteal levels of P, 20α-OHP, T, and E2 and in vitro production of these hormones in both groups. The present study indicates that the corpus luteum of the rat secretes a large amount of 20α-OHP and T in addition to small amounts of P and E2 for at least 40 days after deprivation of gonadotropins and that the corpora lutea and nonluteal ovary are still capable of responding to exogenous LH until at least 10 days after hypophysectomy.