Impact of antihypertensive therapy with isradipine and metoprolol on early markers of hypertensive nephropathy

[Factors associated with changes in microalbuminuria during antihypertensive treatment]

BACKGROUND

The objective of the present study was to analyze the factors related with changes of microalbuminuria during antihypertensive treatment in patients with essential hypertension.

METHODS

One hundred and six patients (57 men, mean age 40.8 [SD 6.6] years) never treated with antihypertensive treatment were included. At the beginning and after one year, blood pressure biochemical profile and urinary albumin excretion (UAE) were measured. After the initial evaluation, 53 patients received angiotensin converting enzyme inhibitors (ACEi) and 53 beta-blockers (BB). Hydrochlorothiazide was added to achieve the blood pressure target < 140/90 mmHg.

RESULTS

The average of UAE was 32.1 (43.1) mg/24 h, and 41 (39%) patients had microalbuminuretics. After 12 months of treatment, a significative fall of systolic BP (-20.6 [8.03] mmHg, p < 0.001), and diastolic BP (-14.18 [10.34] mmHg, p < 0.001) were observed, whereas baseline glucose increases (3.08 [11.07] mg/dl, p = 0.006). The changes of UAE were only related with the baseline UAE values. Neither, age, sex, baseline diastolic BP and changes in diastolic BP were significantly related with the changes in UAE. In spite of similar mean BP reduction (medial BP 17.4 [10.9] vs 14.8 [10.4] mmHg), UAE only was reduced in patients treated with ACEi (LogUAE: 0.203 [0.872] mg/24 h; p < 0.04). In addition, in patients treated with BB a significative increase in baseline glucose (4.4 [12.3] mg/dl; p = 0.013) and uric acid (1.18 [4.18]; p = 0.031) were observed.

CONCLUSIONS

In patients with essential hypertension, changes in microalbuminuria depends of the initial UAE values and the kind of antihypertensive treatment. ACEi produced higher UAE reduction and lower derangement of the glucose metabolism than BB.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Microalbuminuria in essential hypertension

Urinary excretion of albumin exceeds normal values in 10 to 25% of patients with essential hypertension. The level of albuminuria is highly correlated with arterial pressure, and more closely with ambulatory arterial pressure. The interaction between albuminuria and arterial pressure is enhanced by overweight, smoking, protein intake, insulin resistance, lipid abnormalities, and possibly genotypes of the components of the renin-angiotensin system. The renal mechanisms of microalbuminuria are not well elucidated. Notably, an increase in filtration fraction suggestive of intraglomerular hypertension was observed in patients with hyperfiltration. Microalbuminuria may be a marker of diffuse vascular abnormalities predisposing to cardiovascular disease and/or hypertensive renal disease heralding future renal failure, but its predictive value needs to be tested in more long-term follow-up studies. Antihypertensive treatment has a varied influence on albuminuria; angiotensin-converting enzyme inhibitors may correct this abnormality (at least partially) better than other agents.

Renal protection by antihypertensive drugs: insights from microalbuminuria studies

During the last few years there has been a renewed interest in blood-pressure (BP)-induced kidney damage, owing to a progressive increase in the incidence and prevalence of hypertension and vascular diseases as a cause of end-stage renal disease (ESRD). The need to prevent ESRD demands continued efforts so as to identify early those people with hypertension who are at risk and to provide them with effective antihypertensive therapy. This review analyses what is needed in terms of surrogate endpoints for monitoring kidney damage and what is known about the impact of antihypertensive treatments in reducing the BP burden on the kidney in non-diabetic subjects. Although glomerular filtration rate (GFR) and proteinuria are useful surrogate endpoints for patients with nephropathy and GFR below or close to the threshold value for renal insufficiency, it is clear that monitoring changes in either GFR or proteinuria does not provide a sensitive endpoint for subjects with the mildest forms of renal disease, e.g. essential hypertensive patients who are at risk of developing kidney damage. In this case microalbuminuria may be useful, although unequivocal evidence demonstrating that microalbuminuria is a risk marker for developing renal insufficiency in non-diabetic renal diseases has not existed until now, and whether a decrease in microalbuminuria is of prognostic significance in patients with essential hypertension remains to be demonstrated. The beneficial effects of the antihypertensive agents on microalbuminuria are also proportional to BP reduction. If a large enough BP reduction is achieved there seem to be, at most, only minimal differences among the antihypertensive drug classes. Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers have additional beneficial effects on microalbuminuria independent of the BP reduction, owing to their direct role in glomerular haemodynamics. The heterogeneity in the changes in urinary albumin excretion during antihypertensive treatment may be related to the different factors involved in the presence of microalbuminuria or structural end-organ damage, or both.

