An Epinephrine-sensitive Lipolytic Activity in Adipose Tissue* 7

Adipose tissue has two principal functions: to store excess nutrients as fat, and to release fatty acids on demand. These processes are controlled by the concentration of nutrients in the circulation, by the secretion of various hormones, and by nervous stimuli (2). The purpose of the work to be described was to investigate the mechanism which controls the release of fatty acids from adipose tissue. The intact animal fed with glucose or injected with insulin releases fatty acids from its adipose tissue at a reduced rate (3). An isolated piece of adipose tissue responds in a similar manner when glucose or insulin is added to the incubation medium (4) ; the release of fatty acids from the tissue is reduced or abolished, and the tissue takes up an increased amount of glucose. Conversely, starvation, which stimulates the release of fatty acids from adipose tissue, inhibits the uptake of glucose. These observations seem to indicate that the release of fatty acids from adipose tissue results from a decrease in the uptake and utilization of glucose. This theory, however, fails to explain the action of epinephrine, which stimulates fatty acid release and also stimulates glucose uptake (5). Fatty acids in adipose tissue are stored almost exclusively as esters (triglycerides) (6), but are released only as nonesterified fatty acids. Therefore, lipolysis is an essential step in the release process. It seems likely that one of the factors that regulates fatty acid release would be a lipase. Control could be exerted by the activation and inactivation of this lipase. The work to be presented demonstrates the presence in adipose tissue of a lipolytic system with these properties.