EXPRESSION OF OREXIN A AND B IN THE PORCINE HYPOTHALAMUS DURING THE OESTROUS CYCLE

Orexins A and B are hypothalamic peptides engaged in a variety of physiological functions related to the control of energy homeostasis, sleep and wakefulness. The presence of orexin receptors in the tissues of the hypothalamus-pituitary-gonadal axis indicates that these hormones are also involved in the control of the reproductive system. The aim of this study was to compare the expression levels of prepro-orexin (a precursor of orexins A and B) mRNA in the porcine hypothalamic structures involved in reproductive processes - mediobasal hypothalamus (MBH), preoptic area (POA) and stalk median eminence (SME), during four stages (days 2-3, 10-12, 14-16, 17-19) of the oestrous cycle. In MBH, lower concentrations of PPO mRNA were observed on days 2-3 than in the remaining stages. In POA, the highest mRNA expression of PPO was noted on days 17-19. In SME, the highest concentrations of PPO was observed on days 2-3, and the lowest on days 14-16. We also investigated the intensity of OXA and OXB immunoreactivity and detected both peptides in all examined structures. In MBH, signal intensity for OXA was highest on days 14-16 and lowest on days 17-19. The highest levels of immunoreactivity were noted on days 2-3 and 10-12 in POA, and in SME additionally on days 17-19. OXB immunoreactivity in hypothalamic tissues also changed during the cycle, and the highest signal intensity was reported on days 10-12 in MBH, on days 14-16 in POA, and on days 14-16 and 17-19 in SME. The results of our study indicate that orexins A and B are produced in the porcine hypothalamus and that their concentrations vary subject to the pig's hormonal status. Our findings also suggest that orexins may affect reproductive functions at the highest level of the hypothalamus-pituitary-gonadal axis.