EFFECTS OF ETHACRYNIC ACID (A NEW SALURETIC AGENT) ON RENAL DILUTING AND CONCENTRATING MECHANISMS: EVIDENCE FOR SITE OF ACTION IN THE LOOP OF HENLE

Emerging and Re-emerging Warheads for Targeted Covalent Inhibitors: An Update

Covalent inhibitors and other types of covalent modalities have seen a revival in the past two decades, with a variety of new targeted covalent drugs having been approved in recent years. A key feature of such molecules is an intrinsically reactive group, typically a weak electrophile, which enables the irreversible or reversible formation of a covalent bond with a specific amino acid of the target protein. This reactive group, often called the "warhead", is a critical determinant of the ligand's activity, selectivity, and general biological properties. In 2019, we summarized emerging and re-emerging warhead chemistries to target cysteine and other amino acids (Gehringer, M.; Laufer, S. A. J. Med. Chem. 2019, 62, 5673-5724; DOI: 10.1021/acs.jmedchem.8b01153). Since then, the field has rapidly evolved. Here we discuss the progress on covalent warheads made since our last Perspective and their application in medicinal chemistry and chemical biology.

Ethacrynic Acid: A Promising Candidate for Drug Repurposing as an Anticancer Agent

Ethacrynic acid (ECA) is a diuretic that inhibits Na-K-2Cl cotransporter (NKCC2) present in the thick ascending loop of Henle and muculo dens and is clinically used for the treatment of edema caused by excessive body fluid. However, its clinical use is limited due to its low bioavailability and side effects, such as liver damage and hearing loss at high doses. Despite this, ECA has recently emerged as a potential anticancer agent through the approach of drug repositioning, with a novel mechanism of action. ECA has been shown to regulate cancer hallmark processes such as proliferation, apoptosis, migration and invasion, angiogenesis, inflammation, energy metabolism, and the increase of inhibitory growth factors through various mechanisms. Additionally, ECA has been used as a scaffold for synthesizing a new material, and various derivatives have been synthesized. This review explores the potential of ECA and its derivatives as anticancer agents, both alone and in combination with adjuvants, by examining their effects on ten hallmarks of cancer and neuronal contribution to cancer. Furthermore, we investigated the trend of synthesis research of a series of ECA derivatives to improve the bioavailability of ECA. This review highlights the importance of ECA research and its potential to provide a cost-effective alternative to new drug discovery and development for cancer treatment.

Chemoproteomic Profiling Reveals Ethacrynic Acid Targets Adenine Nucleotide Translocases to Impair Mitochondrial Function

Ethacrynic acid (EA) is a diuretic drug that is widely used to treat high-blood pressure and swelling caused by congestive heart failure or kidney failure. It acts through noncovalent inhibition of the Na⁺-K⁺-2Cl^- cotransporter in the thick ascending limb of Henle's loop. Chemically, EA contains a Michael acceptor group that can react covalently with nucleophilic residues in proteins; however, the proteome reactivity of EA remains unexplored. Herein, we took a quantitative chemoproteomic approach to globally profile EA's targets in cancer cells. We discovered that EA induces impaired mitochondrial function accompanied by increased ROS production. Our profiling revealed that EA targets functional proteins on mitochondrial membranes, including adenine nucleotide translocases (ANTs). Site-specific mapping identified that EA covalently modifies a functional cysteine in ANTs, a mutation of which resulted in the rescuing effect on EA-induced mitochondrial dysfunction. The newly discovered modes of action offer valuable information to repurpose EA for cancer treatment.

