Preferential localization of 3H-pentosanpolysulphate to the urinary tract in rats

Endogenous glycosaminoglycans probably have a protective effect in the urinary tract, e.g. against stone formation. The synthetic sulphated polysaccharide pentosanpolysulphate (PPS) has been suggested to exert a similar protective effect e.g. by inhibition of crystallization and bacterial anti-adhesion. We have studied the distribution in rats of tritium-labelled PPS. Chromatography showed this material to contain two distinct peaks with approximate molecular weight around 2.700 (60-70%) and 1.000 (30-40%) daltons. PPS was administered orally and intravenously (5 mg/kg b.wt.) to Sprague-Dawley rats, which were killed 1 and 4 hours later, respectively, and subjected to whole-body autoradiography. Autoradiograms of sections from intravenously injected rats showed an extensive distribution of radioactivity in the whole animal, with a notable labelling of connective tissues, while bone and cartilage had low activity. There was upper intestine activity, suggesting some hepatic excretion. The most conspicuous finding, however, was the high concentration in urine and a preferential localization of activity corresponding to the lining of the urinary tract (pelvis, ureter, and bladder). The distribution was similar, but the activity lower after oral administration. In one experiment, PPS was applied intravesically under anaesthesia, with and without epithelial destruction caused by instillation of 0.4 M HCl. After vigorous rinsing, with saline, the radioactivity was still retained in the bladder wall. In other intravenous experiments, the bladder was extirpated, everted and rinsed in saline or urea of increased osmolality. High amount of radioactivity could be rinsed off by 0.5 M saline. Chromatography of the rinsing solution showed presence of both fractions of PPS previously found in the injection solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of ischaemic acute renal failure with superoxide dismutase and sucrose

The preventive effects of intravenously administered superoxide dismutase (SOD) and of SOD combined with sucrose on acute renal failure were investigated in rat kidneys exposed to 45 min of warm ischaemia. Superoxide dismutase (20 mg) given just before primary ischaemia and in the early recirculation phase was found to ameliorate the red cell aggregation in the renal medulla, in particular, in the inner stripe of the outer zone the volume of trapped red cells decreased from 11.2 +/- 1.6% in untreated animals to 0.02 +/- 0.001%, thus allowing improved restoration of medullary blood flow. This was also accompanied by an expected restoration of the urine osmolality reaching almost 400 mOsm kg-1 after administration of SOD + sucrose. Superoxide dismutase also restored the capillary macromolecular permeability as evidenced by normalization of plasma to lymph transport of proteins. Micropuncture studies showed that in ischaemically damaged but untreated kidneys the tubules were obstructed and that the proximal tubular pressure rose to such a level that the net driving force for filtration approached zero. This explains the marked decrease in glomerular filtration rate (GFR) from a normal value of about 1 ml min-1 to 0.01 +/- 0.02 ml min-1. After treatment with SOD the tubules were still largely obstructed, resulting in a depression of the net driving force and a decrease in single nephron glomerular filtration rate (SNGFR) to about 11 nl min-1, that is, to only 25% of the normal SNGFR. The total filtration was 0.09 +/- 0.04 ml min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic-pharmacodynamic relationship of piretanide in healthy and uremic subjects. Determinants of the diuretic effect of a loop diuretic

The pharmacokinetics of the loop diuretic piretanide and its diuretic effects were studied in 6 healthy volunteers, 12 pre-dialysis (GFR 7-28 ml/min) and 10 dialysis patients (c-creat. 1-7 ml/min). Single doses up to 96 mg i.v. and orally were well tolerated and audiometry showed no hearing changes. Pharmacokinetic data showed rapid and almost complete absorption (bioavailability 92%) and a rapid elimination with renal clearance of 50% of the total 200 ml/min in the normals and renal clearance of about 50% of actual GFR in the patients. Extrarenal clearance was the same in normals and patients. The rapid extrarenal elimination reduces the risk of accumulation in renal patients but also reduces the active fraction of the dosage being cleared by the kidneys. Therefore, a high dosage and high plasma levels of piretanide were necessary for diuretic effect in uremic patients. The relation between the urinary piretanide excretion rate and the chloruretic effect was similar in normals and uremic patients; Cl- excretion increased 40 mMol per mg piretanide excreted.

