Involvement of the vagus nerves in the regulation of basal hepatic glucose production in conscious dogs

We determined if blocking transmission in the fibers of the vagus nerves would affect basal hepatic glucose metabolism in the 18-h-fasted conscious dog. A pancreatic clamp (somatostatin, basal portal insulin, and glucagon) was employed. A 40-min control period was followed by a 90-min test period. In one group, stainless steel cooling coils (Sham, n = 5) were perfused with a 37degreesC solution, while in the other (Cool, n = 6), the coils were perfused with -20degreesC solution. Vagal blockade was verified by heart rate change (80 +/- 9 to 84 +/- 14 beats/min in Sham; 98 +/- 12 to 193 +/- 22 beats/min in Cool). The arterial glucose level was kept euglycemic by glucose infusion. No change in tracer-determined glucose production occurred in Sham, whereas in Cool it dropped significantly (2.4 +/- 0.4 to 1.9 +/- 0.4 mg.kg(-1).min(-1)). Net hepatic glucose output did not change in Sham but decreased from 1.9 +/- 0.3 to 1.3 +/- 0.3 mg.kg(-1).min(-1) in the Cool group. Hepatic gluconeogenesis did not change in either group. These data suggest that vagal blockade acutely modulates hepatic glucose production by inhibiting glycogenolysis.