Interaction Between Prolactin, LH, Neurohypophysial Hormones and Hysterectomy on Luteal Function in Rats1

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Abstract
Functional corpora lutea (CL), which were capable of sustaining high levels of plasma progesterone, were maintained in hypophysectomized rats by transplantation of the pituitary or by daily treatment with exogenous prolactin. Treatment of autografted rats with exogenous LH (20 μg/day) for 6 days greatly reduced the plasma concentration of progesterone. Injections of LH to autografted rats for only 2 days markedly reduced progesterone in one half of the experimental animals. Even though exogenous LH was clearly luteolytic in autografted rats, the response in prolactin-treated, hypophysectomized rats depended upon the exact timing of each LH injection relative to each prolactin injection. Exogenous LH for 6 days greatly decreased plasma progesterone when each LH injection (1100 and 2000 hr) occurred 3 hr after a prolactin injection (0800 and 1700 hr). Injection of LH 3 hr before each prolactin injection had no effect on the concentration of plasma progesterone which was the same as in controls treated only with prolactin. Simultaneous injection (0800 and 1700 hr) of LH and prolactin produced an intermediate effect characterized by a slight reduction in progesterone concentration in some rats. The permissive effects of endogenous prolactin and of exogenous prolactin injected 3 hr before LH were manifested in the ability of exogenous LH, given for several days, to induce functional luteolysis and decrease plasma progesterone. Treatment of autografted rats with large dosages of neurohypophyseal hormones did not affect the plasma concentration of progesterone. Hysterectomy of pituitary intact, pseudopregnant rats had no effect on plasma progesterone on days 8 and 10. Plasma progesterone in hysterectomized animals remained elevated on days 12 and 14 whereas the levels in sham-operated controls declined.

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