[An analysis of the structural characteristics of the tight junction of the enterocytes of the rat small intestine during nutrient absorption (immunoelectron microscopic research)].

To analyze structural changes of intercellular relationships of the enterocytes during glycine, glucose, and triolein absorption the structural and immunocytochemical methods of electron microscopy were used. The study was carried out on the proximal part of the rat small intestine in acute and chronic experiments. In the acute ones glucose or glycine solutions (both of 10 and 40 mM) or triolein emulsion (0.5%) were inserted into the isolated small intestinal segments for 20 min. In chronic experiments the isolated loop of the small intestine was perfused with glucose solution (40 mM). Then the corresponding pieces of the intestinal tissue were fixed for structural and immunocytochemical studies. Rarely (in 1% of all cases), and only in chronic experiments, structural changes in the tight junctions--"blisters" and dilatations--were found. At the same time the analysis of the spatial distribution of actin filaments showed that during glucose and glycine absorption the antiactin tracers were found not only within microvilli and on the "root" filaments but also in vicinity of the tight junction and between terminal filaments. The results obtained agree with the hypothesis about the possibility of paracellular transport of some nutrients induced by sodium-dependent transport of glucose and glycine.