Restoration of Leydig cells after repeated administration of ethane dimethanesulfonate in adult rats

Adult male rats were repeatedly treated with ethane dimethanesutfonate (EDS), an agent known to destroy Leydlg cells selectively. Following a second Injection, changes In serum testostemna levels and histological and morphametric changes of Leydlg cells showed the time course to be similar to those after the flrst treatment. The number and volume of Leydlg cells markedly decreased at day 2, began to increase from day 7, and recovered to the values of the contml rats at day 30, concomitant with the changes of serum testosterone levels. Cells in the interstitial tlssue labeled wlth bromodeoxyuridlne markedly increased In number at day 2, gradually decreased thereafter, and returned to the values of the controls at day 14. During this period, cells undergoing mltosls were seen, their type unable to be determined, but were presumed to be regenerating Leydlg cells. Even 30 days following four treatments with Intervals of 30 days each, serum testosterone levels were the same as those in the controls. Also the numerlcal and volume denstties of Leydig cells and the volume of an average Leydlg cell were the same as those of the controls. Mttosis was observed In mature Leydig cells at this perlod, if any. It appears that new Leydig cells began to proliferate by division earller than 14 days after EDS, allowing that there were several stages of proliferation, and that the source of reappearing Leydig cells may not be a limited number of precursor cells, impiying the presence of stem cells for Leydig cells.