Smooth muscle cell hypertrophy and hyperplasia in the partially obstructed gut of the rat: a quantitative evaluation.

Partial surgical stenosis of the gut induces smooth muscle cell hypertrophy and hyperplasia in the loops upstream from the obstruction in a few days. In the present study we report a quantitative evaluation of these phenomena in the circular smooth muscle layer of the small intestine of the rat 7 days after a subtotal stenosis. In the loops upstream from the obstruction, lumen diameter and muscle wall thickness were found to be increased in comparison with downstream tracts. Morphometrical analysis showed that cross-sectional profile areas of smooth muscle cells, within the circular layer of upstream loops, significantly increased in size. Moreover, smooth muscle underwent a marked cell hyperplasia; in fact, estimates of the number of smooth muscle cell nuclear profiles turned out to be from 2.0 to 3.8 times greater in upstream loops than in downstream loops. The relation between the degree of lumen dilatation and the degree of the increase of the circular muscle layer thickness and of hypertrophic and hyperplastic response is discussed.