Mucosal Protein Synthesis Research Articles

Effect of medium chain triglycerides (MCT) on jejunal mucosa mass and protein synthesis.

The effects of medium chain triglycerides (MCT) on jejunal mucosa mass and protein synthesis were compared with results from previous experiments with rats fed by parenteral nutrition or enteral nutrition. Other published studies have also been analysed. Three experimental models were studied. In the traumatic model, production of a femoral fracture was followed by Kirschner pin insertion into the medullary canal of both fragments at reduction. (Forty ras were fed enteral nutrition and 93 were given parenteral nutrition.) A second model entailed resection under ether anaesthesia using the technique described by Higgins. (Fifty five rats were fed enteral nutrition and 28 with parenteral nutrition.) A third model entailed a terminolateral portocaval shunt under anaesthesia with pentobarbital. (Sixty nine rats were treated this way and then given enteral nutrition.) Proportions of medium chain/long chain triglycerides (LCT) were as follows: 0/100, 20/80, 40/60, 50/50, and 92/8 for enteral nutrition and 0/100, 30/70, 50/50, and 70/30 for parenteral nutrition. Faecal losses of alpha amino nitrogen, protein, total fats, and free fatty acids were analysed together with the quantitative intake, weight gain of the rats, jejunal mucosal mass, and protein synthesis in relation to the MCT proportion ingested or given by enteral nutrition or parenteral nutrition. From analysis of our results and those of others, several conclusions could be drawn. Firstly, the route of administration of MCT is extremely important and enterocytes might be considered one of the main target sites. Secondly, a high proportion of MCT (more than 80%) offers no advantage for jejunal mucosa and produces undesirable side effects. Thirdly, the effect of MCT on jejunal mucosal protein synthesis depends on the metabolic state. Finally, an increase in jejunal mucosal mass directly correlated with MCT concentrations, but no correlation was found between mass and protein synthesis. A positive correlation, however, between MCT proportion and enzyme activity (alkaline phosphatase and sucrase) in the brush border membrane was seen as well as a positive correlation with the concentration of phospholipids in the microvilli.

In vivo rates of mucosal protein synthesis in patients with Barrett’s oesophagus

In vivo rates of mucosal protein synthesis in patients with Barrett’s oesophagus

Measurement of duodenal mucosal protein synthesis in patients with coeliac disease

Measurement of duodenal mucosal protein synthesis in patients with coeliac disease

Increased intestinal protein synthesis during sepsis and following the administration of tumour necrosis factor α or interleukin-1 α

The influence of sepsis on intestinal protein synthesis was studied in rats. Sepsis was induced by caecal ligation and puncture (CLP); control rats were sham-operated. Protein synthesis was measured in vivo in the jejunum and ileum following a flooding dose of [14C]leucine. At 8 h after CLP the protein synthesis rate was increased by approx. 15% in jejunal mucosa, and at 16 h after CLP, the protein synthesis rate was increased by 50-60% in the mucosa and seromuscular layer of both jejunum and ileum. In a second series of experiments, rats were treated with recombinant tumour necrosis factor alpha (rTNF alpha) or recombinant interleukin-1 alpha (rIL-1 alpha) administered at a total dose of 300 micrograms/kg body weight over 16 h. Control rats received corresponding volumes of solvent. Treatment with rTNF alpha resulted in an approx. 25% increase in mucosal protein synthesis in jejunum. Following treatment with rIL-1 alpha, protein synthesis increased by 25% in jejunal mucosa and almost doubled in ileal mucosa. The results suggest that sepsis stimulates intestinal protein synthesis and that this response may, at least in part, be mediated by TNF and/or IL-1.

Effect of total parenteral nutrition, systemic sepsis, and glutamine on gut mucosa in rats.

The effect of the combination of total parenteral nutrition (TPN) and systemic sepsis on mucosal morphology and protein synthesis was investigated. Rats were given a standard TPN mixture consisting of glucose (216 kcal.kg-1.day-1), lipid (24 kcal.kg-1.day-1), and amino acids (1.5 g N.kg-1.day-1) for 5 days. On the 5th day the rats (n = 37) were randomized into four groups according to diet as follows: 1) control nonseptic on standard TPN, 2) control nonseptic on TPN with glutamine, 3) septic on standard TPN, and 4) septic with the TPN supplemented with glutamine. Twenty hours after the injection of Escherichia coli, the rats were given a 4-h constant infusion of [U-14C]leucine to determine the mucosal fractional protein synthesis rates. The following results were obtained. 1) Histological examination showed that systemic sepsis caused tissue damage to the ileum and jejunum. 2) Glutamine supplementation attenuated these changes. 3) There were no visible changes to the colon either from glutamine supplementation or sepsis. 4) Sepsis was associated with an increase in mucosal protein synthesis and decreased muscle synthesis. 5) Addition of glutamine to the TPN mix further increased protein synthesis in the intestinal mucosa of septic rats.

