Subcellular Localization of the Prostaglandin System in the Rabbit Renal Papilla

Abstract

Abstract The occurrence of prostaglandins (PG), prostaglandin precursor acids, prostaglandin synthetase and 15‐hydroxy prostaglandin dehydrogenase was studied in subcellular fractions isolated from homogenates of rabbit renal papilla by sucrose density gradient centrifugation. The investigated fractions were lipid droplets, supernatant, microsomes and mitochondria as verified by electron microscopy. Most of the prostaglandins was found to be prostaglandin E 2 and was present in the supernatant whereas the prostaglandin synthetase occurred most abundantly in the microsomal fraction.‐Nearly all of the recovered prostaglandins were formed during the preparation of the subcellular fractions. Arachidonic acid was the major esterified C 20 acid and had the highest relative concentrations in the supernatant, microsomes, and mitochondria, whereas the lipid droplets had lower concentrations. No detectable 15‐hydroxy prostaglandin dehydrogenase was present in the supernatant fraction of the papilla. The results indicate that in the rabbit renal papilla prostaglandin E2 is formed mainly from locally available arachidonate in membranes which sediment in the microsomal fraction and which may be derived from either cell membranes or membranes of the endoplasmic reticulum. After their formation the prostaglandins are probably released into the cytoplasm of the cells rather than being concentrated within specific subcellular particles and may leave the papilla without undergoing metabolic inactivation.