INSULIN AND INCORPORATION OF AMINO ACIDS INTO PROTEIN OF MUSCLE. 1. ACCUMULATION AND INCORPORATION STUDIES WITH THE PERFUSED RAT HEART

Sites of superoxide and hydrogen peroxide production by muscle mitochondria assessed ex vivo under conditions mimicking rest and exercise

The sites and rates of mitochondrial production of superoxide and H2O2 in vivo are not yet defined. At least 10 different mitochondrial sites can generate these species. Each site has a different maximum capacity (e.g. the outer quinol site in complex III (site IIIQo) has a very high capacity in rat skeletal muscle mitochondria, whereas the flavin site in complex I (site IF) has a very low capacity). The maximum capacities can greatly exceed the actual rates observed in the absence of electron transport chain inhibitors, so maximum capacities are a poor guide to actual rates. Here, we use new approaches to measure the rates at which different mitochondrial sites produce superoxide/H2O2 using isolated muscle mitochondria incubated in media mimicking the cytoplasmic substrate and effector mix of skeletal muscle during rest and exercise. We find that four or five sites dominate during rest in this ex vivo system. Remarkably, the quinol site in complex I (site IQ) and the flavin site in complex II (site IIF) each account for about a quarter of the total measured rate of H2O2 production. Site IF, site IIIQo, and perhaps site EF in the β-oxidation pathway account for most of the remainder. Under conditions mimicking mild and intense aerobic exercise, total production is much less, and the low capacity site IF dominates. These results give novel insights into which mitochondrial sites may produce superoxide/H2O2 in vivo.

Cancer cachexia prevention via physical exercise: molecular mechanisms

Cancer cachexia is a debilitating consequence of disease progression, characterised by the significant weight loss through the catabolism of both skeletal muscle and adipose tissue, leading to a reduced mobility and muscle function, fatigue, impaired quality of life and ultimately death occurring with 25-30 % total body weight loss. Degradation of proteins and decreased protein synthesis contributes to catabolism of skeletal muscle, while the loss of adipose tissue results mainly from enhanced lipolysis. These mechanisms appear to be at least, in part, mediated by systemic inflammation. Exercise, by virtue of its anti-inflammatory effect, is shown to be effective at counteracting the muscle catabolism by increasing protein synthesis and reducing protein degradation, thus successfully improving muscle strength, physical function and quality of life in patients with non-cancer-related cachexia. Therefore, by implementing appropriate exercise interventions upon diagnosis and at various stages of treatment, it may be possible to reverse protein degradation, while increasing protein synthesis and lean body mass, thus counteracting the wasting seen in cachexia.

Accumulation of amino acids in muscle of perfused rat heart. Effect of insulin in the presence of puromycin

1. Rat heart was perfused with a mixture of amino acids and other ninhydrin-positive substances in the same concentrations as they are found in plasma, and with or without sufficient puromycin to suppress protein synthesis all but completely. 2. In the presence of puromycin, but not in its absence, insulin increased the concentrations of most of the individual amino acids in the intracellular water of heart. 3. The results accord with the conclusion that insulin increases the entry of most, if not all, amino acids into muscle.

Accumulation of amino acids in muscle of perfused rat heart. Effect of insulin

1. Rat heart perfused with Krebs-Henseleit bicarbonate buffer released material containing ninhydrin-positive nitrogen, but the amount was less than that reported to be released by diaphragm; glucose, but not insulin, decreased the release of ninhydrin-positive nitrogen and increased the concentration of the same material in the intracellular water of heart. 2. When heart was perfused with a mixture of amino acids and glucose, there was actually a net uptake, and an increase in intracellular concentration, of ninhydrin-positive nitrogen. Changes in the concentration of ninhydrin-positive nitrogen did not accurately reflect changes in concentration of amino acids. 3. The effect of insulin on the actual concentration of individual amino acids in heart muscle was examined by perfusing the heart with a mixture of amino acids and other ninhydrin-positive substances in the same concentration as they are found in plasma. 4. The effect of insulin on the concentrations of amino acids in the medium and in the intracellular water of the heart was determined after perfusion for different periods of time. No clear or meaningful effect of insulin was observed, despite the fact that insulin significantly increased the accumulation, in each of the same hearts, of radioactivity from amino[(14)C]isobutyric acid.

