Induction of Pseudopregnancy and Prolactin Surges by a Single Injection of Progesterone

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Abstract
Preovulatory rat follicles matured during normal cycles go gradually into atresia if ovulation is inhibited by injections of sodium pentobarbital from proestrus for 2 or more days. The gradual process of atresia is characterized by a rapid decrease of follicular estrogen secretion within 1 day after the start of pentobarbital injections. Furthermore, structural signs of atresia appear in predictable order during the ensuing 3 days. In the present study experiments are described demonstrating clear and reproducible effects of daily treatment with bromocriptine on the above processes. Bromocriptine delayed the decrease of follicular estrogen production by about 1 day and also delayed the occurrence of structural signs of atresia. Further study revealed that the effect on estrogen secretion was likely through the action of bromocriptine to suppress prolactin secretion. It thus seems that prolactin is involved in the mechanisms whereby preovulatory follicles lose their capacity to secrete estrogen. This effect of prolactin may occur at the ovarian level and, thus, be involved in reduced secretion of estrogen by the ovaries during physiological or pathological hyperprolactinemic states.