Dual effect of potent diuretics on renal handling of phosphate in man

Diuretic Use and Serum Phosphate: Rotterdam Study and UK Biobank

Purpose

Hypophosphatemia (serum phosphate < 0.80 mmol/L) leads to musculoskeletal complaints. The most common drugs linked to hypophosphatemia are thiazide and loop diuretics, but studies in the general population are lacking. Our aim was to study associations between diuretic use and serum phosphate in the Rotterdam Study (RS), a population-based cohort study, with replication in UK Biobank (UKBB).

Methods

Associations between thiazide and loop diuretic use and serum phosphate and odds of hypophosphatemia were analyzed with cross-sectional multivariate linear and logistic regression in participants without chronic kidney disease in the RS and UKBB. Analyses were adjusted for age, sex, and body mass index (BMI) and pooled in 3 RS cohorts with further adjustment for cohort and serum potassium, which was not available in UKBB.

Results

Thiazide diuretics were associated with lower serum phosphate in both sexes. This association lost significance in RS females after adjustment for BMI and in males after adjustment for serum potassium. Thiazide diuretics increased odds of hypophosphatemia in females in both cohorts and in males in UKBB only. Loop diuretics were associated with lower serum phosphate in females but not males. Adjustment for BMI attenuated these associations. Associations between loop diuretics and increased odds of hypophosphatemia in females lost significance after BMI adjustment.

Conclusion

Thiazides, but not loop diuretics, and increased BMI and decreased serum potassium should be considered as contributing factors in subjects with hypophosphatemia. Further studies are needed to replicate the findings and elucidate the potential role of hypokalemia as a mediator of this effect.

NHE3 in the thick ascending limb is required for sustained but not acute furosemide-induced urinary acidification

The Na⁺/H⁺ exchanger isoform 3 (NHE3) facilitates Na⁺ reabsorption and H⁺ secretion by the kidneys. Despite stronger NHE3 abundance in the thick ascending limb (TAL) compared to the S1 and S2 segments of the proximal tubule, the role of NHE3 in the TAL is poorly understood. To investigate the role of NHE3 in the TAL, we generated and phenotyped TAL-specific NHE3 knockout mice (NHE3^TAL-KO). Compared to control mice, NHE3^TAL-KO mice did not show significant differences in body weight, blood pH or plasma Na⁺, K⁺ or Cl^- levels. Fluid intake trended to be higher and urine osmolality was significantly lower in NHE3^TAL-KO mice. Despite a similar GFR, NHE3^TAL-KO mice had a greater urinary K⁺/creatinine ratio. One proposed role of NHE3 relates to furosemide-induced urinary acidification. Acute bolus treatment with furosemide under anesthesia did not result in differences in the dose dependence of urinary flow rate, Cl^- excretion or maximal urinary acidification between genotypes; however, in contrast to control mice, urinary pH returned immediately towards baseline levels in NHE3^TAL-KO mice. Chronic furosemide treatment reduced urine osmolality similarly in both genotypes but metabolic alkalosis, hypokalemia and calciuresis were absent in NHE3^TAL-KO mice. Compared to vehicle, chronic furosemide treatment in control mice resulted in greater NKCC2 and lower Npt2a abundances, effects that were absent in NHE3^TAL-KO mice. In summary, NHE3 in the TAL plays a role for the sustained acidification effect of furosemide. Consistent with this, long-term treatment with furosemide did not result in metabolic alkalosis in NHE3^TAL-KO mice.

Hydrochlorothiazide and potassium chloride in comparison with hydrochlorothiazide and amiloride in the treatment of mild hypertension

A randomized, double-blind, cross-over study comparing 50 mg hydrochlorothiazide plus 5 mg amiloride (HCTZ/A) with 50 mg hydrochlorothiazide plus 26 mmol potassium chloride (HCTZ/K) was conducted in 18 patients with mild essential hypertension (diastolic pressure 90-105 mmHg). The sequence of treatment was: placebo for 2 weeks, one active drug for 3 weeks, placebo for 2 weeks, the other active drug for 3 weeks. The two agents were significantly and equally efficacious in lowering the systolic and diastolic blood pressure. Baseline vs. treatment mean serum potassium levels were 3.82 vs. 3.78 mmol/l for HCTZ/A and 3.82 vs. 3.70 mmol/l for HCTZ/K. The decrease in serum potassium level from baseline was significant for both agents but not significantly different when the two treatment forms were compared. Both treatment forms elevated fasting serum cholesterol and glucose. Serum triglycerides and uric acid rose significantly with HCTZ/K. Amiloride may affect the tubular handling of uric acid causing increased uric acid excretion, thus counteracting thiazide-induced hyperuricemia. During 3 weeks' extension of the main study, 5 patients received HCTZ/A in double the original dose (100 mg/10 mg) and 6 patients received HCTZ/K in double the original dose (100 mg/52 mmol). No further blood pressure reduction was observed on treatment with these doses. The mean serum potassium levels did not decrease further on doubling the HCTZ/A dose, while a significant fall was observed for HCTZ/K (3.60 vs. 3.42 mmol/l) (p less than 0.05, single tailed t-test). Both drug combinations were well tolerated and side-effects were not significantly different from those during placebo administration. This study demonstrates that 50 mg hydrochlorothiazide plus 26 mmol potassium chloride are as effective as 50 mg hydrochlorothiazide plus 5 mg amiloride, both in reducing blood pressure and preventing hypokalaemia in the treatment of essential hypertension. A small extension study indicates that amiloride might be more effective than potassium chloride in preventing hypokalaemia when high doses (100 mg/day) of hydrochlorothiazide are administered.

