Tubular chloride transport and the mode of action of some diuretics

Absence of interaction between furosemide and mitomycin C

The possible interaction between furosemide and mitomycin C (MMC) was studied in five patients. The pharmacokinetics of MMC were studied using an HPLC assay. Furosemide was administered prior to, or 120 min after MMC. Furosemide did not change the pharmacokinetics of MMC, nor did it change the amount of MMC excreted in the urine. There appears to be no interaction between the two drugs.

A search for a model tissue for studying effects of thiazide diuretics

A search was made for a model tissue of NaCl absorption which would be sensitive to inhibition by diuretics of the thiazide type. A lack of such a model through the years has hampered the analysis of the cellular mechanism of action of this important class of drugs. Using the short-circuit current technique, the urinary bladders of the toads Bufo spinosus and Bufo marinus, and the frog Rana temporaria were investigated regarding the effects of various thiazides. These bladders have NaCl absorptive properties similar to those of the distal renal tubules, and are claimed to be sensitive to the inhibitory effect of thiazides on sodium transport. The short-circuit current (SCC), which is representative of the sodium transport across the epithelium, was reduced by cyclopenthiazide and polythiazide, but only at high concentrations (above 0.1 mM). To rule out the possibility that this was an unspecific effect, attempts were made to block the effect by the 'thiazide blocker' Ex 4877, but without success. This finding, together with the fact that dose-response curves were difficult to obtain, would indicate that these epithelia are not suitable for the stated purpose. Preliminary studies were also conducted on the urinary bladder of the plaice, Pleuronectes platessa, which has a different system of NaCl absorption that is claimed to be rapidly and reversibly inhibited by thiazides. Polythiazide, added to both sides of the bladder, had no effect on SCC.

Treatment of mineralocorticoid-resistant renal hyperkalemia with hypertension (type II pseudohypoaldosteronism)

A 16 year old girl with the rare syndrome characterised by hypertension, hyperkalemia, and acidosis was treated with a range of drugs, including thiazides, frusemide, and beta-adrenoceptor antagonists. None of the agents normalised the hypertension and biochemical abnormalities. Best results were obtained with methyclothiazide in full dosage, which normalised the blood pressure, serum potassium level, and bicarbonate level in the face of increased plasma renin activity. Empirical treatment with thiazides is the most satisfactory method for long term management.

Cellular mechanism of action of loop diuretics: implications for drug effectiveness and adverse effects

The loop diuretics inhibit a transport system that moves sodium, potassium and chloride across cell membranes of many tissues, including the thick ascending loop of Henle. This inhibitory effect is responsible for their natriuretic effect. Of the agents available for clinical use, bumetanide is the most powerful; it has an in vitro transport inhibitory potency and an in vivo natriuretic effectiveness that is approximately 50-fold that of furosemide. This increased potency and the consequent decreased dose requirement give bumetanide the potential for increased effectiveness and decreased incidence of adverse effects.

Drug-drug and drug-disease interactions with nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs may cause a number of drug interactions. They can displace other drugs from serum proteins, and some can affect the metabolism or decrease the renal elimination of other drugs. In addition, they can attenuate the pharmacologic effect of other drugs, such as diuretic and antihypertensive agents, without affecting their disposition. Lastly, many disease states and aging can affect the handling of nonsteroidal anti-inflammatory drugs, mandating dose adjustment of some of these agents in certain clinical conditions. Some drugs may require more of these adjustments than others.

