Acid Concentration In Rats Research Articles

Influence de la cinétique d'évacuation gastrique de l'aliment sur l'insulinémie chez le veau préruminant

The aim of this work was to clarify the possible role of blood metabolites (glucose, aminoacids, triglycerides) in the regulation of postprandial blood insulin in the preruminant calf. The animals used were 6 male Friesian bull calves with an average weight of 80 kg. They were divided into groups I and II. During the first experimental period (A), group I received a control diet that contained skim-milk powder as the only protein source, whereas group II received an experimental diet containing fish protein concentrate as the main protein source. During the second experimental period (B), the diets were switched. It was previously shown that the rate of fat and amino acid absorption increased when milk proteins in such milk substitutes were replaced by hydrolyzed fish proteins (Guilloteau et al., 1975). The results showed that during any experimental period in the control group, there was a decrease in the postprandial blood free amino nitrogen. Blood triglycerides exhibited a small increase at 0.5 h after the meal but a large decrease at 1-4.5 h. The meal also resulted in a very large increase in blood glucose with maximal values occurring at 1-4.5 h. Blood insulin showed a large increment at 0.5 h then increased slowly, peaking at 2-3 h. The postprandial increase in blood insulin was less during the first experimental period than during the second one. In calves fed the fish diet, blood free amino nitrogen and blood triglycerides showed a large postprandial increase. Blood glucose exhibited a smaller postprandial increment than in the controls and began to decrease at half an hour. In contrast, the trend of changes in blood insulin was the same as in the controls (i.e. a maximum at 3 h occurring after a large increase at 0.5 h). There were no significant differences in blood insulin between the two experimental periods. It was lower in the calves fed the fish diet than in the controls during the first experimental period; during the second period, it was similar in both groups. From these observations, it may be inferred that, as compared to the control diet, the fish diet resulted in a decrease in glucose stimulation of postprandial insulin secretion; in contrast, the effect of aminoacids and lipids may be increased.

Mechanisms for reduced hepatic clearance and elevated plasma levels of bile acids in cirrhosis: A study in patients with an end-to-side portacaval shunt

The mechanisms for reduced hepatic clearance and for elevated levels of plasma bile acids were investigated in cirrhotic patients having an end-to-side portacaval shunt. The liver plasma flow and the concentration and relative composition of total bile acids in the systemic and hepatic venous blood were determined in the fasting state. Mean values for liver plasma flow, hepatic extraction ratio, hepatic clearance and Vmax/Km of total bile acids were respectively: 395 ± 37 ml/min (mean ± SEM), 0.48 ± 0.08, 184 ± 36 ml/min, and 287 ± 74 ml/min. These values are lower than those estimated in healthy subjects assuming a mean liver plasma flow of 600 ml/min and a mean hepatic extraction ratio of 0.80. It was shown that the hepatic clearance of bile acids depends on Vmax/Km, i.e., on the inherent ability of the liver to remove bile acids from the blood rather than on liver plasma flow. Chenodeoxycholic acid was the major bile acid in both the hepatic and systemic venous blood. The hepatic clearance of total bile acids therefore mainly reflected the hepatic clearance of chenodeoxycholic acid. The respective contribution to plasma bile acid levels of: (a) the hepatic clearance and its two biologic determinants, i.e., liver plasma flow and Vmax/Km, (b) the total extrahepatic portosystemic shunting, and (c) the intestinal absorption rate of bile acids were quantitated. A significant and hyperbolic relationship existed between bile acid levels and Vmax/Km values. The largest relative contribution to bile acid levels due to portacaval shunting was found in those subjects with the greatest hepatic clearances. The intestinal absorption rate of bile acids varied in a narrow range (5.7–9.5 μmol/min) despite wide variations in bile acid levels; no significant relationship was found between these two parameters. Finally, the results of this study show that altered hepatic elimination of bile acids and of drugs which are fully absorbed by the intestine and completely metabolized by the liver share common mechanisms in liver cirrhosis.

Effects of Ethionine Feeding on Urinary and Tissue Ascorbic Acid Concentrations in Rats

The effect of feeding 0.25% ethionine for 3–10 weeks to male and female rats on urinary and tissue ascorbate contents were studied. The concentrations of ascorbic acid in the urine, blood, liver and adrenals were significantly reduced in the rats receiving ethionine as compared to those receiving stock diet. This decrease was not apparently due to feed intake, not reversed by supplementation of methionine, but can be partially restored by removing ethionine from stock diet. The response to trichloro-2-methyl-2-propanol stimulation of urinary ascorbic acid was considerably suppressed by ethionine administration. In vitro the enzymatic synthesis of the vitamin from glucuronolactone by liver homogenate of ethionine-fed rats was significantly decreased from that of stock diet-fed controls. These results indicate that ethionine reduces the capacity to synthesize ascorbate which, in turn, causes a decrease of ascorbic acid contents in the urine, blood, liver and adrenals.ethionine ascorbic acid

A dual, concentration-dependent absorption mechanism of linoleic acid by rat jejunum in vitro.

