Effects of Bixa orellana leaves extract on increased paw volume and peritoneal vascular permeability induced by 5-HT in rats

It has been shown that Bixa orellana leaves exhibited anticonvulsant, analgesic and antidiarrhoeal [1] as well as antimicrobial activities [1,2]. In the present study, the effects of aqueous extract of Bixa orellana (BOE) were studied on paw edema and increased peritoneal vascular permeability induced by 5-Hydroxytryptamine (5-HT). Concentrations of nitrate and nitrate were also determined from paw tissues as indicators of nitric oxide production. Briefly, right hind paw volume of Sprague-Dawley rats was measured before 5-HT injection and each hour after for a period of 5 hours by means of volume displacement method by using plethysmometer. 50mg/kg and 150mg/kg BOE significantly reduced 5-HT (0.08mg/kg)-induced paw edema at first hour time point, when maximal paw volume was achieved, from 3.45±0.18 to 2.45±0.18 & 2.59±0.16ml respectively (n=6, p<0.05). Levels of nitrate/nitrite, measured through Griess reaction in inflamed paw tissues, were significantly lowered by 50 & 150mg/kg BOE (2.71µmol g-1±0.10, and 1.79µmol g-1±0.13, P<0.05) respectively, compared to control (4.12µmol g-1±0.11). In another set of rats (n=6 per group), increased peritoneal vascular permeability indicated from leakage of Evans blue dye into the peritoneal cavity was determined spectrophotometrically. BOE significantly reduced Evans blue dye leakage induced by 5-HT from 3.99±0.58µg rat-1 to 2.25±0.18µg rat-1and 2.17±0.18µg rat-1, 43.63 & 45.68% reductions respectively by 50mg/kg & 150mg/kg BOE. 1mg/kg 5-HT2 antagonist, Mianserin, reduced Evans blue dye leakage by 59.22% to 1.63±0.23µg rat-1. This data indicates that 50 and 150mg/kg BOE reduce paw edema and leakage of Evans Blue dye caused by 5-HT and it is possible that the reduction of paw volume may be associated with inhibitions of levels of nitrate/nitrite, and therefore nitric oxide, in tissues.