ADAPTATION OF Β-Amino ACID TRANSPORT TO DIETARY CHANGE IN 2, 4 AND 8 WEEK RATS

Abstract

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 ...

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

“…This observation was previously made in 4-and 8-week animals (8,9). A major component of the tubular transport of taurine by isolated cortical tubules occurs across the luminal membrane.…”

“…Therefore, 14 days of dietary taurine manipulation ensures full expression of this renal adaptive response (10). Lifelong exposure to the LTD results in animals that are significantly smaller than normal (8,9), since they receive inadequate concentrations of methionine and cysteine in their diet during a critical growth period (17). In this study, 70-day animals have been fed on the LTD only from Days 56 to 70; thus, they are fully grown prior to initiating the diet with reduced values for sulfur amino acids.…”

“…We have recently demonstrated that renal adaptation of P-amino acid transport can be found if animals are placed on a diet with minimal quantities of methionine and cysteine and devoid of taurine, or if they are given a diet containing large amounts (3%) of taurine (8)(9)(10). Similar adaptive responses have been reported by Rozen et al…”