Interleukin-6 Enhances Glucagon Secretion: Amplification via the Pancreas and Brain

Abstract

Inappropriate glucagon secretion contributes to hyperglycemia in inflammatory disease. Previous work implicates the pro-inflammatory cytokine, interleukin-6 (IL-6), in glucagon secretion. IL-6 knock-out mice have a blunted glucagon response to lipopolysaccharide (LPS) that is restored by intravenous replacement of IL-6. Given that IL-6 has previously been demonstrated to have a transcriptional (i.e. slow) effect on glucagon secretion from islets, I hypothesized that the rapid increase in glucagon following LPS occurred by a faster mechanism such as by action within the brain. Using chronically catheterized, conscious mice, it was found that central IL-6 stimulates glucagon secretion uniquely in the presence of an accompanying stressor (hypoglycemia or LPS). Contrary to the original hypothesis, however, IL-6 was found to amplify glucagon secretion in two ways: IL-6 not only stimulates glucagon secretion via the brain but also by direct action on islets. Interestingly, IL-6 augments glucagon secretion from both sites only in the presence of an accompanying stressor (such as epinephrine). Given that both adrenergic tone and plasma IL-6 are elevated in multiple inflammatory diseases, the interactions of the IL-6 and catecholaminergic signaling pathways in regulating GCG secretion may contribute to our present understanding of these diseases.