Progesterone and oestrogen receptors in the female genital tract throughout pregnancy in tammar wallabies

The tammar, Macropus eugenii, is a monovular macropodid marsupial which has a postpartum oestrus and an 11 month embryonic diapause. Progesterone and oestradiol cytosol receptors were measured by Scatchard analyses and single point analysis in the lateral vagina, endometrium and myometrium of the gr avid and contralateral nongravid uterus throughout pregnancy, immediately a fter parturition and during seasonal reproductive quiescence. In endometria l tissues, both progesterone and oestradiol receptors doubled in concentrat ion in both gravid and non-gravid uteri between day 0 and day 5 of pregnanc y, coinciding with previously described peak values in peripheral plasma pr ogesterone and oestrogen. Receptor concentrations in endometrial tissue dur ing seasonal quiescence were not significantly different from those immedia tely after reactivation. After day 12 of pregnancy, downregulation of both progesterone and oestradiol cytosolic receptors occurred concomitant with t he increase in progesterone in the peripheral plasma.:However, there was a unilateral increase in oestradiol receptor concentrations in endometrium ob tained from the nongravid uterus between day 25 of the 26.5 day gestation a nd immediately after parturition Myometrial receptor concentrations mirrore d those of the endometrium but were lower. Concentrations of progesterone r eceptor in the lateral vaginae were at the lower limit of detection, while the oestradiol cytosol receptor concentrations were even lower in this tiss ue. Thus, the steroid receptor concentrations provide another example of lo cal unilateral endocrine responses in the reproductive tract of the tammar. These results also indicate that the downregulation of progesterone and oe stradiol receptors that occurs in both uteri in mid- and late-pregnancy is selectively and locally reversed before parturition in the non-gravid endom etrium in response to the local effects of follicular oestradiol from the i psilateral ovary.