Vagal mediation of hypothalamic obesity but not of supermarket dietary obesity

Effects of subdiaphragmatic vagotomy on energy balance and thermogenesis in the rat

Subdiaphragmatic vagotomy caused chronic gastric distension and hypertrophy, and a reduction in voluntary food intake in rats fed a pelleted stock diet. These effects were minimized by feeding a more digestible semisynthetic diet. Vagotomized rats fed the pelleted diet showed lower rates of oxygen consumption than pair-fed controls, and the rise in metabolic rate (thermic response) following gastric intubation with a carbohydrate meal was diminished. This could be restored to normal by simultaneous injection of insulin. Thermic responses to fat and noradrenaline were normal in the vagotomized group. On the powdered semisynthetic diet, vagotomized rats gained more weight and showed greater efficiency of energy gain than pair-fed controls. The thermic response to a single meal of the semisynthetic diet was depressed in these vagotomized rats, but restored to normal by acute insulin treatment. The activity of the thermogenic proton conductance pathway in brown adipose tissue mitochondria (assessed from purine nucleotide binding) was reduced by vagotomy in animals on both diets, but was restored to normal by chronic insulin treatment, which also slightly raised brown fat activity in sham-operated rats. These results demonstrate that the reduced gastric activity and food intake following vagotomy is dependent on the digestibility and/or composition of the diet. When differences in food intake are abolished by pair feeding, vagotomy reduces thermogenic responses to carbohydrate, probably as a result of impaired insulin release. This may be responsible for the enhanced energetic efficiency and elevated weight and energy gains seen after vagotomy.