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Effects of Dietary Protein, Energy and Tyrosine on Central and Peripheral Norepinephrine Turnover in Mice^1,2,

Department of Foods and Nutrition, University of Alberta, Edmonton, Alberta, Canada T6G 2M8

Norepinephrine (NE) turnover rate and tyrosine concentrations were assessed in several tissues of 5-wk-old female lean mice that were fed diets of 20% protein (1.2% tyrosine), 40% protein (2.4% tyrosine) or tyrosine-supplemented diets of 40% protein with 4 or 8% tyrosine or 20% protein with 4% tyrosine for 4 d. Mice fed the 40% protein diet had significantly lower NE turnover rates in interscapular brown adipose tissue, heart and kidney (66, 64 and 49%, respectively) and nonsignificantly lower (84%) turnover rate in brain than did mice fed the 20% protein diet, but plasma and tissue tyrosine concentrations did not differ. When energy intake of the 20% protein-fed mice was restricted to 92% of the 40% protein-fed mice, tyrosine concentration in plasma and tissues was lower by half, but NE turnover rate did not differ between the two groups. Supplementation of the 40 or 20% diets with tyrosine, resulting in twofold higher plasma and tissue tyrosine concentrations, had no effect on NE turnover rate in any organ examined. We conclude that both energy intake and dietary protein concentration affect sympathetic nervous system activity in young mice. Tyrosine does not mediate or alter these changes.

KEY WORDS: • dietary protein • energy intake • tyrosine supplementation • norepinephrine turnover

¹ Presented in part at the 70th Annual Meeting of the Federation of American Societies for Experimental Biology, St. Louis, MO, 17 April 1986 and the 28th Annual Meeting of the Canadian Federation of Biological Societies, Guelph, Ontario, Canada, 16 June 1986.

² Supported by Natural Sciences and Engineering Council of Canada and Central Research Fund, University of Alberta.

³ To whom correspondence should be sent.

Manuscript received 22 January 1987. Revision accepted 20 August 1987.

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