Increased sympathetic nervous system activity in rats fed a low-protein diet

J. B. Young, L. N. Kaufman, M. E. Saville, L. Landsberg

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54 Scopus citations

Abstract

To examine the state of sympathetic nervous system (SNS) function in animals fed a protein-restricted diet, [3H] norepinephrine ([3H]-NE) turnover was measured in heart and interscapular brown adipose tissue (IBAT) of rats fed synthetic diets of equal caloric density containing 22% protein (as casein) or 7% protein (the difference being made up by sucrose). Because dietary availability of tyrosine is a potential mediator of SNS responses to protein ingestion, a third diet (7% protein supplemented with tyrosine) was also tested. After 12 days dietary preparation [3H]-NE turnover was increased 35-70% in heart by 7% protein feeding and 93-103% in IBAT. When smaller animals were fed the synthetic diets for 4-5 wk, sympathetic stimulation in those given the protein-restricted formula was also apparent, although demonstration of this response was complicated by comparative problems due to the marked differences in body size between normal and protein-restricted groups. Addition of tyrosine (sufficient to normalize plasma and brain tyrosine levels) was without effect on the stimulation of NE turnover induced by the protein-deficient diet. Similarly, augmented urinary NE excretion observed in animals consuming the 7% protein diet was unaffected by supplemental tyrosine. Urinary dopamine excretion, however, was uniquely and strikingly elevated with restoration of dietary tyrosine to animals fed the low-protein diet. Thus isocaloric substitution of sucrose for casein in the diet activates the SNS in heart and IBAT, a response unrelated to limitation of dietary tyrosine.

Original languageEnglish (US)
Pages (from-to)R627-R637
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume17
Issue number5
DOIs
StatePublished - 1985

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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