Citation Information: J Clin Invest. 1978;62(3):623-632. https://doi.org/10.1172/JCI109169.
Abstract
The kinetics and factors regulating alanine and glutamine formation and release were investigated in skeletal muscle preparations from control and experimentally uremic rats. These preparations maintained phosphocreatine and ATP levels in vitro which closely approximated levels found in vivo. Alanine and glutamine release from uremic muscle were increased 45.8 and 36.0%, respectively, but tissue levels were unaltered. The increased release of alanine by uremic muscle was not accounted for by decreased rates of medium alanine reutilization via oxidation to CO2 or incorporation into muscle protein. The maximal capacity of added amino acids such as aspartate, cysteine, leucine, and valine to stimulate net alanine and glutamine formation was the same in uremic and control muscle. Epitrochlearis preparations were partially labeled in vivo with [guanido-14C]-arginine. On incubation, preparations from uremic animals showed a 54.6% increase in the rate of loss of 14C-label in acid precipitable protein. Correspondingly, these same uremic preparations showed a 62.7% increase in 14C-label appearance in the acid-soluble fraction of muscle and in the incubation media. Insulin decreased alanine and glutamine release to an extent threefold greater in uremic than in control preparations, and increased muscle glucose uptake approximately threefold in all preparations. Although basal rates of [4,5-3H]leucine incorporation into protein were decreased 25% in uremic muscles as compared with control muscles, insulin stimulated [3H]leucine incorporation nearly equally in both preparations.
Authors
Alan J. Garber
Citation Information: J Clin Invest. 1978;62(3):633-641. https://doi.org/10.1172/JCI109170.
Abstract
The mechanism of the increased alanine and glutamine formation and release from skeletal muscle in experimental uremia was investigated using epitrochlearis preparations from control and chronically uremic rats. In uremic muscle, insensitivity to epinephrine or serotonin suppression of alanine and glutamine release was observed. With control muscles, 1 nm or greater, epinephrine inhibited alanine and glutamine release, whereas with uremic muscles, epinephrine concentrations <1 μM did not alter amino acid release. Decreased alanine and glutamine release with 1 nM serotonin was observed in control muscles, but no inhibition was observed with concentrations <1 μM in uremic muscle. Muscle amino acid levels were the same in control and uremic muscles in the presence or absence of epinephrine or serotonin. The reutilization of released alanine by protein synthesis or oxidation to CO2 was not differentially affected by epinephrine in uremic muscles as compared with control muscle. Dibutyryl-cAMP inhibited amino acid release equally in uremic and control muscles. Epinephrine or serotonin increased cAMP levels two- to four-fold or more in control than in uremic muscle. Basal- and fluoride-stimulated adenylate cyclase activities were equal in uremic and control muscle homogenates and in membrane fractions, but 10 μM epinephrine-stimulated adenylate cyclase was reduced 30-60% with uremia. At any concentration of epinephrine (0.001—100 μM), the stimulation of membrane adenylate cyclase activity was one- to twofold greater with control membranes than with uremic muscle membranes. With either control or uremic muscle, peak adenylate cyclase activity was observed at 1 μM epinephrine.
Authors
Alan J. Garber
Citation Information: J Clin Invest. 1978;62(3):692-701. https://doi.org/10.1172/JCI109177.
Abstract
Electrolyte fluxes are fundamental to normal endocrine pancreatic function. Adenosine triphosphatases (ATPases) are enzyme systems believed to modulate electrolyte movements across membranes in a number of cell types. This study was undertaken to measure cation-dependent ATPases of rat pancreatic islets. In addition, we compared effects of substances which influence endocrine pancreatic function upon ATPases in homogenates of islets and kidney, the latter being a tissue which would not be expected to have a stimulus-secretion response to substances which activate islets.
Authors
Seymour R. Levin, Barry G. Kasson, June F. Driessen
Citation Information: J Clin Invest. 1978;62(2):271-280. https://doi.org/10.1172/JCI109126.
