DIETARY-FAT AND FIBER ALTER RAT COLONIC MUCOSAL LIPID MEDIATORS AND CELL-PROLIFERATION

To better understand the biochemical mechanisms by which dietary fat and fiber modulate colonic cell proliferation, we determined the effect of dietary fats and fibers on rat colonic epithelial cell phospholipid mass and composition and on two metabolic products of phospholipids, prostaglandins and diacylglycerol (DAG). In a 3 x 3 factorial design, groups of 10 male Sprague-Dawley rats were fed one of nine experimental diets for 3 wk: three types of fat at 15 g/100 g (beef tallow, corn oil or fish oil) x two types of fiber (pectin or cellulose) or fiber-free as a control group. Dietary treatment did not alter phospholipid or DAG mass, although the fatty acid compositions of membrane phospholipids and DAG were altered by dietary treatment. Arachidonic acid 120:4(n-6)] and eicosapentaenoic acid [20:5(n-3)] in colonic mucosal phospholipid and DAG were associated with higher and lower indices of cell proliferation, respectively. These correlations were specific for the distal colon, which was the principle site of dietary fat effects on cell proliferation. Prostaglandin E and prostacyclin synthesis in colonic mucosa and muscle was significantly lower in fish oil-fed compared with beef tallow- and corn oil-fed animals (by 46-90%, P < 0.001), in both the proximal and distal colon. Correlations between prostaglandin production and cell proliferation, however, were significant only in the distal colon. These data raise the possibility that dietary fat and fiber may modulate intracellular events related to cell proliferation via their effects on epithelial cell phospholipid fatty acid composition, and subsequently on prostaglandin production and DAG composition.