Tissue and organ distribution of radioactive carbon from 14C-labeled tryptophan in the mouse was studied by whole-body autoradiography and biochemical analysis. The mice injected intravenously with L-[side chain-3-14C]tryptophan were sacrificed at various intervals. Examination of autoradiographs disclosed that the injected 14C-tryptophan was rapidly taken up from the blood by the organs. The radioactivity in the pancreas was the highest and predominant throughout the intervals after injection in this investigation.The comparative values among radioactivity in various organs estimated by a liquid scintillation counter were consistent with those obtained from whole-body autoradiographs. Radioactivity in the acid-insoluble fractions was increased with time in all organs examined. High-performance liquid chromatography of the acid-soluble fractions disclosed radioactive tryptophan and alanine in the blood, liver, kidney and small intestine, while radioactive alanine was not detected in the brain.Tryptophan is distributed in tissues and body fluids, in a free form and incorporated into protein molecules. There are three principal metabolic fates of dietary tryptophan: it may be incorporated into tissue proteins, or it may be metabolized, either by way of the 5-hydroxyindole pathway, leading to the neurotransmitter serotonin (5-hydroxytryptamine), or by way of the oxidative pathway which leads to complete oxidation (2). The distribution and metabolic fates of tryptophan have been extensively studied, but not satisfactorily in the whole-body. In the meantime, whole-body autoradiography has been used for investigation of the distributions of hexoses (12, 23) and hexosamines (7,8) in mice in our laboatory. The distributions of methionine (1), glutamine (3), tyrosine (14) and other amino acids (11, 15) and 5-hydroxytryptophan and 5-hydroxytryptamine (22) have been studied by this method. In the present study, we report the distribution of radioactive tryptophan and/or its metabolites in mice by whole-body autoradiography and biochemical analysis. MATERIALS AND METHODSAnimals. Adult male albino mice of ICR strain, weighing approx. 25 g, were used.
Tissue and organ distribution of radioactive carbon from 14C-tyrosine in the mouse was studied by whole-body autoradiography and biochemical analysis. The mice injected intravenously with L-[U-14C]tyrosine were sacrificed at various intervals. Examination of autoradiographs disclosed that the injected 14C-tyrosine was rapidly taken up from the blood by the tissues. The radioactivity in the pancreas was the highest and predominant throughout the intervals after injection in this investigation.The comparative values among radioactivity in the organs estimated by a liquid scintillation counter were approximately consistent with those obtained from the whole-body autoradiographs. Radioactivity in the acid-insoluble fractions was increased with time in all organs examined. High-performance liquid chromatography of the acid-soluble fractions disclosed that the amounts of the radioactive tyrosine and its metabolites and/or their molar ratios were different among the organs.Tyrosine is distributed in tissues and body fluids, in a free form and incorporated into protein molecules. It is generally accepted that tyrosine is a precursor of catecholamines, thyroxine and tyramine. The distribution and metabolic fates of tyrosine have been extensively studied, but not satisfactorily in the whole-body. In the meantime, whole-body autoradiography has been used for investigation of the distributions of hexoses (13, 21) and hexosamines (7,8) in mice in our laboratory. In the recent report (9), the distribution of radioactive tryptophan and/or its metabolites in mice was examined by this method. To our knowlege, the distribution of tyrosine in the whole body has not been reported by this method, although those of the amino acids such as methionine (1), glutamine (3) and other amino acids (12, 15) and dopa (22) have been studied. The present report deals with the tissue distribution in mice by means of whole-body autoradiography and biochemical analysis at several intervals after injection of L-[U-14C]tyrosine. MATERIALS AND METHODSAnimals. Adult male albino mice of ICR strain, weighing approx. 30 g, were used. Materials. L-[U-14C]tyrosine (specific activity: 493.0 mCi/mmol) was purchased from New England Nuclear, U. S.A. The substance was lyophilyzed and dissolved in physiological saline solution (50 iCi/ml).
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