Intracellular monosaccharide and amino acid concentrations and activities and the mechanisms of insulin action

Current amino acid and monosaccharide transport models are based on an assumption which equates the intracellular chemical activity of a solute with its concentration. This assumption was tested for alpha-aminoisobutyric acid and 3-O-methylglucose in a giant cell, the amphibian oocyte, by using recently developed cryomicrodissection and internal reference phase techniques. We found the following. (i) alpha-Aminoisobutyric acid and 3-O-methylglucose activities were much greater in cytoplasm than was suggested by concentration data; i.e., activity coefficients were higher than in ordinary water solutions. This is attributable to the inaccessibility of considerable water as solvent (solute exclusion). (ii) Solute concentrations varied regionally as follows: nucleus > > animal cytoplasm > vegetal cytoplasm. Insulin increased the nucleus/cytoplasm concentration asymmetry, apparently by increasing cytoplasmic solute exclusion. (iii) Nuclear activity coefficients more closely resembled those of ordinary saline solutions so that nucleus/ extracellular concentration ratios reflected transmembrane activity gradients better than did cytoplasm (or whole cell)/extracellular ratios. (iv) Mediated passive alpha-aminoisobutyric acid and 3-O-methylglucose transport were constituent oocyte membrane properties. Membrane active transport was initiated with time (in the presence of substrate) and by insulin. (v) Increased temperature mimicked insulin in enhancing transmembrane alpha-aminoisobutyric acid activity gradients and increasing the nucleus/cytoplasm concentration asymmetry. These results indicated that concentration data are a misleading measure of cellular amino acid and monosaccharide activity; some consequences of this observation were explored. A model is proposed in which cell water has reduced solvent capacity or is compartmentalized (considered less likely) and is susceptible to physiological modulation. The model accounts for many observations in small cells, suggesting generality of the exclusion phenomenon and a previously unrecognized metabolic control mechanism.

Competition for transport of amino acids into rat heart: effect of competitors on protein synthesis and degradation

Transport of the neutral amino acids, 2-(methylamino)isobutyrate (MeAIB) and Phe, was examined in isolated rat hearts perfused by the Langendorff method. Hearts were perfused by recirculating for various time periods buffer containing [14C]-MeAIB or [14C]-Phe plus desired additions. Uptake of MeAIB was linear for approximately 30 minutes; Phe uptake was linear for a maximum of 5 minutes, and reached a steady state after 15 minutes. Km and Vmax for MeAIB were 1.1 +/- 0.03 mmol/L and 37.7 +/- 0.4 pmol/microL intracellular fluid (ICF)/min; values for Phe were 1.8 +/- 0.02 mmol/L and 364 +/- 5 pmol/microL ICF/minute. Uptake of MeAIB (0.2 mmol/L) was reduced 95% in the presence of Ser (10 mmol/L), and less severely by large neutral amino acids ([LNAA], 10 mmol/L) such as Phe and Leu (by 46% and 54%, respectively). Uptake of Phe (0.2 mmol/L) was reduced by LNAA such as Val, Leu, and Ile (by 51%, 78%, and 81%, respectively), or by commercial preparations used in parenteral nutrition, eg, Travasol or Travasol plus extra branched-chain amino acids (BCAA) (Branchamin); Ser had little effect (8% reduction). Insulin in the perfusion medium increased the fractional rate of protein synthesis. Individual BCAA at physiological concentrations (0.2 mmol/L) did not alter the rate of protein synthesis. Branchamin or Travasol plus Branchamin also had no effect on the rate of protein synthesis in heart, but did depress the rate of degradation. These studies suggest that amino acid transport into heart may be affected by normal levels of plasma amino acids, whereas protein synthesis is not.

