Effect of excess dietary calcium on colon mucosal membranes and fecal lipids.

The objective of the present studies was to examine the biochemical alterations in colon apical membranes upon feeding excess calcium to animals on a saturated fatty acid-rich diet. It has been suggested recently that excess dietary calcium may offer a protection to colon membranes as judged by histologic examination. Sprague-Dawley weanling male rats were fed a semisynthetic diet containing 14% beef fat plus 2% corn oil and either the calcium requirement or excess calcium in the form of calcium carbonate. Animals were fed the diets for 4 weeks. Feces were collected in the last 3 days. The results indicate that excess dietary calcium resulted in alteration in the density of 4 protein bands of colon apical membranes upon examination on SDS-gel electrophoresis. These bands contain 20% of membrane proteins. The diet had no effect on either the lipid content or fatty acid composition of the membranes. Excess dietary calcium resulted in a 54% reduction in fecal water bile acids and a 44% reduction in fecal water free fatty acids. The reduction in fecal water lipids was due to alterations in the solubility of these lipids. This was not mediated through alterations in the pH of fecal water. The observed alterations in protein patterns of these membranes may be due to either the reduction of fecal water bile acids and free fatty acids or may be a direct effect of dietary calcium on membrane proteins.