Increased sympathetic nervous system activity in rats fed a low-protein diet.
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.
D002001:Adipose Tissue, Brown / Q000502:physiology; D000818:Animals; D001835:Body Weight; D002714:Chlorisondamine / Q000494:pharmacology; D004044:Dietary Proteins / Q000008:administration & dosage*; D004298:Dopamine / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D006329:Heart Conduction System; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D009929:Organ Size; D051381:Rats; D011919:Rats, Inbred Strains; D013564:Sympathetic Nervous System / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism
D004044:Dietary Proteins; D014443:Tyrosine; D002714:Chlorisondamine; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine