Mechanisms of adaptation in rat small intestine: regional differences in quantitative morphology during normal growth and experimental hypertrophy.

The gross and microscopical dimensions of small intestines from three groups of rats were investigated by morphometric (mainly stereological) methods. The groups were chosen to represent relatively 'steady state' situations: normal growth (over a 12 week period) and intestinal hyperplasia due to streptozotocin-diabetes of 12 weeks duration. Four intestinal segments were sampled along each intestine. For normal groups, no interaction effects were found, suggesting that growth affected all regions of the small intestine in the same way. Older rats were heavier and their intestines were longer and narrower. In addition, villous surface area was more extensive and the villi differed in shape. Volumes of crypts, submucosa and muscularis externa were all reduced. Diabetic animals weighed less than age-matched controls and their intestines were wider but not significantly longer. All surface areas and volumes were increased substantially. However, hypertrophy of the muscularis externa was not detected by measuring muscularis thickness. Villi altered their shape. At least for villous height, the effects of diabetes were greater in terminal segments. These findings are discussed in the context of the reported effects of age and experimental hyperplasia (including diabetes) on intestinal architecture and behaviour.