Acids In Skeletal Muscle Research Articles

Alanine and glutamine synthesis and release from skeletal muscle. II. The precursor role of amino acids in alanine and glutamine synthesis.

The synthesis and release of alanine and glutamine have been studied in the intact rat epitrochlaris skeletal muscle preparation. Aspartate, cysteine, leucine, valine, methionine, isoleucine, serine, theronine, and glycine increased significantly the formation and release of alanine from muscle. Cysteine, leucine, valine, methionine, isoleucine, tyrosine, lysine, and phenylalanine increased the rate of glutamine synthesis. Only ornithine, arginine, and tryptophan were without effect on the synthesis of either alanine or glutamine. Half-maximal stimulation of alanine and glutamine formation by added amino acids was observed with concentrations ranging between 0.5 and 1.0 mM. Increases in alanine and glutamine formation were not accompanied by changes in pyruvate production or glucose uptake. The progressive decline in alanine and glutamine synthesis noted on prolonged incubation was prevented by the addition of amino acids to the incubation medium. Stimulation of alanine synthesis by added amino acids was unaffected by inhibition of glycolysis with iodoacetate. Inhibition of alanine aminotransferase with aminooxyacetate significantly decreased alanine formation. Pyruvate and ammonium chloride did not increase further the rate of either alanine or glutamine formation above that produced by added amino acids. These data indicate that most amino acids are precursors for alanine and glutamine synthesis in skeletal muscle. A general mechanism is presented for the de novo formation of alanine from amino acids in skeletal muscle, and the importance of proteolysis for the supply of amino acid precursors for alanine and glutamine synthesis is discussed.

Action of epinephrine on the distribution of two model amino acids in the diabetic rat.

The injection of epinephrine (1.0 mg/kg) into alloxan-diabetic, fasted rats depressed the serum concentration of previously administered α-aminoisobutyric acid (AIB) and 1-aminocyclopentanecarboxylic acid (ACPC) within 2 h and simultaneously increased the concentration of these amino acids in the liver. The increase of ACPC and AIB concentrations in the liver following epinephrine injection was nearly 3 times as great in the alloxan-diabetic rats as in normal intact rats. The levels of the two amino acids in skeletal muscle, heart, and diaphragm of the alloxanized rats were unchanged following epinephrine injection, but the distribution ratios in these tissues were raised because the serum concentration decreased 20%.Further studies were carried out employing rats that were treated 1 h before epinephrine injection, with mannoheptulose, a compound which blocks insulin release. The concentration of ACPC and AIB in the serum 2 h after epinephrine injection were lowered. At the same time the concentrations of ACPC in liver and heart were raised, as was the concentration of AIB in heart. The levels of the two amino acids in skeletal muscle and diaphragm were unaltered. However, distribution ratios were raised in the four tissues. These results demonstrate that epinephrine enhances AIB and ACPC transport into the tissues of the insulin-deficient rats <i>in vivo</i> and suggest that epinephrine-stimulated amino acid transport is not due indirectly to insulin.

Vitamin E Deficiency and the Accumulation of Amino Acids in Skeletal Muscle

The movements of 14C-labeled glycine and α-aminoisobutyric acid (AIB) into and out of skeletal muscle slices from control and vitamin E-deficient rabbits were studied. Vitamin E deficiency increased 14C-amino acid accumulation at 60 minutes of incubation without having any demonstrable effect either on the early phase of entry (zero to 30 minutes) or on the efflux of 14C-amino acids. Inhibition of 14C-glycine incorporation into protein by puromycin had no effect either on the early phase of entry or on the accumulation of 14C-glycine by control or vitamin E-deficient muscle. The early phase of 14C-glycine entry followed first-order kinetics; its rate constant in sec-1 was 5.5 × 10-4. Whereas steady-state distribution ratios of 14C-amino acids were reached by control muscle in about 30 minutes, dystrophic muscle continued to accumulate the 14C-amino acids for 60 minutes or more. Small differences in influx, efflux, or both, can result in significant differences in net accumulation with extended time. Thus, we suggest that vitamin E-deficient muscle has one or more compartments capable of increasing the accumulation of 14C-glycine and 14C-AIB due to a change either in influx or efflux which is too small to demonstrate. These compartments may be located in regenerating muscle cells, or in other cell types more abundant in the dystrophic muscle.

Vitamin E deficiency and metabolism of amino acids in skeletal muscle.

Vitamin E deficiency and metabolism of amino acids in skeletal muscle.

Free amino acids in liver, plasma, and muscle of patients with cirrhosis of the liver

A significant decrease in concentration of branched-chain amino acids in skeletal muscle of cirrhotic patients has been observed. These data are presented in further support of the concept that a relative deficiency of these amino acids may be present in cirrhotic patients.

Autoradiography of Injected Albumin‐Bound l‐C14‐‐Palmitate in Pigeon Pectoralis Muscle

AbstractWirsén, C. Autoradiography of injected albumin‐bound 1‐C14‐palmilate in pigeon pectoralis muscle. Acta physiol. scand. 1965. 65. 120–125. — Labeled albumin‐bound palmitate was injected i. v. into laboratory pigeons and specimens from pectoralis major and minor removed after 3, 6 and 15 min. Autoradiography on fresh‐frozen sections was performed with the method developed by Ullberg 1954. The activity was distinctly stronger in red muscle fibers than in white. It is suggested that the uptake of palmitic acid in skeletal muscle is a selective process.

Effects of cortisol on amino acids in skeletal muscle and plasma.

Effects of cortisol administration on concentrations of free amino acids and other ninhydrin reacting substances (NRS) were determined in plasma of fasted mice and skeletal muscle of fasted and nonfasted mice by column chromatography. The following amino acids were found: alanine, arginine, aspartic acid, glutamic acid, glycine, glutamine, histidine, isoleucine, leucine, lysine, methionine, proline, serine, threonine, tryptophan and valine. Cystine and cysteine were absent and traces of phenylalanine and tyrosine were present. Non-amino acid NRS found included carnosine, glycerophosphoethanolamine, phosphoethanolamine, phosphoserine, taurine and urea. Taurine accounted for more than half the total NRS. Administration of cortisol appeared to result in increased concentration of virtually all amino acids and urea in both fasted and nonfasted animals. In the fed group, the difference between the sums of amino acids present was significant. Cortisol injection also increased plasma amino acids but to a lesser ...