Lactase is unchanged in suckling mice fed with lactose-free milk

At weaning, mammals switch from milk to complex adult food and change from a lactose-rich to a lactose-free diet. At the same time, the small intestin e matures resulting in changes in lactase expression and the onset of sucra se. The aim of this study was to analyze the effect of premature and specif ic depletion of lactose on maturation of the small intestine and on lactase expression in suckling mice. For this purpose, from postnatal days 10 to 1 6, suckling mice were fed by transgenic alpha-lactalbumin-deficient females that produce lactose-free milk. Pups fed with lactose-free milk had a lowe r body weight than controls fed by wildtype females. They also displayed hy potrophy of intestinal muscle layers, but no obvious alterations in the mor phology of the intestinal epithelium. The level of lactase activity as well as the longitudinal distribution of corresponding mRNA were unchanged comp ared to suckling animals nourished with normal lactose-containing milk. Fin ally, there was no premature onset of sucrase expression. We conclude that feeding suckling mice for six days with lactose-free milk does not provoke any premature maturation of the small intestine. Thus, decreasing lactose i ntake is not a major cause for the modifications of lactase expression whic h occur at weaning.