Myofibril membranes in relation to the neuromuscular weakness of acute monocrotophos poisoning.

Organophosphate poisoning is a common method of deliberate self-harm in countries where the pesticides are readily available. The severity of neuroparalysis and myopathy occurring in acute organophosphate poisoned patients is determined by the severity of poisoning and is associated with morbidity and mortality. Molecular mechanisms that underlie severe paralysis are not well delineated but are essential to know to improve treatment. In this study rats were subjected to increasing doses (0.25 to 0.8 LD(50)) of monocrotophos, and cell membrane lipid profiles, particularly those of myofibril membranes, were examined in relation to neuromuscular weakness occurring in poisoning. Increasing doses of monocrotophos inhibited brain and RBC acetylcholinesterase >/=60% early in the poisoning. RBC acetylcholinesterase levels recovered to 70% to 80% of normal while brain acetylcholinesterase remained 44% to 67% inhibited 1 week after poisoning. Increasing severity of poisoning led to significant changes in myofibril membrane lipid composition with cholesterol to phospholipid ratios increasing from 0.029 +/- 0.008 in controls to 0.063 +/- 0.023 in severe poisoning (p > 0.05). These changes were associated with neuromuscular weakness in the first day of poisoning. Membrane changes were reversible and rats recovered muscle strength in 1 week with no treatment. Lipid compositions of the intestine, brain, and muscle mitochondrial membranes were not affected by monocrotophos. The study indicated that neuromuscular weakness was associated with muscle membrane disorganization early in the course of acute organophosphate poisoning and that subclinical neurotoxicity of long duration may be a consequence of acute organophosphate poisoning. Controlling the severity of poisoning early in the course of acute organophosphate poisoning appears to be important for clinical recovery.