The clinical pharmacology of ethacrynic acid

Ethacrynic acid (Edecrin) is a loop diuretic that produces a prompt and profound diuresis. The primary action of ethacrynic acid is the inhibition of the activity of the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle. The onset of action is usually within 30 minutes after an oral dose and within 5 minutes after an intravenous injection. After oral administration, peak diuretic effect occurs in about 2 hours and the effect lasts about 6-8 hours. After intravenous administration, peak diuretic effect occurs within 30 minutes and the diuretic effect is virtually completed in 2-4 hours. The bioavailability of ethacrynic acid approximates 100%, with maximal blood level between 40 and 92 minutes. The elimination half-life has been reported to be less than 1 hour, but highly variable (average 30 minutes with a range of 12-160 minutes). Intravenous ethacrynic acid has a prompt venous dilatory effect and immediately relieves symptoms of pulmonary congestion, before a diuresis can occur. Ethacrynic acid is effective in all types of edema whether there is clinical acidosis, alkalosis, or electrolyte imbalance. Most side effects of ethacrynic acid can be attributed to its effectiveness (volume depletion); however, it may cause metabolic alkalosis that is preventable by KCl replacement. Ethacrynic acid has ototoxic effect that occasionally results in temporally or permanent deafness. Despite limitations, ethacrynic acid has been employed in the treatment of congestive heart failure and other edematous states, especially in patients allergic to sulfa-containing drugs because all the other loop diuretics have a sulfa moiety.

Pharmacokinetics and pharmacodynamics of azosemide

Azosemide is used in the treatment of oedematous states and hypertension. The exact mechanism of action is not fully understood, but it mainly acts on both the medullary and cortical segments of the thick ascending limb of the loop of Henle. Delayed tolerance was demonstrated in humans by homeostatic mechanisms (principally an increase in aldosterone secretion and perhaps also an increase in the reabsorption of solute in the proximal tubule). After oral administration to healthy humans in the fasting state, the plasma concentration of azosemide reached its peak at 3-4 h with an absorption lag time of approximately 1 h and a terminal half-life of 2-3 h. The estimated extent of absolute oral bioavailability in humans was approximately 20.4%. After oral administration of the same dose of azosemide and furosemide, the diuretic effect was similar between the two drugs, but after intravenous administration, the effect of azosemide was 5.5-8 times greater than that in furosemide. This could be due to the considerable first-pass effect of azosemide. The protein binding to 4% human serum albumin was greater than 95% at azosemide concentrations ranging from 10 to 100 microg/ml using an equilibrium dialysis technique. The poor affinity of human tissues to azosemide was supported by the relatively small value of the apparent post-pseudodistribution volume of distribution (Vdbeta), 0.262 l/kg. Eleven metabolites (including degraded products) of azosemide including M1, glucuronide conjugates of both M1 and azosemide, thiophenemethanol, thiophencarboxylic acid and its glycine conjugate were obtained in rats. Only azosemide and its glucuronide were detected in humans. In humans, total body clearance, renal clearance and terminal half-life of azosemide were 112 ml/min, 41.6 ml/min and 2.03 h, respectively. Azosemide is actively secreted in the renal proximal tubule possibly via nonspecific organic acid secretory pathway in humans. Thus, the amount of azosemide that reaches its site of action could be significantly modified by changes in the capacity of this transport system. This capacity, in turn, could be predictably changed in disease states, resulting in decreased delivery of the diuretic to the transport site, as well as in the presence of other organic acids such as nonsteroidal anti-inflammatory drugs which could compete for active transport of azosemide. The urinary excretion rate of azosemide could be correlated well to its diuretic effects since the receptors are located in the loop of Henle. The diuretic effects of azosemide were dependent on the rate and composition of fluid replacement in rabbits; therefore, this factor should be considered in the evaluation of bioequivalence assessment.

Diuretic use in the elderly: potential for diuretic-induced hypokalemia

The more potent "loop" diuretics are being used with increasing frequency. The elderly constitute a growing portion of the population undergoing treatment with diuretics. The alterations in renal function and pharmacokinetics in the elderly (over 60 years of age) may result in the development of certain adverse effects. In patients over 70 years old, there is a progressive decline in overall renal function, resulting in a more than 50% decrease in glomerular filtration rate. Most of the pharmacokinetic changes in the elderly consist of alterations resulting in enhanced plasma levels of any given drug; diminished hepatic drug extraction, detoxification/metabolism or prodrug conversion; decreased renal excretion of drug; and diminished volume of distribution of drug. Adverse reactions to diuretics may be grouped into metabolic changes (e.g., hypokalemia), physiologic alteration (e.g., volume contraction), toxic manifestation (e.g., interstitial nephritis) and allergic or idiosyncratic phenomena (e.g., rash or thrombocytopenia). There is general agreement that significant hypokalemia, particularly among elderly patients receiving digitalis glycosides, is significant and requires therapy. Diuretic-associated hypokalemia reflects the potency and duration of action of a diuretic, factors modulating potassium balance including dietary intake and concurrent medical processes. The short duration of action and greater natriuresis relative to kaliuresis characteristic of loop diuretics may result in a lesser degree of hypokalemia than that seen with traditional thiazide diuretics.

