Carboxylesterase in the liver and small intestine of experimental animals and human

Native polyacrylamide gel electrophoresis showed carboxylesterase (CES) to be the most abundant hydrolase in the liver and small intestine of humans, monkeys, dogs, rabbits and rats. The liver contains both CES1 and CES2 enzymes in all these species. The small intestine contains only enzymes from the CES2 family in humans and rats, while in rabbits and monkeys, enzymes from both CES1 and CES2 families are present. Interestingly, no hydrolase activity at all was found in dog small intestine. Flurbiprofen derivatives were R-preferentially hydrolyzed in the liver microsomes of all species, but hardly hydrolyzed in the small intestine microsomes of any species except rabbit. Propranolol derivatives were hydrolyzed in the small intestine and liver microsomes of all species except dog small intestine. Monkeys and rabbits showed R-preferential and non-enantio-selective hydrolysis, respectively, for propranolol derivatives in both organs. Human and rat liver showed R- and S-preferential hydrolysis, respectively, in spite of non-enantio-selective hydrolysis in their small intestines. The proximal-to-distal gradient of CES activity in human small intestine (1.1-1.5) was less steep than that of CYP 3A4 and 2C9 activity (three-fold difference). These findings indicate that human small intestine and liver show extensive hydrolase activity attributed to CES, which is different from that in species commonly used as experimental animals.     

黑麂肝、小肠和大肠的组织学结构及Ghrelin的分布

研究了成年雌性黑麂(Muntiacus crinifrons)的肝、小肠和大肠的组织学结构及Ghrelin的分布。采用H.E染色法观察组织学结构,免疫组化PV-9000两步法并结合DAB显色技术确定Ghrelin的分布。结果表明,黑麂的肝组织分为被膜、肝小叶、肝中央静脉、门管区等结构。被膜为浆膜结构,肝小叶不明显。肝细胞以中央静脉为中心,呈放射状排列。肝血窦的形状不规则。肠黏膜上皮为单层柱状上皮,小肠、盲肠和结肠的黏膜肌层很薄,管壁皱襞与肠绒毛等形态在消化道各部也存在差异。免疫组化结果显示肝细胞中有Ghrelin阳性细胞的表达;在肠道,免疫阳性细胞在十二指肠、空肠、回肠、盲肠和直肠的黏膜、黏膜下层和肌层均有分布,尤其在肠绒毛上皮和黏膜下层分布较多。黑麂肝、小肠和大肠结构与哺乳动物基本相似,但无十二指肠腺;Ghrelin阳性细胞在肝、小肠和大肠均有分布,这表明Ghrelin可能对消化有一定的调节作用。     

Dietary regulation of ornithine transcarbamylase mRNA in liver and small intestine

In the rat, changes in dietary protein intake give rise to changes in the levels of ornithine transcarbamylase (OTC) in liver and small intestine--an increase in liver and decrease in small intestine. The changes in enzyme level are accompanied by similar changes in levels of specific mRNA. Thus in liver, there is an increase in the level of specific mRNA when protein intake is increased, whereas in small intestine there is a small decrease. Comparison of changes in specific mRNA with total poly-A-containing RNA showed that the change in OTC mRNA in liver paralleled the change in total RNA levels. In contrast, in small intestine the small decrease in OTC mRNA levels when protein intake was increased was in the face of an increase in the level of total mRNA. Whereas the level of OTC is 20-fold higher in liver than in small intestine, the mRNA level for the enzyme differs by only 2.5-fold.     

