Abnormal regulation of HGP by hyperglycemia in mice with a disrupted glucokinase allele

Luciano Rossetti, Wei Chen, Meizhu Hu, Meredith Hawkins, Nir Barzilai, Shimon Efrat

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

Glucokinase (GK) catalyzes the phosphorylation of glucose in β-cells and hepatocytes, and mutations in the GK gene have been implicated in a form of human diabetes. To investigate the relative role of partial deficiencies in the hepatic vs. pancreatic GK activity, we examined insulin secretion, glucose disposal, and hepatic glucose production (HGP) in response to hyperglycemia in transgenic mice 1) with one disrupted GK allele, which manifest decreased GK activity in both liver and β-cells (GK+/-), and 2) with decreased GK activity selectively in β-cells (RIP-GKRZ). Liver GK activity was decreased by 35-59% in the GK+/but not in the RIP-GKRZ compared with wild type (WT) mice. Hyperglycemic clamp studies were performed in conscious mice with or without concomitant pancreatic clamp. In all studies [3-3H]glucose was infused to measure the rate of appearance of glucose and HGP during 80 min of euglycemia (Glc ~5 mM) followed by 90 min of hyperglycemia (Glc ~17 mM). During hyperglycemic clamp studies, steady- state plasma insulin concentration, rate of glucose infusion, and rate of glucose disappearance (R(d)) were decreased in both GK+/- and RIP-GKRZ compared with WT mice. However, whereas the basal HGP (at euglycemia) averaged ~22 mg·kg-1·min-1 in all groups, during hyperglycemia HGP was suppressed by only 48% in GK+/- compared with ~70 and 65% in the WT and RIP- GKRZ mice, respectively. During the pancreatic clamp studies, the ability of hyperglycemia per se to increase R(d) was similar in all groups. However, hyperglycemia inhibited HGP by only 12% in GK+/-, vs. 42 and 45%, respectively, in the WT and RIP-GKRZ mice. We conclude that, although impaired glucose-induced insulin secretion is common to both models of decreased pancreatic GK activity, the marked impairment in the ability of hyperglycemia to inhibit HGP is due to the specific decrease in hepatic GK activity.

Original languageEnglish (US)
Pages (from-to)E743-E750
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume273
Issue number4 36-4
DOIs
StatePublished - 1997

Keywords

  • Gluconeogenesis
  • Glucose cycling
  • Glycogen
  • Maturity-onset diabetes of the young
  • Transgenic mice

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

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