Role of enhanced arachidonate availability through phospholipase A2 pathway in mediation of increased prostaglandin synthesis by glomeruli from diabetic rats.

Abstract

Prostaglandin E2 (PGE2) production by superfused glomeruli from rats made diabetic for 2 wk by streptozocin injection is twofold higher than that by glomeruli from normal rats. The higher rates of PGE2 production by glomeruli from diabetic rats are associated with higher levels of labeled free arachidonate in glomeruli prelabeled with [3H]arachidonate, both basally and after stimulation with Ca2+ ionophore A23187. The difference between release of labeled arachidonate from phospholipids of diabetic versus normal glomeruli is likely underestimated by measurements of arachidonate alone due to more rapid incorporation of released arachidonate into triacylglycerol of diabetic glomeruli. A23187 induced a fall in labeled phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol in glomeruli that had been prelabeled with [3H]arachidonate and also induced a reduction in the mass of these phospholipids. Consistent with the higher levels of labeled arachidonate, the reduction in both labeled phospholipids and phospholipid mass with A23187 was greater in glomeruli from diabetic than normal rats. Furthermore, the reduction in labeled phospholipids and phospholipid mass with A23187 was largely (62-80%) accounted for by a fall in phosphatidylcholine plus phosphatidylethanolamine in glomeruli from both normal and diabetic rats. These results suggest a primary role for phospholipase A2 in A23187 actions on glomerular arachidonate release in normal rats and for the higher levels of arachidonate found in glomeruli from diabetic rats. Nevertheless, A23187 also stimulated the production of inositol phosphates--a measure of cellular phospholipase C activity.(ABSTRACT TRUNCATED AT 250 WORDS)