Metabolic fates of isovaleric acid and isovalthine in rats

1. Isovaleric acid-1-C14, -4-C14, or C14-CaC03 with or without non-isotopic isovaleric acid was orally administered to rats and the incorporation of these isotopes into liver cholesterol, fatty acid, or urinary isovalthine was examined. 2. Isopropyl group of isovaleric acid was more efficiently utilized for cholesterol synthesis than carboxyl group, and also for cholesterol synthesis than for fatty acid. These results indicate that isovaleric acid is cleaved into two fragments before it is utilized for cholesterol synthesis. 3. Carbon dioxide was used for the synthesis of liver cholesterol and of liver fatty acid. Isovaleric acid seems to enhance the incorporation of carbon dioxide into cholesterol. 4. All the experimental rats received isotopic or non-isotopic isovaleric acid excreted isovalthine, but no radioactivity was found in it. Thus, isovaleric acid residue of urinary isovalthine molecule is not derived from isovaleric acid administered, and carbon dioxide is not the carbon source of urinary isovalthine. 5. Suspicious metabolism of isovaleric acid or of carbon dioxide was discussed. 6. Isotopic isovalthine which was synthesized from (± ) α-bromoisovaleric acid-4-C14 is administered to rat and it was found that the isotope did not incorporate into cholesterol or fatty acid of liver and of brain. About 15% of isotopic isovalthine was recovered in urine up to the next day after injection. The large part of isovalthine was missing.