Response of phosphoenolpyruvate cycle activity to fasting and to
hyperinsulinemia in human subjects.
Wolfe, Robert R., David Chinkes, Hidefumi Baba, Judah Rosenblatt, and
Xiao-Jun Zhang.
Metabolism Unit, Shriners Burns Institute and University of Texas
Medical Branch, 815 Market Street, Galveston, Texas 77550
APStracts 3:0044E, 1996.
We have used a new isotopic tracer technique to investigate the
physiological role of the phosphoenolpyruvate (PEP) cycle in
metabolic adaptation to fasting and to hyperinsulinemia. The forward
direction of the PEP cycle is the conversion of oxaloacetate (OAA) to
PEP, and the net flux of the cycle is the rate at which PEP from OAA
goes on to form glucose or glycogen, as opposed to being recycled to
pyruvate, then OAA. Normal volunteers (n = 6) were studied after an
overnight fast and then again after three days of fasting, and five
additional subjects were studied during a hyperinsulinemic clamp
(insulin concentration = 568 +/- 25 _U/ml, glucose infusion = 14.2
+/- .55 mg/kg x min). After an overnight fast, 35.4 +/- 6.7% of PEP
from OAA was recycled to pyruvate/lactate. Short-term fasting caused
a significant increase in the conversion of OAA to PEP, and also a
drop in the percent PEP from OAA that went to pyruvate/lactate to
15.2 +/- 4.0%. The principal response to hyperinsulinemia was a
decrease in the recycling of OAA to lactate, as there was no
significant change in the conversion of OAA to PEP. We conclude that
changes in both directions of the PEP cycle are important in
regulating gluconeogenic/glycogeneogenic flux.
Received 2 October 1995; accepted in final form 19 February 1996.
APS Manuscript Number E483-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96