Colite experimental induzida pelo ácido trinitrobenzeno sulfônico em ratos reduz a resposta hipernociceptiva inflamatória : papel das vias endocanabinóides, opióides endógenos e NO/GMPC/PKG/K+ATP

Abstract

The aim of this study was to investigate a possible involvement of the opioids, endocannabinoids and NO/cGMP/PKG/K+ATP pathway in the antinociception of the Crohn´s experimental model in hypernociception induced by carragenan ou PGE2. Colitis was induced in the male Wistar rats (200-250) by intracolonic administration of 20 mg of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in 50% ethanol, ethanol 50% or an equivalent volume of saline. Three or fourteen days after the colitis induction several parameters were evaluated: paw edema induced by carrageenan (Cg; 500μg/hind paw) or dextran (Dxt, 500μg/hind paw), myeloperoxidase activity (MPO), neutrophil migration to pleural cavity. Paw edema was evaluated the right hind paw and measured by plethysmometry. Neutrophil migration was induced by Cg injection in the right hind paw or in the peritoneal cavity. After 4h, rats were sacrificed and the skin of the right hind paw was harvested to measure neutrophil infiltration by MPO assay. Neutrophil migration induced by Cg was also evaluated in the pleural cavity, with the total e differential leucocytes counted. The mechanical behavioral tests were performed by measuring the force in grams (g) applied through a digital analgesymeter (Insight®). In this test the rats received PGE2 (100ng/paw) or carrageenan (Cg; 500μg/paw) into the plantar surface. In order to investigate the involvement of the NO/cGMP/PKG/K+ATP pathway in this event there were used L-Noarg (antagonist of iNOS; 100ng/paw), ODQ ( guanilate ciclase blocker; 8μg/paw), L-Arg (200mg/kg), KT5823 ( PKG blocker; 1.5 μg/paw) and Glibenclamide ( K+ATP channels blocker; 160μg/paw). To evaluated the involvement of the opioids and cannabinoids in this event naloxone (opioids receptor blocker; 1 μg/paw) or AM251 ( cannabinoid receptor blocker type I; 80 μg/paw) or AM630 (cannabinoid receptor blocker type II; 25 μg/paw) were inject respectively. Our results shows that, in animals with TNBS-induced colitis, there was a significant inhibition in the Cg (3rd or 14th after colitis induction) and Dxt (3rd after colitis induction)-induced paw edema. There were no differences in MPO activity and neither in the pleural neutrophil infiltration induced by Cg in rats inoculated with TNBS -induced colitis (3rd after colitis induction) when compares to normal animals. Rats with colitis induced by TNBS showed an increased nociceptive threshold when induced by CG and PGE2. Treatment with ODQ, KT5823 and glibenclamide, naloxone, AM251 and AM630 decreased the nociceptive threshold when compared with TNBS colitis. L-NOARG decrease the nociceptive threshold in rats with colitis induced by TNBS and L-arginine reversed this effect. Our results suggest that the antinociceptive effect of the experimental model of Crohn´s disease induced by TNBS seemed to be mediated a decrease of inflammatory response independent of neutrophil migration and activation of the NO⁄cGMP/PKG pathway followed by the opening of K+ ATP channels and activation of opioid and cannabinoid system.