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1 Gifford Laboratories for Diabetes Research and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75235; and 2 Department of Pathology and Pharmacology, University of Washington, Seattle, Washington 98195
The effect of
moderate hyperleptinemia (~20 ng/ml) on liver and skeletal muscle
glycogen metabolism was examined in Wistar rats. Animals were studied
~90 h after receiving recombinant adenoviruses encoding rat leptin
(AdCMV-leptin) or
-galactosidase (AdCMV-
Gal). Liver and skeletal
muscle glycogen levels in the fed and fasted (18 h) states were similar
in AdCMV-leptin- and AdCMV-
Gal-treated rats. However, after delivery
of a glucose bolus, liver glycogen levels were significantly greater in
AdCMV-leptin compared with AdCMV-
Gal rats
(P < 0.05). To investigate the
mechanism(s) of these differences, glycogen levels were measured
immediately after the cessation of a 3- or 6-h glucose infusion or 3, 6, and 9 h after the cessation of a 6-h glucose infusion. Similar
increases in liver and skeletal muscle glycogen occurred in
hyperleptinemic and control rats in response to glucose infusions.
However, 3 and 6 h after the cessation of a glucose infusion, liver
glycogen levels were approximately twofold greater
(P < 0.05) in AdCMV-leptin-treated compared with AdCMV-
Gal-treated animals. Skeletal muscle glycogen levels were similar in AdCMV-leptin-treated and AdCMV-
Gal-treated animals at the same time points. Glycogen phosphorylase,
phosphodiesterase 3B, and glycogen synthase activities were unaltered
by hyperleptinemia. We conclude that moderate increases in plasma
leptin levels decrease liver glycogen degradation during the
fed-to-fasted transition.
glucose metabolism; metabolic regulation
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