TURTLE OVIDUCT PROGESTERONE-RECEPTOR - RADIOLIGAND AND IMMUNOCYTOCHEMICAL STUDIES OF CHANGES DURING THE SEASONAL CYCLE

In order to determine the regulation of the oviduct progesterone recep tor in Chrysemys picta, radioligand binding studies were performed to determine changes in the high and lower affinity binding sites during the seasonal cycle. Lower affinity sites were present in both cytosoli c and nuclear fractions during the cycle and peaked during the peri-ov ulatory/early luteal periods. The high affinity sites, present exclusi vely in the nuclear fraction, increased following the preovulatory pea k in plasma estradiol, remained elevated during the early luteal phase following the post-ovulatory peak in progesterone, and declined to no ndetectable levels just before egg-laying. DNA-cellulose affinity chro matography showed that both high and low affinity binding sites were i ntegral to both progesterone receptor and and A isoforms. Western blot analysis confirmed the binding studies and showed that PR-B (115 kDa) was present in greatest amounts during the peri-ovulatory and luteal periods, whereas PR-A (88 kDa) increased during those periods and was present following egg-laying. Immunocytochemical analysis revealed inc reased progesterone receptor immunostaining from the winter to the per i-ovulatory period in the three major zones (luminal epithelium, submu cosal glands and the myometrium) following the preovulatory peak in es tradiol, a decrease in all three zones, especially the myometrium, in the late luteal period following the post-ovulatory peak in progestero ne, and an increase again during fall recrudescence. Competition studi es demonstrated that progesterone was the most effective competitor fo llowed by pregnenolone, R5020 and deoxycorticosterone. RU 486 does not bind to the high affinity site, but binds quite well to the lower aff inity site. This study suggests that progesterone receptor isoforms in the turtle oviduct may be under the regulation of changing estrogen/p rogesterone ratios during the cycle.