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The secretory rates of progesterone and pregn-4-en-20α-ol-3-one (20α-OH P) in ovarian venous blood were investigated in various reproductive states of individual rats. In rats with 4-day estrous cycles, 2 peaks of progestin secretion were observed, one in the evening of proestrum and another during early diestrum. The progesterone level in the evening of proestrum was twice that during early diestrum. The level of progesterone in pseudopregnant animals increased to day 6, and then declined by day 13. During pregnancy venous blood progesterone was higher than in pseudopregnancy. By day 11, the progesterone level had reached a plateau higher than the maximum level in rats with both uterine horns traumatized. This plateau was followed by a further increase by day 14. After parturition, an increase in 20α- OH P was observed, while progesterone declined. In pseudopregnant rats which were hysterectomized on day 5, progesterone values obtained at various stages were greater than those obtained from pseudopregnant intact rats. Progesterone declined, however, from days 6 to 21 in the hysterectomized pseudopregnant animals. After induction of deciduomata on day 4 of pseudopregnancy, there was an increase in the venous blood progesterone by day 9 and a decline thereafter to day 21. An inverse relationship existed in the secretion of progesterone and 20α- OH P during pseudopregnancy in intact and hysterectomized rats as well as in animals with decidual tissue. The same relationship was found during the first half of pregnancy. The secretory patterns of progesterone and 20α-OH P were similar, though of different magnitudes, during the estrous cycle and during the second half of pregnancy. (Endocrinology82: 333, 1968)
HASHIMOTO et al. (Thu,) studied this question.