Effect of hepatic vagotomy on plasma catecholamines during exercise-induced hypoglycemia

The existence of a hepatosympathetic reflex active during insulin-induced hypoglycemia has recently been reported. The purpose of the present investigation was to test the hypothesis that the liver, through the afferent innervation of the vagus nerve, contributes to plasma epinephrine and norepinephrine responses during exercise-induced hypoglycemia. Hepatic vagotomized and sham-operated rats were killed at rest or after 30, 60, and 120 min of running exercise (26 m/min, 0% grade). At the end of the 120-min exercise period, liver glycogen, glucose, and insulin levels measured in the portal and peripheral plasma were all significantly reduced (P < 0.05) while epinephrine and norepinephrine concentrations, beta-hydroxybutyrate, lactate, and portal and peripheral glucagon plasma levels were all significantly increased (P < 0.05). However, no significant differences were observed between hepatic vagotomized and sham-operated rats at rest and after exercise for the metabolic and hormonal responses. These results suggest that if a hepatosympathetic reflex is active during an exercise-induced hypoglycemia situation, then this contribution is probably hidden by more important regulatory mechanisms.