Some effects of metolazone on electrolyte transport

Metolazone action was studied 1) in vitro on isolated operculum of Fundulus heteroclitus (active chloride transport) using an Ussing chamber (metolazone conc 500 microM) and in vivo 2) using the modified Sperber technique in the hen (metolazone infusion rate 0.75-1.2 micrograms/kg/min) and 3) in healthy volunteers using clearance techniques (metolazone infusion rate 10 mg/h). Metolazone reduced (p less than 0.05) short circuit current potential differences with 20% from average control values (p less than 0.05), while direct current resistance was unchanged. This is comparable to thiazide but much lower than loop diuretic effects. True tubular excretion fraction of metolazone before and after novobiocin (2.7 mumol/kg/min coinfusion averaged 14.1 and 4.5%, resp. (p less than 0.01; n = 8). Thus metolazone is partly eliminated by renal tubular secretion. However, the diuretic effect (sodium, chloride and potassium excretion)--and clearances of Cr51-EDTA and I125-Na-o-iodohippurate--were symmetrical, i.e. independent of metolazone urinary excretion rate, as previously shown for thiazides. Renal clearance of metolazone in healthy volunteers. (HPLC-method) averaged 173 +/- 20 ml/min (n = 8). Probenecid (1 g iv.) significantly reduced the renal clearance of metolazone to 33 +/- 7 ml/min and potassium excretion with maximum 30%, while diuretic and saluretic effects were significantly increased with maximum 30%. Thus, also in humans the diuretic effect of metolazone is not coupled to the urinary excretion rate of the drug, but suggests that its diuretic effect is elicited primarily from the peritubular side of the nephron. Probenecid apparently dissociates sodium from potassium excretion effects of metolazone. This implies a luminal, sodium-independent kaliuretic effect of the drug.

Renal handling and effects of [3H]digoxin and interactions with quinidine in the avian kidney

Renal handling and effects of tritium digoxin and interactions with quinidine in the avian kidney were studied using a modified Sperber technique. Results showed that tritium digoxin was extracted at the peritubular side of the nephron in a process competitively inhibited by increasing amounts of unlabelled digoxin. Light microscope autoradiography showed distinct concentrations of silver grains only over distal tubules in the injected kidney. Inhibition of the proximal tubular transport systems for organic anions and cations, respectively, did not change extraction. Addition of quinidine to the injection solution up to an estimated concentration of 1.4 X 10(-5) M in systemic blood significantly lowered 1 min peritubular extraction of tritium digoxin. However, when the amount of quinidine was further increased, extraction of tritium digoxin augmented significantly. Tritium recovery in urine after renal portal bolus injection of tritiated and unlabelled digoxin already showed a distinct ipsilateral peak 2 min after injection with an equally distinct peak of ipsilateral sodium excretion appearing 1 min later. When quinidine was added to the bolus ipsilateral tritium recovery in urine (0-7 min) was halved, with the true tubular excretion fraction (TTEF) lowered by two-thirds, but without changes in the magnitude of ipsilateral natriuresis. Contralateral natriuresis increased more than four-fold with quinidine in the bolus in spite of unchanged tritium recovery in the urine. Thus, our results show tritium digoxin to be extracted from peritubular blood through a specific process probably localized to the distal nephron of the avian kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum azathioprine and 6-mercaptopurine levels and immunosuppressive activity after azathioprine in uremic patients

The pharmacokinetics of azathioprine (AZA) and 6-mercaptopurine (6-MP) was studied in uremic patients after 100 mg AZA intravenously (fifteen patients) and orally (eight patients). 6-MP was analysed with gas chromatography mass spectrometry following extractive alkylation. AZA was determined indirectly assuming quantitative conversion to 6-MP in whole blood. The plasma concentration of AZA fell rapidly after i.v. administration. The mean half-time of elimination for the first rapid phase (t1/2 alpha) was 6.1 min (S.D. +/- 4.1) and for the terminal phase (t1/2 beta) 50 min (+/- 31). The total plasma clearance (Cl) was 6.9 1./min (+/- 3.0). AZA was rapidly converted to 6-MP in vivo, and maximal plasma concentrations of 6-MP were found as early as 5 min after i.v. injection of AZA. The mean t1/2 alpha was 4.6 min (+/- 2.2), t1/2 beta 74 min (+/- 58) and Cl 8.0 1./min (+/- 5.8). The plasma levels of both AZA and 6-MP were either low or undetectable 4-6 h after dose. In erythrocytes AZA levels were low or undetectable indicating rapid conversion to 6-MP in these cells. 6-MP concentration - time curve in erythrocytes was similar to that in plasma, except for a somewhat slower terminal phase of elimination. Oral administration of AZA generated flat plasma curves for AZA and 6-MP. The area under the concentration - time curve (AUC) was considerably smaller than after i.v. administration, 18 and 41% for AZA and 6-MP, respectively. There seems to be little danger of accumulation of AZA/6-MP in uremia. We also studied inhibition of Leucoagglutin (LA) stimulated lymphocyte proliferation by patient plasma at different times in six of the patients following AZA i.v. Sera drawn at 5, 10 and 30 min significantly inhibited the LA-induced proliferation, with an estimated minimum effective concentration of 6-MP in the cultures of about 0.02-0.04 microM. This suggests the possibility of a therapeutic effect even of the low plasma levels of 6-MP obtained after AZA orally. The combined use of sensitive pharmacokinetic and immunological assays as described should be useful in studying the relationship between plasma levels of AZA/6-MP and their immunosuppressive effect and toxicity.

