Influence of subdiaphragmatic vagotomy and brown fat sympathectomy on thermogenesis in rats.

Infusion of rats with insulin (8 U/day via implanted minipump) for 7 days caused a 22% rise in resting oxygen consumption, which was inhibited by acute injection of the beta-adrenergic antagonist propranolol. Insulin treatment produced significant increases in brown fat mass, protein content, and total thermogenic activity (assessed from binding of guanosine diphosphate to isolated brown fat mitochondria), but these responses were inhibited by prior surgical sympathectomy of the tissue. Animals subjected to subdiaphragmatic vagotomy gained more weight than pair-fed, sham-operated controls and showed reductions in total energy expenditure, the acute thermogenic response to a meal and brown adipose tissue activity. Daily injections of insulin (1 U/day) prevented all of these effects of vagotomy. These data demonstrate that the changes in brown fat activity induced by exogenous insulin are mediated by the sympathetic nervous system and that the depressed thermogenesis and brown fat activity associated with vagotomy appear to be due to a relative insulin deficiency and can be reversed by treatment with the hormone.