Short-term and sustained renal effects of angiotensin II receptor blockade in healthy subjects

Circulating Dipeptidyl Peptidase 3 Modulates Systemic and Renal Hemodynamics Through Cleavage of Angiotensin Peptides

BACKGROUND

High circulating DPP3 (dipeptidyl peptidase 3) has been associated with poor prognosis in critically ill patients with circulatory failure. In such situation, DPP3 could play a pathological role, putatively via an excessive angiotensin peptides cleavage. Our objective was to investigate the hemodynamics changes induced by DPP3 in mice and the relation between the observed effects and renin-angiotensin system modulation.

METHODS

Ten-week-old male C57Bl/6J mice were subjected to intravenous injection of purified human DPP3 or an anti-DPP3 antibody (procizumab). Invasive blood pressure and renal blood flow were monitored throughout the experiments. Circulating angiotensin peptides and catecholamines were measured and receptor blocking experiment performed to investigate the underlying mechanisms.

RESULTS

DPP3 administration significantly increased renal blood flow, while blood pressure was minimally affected. Conversely, procizumab led to significantly decreased renal blood flow. Angiotensin peptides measurement and an AT1R (angiotensin II receptor type 1) blockade experiment using valsartan demonstrated that the renovascular effect induced by DPP3 is due to reduced AT1R activation via decreased concentrations of circulating angiotensin II, III, and IV. Measurements of circulating catecholamines and an adrenergic receptor blockade by labetalol demonstrated a concomitant catecholamines release that explains blood pressure maintenance upon DPP3 administration.

CONCLUSIONS

High circulating DPP3 increases renal blood flow due to reduced AT1R activation via decreased concentrations of circulating angiotensin peptides while blood pressure is maintained by concomitant endogenous catecholamines release.

Losartan and Eprosartan Induce a Similar Effect on the Acute Rise in Serum Uric Acid Concentration after an Oral Fructose Load in Patients with Metabolic Syndrome

Introduction

Excessive intake of fructose increases serum uric acid concentration. Hyperuricemia induces a negative effect on atherosclerosis and inflammation. Hyperuricemia is common in patients with arterial hypertension. Several antihypertensive drugs including diuretics increase serum uric acid concentration. In contrast, the angiotensin II receptor antagonist (ARB) losartan was found to lower serum uric acid though it may increase renal excretion while other ARBs showed mostly a neutral effect. In this study, effects of two AT1 receptor antagonists losartan and eprosartan on serum uric acid changes induced by oral fructose load were directly compared.

Methods

The randomized, crossover, head-to-head comparative study comprised 16 ambulatory patients (mean age 64.5 ± 9.8 years). The patients fulfilled AHA/NHLBI 2005 criteria of metabolic syndrome. A daily single morning dose of each study drug (50 mg of losartan or 600 mg of eprosartan) was given during two 3-month periods in a random order separated by 2-week washout time. The oral fructose tolerance test (OFTT) was performed at baseline and after each two 3-onth treatment periods. Before and during OFTT, urine excretion of uric acid and creatinine was assessed in the first morning portion of urine. Blood samples for the measurement of serum uric acid and lipids were taken at baseline and 30, 60, and 120 minutes after oral intake of 75 g of fructose.

Results

After 3-month treatment with eprosartan and losartan, both systolic and diastolic blood pressure decreased significantly and to a similar extent. After the treatment, serum uric acid and its baseline and postfructose urine excretion were unchanged. No significant changes of plasma lipids before and after OFTT were observed throughout the study.

Conclusions

The study showed that in patients with hypertension and metabolic syndrome, both losartan and eprosartan have a neutral effect on fasting and postfructose load serum uric acid concentration and its urinary excretion. This trial is registered with NCT04954560.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Acute eprosartan-induced intrarenal vasodilation in hypertensive humans is not influenced by dietary sodium intake or angiotensin II co-infusion

BACKGROUND

Angiotensin II (Ang II) is thought to play an important role in the development of hypertension. Nevertheless, knowledge on the angiotensin II type-1-receptors (AT1Rs) in the hypertensive kidney and the influence of sodium intake and renin-angiotensin system activity on intrarenal AT1R blockade is scarce. To improve our understanding of renal AT1Rs in hypertensive patients, we studied the effects of acute, local administration of AT1R-blocker eprosartan in kidneys of patients with essential hypertension (off medication).

METHOD

In 73 hypertensive patients who were scheduled for diagnostic renal angiography, we measured renal blood flow (Xenon washout method) before and during intrarenal infusion of two incremental doses of eprosartan (3 and 10 μg/kg/min for 15 min per dose). We hypothesized that the vasodilatory effects of eprosartan would be enhanced by low sodium intake and would be reduced during Ang II co-infusion. Therefore, we allocated the patients to either a high or a low sodium diet and coinfused Ang II (1 ng/kg/min) in a subgroup.

RESULTS

Eprosartan infusion resulted in intrarenal vasodilation in all groups. No differences in the magnitude of this effect were found between the groups. No correlation was found between 24-h urinary sodium excretion (a proxy for dietary sodium intake) and the effect of eprosartan.

CONCLUSION

Eprosartan-induced vasodilation is not influenced by sodium intake and/or co-infusion of Ang II. These rather unexpected findings could be explained by differences between circulating and tissue Ang II levels, variations in AT1R expression, and/or stimulation of other vasodilatory pathways.

Hemodynamic effect of angiotensin II receptor blockade in postmenopausal women on a high-sodium diet: A double-blind, randomized, placebo-controlled study

BACKGROUND

Hypertension becomes increasingly prevalent after menopause. Postmenopausal women are more responsive to salt than premenopausal women, and they have been reported to develop marked renal vasoconstriction on a high-sodium diet.

OBJECTIVE

The aim of this study was to assess whether angiotensin II receptor blockade can restore a normal pattern of renal response to salt in postmenopausal women on a high-sodium diet. We also assessed segmental renal sodium handling in that population.

METHODS

Normotensive and hypertensive postmenopausal women not receiving hormone replacement therapy were enrolled in this prospective, double-blind, placebo-controlled, crossover study. They were assigned to receive irbesartan 150 mg or placebo for 6 weeks; the sequence in which they received irbesartan or placebo was randomized. During the last week of treatment, they received a high-sodium diet (250 mmol/d). Ambulatory blood pressure (ABP), glomerular filtration rate (GFR), and effective renal plasma flow (ERPF) were measured using sinistrin and para-amino-hippurate clearances. Renal sodium handling was assessed by measuring endogenous lithium clearance on day 7 of the high-salt diet.

RESULTS

Nineteen women (mean age, 54.7 years; range, 43-72 years; 7 normotensive subjects [mean age, 53.4 years; range, 47-61 years] and 12 hypertensive subjects [mean age, 55.4 years; range, 43-72 years]) were included in the study. When the data for all 19 subjects were pooled, ABP was significantly lower with irbesartan than placebo both during the day (120 [3]/79 [2] vs 127 [3]/85 [2] mm Hg; both, P < 0.01) and at night (systolic BP, 107 [4] vs 111 [4] mm Hg [P < 0.01] and diastolic BP, 71 [2] vs 75 [2] mm Hg [P < 0.05]). Compared with placebo, irbesartan was not associated with a significant change in GFR in either the normotensive or the hypertensive women. When the data for all 19 subjects were pooled, irbesartan was associated with a significant increase in ERPF compared with placebo (372 [21] vs324 [18] mL/min · 1.73 m(2); P < 0.05). When the hypertensive and normotensive women were considered separately, the effect was more pronounced in the hypertensive women than in the normotensive women, but the changes did not reach statistical significance. When the data for all subjects were pooled, irbesartan was associated with a significant increase in daytime urinary sodium excretion compared with placebo (135 [13] vs 106 [13] μmol/min; P < 0.05) and a significant decrease at night (109 [13] vs 136 [19] μmol/min; P < 0.05). Fractional excretion of lithium (FELi), an inverse marker of proximal sodium reabsorption, increased significantly during the daytime with irbesartan compared with placebo (47% [6.5%] vs 35% [4.7%]; P < 0.05). At nighttime, FELi was significantly higher in the hypertensive subjects receiving irbesartan compared with placebo (43% [7.2%] vs 29% [6.5%]; P < 0.05). The fractional distal reabsorption of sodium did not change significantly with irbesartan compared with placebo.

