The overall aim in this proposal is to elucidate both the physiological significance and the biochemical mechanism of the phosphatidyl inositol (PI) phosphatidic acid cycle in different test systems. Initially three model systems-the exocrine pancreas in response to caeruleim, brain cortex in response to acetylcholine (ACh), and pancreatic islets in response to high glucose - will be used to test the general validity of the hypothesis that PI breakdown is a prostaglandin (PG) generator, which in turn modulates agonist-evoked responses. We will also study in detail biochemical aspects of the PI effect in these systems. The basic technique will be prelabelling with [14C]arachidonic acid (AA), preferably under stimulating conditions, quenching with albumin and an antagonist of the first agonist (or washing), and finally incubating with a second agonist (or the first agonist after washing). The changes in radioactivity in all of the phospholipids, neutral lipids, and PGs will be determined (over 95% of total lipid radioactivity recovered) and a balance sheet drawn up. In this way, the flow of radioactivity from PI to other lipids and/or PGs can be determined. The contribution of phospholipase C and phospholipase A pathways to the release of AA and its metabolites will be determined. The putative stimulation of insulin secretion by aspirin-like drugs will be studied. The preliminary demonstration that triglyceride (TG) shows a massive release of AA on stimulation of brain cortex slices with ACh - associated with a marked increase in the formation of PGF2Alpha - will be further studied. The possible negative feedback of insulin secretion by PGs and the blockade of this negative feedback by aspirin-like drugs may be important in our understanding and treatment of Type II diabetes mellitus. Studies in brain cortex may throw light on Alzheimer's disease, which shows deficiency of ACh in brain cortex. Since the stimulated PGE2 formation from PI augments secretion in the exocrine pancreas by dilation of ducts, these studies may have implications for acute pancreatitis.
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