Amino acid content of rat renal cortex and the response to in vitro incubation.

The concentration of aspartic acid, threonine, serine, glycine, and alanine is significantly higher in newborn rat renal cortex than in the adult tissue, while phenylalanine and histidine are higher in the adult. When adult cortical slices are placed in bicarbonate buffer at room temperature for 20 min there is a 30-60% decrease in the levels of all amino acids except for lysine, which is slightly higher, and methionine and serine, which do not change. Under the same conditions, newborn cortical slices reveal a similar decrease in only glycine, tyrosine, histidine, and the branched-chain amino acids. On subsequent in vitro incubation of the cortical slices at 37 degrees C for 120 min the concentrations in adult tissue remain at the lower values observed on removal from buffer at room temperature except that glutamic acid, glycine, and lysine levels decrease further and serine increases to the concentration found in fresh tissue. Newborn tissue when incubated at 37 degrees C for 120 min shows amino acid concentrations comparable to unincubated fresh tissue for all except aspartic acid, glutamic acid, serine, and phenylalanine, which reach levels higher than unincubated tissue. The ability of newborn tissue to maintain amino acid pools may play a role in the enhanced transport of some amino acids resulting from preincubation at 37 degrees C (Reynolds et al. Science 184: 68-69, 1974; Reynolds and Segal, Biochim. Biophys. Acta 406: 513-525, 1976).