Effect of the placenta on the growth and function of artificially formed secondary corpora lutea of pregnancy in rats.

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Abstract
Pregnant mare serum gonadotropin-induced prepubertal pregnant rats were injected with human chorionic gonadotropin on day 7 of pregnancy to induce the formation of secondary corpora lutea (CL) in addition to the primary CL of pregnancy. The rats bearing 2 sets of CL were hypophysectomized on day 11 of pregnancy (day 3 of the secondary CL age) and their primary CL were removed on day 13 of pregnancy (day 5 of the secondary CL age). The operations did not affect the fetal growth until day 18 of pregnancy when the weight and progesterone secretion of the secondary CL rapidly increased. Hysterectomy on day 18 of pregnancy (day 10 of the secondary CL age), induced regression of CL and rapidly decreased the progesterone secretion. These results suggest that placentas between days 15 and 18 of pregnancy could maintain the function of CL at days 7-10 of CL age when lutropin is indispensable as a luteotropic hormone, and that placentas at days 18-21 of pregnancy could support the rapid growth of CL at day s 10-13 of CL age. Placental hormones which might participate in these luteotropic events were discussed.

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