Evaluation of cytotoxic effects of different doses of vinblastine on mouse spermatogenesis by flow cytometry

The cytotoxic effects of different doses (0 to 8 mg/kg body weight) of vinblastine on mouse spermatogenesis were studied at 7 to 70 days post-treatment. First the gross changes in testicular weight were studied: the doses from 0.05 to 0.5 mg/kg body weight of vinblastine did not show any significant change in testicular weight. However, a dose of 1 mg/kg at day 21 and 28, and 2 mg/kg at all the intervals studied showed a significant decline in testicular weight (P < 0.003 and < 0.03 for 1 and 2 mg/kg, respectively). A further increase in vinblastine dose resulted in a significant decline in testis weight from 7 to 35 days post-treatment. Flow cytometric DNA content measurements were carried out in monocellular suspensions of mouse testis that revealed five quantifiable populations: elongated spermatids (HC), round spermatids (1C), spermatogonia (2C), gonial cells and primary spermatocytes synthesizing DNA (S-phase), and primary spermatocytes (4C) in the control animals. Administration of vinblastine resulted in significant changes in the relative percentages of different germ cell populations as a consequence of which the complete germ cell transformation ratio (HC:2C) declined significantly (P < 0.04) at 21 and 35 days post-treatment (1 and 2 mg/kg). The HC:2C ratio is further divided into 4C:2C, 1C:4C and 1C:2C ratios. The 4C:2C ratio (transformation of spermatogonia to primary spermatocyte) significantly declined at all the post-treatment intervals for 1 and 2 mg/kg vinblastine (P < 0.01). A significant decline in 1C:4C ratio (meiotic transformation) was observed at all the intervals for 0.5 mg/kg (P < 0.004, 0.05, 0.001 and 0.0002 at 7, 14, 21, 28 and 35 days, respectively). This decline in 1C:4C ratio continued at higher doses, i.e. 1 mg/kg (P < 0.0001) and 2 mg/kg (P < 0.0001, 0.005 and 0.0001, respectively) at 14, 21 and 28 days post-treatment. The 1C:2C ratio (spermatocytogenesis) decreased significantly for all the doses by day 14 and 35, except for 0.01 mg/kg (P < 0.04 to 0.0001). Our data suggest that doses of 0.5 mg/kg vinblastine were already cytotoxic to various germ cell populations.