Evidence for an Na(+)-K(+)-Cl- cotransporter in mammalian type I vestibular hair cells

Diuretic Treatment in Patients with Heart Failure: Current Evidence and Future Directions-Part II: Combination Therapy

PURPOSE OF REVIEW

Fluid retention or congestion is a major cause of symptoms, poor quality of life, and adverse outcome in patients with heart failure (HF). Despite advances in disease-modifying therapy, the mainstay of treatment for congestion-loop diuretics-has remained largely unchanged for 50 years. In these two articles (part I: loop diuretics and part II: combination therapy), we will review the history of diuretic treatment and current trial evidence for different diuretic strategies and explore potential future directions of research.

RECENT FINDINGS

We will assess recent trials, including DOSE, TRANSFORM, ADVOR, CLOROTIC, OSPREY-AHF, and PUSH-AHF, and assess how these may influence current practice and future research. There are few data on which to base diuretic therapy in clinical practice. The most robust evidence is for high-dose loop diuretic treatment over low-dose treatment for patients admitted to hospital with HF, yet this is not reflected in guidelines. There is an urgent need for more and better research on different diuretic strategies in patients with HF.

The Impact of Glucocorticoid Therapy on Guideline-Directed Medical Treatment Titration in Patients Hospitalized for Heart Failure with Low Blood Pressure: A Retrospective Study

Background

Positive inotropic and renal protective actions of glucocorticoids have been observed clinically. Therefore, glucocorticoids may be used in patients with heart failure and low blood pressure (HF-LBP).

Methods

The medical records of 144 consecutive patients with HF-LBP who received glucocorticoids as an adjunctive treatment to facilitate the up-titration of β-blocker and angiotensin-converting enzyme inhibitor were reviewed.

Results

After four weeks of treatment, the metoprolol and captopril (or equivalent) dosages were progressively and consistently increased from 25 (interquartile range [IQR] = 12.5-75 mg/day) to 100 mg/day (IQR = 50-178.8 mg/day) and from 0 (IQR = 0-25 mg/day) to 12.5 mg/day (IQR = 0-50 mg/day), respectively. There was a remarkable beneficial hemodynamic response to the glucocorticoid treatment signified by an increase in blood pressure and decrease in heart rate. The average heart rate decreased by 6 beat per minute (bpm) (0.5-16 bpm), and the mean arterial blood pressure increased from 74.06 ± 7.81 to 78.85 ± 7.91 mmHg. We also observed an improvement in renal function and an increased diuretic response following glucocorticoid treatment. As a result, the left ventricular ejection fraction increased from 28.92 ± 8.06% to 33.86 ± 8.76%, and the diuretic response increased from 776.7 mL/40 mg furosemide (IQR = 133.8-2000 mL) to 4000 mL/40 mg furosemide on day 28 (IQR = 2200-5925 mL).

Conclusion

The use of glucocorticoid treatment to maintain hemodynamic and renal functional targets when titrating guideline-directed medical treatment in patients with HF-LBP may be safe, effective, and feasible.

Evaluation of dose-response effects of short-term oral prednisone administration on clinicopathologic and hemodynamic variables in healthy dogs

OBJECTIVE

To determine whether a dose-response relationship exists between short-term oral prednisone administration and common clinicopathologic variables, cardiovascular biomarkers, and systolic arterial blood pressure (SAP) in healthy dogs.

ANIMALS

8 healthy Beagles.

PROCEDURES

Dogs underwent five 5-day experiments (no prednisone treatment [control condition] and prednisone administration at 0.5, 1, 2, and 4 mg/kg, PO, q 24 h), with a 9-day washout period between protocols. Analyses performed before and after treatments included a CBC, serum biochemical analysis, and determination of SAP, fractional excretion of electrolytes, urine protein-to-creatinine ratio, glomerular filtration rate (GFR), serum N-terminal pro B-type natriuretic peptide (NT-proBNP) and plasma cortisol concentrations, and plasma renin activity. Linear mixed-effects modeling was used to compare changes in variables from baseline (day 1 for the same experiment) among treatment conditions.

RESULTS

Changes in serum glucose concentration and GFR were significantly greater after administration of prednisone at 4 mg/kg than for the control condition. Fractional excretion of sodium was decreased from baseline when dogs received 0.5, 1, or 4 mg of prednisone/kg, compared with results for the control condition. Several expected changes in clinicopathologic values were observed after prednisone administration at any dose. Changes in serum NT-proBNP concentration, plasma renin activity, and SAP did not differ from changes for the control condition at any prednisone dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral prednisone administration did not affect SAP, NT-proBNP concentration, or measures of renin-angiotensin-aldosterone system activation in healthy laboratory-housed dogs but was associated with relative increases in GFR and serum glucose concentration.

