Response of liver glycogen synthase and phosphorylase to in vivo glucose and glucose analogues

F. Q. Nuttall, J. W. Theen, C. Niewoehner, D. P. Gilboe

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Glucose causes a rapid increase in the proportion (%) of glycogen synthase in the active (I) form and a rapid decrease in the proportion of phosphorylase in the active (a) form in both fed and fasted rats. The changes in synthase I and phosphorylase a are more rapid in fasted animals. With graded doses of glucose, the maximal decrease in phosphorylase a occurred at a dose that was considerably smaller than that required to maximally stimulate an increase in % synthase I. Thus, in the intact animal a dissociation between the effects of glucose on the synthase and lactose, and arabinose all stimulated an increase in synthase I but did not significantly affect the proportion of phosphorylase in the a form. The % synthase I was not significantly affected by a number of other glucose homologues, pentoses, or three-carbon gluconeogenic substrates. The ketoses fructose and mannoheptulose both caused a striking increase in % phosphorylase a and a decrease in % synthase I, i.e., results opposite to those of glucose. The mechanism by which fructose induces these changes is not known, but the mannoheptulose effects may be accounted for by a rise in liver cAMP concentration.

Original languageEnglish (US)
Pages (from-to)E521-E527
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number5
StatePublished - 1983

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