Mechanism of actions of adrenaline and ACTH in fat mobilization.

Starvation did not cause increase of hormone-sensitive lipase in rat epididymal adipose tissue. Adrenaline did not activate lipase in the fat cells, although it accelerated the release of free fatty acids from the cells. The results suggest that the mechanism of the stimulation of lipolysis by adrenaline is different from that in the cyclic AMP theory. Adrenaline-sensitive fat globules were prepared by hypotonic treatment of fat cells. Lipolysis in the fat globules was stimulated by adrenaline. It was shown that adrenaline-induced lipolysis in the fat globules was not due to activation of lipase but to initiation of a reaction between lipase and triglyceride. It is well known that calcium ions are essential for ACTH-induced lipolysis and that the hormone stimulates calcium uptake into adipose tissue. It was demonstrated that calcium ions accelerated formation of a complex between fat and lipase. The mechanism of the actions of adrenaline and ACTH are discussed on the basis of these results.