Prednisone lowers serum uric acid levels in patients with decompensated heart failure by increasing renal uric acid clearance

Clinical studies have shown that large doses of prednisone could lower serum uric acid (SUA) in patients with decompensated heart failure (HF); however, the optimal dose of prednisone and underlying mechanisms are unknown. Thirty-eight patients with decompensated HF were randomized to receive standard HF care alone (n = 10) or with low-dose (15 mg/day, n = 8), medium-dose (30 mg/day, n = 10), or high-dose prednisone (60 mg/day, n = 10), for 10 days. At the end of the study, only high-dose prednisone significantly reduced SUA, whereas low- and medium-dose prednisone and standard HF care had no effect on SUA. The reduction in SUA in high-dose prednisone groups was associated with a significant increase in renal uric acid clearance. In conclusion, prednisone can reduce SUA levels by increasing renal uric acid clearance in patients with decompensated HF.

Cardiac outcome prevention effectiveness of glucocorticoids in acute decompensated heart failure: COPE-ADHF study

INTRODUCTION

Newly emerging evidence showed that glucocorticoids could potentiate natriuretic peptides' action by increasing the density of natriuretic peptide receptor A, leading to a potent diuresis and a renal function improvement in patients with acute decompensated heart failure (ADHF). Therefore, glucocorticoid therapy may be used in patients with ADHF.

METHODS

One hundred two patients with ADHF were randomized to receive glucocorticoids or standard treatment. Change from baseline in serum creatinine (SCr) at day 7 and cardiovascular death within 30 days were recorded. The study was terminated early because of slow site initiation and patient enrolment.

RESULTS

Glucocorticoid therapy seemed to be well tolerated. There was a remarkable SCr reduction after 7 days treatment. The change from baseline in SCr is -0.14 mg/dL in glucocorticoid group versus -0.02 mg/dL in standard treatment group (P < 0.05). Although sample size is limited, a cardiovascular death reduction at 30 days was observed in glucocorticoid group with odds ratio of 0.26 (3 deaths in glucocorticoid vs. 10 deaths in standard treatment group, P < 0.05). The survival benefit associated with glucocorticoid therapy persisted during the follow-up. Patient-assessed dyspnea and physician-assessed global clinical status were also improved in glucocorticoid group.

CONCLUSIONS

Limited data indicate that glucocorticoid therapy may be used safely in patients with ADHF in short term. Glucocorticoid therapy did not cause heart failure deterioration. Further investigations are warranted.

Excitatory actions of GABA in developing chick vestibular afferents: effects on resting electrical activity

The aim of this study was to characterize the effect of γ-aminobutyric acid (GABA) in the resting multiunit activity of the vestibular afferents during development using the isolated inner ear of embryonic and postnatal chickens (E15-E21 and P5). GABA (10(-3) to 10(-5) M; n = 133) and muscimol (10(-3) M) elicited an increase in the frequency of the basal discharge of the vestibular afferents. We found that GABA action was dose-dependent and inversely related to animal age. Thus, the largest effect was observed in embryonic ages such as E15 and E17 and decreases in E21 and P5. The GABAA receptor antagonists, bicuculline (10(-5) M; n = 10) and picrotoxin (10(-4) M; n = 10), significantly decreased the excitatory action of GABA and muscimol (10(-3) M). Additionally, CNQX 10(-6) M, MCPG 10(-5) M and 7ClKyn 10(-5) M (n = 5) were co-applied by bath substitution (n = 5). Both the basal discharge and the GABA action significantly decreased in these experimental conditions. The chloride channel blocker 9-AC 0.5 mM produced an important reduction in the effect of GABA 10(-3) (n = 5) and 10(-4) M (n = 5). Thus, our results suggest an excitatory role of GABA in the resting activity of the vestibular afferents that can be explained by changes in the gradient of concentration of Cl(-) during development. We show for the first time that the magnitude of this GABA effect decreases at later stages of embryonic and early postnatal development. Taking into account the results with glutamatergic antagonists, we conclude that GABA has a presynaptic action but is not the neurotransmitter in the vestibular afferent synapses, although it could act as a facilitator of the spontaneous activity and may regulate glutamate release.

