title: Severity of hyperammonemic encephalopathy correlates with brain ammonia level and saturation of glutamine synthetase in vivo.
abstract: Correlation among in vivo glutamine synthetase (GS) activity, brain ammonia and glutamine concentrations, and severity of encephalopathy was examined in hyperammonemic rats to obtain quantitative information on the capacity of GS to control these metabolites implicated in the etiology of hepatic encephalopathy. Awake rats were observed for neurobehavioral impairments after ammonium acetate infusion to attain a steady-state blood ammonia concentration of 0.9 (group A) or 1.3 mumol/g (group B). As encephalopathy progressed from grade III to IV, brain ammonia concentration increased from 1.9 to 3.3 mumol/g and then decreased to 1.3 mumol/g on recovery to grade III. In contrast, brain glutamine concentration was 26, 23, and 21 mumol/g, respectively. NH(4+)-infused rats pretreated with L-methionine DL-sulfoximine reached grade IV when brain ammonia and glutamine concentrations were 3.0 and 5.5 mumol/g, respectively; severity of encephalopathy correlates with brain ammonia, but not glutamine. In vivo GS activity, measured by NMR, was 6.8 +/- 0.7 mumol/h/g for group A and 6.2 +/- 0.6 mumol/h/g for group B. Hence, the in vivo activity, shown previously to increase with blood ammonia over a range of 0.4-0.64 mumol/g, approaches saturation at blood ammonia > 0.9 mumol/g. This is likely to be the major cause of the observed accumulation of brain ammonia and the onset of grade IV encephalopathy.
authors.affiliation: Magnetic Resonance Spectroscopy Laboratory, Huntington Medical Research Institutes, Pasadena, California 91105, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kanamori
authors.forename: B D
authors.initials: BD
authors.lastname: Ross
authors.forename: J C
authors.initials: JC
authors.lastname: Chung
authors.forename: E L
authors.initials: EL
authors.lastname: Kuo
mesh_terms: D000641:Ammonia / Q000097:blood / Q000378:metabolism* / Q000633:toxicity*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism*; D006501:Hepatic Encephalopathy / Q000378:metabolism* / Q000503:physiopathology; D007700:Kinetics; D008297:Male; D008717:Methionine Sulfoximine / Q000494:pharmacology; D009043:Motor Activity; D011187:Posture; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex; D013997:Time Factors
chemical_list: D005973:Glutamine; D008717:Methionine Sulfoximine; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase