Intestinal brush border membrane marker enzymes, lipid composition and villus morphology: effect of fasting and diabetes mellitus in rats.

Diabetes mellitus is associated with enhanced passive intestinal uptake of cholesterol and fatty acids. In order to determine the basis for these changes in intestinal permeability, the jejunal morphology and the lipid content of purified brush border membranes (BBM) were measured in fasted and fed control (C) and streptozotocin diabetic (DM) rats. There was no difference between C and DM in BBM sucrase or alkaline phosphatase; fasting had no effect on BBM enzymes in C, but in DM fasting was associated with increased sucrase activity per length of jejunum. In C fasting was associated with higher levels of BBM total phospholipid, lecithin, choline and amine phospholipids, whereas fasting in DM was associated with higher BBM cholesterol and lower free fatty acids. In the fasting DM, there was a greater villus and mucosal surface area than in the fasting C. A previous study demonstrated that with fasting in DM versus C, cholesterol uptake was unchanged, but when animals were fed, cholesterol and fatty acid uptake were greater into the jejunum of fed DM as compared with fed C. In the BBM of fed DM as compared with C, there was a significant increase in total phospholipid, lecithin, phosphatidyl ethanolamine, choline and amine phospholipids, and phospholipid/cholesterol ratio. Thus, (1) fasting is associated with changes in intestinal morphology, BBM lipids; (2) the effect of fasting is different in DM and C; (3) the enhanced uptake of lipids into the jejunum of fed diabetic rats is not due to changes in villus morphology, but may be due to alterations in the BBM phospholipids.