Kenneth C. Bovee

Renal Clearance of Amino Acids in Canine Cystinuria

Abstract The renal clearances of cystine, the dibasic, acidic, and neutral amino acids have been compared with simultaneously determined clearance of inulin in six cystinuric and three normal dogs. The plasma levels of cystine and the dibasic amino acids were comparable in cystinuric and normal dogs; plasma methionine was elevated in cystinuric dogs and was positively correlated with plasma cystine levels. In the cystinuric animals the renal clearance of cystine varied from a minor reabsorptive defect in some animals to a complete reabsorptive defect in others. There was a positive multiple correlation between plasma cystine, plasma methionine levels, and fractional reabsorption of cystine. In one cystinuric animal, cystine clearance exceeded inulin clearance. Lysine reabsorption was normal in two and slightly depressed in four of the cystinuric animals. Abnormal clearances of other amino acids were only randomly observed. The clearance of cystine and of the dibasic amino acids may vary independently in canine cystinuria. Our data suggest that canine cystinuria may be a metabolic disease manifested as a tubular reabsorptive defect.

Comparison of Power Doppler and B-Scan Sonography for Renal Imaging Using a Sonographic Contrast Agent

The goal of this study was to evaluate the relative performance of power Doppler and B‐scan imaging modes in detecting vascular perfusion changes resulting from injection of a contrast agent. To allow this comparison the imaging plane and the contrast agent injection must be the same for both modes. We achieved this by using a rigid transducer holder and simultaneously recording power Doppler and B‐scan images on separate videotapes. The kidneys of five adult beagles were scanned to allow a comparison of how power Doppler and B‐scan imaging methods monitor changes during the injection of 0.1 ml/kg of a contrast agent, EchoGen emulsion (Sonus Pharmaceuticals, Bothell, WA). The changes in the images were assessed qualitatively by three radiologists and quantitatively using a custom‐designed image analysis software. All of the radiologists agreed that no visually detectable changes occurred in B‐scan images but that significant changes could be observed in power Doppler images. Image analysis also indicated a difference between power Doppler and B‐scan images. The change in mean color level of power Doppler images could be displayed as an indicator dilution curve with a peak enhancement of 46 +/‐ 16 above the preinjection value. The time at which mean color level peaked was 18 +/‐ 13 s. The mean color level returned to half of the peak value by 69 +/‐ 42 s and returned to the preinjection baseline value by 148 +/‐ 73 s. Conversely, B‐scan images showed statistically insignificant changes, and time measurements could not be made. By all measures used to evaluate images, power Doppler imaging had a greater sensitivity in detecting changes resulting from contrast agent injection than B‐scan imaging. This finding indicates that power Doppler imaging of contrast agent injections can be used to map regional differences in flow as well as quantitative measurements of a contrast agents transit time and has the potential to assess kidney abnormalities associated with renal blood flow.

Renal Function and Laboratory Evaluation

This paper reviews the normal renal function in relation to common functional tests helpful to detect nephrotoxicity. The measurement of renal blood flow, intrarenal distribution of blood flow, and glomerular filtration rate remain the basic parameters of nephrotoxicity. Renal tubular function is accurately measured by standard clearance tests for solutes including electrolytes, glucose and amino acids. The renal concentrating capacity serves as a sensitive but non-specific measure of renal integrity. The measurement of plasma concentration of some solutes is helpful to identify nephrotoxicity, but is most effective when a profile of solutes is measured over a time period. Urinary protein excretion and particularly the excretion of enzymes may localize the nephrotoxicity in certain tubular segments. Due to the multiple functions of the kidney, no single test or group of tests can be relied upon to detect nephrotoxicity. A battery of tests including screening tests and specific tests to measure glomerular or tubular function must be selected to match the pattern of nephrotoxicity.

Amino Acid Uptake by Kidney and Jejunal Tissue from Dogs with Cystine Stones

Cystine and lysine accumulation in vitro in intestinal and renal tissue was studied in eight dogs that form cystine stones. Under conditions which demonstrate in vitro defects in tissue obtained from humans with cystinuria, normal amino acid accumulation occurred in six dogs with the canine disorder. Normal amino acid uptake in tissue and the demonstration of normal to minimum increases in excretion of lysine suggest that the canine disorder is not similar to the human syndrome.

Characteristics of cystine and lysine transport in renal and jejunal tissue from cystinuric dogs

Abstract Canine cystinuria differs from the human situation in two respects. Lysinuria was present in 10 of 14 cystinuric dogs, however the molar ratio of lysine excretion did not exceed that of cystine, although it commonly does in the human disease. Excessive excretion of other dibasic amino acids, ornithine and arginine, was not found in the dogs. Using conditions which demonstrate an in vitro transport defect in intestinal epithelial cell accumulation of cystine and lysine by human cystinuric jejunal mucosa, cystine and lysine accumulation by jejunal mucosa from cystinuric dogs was normal. No defect in cystine or lysine accumulation by renal cortical slices was demonstrated. It appears that isolated cystinuria occurs more frequently in the canine population than in humans, and epithelial cell transport defects of cystine and lysine cannot be demonstrated.

Evaluation of change in blood flow by contrast-enhanced power Doppler imaging during norepinephrine-induced renal vasoconstriction.