Clinical pharmacologic implications in diuretic selection

Logical and comprehensive diuretic therapy is based on a sound knowledge of renal physiologic principles. Knowledge of the sites within the nephron at which the currently available diuretics work and their modes of action provide the clinician with a basis upon which to arrive at therapeutic decisions. True diuretic resistance is uncommon, but when it occurs, sequential nephron blockade can frequently reverse the refractoriness initially exhibited by the patient.

Site of action of torasemide in man

The effect of torasemide, a new orally and parenterally active diuretic agent, on the renal mechanisms of dilution and concentration was studied in 6 healthy volunteers. The experimental conditions included water and osmotic diuresis. Torasemide caused maximal chloruresis and natriuresis during the 20-40 min after administration. The effect was more pronounced under osmotic diuresis and persisted throughout the 100 min of those experiments. A distinct effect both on free water clearance (CLH2O) during water diuresis and tubular reabsorption of solute free water (TcH2O) during osmotic diuresis strongly suggests that the major site of action of torasemide is the ascending limb of the loop of Henle. Comparison with furosemide under osmotic diuresis indicates longer abolition of TcH2O/GFR by torasemide in keeping with the fact that its half-life is 2- to 3-times longer than that of furosemide.

Diuretics. Clinical pharmacology and therapeutic use (Part I)

25 years have elapsed since the introduction of the first effective oral diuretic, chlorothiazide. Diuretics are now amongst the most widely prescribed drugs in clinical practice worldwide. Availability of these drugs has not only brought therapeutic benefit to countless numbers of patients but it has at the same time provided valuable research tools with which to investigate the functional behaviour of the kidney and other electrolyte-transporting tissues. Despite many remaining gaps in our knowledge of the biochemical processes involved in diuretic drug action, available compounds can be divided into 5 groups on the basis of their preferential effects on different segments of the nephron involved in tubular reabsorption of sodium chloride and water. Firstly, there is heterogeneous group of chemicals that share the common property of powerful, short-lived diuretic effects that are complete within 4 to 6 hours. These agents act on the thick ascending limb of Henle's loop and are known as 'high ceiling' or 'loop' diuretics. The second group are the benzothiadiazines and their many related heterocyclic variants, all of which localise their effects to the early portion of the distal tubule. The third group comprises the potassium-sparing diuretics which act exclusively on the Na+-K+/H+ exchange mechanisms in the late distal tubule and cortical collecting duct. The action of drugs in groups 2 and 3 is prolonged to between 12 and 24 hours. The fourth group consists of diuretics that are chemically related to ethacrynic acid but have the unusual property of combining within the same molecule the property of saluresis and uricosuria. These compounds have actions, to different individual extents, in the proximal tubule, thick ascending limb, and early distal tubule and are known as 'polyvalent' diuretics. Finally, there is a mixed group of weak or adjunctive diuretics which includes the vasodilator xanthines such as aminophylline, and the osmotically active compounds such as mannitol. Available evidence on the molecular mechanisms of action of diuretics in each group is reviewed. The haemodynamic, humoral and physical factors involved in control of electrolyte and fluid handling by the kidney in normal conditions and pathological states are discussed in relation to rational choices of different diuretics in the treatment of various oedematous and non-oedematous conditions.

