Characterization of the regenerated Leydig cell population of the rat after destruction by ethylene-1,2-dimethanesulphonate.

The Leydig cells repopulating the adult rat testis after destruction by a single injection of the cytotoxic ethylene-1,2-dimethanesulphonate (EDS) were investigated. After 14 days, serum concentrations of LH and FSH were significantly raised and concentrations of testosterone in the serum and testis reduced. At 21 days, hormone concentrations had returned to within the normal range. Binding of 125I-labelled human chorionic gonadotrophin (hCG) to testis homogenate, however, was still less than 10% of normal. After 21 or 28 days the 125I-labelled hCG binding profiles of isolated Leydig cells from EDS-treated rats, separated on a Percoll gradient, showed a single peak similar to that of immature (25 days old) rats. After 49 days, 125I-labelled hCG binding resolved into two peaks more like that of normal adult rats. Using a quantitative cytochemical method, 3 beta-hydroxysteroid dehydrogenase activity in individual Leydig cells of unfixed testis sections was determined. Activity was increased by 70% (P less than 0.05) in repopulating Leydig cells 21 days after EDS treatment compared with cells from vehicle-treated rats. In addition, Leydig cells were still capable of further 'in-vivo' stimulation by pharmacological doses of hCG. These data indicate that Leydig cells repopulating the testis are homogeneous. Fewer cells from the newly formed population are capable of maintaining normal serum concentrations of testosterone and must thus be individually more active in secreting testosterone. In these respects, the Leydig cells repopulating the adult rat testis after EDS treatment more closely resemble those of the fetal rat testis.