Expression of calbindin-D9k and vitamin D receptor in the uterus of Egyptian buffalo during follicular and luteal phases

Uteri of mature Egyptian buffalo cows (5–10 years old) were collected at follicular (n = 12) and luteal (n = 16) phases of estrous cycle to investigate the expression of calbindin-D9k (CaPB-9k) and vitamin D receptor (VDR). This study was done using avidin-biotin immunohistochemistry method. In addition, blood levels of calcium (Ca), vitamin D3 (Vit D), estrogen (E2) and progesterone (P4) were measured. The immunohistochemical findings restricted the expressions of CaBP-9k and VDR to the luminal and glandular epithelia of the endometrium implicating the importance of CaBP-9K and VDR in the function of endometrial epithelium, especially the glandular one, in order to prepare a receptive uterus. On the other hand, the myometrium did not express CaBP-9k or VDR that denies the potential role of CaBP-9k and VDR in the uterine contractility during the estrous cycle of Egyptian buffalo. All of Ca, Vit D, and P4 blood levels significantly (P < 0.05) increased during luteal phase however, blood level of E2 significantly (P < 0.05) increased during follicular phase. The expressions of CaBP-9k and VDR in the uterus of Egyptian buffalo were significantly (P < 0.05) higher during luteal (P4 dominant) phase than during the follicular (E2 dominant) phase indicating that P4 up-regulates the expressions of CaBP-9k and VDR. In view of these observations, this study represents the first characterization of CaBP-9K and VDR expression in the uterus of Egyptian buffalo and suggests the pivotal role of CaBP-9k and VDR in the uterine receptivity. Furthermore, it demonstrates the regulatory role of P4 for expressions of CaBP-9k and VDR in buffalo uterus.