Gamma-glutamyl transpeptidase activity in the developing rat testis. Enzyme localization in isolated cell types.

Abstract

The purpose of this study was to correlate gamma glutamyl transpeptidase (γ-GTP) activity with the morphological changes occurring in the rat testis during sexual maturation and to determine the cell type(s) responsible for the activity of this enzyme. The γ-GTP activity was measured at different ages in whole testis homogenates, isolated specific cell types and cultured Sertoli cells. The specific activity of γ-GTP, expressed as units per mg of protein (U/mg P), in whole testis homogenates increased with age of animals, reaching maximum value (0.60 ± 0.03 U/mg P) by the 20th day, thus, prior to the formation of spermatids, and then remained essentially unchanged until Day 100. When individual cell types were isolated from 30-day-old rat testis, the specific activities of γ-GTP in the Sertoli cells and the germ cells respectively were 0.93 ± 0.07 U/mg P and 0.12 ± 0.05 U/mg P. The peritubular cells and interstitial cells contained non-detectable γ-GTP activity. These results indicate that in 30-day-old rat testis the γ-GTP activity is associated mainly with the Sertoli cells. The γ-GTP activity of the isolated Sertoli cells was also investigated after various culture periods at 34°C. The specific activity of γ-GTP in the cultured Sertoli cells increased with culture age, showing a 5-fold increase after three days of incubation and a 20-fold increase after seven days of culture. The physiological significance of γ-GTP activity in the Sertoli cells and its increase under culture conditions remain unclear, but the enzyme may play a role in the synthesis of specific proteins known to be secreted by the Sertoli cells.