Lactulose-induced diarrhoea in rats: effects on caecal development and activities of microbial enzymes

The intake of large amounts of lactulose and other non-digestible oligosaccharides can cause diarrhoea in rats and humans. The purpose of our study was to estimate tendency and scope of changes in caecum development, amount and composition of caecal digesta and activity of caecal microbial enzymes under the influence of lactulose-rich diet evoking or not evoking diarrhoea. Male Wistar rats were fed on 8%-lactulose diet for 4 weeks. Feeding with lactulose induced enlargement of the caecum (digesta and wall) compared to the control group. However, the hypertrophy of the caecal wall in rats with diarrhoea was less than in these without that ailment. Dry matter of caecal digesta was significantly decreased in rats with diarrhoea. Diarrhoea lowered concentrations of enzymatic protein and short-chain fatty acids in the caecum, and the activity of bacterial beta-glucuronidase, alpha- and beta-galactosidase, alpha- and beta-glucosidase in caecal digesta, compared to rats without diarrhoea. The ammonia concentration in the caecum was enhanced by diarrhoea symptoms. Occurrence of diarrhoea significantly deteriorated functioning of the caecal ecosystem what in turn limited potential benefits of diet supplementation with lactulose.