Linoleic acid absorption was studied using everted rat jejunal sacs. At low concentrations (42-1260 microM), the relationship between linoleic acid concentration and its absorption rate fitted best to a rectangular hyperbola. At high concentrations (2.5-4.2 mM) the relationship between the two parameters was linear. The separate additions of 2,4-dinitrophenol, cyanide, or azide, or decrease in the incubation temperature from 37 to 20 degrees C did not change the absorption rate of linoleic acid. Absorption rate of linoleic acid at low concentrations increased as the hydrogen ion and taurocholate concentrations were increased or as the unstirred water layer thickness was decreased. Linoleic acid absorption rate was decreased after the additions of lecithin, oleic, linolenic, and arachidonic acids or the substitution of taurocholate with the nonionic surfactant Pluronic F 68. These observations indicate that a concentration-dependent, dual mechanism of transport is operative in linoleic acid absorption. Facilitated diffusion is the predominant mechanism of absorption at low concentrations, while at high concentrations, simple diffusion is predominant. At low concentrations, the absorption rate of linoleic acid is influenced by the pH, surfactant type and concentration, the simultaneous presence of other polyunsaturated fatty acids, and the thickness of the unstirred water layer.

Balance of net base in the rat. IV. Effects of oral calcium and phosphate loading.

Mineral and net base balances were studied in groups of male weanling Wistar rats given oral loads of calcium chloride, monocalcium phosphate plus monosodium phosphate, and disodium phosphate plus monopotassium phosphate, respectively. A group of adult nongrowing rats loaded with calcium chloride was included for comparison. In response to CaCl2 loading, gastrointestinal net base absorption was inhibited due, largely, to luminal precipitation of tertiary phosphates of calcium and magnesium. In the weanling animal, however, a rise in the rate of renal net acid excretion matched the concomitant decrement in the rate of net base absorption, permitting of continued skeletal net base storage. Similarly, in the adult animals augmented renal net acid excretion offset a positive rate of gastrointestinal net acid absorption with a resultant (normal) zero net base balance. Loading with monocalcium phosphate and disodium phosphate at a constant oral net base intake did not influence the overall net base balance, but disodium phosphate loading caused significant sodium retention.

Motility‐ and blood flow‐dependent absorption of amino acids in canine small intestine*

A relationship between L-phenylalanine and L-serine absorption, intestinal motility and blood flow has been studied with a canine in situ isolated jejunal loop in acute experiments and in chronic preparations in conscious dogs. During spontaneous rhythmic contractions, as well as after mechanical and pharmacological stimuli, rhythmic changes in blood flow, related to intestinal contractions, were observed. They had no bearing on mean blood flow or absorption as long as they did not occur together with tonic contractions. The tonic contractions resulted in a prolonged decrease in jejunal blood flow ano diminished amino acid absorption rate. Absorption and motility index, as well as blood flow and motility were negatively correlated. There was a positive rectlinear correlation between intestinal blood flow and absorption, regardless of whether changes in blood flow resulted from the increase in motility or were induced by intestinal artery occlusion. These correlations suggest that changes in amino acid absorption during increased motility depend on changes in blood flow. This relationship may be important in clinical syndromes with hypermotility.

Concomitant elevations in serum sialytransferase activity and sialic acid content in rats with metastasizing mammary tumors.

Rats with transplantable spontaneously metastasizing mammary tumors have elevated levels of both serum sialoglycoconjugate and serum sialytransferase activity compared with normal female rats or rats with various nonmetastasizing mammary tumors. A direct relationship was observed between the amount of serum protein-bound sialic acid and serum sialyltransferase activity in all rats studied. Serum sialyltransferase activity in rats with a representative metastasizing mammary tumor, SMT-2A, was also correlated with tumor age. Microsomes prepared from the SMT-2A tumor have a sixfold higher sialyltransferase activity than do microsomes prepared from the nonmetastasizing mammary tumor MT-W9B. Normal rat liver microsomes have the same level of activity as microsomes prepared from livers of animals with either SMT-2A or MT-W9B tumors. The data indicate that spontaneously metastasizing mammary tumor cells have an increased production and release, perhaps through cell surface shedding, of a sialyltransferase. It is suggested that this sialyltransferase may increase the serum half-life of certain tumor-specific circulating glycoconjugates by increasing the content of protein-bound sialic acid and may thereby play a role in the immune escape mechanism of metastasizing tumor cells.

