Neuromuscular effects of chronic exposure to fenthion in dogs and predictive value of electromyography.
Chronic exposure to organophosphates (OP) can result in nonspecific neurologic signs in both man and animals. Improved methods are needed to predict toxicity and to better characterize neuromuscular effects. In this study, dogs were exposed to an OP (fenthion) by weekly dermal application of a 20% solution at a dosage of 44 mg/kg. This dosage does not produce signs of acute OP toxicity in dogs, although plasma cholinesterase (ChE) levels are significantly decreased. Electromyograms (EMG) were used to monitor motor unit potential (MUP) activity at minimal and submaximal contractile effort in four different muscles. At 1-month intervals, muscle biopsies were obtained and plasma ChE levels were determined. At 3 months, hyperreflexia and/or mild proprioceptive deficits were observed. The dosage was reduced to 22 mg/kg for the remaining 3 months of the study. At the end of this 6-month study, nerve and muscle biopsies were obtained. Mean plasma ChE levels were decreased (preexposure value of 1775 IU/liter to low of 310 IU/liter) and correlated with duration of exposure and change in dosage level. Fourier analysis of EMG indicated some increase in higher frequency components of the power spectrum with time, and analysis of individual MUPs revealed a significant (p less than 0.05) increase in the product of the amplitude times the duration of the potentials in all muscles examined. Biopsy results were supportive of EMG findings of altered neuromuscular function and loss of small motor units. The EMG changes were most consistent in the gastrocnemius muscle and were detected prior to development of clinical signs. These results indicate that EMG can be useful in monitoring OP exposure and predicting toxicity.
Tuler
S M
SM
Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens 30602.
Febles
D
D
Bowen
J M
JM
D000818:Animals; D001259:Ataxia / Q000503:physiopathology; D001679:Biogenic Amines / Q000378:metabolism; D002091:Butyrylcholinesterase / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000633:toxicity; D004285:Dogs; D004576:Electromyography; D005260:Female; D005284:Fenthion / Q000633:toxicity*; D006651:Histocytochemistry; D007958:Leukocyte Count / Q000187:drug effects; D009132:Muscles / Q000378:metabolism / Q000473:pathology; D009135:Muscular Diseases / Q000139:chemically induced* / Q000503:physiopathology; D009422:Nervous System Diseases / Q000139:chemically induced* / Q000503:physiopathology; D018377:Neurotransmitter Agents / Q000378:metabolism; D011237:Predictive Value of Tests
D001679:Biogenic Amines; D018377:Neurotransmitter Agents; D005284:Fenthion; D002265:Carboxylic Ester Hydrolases; C021859:neurotoxic esterase; D002091:Butyrylcholinesterase