CHOLINESTERASE INHIBITION - COMPLEXITIES IN INTERPRETATION

Cholinesterases are measured to assess exposures to or effects of orga nophosphorus esters and carbamates. Plasma butyrylcholinesterase is us ually most sensitive to inhibitors, but it has no known physiological function(s); its inhibition reflects exposure. The physiological funct ion of erythrocyte acetylcholinesterase (AChE) also is not known, but the enzyme is the same as that involved in synaptic transmission and i ts measurement is used to mirror effects on the nervous system. Erythr ocyte AChE has large inter- and intraindividual variation, and small c hanges are detectable by comparison with preexposure values. The relat ion between inhibition of erythrocytes and nervous tissue AChE depends on the pharmacokinetics of inhibitors. Usually, erythrocyte AChE inhi bition overestimates that in the nervous system. Pharmacodynamic facto rs such as spontaneous reactivation and aging of inhibited enzyme shou ld also be considered in assessing AChE inhibition. Other factors, suc h as timing of measurement, add complexity because erythrocyte AChE in hibition persists longer than that in the nervous tissues. Cholinergic transmission might also be impaired because of direct effects of orga nophosphorus esters and carbamates on receptors.