The Pattern of Progesterone Secretion in Hypophysectomized Rats Bearing Pituitary Transplants: Effects of Hysterectomy, Estrogen, and Indomethacin*

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Abstract
Cyclic rats were hypophysectomized and their pituitaries transplanted beneath the kidney capsule on day 2 (day 1, ovulation); they were then either hysterectomized or sham hysterectomized (uterus intact rats) and injected s.c. daily with either 1.0 .mu.g 17.beta.-estradiol (E1) or with the sesame oil vehicle until autopsy on day 105. Blood samples were drawn by jugular venipuncture every 2 to 3 days until day 21 and once weekly thereafter. In these rats the serum progesterone level rose until about day 8 and tended to reach a plateau between days 8 and 14. The regression phase began, in general, after days 8 to 14 and continued, without change in rate, for at least 3 mo. In both the uterus-intact and the hysterectomized rats, E1 seemed to induce an earlier onset of regression and a brief increase in its rate, but did not otherwise affect the rate of regression. In the hysterectomized rats regression began later than in the uterus-intact rats, but its rate was also not different from the latter. The serum progesterone pattern of rats subjected to pituitary autotransplantation on day 2 was compared with that of pseudopregnant rats which were either subjected to pituitary autotransplantation on day 2, 5, 7 or 9, or were given a pituitary homotransplant on day 2, and then hypophysectomized on day 2, 3, 5 or 7. A group of rats with sham operations served as additional controls. In these rats, the same pattern of serum progesterone already described was seen in those subjected to either pituitary autotransplantation on or before day 5, or to pituitary homotransplantation, and to hypophysectomy on or before day 5. When the pituitary was autotransplanted on day 7 or day 9, or when the pituitary homotransplant-bearing rat was hypophysectomized on day 7, regression began earlier and was more rapid than in rats operated on on or before day 5. In fact, in the rats operated on day 9, regression was as rapid as it was in the intact (sham operation) controls. Another group of rats subjected to pituitary autotransplantation and hysterectomy on day 2 was divided into 4 subgroups on day 21. In 2 of these, the rats received indomethacin-containing Silastic capsules inserted into each ovarian bursa; in the other 2 groups blank capsules were similarly inserted. The rats in each of these groups were then injected s.c. daily with either E1 or oil; serum progesterone levels were determined on days 21, 22, 24, 28 and once weekly until day 63. E1 had the same effect as in the 1st experiment, but hysterectomy did not change the serum progesterone level from that of the uterus-intact rats of the 1st experiment. Indomethacin completely blocked the effect of E1 but had no significant effect on the serum progesterone levels in the oil-treated rats. The serum PRL level in the rats with pituitary transplants rose to a broad peak between 9 and 18 days after transplantation and then fell to and remained at a slightly lower plateau. Hysterectomy did not affect it, but E1 treatment almost doubled it. Corpora lutea that were removed from the influence of the in situ pituitary (LH?) soon after their formation and maintained under the influence of PRL apparently undergo a profound reduction in the rate of regression of progesterone secretion.