TY - JOUR
T1 - Short-term metabolic fate of 13N-labeled glutamate, alanine, and glutamine(amide) in rat liver
AU - Cooper, A. J.L.
AU - Nieves, E.
AU - Rosenspire, K. C.
AU - Filc-DeRicco, S.
AU - Gelbard, A. S.
AU - Brusilow, S. W.
N1 - Copyright:
Copyright 2004 Elsevier B.V., All rights reserved.
PY - 1988
Y1 - 1988
N2 - Tracer quantities (in 0.2 ml) of 13N-labele glutamate, alanine, or glutamine(amide) were administered rapidly (≤ 2 s) via the portal vein of anesthetized adult male rats. Liver content of tracer at 5 s was 57 ± 6 (n = 6), 24 ± 1 (n = 3), and 69 ± 7 (n = 3) % of the injected dose, respectively. Portal-hepatic vein differences for the corresponding amino acids were 17 ± 6, 26 ± 8, and 19 ± 9% (n = 4), respectively, suggesting some export of glutamate and glutamine, but not of alanine, to the hepatic vein. Following L-[13N]glutamate administration, label rapidly appeared in liver alanine and aspartate (within seconds). The data emphasize the rapidity of nitrogen exchange via linked transaminases. By 30 s following administration of either L-[13N]glutamate or L-[13N]alanine, label in liver glutamate was comparable; yet, by 1 min ≥ 9 times as much label was present in liver glutamine(amine) following L-[13N]glutamate administration than following L-[13N]alanine administration. Conversely, label in liver urea at 1 min was more pronounced in the latter case despite: (a) comparable total pool sizes of glutamate and alanine in liver; and (b) label incorporation from alanine into urea must occur via prior transfer of alanine nitrogen to glutamate. The data provide evidence for zonal differences in uptake of alanine and glutamate from the portal vein in vivo. The rate of turnover of L-[amide-13N]glutamine was considerably slower than that of L-[13N]alanine or of L-[13N]glutamate, presumably due in part to the higher concentration of glutamine in that organ. Nevertheless, it was possible to show that despite occasional suggestions to the contrary, glutamine(amide) is a source of urea nitrogen in vivo. The present findings continue to emphasize the rapidity of nitrogen exchange reactions in vivo.
AB - Tracer quantities (in 0.2 ml) of 13N-labele glutamate, alanine, or glutamine(amide) were administered rapidly (≤ 2 s) via the portal vein of anesthetized adult male rats. Liver content of tracer at 5 s was 57 ± 6 (n = 6), 24 ± 1 (n = 3), and 69 ± 7 (n = 3) % of the injected dose, respectively. Portal-hepatic vein differences for the corresponding amino acids were 17 ± 6, 26 ± 8, and 19 ± 9% (n = 4), respectively, suggesting some export of glutamate and glutamine, but not of alanine, to the hepatic vein. Following L-[13N]glutamate administration, label rapidly appeared in liver alanine and aspartate (within seconds). The data emphasize the rapidity of nitrogen exchange via linked transaminases. By 30 s following administration of either L-[13N]glutamate or L-[13N]alanine, label in liver glutamate was comparable; yet, by 1 min ≥ 9 times as much label was present in liver glutamine(amine) following L-[13N]glutamate administration than following L-[13N]alanine administration. Conversely, label in liver urea at 1 min was more pronounced in the latter case despite: (a) comparable total pool sizes of glutamate and alanine in liver; and (b) label incorporation from alanine into urea must occur via prior transfer of alanine nitrogen to glutamate. The data provide evidence for zonal differences in uptake of alanine and glutamate from the portal vein in vivo. The rate of turnover of L-[amide-13N]glutamine was considerably slower than that of L-[13N]alanine or of L-[13N]glutamate, presumably due in part to the higher concentration of glutamine in that organ. Nevertheless, it was possible to show that despite occasional suggestions to the contrary, glutamine(amide) is a source of urea nitrogen in vivo. The present findings continue to emphasize the rapidity of nitrogen exchange reactions in vivo.
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M3 - Article
C2 - 2900834
AN - SCOPUS:0024253774
SN - 0021-9258
VL - 263
SP - 12268
EP - 12273
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 25
ER -