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UMMARY

At weaning, mammals switch from milk to complex adult food, and change from alactose-rich to a lactose-free diet. At the same time, the small intestine maturesresulting in changes in lactase expression and the onset of sucrase. The aim of this studywas to analyze the effect of premature and specific depletion of lactose on maturation ofthe small intestine and on lactase expression in suckling mice. For this purpose, frompostnatal days 10 to 16, suckling mice were fed by transgenicalpha-lactalbumin-deficient females that produce lactose-free milk. Pups fed withlactose-free milk had a lower body weight than controls fed by wildtype females. They alsodisplayed hypotrophy of intestinal muscle layers, but no obvious alterations in themorphology of the intestinal epithelium. The level of lactase activity as well as thelongitudinal distribution of corresponding mRNA were unchanged compared to sucklinganimals nourished with normal lactose-containing milk. Finally, there was no prematureonset of sucrase expression. We conclude that feeding suckling mice for six days withlactose-free milk does not provoke any premature maturation of the small intestine. Thus,decreasing lactose intake is not a major cause for the modifications of lactase expressionwhich occur at weaning.

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