Expression of estrogen and progesterone receptors in the bovine ovary during estrous cycle and pregnancy.

The objective of the study was to demonstrate the mRNA expression of estrogen receptor a (ERa), ERbeta, and progesterone receptor (PR) by block reverse transcription-polymerase chain reaction(RT-PCR) and real-time RT-PCR (LightCycler) in bovine ovarian follicles and in corpus luteum during the estrous cycle and pregnancy. The mRNA expression of ERalpha and ERbeta mRNA in theca interna tissue (TI) (lower pg/microg RNA) increased continuously and significantly during final growth of follicles, with much higher levels for ERalpha. The mRNA expression of ERalpha and ERbeta in granulosa cells (GC) (fg/microg RNA) increased continuously during follicle growth but without any significant change. The expression of mRNA for PR in follicles (lower fg/microg RNA) increased continuously to maximum level in preovulatory follicles with a significant change only in TI. The highest mRNA expression for ERalpha (fg/microg RNA) was detected in corpus luteum (CL) during the early luteal phase, following by a significant decrease of expression during the mid, late, and regression phases. In contrast, ERbeta mRNA expression is relatively high during the early stage, decreased during the late early and mid luteal phase, and increased significantly again during the late luteal phase and after CL regression. During pregnancy (>3 mo), low levels of ERalpha and ERbeta mRNA expression (<25 fg/microg RNA) with no significant changes were measured. No significant change in PR mRNA expression (levels <13 fg/microg RNA) during the estrous cycle and pregnancy in bovine CL were found. The results suggest an autocrine/paracrine role of steroid receptors in the regulation of final follicle growth and corpus luteum formation and function.