Reproductive toxicity of methomyl insecticide in male rats and protective effect of folic acid.

The acute toxicity (LD(50)) of insecticide methomyl and its effects on male reproduction in rats were carried out. Methomyl was given orally to male rats daily for 65 successive days at two doses (0.5 and 1.0 mg kg(-1) b.wt., corresponding to 1/40 and 1/20 LD(50)) alone and in combination with folic acid (1.1 mg kg(-1) b.wt., corresponding to acceptable daily intake, ADI). Fertility index, weight of sexual organs, semen picture, serum testosterone level and histopathology of testes were the parameters used to evaluate the reproductive efficiency of treated rats. The reversibility of methomyl effects was also studied after 65 days post-administration. The oral LD(50) of methomyl was 20.0 mg kg(-1) b.wt. in male rats. Methomyl significantly decreased the fertility index, weight of testes and accessory male sexual glands, serum testosterone level and sperm motility and count, but increased sperm cell abnormality. It induced testicular lesions characterized by moderate to severe degenerative changes of seminiferous tubules and incomplete arrest of spermatogenesis. These toxic effects were not persistent (reversible). Coadministration of folic acid with methomyl decreased its reproductive toxicity. A great attention should be taken during field application of methomyl to avoid its deleterious effects in farm animals and occupationally exposed humans.