Immunohistochemical localization of glucose transporter 1 and 3 in the scrotal and abdominal testes of a dog.

Glucose is essential for testicular function; the uptake of carbohydrate-derived glucose by cells is mediated by glucose transporters (GLUTs). In the present study, we investigated the activity of GLUT1 and GLUT3, the two main isoforms of GLUTs found in testes, in the left scrotal and right abdominal testes of a German Shepherd dog. Immunohistochemical analysis showed that GLUT1 immunoreactivity was absent in the scrotal and abdominal testes. In contrast, weak to moderate GLUT3 immunoreactivity was observed in mature spermatocytes as well as spermatids in the scrotal testis. In the abdominal testis, relatively strong GLUT3 immunoreactivity was detected in Leydig cells only and was absent in mature spermatocytes and spermatids. GLUT3 immunoreactivity was significantly decreased in the tubular region of abdominal testis and significantly increased in the extra-tubular (interstitial) region of abdominal testis compared to observations in the each region of scrotal testis, respectively. These results suggest that GLUT3 is the major glucose transporter in the testes and that abdominal testes may increase the uptake of glucose into interstitial areas, leading to an increased risk of developing cancer.