Luteal function during the periimplantation period and requirement for estrogen for implantation and pregnancy maintenance in the non-human primate

Abstract

An attempt has been made in this paper to review our present understanding of luteal function during the periimplantation period and in particular hormonal requirement for implantation and maintenance of early pregnancy in the non-human primate. In a fertile cycle thecorpus luteum is apparently rescued from luteolysis by chorionic gonadotropin secreted by the implanted blastocyst, In the bonnet monkey the serum progesterone titers during the luteal phase of a fertile cycle seems higher compared to that of nonmated cycling monkeys. This suggested that thecorpus luteum is receiving some stimulatory signal from the blastocyst even prior to implantation. The recent demonstration that human blastocyst in culture secretes into the medium human chorionic gonadotropin essentially support the above assumption. However, attempts to extend the luteal phase of cycling unmated monkeys with exogenous human chorionic gonadotropin injection has hitherto not met with complete success suggesting that there could be other than chorionic gonadotropin, additional luteal stimulatory factors the unimplanted blastocyst is secreting. Corpus luteum is the principle source of both progesterone and estrogen produced during the periimplantation period and dysruption of luteal function, brought about by either lutectomy or ovariectomy or luteinizing hormone antiserum treatment, followed by progesterone supplementation leads to maintenance of pregnancy. This has lead to questioning the need for estrogen in the maintenance of early pregnancy. Recent work using Zuclomiphene, an antiestrogen during days 5-11 of cycle in rhesus monkeys mated between day 9-14, has however, suggested that estrogen may be required for implantation. Further work is needed to arrive at an unequivocal decision regarding the need for estrogen in maintenance of early pregnancy in the primate.