Relationship between central nervous system hydrogen ion regulation and amino acid metabolism in hypercapnia, II.
Resting level of ventilation is affected by change in extracellular fluid hydrogen ion concentration [H+] in the central nervous system (CNS) and by certain amino acid neurotransmitters within or near the medulla oblongata. Hypercapnia alters both cerebrospinal fluid (CSF) [H+] and CSF ammonia metabolized to glutamine, a precursor of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Therefore, the effect of 1 to 2 h of hypercapnia on cerebral cortical and medullary contents of selected amino acids and bicarbonate (HCO-3) fixation rates was studied in anesthetized mongrel dogs using 11C-labeled HCO-3. Medullary taurine, glycine, alanine, and glutamate concentrations were not significantly altered by hypercapnia, but mean medullary glutamine and GABA concentrations both increased significantly (p less than 0.05), with a high correlation (r = 0.82, n = 8) between individual values. Medullary GABA and glutamine increased linearly with CSF [H+]. The rate of CNS HCO-3 fixation into CSF glutamine was negligibly small and decreased during hypercapnia, compared with the rate of medullary tissue HCO-3 fixation, which increased linearly with CSF [H+]. These observations show that there is a significant interrelationship between medullary metabolism of GABA, glutamine, bicarbonate, and CNS hydrogen ion regulation during hypercapnia.
Hoop
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B
Shih
V E
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Kazemi
H
H
D000136:Acid-Base Equilibrium; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D004285:Dogs; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D005973:Glutamine / Q000378:metabolism; D006935:Hypercapnia / Q000134:cerebrospinal fluid / Q000378:metabolism* / Q000503:physiopathology; D008526:Medulla Oblongata / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D001639:Bicarbonates; D005971:Glutamates; D018377:Neurotransmitter Agents; D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid