Abstract: The aim of this study was to compare the distribution of endothelin-1 (ET-1) and endothelial nitric oxide synthase (eNOS) in the normal testes and cryptorchidism of yak, and analyze the role of ET-1/eNOS differences in cryptorchidism of yak. The 20 pairs of healthy and pathological adult (4-year-old) male yak testes were collected and divided into three groups: the normal group (10 pairs), the unilateral descent group (6 pairs), and the cryptorchidism group (4 pairs). The H.E, Masson’s and Gomori’s staining were used to compare the histochemical characteristics; Immunohistochemical methods, immunofluorescence techniques and quantitative real-time PCR (qPCR) were used to detect the expression levels of ET-1 and eNOS in different groups testes, and morphometric statistical software was used to compare the differences.The results showed that, compared with the normal group, there was no significant difference in the ratio of interstitial to luminal area in the unilateral descent group of yaks (P>0.05); In the cryptorchidism group, the luminal area was significantly reduced, and the content of collagen and reticular fibers were increased. Immunohistochemistry and immunofluorescence results showed: The ET-1 was expressed in leydig cells, spermatogenic cells at different stages, while mainly expressed in leydig cells and no significant expression was observed in the cryptorchidic epithelium, the difference in average optical density of ET-1 between the normal and unilateral descent groups was significant (P<0.05), also the difference between the normal and cryptorchidism groups was extremely significant (P<0.01). The eNOS was expressed in seminiferous tubules and leydig cells. Compared with the normal group, the difference in eNOS expression was extremely significant in the unilateral descent group (P<0.001) and significant in the cryptorchidism group (P<0.05). qPCR results showed that the relative expression of ET-1 in normal group was significantly higher than that in unilateral descent and cryptorchidism group (P<0.01), the relative expression of eNOS in unilateral descent group was higher than that in normal group (P<0.05). Yaks living in a hypoxic environment on the plateau, the seminiferous tubules are atrophied and interstitial cells decreased in the cryptorchidism testes of yak, ultimately leading to the local secretion regulation inhibited and sperm development obstructed. ET-1 and eNOS are co-located in leydig cells, the expression imbalance in interstitial cells in the unilateral descent group and cryptorchidism group should be caused by abnormal distribution in interstitial cells and blood vessels.

Key words: yak, endothelin-1, endothelial nitric oxide synthase, testis, cryptorchidism