ABSORPTION OF UPID BY THE SMALL INTESTINAL ENTEROCYTES OF THE CmCKEN

Holman J.: Absorption of Lipid by the Small Intestinal Enterocytes of the Chicken. Acta vet. Brno, 48, 1979: 9-13. Experiments were conducted to study the way of lipid absorption in the chicken small intestinal epithelium after peroral administration of sunflower oil. Chickens aged 14-to-23 days were used. The electron-microscopical examination showed that the lipids were absorbed by selective diffusion of monoglycerides and fatty acids by the entire free surface of enterocytes. Pinocytosis of non-hydrolyzed triglycerides was not observed. During lipid absorption in the apical ponion of enterocytes there was no increased occurrence of pinocytotic invaginations or pinocytotic vesicles detectable. Microvilli, plasma membrane, pinocytosis, monoglycerides, fatty acids,rchylomicrons. The way of enteral absorption of lipids in mammals has been a matter of discussion since a long time. Hewitt (1953) admitted that a pan oftriglycerides is absorbed in the nonhydrolyzed form. Palay and Karlin (1959) after peroral administration of lipids to rats found well visible pinocytotic vesicles with lipid panicles in the brush border of enterocytes just beneath the terminal web. Also Mohiuddin (1964) found the lipid droplets to be taken into the epithelial absorptive cells of the intestine by pinocytosis and to be given off by retropinocytosis. The more recent studies based on introduction of ultrathin sections and elaborate biochemical methods have created the new lipolytic theory of lipid absorption. Lipids hydrolyzed in the intestinallumen diffuse into the epithelial cells in form of glycerol and fatty acids. Within these cells their resynthesis occurs (Hofmann and Borgstrom 1962; Johnston and Borgstrom 1964; Senior 1964). This theory received much suppon by the morphological findings. Lipids were found to enter the epithelial cells through their microvilli in particularly small form approaching the size of molecules (Lacy and Taylor 1962). Lipid panicles 50 A to lOOO A in size stained with Pb++ were identified between, on or within the microvilli of the absorptive cells (Rostgaard and Barrnett 1965). These finding compared with micellar solutions stained in vitro indicated that lipids can be absorbed by diffusion in form of lipid particles according to the above-mentioned authors. Similarly, incubation of small intestinal segments in artificially prepared micellar solution showed that the lipids are absorbed by diffusion in form of panicles of micellar or molecular size (Strauss 1966). According to Cardell et a1. (1967) monoglycerides and fatty acids diffUse from micelles during their connection with microvillous membrane of the enterocyte. In rats, the enteral absorption of products of sunflower oil hydrolysis was studied by Dermer (1967). On the surface of fat-absorbing rat intestinal microvilli he found panicles 100 A in size. Indentations between the microvilli and vesicles within the terminal web area, each surrounded by a membrane, did not contain globular material and they were observed in both experimental and control animals. Sjostrand and Bergstrom (1967) found after the fractionated centrifugation ofhomogenates from intestinal epithelial cells of the rat the labelled oleic acid and cholesterol in the smooth-surfaced vesicles of the apical part of enterocytes. These ~esults support the view on resynthesis of triglycerides in the vesicles. Zilversmit (1967) found the chylomicrons originating in the intestinal cells to consist of a network of triglyceride which is, according to its fatty acid composition, similar to the lipids derived from the food.