Free amino acids in rat blood serum during A-hypovitaminosis]

A pool of free aminoacids of the blood serum has been studied in growing rats with a decreased retinol content in the liver tissue (to 5 g/g). The study shows a reliable drop in the concentrations of all essential aminoacids, except for phenylalanine. It is determined that the total amount of essential aminoacids decreases by 31%. At the same time concentrations of replaceable aminoacids increase, namely: glutamic acid and arginine--by 15.7%, ornithine and histidine--by 24%-45%, though proline concentration decreases abruptly by 31%. A disturbance in ultrastructural organization of microvilli in the apical membrane cells absorptive epithelium of the small intestine has been found. The results of the study confirm changes in a free aminoacid pool of the blood serum in growing rats and these changes occur first of all due to the disturbance of the absorption processes in the small intestine.     

Effect of exogenous cortisone on amino acid metabolism in rats

1. The effect of exogenous cortisone on concentration of free amino acids in serum, skeletal muscle, kidney, small intestine and liver was studied. 2. The amino acid pool in serum, skeletal muscle and small intestine decreased significantly. 3. Glutamine synthesis increased significantly in skeletal muscle. 4. Levels of branched amino acids increased in serum and small intestine. 5. Levels of alanine increased in kidney and liver.     

Intestinal apical amino acid absorption during development of the pig

Amino acids originating from the diet are the principal metabolic fuels for the small intestine, and although the developing intestine is exposed to dramatic changes in the types and amounts of protein, there is little known about rates of amino acid absorption across the apical membrane during development. Therefore, rates of absorption were measured for five amino acids that are substrates for the acidic (aspartate), basic (lysine), neutral (leucine and methionine), and imino (proline) amino acid carriers using intact tissues from the proximal, mid-, and distal small intestines of pigs ranging in age from 90% of gestation to 42 days after birth (12 days after weaning). Rates of absorption (sum of carrier-mediated and apparent diffusion) were highest at birth (except for proline) and declined by an average of 30% during the first 24 h of suckling. There were continuing declines for leucine, methionine, and proline but not for aspartate and lysine. Due to rapid growth of the intestine, absorption capacities for all amino acids increased faster than predicted from gains in metabolic mass. Regional differences for rates of absorption were not detected until after birth, and only for aspartate and proline. Maximum rates of saturable absorption (nmol. min(-1). mg tissue(-1)) by the midintestine increased during the last 10% of gestation, were highest at birth, and then declined. The contribution of apparent diffusion to amino acid absorption was lowest at birth, then increased after onset of suckling.     

Hind leg muscle amino acid balances in cold-exposed rats

The changes in hind leg tissue (muscle and skin) amono acid pool size and arteriovenous balance were measured in rats subjected to 0–90 min of cold exposure (4°C). Tissue free amino acid pools presented a different composition pattern from protein amino acids. Muscle rapidly reacted to cold exposure by releasing small amounts of some amino acids (alanine, aspartate), with only small changes in pool size during the first 30 min. Amino acid oxidation was very limited during the whole period of cold exposure, since at all times tested there was either nil ammonia efflux or net absorption of ammonia and glutamine; i.e. the muscle was in positive nitrogen balance throughout the period studied. Thus most of the amino acid nitrogen taken up from the blood and not found in the free amino pools must have been incorporated into protein, since it was not oxidized, as shown by the glutamine and ammonia blance. The data on amino acid incorporation into proteins indicate that hind leg protein turnover is rapidly and widely modulated from a low initial setting upon cold exposure to a higher protein synthesis rate immediately afterwards, suggesting that protein turnover may have an important role in short-term events in cold-exposed muscle, in addition to its influence in long-term adaptation.     

