Structural and functional analysis of glucose absorption mechanisms in the rat small intestine in vivo.

The absorption of glucose (free, and released from membrane hydrolysis of maltose) and water in the isolated loop of the rat small intestine was studied in chronic experiments. Even at maximum glucose (75 mmol/l) or maltose (37.5 mmol/l) concentrations the rate of glucose transfer by solvent drag and by diffusion did not exceed 13% and 25%, respectively, of the total rate of glucose absorption. Electron microscopic and immunocytochemical analysis revealed a significant widening of intercellular gaps in the basal epithelium region and an increase of actin density in the vicinity of the tight junctions and between the apical root filaments in enterocytes after glucose or glycine load in chronic and acute experiments. However, very rarely (in 1% of all cases), and only in chronic experiments, structural changes in the tight junctions such as "blisters" and dilatations were also recognised. It is concluded that under normal physiological conditions the absorption of glucose (free, and released from maltose hydrolysis) mainly uses active transport across the apical membrane of the enterocytes.

[Isolated enterocytes as an object of functional morphology]. / Izolirovannye énterotsity kak ob''ekt funktsional'noi morfologii.

Morphological examination of isolated enterocytes obtained-from the rat jejunum initial region by mechanical method after the previous treatment with ethylendiamintetracetic acid disodium salt included staining with hematoxylin, carmin and janus green. Histochemical reaction to alcaline phosphatase, succinate dehydrogenase, lactate dehydrogenase, ATP-ase and glycosaminoglycans were performed. Significant resemblance between the main cytological and cytochemical characteristics of the isolated enterocytes and those of the intestinal epithelium was demonstrated. Morphophysiological examination of isolated enterocytes, incubated in media, containing different substrates (glucose, maltose, glycine, trioleine) and under effect of oxygenated and not-oxygenated media demonstrated that mitochondria intracellular topography and succinate dehydrogenase activity significantly depend on their functional state.

[Proteases of the large intestine]. / Proteazy tolstoi kishki.

The large intestine was found to reveal an obvious activity of various aminopeptidases and genuine dipeptidases in dogs and in humans. A dipeptidase was found specific by its independence of the C-terminal configuration of the peptide. This peptidase in an intrinsic membrane protein. Physiological significance of these enzymes is discussed.

[An analysis of the structural characteristics of the tight junction of the enterocytes of the rat small intestine during nutrient absorption (immunoelectron microscopic research)]. / Analiz strukturnykh kharakteristik plotnogo kontakta énterotsitov tonkoi kishki krys v protsesse vsasyvaniia nutrientov (immunoélektronno-mikroskopicheskoe issledovanie).

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.

[Circadian rhythm of intestinal glucose absorption in fasting and fed rats]. / Sutochnye kolebaniia skorosti vsasyvaniia gliukozy v tonkoi kishke golodnykh i sytykh krys.

Under conditions of chronic experiment the circadian cycle of glucose transport was determined. An isolated proximal area of the small intestine was perfused by glucose, fructose, medical bile and Ringer's solutions in various intervals of the 24 hour period. The circadian cycle of glucose absorption is disturbed in the fasting rats. Various substrates differently alter their amplitude and acro-phase of absorption. Ringer's solution perfusion shifts the acro-phase absorption to evening time, while that of fructose occurs during day time and that of bile takes place at night. The circadian cycle of the fed rats is less subject to shifts. Fasting is a powerful exogenous factor causing structural changes in the small intestine and altering the circadian cycle of glucose absorption.

[The digestive enzymes in the gastrointestinal tract, kidney, liver and spleen in different functional states]. / Pishchevaritel'nye fermenty v zheludochno-kishechnom trakte, pochke, pecheni i selezenke pri razlichnykh funktsional'nykh sostoianiiakh.

A wide range of digestive enzymes with different cellular location (membrane, intracellular, Lysosomal) was determined in gastrointestinal organs (stomach, duodenum, jejunum, ileum, colon) as well as in undigestive organs (liver, kidney, spleen) in normal conditions and in altered functional states (fasting, refeeding). High levels of peptidase activity was noted in undigestive organs and the colon as compared to that in the small intestine. Adaptive responses were (revealed not only for a number of membrane enzymes but also for intracellular ones including those in undigestive organs.

[The enzymatic barrier of the small intestine]. / Enzimaticheskii bar'er tonkoi kishki.

The small intestine's barrier functions are reviewed. The data on mechanical (passive) and active protective systems of the organism against various antigens, toxic substances and proteins, is presented. An important role of these protective systems as an enzyme apparatus of epithelial and postepithelial layers of the small intestine's mucose, is shown.

[The detailed characteristics of the enzyme spectrum of the small intestine in rats in the early postnatal period]. / Detal'naia kharakteristika fermentnogo spektra tonkoi kishki krys v rannem postnatal'nom periode.

The activity of the small intestine's peptide hydrolases is higher in 1-day old rats than in adult rats, whereas levels of activity of alkaline phosphatase and diglycyl glycine peptidase do not differ significantly in these two groups of the rats. Our own data on carbohydrases corroborate other authors' evidence and reveals that activities of lactase, sucrase and maltase are either absent or very low in the first days of life and sharply increase by the third week of postnatal development. Adaptive changes of regulatory properties of lactase and alkaline phosphatase are revealed.

[The enzyme-transport characteristics of the small intestine of rats during aging]. / Fermentativno-transportnye kharakteristiki tonkoi kishki krys pri starenii.

