Although amino acid mixtures enriched in branched-chain amino acids (BCAA) and deficient in aromatic amino acids (AAA) are often used together with insulin and glucose in clinical nutrition, their physiological effects on muscle protein anabolism are not known. To this aim, we studied forearm leucine kinetics in post-absorptive volunteers, before and after the systemic infusion of BCAA-enriched, AAA-deficient amino acids along with insulin and the euglycaemic clamp. The results were compared with the effects of insulin infusion alone. A compartmental leucine forearm model was employed at steady state. Hyperaminoacidaemia with hyperinsulinaemia (to ≈ 80–100 μ-units/ml) increased the leucine plasma concentration (+70%; P< 0.001), inflow into the forearm cell (+150%; P< 0.01), disposal into protein synthesis (+100%; P< 0.01), net intracellular retention (P< 0.01), net forearm balance (by ≈ 6-fold; P< 0.01) and net deamination to α-ketoisocaproate (4-methyl-2-oxopentanoate) (+9%; P< 0.05). Leucine release from forearm proteolysis and outflow from the forearm cell were unchanged. In contrast, hyperinsulinaemia alone decreased plasma leucine concentrations (-35%; P< 0.001) and leucine inflow (-20%; P< 0.05) and outflow (-30%; P< 0.01) into and out of forearm cell(s), it increased net intracellular leucine retention (P< 0.03), and it did not change leucine release from forearm proteolysis (-20%; P = 0.138), net leucine deamination to α-ketoisocaproate, leucine disposal into protein synthesis or net forearm protein balance. By considering all data together, leucine disposal into protein synthesis was directly correlated with leucine inflow into the cell (r = 0.71; P< 0.0001). These data indicate that the infusion of BCAA-enriched, AAA-deficient amino acids along with insulin is capable of stimulating forearm (i.e. muscle) protein anabolism in normal volunteers by enhancing intracellular leucine transport and protein synthesis. These effects are probably due to hyperaminoacidaemia and/or its interaction with hyperinsulinaemia, since they were not observed under conditions of hyperinsulinaemia alone.
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August 27 1999
Effects of branched-chain-enriched amino acids and insulin on forearm leucine kinetics
Michela ZANETTI;
Michela ZANETTI
1Cattedra di Malattie del Metabolismo, Dip. di Medicina Clinica e Sperimentale, Policlinico Universitario, via Giustiniani 2, 35128 Padova, Italy
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Rocco BARAZZONI;
Rocco BARAZZONI
1Cattedra di Malattie del Metabolismo, Dip. di Medicina Clinica e Sperimentale, Policlinico Universitario, via Giustiniani 2, 35128 Padova, Italy
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Edward KIWANUKA;
Edward KIWANUKA
1Cattedra di Malattie del Metabolismo, Dip. di Medicina Clinica e Sperimentale, Policlinico Universitario, via Giustiniani 2, 35128 Padova, Italy
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Paolo TESSARI
1Cattedra di Malattie del Metabolismo, Dip. di Medicina Clinica e Sperimentale, Policlinico Universitario, via Giustiniani 2, 35128 Padova, Italy
Correspondence: Dr Paolo Tessari (e-mail [email protected]).
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Publisher: Portland Press Ltd
Received:
May 05 1999
Revision Received:
May 28 1999
Accepted:
June 23 1999
Online ISSN: 1470-8736
Print ISSN: 0143-5221
The Biochemical Society and the Medical Research Society © 1999
1999
Clin Sci (Lond) (1999) 97 (4): 437–448.
Article history
Received:
May 05 1999
Revision Received:
May 28 1999
Accepted:
June 23 1999
Citation
Michela ZANETTI, Rocco BARAZZONI, Edward KIWANUKA, Paolo TESSARI; Effects of branched-chain-enriched amino acids and insulin on forearm leucine kinetics. Clin Sci (Lond) 1 October 1999; 97 (4): 437–448. doi: https://doi.org/10.1042/cs0970437
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