Abstract
Summary
Levels of estrone and progesterone have been determined which, when given in combination to rats oöphorectomized and hypophysectomized on day 7 or 8 of pregnancy, will permit most of them to carry a slightly less than average number of apparently normal young through the usual gestational period. Of 7 rats given 1 fxg of estrone and 4 mg of progesterone daily, one died on day 22 following an attempt to deliver 6 large and 2 resorbing fetuses, and the other 6 when sacrificed on days 22 or 23 were found to have a total of 39 (3 to 9) living young and 16 (1 to 6) fetuses in various stages of resorption. Of the 10 rats given 1 μg of estrone and 3 mg of progesterone, one died on day 21 without being able to deliver 9 term-size fetuses, 6 when sacrificed on days 21 or 22 were found to have a total of 36 (4 to 8) living young and 8 either recently dead or in various stages of resorption, and the remaining 3 when sacrificed on days 22 or 23 were found to have resorbing implants or no visible-implantation sites. It may be concluded, therefore, that 1 μg of estrone and 4 mg of progesterone substituted for the ovaries and pituitary during the period of pregnancy between days 7 and 11, and for the ovaries alone from day 11 until term. The pituitary is only necessary during the first half of pregnancy in the rat, and then probably because of its gonadotrophs triad, FSH, ICSH and lactogenic hormone.
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