Fasting Reverses the Renal Adaptation to Altered Dietary Sulfur Amino Acid Intake 1

Abstract

Abstract

We have previously shown that there is renal adaptation to alterations in dietary sulfur amino acid intake. While ingesting a low-methionine, low-taurine diet, urinary and plasma taurine concentrations fall, and the accumulation of taurine by collagenaseisolated tubules is greatly enhanced. On a taurine and methionine-supplemented diet (3%, w/w), urinary and plasma taurine values are increased, and accumulation by tubules is diminished. This study was planned to evaluate the effect of fasting on the adaptation to dietary intake change. Rats were given a high-taurine diet (HTD), low-taurine diet (LTD), or a normal diet (NTD) from age 56 to 70 days of life. Half of the rats in each dietary group were fasted for 72 hr and they lost 13 ± 1% of body weight. Plasma taurine values fell in all three fasted groups, and urinary taurine excretion rose in LTD and fell in HTD-fasted animals. Renal cortex taurine fell in all fasted groups, indicative of taurine release. The in vivo tissue distribution ratio remained unchanged in fasted LTD and NTD animals, but rose into the normal range in fasted HTD animals. The initial rate of uptake (5 min) by isolated tubules was reduced in LTD-fasted and increased in HTD-fasted cortex. Kinetic analysis indicated that the K _m of uptake was unaffected, but the V _max was changed after fasting. Fasting also reverses the adaptive response detected in isolated renal brush border membranes. The renal adaptive response is found at the level of the isolated brush border membrane vesicle, indicating that this membrane surface is involved. A 72-hr fast appears to blunt the adaptive response of the kidney to altered dietary amino acid intake at the level of the luminal surface. The signal for this adaptation and its blunting remains uncertain.