Acute natriuretic effect of nifedipine in hypertensive patients and normotensive controls--a proximal tubular effect?

Nifedipine or hydralazine as a first-line agent to control hypertension in severe preeclampsia

BACKGROUND

Pre-eclampsia is one of the most serious and common complications of pregnancy. Nifedipine, a calcium channel blocker, and the vasodilator hydralazine have both been used as antihypertensive agents in this condition. The aim of this study was to determine which of these two agents is the most appropriate antihypertensive in the management of severe pre-eclampsia.

METHODS

One hundred and twenty-six pre-eclamptic patients with a gestational age of more than 20 weeks were randomized to receive either 8 mg nifedipine sublingually or 5-10 mg intravenous hydralazine. Women with a history of heart failure and women receiving antihypertensive treatment during the course of the current pregnancy were excluded. For each patient the following data were recorded; the number of drug administrations, the time needed to control blood pressure, mean urinary output, the time interval between effective control and a new hypertensive crisis after each drug administration and relevant adverse effects in mother or fetus.

RESULTS

Effective control of blood pressure was achieved in both treatment arms. Data analysis indicated significantly fewer drug administrations in the nifedipine arm of the study. The time interval before a new hypertensive crisis following initial effective control of blood pressure was significantly longer in the nifedipine group when compared with hydralazine. Effective control of blood pressure was achieved more rapidly in multiparous patients receiving nifedipine (p=0.026). Mean urinary output before and after delivery was greater in the nifedipine arm of the study. There were no significant differences between the two groups in other variables. In addition, in neither group were there any serious adverse effects in mother or fetus.

CONCLUSION

Nifedipine is safe and more effective than hydralazine in controlling blood pressure in severe pre-eclampsia. It has the added advantage of being cheaper and more widely available than the latter and is easily administered.

Altered expression of renal aquaporins and Na+ transporters in rats treated with L-type calcium blocker

Nifedipine, a calcium antagonist, has diuretic and natriuretic properties. However, the molecular mechanisms by which these effects are produced are poorly understood. We examined kidney abundance of aquaporins (AQP1, AQP2, and AQP3) and major sodium transporters [type 3 Na/H exchanger (NHE-3); type 2 Na-Pi cotransporter (NaPi-2); Na-K-ATPase; type 1 bumetanide-sensitive cotransporter (BSC-1); and thiazide-sensitive Na-Cl cotransporter (TSC)] as well as inner medullary abundance of AQP2, phosphorylated-AQP2 (p-AQP2), AQP3, and calcium-sensing receptor (CaR). Rats treated with nifedipine orally (700 mg/kg) for 19 days had a significant increase in urine output, whereas urinary osmolality and solute-free water reabsorption were markedly reduced. Consistent with this, immunoblotting revealed a significant decrease in the abundance of whole kidney AQP2 (47 ± 7% of control rats, P< 0.05) and in inner medullary AQP2 (60 ± 7%) as well as in p-AQP2 abundance (17 ± 6%) in nifedipine-treated rats. In contrast, whole kidney AQP3 abundance was significantly increased (219 ± 28%). Of potential importance in modulating AQP2 levels, the abundance of CaR in the inner medulla was significantly increased (295 ± 25%) in nifedipine-treated rats. Nifedipine treatment was also associated with increased urinary sodium excretion. Consistent with this, semiquantitative immunoblotting revealed significant reductions in the abundance of proximal tubule Na+ transporters: NHE-3 (3 ± 1%), NaPi-2 (53 ± 12%), and Na-K-ATPase (74 ± 5%). In contrast, the abundance of the distal tubule Na-Cl cotransporter (TSC) was markedly increased (240 ± 29%), whereas BSC-1 in the thick ascending limb was not altered. In conclusion, 1) increased urine output and reduced urinary concentration in nifedipine-treated-rats may, in part, be due to downregulation of AQP2 and p-AQP2 levels; 2) CaR might be involved in the regulation of water reabsorption in the inner medulla collecting duct; 3) reduced expression of proximal tubule Na+ transporters (NHE-3, NaPi-2, and Na, K-ATPase) may be involved in the increased urinary sodium excretion; and 4) increase in TSC expression may occur as a compensatory mechanism.

Antihypertensive treatment of patients with proteinuric renal diseases: risks or benefits of calcium channel blockers?

In patients with proteinuric renal diseases the rate of progression of renal insufficiency is determined by the level of blood pressure and proteinuria. It has been demonstrated that strict blood pressure control with angiotensin converting enzyme (ACE)-inhibitors or beta-blockers, aimed at reaching values below 130/80 mm Hg, attenuates the deterioration of renal function. In general, the beneficial effects of these drugs are reflected in a parallel lowering of proteinuria. Calcium channel blockers are effective antihypertensive drugs, however, their safety in patients with proteinuric renal diseases and renal insufficiency may be questioned because of reported untoward effects on urinary protein excretion. The present review discusses the potential benefits and risks of calcium channel blockers (CCBs) in the treatment of patients with renal diseases. To this end we have evaluated the effects of these drugs in animal models of progressive renal injury. In these animal models adverse effects of CCBs have been reported which are attributed to an impairment of autoregulation. In patients with proteinuria, the dihydropyridine CCBs do not lower proteinuria despite a reduction of blood pressure. Studies on the effects on the course of renal function are limited, however, the available data do suggest that this class of CCBs may be less advantageous than other antihypertensive drugs, thus arguing against the use of these agents as first-line drugs in patients with proteinuric renal diseases. Information on the effects of the non-dihydropyridine CCBs is limited to a small number of studies in patients with diabetic renal disease. Although the data suggest that these classes of CCBs might be more beneficial, more studies are needed, particularly in patients with non-diabetic renal diseases, before founded conclusions can be reached.