Urinary protein binding, kinetics, and dynamics of furosemide in nephrotic patients

The urinary protein binding, kinetics, and dynamics of furosemide were studied in five nephrotic patients after intravenous dosing. Serial plasma and urine samples containing furosemide were analyzed by HPLC, and drug binding to plasma and urinary proteins was determined using equilibrium dialysis techniques. In comparison to data reported previously in healthy subjects, the steady-state volumes of distribution and nonrenal plasma clearances were significantly increased in nephrotic patients, reflecting the reduced binding of furosemide to plasma proteins. Although there was no significant difference in renal clearance between these two groups, the unbound renal clearance of furosemide was significantly reduced in nephrotic patients even when compensated for by the number of functioning nephrons. Furosemide was extensively bound to urinary protein (19.6-78.4%), and the binding was dependent on the degree of proteinuria. Nevertheless, dose-response analyses, in which the response was represented by sodium excretion rate and the dose by urinary excretion rate of unbound drug, demonstrated that nephrotic patients were less responsive to equivalent amounts of unbound diuretic as compared to healthy subjects.

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.

Effects of standard diuretics and ortho-vanadate on sodium transport across isolated frog skin

Frog (Rana temporaria) skins were studied in an Ussing type lucite chamber adapted to diminish tissue edge damage. The transepithelial electrical potential difference, short circuit current and direct current (DC) resistance of skins mounted in this chamber were 56, 20 and 24% higher, respectively, than those of skins mounted in a conventional chamber. Amiloride, triamterene, ouabain and ortho-vanadate inhibited short circuit current and net mucosal to serosal flux of 22Na. Amiloride and triamterene had rapid onsets of action and were effective only when administered to the mucosal (pond) side of the skin. Ouabain and ortho-vanadate had slower onsets of action and were effective only when administered to the serosal side of the skin. Steady state of effects of these drugs was not reached within the three-hour period of the experiments. The inhibitory effect of ortho-vanadate was blocked by adding a disulfonic stilbene derivative (DIDS) to the serosal side of the skin. Serosal prostaglandin E2 stimulated the short-circuit current and decreased the DC resistance. Thiazides, acetazolamide and loop diuretics had no effects on Na+ transport by frog skin. Thus, frog skin seems to be a useful model only in studies of the mode of action and the structure-activity relationship of diuretic which act by inhibiting sodium entry or Na+-K+-ATPase activity.

Clinical syndromes associated with disorders of renal tubular chloride transport: excess and deficiency of a circulating factor?

Two contrasting patients are described, one with pseudo-Bartter's syndrome induced by frusemide abuse and the other a case of hyporeninaemic hypoaldosteronism. The clinical and biochemical features of these two conditions are the opposite of each other and, in the first patient, the effects of frusemide were antagonised by treatment with indomethacin while in the second frusemide itself corrected the syndrome. The decreased pressor sensitivity to infused angiotensin II seen in the patient with pseudo-Bartter's syndrome was corrected with indomethacin and the enhanced pressor sensitivity seen in hyporeninaemic hypoaldosteronism was reversed with frusemide. Frusemide, an agent which blocks chloride transport at the ascending limb of Henle's loop, was respectively thus the cause and the cure of these conditions. On the basis of this the suggestion is made that Bartter's syndrome and hyporeninaemic hypoaldosteronism represent respectively an excess and a deficiency of a circulating factor similar to frusemide capable of blocking renal tubular chloride transport.

Glomerular filtration rate and PCO2 as determinants of lithium reabsorption

To examine whether lithium reabsorption varies in proportion to the bicarbonate-dependent reabsorption of water and chloride, reabsorption was altered by varying PCO2 and glomerular filtration rate (GFR) in volume-expanded, anesthetized dogs during ethacrynic acid infusion. At constant GFR and plasma bicarbonate concentration, lithium, bicarbonate, chloride and water reabsorption were inversely related to plasma pH during variations in PCO2. Lithium and bicarbonate reabsorption varied by 9 +/- 1% and chloride reabsorption by 7 +/- 1% as plasma pH was altered by 0.1 unit from plasma pH 7.5. Calculation of reabsorbate concentrations indicated that lithium was reabsorbed as readily as water (reflection coefficient = 0). During mechanical constriction of the suprarenal aorta, GFR was reduced at constant plasma pH. Bicarbonate reabsorption fell more than chloride, water and lithium reabsorption. Lithium reabsorption was not significantly reduced until GFR was reduced by 35%. In stop-flow studies during ouabain infusion, urinary lithium concentrations were reduced below plasma concentrations. This is compatible with passive diffusion of lithium along a lumen-positive potential exceeding 10 mV in the diluting segment. Thus, lithium reabsorption behaved as expected for bicarbonate-dependent paracellular reabsorption during variations in PCO2; when GFR is reduced, an additional component of lithium reabsorption is disclosed.

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.

Bumetanide inhibits (Na + K + 2Cl) co-transport at a chloride site

Chloride-dependent cation transport systems in a number of cells and tissues are inhibited by 5-sulfamoylbenzoic acid loop diuretics, such as furosemide and bumetanide. Interactions between chloride and bumetanide have been examined in the catecholamine-activated (Na + K + 2Cl) co-transport pathway of the duck red blood cell. Levels of chloride were varied while maintaining a constant ratio of internal to external chloride across the cell membrane. Increasing external chloride from 20 to 100 mM shifted the dose-response curve for the effect of bumetanide on co-transport toward higher concentrations of the drug. The bumetanide concentration producing half-maximal inhibition (IC50) was increased from approximately 6 X 10(-8) to approximately 2 X 10(-7) M. When cells were incubated in the presence of a constant, submaximal inhibitory dose of bumetanide (10(-8) M), increasing external chloride (in increments of 20 mM) from 20 to 140 mM progressively decreased the level of inhibition of the co-transport system. Kinetic analysis of the data demonstrates that bumetanide and chloride compete for a common site.

Changes in pharmacokinetics and in effect of furosemide in the elderly

In this paper the general changes in the pharmacokinetics of drugs in the elderly are summarized. The suggestion is proposed, that in the case of diuretics--which act after renal excretion--the results of these changes are totally different: contrary to other drugs the standard dose of a diuretic must have less saliuretic effect instead of more effect. This thesis is supported by the results of experiments with furosemide in old patients: the kinetics are changed as expected, leading to higher plasma levels and increased Area Under the (plasma level versus time) Curve (AUC), but the effects are--dependent on renal function--decreased. To a certain degree kinetics and dynamics of furosemide can be explained and predicted on the basis of simple patient parameters. If diuretics are used in old people to treat congestive heart failure, the normal adult dose has to be used, and occasionally a larger dose has to be given.

Plasma protein binding of furosemide in kidney transplant patients

The present investigation was undertaken in order to determine the in vivo plasma protein binding of furosemide in kidney transplant patients and its possible consequence on furosemide effect. Using an equilibrium dialysis technique, serial plasma samples of furosemide taken after intravenous administration were dialyzed against an equal volume of isotonic Krebs Ringer bicarbonate buffer (pH 7.4). Dialysis was performed at 37 degrees C for 5 hr, and furosemide concentrations (total as well as free) were analyzed by HPLC using fluorescence detection. It was observed that kidney transplant patients on concomitant sulfisoxazole treatment (KT+) had a significantly greater value for percent free of furosemide as compared to transplant patients not on sulfisoxazole (KT-) (4.4 +/- 0.8 for KT+ vs. 1.7 +/- 0.3% for KT-; p less than 0.01) as well as to healthy volunteers (4.4 +/- 0.8 for KT+ vs. 1.2 +/- 0.2% for controls; p less than 0.01). In addition, kidney transplant patients not on concomitant sulfisoxazole treatment had a significantly higher value for percent free of furosemide with respect to healthy volunteers (p less than 0.05). Nonlinear plasma protein binding was also observed for one patient, who had values for percent free of furosemide ranging from 1.3 to 12.9%. However, no significant correlation was found between the fraction of the dose excreted unchanged in the urine and percent free of furosemide.