Bumetanide. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use

Bumetanide is a potent 'loop' diuretic for the treatment of oedema associated with congestive heart failure, hepatic and renal diseases, acute pulmonary congestion and premenstrual syndrome and in forced diuresis during and after surgery. Bumetanide may be given orally, intravenously or intramuscularly and produces a rapid and marked diuresis, and increased urinary excretion of sodium, chloride and other electrolytes (within 30 minutes) which persists for 3 to 6 hours. Its principal site of action is on the ascending limb of the loop of Henle, with a secondary action on the proximal tubule. Pharmacologically, bumetanide is about 40-fold more potent than frusemide (furosemide), with the exception of its effects on urinary potassium excretion where its potency is lower. Studies in patients with oedema due to congestive heart failure, pulmonary oedema or hepatic disease show that oral or intravenous bumetanide 0.5 to 2 mg/day produces results comparable to those with frusemide 20 to 80 mg/day. In acute pulmonary oedema, intravenous bumetanide produces a very rapid diuresis. Higher doses of bumetanide may be required (up to 15 mg/day) in patients with chronic renal failure or nephrotic syndrome. In these patients muscle cramps are not uncommon with bumetanide, but glomerular filtration rates are unaffected. In most studies, diuretic effects were accompanied by decreased bodyweight, abdominal girth and improvements in a variety of haemodynamic parameters. Comparison of bumetanide with frusemide at a dose ratio of 1 : 40 reveals no significant differences in clinical response with the exception of renal disease, where patients with oedema appear to respond better to bumetanide. Combination with thiazide diuretics enhances the clinical response to bumetanide. Potassium supplements and spironolactone may be beneficial additions to bumetanide where patients at risk of hypokalaemia can be identified. Clinically important side effects are infrequent, with audiological impairment occurring to a lesser extent than with frusemide. Bumetanide thus offers an important alternative to frusemide when a 'loop' diuretic is indicated.

Effects of ethacrynic acid in the newborn infant

The effects of ethacrynic acid on electrolyte and water excretion were examined in 10 neonates with fluid overload states. Ethacrynic acid (1 mg/kg IV) produced a 10-fold increase in FENa+ and FECl - and a sixfold increase in urine volume and osmolar clearance. These effects peaked within 1 hour of ethacrynic acid administration, and progressively decreased to the baseline value by 5 hours after drug administration. The mean excretion of potassium increased by 280% in 1 hour, and returned to baseline value after 5 hours. The mean Ca++ excretion increased fourfold after 1 hour, and the effect lasted for 4 hours. Two infants developed mild hyponatremia. Our data emphasize the prolonged diuretic and saluretic effect of ethacrynic acid in neonates.

Renal actions of a uricosuric diuretic, racemic indacrinone, in man: comparison with ethacrynic acid and hydrochlorothiazide

The effects of indacrinone (IND) have been investigated in a two part study. First, a total of 36 clearance studies have been performed in 14 healthy volunteers, under conditions of either maximal hydration or hydropenia, to compare the renal sites of action of single oral doses of IND, 20 mg, ethacrynic acid (EA), 100 mg, and hydrochorothiazide (HCTZ), 100 mg. Under conditions of maximal water hydration, IND increased fractional Na+ excretion from a mean of 1.19 +/- 0.05 to 4.93 +/- 0.67% of GFR. This was similar to the response seen with HCTZ, which increased fractional Na+ clearance up to 3.16 +/- 0.17% of GFR; EA increased fractional Na+ excretion up to 14.5 +/- 2.5% of GFR. The mean reduction in fractional free-water clearance (CH2O/GFR X 100%) invoked by IND, (delta = -34.8% of control) was similar to that produced by EA, (delta = -27.2% of control), and by HCTZ, (delta = -26.6% of control). During hydropenia with superimposed mannitol diuresis, both IND and EA caused a fall in fractional free-water reabsorption (TcH2O/GFR X 100%), delta IND = -20.3% of control, delta EA = -70.1% of control. HCTZ produced a significant increase in fractional free-water reabsorption, delta HCTZ = -20.7% of control. In all studies, single doses of IND were both uricosuric and hypouricaemic. Fractional urate excretion increased from a mean 6.7 +/- 0.1 to 15.2 +/- 2.1% of GFR whilst plasma urate concentration fell from a mean of 0.36 +/- 0.03 to 0.34 +/- 0.03 mM (P less than 0.05) within 2-3 h post drug. HCTZ and EA, in single doses, had little effect on urate excretion. In the second part of the study, a total of 16 healthy volunteers received either IND, 10 mg, or HCTZ 50 mg, orally for 8 days, whilst on a diet of controlled electrolyte content. Both drugs were well tolerated by both sets of subjects with no adverse clinical or pathological findings. Both IND and HCTZ caused a significant reduction in weight and standing systolic blood-pressure during the first 48 h of therapy. At the doses administered, IND and HCTZ displayed similar diuretic responses with respect to water, Na+, Cl-, Ca2+ and PO4(3-) excretion. IND produced less kaliuresis than HCTZ during the first treatment day but cumulative K+ loss was similar for both drugs over the eight days of therapy. Fractional urate excretion after IND remained elevated throughout the 8 days of therapy and the subjects remained isouricaemic for 7 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Bumetanide: a new loop diuretic (Bumex, Roche Laboratories)

