The production and release of glycerol by adipose tissue incubated in vitro.

Lipolysis of triglycerides goes on constantly in adipose tissue producing glycerol and free fatty acids. The fatty acids can be activated and reesterified. Glycerol, on the other hand, is not metabolized to any significant extent (1-3). Glycerokinase, the enzyme that catalyzes the formation of a-glycerophosphate from glycerol and adenosine triphosphate, is apparently absent and glycerol is not converted to a-glycerophosphate for use in triglyceride synthesis (4, 5). When adipose tissue is incubated in vitro, glycerol is released into the medium (3, 6,7), along with free fatty acids when the medium contains albumin. Whereas net changes in the amount of free fatty acids in such a system represent the difference between the amount formed by lipolysis and the amount reesterified, it is probable that the accumulation of glycerol is a reflection of the rate of lipolysis. In the experiments reported below the relationship between glycerol release and free fatty acid (FFA)’ release was determined under differing conditions making it possible to draw certain inferences concerning qualitative changes in the rates of lipolysis and/or esterification. In some experiments the concentrations of FFA and of glycerol in the tissue also were determined. In the latter studies, by making certain assumptions discussed below, the rate of esterification of FF.4 has been calculated.