The Anatomy of the Oesophagus,Stomach and Intestine in Common Wolffish (Anarhichas lupus L.): A Basis for Diagnostic Work and Research

The alimentary canal of laboratory-reared common wolffish (Anarhichas lupus L.) was studied using light and electron microscopy. In the oesophagus, a simple columnar microvillous epithelium with transport characteristics was observed in addition to the main striated squamous epithelium. An osmoregulatory function is proposed for the simple columnar epithelium, which was supported by wide, thin-walled vessels. In the stomach, a separate type of neck cells was observed leading into the acinar gastric glands, which morphologically consist of one cell type: chief cells. The intestine was divided into a proximal and distal segment by an intestinal valve. Pyloric caeca were not present. We propose that shallow, crypt-like structures in the intestinal mucosa are the sites of epithelial-cell proliferation in juveniles and adults. The length of microvilli decreased from approximately 4 μm in the cranial part of the proximal intestine, to 1.5 μm in the distal intestine. In the distal intestine, rod-shaped bacteria were observed between microvilli. An extensive system of thin-walled vessels was observed in the submucosa of juvenile and adult wolffish stomach and intestine. Eosinophilic granular cells were numerous in the perivascular connective tissue in the gastric and intestinal submucosa of adults and juveniles, but were not observed in larvae.     

Tissue amino acid pool changes during the perinatal period of the rat

Total free amino acid content in foetal liver, kidney, skin and striated muscle increases sharply during pregnancy. After delivery, there is no significant change in tissue total amino acid pools. The essential free amino acid pool in striated muscle decreases after delivery. This decrease suggests a relationship with the increased protein content in striated muscle.     

Effect of parenteral nitrogen feeding on the free amino acid composition of the blood serum and liver tissue in irradiated rats

A considerable change in the free amino acid composition of blood serum and hepatic tissue was noted on the 7th and 14th days following total-body X-irradiation of rats with a dose of 2.9 Gy. The total free amino acid content of blood serum increased and that of hepatic tissue decreased by 85% (on an average) as compared to the intact controls. Quantitative changes in the content of individual amino acids were analysed. Polyamine injected enterally for 7 days and parenterally for 3 days after irradiation aids the elimination of the postirradiation changes in the amino acid balance.     

Effect of 24-hour starvation on amino acid pool composition and enzyme activities of rat brown adipose tissue

The effect of 24-hr starvation on the amino acid pool composition and its concentration ratios with respect to blood and plasma as well as the activities of alanine, aspartate and branched chain amino acid transaminases, glutamate dehydrogenase, glutamine synthetase and adenylate deaminase have been studied in rat brown adipose tissue. Starvation induced a considerable decrease of pool amino acid concentration. Alanine and taurine were the amino acids in which the decrease was more marked. Small changes were observed in the activities of the enzymes studied, with decreases only in glutamate dehydrogenase and adenylate deaminase. These changes agree with a decrease in amino acid utilization in this tissue induced by starvation.     

Site differences of Toll-like receptor expression in the mucous epithelium of rat small intestine

Toll-like receptors (TLRs) are known to recognize pathogen-associated molecular patterns and might function as receptors to detect microbes. In this study, the distribution of TLR-2, -4 and -9 were immunohistochemically investigated in the rat small intestine. As a result, TLR-2 was detected in the striated borders of villous columnar epithelial cells throughout the small intestine, except for the apices of a small number of intestinal villi. TLR-4 and -9 were detected in the striated borders of the villous columnar epithelial cells only in the duodenum. TLR-4-immunopositive minute granules were found in the apical cytoplasms of epithelial cells, subepithelial spaces and blood capillary lumina. TLR-2 and -4 were detected in the striated borders of undifferentiated epithelial cells and in the luminal substances of the intestinal crypts throughout the small intestine, but TLR-9 was not detected in the crypts throughout the small intestine. Only TLR-4 was detected in the secretory granules of Paneth cells in both the jejunal and ileal intestinal crypts. These findings suggest that duodenal TLRs might monitor indigenous bacteria proliferation in the upper alimentary tract, that TLR-2 might also monitor the proliferation of colonized indigenous bacteria throughout the small intestine, that the lack of TLR-2 at the villous apices might contribute to the settlement of indigenous bacteria, and that TLR-2 and -4 are secreted from intestinal crypts.     

Inhibition of intestinal uptake of amino acids by unconjugated bile salt.