Dose-dependent pharmacokinetics of furosemide in the rat

The pharmacokinetics of furosemide were investigated in the rat at doses of 10 and 40 mg kg-1 corresponding to doses of 80 and 320 mg given to humans based on body surface area. A three-compartment open model with renal excretion taking place from the shallow peripheral compartment gave the best fit to the data. The terminal half-life of furosemide was found to change from 29 min for the 10 mg kg-1 dose to 49 min for the 40 mg kg-1 dose. This change could be detected as a change in the apparent volume of distribution caused by decreased protein binding at increasing plasma concentrations of furosemide. The total plasma clearance did not change significantly although metabolic and renal clearance both changed. The renal clearance was found to be dependent on the free fraction of furosemide in plasma and thus increased with increasing plasma concentrations. The metabolic clearance decreased with increasing dose indicating a saturable metabolism of furosemide.

A survey of the effects of loop diuretics on the zonulae occludentes of the perilymph-endolymph barrier by freeze fracture

The acute (30 min) effects of the loop diuretics piretanide, ethacrynic acid, bumetanide, furosemide, and azosemide, and the chronic (8 days) effects of furosemide and bumetanide on the zonulae occludentes (tight junctions) of the perilymph-endolymph barrier in the stria vascularis and in Reissner's membrane of the basal cochlear turns were studied by freeze-fracture. Quantitative analysis of their effects indicated that the structural integrity of the barrier was modified by either as increase or a decrease in the number, depth, and density of the strands of the tight junctions of the strial marginal cells. Only azosemide appeared to modify the tight junctions between the epithelial cells of Reissner's membrane, but it had little effect on the strial junctions. The tight junctions between the basal cells of the stria appeared to be the least affected by the various loop diuretics, although piretanide appeared to increase randomly the intercellular spaces lying between the strands.

Heterogeneity in the distal nephron of the salamander (Ambystoma tigrinum): a correlated structure function study of isolated tubule segments

Studies on isolated perfused tubules of the tiger salamander (Ambystoma tigrinum) have shown that the distal nephron is heterogeneous with respect to function (Stoner, 1977). In this study, the initial portion of the distal tubule (diluting segment) exhibited a voltage, positive in the lumen, and a net absorption of chloride. Since the chloride was transported against an electro-chemical gradient, its transport was active. More distad, the junctional segment exhibited a lumen-negative voltage and sodium, rather than chloride, was transported actively. More recently Delaney and Stoner (1981) have demonstrated in vitro that the collecting duct of this species also has a lumen-negative voltage which is probably associated with active sodium reabsorption. The primary objective of the present paper was to correlate the morphology of the diluting and junctional segments of the Ambystoma distal tubules with the physiologic data from the same isolated perfused tubules. The results indicate that the morphological heterogeneity previously demonstrated in distal tubules of Necturus exists with respect to both structure and function in Ambystoma. The cell types found in the amphibian distal nephron appear to be homologous to those seen in the mammalian nephron.

The time course of delivery of furosemide into urine: an independent determinant of overall response

After an oral or intravenous dose of furosemide, there is considerable interindividual variability in the amount of unchanged drug delivered into the urine. On average, approximately half as much reaches the intraluminal site of action with an oral compared to an intravenous dose. However, the natriuretic response to the same dose administered by either route is virtually the same. Similarly, after pretreatment with probenecid, the same total amount of furosemide in urine causes a greater overall response. It has been presumed that this paradox is accounted for by differences in rate of delivery of furosemide to the active site such that after an oral dose, or after pretreatment with probenecid, amounts of drug are for longer periods of time at the "steep" portion of the dose-response curve. Our analysis shows this not to be the case. For furosemide, the "slope factor" of the dose-response curve is such that the amount of diuretic delivered into the urine which is maximally efficient (21.5 micrograms/min) is considerably less than the amount causing half-maximal response (69.8 micrograms/min). Oral administration or pretreatment with probenecid maintains drug close to this maximally efficient amount more persistently than does intravenous administration. By so doing, total response to an oral dose approaches that of intravenous dosing despite delivering half the amount of drug to the active site, and after probenecid an intravenous dose causes a greater response than intravenous dosing alone despite delivering the same amount of drug to the active site. These data emphasize the importance of the time course of delivery of drug to the active site as an independent determinant of overall response.

