Insights into the biochemical mechanism of maleic acid-induced Fanconi syndrome

Maleic acid administration is known to produce the Fanconi syndrome, although the biochemical mechanism is incompletely understood. In this study the effect of a single injection of maleic acid (50 mg/kg body wt, i.v.) on the rat renal ATPases was examined. Maleic acid rapidly caused bicarbonaturia, natriuresis, and kaliuresis. When nephron segments were microdissected, there was an 81 +/- 2% reduction in proximal convoluted tubule (PCT) Na-K-ATPase activity (P < 0.005) and a 48 +/- 4% reduction in PCT H-ATPase activity (P < 0.01). Enzyme activity (Na-K-ATPase, H-ATPase, H-K-ATPase) in the medullary thick ascending limb of Henle's loop and distal nephron segments was normal. In vitro, maleic acid (1 and 10 mM) inhibited Na-K-ATPase in PCT, but it had no effect on H-ATPase in PCT. Prior phosphate infusion to maleic acid-treated rats attenuated urinary bicarbonate wastage by 50% (P < 0.05); activity of proximal tubule Na-K-ATPase and H-ATPase activities were partially protected as compared to the animals given maleic acid alone (P < 0.05). Renal cortical ATP levels were not altered at the concentration of maleic acid used in this study (that is, 50 mg/kg body wt), but higher doses of maleic acid (that is, 500 and 1000 mg/kg body wt) caused ATP levels to fall. Maleic acid did not affect cortical medullary total phosphate concentration, however, P32 turnover (1 and 24 hr) was altered by prior phosphate infusion. A protective effect of prior phosphate loading on the membrane bound Pi pool (insoluble) was seen while the cytosolic Pi pool (soluble) was not different from control. Thus, maleic acid-induced "Fanconi" syndrome likely results from both direct inhibition of proximal tubule Na-K-ATPase activity and membrane-bound phosphorus depletion. The former mechanism would reduce activity of the sodium-dependent transporters (that is, Na/H antiporter), while the latter would inhibit the electrogenic proton pump (H-ATPase). The combination of reduced proximal tubule Na-H exchange and H-ATPase activities would markedly inhibit bicarbonate reabsorption and result in the metabolic acidosis universally seen in the Fanconi syndrome.

Effect of respiratory acidosis and respiratory alkalosis on renal transport enzymes

We studied the effect of respiratory acidosis and respiratory alkalosis on acid-base composition and on microdissected renal adenosinetriphosphatase (ATPase) enzymes. Rats were subjected to hypercapnia or hypocapnia of 6, 24, and 72 h duration. After 6 h of hypercapnia, collecting tubule (CT) ATPases were not changed. At 24 h, plasma bicarbonate was 35 +/- 1 meq/l (P < 0.01) and CT H-ATPase and H-K-ATPase activities were 90% greater than controls (P < 0.01). By 72 h, plasma bicarbonate was 37 +/- 1 meq/l (P < 0.005 vs. control) and CT enzyme activity had increased even more, averaging approximately 130% of control (P < 0.05). Significant increases in enzyme activities were also observed in the proximal convoluted tubule and medullary thick ascending limb. Plasma aldosterone was three to four times that of control at all three time periods. In hormone-replete adrenalectomized rats, acid-base parameters and ATPase activities were the same as those seen in adrenal intact animals. After 6 h of hypocapnia, plasma bicarbonate was not significantly changed, but H-ATPase and Na-K-ATPase activities were decreased by 35% along the entire nephron (P < 0.05). H-K-ATPase activity in CT also decreased by 35%. At 24 h, plasma bicarbonate was 20.5 +/- 0.5 meq/l (P < 0.05 vs. control) and CT H-ATPase and H-K-ATPase activities were 60% less than control (P < 0.01). By 72 h, plasma bicarbonate was 18.5 +/- 0.5 meq/l (P < 0.05); however, only CT H-ATPase activity continued to fall, averaging 75% less than control (P < 0.005). Hypocapnia had no effect on plasma aldosterone or potassium. These results demonstrate that chronic, but not acute, respiratory acidosis stimulates activity of both renal proton ATPases. By contrast, both acute and chronic respiratory alkalosis decrease the two renal proton pumps. The stimulatory effect of hypercapnia and the inhibitory effect of hypocapnia on the renal ATPases appear to be potassium and aldosterone independent. Although the precise mechanisms for these results are not known, a direct effect of PCO2, pH, or changes in bicarbonate delivery may be involved.

Biochemistry and pathophysiology of vanadium

The biochemistry and function of vanadate and its possible role in health as well as in disease remains one of the most fascinating stories in biology. This review has surveyed the pertinent literature regarding its effect in the normal kidney and other tissues. While inhibition of the Na(+)-K+ ATPase enzyme was the first described and perhaps the most widely studied, the element clearly has other actions. Speculation as to whether vanadate is a part of the pathogenesis of the 'uremic syndrome', acquired cystic kidney disease, depression, and bone disease should provoke the clinical investigator and the basic researcher alike to a myriad of new and intriguing experiments.

Women, medicine and life in the Middle Ages (500-1500 AD)

The status of women in the Middle Ages was ambiguous, because although they had great responsibility and expertise in practical affairs they were viewed as chattel and inferior to men. They were skilled in cookery, often of highly spiced dishes using a variety of ingredients and flavorings, and they were taught the use of medicinal herbs. They were often skilled in simple first aid, though they were not allowed to practise outside the home. An important exception of this was Hildegarde von Bingen, whose Physica brought her great renown. In it she became the first woman to discuss plants in relation to their medicinal properties. For most people in the Middle Ages, treatment revolved around herbs and diet, together with faith and holy relics and the use of (forbidden) pagan incantation and ritual. Astrology was often a necessary adjunct to treatment. In Salerno, however, medicine had been practised from classical times, and medical training could last for 7 years or more. One of the greatest medieval medical texts is the Tacuinum Sanitatis, which describes in detail the 6 essentials for the preservation of man's health. Several vegetables and herbs are mentioned in connection with the kidneys, the picking and preparation of which are imbued with magic.

H-K-ATPase in distal renal tubular acidosis: urinary tract obstruction, lithium, and amiloride

In previous studies we suggested that urinary tract obstruction and chronic administration of lithium or amiloride were models of "voltage-dependent" distal renal tubular acidosis (DRTA). Subsequently, differences among these three models suggested that the pathogenesis was far more complex than we originally proposed. A recent study showed that H-adenosinetriphosphatase (H-ATPase) activity was decreased in all three experimental models. In the current experiments we examined the effect of 24-h unilateral ureteral obstruction (UUO) and chronic administration of amiloride and lithium on collecting tubule H-K-ATPase, the other renal H-ATPase enzyme. In the obstructed kidney, cortical collecting tubule (CCT) H-K-ATPase activity was enhanced by 73 +/- 10.0%, whereas the enzyme activity in medullary collecting tubule (MCT) was decreased by 67 +/- 5.4%. In the normal contralateral kidney, activities of H-ATPase, H-K-ATPase, and Na-K-ATPase were increased by approximately 30% in both CCT and MCT. Following amiloride (3 mg.kg-1.day-1 x 3 days ip), rats had normal acid-base status, slight hyperkalemia, and markedly elevated plasma aldosterone levels. Both CCT and MCT H-K-ATPase activities in amiloride-treated rats were unchanged. After LiCl (4 meq.kg-1.day-1 x 3 days ip), rats developed mild metabolic acidosis and had normokalemia and normal aldosterone status. CCT H-K-ATPase activity in lithium-treated rats was decreased by 64 +/- 8.8%, whereas the enzyme activity in MCT remained unchanged. Lithium in vitro (30 meq/l) inhibited CCT, but not MCT, H-K-ATPase activity, whereas amiloride had no effect on the enzyme activity. (ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of and therapeutic strategies for hypertension in pregnancy

Approximately 8% to 10% of pregnancies are complicated by hypertension. The disease, whether it first appears during gestation or was present prior to conception, puts both mother and baby at risk. The fetal risks include death in utero, poor growth, and prematurity. The risks to the mother are more difficult to assess, but intracranial bleeding is the most common cause of death. This review examines some of the physiological changes that occur in normal pregnancy and defines the hypertensive disorders of pregnancy. The recent data regarding pharmacologic and nonpharmacologic therapies for the treatment of hypertension in pregnancy are discussed, and comments as to the prophylaxis of preeclampsia are noted.

