Vitamin D(3) Metabolic Enzymes in the Porcine Uterus: Expression, Localization and Autoregulation by 1,25(OH)(2)D(3) In Vitro

The role of vitamin D(3) has been confirmed in female reproductive organs. This study aimed to examine vitamin D(3) metabolic enzymes, i.e., CYP27B1 and CYP24A1, mRNA transcript and protein abundance, and protein localization in the uterus of pigs on days 2–5, 10–12, 15–16 and 18–20 of the estrous cycle. Additionally, we determined 1,25(OH)(2)D(3) concentration in uterine flushings and the effect of 1,25(OH)(2)D(3) (10, 50 and 100 ng/mL) in vitro on CYP27B1 and CYP24A1 mRNA transcript abundance in endometrial and myometrial slices. In the endometrium, a greater CYP27B1 mRNA transcript abundance was noted on days 10–12 and 18–20 than on days 15–16, whereas encoded protein abundance was greater on days 18–20 when compared to days 15–16. Endometrial CYP24A1 mRNA transcript abundance was greater on days 18–20 than on days 10–12 and 15–16. In the myometrium, CYP27B1 mRNA transcript abundance was greater on days 18–20 than on days 2–5 and 15–16, while protein abundance was larger in slices collected on days 18–20 than on days 15–16. Neither CYP24A1 mRNA transcript nor encoded protein abundance were detected in the myometrium. The highest 1,25(OH)(2)D(3) concentration in uterine flushings was observed on days 18–20. Furthermore, the 1,25(OH)(2)D(3) increased the abundance of the CYP24A1 mRNA transcript in endometrial slices. Overall, our results suggest that porcine uterus is an extra-renal site of vitamin D(3) metabolism. Both the endometrium and the myometrium possess the ability to synthesize vitamin D(3), while only the endometrium contributes to its catabolism.