Factors controlling the level and determination of D-amino acids in the urine and plasma of laboratory rodents.

Unambiguous methodologies were developed for the accurate and reproducible determination of specific D-amino acids in the physiological fluids of common laboratory rodents. Depending on the strain of rodent and the type of amino acid examined, excreted D-amino acids ranged from the low percent levels to over 40 percent of the total specific amino acid level. Relative plasma levels tended to be considerably lower, typically an order of magnitude less. A number of factors were found to alter the relative amounts of excreted D-amino acids. This included: diet, age, pregnancy, advanced cancer, and antibiotics. The two factors that seemed to result in substantially lower levels of excreted D-amino acids were fasting and young age. Pregnancy was the only factor that consistently resulted in higher relative D-amino acid excretion. Much of the observed data are believed to be related to the efficiency with which the kidney reabsorbs L-amino acids. No claims are made as to the meaning and/or importance of free D-amino acids in regards to pathology, age, clinical usefulness and so forth. However, a knowledge of normal D-amino acid levels and dynamics is necessary before it is possible to identify perturbations caused by either natural or pathological conditions. The techniques are now available that should allow these topics to be addressed properly.