We evaluated the changes in flow induced by intrarenal infusion of norepinephrine by an ultrasonographic contrast agent and power Doppler imaging. Hypoperfusion was induced in dogs (N = 5) by infusing norepinephrine directly into the renal artery for 30 min at doses of 0.7 microg/kg/min, 1.0 microg/kg/min, and 1.9 microg/kg/min. Contrast agent injections were made before and after each infusion of norepinephrine. The transit of contrast agent through the kidney and color enhancement were measured by computer analysis of power Doppler images. Mean transit time and effective renal plasma flow were measured. The effective renal plasma flow decreased by 29%, 30%, and 64%, respectively, with the increasing doses of norepinephrine. Paralleling this change, the mean transit time, which corresponds to reduction in renal blood flow, increased by 26%, 43%, and 77%, respectively, from the preinfusion value. Regression analysis shows renal blood flow to decrease exponentially with norepinephrine dose. Renal blood flow changes measured by contrast‐enhanced imaging correlated closely with the effective renal plasma flow measurements. Computer analysis of contrast‐enhanced power Doppler images allowed measurement of renal blood flow. This technique may be useful in assessing renal perfusion during pharmacologic and other therapeutic interventional procedures.

Spontaneous Fanconi syndrome in the dog.

Three dogs with spontaneous renal tubular defects similar to idiopathic Fanconi syndrome are characterized. Renal clearance studies revealed a fractional reabsorption of glucose ranging from 31% to 82%. Abnormal glucose thulium values were present in all dogs. A generalized aminoaciduria occurred in two dogs while one had aminoaciduria characteristic of canine cystinuria. Fractional reabsorption of phosphate ranged from 47% to 79%. In vitro uptake of alpha-methyl-D-glucoside was significantly depressed (p less than 0.001). In vitro uptake of amino isobutyric acid was similar to controls. Renal biopsy revealed nonspecific interstitial change in two dogs and normal histology in the other. These animals represent a useful new model for the study of renal tubular transport defects.

Cystinuria in dogs: Comparison of the cystinuric component of the Fanconi syndrome in Basenji dogs to isolated cystinuria☆

Two animal models for cystinuria have been examined: the Basenji dog with Fanconi syndrome and cystine stone-forming dogs of various breeds. Brush-border membranes were isolated from these animals and uptake of D-glucose and L-cystine was characterized. Experiments with isolated brush-border vesicles from Basenji dogs with cystinuria as a component of the Fanconi syndrome showed diminished sodium-dependent D-glucose uptake but no decrease in L-cystine uptake even though the cystine defect in vivo was as high as 94% (ie, 6% reabsorption). In contrast, brush-border vesicles isolated from the kidney of a cystine stone-forming dog (Welsh Corgi) with a cystine defect of only 16% (ie, 84% reabsorption) had decreased uptake of cystine compared to values found for Beagle and Basenji vesicles. Thus, cystinuria found in Basenji dogs with the Fanconi syndrome differs from that in classic stone-forming cystinuric dogs. The alteration responsible for the cystinuria of Basenji dogs with Fanconi syndrome does not appear to have a membrane locus and may reflect altered energetics for transport, which are not detected in isolated vesicles. The cystine defect in cystinuric stone-forming dogs does appear to be reflected in the isolated membrane.

DEVELOPMENTAL ASPECTS OF CYSTINE TRANSPORT IN THE DOG

ABSTRACT. Developmental changes in cystine transport by the canine kidney were examined both in vivo and in vitro. Renal clearance studies indicated that cystine was one of the more incompletely reabsorbed amino acids at birth, but its reabsorption approaches adult levels by 21 days. Concomitantly, cystine uptake by isolated renal cortical tubule fragments from immature dogs was slower than that by renal tubules from adult dogs. Both age groups rapidly metabolized the transported cystine. This metabolism was principally to cysteine, but also small amounts of reduced glutathione were formed from the transported cystine. Concentration dependence studies indicated two transport systems for cystine uptake in both the immature and the adult dog. Both transport systems in the 1-wk-old dog had a somewhat greater affinity for cystine than the corresponding system in the adult, but this was offset by the markedly lower maximal transport rates for these, systems in the 1-wk-old dog. The high affinity system was inhibited by lysine in tubules from both age groups. In the dog, the rise in the tubular reabsorption of cystine with maturation could, in part, be explained by an increase in the number of transport sites for cystine.

Renal tubule reabsorption of amino acids after lysine loading of cystinuric dogs

The renal reabsorption of cystine, lysine, arginine, and ornithine as well as other amino acids has been determined before and after lysine infusion in four normal and five cystinuric dogs. The large filtered load of lysine caused defective reabsorption of cystine in three of four normals and augmented the basal defect in all of the cystinuric dogs. Two of the cystinuric dogs responded with cystine clearances in excess of the glomerular filtration rate. The magnitude of increase of the reabsorptive defect for cystine observed after lysine infusion into the cystinuric dogs was unrelated to the extent of the basal defect. Two of the normal dogs and four of the five cystinuric dogs demonstrated defective arginine reabsorption after lysine loading, one of the cystinuric dogs having greater arginine excretion than the filtered load. Although normal dogs showed a moderate inability to reabsorb the large filtered load of lysine, three of the cystinuric dogs exhibited a -60 to -70% reabsorption, consistent with lysine secretion. Both normal and cystinuric dogs showed defective glycine absorption after lysine loading, but only cystinuric dogs showed variable defects in threonine, serine, histidine, methionine, and tyrosine when the basic amino acid was infused. Each cystinuric dog responded to lysine infusion in a different way, and the overall pattern of response differed from the normal, with evidence of induced secretion of cystine, lysine, and arginine in the affected dogs.