The distribution of radioactive carbon from L-(U-14C)tyrosine in mice.

Abstract

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).

Distribution and metabolic fate of radioactive carbon from L-(U-14C)arginite administered into mice.

“…The finding at 180 min after injection indicates that most of the radioactive substances remained as proteins in the organs at this time. This finding that the pancreas had the highest radioactivity during the intervals tested is consistent with other reports about glutamine (3), tryptophan (8) and tyrosine (9), and different from those about methionine (1) and aspartic acid (16). This may imply the differences of the pool size of amino acids and/or the requirement for protein synthesis in the pancreas.…”

“…In this investigation, most of the radioactivity in the pancreas may be responsible for that in the exocrine part of this organ, as several investigators (3,12) reported that there was a high concentration of radioactivity in the exocrine part of this organ but little or no radioactivity in the islands of Langerhans. The general pattern of the autoradiographs obtained after injection of radioactive arginine had a resemblance to those reported about tryptophan (8) and other amino acids (9,12,16), and was different from those about hexoses (14,25) and hexosamines (10,11).…”

“…With regard to the radioactivity in the organs at 5 min and 30 min after injection, the results shown in Table 1 are approximately consistent with those obtained by whole-body autoradiography stated above. The findings that the radioactivity in the blood and kidney decreased with time are coincident with those about tryptophan (8) and tyrosine (9) and indicate that the radioactive substances in the blood are rapidly taken up by the tissues and/or excreted in the urine.…”

“…The significant radioactivity for spermine, spermidine (17 min of the retention time) and creatinine (21 min of the retention time) was not detected in any of the organs at any intervals after injection. other amino acids reported (3,8,9). The findings on the brain and testis at an early time after injection indicate that it is difficult for arginine to be incorporated into these organs and may reflect the concepts of the blood-brain barrier (18) and the blood-testis barrier (5).…”

“…In addition, using different post-injection times, the change in distribution with time can be followed. The distributions of methionine (1), glutamine (3), tryptophan (8), tyrosine (9) and other amino acids (12,16) …”