QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Torres, N. Articles by Harper, A. E. Search for Related Content PubMed PubMed Citation Articles by Torres, N. Articles by Harper, A. E.

Leucine Affects the Metabolism of Valine by Isolated Perfused Rat Hearts: Relation to Branched-Chain Amino Acid Antagonism^1,2,3,

Departments of Nutritional Sciences and Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI 53706

This study was conducted to determine the effects of different concentrations of leucine on the transport, transamination and oxidation of valine and on incorporation of valine into heart proteins in the isolated perfused rat heart. Valine metabolism was studied in rat hearts perfused with medium containing glucose and graded levels of L-leucine. In transport studies L-phenylalanine was also tested. Uptake of L-[1-¹⁴C]valine (0.2 mmol/L) was significantly reduced (50%) by inclusion of 0.2 mmol/L phenylalanine or leucine, and by 70% by inclusion of 1.0 mmol/L phenylalanine or leucine in the perfusate. Transamination of valine decreased by 37 and 48%, and oxidation of valine by 53 and 71%, respectively, when 0.2 or 1.0 mmol/L leucine was included in the perfusate. Tissue concentrations of valine decreased by 43, 48 and 62% in the presence of 0.2, 0.5 and 1.0 mmol/L leucine, respectively; tissue concentrations of leucine, glutamate and alanine increased 11-fold, 1.2-fold and 0.5-fold, respectively, when 1.0 mmol/L leucine was present in the perfusate. Addition of 0.2–1.0 mmol/L leucine did not affect incorporation of valine into heart proteins. We conclude that 1) competition among large neutral amino acids for transport into heart occurs at physiological concentrations of these amino acids in plasma; 2) inhibition of valine uptake by leucine can limit the rate of valine catabolism in heart; and 3) depletion of tissue valine concentration by an excess of leucine did not affect the rate of protein synthesis.

KEY WORDS: • valine catabolism • protein synthesis • branched-chain amino acids • transport • rats

¹ Presented in part at the 76th Annual Meeting of the Federation of American Societies for Experimental Biology, April 1992, Anaheim, CA [Torres, N., Tovar, A. & Harper, A. E. (1992) Effect of leucine on the transport, transamination, oxidation, and incorporation of valine into proteins in isolated perfused rat heart. FASEB J. 6: A1967 (abs.)].

² Supported in part by funds from The College of Agriculture and Life Sciences, Madison, WI, the Coca-Cola Foundation, Atlanta, GA and Clintec Nutrition, Deerfield, IL.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

⁵ Current address: Department of Physiology of Nutrition, Instituto Nacional de la Nutrición, México, D.F. 14000, México.

⁶ Current address: 381 N.W. 112th Street, Seattle, WA 98177-4840.

Manuscript received 21 June 1994. Revision accepted 17 January 1995.