The loop diuretic furosemide as non-competitive inhibitor of C1-/HCO3-ATPases of vertebrate kidneys and insect rectum

1. The effect of the diuretic drug furosemide was studied in detail on ouabain-insensitive, SCN- and OCN- -sensitive C1-/HCO-3-ATPase in homogenates from larval dragonfly rectum (Aeshna cyanea), frog (Rana temporaria) and mouse (Mus musculus) kidney. 2. The in vitro inhibition by the drug studied on the HCO-3-activated enzyme is non-competitive with an inhibitor constant of Ki=4.3 mM furosemide in the case of insect rectum and Ki=0.9 mM furosemide in the case of frog and mouse kidney. 3. Furosemide even at 10 mM concentration which completely inhibits the anion-dependent ATPase has only a little inhibitory effect on the Na+/K+-ATPase of the 3 tissues. 4. The data suggest that furosemide may affect an active chloride transport system involving a C1-/HCO-3-ATPase.

Micropuncture study of changes in glomerular filtration and ion and water handling by the rat kidney during pregnancy

1. In rats receiving 200 mul. min(-1) sodium chloride, glomerular filtration rate, single nephron glomerular filtration rate, and fractional reabsorption were measured at various points along the nephron, and ionic concentrations measured in early distal tubular fluid in virgin and 6, 12 and 19 day pregnant rats.2. Glomerular filtration increased progressively until the twelfth day of pregnancy. At 19 days of pregnancy the glomerular filtration rate, while still above virgin levels, was reduced below 12 day pregnant levels.3. Single nephron glomerular filtration rates measured in proximal and distal tubules were different at both 12 and 19 days of pregnancy, indicating an alteration of tubuloglomerular feed-back.4. A change in the ratio of glomerular filtration rate: distal single nephron filtration rate indicated a redistribution of glomerular filtrate to juxtamedullary nephrons by the sixth day of pregnancy.5. Fluid reabsorption is similar up to the early distal tubule but it is not possible to say whether reabsorption is the same in proximal tubules. More fluid is reabsorbed by late distal tubules and collecting ducts in 12 and 19 day pregnant animals than in the virgin and 6 day pregnant animals.6. Changes in ion reabsorption by the loop of Henle occurred during pregnancy; sodium reabsorption was increased by the sixth day of pregnancy and potassium reabsorption by the twelfth day.

The effect of loop diuretics on the excretion of Na+, Ca2+, Mg2+, and Cl-

Bumetanide, ethacrynic acid, and furosemide were administered in two equipotent doses to the same five dogs in three separate studies. Intravascular volume was maintained by the replacement of urinary losses. Fractional chloride excretion was used as a marker of diuretic effect. Comparison of absolute and fractional excretion of Na+, Cl-, Ca2+, and Mg2+ did not demonstrate a significant difference among the three diuretics.

The effect of intravenous bumetanide in man with normal and low renal function

Bumetanide was administered intravenously to four groups of patients with varying levels of glomerular filtration rate (average 10 to 108 ml/min/1.73 m2 B.S.A.). The dose of bumetanide was either 0.25, 0.5, 1.0, or 2.0 mg administered by intravenous "push." The intravenous administration produced a prompt and marked increase in sodium, chloride, and calcium excretion. The effect was brief, lasting 30 to 60 minutes, but persisted to some extent with the 2.0 mg dose beyond 120 minutes. There was no effect on phosphate excretion or on the parameters of net acid excretion.

Effects of amiloride and SITS on branchial ion fluxes in rainbow trout, Salmo gairdneri

The effects of amiloride and SITS on branchial ion fluxes in rainbow trout were examined. Each drug was found significantly to inhibit both influx of Na+ and Cl- ions. It is postulated that the inhibitory effects on the contralateral exchange processes result from changes in gill epithelial cell pH.