CONCLUSIONS

The results from this study suggest that angiotensin II receptor blockade had a favorable impact on BP, renal hemodynamics, and renal sodium handling in these salt-replete postmenopausal women. Blockade of the renin-angiotensin system restored the normal pattern of renal response to high sodium intake in these women.

Long-term use and tolerability of irbesartan for control of hypertension

In this review, we discuss the pharmacological and clinical properties of irbesartan, a noncompetitive angiotensin II receptor type 1 antagonist, successfully used for more than a decade in the treatment of essential hypertension. Irbesartan exerts its antihypertensive effect through an inhibitory effect on the pressure response to angiotensin II. Irbesartan 150-300 mg once daily confers a lasting effect over 24 hours, and its antihypertensive efficacy is further enhanced by the coadministration of hydrochlorothiazide. Additionally and partially beyond its blood pressure-lowering effect, irbesartan reduces left ventricular hypertrophy, favors right atrial remodeling in atrial fibrillation, and increases the likelihood of maintenance of sinus rhythm after cardioversion in atrial fibrillation. In addition, the renoprotective effects of irbesartan are well documented in the early and later stages of renal disease in type 2 diabetics. Furthermore, both the therapeutic effectiveness and the placebo-like side effect profile contribute to a high adherence rate to the drug. Currently, irbesartan in monotherapy or combination therapy with hydrochlorothiazide represent a rationale pharmacologic approach for arterial hypertension and early-stage and late-stage diabetic nephropathy in hypertensive type II diabetics.

Renal effects of urodilatin in healthy subjects are independent of blockade of the cyclooxygenase and angiotensin II receptor

OBJECTIVE

Little is known about the role of the renin-angiotensin-aldosterone system and the renal prostaglandins in modulating the renal vasoconstrictive and natriuretic effects of synthetic urodilatin (URO) in healthy humans.

MATERIAL AND METHODS

Twelve volunteers were pretreated in a randomized, single-blind, crossover study with losartan 50 mg a day or placebo for 5 days. Another 12 healthy subjects received indomethacin 25 mg three times a day or placebo for 4 days and a single dose on day 5. All subjects received a URO infusion (15 ng kg(-1) min(-1)) on day 5. Radioactive tracers and the lithium clearance technique were used.

RESULTS

The effective renal plasma flow (ERPF) decreased significantly during URO infusion: losartan pretreatment 573+/-63 to 461+/-76 mL/min versus placebo 540+/-89 to 432+/-90 mL/min. The urinary sodium excretion rate (UNa) increased significantly during URO infusion: losartan 335+/-115 to 502+/-134 umol/min (micromol/min) (UNa) versus placebo 386+/-142 to 476+/-137 umol/min (micromol/min) (UNa). In the indomethacin pretreated subjects, ERPF decreased significantly from 530+/-109 to 446+/-55 mL/min versus 533+/-89 to 449+/-69 mL/min in the placebo group. UNa increased significantly from 395+/-142 to 768+/-254 umol/min (micromol/min) (UNa) in the indomethacin group versus 282+/-117 to 552+/-242 umol/min (micromol/min) (UNa) in placebo.

CONCLUSION

The renal vasoconstrictive and natriuretic effects of synthetic URO are not modified by sustained inhibition of the angiotensin II receptor or the cyclooxygenase in man in a sodium replete state.

The role of angiotensin II in stress urinary incontinence: A rat model

AIMS

Pharmacological treatment for stress urinary incontinence (SUI) is limited to the use of non-selective alpha-agonists, which are often ineffective. Non-adrenergic mechanisms have also been implicated in urethral closure, including angiotensin II (Ang-II), which has been demonstrated throughout the urinary tract. We investigate the role of Ang-II in urethral tone in a rat model of SUI.

METHODS

Abdominal leak point pressure (ALPP) and retrograde urethral pressure profilometry (RLPP) were measured in 70 female virgin rats. Thirty rats underwent pudendal nerve injury (PNT), 30 had circumferential urethrolysis (U-Lys), and 10 had sham surgery. Rats received daily doses of Angiotensin Type 1 (AT-1) receptor inhibitor (20 mg/kg), Angiotensin Type 2 (AT-2) receptor antagonist (10 mg/kg), or Ang-II (2 mg/kg).

RESULTS

Following U-Lys, RLPP and ALPP decreased from 21.4 +/- 2.0 and 39.2 +/- 3.3 mm Hg, to 13.1 +/- 1.5 and 21.6 +/- 1.9 mmHg, respectively (P < 0.01). After PNT, RLPP, and ALPP decreased from 21.0 +/- 1.6 and 41.9 +/- 3.0 mmHg to 13.1 +/- 1.5 and 24.7 +/- 3.3 mmHg, respectively (P < 0.01). AT-1 inhibitor caused significant decrease in RLPP and ALPP from 21.0 +/- 6.2 and 41.8 +/- 9.4 mmHg, to 12.0 +/- 3.8 and 25.6 +/- 6.6 mmHg, respectively (P < 0.01). Likewise, AT-2 treatment reduced RLPP and ALPP from 21.4 +/- 6.3 and 40.1 +/- 1.7 mmHg, to 13.5 +/- 5.7 and 31.0 +/- 7.2 mmHg, respectively (P < 0.01). Following surgery, Ang-II administration restored RLPP and ALPP to baseline presurgical values.

CONCLUSIONS

AT-1 and AT-2 receptor inhibition significantly lowers urethral resistance, comparable to either neurogenic or urethrolytic injury. Ang-II treatment restored urethral tone in rats with intrinsic sphincter dysfunction. Ang II appears to serve a functional role in the maintenance of urethral tone and stress continence.

Irbesartan reduces creatinine clearance in type 1 diabetic children with renal hyperfunction: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Previous studies in type 2 diabetes have demonstrated the renoprotective effect of AT(1)-receptor antagonist drugs, but data on type 1 diabetic (T1DM) children are scarce. The aim of this study was to evaluate the effectiveness of the AT(1)-receptor antagonist irbesartan in reducing creatinine clearance rate (CCR) in non-hypertensive T1DM children with renal hyperfunction.

METHODS

In this randomized, double-blind, placebo-controlled trial we enrolled 20 T1DM children aged 6-16 years and randomly allocated them to receive either irbesartan (1 mg/kg body weight) or placebo daily for 12 weeks. Children were eligible to participate if they had renal hyperfunction, defined as a CCR >20 ml/min/1.73 m(2) body surface area. In addition, the participants could not have high blood pressure or renal failure and they could not be receiving diuretics or angiotensin-converting enzyme inhibitors. The primary endpoint of the trial was the change in CCR.

RESULTS

There were no significant differences in age, duration of diabetes or body mass index between the two groups. No subject dropped out, withdrew consent or had side effects or adverse events attributable to irbesartan or the placebo. In the irbesartan group, CCR decreased from 155.0+/-6.6 to 86.2+/-7.4 ml/min (P<0.0001); CCR did not change significantly in the control group (154.1+/-13.1 to 172.0+/-15.5 ml/min; P = 0.86). Blood pressures at baseline and throughout the study were similar in both groups.

