Effects of etoposide on stage-specific DNA synthesis during rat spermatogenesis

The stage-specific effect of etoposide on spermatogenic DNA synthesis was measured 1, 3 and 18 days after a single intraperitoneal injection of etoposide inhibited premitotic DNA synthesis most effectively at stages II–III and IV–V of the seminiferous epithelial cycle in which DNA synthesis of late spermatogonia takes place. Compared with control levels, DNA synthesis at stages II–III was maximally inhibited 43% and 57% at doses of 5 and 10 mg/kg, respectively, and at stages IV–V the maximal inhibition was 67% and 62%, at doses of 5 and 10 mg/kg respectively. Premeiotic DNA synthesis was not as vulnerable to the etoposide action as premitotic DNA synthesis, the maximal inhibition of premeiotic DNA synthesis was 39% and 41% compared with control at doses of 5 and 10 mg/kg, respectively. Induction of most probably repair-type DNA synthesis was demonstrated in stages I–III, VIIa–b and XII of the cycle. All the effects of etoposide were most apparent 1 and 3 days after treatment but had not totally disappeared 18 days after the treatment.