The effect of estrone and estradiol on the expression of the orexin/hypocretin system in the porcine uterus during early pregnancy.

Orexin A and B (OXA, OXB) are hypothalamic neuropeptides acting via two receptors, type 1 (OX1R) and 2 (OX2R). Orexins, also known as hypocretins, take part in a common endocrine system regulating metabolism and reproductive functions. Changes in the orexin system expression during the estrous cycle and pregnancy suggest dependence on the local hormonal milieu. Estrogens are the key hormones controlling reproductive functions, including maternal recognition of pregnancy and implantation. We hypothesize that estrogens may affect orexin system expression in the early pregnant uterus. The aim of this study was to investigate the influence of estrogens on prepro-orexin (PPO), OX1R, and OX2R gene expression, OX1R and OX2R protein content in the porcine uterine tissue, as well as OXA and OXB secretion on days 10-11, 12-13, 15-16, and 27-28 of pregnancy and on days 10-12 of the estrous cycle (n = 5 per group). The expression of PPO, OX1R, and OX2R genes was examined using qPCR, OX1R and OX2R protein content was evaluated using western blotting, and orexins secretion was determined with ELISA. This is the first study to describe the influence of estrogens on orexin system expression in the porcine uterus. Obtained results revealed that estrogens significantly affect the expression of orexin system and orexins secretion. The influence of estrogens varied between different stages of early pregnancy and the estrous cycle. The steroids showed a tissue-specific and dose-dependent effect. Our findings suggest that orexins could act as a "molecular switch" for estrogen activation in the processes of endometrial decidualization and rapid uterine enlargement during early pregnancy.