A Preliminary Study on the Role of Orexin A in Leydig Cell Steroidogenesis and Its Implications for Fertility in Alpacas (Vicugna pacos).

In Italy, the breeding of alpacas (Vicugna pacos) is on the rise, driven by the value of their precious wool and their docile temperament. This growth is, however, severely limited by the species' reproductive inefficiency. This study aimed to investigate the specific role of the neuropeptide orexin A (OxA) and its receptor OX1R in modulating testicular steroidogenesis in the alpaca, testing the hypothesis that the OxA/OX1R pathway stimulates testosterone production. Using testicular tissue from two groups of adult male alpacas (five- and seven-year-olds, n = 6 per group), we combined immunohistochemistry with ex vivo functional assays. Immunohistochemical analysis confirmed the expression of both OxA and OX1R in Leydig cells. Functional studies on testicular fragments demonstrated that OxA enhanced testosterone synthesis via OX1R activation. Furthermore, OxA reduced estradiol levels by suppressing aromatase activity and counteracted the inhibitory effect of Müllerian inhibiting substance (MIS) on testosterone secretion. These results provide the first evidence that the peripheral OX1R pathway is functionally involved in promoting a testosterone-dominant steroidogenic milieu in alpaca testes. This preliminary study identifies the orexin system as a potential target for developing strategies to improve reproductive management in this species.