Bumetanide is a recently introduced diuretic that inhibits sodium transport in the thick ascending limb of the loop of Henle. It is structurally and pharmacologically similar to furosemide, but is approximately 40 times as potent on a milligram-for-milligram basis. After oral administration, it is rapidly absorbed, with peak serum concentrations attained at approximately 30 minutes. Its pharmacokinetic parameters are similar to those of furosemide. Bumetanide has demonstrated efficacy in the management of edema associated with congestive heart failure, hepatic cirrhosis, and renal insufficiency. Bumetanide has demonstrated an adverse-reaction profile similar to that of furosemide, although the incidence of hypochloremia and hypokalemia is greater with bumetanide. The incidence of hyperglycemia and ototoxicity is greater with furosemide. The principal indication for bumetanide may be in patients with increased risk of ototoxicity. Cost considerations should relegate bumetanide to a secondary role for the treatment of sodium and fluid retention in most clinical settings.

Pharmacology of bumetanide

The diuretic action of bumetanide was compared with that of furosemide following oral and intravenous administration of equipotent doses in the rat, mouse, cat, rabbit, and dog. The onset of the bumetanide-induced diuresis was rapid and lasted 4 to 6 hours. In studies of selective renal uptake, the ratio of tissue concentration to plasma concentration of bumetanide was three times greater than that of furosemide. Protein binding and metabolism studies did not reveal significant differences between the two diuretics. Bumetanide and Furosemide were excreted in dog urine as unchanged drug. Data obtained by various procedures to determine renal sites of action indicate a direct action of bumetanide at the ascending limb of Henle's loop and the proximal convoluted tubule. The altered blood flow induced by bumetanide does not per se account for the natriuretic response, but the increase in renal electrolyte excretion is thought to be linked to a prostaglandin--reninbradykinin system.

Studies on the mechanism and characteristics of action of a uricosuric diuretic, indacrinone (MK-196)

1 The renal action of indacrinone (MK-196), a phenoxyacetic acid derivative with diuretic and uricosuric properties, has been studied in fifteen male subjects. 2 Increasing single doses of up to 60 mg of oral indacrinone produced a linear increase in urinary volume and excretion of Na+ and Cl-, whilst the responses of urinary K+, Ca2+, Mg2+ and uric acid excretion, rose to a plateau at the 40 mg dose. 3 Indacrinone evoked a rapid diuretic response which reached a maximum of 2-4 h and was largely complete at 8-12 h after administration. 4 During maximal hydration, indacrinone produced a substantial fall in fractional free water clearance (CH2O), from 8.89% to 5.83% of the filtered load of water, associated with an increase in osmolal clearance, from 1.38% to 5.78% of the filtered load of solute. The reduction in CH2O was of the same order as that produced by a dose of ethacrynic acid with comparable saluretic activity and significantly greater than that produced by an equi-saluretic dose of hydrochlorothiazide. These findings imply an action of indacrinone upon solute transport in the diluting segments of the distal tubule. 5 At the time of maximal indacrinone-induced saluresis, which amounted to an increase from 0.48% to 4.61% of the filtered load of NaCl, fractional urate clearance increased from 5.16% to 12.24% of the filtered load of uric acid. 6 Indacrinone is a long acting diuretic, sharing some properties in common with both loop diuretics and benzothiadiazines. The results are discussed in relation to structure-activity amongst derivatives of phenoxyacetic acid.

