The morphometry and biomechanical properties of the rat small intestine after systemic treatment with epidermal growth factor.

Morphometric and passive biomechanical properties were studied in isolated segments of the duodenum, jejunum and ileum in 22 EGF-treated rats and 12 control rats. The rats were allocated to groups with EGF treatment for 2, 4, 7, and 14 days (n = 6 for each EGF treatment group except n = 4 for the 14 days group) or saline treatment (n = 3 for each group). The intestinal segments were pressurized with Krebs solution from 0 to 8 cmH2O for duodenum and 0 to 6 cmH2O for jejunum and ileum using a ramp distension protocol. The diameter and length were recorded at different pressure levels. Circumferential and longitudinal stresses (force per area) and strains (deformation) were computed from the length, diameter, pressure and the zero-stress state data. EGF treatment was associated with pronounced morphometric changes, e.g., the wall thickness, wall area, and the circumferential lengths significantly increased during EGF treatment in all intestinal segments (P < 0.05). Histological analysis showed that the thickness and area of the layers increased after EGF treatment. With respect to the biomechanical data, the opening angle increased in all segments during EGF treatment with the highest value in the 14 days EGF treatment group (P < 0.05). The same result was found for residual strain and the residual strain gradient through the intestinal wall. Linear regression analysis demonstrated that the opening angle mainly depended on the mucosa thickness and area. Furthermore, the circumferential stiffness increased in the duodenum and decreased in the jejunum and ileum during EGF treatment. A plateau was reached after 7 days where after it started to normalize (P < 0.01). In the longitudinal direction, all intestinal segments became stiffer after EGF treatment for 7 days. After 14 days the curve started to normalize in duodenum and jejunum but not in the ileum.