OBJECTIVETo assess the joint toxicity of phoxim (Pho) and fenvalerate (Fen) on the spermatogenesis of male rats and to clarify its mechanism.

METHODSBased on the three administrative levels of factorial analysis (3 x 3) of Pho and Fen, i. e. their half lethal dose (LD50) 1/250 LD50 (5.9, 2.4 mg/kg) and 1/50 LD50 (29.4, 12.0 mg/kg) and the control, 135 adult male SD rats were randomly assigned to9 groups, the control (0.0 mg/kg), Pho (5.9, 29.4 mg/kg), Fen (2.4, 12.0 mg/kg), Pho + Fen (5.9 + 2.4, 5.9 + 12.0, 29.4 + 2.4, 29.4 + 12.0 mg/kg), and treated intragastrically with different doses of Pho, Fen and Pho + Fen for 15 and 30 days. The levels of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T) and testis homogenate T were determined by radioimmunoassay (RIA), the activity of testicular marker enzymes such as acid phosphatases (ACP) and gamma-glutamyl transpeptidase (gamma-GT) examined, and the sperm head count measured for the changes of daily sperm production (Spr).

RESULTSAt 15 days, obvious interaction was observed between Pho and Fen in both serum LH and FSH (P < 0.05), as well as between their reproductive toxicities. With the increase in doses, the joint action was synergistic in LH (P < 0.05) and antagonistic in FSH (P < 0.01) at a high dose ( 29.4 + 12.0 mg/kg). At 30 days, marked interaction between Pho and Fen was noted in the content of homogenate T (P < 0.05) , with a joint synergistic effect. At 15 and 30 days, with the increase of doses, both Pho and Fen reduced Spr and the activity of ACP and gamma-GT, but Pho + Fen showed no obvious interaction in them (P > 0.05) , and their joint action was an additive effect.

CONCLUSIONPho and Fen jointly impaired spermatogenesis in a dose- and time-dependent manner. Their joint action exhibited mainly as a synergistic effect, an additive effect and increased toxicity.