Preprogramming Mechanism of Luteinizing Hormone in the Determination of the Lifespan of the Rat Corpus Luteum*

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Abstract
Luteal regression was studied in female rats bearing an isografted pituitary under the renal capsule and the day of ovulation was designated as day 0. These females had pseudopregnancy-like cycles and ovulations at 16-day intervals. After each ovulation, corpora lutea were activated and progesterone concentrations increased in peripheral blood until day 5, after which concentrations gradually decreased. Removal of the in situ pituitary on day 0 or 1 resulted in maintenance of luteal function; progesterone concentrations were sustained. This effect of hypophysectomy on day 0 was prevented by daily administration of small amounts of LH [luteinizing hormone] from days 0-5; however, luteal regression occurred if hypophysectomy was performed on day 4 or later and progesterone concentrations decreased. Luteal regression was prevented if anti-LH serum was administered from days 1-5 to pituitary-isografted rats and was followed by hypophysectomy on day 5. The lifespan of corpora lutea in pseudopregnant rats is programmed between days 2-4 after ovulation through the hypothalamohypophysial axis via secretion of LH.