Effects of calcium antagonists on renal hemodynamics and progression of nondiabetic chronic renal disease

[Hypertension and chronic renal insufficiency]

In the last ten years the incidence of patients with terminal renal insufficiency has been continuously rising. A decrease in numbers is expected through vigorous treatment of systolic and diastolic blood pressure. Any antihypertensive therapy--independent of the substance group used--decreasing blood pressure, will slow down the progression of renal insufficiency. Whenever possible, an angiotensin-converting enzyme inhibitor should be part of the treatment, since these drugs have been shown to be renoprotective beyond their antihypertensive effect in certain renal diseases. This review will discuss pathogenesis, treatment and the use of renoprotective drugs in hypertensive patients with chronic renal failure.

Effects of angiotensin-converting enzyme inhibitor, angiotensin II receptor antagonist and calcium antagonist on urinary podocytes in patients with IgA nephropathy

The urinary podocyte is postulated to be a marker for estimation of the severity of active glomerular injury and a predictor of disease progression in children with glomerulonephritis. Non-dihydropyridine calcium antagonist, including verapamil, reduce proteinuria to an extent similar to that of the angiotensin-converting enzyme inhibitor (ACEI), including trandolapril, but to a greater extent than other antihypertensives. Angiotensin (Ang) II receptor antagonists, including candesartan cilexetil, show potent and long-term preventive effects against the progression of renal injury. The aim of the present study is to assess whether verapamil, trandolapril and candesartan cilexetil affect proteinuria and urinary podocytes in patients with IgA nephropathy. Thirty-two normotensive patients aged 18-54 years with biopsy-proven IgA nephropathy, nonnephrotic proteinuria (1-3 g/day), and normal renal function (creatinine clearance >80 ml/min) were studied. Twenty patients with diffuse mesangial proliferative glomerulonephritis (non-IgA PGN) and 20 healthy controls were also included in this study. The number of urinary podocytes in patients with advanced IgA nephropathy (n = 16) was significantly higher than that in patients with the disease in the mild stage (n = 16) (p < 0.01) or in patients with non-IgA PGN (p < 0.01). Urinary podocytes were not detected in healthy controls. The 32 patients with IgA nephropathy were randomly divided into four treatment groups: those treated with verapamil (120 mg/day, n = 8); those treated with trandolapril (2 mg/day, n = 8); those treated with candesartan cilexetil (8 mg/day, n = 8), and those given a placebo (n = 8). Treatment continued for 3 months. Antiproteinuric response in the trandolapril group was similar to that in the candesartan cilexetil group (-38 vs. -40%). The action of trandolapril or candesartan cilexetil was greater than that of verapamil (p < 0.01). Reduction in the number of urinary podocytes from baseline was significantly greater in patients treated with trandolapril or candesartan cilexetil than in patients treated with verapamil (p < 0.01). However, there was no difference between patients treated with trandolapril and those treated with candesartan cilexetil. Proteinuria and urinary podocytes were unaffected in the placebo group. These data suggest that urinary podocytes may be a marker of disease activity in adult patients with IgA nephropathy and that trandolapril and candesartan cilexetil are more effective than verapamil in reducing the number of podocytes.

Nephroprotective effect of antihypertensive drugs in essential hypertension

BACKGROUND

Effective antihypertensive treatment has prevented target-organ involvement in hypertension, markedly reducing morbidity and mortality from strokes, coronary heart disease, cardiac failure, and hypertensive emergencies. However, the incidence of hypertension-related end-stage renal disease continues to increase, suggesting that therapeutic reduction in arterial pressure by itself is not sufficient to prevent the development of hypertensive renal failure.

OBJECTIVE

To examine experimental and clinical data concerning the protective effect of reduction of arterial pressure on the progression of hypertension-related renal disease, and the evidence indicating that some antihypertensive agents may afford more nephroprotection, over and above that attributable to reduction of arterial pressure.

RESULTS

Results of numerous studies clearly indicate that adequate control of arterial pressure, irrespective of the antihypertensive agent used, slowed the progression of renal disease. Results of some studies suggest that lowering arterial pressure below the level that is usually considered adequate has an additional beneficial effect by slowing the progression of renal injury.

CONCLUSION

Results of a number of studies evaluating nephroprotective effects of various drugs and regimens have indicated that certain agents, most notably angiotensin converting enzyme inhibitors and their combination with calcium antagonists, afford more protection than do others at similar levels of reduction of arterial pressure. Results of still other studies suggest that certain agents that exert greater nephroprotection are more efficient at controlling arterial pressure. Therefore, further data are needed before any final conclusion can be drawn. However, it is clear that, in order to establish nephroprotection in patients with essential hypertension, the problem should not be further complicated by additional comorbid diseases such as diabetes mellitus.

Diversity of calcium antagonists

Calcium antagonists (CAs) are widely used in the management of hypertension and chronic stable angina pectoris. Currently available CAs fall into three distinct structural classes--the dihydropyridines, the benzothiazepines, and the phenylalkylamines. The diversity of these agents, even among drugs within a structural group, is apparent in their pharmacology, physiologic effects, and therapeutic uses. Traditional CAs produce their effects through blockade of the L-type calcium channel. Recently, a new CA has been developed. Mibefradil, the first member of a new class of CAs, is a tetralol derivative. It is characterized by its selective blockade of T-type calcium channels. It differs from existing CAs and may offer important therapeutic advantages.