Amphibolic role of the Krebs cycle in the insulin-stimulated protein synthesis

It has been a generally held view that insulin does not significantly affect the incorporation of amino acids into liver protein. This interpretation was based on data obtained from studies using the branched chain amino acids, which are poorly metabolized by the hepatic tissue. The effect of insulin on 14CO2 formation and protein incorporation of several 1-14C-labeled or U-14C-labeled amino acids was studied in isolated rat hepatocytes and diaphragm pieces. It was shown that insulin enhanced 14CO2 formation and protein incorporation primarily of those carbons of amino acids which are metabolized through the mitochondrial Krebs cycle. Using aminooxyacetic acid (0.5 mM), a potent inhibitor of the transamination reaction, it was shown that there exists an "insulin-sensitive" pool of glutamate which is preferentially utilized for protein synthesis in the presence of insulin. The insulin effect on protein incorporation of 14C-labeled glutamate generated in the Krebs cycle was abolished in the presence of aminooxyacetic acid. We interpret these results to signify that mitochondrial transamination of alpha-ketoglutarate to glutamate is essential for insulin stimulation of 14C incorporation into hepatocyte protein.

Prostacyclin-inhibition of lysine accumulation by the rat left ventricle

1. Left ventricular slices of male Sprague-Dawley rats were incubated with a fixed concentration of 0.5 microCi/ml 3H-lysine and several concentrations of unlabelled lysine ranging from 0.2 to 5.0 mM in control and prostacyclin-treated experiments. The time of incubation ranged from 0.5 to 90 min. 2. Left ventricular slices were cut to have an optimal thickness of 0.47 +/- 0.09 mm. 3. Lysine was taken up against a concentration gradient. Saturation was reached at 0.5 mM and steady state accumulation of lysine was attained within 60 min. 4. Prostacyclin in concentrations ranging from 1.2 x 10(-8) to 4.8 x 10(-8) M inhibited lysine transport in left ventricular slices significantly (P less than 0.01).

Purine biosynthesis de novo in rat skeletal muscle

Purine biosynthesis by the 'de novo' pathway was demonstrated in isolated rat extensor digitorum longus muscle with [1-14C]glycine, [3-14C]serine and sodium [14C]formate as nucleotide precursors. Evidence is presented which suggests that the source of glycine and serine for purine biosynthesis is extracellular rather than intracellular. The relative incorporation rates of the three precursors were formate greater than glycine greater than serine. Over 85% of the label from formate and glycine was recovered in the adenine nucleotides, principally ATP. Azaserine markedly inhibited purine biosynthesis from both formate and glycine. Cycloserine inhibited synthesis from serine, but not from formate. Adenine, hypoxanthine and adenosine markedly inhibited purine synthesis from sodium [14C]formate.

The effects of insulin on glucose uptake and lactate release in perfused working rat heart preparations

The effects of insulin on glucose uptake and lactate release in the perfused working rat heart have been investigated in three types of preparation: (i) a control low-workload preparation; (ii) an increased-pressure-workload preparation, simulating conditions of aortic pressure encountered in vivo; (iii) an increased-volume-workload preparation, where pumping work done is approximately the same as (ii) but coronary flow is restricted because of the decreased aortic pressure. Insulin stimulated glucose uptake and lactate release in preparations (i) and (ii), but failed to do so in preparation (iii). It was considered possible that preparation (iii) was hypoxic, thus necessitating a maximal stimulation of glucose uptake. This was confirmed by improving cardiac oxygenation by addition of stroma-free haemoglobin to the perfusate in preparation (iii). Under these conditions in the absence of insulin, glucose uptake and lactate release were decreased compared with perfusions in the absence of haemoglobin. Insulin stimulation of both processes was restored. We conclude that the failure of other workers to observe insulin effects on glucose uptake and lactate release under physiological workloads [preparation (ii)] may be a consequence of intracellular hypoxia in their preparations.

