Calcium antagonists and the kidney. Implications for renal protection

Serum uric acid change in relation to antihypertensive therapy with the dihydropyridine calcium channel blockers

PURPOSE

We investigated serum uric acid changes in relation to the achieved clinic and ambulatory blood pressure after 8 weeks of antihypertensive therapy with two dihydropyridine calcium channel blockers.

MATERIALS AND METHODS

The study participants were patients with clinic and ambulatory hypertension, enrolled in a randomised controlled trial that compared amlodipine (5-10 mg, n = 215) and nifedipine gastrointestinal therapeutic system (GITS, 30-60 mg, n = 203). Hyperuricaemia was defined as a serum uric acid concentration of ≥420 µmol/L in men and ≥360 µmol/L in women. Analysis of covariance and multiple regression analyses were performed to study the associations between serum uric acid changes and the achieved clinic and ambulatory blood pressure during follow-up.

RESULTS

At baseline, 67 (16.0%) of the 418 patients had hyperuricaemia. Antihypertensive treatment reduced clinic and 24-h daytime and night-time systolic/diastolic blood pressure by a mean (±standard error [SE]) change of -17.4 ± 0.6/-8.6 ± 0.4 mm Hg and -13.7 ± 0.5/-8.3 ± 0.3 mm Hg, -13.8 ± 0.6/-8.4 ± 0.4 mm Hg, and -12.7 ± 0.7/-8.0 ± 0.4 mm Hg, respectively. Antihypertensive treatment reduced serum uric acid by a mean (±SE) change of -9.3 ± 2.8 μmol/L. The serum uric acid changes differed according to the achieved clinic and ambulatory blood pressure, and were statistically significant (mean ± SE -20.6 ± 6.6 to -10.7 ± 2.9 μmol/L, p ≤ 0.04) at the systolic/diastolic ranges of 130-139/≥90 mm Hg in clinic pressure, and <130/75-84 mm Hg, <145/80-84 mm Hg and <120/65-69 mm Hg in 24-h, daytime and night-time ambulatory pressure.

CONCLUSION

Our study showed that antihypertensive therapy with a dihydropyridine calcium channel blocker was associated with reduced serum uric acid, especially when 24-h ambulatory systolic blood pressure was controlled.

Radiocontrast-induced nephrotoxicity and urinary alpha-glutathione S-transferase levels: effect of amlodipine administration

AIMS

The exact pathogenesis and prophylaxis concerning radiocontrast-induced nephrotoxicity (RCIN) was unclear. Short-acting calcium antagonists were used to prevent RCIN. This study was designed to evaluate the role of a long-acting calcium antagonist (amlodipine) administration by determining serum creatinine (SCre) levels and 24 hour urinary excretion rates of glutathione S-transferase alpha (GST-alpha) which has a selective localization only to proximal tubular epithelium.

METHODS

In a prospective trial, 29 outpatients (19 M, 10 F) undergoing coronary angiography were randomized and either amlodipine 10 mg/day (n = 15) or placebo (n = 14) were administered prior to angiography and continued thereafter. All patients had normal basal renal function and none of them had any risk factor for RCIN. A low osmolar, nonionic contrast media (iopamidol 76%) was administered to all patients. Creatinine clearance (CCre), SCre and 24-hour urinary GST-alpha levels were measured before, 24 hours and 7 days after angiography.

RESULTS

SCre and 24 hour urinary GST-alpha values increased on 24th hour following the angiography in both groups (p < 0.017 and 0.001, respectively). Pretreatment with amlodipine created no difference in both variables (p > 0.05).

CONCLUSIONS

A reversible tubular dysfunction occurs following radiocontrast administration which was manifested by an increase in urinary GST-alpha excretion rates. Pretreatment with a long acting calcium antagonist amlodipine has no effect on the course of enzyme excretion and alteration observed in SCre.

Effects of manidipine and nifedipine on blood pressure and renal function in patients with chronic renal failure: a multicenter randomized controlled trial

Several studies suggest the distinctive advantages of ACE-inhibitors and calcium-channel blockers in protecting the residual renal function in hypertensive patients. Pre-clinical and clinical studies have shown rare adverse events in the treatment with manidipine, which is commonly used as antihypertensive drug. We therefore decided to compare the effects of manidipine and nifedipine, on blood pressure, and renal function. One hundred and one hypertensive patients with chronic renal failure were randomly assigned to receive either manidipine 20 mg daily or nifedipine 60 mg daily, respectively. Patients were assessed every two weeks during the active treatment period with the final follow-up after three months. The primary endpoint was the achievement of DBP < or = 90 mmHg or a 10 mmHg DBP reduction from the baseline values, whilst the secondary endpoints was the improvement of the renal function assessed through the creatinine clearance, creatinine blood levels, protein and sodium urine excretion. Significant reduction in SBP (p < 0.001) and DBP (p < 0.001), compared to the baseline values, was reached in both treatments. Creatinine blood levels (p < 0.05) and creatinine clearance (p < 0.01) significantly increased in the manidipine group. Protenuria did not significantly change in the manidipine group but increased in the nifedipine group (p < 0.05). The number of patients with severe adverse reactions differed significantly (p < 0.01) between the groups with the highest frequency for nifedipine (14.5%) compared to manidipine (8.5%). The withdrawal rate was not significantly different between the groups. Manidipine is equally safe and effective as nifedipine and it may have more activity on renal function and less severe side effects compared to nifedipine.