Regulation of collecting tubule adenosine triphosphatases by aldosterone and potassium

To examine the precise role of potassium and aldosterone on acid-base composition and on collecting tubule ATPases, glucocorticoid-replete adrenalectomized rats were replaced with zero, physiological, or pharmacological doses of aldosterone and were fed varying potassium diets to produce hypokalemia, normokalemia, or hyperkalemia. Radiochemical measurement of ATPase activities showed that collecting tubule H/K-ATPase changed inversely with potassium and not with aldosterone whereas H-ATPase changed directly with aldosterone but not with potassium. When both enzymes changed in the same direction, alterations in acid-base composition were profound; however, when these two acidifying enzymes changed in opposite directions or when only one enzyme changed, the effect on acid-base balance was modest. Serum bicarbonate was approximately 45 meq/liter when aldosterone was high and potassium was low; it was only 29 meq/liter when aldosterone was high but potassium was normal or when aldosterone was normal and potassium was low. Our observations may help explain the metabolic alkalosis of primary aldosteronism in which aldosterone excess and hypokalemia are combined and the metabolic acidosis of aldosterone deficiency in which hypoaldosteronism and hyperkalemia are paired. The present study also demonstrated that aldosterone plays the major role in controlling Na/K-ATPase activity in cortical collecting tubule. Hypokalemia stimulates Na/K-ATPase activity in the medullary collecting tubule; this stimulatory effect of hypokalemia supports the hypothesis that the enzyme is present on the apical membrane at this site.

Effect of furosemide-induced hypokalemic metabolic alkalosis on renal transport enzymes

Hypokalemic metabolic alkalosis is one of the most common complications of chronic furosemide administration. In this study we examined acid-base composition and ATPase enzyme activities in medullary thick ascending limb of Henle's loop (MTAL) and collecting tubule (CCT and MCT) after seven days of chronic furosemide therapy. All of the studies were conducted in adrenal intact (AI) rats or in adrenalectomized (ADX) glucocorticoid replete rats replaced with a physiological dose of aldosterone (Aldo). Furosemide (F) was administered to each rat by mini-osmotic pump. In the AI+F group, plasma Aldo was high and obvious metabolic alkalosis occurred (HCO3- = 37 +/- 2 mEq/liter vs. 22 +/- 2 mEq/liter in controls, P < 0.005); activities of H-K-ATPase, H-ATPase, and Na-K-ATPase were increased approximately twofold in both CCT and MCT. In the ADX+F group (HCO3- = 28 +/- 2 mEq/liter, P < 0.05 from control), H-ATPase activity was normal in CCT and it was slightly increased in MCT. CCT and MCT H-K-ATPase activities were markedly increased (approximately twofold). Na-K-ATPase activity was the same as control in CCT but it was increased in MCT. In ADX+F+Vanadate (V) group which also had normal Aldo levels, acid-base changes were modest (20 +/- 2 mEq/liter, NS from control); in CCT and MCT H-K-ATPase and Na-K-ATPase activities were markedly reduced, but H-ATPase activity in MCT was increased. In all three experimental groups Na-K-ATPase activity in MTAL was reduced fivefold. Hypokalemia developed in both intact and ADX animals receiving furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosterone metabolism and membrane transport

