Bayesian sample sizes for exploratory clinical trials comparing multiple experimental treatments with a control.

In this paper, a Bayesian approach is developed for simultaneously comparing multiple experimental treatments with a common control treatment in an exploratory clinical trial. The sample size is set to ensure that, at the end of the study, there will be at least one treatment for which the investigators have a strong belief that it is better than control, or else they have a strong belief that none of the experimental treatments are substantially better than control. This criterion bears a direct relationship with conventional frequentist power requirements, while allowing prior opinion to feature in the analysis with a consequent reduction in sample size. If it is concluded that at least one of the experimental treatments shows promise, then it is envisaged that one or more of these promising treatments will be developed further in a definitive phase III trial. The approach is developed in the context of normally distributed responses sharing a common standard deviation regardless of treatment. To begin with, the standard deviation will be assumed known when the sample size is calculated. The final analysis will not rely upon this assumption, although the intended properties of the design may not be achieved if the anticipated standard deviation turns out to be inappropriate. Methods that formally allow for uncertainty about the standard deviation, expressed in the form of a Bayesian prior, are then explored. Illustrations of the sample sizes computed from the new method are presented, and comparisons are made with frequentist methods devised for the same situation.

Cooperative mechanisms involved in chronic antidiuretic response to bendroflumethiazide in rats with lithium-induced nephrogenic diabetes insipidus.

Previous studies of central diabetes insipidus suggested that thiazides acutely exerted a paradoxical antidiuresis by either indirectly activating volume-homeostatic reflexes to decrease distal fluid-delivery, or directly stimulating distal water-reabsorption. This study investigated whether the direct and indirect actions of bendroflumethiazide (BFTZ) simultaneously cooperated and also whether the renal nerves were involved in inducing long-term antidiuresis in nephrogenic diabetes insipidus (NDI). BFTZ or vehicle was gavaged into bilateral renal denervated and innervated rats with lithium-induced NDI for 10 days, constituting four groups. At one day before (D0) and one, five and ten days after starting administration of BFTZ or vehicle, rats were placed in metabolic cages to collect urine for 6 hours. BFTZ-treatment in both renal innervated and denervated rats caused equivalent reductions in urine-flow, creatinine clearance, lithium clearance and free-water clearance, but rises in urine-osmolality, fractional proximal reabsorption and fractional distal reabsorption at all days compared to D0, as well as to those of their relevant vehicle-received group. Therefore, the chronic antidiuretic response to BFTZ in conscious NDI rats was exerted through a concomitant cooperation of its direct distal effect of stimulating water-reabsorption and its indirect effect of reducing distal fluid-delivery by activating volume-homeostatic mechanisms, which appeared independent of the renal nerves.

Emerging role of calcium-activated potassium channel in the regulation of cell viability following potassium ions challenge in HEK293 cells and pharmacological modulation.

Emerging evidences suggest that Ca(2+)activated-K(+)-(BK) channel is involved in the regulation of cell viability. The changes of the cell viability observed under hyperkalemia (15 mEq/L) or hypokalemia (0.55 mEq/L) conditions were investigated in HEK293 cells expressing the hslo subunit (hslo-HEK293) in the presence or absence of BK channel modulators. The BK channel openers(10(-11)-10(-3)M) were: acetazolamide(ACTZ), Dichlorphenamide(DCP), methazolamide(MTZ), bendroflumethiazide(BFT), ethoxzolamide(ETX), hydrochlorthiazide(HCT), quercetin(QUERC), resveratrol(RESV) and NS1619; and the BK channel blockers(2 x 10(-7)M-5 x 10(-3)M) were: tetraethylammonium(TEA), iberiotoxin(IbTx) and charybdotoxin(ChTX). Experiments on cell viability and channel currents were performed using cell counting kit-8 and patch-clamp techniques, respectively. Hslo whole-cell current was potentiated by BK channel openers with different potency and efficacy in hslo-HEK293. The efficacy ranking of the openers at -60 mV(Vm) was BFT> ACTZ >DCP ≥RESV≥ ETX> NS1619> MTZ≥ QUERC; HCT was not effective. Cell viability after 24 h of incubation under hyperkalemia was enhanced by 82+6% and 33+7% in hslo-HEK293 cells and HEK293 cells, respectively. IbTx, ChTX and TEA enhanced cell viability in hslo-HEK293. BK openers prevented the enhancement of the cell viability induced by hyperkalemia or IbTx in hslo-HEK293 showing an efficacy which was comparable with that observed as BK openers. BK channel modulators failed to affect cell currents and viability under hyperkalemia conditions in the absence of hslo subunit. In contrast, under hypokalemia cell viability was reduced by -22+4% and -23+6% in hslo-HEK293 and HEK293 cells, respectively; the BK channel modulators failed to affect this parameter in these cells. In conclusion, BK channel regulates cell viability under hyperkalemia but not hypokalemia conditions. BFT and ACTZ were the most potent drugs either in activating the BK current and in preventing the cell proliferation induced by hyperkalemia. These findings may have relevance in disorders associated with abnormal K(+) ion homeostasis including periodic paralysis and myotonia.

