The R6le of the Phospholipids of the Intestinal Mucosa in Fat Absorption

It is almost universally believed that neutral fat must undergo saponification in the lumen of the small intestine before it is absorbed. It has been known since the time of Munk (1880) that the lipid of the thoracic lymph, which acts as the chief vehicle for the transportation of absorbed fat into the blood, consists mainly of neutral fat. Furthermore, the analysis of the chyle from the mesenteric lymphatics has shown that 95 to 97 per cent of the fatty acids is in the form of the triglycerides (Moore, 1903). In 1842 Goodsir discovered that there is an accumulation of fat-like droplets within the epithelial cells of the intestinal mucosa during fat absorption, and some years later Perewoznikoff (1876) observed that the same phenomenon occurs after feeding fatty acids and glycerol, but it was not until chemical methods were applied (Moore, 1903; Noll, 1910) that it was proved that this accumulated material consists mainly of neutral fat. These facts led to the conclusion that there is a resynthesis of neutral fat from its absorbed constituents within the intestinal mucosa, presumably in the epithelial cells. It has been tacitly assumed that this resynthesis is simply a reversal of the hydrolysis which takes place in the lumen of the intestine; that is, it is enzymic in nature. Nevertheless, attempts to demonstrate in vitro the synthesis of fat from its split products in the presence of hashed mucosa have been either inconclusive or definitely unsuccessful. Ewald (1883) and Hamburger (1900) believed that their experiments proved that such a synthesis did occur in vitro but their technique has been severely criticized by Moore (1903) whose own experiments gave negative results. Likewise