Losartan decreases glomerular filtration rate in isolated perfused porcine slaughterhouse kidneys

We investigated whether Losartan, an angiotensin II (Ang II) AT1 receptor antagonist, decreases renal vascular resistance (RVR) and increases glomerular filtration rate (GFR) in isolated perfused porcine slaughterhouse kidneys (11 control experiments and 11 Losartan experiments with 7.5mg Losartan in the preservation solution and 100(g/minute Losartan infused during perfusion). With perfusion, plasma renin activity (PRA) increased markedly from 3 +/- 1 to 90 +/- 17 ng Ang I/ml/h (control), and from 4 +/- 1 to 70 +/- 8 ng Ang I/ml/h (Losartan), plasma Ang II increased from 86 +/- 63 to 482 +/- 111 pg/ml (control), and from 73 +/- 42 to 410 +/- 91 pg/ml (Losartan). The GFR was decreased in Losartan experiments as compared with control experiments (5 +/- 1 versus 10 +/- 2 ml/min/100g kidney wt; p < 0.05). The RVR was the same in both groups (0.2 +/- 0.01 mm Hg/100g kidney wt/min/ml). Tubular sodium reabsorption was decreased in Losartan experiments as compared with control experiments (0.7 +/- 0.1 versus 1.4 +/- 0.3 mmol/min/100g kidney wt). Overall, Losartan accentuated pathophysiological signs of acute renal failure. Although other drugs have to be investigated, these results suggest that porcine slaughterhouse kidneys could be useful as a tool for research in areas such as transplantation and intensive-care medicine.

Calcium channel blockers in veterinary medicine

Calcium channel blockers are becoming increasingly popular in veterinary medicine for the treatment of systemic hypertension, cardiac arrhythmias, and hypertrophic cardiomyopathy. Calcium is vital to many cellular functions and thus stringent regulation of intracellular calcium concentrations is required. Pharmacologic manipulation of the regulatory mechanisms has the potential to alter cellular function in all body systems. In human medicine, calcium channel blockers are being evaluated for, among other things, use in treating glaucoma, deep vein thrombosis, and pulmonary hypertension, in renal transplantation, and for prevention of reperfusion injury. The potentially beneficial effects of these drugs have often been overshadowed by adverse effects including hypotension, inappetence, bradycardia, conduction abnormalities, and decreased cardiac output. With the introduction of sustained-release formulations (diltiazem) and 2nd generation calcium channel blockers (amlodipine) many of these effects have been attenuated or eliminated. This paper will review the functions of calcium and the calcium channels as well as discussing the classes and current and potential uses of the various calcium channel blockers.

Acute renal failure in infants, children and adults

Acute renal failure (ARF) occurs in many critically ill patients regardless of age. A combination of events often seen in critical care settings, including shock, sepsis, hypoxia, and the use of potentially nephrotoxic medications, combine to make ARF an ongoing and important management issue in critical care medicine. Since the events leading to the development of ARF differ in infants, children, adults, and the elderly, the pathophysiology, clinical features, and treatment modalities do indeed have remarkable similarities among the different age groups.

Role of intracellular calcium stores in contrast medium-induced renal vasoconstriction

RATIONALE AND OBJECTIVES

Renovascular smooth muscle contractility, an important factor in contrast media-induced nephrotoxicity, depends on intracellular Ca2+ concentration, which is composed of extracellular Ca2+ influx and intracellular Ca2+ release. These factors were investigated in contrast media-induced renal vasoconstriction in an in vitro model.

METHODS

KCl-induced isometric contractions of rabbit renal artery were compared with contractions elicited by contrast media (diatrizoate, iohexol, iopamidol). Measurements were made after incubation with the Ca2+ channel blockers nifedipine, verapamil, and diltiazem to assess the role of extracellular Ca2+ influx and after ryanodine and thapsigargin to investigate the role of intracellular Ca2+ release.

RESULTS

The Ca2+ channel blockers partially inhibited contractions induced by contrast media, while KCl-induced contractions were completely abolished. Ryanodine and thapsigargin also markedly inhibited contrast media-induced contractions.

CONCLUSION

Ionic and nonionic contrast media induced quantitatively different renal vasocontractions. Ca2+ channel blockers inhibited this vasocontraction only slightly compared with intracellular Ca2+ release blockers.

