OBJECTIVETo investigate the effects of malathion on the testicular spermatogenic function of male rats and its working mechanism.

METHODSForty specific pathogen-free male Wistar rats were randomly and equally divided into four groups: three exposure groups and a control group. Malathion was administered orally to male rats in the exposure groups at 33.75, 54, and 108 mg/kg (1/32 LD₅₀, 1/20 LD₅₀, and 1/10 LD₅₀) for 60 days. Rats in the control group received an equal volume of water. The body weights of rats were measured after exposure. The organ weights and coefficients of the testes and epididymes were determined as soon as rats were sacrificed. The sperm motility, counts, and malformation rates were measured in the left epididymis. Histopathological changes, cell apoptosis, and the expression levels of Bcl-2/Bax in the testes of rats were observed using HE staining, terminal deoxynucleotidyl transferase-mediated dUPT-biotin nick end labeling, and immunohistochemistry SABC method.

RESULTSThe body weights and the testis weights in the exposure groups were significantly lower than those in the control group (P < 0.01). The exposure groups had significantly lower sperm motility and significantly higher sperm malformation rates than the control group (P < 0.01). The sperm counts were significantly lower in the exposure groups than in the control group (P<0.01). The sperm counts and motility were negatively correlated with exposure dose (r = -0.81, P < 0.01; r = -0.51, P < 0.01), while the sperm malformation rate was positively correlated with exposure dose (r = 0.85, P 0.01). The exposure groups had significantly higher spermatogenic cell apoptosis rates than the control group (P<0.01). The expression level of Bax was significantly higher in the exposure groups than in the control group (P<0.01), while the expression level of Bcl-2 was significantly lower in the exposure groups than in the control group (P < 0.01). Histopathological examination of the testes showed degenerative changes in the seminiferous tubules at various doses along with the increase in malathion exposure dose.

CONCLUSIONMalathion affects the testicular spermatogenic function of male rats and its working mechanism may involve cell apoptosis induced by down-regulation of Bcl-2 and up-regulation of Bax.