Potassium-sparing effects of furosemide in mice on high-potassium diets.

In individuals on a regular "Western" diet, furosemide induces a kaliuresis and reduction in plasma K concentration by inhibiting Na reabsorption in the thick ascending limb of Henle's loop, enhancing delivery of Na to the aldosterone-sensitive distal nephron. In the aldosterone-sensitive distal nephron, the increased Na delivery stimulates K wasting due to an exaggerated exchange of epithelial Na channel-mediated Na reabsorption of secreted K. The effects of furosemide are different in mice fed a high-K, alkaline (HK) diet: the large-conductance Ca-activated K (BK) channel, in conjunction with the BK ß4-subunit (BK-α/ß4), mediates K secretion from intercalated cells (IC) of the connecting tubule and collecting ducts. The urinary alkaline load is necessary for BK-α/ß4-mediated K secretion in HK diet-fed mice. However, furosemide acidifies the urine by increasing vacuolar ATPase expression and acid secretion from IC, thereby inhibiting BK-α/ß4-mediated K secretion and sparing K. In mice fed a low-Na, high-K (LNaHK) diet, furosemide causes a greater increase in plasma K concentration and reduction in K excretion than in HK diet-fed mice. Micropuncture of the early distal tubule of mice fed a LNaHK diet, but not a regular or a HK diet, reveals K secretion in the thick ascending limb of Henle's loop. The sites of action of K secretion in individuals consuming a high-K diet should be taken into account when diuretic agents known to waste K with low or moderate K intakes are prescribed.

Hydrochlorothiazide vs chlorthalidone, indapamide, and potassium-sparing/hydrochlorothiazide diuretics for reducing left ventricular hypertrophy: A systematic review and meta-analysis.

Left ventricular hypertrophy develops in 36%-41% of hypertensive patients and independently predicts cardiovascular events and total mortality. Moreover, drug-induced reduction in left ventricular mass (LVM) correlates with improved prognosis. The optimal thiazide-type diuretic for reducing LVM is unknown. Evidence regarding potency, cardiovascular events, sodium, and potassium suggested the hypothesis that "CHIP" diuretics (CHlorthalidone, Indapamide, and Potassium-sparing diuretic/hydrochlorothiazide [PSD/HCTZ]) would reduce LVM more than HCTZ. Systematic searches of five databases were conducted. Among the 38 randomized trials, a 1% reduction in systolic blood pressure (SBP) predicted a 1% reduction in LVM, P = 0.00001. CHIP-HCTZ differences in reducing LVM differed across trials (ie, heterogeneity), making interpretation uncertain. However, among the 28 double-blind trials, heterogeneity was undetectable, and HCTZ reduced LVM (percent reduction [95% CI]) by -7.3 (-10.4, -4.2), P < 0.0001. CHIP diuretics surpassed HCTZ in reducing LVM: chlorthalidone -8.2 (-14.7, -1.6), P = 0.015; indapamide -7.5 (-12.7, -2.3), P = 0.005; and all CHIP diuretics combined -7.7 (-12.2, -3.1), P < 0.001. The comparison of PSD/HCTZ with HCTZ had low statistical power but favored PSD/HCTZ: -6.0 (-14.1, +2.1), P = 0.149. Thus, compared to HCTZ, CHIP diuretics had twice the effect on LVM. CHIP diuretics did not surpass HCTZ in reducing systolic or diastolic blood pressure: -0.3 (-5.0, +4.3) and -1.6 (-5.6, +2.4), respectively. The strength of evidence that CHIP diuretics surpass HCTZ for reducing LVM was high (GRADE criteria). In conclusion, these novel results have demonstrated that CHIP diuretics reduce LVM 2-fold more than HCTZ among hypertensive patients. Although generally related to LVM, blood pressure fails to explain the superiority of CHIP diuretics for reducing LVM.

Diuretic, natriuretic and potassium-sparing effect of nothofagin isolated from Leandra dasytricha (A. Gray) Cogn. leaves in normotensive and hypertensive rats.

