Use of 3H and 14C doubly labeled glucose and amino acids in the study of hormonal regulation of gluconeogenesis in rats
Dunn, A.; Chenoweth, M.; Bever, K.
Federation Proceedings 36(2): 245-252
1977
ISSN/ISBN: 0014-9446 PMID: 190046 Document Number: 112882
[U-14C,6-3H]Glucose was given to normal and adrenalectomized rats. No effect was observed on the [6-3H]glucose half-life, suggesting the dicarboxylic acid shuttle is not affected by adrenalectomy; the Cori cycle also is not influenced. Loads of [14C]aspartate, [14C]glutamate, or [14C]alanine were given to normal and adrenalectomized rats. Simultaneously, transaminase activity was studied by measuring the appearance of 3H2O in body water after administration of [2-3H]aspartate, [2-3H]glutamate, or [2-3H]alanine. Adrenalectomy has no influence on the incorporation of glutamate or aspartate into glucose or on their transaminases. Diminution of incorporation of [14C]alanine into glucose and alanine transaminase activities occurs only when rats are given unphysiological loads. These studies support the contention that glucocorticoid rate-limiting actions occur in extrahepatic tissues to produce an increased flow of glucose precursors to the liver. [U-14C,3-3H]Glucose was used to investigate the effect of glucagon on the hepatic fructose-6-phosphate cycle. Glucagon administration resulted in a rapid drop in the 3H/14C ratio of circulating glucose, suggesting an increase in fructose-6-phosphate recycling caused by activation of FDPase with little or no decrease in phosphofructokinase. Such a change would direct substrate flux toward gluconeogenesis.