Measurement of duodenal mucosal protein synthesis after delivery of [ 13C]leucine and [ 13C]valine by IV and IG routes

Measurement of duodenal mucosal protein synthesis after delivery of [ 13C]leucine and [ 13C]valine by IV and IG routes

Stimulation of jejunal mucosal protein synthesis by luminal glucose: Effects with luminal and vascular leucine in fed and fasted rats

This study was conducted to determine whether short-term (1.75 h) luminal glucose perfusion increases the mucosal protein synthesis rate in rat small intestine. A luminal perfusate containing 56 mM glucose was compared with a control perfusate containing mannitol in two jejunal segments constructed in the same animal. Mucosal protein synthesis rates were determined when the tracer amino acid was administered intravenously and intraluminally. The results indicated that luminal glucose perfusion rapidly stimulated mucosal protein synthesis in the fed state by 20% and 37% with the labeled amino acid derived from the vascular and luminal compartment, respectively. A 16-h fast abolished the stimulatory effect of glucose when the labeled amino acid was given intravascularly but not intraluminally. These effects of glucose could be ascribed to a direct alteration of mucosal metabolism rather than to indirect systemic effects.

Stimulation of jejunal Mucosal Protein Synthesis by Luminal Glucose: Effects With Luminal and Vascular Leucine in Fed and Fasted Rats

This study was conducted to determine whether short-term (1.75 h) luminal glucose perfusion increases the mucosal protein synthesis rate in rat small intestine. A luminal perfusate containing 56 mM glucose was compared with a control perfusate containing mannitol in two jejunal segments constructed in the same animal. Mucosal protein synthesis rates were determined when the tracer amino acid was administered intravenously and intraluminally. The results indicated that luminal glucose perfusion rapidly stimulated mucosal protein synthesis in the fed state by 20% and 37% with the labeled amino acid derived from the vascular and luminal compartment, respectively. A 16-h fast abolished the stimulatory effect of glucose when the labeled amino acid was given intravascularly but not intraluminally. These effects of glucose could be ascribed to a direct alteration of mucosal metabolism rather than to indirect systemic effects.

Intestinal mucosa in diabetes: synthesis of total proteins and sucrase-isomaltase.

The effects of insulin deficiency on nitrogen metabolism in muscle and liver have been extensively studied with recent in vivo demonstration of impaired protein synthesis in rats with streptozotocin-induced diabetes. Despite the significant contribution of small intestinal mucosa to overall protein metabolism, the effects of insulin deficiency on intestinal protein synthesis have not been completely defined. We studied the effects of streptozotocin-induced diabetes on total protein synthesis by small intestinal mucosa and on synthesis of a single enzyme protein of the enterocyte brush-border membrane sucrase-isomaltase. We used the flooding-dose technique of McNurlan, Tomkins, and Garlick (Biochem. J. 178: 373-379, 1979) to minimize the difficulties of measuring specific radioactivity of precursor phenylalanine and determined incorporation into mucosal proteins and sucrase-isomaltase 20 min after injection of the labeled amino acid. Diabetes did not alter mucosal mass as determined by weight and content of protein and DNA during the 5 days after injection of streptozotocin. Increased rates of sucrase-isomaltase synthesis developed beginning on day 3, and those of total protein developed on day 5. Thus intestinal mucosal protein synthesis is not an insulin-sensitive process.

Role of dietary iron in maturation of rat small intestine at weaning.

The weanling process is characterized by the transition from a liquid diet poor in iron (rat milk) to a solid diet high in iron (chow pellets). To examine the effects of iron content of the weanling diet on terminal maturation of rat small intestine, suckling pups, nursed by iron-sufficient mothers, were weaned by day 16 onto a solid basal diet that was either deficient [low-iron diet (LID): 0.5 mg iron/100 g solid] or high [high-iron diet (HID) controls: 30 mg iron/100 g solid] in iron. The animals were studied during or at the end of the 4th postnatal wk. By day 17 rats weaned onto the LID exhibited an initial rise in jejunal sucrase activity as did their controls, but the activity plateau of the enzyme was reduced to a level 60% of the controls. On day 28 iron-deprived rats were anemic and showed significant decreases (P less than 0.01 compared with HID rats) in the activity of jejunal sucrase (-57%), neutral lactase (-83%), and maltase (-46%), whereas villus height, crypt depth, mucosal mass parameters, ileal acid beta-galactosidase activity, mucosal protein, and DNA synthesis rates were equivalent in LID and HID groups. The concentration of the secretory component, a glycoprotein synthesized by the intestinal crypt cell, was markedly depressed (P less than 0.01 vs. controls) in the jejunum (-54%) and ileum (-79%) of iron-deprived rats. When D-[1-14C]glucosamine was injected intraperitoneally, incorporation of the label into jejunal and ileal brush-border proteins was two to three times lower for iron-deficient rats than for controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of feeding t-2 toxin on rna, dna and protein contents of liver and intestinal mucosa of rats