Renal handling of 125I-labelled insulin in the hen

Renal handling of 125I-insulin was studied using a modification of the Sperber technique. Results showed 125I-insulin to be extracted at the peritubular side of the nephron in a process that was competitively inhibited by increasing amounts of unlabelled insulin, but not ACTH, in the injection mixture. When unlabelled insulin instead was injected 30 sec after the labelled insulin it showed significantly less interference with peritubular extraction of 125I-insulin, indicating strong attachment to the cell membrane or possible internalization of 125I-insulin into proximal tubular cells. Light microscope autoradiography 1 min after injection of 125I-insulin showed grains over proximal tubules only. On the ligated side localization was preferably peritubular while on the control side it was luminal. Electron microscope autoradiography showed sparsely distributed grains, however, frequently located over basal parts of proximal tubular cells. Pretreatment with lysine hydrochloride lowered renal extraction of 125I-insulin and increased urinary recovery of iodine label bilaterally. 125I-glucagon and 125I-C-peptide were not extracted from the peritubular circulation. In conclusion, the model has provided evidence of a rapid and significant peritubular extraction of 125I-insulin by proximal tubular cells in a process probably involving specific insulin receptors. Following receptor binding probably only minor amounts of 125I-insulin enters the proximal tubular cells, while the greater part is degraded at the cell surface or released into the circulation.

Acute tolerance to furosemide diuresis in humans. Pharmacokinetic-pharmacodynamic modeling

Furosemide, 40 mg, was given to eight healthy volunteers as an i.v. dose and as oral doses (tablet and solution) with and without food intake. The urine and plasma were sampled frequently and analyzed on their content of furosemide (high-performance liquid chromatography). The urine flow and chloride excretion rate were used as measures of the effect. In spite of a 3-fold difference (28 vs. 9 mg/8 hr, P less than .001) in the cumulative urinary excretion of furosemide between i.v. and postprandial oral administration, no significant difference in the diuretic effect was found (2-2.2 liters/8 hr). The drug excretion-response curves showed parallel shifts depending on mode of administration of furosemide. Clockwise hysteresis, indicating acute tolerance development to the diuretic effect, was seen after the oral doses after food intake. This within-dose development of tolerance was modeled with an extended Hill equation. The tolerance development seems to have a near relationship to acute volume depletion (inadequate substitution of urine losses), probably activating some intrarenal mechanism for extracellular fluid volume preservation. Thus, the time course of furosemide excretion, as well as the degree of renal compensation, determine the renal sensitivity to furosemide. This has important implications for the proper design and interpretation of studies of the excretion-response relationship of diuretics.

Renal tubular accumulation of organic substances: a new in vivo method which differentiates between luminal and peritubular uptake

Using a modification of the Sperber technique we studied cellular uptake of organic substances in the kidney. A test substance was mixed with an extracellular marker (ethylenediaminetetraacetate or inulin), both radiolabelled with an activity ratio close to I, and injected into the renal portal system on one side via a leg vein. The animals were killed 1-10 min after injection and the radioactivity in different organs determined. Results showed significantly higher ipsilateral (injection) to contralateral (control) kidney ratios (substance to marker) at 1 min after injection for 125I-Na-o-iodohippurate (125I-Hipp; P less than 0.001), 14C-tetraethylammonium bromide (14C-TEA; P less than 0.001), 3H-dihydromorphine (3H-DHM; P less than 0.01), and 125I-iothalamate (P less than 0.01), with a progressive decrease in injection kidney ratios for 125I-Hipp and 14C-TEA when death occurred after a longer period. Inhibition of renal tubular transport with novobiocin or mepiperphenidol markedly reduced 1- and 4-min injection kidney ratios for 125I-Hipp and 14C-TEA, respectively. When death occurred after a longer period, ratios in both kidneys increased significantly for 125I-iothalamate. A good correlation was found between peak cellular accumulation in the kidney and excretion efficiency of test substances. Thus, the results indicate that 125I-Hipp, 125I-iothalamate, 14C-TEA, and 3H-DHM were accumulated from the peritubular side of the nephron through the transport systems for organic acids and bases, respectively, and that 125I-iothalamate also showed luminal uptake. In conclusion, this new in vivo technique is simple and well suited for studying renal tubular accumulation of organic substances and offers the advantage of being able to distinguish luminal from peritubular uptake.

