Altered prejunctional modulation of intestinal cholinergic and noradrenergic pathways by α2‐adrenoceptors in the presence of experimental colitis

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Abstract
This study investigates the influence of intestinal inflammation on: (1) the control of intestinal neurotransmission and motility by prejunctional α2‐adrenoceptors and (2) the expression of intestinal α2‐adrenoceptors. Experimental colitis was induced by intrarectal administration of 2,4‐dinitrobenzenesulphonic acid (DNBS) to rats. UK‐14,304 inhibited atropine‐sensitive electrically evoked contractions of ileal and colonic longitudinal muscle preparations. UK‐14,304 acted with similar potency, but higher efficacy, on tissues from DNBS‐treated animals; its effects were antagonized with greater potency by phentolamine than rauwolscine. Electrically induced [3H]noradrenaline release from ileal preparations was reduced in the presence of colitis. Tritium outflow was decreased by UK‐14,304 and stimulated by rauwolscine or phentolamine: these effects were enhanced in preparations from animals with colitis. Reverse transcription–polymerase chain reaction and Western blot assay demonstrated the protein expression of α2A‐adrenoceptors in mucosal and muscular tissues isolated from ileum and colon. The induction of colitis increased α2A‐adrenoceptor expression in both ileal and colonic muscular layers, without concomitant changes in mucosal tissues. Induction of colitis reduced gastrointestinal propulsion of a charcoal suspension in vivo. In this setting, the gastrointestinal transit was inhibited by intraperitoneal (i.p.) UK‐14,304 and stimulated by i.p. rauwolscine. After pretreatment with guanethidine, the stimulant action of rauwolscine no longer occurred, and UK‐14,304 exerted a more prominent inhibitory effect that was antagonized by rauwolscine. The present results indicate that, in the presence of intestinal inflammation, prejunctional α2‐adrenoceptors contribute to an enhanced inhibitory control of cholinergic and noradrenergic transmission both at inflamed and noninflamed distant sites. Evidence was obtained that such modulatory actions depend on an increased expression of α2A‐adrenoceptors within the enteric nervous system. British Journal of Pharmacology (2003) 139, 309–320. doi:10.1038/sj.bjp.0705249