Diuretics prime plant immunity in Arabidopsis thaliana.

Plant activators are agrochemicals that activate the plant immune system, thereby enhancing disease resistance. Due to their prophylactic and durable effects on a wide spectrum of diseases, plant activators can provide synergistic crop protection when used in combination with traditional pest controls. Although plant activators have achieved great success in wet-rice farming practices in Asia, their use is still limited. To isolate novel plant activators applicable to other crops, we screened a chemical library using a method that can selectively identify immune-priming compounds. Here, we report the isolation and characterization of three diuretics, bumetanide, bendroflumethiazide and clopamide, as immune-priming compounds. These drugs upregulate the immunity-related cell death of Arabidopsis suspension-cultured cells induced with an avirulent strain of Pseudomonas syringae pv. tomato in a concentration-dependent manner. The application of these compounds to Arabidopsis plants confers disease resistance to not only the avirulent but also a virulent strain of the pathogen. Unlike salicylic acid, an endogenous phytohormone that governs disease resistance in response to biotrophic pathogens, the three diuretic compounds analyzed here do not induce PR1 or inhibit plant growth, showing potential as lead compounds in a practical application.

AT2 receptor non-peptide agonist C21 promotes natriuresis in obese Zucker rats.

Previously, we demonstrated that angiotensin II type 2 (AT(2)) receptors have a role in natriuresis in obese Zucker rats (OZR). In the present study, we investigated the role of a novel, non-peptide agonist, C21, in natriuresis via AT(2) receptor activation in OZR. Infusion of C21 (1 and 5 µg kg(-1) min(-1)) into rats under anesthesia caused a dose-dependent increase in urine flow (UF) and urinary Na volume (U(Na)V). These effects of C21 were blocked by pre-infusion of the AT(2) receptor antagonist, PD123319, (50 µg kg(-1) min(-1)), suggesting involvement of the AT(2) receptor. Infusion of C21 (5 µg kg(-1) min(-1)) significantly increased the fractional excretion of sodium without changing the glomerular filtration rate or blood pressure, suggesting a tubular effect. Similarly, C21 infusion increased the fractional excretion of lithium, suggesting a proximal tubular effect. Furthermore, we tested the effect of C21 on natriuresis after blocking two main, distal-nephron Na transporters, the epithelial Na channels (ENaC), with amiloride (AM, 3 mg kg(-1) body wt), and the NaCl cotransporters (NCC), with bendroflumethiazide (BFTZ, 7 mg kg(-1) body wt). Infusion of AM + BFTZ caused significant increases in both diuresis and natriuresis, which were further increased by infusion of C21 (5 µg kg(-1) min(-1)). Natriuresis in response to C21 was associated with increases in urinary NO and cGMP levels. The data indicate that the AT(2) receptor agonist, C21, promotes natriuresis via AT(2) receptor activation and that this effect is potentially based in the proximal tubules and linked to the nitric oxide/cyclic guanosine monophosphate pathway. The natriuretic response to C21 may have therapeutic significance by improving kidney function in obesity.

Cooperative mechanisms of acute antidiuretic response to bendroflumethiazide in rats with lithium-induced nephrogenic diabetes insipidus.

