Metabolism of labeled dihydrosphingomyelin in vivo.

Tritiated dihydrosphingomyelin was injected into rats, and after various time intervals the distribution of radioactivity in various organs and in the blood and urine was determined. The rate of catabolism of the administered dihydrosphingomyelin was relatively rapid, since about one-fifth of the tritium was recovered as body water after 6 hr. The liver appeared to be the principal site of metabolism of injected dihydrosphingomyelin, although other tissues were also labeled. The radioactive lipids were extracted from each organ and fractionated by chromatography. The tritium label was found in diminishing amounts in the sequence dihydrosphingomyelin, dihydroceramide, dihydrosphingosine, which suggests that the catabolism of dihydrosphingomyelin proceeds in that sequence. An extensive incorporation of label into lipids other than sphingolipids was also observed.