Glucose transport by short loops of Henle in the rat

1. Short loops of Henle were artificially perfused with saline solutions containing 5 or 0 mM-glucose in the presence and absence of phlorizin. 2. Net fluid reabsorption was greater when glucose but no phlorizin was present than in all other series. 3. Glucose was reabsorbed from glucose-containing perfusate and this was abolished by phlorizin. Secretion of glucose occurred into the perfusate which initially contained no glucose and this secretion was enhanced by phlorizin. 4. Sodium reabsorption was inhibited by phlorizin, when glucose was present, but enhanced by phlorizin when glucose was absent. 5. It can be shown that there is secretion of some osmotically active solute in all series. Its secretion is enhanced by phlorizin in the absence of glucose.

Vanadate-induced inhibition of sodium transport and of sodium-independent anion transport in turtle bladder

Vanadate in the serosal bathing fluid of turtle bladders inhibits the Na+ moiety of the short-circuiting current (Isc), the anion (Cl-, HCO3-) moiety of Isc, and net Cl- flux. Since the anion transport is Na+-independent and ouabain-insensitive, its inhibtion by vanadate is uniquely different from the well known vanadate-induced inhibition of (Na++K+)-ATPase and Na+ transport-dependent anion movement of some other epithelia. Vanadate also generates damped oscillations in the bladders' electrical parameters, an unusual effect by an ion in epithelial systems.

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.

Diuretics stimulate H+ secretion in turtle urinary bladder

The effect of various diuretics on H+ secretion was studied in the isolated short-circuited urinary bladder of the turtle. Mucosal (urinary) chlorothiazide stimulated H+ secretion promptly, from 1.33 +/- 0.24 to 3.03 +/- 0.25 mueq/h (P less than 0.001). The effect was rapidly reversible upon washout of the drug, H+ returning to control levels, 1.37 +/- 0.26 mueq/h (P less than 0.001). Similar effects were observed with mucosal hydrochlorothiazide and mucosal ethacrynic acid/cysteine. Stimulation of H+ secretion occurred in the presence or the absence of exogenous CO2, in the presence or absence of mucosal Na+ and during inhibition of Na+ transport by ouabain. There was no stimulation of H+ secretion by uncomplexed ethacrynic acid or by mucosal furosemide. The nondiuretic sulfonamide, sulfasoxizole, and the nonsulfonamide buffer, borate, had no effect on H+ SECRETION. These observations indicate that the stimulatory effect of diuretics on H+ secretion is not related to active sodium transport, transepithelial electrical potential, or the buffering capacity of the drugs. Since the transepithelial pH gradient at which active H+ secretion was abolished was identical for chlorothiazide-treated tissues (2.68 pH U) as for control tissues (2.65 pH U, NS), the data suggest that the protonmotive force of the H+ pump was unaffected by the diuretic. This observation, plus the rapid onset and reversibility of the drugs, is consistent with an effect on the mucosal membrane to increase H+ conductance (K). The findings raise the possibility that direct enhancement of renal H+ secretion may play a role in the metabolic alkalosis induced by some diuretics.

Preliminary evaluation of furosemide-probenecid interaction in humans

The pharmacokinetics and pharmacodynamics of intravenous furosemide, 40 mg, were studied in four healthy male subjects in a crossover fashion with and without probenecid pretreatment. In each study, 16 plasma and 10 urine samples were collected over 24 hr. Fluid and electrolyte urinary losses were replaced orally throughout the study. Unchanged furosemide and probenecid were measured using high-pressure liquid chromatography; urinary sodium was measured by flame photometry. Although probenecid caused marked changes in the pharmacokinetic parameters of furosemide (increased area under the curve, decreased plasma and renal clearance, increased half-life, and decreased fraction excreted unchanged in the urine), there was no significant difference in its gross 8-hr natriuretic and diuretic effect. However, analysis of the time course of natriuresis showed a pattern similar to that of the urinary furosemide excretion rate, whereas the plasma concentration was poorly correlated over the entire dose-response curve.

