S-(+)-Linalool from Lippia alba: sedative and anesthetic for silver catfish (Rhamdia quelen).

Objective: The present study describes the isolation of linalool from the essential oil of Lippia alba (Mill.) N. E. Brown, and its anesthetic effect in silver catfish (Rhamdia quelen) in comparison with essential oil. The potentiation of depressant effects of linalool with a benzodiazepine (BDZ) and the involvement of GABAergic system in its antagonism by flumazenil were also evaluated.

Study Design: Prospective experimental study.

Animals: Juvenile silver catfish unknown sex weighing mean 9.24 ± 2.83 g (n = 6 for each experimental group per experiment).

Methods: Column chromatography was used for the isolation of S-(+)-linalool. Fish (n = 6 for each concentration) were transferred to aquaria with linalool (30, 60, and 180 μL L(-1)) or EO of L. alba (50, 100, and 300 μL L(-1)) to determine the induction time for anesthesia. After induction, the animals were transferred to anesthetic-free aquaria to assess their recovery time. To observe the potentiation, fish were exposed to linalool (30, 60, and 180 μL L(-1)) in the presence or absence of BDZ (diazepam 150 μm). In another experiment, fish exposed to linalool (30 and 180 μL L(-1) or BDZ were transferred to an anesthetic-free aquaria containing flumazenil (5 μm) or water to assess recovery time.

Results: Linalool had a similar sedation profile to the essential oil at a proportional concentration in silver catfish. However, the anesthesia profile was different. Potentiation of linalool effect occurred only when tested at low concentration. Fish exposed to BDZ showed faster anesthesia recovery in water with flumazenil, but the same did not occur with linalool.

Conclusions And Clinical Relevance: The use of linalool as a sedative and anesthetic for silver catfish was effective at 30 and 180 μL L(-1), respectively. The mechanism of action seems not to involve the benzodiazepine site of the GABAergic system.