Potassium accumulation between type I hair cells and calyx terminals in mouse crista

The mode of synaptic transmission in the vestibular periphery, between type I hair cells and their associated calyx terminal, has been the subject of much debate. The close and extensive apposition of pre- and post-synaptic elements has led some to suggest potassium (K(+)) accumulates in the intercellular space and even plays a role in synaptic transmission. During patch clamp recordings from isolated and embedded hair cells in a semi-intact preparation of the mouse cristae, we noted marked differences in whole-cell currents. Embedded type I hair cells show a prominent droop during steady-state activation as well as a dramatic collapse in tail currents. Responses to a depolarizing voltage step (-124 to +16 mV) in embedded, but not isolated, hair cells resulted in a >40 mV shift of the K(+) equilibrium potential and a rise in effective K(+) concentration (>50 mM) in the intercellular space. Together these data suggest K(+) accumulation in the intercellular space accounts for the different responses in isolated and embedded type I hair cells. To test this notion, we exposed the preparation to hyperosmotic solutions to enlarge the intercellular space. As predicted, the K(+) accumulation effects were reduced; however, a fit of our data with a classic diffusion model suggested K(+) permeability, rather than the intercellular space, had been altered by the hyperosmotic change. These results support the notion that under depolarizing conditions substantial K(+) accumulation occurs in the space between type I hair cells and calyx. The extent of K(+) accumulation during normal synaptic transmission, however, remains to be determined.

Is race a risk factor for the development of renal artery stenosis?

Atherosclerotic renal artery disease is a common cause of hypertension and chronic kidney disease that may progress into end stage renal failure if not diagnosed and treated early. Renal artery stenosis (RAS) has been shown to be an independent risk factor for mortality in patients with coronary artery disease. We sought to determine whether race is an independent risk factor for developing RAS. A retrospective study was conducted including 324 patients with resistant hypertension who underwent renal angiography with or without coronary angiography. In univariate analysis, Caucasian race was associated with significant risk of RAS (OR = 2.3, P = .01). However, this association was no longer significant after correcting for additional clinical variables in a multivariate model (OR = 1.5, P = .07). There was a strong association between smoking and RAS (OR 2.0, P = .02). We conclude that traditional risk factors, especially smoking, rather than race, are the most important predictors of RAS development.

Prednisone adding to usual care treatment for refractory decompensated congestive heart failure

The aim of the present study was to determine if prednisone, a glucocorticoid, added to conventional treatment for patients with decompensated congestive heart failure (DCHF) refractory to the conventional care, results in significant relief of congestive symptoms and improvement of clinical status. Diuretic-based strategies, as the mainstay in DCHF management, are not always effective in eliciting diuresis. However, the addition of prednisone to standard care may induce potent diuresis in this clinical setting. Thirty-five patients with DCHF were enrolled in the study, and prednisone (1 mg/kg/day with maximum dosage of 60 mg/day) was added to the standard treatment. Primary endpoints were the effects on daily urine volume, patient and physician assessed dyspnea and global clinical status, and changes in renal function. The addition of prednisone induced potent diuresis with time. As a result of the diuresis, congestive symptoms improved markedly in 80% and global clinical status improved markedly in 68.6% of the DCHF patients at the end of the study (P < 0.001). The change in serum creatinine from baseline was -12.21 micromol/L (P < 0.05). Adding prednisone to conventional care in the patients with refractory DCHF induced potent diuresis accompanied by a dramatic relief of congestive symptoms and improvements in clinical status and renal function.

Interaction of Endothelial Nitric Oxide and Angiotensin in the Circulation

Discovery of the unexpected intercellular messenger and transmitter nitric oxide (NO) was the highlight of highly competitive investigations to identify the nature of endothelium-derived relaxing factor. This labile, gaseous molecule plays obligatory roles as one of the most promising physiological regulators in cardiovascular function. Its biological effects include vasodilatation, increased regional blood perfusion, lowering of systemic blood pressure, and antithrombosis and anti-atherosclerosis effects, which counteract the vascular actions of endogenous angiotensin (ANG) II. Interactions of these vasodilator and vasoconstrictor substances in the circulation have been a topic that has drawn the special interest of both cardiovascular researchers and clinicians. Therapeutic agents that inhibit the synthesis and action of ANG II are widely accepted to be essential in treating circulatory and metabolic dysfunctions, including hypertension and diabetes mellitus, and increased availability of NO is one of the most important pharmacological mechanisms underlying their beneficial actions. ANG II provokes vascular actions through various receptor subtypes (AT1, AT2, and AT4), which are differently involved in NO synthesis and actions. ANG II and its derivatives, ANG III, ANG IV, and ANG-(1-7), alter vascular contractility with different mechanisms of action in relation to NO. This review article summarizes information concerning advances in research on interactions between NO and ANG in reference to ANG receptor subtypes, radical oxygen species, particularly superoxide anions, ANG-converting enzyme inhibitors, and ANG receptor blockers in patients with cardiovascular disease, healthy individuals, and experimental animals. Interactions of ANG and endothelium-derived relaxing factor other than NO, such as prostaglandin I2 and endothelium-derived hyperpolarizing factor, are also described.