The mammalian kidney metabolizes virtually all of the steroid hormones. Corticosterone receptors have been found in the cortical collecting tubule, and at least four metabolites of the hormone have been identified in rat renal tissue and urine. The biologic activity of these metabolites is not completely known. In this study, we examined the functional effects of three of the metabolites of corticosterone on membrane transport in toad and turtle bladders; we also analyzed the oxidoreductase pathways for corticosterone metabolism. In the toad bladder, maximal water flow (vasopressin- and cyclic AMP-stimulated) was unaffected by corticosterone, 11-dehydro-20-dihydrocorticosterone (metabolite I) and 11-dehydrocorticosterone (metabolite IV); maximal water flow was significantly inhibited by 20-dihydrocorticosterone (metabolite II). Sodium transport in the toad bladder was stimulated by corticosterone, 11-dehydrocorticosterone and 20-dihydrocorticosterone. Analysis of the oxidoreductase pathways in this tissue revealed that most of the corticosterone was oxidized to 11-dehydrocorticosterone, a biologically active compound; 11-dehydrocorticosterone was further metabolized to 11-dehydro-20-dihydrocorticosterone, a biologically inactive compound. Only 6% of the parent compound was converted to 20-dihydrocorticosterone. In the turtle bladder, none of the metabolites tested altered hydrogen ion secretion over the time period studied; no significant biotransformation of corticosterone occurred in this tissue. As the metabolites of corticosterone found in toad bladder are the same as those identified in mammalian tissues, our studies suggest that some of them may be important modulators of sodium and water transport in the distal nephron. Our data further suggest that these compounds are likely not involved in the regulation of urinary acidification.

Vanadate causes hypokalemic distal renal tubular acidosis

Pages F449–F453: E. Dafnis, M. Spohn, B. Lonis, N. A. Kurtzman, and S. Sabatini. “Vanadate causes hypokalemic distal renal tubular acidosis.” The value for urine anion gap in NH4Cl-treated animals on page F450 (last sentence in first paragraph of results), as well as on page F51 (Table 2, last value in last line), should be -82 ± 7 meq/l instead of -232 ± 27 meq/l.

Vanadate causes hypokalemic distal renal tubular acidosis

Pages F449–F453: E. Dafnis, M. Spohn, B. Lonis, N. A. Kurtzman, and S. Sabatini. “Vanadate causes hypokalemic distal renal tubular acidosis.” The value for urine anion gap in NH4Cl-treated animals on page F450 (last sentence in first paragraph of results), as well as on page F51 (Table 2, last value in last line), should be -82 ± 7 meq/l instead of -232 ± 27 meq/l.

Effect of lithium and amiloride on collecting tubule transport enzymes

In humans and animals, the administration of Li or amiloride results in a defect in urinary acidification. Both agents are thought to cause this by a voltage-dependent mechanism in the distal nephron. This study was designed to determine the effects of chronic Li and amiloride administration on the two main transport enzymes in rat nephron collecting tubule, the Na-K-adenosine triphosphatase (ATPase) and the H(+)-ATPase. We also examined the effects of both agents on these enzymes in vitro. Amiloride administration resulted in a decrease in Na-K-ATPase and H(+)-ATPase activities in cortical collecting tubule and medullary collecting tubule. Therapeutic concentrations of amiloride in vitro inhibited Na-K-ATPase activity, but only in cortical collecting tubule. The effects of Li administration were different; it decreased Na-K-ATPase and H(+)-ATPase in both cortical collecting tubule and medullary collecting tubule. In cortical collecting tubule, the inhibitory effect on H(+)-ATPase activity was seen in vitro at a Li concentration similar to that found in urine. In contrast to the effect of Li on the H(+)-ATPase, in vitro Li stimulated Na-K-ATPase activity. These results suggest that the mechanism of action whereby these two agents result in distal renal tubular acidosis in humans and animals are different. In the collecting tubule, amiloride appears to act solely through a voltage-dependent mechanism by inhibiting cortical collecting tubule Na-K-ATPase. Li, by contrast, appears to have an additional effect in the cortical collecting tubule to inhibit the H(+)-ATPase. The biochemical differences seen with these drugs may explain the more severe acidemia universally found in animals after chronic Li administration.

