Expression of irisin in the porcine pituitary gland during the oestrous cycle and early pregnancy: the role of GnRH, gonadotropins, and insulin

Context Metabolic status significantly affects female reproductive function, with both excess and deficiency of body fat negatively affecting fertility. Irisin, a hormone secreted by muscle and fat tissue, is linked to metabolism and reproduction, but its role in the pituitary gland remains unclear. Aims This study investigated the expression of irisin and its receptor (integrin αV/β5) in the anterior (AP) and posterior (PP) lobes of the porcine pituitary during the oestrous cycle and early pregnancy. We hypothesised that they are localised in specific pituitary cell types and that gonadotropin-releasing hormone (GnRH), luteinising hormone (LH), follicle-stimulating hormone (FSH), and insulin modulate irisin expression and secretion by AP cells. Methods The expression of irisin and integrin αV/β5 was analysed using quantitative real-time polymerase chain reaction (qPCR) and western blotting. Immunofluorescence was used to determine colocalisation with pituitary hormones. AP cells were cultured in vitro and treated with GnRH, LH, FSH, or insulin to assess their effects on irisin protein concentrations and secretion. Key results Irisin and its receptor were expressed in both AP and PP lobes and colocalised with all major trophic cell types. Their expression varied depending on the reproductive stage. GnRH, LH, FSH, and insulin inhibited irisin secretion by AP cells during the luteal phase, whereas only insulin had an effect during the follicular phase. Conclusions Irisin and its receptor are expressed in a hormone-dependent manner and localise to specific pituitary cell types, suggesting intra-pituitary regulatory roles. Implications These findings indicated that irisin may act as a local modulator of pituitary function and reproductive hormone regulation, linking metabolic and reproductive health.