Field results using cholinesterase reactivation techniques to diagnose acute anticholinesterase poisoning in birds and fish

Abstract

The inhibition of brain cholinesterase (ChE) activity in organophosphate (OP)- or carbamate (CB)-poisoned animals is usually determined by comparison with the normal activity in control specimens. Alternatively, the activity of pesticide-inhibited ChE can be restored, ideally up to normal levels, using simple in vitro procedures, thereby providing a reference value against which ChE inhibition can be estimated. The activity of phosphorylated ChE can be increased by the addition of the nucleophilic reagent pyridine 2-aldoxime methiodide (2-PAM), while the spontaneous reactivation of carbamylated ChE can be enhanced by dilution. These procedures can also be used to differentially diagnose OP and CB poisoning. Brain ChE inhibition in birds and fish from field poisoning incidents was determined using reactivation techniques and normal activity data from separate control specimens. In OP-poisoned birds, the mean inhibition relative to 2-PAM-treated samples and controls ranged from 77–82% and 84–87%, respectively. The corresponding values for OP-poisoned fish were 48–82% and 66–86%, respectively. In CB-poisoned birds, the mean inhibition relative to diluted samples and controls ranged from 22–56% and 33–76%, respectively. The reactivation of carbamylated ChE was further enhanced by increasing the dilution ratio and lengthening the incubation period. Although ChE activity was not fully restored to normal levels in many individuals, diagnostically significant inhibition was demonstrated in most cases. In OP-poisoned fish held 24 h postmortem at 20°C, 2-PAM restored brain ChE activity to that of similarly handled, unexposed controls. After postmortem storage for 48 h, ChE activities in reactivated and inhibited samples were statistically indistinguishable due to the aging of the phosphorylated ChE. Despite the limitations imposed by aging, ChE reactivation is a potentially useful diagnostic technique, particularly when control data are unavailable or difficult to obtain.