Vascular perfusion of the isolated rat stomach with a fluorocarbon emulsion

A constant-pressure system using a fluorocarbon (FC-75) containing artificial medium was used for vascular perfusion of the isolated rat stomach. A 10% emulsion of FC-75 in a modified Tyrode solution, containing 3.5% bovine serum albumin, amino acids, nucleosides, and beta-hydroxybutyrate appeared to allow an adequate perfusion for at least seven hours. The following criteria were used to estimate for functional state of the perfused stomach: (1) venous flow, (2) oxygen consumption, (3) leakage from the blood vessels to the gastric lumen, (4) ultrastructure, (5) secretion of H+ and pepsinogen after stimulation, and (6) transport of labelled macromolecules. During perfusion oxygen consumption and venous flow remained, after an initial high value, constant for at least seven hours. Leakage from the vascular bed was absent. Ultrastructure was preserved for at least seven hours. Administration of pilocarpine led to secretion of HCl ad pepsinogen. Pentagastrin and histamine stimulated HCl secretion in only some of the preparations. [3H]-galactose was incorporated into macromolecules and transported from the Golgi-region towards the apex of the cell. These observations led to the conclusion that the described vascular perfusion system in at least an appropriate model for studying glycoprotein synthesis.

Intracellular monosaccharide and amino acid concentrations and activities and the mechanisms of insulin action

Current amino acid and monosaccharide transport models are based on an assumption which equates the intracellular chemical activity of a solute with its concentration. This assumption was tested for alpha-aminoisobutyric acid and 3-O-methylglucose in a giant cell, the amphibian oocyte, by using recently developed cryomicrodissection and internal reference phase techniques. We found the following. (i) alpha-Aminoisobutyric acid and 3-O-methylglucose activities were much greater in cytoplasm than was suggested by concentration data; i.e., activity coefficients were higher than in ordinary water solutions. This is attributable to the inaccessibility of considerable water as solvent (solute exclusion). (ii) Solute concentrations varied regionally as follows: nucleus > > animal cytoplasm > vegetal cytoplasm. Insulin increased the nucleus/cytoplasm concentration asymmetry, apparently by increasing cytoplasmic solute exclusion. (iii) Nuclear activity coefficients more closely resembled those of ordinary saline solutions so that nucleus/ extracellular concentration ratios reflected transmembrane activity gradients better than did cytoplasm (or whole cell)/extracellular ratios. (iv) Mediated passive alpha-aminoisobutyric acid and 3-O-methylglucose transport were constituent oocyte membrane properties. Membrane active transport was initiated with time (in the presence of substrate) and by insulin. (v) Increased temperature mimicked insulin in enhancing transmembrane alpha-aminoisobutyric acid activity gradients and increasing the nucleus/cytoplasm concentration asymmetry. These results indicated that concentration data are a misleading measure of cellular amino acid and monosaccharide activity; some consequences of this observation were explored. A model is proposed in which cell water has reduced solvent capacity or is compartmentalized (considered less likely) and is susceptible to physiological modulation. The model accounts for many observations in small cells, suggesting generality of the exclusion phenomenon and a previously unrecognized metabolic control mechanism.

Effect of diet composition on the protein synthetic pattern of the rat pancreas after a feeding period of five days

Rats were fed for five days on a protein-rich and on a carbohydrate-rich diet, respectively. One half of the pancreas of these rats was incubated with [3H]leucine and the other half with [14C]leucine and extracts from these pancreas halves were prepared. Mixtures of the differently labeled extracts were subjected to electrophoresis towards the anode as well as towards the cathode on a polyacrylamide gel containing urea at pH 8.5. Several secretory enzymes could be identified on the gels. Along the gels the 3H : 14C ratio was determined in 1 mm slices. The results show that after five days of feeding a diet there is some adaptation to diet composition. Generally rather small changes in synthetic rate occur. Only one component, the cathodic chymotrypsinogen shows an important difference in synthetic rate under the two circumstances.

Glycoprotein synthesis in the mucous cells of the vascularly perfused rat stomach. I. Surface mucous cells

We developed a constant-pressure vascular perfusion system of the isolated rat stomach, utilizing an artificial, fluorocarbon (FC-75)-containing medium. Perfusion could be maintained for at least six hours, as demonstrated by the ultrastructure of the mucosal cells and by the constant incorporation of [3H]-galactose in the surface mucous cells. Moreover all mucous cell types in tissue fixed after six hours of perfusion showed the same histochemical reactions for glycoproteins as in tissue fixed shortly after decapitation of the animal. The surface mucous cells of the antrum incorporated 30% less [3H]-galactose, [3H]-serine and [35S]-sulphate than those of the fundus. The amount of radioactivity incorporated per cell did not decrease during a subsequent 2 hour chase.

