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

The role of vitamin D has been confirmed in female reproductive organs. This study aimed to examine vitamin D 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)D concentration in uterine flushings and the effect of 1,25(OH)D (10, 50 and 100 ng/mL) in vitro on and mRNA transcript abundance in endometrial and myometrial slices. In the endometrium, a greater 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 mRNA transcript abundance was greater on days 18-20 than on days 10-12 and 15-16. In the myometrium, 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 mRNA transcript nor encoded protein abundance were detected in the myometrium. The highest 1,25(OH)D concentration in uterine flushings was observed on days 18-20. Furthermore, the 1,25(OH)D increased the abundance of the mRNA transcript in endometrial slices. Overall, our results suggest that porcine uterus is an extra-renal site of vitamin D metabolism. Both the endometrium and the myometrium possess the ability to synthesize vitamin D, while only the endometrium contributes to its catabolism.