Long-term effect of manidipine on renal function and structure in uninephrectomized spontaneously hypertensive rats

1. Long-term effects of manidipine hydrochloride (MAN), a calcium channel blocker, were examined in three groups of spontaneously hypertensive rats (SHR). Group 1 was given uninephrectomy (UNX) and MAN treatment, group 2 was given UNX and was not treated with MAN and group 3 was given neither UNX nor MAN treatment. 2. At week 15 after UNX, inulin clearance in group 1 rats decreased compared with rats in groups 2 and 3, but remained at the same level at week 40, when the level in group 2 rats declined below that in rats in groups 1 and 3. 3. Glomerular and tubulointerstitial lesions did not differ at week 15 after UNX among the three groups, whereas at week 40 both were advanced in the order of groups 2, 1 and 3. 4. Proteinuria did not differ between rats in groups 1 and 2 over the experimental period. 5. At week 15, the kidney weights of group 1 rats were greater than those of group 2 rats, indicating more prominent tubular hypertrophy in the former group. This was confirmed by morphometry of the proximal tubuli. In contrast, the glomerular volumes of rats in groups 1 and 2 were enlarged compared with that of rats in group 3, with no difference between the former two groups. 6. The findings suggest that MAN exerts renoprotective effects in SHR, both with regard to function and morphology. An effect on glomerular haemodynamics was considered to more likely be the mechanism underlying the renoprotective effect of MAN rather than that of a lowering of systemic blood pressure. 7. Augmented tubular hypertrophy after MAN treatment was an unexpected finding of the present study and the biological significance of this finding remains to be explored.

Prevention and slowing down the progression of the diabetic nephropathy through antihypertensive therapy

Diabetic nephropathy is the major cause of illness and premature death in people with diabetes, largely through accompanying cardiovascular disease and end-stage renal failure. Diabetic patients are several times as prone to kidney disease as nondiabetic people and the accumulative risk of diabetic nephropathy in insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) is about 30%-50% after 25 years of disease. Diabetic nephropathy is a progressive disease that takes several years to develop, ending in chronic renal insufficiency. Proteinuria heralds the onset of diabetic nephropathy, and the worsening of proteinuria parallels the progression of renal disease. The main risk factors for the frequency, severity, and progression of diabetic nephropathy are the degree of hyperglycemia and associated metabolic disturbances, hypertension, protein overload, cigarette smoking, as well as the duration of diabetes. Interventional strategies for primary, secondary, and tertiary prevention of diabetic nephropathy therefore include meticulous glycemic control, appropriate treatment of associated lipid abnormalities, rigorous control of the blood pressure, reduction in dietary protein intake, in particular animal protein, and of fat intake, and stopping cigarette smoking. Randomized clinical trials indicate that antihypertensive therapy is beneficial in preventing and slowing down the progression of diabetic nephropathy. There is now increasing evidence that angiotensin-converting enzyme inhibitors and certain calcium antagonists produce a more beneficial effect on diabetic nephropathy in terms of reducing proteinuria and slowing the progression to diabetic renal failure. These drugs are attributed nephroprotective capacity beyond their blood pressure lowering capacity and initial clinical trials with combinations have revealed even additive protective effects on end organs.

Angiotensin II receptor antagonism: losartan - sites and mechanisms of action

This review surveys the basic pharmacology of angiotensin II receptors and their antagonism; reviews the existing clinical experience with losartan, the first approved nonpeptide angiotensin II antagonist; suggests other possible clinical areas for angiotensin II receptor antagonism; and compares angiotensin-converting enzyme inhibition with angiotensin receptor antagonism.

Renoprotective effect of enalapril in uninephrectomized spontaneously hypertensive rats with neonatal streptozotocin-induced diabetes

We compared the renoprotective effect between angiotensin-converting enzyme inhibitor, enalapril, and a dihydropyridine-type calcium channel blocker, nicardipine, in a severe form of renal injury in rats. Two-day-old spontaneously hypertensive rats (SHR) were injected with streptozotocin or vehicle as control. UNX was performed at 3 weeks of age, and enalapril or nicardipine was administered in drinking water from 7 weeks of age. Uninephrectomy (UNX) markedly exacerbated hypertension and renal injury in the nondiabetic and diabetic SHR. Enalapril and nicardipine comparably reduced blood pressure in UNX diabetic SHR. However, serum creatinine was significantly elevated in the nicardipine-treated group as compared with the enalapril-treated group at 24 weeks of age (nicardipine-treated group, 67 +/- 4 microM; enalapril-treated group, 49 +/- 3 microM; P < 0.01; untreated group 57 +/- 4 microM). Furthermore, the incidence of glomerular sclerosis was similar between untreated and nicardipine-treated groups, whereas it tended to be reduced in the enalapril-treated group. In a separate experiment of diabetic SHR without UNX, enalapril therapy significantly ameliorated hyperglycemia and albuminuria (P < 0.01). This study showed that a renoprotective effect was seen in enalapril but not in nicardipine in UNX diabetic SHR despite the comparable reduction of blood pressure. This suggests that enalapril may be more effective than nicardipine in delaying the progression of a severe form of diabetic nephropathy.