Female undernutrition during early pregnancy may affect the physiological pattern of genomic DNA methylation. We hypothesised that in utero DNA methylation may be impaired in females fed a restrictive diet in early pregnancy. In this study we evaluated whether poor maternal nutritional status, induced by applying a restricted diet during the peri-conceptional period, may influence: (1) the potential for in utero DNA methylation, expressed as changes in the mRNA expression and protein abundance of methyltransferases: DNA methyltransferase 1 (DNMT1) and DNMT3a in the endometrium and the myometrium, (2) the intrauterine microenvironment, measured as oestradiol 17ß (E2) and progesterone (P4) concentrations in uterine flushings and (3) plasma concentration of E2 and P4 during the peri-implantation period. Our results indicate that maternal peri-conceptional undernutrition affects maintenance and de novo DNA methylation in the endometrium, de novo methylation in the myometrium and a results in a decrease in intrauterine E2 concentration during the peri-implantation period. The intrauterine concentration of P4 and plasma concentrations of E2 and P4 did not change. These findings suggest that undernutrition during the earliest period of pregnancy, and perhaps the pre-pregnancy period, may create changes in epigenetic mechanisms in the uterus and intrauterine milieu of E2 during the peri-implantation period.

The endometrium of pregnant and cyclic pigs is a source of oestrone (E1) and 17ß-oestradiol (E2). However, the roles of LH, FSH and prolactin (PRL) as regulators of endometrial steroidogenesis, and the presence of 17ß-hydroxysteroid dehydrogenase (17ß-HSD) in the porcine endometrium, remain unknown. Therefore, in the present study we examined 17ß-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 17ß-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.