Is 125I iothalamate an ideal marker for glomerular filtration?

The triiodinated angiographic contrast medium, iothalamate, has (usually labelled 125I) been used extensively as a marker for glomerular filtration. We have studied the renal handling of 125I iothalamate (IOT) in vivo and in vitro in several species. In renal cortical slices from chicken, rabbit, rat, and monkey, the tissue-to-medium ratio of IOT was twice that of 51Cr-EDTA (EDTA) at 37 degrees C; a difference that was abolished at 0 degree C and markedly reduced by added o-iodohippurate or iodipamide. In five chickens the steady-state renal clearance of IOT (CIOT) was twice (P less than 0.05) that of EDTA (CEDTA) or 3H inulin (C1); a difference that was abolished by administration of 100 mg/kg/hr of novobiocin, an organic anion transport inhibitor. CEDTA was similar to C1 before as well as after transport inhibition. Utilizing the Sperber technique the mean apparent tubular excretion fraction (ATEF) of IOT was 8%, while that of EDTA was 1% (P less than 0.01; N = 10). After novobiocin coinfusion (new steady-state) ATEFIOT was significantly reduced (P less than 0.01) and not different from that of EDTA (-1%). In the same animals the total urinary recovery of IOT was 84 and 57% (P less than 0.01) before and after novobiocin, respectively, while corresponding values for EDTA was unchanged by the inhibitor. In seven rats the renal extraction of IOT was reduced from 29 to 17% (P less than 0.05) by coinfusion of probenecid (5 mg/kg/hr). Corresponding extractions were 82 to 34% (P less than 0.005) and 22% (unchanged) for PAH and EDTA, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of furosemide in man after intravenous and oral administration. Application of moment analysis

Furosemide 40 mg was administered to 8 healthy subjects as an i.v. bolus dose, as 1 tablet in the fasting state, and as 1 tablet and a solution after food intake. The i.v. data gave a total body clearance of 162 +/- 10.8 ml/min and a renal clearance of 117 +/- 11.3 ml/min; the volume of distribution at steady state was 8.3 +/- 0.61. Oral administration gave a bio-availability of the tablet (fasting) of 51%. Food intake slightly reduced the bioavailability, but not to a significant extent. There was no significant difference in availability between the tablet and the solution. Moment analysis gave a mean residence time after the i.v. dose, MRTi .v., of 51 +/- 1.5 min. The mean absorption times (MAT) for all oral doses were significantly longer than the MRTi .v., indicating absorption rate-limited kinetics of furosemide. On average, food delayed the absorption by 60 min. The MAT for the tablet in the postprandial state was significantly longer than for the solution, indicating dissolution rate-limited absorption of the tablet.

Steady state pharmacokinetics of trimethoprim 300 mg once daily in healthy volunteers assessed by two independent methods

The steady state pharmacokinetics of trimethoprim was determined after 300 mg orally once daily to 6 healthy volunteers for 9 days. The microbiological assay of plasma level was unreliable at trimethoprim concentrations greater than 4 micrograms/ml, so results from an HPLC-assay are given. Steady state was present after 3 days. The plasma concentration peaked 1 to 4 h (mean 2.0 h) after the dose at a mean of 6.0 micrograms/ml (range 3.1-9.5 micrograms/ml); the minimum value was 1.5 micrograms/ml (range 0.6-2.9 micrograms/ml). The mean AUCss was 77 micrograms/ml X h and the mean plasma clearances was 67 and 74 ml/min on Days 8 and 9. Renal clearance was about 60% of the plasma clearance. The average plasma half life was 10.6 h (range 8.7-15.3 h). Thus, there was considerable interindividual variation in all pharmacokinetic parameters. 72 h after the last dose trimethoprim was detectable in plasma in only 1 of the 6 subjects. The minimum urinary concentration of trimethoprim during treatment was always well above (range 22 to 220 micrograms/ml) the MIC values for most urinary tract pathogens. Therefore, a daily dose of 300 mg trimethoprim results in a therapeutic concentration in urine at steady state that lasts throughout the dosing interval and in most subjects probably lasts also for a further 24 h. Trimethoprim administration raised mean serum creatinine from 67 to 97 mumol/l, probably due to competitive inhibition of the tubular secretion of creatinine.

