Effect of Hypophysectomy on Day 12 of Pregnancy on Ovarian Steroidogenesis in the Rat

Corpora lutea (CL) and nonluteal ovarian tissues (NLO) were removed from pregnant rats hypophysectomized (H) or sham-hypophysectomized (sham H) on Day 12 of pregnancy and killed on Days 14, 16, 18, 20, or 22 (Day 1 = day of sperm-positive vaginal smear). The tissues were incubated separately for 2 h to examine their ability to produce steroids in vitro. Progesterone (P), 20α-dihydroprogesterone (20α-OHP), testosterone (T), and estradiol-17β (E2) in sera, tissues, and media were measured by radioimmunoassay. On Days 14–20, serum and luteal levels of P, 20α-OHP, and T were the same in H and sham H rats. However, at Day 22 significant differences in serum P and 20α-OHP and in luteal levels of 20α-OHP and T were apparent. Serum and luteal levels of E2 in both groups did not differ on Days 14 and 16 but decreased after Day 18 in the H rat whereas the levels continued to rise in the controls. In vitro production of P, 20α-OHP, and T by CL was similar in both groups on Days 14 through 20, but significantly different on Day 22. On Days 18–22 of pregnancy, luteal production of E2 in H rats was significantly lower than in sham H rats. The pituitary, therefore, plays no part in luteal P, 20α-OHP, and T production from Days 14 to 20 and in luteal production of E2 on Days 14 and 16 of pregnancy. However, the pituitary was responsible for the NLO secretion of T and E2 in the second half of pregnancy. The NLO of both groups produced small amounts of P with no significant differences until Day 22. The NLO of H rats produced significantly less amounts of T from Days 14 to 22. In H rats the NLO always produced only small amounts of E2 throughout the period of observation whereas marked increases in E2 concentration and production were observed on Days 20 and 22 in the controls.