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

Abstract

A modified electrometric method was described in sheep, goats and cattle and used to demonstrate in vitro inhibition of plasma and erythrocyte cholinesterase activities by the organophosphate and carbamate insecticides dichlorvos and carbaryl, respectively. A typical reaction mixture for the measurement of cholinesterase activity 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<sup>ο</sup>C for 30 min in sheep, 40 min in goats and 20 min in cattle. The pH of the reaction mixture was determined by a pH meter before and after the incubation. The initial pH was measured before the substrate addition. The enzyme activity was expressed as ∆pH/incubation time = (pH1 – pH2) – ∆pH of blank. The method of inhibitor-cholinesterase incubation was used to measure the in vitro inhibition of plasma and erythrocyte cholinesterase activities. Dichlorvos in concentrations of 0.5 and 1 μm inhibited plasma and erythrocyte cholinesterase activities by 24–85%, whereas carbaryl in concentrations of 5 and 10 μm inhibited them by 50–89%. The results suggest that the described electrometric method could be efficiently used for detecting cholinesterase inhibition in ruminants, and further point to the value of the present experimental protocol of in vitro cholinesterase inhibition in preliminary toxicological examinations of anticholinesterase compounds