Coupling between renal tubular secretion and effect of bumetanide

The relationship between renal tubular secretion of bumetanide and its saluretic effect was studied in six healthy subjects before and after probenecid (1 gm IV). Bumetanide was determined in serum and urine by HPLC. Continuous intravenous infusion of bumetanide (200 micrograms/hr) gave an average diuresis at steady state of 15 +/- 3 ml/min. Corresponding plasma concentration, urinary excretion rate, and renal clearance of bumetanide averaged 14.3 +/- 2.3 ng/ml, 64 +/- 31 micrograms/30 min, and 145 +/- 59 ml/min. After probenecid there was a marked change in bumetanide kinetics. Average plasma concentration rose to 41.7 +/- 8.1 ng/ml, whereas renal clearance and urinary excretion rate fell to 15.1% and 29.5% of control. There was also a concomitant decrease in diuresis and saluresis to 47% and about 40% of control. Probenecid also reduced the renal clearance of para-aminohippurate and inulin to 67% and 75% of control. Since the fractional water and sodium chloride excretion was also reduced about 33% and 42%, it is concluded that a large part of the diuretic effect of bumetanide depends on its active tubular secretion. As with furosemide and piretanide, bumetanide diuresis is elicited from the luminal side of the human nephron.

Renal tubular secretion of piretanide and its effects on electrolyte reabsorption and tubuloglomerular feedback mechanism

Piretanide [HOE 118; 4-phenoxy-3-(1-pyrrolidinyl)-5-sulfamoxylbenzoic acid] is a new diuretic with a saluretic effect similar to that of furosemide. The present experiments were undertaken to investigate if transport of piretanide into the tubular lumen determines the diuretic response and what effect piretanide has on the tubuloglomerular feedback control and loop of Henle electrolyte transport. To study the first question, five healthy subjects were investigated. Piretanide, inulin and p-aminohippuric acid were continuously infused. After equilibration, 1 g of probenecid was given which reduced the tubular secretion of piretanide to one-sixth of control level. The reduction in diuresis was 41.4% while it was 59.5, 63.9 and 45.8% for the urinary excretion of chloride, sodium and potassium, respectively. In a second series of experiments in rats a proximal tubular stop-flow pressure response at increased distal delivery of fluid was measured when Ringer's solution, Ringer's solution plus furosemide (10(-4) M) or bumetanide (5 X 10(-5) M) or piretanide (10(-4) M and 5 X 10(-5) M) was added to the tubular perfusion solution. The results indicate that the feedback could be completely blocked by any of these diuretics. The fluid absorption in the loop of Henle was studied in separate experiments and the addition of piretanide (10(-4) M) greatly reduced chloride and absolute fluid absorption from this nephron segment. The present results indicate that tubular secretion of piretanide is important for the diuretic response and that piretanide inhibits the fluid absorption in the loop of Henle and the tubuloglomerular feedback control which would otherwise blunt the diuretic response with a reduction in glomerular filtration rate.

Determinants of access of diuretics to their site of action

For consideration of the determinants of access of diuretics to their site of action to be meaningful, one must understand molecular modes of action of diuretics and the anatomic site of effect along the nephron in addition to determinants of the renal handling of diuretics. Although the molecular mode of action is known for a number of drugs, such as the inhibition of carbonic anhydrase by acetazolamide, that for loop diuretics remains obscure. Sites of diuretic action along the nephron have been well delineated through collation of results from in vitro and in vivo techniques in a variety of species. Loop diuretics clearly block chloride reabsorption throughout the thick ascending limb of the loop of Henle. Access of diuretics to their renal tubular sites of action varies among drugs. Important determinants are plasma protein binding, active tubular secretion, nonionic diffusion, and intrarenal metabolism.