The exact mechanism underlying thiazides-induced paradoxical antidiuresis in diabetes insipidus is still elusive, but it has been hypothesized that it is exerted either via Na+-depletion activating volume-homeostatic reflexes to decrease distal delivery, or direct stimulation of distal water reabsorption. This study examined how these two proposed mechanisms actually cooperate to induce an acute bendroflumethiazide (BFTZ)-antidiuretic effect in nephrogenic diabetes insipidus (NDI). Anaesthetized rats with lithium (Li)-induced NDI were prepared in order to measure their renal functional parameters, and in some of them, bilateral renal denervation (DNX) was induced. After a 30 min control clearance period, we infused either BFTZ into 2 groups, NDI+BFTZ and NDI/DNX+BFTZ, or its vehicle into a NDI+V group, and six 30 min experimental clearance periods were taken. During BFTZ infusion in the NDI+BFTZ group, transiently elevated Na+ excretion was associated with rapidly increased urinary osmolality and decreased free water clearance, but Li clearance and urine flow declined in the later periods. However, in the NDI/DNX+BFTZ group, there was persistently elevated Na+ excretion with unchanged Li clearance and urine flow during the experimental period, while alterations in free water clearance and urinary osmolality resembled those in the NDI+BFTZ group. In conclusion, BFTZ initially exerted two direct effects of natriuresis-diuresis and stimulating free water reabsorption at the distal nephron in NDI, which together elevated Na+ excretion and urinary osmolality but kept the urine volume unchanged in the first hour. Thereafter, the resultant sodium depletion led to the activation of neural reflexes that reduced distal fluid delivery to compensate for BFTZ-induced natriuresis-diuresis which, in cooperation with the direct distal BFTZ-antidiuretic effect, resulted in excretion of urine with a low volume, high osmolality, and normal sodium.

ANP-mediated inhibition of distal nephron fractional sodium reabsorption in wild-type and mice overexpressing natriuretic peptide receptor.

Atrial natriuretic peptide (ANP) elicits natriuresis; however, the relative contributions of proximal and distal nephron segments to the overall ANP-induced natriuresis have remained uncertain. This study was performed to characterize the effects of ANP on distal nephron sodium reabsorption determined after blockade of the two major distal nephron sodium transporters with amiloride (5 microg/g body wt) plus bendroflumethiazide (12 microg/g body wt) in male anesthetized C57/BL6 and natriuretic peptide receptor-A gene (Npr1) targeted four-copy mice. The lower dose of ANP (0.1 ng x g body wt(-1) x min(-1), n = 6) increased distal sodium delivery (DSD, 2.4 +/- 0.4 vs. 1.6 +/- 0.2 mueq/min, P < 0.05) but did not change fractional reabsorption of DSD compared with control (86.3 +/- 2.0 vs. 83.9 +/- 3.6%, P > 0.05), thus limiting the magnitude of the natriuresis. In contrast, the higher dose (0.2 ng x g body wt(-1) x min(-1), n = 6) increased DSD (2.8 +/- 0.3 mueq/min, P < 0.01) and also decreased fractional reabsorption of DSD (67.4 +/- 4.5%, P < 0.01), which markedly augmented the natriuresis. In Npr1 gene-duplicated four-copy mice (n = 6), the lower dose of ANP increased urinary sodium excretion (0.6 +/- 0.1 vs. 0.3 +/- 0.1 mueq/min, P < 0.05) and decreased fractional reabsorption of DSD compared with control (72.2 +/- 3.4%, P < 0.05) at similar mean arterial pressures (91 +/- 6 vs. 92 +/- 3 mmHg, P > 0.05). These results provide in vivo evidence that ANP-mediated increases in DSD alone exert modest effects on sodium excretion and that inhibition of fractional reabsorption of distal sodium delivery is requisite for the augmented natriuresis in response to the higher dose of ANP or in Npr1 gene-duplicated mice.

Comparison of the effects of diuretics on blood pressure and arterial stiffness in patients with stroke.

