Influence of hepatic vagus nerve on pancreatic hormone secretion during exercise

There has been recent evidence that the liver through the hepatic vagus nerve may influence the resting levels of plasma insulin in adrenalectomized rats. The present investigation was designed to evaluate whether such a relationship exists during physical exercise. To this end, the effects of a selective hepatic vagotomy on portal and peripheral insulin and on peripheral glucagon concentrations were studied after a 30-min treadmill run (26 m/min, 0% grade) in adrenodemedullated rats. Hepatic vagotomy was associated with small but significantly higher (P < 0.05) levels of liver glycogen and blood glucose at rest and after exercise. No significant differences were observed between hepatic-vagotomized and sham-operated rats in resting insulin, glucagon, and plasma norepinephrine concentrations. Peripheral plasma insulin levels after exercise were significantly higher (P < 0.01) in hepatic-vagotomized than in sham-operated rats [172 ± 20 vs. 108 ± 10 (SE) pmol/l]. Exercise was also associated with a significantly lower peripheral glucagon (P < 0.01) and norepinephrine (P < 0.05) levels in hepatic-vagotomized compared with sham-operated rats. These results indicate a role for the hepatic vagus nerve in the regulation of pancreatic islet secretion during exercise, possibly by contributing to the increase in sympathetic activity.