Multiple forms of mutarotases from the kidney, liver, and small intestine of rats: purification, properties, subcellular localization and developmental changes

Comparative studies of mutarotase [aldose 1-epimerase, EC 5.1.3.3] from the kidney, liver and small intestine of rats were performed placing in the focus on the study of multiple forms. The findings obtained are as follows. Mutarotases from the kidney and liver of adult rats were both separated into four forms (types I-IV) by DEAE-cellulose column chromatography, whereas only two forms (types I and II) were detected in the small intestine. Liver mutarotase type I was further separated into types I1 and I2 by column chromatography on hydroxylapatite. Types I and II from the kidney and type II from the liver were purified to homogeneity as judged by isoelectric focusing on thin layer polyacrylamide gel. Of various physicochemical properties, only the Km for alpha-D-xylose and the isoelectric point were different among the multiple forms. Liver mutarotase was immunohistochemically localized in the nuclei of parenchymal cells and small intestine enzyme in the nuclei of mucosal cells, indicating similarity with the localization of kidney enzyme (in the nuclei of epithelial cells of renal tubules and glomeruli) which was reported in our previous paper [Experientia (1979) 35, 1094-1097]. The kidney mutarotase level increased gradually after birth and reached a maximum near adult level within 20 days. This developmental pattern was essentially the same as that in the liver but clearly different from that in the small intestine, in which the mutarotase activity of suckling rats was several times higher than that of adult rats. Distribution patterns of multiple forms (types I-IV) of the enzyme in the kidney and liver of 10-day-old rats were similar to those in respective tissues of adult rats. On the other hand, the small intestine of 10-day-old rats contained four forms (types I-IV), whereas there were only two forms (types I and II) in adult rats.     

Function and regulation of hepatic and intestinal fatty acid binding proteins

Two structurally different fatty acid binding proteins (FABP) have been isolated from rat liver and small intestinal epithelium. hFABP is a 14 184 Da protein found in abundance in both liver and small intestine, whereas gFABP (15 063 Da) is abundantly present only in small intestine. This review discusses studies which have provided insight into the physiological functions of these proteins. These include analyses of endogenous and exogenous ligand binding to FABP in vitro; examination of the modulating effect of FABP preparations on enzyme activities in vitro; exploration of relationships between alterations in cytosolic FABP content in response to hormonal, pharmacological, and dietary manipulations and changes in the rates of cellular fatty acid uptake and utilization; and studies of hFABP turnover and the mechanisms of FABP regulation. These experiments provide compelling evidence for a broad role of the FABPs in the transport, utilization and cellular economy of free fatty acids in the liver and small intestine, and also in protecting several aspects of cellular function against the modulatory effects of fatty acids, fatty acyl-CoA esters, and other ligands. Studies of FABP regulation also suggest a role in long-term rather than short-term modulation of hepatic fatty acid metabolism and indicate that hFABP and gFABP may perform different functions in the small intestine.     

Two different gamma-glutamyltransferases during development of liver and small intestine: a fetal (sialo-) and an adult (asialo-) glycoprotein.

Depending on the developmental stage, the gamma-glutamyltransferase (E.C. 2.3.2.2) exists in two different types in the liver and in the small intestine: a sialic acid-rich fetal type and a sialic acid-poor adult type. The fetal type could be detected in the undifferentiated cryptal cells, in the fetal small intestine and in the fetal liver, and the adult type in the differentiated villous cells and in the adult liver. The separation of both types was performed using ConA-sepharose, which does not bind the fetal type but the adult type. Binding was reached by neuraminidase treatment.     

Enzymes of ornithine metabolism in adult and developing rat intestine.

The levels of 11 enzymes, most of them involved in the metabolism of ornithine, were measured in whole upper intestine, or in duodenum, small intestine and colon of adult rats. The developmental formations in small intestine of arginase, ornithine aminotransferase, and ornithine transcarbamylase were compared with those in liver. Changes with age (late gestation of adult) of the intestinal activities of pyrroline-5-carboxylate reductase, proline oxidase and glutamyl transpeptidase are also described. The results suggest that the proximal part of the intestine is well endowed with enzymes involved in the conversion of ornithine to proline as well as to citrulline. Fetal intestine is rich in proline oxidase and pyrroline-5-carboxylate reductase. The peak levels of ornithine aminotransferase found in intestine in the first 3 postnatal weeks were higher than seen in any other rat tissue. Some of the properties of arginase, ornithine aminotransferase and pyrroline-5-carboxylate reductase in small intestine were compared with those in liver. Isozymes of arginase in small intestine differed from those in liver; the kinetic properties of ornithine aminotransferase were similar in the two tissues. In intestine of 14-day-old rats, the ornithine aminotransferase reaction was reversible, forming ornithine from pyrroline-5-carboxylate. The intestinal pyrroline-5-carboxylate reductase was cold-labile as was the hepatic enzyme in rat.     