OBJECTIVES: Indapamide (IND) and bendroflumethiazide (BDZ) are both widely used in patients with stroke. We compared their effects on arterial blood pressure (BP) and arterial stiffness in a group of patients with stroke. METHODS: In a prospective, randomized, double-blinded study we investigated the effect of 28-day treatment with BDZ (2.5 mg once daily) or IND (2.5 mg once daily) on BP and arterial stiffness in a group of patients with first-ever ischemic stroke. RESULTS: All data are expressed as mean (SD). In all, 23 patients completed the protocol (age 70.0 +/- 9.55 years). Group I (IND) and group B (BDZ) comprised 13 and 10 patients, respectively. Groups were well matched for demographics and baseline characteristics. Mean arterial pressure reduction from baseline was I = 14.3 +/- 10.3 mm Hg (P < .001) versus B = 9.1 +/- 11.2 mm Hg (P = .03). Augmentation index (AI) was reduced by: I = 4.94 +/- 7.22% (P = .037) versus B = 6.17 +/- 7.85% (P = .035). Time to reflection was increased by I = 3.22 +/- 9.57 milliseconds (P = .268) versus B = 4.71 +/- 5.30 milliseconds (P = .020). There was no significant difference between the two drugs with regard to change in BP or arterial stiffness. Pooled data showed a reduction in mean arterial pressure by 12.1 +/- 10.77 mm Hg (P < .0001) and in AI by 5.5 +/- 7.36% (P = .002), and a small increase in time to reflection by 3.9 +/- 7.79 milliseconds (P = .029). The change in BP explained up to 28% of the change in AI. CONCLUSION: Both diuretics altered hemodynamic parameters to a similar extent. The results are consistent with a direct effect of diuretic therapy on vascular function. The influence of both diuretics on arterial stiffness was similar.

Acetazolamide prevents vacuolar myopathy in skeletal muscle of K(+) -depleted rats.

BACKGROUND AND PURPOSE: Acetazolamide and dichlorphenamide are carbonic anhydrase (CA) inhibitors effective in the clinical condition of hypokalemic periodic paralysis (hypoPP). Whether these drugs prevent vacuolar myopathy, which is a pathogenic factor in hypoPP, is unknown. The effects of these drugs on the efflux of lactate from skeletal muscle were also investigated. EXPERIMENTAL APPROACH: For 10 days, K(+)-depleted rats, a model of hypoPP, were administered 5.6 mg kg(-1) day(-1) of acetazolamide, dichlorphenamide or bendroflumethiazide (the last is not an inhibitor of CA). Histological analysis of vacuolar myopathy and in vitro lactate efflux measurements were performed in skeletal muscles from treated and untreated K(+)-depleted rats, and also from normokalemic rats. KEY RESULTS: About three times as many vacuoles were found in the type II fibres of tibialis anterioris muscle sections from K(+)-depleted rats as were found in the same muscle from normokalemic rats. In ex vivo experiments, a higher efflux of lactate on in vitro incubation was found in muscles of K(+)-depleted rats compared with that found in muscles from normokalemic rats. After treatment of K(+)-depleted rats with acetazolamide, the numbers of vacuoles in tibialis anterioris muscle decreased to near normal values. Incubation with acetazolamide in vitro inhibited efflux of lactate from muscles of K(+)-depleted rats. In contrast, bendroflumethiazide and dichlorphenamide failed to prevent vacuolar myopathy after treatment in vivo and failed to inhibit lactate efflux in vitro. CONCLUSIONS AND IMPLICATIONS: Acetazolamide prevents vacuolar myopathy in K(+)-depleted rats. This effect was associated with inhibition of lactate transport, rather than inhibition of CA.

Overlapping in vitro and in vivo specificities of the organic anion transporters OAT1 and OAT3 for loop and thiazide diuretics.

