Studies on Lipid Metabolism in the Small Intestine With Observations on the Role of Bile Salts*†

It is now well established that the esterification of long chain fatty acids is an important step in their transport across the small intestinal mucosa before they appear in the lymph in chylomicrons.Evidence for this process has been well reviewed recently (1, 2).The main ester formed by the mucosa is triglyceride but a small proportion of the fatty acids is incorporated into phospholipids and cholesterol esters.We have recently re- ported some in vitro studies on the incorporation of long chain fatty acids into glycerides using ho- mogenates of rat and human small intestine mu- cosa and have delineated some of the cofactor re- quirements involved (3).This work has now been extended to the intact mucosa of the rat.Observations are presented on factors influencing the uptake and esterification of palmitate-1-C4 and the incorporation of label into lipid from C14- glucose.In addition, evidence is presented for the concept that conjugated bile salts directly stimulate glyceride metabolism in the intestinal mucosa. MATERIALS AND METHODSPalmitic acid-1-C14 and uniformly labeled glucose-C4 were obtained from the Volk Radiochemical Company, Chicago, Illinois.The C14-labeled palmitate was purified and made up into a solution as previously described (2).Crystalline bovine albumin was obtained from Nutritional Biochemicals Corporation, Cleveland, Ohio.Cholic acid and desoxycholic acid were obtained from Matheson, Coleman and Bell, Norwood, Ohio and the cholic acid was recrystallized from 70 per cent ethanol.The taurine derivatives of these acids and glycocholic acid were prepared according to Norman (4) and their * Presented in part before the American Society for Clinical Investigation, Atlantic City, New Jersey, May, 1959.