A role for vagal activity in preventing the suppression of glucagon secretion by GLP-1 during hypoglycemia.

Abstract

Glucagon-like peptide 1 (GLP-1) is generally safe against hypoglycemia, although it stimulates insulin and inhibits glucagon secretion. One explanation is that glucagon secretion is not inhibited by GLP-1 during hypoglycemia. We aimed at understanding the lack of suppression of glucagon secretion by GLP-1 by exploring the paracrine and neural regulation of pancreatic hormone secretion during hypoglycemia. Isolated rat pancreas (A) and an organ block comprising pancreas and stomach (B) were perfused. We performed 1) dose-response studies with GLP-1 (7-36) at hypoglycemia; 2) studies with GLP-1 (7-36) with and without blockage of somatostatin (SST) activity (with SST receptor antagonists); 3) and 4) dose-response experiments with acetylcholine at euglycemia and studies under hypoglycemia; and 5) finally, we studied the role of cholinergic signaling for modulation of GLP-1 activity under hypoglycemia. We measured glucagon, SST, and insulin levels. The secretion of SST was dependent on surgical preparation (A or B, P = 0.0006) and on cholinergic stimulation (P < 0.0001), rather than on glucose levels (P > 0.05). The infusion of SSTR antagonists in the isolated perfused rat pancreas blocked the paracrine effects of SST (P = 0.0041) and stimulated glucagon secretion (P = 0.0023). Cholinergic activity stimulated glucagon secretion during hypoglycemia through suppression of SST secretion. Cholinergic signaling delivered through the gastric intramural autonomic ganglia and/or vagus nerve efferents to the pancreas appears to be crucial for preventing GLP-1-induced inhibition of glucagon secretion during hypoglycemia.NEW & NOTEWORTHY Autonomic signaling suppresses somatostatin secretion, crucial for paracrine stimulation of glucagon secretion. SST mediates GLP-1-induced inhibition of glucagon secretion, but autonomic signaling may interfere with this mechanism. Activation of cholinergic pathways in a preparation with prepancreatic parasympathetic structures suppresses SST secretion in response to GLP-1 and potentiates glucagon secretion during hypoglycemia. These findings support the clinical importance of autonomic signaling in regulating pancreatic hormone secretion and hypoglycemia risk in some patients on GLP-1 receptor agonists.