Background: Cryptorchidism is one of the most common birth disorders of the male reproductive system identified in
dogs and other mammals. This condition is characterised by the absence of one (unilateral) or both (bilateral) gonads
from the scrotum. The peptides orexin A (OxA) and B (OxB) were obtained by post-transcriptional proteolytic cleavage
of a precursor molecule, called prepro-orexin. These substances bind two types of G-coupled receptors called receptor
1 (OX1R) and 2 (OX2R) for orexins. OX1R is specific to OxA while OX2R binds the two peptides with equal affinity.
Orexins modulate a great variety of body functions, such as the reproductive mechanism. The purpose of the present
research was to study the presence of OxA and its receptor 1 and their possible involvement in the canine testis under
healthy and pathological conditions.
Methods: This study was performed using adult male normal dogs and male dogs affected by unilateral cryptorchidism.
Tissue samples were collected from testes and were divided into three groups: normal, contralateral and cryptic. The
samples were used for immunohistochemistry, Western blot and in vitro tests for testosterone evaluation in normal and
pathological conditions.
Results: OxA-immunoreactivity (IR) was described in interstitial Leydig cells of the normal gonad, and Leydig, Sertoli cells
and gonocytes in the cryptic gonad. In the normal testis, OX1R-IR was described in Leydig cells, in pachytene and
second spermatocytes and in immature and mature spermatids throughout the stages of the germ developing
cycle of the male gonad. In the cryptic testis OX1R-IR was distributed in Leydig and Sertoli cells. The presence of
prepro-orexin and OX1R was demonstrated by Western blot analysis. The incubation of fresh testis slices with
OxA caused the stimulation of testosterone synthesis in the normal and cryptic gonad while the steroidogenic
OxA-induced effect was cancelled by adding the selective OX1R antagonist SB-408124.
Conclusions: These results led us to hypothesise that OxA binding OX1R might be involved in the modulation of
spermatogenesis and steroidogenesis in canine testis in healthy and pathological conditions