The diuretic response in normal volunteers to a new benzylamine, 2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol HCl

A phase I dose-response study of 2-aminomethyl-4-(1,1-dimethylethyl)-6-iodophenol HCl (MK-447) was performed with the following oral doses: 6.25, 12.5, 25, 50, and 100 mg. Each volunteer served as his own control. The study was carried out in double-blind fashion on a 5-Gm Na and K diet with a minimum 2000 ml fluid intake. Urine was fractionated and analyzed for sodium, chloride, potassium, calcium, uric acid, and volume. Comparisons (MK-447 minus control values) of the 24-hour total sodium, calcium, potassium, and volume excretion rates at 6.25, 25 and 100 mg MK-447 were as follows: sodium, 195, 345, and 528 muEq/min; chloride, 191, 365, and 756 muEq/min; potassium, 77, -3, and 65 muEq/min; and volumes, 1, 3.4 and 11.7 ml/min. MK-447 did not alter calcium excretion. Uric acid excretion was observed to decrease as the dose of MK-447 was increased, however, the serum uric acid level always remained within normal limits. MK-447 did not alter the physiologic parameters but did produce symptoms of volume contraction at 100 mg. Because no further dose increase was attempted, a plateau in the dose-response curve was not reached. Comparison of 100 mg MK-447 with 80 mg oral furosemide revealed similar potency and a somewhat longer duration of action for MK-447.

Natriuretic and phosphaturic response to diuretics after parathyroidectomy in dogs

Intact and acutely parathyroidectomized (TPTX) dogs were studied during hydropenia, volume expansion (VE), volume expansion plus ethacrynic acid (EA), and volume expansion plus acetazolamide (AZ). In intact dogs, VE produced marked increases in both Na+ and phosphate (Pi) excretion; in TPTX dogs, Na+ excretion increased but phosphaturia was minimal. Addition of EA increased Na+ but not Pi excretion in both groups. Discontinuing EA and substituting AZ in intact dogs produced a marked increase in Pi excretion compared to both VE and VE + EA. In TPTX dogs, AZ failed to increase Pi excretion compared to VE alone. The results suggest that increased distal Pi absorption in acutely TPTX dogs is not associated with NaCl reabsorption in the thick ascending loop of Henle or may occur at an alternative nephron site. Furthermore, the increased distal Pi reabsorptive capacity revealed by TPTX can overcome the increased distal Pi delivery produced by the superimposition of AZ on VE.

Diuretic effects of Bay g 2821 in patients with advanced renal failure

Clearance studies were carried out in 18 non-oedematous patients with advanced renal failure (glomerular filtration rate less than 12 ml/min) to assess the diuretic effects of Bay g 2821 given different oral doses (120 mg to 360 mg). The results showed a significant increase in urinary volume and in clearances of sodium, calcium, magnesium, chloride, inorganic phosphorus and 51CrEDTA. There were no significant changes, however, in clearance of PAH, urea and uric acid. The diuretic response started in the first hour after drug intake, reached a maximum after 3 to 5 hours, and declined slowly in the following 3 to 4 hours. In patients with a glomerular filtration rate less than 3 ml/min the drug lost its effect. In rates between 5 to 10 ml/min the efficacy of Bay g 2821 was comparable to that of furosemide and ethacrynic acid. No side-effects were reported.

A method for screening diuretic agents in the mouse: an investigation of sexual differences

Acetazolamide, aminophyline, frusemide, ethacrynic acid and triamterene were tested for diuretic action at dosages of 3, 10 and 30 mg kg-1 (s.c.) in male and female mice. Each drug significantly raised sodium excretion and all but acetazolamide elevated urine volume and chloride excretion. Potassium excretion was significantly raised by acetazolamide and frusemide. Acetazolamide and triamterene evoked urinary alkalinization whereas frusemide and ethacrynic acid reduced urinary pH. Female mice were markedly more sensitive than males to the diuretic, natriuretic, chloruretic and urinary acidfying actions of ethacrynic acid.

Laboratory tests of renal function

There are several tests available to evaluate renal function. Because the kidney has such complex and varied functions, no one test can adequately measure them. A rough measure of renal function can be obtained by examining the constituents of the urine. More specific aspects of tubular and glomerular function require more complex tests. Proper interpretation of these tests, however, requires knowledge of the patient's status and clinical course.

