AIM: To measure the time-dependent (viscoelastic) behavior in the change of the small intestinal opening angle and to test how well the behavior could be described by the Kelvin model for a standard linear solid. METHODS: Segments from the duodenum, jejunum, and ileum were harvested from 10 female Wistar rats and the luminal diameter, wall thickness, and opening angle over time (theta(t)) were measured from rings cut from these segments. RESULTS: Morphometric variations were found along the small intestine with an increase in luminal area and a decrease in wall thickness from the duodenum to the ileum. The opening angle obtained after 60 min was highest in the duodenum (220.8 +/- 12.9 degrees) and decreased along the length of the intestine to 143.9 +/- 8.9 degrees in the jejunum and 151.4 +/- 9.4 degrees in the ileum. The change of opening angle as a function of time, fitted well to the Kelvin model using the equation theta(t)/theta(0) = [1-eta exp (-lambda t)] after the ring was cut. The computed creep rate lambda did not differ between the segments. Compared to constant calculated from pig aorta and coronary artery, it showed that alpha agreed well (within 5%), lambda was three times larger than that for vascular tissue, and lambda ranged +/- 40% from the value of the pig coronary artery and was a third of the value of pig aorta. CONCLUSION: The change of opening angle over time for all the small intestine segments fits well to the standard linear spring-dashpot model. This viscoelastic constant of the rat small intestine is fairly homogenous along its length. The data obtained from this study add to a base set of biomechanical data on the small intestine and provide a reference state for comparison to other tissues, diseased intestinal tissue or intestinal tissue exposed to drugs or chemicals. (C) 2005 The WJG Press and Elsevier Inc. All rights reserved.