Abstract
PMSG-induced prepubertal pregnant rats were injected with hCG 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 two 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 of and progesterone secretion of the secondary CL rapidly increased. Hysterectomy on Day 18 of pregnancy (Day 10 of the secondary CL age), however, 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 LH is indispensable as a luteotropic hormone, and that placentas between Days 18 and 21 of pregnancy could support the rapid growth of CL at Days 10-13 of CL age. Placental hormones which would participate in these luteotropic events have been discussed.