The unconjugated bile salt, sodium deoxycholate, at a concentration of 0.5 mM was shown to inhibit the intestinal uptake of the amino acids L-glycine, L-leucine, L-proline, L-lysine and L-tyrosine in rats in vitro. This effect was acutely reversible except for the basis amino acid L-lysine and is therefore not simply due to tissue damage. These results, and the recent finding that sodium deoxycholate inhibits intestinal absorption of amino acids in vivo, suggest that impaired intestinal amino acid transport may contribute to hypoproteinaemia in patients with bacterial overgrowth in the upper small intestine in whom deoxycholate is present in the small intestinal lumen in excessive concentrations.     

Effect of tryptophan excess in a diet on amino acid composition of skin collagen and on an initial stage of protein biosynthesis in rat liver

Protein deficiency and tryptophane load against its background lead to the acid-soluble collagen synthesis in the rat skin. The amino acid composition of the collagen differs from the norm. This is accompanied by changes in the free amino acid pool of blood serum and liver, under tryptophane load the free amino acids pool of the liver increasing twice as high. At the same time protein deficiency increases and tryptophane load decreases the level of tRNA amino acylation with tryptophane in the animal liver. Thus, protein deficiency and tryptophane load against its background cause deep changes in the protein biosynthesis.     

Ultrastructural features of the gut in the white sturgeon, Acipenser transmontanus

Electron-microscopic examinations of the sturgeon gut were performed. Oesophageal goblet cells were abundant in the stratified epithelium. The ultrastructural features of the secretory granules of the oesophageal and intestinal goblet cells were quite similar to those of other vertebrates. Lobules of multilocular adipose tissue were observed in the deep tunica propriasubmucosa of the oesophagus, in close association with vasculature and large fibre bundles of myelinated and unmyelinated axons. Similarly composed nerve fibre bundles were observed in the cardiac stomach, too. The presence of myelinated axons is an unusual feature in the vertebrate enteric nervous system. Cardiac and fundic zones of the stomach showed an epithelium with columnar ciliated and non-ciliated cells, the latter equipped with fuzzy microvilli. Cells lining the tubular gastric proper glands were markedly granulated. Intestinal superficial epithelium was columnar and contained ciliated, as well as non-ciliated and goblet cells. In the tunica propria all over the intestine, the presence and ultrastructure of granulated cells was in addition described. Intraepithelial granulated leukocytes were seen throughout the alimentary canal. Various types of endocrine cells were seen both in the stomach and in the intestine, the size of their granules was measured and their ultrastructure described and compared to that of mammalian cell types.     

The digestive tract of the amberjack Seriola dumerili, Risso: a light and scanning electron microscope study

The histology of the digestive tract of the amberjack ( Seriola dumerili , Risso) was studied using light and scanning electron microscopy. The anterior oesophagus mucosa displays primary and secondary folds lined with a stratified squamous epithelium with fingerprint-like microridges which is substituted, on the top of the oesogaster folds, by a simple columnar epithelium with short microvilli. Only primary folds are present in the stomach. The anterior portion is rich in simple tubular glands, whereas the oesogaster and the pyloric region are devoid of them. Pyloric caeca and anterior and middle intestine mucosa display the same pattern of folding. The dominant cell type is the enterocyte, which exhibits larger and thinner microvilli in the caeca than in the intestine. The columnar epithelium of the rectum is replaced, in the anal sphincter, by a stratified flattened epithelium. Goblet cells are numerous throughout the whole length of the tract with the exception of the initial part of the oesophagus, the oesogaster, the stomach and the anal sphincter. Mucosubstances have been shown to vary in the different regions of the gut: acid mucines are found in the oesophagus, pyloric stomach, caeca, intestine and rectum, whereas neutral mucosubstances dominate in the anterior portion of the stomach. The muscularis is well developed throughout the length of the tract: two layers of striated muscle at the oesophageal level; two layers of smooth muscle in the stomach wall and three at the intestinal level.     