Organic anion transporter (OAT) genes have been implicated in renal secretion of organic anions, but the individual in vivo contributions of OAT1 (first identified as NKT) and OAT3 remain unclear. Potential substrates include loop diuretics (e.g., furosemide) and thiazide diuretics (e.g., bendroflumethiazide), which reach their tubular sites of action mainly by proximal tubular secretion. Previous experiments in Oat1 knockout (-/-) mice revealed an almost complete loss of renal secretion of the prototypic organic anion p-aminohippurate (PAH) and a role of OAT1 in tubular secretion of furosemide (Eraly SA, Vallon V, Vaughn D, Gangoiti JA, Richter K, Nagle M, Monte JC, Rieg T, Truong DM, Long JM, Barshop BA, Kaler G, Nigam SK. J Biol Chem 281: 5072-5083, 2006). In this study we found that both furosemide and bendroflumethiazide inhibited mOat1- and mOat3-mediated uptake of a labeled tracer in Xenopus oocytes injected with cRNA, consistent with their being substrates for mouse OAT1 and OAT3. Experiments in Oat3(-/-) mice revealed intact renal secretion of PAH, but the dose-natriuresis curves for furosemide and bendroflumethiazide were shifted to the right and urinary furosemide excretion was impaired similar to the defect in Oat1(-/-) mice. Thus, whereas OAT1 (in contrast to OAT3) is the classic basolateral PAH transporter of the proximal tubule, both OAT1 and OAT3 contribute similarly to normal renal secretion of furosemide and bendroflumethiazide, and a lack of either one is not fully compensated by the other. Although microarray expression analysis in the kidneys of Oat1(-/-) and Oat3(-/-) mice revealed somewhat altered expression of a small number of transport-related genes, none were common to both knockout models. When searching for polymorphisms involved in human diuretic responsiveness, it may be necessary to consider both OAT1 and OAT3, among other genes.

Effects of "newer" and "older" antihypertensive drugs on hemorrheological, platelet, and endothelial factors. A substudy of the Anglo-Scandinavian Cardiac Outcomes Trial.

BACKGROUND: Different antihypertensive therapies may exert benefits via not only a reduction in blood pressure but also in improving the risk of thrombosis. METHODS: We tested the hypothesis that a more modern antihypertensive drug regimen (ie, amlodipine +/- perindopril) would have a more beneficial effect on hemorheological markers (white blood-cell count [WCC], plasma viscosity [PV], hematocrit [HCT], and fibrinogen)--and on plasma von Willebrand factor (vWf, an index of endothelial damage and dysfunction) and soluble P-selectin (sP-sel, an index of platelet activation), compared with an older antihypertensive drug regimen (ie, atenolol +/- bendroflumethiazide). RESULTS: After 6 months, PV, sP-sel, and HCT fell in both groups (P < .01), while fibrinogen was unchanged. However, those 74 patients randomized to amlodipine +/- perindopril had significant reductions in WCC (P = .005), with no significant changes in vWF or platelet count. Conversely, in those 85 patients randomized to atenolol +/- bendroflumethiazide, there were significant reductions in vWF (P = .001) and platelet count (P = .011) but no significant reductions in WCC. There were no significant differences in the levels of any of the variables between the two arms of the trial, nor a significant difference in the magnitude of reduction between the two treatment arms. CONCLUSIONS: Within the constraints of this substudy design, there was no differential effect apparent of the two antihypertensive treatment arms on hemorheological parameters or endothelial and platelet function (as assessed by vWF and sP-sel), suggesting that other pathophysiological mechanisms may be involved.

Does the aldosterone:renin ratio predict the efficacy of spironolactone over bendroflumethiazide in hypertension? A clinical trial protocol for RENALDO (RENin-ALDOsterone) study.

BACKGROUND: High blood pressure is an important determinant of cardiovascular disease risk. Treated hypertensives do not attain a risk level equivalent to normotensives. This may be a consequence of suboptimal blood pressure control to which indiscriminate use of antihypertensive drugs may contribute. Indeed the recent ALLHAT1study suggests that thiazides should be given first to virtually all hypertensives. Whether this is correct or whether different antihypertensive therapies should be targeted towards different patients is a major unresolved issue, which we address in this study. The measurement of the ratio of aldosterone: renin is used to identify hypertensive subjects who may respond well to treatment with the aldosterone antagonist spironolactone. It is not known if subjects with a high ratio have aldosteronism or aldosterone-sensitive hypertension is debated but it is important to know whether spironolactone is superior to other diuretics such as bendroflumethiazide in this setting. METHODS/DESIGN: The study is a double-blind, randomised, crossover, controlled trial that will randomise 120 hypertensive subjects to 12 weeks treatment with spironolactone 50 mg once daily and 12 weeks treatment with bendroflumethiazide 2.5 mg once daily. The 2 treatment periods are separated by a 2-week washout period. Randomisation is stratified by aldosterone: renin ratio to include equal numbers of subjects with high and low aldosterone: renin ratios. Primary Objective--To test the hypothesis that the aldosterone: renin ratio predicts the antihypertensive response to spironolactone, specifically that the effect of spironolactone 50 mg is greater than that of bendroflumethiazide 2.5 mg in hypertensive subjects with high aldosterone: renin ratios. Secondary Objectives--To determine whether bendroflumethiazide induces adverse metabolic abnormalities, especially in subjects with high aldosterone: renin ratios and if baseline renin measurement predicts the antihypertensive response to spironolactone and/or bendrofluazide. DISCUSSION: The numerous deleterious effects of hypertension dictate the need for a systematic approach for its treatment. In spite of various therapies, resistant hypertension is widely prevalent. Among various factors, primary aldosteronism is an important cause of resistant hypertension and is now more commonly recognised. More significantly, hypertensives with primary aldosteronism are also exposed to various other deleterious effects of excess aldosterone. Hence treating hypertension with specific aldosterone antagonists may be a better approach in this group of patients. It may lead on to better blood pressures with fewer medications.

