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Brain insulin action augments hepatic glycogen synthesis without suppressing glucose production or gluconeogenesis in dogs
Christopher J. Ramnanan, … , Alan D. Cherrington, Dale S. Edgerton
Christopher J. Ramnanan, … , Alan D. Cherrington, Dale S. Edgerton
Published August 25, 2011
Citation Information: J Clin Invest. 2011;121(9):3713-3723. https://doi.org/10.1172/JCI45472.
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Research Article

Brain insulin action augments hepatic glycogen synthesis without suppressing glucose production or gluconeogenesis in dogs

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Abstract

In rodents, acute brain insulin action reduces blood glucose levels by suppressing the expression of enzymes in the hepatic gluconeogenic pathway, thereby reducing gluconeogenesis and endogenous glucose production (EGP). Whether a similar mechanism is functional in large animals, including humans, is unknown. Here, we demonstrated that in canines, physiologic brain hyperinsulinemia brought about by infusion of insulin into the head arteries (during a pancreatic clamp to maintain basal hepatic insulin and glucagon levels) activated hypothalamic Akt, altered STAT3 signaling in the liver, and suppressed hepatic gluconeogenic gene expression without altering EGP or gluconeogenesis. Rather, brain hyperinsulinemia slowly caused a modest reduction in net hepatic glucose output (NHGO) that was attributable to increased net hepatic glucose uptake and glycogen synthesis. This was associated with decreased levels of glycogen synthase kinase 3β (GSK3β) protein and mRNA and with decreased glycogen synthase phosphorylation, changes that were blocked by hypothalamic PI3K inhibition. Therefore, we conclude that the canine brain senses physiologic elevations in plasma insulin, and that this in turn regulates genetic events in the liver. In the context of basal insulin and glucagon levels at the liver, this input augments hepatic glucose uptake and glycogen synthesis, reducing NHGO without altering EGP.

Authors

Christopher J. Ramnanan, Viswanathan Saraswathi, Marta S. Smith, E. Patrick Donahue, Ben Farmer, Tiffany D. Farmer, Doss Neal, Philip E. Williams, Margaret Lautz, Andrea Mari, Alan D. Cherrington, Dale S. Edgerton

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Figure 1

Plasma insulin and glucagon concentrations in dogs subjected to the i.c.v. insulin protocol.

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Plasma insulin and glucagon concentrations in dogs subjected to the i.c....
As illustrated above the graphs, 18-hour fasted conscious dogs received peripheral infusion of somatostatin (SRIF) and were maintained on a pancreatic clamp at basal levels of hepatic insulin and glucagon, then exposed to i.c.v. infusion of either aCSF or aCSF plus insulin. (A) Arterial plasma insulin. (B) Hepatic sinusoidal plasma insulin. (C) Arterial plasma glucagon. (D) Hepatic sinusoidal plasma glucagon. Values are mean ± SEM. n = 5 per group.

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