Mecanismo de ação de monoterpenoides com atividade sedativa e anestésica em jundiás (Rhamdia quelen)

Abstract

Monoterpenoids are present in a large proportion in essential oils of aromatic plants and are important sources of bioactive molecules. Thymol, carvacrol and linalool are examples of these compounds and among their biological properties the depressant activity in the central nervous system stands out. In this context, the objective of this study was to evaluate the anesthetic potential of thymol and carvacrol, and their influence on acetylcholinesterase (AChE) activity in the muscle and brain of silver catfish (Rhamdia quelen). The AChE activity of S-(+)-linalool was also evaluated. We subsequently assessed the effects of thymol and S-(+)-linalool on the GABAergic system. Fish were exposed to thymol and carvacrol (25, 50, 75 and 100 mg L-1) to evaluate time for anesthesia and recovery. Both compounds induced sedation at 25 mg L-1 and anesthesia with 50–100 mg L-1. However, fish exposed to carvacrol presented strong muscle contractions and mortality. AChE activity increased about two-fold in the brain of fish exposed to 50 mg L -1 carvacrol and about three-fold at 100 mg L -1 thymol, however AChE activity decreased (about five-fold) in the muscle of silver catfish exposed to 100 mg L -1 carvacrol. S-(+)-linalool did not alter AChE activity. Anesthesia with thymol was reversed by exposure to picrotoxin (GABAA antagonist), similar to the positive control propofol, but was not reversed by flumazenil (antagonist of benzodiazepine binding site), as observed for the positive control diazepam. Picrotoxin did not reverse the effect of S-(+)- linalool. Thymol 50 mg L-1 is more suitable than carvacrol for anesthesia in silver catfish, as we observed good anesthetic performance and no interference with AChE activity. Its anesthetic effect appeared to involve the GABAA receptors, but was not related to the benzodiazepine site. Therefore, the anesthetic effect of S-(+)-linalool in silver catfish does not appear to involve the GABAA receptors.