AJP - Endocrinology and Metabolism, Vol 266, Issue 3 E433-E437, Copyright © 1994 by American Physiological Society
Use of 2H2O to study labeling in plasma glucose and hepatic glycogen during a hyperglycemic clamp
R. A. Shalwitz, T. J. Beth, A. M. MacLeod, S. J. Tucker and G. G. Rolison
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri.
In this study, we demonstrate the use of 2H2O, in a manner analogous to
3H2O, to study gluconeogenic flux (deuterium labeling at the carbon-6
position of glucose) relative to overall flux through glucose 6-phosphate
(deuterium labeling at the carbon-2 position of glucose) into glucose
output and glycogen synthesis during hyperglycemia. Before the study (4
days), jugular and carotid catheters were placed. Rats were fasted for 17 h
before the study. 2H2O was infused for 2 h at 3 ml/h, with a subsequent 1-h
equilibration period. A hyperglycemic clamp at 180 mg/dl (10 mM) was then
performed for 90 min (plasma samples obtained at 10-min intervals). At the
end of the experiment, anesthesia was induced and the liver removed. Gas
chromatography-mass spectroscopy isotopomer analysis of four different mass
clusters from glucose was used to determine deuterium enrichment on the
carbon-2 (E2D) and carbon-6 (E6D) positions of plasma glucose and
glycogen-glucose. The results show that the labeling pattern in glycogen
and plasma glucose was virtually identical. In addition, the E6D-to-E2D
ratio in plasma glucose did not change during hyperglycemia. Additional
studies were performed to show that the E6D-to-E2D ratio was decreased in
the fed state and that the fed animal, compared with the fasted rat, had a
marked increase in the ratio when given an epinephrine infusion. Thus it
was concluded that this was a robust new technique for analyzing glucose
and glycogen metabolism in rats.(ABSTRACT TRUNCATED AT 250 WORDS)