CONCLUSIONS

Irbesartan significantly reduces CCR in non-hypertensive, non-controlled T1DM children; the clinical significance of this finding, however, remains to be established.

Effects of Candesartan on Glomerular Hemodynamics and Permselectivity in Patients with Favorable Renal Allograft Function

BACKGROUND

Distinct effects of angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers on glomerular perfusion and permselectivity are important determinants of the substances nephroprotective quality. In renal allograft recipients, however, specific effects of angiotensin antagonism on glomerular function have not been evaluated so far.

METHODS

Twenty patients with favorable allograft function were included into a prospective study within the first year after renal transplantation. Glomerular filtration rate, renal plasma flow, albuminuria, and the fractional clearances of neutral dextrans were determined at baseline and after 3 months of treatment with candesartan. Ten individuals after renal donation served as controls for the baseline evaluation.

RESULTS

Compared with the control group, the allograft recipients had a higher renal-vascular resistance and a lower glomerular filtration rate. Albuminuria was significantly higher; however, the difference in the dextran sieving curve was not statistically significant. Apart from mild changes in biochemical parameters, the therapy with candesartan led to a rise in serum creatinine along with a nonsignificant drop in the glomerular filtration rate. There was a highly significant drop in filtration fraction and albuminuria. Glomerular permselectivity clearly improved for a range of dextran molecular diameters from 43 Angstrom up to 73 Angstrom.

CONCLUSION

A therapy with candesartan has distinct effects on glomerular function in patients after renal transplantation. A drop in filtration fraction along with an improvement in glomerular permselectivity and albuminuria point to a nephroprotective quality that should lead to a systematic clinical evaluation of candesartan even in patients with favorable renal allograft function.

Irbesartan: a review of its use in hypertension and in the management of diabetic nephropathy

Irbesartan (Avapro, Aprovel) is a potent and selective angiotensin II subtype 1 receptor antagonist indicated for use in patients with hypertension, including those with type 2 diabetes mellitus and nephropathy. Once-daily administration of irbesartan provided 24-hour control of blood pressure (BP). In patients with mild-to-moderate hypertension irbesartan was as effective as enalapril, atenolol and amlodipine, and more effective than valsartan in terms of absolute reduction in BP and response rates. Irbesartan produced a greater reduction in diastolic BP at trough than once-daily losartan, but had a smaller effect than olmesartan; the reduction in systolic BP achieved with irbesartan was similar or greater than that with losartan and similar to that seen with olmesartan. The combination of irbesartan with hydrochlorothiazide produced additive effects on BP reduction. Irbesartan also induced regression of left ventricular mass in patients with hypertension and left ventricular hypertrophy. In two large studies (IRbesartan MicroAlbuminuria type 2 diabetes mellitus in hypertensive patients [IRMA 2] and the Irbesartan Diabetic Nephropathy Trial [IDNT]) irbesartan exerted a renoprotective effect in hypertensive patients with type 2 diabetes at both the early and later stages of diabetic nephropathy. The renoprotective effect was at least partly independent of the BP-lowering effect. In the IRMA 2 trial, the proportion of patients progressing to overt nephropathy was significantly lower for recipients of irbesartan 300mg once daily than placebo. In patients with overt nephropathy in the IDNT, irbesartan 300mg once daily provided significantly greater renoprotection than amlodipine 10mg once daily or placebo. The relative risk of doubling of serum creatinine was significantly lower with irbesartan than amlodipine or placebo. Irbesartan is well tolerated in hypertensive patients, including those with type 2 diabetes and incipient or overt nephropathy. The overall incidence of adverse events with irbesartan was similar to that with placebo. Irbesartan was associated with a lower incidence of cough than enalapril and was not associated with ankle oedema or with any clinically significant drug interactions. In conclusion, irbesartan is a well tolerated and effective antihypertensive agent. It also slows the progression of renal disease in hypertensive patients with type 2 diabetes at both the early and later stages of diabetic nephropathy. Thus, irbesartan is a valuable agent in the management of patients with these indications.

Angiotensin II receptor blockers in heart failure

Heart failure remains a significant cause of morbidity and mortality, despite major advances in therapy. Angiotensin II, the principal mediator of the renin-angiotensin system, exerts both short-term (e.g., hemodynamic, renal) and long-term (e.g., inflammation, cardiac remodeling) effects in the pathophysiology of cardiovascular disease. The effects of angiotensin II appear to be more completely inhibited by angiotensin II receptor blockers (ARBs), which act at the subtype 1 receptor level, than by angiotensin-converting enzyme (ACE) inhibitors because pathways other than that of ACE contribute to the generation of angiotensin II. Evidence demonstrates that ARBs, when added to conventional treatment for patients with heart failure, are associated with a reduction in morbidity and mortality as well as an improvement in quality of life. Clinical trials of ARB therapy indicate that these agents are generally well tolerated, both alone and in combination with other neurohormonal inhibitors. The current role of ARBs in heart failure is as an alternative for patients who cannot tolerate therapy with an ACE inhibitor. A number of ongoing clinical studies are likely to further define or expand the role of ARBs in the treatment of cardiovascular disease.

Effects of angiotensin II receptor antagonism on the renal hemodynamic response to cardiovascular stress

BACKGROUND

To elucidate the effect of the angiotensin type 1 (AT1) receptor antagonist (AT1RA) eprosartan (E) on renal hemodynamics in normotensive and borderline hypertensive subjects, we investigated the hormonal and renal hemodynamic responses during cardiopulmonary stress testing.

METHODS

In a prospective, double-blind, randomized, placebo-controlled crossover study, the effects of E on renal plasma flow (RPF), renal blood flow (RBF), glomerular filtration rate (GFR), and the concentration of angiotensin II (Ang II) levels were measured with the subjects at rest and during perturbation of cardiopulmonary baroreceptors using lower body negative pressure (LBNP). Ten normotensive male subjects (NT) versus 14 males with mild hypertension (HT), matched for age and body mass index, who were all free of any medication, were randomly assigned to receive placebo or E 600 mg/day PO for seven days (intake phase 1). After a washout period of four weeks the subjects started the intake of the other substance for seven days in a crossover manner (intake phase 2). The measurements were taken on day 7 of both intake phases.

RESULTS

During the LBNP test, RPF and RBF were reduced significantly in all subjects; GFR, however, decreased significantly during cardiopulmonary stress testing in the subjects taking the placebo (P < 0.05) and remained unchanged in those under treatment with AT1RA. Ang II levels increased significantly during cardiopulmonary stress test only in the subjects with hypertension who were on placebo, whereas the Ang II levels did not change in normotensive subjects or those treated with the AT1RA.

CONCLUSIONS

The data confirm that with cardiovascular stress simulating orthostasis or volume depletion, subjects with AT1RA can maintain their GFR level, suggesting that AT1RA potentially is renoprotective. Additionally, the neurohumoral system is activated after cardiovascular stress in subjects even at an early stage of hypertension.

Part 1. Uric acid and losartan

PURPOSE OF REVIEW

To characterize the mechanism and clinical impact of the angiotensin-receptor blocker losartan on both renal uric acid handling and thereby serum uric acid.

RECENT FINDINGS

Losartan effect on serum uric acid has been demonstrated at various stages of renal failure including most recently observations obtained in end-stage renal disease patients. Other angiotensin-receptor blockers do not alter renal handling of uric acid. The uricosuria, which accompanies losartan administration, has not been associated with adverse renal consequences, in part, because of the increase in urinary pH that follows its administration.

