RADIOLIGAND AND IMMUNOCHEMICAL STUDIES OF TURTLE OVIDUCT PROGESTERONEAND ESTROGEN-RECEPTORS - CORRELATIONS WITH HORMONE-TREATMENT AND OVIDUCT CONTRACTILITY

Progesterone (PR) and estrogen (ER) receptors were previously identifi ed and characterized in the reproductive tract of the turtle, Chrysemy s picta, and changes in PR levels were monitored during the seasonal c ycle. To understand the hormonal regulation of PR, intact and ovariect omized animals were treated with estradiol, progesterone, and a combin ation of estradiol and progesterone, and high affinity PR and ER level s were determined by radioligand binding studies. Ovariectomy signific antly decreased ER levels; in contrast, PR levels increased following ovariectomy. In both intact and ovariectomized animals, estradiol alon e did not elevate PR levels above control; however, the PR was down-re gulated by progesterone. ER levels in ovariectomized animals were not restored by any of the steroid regimens. By Western blot analysis, PR levels appeared to increase following ovariectomy, were unaffected by estradiol, and were somewhat decreased following progesterone treatmen t in estradiol-primed ovariectomized animals. While not quantitative, these results are supportive of radioligand binding studies. Immunocyt ochemical studies of oviduct PR followed the same pattern showing incr eased immunoreactivity following ovariectomy, no change with estradiol , and a decrease following progesterone treatment of estradiol-primed animals. Oviduct contractility was monitored as a physiological index of progesterone action. Estradiol significantly increased the amplitud e of the contractions both in vivo and in vitro, whereas progesterone in combination with estradiol significantly inhibited the estrogen eff ect. This study suggests that estradiol alone may not be adequate for regulation of both ER and PR. While progesterone down-regulates its ow n receptor, it does not appear to influence the ER. These data are in contrast to mammalian and avian studies which show that estradiol incr eases both the ER and PR in the reproductive tract, and progesterone d own-regulates both receptors. (C) 1996 Academic Press, Inc.