Compensatory hypertrophy of skeletal muscle fibers in streptozotocin-diabetic rats

Previous studies have demonstrated an apparent differential response of the fiber types in mixed skeletal muscles of rats to streptozotocin diabetes. The purpose of the present study was to examine the ability of the different fiber types to hypertrophy in muscles from diabetic rats, which should further clarify the apparent differential trophic influence of insulin on the fibers. One group of rats was injected with streptozotocin to induce diabetes. The gastrocnemius muscle was then removed from one hindlimb of rats of both the diabetic and a second, normal group, resulting in compensatory growth of ipsilateral plantaris muscle. Rats were sacrificed 60 days following the surgery. Experimental muscles in normal and diabetic rats enlarged 79% and 61% over control muscles, respectively. In normal hypertrophied muscles there was an 8% increase in relative cross-sectional area composed of slow-twitch fibers, whereas in diabetic rats the slow-twitch component increased 17%. The results indicate that slow-twitch fibers in diabetic rats were capable of responding to the chronic power overloaded condition, but that the fast-twitch fibers had a reduced capacity to undergo compensatory growth. These findings support our previous observations suggesting that insulin may exert a differential trophic effect upon the muscle fiber types.

Glycoprotein transport in the surface mucous cells of the rat stomach

The intracellular transport of glycoproteins pulse-labeled in vitro with tritiated leucine and galactose in the surface mucous lining cells (SMC) of the fundus of the rat stomach was studied by electron microscope autoradiography. The SMC survive for several hours in pieces of the fundus incubated in a bicarbonate-buffered medium. The SMC have a normal ultrastructure for at least 4 h of incubation. Kinetic activity is normal for at least 5 h, as demonstrated by the normal nuclear incorporation of tritiated thymidine; The SMC incorporate labeled leucine and galactose at normal rates up to 4 h and 6 h, respectively. In contrast to the SMC, the cells of the gastric glands show signs of degeneration within 1 h after the start of incubation. In the SMC the secretory protein forms a smaller part of the total protein synthesized than in other secretory cells studied. The intracellular tranpsort of the leucine-labeled moiety of the glycoproteins follows the normal pathway. The RER loses 35% of its transportable labeled protein within 30 min. The Golgi complex is maximally labeled at 40 min and the mucous granules after 120 min. Galactose is attached to the glycoproteins mainly in the Golgi complex. Glycoproteins are not secreted within 2 h after synthesis of their protein moiety.

Insulin regulation of amino acid transport in mesenchymal cells from avian and mammalian tissues

Insulin regulation of amino acid transport across the cell membrane was studied in a variety of mesenchymal cell directly isolated from avian and mammalian tissues or collected from confluent cultures. Transport activity of the principal systems of mediation in the presence and absence of insulin was evaluated by measuring the uptake of representative amino acids under conditions approaching initial entry rates. Insulin enhanced the transport rate of substrate amino acids from the A system(alpha-aminoisobutyric acid, L-proline, glycine, L-alanine and L-serine) in fibroblasts and osteoblasts from chick-embryo tissues, in mesenchymal cells (fibroblasts and smooth muscle cells) from immature rat uterus, in thymic lymphocytes from young rats and in chick-embryo fibroblasts from confluent secondary cultures. In these tissues, the uptake of amino acid substrates of transport systems L and Ly+ (L-leucine, L-phenylalanine, L-lysine) was not affected by the presence of the hormone. No insulin control of amino acid transport was detected in chick-embryo chondroblasts and rat peritoneal macrophages. These observations identify the occurrence of hormonal regulatory patterns of amino acid transport for different mesenchymal cells types and indicate that these properties emerge early during cell differentiation.