Effects of ethacrynic acid on the isolated collecting tubule

Effects of the diuretic ethacrynic acid on osmotic water permeability were investigated in the isolated perfused collecting tubule of the rabbit kidney. The base-line water permeability of the collecting tubule was not affected when the drug (10(-4)M) alone was added to the bathing medium. Vasopressin alone in the bathing medium (2, 5 muU/ml) elicited a significant increase in osmotic water absorption. With vasopressin kept in the bathing medium, the addition of 10(-5)M ethacrynic acid depressed the hydro-osmotic effect of vasopressin by 50%. This inhibitory effect of low concentrations of ethacrynic acid could be surmounted by high, supramaximal dosage levels of vasopressin. When 10(-4)M ethacrynic acid was added to the bathing medium before vasopressin, the hydro-osmotic effect of vasopressin and the diuretic in combination was insignificant.Dibutyryl adenosine 3'5'-monophosphate (10(-4)-10(-2)M) alone in the bathing medium significantly increased baseline osmotic water flow, mimicing the effect of antidiuretic hormone. When ethacrynic acid was added together with the nucleotide, the permeability remained at the same high level. Theophylline, like the nucleotide and vasopressin, produced a significant hydro-osmotic effect. The magnitude of this response was not affected by further addition of ethacrynic acid (10(-4)M). It was concluded that ethacrynic acid is an antagonist of antidiuretic hormone. The antagonism probably occurs at the level of the receptor site of the hormone on the peritubular membrane. Antagonism to circulating antidiuretic hormone may therefore be one of the factors involved in the loss of renal concentrating ability brought about by ethacrynic acid diuresis.

Acute effect of prednisolone on renal handling of sodium

The effect of prednisolone on renal handling of sodium (Na) was studied in rats under three experimental conditions: 1) hydropenia, 2) water diuresis, and 3) distal tubular blockade (DTB). Prednisolone, 0.25 mg/100 g per hr, was infused directly into left renal artery and urine was collected separately from each kidney. Predominantly unilateral increases in urine flow (V) and Na excretion were noticed in all experiments during prednisolone infusion. In the hydropenic rats the maximal increments on the infused side were, for V (mean ± SD), from 9.3 ± 1.5 to 21.4 ± 0.8 μl/min (P < 0.001); for C_Na/C_In, from 0.28 ± 0.11 to 2.97 ± 0.71 % (P < 0.005); and for TH2Oc/CIn, from 2.93 ± 2.26 to 5.32 ± 1.92% (P < 0.05). In the rats with water diuresis, the maximal increases were, for V/C_In, from 5.87 ± 1.97 to 10.1 ± 6.0% (P < 0.005); for C_H2O/C_In, from 4.09 ± 0.68 to 6.00 ± 0.44% (P < 0.0005); and for C_Na/C_In, from 0.22 ± 0.07 to 0.70 ± 0.38% (P < 0.01). In DTB-rats the maximal increases were for V from 48.6 ± 9.0 to 72.7 ± 14.1 μl/min (P < 0.0005) and for C_Na/C_In from 9.42 ± 2.97 to 20.23 ± 7.34% (P < 0.005). In the contralateral kidney these changes were less pronounced. These observations suggest that prednisolone depresses directly Na reabsorption. The association of natriuresis with augmented TH2Oc/CIn and C_H2O/C_In during hydropenia and water diuresis, respectively, and the increases in V and C_Na/C_In during DTB, all are consistent with inhibition of Na reabsorption in the proximal tubule.