Treatment of patients with essential hypertension and microalbuminuria

There has been increasing interest in the question of whether microalbuminuria can be used in the risk stratification of patients with essential hypertension. A cluster of cardiovascular and/or renal risk factors may be associated with microalbuminuria in hypertension. Despite this, prospective data about the potential role of microalbuminuria as a prognostic marker of cardiovascular and/or renal risk have been sparse and inconclusive until now. Blood pressure values have been considered the most important determinant of microalbuminuria in essential hypertension; however, hyperinsulinaemia--a metabolic component-was noted to be present in conjunction with high blood pressure. Furthermore, 2 other factors may be also related to microalbuminuria: salt sensitivity and renal structural changes (nephrosclerosis). We are now aware that the clinical and physiological implications of abnormal urinary albumin excretion (UAE) are much broader than anticipated, possibly involving haemodynamic, metabolic and vascular components overlapping several clinical syndromes. Achievement of short term UAE reduction with antihypertensive treatment depends on structural abnormalities established in the glomerulus, the extent of blood pressure reduction and the antihypertensive drug class used. In terms of UAE reduction, better results are obtained with ACE inhibitors or angiotensin II antagonists such as losartan and valsartan, than with other antihypertensive classes, although their true impact in preserving renal function needs to be assessed. The capacity of new calcium antagonists, such as amlodipine, lacidipine or mibefradil, to reduce UAE also needs to be assessed further. Thus, microalbuminuria may be seen as an integrated marker of risk and should be assessed in recently diagnosed patients with essential hypertension. In microalbuminuric patients, the target should be to decrease blood pressure < 135/85 mm Hg, reduce salt intake to around 100 mmol/day and prescribe a low-calorie diet if obesity is present. ACE inhibitors or angiotensin II antagonists have more potential benefits than the other classes of antihypertensive drugs in reducing UAE. Finally, a yearly assessment of microalbuminuria is recommended during treatment, to monitor the impact of therapy.

Microalbuminuria in essential hypertension

The prevalence of microalbuminuria in patients with essential hypertension ranges between 10 and 25%. The level of albuminuria is highly correlated with arterial pressure and more closely ambulatory arterial pressure. The interaction between albuminuria and arterial pressure is enhanced by overweight and smoking. The renal mechanisms of microalbuminuria are not well elucidated; however, an increase in filtration fraction suggestive of intraglomerular hypertension was observed in patients with hyperfiltration. The significance of microalbuminuria as a marker of cardiovascular risk or hypertensive renal damage needs to be confirmed through long-term follow-up studies. Antihypertensive treatment has variable influence on albuminuria; and angiotensin-converting enzyme inhibitors and to a lesser extent other agents, tend to partially correct this abnormality.

High altitude-induced albuminuria in normal man is enhanced by infusion of low-dose dopamine

Renal function and the urinary excretion rate of albumin (Ualb) at rest and during infusion of dopamine (3 micrograms kg-1 min-1) were investigated in eight normal volunteers at sea level and 48 h after a rapid, passive ascent to an altitude of 4350 m. Oxygen saturation decreased to 81% (77-85) (median with quartiles in parentheses) at high altitude. High altitude hypoxia increased Ualb from 3.2 micrograms min-1 (2.7-3.5) to 5.0 micrograms min-1 (3.3-6.6) (p < 0.05); increased mean arterial blood pressure from 80 mmHg (73-95) to 102 mmHg (96 108) (p < 0.01); decreased the effective renal plasma flow (ERPF) from 465 ml min-1 (412-503) to 410 ml min-1 (385-451) (p < 0.05), and increased the filtration fraction from 24% (22-27) to 28% (26-29) (p < 0.01). Glomerular filtration rate (GFR), and the renal clearances of lithium (CLi) and sodium (CNa) remained unchanged at high altitude. Dopamine increased ERPF, GFR, CLi, CNa, and decreased the filtration fraction in both environments. Infusion of dopamine further increased Ualb to 10.5 micrograms min-1 (5.5-64.8) (p < 0.05) at high altitude, but had no effect on Ualb at sea level. In conclusion, high altitude hypoxia per se increases the urinary excretion rate of albumin, which is further increased by the renal vasodilating drug dopamine. This effect of dopamine at high altitude may result from combined effects of the increase in renal plasma flow and a hypoxia-induced increase in the glomerular capillary permeability to albumin.

