The effect of ethyl-, methyl- and hydroxyethyl-nitrosourea on the mouse testis.

Hybrid male 101 X C3HF1 mice were given intraperitoneal injections of methyl-, ethyl- and hydroxyethyl-nitrosourea and killed 3-16 days later. All compounds were similar in that all differentiating spermatogonia from type A1 to early type B were killed by 50 mg/kg and higher doses of ENU and by 75 mg/kg MNU. Cells exposed in leptotene to 100 and 250 mg/kg ENU and 455 mg/kg HENU showed a delayed response with degeneration in pachytene 5 days later. Labeling prior to exposure to ENU indicated that the effect of stage of the mitotic cycle on sensitivity to cell killing is less marked than for radiation. This may be the explanation for the s-shaped mutation induction curve obtained with ENU in contrast to the humped dose-response curve observed for radiation.