Vanadate causes hypokalemic distal renal tubular acidosis

Considerable evidence supports the presence of an H(+)-K(+)-ATPase along the mammalian nephron. Inhibition of this enzyme might be expected to reduce acid excretion while increasing potassium excretion, thus causing hypokalemic distal renal tubular acidosis (RTA). In this study we administered vanadate at a dose of 5 mg/kg ip for 10 days to rats. These animals developed hypokalemic distal RTA with a blood pH of 7.22 +/- 0.01, a plasma bicarbonate of 15.2 +/- 0.6 meq/l, and a plasma potassium of 3.28 +/- 0.06 meq/l. The vanadate-treated animals had a urine pH of 6.70 +/- 0.09, a value significantly higher than NH4Cl-treated animals with the same degree of acidemia (urine pH = 5.25 +/- 0.04). When cortical collecting tubules (CCT) from these animals were microdissected and H(+)-K(+)-ATPase was measured, it was decreased by approximately 75% (P less than 0.001); but H(+)-ATPase was no different from control. In medullary collecting tubule, H(+)-K(+)-ATPase was also decreased but less than in CCT. Muscle potassium concentration in the vanadate-treated animals was significantly lower than in controls. These results demonstrate that vanadate causes hypokalemic distal RTA in association with inhibition of collecting tubule H(+)-K(+)-ATPase activity.

The effect of pregnancy on renal function: physiology and pathophysiology

Marked changes in renal function occur with pregnancy. We present a summary of these changes in this review and give insight into possible mechanisms if they are known. Controversies exist regarding the therapy of pregnancy-induced hypertension and asymptomatic and recurrent bacteriuria. The current views on these topics are given. Specific renal diseases are summarized, including transplantation, and optimum management strategies and maternal and fetal prognosis during pregnancy are given.

NEM-sensitive ATPase activity in rat nephron: effect of metabolic acidosis and alkalosis

The present study was designed to quantitate the amount and to map the localization of N-ethylmaleimide (NEM)-sensitive adenosinetriphosphatase (ATPase) activity in microdissected segments of the rat nephron. After complete nephron mapping the effect of chronic metabolic acidosis and alkalosis on enzyme activity was determined. In control animals the highest enzyme activity was found in the early proximal convoluted tubule of juxtamedullary nephrons; superficial early proximal tubule as well as medullary and cortical thick ascending limbs and collecting ducts also contained substantial activity. Enzyme activity in the papillary collecting duct before entry into the ducts of Bellini was 329 +/- 93 pmol.mm-1.h-1 (n = 8); after entry, however, enzyme activity was approximately one-fourth that value (60 +/- 9 pmol.mm-1.h-1, n = 8, P less than 0.01). No NEM-sensitive ATPase activity was found in the thin limbs of the loop of Henle. Enzyme activity increased in both the medullary and cortical thick ascending limbs as well as in the cortical collecting tubule in response to NH4Cl-induced chronic metabolic acidosis; in the cortical collecting duct, metabolic acidosis increased maximum activity (Vmax) but did not change Michaelis-Menten constant (Km). In the proximal convoluted tubule, enzyme activity decreased with metabolic acidosis. Bicarbonate loading had no effect on enzyme activity except in the most distal portion of the collecting duct where it was stimulated. These results show that NEM-sensitive ATPase activity exists throughout much of the rat nephron. These data suggest that both the cortical collecting tubule and thick ascending limb are regulatory sites of distal urinary acidification during acid loading.

Enzyme activity in obstructive uropathy: basis for salt wastage and the acidification defect

Unilateral ureteral obstruction results in marked changes in renal function throughout the nephron, including impaired acid and potassium secretion and salt wastage. The nephron site believed responsible for the acidification defect is the collecting duct. It has been presumed, although not demonstrated, that the cellular mechanism for the acidification defect is both a decrease in transepithelial voltage and a decrease in activity of the proton pump located at the luminal membrane. The mechanism for the abnormalities in sodium handling are thought due to alterations in Na-K ATPase activity. Our laboratory has recently mapped the profile of the N-ethylmaleimide (NEM)-sensitive ATPase and Na-K ATPase in microdissected rat nephron, documenting their presence throughout much of the nephron. In animals with acute unilateral ureteral obstruction for 18 to 24 hours, we measured NEM-sensitive ATPase and Na-K ATPase activities in several nephron sites. In all nephron segments Na-K ATPase activity was markedly decreased. In the medullary collecting duct, NEM-sensitive ATPase activity was also markedly reduced in animals with acute ureteral obstruction; in the cortical collecting duct, activity fell significantly, but to a lesser degree than was observed in the medullary collecting duct. NEM-sensitive ATPase activity was unchanged from control in the proximal convoluted tubule and in the medullary thick ascending limb; in the cortical thick ascending limb enzyme activity increased. These results demonstrate a change in both Na-K ATPase and NEM-sensitive ATPase activities as a direct consequence of a defect known to result in salt wastage and an acidification defect in humans and animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Peculiar effects of temperature and polyvinylalcohol on the activity of bovine serum amine oxidase

