Orexin A promotes granulosa cell secretion of progesterone in sheep

Background: Orexin A, a small-molecule peptide, can regulate female hormones, but limited evidence for its mechanism of activity exists in ovine. Aims: The objective of this study was to investigate the effect of orexin A on progesterone (P4) secretion in cultured granulosa of sheep follicles. Methods: Sheep ovarian granulosa were isolated and identified, pre-incubated with luteinizing hormone (LH) (2.5 IU/ml), follicle-stimulating hormone (FSH) (2.5 IU/ml), or oestrogen (1 µg/ml); and cultured in vitro. The pretreated sheep ovarian granulosa were subsequently cultured with different concentrations (1 nM, 10 nM, 58 nM, 100 nM, and 145 nM) of orexin A for varying amounts of time (0 h, 24 h, 48 h, and 72 h). Then, the expression levels of P4, steroidogenic acute regulatory protein (StAR), 3β-Hydroxysteroid dehydrogenase (3β-HSD) and cytochrome P450 (CYP11) were determined. Results: The results showed that the sheep ovarian granulosa were correctly identified. The different concentrations of orexin A promoted the secretion of P4 from granulosa in the ovine ovary compared with that in the control. The expression of StAR, 3β-HSD and P450 (CYP11) gradually increased, and then decreased with increasing concentrations of orexin A, but the expression of P450 (CYP11) decreased with the increase of time. Conclusion: These results revealed that orexin A promotes the secretion of P4 by regulating the expression of StAR, 3β-HSD, and P450 (CYP11). Understanding the mechanism underlying the promotion of P4 by orexin A could open new therapeutic possibilities in the treatment of hormone homeostasis.