Diuretic effect and pharmacokinetics of tizolemide in subjects with normal and decreased renal function

Tizolemide, a new sulphonamide diuretic, has alkaline properties and is cleared by a tubular transport system which differs from the PAH-excreting system which transports thiazide diuretics. The effect of this drug on the excretion of sodium and other electrolytes, and its pharmacokinetics, were evaluated in 5 healthy volunteers and in 10 patients with renal disease who had GFRs ranging from 5-98 ml/min. The saluretic effect of tizolemide was compared with that of placebo. The increase in sodium and chloride excretion after a single dose of 50 mg i.v. was clearly dependent on residual renal function but could be observed in all except one patient. It remains to be assessed whether a full diuretic effect can be achieved in patients with renal insufficiency if higher doses are used. The plasma half-life was 3.0 hours in healthy subjects but increased in patients with renal insufficiency to a maximum of 52 hours. In normal subjects total plasma clearance (611 ml/min) mainly depended on the renal clearance (564 ml/min) which decreased in proportion to GFR, whereas non-renal clearance remained unchanged. The large apparent volume of distribution of the drug (166 l/1.73 m2 BSA) did not increase significantly in uremia. Clinical trials with this drug in patients with reduced renal function must take into account the expected prolongation of its half-life.

Total serum IgE in uremia and after renal transplantation

Uremic patients on maintenance hemodialysis, but without clinical evidence of atopy or diabetes mellitus, had serum levels of total IgE significantly lower than in healthy controls matched for age and sex. Patients with uremia due to diabetic nephropathy had higher IgE levels than the reference group. No correlation was found between total IgE levels and length of dialysis treatment. After renal transplantation, the IgE levels decreased on average to 31% of the pretransplant values over a 60-day observation period. Bacterial or viral infections or episodes of kidney rejection had no apparent influence on the IgE synthesis in the patients with transplant. No correlation was detectable between pretransplant IgE levels and six-month survival of the kidney graft. The low IgE concentrations in uremia are suggested to reflect altered T-cell regulation of the IgE production. The raised IgE levels in diabetic patients could not be explained by specific reagins against insulin, but may have reflected an influence of abnormal carbohydrate metabolism on IgE synthesis. The fall in IgE levels following transplantation is proposed to be attributable to the combined corticosteroid-azathioprine treatment.

Renal tubular secretion and effects of chlorothiazide, hydrochlorothiazide and clopamide: a study in the avian kidney

The relationship between renal tubular secretion and saluretic effects of two thiazides (chlorothiazide and hydrochlorothiazide) and clopamide was studied using a modified Sperber technique. The distribution of carbonic anhydrase in the avian kidney was studied by a histochemical method. The modified Sperber technique allows an absolute estimation of the tubular excretion efficiency of a substance, as determined by its True Tubular Excretion Fraction (TTEF). The TTEF values were for chlorothiazide 59%, hydrochlorothiazide 22% and clopamide 10%. Thus, they were all actively secreted by renal tubular cells; most likely through organic anion transport since novobiocin markedly reduced the TTEF values. After infusion of the diuretics into the renal portal system on one side there was only a small ipsilateral excess natriuresis and chloruresis, in spite of their different tubular excretion efficiencies. For hydrochlorothiazide, and especially for chlorothiazide the saluretic effect therefore appears to be largely independent of the tubular fluid concentration of the diuretic and primarily evoked from the peritubular side of the avian nephron. This is a sharp contrast to the primarily luminally induced saluretic effects of furosemide, ethacrynic acid and piretanide. Only chlorothiazide caused an ipsilateral excess excretion of potassium and bicarbonate, probably due to inhibition of carbonic anhydrase since similar effects were seen after acetazolamide. This effect was coupled to tubular secretion of the diuretic, and probably reflects an inhibition of carbonic anhydrase in cortical distal tubules, where the enzyme is present in the apical region of most cells and could be reached by chlorothiazide present in the tubular fluid.

Effects of bendroflumethiazide on urate metabolism during treatment of patients with renal stones

Treatment with bendroflumethiazide (2.5 mg, twice daily with potassium supplements) in 63 patients with calcium-containing renal stones for a minimum period of 1 year (average duration of treatment 2.6 years) increased the serum urate values in all patients with an average of 90 mumol./l. (conversion factor: 1 mmol. urate = 183 mg.). Despite this the mean urinary urate excretion was unchanged. In the individual patient a systematic effect of therapy was evident since in patients with low pretreatment values the thiazide increased the urate output while in those with the highest levels before therapy it caused a reduction. In most patients there was a reduction of the urate clearance during therapy, which was most evident in those with the highest pretreatment clearance values. In patients with incomplete types of renal acidification defects the same effects were seen on urate metabolism during thiazide treatment as in the other, idiopathic, stone formers. Although the possible role of urate in calcium stone formation has not been definitely settled this study shows that thiazides do not cause hyperuricosuria and hence their beneficial effects on calcium excretion are not counteracted.