An inflexion point of enzyme activity at 38 - 42 degrees C of the bovine serum amineoxidase was found. This result, associated with non-strict Arrhenius curves and slightly different activation energies in various temperature intervals, suggests some conformational transitions at the mentioned temperatures. The high molecular weight polyvinylalcohol (100,000 Da) generated an activatory effect and a sigmoidal (non-Michaelis) curve of the dependence of the activity on the substrate concentrations, while the low molecular weight polyvinylalcohol (20,000 Da) does not produce this effect. The different ratio of the two types of polyvinylalcohol/enzyme monomer sizes is considered to be responsible for these different effects on the enzyme kinetics.

Effect of phthalate acid esters on transport in toad bladder membrane

Sclerosing peritonitis is a serious complication in patients on long-term peritoneal dialysis; it markedly decreases transport of water and solute across the peritoneal membrane. Although the precise mechanism is unknown, organic compounds (i.e., plasticizers) from plastic tubing and dialysis bags have been suggested to be a cause of the syndrome. The effects of three such compounds on water and sodium transport in vitro were studied in the toad bladder. The compounds studied were didodecylphthalate, dioctylphthalate, and benzylbutylphthalate. After 4 hr incubation in vitro, dioctylphthalate and benzylbutylphthalate significantly inhibited vasopressin-stimulated water flow in toad bladder. Basal water flow was not affected by any of the three compounds. Sodium transport, as measured using short-circuit current, was decreased to an equivalent degree by all compounds; inhibition of short-circuit current was dose dependent and was approximately 30% at 10(-3) M. The onset of action was between 3.5 and 4 hr, and the effect on short-circuit current was not reversible. These results demonstrate that the plasticizers (to which patients of all sorts are commonly exposed) inhibit transport across living membranes. In the toad bladder these compounds decrease sodium transport and maximal water flow. Although other evidence suggests that the cumulative toxic effects of these compounds may play a causal role in sclerosing peritonitis in patients on peritoneal dialysis, our study suggests that chronic exposure to the phthalate acid esters in patients with normal renal function may result in sodium wastage, polyuria, and a concentrating defect resistant to AVP.

Vanadate stimulates the N-ethylmaleimide-sensitive adenosine triphosphatase in rat nephron

Vanadate has been used in many cellular systems to elucidate mechanisms of enzyme action. Vanadate inhibits Na-K adenosine triphosphatase (ATPase) activity in many tissues. In isolated collecting tubule it inhibits sodium transport and vasopressin-stimulated water flux, the latter presumably distal to cyclic AMP formation. Depending upon the tissue studied, vanadate also stimulates a variety of cellular reactions including adenylate cyclase, glucose oxidation and glycogen synthesis. We studied the effect of varying concentrations of vanadate on N-ethylmaleimide (NEM)-sensitive ATPase activity in microdissected segments of rat nephron. In proximal convoluted tubule and in cortical, medullary and papillary collecting ducts vanadate had no effect on enzyme activity. In medullary and cortical thick ascending limbs, however, vanadate significantly stimulated NEM-sensitive ATPase activity (medullary thick ascending limb, 241 +/- 14 pmol/mm/hr vs. 531 +/- 74 pmol/mm/hr; control vs. (1 mM) vanadate, respectively; n = 14, P less than 0.01). The stimulatory effect of vanadate on NEM-sensitive ATPase activity was present at 5 microM vanadate, a concentration that inhibited Na-K ATPase activity approximately 80%. Metabolic acidosis also stimulated enzyme activity in the thick ascending limb, and the effect of vanadate was not additive. Metabolic alkalosis had no effect on NEM-sensitive ATPase in the thick ascending limb, but the stimulatory effect of vanadate was still seen. These data document that the NEM-sensitive ATPase in thick ascending limb is different from that found in other nonmammalian proton secretory epithelia which are vanadate inhibitable. The results with vanadate plus metabolic acidosis suggest that both are acting via the same mechanism.