SUMMARY

Hyperuricemia is closely linked to both hypertension and cardiovascular disease. The development of hyperuricemia and its persistence are clearly renal processes. Likewise, the correction of hyperuricemia is often accomplished by increasing its renal excretion. A number of medications, by way of varying mechanisms, can alter renal urate handling and thereby influence serum uric acid values. Most recently, the angiotensin-receptor blocker losartan has been shown to reduce serum uric acid. The mechanism of this process relates to losartan alone and does not involve the E-3174 metabolite of this compound. This probenecid-like effect of losartan occurs shortly after drug administration, and is both transient and dose-dependent. This property of losartan, touted by some as a meaningful pharmacological distinction among the angiotensin-receptor blockers, remains to be proved, since, to date, the hypothesis that a reduction in serum uric acid alters the natural history of cardiovascular disease has not been formally tested.

Efficacy of irbesartan, a receptor selective antagonist of angiotensin II, in reducing portal hypertension

The use of angiotensin II antagonists in the treatment of portal hypertension remains controversial. Our aims were to assess the effect of Irbesartan on portal pressure and to evaluate its safety in cirrhotic patients with portal hypertension. Twenty-five cirrhotic patients were treated in a pilot study with Irbesartan 300 mg orally once daily for 60 days. Hemodynamic evaluations and biochemical tests were performed before therapy and after two months of treatment. Three patients (12%) discontinued treatment for symptomatic arterial hypotension (mean arterial pressure -26.% +/- 3.1 versus basal). In the 18 responders, the hepatic venous pressure gradient diminished by a mean of 18.1% +/- 10.5 from baseline (p = 0.02); the gradient decreased by 20% or more in only 5 patients (23%). The mean arterial pressure decreased significantly during therapy (92 +/- 7 vs 109 +/- 25 mm Hg, P < 0.001). In conclusions, Irbesartan induced a marginal reduction in portal pressure and its safety was limited by the pronounced effects on arterial pressure.

Renal effects of angiotensin II receptor antagonists

Among the many roles that angiotensin II plays in the kidney, one of the most important is the direct and indirect regulation of sodium excretion. Angiotensin II is produced within the kidney, where concentrations appear to be far in excess of those detected in plasma. High levels of angiotensin II subtype 1 receptors have been detected on the luminal side of the tubular cells in the proximal convoluted tubule, and these have been implicated in the regulation of sodium excretion. This portion of the nephron is responsible for the reabsorption of 65% of filtered sodium. It is, therefore, reasonable to assume that blockade of these receptors, using non-peptide angiotensin II receptor antagonists, will bring about an increase in renal excretion of sodium. There is, however, the possibility that, if the effect is small, downstream sites will have the capacity to reabsorb the increased sodium delivered to the distal nephron. Studies in hypertensive animal models have established that angiotensin II subtype 1 receptor antagonists stimulate natriuresis. However, the studies that have been performed to date in humans are deficient in that they have been conducted in normotensive subjects. Also, subjects have only been followed up for 6 or 8 h and thus these studies did not examine whether the observed short-term natriuresis was followed by an enhanced reabsorption of sodium. Another study, designed to overcome the deficiencies of previous studies, has investigated the natriuretic effect of telmisartan in hypertensive patients.

New perspectives on the role of aldosterone excess in cardiovascular disease

1. Evidence from recent experimental and clinical studies suggests that excessive circulating levels of aldosterone can bring about adverse cardiovascular sequelae independent of the effects on blood pressure. Examples of these sequelae are the development of myocardial and vascular fibrosis in uninephrectomized, salt-loaded rats infused with mineralocorticoids and, in humans, an association of aldosterone with left ventricular hypertrophy, impaired diastolic and systolic function, salt and water retention causing aggravation of congestion in patients with established congestive cardiac failure (CCF), reduced vascular compliance and an increased risk of arrhythmias (resulting from intracardiac fibrosis, hypokalaemia, hypomagnesaemia, reduced baroreceptor sensitivity and potentiation of catecholamine effects). 2. These sequelae of aldosterone excess may contribute to the pathogenesis and worsen the prognosis of CCF and hypertension. 3. The heart and blood vessels may be capable of extra-adrenal aldosterone biosynthesis, raising the possibility that aldosterone may have paracrine or autocrine (and not just endocrine) effects on cardiovascular tissues. 4. The high prevalence of CCF, which is associated with secondary aldosteronism, and primary aldosteronism (PAL; recently recognized to be a much more common cause of hypertension than was previously thought) argue for an important role for aldosterone excess as a cause of cardiovascular injury. 5. The recognition of non-blood pressure-dependent adverse sequelae of aldosterone excess raises the question as to whether normotensive individuals with PAL, who have been detected as a result of genetic or biochemical screening among families with inherited forms of PAL, are at excess risk of cardiovascular events. 6. Provided that patients are carefully investigated in order to permit the appropriate selection of specific surgical (laparoscopic adrenalectomy for PAL that lateralizes on adrenal venous sampling) or medical (treatment with aldosterone antagonist medications) management and safety considerations for the use of aldosterone antagonists are kept in mind, the appreciation of a widening role for aldosterone in cardiovascular disease should provide a substantially better outlook for many patients with CCF and hypertension.

Uricosuric effect of losartan in patients with renal transplants

BACKGROUND

The aim of the study was to evaluate the uricosuric effect of the angiotensin II receptor antagonist, losartan, in hypertensive patients with renal transplants who are treated with cyclosporin A (CsA).

METHODS

Twenty-six patients with stable renal function and hypertension, 16 men and 10 women, median age 47 years (range, 25-63 years), were studied in an open randomized crossover trial, comparing a 2-week control period with a 2-week period of once-daily administration of 50 mg of losartan. The main outcome measurements were fractional excretion of uric acid (FE(uric acid)) based on 24-hr urine collections and plasma uric acid.

RESULTS

The median FE(uric acid) was 5.7% (range, 2.4-10.4%) in the control period with a median change of +0.84% (range, -1.15% to +2.77%) in the losartan period (P<0.0002). Plasma uric acid was 0.47 mM (0.29-0.69 mM) in the control period with a change of -0.03 mM (-0.10 to 0.06 mM) in the losartan period (P<0.002). Diastolic blood pressure was 87 mmHg (70-97 mmHg) in the control period with a change of -3 mmHg (-13 to +6 mmHg) in the losartan period (P<0.005). There was no difference in systolic blood pressure between the two study periods. Plasma creatinine was 165 microM (102-356 microM) in the control period with a change of +9 microM (-36 to +60 microM) in the losartan period (P<0.01). Plasma potassium was 4.2 mM (3.0-4.7 mM) in the control period with a change of + 0.2 mM (-0.2 to +0.9 mM) in the losartan period (P<0.0005).

CONCLUSIONS

Once-daily administration of 50 mg of losartan in hypertensive CsA-treated patients with renal transplants caused a 17% increase in FE(uric acid) and an 8% fall in plasma uric acid.

Comparison of angiotensin II receptor antagonists

Nonpeptide orally active angiotensin II type 1 (AT1) receptor antagonists are the most specific means presently available to block the renin-angiotensin enzymatic cascade. Six of these drugs have already been licensed in Europe and in the United States for the treatment of high blood pressure, and additional candidates are in the pipeline. The World Health Organisation has also recently endorsed their use for this condition. Inasmuch as AT1 receptor antagonists have proven themselves the equals of angiotensin converting enzyme inhibitors with respect to antihypertensive efficacy, but demonstrated better safety profiles, this class of drugs may be considered to be a qualitative improvement in the treatment of essential hypertension. Interestingly, the six agents now on the market diverge considerably with respect to their pharmacokinetic and pharmacodynamic properties, although it is not certain whether such differences are clinically relevant. A considerable number of large, multicentre trials are in progress to ascertain the possible longer-term organoprotective effects of these substances on cardiovascular morbidity and mortality. Because of their noteworthy safety record to date, and simple once-a-day dosage regimen, AT1 receptor antagonists have the potential to improve compliance in patients with chronic hypertension.