Lithium-induced nephrogenic diabetes insipidus: in vivo and in vitro studies

The physiological basis for the polyuria and polydipsia occurring in some manic-depressive patients treated with lithium salts was studied in vivo and in vitro. Three lithium-treated polyuric patients, in whom other causes of a concentrating defect were excluded, had abnormal urinary concentrating abilities after a standard water depreviation test. Two of these patients failed to respond to exogenous vasopressin (ADH) and one had a subnormal response. The abilities of these patients to excrete solute-free water (C(H2O)) was comparable to normal subjects during steady-state water diuresis, suggesting no gross abnormalities in sodium transport. However, each of these patients demonstrated abnormally low capacities to reabsorb solute-free water (T(C) (H2O)) under hydropenic conditions after administration of hypertonic saline and vasopressin. These in vivo findings demonstrate at least a nephrogenic basis for the diabetes insipidus syndrome manifested by these three patients. The defect in water transport was further characterized in toad urinary bladders in vitro. Short-circuit current (I) and water flow (W) were studied under basal, ADH-stimulated, and cyclic adenosine 3',5'-monophosphate (c-AMP)-stimulated conditions. Increasing mucosal [Li(+)] progressively inhibited basal I, and both I and W induced by ADH. Significant inhibition of basal and ADH-induced I was observed at mucosal [Li(+)] < 1.1 mEq/liter, and of ADH-induced W at mucosal [Li(+)] = 11 mEq/liter. On the other hand, at these lithium concentrations, neither c-AMP-stimulated W nor I was inhibited. Increasing serosal [Li(+)] produced significant inhibition of basal I only at [Li(+)] at least 50-fold greater than at the mucosal (urinary) surface. These in vitro studies confirm that mucosal lithium inhibits the action of ADH, but not c-AMP. Hence, lithium appears to be a significant inhibitor of ADH-stimulated water flow, probably acts from the urinary surface, and appears to exert its effect at a site biochemically proximal to c-AMP action.

Role of antidiuretic hormone in the abnormal water diuresis of anterior hypopituitarism in man

To evaluate the role of antidiuretic hormone (ADH) in the defect in water excretion which is characteristic of glucocorticoid deficiency, the effects of hydrocortisone and ethanol upon urinary dilution during a sustained water load were studied in patients with anterior hypopituitarism. A spectrum of defects in urinary dilution was found in the seven patients with anterior hypopituitarism, and the subjects were separable into two groups. Four patients were unable to excrete a urine hypotonic to plasma (group I) while three diluted the urine (group II). In two of the group II patients, despite maintenance of hydration, urinary osmolality later rose to hypertonicity. Physiological doses of hydrocortisone improved urinary dilution in all patients. Submaximal doses of oral hydrocortisone, when given to the group I patients, converted their response to hydration to one characteristic of the group II patients, i.e., an initial hypotonic urine followed by a secondary rise to hypertonicity. Ethanol, a known inhibitor of ADH secretion, had no effect in the group I patients. When two of these patients were pretreated with sub-maximal doses of hydrocortisone, however, so that they were able to transiently dilute the urine, ethanol prevented the secondary rise in urine osmolality. Similarly, the administration of ethanol to the untreated group II patients, when the urine was hypotonic, improved diluting ability as characterized by a lowering of urinary osmolality and an increased excretion of solute-free water in all three patients. Hydrocortisone did not improve urinary dilution in three patients with complete hypophyseal diabetes insipidus and one with both anterior and posterior insufficiency receiving constant infusions of vasopressin. These data suggest, therefore, that inappropriately elevated levels of ADH play a major role in the defect in water excretion of anterior hypopituitarism. Glucocorticoids appear to be necessary for a normal neurohypophyseal response to inhibitory stimuli.

The postobstructive kidney. Observations on nephron function after the relief of 24 hr of ureteral ligation in the dog

After the relief of 24 hr of complete unilateral ureteral obstruction in the dog, the experimental kidney is characterized by a decrease in filtration rate and an increase in fractional and often absolute excretion of sodium before and after the administration of mannitol. In the hydrated state, the failure to conserve sodium is associated with increases in fractional free water clearance and fractional sodium supply to water-freeing sites signifying that the augmented sodium excretion is derived from a proximal source. In the hydropenic state there is decreased fractional free water reabsorption, and sometimes free water excretion, in the postobstructive kidney. An early plateau in free water reabsorption is associated with an increased fractional excretion of sodium. These findings are attributed to the early development of distal nephron impermeability to water as a result of enhanced distal tubular supply and transport of sodium. There is a decrease in maximal tubular reabsorptive capacity (Tm) of glucose in the post-obstructive kidney which is, however, less marked than the decrease in filtration rate. The fall in filtration rate is to some extent likely due to a dropping out of nephrons from the circulation while the remaining nephrons are hypoperfused. The magnitude of the sodium reabsorptive defect is markedly exaggerated as the concentration of nonreabsorbable solute (mannitol) in the glomerular perfusate is increased. It is concluded that the postobstructive increase in sodium excretion during mannitol administration is in part due to a limit in the capacity to reabsorb sodium against a concentration gradient in the proximal tubule.