Distribution of estrogen receptor alpha in the dominant follicles and corpus luteum at the three stages of estrous cycle in Japanese Black cows

Distribution of estrogen receptor alpha (ERalpha) in the dominant follicle (DF) and corpus luteum (CL) at the three stages of estrous cycle in Japanese Black cows was evaluated by means of immunohistochemistry. Ovarian dynamics were observed twice daily using ultrasonography until the ovariectomy performed on Day 7 (First group, n=3), Day 10 (Second group, n=3) and Day 18 (Third group, n=3) (Day 0=estrus). Expression of ERalpha represented by immunohistological staining intensity in cells was determined using a light microscope equipped with a digital camera. A tendency toward higher expression were observed in theca interna (TI) of DF when compared with those in mural granulosa cells (mGC), antral granulosa cells (aGC) and theca externa (TE). ERalpha expression in the Third group was lower than that in the First Group in mGC, and it was also lower than that in the second group in TE (P<0.05). ERalpha expression in lineal cells was higher than those in the stromal cells in CL. No significant difference of ERalpha expression was observed within luteal or stromal cells, except in the Second group in the luteal cells, in which significantly higher expressions than that in the Third group (P<0.05) were observed. The results showed that, 1) ERalpha was present in developing DF on Day 7, early regressing DF on Day 10 and preovulatory DF on Day 18, especially in the TI, and a few were localized in the mGC, and 2) ERalpha was highly expressed in the luteal cells and the expression decreased in combination with regression of CL.