Effect of verapamil on organophosphorus-induced delayed neuropathy in hens

Verapamil, a calcium channel blocker, was administered to adult white leghorn hens to determine if inhibition of calcium entry could alter delayed neuropathy induced by administration of phenyl saligenin phosphate (PSP). Verapamil was given im in doses of 7 mg/kg/day for 4 days beginning 24 hr before administration of PSP (2.5 mg/kg im). Ataxia was less pronounced in hens given PSP plus verapamil than in hens given PSP alone during observations made 8-28 days after PSP administration. Myelinated fiber lesions were less extensive and regeneration more notable in the biventer cervicis nerve in chickens given PSP plus verapamil, with samples obtained both 17 and 28 days after PSP. In the absence of verapamil, rheobase and chronaxie values of strength-duration curves were higher and shorter, respectively, and sensitivity to acetylcholine was increased in biventer cervicis nerve-muscle preparations from hens given PSP. Verapamil did not alter PSP-induced inhibition of neurotoxic esterase, indicating that the mechanism involved in amelioration of these indices of delayed neuropathy was not associated with initial enzyme inhibition caused by this organophosphorus ester.