Renal adaptation to alteration in dietary amino acid intake

The nonessential beta-amino acid taurine, which is inert in renal tissue, was used to study the renal adaptation to dietary taurine change. Three isoproteinic diets were employed: HTD--high in taurine, NTD--normal taurine, and LTD--deficient in the taurine precursors cysteine and methionine. When compared with NTD, HTD resulted in an increase in the urinary excretion and fractional excretion of taurine, whereas LTD led to a decrease in urinary excretion and fractional excretion of taurine. In vitro studies demonstrated an increase in the Vmax of the high-affinity, low-capacity uptake system with no change in "apparent" Km following LTD. Complete adaptation developed within days after the diet was changed (NTD to HTD = 3 days; NTD to LTD = 3-6 days). These studies demonstrate that the renal response to altered dietary amino acid can be evaluated and that adaptation occurs for the beta-amino acid taurine. The renal response serves to conserve taurine during periods of deprivation and to dispose of taurine during periods of excess. The renal adaptation to restricted taurine intake seems to occur through an increase in transport sites (increased Vmax) or change in flux at the transport sites, with no change in transport affinity (unaltered apparent Km).