title: The exchange between proglycogen and macroglycogen and the metabolic role of the protein-rich glycogen in rat skeletal muscle.
abstract: The aim of this study is to determine if proglycogen and macroglycogen are kinetically related in rat skeletal muscle. Eight groups of anesthetized fasted rats (seven hepatic-occluded and one nonoccluded) were intravenously infused with [3-3H]glucose at a rate of 1.7 microCi x min(-1) for 20 min. At the end of infusion, hindlimb muscles were excised and rapidly frozen in liquid nitrogen. Proglycogen was extracted by precipitation in 10% TCA; and macroglycogen as a part of total glycogen by precipitation in 20% KOH-65% ethanol. Along with the tracer, the occluded rats were also infused with: saline (group 1); insulin at rates ranging from 5 to 50 mU x min(-1) (groups 2 to 5); and insulin at a rate of 10 mU x min(-1) plus glucose at rates of 10.2 and 20.4 micromol x min(-1), respectively (groups 6 and 7). The infusion regimens resulted in up to 30-fold difference in whole-body glucose utilization among the rats. In the rats infused with saline and insulin at a rate of 5 mU x min(-1), [3H]glucose was found to be exclusively incorporated into proglycogen. Incorporation into macroglycogen was found in the rats infused with insulin at rates > 10 mU x min(-1). Supplementary glucose infusion increased the synthesis of [3H]proglycogen (four- to sixfold), and equilibrated the two extractable forms of glycogen in the insulin-infused rats. In the saline-infused nonoccluded rats, only proglycogen was found to be labeled. In conclusion, our data indicate that in the intact and hepatic-occluded rats, proglycogen in the skeletal muscles may undergo synthesis and degradation of its own more readily than exchange between itself and depot macroglycogen.
authors.affiliation: Department of Biochemistry, Chang Gung College of Medicine and Technology, Kwei-san, Tao-yuan, Taiwan. mthuang@cguaplo.cgu.edu.tw
authors.forename: M
authors.initials: M
authors.lastname: Huang
authors.forename: C
authors.initials: C
authors.lastname: Lee
authors.forename: R
authors.initials: R
authors.lastname: Lin
authors.forename: R
authors.initials: R
authors.lastname: Chen
mesh_terms: D000818:Animals; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006003:Glycogen / Q000032:analysis / Q000145:classification / Q000378:metabolism*; D006614:Hindlimb / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008099:Liver / Q000098:blood supply; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010949:Plasma / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D006003:Glycogen; D005947:Glucose