LUTEOTROPIC HORMONE RECEPTORS IN THE OVARY OF THE MINK (MUSTELA-VISON) DURING DELAYED IMPLANTATION AND EARLY-POSTIMPLANTATION GESTATION

The reproductive cycle of the mink displays rigid seasonality and obli gate embryonic diapause. After ovulation, the corpus luteum (CL) invol utes, and it secretes basal progesterone until activated prior to impl antation. To study changes in the relative abundance of luteal prolact in and LH receptor mRNA through gestation, ovaries and serum were coll ected from pregnant female mink at 2-day intervals (n = 3 per date) th rough embryonic diapause and CL activation (March 19-31) and at 5-day intervals through implantation and early-postimplantation gestation (M arch 31-April 15). To determine the effect of endogenous prolactin, mi nk received Alzet osmotic minipumps releasing 2 mg/day 2-bromo-alpha-e rgocryptine (bromocriptine) or saline on March 19. Ovaries and serum w ere taken from 3 animals every 2 days until March 31. Prolactin recept or mRNA in ovaries was low during CL activation but increased 3-fold t hrough embryo implantation. Its abundance correlated with prolactin bi nding to ovarian membranes and with circulating prolactin. Bromocripti ne suppressed endogenous prolactin levels and prevented the increase i n prolactin receptor mRNA. There was a transient peak in LH receptor m RNA in the ovaries at March 19-23, which declined to basal levels by M arch 25 and remained constant through midgestation. Bromocriptine prev ented the preimplantation peak in LH receptor mRNA and reduced its abu ndance below pretreatment levels. The results suggest that prolactin u p-regulates its receptor and maintains the LH receptor in the mink CL. The pattern of LH receptor mRNA argues for a role for LH in CL reacti vation and termination of embryonic diapause in mink.