15N-NMR spectroscopy studies of ammonia transport and glutamine synthesis in the hyperammonemic rat brain.
Ammonia transport and glutamine synthesis were studied in the hyperammonaemic rat brain in vivo using 15N-NMR spectroscopy at a plasma ammonia level of approximately 0.39 mM raised via an intravenous [15N]-ammonium acetate infusion. The initial slope of the time course of the summed cerebral 15N-labelled metabolites was used to determine the rate of ammonia net transport during hyperammonemia as 0.13 +/- 0.02 micromol/min/g (mean +/- SD; n = 5). Based on the total accumulation of glutamine and the 1:2 stoichiometric relationship between fluxes of four-carbon skeletons and nitrogen atoms, the rate of de novo glutamine synthesis through anaplerosis and subsequent glutamate dehydrogenase action was calculated to be 0.065 +/- 0.01 micromol/min/g. The rate of total glutamine synthesis was estimated to be 0.20 +/- 0.06 micromol/min/g (n = 5) by fitting the [5-15N]glutamine time course to a previously described model of glutamate-glutamine cycling between astrocytes and neurones. A large dilution was also observed in [2-15N]glutamine, which supports the glutamate-glutamine cycle as being an important pathway for neuronal glutamate repletion in vivo.
Shen
J
J
Department of Internal Medicine, Yale University School of Medicine, New Haven, Conn., USA.
Sibson
N R
NR
Cline
G
G
Behar
K L
KL
Rothman
D L
DL
Shulman
R G
RG
D000085:Acetates / Q000494:pharmacology; D000641:Ammonia / Q000097:blood / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000096:biosynthesis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008954:Models, Biological; D009587:Nitrogen Isotopes; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley
D000085:Acetates; D009587:Nitrogen Isotopes; D005973:Glutamine; D018698:Glutamic Acid; D000641:Ammonia; C018824:ammonium acetate