CaBP9K levels during the luteal and follicular phases of the estrous cycle in the bovine uterus

The expression of calbindin-D(9K) (CaBP(9K)) and calbindin-D(28K) (CaBP(28K)) genes in the reproductive system is well established for rodent and avian species, but not for domestic livestock. This investigation expanded the study of these proteins to include the bovine uterus and examined the levels of CaBP(9K) and CaBP(9K) mRNA in the nonpregnant bovine uterus during the estrous cycle. Immunohistochemical studies revealed that CaBP(9K) was present in all uterine glandular and luminal epithelial cells. In contrast, the closely related calcium binding protein CaBP(28K) was present in only one to two glandular cells in all the samples examined. Neither protein was localized in the myometrium or in the stromal cells of the endometrium. RIA and dot blot hybridization were used to quantify the amount of CaBP(9K) and CaBP(9K) mRNA. The levels of both the protein and its mRNA were threefold higher during the luteal phase than during the follicular phase. RIA was also used to determine bovine uterine levels of 17 beta-estradiol and progesterone. Progesterone levels were higher during the luteal phase than during the follicular phase, while 17 beta-estradiol levels were higher during the follicular phase. This investigation represents the first characterization of CaBP(9K) gene expression in the bovine uterus. It demonstrated that the expression of CaBP(9K) and CaBP(9K) mRNA was greatest during the progesterone-dominated luteal phase of the bovine estrous cycle. These results indicated that CaBP(9K) may be involved in uterine glandular function during the luteal phase