Application of an electrometric method for measurement of in vitro inhibition of blood cholinesterases from sheep, goats and cattle by dichlorvos and carbaryl

A modified electrometric method was used to demonstrate in vitro inhibition of plasma and erythrocyte cholinesterase activities by the insecticides dichlorvos and carbaryl in sheep, goats and cattle. A typical reaction mixture contained 3 mL distilled water, 3 mL barbital-phosphate buffer (pH 8.1), 0.2 mL plasma or erythrocytes and 0.1 mL acetylthiocholine iodide (7.5%) as a substrate. The mixture was incubated at 37 deg C for 30 min in sheep, 40 min in goats and 20 min in cattle. The pH of the mixture was determined before and after the incubation. The enzyme activity was expressed as deltapH/incubation time = (pH1-pH2) - deltapH of blank. Dichlorvos in concentrations of 0.5 and 1 microm inhibited plasma and erythrocyte cholinesterase activities by 24-85%, whereas carbaryl in concentrations of 5 and 10 microm inhibited them by 50-89%. The electrometric method could be efficiently used for detecting cholinesterase inhibition in ruminants.