Effects of telmisartan on renal excretory function in conscious dogs

The present study investigated the effects of telmisartan, a selective AT1 receptor antagonist, on renal function in dogs. Conscious female dogs were treated with (i) vehicle (controls) and three doses of telmisartan (0.03 mg/kg, 0.1 mg/kg and 0.3 mg/kg) administered intravenously; (ii) vehicle and three doses of telmisartan (0.3 mg/kg, 1.0 mg/kg and 3.0 mg/kg) administered orally; or (iii) 1.0 mg/kg per day telmisartan orally for 12 days. Eight dogs were used for each experiment. Each of the four treatments in (i) and (ii) was administered 7 days apart. During the 6 h after intravenous administration, urine volume was significantly higher in dogs treated with telmisartan 0.1 mg/kg (8.5 +/- 1.6 ml/kg) and 0.3 mg/kg (7.0 +/- 0.9 ml/kg) than controls (2.7 +/- 0.3 ml/kg; P < 0.05), and renal sodium excretion was increased significantly with telmisartan 0.03 mg/kg (803 +/- 124 micromol/kg), 0.1 mg/kg (1039 +/- 213 micromol/kg) and 0.3 mg/kg (966 +/- 161 micromol/kg) versus controls (159 +/- 21 micromol/kg; P < 0.05). Oral telmisartan at doses of 1.0 mg/kg and 3.0 mg/kg also produced significant increases in urine volume (7.2 +/- 1.1 ml/kg and 6.6 +/- 1.2 ml/kg, respectively) and renal sodium excretion (599 +/- 146 micromol/kg and 555 +/- 131 micromol/kg, respectively) compared with controls (2.8 +/- 0.5 ml/kg and 80 +/- 33 mciromol/kg; P < 0.05) over the 6-h post-dose period. Telmisartan at all intravenous doses and at 3.0 mg/kg orally increased the urinary excretion of chloride significantly over the 6-h post-dose period compared with vehicle alone. The excretion of potassium and creatinine were unchanged by any treatment. Telmisartan 1.0 mg/kg administered orally for 12 days produced similar results. In conclusion, acute intravenous or oral as well as subchronic oral administration of telmisartan to conscious dogs promotes diuresis and natriuresis without affecting potassium or creatinine excretion.

End-stage renal failure after irbesartan prescription in a diabetic patient with previously stable chronic renal insufficiency

We report the case of a 78-year-old hypertensive diabetic patient without evidence of renal artery stenosis who had moderate chronic renal insufficiency, which had been stable for several years under low-dose captopril therapy, and who rapidly developed acute renal failure when irbesartan was prescribed. Unfortunately the medication was not stopped promptly and the patient never recovered his basal renal function and had to undergo chronic hemodialysis. This observation emphasizes the importance of a careful monitoring of renal function in patients receiving angiotensin II receptor antagonists.

Treatment of hypertension in diabetes mellitus

In this article we emphasize the need for prompt intervention in diabetic patients with high blood pressure in order to protect the heart, brain, kidney, and the vascular tree against arteriosclerotic damage, which is the main cause of mortality in type 1, and particularly type 2 diabetes mellitus. Recent placebo-controlled, randomized trials indicate that compared with the nondiabetic population, a lower blood pressure threshold for intervention and a lower target blood pressure are adequate in terms of target organ protection. Although all major classes of antihypertensive drugs have demonstrated a potential benefit in treating diabetic hypertensive patients, blocking the renin-angiotensin system with angiotensin converting enzyme (ACE) inhibitors is especially useful in patients at high risk for myocardial infarction and/or renal damage. The new class of antihypertensive agents that block the angiotensin II receptor have renal effects very close to those observed with ACE inhibitors. The potential role of this new class in the treatment of hypertension in diabetes will depend on the results of ongoing trials.

Renoprotective benefits of RAS inhibition: from ACEI to angiotensin II antagonists

In landmark clinical trials, pharmacological inhibition of the renin-angiotensin system (RAS) with angiotensin-converting enzyme inhibitors (ACEIs) attenuated the decline in renal function associated with chronic renal disease (CRD). Hemodynamic and nonhemodynamic effects of angiotensin II (Ang II) attest to its central role in the pathogenesis of CRD. Angiotensin II subtype 1 receptor antagonists (AT1RA) differ from ACEI in their effects on the RAS and on bradykinin metabolism. Elevations in bradykinin levels associated with ACEI and stimulation of angiotensin subtype 2 receptors resulting from AT1RA may produce therapeutic effects unique to each class of drug. Nevertheless, in animal models of CRD, ACEI and AT1RA exert equivalent renoprotection, implying that their renoprotective effects result primarily from inhibition of Ang II-mediated stimulation of angiotensin subtype 1 receptors. Clinical data comparing ACEI and AT1RA therapy in renal disease are limited to short-term studies, which indicate that AT1RAs have equivalent effects to ACEI on the major determinants of CRD progression, namely blood pressure and proteinuria. AT1RAs were well tolerated, with side-effect profiles similar to placebo. Taken together, available evidence suggests that AT1RAs will share the renoprotective properties of ACEI in human CRD. Nevertheless, the results of long-term clinical trials are required before AT1RA can be recommended as an alternative to ACEI in renoprotective therapy.

Angiotensin II receptor antagonists

Blockade of the renin-angiotensin system began as a way of studying the pathogenesis of cardiovascular disease with specific pharmacological probes. Oral activity, achieved by shortening the original peptide structures, transformed the probes into therapeutic agents, the angiotensin-converting enzyme (ACE) inhibitors. However, ACE is a non-specific target for blocking the renin-angiotensin enzymatic cascade. The availability of orally active drugs turned ACE inhibition into a therapeutic breakthrough but more specific blockade always seemed desirable. This goal has now been achieved with the orally active angiotensin II receptor antagonists; six are on the market and more are under development. This new class of drugs is equal in efficacy to ACE inhibitors, at least in hypertensive patients. Trials now underway will demonstrate whether angiotensin II receptor antagonists can prevent target-organ damage and reduce cardiovascular morbidity and mortality. If they do, these compounds might one day replace ACE inhibitors.

Pharmacologic, pharmacokinetic, and therapeutic differences among angiotensin II receptor antagonists

Over the past 4 years, six angiotensin II receptor antagonists (ARBs) were approved for treating essential hypertension. They differ with respect to dosing, metabolism, elimination, clinical efficacy, and investigational applications. Candesartan cilexetil is the only prodrug among the agents. Losartan is distinguished from other ARBs by cytochrome P450 (CYP) 3A4- and CYP2C9-mediated biotransformation to its active metabolite EXP-3174. No ARB requires dosage adjustment for renal impairment, but the initial dose of losartan should be reduced 50% in hepatically impaired patients. None of the drugs is significantly cleared by hemodialysis. Completion of continuing trials will elucidate the drugs' role in treating heart failure, cerebral stroke, and myocardial infarction.

