Renal tubular biochemistry during acute and chronic metabolic alkalosis in the dog

Diet and nephrolithiasis

Pharmacologic therapy of recurrent nephrolithiasis continues to be the mainstay of the strategy to prevent recurrence. This approach persists even in the face of increasing evidence of a marked benefit of mere entry into a nonpharmacologic diet and fluid modification protocol at a clinic specializing in the evaluation and therapy of recurrent nephrolithiasis (the "Stone Clinic effect"). This review examines the role of diet in the pathogenesis of various forms of nephrolithiasis and the effectiveness of dietary therapy in preventing new stone formation. Recent and older evidence support a primary role for modification of diet, particularly diet protein and sodium intake, in the prevention of recurrent nephrolithiasis.

Changes in urinary magnesium, citrate, and oxalate levels due to cola consumption

The serum concentration and urinary excretion of four potential stone constituents: calcium, oxalate, phosphate, and uric acid; and of two potential inhibitors of urinary stone formation, citrate and magnesium, were studied before and during ingestion of a carbonated cola beverage. Four participants, after baseline serum determinations, abstained for forty-eight hours from cola consumption and then attempted to drink 3 quarts per day of cola in the following forty-eight hours. One participant failed to drink more than two quarts per day of cola. In all 4 participants twenty-four-hour urinary excretion of magnesium decreased by an average of 2.6 mg. In the 3 participants who succeeded in drinking 3 quarts of cola per day, twenty-four-hour urinary excretion of oxalate increased an average of 8.3 mg and excretion of citrate decreased an average of 122 mg. These results demonstrate changes in urine constituents which could contribute to enhanced kidney stone formation in patients who drink large quantities of cola-flavored carbonated beverages.

Response of ammonia metabolism to acute acidosis: insights from cultured renal epithelium

LLC-PK1 kidney epithelial cell lines cultured under the condition of continuous rocking exhibit both acute and adaptive changes in glutamine-dependent ammonia metabolism in response to acid-base manipulations in the media pH. Pulse-chase studies with 14C-glutamine as well as studies with various metabolic inhibitors of the ammoniagenic pathways suggest that glutamine in LLC-PK1 cells is metabolized via mitochondrial pathway and that intramitochondrial phosphate-dependent glutaminase pathway plays a predominant role in the regulation of ammoniagenesis to acute acidosis. Furthermore, the measurements of intracellular pH under both basal and acute low pH conditions resulted in the estimation of intracellular pH, which paralleled the alterations in media pH. Therefore, a change in intracellular pH appears to act as a direct signal for alterations in ammonia metabolism in LLC-PK1 cells. Thus, LLC-PK1 cultures provide an excellent model system to investigate renal ammoniagenesis and the intracellular signals that modulate this process.

Effects of potassium bicarbonate on distal nephron Na-K-ATPase in adrenalectomized rabbits

Na-K-ATPase activity in the connecting tubule (CNT) and cortical collecting duct (CCD) has been shown to be influenced by KCl both in the presence and in the absence of aldosterone. To investigate if the aldosterone-independent effect of K+ on Na-K-ATPase can be produced by other K+ salts, we studied the effects of dietary KHCO3 on Na-K-ATPase and ouabain-insensitive Mg-ATPase activities in four nephron segments of adrenalectomized (ADX) rabbits. The segments examined were: the distal convoluted tubule (DCT), CNT, CCD and medullary collecting duct (MCD). All diets were similar in composition except their KHCO3 contents which were 100, 300, 500 and 700 meq/kg in groups 1 to 4 respectively. Increasing KHCO3 in the diet increased K+ excretion (7 X) and urine pH (6.6 to 8.3). Na-K-ATPase activity in the CCD increased greater than 200% as dietary KHCO3 was increased to 700 meq/kg. There was a linear relation between Na-K-ATPase activity in this segment and steady state plasma K+ as well as K+ excretion in the urine. However, Na-K-ATPase activity in the CCD was lower in KHCO3-fed ADX rabbits than the KCl-fed animals studied previously under similar conditions. There were no significant differences in Na-K-ATPase activities in DCT, CNT and MCD among the four groups given different KHCO3-diets. It is concluded that dietary intake of KHCO3 can also influence Na-K-ATPase activity in the CCD independent of aldosterone.

Effect of acetazolamide on renal metabolism and ammoniagenesis in the dog

The effect of acetazolamide (ACZ) on renal metabolism and ammoniagenesis was studied in the dog in vivo and in vitro. ACZ was administered to 10 dogs with normal acid-base status and five with chronic metabolic acidosis induced by NH4Cl. In both groups of dogs, the acute administration of ACZ markedly reduced the urinary excretion of ammonium (from 33 to 10 in normal dogs and from 100 to 23 mumoles/100 ml GFR in acidotic dogs) whereas its release into the renal vein was increased in a reciprocal fashion (from 69 to 95 in normal dogs and from 91 to 152 mumoles/100 ml GFR in acidotic dogs). ACZ did not change the total ammonium production nor the renal glutamine utilization. The renal utilization or production of glutamate, alphaketoglutarate, alanine and citrate also remained unchanged. Despite a marked urinary alkalinization, citraturia remained minimal. However, the renal cortical concentrations of glutamine, glutamate, succinate, fumarate, malate, aspartate and phosphoenolpyruvate fell following ACZ administration, especially in acidotic dogs showing rapid renal utilization of glutamine. ACZ had no effect on the same metabolites in the kidney of normal dogs even when lactate utilization was enhanced by lactate infusion. This study demonstrates that an accelerated ammoniagenic flux can proceed in the dog kidney without the renal cortical changes produced by metabolic acidosis in this species. In vitro, using dog tubules, a selective effect of ACZ on glutamine metabolism as compared to lactate was observed. ACZ reduce the rate of the reactions catalyzed by alphaketoglutarate dehydrogenase and by succinyl CoA synthetase. Other enzymes of the ammoniagenic and gluconeogenic pathways (glutaminase, GLDH, malic enzyme, PEPCK) were not changed by ACZ. The metabolic effects of ACZ observed in the intact kidney in vivo or with tubules in vitro may be in part related to the effect of ACZ on these enzymes critical for the ammoniagenic process.