Effect of Glucagon on the Metabolism of Adipose Tissue*

In previous studies (1) it was found that adrenaline had a marked stimulatory action upon the respiration of rat epididyma1 adipose tissue in vitro. In view of the many similarities between the metabolic actions of adrenaline and of glucagon it was of interest to study the action of glucagon upon the metabolism of adipose tissue in vitro. Glucagon is now known to cause the release of free fatty acids from adipose tissue in U&O (2) and to activate phosphorylase in adipose tissue (2, 3); it has been suggested that its lipolytic activity is related to its action on phosphorylase (3, 4). In addition, glucagon increases glucose uptake by adipose tissue (2, 5), although there is still some doubt whether this effect is characteristic of glucagon or is an effect of insulin contamination (5). Also, qlucagon has been reported to increase the oxygen uptake of adipose tissue incubated with glucose, succinate, and acetate (6) and to decrease the incorporation of acetate-l-U4 into adipose tissue lipid (6). Glucagon is known to influence both carbohydrate and fat metabolism in other tissues in vitro. Fatty acid synthesis from acetate (7) and from glucose (8, 9) by liver slices is inhibited by glucagon, and fatty acid oxidation is increased, as indicated by increased ketone body formation (8, 10). In the experiments to be reported it is shown that glucagon increases the oxygen consumption of adipose tissue. Glucose is required for this effect of glucagon and the stimulation of glucose uptake parallels the stimulation of oxygen consumption. In addition glucagon causes a simultaneous release of free fatty acids and glycerol from tissue incubated in the absence of glucose. A preliminary report of some of this work has been made (11).