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.