Young male albino rats were fed 1.5 mg T-2 toxin/kg body weight daily for 4 days and the effects on body weight, liver weight and protein, RNA, and DNA contents of liver and intestinal mucosa were studied. A significant decrease in body weight and an increase in liver weight were observed. Liver protein and DNA and intestinal mucosal protein contents were significantly decreased, whereas intestinal mucosal RNA content was increased. Decreased liver and intestinal mucosal protein synthesis in T-2 toxin-fed rats was inferred from the [ 14C]leucine incorporation studies.

Increased intestinal uptake of cobalamin in pregnancy does not require synthesis of new receptors

Increased intrinsic factor cobalamin binding to receptors present in ileal mucosa from mice in the late stages of pregnancy is regulated by placental lactogen. In mice at day 18–20 of pregnancy given an intraperitoneal injection of cycloheximide, 0.5 mg/kg, receptor binding was reduced from 0.42 ng/mg protein to 0.18 ng/mg protein 4 h later. Intestinal mucosal protein synthesis was less than 20% of control values after this dose of cycloheximide. Although this result could be interpreted to mean that the increase in receptors in pregnancy was due to new protein synthesis, cycloheximide-treated mice also had reduced concentrations of placental lactogen in serum. Supplementation with the hormone in cycloheximide-treated mice maintained receptor binding at pregnant levels. Analysis of binding data showed receptor number to be 3.1·10 11/mg protein and the binding constant ( K a) to be 0.5·10 12 M −1, which were similar to values found in untreated pregnant mice. It is concluded that, because the increase in receptors cannot be explained on the grounds of new protein synthesis, placental lactogen may recruit cryptic intrinsic factor cobalamin receptors.

Gastrin stimulation of gastric mucosal protein synthesis

Gastrin stimulation of gastric mucosal protein synthesis

Stimulation of gastric mucosal protein synthesis by different molecular forms of gastrin.

Protein synthesis in gastric mucosa was studied by measuring the incorporation of labeled amino acids into protein by isolated gastric mucosal ribosomes in a cell-free system. In 48-hour fasted rats, administration of the synthetic analogues pentagastrin, tetragastrin and gastrin-17 or naturally occurring molecular forms of human gastrin (G-14, G-34) markedly enhanced (23-123%) the capacity of the gastric mucosal ribosomes to synthesize endogenous mRNA-directed protein in a cell-free system. In the presence of exogenous mRNA (poly-U), the gastric mucosal ribosomes from the saline-treated controls showed a higher poly(U)-directed protein synthesis, compared to each fo the gastrin-treated groups. The protein/polyphenylalanine ratio which represents a ratio of polysomes to monosomes was found increased in ribosomes from the gastrin-treated groups.

Chronic administration of pentagastrin: Effect on gastric mucosal protein synthesis in rats

Groups of adult rats were injected with either saline or pentagastrin (500 μg/kg) for 14 days. The capacity of the gastric mucosal ribosomes to synthesize endogenous and exogenous mRNA-directed protein in a cell-free system was then investigated. Polyribosomal profiles were also analysed on sucrose gradients. The endogenous mRNA-directed incorporation of 14C-labelled amino acids into protein by the gastric mucosal ribosomes from the pentagastrin-injected rats was found to be considerably greater than that of the control. In the presence of exogenous mRNA (poly-U) the polyribosomes as well as the endogenous mRNA-free ribosomes (run-off ribosomes) from the pentagastrin-treated group showed 86% and 136% increment in [ 14C]-phenylalanine incorporation as compared to the corresponding control preparation. The ribosomal ribonuclease activity between the groups was found to be the same. The results of the present investigation indicate that an enhancement in the translational capacity of the ribosomes is in part responsible for stimulation of gastric mucosal protein synthesis after chronic administration of pentagastrin.

