INFLUENCE OF DIETARY-FAT AND FEEDING PERIOD ON PHOSPHOINOSITIDE METABOLISM IN RAT COLONOCYTES

The objective of the present study was to examine the effect of dietar y fat content on phosphoinositide (PI) metabolism, fatty acid composit ion in calonocytes, and colonic luminal content of bile acids (BA) and free fatty acids (FFA) in rats. Male Sprague-Dawley rats weighing app roximately 166 g were fed a semipurified diet containing 3% or 21.5% b eef fat and 2% corn oil. The nonfat ingredients were adjusted to corre ct for differences in food consumption of these diets. Animals were fe d these diets ad libitum for one or four weeks. The isolated colonocyt es had a viability of 88.9% in all groups. PI metabolism was examined in the absence (basal) or presence of agonists, 2 mM deoxycholic acid or 10 mu M A(23187). Dietary fat concentration had no effect on PI met abolism, but the length of feeding had a significant effect on basal a nd stimulated PI metabolism. Colonocytes of animals fed the diets for four weeks were less sensitive to stimulation of PI cycle by agonists than those of animals fed for one week. Colonocyte fatty acid composit ion was influenced by dietary fat and feeding period. Only the relativ e percentage of 20:3(n-6) was significantly lower in rats fed the high -fat diet far one week; 18:0 was lower and 18:3(n-6) was higher in col onocytes of animals fed the diets for one week than in those fed for f our weeks. Several colonic fatty acids, namely, 16:0, 20:3(n-6), and 2 2:5(n-6), also exhibited diet-by-feeding period interaction. Intracolo nic luminal contents from rats fed the high-fat diet contained elevate d concentrations of BA and FFA (44% and 62%, respectively). It was con cluded that despite the effects of dietary fat concentration on increa sed colonic BA and FFA and an altered membrane fatty acid composition, dietary fat had no effect on PI metabolism in colonocytes under the c onditions in the present experiment. A difference in components betwee n the purified diet and the commercial rat chaw and/or an aging effect of the rats may alter the PI cycle of colonocytes.