Systemic treatment with epidermal growth factor in the rat. Biomechanical properties of the growing small intestine.

Prolonged treatment with epidermal growth factor (EGF) in the rat provides an experimental model to growth of the gastrointestinal tract. We treated female Wistar rats for 0 (n = 15), 1 (n = 8), 2 (n = 8), and 4 (n = 8) weeks with subcutaneous EGF (i50 micrograms.kg-1.day-1). Segments were taken from locations at 10, 50 and 90% along the length of the small intestine, weighed, the wall thickness was measured and the luminal cross-sectional area and passive biomechanical properties were assessed using impedance planimetry. In addition, the wall composition was evaluated on histological sections. The weight of the total small intestine and of the three segments (measured in mg.cm-1) increased with the duration of the EGF treatment due to mucosal and muscular growth. After 1 week of treatment the wall thickness increased. After 2 weeks of treatment the cross-sectional area began to increase. The circumferential stress-strain distributions revealed translation of the curves to the right in the graphs implying reduced wall stiffness during EGF treatment. In conclusion EGF treatment for 1 to 4 weeks caused a time-dependent increase in intestinal weight. The growth was characterized by increased wall thickness, increased cross-sectional area and reduced wall stiffness.