Effects of in Vivo Administration of Pentagastrin, Secretin, and 13-Nle-Motilin on the in Vitro Incorporation of14C-Leucine into Protein of Human Gastric Mucosa

Mitznegg, P., Domschke, W., Domschke, S., Belohlavek, D., Sprügel, W., Strunz, U., Wünsch, E., Jaeger, E. & Demling, L. Effects of in vivo administration of pentagastrin, secretin, and 13-nle-motilin on the in vitro incorporation of 14C-leucine into protein of human gastric mucosa. Scand. J. Gastroent. 1976, 11, 657-660Under endoscopic control, biopsy specimens were taken from the oxyntic gland area of the stomach before and after administration of pentagastrin, synthetic secretin, and 13-norleucine motilin (13-nle-motilin), respectively. In 29 volunteers, the basal rate of 14C-leucine incorporation into mucosal protein averaged 41.2 ± 7.7 × 103 cpm/mg protein (mean ± S.D.). One and 4 hours after s.c. administration of pentagastrin (6 µg/kg body weight), values were significantly increased (p<0.05) by 18.9 and 21.8 %, respectively, with respect to the basal level. One hour after an intravenous shot of 2 CU per kg body weight of secretin, gastric mucosal protein synthesis was not substantially inhibited, whereas a 1-hour continuous i.v. infusion of 13-nle-motilin (0.4 μg/kg body weight, hr) significantly decreased 14C-leucine incorporation rates by 17.5% (p<0.05). In contrast to rats, 1 hour after s.c. pentagastrin, protein synthesis in human duodenal mucosa was not altered. From these results it may be concluded that pentagastrin has a trophic influence on gastric mucosa in man. Moreover, the data presented are compatible with the hypothesis that gastrin and motilin may be involved in the regulation of human gastric mucosal protein synthesis.

Protein synthesis by human intestinal mucosa: Variations with diseases of the gut

Studies of protein synthesis by human intestinal mucosa were performed by determining the in vitro incorporation of l-leucine-U- 14C into the total proteins of peroral mucosal biopsy specimens. The mean value for normal mucosa was 1483 dpm/mg/30 min ± 402. In mucosa from patients with sprue the mean value for mucosal protein synthesis was 3056, a significant elevation which might reflect abnormally high cell turnover in this disease. In mucosa from patients with abetalipoproteinemia the mean value for protein synthesis was 535. This value, which is significantly lower than normal, may be related to diminished or absent synthesis of betalipoproteins by the intestine in this disease. The mean value for mucosal protein synthesis among patients with treated Whipple's disease in remission was normal. Measurement of protein synthesis by intestinal mucosa, obtained by peroral biopsy, appears to be useful in assessing metabolic aberrations and adaptations of the gut.

RNA and DNA of gastric and duodenal mucosa in antrectomized and gastrin-treated rats.

RNA and DNA of gastric and duodenal mucosa in antrectomized and gastrin-treated rats.

Carbohydrate dependent protein synthesis and enzyme activity in the jejunum

The mechanism by which dietary carbohydrate (CH) regulates jejunal disaccharidase activity has not been elucidated. Studies were undertaken to determine whether adaptive changes in disaccharidase levels were accompanied by variations in protein synthesis; and if so, whether they were related to cell migration and RNA synthesis. 200 g rats were fed a CH-free diet (with isocaloric protein replacement) for 7 days and then fed a diet rich in either sucrose (68% cal) or starch (51% cal). Incorporation of 14C amino acids into total mucosal and brush border (BB) proteins (TCA insoluble) was measured. Both sucrose and starch stimulated an increase of 30% in the labeling of total mucosal proteins and greater than 100% rise in that of BB proteins. Simultaneously, there was 100% rise in sucrose and lactase activity and 60% increase in maltase activity in crude jejunal homogenate and BB. When actinomycin-D was injected IP 6 hrs prior to feeding sucrose, RNA synthesis measured 24 hrs later was reduced 50%, and cell migration was arrested. Although neither basal rates of total mucosal protein synthesis nor the increase stimulated by CH feeding were inhibited, 14C labelling of the BB was reduced. Sucrase, lactase and maltase levels in the crude homogenates rose 75–100%, but these activities in the BB did not increase in actinomycin-D treated animals. The data suggest that dietary CH controls disaccharidase acitivity by changes in protein synthesis independent of RNA synthesis and cell migration, and support the concept that there is an RNA-dependent step required for the transfer of newly formed disaccharidases from sites of synthesis to the BB.

Inhibition of protein synthesis and absorption of lipid into thoracic duct lymph of rats.

SummaryAbsorption of micellar lipid into thoracic duct lymph of unanesthetized rats was studied after administration of actinomycin D or cycloheximide, agents known to inhibit protein synthesis. Micellar lipid was infused steadily into the upper small intestine to avoid complications by defective gastric emptying or defective lipolysis. Actinomycin D, 50 μg/rat, inhibited mucosal protein synthesis, but absorption of fat into the lymph was unimpaired after this dosage. Malabsorption produced by larger doses of actinomycin D or cycloheximide was accompanied by a marked decline in lymph flow. The change in lymph flow was closely related to decreased recoveries of lipid in the lymph, and reduced flow appeared to be more important than suppression of mucosal protein synthesis. The results indicate that chylomicron formation is not dependent on normal mucosal protein synthesis.