The mechanism of lincomycin‐induced diarrhoea

Metabolic studies were performed before and seven days after treating rats orally with lincomycin. Following the treatment the mean faecal weight increased from 302.2 g/72 hr +/- 3.8 (S.D.) to 65.5 +/- 8.2. The faecal fat excretion was unchanged, and the weight increase was mainly due to increased water content. To find whether the watery diarrhoea was due to bile acid malabsorption, the absorption rate of [14C]-taurocholic acid was measured in untreated rats and rats treated with lincomycin using an in vivo perfusion technique. There was no significant difference in bile acid absorption rate measured at three different concentrations of bile acid in the perfusate. Alternative mechanisms of lincomycin-associated diarrhoea are discussed.

Absorption of xylose, glucose, glycine, and folic (pteroylglutamic) acid in Zambian Africans with anaemia.

Rates of glucose, glycine, and folic (pteroylglutamic) acid absorption were determined for a 30 cm jejunal segment in vivo, with a double-lumen tube perfusion system, in 10 Zambian African women with a mean haemoglobin concentration of 5-1 (3-5-9-2) g/dl. In four the anaemia was megaloblastic (due to folate deficiency) and in six hypochromic. Perfusion solutions contained (1) glucose 200 mmol/1, (2) glycine 100 mmol/1, and (3) folic acid 250 mug/1. D-xylose absorption after a 25 g oral load was determined in them, and also in 18 additional patients (11 had megaloblastic and seven either hypochromic or haemolytic anaemia). Xylose absorption tests were significantly impaired in the patients with megaloblastic compared with hypochromic or haemolytic anaemia (P less than 0-001); those with untreated megaloblastic anaemia had a greater abnormality than those who had started treatment. Mean glucose, glycine, and folic acid absorption rates were similar to those in controls, and the rates in patients with megaloblastic and hypochromic anaemia were not significantly different. Correlation between glucose absorption rate and xylose excretion was, however, significantly (P less than 0-02). If more patients had been studied it seems likely therefore that a significant impairment of glucose absorption rate in the presence of megaloblastic anaemia would also have been demonstrated. In this investigation anaemia per se did not affect glucose, glycine, or folic acid absorption rates or xylose absorption, but xylose absorption was reduced in patients with megaloblastic anaemia. That abnormality was probably related to folate deficiency, and the underlying mechanism seems to be different from that causing impairment of monosaccharide absorption in patients with systemic bacterial infections. Mean glycine and folic acid absorption rates were not altered by megaloblastic anaemia, indicating that folate deficiency does not cause a general depression of absorption.

Influence of diet on the induction of hepatic ceroid pigment in rats by polychlorinated biphenyls

The effects of differences in diet composition on polychlorinated biphenyl (PCB) poisoning was studied in four groups of male Wistar rats fed two different diets for 30 days. In rats fed a commercial diet, normal growth was observed, whereas rats fed this diet with PCB added had markedly depressed growth. The growth of rats fed a synthetic diet was lower than that of the group fed commerical diet. The weight of the liver increased significantly in PCB-treated rats. In rats given PCB and fed a commercial diet, the liver showed prominent dark brown pigmentation which was identified histochemically as ceroid. The liver of rats given PCB and fed a synthetic diet had a pale yellow color due to an accumulation of lipids. Serum cholesterol was increased in both PCB-fed groups; serum triglyceride concentrations were increased only in rats given PCB and fed commercial diet. Liver linoleic acid concentrations in rats given PCB and fed a commercial diet, and the oleic acid concentrations in rats given PCB and fed a synthetic diet were elevated. Thus, the toxic manifestations of PCB in rats differ significantly when different dietary regimens are used.

Effects of diet, age, strain and anatomical site on fat depot triglyceride and fatty acid content in rats.

OM rats fed a high fat ration were heavier, fatter and had fat depots which weighed at least three times as much as those fed a low fat (grain) ration. S rats fed a high fat ration showed slight increase in fat depot weights and no increase in body weight or fat when compared to rats of the same strain fed grain. For both strains of rats fed either diet for 4, 10 or 20 wk following weaning, there was a lower percentage of TG in the inguinal depot than in the epididymal or perirenal-retroperitoneal fat depots. There was a tendency for rats fed a high fat ration to have a higher percentage of TG in adipose tissues than rats fed grain, but the differences were not significant as long as age, anatomical site and strain were constant. Strain and age had no significant effect on the percentage of TG in fat depots. The fatty acid composition of the fat depots was effected by ration, but not by age, strain or anatomical site of the fat depot.