Salt- and angiotensin II-dependent variations in amiloride-sensitive rectal potential difference in mice

1. In the rectum and distal nephron, sodium reabsorption is mediated by the amiloride-sensitive epithelial sodium channel (ENaC). The ENaC-mediated sodium transport is electrogenic and creates an amiloride-sensitive transepithelial potential difference (PD). 2. We have evaluated the salt- and angiotensin (Ang)II-dependent variations in amiloride-sensitive rectal PD in mice and assessed their relationship with renal sodium handling. 3. Rectal PD was measured in vivo in mice maintained on a medium-, low- or high-sodium diet. On a medium-salt diet, the mean (+/- SEM) amiloride-sensitive PD was larger in the afternoon than in the morning (-26.1 +/- 0.9 and -11.2 +/- 0.7 mV, respectively; P = 0.001), indicating a circadian cyclicity. Rectal PD increased on a low-sodium diet and decreased on a high-sodium diet. 4. Amiloride-sensitive rectal PD correlated significantly with the urinary Na+/K+ ratio (P < 0.001) and with sodium reabsorption in the distal nephron as measured by the lithium clearance technique (P < 0.001). 5. In mice treated with an AngII AT1 receptor antagonist, amiloride-sensitive rectal PD was increased in the afternoon compared with controls (-32.8 +/- 2.0 vs -24.4 +/- 0.9, respectively; P < 0.001). 6. At high doses, AngII decreased the amiloride-sensitive rectal PD and this effect was blunted by an AT1 receptor antagonist. 7. These results show the presence of a salt-dependent daily cyclicity of sodium transport in the mouse rectum that follows circadian changes in sodium handling in the distal nephron. Angiotensin II appears to modulate this diurnal pattern of rectal amiloride-sensitive sodium transport.

Angiotensin II receptor antagonists and hypertension

Over recent years, a number of imidazole derivatives that specifically bind to the angiotensin II type 1 receptor, thereafter called sartans, have been developed and made available to the clinician. Whether targeting antihypertensive treatment with such a high specificity within the renin cascade may carry major clinical advantage over inhibiting angiotensin converting-enzyme remains to be demonstrated. In short-term studies, the efficacy of these drugs at reducing blood pressure was similar to that of established comparators, whereas overall side effect profile was comparable to that of placebo.

Non-peptide angiotensin type 1 receptor antagonists in the treatment of hypertension

Angiotensin II (Ang II) acts at the cellular level on two receptor subtypes: the AT1 receptor which can be blocked by losartan and its analogues (the 'sartan family'), and the AT2 receptor that does not react with the above antagonists but which can be blocked by different compounds, such as PD123319. AT1 receptor blockade has proven to be a highly effective means of interference with the renin-angiotensin system (RAS) and hence of reducing high blood pressure. As a result of the terminal blockade of the RAS cascade, circulating Ang II levels tend to rise two- to threefold. The free access of such enhanced levels to uninhibited AT2 receptors may be clinically relevant, as argued in the present review. The most extensive experimental and clinical experience with AT1 receptor blockade so far has been obtained with the pioneer drug losartan, although major contributions have also been made on candesartan cilexetil, irbesartan and valsartan. All of these four drugs have been instrumental in substantial clinical trials, serving as sources of information in the clinically oriented part of this review. AT1 receptor blocking drugs generally provide a relatively gradual decrease in blood pressure, which is comparable to that obtained with conventional anti-hypertensive drugs. Clinical trials reveal an astounding lack of drug-related adverse effects, scoring even better than placebo in terms of frequencies and sometimes patterns. The trough/peak ratio on single dosages seems to have been mastered, particularly with the second generation of AT1 receptor blockers, as is evident from 24 h ambulatory blood pressure monitoring. Combination with low-dose thiazide regimens is well established. Intermediate endpoints (micro-albuminuria and left ventricular hypertrophy) appear to be controllable. Morbid cardiovascular sequelae are currently under study in comparison with beta- and calcium channel blockade.

Effect of eprosartan and losartan on uric acid metabolism in patients with essential hypertension

OBJECTIVE

The influence of angiotensin II AT-1 receptor antagonists on uric acid metabolism, and the potential differences among them with regard to this effect, remains to be precisely established. This study was designed to compare the effects of losartan and eprosartan on uric acid metabolism in patients with mild to moderate essential hypertension.

DESIGN

Randomized, double-blind, parallel-group study in hypertensive patients.

SETTING

Outpatient clinic.

PATIENTS

Following a 2- to 3-week single-blind placebo run-in period, 60 patients with sitting diastolic blood pressure > or = 95 and < or = 114 mmHg were randomized. Fifty-eight patients completed the study.

INTERVENTIONS

Patients were randomized to receive losartan 50 mg or eprosartan 600 mg once daily for 4 weeks.

MAIN OUTCOME MEASURES

The primary endpoint was the change in the ratio of urinary uric acid/creatinine in the period 0-4 h of a 24 h urine collection after 4 weeks of treatment. Secondary endpoints included 24 h urinary uric acid excretion, as well as serum urate and anti-hypertensive efficacy.

RESULTS

Mean urinary uric acid/creatinine changes from baseline were 0.14 (day 1) and 0.11 (week 4) for losartan and -0.04 for eprosartan (at both day 1 and week 4; P < 0.01 between groups at both time-points). The mean increase in 24 h urinary uric acid excretion with losartan was 0.7 mmol/24 h (25% increase from baseline) at both day 1 and week 4. No significant difference was observed in the change of serum urate levels versus baseline between both treatment groups after 4 weeks (- 23.4 and - 19.5 micromol/l for losartan and eprosartan, respectively). Patients with hyperuricaemia in both treatment groups showed similar modifications of uric acid metabolism compared with non-hyperuricaemic subjects. Blood pressure control (sitting diastolic blood pressure < 90 mmHg or < 100 mmHg with a decrease of at least 10 mmHg from baseline) was achieved in 22 patients (73%) with eprosartan and in 16 (53%) with losartan.

CONCLUSIONS

Losartan increased uric acid excretion in hypertensive patients, whilst eprosartan did not Neither AT-1 receptor antagonist substantially modified serum urate concentrations.

Additive antiproteinuric effect of converting enzyme inhibitor and losartan in normotensive patients with IgA nephropathy

We tested the hypothesis that the combination of converting enzyme inhibitor (CEI) with losartan (LOS) produces a more profound antiproteinuric effect than either drug alone in normotensive patients with immunoglobulin A (IgA) nephropathy. Eight normotensive (mean blood pressure, 88.9 +/- 2.1 mm Hg) patients with biopsy-proven IgA nephropathy, nonnephrotic proteinuria (protein, 1 to 3 g/d), and normal or slightly reduced creatinine clearance (range, 69 to 119 mL/min) were studied. Clinical evaluations and laboratory tests were performed (1) before CEI treatment (basal) and after (2) CEI alone (CEI, 12 weeks); (3) the combination of CEI and LOS, the latter at a dosage of 50 mg/d (CEI + LOS, 4 weeks); (4) LOS alone (LOS; 50 mg/d; 12 weeks); (5) the combination of LOS and CEI (LOS + CEI, 4 weeks, at the same dosage as CEI + LOS); and (6) a doubled dose of either CEI alone or LOS alone for 4 weeks. CEI and LOS as monotherapy significantly reduced proteinuria by 38% and 30%, respectively. No further reduction of proteinuria was achieved by doubling the dose of CEI or LOS. Both combinations induced a more remarkable reduction of proteinuria (73%; P < 0.05 v other periods) than either drug administered alone. The antiproteinuric effect of CEI or LOS and the more remarkable effect achieved with both combinations was not dependent on the reduction of blood pressure and/or creatinine clearance. In conclusion, this study provides first-time evidence that the combination of CEI and LOS in normotensive patients with IgA nephropathy produces a more profound decrease in proteinuria than either drug. This additive antiproteinuric effect is not dependent on changes in systemic blood pressure and creatinine clearance. Nevertheless, a larger controlled study is required to confirm this novel observation.

