The Kinetics of Excretion of Alpha-Aminoisobutyric Acid in Rats. Potential Use as an Indicator for Nitrogen Metabolism

摘要

The possibility of devising a simpler method of monitoring nitrogen metabolism than the arduous and costly balance technique was explored in rats. The synthetic, non-metabolizable analog of natural amino acids, alpha amino-isobutyric acid-1-14C (A1B), was the indicator substance used. The balance technique was employed and nitrogen and A1B excretion were studied in parallel for 154 days (22 weeks). Two experiments were performed, in the first the A1B was administered intramuscularly (I.M.) and in the second it was administered intravenously (I.V.). In both the control and T.P. rats of the I.M. and I.V. groups there was an excellent degree of correlation between native nitrogen and A1B excretion (r = 0.99). The duration of action of the T.P. as determined from the changes in A1B excretion was identical to that determined from the changes in nitrogen excretion, 9 days for each. The decrease in nitrogen excretion induced by the T.P. was 22.0% and identical to that previously found in clinical studies in this laboratory with T.P. and four synthetic anabolic steroids. Recovery of A1B was almost complete and up to 95% of the amount administered. The simplicity of A1B determination, the single exponential disappearance and its constancy, the high degree of correlation between nitrogen excretion and A1B and the prolonged period available for experimental manipulation all suggest that A1B should be useful as an indicator for nitrogen excretion and, indirectly, for nitrogen metabolism. (Author)