How to express pharmacological contractions of the inflamed rat intestine

Inflammation leads to intestinal dysmotility which can be due to both funct ional and trophic alterations of the neuromuscular apparatus. To discrimina te between trophic and functional changes, several normalization procedures are used in contractility studies. It is important to know how normalizati on procedures may influence the obtained results. In a rat model of TNBS-induced ileitis, we compared seven known normalizati on procedures for pharmacological contractions of longitudinal muscle strip s. During acute ileitis, contractility was significantly decreased, irrespecti ve of the normalization procedure used. During the post-inflammation phase, hypertrophy and hyperplasia of smooth muscle cells led to increased contra ctility on raw strip chart recordings. However, when contractions were corr ected for the increase in muscle mass, the contractility was either normal or decreased, depending on the normalization procedure used. Normalization of contractions to the cross-sectional area (CSA) of the longitudinal muscl e is the gold standard. Comparison of three methods to determine the CSA, s howed that the commonly used equation to calculate the CSA, based on the ti ssue weight, length and density, might overestimate the CSA. We conclude th at this equation should be adapted by a muscle thickness ratio, or alternat ively the CSA can be determined on histological sections.