Expression of Orexin A and its Receptor 1 in the Epididymis of the South American Camelid Alpaca (Vicugna pacos)

Orexins A (ox A) and B are two peptides originally discovered in neurons of rat hypothalamus, and later found in different cellular types of the gastrointestinal and genital tracts. They arise from the proteolytic cleavage of a common precursor molecule, prepro‐orexin, and bind to two receptors, namely receptor 1 (ox1r) and receptor 2 for orexins, that show different binding affinity. The central role of the two peptides has been extensively studied, whereas their activity in the periphery is still poorly known. Here, we investigated the presence of ox A and ox1r in the epididymis of a South American camelid species, the alpaca, by immunohistochemistry, and we also assessed the expression of prepro‐orexin and ox1r in tissue extracts by Western blotting analysis. Ox A‐ and ox1r‐immunoreactivity was found in the cytoplasm of principal cells of the caput epididymis. A prevalent supranuclear localization of granular‐shaped positive material was observed. No positivity was present in the other cytotypes of epididymis. The expression of two peptides with molecular weight corresponding to those of prepro‐orexin and ox1r, respectively, was detected in the tissue extracts from the organ.