Comparison of ET‐1 and eNOS expressions in yak testes at different developmental stages.

Yak has strong adaptability to plateau hypoxia environment. However, the endothelin‐1 (ET‐1) and endothelial nitric oxide synthase (eNOS) are important regulators in blood oxygen transportation. Yak testes: newborn (3 days), young (1 years), adult (4 years) and old (9 years) were collected for microscopic analyses using haematoxylin and eosin staining (H&E), immunohistochemistry and immunofluorescence, as well as Western blot to compare the expression of ET‐1 and eNOS. Furthermore, the levels of ET‐1 mRNA and eNOS mRNA was detected by real‐time quantitative polymerase chain reaction (RT‐qPCR). The results showed that ET‐1 mRNA and eNOS mRNA in old yaks were higher than other developmental stages (p <.01). And the levels of ET‐1 and eNOS protein increased with age. Immunohistochemistry and immunofluorescence showed that ET‐1 and eNOS were mainly localized in gonocytes and spermatogenic membrane of newborn yaks. These two factors were expressed in both Leydig cells of young yaks and endothelial cells of adult yaks. In old yaks, ET‐1 was mainly expressed in Sertoli cells, while eNOS was obviously positive in capillaries and Leydig cells. Therefore, the positive results of ET‐1 and eNOS in gonocyte and spermatogenic basement were closely related to the development of testes. The expression of Leydig and Sertoli cells indicated that they played an important role in testes function. The expression in endothelial cells or interstitial capillaries, suggesting that they are involved in the regulation of microcirculation in yak testes. This study could provide clues for further revealing the regulation of yak testicular blood vessels in alpine cold and hypoxic environments. [ABSTRACT FROM AUTHOR]