Role of tachykinin NK2 receptors in normal and altered rectal sensitivity in rats

1 Irritable bower syndrome is characterized by visceral hyperalgesia common ly associated with stress and inflammatory processes. We investigated the r ole of tachykinin NK2 receptors in the ability of trinitrobenzenesulphonic acid (TNBS) and stress to enhance the sensitivity of the rat rectum to dist ension using a selective tachykinin NK2 receptor antagonist (MEN 11420). 2 Rats were fitted with electrodes implanted in the striated muscles of the abdomen. Rectal distension (RD) was performed with a balloon inflated by s teps of 0.4 ml from 0 to 1.6 ml. Five groups were submitted to RD performed 3 days before and after intrarectal instillation of TNBS. Fifteen minutes before RD, rats were treated with saline or MEN 11420 (5-100 mu g kg(-1) i. v.). Two other groups, submitted to 2 h restraint or sham stress sessions w ere randomly treated i.v. with saline or MEN 11420 (10-200 mu g kg(-1)) pri or to RD applied 20 min later. 3 The basal response to RD was characterized by a significant increase in t he number of abdominal contractions. This response occurred with a threshol d volume of 0.8 ml and was dose-dependently reduced by MEN 11420 (5-100 mu g kg(-1) i.v.). Rectal inflammation lowered the volume of distension produc ing abdominal contractions to 0.4 ml (allodynia). This effect was either re duced or suppressed by MEN 11420. A similar allodynia was observed after a stress session and this effect was reduced (49%) or suppressed by MEN 11420 at 200 and 100 mu g kg(-1), respectively. 4 Tachykinin NK2 receptors are involved in rectal hypersensitivity associat ed with inflammation and stress.