Morphometric and biomechanical remodeling of the small intestine during aging in rats

The present study aimed to study the morphometric and biomechanical remodeling of the small intestine during aging in rats. Twenty-four male Wistar rats, aged from 6 to 22 months, were used in the study. The body weight and the wet weight per length of duodenal and ileal segments were measured at the termination of the experiments. Morphometry data was obtained by measuring the wall thickness and cross-sectional area. The mechanical test was done as a step-wise distension experiment. The intestinal diameter and length were obtained from digitized images of the segments at pre-selected pressure levels and at the no-load and zero-stress states. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter and pressure data and from the zero-stress state geometry. The duodenal and ileal dimensions increased slightly from 6 to 22 months, e.g. the wall thickness and the wall cross-sectional area increased about 4% and 25% for duodenum and 5% and 8% for ileum. The opening angle gradually decreased from 154 to 117 degrees for duodenum and from 144 to 87 degrees for ileum during aging. The circumferential stress-strain curves significantly shifted to the left after 22 months (p<0.05) whereas the longitudinal stress-strain curves significantly shifted to the left after 18 months (p<0.01) both for duodenum and ileum. The intestinal wall became stiffer circumferentially and longitudinally during the aging. Furthermore, the intestinal wall was stiffer longitudinally than circumferentially. In conclusion, pronounced morphometric and biomechanical remodeling occurred in the rat intestine during aging.