光唇鱼消化道的形态结构特征

采用解剖及石蜡切片显微技术,观察研究了光唇鱼消化道的形态结构特征。消化道由口咽腔、食道、肠构成。口下位、马蹄形,无颌齿,具咽齿,齿式为4/4。舌较小,前端游离,舌粘膜表层为复层鳞状上皮,有较多的杯状细胞和味蕾。食道及肠均由粘膜层、粘膜下层、肌层及外膜构成。食道内皱襞发达,粘膜层有大量杯状细胞。肠道盘曲,由前、中、后肠组成,肠长/体长为1.84±0.24;前肠管腔较大,中、后肠管腔渐变小;前、中肠皱襞及纹状缘比后肠发达;前肠及后肠杯状细胞较少,中肠杯状细胞较多。光唇鱼消化道的形态结构特征与其食性相适应。     

A study of the anatomy, histology and ultrastructure of the digestive tract of Orthrias angorae Steindachner, 1897

The anatomy, histology and ultrastructure of the digestive tract of Orthrias angorae (Steindachner, 1897) were investigated using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The histological structure consists of four layers: mucosa, submucosa, muscularis and serosa. The esophageal mucosa consists of undifferentiated basal epithelial cells, mucous cells and surface epithelial cells. It was observed that the J-shaped stomach had a meshwork of folds in the cardiac region, and longitudinal folds in the fundic and pyloric regions. A single layer of columnar cells, PAS positive only in their apical portions, forms the epithelium. The convoluted tube-shape intestine is lined by simple columnar epithelial cells, which have microvilli at the apical surface. The wall of the esophagus and stomach are thicker than that of the intestine because of the thick muscle layer. There were numerous goblet cells in the intestine. There were numerous gastric glands in the submucosa layer ofthe cardiac stomach, but none were present in the pyloric region of the stomach. There were no pyloric caeca between the stomach and intestine. The enterocytes with microvilli contained rough endoplasmic reticulum, ribosomes and rounded bodies, and the gastric cells contained a well-developed Golgi apparatus.     

The current concepts on the absorption of monosaccharides, amino acids and peptides in the mammalian small intestine

The review is mainly devoted to the development of ideas about absorption, or transport, of basic nutrients in the small intestine in humans and higher animal. The absorption processes have been characterized on the example of such substances, vital for organism, as carbohydrates and proteins. The review considers a molecular structure of transporters--protein molecules, which take part in a transfer of the products of lumenal and membrane digestion of carbohydrates (glucose, galactose, fructose) and proteins (amino acids, oligopeptides) across the enterocyte membranes. An information is presented about genetic disturbances of transport of certain amino acids during such diseases as Hartnup disease, cystinuria, and iminoglycineuria.     

Basolateral aromatic amino acid transporter TAT1 (Slc16a10) functions as an efflux pathway

Basolateral efflux is a necessary step in transepithelial (re)absorption of amino acids from small intestine and kidney proximal tubule. The best characterized basolateral amino acid transporters are y+LAT1-4F2hc and LAT2-4F2hc that function as obligatory exchangers and thus, do not contribute to net amino acid (re)absorption. The aromatic amino acid transporter TAT1 was shown previously to localize basolaterally in rat's small intestine and to mediate the efflux of L-Trp in the absence of exchange substrate, upon expression in Xenopus oocytes. We compared here the amino acid influx and efflux via mouse TAT1 in Xenopus oocytes. The results show that mTAT1 functions as facilitated diffusion pathway for aromatic amino acids and that its properties are symmetrical in terms of selectivity and apparent affinity. We show by real-time RT-PCR that its mRNA is highly expressed in mouse small intestine mucosa, kidney, liver, and skeletal muscle as well as present in all other tested tissues. We show that mTAT1 is not N-glycosylated and that it localizes to the mouse kidney proximal tubule. This expression is characterized by an axial gradient similar to that of the luminal neutral amino acid transporter B0AT1 and shows the same basolateral localization as 4F2hc. mTAT1 also localizes to the basolateral membrane of small intestine enterocytes and to the sinusoidal side of perivenous hepatocytes. In summary, we show that TAT1 is a basolateral epithelial transporter and that it can function as a net efflux pathway for aromatic amino acids. We propose that it, thereby, may supply parallel exchangers with recycling uptake substrates that could drive the efflux of other amino acids.