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Journal of Nutrition Vol. 114 No. 5 May 1984, pp. 835-839
Copyright © 1984 by American Society for Nutrition
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Free Tyrosine Levels of Rat Brain and Tissues with Sympathetic Innervation following Administration of L-Tyrosine in the Presence and Absence of Large Neutral Amino Acids1,2,

Richard F. Ablett, Margaret MacMillan, Michael J. Sole, Corey B. Toal and G. Harvey Anderson3

Departments of Nutritional Sciences and Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada M5S 1A8

The tyrosine concentration of fasted rats was measured in plasma, brain and tissues receiving sympathetic innervation after L-tyrosine (200 mg/kg) was administered alone or in the presence of an equimolar cocktail containing isoleucine, leucine and valine. In the samples taken at 15, 30, 45, 60, 120 or 180 minutes, the highest concentrations of L-tyrosine were observed in plasma, heart, adrenal gland and kidney at 15 minutes, but in interscapular brown adipose tissue at 15 and 30 minutes and in brain at 15–60 minutes. The decline from peak concentrations was slower in brain, kidney and interscapular brown adipose tissue than in plasma, but in all tissues examined, control levels of free tyrosine were attained by 180 minutes postadministration. Competing large neutral amino acids reduced the maximal uptake of tyrosine in the brain by 48% but had no effect in the other tissues examined.

KEY WORDS: • tyrosine • isoleucine • leucine • valine • brain

1 Supported by the Ontario Heart Foundation and Natural Sciences and Engineering Research Council (Canada).

2 Presented at the Federation of American Societies for Experimental Biology meetings in Chicago, IL, April 1983.

3 Address reprint requests to G. H. Anderson.

Manuscript received 21 September 1983.




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