The effect of branched-chain amino acids on ammonia metabolism in rat skeletal muscle

To compare the contributions of splanchnic and skeletal muscle tissues to the disposal of intravenously administered amino acids, regional amino acid exchange was measured across the splanchnic bed and leg in 11 normal volunteers. Postabsorptively, net release of amino acids by leg (largely alanine and glutamine) was complemented by the net splanchnic uptake of amino acids. Amino acid infusion via peripheral vein (0.2 g X kg-1 X h-1) caused a doubling of plasma insulin and glucagon levels and a threefold rise in blood amino acid concentrations. Both splanchnic and leg tissues showed significant uptake of infused amino acids. Splanchnic tissues accounted for approximately 70% of the total body amino acid nitrogen disposal; splanchnic uptake was greatest for the glucogenic amino acids but also included significant quantities of branched-chain amino acids. In contrast, leg amino acid uptake was dominated by the branched-chain amino acids. Based on the measured leg balance, body skeletal muscle was estimated to remove approximately 25-30% of the total infused amino acid load and approximately 65-70% of the infused branched-chain amino acids. Amino acid infusion significantly stimulated both the leg efflux and the splanchnic uptake of glutamine (not contained in the infusate). We conclude that when amino acids are infused peripherally in normal humans, splanchnic viscera (liver and gut) are the major sites of amino acid disposal.

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Interorgan metabolism of amino acids in streptozotocin-diabetic ketoacidotic rat

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1983.244.2.e151 ◽

1983 ◽

Vol 244 (2) ◽

pp. E151-E158 ◽

Cited By ~ 10

Author(s):

J. T. Brosnan ◽

K. C. Man ◽

D. E. Hall ◽

S. A. Colbourne ◽

M. E. Brosnan

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Amino Acid ◽

Branched Chain Amino Acids ◽

Diabetic Rats ◽

Normal Rat ◽

Diabetic Brain ◽

Streptozotocin Diabetic Rats ◽

Branched Chain ◽

Amino Acid Concentrations

Amino acid concentrations in whole blood, liver, kidney, skeletal muscle, and brain were measured and arteriovenous differences calculated for head, hindlimb, kidney, gut, and liver in control and streptozotocin-diabetic rats. In the control rats, glutamine was released by muscle and utilized by intestine, intestine released citrulline and alanine, liver removed alanine, and the kidneys removed glycine and produced serine. In diabetic rats, the major changes from the pattern of fluxes seen in the normal rat were the release of many amino acids from muscle, with glutamine and alanine predominating, and the uptake of these amino acids by the liver. Glutamine removal by the intestine was suppressed in diabetes, but a large renal uptake of glutamine was evident. Branched-chain amino acids were removed by the diabetic brain, and consequently, brain levels of a number of large neutral amino acids were decreased in diabetes.

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