Which of the following regulates lipolysis in adipocytes?
|A||Activation of fatty acid synthesis mediated by cyclic AMP|
|B||Activation of triglyceride lipase as a result of hormone-stimulated increases in cyclic AMP levels|
|C||Glycerol phosphorylation to prevent futile esterification of fatty acids|
|D||Activation of cyclic AMP production by insulin|
increases in cyclic AMP levels
a. Lipolysis is directly regulated by hormones in adipocytes. Epinephrine stimulates adenylatecyclase to produce cyclic AMP, which in turn stimulates a protein kinase.
b. The kinase activates triglyceride lipase by phosphorylating it. Lipolysis then proceeds and results in the release of free fatty acids and glycerol.
c. A futile re esterification of free fatty acids is prevented, since adipocytes contain little glycerol kinase to phosphorylate the liberated glycerol, which must be processed in the liver.
d. Inhibition of lipolysis occurs in the presence of insulin, which lowers cyclic AMP levels. Lipoprotein lipase is not an adipocyte enzyme.