Mode of action of furosemide on the chloride-dependent short-circuit current across the ciliary body epithelium of toad eyes

The effects of furosemide on the chloride-dependent short-circuit current across the toad ciliary epithelium were examined. Under control conditions, the short-circuit current obeyed Michaelis-Menten kinetics against medium chloride concentration, the Michaelis constant (Km) for chloride being 90 mM and the maximal short-circuit current (Vmax) 128 mu A/cm2. Furosemide added to the aqueous side of the epithelium rapidly reduced the short-circuit current; the effect was reversible. The effect of furosemide addition to the stromal side was much smaller and slower than that from the aqueous side. The dose-dependent range of furosemide action was from 0.1 micro M to 1 mM with 50% inhibition occurring at about 3 micro M. Lineweaver-Burk plot of the short-circuit current against the chloride concentration showed that furosemide decreased the value of Vmax and increased the Km; the inhibition being of mixed type. A Hill plot of the dose-response curve yielding a slope of unity suggested one furosemide molecule combines with one chloride transport site. Probenecid, a competitive inhibitor of organic acid transport reduced the effects of furosemide significantly when added simultaneously. The involvement of organic acid transport system in the mechanism of furosemide action on chloride transport was suggested.

Studies with the optically active isomers of the new diuretic drug ozolinone. I. Differences in stereoselectivity of the renal target structures of ozolinone

The renal actions of the optically active isomers of the new diuretic drug ozolinone were studied by clearance, flowmeter and micropuncture techniques in rats. The levorotatory, but not the dextrorotatory isomer of ozolinone increased urine flow, urinary sodium and chloride excretion and enhanced sodium and chloride concentrations in early distal tubular fluid as checked by in situ microperfusion of Henle's loops. This indicates stereospecificity of the drug's diuretic action. However, both isomers of ozolinone equally inhibited maximal tubular secretion of paraaminohippurate and increased renal blood flow as measured by an electromagnetic flowmeter. Thus, the different renal target structures of ozolinone differ markedly with respect to stereoselectivity.

Pathophysiology of Tamm-Horsfall protein

Tamm-Horsfall protein, a renal glycoprotein present in normal urine, is the primary constituent of urinary casts. Immunoelectron microscopy has shown that this protein is localized selectively along surface membranes of the thick ascending loop of Henle. In this surface membrane site, the unique aggregation and gel formation of Tamm-Horsfall protein in response to increasing concentrations of electrolytes within physiologic ranges may influence the permeability characteristics of this nephron segment. These aggregation characteristics also play a role in pathologic conditions and lead to the prolonged persistence of interstitial Tamm-Horsfall protein deposits in several tubulointerstitial diseases. Recent studies have demonstrated immunologic responses to this protein, including an immune complex tubulointerstitial nephritis in rats mediated by autoantibodies to Tamm-Horsfall protein.

Disorders of chloriuretic hormone secretion

Experimental evidence supports the existence of a circulating substance, natriuretic hormone, which augments electrolyte excretion. Because such a hormone probably acts by inhibiting chloride reabsorption in the thick, ascending limb of the loop of Henle it would more accurately be called chloriuretic hormone. Chloriuretic hormone must have an action which resembles that of loop diuretics such as frusemide and ethacrynic acid. An excess of chloriuretic hormone could explain all the manifestations of Bartter's syndrome, whereas a deficiency could account for Gordon's syndrome. Hyporeninaemic hypoaldosteronism may develop in subjects who are unable to increase chloriuretic hormone concentrations appropriately in response to progressive impairment of renal function.

Pharmacokinetics/pharmacodynamics of furosemide in man: a review

The pharmacokinetics of furosemide and the attempt to correlate biological fluid measurements with diuretic response have been the subject of a large number of studies since the original reports of Hajdú, Rupp, and coworkers in the mid-1960s. This article attempts to critically review these studies under seven different sections: furosemide pharmacokinetics in normal volunteers, furosemide pharmacokinetics in patients with decreased renal function, furosemide pharmacokinetics in patients with congestive heart failure, furosemide metabolism and assay methods, furosemide bioavailability, dose-response relationships, and the role of inhibitors and mediators on furosemide effects. The literature is reviewed through August 1978.

