The role of the sympathetic nervous system in the metabolism of free fatty acids

Norepinephrine and epinephrine increased circulating levels of free fatty acids in humans and dogs. The increase was sustained in dogs during infusion of norepinephrine, but transient during epinephrine infusion, which also increased plasma sugar concentration. Anxiety or discomfort in humans and decrease in depth of pentobarbital anesthesia in dogs were accompanied by increased free fatty acid concentration, whereas ganglionic blockade with hexamethonium in dogs resulted in a prompt and sustained fall. In intact and adrenalectomized dogs receiving constant infusions of palmitic acid-1-C14, the decrease in free fatty acid concentration following hexamethonium was shown to result from a reduction in the rate at which they were added to plasma. Only a slight additional reduction was produced by insulin. The effects of norepinephrine and epinephrine on free fatty acid concentration were readily demonstrated during ganglionic blockade, whereas peripheral adrenergic blockade with dibenamine inhibited the response to these amines. The response of free fatty acids to sympathetic amines was also diminished in adrenalectomized dogs maintained with desoxycorticosterone alone. The concept is proposed that the sympathetic nervous system exerts a tonic action on the mobilization of fatty acids from adipose tissuc which may be altered by central stimuli as well as by hormonal factors.