Abstract
During osmotic diarrhea, loss of water and electrolytes appears to be greater in infants than in adults. In 2-, 3-, and 7-wk-old rats, we studied net transport of H2O, Na, and Cl, during in vivo perfusion of segments of the jejunum and ileum, from solutions with osmolalities of 300, 375, 500, or 700 mosmol/kg. In the jejunal segments, from the hypertonic solutions net transport of H2O, Na, and Cl was into the lumen and greater in the 2- than 7-wk-old rats. In the ileal segments, transport of water was into the lumen, transport of Na was minimal and variable, whereas transport of Cl was usually out the lumen. In 3-wk-old rats, transport rates were intermediate between those in 2- and 7-wk-old rats. The calculated filtration coefficient (microliters of H2O transported per hour per unit osmolality gradient—lumen-serum—per gram dry weight) of water suggested that the resistance to water flow did not increase with rise in luminal hypertonicity in the jejunum of the 2- and 3-wk-old rats, whereas in jejunum of the 7-wk-old rats and in ileum of rats in all three ages, the resistance to water flow increased with the rise in luminal osmolality. The differences in the transport rates and the resistance to water flow, between segments of the 2-, 3-, and 7-wk-old rats, suggested a maturational phenomenon that appears to continue beyond the 3rd wk of life and could have been due to differences in some physical property of the mucosal membrane.
Authors
M. K. Younoszai, R. S. Sapario, M. Laughlin
Abstract
Highly purified, polymyxin-released, low molecular weight Escherichia coli heat-labile enterotoxin (LT) catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. This NAD glycohydrolase activity was stimulated by dithiothreitol and was independent of cellular components. Nicotinamide formation was enhanced by arginine methyl ester > d-arginine ≅ l-arginine ≅ guanidine. A 20-fold increase in activity was noted with arginine methyl ester, and maximal activity again required dithiothreitol. When the reaction was initiated with toxin, a delay was observed before a constant rate was established. The reaction products found after incubation of [adenine-U-14C]NAD and l-[3H]arginine or unlabeled arginine methyl ester with the enterotoxin had mobilities on thin-layer chromatograms similar to the reaction products obtained after incubation of choleragen with these substrates and are consistent with the formation of ADP-ribose-l-arginine and ADP-ribose-l-arginine methyl ester, respectively. Both toxins, which catalyze the NAD-dependent activation of adenylate cyclase, thus appear to possess NAD glycohydrolase and ADP-ribosyltransferase activities. Although the activities of both toxins are dependent on dithiothreitol, Escherichia coli enterotoxin exhibited optimal activity in Tris (Cl−) (pH 7.5) and was inhibited by high concentrations of potassium phosphate (pH 7.0) or low pH (sodium acetate, pH 6.2). It appears that the optimal assay conditions as well as the kinetic constants for the reactants differ from those previously noted with choleragen. It is probable therefore that although the two toxins catalyze similar reactions, they differ in primary structure. The presence of transferase and glycohydrolase activities in structurally distinct toxins that activate adenylate cyclase strengthens our hypothesis that the ADP-ribosylation of arginine is a model for the NAD-dependent activation of adenylate cyclase; activation may result from ADP-ribosylation of the cyclase itself or of a protein that regulates its activity.
Authors
Joel Moss
Citation Information: J Clin Invest. 1978;62(2):425-435. https://doi.org/10.1172/JCI109144.
Abstract
The relative contributions of impaired insulin secretion and of tissue insensitivity to insulin to the carbohydrate intolerance of uremia were investigated in 10 chronically uremic subjects. Two types of glucose-clamp experiments were performed in each patient before and after 10 wk of thrice weekly hemodialysis. In both types the blood glucose concentration was maintained at a constant level by the periodic adjustment of a variable glucose infusion with a negative feedback formula.
Authors
Ralph A. Defronzo, Jordan D. Tobin, John W. Rowe, Reubin Andres
Citation Information: J Clin Invest. 1978;62(2):480-486. https://doi.org/10.1172/JCI109149.
