The effect of interleukin 1β and interleukin 6 on estradiol-17β secretion in the endometrium of pig during early pregnancy and the estrous cycle

Abstract

Estrogens are produced by porcine embryos during early pregnancy. It was found that the uterus of pigs might be a source of steroid hormones, including estrogens. However, the factors involved in the regulation of endometrial steroidogenesis remain unknown. We hypothesize that interleukin (IL) 1β and IL6, which are cytokines produced by porcine embryos and uterine cells, might be involved in the regulation of endometrial estrogen synthesis. Porcine endometrial explants were harvested from gravid (N = 15) and cyclic (N = 15) pigs on days 10 to 11, 12 to 13, and 15 to 16. Samples were analyzed to determine: (1) the expression of CYP19 mRNA and the presence of aromatase cytochrome P450 protein in the tissue; and (2) the release of endometrial estradiol-17β (E2) in response to IL1β and IL6 after 6 and 12 hours of in vitro incubation. The effects observed in pregnant gilts were compared with the effects in nonpregnant gilts on corresponding days of the estrous cycle. On days 15 to 16 of pregnancy the expression of CYP19 in the endometrium was markedly decreased when compared with other periods, and the quantity of endometrial P450 aromatase protein was higher on these days than on days 12 to 13. In nongravid pigs, the expression of CYP19 was lower on days 15 to 16 when compared with days 12 to 13 and the quantity of P450 aromatase protein did not differ during the studied days of the estrous cycle. Basal endometrial E2 release was higher in pregnant gilts when compared with cyclic gilts only on days 15 to 16. In gravid pigs IL1β and IL6 did not affect endometrial E2 release on days 10 to 11 and 12 to 13 of pregnancy (P > 0.05); however, increased E2 release was observed on days 15 to 16 (P < 0.05). In cyclic pigs neither IL1β, nor IL6 affected endometrial E2 release (P > 0.05). These results provide evidence that: (1) the endometrium possesses a potential for steroidogenesis and produces E2in vitro in gravid and nongravid pigs between days 10 to 16; and (2) IL1β and IL6 increase in vitro endometrial synthesis of E2 in pregnant pigs on days 15 to 16. Therefore, IL1β and IL6 might act as stimulators of endometrial E2 secretion in vitro during the time of decreased production of embryonic estrogens. This correlates with a rapid remodeling of the endometrial tissue and the beginning of hemotrophic nutrition of the embryos occurring on days 15 to 16 of pregnancy.