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).

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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 k 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, of uptake was unaffected, but the V,,, 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. 4930037-9727/8U080493-099$01. W O

Glomeruli and tubules were isolated with a graded sieving procedure from the same renal cortex of men of premature age up to 80 years. Glomerular and tubular basement membranes (GEM and TBH, respectively) were obtained with a detergent procedure. Purity was controlled with light and electron microscopy and by estimating total phosphorus content. Amino acid and carbohydrate composition, including 3-hydroxyproline and sialic acid, were determined. Comparison of GBM and TBH from the same kidneys showed at all ages, that GBM contains nore 3-hydroxyproline, sialic acid, mannose and hexosamine than TBM. Significant changes in the chemical composition were found during the first period of life, in GEM immediately after birth and in TBM during growth up to 10 years. The changes include an increase of the contents of 3-and 4-hydroxyproline, glycine, hydroxylysine, glucose, galactose and hexosamine and a decrease in the contents of histidine and lysine. These data indicate, that changes in collagenous and non-collagenous components arise with maturation. The results will be used for comparison with the chemical composition of renal basement membranes from different patients with congenital renal dl seases . Renal adaptation to deprivation of inorganic solutes has been observed, but adaptation to altered dietary intake of amino acid has not been studied. Using isolated renal cortical tubule segments the uptake of taurine (T) in breast fed (2 wk), weanling (w) (4 wk) and adult (A) (8 wk) rats under 3 dietary states was Findings suggest renal adaptation to increased or decreased dietary amino acid occurs within 1 week of weaning. In the 2 wk rat there is decreased uptake with HTD and no difference between PITI) and LTD. This sup,t;ests that adaptation to HTD is transmitted throwh breast milk but the tocsin for renal adaptation to LTD present in (A) and (w) is not transmitted to the 2 wk rat. This study was performed to evaluate renal transport of taurine in the human kidney. Previous studies suggested that normal individuals have three distinct excretion classes which are under genetic control. _ --Four normal volunteers were given an oral load of taurine (260 mg/l. 73 ~2 ) and urinary excretion measured. Then they were ntudied hy clannical clearance techniques using inulin as a marker of glomerulsr filtration. Following baseline dererminarions of taurine clearance, each subject was given increasing intravenous doses of B-alanine.Following oral loading, three subjects excreted taurine at a rate of 3.8-5.6 uM/min, while one subject had an excretion rate of 0.14-0.34 uM/min. During baseline conditions. fractional reabsorption of taurine in the three high excretors ranged from 0.65 to 0.80. With B-alanine loading, fractional reabsorption of taurine decreased to 0.13 to 0. In the low excretor, fractional reabsorption of taurine under baseline conditions was 0.99 and decreased to only 0.55 during B-alanine loading.These studies suggest the presence of both a high and low Km transport system for taurine in the human kidney which ...

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