Role of Intraluteal Estrogen in the Regulation of the Rat Corpus Luteum during Pregnancy*

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Abstract
The pronounced aromatizing ability of the rat corpus luteum and the ability of estradiol to maintain luteal progesterone synthesis suggest that estrogen formed within the luteal cell might act locally to maintain luteal function. To examine this hypothesis, rats were treated with either estradiol (100 .mu.g/day), high or low levels of testosterone via Silastic capsules (20 cm or 1 cm in length), or dihydrotestosterone (20 cm capsule) after hypophysectomy and hysterectomy on day 12 of pregnancy. Hypophysectomy and hysterectomy caused serum progesterone and androgen levels, estradiol concentrations in the corpora lutea, and the content of estradiol receptor in luteal cell nuclei to decrease significantly, and caused the cessation of luteal growth. The daily administration of 100 .mu.g estradiol or of high levels of testosterone via the 20 cm Silastic capsule increased the estradiol concentration in the corpora lutea dramatically, maintained serum progesterone from day 12 through day 15 at concentrations similar to those in pregnant, sham-operated animals, and increased the nuclear content of estradiol receptor in the corpora lutea. Treatment with the small testosterone capsule maintained the serum androgen and progesterone levels, estradiol concentrations in the corpora lutea, and luteal growth at levels observed in pregnant, sham-operated animals. Treatment with the 20 cm dihydrotestosterone capsule did not sustain progesterone secretion and luteal growth. These results suggest that estrogen formed by aromatization within the corpora lutea may play an important role in the regulation of luteal function during pregnancy in the rat.