Atividade anestésica de óleos essenciais e constituintes isolados de plantas medicinais brasileiras em Rhamdia quelen

Abstract

The aim of this study was to obtain new fish anesthetic and sedative drugs from Brazilian medicinal plants: Ocimum gratissimum (OG), Ocimum americanum (OA) e Hyptis mutabilis (HM). Essential oils from these plants were obtained by hydrodestilation and analysed by gas chromatography coupled to mass spectrometry (GC-MS). The chirality of one constituent of OA oil was also determined. Isolation process from essential oil of OA and HM was conduced and the isolated compounds were analyzed by spectroscopic methods. To determine the point at which anesthesia was induced and the length of the recovery period, juvenile silver catfish (Rhamdia quelen) were placed in aquaria containing essential oil or isolated compounds. The mechanism of action of the essential oil of OG and (-)-globulol was evaluated through association with diazepam (150 μM) and reversion with flumazenil (5μM). The evaluation of tolerance development was performed to OG oil using re-exposure after 30 days or at week intervals. The effects of OA oil (300 and 500 mg L-1) exposure on stress parameters (plasma cortisol, glucose and sodium levels) after handling were also assayed. The major compounds of the essential oils were eugenol (73.6%) in OG, 1,8-cineol (21% in the leaf) and linalool (20.2% in the leaf; 46.6% in the inflorescence) in OA, globulol (26.6% in the leaf) and germacrene D (15% in the inflorescence) in HM. Anesthetic effects were detected to all samples in silver catfish in concentration ranges of 30-300 mg L-1 of OG, 200- 500 mg L-1 of OA and 344 mg L-1 of HM. Fractionation of the essential oil of HM furnished (+)-1-terpinen-4-ol and (-)-globulol, which demonstrated sedative effect at 10 mg L-1. Anesthesia was obtained with 83-190 mg L-1 of (-)-globulol, but animals showed loss of mucus during induction and mortality at these concentrations. Benzodiazepinic-like action on receptor GABAA was detected to the essential oil of OG, as well as tolerance development. The same pattern could not be observed to (-)-globulol. The R-(-)-linalool detected in essential oil of OA demonstrated higher anesthetic effect in silver catfish in relation to the S- (+)-form isolated from the essential oil of Lippia alba, which was the only active against Aeromonas hydrophila in vitro. Regarding to the stress parameters, previous exposure to the essential oil of OA was able to prevent handling-induced stress.