The hepatic vagus nerve in the control of insulin sensitivity in the rat

Abstract

The objective was to determine if the cervical vagus or hepatic branch of the vagus nerve is a suitable site to produce functional parasympathetic denervation of the liver in the rat as assessed from the ability to produce insulin resistance. Anterior plexus denervation in both anesthetized rats and cats results in insulin resistance as assessed by the rapid insulin sensitivity test (RIST). This diagnostic test is a modified euglycemic clamp using the amount of glucose required to be infused to maintain euglycemia following a bolus administration of insulin (50 mU kg −1 over 5 min, 0.1 ml min −1 infusion) as the index of insulin sensitivity. Blood sampling was achieved through an arteriovenous silicone vascular shunt connecting the left carotid artery and the right jugular vein and allowed the close monitoring of blood glycemia throughout the test (every 2 min). The control RIST index (249.2±10.2 mg kg −1) was significantly decreased ( P<0.001) following hepatic vagotomy (134.0±13.9). The intraportal infusion of 2.5 μg kg −1 min −1 of acetylcholine partially reversed (202.1±12.3) the insulin resistance. Intravenous atropine (1 mg kg −1) or hepatic anterior plexus denervation did not produce significant further insulin resistance. A similar degree of insulin resistance was produced by bilateral cervical vagotomy which was also partially reversed by acetylcholine. Complete hepatic parasympathetic denervation was achieved by selective hepatic vagal branch section. The data suggest that all of the parasympathetic nerves that regulate hormonal control of insulin resistance pass through the cervical vagus and the hepatic branch, and finally, through the anterior hepatic plexus along the common hepatic artery and that denervation at any of these sites leads to functional elimination of all hepatic parasympathetic input regulating insulin sensitivity. This approach provides an additional research tool to study the hepatic parasympathetic reflex control of peripheral insulin action.