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

## TL;DR

This study explores how orexin A affects testosterone production in alpaca testes, offering insights for improving alpaca fertility.

## Contribution

The study is the first to demonstrate the role of the orexin A/OX1R pathway in promoting testosterone production in alpaca Leydig cells.

## Key findings

- Orexin A increases testosterone synthesis in alpaca testicular tissue via OX1R activation.
- Orexin A reduces estradiol levels by suppressing aromatase activity.
- Orexin A counteracts the inhibitory effect of Müllerian inhibiting substance on testosterone secretion.

## Abstract

To support the sustainable growth of alpaca farming in Italy, hindered by the species’ reproductive challenges, this study examined a natural signaling system involving orexin A (OxA). Investigations using testicular tissue revealed that this system is active in the hormone-producing cells of alpacas. The research demonstrated that OxA effectively increases testosterone levels and reduces the action of other substances that inhibit this key fertility hormone. This evidence identifies the orexin pathway as an important regulator of testicular function, offering a scientific foundation for future approaches to enhance reproductive management in alpaca breeding.

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.