Pharmacodynamics and Pharmacokinetics of Irbesartan in Patients With Mild to Moderate Hypertension

BACKGROUND: The pharmacodynamics (plasma angiotensin II [AII], plasma renin activity [PRA], renal function, blood pressure [BP], urinary excretion of major metabolites of prostacyclin [PGI(2)-M], and thromboxane A(2) [TXA(2)-M]) and pharmacokinetics of irbesartan were assessed in hypertensive patients. METHODS AND RESULTS: Twenty-four white patients with seated diastolic blood pressure 95 to 110 mmHg were randomized to double-blind irbesartan 300 mg or placebo once daily for 4 weeks, following a placebo lead-in. Irbesartan-treated patients had significantly greater 24-hour area under the curve values for mean change from baseline in AII and PRA versus placebo-treated patients on day B15 (AII [pg |mZ h/mL]: 261 +/- 515 vs 12 +/- 51; PRA [(ng/mL/h); h]:74 +/-162 vs -2 +/-14; P values >.05). Irbesartan significantly lowered BP without clinically important changes in renal function. Irbesartan had no effect on 24-hour urinary TXA(2)-M excretion, but significantly increased 24-hour PGI(2)-M excretion versus placebo on day B29 (20.7 +/- 23 pg/mg creatinine vs _2.3 +/- 43 pg/mg creatinine; P <.05). Pharmacokinetics were comparable to those from previous studies. The hourly relationship between plasma irbesartan concentration and antihypertensive effect indicated a broad, clockwise hysteresis, with peak concentration occurring at 1.5 hours, whereas peak antihypertensive effect occurred at 4 hours. CONCLUSIONS: Irbesartan increases plasma AII and PRA and lowers BP consistent with AT(1) receptor blockade, without clinically important effects on renal function.

Valsartan and the kidney: present and future

Angiotensin (Ang) II type 1 (AT1) receptor antagonists are orally active drugs that specifically block the subtype 1 of Ang receptors. In contrast to AT1 receptor antagonists, angiotensin-converting enzyme (ACE) inhibitors block the actions of Ang II incompletely. Furthermore, the bradykinin-potentiating effects of ACE inhibitors may contribute to the mechanism of action of ACE inhibitors. Data in experimental animals suggest that AT1 receptor antagonists decrease the glomerular filtration rate (GFR) to a lesser degree than ACE inhibitors. The greater effect of ACE inhibitors in decreasing glomerular pressure was attenuated with a bradykinin antagonist. In rat models of renal damage with proteinuria, acute reduction of proteinuria was seen with ACE inhibitors but not with AT1 receptor antagonists, whereas long-term reductions of proteinuria were of similar magnitude with both agents. Renal histology after several months revealed that AT1 receptor antagonists and ACE inhibitors were equally renoprotective in various renal damage models. AT1 receptor antagonists, like ACE inhibitors, exhibit a natriuretic effect equal to moderate doses of a thiazide diuretic. In patients with severe volume depletion, use of AT1 receptor antagonists may lead to acute renal failure. Valsartan was tested in a double-blind trial in patients with moderate to severe renal failure and led to a substantial decrease in diastolic and systolic blood pressure, whereas there was no difference from placebo for changes in GFR. Urine protein increased with placebo and decreased with valsartan. The data indicate that valsartan in renal failure patients is effective in lowering blood pressure while leaving renal excretory function unaltered. Whether there is a renoprotective effect can only be shown in long-term trials, which are under way.

Reappraisal of the pathogenesis and consequences of hyperuricemia in hypertension, cardiovascular disease, and renal disease

An elevated uric acid level is associated with cardiovascular disease. Hyperuricemia is predictive for the development of both hypertension and coronary artery disease; it is increased in patients with hypertension, and, when present in hypertension, an elevated uric acid level is associated with increased cardiovascular morbidity and mortality. Serum uric acid level should be measured in patients at risk for coronary artery disease because it carries prognostic information. Hyperuricemia is caused by decreased renal excretion. In this article, we suggest that this may be mediated by intrarenal ischemia with lactate generation and the inhibition of the secretion of urate by the anion-exchange transport system. The possibility that hyperuricemia directly contributes to cardiovascular or renal disease needs to be reconsidered. Although hyperuricemia is associated with a number of cardiovascular or renal risk factors, several studies have found uric acid level to be independently associated with increased mortality by multivariate analysis. If hyperuricemia is directly toxic, the most likely site is the kidney. Chronic hyperuricemia is strongly associated with chronic tubulointerstitial disease, and many of these patients have decreased renal function. Although it is possible that the hyperuricemia could simply be the consequence of the renal disease, further studies are necessary to rule out a pathogenic role for uric acid in the development of renal disease and salt-dependent hypertension.

Angiotensin II receptor antagonists in hypertension

Blockade of the renin-angiotensin system is now recognized as an effective approach to the treatment of hypertension and congestive heart failure. Today, it is possible to antagonize the effects of angiotensin II more specifically by blocking its receptors by using nonpeptide receptor antagonists. These compounds that first have been used to recognize the various subtypes of angiotensin II receptors are now available clinically. Four of them have recently been launched on the market and several others are preregistered for the treatment of hypertension. These new molecules are as effective as ACE inhibitors, calcium antagonists and beta-blockers in lowering blood pressure in hypertensive patients. When compared to ACE inhibitors, they appear to have comparable favorable effects on systemic and renal hemodynamic properties. One of the major characteristics of angiotensin II receptor antagonists as a class is the excellent tolerability with an incidence of side effects that is generally similar to that of placebo. Large clinical trials are now underway to demonstrate the long-term benefits of these agents in hypertension, heart failure and type II diabetic nephropathy.

Effect of indomethacin on the renal response to angiotensin II receptor blockade in healthy subjects

BACKGROUND

Non-steroidal anti-inflammatory drugs are known to promote sodium retention and to blunt the blood pressure lowering effects of several classes of antihypertensive agents including beta-blockers, diuretics and angiotensin converting enzyme (ACE) inhibitors. The purpose of the present study was to investigate the acute and sustained effects of indomethacin on the renal response to the angiotensin II receptor antagonist valsartan and to the ACE inhibitor enalapril.

METHODS

Twenty normotensive subjects maintained on fixed sodium intake (100 mmol sodium/day) were randomized to receive for one week: valsartan 80 mg o.d., enalapril 20 mg o.d., valsartan 80 mg o.d. + indomethacin 50 mg bid and enalapril 20 mg o.d. + indomethacin 50 mg bid. This single-blind study was designed as a parallel (valsartan vs. enalapril) and cross-over trial (valsartan or enalapril vs. valsartan + indomethacin or enalapril + indomethacin). Renal hemodynamics and urinary electrolyte excretion were measured for six hours after the first and seventh administration of each treatment regimen.

RESULTS

The results show that valsartan and enalapril have comparable renal effects characterized by no change in glomerular filtration rate and significant increases in renal plasma flow and sodium excretion. The valsartan- and enalapril-induced renal vasodilation is not significantly blunted by indomethacin. However, indomethacin similarly abolishes the natriuresis induced by the angiotensin II antagonist and the ACE inhibitor.

CONCLUSIONS

This observation suggests that although angiotensin receptor antagonists do not affect prostaglandin metabolism, the administration of a non-steroidal anti-inflammatory drug blunts the natriuretic response to angiotensin receptor blockade.

