Our objective is to study the regulation of prostacyclin (PGI2) production in the isolated adipocyte of the normal and diabetic organism. We recently showed (a) that isolated rat adipocytes produce PGI2 in large quantities during norepinephrine-induced lipolysis, (b) that insulin inhibits this production, (c) that high levels of stable derivatives of PGI2 and PGE2 circulate in patients and in rats with diabetic ketoacidosis (DKA), (d) that the adipocyte is an important source of these derivatives, and (e) that insulin inhibits the production of these derivatives. Increased PGI2 production may mediate important hemodynamic and gastrointestinal features of DKA. Although decreased PGI2 production by endothelium and increased thromboxane A2 production by platelets may promote diabetic vascular disease, any valid model of prostaglandins in diabetics may also consider PGI2 production by adipocytes. We propose (and have tested) a model that accounts for all these findings. Studies of PGI2 production in the adipocyte is important because (a) this cell appears to be one of the major sources (along with endothelium) of this highly potent substance in the body, (b) any valid model of the pathogenesis of DKA and diabetic vascular disease must consider PGI2 production by the adipocyte, (c) such investigations can serve as a model for understanding the effects of insulin on prostaglandin synthesis in other target cells such as platelets, and (d) these studies can thereby provide the molecular basis for understanding the role of protaglandins in DKA and diabetic vascular disease.
Our specific aims are as follows: 1) To explore the mechanism of hormone-induced production of PGI2 (and PGE2 and PGF2Alpha where appropriate) in the isolated rat adipocyte, with emphasis on (a) the cellular site of origin of the arachidonic acid that serves as precursor for synthesis of PGI2 and other prostaglandins, (b) the identity of the adrenergic receptor that mediates norephinephrine-induced prostaglandin production (c) the role of cAMP, (d) the effect of calcium, (e) the possible role of the phospholipase inhibitory protein, and (f) the mechanism by which insulin inhibit PGI2 production; 2) to define the hormonal regulation of arachidonic acid and PGI2 metabolism in the adipocyte, with emphasis on hormones known to regulate lipolysis, such as glucocorticoids; 3) to explore these questions in adipocytes from normal rats and rats with experimental diabetes and DKA; and 4) to pursue these questions in human adipocytes from normal and diabetic subjects.