Ageing was shown to be accompanied by changes of the activity levels of the small intestine's carbohydrases, dipeptidases, and alkaline phosphatases. The changes occurred both under normal conditions and after operations on the small intestine. In ageing, the small intestine's capacity for the homeomorphosis decreases irrespective of either increase or decrease in the functional loading. The age involution of the gastrointestinal tract is followed by disturbances not only in hydrolytic processes but in transport those as well: particularly deceleration of glucose accumulation in preparations of the rat intestine mucose. Regulatory properties of some enzymes were changed, too, in old rats.

[Trans-sorption as an important mechanism of molecular transport in biological systems]. / Transsorbtsiia kak vazhnyi mekhanizm molekuliarnogo transporta v biologicheskikh sistemakh.

The mechanism of trans-sorption was shown to be based on mobile adsorption of various substances at specific and unspecific sites localised in spatially organised systems integrated within premembrane structures. Some specifics and possible physiological significance of trans-sorption are discussed using mathematical models of nutrients transfer across autonomous premembrane layer in the small intestine.

[The transport system that pumps monosaccharides from enterocytes across the basolateral membrane]. / Transportnaia sistema, otkachivaiushchaia monosakharidy iz énterotsitov cherez bazolateral'nuiu membranu.

Using a new, in vitro, experimental approach the transport of glucose, galactose, fructose and glycine in seroso-mucosal direction in the small intestine, was studied under different modes of oxygenation. In case of monosaccharides under the oxygenation from serosal surface, the substrate concentration is lower in the small intestine tissue than under anoxia. The effect of the oxygenation from serosal surface on the galactose transport was shown to be sensitive to absence of sodium ions, ouabain, phloretin, and not sensitive to phlorizin. The data obtained corroborate the hypothesis of the existence of a mechanism pumping off monosaccharides enterocytes through the basolateral membrane.

[The characteristics of the absorption in the small intestine of 2 casein hydrolysates and of an equivalent amino acid mixture]. / Nekotorye osobennosti vsasyvaniia v tonkoi kishke dvukh gidrolizatov kazeina i ékvivalentnoi smesi aminokislot.

Using casein hydrolysates and the amino-acid mixture applied to mucosal or serosal surfaces, their effect on the transport of free glycine, glycine formed during glycyl glycine hydrolysis, and galactose, was studied in the small intestine. The data obtained suggest a mechanism of peptide transport in the enterocytes as well as a possibility of a regulatory effect of the peptides contained in casein hydrolysates on the transport of some basic nutrients.

[Theory of universal functional blocks and fundamental biomedical problems]. / Teoriia universal'nykh funktsional'nykh blokov i fundamental'nye biomeditsinskie problemy.

The paper presents the main aspects of the theory of elementary functional blocks. In accordance with the theory considered high specialization of the complex functions could be reached due to the recombination and transposition of a large though limited set of molecular machines realizing elementary biological operations. The authors proved that the theory of universal functional blocks became a fundamental aspect of the medical theory as it permitted one not only to explain and classify a certain part of clinical and clinicophysiological phenomenology but was of significant prognostic value.

[The effect of stress on the enzyme systems of the enterocyte microvilli in rat pups and the possible mechanism of the transmission of stress effects from dam to progeny]. / Vliianie stressa na fermentnye sistemy mikrovorsinok énterotsitov u krysiat i vozmozhnyi mekhanizm peredachi stressornykh éffektov ot materi k potomstvu.

In suckling rats whose mothers had had an immobilisation stress or been injected HC and T4 at the last day of their pregnancy, the sucrase induction decreased in the small intestine, if the HC was injected on the 10th day of life. The hormone injection to 1-day suckling rats did not affect the induction. These effects seem to be exerted not by the direct permeation of hormone from mother to litter but to be mediated rather by a special factor "stressin". The latter is transferred from mother to litter and decreases the sensitivity of intestinal enzymes to exogenous HC, thus exerting an antistressor effect.

[The endorphins of the epithelial and subepithelial structures of the rat small intestine and the evolutionary hypotheses of the formation of the mechanisms of the negative regulation of their synthesis]. / Endorfiny épitelial'nykh i subépitelial'nykh struktur tonkogo kishechnika krys i nekotorye évoliutsionnye gipotezy formirovaniia mekhanizmov negativnoi reguliatsii ikh sinteza.

The effects of the agonist of the glucocorticoid hormones dexamethasone and dopamine antagonist--haloperidol on the concentration of immunoreactive alpha-, beta- and gamma-endorphins in duodenum, ileum, and jejunum of rats were studied. Besides the extracts of the intestines, the immunoreactive endorphins were measured in the extracts of their mucosa-submucosa and muscle-serous layers, that allowed to separate the endorphin-producing cells of the nervous system (muscle-serous layer) from endorphin producing cells of endocrine and immune systems (mucosa-submucosa layer). The injection of dexamethasone (0.2 mg per rat, daily for 6 days) caused the reliable decrease in concentrations of all three types of endorphins in mucosa-submucosa and muscle-serous layer of duodenum, ileum, and jejunum. Under the action of haloperidol (0.6 mg per rat, daily for 6 days) the reliable increase of beta-endorphin concentration was noticed only in jejunum. The suggestion is made that two distinct subpopulations of endorphin-producing cells exist in the intestine: in one cells endorphin synthesis is regulated by glucocorticoids, as in the anterior lobe of pituitary, in the other cells the synthesis of endorphins is regulated by dopamine, as in the cells of the intermediate lobe of pituitary. It is suggested that both glucocorticoid and dopamine types of regulation of endorphins synthesis were formed in the intestine or even in the gastric cavity. In process of evolution the cells with glucocorticoid type of regulation gave rise to the anterior lobe of pituitary, the cells with the dopamine type of regulation--to the intermediate lobe.