Effects of methyl parathion (o,o-dimethyl o-4-nitrophenyl phosphorothioate) on rat sperm morphology and sperm count, but not fertility, are associated with decreased ascorbic acid level in the testis

Methyl parathion (MP; o,o-dimethyl o-4-nitrophenyl phosphorothioate) is an organophosphorous pesticide used world wide to spray agricultural crops. The present study was aimed to investigate the genotoxic and cytotoxic effects on male germ cells and their possible relation with testicular ascorbic acid levels. Adult male Wistar rats (n=5/group) received MP at 0, 0.5, or 1 mg/kg (experiments 1 and 2) for 12 days and 0, 0.75 or 1.5 mg/kg (experiment 3) for 25 days (i.p.) everyday at intervals of 24 h. The epididymal sperm count, sperm abnormalities and testicular ascorbic acid levels (by 2,4-dinitrophenyl hydrazine method) were estimated on days 130, 77 and 17 following the last exposure in experiments 1, 2, and 3, respectively. Virgin untreated female rats were mated with treated males from experiments 2 and 3 for a week effective from day 35 to 41 after the first treatment, and fertility indices were measured after the birth of pups. Sperm count was decreased in experiments 2 and 3 (P<0.01), and in all three experiments, the abnormal sperms increased (P<0.001). Concomitantly, the ascorbic acid levels decreased in the testis (P<0.05-0.001; one-way ANOVA and Bonferroni's post hoc test). The body weights of offspring of treated males did not show significant changes from those of the controls, although there were some decreases observed. MP reduced the lactation index in experiment 2 (P<0.001; Chi-square test). The number of pups/parent along with fertility indices showed some numerical decrease but without any statistical significance. The present findings suggest that MP is a weak genotoxic and cytotoxic agent in the rat exposed to human exposure dose-levels, and that these effects, except the fertility are well correlated with decreased ascorbic acid level in the testis. Furthermore, MP-induced changes in the germ cells do not have any significant effects on F1 generation.