Anti-inflammatory effects of methyl cinnamate, the major constituent of the essential oil of Ocimum micranthum, on the gastrointestinal tract of rats submitted to acetic acid-induced colitis

Abstract

The essential oil of Ocimum micranthum Willd. has analgesic properties in nociception of inflammatory origin and exerts antispasmodic actions on rat airways after inflammatory stimulus (Planta Med. 2012;78:681). Its effects involve methyl cinnamate (MC), a compound potentially interesting for studies involving conjunctly smooth muscle cells, nociception, and inflammation. Thus, this study was designed to observe whether MC impairs the deleterious effects caused in acetic acid-induced colitis. Wistar rats of the colitis group (CG) were instilled with acetic acid (5%) by rectal route, while control group (S) received saline. Animals received (p.o.) saline or MC (50 mg/kg) daily for 3 days after instillation procedure. Positive control was prednisolone (P; 1 mg/kg, i.p.). At the 3rd day, the rats were sacrificed in order to obtain blood samples and colon strips that were disposed in bath chamber to construct concentration-effect curves to KCl (1 – 140 mM). Rats of CG showed intense inflammatory process at visual inspection, which was confirmed by the increased levels of leukocytes in blood samples (5.6 ± 0.5 × 103 cells/µl in S [n = 10]; 8.6 ± 0.7 × 103 cells/µl in CG [n = 9]; p < 0.05). MC or P significantly decreased the leukocyte levels in CG to 6.4 ± 0.4 × 103 cells/µl [n = 9] and 5.4 ± 0.6 × 103 cells/µl [n = 6] (p < 0.05), respectively. The levels of IL-1β, which were 737.3 ± 81.4 pg/ml (n = 5) in CG, were significantly (p < 0.05) decreased by MC and P to 511.0 ± 75.7 pg/mL (n = 5) and 317.4 ± 23.9 pg/ml (n = 6), respectively (S group = 434.1 ± 22.9 pg/ml; n = 7). Maximal contraction induced by KCl was 0.05 ± 0.01 g/mg of tissue (n = 5) in CG, value significantly lower than 0.21 ± 0.03 g/mg of tissue (n = 5) in S. MC and P reverted partially the detrimental effects on KCl-induced contractions in CG (Emax = 0.14 ± 0.03 g/mg of tissue (n = 5) and 0.11 ± 0.01 g/mg of tissue (n = 6), respectively). Thus, MC has protective effects against the deleterious actions of acetic acid instilled on gastrointestinal tract of rats.