Effect of protein restriction on (15)N transfer from dietary [(15)N]alanine and [(15)N]Spirulina platensis into urea.
Six normal men consumed a mixed test meal while adapted to high (1.5 g. kg(-1) x day(-1)) and low (0.3 g. kg(-1) x day(-1)) protein intakes. They completed this protocol twice: when the test meals included 3 mg/kg of [(15)N]alanine ([(15)N]Ala) and when they included 30 mg/kg of intrinsically labeled [(15)N]Spirulina platensis ([(15)N]SPI). Six subjects with insulin-dependent diabetes mellitus (IDDM) receiving conventional insulin therapy consumed the test meal with added [(15)N]Ala while adapted to their customary high-protein diet. Protein restriction increased serum alanine, glycine, glutamine, and methionine concentrations and reduced those of leucine. Whether the previous diet was high or low in protein, there was a similar increase in serum alanine, methionine, and branched-chain amino acid concentrations after the test meal and a similar pattern of (15)N enrichment in serum amino acids for a given tracer. When [(15)N]Ala was included in the test meal, (15)N appeared rapidly in serum alanine and glutamine, to a minor degree in leucine and isoleucine, and not at all in other circulating amino acids. With [(15)N]SPI, there was a slow appearance of the label in all serum amino acids analyzed. Despite the different serum amino acid labeling, protein restriction reduced the postmeal transfer of dietary (15)N in [(15)N]Ala or [(15)N]SPI into [(15)N]urea by similar amounts (38 and 43%, respectively, not significant). The response of the subjects with IDDM was similar to that of the normal subjects. Information about adaptive reductions in dietary amino acid catabolism obtained by adding [(15)N]Ala to a test meal appears to be equivalent to that obtained using an intrinsically labeled protein tracer.
Hamadeh
M J
MJ
Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Quebec, Canada H3T 1E2.
Hoffer
L J
LJ
D000409:Alanine / Q000378:metabolism*; D001224:Aspartic Acid / Q000097:blood; D001426:Bacterial Proteins; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism*; D018753:Diet, Protein-Restricted; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005973:Glutamine / Q000097:blood; D005998:Glycine / Q000097:blood; D006801:Humans; D007532:Isoleucine / Q000097:blood; D007930:Leucine / Q000097:blood; D008297:Male; D008715:Methionine / Q000097:blood; D009587:Nitrogen Isotopes / Q000032:analysis / Q000378:metabolism*; D019518:Postprandial Period / Q000502:physiology; D053545:Spirulina; D014508:Urea / Q000378:metabolism*
D001426:Bacterial Proteins; D009587:Nitrogen Isotopes; D007532:Isoleucine; D005973:Glutamine; D001224:Aspartic Acid; D014508:Urea; D008715:Methionine; D007930:Leucine; D000409:Alanine; D005998:Glycine