Comparison of the effect of diuretics on carotid blood flow in stroke patients.

OBJECTIVES: Indapamide (IND) and bendroflumethiazide (BDZ) are both widely used in the management of blood pressure after stroke. There are theoretical reasons why these agents may differ with regard to their cardiovascular effects. We compared the effect of these agents on blood pressure and cerebral blood flow in a group of stroke patients. METHODS: In a prospective, randomized, double-blinded study we investigated the effect of 28 days' treatment with BDZ 2.5 mg od or IND 2.5 mg od on blood pressure and cerebral blood flow in a group patients with recent first-ever ischemic stroke. Using extracranial carotid and transcranial ultrasound we assessed carotid blood flow and intracranial hemodynamics. RESULTS: All data are expressed as mean (SD). Twenty-five patients completed the protocol (age 68.8 +/- 10.6 y). Groups I (IND) and B (BDZ) comprised 13 and 12 patients, respectively. Groups were well matched for demography and baseline characteristics. Percent change in mean arterial pressure reduction from baseline was (I = -14.7 +/- 12.5, P < 0.001 vs. B = -7.7 +/- 9.16 mm Hg, P = 0.02). There was a trend toward increased carotid blood flow in both groups (I = +10% +/- 47, P = 0.4 vs. B = +33% +/- 47, P = 0.12). No significant change in middle cerebral artery mean flow velocity or pulsatility index was observed. There was no significant difference between the 2 drugs with regard to change in blood pressure (95% confidence interval for difference -2.5 to 16.3 mm Hg, P = 0.14) or carotid blood flow (95% confidence interval for difference -58 to 27 mL/s, P = 0.45). CONCLUSIONS: Both diuretics reduced blood pressure to a similar and significant degree. There was no evidence of an adverse effect on cerebral blood flow or intracranial hemodynamics induced by either agent. No significant difference between the effect of IND and BDZ was observed.

Blunted non-nitric oxide vasodilatory neurotransmission in penile arteries from renal hypertensive rats.

The present study was designed to explore whether there are any effects on neurogenic responses in penile small arteries during the development of hypertension in a one-kidney, one-clip (1K1C) model, a non-renin-dependent model of renovascular hypertension. Five weeks after surgery, male Sprague-Dawley rats were given vehicle, bendroflumethiazide (7.5 mg/kg/day), or L-arginine (2 g/kg/day) in their drinking water for five weeks. Experiments were performed on penile small artery rings (150-200 microm) mounted on microvascular myographs for electrical field stimulation (EFS), and erectile tissue was processed for immunohistochemistry. Maximal neurogenic contractions were unmodified in penile preparations. Relaxations induced by EFS were reduced in the presence of ADMA. In 1K1C rats, neurogenic vasorelaxation mediated by nitric oxide (NO) was unaltered, while relaxation resistant to NO synthase inhibition was blunted. L-arginine and bendroflumethiazide lowered blood pressure in 1K1C rats, but vasodilation was still blunted in the penile arteries. Immunoreactivity for factor VIII and neuronal NO synthase was unaltered in penile arteries from 1K1C animals. Endothelium-dependent vasorelaxation evoked by acetylcholine was also blunted in preparations from 1K1C rats, while exogenous NO relaxation was unaffected. Plasma concentrations and urinary excretion of ADMA did not differ among the experimental animals. Our findings indicate that the reduced release of a non-NO vasodilatory neurotransmitter accounts for the impaired neurogenic vasodilation of the penile arteries. Although ADMA inhibits penile vasorelaxation, it is unlikely to affect erectile function in 1K1C rats.

