NUTRITIONAL-STATUS INFLUENCES THE INSULIN-RESPONSE PRODUCED BY ACUTE HEPATIC VAGOTOMY

It has been established that the liver, through the afferent pathway o f the vagus nerve, can influence insulin secretion. The purpose of the present study was to determine if this influence can be altered by di fferent nutritional status aimed at inducing metabolic changes in the liver. This was carried out by comparing the insulin response 30 min a fter sectioning of the hepatic vagus branch in five experimental condi tions: a normal (NCD) and a medium-fat diet (MFD) for 3 weeks, both wi th and without an overnight fast, and after an overloading liver glyco gen protocol (normal diet). All experiments were conducted using anest hetized, adrenodemedullated rats. Blood was collected before and after (30 min) the hepatic vagotomy (HV) or a sham operation (SHM). As expe cted, liver glycogen levels were significantly (p < 0.01) lower in the fasted than in the fed condition, and were approximately 50% higher ( p < 0.01) in the overloaded than in the normally fed condition. Basal insulin concentrations were also lower (p < 0.01) in the fasted compar ed to the fed groups, but were significantly (p < 0.01) increased by t he medium-fat diet. Plasma glucose levels were significantly (p < 0.01 ) decreased by the overnight fast, but were not affected by the hepati c vagotomy. Plasma catecholamine concentrations were similar in all ex perimental conditions. Insulin concentrations were significantly (p < 0.05) increased by the HV, compared to SHM rats, in all experimental c onditions (from 50% to 75%). The extent of this response was altered b y the diet manipulations as the HV-induced insulin increase was greate r (p < 0.01) in the MFD than in the NCD groups, whether fed or fasted. Furthermore, and contrary to our expectations, high hepatic glycogen contents did not reduce the insulin response to an acute hepatic vagot omy. These results indicate that the insulin increase induced by an ac ute HV is influenced by the prevailing metabolic conditions, and sugge st that the hepatic vagus nerve exerts a constant inhibition on insuli n secretion, independently of the hepatic glycogen content.