Active constituents from natural origin have long been used for the treatment of patients suffering from cardiovascular and renal diseases. This study therefore aimed to investigate the diuretic and natriuretic properties of nothofagin, a dihydrochalcone isolated from Leandra dasytricha (A. Gray) Cogn. leaves in normotensive and hypertensive rats. Male Wistar normotensive rats were orally treated with vehicle (1 ml/kg); hydrochlorothiazide (HCTZ; 25 mg/kg); ethyl acetate fraction from L. dasytricha (EALD; 3-30 mg/kg) and nothofagin (NOT; 0.3-3 mg/kg). Spontaneously hypertensive rats (SHR) received NOT (1 mg/kg), HCTZ (25 mg/kg) or vehicle. The cumulative diuretic index, urinary electrolytes excretion (Na+ and K+), pH, density and conductivity were measured at the end of the experiment (after 8 h). A7r5 and L929 cell lines were used to measure cell viability after exposure to NOT. Nitric oxide generation was quantified in A7r5 cell supernatant, and DPPH assay was used for evaluating the antioxidant properties of NOT. The urinary volume of normotensive rats were increased after the treatment with EALD, without any changes in Na+ or K+ excretion. NOT was able to induce diuresis and natriuresis, but not kaliuresis, in both normotensive and hypertensive rats. The reduction in prostanoids generation through cyclooxygenase inhibition, as well as the muscarinic receptor antagonism, fully avoided NOT-induced increases in diuretic index. NOT, which did not interfere with L929 or A7r5 cell viability, was able to stimulate nitric oxide generation in A7r5 cell, besides showing an antioxidant effect in scavenging the free-radical DPPH. Taken together, our study shows, for the first time, the diuretic, natriuretic and potassium-sparing effect of nothofagin in rats, which was associated with prostanoids generation, muscarinic receptor activation and antioxidant properties.

The effect of co-trimoxazole on serum potassium concentration: safety evaluation of a randomized controlled trial.

AIMS: Co-trimoxazole maintains a well-established role in the treatment of Pneumocystis jirovecii and Toxoplasma gondii, as well as urinary tract infections. Observational studies report hyperkalaemia to be associated with co-trimoxazole, which may stem from an amiloride-like potassium-sparing effect. The current study investigated changes in serum potassium in patients without acute infections, and the influence of concomitant antikaliuretic drugs on this effect. METHODS: A post hoc analysis was carried out of a randomized controlled trial in patients with interstitial lung disease who were assigned to placebo or 960 mg co-trimoxazole twice daily. Serum potassium and creatinine were measured at baseline, 6 weeks, and 6, 9 and 12 months. The primary outcome was the difference in mean serum potassium concentrations between co-trimoxazole and placebo at 6 weeks. RESULTS: Mean serum potassium levels were similar at baseline: 4.24 (± 0.44) mmol l-1 in the 87 co-trimoxazole group participants and 4.25 (± 0.39) mmol l-1 in the 83 control participants. Co-trimoxazole significantly increased mean serum potassium levels at 6 weeks, with a difference between means compared with placebo of 0.21 mmol l-1 [95% confidence interval (CI) 0.09, 0.34; P = 0.001). This significant increase in serum potassium was detectable even after exclusion of patients on antikaliuretic drugs, with a difference between means for co-trimoxazole compared with placebo of 0.23 mmol l-1 (95% CI 0.09, 0.38; P = 0.002). There were 5/87 (5.7%) patients on co-trimoxazole whose serum potassium concentrations reached ≥5.5 mmol l-1 during the study period. CONCLUSIONS: Co-trimoxazole significantly increases serum potassium concentration, even in participants not using antikaliuretic drugs. While the magnitude of increase was often minor, a small proportion in our outpatient cohort developed hyperkalaemia of clinical importance.

Block of human CaV3 channels by the diuretic amiloride.

Previous studies in native T-type currents have suggested the existence of distinct isoforms with dissimilar pharmacology. Amiloride was the first organic blocker to selectively block the native T-type calcium channel, but the potency and mechanism of block of this drug on the three recombinant T-type calcium channels (Ca(V)3.1, Ca(V)3.2, and Ca(V)3.3) have not been systematically determined. The aim of the present study was to investigate whether there is differential block of Ca(V)3 channels by amiloride, to establish the mechanism of block, and to obtain insights into the amiloride putative binding sites in Ca(V)3 channels. By performing whole-cell patch-clamp recordings of human embryonic kidney 293 cells stably expressing human Ca(V)3 channels, we found that amiloride blocked the human Ca(V)3 channels in a concentration-response manner; the IC50 for Ca(V)3.2 channels (62 µM) was 13-fold lower than that for Ca(V)3.1 and Ca(V)3.3. Block is voltage-independent (except for Ca(V)3.3 channels) and targets mainly closed-state channels, although a small use-dependent component was observed in Ca(V)3.1 channels. In addition, amiloride block of Ca(V)3.2 channels is mainly due to an extracellular effect, whereas in Ca(V)3.1 and Ca(V)3.3 channels, the amiloride inhibition is equally effective from both sides of the membrane. The results demonstrate that amiloride blocks human Ca(V)3 channels differentially through a mechanism involving mainly the closed state of the channel and suggest a negative allosteric interaction with at least two putative binding sites with different affinities. The preferential block of Ca(V)3.2 channels labels amiloride as the only organic blocker to be selective for any T-type channel.