Identification of markers for precursor and Leydig cell differentiation inthe adult rat testis following ethane dimethyl sulphonate administration

Administration of ethane dimethane sulphonate (EDS) to adult rats results i n the destruction of all Leydig cells, followed by a complete regeneration. We investigated this regeneration process in more detail, using different markers for precursor and developing Leydig cells: the LH receptor, 3 beta- hydroxysteroid dehydrogenase (3 beta-HSD), transforming growth factor alpha (TGF alpha), and a new marker for Leydig cell maturation, relaxin-like fac tor (RLF). LH receptor immunoreactivity was found in Leydig cell-depleted testes at 3 and 8 days after EDS administration. The positive (precursor) cells had a m esenchymal-like morphology. The number of LH receptor-positive cells 8 days after EDS administration was 15 +/- 4 per 500 Sertoli cell nuclei. Fifteen days after EDS administration, the first new Leydig cells could be observe d. These cells stained positively with both the antibodies against the LH r eceptor and SP-HSD, while some cells also stained positively for TGF alpha. After EDS administration, RLF mRNA disappeared from the testis and reappear ed again at the time of the appearance of the first Leydig cells. Concomita nt with the increase in the number of Leydig cells, the number of RLF-expre ssing cells increased. The observations of the present study give further support to the hypothesi s that Leydig cell development in the prepubertal testis, and in the adult testis following EDS administration, takes place along the same cell lineag e and suggest, therefore, that the adult EDS-treated rat can serve as a mod el for studying the adult-type Leydig cell development that normally occurs in the prepubertal rat testis.