Abstract
Clinical isolates of enterococci (Streptococcus faecalis) with high-level resistance to both streptomycin and kanamycin (minimal inhibitory concentration >2,000 μg/ml), and resistant to synergism with penicillin and streptomycin or kanamycin were examined for aminoglycoside-inactivating enzymes. All of the 10 strains studied had streptomycin adenylyltransferase and neomycin phosphotransferase activities; the latter enzyme phosphorylated amikacin as well as its normal substrates, such as kanamycin. Substrate profiles of the neomycin phosphotransferase activity suggested that phosphorylation occurred at the 3′-hydroxyl position, i.e., aminoglycoside 3′-phosphotransferase. A transconjugant strain, which acquired high-level aminoglycoside resistance and resistance to antibiotic synergism after mating with a resistant clinical isolate, also acquired both enzyme activities. Quantitative phosphorylation of amikacin in vitro by a sonicate of the transconjugant strain inactivated the antibiotic, as measured by bioassay, and the phosphorylated drug failed to produce synergism when combined with penicillin against a strain sensitive to penicillin-amikacin synergism.
Authors
Donald J. Krogstad, Thomas R. Korfhagen, Robert C. Moellering Jr., Christine Wennersten, Morton N. Swartz
Citation Information: J Clin Invest. 1978;62(1):124-132. https://doi.org/10.1172/JCI109096.
Abstract
The anatomical sites and the rates of extrapancreatic secretion of glucagon and of glucagon-like immunoreactivity (GLI) were assessed in dogs 2 h after pancreatectomy by catheterization of the gastrosplenic and mesenteric veins.
Authors
Walter A. Muller, Lucien Girardier, Josianne Seydoux, Michael Berger, Albert E. Renold, Mladen Vranic
Citation Information: J Clin Invest. 1978;62(1):14-19. https://doi.org/10.1172/JCI109098.
Abstract
The effect of 8 mg/kg of indomethacin on uterine blood flow, prostaglandin production, and intraamniotic fluid pressure was examined in late pregnant dogs. Uterine blood flow was measured with 15 μm radiolabeled microspheres. Because we found that a significant percentage of the microspheres shunted through the placental circulation into the lungs, we calculated placental blood flow by adding the shunted microspheres through the placenta to the nonshunted microspheres in the placenta. Total uterine blood flow significantly increased from 271±69 ml/min during control period to 371±72 ml/min (P < 0.01) 30 min after indomethacin. This increase was attributable to the change in blood flow to the placental circulation (222±58 to 325±63 ml/min; P < 0.01). Associated with these hemodynamic changes we found an almost complete suppression of uterine prostaglandin E2 production (1,654±305 to 51±25 pg/ml; P < 0.01) as measured by gas chromatography-mass spectrometry. In addition, we found that indomethacin treatment resulted in uterine relaxation as measured by intraamniotic fluid pressure changes (11.2±1.3 mm Hg to 8.5±1.2 mm Hg; P < 0.001).
Authors
John G. Gerber, Robert A. Branch, Walter C. Hubbard, Alan S. Nies
Citation Information: J Clin Invest. 1978;62(1):152-161. https://doi.org/10.1172/JCI109100.
Abstract
Gastric inhibitory polypeptide, or GIP, has been postulated as the major enteric hormonal mediator of insulin release. The release of immuno-reactive GIP (IR-GIP) after oral glucose and its role in insulin release was studied in normal men by the glucose clamp technique. In 24 subjects studied with the hyperglycemic clamp, blood glucose was maintained at 125 mg/dl above basal for 2 h via a primed-continuous IV glucose infusion coupled to a servo-controlled negative feedback system. 40 g glucose per m2 surface area was ingested at 60 min, and the blood glucose was maintained at the steady-state hyperglycemic level. Plasma IR-GIP and insulin (IRI) levels were measured throughout the 2-h period. IR-GIP levels changed little when IV glucose alone was given; the mean basal value was 305±34 (SEM) pg/ml. After oral glucose, IR-GIP levels began to rise within 10 min and reached a peak within 40 min of 752±105 pg/ml. Plasma IRI responded initially to the square wave of hyperglycemia in the typical biphasic pattern. After oral glucose, plasma IRI levels rose strikingly above the elevated levels produced by hyperglycemia alone, reaching a peak of 170±15 μU/ml within 45 min. The time course of the rise in IR-GIP and IRI was nearly identical.
Authors
Dana K. Andersen, Dariush Elahi, John C. Brown, Jordan D. Tobin, Reubin Andres
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