Effect of bradykinin-receptor blockade on the response to angiotensin-converting-enzyme inhibitor in normotensive and hypertensive subjects

BACKGROUND

Angiotensin-converting-enzyme (ACE) inhibitors not only decrease the production of angiotensin II but also decrease the degradation of bradykinin. In this study, a specific bradykinin-receptor antagonist, icatibant acetate (HOE 140), was used to determine the contribution of bradykinin to the short-term effects of ACE inhibition on blood pressure and plasma renin activity in both normotensive and hypertensive subjects.

METHODS

We compared the hemodynamic, renal, and endocrine effects of captopril alone (25 mg), captopril plus icatibant (100 microg per kilogram of body weight), the angiotensin II subtype 1-receptor antagonist losartan (75 mg), and placebo in 20 subjects with normal blood pressure and 7 subjects with hypertension. The subjects were studied while they were salt depleted (i.e., in balance on a diet in which they were allowed 10 mmol of sodium per day). The drugs were administered on four separate study days in a single-blind, randomized fashion.

RESULTS

The coadministration of icatibant significantly attenuated the hypotensive effect of captopril (maximal decrease in mean arterial pressure for all subjects combined, 10.5+/-1.0 mm Hg, as compared with 14.0+/-1.0 mm Hg for captopril alone; P=0.001), in such a way that the decrease in blood pressure after the administration of captopril plus icatibant was similar to that after the administration of losartan (maximal decrease in mean arterial pressure, 11.0+/-1.7 mm Hg). Icatibant did not alter the renal hemodynamic response to captopril, but it significantly altered the change in plasma renin activity in response to ACE inhibition (-0.4+/-0.4 ng of angiotensin I per milliliter per hour, as compared with 2.0+/-0.7 ng per milliliter per hour for captopril alone; P=0.007). The magnitude of these effects was similar in both the normotensive and the hypertensive subjects, as well as in both the black subjects and the white subjects.

CONCLUSIONS

These data confirm that bradykinin contributes to the short-term effects of ACE inhibition on blood pressure in normotensive and hypertensive persons and suggest that bradykinin also contributes to the short-term effects of ACE inhibition on the renin-angiotensin system.

Does blockade of angiotensin II receptors offer clinical benefits over inhibition of angiotensin-converting enzyme?

Angiotensin AT1 receptor antagonists represent a new class of drugs for the treatment of hypertension. They are specific for the renin-angiotensin system, selective for the angiotensin AT1 receptor, and act independently of the angiotensin II synthetic pathway. Blockade of the renin-angiotensin system at the receptor level should therefore be more complete. The high circulating levels of angiotensin II following angiotensin AT1 receptor blockade could be beneficial in stimulating other unblocked angiotensin receptors, especially the AT2 receptor. It has been proposed that the angiotensin AT2 receptor, which is re-expressed or up-regulated during pathological circumstances, counterbalances the effect of the stimulation of the angiotensin AT1 receptor. Through this mechanism, angiotensin AT1 antagonists may be superior to ACE inhibitors in cardiac and vascular remodelling as well as in kidney insufficiency. Long-term trials are required to demonstrate the possible clinical superiority of this new class of antihypertensive agents.

Pharmacokinetics and pharmacodynamics of irbesartan in patients with hepatic cirrhosis

The effect of hepatic impairment on the clinical pharmacology of the angiotensin II (AII) receptor antagonist irbesartan was assessed by comparing pharmacokinetic and pharmacodynamic parameters in 10 patients with hepatic cirrhosis with a matched group of 10 healthy volunteers. The pharmacokinetics and pharmacodynamics of irbesartan, 300 mg taken orally once daily, were evaluated after single- and multiple-dose (7 consecutive days) administration to normotensive subjects in an open-label, multiple-dose, parallel group study. Pharmacokinetic data obtained after administration of single and multiple doses of irbesartan showed no significant difference between the two groups in time to maximum observed plasma concentration of drug (tmax), half-life (t1/2), area under the plasma concentration-time curve (AUC), apparent oral clearance (Cl(t)/F), renal clearance (Cl(r)), and accumulation index (AI). Steady-state levels of irbesartan were reached within 3 days in both treatment groups. After irbesartan administration on day 1, mean increases from baseline in plasma AII levels and plasma renin activity (PRA) were greater in the group with cirrhosis than in the control group. On day 7, mean increases from baseline in PRA were greater in the control group than in the group with cirrhosis. No discontinuations or serious adverse events occurred during the study. The pharmacokinetics of irbesartan after repeated oral administration were not significantly affected in patients with mild-to-moderate cirrhosis of the liver. No dosage adjustment is necessary in patients with hepatic insufficiency.

Renal response to the angiotensin II receptor subtype 1 antagonist irbesartan versus enalapril in hypertensive patients

OBJECTIVE

To compare the acute and sustained renal hemodynamic effects on hypertensive patients of 100 mg irbesartan and 20 mg enalapril each once daily.

PATIENTS

Twenty patients (aged 35-70 years) with uncomplicated, mild-to-moderate essential hypertension and normal serum creatinine levels completed this study.

STUDY DESIGN

After random allocation to treatment (n=10 per group), administration schedule (morning or evening) was determined by further random allocation, with crossover of schedules after 6 weeks' therapy. Treatment and administration assignments were double-blind. Twenty-four-hour ambulatory blood pressure was monitored before and after 6 and 12 weeks of therapy. Renal hemodynamics were determined on the first day of drug administration and 12 and 24 h after the last dose during chronic treatment.

RESULTS

Administration of each antihypertensive agent induced a renal vasodilatation with no significant change in glomerular filtration rate. However, the time course appeared to differ: irbesartan had no significant acute effect 4 h after the first dose, but during chronic administration a renal vasodilatory response was found 12 and 24 h after the dose; enalapril was effective acutely and 12 h after administration, but no residual effect was found 24 h after the dose. Both antihypertensive agents lowered mean ambulatory blood pressure effectively, with no significant difference between treatments or between administration schedules (morning versus evening).

CONCLUSIONS

Irbesartan and enalapril have comparable effects on blood pressure and renal hemodynamics in hypertensive patients with normal renal functioning. However, the time profiles of the renal effects appear to differ, which might be important for long-term renoprotective effects.

Pharmacokinetics and pharmacodynamics of irbesartan in healthy subjects

The safety, pharmacokinetics, and pharmacodynamics of single and multiple doses of the angiotensin II (AII) AT1 blocker irbesartan were assessed in healthy subjects. In this single-center, placebo-controlled, double-blind within dose group, sequential, dose-ascending study, 48 men were randomized to receive irbesartan at doses of 150 mg, 300 mg, 600 mg, or 900 mg daily. Subjects received a single dose of irbesartan (n = 9 per group) or placebo (n = 3 per group), followed by 3 days of placebo, and then multiple doses of irbesartan or placebo once daily for 7 days. The values for plasma area under the concentration-time curve (AUC) of irbesartan were dose proportional up to 600 mg. There were no significant differences between the dose groups in time to maximum concentration (tmax) or half-life (t1/2) after single and multiple doses. After multiple doses, urinary recovery was significantly lower in the 600-mg and 900-mg dose groups compared with the 150-mg and 300-mg dose groups. Steady-state concentrations of irbesartan were achieved within 3 days of administration with no clinically important accumulation. Irbesartan produced dose-dependent increases in plasma renin activity and AII levels. Irbesartan was well tolerated at doses from 150 mg to 900 mg daily; a maximally tolerated dose was not reached. Modest decreases in blood pressure without orthostatic symptoms were observed at irbesartan doses of 300 mg or higher. These results demonstrated the dose-proportionality of irbesartan 150 mg to 600 mg and indicated that doses up to 900 mg daily were well tolerated.