AMINO ACID EXCRETION PATTERNS IN DEVELOPING RATS

1967 ◽  
Vol 45 (5) ◽  
pp. 867-872 ◽  
Author(s):  
William A. Webber
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Rat Kidney ◽  
Kidney Cortex ◽  
Acid Excretion ◽  
Human Infants ◽  
Rat Kidney Cortex ◽  
Progressive Development ◽  
Cortex Slices ◽  
Amino Acid Concentrations

Amino acid excretion patterns were studied in rats 2 to 12 weeks old. In general there was a decline in amino acid excretion over this period which paralleled that reported in human infants by other workers. The decrease was most marked for certain amino acids (glycine, histidine, and arginine). These changes in excretion are not explicable in terms of changes in plasma amino acid concentrations, nor is it likely that they result from differences in filtered load. They may reflect a progressive development of transport mechanisms for some amino acids over the period studied, in which case similar changes in the concentrating ability of rat kidney cortex slices would be predicted. Other possible explanations which are less readily tested include changes in permeability of the tubular cell membranes and differences in the glomerular filtering capacity relative to the amount of tubular tissue which has developed.

A comparison of the amino acid concentrating ability of the kidney cortex of newborn and mature rats

1968 ◽  
Vol 46 (2) ◽  
pp. 165-169 ◽  
Author(s):  
W. A. Webber ◽  
J. A. Cairns
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Cell Layer ◽  
Rat Kidney ◽  
The Other ◽  
Kidney Cortex ◽  
Acid Transport ◽  
Newborn Rat ◽  
Rat Kidney Cortex ◽  
A Cell

It has frequently been demonstrated that there are multiple mechanisms for amino acid transport and that these function to maintain a favorable intracellular level of amino acids within cells. In some instances they also make possible the transport of amino acids from one face of a cell layer to the other. In general, developing tissues have a higher concentrating ability than mature tissues. In the kidney, however, it has been observed that the ability to reabsorb amino acids may be less effective in developing than in mature organisms. Studies were carried out to determine whether the newborn rat kidney cortex differed from mature cortex in its ability to concentrate a representative group of amino acids. In general, the patterns observed for the concentrative uptake of glycine, L-leucine, α-aminoisobutyric acid, L-aspartic acid, and L-lysine were the same. In all cases uptake was initially more rapid in the mature tissue, but the concentration ratios ultimately reached were higher in the newborn tissues. It is concluded that, as in other developing tissues, newborn rat kidney cortex has a high concentrating ability and might therefore be expected to reabsorb amino acids at least as effectively as mature cortex. However the observation that uptake is relatively slow initially suggests that although the ability to establish a gradient at equilibrium is high the capacity of the system is relatively low and this may account for the apparent low capacity of the immature kidney to reabsorb amino acids.

SOME EFFECTS OF PHLORIZIN AND PHLORETIN ON RENAL AMINO ACID REABSORPTION IN THE DOG

1965 ◽  
Vol 43 (1) ◽  
pp. 79-87 ◽  
Author(s):  
William A. Webber
Keyword(s):  
Amino Acid ◽  
Aspartic Acid ◽  
Rat Kidney ◽  
Kidney Cortex ◽  
Rat Kidney Cortex ◽  
Site Of Action ◽  
Proximal Tubular ◽  
Amino Acid Levels ◽  
Amino Acid Concentrations

The effects of phlorizin and phloretin on amino acid reabsorption were studied using clearance techniques in dogs. At endogenous plasma amino acid concentrations no effects were demonstrable. At elevated amino acid levels phlorizin depressed the reabsorption of L-aspartic acid and L-lysine. Phloretin depressed the reabsorption of L-aspartic acid but had a slight enhancing effect on that of L-lysine. No definite effects were observed on L-alanine or glycine reabsorption. These results are not predictable from the observations of other workers that in the in vitro rat kidney cortex phlorizin increases amino acid concentrating ability while phloretin depresses it. Our results are not, however, incompatible with the in vitro observations since it is theoretically possible for an agent to enhance the concentrating ability of kidney cortex, and either depress or increase tubular reabsorption, depending on whether the predominant site of action is on the luminal or basal side of the proximal tubular cells.

A comparison of the efflux rates of AIB from kidney cortex slices of mature and newborn rats

1968 ◽  
Vol 46 (5) ◽  
pp. 765-769 ◽  
Author(s):  
W. A. Webber
Keyword(s):  
Amino Acid ◽  
Initial Rate ◽  
Rat Kidney ◽  
Kidney Cortex ◽  
Newborn Rats ◽  
Rat Kidney Cortex ◽  
The Difference ◽  
Cortex Slices ◽  
Kidney Cortex Slices ◽  
Newborn Animals

Earlier observations of the pattern of uptake of amino acids by rat kidney cortex slices taken from mature and from newborn animals indicated that although the initial rate of entry was invariably more rapid in the mature tissue, the concentration gradient eventually achieved was consistently higher in the newborn tissues. Assuming that the rate of entry was relatively constant, the final concentration differences could only be explained if there was a significantly more rapid efflux of amino acid from the mature tissues. Studies were therefore carried out to measure the rate of efflux of 14C-labelled α-aminoisobutyric acid (AIB) from newborn and mature tissues previously loaded with this nonmetabolized amino acid. It was observed that the rate of efflux was markedly greater in the case of the mature tissues. At 1 h the proportion of AIB which had effluxed was about twice as great in the mature as compared with the newborn tissue. A comparatively small fraction of the efflux from both types of tissue was shown to be dependent on the concentration of external AIB and may have resulted from an exchange diffusion process. This fraction did not account for any significant part of the difference in efflux rates, which probably was the result of different rates of passive diffusion.

Effect of metal ions on in vitro gluconeogenesis in rat kidney cortex slices

1965 ◽  
Vol 208 (5) ◽  
pp. 841-846 ◽  
Author(s):  
Julia Z. Rutman ◽  
Lawrence E. Meltzer ◽  
J. Roderick Kitchell ◽  
Robert J. Rutman ◽  
Philip George
Keyword(s):  
Amino Acids ◽  
Metal Ions ◽  
Tricarboxylic Acid Cycle ◽  
Rat Kidney ◽  
Kidney Cortex ◽  
Rat Kidney Cortex ◽  
In Vitro Systems ◽  
Cortex Slices ◽  
Kidney Cortex Slices

The effect of metal ions on glucose formation from amino acids and glycolytic and tricarboxylic acid cycle intermediates has been examined in rat kidney cortex slices in vitro. Of the metals tested, only Mn++ and Ca++ have been shown to be stimulatory, while Zn++, Cu++, and Cd++ are inhibitory. The case of Mn++ activation is of particular interest because Mg++ ions are inactive in this system, despite the similarities usually observed in the in vitro systems. The stimulation of gluconeogenesis from α-keto acids is comparable for both Ca++ and Mn++, in contrast to the lack of a Mn++ effect with the homologous l-α-amino acids. Evidence is presented as to the possible significance of metal ions in regulating carbohydrate metabolism.

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