Journal of Applied Physiology, Vol 44, Issue 3 333-339, Copyright © 1978 by American Physiological Society
Selected brain amino acids and ammonium during chronic hypercapnia in conscious rats
J. Weyne, F. Van Leuven, H. Kazemi and I. Leusen
Glutamic, aspartic, and gamma-aminobutyric acid (GABA), glutamine, and
ammonium were measured in the brains of unanesthetized normocapnic and
hypercapnic (10% CO2; 5 min to 3 wk) rats. Hypercapnia increased glutamine
and GABA and decreased glutamic and aspartic acids. Changes occurred within
1 h and were maintained during the observation period of 3 wk. On return to
normocapnia amino acid concentrations were almost normal after 1 h. Based
on the time course it is concluded that intracerebral hypercapnia is more
likely the stimulus for change than acidosis. Ammonium content was
unchanged for at least 1 h after the onset of hypercapnia but increased
thereafter. Experiments in which glutamine synthesis by brain was impeded
by inhibiting the enzyme glutamine synthetase favor the hypothesis that the
rise of ammonium content in hypercapnia is initially not seen because of
increased glutamine synthesis. The changes observed may have a role in
metabolic pH homeostasis of brain tissue and may also be relevant to the
modified brain excitability in hypercapnia.
