INTESTINAL CALCIUM-ABSORPTION IN RATS IS STIMULATED BY DIETARY LACTULOSE AND OTHER RESISTANT SUGARS

Lactulose is a disaccharide analogue of lactose that is resistant to m etabolism in the small intestine but not in the large intestine. The e ffects of lactulose and other sugars on intestinal Ca absorption were determined from the decrease in the 47Ca:Sc-47 ratio between diet and feces after feeding male rats diets containing these sugars during a s ingle night. Dietary lactulose was more potent than lactose in stimula ting Ca absorption and was effective between 5 and 38 wk of age. The c omponent sugars of lactulose, galactose and fructose, did not influenc e Ca absorption when provided together at concentrations equimolar to that of lactulose. The stimulation of Ca absorption by dietary lactulo se increased as dietary Ca concentration was raised and was not influe nced by prior injections of calcitriol. Lactulose must be present in t he same meal as Ca to stimulate Ca absorption, but this stimulation wa s lost if the rats were fed lactulose continuously for 2 or 7 d prior to the test diet. Other sugars thought to be poorly absorbed in the sm all intestine (xylitol, lactobionate, arabinose, raffinose, pyroglutam ate, sorbitol, gluconate and raftilose) stimulated Ca absorption to an identical extent as lactulose. Cecectomy did not influence the enhanc ement of Ca absorption by lactulose. These results indicate that sugar s resistant to metabolism and absorption in the small intestine but no t the large intestine stimulate Ca absorption in the small intestine.