G. Giannoukos et al., TURTLE OVIDUCT PROGESTERONE-RECEPTOR - RADIOLIGAND AND IMMUNOCYTOCHEMICAL STUDIES OF CHANGES DURING THE SEASONAL CYCLE, Endocrine, 3(6), 1995, pp. 429-437
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.