Characterization of Rat Placental Luteotropin, Physiological and Physicochemical Properties1

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Abstract
Extracts of placentae and sera from rats 11, 12, and 13 days pregnant supported the decidual reaction in mature, hypophysectomized, pseudopregnant rats, with maximal potency noted on Day 12. Extracts of tissues or sera obtained on Days 10, 14, and 16 of pregnancy did not sustain deciduomata. Serum progesterone levels in decidualized rats were elevated as opposed to rats not supporting the decidual reaction. The luteotropic activity of rat placentae was also demonstrated following administration of placental tissue to the hypophysectomized pregnant rat. Placental luteotropic activity was dose-related, and the active factor could be lyophilized repeatedly without loss of activity. The biologically active placental component(s) was characterized as a heat-labile protein of approximately 25,000–50,000 molecular weight. These data affirm the critical endocrine role of the rat placenta in supplanting the pituitary and maintaining corpus luteum functions.

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