Quantitative and qualitative analyses of isolated lipid droplets from interstitial cells in renal papillae from various species

The lipid droplets of renal papillae homogenates from four different species were obtained by ultracentrifugation. Ca. 80–98% of the lipids (triglycerides, phospholipids, free fatty acids, and cholesterol esters) consist of triglycerides. The triglycerides were fractionated by argentation thin layer chromatography and each fraction characterized by gas liquid chromatography. No fraction contained any unique triglyceride. The fatty acid composition of the total triglycerides, as analyzed by gas liquid chromatography and ozonolysis, differed markedly from the fatty acid composition of the corresponding plasma triglycerides. The papillary triglycerides were characterized by higher concentrations of stearic acid, arachidic acid, and polyunsaturated acids with 20 or more carbon atoms. Particularly interesting was the presence in the lipid droplets of docosa-7,10,13,16-tetraenoic acid. This acid has been shown to be a major component in the cholesterol ester fraction of rat and canine adrenal lipids. In the papillary triglycerides, this acid accounted for 7%, 15%, and more than 20% of the total fatty acids in the dog, rat, and rabbit, respectively. The pig differs from these three species in having only ca. 1% of this acid. These observations suggest that the interstitial cells produce these triglycerides. This production could occur either by a transacylation from phospholipids and cholesterol esters and by a de novo synthesis from locally produced fatty acids. The possibility that the triglyceride production may be involved in a control of the prostaglandin production of the renal medulla is discussed.