A synthetic orally-active progestin, 17α-acetoxyprogesterone (17-ap), given to pregnant rats for the first 13 days of gestation had no apparent effect on ovary, uterus, or implant (the foetus and its membranes) weights, or uterine acid and alkaline phosphatase activity. No follicular cysts were observed in these rats, in contrast to the incidence of follicular cysts observed in pigs in similar experiments. Pituitary luteotropic hormone (probably prolactin) was increased while pituitary luteinizing hormone (lh) was decreased. The theoretical implications of these findings, and the possible role of prolactin in preventing follicular cysts and luteal regression in progestin-treated rats, are discussed.
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