Gender related differential effect of tachykinin NK2 receptor-mediated visceral hyperalgesia in guinea pig colon.

Background and PurposeThe tachykinin NK2 receptor antagonist ibodutant is under Phase III clinical investigation to treat female patients with irritable bowel syndrome. The aim of this study was to investigate the NK2 receptor-related gender specificity in a model of colitis. Experimental ApproachColitis was induced by rectal instillation of 2,4,6-trinitrobenzenesulfonic acid (TNBS, 0.5mL, 30mgmL(-1) in 30% ethanol) in female and male guinea pigs. Electromyographic recording of the responses to colorectal distension (CRD) was made 3days later. Ibodutant (0.33 , 0.65, 1.9 and 6.5mgkg(-1)) was given s.c., 30min before CRD. Release of neurokinin A and substance P from isolated mucosal and smooth muscle tissues following treatment with KCl (80mM) or capsaicin (10M) was measured by EIA. Plasma pharmacokinetics of ibodutant following a single s.c. administration (0.73 or 2.1mgkg(-1)) were measured over 24h. Key ResultsIbodutant did not affect abdominal contractions in control animals. After TNBS-induced colitis, ibodutant prevented the increased visceral hypersensitivity to CRD in females, at lower doses than in males. Ibodutant pharmacokinetics did not differ between females and males. Tachykinins release was greater in smooth muscle than in mucosal samples. Capsaicin-stimulated release of tachykinins from inflamed mucosal samples from females was significantly lower than in males. Conclusions and ImplicationsIbodutant prevented abdominal nociception in a model of visceral hypersensitivity in guinea pigs with a greater efficacy in females than in males. Our results highlight a gender-related difference in colonic visceral hypersensitivity and mucosal nerve activation.