ROLE FOR AUTONOMIC NERVOUS-SYSTEM TO INCREASE PANCREATIC GLUCAGON-SECRETION DURING MARKED INSULIN-INDUCED HYPOGLYCEMIA IN DOGS

To determine the role of the autonomic nervous system (ANS) in mediating the glucagon response to marked insulin-induced hypoglycemia in dogs, we measured arterial and pancreatic venous glucagon responses to insulin-induced hypoglycemia during acute, terminal experiments in halothane-anesthetized dogs in which the ANS was intact (control; n = 9), pharmacologically blocked by the nicotinic ganglionic antagonist hexamethonium (n = 6), or surgically ablated by cervical vagotomy and cervical spinal cord section (n = 6). In control dogs, insulin injection caused plasma glucose to fall by 4.4 +/- 0.2 mM to a nadir of 1.7 +/- 0.2 mM. Arterial epinephrine (EPI) levels increased by 13,980 +/- 1860 pM (P < 0.005), confirming marked activation of the ANS. Pancreatic output of glucagon increased from 0.53 +/- 0.12 to 2.04 +/- 0.38 ng/min during hypoglycemia (change [DELTA] +1.51 +/- 0.33 ng/min, P < 0.005). This increased arterial plasma glucagon from 27 +/- 3 to 80 +/- 15 ng/L (DELTA-+52 +/- 14 ng/L, P < 0.025). Hexamethonium markedly reduced the ANS response to insulin injection (DELTA-EPI +2130 +/- 600 pM, P < 0.025 vs. control) despite a similar fall of plasma glucose (DELTA -4.1 +/- 0.2 mM) and a lower nadir (0.6 +/- 0.1 mM). Both the pancreatic glucagon response ( glucagon output +0.45 +/- 0.24 ng/min) and the arterial immunoreactive glucagon response (DELTA +5 +/- 4 ng/L) were substantially reduced by hexamethonium (P < 0.025). Vagotomy plus spinal cord section totally abolished the arterial EPI response to insulin injection despite a larger fall of plasma glucose (DELTA -5.4 +/- 0.4 mM) and a lower nadir (0.9 +/- 0.2 mM). Again, both the pancreatic glucagon response (DELTA-glucagon output +0.27 +/- 0.23 ng min) and the arterial glucagon response (DELTA +5 +/- 2 ng/L) were significantly reduced (both P < 0.025 vs. control). We conclude that autonomic activation contributes to the glucagon response to marked insulin-induced hypoglycemia in dogs.