Calcium-channel entry blocker therapy for hypertensive patients with concomitant renal impairment: a focus on isradipine

In the treatment of hypertension in renally impaired patients, normalization of blood pressure alone may not be sufficient to prevent significant morbidity to the kidneys. Treatment must reduce pressure in the renal vasculature, otherwise glomerular filtration rate and renal plasma flow will continue to deteriorate. Isradipine a dihydropyridine calcium-channel blocker, has been investigated as a suitable treatment in this setting. Isradipine maintains glomerular filtration rate, preserves or enhances renal plasma flow, decreases renal vascular resistance, maintains or reduces filtration fraction, and exerts a sustained natriuretic effect, all of which may enable isradipine to slow the rate of progression of renal deterioration. In addition, isradipine may decrease proteinuria and may decrease glomerular capillary pressure by dilating both the efferent and afferent arterioles. Unlike older calcium-channel blockers, isradipine exhibits minimal cardiodepressant activity and is not associated with any negative inotropic effects. It is metabolized in the liver and dosage adjustments may not be necessary when administered to patients with renal insufficiency. Isradipine has a favorable renal effect profile and also has several properties that meet the requirements of other patient populations where an extra measure of antihypertensive safety is required, such as diabetics, dialysis patients, and transplant recipients. Side effects with isradipine are usually mild and transient, occurring in a dose-dependent manner.

Antihypertensive therapy with isradipine in patients with special safety concerns

Treatment of hypertension in the complicated patient requires a specialized approach focusing on the treatment of the blood pressure and concurrent medical problems. Therapy must be chosen in consideration of the patient's age, multiple illnesses, declining organ function, and possible drug interactions. This requires that the antihypertensive agent chosen have a demonstrated safe profile. In clinical trials, monotherapy with the calcium channel blocker (CCB) isradipine (ISR) at a recommended therapeutic dosage has controlled blood pressure with an excellent level of safety. In these studies, ISR had no significant effect on heart rate, cardiac conduction, or cardiac contractility and no negative effect on renal function. In hypertensive patients with both normal and impaired renal function, ISR significantly increased renal plasma flow while decreasing renal vascular resistance without decreasing glomerular filtration rate and filtration fraction. ISR has long-term natriuretic effects that may provide additional benefits in antihypertensive therapy. Most adverse effects associated with ISR are mild, transient, and related to vasodilation. The most frequently reported adverse reactions are headache, dizziness, and edema. ISR does not affect glycemic control or lipid metabolism in either diabetic or nondiabetic patients. It has no reported adverse interaction with some of the most commonly used medications for elderly patients, including digoxin, nitroglycerin, oral hypoglycemics, and hydrochlorothiazide. ISR may be used as a first-line agent for the treatment of hypertension in complicated patients.

Microalbuminuria in essential hypertension

The prevalence and significance of microalbuminuria is not well elucidated in patients with essential hypertension. In newly detected hypertension, its prevalence ranges between 23 and 37% and albuminuria is usually well correlated with the level of arterial pressure. Interestingly, albuminuria is enhanced in overweight hypertensive patients. Antihypertensive treatment has variable influence on albuminuria, and converting enzyme inhibitors, in contrast to other agents, tend to partially correct this abnormality. Whether microalbuminuria represents a predictor of the future development of nephrosclerosis and ultimately renal failure, or a predictor of cardiovascular morbidity deserves to be investigated.

Calcium antagonists and the kidney: future therapeutic perspectives

During the past decade, attention has focused on the effects of calcium antagonists on renal function. Recent studies using diverse videomicroscopic techniques including the isolated perfused hydronephrotic rat kidney model, which permits direct visualization of afferent and efferent arterioles, have demonstrated that calcium antagonists acutely antagonize preglomerular vasoconstriction. In contrast, most studies suggest that the efferent arteriole appears to be refractory to the vasodilatory effects of these agents. Although the clinical implications of such observations have not been fully delineated, the results of recent studies indicate that calcium antagonists exert salutary effects on renal function in clinical settings characterized by impaired renal hemodynamics, including transplant-associated acute renal insufficiency and, possibly, cyclosporine nephrotoxicity. Evidence has accrued to suggest that calcium antagonists also may be protective against acute radiocontrast-induced nephrotoxicity. Finally, the renal hemodynamic and natriuretic effects of calcium antagonists commend their use as antihypertensive agents in the management of essential hypertension and transplant-associated hypertension.