Developmental Aspects of Renal β-Amino Acid Transport I. Ontogeny of Taurine Reabsorption and Accumulation in Rat Renal Cortex

Abstract

Summaryevidence that breast milk is a dietary source of taurine in the weanling rat, several studies have suggested fully developed tauNewborn Sprague-Dawley rat pups were found t' have reduced rine synthetic capacity in the neonatal rat in contrast to the net tubular reclamation of the p-amino acid taurine in vivo. The ,itUation in man (34,35). reabsorption of this compound increased between the 2nd and 4thThe renal uptake of taurine both in viva and in vitro has been week of life and the excreted taurine fell despite a rise in glomer-defined in adult mouse (10) and in adult rat kidney cortex (7, 9). ular filtration rate indicative of increased transport with matura-Endogenous clearance of tauhe in rat may be as high as 40% tion.(19), but most studies utilizing free flow micropuncture (13) or cortex in viva taurine from plasma against continuous microperfusion (1 1) have consistently found a cleara large chemical gradient. Newborn cortex slices in vitro accu-ance of s% of filtered load, a value akin to that found in A,J mutated taurine to higher levels at steady state at 4 . 4 mM, but mouse (10). ~h~ t a u h e reabsorptive system, in contrast to net uptake was less efficient at higher taurine concentrations. Further reclamation for most a-amino acids, demonstrates a high cortex 'Iices was not found at any age. but low capacity for uptake; thus, reabsorption of only 9&95% of in and newborn was greatest at filtered load has been found (9,11,30). Uptake by cortex slices, mEq/liter K in the external medium. Slices from younger animals indicative .of antiluminal membrane transport (41, 421, took place had 'lightly higher pH 'ptima for 'ptake and temperature by at least two t a u h e carriers in both mouse and rat (7, 9, 10). tion increases uptake more in neonatal than in adult kidney.Each site was sodium-dependent, required aerobic metabolism, and, of all amino acids tested, only /?-amino acids, such as /?-Speculation alanine, prevented taurine uptake in a competitive fashion (9, 10, If the newborn rat is in part dependent on the transfer of taurine 16). Glutathione oxidation inhibited taurine accumulation by the from mother to pup via milk, the process of weaning may require first (low Km, high affinity) transport system possibly by enhanced greater renal tubular reabsorption in order to maintain tissue and taurine efflux (7, 9). The pattern of taurine excretion and the plasma pools of taurine. The improved reabsorption of taurine tissue levels of this amino acid over the first few weeks of life found in 4-week-old and adult animals may reflect maturational be to the Ontogeny of changes brought about by the reduction in dietary taurine (and mechanisms, particularly because amino acid hyperexcretion is other sulfur containing amino acids) after weaning. characteristic of the early postnatal period in man and other mammals (1, 30). In this paper, the authors discuss the development of the in vivo taurine renal transport system during the first Taurine (2-aminoethanesulfonic acid), the amino acid charac-month of life....

Developmental Aspects of Renal β-Amino Acid Transport. VI. The Role of Membrane Fluidity and Phospholipid Composition in the Renal Adaptive Response in Nursing Animals

“…(Pediatr Res 22: 163-167,1987) Immature animals of virtually all mammalian species have a "physiologic" generalized aminoaciduria which results in excretion of a higher fraction of the filtered amino acid load of all amino acid classes (1,2). Our laboratory has focused on physiologic factors that modify the development of amino acid transport systems in order to better understand the processes by which these transport sites achieve a mature transport profile (3)(4)(5)(6)(7). For an appropriate transport probe , we have used the l3-amino acid taurine, since it is relevant in the nutrition of young animals (8) and since one can manipulate the dietary level of sulfur amino acids to alter the renal handling of taurine (5,(9)(10)(11)(12)(13)(14).…”

Developmental Aspects of Renal β-Amino Acid Transport II. Ontogeny of Uptake and Efflux Processes and Effect of Anoxia

“…A possibly completely unrelated finding was that the initial rate of uptake was reduced in tissue from younger animals. Both these findings cannot fully account for the increased taurinuria of young animals because efflux was reduced and initial uptake rate was slower in slices from 28-dav-old animals who demonstrate entirelv normal taurine reclamation (6). As previously suggested (9), luminal brush border u~t a k e mav be decreased in immature animals.…”

“…Tissue was incubated as described (7-9) and a Tris-Ringer glucose medium was used as described before (6). Slices were removed, blotted, weighed, boiled, and the supernate counted as described (7,8).…”

Development Aspects of Renal β-Amino Acid Transport. V Brush Border Membrane Transport in Nursing Animals—Effect of Age and Diet

“…Urine taurine was measured by a high performance liquid chromatography method after post column derivatization with phenyl-iso-thiocyanate as described elsewhere (14), urine creatinine concentrations were measured by a previously described method (3).…”