Fatty acids (FA) and monoacylglycerol (MAG) produced during absorption of dietary fat are generally thought to be solubilized and transported in intestinal contents as micelles formed with bile salts. Recent findings elsewhere indicate that lamellar structures coexist with mixed micelles and could be involved in transport of lipolytic products into intestinal cells. We investigated this possibility by studying, with a flow-through chamber and phase microscope, effects of various substances on hydrolysis of long chain triacylglycerol (TAG) by pancreatic lipase and transport of lipolytic products in aqueous medal at pH 7.4. We found that FA and MAG produced by lipolysis were insoluble in aqueous media at pH 7.4. Calcium enhanced lipolysis but had no effect on release. of lipolytic product to the media, whereas sodium taurodeoxycholate (TDC) caused release of lipolytic product to the media without affecting lipolysis. Release of lipolytic products by TDC, however, was slow with only 1/3 released in 30 min. TDC enhanced by 60% the stimulatory effect of calcium on lipolysis. Our morphological observations indicated that FA- and MAG formed bilayered (lamellar) structures before they were dispersed by KTDC in the aqueous medal. Findings elsewhere in patients with bile salt deficiencies showed bile salts are not necessary for digestion and absorption of dietary fat. Earlier studies showed in rats and fish that dietary fat droplets undergoing lipolysis were attached to the luminal surface of intestinal cells. Thus, we propose that FA and MAG may be transported from dietary fat droplets into intestinal epithelial cells, in the presence of bile salts, by lateral flow in an interfacial continuum composed of the monolayer surrounding the droplets and the outer leaflets of cell membranes, a process similar to that observed for transport of lipolytic products from chylomicrons in plasma to the interior of parenchymal cells.