Aldosterone acts on the kidney, not the brain, to cause mineralocorticoid hypertension in sheep

OBJECTIVE

To determine the extent to which mineralocortioid hypertension depends on a direct action of aldosterone on the kidney or on the brain.

METHODS

Studies were performed in conscious sheep that were previously uninephrectomized, implanted with silastic cannulae in the renal artery of the remaining kidney, and had guide tubes implanted over the lateral cerebral ventricles. The effect of aldosterone, infused either intrarenally (i.r.; 2 microg/h) or intravenously (i.v.; 2 and 10 microg/h) for 10 days (n = 5), on arterial pressure and fluid and electrolyte balance was determined. The i.r. (2 microg/h) and i.v. (10 microg/h) doses were calculated to give similar intrarenal concentrations of aldosterone. In a further study, the effect of intracerebroventricular (i.c.v.) infusion of aldosterone (2 microg/h for 21 days) on arterial pressure was examined (n = 5).

RESULTS

Infusion of aldosterone caused a progressive increase in mean arterial pressure from 83 +/- 3 mmHg to a maximum of 100 +/- 4 mmHg (P < 0.001) with 2 microg/h i.r. and from 84 +/- 3 mmHg to a maximum of 104 +/- 4 mmHg (P < 0.001) with 10 microg/h i.v., both by day 7. With both infusions there were similar increases in plasma [Na+] and decreases in plasma [K+] and total protein concentration (P < 0.05) between days 3 and 5; these were maintained throughout the infusion. There were no significant changes with i.v. aldosterone (2 microg/h). Long-term i.c.v. infusion of aldosterone (2 microg/h for 21 days) caused no change in arterial pressure.

CONCLUSIONS

In conscious sheep the hypertensive response to aldosterone resulted from an action on the kidney, with no evidence for a direct action on the brain.

Glycine induced calcium concentration changes in vestibular type I sensory cells

Glutamate is the neurotransmitter of the synapse between vestibular type I hair cells and the afferent nerve calyx. This calyx may also be involved in local feedback, which may modify sensory cell activity via N-methyl-D-aspartate (NMDA) receptors. Glycine is the co-agonist of glutamate in NMDA receptor activation. Both agents have been detected by immunocytochemistry in the nerve calyx. Glutamate and NMDA stimulations cause changes in the intracellular calcium concentration ([Ca(2+)](i)) of isolated type I sensory cells. We investigated the effect of glycine stimulation on [Ca(2+)](i) in guinea pig type I sensory cells by spectrofluorimetry with fura-2. Glycine application to isolated type I sensory cells induced a rapid and transient increase in [Ca(2+)](i). The fluorescence ratio increased by 55% above the resting level. The peak was reached in 9 s and the return to basal level took about 20 s. A specific antagonist of the glycine site on NMDA receptors, 7-chlorokynurenate (10 microM), decreased the calcium response to glycine by 60%. Glycine may activate NMDA receptors. Glycine may also activate the strychnine-sensitive glycine receptor-gated channel. Strychnine (50 microM) decreased the calcium response to glycine by 60%. Thus, glycine probably induces calcium concentration changes in type I vestibular sensory cells via NMDA receptors and/or glycine receptors.

Effect of dexamethasone on the lymphocytic Na+/H+ antiporter activity

OBJECTIVE

The effects of short-term administration of dexamethasone on sodium/proton antiporter (Na+/H+ antiporter) in human lymphocytes were investigated in vitro.

METHODS

Cytosolic pHi in lymphocytes was measured spectrophotometrically using the pH-sensitive fluorescent dye 2'-7'-bis-carboxyethyl-5(6)-carboxyfluorescein at 530 nm with excitation wavelengths of 440 and 530 nm. The Na+/H+ antiporter activity was determined after intracellular acidification using 100 mmol/l propionic acid.

RESULTS

The addition of 1 micromol/l dexamethasone significantly reduced cytosolic pHi from 7.44+/-0.03 to 7.25+/-0.05 (mean +/- SEM; P<0.01). Incubation with dexamethasone for 40 min significantly reduced the Na+/ H+ antiporter activity from (9.19+/-0.61)x10(-3) pHi/s (n = 22) to (7.23+/-0.49)x10(-3) pHi/s (n = 22; P<0.01). The effect of dexamethasone was time and concentration dependent The apparent affinity of the Na+/H+ antiporter was not significantly different in the absence or presence of dexamethasone. The inhibition of the Na+/H+ antiporter by dexamethasone was abolished in the presence of the glucocorticoid receptor blocker, mifepristone.

CONCLUSION

Dexamethasone directly inhibits the Na+/H+ antiporter using a receptor-dependent pathway. This effect may be important for pharmacological side effects such as glucocorticoid-induced hypertension.