Dietary potassium influences kidney maintenance of serum phosphorus concentration

In studying the metabolic effects of diet potassium (K+) variation in normal humans, we noted that varying diet K+ within its normal range influenced inorganic phosphorus (Pi) homeostasis and serum calcitriol (1,25-dihydroxyvitamin D) levels. In six men who ingested a constant whole-foods diet containing (per 70 kg body wt) 27 mmol/day Pi and 52 mEq/day K+, we increased diet K+ to 156 mmol/day with supplements first of potassium bicarbonate (KHCO3) alone and then of potassium chloride (KCL) alone, each for eight days interrupted by an eight-day recovery period of no K+ supplement. Urine Pi decreased promptly with either K(+)-salt, each inducing a persisting retention of 7 to 10 mmoles Pi, which was dumped during recovery. Fasting serum [Pi] increased with either K+ supplement (P = 0.022, repeated measures analysis of variance); the composite mean serum [Pi] for the two K(+)-supplement periods exceeded that for the two periods without supplements (P less than 0.01, paired t-test). Conversely, the concentrations of serum calcitriol decreased with either K+ supplement (P = 0.020). Among subjects, the diet K(+)-induced increases in serum [Pi] correlated with those in plasma [K+] (r = 0.64, P = 0.027); the decreases in serum calcitriol concentration correlated with the increases in serum [Pi] (r = -0.69, P = 0.014). There were no significant differences among periods in serum parathyroid hormone, ionized calcium, urine cyclic AMP excretion, plasma renin activity, body weight, serum albumin, or creatinine clearance; plasma volume decreased slightly during KCL but not during KHCO3 periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypophosphatemia in course of chronic obstructive pulmonary disease. Prevalence, mechanisms, and relationships with skeletal muscle phosphorus content

Serum phosphorus levels (Ps), dietary intake of phosphorus, and renal phosphate handling indexes were evaluated in 158 patients with chronic obstructive pulmonary disease (COPD) of varying degrees of severity; moreover, skeletal muscle phosphorus content (Pm) was measured in muscle samples obtained by quadriceps femoris needle biopsy in 14 of the same patients. Hypophosphatemia (Ps less than or equal to 2.5 mg/dl) was found in 34 (21.5 percent) of 158 patients without differences between groups of COPD patients presenting increasing severity of respiratory illness. No relationship was found between serum levels and dietary intake of phosphorus; hypophosphatemia was associated with low renal phosphate threshold (TmPO4/GFR) values in 31 (91 percent) of 34 patients. The prevalence of hypophosphatemia was significantly higher among COPD patients taking one or more drugs commonly used in COPD and known as negatively influencing renal phosphate handling: xanthine derivatives, corticosteroids, loop diuretics, and beta 2-adrenergic bronchodilators. Short-term administration of therapeutic doses of these drugs in COPD patients previously not taking any drug reduced TmPO4/GFR values; phosphaturic effect of short-term theophylline administration on renal phosphate handling was additive to that of long-term assumption of the drug. Muscle phosphorus content was both reduced in COPD patients as compared with control subjects and significantly correlated to serum phosphorus levels and to TmPO4/GFR values. The present investigation revealed a high prevalence of hypophosphatemia among COPD patients as well as a defect in renal phosphate reabsorption secondary, at least in part, to pharmacologic therapy. Moreover, it also suggests that in COPD patients muscle phosphorus content is likely to be reduced in presence of hypophosphatemia.

Metabolic abnormalities associated with phosphoric acid ingestion

A 64-year-old man ingested a phosphoric acid solution in a suicide attempt. He subsequently developed hyperphosphatemia, hypocalcemia, and systemic metabolic acidosis. Local caustic effects of the acid were mild. The patient recovered and was lost to follow-up.

Diuretic activity of torasemide and furosemide in chronic heart failure: a comparative double blind cross-over study

The diuretic effects of torasemide and of furosemide were compared in a double blind cross-over study in 13 patients with stable chronic heart failure. Single doses of 10 mg and 20 mg of torasemide and of 40 mg of furosemide were given orally, in a randomized order on 3 consecutive days. In addition, a placebo was administered on the day preceding the 3 active drug treatment days to obtain control data. Each experimental day was divided into three urine collection periods - 0 to 4 h, 4 to 12 h and 12 to 24 h. Urine output, ion excretion and clearance were measured during each of the 3 periods as well as for the 24-h period. Torasemide 20 mg was distinctly more active in each of the 3 collection periods and in the 24-h period than furosemide 40 mg, whereas no significant difference was found between furosemide 40 mg and torasemide 10 mg for most of the experimental data. From 0 to 4 h, both torasemide and furosemide significantly increased the urinary flow rate and the urinary excretion of sodium, chloride and calcium, while they decreased the urinary osmolality when compared to placebo. All the effects persisted in the 4 to 12 h period after torasemide 20 mg in contrast to furosemide, whose effects were limited to the 0 to 4 h period. In the third period (12-24 h), the urine volume fell below the placebo value after furosemide but not torasemide, and only torasemide 20 mg was followed by a persistent decrease in the urine osmolality.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

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.

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.