The pharmacologic effects of furosemide therapy in the low-birth-weight infant

The pharmacologic effects of furosemide were studied in six infants (mean gestation 30.7 weeks; mean birth weight 1,490 gm) at ages 10 to 57 days. Furosemide (for clinical indication, standardized at 1 mg/kg) was given intravenously over one minute; data were collected over the ensuing 24 hours. For three hours following furosemide administration, a significant diuresis was observed. Sodium excretion, percent fractional sodium excretion, and potassium excretion were significantly increased and urinary pH significantly decreased for six hours following the administration of furosemide. Creatinine and free water clearances were slightly elevated, although not significantly. Furosemide is an effective diuretic, the onset of pharmacologic action was within one hour, the peak action was sustained for three hours, and the duration of action was six hours. The net fluid, sodium, and potassium losses following a 1 mg/kg single dose were 28 ml, and 3.6 and 0.3 mEq/kg, respectively.

Factors affecting the distribution of chloride ions in rat renal outer medulla

1. The intracellular Cl- concentration, [Cl-]1, of rat renal outer medullary slices has been studied in iso-osmolal media containing 42, 93, 144, 189 or 225 mM chloride, [Cl-]0. Equilibrium values for [Cl-]1 were attained within 25-50 min from the start of incubation such that [Cl-]1/[Cl-]0 = 0-46. This ratio was independent of [Cl-]0 within the range studied. Intracellular Na+ was unaffected, and only minor variations of cell volume were observed (calculated from slice weight changes and [14C]carboxyl inulin spaces. 2. When [Cl-]0 = 189 mM, [Cl-]1 remained constant at 87 mM for up to 50 min, indicating that these figures may represnet the interstitial [Cl-] and mean intracellular [Cl-] respectively in outer medulla. 3. Omission of bicarbonate from medium containing 189 mM-Cl- caused an increase in [Cl-]1/[Cl-]0 to 0-58, which was not significantly affected by anoxia or by the presence of arsenite (5 X 10(-3) M) or 2,4-dinitrophenol (10(-3) M). Significant further increases were observed in the presence of iodoacetic acid (5 X 10(-3) M) (0-70), acetazolamide (10(-3) M or 5 M 10(-3) M) (0-71) and iodacetic acid plus 2,4-dinitrophenol (0-85). The addition of the diuretic agents ouabain, ethacrynic acid-cysteine and frusemide (all 10(-3) M) to 189 mM-Cl- media containing bicarbonate reduced [Cl-]1/[Cl-]0 to 0-36, 0-37 and 0-42 respectively. 4. The mean 36Cl- space of outer medulla after 50 min incubation in 189 mM Cl- medium was 49-7 +/- 2-1 micronl./100 mg wet wt. The volume of distribution was not significantly affected by ouabain, ethacrynic acid-cysteine or frusemide (10(-3) mM). 5. Net efflux of 36Cl- from slices loaded with isotope into 'cold' 189 mM Cl medium showed three components with rate constants of 69 X 10(-3), 18 X 10(-3) and 9-9 X 10(-5) sec-1 respectively. Efflux was not affected by ouabain, ethacrynic acid-cysteine or frusemide (10(-3) mM). 6. The main conclusions drawn from this study are: (i) the interstitial fluid Cl- concentration of normally hydrated rat outer medulla is approx. 189 mM; (ii) the [Cl-]1/[Cl-]0 ratio 0-46 may represent a chiefly passive distribution maintained by the opposing gradient of a second anion, probably bicarbonate; (iii) the energy required to maintain unequal distribution of Cl- in the absence of external bicarbonate is derived chiefly from glycolysis, with a small aerobic component; (iv) there may be two intracellular chloride pools whose net rates of Cl- exchange differ by a factor of approx. 180.