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Serum Prolactin Concentrations during Hormonally Induced Pseudopregnancy in the Rat

Department of Endocrinology, Growth, and Reproduction, Erasmus University Rotterdam, The Netherlands

Address all correspondence and requests for reprints to: W. J. de Greef, Department of Endocrinology, Growth, and Reproduction, Erasmus University, P.O. Box 1738, Rotterdam, The Netherlands.

Abstract

Treatment of 5-day cyclic rats with 10 or 100 jug estradiol benzoate on the day of estrus induced a luteal phase in all animals studied. On the other hand, an injection with 1 jug estradiol benzoate given on the same day failed to induce pseudopregnancy. When 10 mg progesterone were injected on the day of estrus, about 50% of the rats became pseudopregnant, whereas most of the remaining rats had a 6-day cycle.

The injection of 10 or 100 fig estradiol benzoate or 10 mg progesterone induced a period of increased PRL secretion which lasted for 2–4 days, followed by twice daily surges of PRL at the end of the dark and light periods, respectively. It is argued that pseudopregnancy induction by estradiol benzoate or progesterone is primarily a result of the induction of a period of increased PRL secretion. In this way, progesterone secretion by the recently formed corpora lutea is induced, and the elevated levels of progesterone in turn generate diurnal surges of PRL.

Received September 1, 1978.