Enzymes of orithine metabolism in adult developing rat intestine

The levels of 11 enzymes, most of them involved in the metabolism of orithine, were measured in whole upper intestine, or in duodenum, small intestine and colon of adult rats. The developmental formations in small intestine of arginase, orithine aminotransferase, and orithine transcarbamylase were compared with those in liver. Changes with age (late gestation to adult) of the intestinal activities of pyrroline-5-carboxylate reductase, proline oxidase and glutamyl transpeptidase are also described.The results suggests that the proximal part of the intestine is well endowed with enzymes involved in the conversion of ornithine to proline as well as to citrulline. Fetal intestine is rich in proline oxidase and pyrroline-5-carboxylate reductase. The peak levels of ornithine aminotraferase found in intestine in the first 3 postnatal weeks were higher than seen in any other rat tissue.Some of the properties of arginase, ornithine aminotransferase and pyrroline-5-carboxylate reductase in small intestine were compared with those in liver. Isozymes of arginase in small intestine differed from those in liver; the kinetic properties of ornithine aminotransferase were similar in the two tissues. In intestine of 14-day-old rats, the orithine aminotransferase reaction was reversible, forming ornithine from pyrroline-5-carboxylate. The intestinal pyrroline-5-carboxylate reductase was cold-labile as was the hepatic enzyme in rat.     

Gene expression in derivatives of embryonic foregut during prenatal development of the rat

Proteins characteristic for the adult cellular phenotype, i.e., carbamoylphosphate synthetase (CPS) for liver and small intestine, arginase for liver, glutamate dehydrogenase (GLDH) for pancreas, liver, and small intestine, and amylase for pancreas were studied immunohistochemically in rat embryos and fetuses. At distinct developmental stages, subsets of enzymes appear synchronously in the foregut derivatives, suggesting that gene expression in the different organs is regulated by common factors. In contrast to the long-held opinion that fetal hepatocytes are a homogeneous cell population, it is shown that arginase and CPS are heterogeneously distributed between ED 16 and ED 20. This heterogeneity is related to the vascular architecture of the liver and disappears perinatally as the result of strong stimulation of enzyme synthesis. In addition, an intercellular heterogeneity in CPS content that is not related to the vasculature is observed between ED 14 and ED 20. This "random" heterogeneity reflects temporal differences in the onset of CPS accumulation in individual cells.     

Transport and metabolism of carnitine precursors in various organs of the rat

Isolated, vascularly perfused small intestine, liver, and kidney were used to investigate their interdependence in the absorption and metabolism of carnitine precursors in the rat. During 30 min of recirculating perfusion, the small intestine absorbed trimethyllysine, hydroxytrimethyllysine, and trimethylaminobutyrate fairly well when they were administered via the lumen or the perfusate. Trimethylaminobutyrate was synthesized from either trimethyllysine or hydroxytrimethyllysine by the small intestine, but further hydroxylation of trimethylaminobutyrate to carnitine did not occur. Trimethyllysine and hydroxytrimethyllysine were not readily absorbed by the liver. In contrast, trimethylaminobutyrate and trimethylaminobutyraldehyde were rapidly absorbed from the perfusate and readily incorporated into carnitine by the liver. Trimethyllysine and hydroxytrimethyllysine were taken up slowly by the kiodney and partially converted to trimethylaminobutyrate during 3409 min of perfusion. Trimethylaminobutyrate was neither absorbed readily by the kidney nor was it hydroxylated to carnitine. These results were compared to whole animal studies performed over an equivalent time period. The data suggest that the isolted small intestine absorbs trimethyllysine well, but it probably plays a minor role in metabolizing physiological quantities of this compound in the whole animal where other organs are competing for the same substrate. In both the isolated organ and in the whole animal, the kidney absorbs and metabolizes trimethyllysine more readily than the liver; whereas the liver absorbs trimethylaminobutyrate more rapidly than either the kidney or the small intestine and, unlike these organs, converts it to carnitine.     

