Effect of beta-naphthoflavone on o-tolyl saligenin phosphate-induced delayed neuropathy in two lines of chickens.

The effect of the microsomal enzyme inducer beta-naphthoflavone (beta NF) on the development of organophosphorus-induced delayed neuropathy (OPIDN) was examined in two laboratories (VPI and MSU), utilizing two strains of White Leghorn hens. A single intraperitoneal injection of beta NF at 80 mg/kg body weight 48 h prior to administration of o-tolyl saligenin phosphate (TSP), the neuroactive metabolite of tri-o-tolyl phosphate (TOTP), caused a significant increase in hepatic microsomal cytochrome P-450 concentrations and aniline hydroxylase activities after 72 h in both strains. Hepatic carboxylesterase and cholinesterase activities were not affected by beta NF treatment in either strain. Administration of TSP in single subcutaneous doses of 20 and 25 mg/kg body weight (VPI) or 30 and 60 mg/kg body weight (MSU) caused significant inhibition of whole-brain neuropathy target esterase (NTE) activity 24 h postdosing, and hens subsequently developed clinical signs characteristics of OPIDN. beta NF had no significant effect on NTE inhibition or on initiation or severity of OPIDN clinical signs. However, OPIDN clinical signs were less severe in the strain of bird (MSU) with the higher intrinsic hepatic carboxylesterase activity and the higher beta NF-induced cytochrome P-450 concentration. The study indicates that microsomal enzyme induction, which has been shown to alleviate TOTP-induced delayed neuropathy, could not alleviate OPIDN resulting from exposure to TSP. This study also suggests that strain may affect susceptibility to TSP-induced delayed neuropathy.