Determination of analgesic potential of Helicteres isora and molecular involvement of opioids and GABA receptors

Herbal medicines are used as a source of therapeutic agents as they are safer and less toxic than synthetic drugs. Several species of Helicteres isora (Sterculiaceae) have been documented in folk medicine to have analgesic properties. This study is aimed to explore possible analgesic potential of Helicteres isora. linn crude extracts (Hi-Crd) and its sub-fractions, ethyl acetate (Hi-Et) and chloroform (Hi-Chl) by using various models for pain such as acetic acid induced writhing model, formalin paw licking test and tail immersion test. A significant decrease was seen in the frequency of writhing in acetic acid-induced writhing model. The crude extracts and chloroform fractions were more effective when compared to standard. The negative control group displayed a writhing frequency of 76.56 ± 1.21, Hi-Crd at dose of 300 mg/kg and Hi-Chl at dose of 75 mg/kg produces writhing of 20.18 ± 2.03 (P < 0.001) and 17.74 ± 2.39 (P < 0.001) respectively. In formalin paw licking model Crude extract at a dose of 300 mg/kg b.w produced licking response of 20.09 ± 1.45 (P < 0.001) in Phase-I with percentage activity of 49.85% and 17.22 ± 1.33 (P < 0.001) in Phase-II with percentage activity of 72.15 %. Hi-Chl at a dose of 75 mg/kg b.w produced licking response of 19.55 ± 1.76 (P < 0.001) in Phase-I with percentage activity of 51.19 % and 16.01 ± 2.21 (P < 0.001) in Phase-II with percentage activity of 74.11 %. The central analgesic potential was determined by tail immersion test in which the Hi-Chl fraction was most potent and delivered percentage activity of 71.64 %. The standard tramadol delivered percentage activity of 82.29 % at a dose of 10 mg/kg. For the involvement of opioid receptors naloxone was co-administered with standard and test sample at a dose of 2 mg/kg, naloxone completely antagonized tramadol. The analgesic effects of Hi-Crd, Hi-Chl and Hi-Et were completely reversed by naloxone, this confirms involvement of opioids receptors in the analgesic effect of the extracts. For the involvement of GABAergic system bicuculline was injected prior to treatment with test samples. The writhing in the absence and in the presence of bicuculline were partially reversed and the involvement of GABAergic system in the analgesic effect of the crude extracts and fractions is testified.