Monitor peptide binding sites are expressed in the rat liver and small intestine.

125I-monitor peptide binding was performed using frozen sections of the rat liver and gut and visualized using autoradiography. Saturable binding was observed in unidentified single cells in the liver and in the mucosa of the small intestine. Epidermal growth factor (EGF) and GTPgammaS did not inhibit 125I-monitor peptide binding indicating that the binding sites are not EGF receptors or G protein-coupled receptors. The liver binding site exhibited an affinity 3.7-4.4-fold higher than those in the small intestine. It has been established that intraluminal monitor peptide releases cholecystokinin from the small intestine. The present results indicate that monitor peptide may also have liver associated functions.     

不同日龄大白猪视黄酸受体α基因组织表达

研究采用RT-PCR方法对大白猪的视黄酸受体α基因在1日龄、90日龄、180日龄、270日龄和360日龄的心、肝、胃、脾、肾、肺、大肠、小肠、肌肉、子宫、卵巢共11个组织的表达情况进行了研究。结果表明,RARαmRNA在肝、脾、肾、大肠、小肠、子宫和卵巢中持续表达,其中脾、大肠和小肠是持续高表达;180日龄时,所有组织的RARαmRNA的表达量普遍降低;360日龄时,所检的11个组织均高水平表达该基因。     

Effect of Exercise on Tissue Protein Synthesis in Rats

The effect of exercise on the protein metabolism in skeletal muscles (gastrocnemius and soleus), liver and small intestine was investigated in rats. Treadmill treatment for 7 d resulted in atrophy of the liver and small intestine, which was associated with a reduction in protein content. The rates of protein synthesis in the liver and small intestine were significantly suppressed in rats subjected to exercise. The change in protein synthesis in the visceral organs was mediated by the change in RNA activity (protein synthesis per unit RNA) but not by the change in RNA concentration. The tissue weight and the rate of protein synthesis in the gastrocnemius and soleus muscles were not affected by exercise. The results suggest that these changes in protein synthesis in the liver and small intestine may explain, at least partly, the atrophy of these organs which was observed after 7 d of exercise.     

Effect of exercise on tissue protein synthesis in rats.

The effect of exercise on the protein metabolism in skeletal muscles (gastrocnemius and soleus), liver and small intestine was investigated in rats. Treadmill treatment for 7 d resulted in atrophy of the liver and small intestine, which was associated with a reduction in protein content. The rates of protein synthesis in the liver and small intestine were significantly suppressed in rats subjected to exercise. The change in protein synthesis in the visceral organs was mediated by the change in RNA activity (protein synthesis per unit RNA) but not by the change in RNA concentration. The tissue weight and the rate of protein synthesis in the gastrocnemius and soleus muscles were not affected by exercise. The results suggest that these changes in protein synthesis in the liver and small intestine may explain, at least partly, the atrophy of these organs which was observed after 7 d of exercise.     

Studies on new intracellular proteases in various organs of rat. 3. Control of group-specific protease under physiological conditions.

