Chronic toxicity of technical fenitrothion in male rats

Abstract

Weanling male Wistar rats were given 0.5, 1.0, 5.0 or 10.0 mg/kg body wt of technical fenitrothion ( O,O-dimethyl O-(4-nitro- m-tolyl) phosphorothioate in peanut oil by daily oral gavage for 12 months. Each month, 10 vehicle-and 5 insecticide-treated rats from each group were killed, tissues (liver, kidney, brain, spinal cord, and sciatic nerve) were preserved for morphological examination and the effects of treatment were assessed by measuring changes in activities of blood plasma pseudocholinesterase, erythrocytic and brain acetylcholinesterase (AChE), and hepatic and renal nonspecific carboxylesterases (CE) as well as routine hematology and serum biochemistry. At 12 months, administration was stopped and the survivors were held for an additional 2 months to monitor the recovery from the biological effects of the treatment. No changes were observed in the routine hematological or serum biochemical parameters measured during the treatment period at any of the doses administered. The morphological changes observed could not be related either to the vehicle or to a dose-dependent effect of fenitrothion. A dose-dependent inhibition of the tissue esterases was observed. Little change was measured at 0.5 and 1.0 mg/kg/day. Marked reductions in hepatic CE, brain, and erythrocytic AChE activities were observed at doses of 5.0 and 10.0 mg/kg/day within 1 month of treatment and remained relatively constant for the duration of treatment. Within 1 month after treatment was stopped, tissue esterase levels were within normal limits with the exception of the brain AChE in rats given the two larger doses. Within 2 months after treatment was terminated, tissue esterase activities of all treated rats were comparable to control activities.