Prostaglandins inhibiting lipolysis

At least seven hormones, including ACTH, epinephrine, and glucagon, attack the adipose tissue and lead to the breakdown of triglycerides to yield free glycerol and fatty acids. After each hormone has attached to its own specific receptor, they all act through a common mechanism—the stimulation of adenyl cyclase— with proportionate elaboration of cAMP. The cAMP activates the lipase, possibly by phosphorylation of the enzyme. Insulin and certain prostaglandins inhibit lipolysis and decrease the level of cAMP in the cell. In contrast, theophylline and caffeine inhibit the phosphodiesterase and thereby increase lipolysis in the fat cells (see Fig. 8-35). 

K. R. Feingold, W. Doereler, C.A. Di-narello, W. Fiers, and C. Gruneeld, Stimulation of lipolysis in cultured fat cells by tumor necrosis factor, interleukin-1, and the interferons is blocked by inhibition of prostaglandin synthesis, Endocrinology, 1992, 130, 10-16. 

Some hormones inhibit adenylate cyclase activity. Such molecules depress cellular protein phosphorylation reactions because their receptors interact with G, protein. When Gi is activated, its ( subunit dissociates from the /fydimer and prevents the activation of adenylate cyclase. For example, because its receptors in adipocytes are associated with G PGK, (prostaglandin H,) depresses lipolysis. (Recall that lipolysis is stimulated by glucagon and epinephrine.)... 

Strong, P., Coleman, R.A., Humphrey, P.P. 1992. Prostanoid-induced inhibition of lipolysis in rat isolated adipocytes probable involvement of EP3 receptors. Prostaglandins 43 559-566. 

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