Cellular proliferation induced in the lung by cadmium aerosol.

Rats were exposed to a polydispersed aerosol of 0.1 per cent cadmium chloride in physiologic saline for a single period of 2 hours, and the evolution of damage was followed for a 10-day period. Control animals were unexposed rats and rats exposed to an aerosol of physiologic saline. Wet lung weight doubled by the fourth day in animals exposed to cadmium chloride, but not in the control groups. Apart from a transient increase in fluid content at 1 day, there was no evidence that the lung weight gain was due to inflammatory edema. Uptake of [3H]thymidine markedly increased during the first four days after exposure to cadmium chloride. Light autoradiography showed that [3H]thymidine labeling occurred almost exclusively in Type II alveolar cells at 1 day: later, the label appeared in interstitial cells and cells lying free within alveoli. These changes correlated well (r=0.70) with the increase in deoxyribonucleic acid on the fourth day after exposure. Uptake of [3H]thymidine and deoxyribonucleic acid content in rats exposed to cadmium chloride showed a significant difference from the control groups (P less than 0.001). These experiments demonstrate that exposure to cadmium chloride aerosol evokes a wave of cellular proliferation in rat lung. This finding is of interest, because heavy industrial exposure to cadmium in humans is known to be associated with severe physiologic impairment and anatomic damage.

Plasma and Tissue Free Amino Acid Concentrations in Rats Fed Tryptophan-imbalanced Diets with or without Niacin

The concentration of free tryptophan and other free amino acids in blood plasma and of free tryptophan and threonine in liver and muscle have been determined in rats fed tryptophan-imbalanced diets ( induced with 7.8% amino acids in a low protein adequate-niacin diet or with threonine or 2.06% amino acids in a low protein niacin-free diet). The concentration of free tryptophan in the plasma and liver of rats fed the threonine-induced niacin-deficient diet was not depressed below that of the control animals. However, tryptophan concentration decreased in the plasma of rats fed the above diet corrected with 2.5 mg nicotinamide/100 g diet. Liver tryptophan concentrations, however, did not decrease in the niacin-corrected group. The only prominent change in other amino acids was that of threonine, which increased markedly in all groups supplemented with threonine. When the 7.8% amino acid-induced un balanced diet containing adequate niacin was fed, the plasma and muscle free trypto phan concentrations of meal-fed rats decreased markedly within 3.5 to 5 hours. Liver concentrations also decreased by 5 hours in the unbalanced group. The concentrations of the amino acids that were added to the diet to cause the imbalance increased con- comitantly with a decrease in plasma tryptophan. These results support the suggestion that in the first situation ( niacin-free diet ) the metabolic response is a result of a deficiency of niacin; whereas, when the tryptophan imbalance is induced in an adequate- niacin diet with 7.8% of an amino acid mixture devoid of tryptophan, the immediate metabolic need is that of tryptophan, the limiting amino acid; a response typical of those observed with other amino acid imbalances. J. Nutr. 104: 1584-1596, 1974.

A comparison of the rate of absorption micellar and nonmicellar oleic acid. A jejunal perfusion study in man.

The influence of physical state on the rate of fatty acid absorption was studied in healthy human volunteers by a perfusion technic featuring a proximal occlusive balloon. Fatty acid was absorbed much faster from a micellar solution than from an emulsion of identical concentration.

Increased glycine absorption rate associated with acute bacterial infections in man.

1. Glycine absorption rate from a 300 mm jejunal segment was determined in vivo in four Zambian African subjects with acute, and four with chronic, respiratory infections. Glycine solutions (100, 150 and 250 mmol/l) were perfused, by means of a double-lumen tube technique. The results were compared with those for four relatively normal Zambian African subjects (‘reference’ group) previously studied. The group with acute-infections had a significantly higher mean absorption rate than the reference or chronic-infection group.2. Glycine absorption results from a 100 mmol/l glycine solution in an additional twenty-four Zambian African subjects have also been analysed. When results for the thirty-six subjects were combined, those with acute bacterial infections had a significantly higher mean absorption rate than the normal subjects or those with chronic infections. For the twenty-one normal subjects there was a significant positive correlation between the individual absorption rates and serum total globulin and γ-globulin concentrations.3. It seems likely that the rapid catabolism of protein associated with infection is counteracted by an increase in amino acid absorption rate. In subjects on a low-protein diet that mechanism would be limited. The deterioration in nutritional status during infections in developing countries could therefore be partly explained by the present observation.

