METABOLISM OF BRAIN SPHINGOMYELINS: HALF‐LIVES OF SPHINGOSINE, FATTY ACIDS AND PHOSPHATE FROM TWO TYPES OF RAT BRAIN SPHINGOMYELIN

Abstract

Abstract— The metabolism of rat brain sphingomyelins containing short‐chain (C16‐C18) and long‐chain (C20‐ C24) fatty acids has been studied by determination of the content of radioactivity in the sphingo‐sinc. fatty acids and phosphate of the sphingomyelins over a period of 60 days following the intracisternal injection of [14C]acetate and [32P]phosphate. From the rate of decrease of the specific radioactivities of the different constituents of short‐chain fatty acid sphingomyelins, we have calculated a half‐life of 65 days for sphingosine. 41 days for fatty acids and 62 days for phosphate. For the long‐chain fatty acid sphingomyelins the half‐life of sphingosine was approximately 465 days. The fatty acids and phosphate from these sphingomyelins had fast and slow turnover pools. The half‐life for the fast pool was 7 days for the two constituents and the estimated half‐lives for the slow pool were 220 days for fatty acids and 480 days for phosphate.These results suggest that one can distinguish at least three metabolic pools of brain sphingomyelins: (a) sphingomyelins with long‐chain fatty acids situated in myelin whose half‐lives are 465 days for sphingosine, 220 days for fatty acids and 480 days for phosphate; (b) sphingomyelins with long‐chain fatty acids located mainly in non‐myelin structures having half‐lives of 465 days for sphingosine. 7 days for fatty acids and 7 days for phosphate; (c) sphingomyeiins with short‐chain fatty acids with half‐lives of 65 days for sphingosine. 41 days for fatty acids and 62 days for phosphate. The differences between the half‐lives of the three metabolic pools of sphingomyelin, together with the subcellular localizations of the two molecular species of these compounds, suggest that the metabolism of the different molecular species of sphingomyelin are independent and that in various subcellular fractions the long‐chain fatty acid and short‐chain fatty acid sphingomyelins have different turnover rates.