TY - JOUR
T1 - Role of the glucose cycle in control of net glucose flux in exercising humans
AU - Weber, J. M.
AU - Klein, S.
AU - Wolfe, R. R.
PY - 1990
Y1 - 1990
N2 - The hepatic glucose cycle involves the production of plasma glucose from glucose 6-phosphate and the simultaneous conversion of glucose back to glucose 6-phosphate. We have evaluated the role of the glucose cycle in the regulation of plasma glucose concentration during exercise at 70% of maximal O2 uptake and during recovery in five normal volunteers. Total glucose flux was measured by use of [2-2H]glucose (Ra2), net glucose flux through the glucose cycle was determined with [6,6-2H2]glucose (Ra6), and the rate of glucose cycling was determined by Ra2 - Ra6. Gas chromatography-mass spectrometry was used for analysis of isotopic enrichment. At rest, 33% of total glucose flux was recycled. In exercise, total flux increased 300%, but so did glucose cycling, which means that there was no change in the percentage of flux recycled. In recovery, both total flux and the rate of recycling returned rapidly to the resting value. We therefore conclude that whereas total glucose production can respond extremely quickly to large changes in energy requirements caused by exercise, thereby enabling maintenance of a constant blood glucose concentration, glucose cycling does not have an important role in amplifying the control of net hepatic glucose flux through the glucose cycle.
AB - The hepatic glucose cycle involves the production of plasma glucose from glucose 6-phosphate and the simultaneous conversion of glucose back to glucose 6-phosphate. We have evaluated the role of the glucose cycle in the regulation of plasma glucose concentration during exercise at 70% of maximal O2 uptake and during recovery in five normal volunteers. Total glucose flux was measured by use of [2-2H]glucose (Ra2), net glucose flux through the glucose cycle was determined with [6,6-2H2]glucose (Ra6), and the rate of glucose cycling was determined by Ra2 - Ra6. Gas chromatography-mass spectrometry was used for analysis of isotopic enrichment. At rest, 33% of total glucose flux was recycled. In exercise, total flux increased 300%, but so did glucose cycling, which means that there was no change in the percentage of flux recycled. In recovery, both total flux and the rate of recycling returned rapidly to the resting value. We therefore conclude that whereas total glucose production can respond extremely quickly to large changes in energy requirements caused by exercise, thereby enabling maintenance of a constant blood glucose concentration, glucose cycling does not have an important role in amplifying the control of net hepatic glucose flux through the glucose cycle.
KW - exercise
KW - stable isotopes
UR - http://www.scopus.com/inward/record.url?scp=0025367539&partnerID=8YFLogxK
U2 - 10.1152/jappl.1990.68.5.1815
DO - 10.1152/jappl.1990.68.5.1815
M3 - Article
C2 - 2361883
AN - SCOPUS:0025367539
SN - 0161-7567
VL - 68
SP - 1815
EP - 1819
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 5
ER -