Growth hormone, cyclic nucleotides and the rapid control of translation in heart muscle

Perfused rat heart incorporated L-[14C]tyrosine into protein at a constant rate for up to 75 min. A purified bovine growth-hormone preparation (1 mug/ml) stimulated the incorporation to a new constant rate that was more than three times the control rate by 10 min after hormone addition to perfusate. The hormone, however, did not alter the intracellular tracer amino acid pool, and the relationship of this to the aminoacyl-tRNA precursor pool is discussed. It is concluded that the increased incorporation largely reflected a rapid increase in protein synthesis at the ribosomes. Measurements of cyclic nucleotide contents during the perfusion showed that these appeared to vary in a systematic way during the perfusion. This strands in contrast with the constant values given by several other parameters measured in this preparation. Futher, the cyclic nucleotide variation seems to be independent of external effectors. The steady-state performance of the heart correlates more closely the [cyclic AMP]/[cyclic GMP] ratio than with the content of the individual cyclic nucleotides. At 10 min after the addition of growth hormone a slight decrese in cyclic AMP content and a large decrease in cyclic GMP were found, suggesting that the hormone's effect in stimulating protein synthesis may be mediated by a decrease in cyclic nucleotide concentrations or an increase in the [cyclic AMP]/[cyclic |p] ratio. The findings are also consistent with an intracellularly directed role for these nucleotides, and the possibility that the cyclic nucleotide changes are an indirect result of growth-hormone action is discussed.

Factors affecting incorporation of (14C) leucine into albumin and transferrin by the liver in the postnatal rat

The mechanisms responsible for the increase in incorporation of radioactive amino acid into albumin, transferrin and total soluble liver protein which occurs in the immediate postnatal period in the rat was investigated in rats delivered surgically in the last 2 days of gestation. The in vivo incorporation of [14C]leucine into the proteins in the liver was low at birth, but increased rapidly during the first half hour after delivery and then more gradually during the subsequent 4.5 h. Neonatal adrenalectomy had no effect on this pattern of results. Intraperitoneal administration of an amino acid supplement had little effect on [14C]leucine incorporation immediately after birth but increased incorporation at 0.5 h and eliminated the second phase of rising incorporation values between 0.5 and 5 h. The in vitro incorporation of 14C into albumin, transferrin and total protein by slices of the liver from animals immediately after delivery was as great as with slices from animals 5 h after delivery. It is concluded that the initial increase in synthesis of proteins in the liver in the first 0.5 h after delivery is probably due to an increase in the supply of metabolic energy due to improved oxygenation of the rats and that the slower increase in protein synthesis between 0.5-5.0 h results from an improved supply of amino acids to liver cells. It is unlikely that changes in the secretion of adrenal hormones in involved.

The specific radioactivity of the tissue free amino acid pool as a basis for measuring the rate of protein synthesis in the rat in vivo

1. Rats were infused in vivo with [U-(14)C]glycine for periods of 2-6h, during which time the specific radioactivity of the free glycine in plasma and tissue approached a constant value. 2. Free serine also became labelled. The ratio of specific radioactivity of serine to that of glycine in the protein of liver, kidney, brain, jejunum, heart, diaphragm and gastrocnemius muscle was closer to the ratio in the free amino acid pool of the tissue than that of the plasma. 3. The kinetics of incorporation of [(14)C]glycine and [(14)C]serine into the protein of gastrocnemius muscle further suggested that the plasma free amino acids were not the immediate precursors of protein. 4. Infusion of rats with [U-(14)C]serine resulted in labelling of free glycine. The ratio of specific radioactivity of glycine to serine in the protein of liver, kidney, brain, jejunum and heart again suggested incorporation from a pool similar to the free amino acid pool of the tissue. 5. Rates of tissue protein synthesis calculated from the incorporation into protein of both radioactive glycine and serine, either infused or derived, were very similar when the precursor specific radioactivity was taken to be that in the total free amino acids of the tissue. Except for gastrocnemius muscle and diaphragm during the infusion of radioactive serine, the rates of tissue protein synthesis calculated from the specific radioactivity of the free glycine and serine in plasma differed markedly.

