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Research Article
Electrometric Determination of Erythrocyte, Plasma and Whole Blood Cholinesterase Activities in Sheep, Goats and Cattle and Their in vitro Inhibition by Anticholinesterase Insecticides

F.K. Mohammad, M.H.I. Al-Zubaidy and A.S. Alias

Journal of Pharmacology and Toxicology, 2007, 2(2), 131-141.

Abstract

Determination of blood cholinesterase activity in animals is used for diagnosis and monitoring poisoning induced by organophosphate and carbamate insecticides. An electrometric method was applied in one step single incubation period (30 min) for measurement of normal reference range values of erythrocyte, plasma and whole blood cholinesterase activities in sheep, goats and cattle, of both sexes. The reaction mixture contained 3 mL distilled water, 3 mL barbital-phosphate buffer (pH 8.1), 0.2 mL erythrocytes, plasma or the whole blood and 0.1 mL acetylcholine iodide (7.5%) as a substrate. The mixture was incubated at 37°C for 30 min in the three animal species. This step avoided variations in enzyme activity across animal species due to differences in the incubation periods found in previous studies. 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 unit of enzyme activity was expressed as Δ pH/30 min. The mean normal reference range values of erythrocytes, plasma and whole blood cholinesterase activities (Δ pH/30 min) in males of the three animal species were as follows, respectively: Sheep (0.306, 0.133 and 0.249), goats (0.366, 0.135 and 0.234) and cattle (0.469, 0.135 and 0.374) whereas those of the females were as follows, respectively: Sheep (0.436, 0.121 and 0.257), goats (0.338, 0.175 and 0.252) and cattle (0.645, 0.137 and 0.450). The method of inhibitor-cholinesterase incubation was used to measure the in vitro inhibition of plasma, erythrocyte and whole blood cholinesterase activities by the organophosphate insecticides chlorpyrifos and methidathion and by the carbamate insecticide carbaryl. Chlorpyrifos in concentrations of 0.5 and 1 μM inhibited plasma, erythrocyte and whole blood cholinesterase activities by 5-30% in sheep, 10-55% in goats and 5-61% in cattle. Methidathion in concentrations of 0.5 and 1 μM inhibited plasma, erythrocyte and whole blood cholinesterase activities by 3-70% in sheep, 8-53% in goats and 6-65% in cattle. Carbaryl in concentrations of 4 and 8 μM inhibited them by 8-54% in sheep, 8-53% in goats and 14-74% in cattle. The study establishes for the first time by using the described electrometric method in a unified way across the three ruminant species sheep, goats and cattle, normal reference range values of erythrocytes, plasma and whole blood cholinesterase activities. The results also suggest that the described electrometric method could be efficiently used for detecting cholinesterase inhibition by organophosphate and carbamate insecticides. Further, the experimental protocol of in vitro cholinesterase inhibition is of value in preliminary toxicological examinations of anticholinesterase pesticides.

ASCI-ID: 55-99

Cited References Fulltext

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