Expression of 17β-hydroxysteroid dehydrogenase and the effects of LH, FSH and prolactin on oestrone and 17β-oestradiol secretion in the endometrium of pigs during early pregnancy and the oestrous cycle.

The endometrium of pregnant and cyclic pigs is a source of oestrone (E1) and 17β-oestradiol (E2). However, the roles of LH, FSH and prolactin (PRL) as regulators of endometrial steroidogenesis, and the presence of 17β-hydroxysteroid dehydrogenase (17β-HSD) in the porcine endometrium, remain unknown. Therefore, in the present study we examined 17β-HSD expression and the effects of LH, FSH and PRL on E1 and E2 release in vitro in endometrial explants harvested from gravid pigs on Days 10-11 (embryo migration within the uterus), 12-13 (maternal recognition of pregnancy) and 15-16 (beginning of implantation) and compared them with results obtained in non-gravid pigs. The results show that: (1) endometrial 17β-HSD activity was decreased on Days 15-16 in pregnant and cyclic pigs compared with the preceding days; (2) LH, FSH and PRL increased endometrial E1 secretion on Days 10-11 and 15-16 of pregnancy and on Days 12-13 and 15-16 of the oestrous cycle; and (3) LH, FSH and PRL increased endometrial E2 secretion on Days 15-16 of pregnancy and during the days studied in the oestrous cycle. In conclusion, data suggest that LH, FSH and PRL affect endometrial secretion of estrogens in pigs.