Dose-effect relations of loop- and thiazide-diuretics on calcium homeostasis: a randomized, double-blinded Latin-square multiple cross-over study in postmenopausal osteopenic women.

BACKGROUND: Thiazide diuretics (TDs) reduce whereas loop diuretics (LDs) increase urinary calcium. We studied the effects of different doses of a TD and LD on electrolytes, calcitropic hormones and biochemical bone markers. SUBJECTS AND METHODS: In a five-period crossover study, comparing four active doses with placebo, 40 postmenopausal women with osteopenia were treated with different doses of LD bumetanide (n = 20, 0.5-2.0 mg per day) or TD bendroflumethiazide (n = 20, 2.5-10 mg per day). Each treatment period lasted 1 week. RESULTS: Urinary calcium decreased dose-dependently in response to the bendroflumethiazide. The best hypocalciuric effect was achieved by 5 mg day-1 of bendroflumethiazide. Total plasma calcium levels increased, whereas ionised calcium at ambient pH-values decreased because of increased pH-values in response to the bendroflumethiazide. Plasma PTH levels did not change, whereas a slight dose-dependent increase occurred in plasma 1,25(OH)2D levels. As a marker of bone formation, plasma osteocalcin levels increased. Conversely, bumetanide dose-dependently increased renal calcium losses with a concomitant increase in plasma PTH and 1,25(OH)2D levels. Plasma osteocalcin levels increased and bone-specific alkaline phosphatase levels decreased dose-dependently. CONCLUSION: Whether a LD or TD is chosen as diuretic therapy affects calcium homeostasis. The effects of LDs are potentially harmful to bone. Further studies are needed to evaluate whether long-term treatment with LDs causes osteoporosis. Until then, we suggest using, if possible, a TD rather than a LD as diuretic therapy in order not to risk deleterious effects on bone metabolism.

Role of sodium depletion in acute antidiuretic effect of bendroflumethiazide in rats with nephrogenic diabetes insipidus.

The mechanisms underlying the acute antidiuretic response to bendroflumethiazide (BFTZ; 0.25 mg/h for 3 h) in rats with nephrogenic diabetes insipidus (NDI) was investigated. NDI was induced in conscious chronically instrumented female Wistar rats either by chronic lithium administration (40-60 mmol Li/kg of diet for 4 weeks) or by acute infusion of V2 antagonist OPC-31260 (0.2 mg/h). Renal clearance experiments were performed in conscious rats instrumented with permanent catheters. During experiments total body water content was held constant by i.v. replacement of urine production (V) with 150 mM glucose. One group in addition received i.v. replacement of urinary sodium losses. In both models of NDI, BFTZ-induced antidiuresis was associated with a decrease in the delivery of tubular fluid to the distal nephron, as measured by lithium clearance (C(Li)). Both the antidiuresis and the decrease in C(Li) could be prevented by sodium replacement. BFTZ did not affect distal water handling as measured by V/C(Li). BFTZ did not induce antidiuresis in normal rats with water diuresis. It is concluded that in rats with NDI, thiazide-induced antidiuresis can be entirely explained by a fall in distal delivery of tubular fluid related to sodium depletion. This contrasts the response in rats with central diabetes insipidus, where thiazides in addition increase distal water reabsorption.

Improvement in midwall myocardial shortening with regression of left ventricular hypertrophy.