1. To study the role of group-specific protease in enzyme degradation, alternation of its activity under various physiological conditions was examined. 2. Studies on the distribution of group-specific protease in various organs of rats showed high activity in skeletal muscle and the muscle layer of small intestine, and rather low activity in liver. The activity varied in different muscles, but red muscle tended to have higher activity than white muscle. Activity was much lower in the muscles of the stomach and colon than in those of the small intestine. 3. Group-specific protease in skeletal muscle increased under various dietary conditions (starvation, protein-free diet or high protein diet), but the activities in the muscle layer of the small intestine and liver were not greatly influenced by dietary conditions. None of the hormones tested (i.e. hydrocortisone, glucagon, insulin, growth hormone and estrogen) influenced the activity of group-specific protease in liver. 4. The level of group-specific protease in skeletal muscle was increased markedly fifteen days after denervation, with a reciprocal decrease in the level of muscle phosphorylase, which is a good substrate of the protease. 5. Liver protease activity appeared in the late suckling period. The activity in skeletal muscle was high at the time of birth and attained the adult level 3 weeks after birth. The activity in the muscle layer of the small intestine did not change after birth. Thus the mechanism for evoking these three specific proteases during development are apparently different. The activity of liver protease began to decrease approximately 12 h after partial hepatectomy and reached a minimum after about 72 h. Recovery of the protease activity was very slow and activity had not returned to the normal value 7 days after the operation. This observation seems to be consistent with the fact that there is little or no protease activity in liver in the neonatal period.     

Naringin protects viscera from ischemia/reperfusion injury by regulating the nitric oxide level in a rat model

We investigated the effects of naringin on small intestine, liver, kidney and lung recovery after ischemia/reperfusion (I/R) injury of the gut. Rats were divided randomly into four groups of eight. Group A was the sham control; group B was ischemic for 2 h; group C was ischemic for 2 h and re-perfused for 2 h (I/R); group D was treated with 50 mg/kg naringin after ischemia, then re-perfused for 2 h. Endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) expressions were detected by immunolabeling. We also measured arginase activity, amounts of nitric oxide (NO) and total protein. iNOS was increased significantly in the small intestine, liver and kidney in group C. iNOS was decreased significantly only in small intestine and lung in group D. eNOS was increased significantly in the small intestine, liver and lung in group C. eNOS was decreased in small intestine, liver and lung in group D; however, eNOS was decreased in the kidney in group C and increased in the kidney in group D. The amount of NO was decreased significantly in all tissues in group D, but arginase activity was decreased in the small intestine and lung, increased in the kidney and remained unchanged in the liver in group D. The total protein increased in the small intestine and liver in group D, but decreased significantly in the kidney and lung in group D. Naringin had significant, salutary effects on the biochemical parameters of I/R by decreasing the NO level, equilibrating iNOS and eNOS expressions, and decreasing arginase activity.     

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.     

The maximal activity of phosphate-dependent glutaminase and glutamine metabolism in late-pregnant and peak-lactating rats.

The maximal activity of phosphate-dependent glutaminase was increased in the small intestine, decreased in the liver and unchanged in the kidney of late-pregnant rats. This was accompanied by increases in the size of both the small intestine and the liver. The maximal activity of phosphate-dependent glutaminase was increased in both the small intestine and liver but unchanged in the kidney of peak-lactating rats. Enterocytes isolated from late-pregnant or peak-lactating rats exhibited an enhanced rate of utilization of glutamine and production of glutamate, alanine and ammonia. Arteriovenous-difference measurements across the gut showed an increase in the net glutamine removed from the circulation in late-pregnant and peak-lactating rats, which was accompanied by enhanced rates of release of glutamate, alanine and ammonia. Arteriovenous-difference measurements for glutamine showed that both renal uptake and skeletal-muscle release of glutamine were not markedly changed during late pregnancy or peak lactation; but pregnant rats showed a hepatic release of the amino acid. It is concluded that, during late pregnancy and peak lactation, the adaptive changes in glutamine metabolism by the small intestine, kidneys and skeletal muscle of hindlimb are similar; however, the liver appears to release glutamine during late pregnancy, but to utilize glutamine during peak lactation.