Compartmentation of free amino acids for protein synthesis in rat liver

The concept that a general intracellular pool serves as the sole precursor of amino acids for protein biosynthesis has been vigorously debated in recent years. To help resolve this controversy, we followed the distribution of intraperitoneally administered [(3)H]valine in the tRNA and the extracellular and intracellular compartments of rat liver. The specific radioactivity of the valine released from isolated tRNA was 2-3 times higher than that of intracellular valine, suggesting that the intracellular pool cannot be the sole precursor of amino acids used for charging tRNA. In addition, the specific radioactivity of the tRNA was only half that of the extracellular valine. Therefore it is unlikely that the valyl-tRNA is charged exclusively with amino acids derived from the extracellular pool. A model is proposed which stipulates that both extracellular and intracellular amino acids contribute to a restricted compartment that funnels amino acids towards protein biosynthesis.

The effect of glucose-insulin-potassium on cardiac ultrastructure following acute experimental coronary occlusion

The effects of glucose-insulin-potassium (GIK) on cardiac ultrastructure following acute experimental coronary occlusion were studied in dogs. Epicardial ST segment elevations at multiple sites on the anterior surface of the left ventricle 15 minutes after ligation of the left anterior descending coronary artery were used to predict infarct development. Biopsies removed from sites of known ST segment elevation were examined with the electron microscope, and the degree of injury was correlated with the ST segment elevation. The animals receiving GIK showed significantly less necrosis than was seen in dogs with occlusion alone at corresponding levels of ST segment elevation. Other evidence suggesting a beneficial effect of GIK was the presence of a fibrillar material in several biopsies from the treated animals, which may indicate the regeneration of myofilaments.

Action of insulin and growth hormone on protein synthesis in muscle from non-hypophysectomized rabbits

The separate effects of insulin and growth hormone on the uptake and incorporation of five amino acids into diaphragm muscle from non-hypophysectomized rabbits has been examined. Both growth hormone and insulin, when present in the medium separately, stimulated the incorporation into protein of the amino acids, leucine, arginine, valine, lysine and histidine. Insulin also stimulated amino acid uptake, but growth hormone did not. When insulin and growth hormone were present in the incubation medium together, the uptake and incorporation of valine, the only amino acid studied under these conditions, tended to be greater than the sum of the separate effects of the two hormones.

Kinetic analysis of insulin action on amino acid uptake by isolated chick embryo heart cells

1. Isolated chick embryo heart cells were used to investigate the mode of action of insulin on the transport of three naturally occurring amino acids: l-proline, l-serine and glycine. Initial velocities of uptake were measured over a period of 5min with an 80-fold range of amino acid concentration. Corrections for amino acid diffusion, incorporation into protein and conversion into carbon dioxide were introduced. 2. The uptake processes approximated Michaelis-Menten kinetics within definite ranges of amino acid concentrations. A single transport system for proline and at least two transport systems for serine and glycine were detected. 3. The kinetic effects of insulin on transport systems for the amino acids tested were consistent with an acceleration of the maximal velocity of the process, without substantial changes in substrate concentration for half-maximal transport velocity. 4. These hormonal effects were not essentially altered by the corrections for amino acid incorporation into protein and conversion into carbon dioxide.

The control by insulin of amino acid accumulation in muscle

1. The capacity of insulin to enhance the accumulation by muscle of several amino acids was studied. Reports that threonine uptake is enhanced by insulin were not confirmed, despite its enhanced incorporation into protein. Uptake of beta-alanine and gamma-aminobutyric acid also did not respond to the hormone. A stimulation of accumulation of alanine, histidine and ethionine was observed. 2. The capacity of inhibitors of protein synthesis to reveal a stimulation by insulin of accumulation of several amino acids, hitherto considered unresponsive to insulin in the absence of inhibitor, was confirmed. Cycloheximide was as effective as puromycin. However, two of these amino acids, alanine and histidine, here showed response to insulin in the absence of inhibitor. The presence of cycloheximide was found to enhance uptake of cycloleucine, ethionine and threonine; in its presence insulin enhanced uptake of beta-alanine and alpha-methyltyrosine. 3. It is concluded that the influence of inhibitors of protein synthesis on amino acid accumulation and the response of amino acid accumulation to insulin are not adequately explained on the basis of inhibition of protein synthesis allowing amino acids to accumulate more readily. 4. The technical problems of whether linear rates of incorporation of amino acids into protein really indicate more than one cell pool are discussed and safeguards suggested. That initial rates of incorporation of label into protein are likely to be non-linear is shown.