Serum B esterases as a nondestructive biomarker in the lizard Gallotia galloti experimentally treated with parathion

Lizards (Gallotia galloti) were given either single or consecutive acute oral treatments of the organophosphorus (OP) insecticide parathion in two different experiments. Brain, serum, and liver microsomal esterase activities and liver microsomal monooxygenase activities were measured 6 and 24 h after the single acute treatment at each of four different doses (Experiment 1) or periodically up to 72 d after a number of consecutive acute treatments at two different doses (Experiment 2). Inhibition of serum butyrylcholinesterase (BChE) and carboxylesterase activities was observed in all treatment groups after 24 h and in the groups treated with 2.5, 5, and 7.5 mg/kg of parathion 6 h after treatment. Brain acetylcholinesterase (AChE) was inhibited at all doses after 6 h but only at the highest dose after 24 h. Highly significant nonlinear correlations, based on a piecewise linear regression model, were obtained between brain AChE activity and serum esterase activities at two sampling times after the single acute treatment. Liver microsomal carboxylesterase was found to be induced at the lower doses 6 and 24 h after treatment. Liver microsomal monooxygenase activity was higher 6 h after treatment than at 24 h, but the difference was not statistically significant. In Experiment 2, serum esterase activities recovered exponentially over a period of weeks. An increase in the recovery time to normal esterase activity was observed after each consecutive acute treatment. Brain AChE activity was inhibited at the end of consecutive administrations of parathion at the higher dose, and liver microsomal monooxygenase activity was inhibited at both doses. Symptoms of poisoning were observed in lizards treated with the higher dose of parathion, but no mortality was recorded. Two main conclusions can be drawn: (1) serum esterase activities recovered extremely slowly after acute treatment with parathion and even more slowly after consecutive acute treatments, and (2) there was a nonlinear correlation between the nondestructive biomarkers, serum "B" esterases, and the destructive biomarker, brain AChE, 6 and 24 h after exposure. These results suggest that G. galloti should be an ideal bioindicator organism to assess OP exposure in the Canary Islands instead of the birds commonly used for this purpose.