Despite normal indices of left ventricular (LV) chamber function, patients with LV hypertrophy (LVH) due to hypertension are thought to have depressed midwall systolic shortening compared with normotensives. The aims of the present study were (1) to confirm this observation and (2) to assess the effects of antihypertensive therapy that cause regression of LVH on LV systolic function assessed at both the midwall and endocardium. Thirty-eight previously untreated hypertensive subjects with LVH underwent echocardiography and were compared with 38 normotensive control subjects. Comparisons between the group with LVH and the control group revealed no significant differences in cardiac output (4. 32+/-0.23 versus 4.55+/-0.21 L/min), ejection fraction (62.5+/-2% versus 66.4+/-1.07%), or endocardial fractional shortening (34.5+/-1.45% versus 37.0+/-0.82%), but shortening assessed at the midwall was significantly less in the group with LVH (17.9+/-1.11% versus 21.6+/-0.63%, P<0.01). Subsequently, 32 patients with uncontrolled hypertension (24 previously untreated and 8 on existing antihypertensive therapy) underwent treatment with ramipril, with the addition of felodipine and bendrofluazide if required, to reduce blood pressure to <140/90 mm Hg. These 32 patients underwent echocardiography at baseline, after blood pressure control, and after an additional 6 months of tight blood pressure control. Good blood pressure control was achieved after 6 months compared with baseline (143/86+/-2.8/1.4 versus 174/103+/-4.1/1.9 mm Hg; P<0.01) with significant regression of LV mass index (124+/-3.4 versus 145+/-3.8 g/m(2), P<0.01). LV fractional shortening assessed at the midwall improved with regression of LVH (21.9+/-0.84 and 18.7+/-1. 19%, P<0.05), with posttreatment midwall shortening being similar to that of the normal control subjects evaluated in the first study. Hypertensive patients with LVH have depressed midwall systolic shortening despite normal indices of LV chamber function. Regression of LVH after good blood pressure control improved midwall shortening to normal levels.

Characterization of the thiazide-sensitive Na(+)-Cl(-) cotransporter: a new model for ions and diuretics interaction.

The thiazide-sensitive Na(+)-Cl(-) cotransporter (TSC) is the major pathway for salt reabsorption in the apical membrane of the mammalian distal convoluted tubule. When expressed in Xenopus laevis oocytes, rat TSC exhibits high affinity for both cotransported ions, with the Michaelis-Menten constant (K(m)) for Na(+) of 7.6 +/- 1.6 mM and for Cl(-) of 6.3 +/- 1.1 mM, and Hill coefficients for Na(+) and Cl(-) consistent with electroneutrality. The affinities of both Na(+) and Cl(-) were increased by increasing concentration of the counterion. The IC(50) values for thiazides were affected by both extracellular Na(+) and Cl(-). The higher the Na(+) or Cl(-) concentration, the lower the inhibitory effect of thiazides. Finally, rTSC function is affected by extracellular osmolarity. We propose a transport model featuring a random order of binding in which the binding of each ion facilitates the binding of the counterion. Both ion binding sites alter thiazide-mediated inhibition of transport, indicating that the thiazide-binding site is either shared or modified by both Na(+) and Cl(-).

Mechanisms of distal-nephron Li(+) reabsorption during dietary K(+) restriction in rats.

The mechanism by which dietary K(+) restriction induces distal-nephron Li(+) reabsorption was investigated by administration of bendroflumethiazide (BFTZ) or vehicle in conscious Wistar rats. Changes in fractional excretion of Li(+) following administration of amiloride (DeltaFE(Li)) were used as an index of distal tubular Li(+) reabsorption. The results revealed an absence of distal tubular Li(+) reabsorption in K(+)-replete rats (DeltaFE(Li) = 3. 6+/-2.4%), in contrast to K(+) restriction in which DeltaFE(Li) was 24.0+/-2.7%. The distal tubular Li(+) reabsorption in K(+)-depleted rats was significantly reduced by preadministration of BFTZ (DeltaFE(Li) = 9.2+/-0.9%). The fractions of Li(+) and Na(+) reabsorbed in the amiloride-sensitive segment were different in K(+)-replete rats (9+/-6 vs. 60+/-6%), but similar in K(+)-depleted rats (61+/-5 vs. 73+/-4%). BFTZ administration to K(+)-depleted rats resulted in a proportional decrease in these fractions, suggesting competition between Na(+) and Li(+) for reabsorption in the distal-nephron segment during K(+) depletion. These results are compatible with the hypothesis that during K(+) depletion the reabsorption of Li(+ )in the distal-nephron segment is competitively inhibited by Na(+).