Sorbitol Dehydrogenase of Rat Testis: Changes of Activity during Development, after Hypophysectomy and following Gonadotrophic Hormone Administration*

Abstract

Sorbitol dehydrogenase (SDH) was examined as a possible marker protein of testicular development and following gonadotrophic stimulation of immature or mature hypophysectomized rats. This enzyme which is localized in a 105,000 supernatant fluid was determined to exhibit a Km for sorbitol of 2.5 X 10-3M. Levels of SDH were correlated with the morphological state of maturation of the germinal epithelium of testicular tubules. SA of SDH increased during testicular development from 0.45 nmoles NAD/min/mg protein at 10 days to maximal activity of 3.2 nmoles NAD/min/mg protein at 60 days. Hypophysectomy of 60–day—old animals initiated a marked and progressive decrease in enzymatic activity between 12 and 39 days postoperatively. Loss of SDH activity paralleled the disappearance of advanced germ cells from the tubules. Daily injections of FSH or LH for 14 days (between 24 and 39 days postoperatively) maintained SDH activity at the level present in 24–day hypophysectomized animals. FSH only maintained the state of the germinal epithelium whereas LH or hCG resulted in significant repair (i.e., from step 6–7 to step 15–19 spermatids). Acutely (4–24 hr) no increase in SDH activity was observed when 15– or 20–day—old animals were injected with gonadotrophins. On the other hand daily injections or FSH, LH or hCG between 15 and 20 days caused 2–fold stimulations of SDH activity. Moreover histological examination of testis from the group of rats treated with FSH for 5 days indicated an increase in the number of primary spermatocytes per tubule. Subsequent histological examination of testis of 16–day—old rats at various times following a single injection of FSH revealed that this hormone (but not LH) stimulated mitotic activity of the germinal epithelium within 9 hr. (Endocrinology91: 147, 1972)