Inhibition and recovery of cholinesterases in Odontophrynus americanus tadpoles exposed to fenitrothion.

We determined the levels of brain acetylcholinesterase (AChE) and tail butyrylcholinesterase (BChE) activities in tadpoles of Odontophrynus americanus exposed to a commercial formulation of fenitrothion. The mean brain AChE activities in the controls tadpoles varied from 6.91 to 6.39 micromol min(-1) mg(-1) protein, whereas tail BChE activities ranged among 0.26 to 0.17 micromol min(-1) mg(-1) protein; the two sublethal concentrations of fenitrothion assayed produced AChE and BChE inhibition (p < 0.01). Brain AChE recovered a substantial level of activity with a maximum of 93.2%; after the transference of tadpoles to a free-pesticide solution, whereas tail BChE recovery showed a smaller increase (39%) in the activity at 168 hr after to transference to clear water. According with our results, we suggest that tadpole's tail BChE presents higher sensibility than brain AChE.