Effects of an angiotensin-converting enzyme inhibitor, a calcium antagonist, and an endothelin receptor antagonist on renal afferent arteriolar structure

Narrowed afferent arteriolar diameter in young, spontaneously hypertensive rats (SHR) may be a contributor to later development of high blood pressure. Thus, treatment that causes dilation of the afferent arterioles in SHR may inhibit the redevelopment of high blood pressure when treatment is withdrawn. We treated SHR with an ACE inhibitor (cilazapril, 5 to 10 mg/kg per day, high; 1 mg/kg per day, low), a calcium antagonist (mibefradil, 20 to 30 mg/kg per day), and an endothelin receptor antagonist (bosentan, 100 mg/kg per day) from age 4 to 20 weeks. Untreated SHR and Wistar-Kyoto rats were also investigated. At 20 weeks, the rats were killed, and morphology of the afferent arterioles was studied. Other SHR (untreated, high cilazapril, low cilazapril, mibefradil) were treated in exactly the same way and then followed to 32 weeks without treatment. The morphometric studies showed that cilazapril increased the lumen diameter in the afferent arterioles and decreased the media-lumen ratio in a dose-dependent manner. On withdrawal of cilazapril treatment, the reduction in blood pressure persisted. Mibefradil tended to increase afferent arteriolar diameter, whereas it did not alter media-lumen ratio. The persistent effect on blood pressure was only moderate after withdrawal of mibefradil. Bosentan had no effect on renal afferent arteriolar structure or blood pressure. In conclusion, cilazapril was more effective than mibefradil in altering afferent arteriolar structure and caused the most persistent effect on blood pressure after treatment withdrawal. The association of increased afferent arteriolar diameter and lower blood pressure level after withdrawal of treatment may suggest a pathogenic role for afferent arteriolar diameter in the development of high blood pressure in SHR.

Effectiveness of enalapril versus nifedipine to antagonize blood pressure and the renal response to endothelin in humans

Endothelin-1 infusion into humans to obtain pathophysiological plasma levels causes mild hypertension, strong renal vasoconstriction, and sodium retention. We studied whether oral use of the angiotensin-converting enzyme inhibitor enalapril (20 mg BID) or the calcium channel blocker nifedipine (60 mg OD) could attenuate these effects of endothelin-1 (2.5 ng/kg per minute for 90 minutes) in six healthy volunteers. Endothelin infusion alone increased plasma endothelin from 3.0 +/- 0.3 to 8.8 +/- 1.0 pmol/L (P < .05). Blood pressure rose by approximately 6 mm Hg (P < .05). Renal function changes were relatively large: Renal blood flow decreased from 941 +/- 76 to 729 +/- 118 mL/min (P < .05) and glomerular filtration rate from 105 +/- 9 to 92 +/- 10 mL/min (P < .05); renal vascular resistance increased from 101 +/- 7 to 152 +/- 20 mm Hg.min/L (P < .05); and sodium excretion decreased from 158 +/- 54 to 86 +/- 27 mumol/min (P < .05). Enalapril treatment reduced blood pressure from 94 +/- 2 to 87 +/- 3 mm Hg (P < .05) and prevented the hypertensive response to endothelin. By contrast, despite renal predilatation, endothelin reduced renal blood flow strongly (from 1063 +/- 127 to 763 +/- 100 mL/min, P < .05), although maximal renal vascular resistance was numerically lower (124 +/- 11 mm Hg.min/L) than during endothelin alone (P < .05). Glomerular filtration rate fell from 118 +/- 11 to 108 +/- 11 mL/min (P < .05). Enalapril did not alter the antinatriuretic effect of endothelin.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension after renal transplantation. Calcium channel or converting enzyme blockade?

We compared the effects of 4 weeks of calcium channel blockade (amlodipine) or converting enzyme inhibition (lisinopril) on blood pressure and renal hemodynamics in a double-blind crossover trial in a group of 20 hypertensive cyclosporine-treated renal transplant patients. Amlodipine (10 mg) was more effective than the same dose of lisinopril in controlling hypertension (mean 24-hour arterial pressure, 111 +/- 9 and 115 +/- 9 mm Hg, respectively; P < .05). Blood pressure during both treatments was lower than during placebo (124 +/- 12 mm Hg, P < .05). Compared with placebo, amlodipine treatment was associated with a significant increase in glomerular filtration rate (10 +/- 20%, P < .05) and effective renal plasma flow (27 +/- 20%, P < .01) and a decrease in renal vascular resistance (23 +/- 18%, P < .01). Renal hemodynamics did not change during lisinopril. Neither drug had an effect on proteinuria. The data indicate that amlodipine is more effective than lisinopril in controlling hypertension in cyclosporine-treated patients and that treatment with amlodipine but not with lisinopril is accompanied by an increase in glomerular filtration rate and effective renal plasma flow and a decrease in renal vascular resistance. The data suggest that the renin-angiotensin system does not play a main role in determining cyclosporine-associated changes in renal hemodynamics and has a limited role in determining cyclosporine-associated hypertension.