Intestinal and systemic effects of oral insulin supplementation in rats after weaning

Oral insulin has intestinal trophic effects in suckling animals. In mice, lower glucose and lipid levels may be seen when oral insulin is given after the weaning period. The purpose of the present study is to examine local and systemic effects of oral insulin supplementation in rats in the postweaning period. Immediately after weaning, Sprague-Dawley rats received either drinking water (controls) or oral insulin in their drinking water (1 U/ml) for either 1 week or 6 weeks. Intestinal mucosal parameters (bowel and mucosal weight, mucosal DNA and protein) and histological changes were examined in all study groups. Glucose levels were monitored weekly, and at the end of the study, blood levels of glucose, lipids, and insulin were measured in the fasting state. After 1 week of insulin supplementation, mucosal weight in duodenum and jejunum as well as jejunal DNA content were significantly higher in insulin-supplemented rats compared to controls. Duodenal circumference and villus height in jejunum were significantly higher in insulin-supplemented rats compared to controls on both day 7 and day 42. Total cholesterol levels were significantly lower in the study group compared with the controls. We conclude that oral insulin supplementation exerts intestinal trophic effects, as well as systemic effects in the postweaning period in rats.