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Sustained endotoxemia leads to marked down-regulation of early steps in the insulin-signaling cascade.

Abstract：

OBJECTIVES:To determine the effects of sustained, 3-day endotoxin infusion on early steps of the insulin-signaling pathway in rat liver and skeletal muscle in vivo; to examine insulin signaling in well-established acute endotoxin models of insulin resistance. DESIGN:Prospective, controlled animal study. SETTING:University research laboratory. SUBJECTS:Male Sprague-Dawley rats: 24 in the 3-day endotoxin study, 22 in each acute endotoxin study. INTERVENTIONS:In prolonged endotoxemia studies, endotoxin (1 mg.kg-1.24 hrs-1) was administered via jugular venous catheter for 74 hrs. Insulin was then injected, and liver and skeletal muscle were removed after 5 mins. In acute endotoxemia studies, an endotoxin bolus (1 mg/kg) was administered, and insulin-signaling responses were studied after 4 hrs. MEASUREMENTS AND MAIN RESULTS:In liver of rats with sustained endotoxemia, there were significant decreases in insulin-stimulated tyrosine phosphorylation of insulin receptors (74%), insulin receptor substrate (IRS)-1 (74%), and IRS2 (53%); binding of the p85 subunit of phosphatidylinositide 3-kinase to IRS1 (80%); and IRS1-precipitable phosphatidylinositide 3-kinase activity (>90%). These findings were associated with significant reductions in abundance of insulin receptors (37%), IRS1 (60%), and IRS2 (23%). Signaling in skeletal muscle was similarly affected, with reduced IRS1 phosphorylation (49%), IRS1 abundance (50%), and binding of p85 to IRS1 (57%). Insulin signaling 4 hrs after endotoxin administration was not different from controls. CONCLUSIONS:Prolonged endotoxemia is associated with marked deficits in early steps of the insulin-signaling pathway, which are at least partly explained by reduced abundance of the insulin receptor and IRS proteins. Signaling defects were not evident 4 hrs after endotoxin administration under conditions of adequate nutrition, indicating that insulin resistance develops gradually, may require concomitant malnutrition, and is not reversed by the development of endotoxin tolerance.

journal_name

Crit Care Med

journal_title

Critical care medicine

authors

McCowen KC,Ling PR,Ciccarone A,Mao Y,Chow JC,Bistrian BR,Smith RJ

doi

10.1097/00003246-200104000-00032

subject

Has Abstract

pub_date

2001-04-01 00:00:00

pages

839-46

issue

eissn

0090-3493

issn

1530-0293

journal_volume

pub_type

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Sustained endotoxemia leads to marked down-regulation of early steps in the insulin-signaling cascade.