|| <p>1. For the settlement of carbon origin of urinary isovalthine, acetic acid-2-C14, valine-U-C14 or leucine-U-C14 was administered to rats together with isovaleric acid as an isovalthinuria inducer, and urinary isovalthine
excreted was tested by autoradiography. As the results of which, it was found that these isotopic compounds were not the precursor of urinary isovalthine. Although the isovalthinuria inducing effect of isovaleric acid was fairly diminished by these isotopic compounds, urinary isovalthine was detected by paper electrophoresis.
2. Some metabolic products of these isotopic compounds were also inquired in urine and some tissues. The results were as follows: a) Acetic acid incorporated into urea, aspartate, serine, glutamate, proline, glycine, alanine, ornithine, ethanolamine, r-amino-buthyric acid (brain only), cholesterol and fatty acids. b) Valine incorporated into urinary glutamate and glycine, and tissue cholesterol and fatty acids. Valine was rapidly excreted in urine and found in a very small amount in liver digest.
c) Leucine incorporated into urinary aspartate, serine, glutamate and glycine, and tissue cholesterol and fatty acids. 3. Several important problems of isovalthine studies to be elucidated were discussed.</p>