A TRACER AMINO ACID AS AN INDICATOR OF NITROGEN METABOLISM

摘要

The experiments being reported are part of a program aimed at devising a simpler method of monitoring nitrogen metabolism. Previous studies with seven different anabolic steroids on the up take of the non-metabolizable amino acid, alpha-aminioiscbutyric acid-l-c14 (AIB), by the levator and muscle of the rat have shown this to be are excel lent indicator of anabolism. The rapidity of the test and its high degree of reproducibility and sensitivity led to study of 1) refinements in the test, 2) determination of the proportionality between the uptake of AIB and glycine in various other tissues and 3) study of the time course of distribution of the AIB in normal and steroid stimulated animals.nThe levator and uptake test has been shortened from 39 to 25 hours without loss of sensitivity or reproducibility. It thus has advantage over the standard amyotrophic tests which require much more time and greater numbers of animals.nThe study of the quantitative relationship between AIB uptake and glycine incorporation into various tissues suggests that a fixed proportionality between the two may exist. The experiment, however, was not entirely satisfactory technically and is to be repeated.nThe time course study of the distribution of AIB in normal and steroid stimulated rats indicates that the maximum general anabolic effect of the four steroids tested does not occur until 96 hours. Up to 2k hours the steroids actually cause a suppression of uptake in the viscera and general muscle and between 2k and 48 hour? the uptake in the treated animals is the same as in the control animals. The importance of r he time chosen at which to study the uptake is thus highlighted Lack of change in bleed leve's over the 9 days of the experiment between the control and experimental groups and the contrasting sharp drop in urinary excretion suggests that blood levels would be appropriate and that excretion levels would be useful as indicators of metabolic charge. The magnitude of the increase in up take by the viscera and general skeletal muscle at 96 hours, 50 to 60%, indicates/that these changes would be useful indicators of "pure" anabolism from the "mixed" anabolic and androgenic effect of the levator and other sexual tissues.