Summary: The morphological responses of smooth muscle cells in the rabbit colon to different degrees of anal stenosis, and the cell changes subsequent to release of that obstruction were studied in both the growing and adult rabbit.
The colon reacted first by dilatation then by thickening of the wall. Microscopically, disruption of the muscle layers, cellular hypertrophy, increased connective tissue and mitosis of smooth muscle cells were apparent. The sequence of cellular hypertrophy was found to be:-cytoplasmic enlargement, nuclear enlargement, mitosis and cellular hyperplasia.
Quantitation showed that cellular hypertrophy up to three times the normal value occurred in proportion to the duration and degree of obstruction. In the adult animal, the muscular thickening was mainly due to hypertrophy with only a 20-30% increase in cell population. In the growing rabbit, hyperplasia and hypertrophy contributed equally to the total muscular thickening. Upon release of obstruction, cell and nuclear size slowly decreased, but the increased cell numbers seemed to remain.
(C) 1973 Royal College of Pathologists of Australasia