Characterization of bile acid absorption across the unstirred water layer and brush border of the rat jejunum.

We have examined the rate-limiting steps involved in bile acid absorption across the unstirred water layer and lipid cell membrane of the jejunal mucosa. Uptake of the polar bile acid taurocholate is limited solely by the cell membrane since this compound permeates the unstirred water layer more rapidly than the lipid cell membrane and stirring does not enhance uptake. With less polar bile acids which permeate the cell membrane relatively more rapidly, however, the unstirred water layer does exert resistance to mucosal uptake of these compounds. That the unstirred water layer is even more rate limiting to uptake from micellar solutions is indicated by the facts that the rate of bile acid absorption from such solutions is lower than from corresponding monomer solutions, stirring markedly enhances uptake from micellar solutions while increases in viscosity of the incubation media depress uptake and expansion of the micelle size further depresses absorption rates. We also have examined the important question of whether the micelle crosses the brush border intact once it reaches the aqueous-lipid interface. The observations that the calculated permeation rate of the micelle should be extremely low, the rate of mucosal cell uptake plateaus at a constant value when the critical micelle concentration is reached at the aqueous-lipid interface, and the different components of a mixed micelle are taken up at different rates indicate that uptake of the intact micelle does not occur; rather, bile acid absorption must be explained in terms of monomers in equilibrium with the micelle. Finally, after correction of the permeability coefficients of the various bile acids for the unstirred layer resistance the incremental partial molar free energy of solution of the hydroxyl group in the brush border membrane was calculated to equal -6126 cal.mole(-1) indicating that passive diffusion of these compounds occurs through a very polar region of the cell membrane.

Sex difference in the liver and plasma free amino acid concentrations in rats.

Sex difference in the liver and plasma free amino acid concentrations in rats.

Intestinal transport of dipeptides in man: relative importance of hydrolysis and intact absorption.

A 30 cm segment of the duodenum, jejunum, or ileum of normal human volunteers was perfused, on separate occasions, with test solutions containing either glycylglycine, free glycine, glycylleucine, or equimolar amounts of free glycine and free leucine. Luminal fluid contained no hydrolytic activity against glycylglycine and minimal activity against glycylleucine. In each intestinal segment, amino acid absorption rates were significantly greater from the test solutions containing the same amount of amino acids in dipeptide than in free form(as high as 185% increase). Perfusion of each intestinal segment with a test solution containing the equimolar mixture of free glycine and free leucine always resulted in a greater leucine than glycine absorption rate. This preferential absorption of leucine, however, was either diminished (jejunum) or almost abolished (duodenum and ileum) when the glycylleucine solution instead of the equimolar mixture was presented to the intestinal mucosa. Among the three segments, the duodenum exhibited the least potential for the disappearance of dipeptides. The jejunal and ileal dipeptide disappearance rates were either similar for glycylleucine (94% vs. 92%) or slightly different for glycylglycine (92% vs. 79%). Despite lack of a remarkable difference in the disappearance rates, absorption rates of constituent amino acids were markedly greater in the jejunum than in the ileum. This reduced amino acid absorption was brought about by a greater accumulation of free amino acids in the lumen of the ileal segment (3 to 10-fold difference). Inhibition of free glycine absorption by leucine during the perfusion of the intestine with a test solution containing glycylglycine and leucine did not result in any greater concentration of free glycine in the lumen than when the glycylglycine test solution did not contain free leucine. Similarly, inhibition of free glycine and free leucine absorption by isoleucine was not accompanied by any remarkable alteration of absorption rates of the constituent amino acids of glycylleucine. The results of these studies suggest that: (a) dipeptide disappearance in the gut lumen is principally accomplished by intact absorption and not by hydrolysis; (b) intracellular hydrolysis of dipeptides is markedly greater in the ileum than in the jejunum, while dipeptide absorption rates are either similar or only slightly different in these two segments; (c) there is no appreciable hydrolysis of glycylglycine by the membrane-bound enzymes and only a small fraction of glycylleucine is hydrolyzed by these enzymes.

Tissue amino acid concentrations in rats during acute ammonia intoxication.

Tissue amino acid concentrations in rats during acute ammonia intoxication.

Effects of Boranes Upon Tissues of the Rat II. Tissue Amino Acid Content in Rats on a Normal Diet

Effects of Boranes Upon Tissues of the Rat II. Tissue Amino Acid Content in Rats on a Normal Diet