STAGE-SPECIFIC DNA-SYNTHESIS OF RAT SPERMATOGENESIS AS AN INDICATOR OF GENOTOXIC EFFECTS OF VINBLASTINE, MITOMYCIN-C AND IONIZING-RADIATION ON RAT SPERMATOGONIA AND SPERMATOCYTES

We have studied the effects of three known mutagens: vinblastine sulphate, mitomycin C and local irradiation of testes on the stage-specific DNA synthesis in the rat testis by using transillumination assisted microdissection of rat seminiferous tubules. It enables us to investigate the sensitivity of different types of spermatogonia and preleptotene spermatocytes to the genotoxic effects of these agents, According to our results, spermatogonia and preleptotene spermatocytes are quite resistant to the action of vinblastine at the treatment times and the doses used, After treatment with mitomycin C, type A(2), A(3) and A(4) spermatogonia seem to be the first cell types affected, which shows itself as a reduction in the DNA synthesis at stages I, II-III, XIII-XIV of the epithelial cycle two and/or three days after the treatment. It also seems that they are mostly affected during the S-phase of their cell cycles. In addition, preleptotene spermatocytes are also sensitive to the action of mitomycin C when they are treated in the G(1) phase of the cell cycle, The local irradiation of 3 Gy has severe effects on the spermatogonia of rat testis which can be seen already 18 h after the treatment and becomes more evident 42 and 66 h after the treatment as a reduction of DNA synthesis at stages XII-V. Type A spermatogonia (A(1)-A(4)) seem to be the most sensitive cell types to the action of irradiation. This study indicates that the novel method of stage-specific DNA synthesis in rat spermatogenesis allows detailed studies of sensitivities in differentiating spermatogonia to genotoxic agents.