Intestinal nutrient uptake measurements and tissue damage: Validating the everted sleeves method

The reliability of methods for nutrient uptake measurements across the inte stinal epithelium relies on the integrity of the mucosal epithelium and the enterocytes. We tested effects of tissue handling during the "everted slee ves method" on the length of intestinal villi, the surface magnification, t he circumference of the gut, and the thickness of the muscle layer in sunbi rds (Nectarinia osea), chicken (Gallus gallus), and mice (Mus domesticus). The sunbird has thin and delicate intestinal villi that are greatly affecte d by the everted sleeves method. After eversion and incubation, villi lost 30% of their original length. The severe tissue damage coincides with uptak e measurements for glucose that were an order of magnitude lower than in ot her nectar-feeding (nectarivorous) birds of similar body size. Tissue handl ing during the everted sleeves method had significant effects on morphometr ic parameters of chicken and mouse intestines, but on a light-microscopical level, the tissue integrity and the cytology of the enterocytes were not a ltered. Therefore, we think that the everted sleeves method renders reliabl e and reproducible measurements of nutrient uptake in those species. We con clude that a histological evaluation is necessary to assess the reliability of the method before it is applied to adults or to the developmental stage of any species.