Antihypertensive and renal effects of acute and chronic therapy with a dihydropyridine Ca-antagonist in patients with different salt sensitivity

We evaluated the effect of the dihydropyridine Ca-channel blocker nitrendipine on blood pressure (BP) and electrolyte urinary excretion after acute and chronic therapy in 33 patients with different NaCl sensitivity as assessed by a modification of the test of Grim and colleagues. Acute nitrendipine administration significantly reduced BP in the group as a whole, although the hypotensive effect was greater in patients with greater NaCl sensitivity; this difference was still evident after 1 month of chronic therapy. Furthermore, urinary sodium and calcium excretion significantly increased in the 3 h after nitrendipine administration during both acute and chronic therapy: these effects on electrolyte excretion were independent of the NaCl sensitivity of the subject.

Combination treatment of enalapril with nitrendipine in rats with renovascular hypertension

We have recently shown that treatment with the calcium channel blocker nitrendipine may aggravate albuminuria and glomerular injury in rats with two-kidney, one clip renovascular hypertension if arterial blood pressure is not reduced. To test whether nitrendipine also exerts its adverse renal effects when normotension is achieved, we examined the effect of combined therapy with nitrendipine and the converting enzyme inhibitor enalapril on blood pressure, albuminuria, glomerular filtration rate, and morphology of the nonclipped kidney. Rats treated with enalapril alone or in combination with the diuretic hydrochlorothiazide or rats treated with nitrendipine alone served as controls. Therapy was started 6 weeks after clipping of one renal artery. Nitrendipine alone did not reduce blood pressure but significantly increased albuminuria, diuresis, glomerular filtration rate, and glomerular volume and injury compared with untreated hypertensive controls. Increase of glomerular filtration rate, diuresis, and albuminuria was reversible after withdrawal of nitrendipine. Treatment with enalapril alone decreased blood pressure significantly but not to normotensive levels and was without significant effect on albuminuria and glomerular morphology. The combination of nitrendipine and enalapril reduced blood pressure to normotensive levels and not only prevented the increase of glomerular volume, glomerular filtration rate, diuresis, and albuminuria caused by nitrendipine alone but furthermore improved glomerular injury and albuminuria to levels not significantly different from normotensive controls. Enalapril in combination with the diuretic had similar beneficial effects on blood pressure, albuminuria, and glomerular injury. These data demonstrate that the adverse effects of nitrendipine monotherapy on glomerular structure and function can be prevented by the combination of nitrendipine and enalapril when blood pressure is normalized.

Proximal renal tubular pressure-natriuresis-relation in essential hypertensives following acute vasodilatation

Blood pressure (BP) and excretory function including lithium clearance were investigated during water-loading and constant infusion of 131I-hippuran and 125I-iothalamate for measurement of renal haemodynamics in 8 untreated essential hypertensives (mean BP +/- SD: 169 +/- 14/107 +/- 6 mmHg) before and after vasodilatation with an i.v. bolus of the potassium-channel opener, pinacidil, 0.01 mg/kg. Systolic BP (-7 +/- 4%; p < 0.05) and diastolic BP (-13 +/- 8%; p < 0.01) decreased significantly and heart rate increased (11 +/- 8%; p < 0.01). Clearance (C) of lithium, sodium, urinary flow rate, potassium and absolute distal reabsorption of sodium all fell significantly. The changes of these variables were significantly correlated with the fall in BP (CLi:r = 0.92, CNa: r = 0.85, V: r = 0.81, CK:r = 0.84), despite no significant changes in renal haemodynamic parameters: glomerular filtration rate, renal plasma flow and renal vascular resistance. A proximal tubular effect was also indicated by a fall in Curic acid and fractional Curic acid. In conclusion, vasodilatation in essential hypertensives following administration of the potassium channel opener, pinacidil, induces a fall in blood pressure with a corresponding fall in fractional proximal tubular excretion of sodium and output of sodium and water from proximal to distal tubular segments, proposing an acute proximal tubular pressure-natriuresis relation.

Influence of antihypertensive therapy on renal function

Antihypertensive therapy influences kidney function by different mechanisms depending on the mode of action of the drug used. The GFR is improved by calcium entry blockers and ACE inhibitors, unaffected by vasodilators, alpha-blockers and centrally acting sympatholytics and impaired by beta-blockers. The same is true for renal blood flow and is due to changes of renal vascular resistance. Renal sodium excretion is impaired mostly by vasodilators, by alpha-blockers, sympatholytics and beta-blockers; in contrast, calcium entry blockers and ACE inhibitors acutely induce natriuresis. The RAAS is stimulated by vasodilators, unaffected by alpha-blockers and sympatholytics and suppressed by beta-blockers. Plasma catecholamines are stimulated by vasodilators and suppressed by centrally acting sympatholytics and unaffected by the others. Induction of acute renal functional impairment is reported for ACE inhibitors under conditions of compromised renal perfusion pressure such as in renal artery stenosis. These data from the literature reviewed are supported by our own experimental data on sodium balance under different drugs and micropuncture data in experimental renal artery stenosis. To achieve effective antihypertensive treatment with a low profile of side effects, careful monitoring of renal function seems to be mandatory.

Dietary sodium intake: influence on calcium channels and urinary calcium excretion in spontaneously hypertensive rats

Binding of the 1,4-dihydropyridine [3H]PN200 110 was employed as an index of cardiac Ca2+ channels in normotensive (WKY) and spontaneously hypertensive (SHR) rats during 4 weeks of normal (0.73% NaCl) and high (8% NaCl) sodium diets when the rats were between 20 and 24 weeks of age. Binding site density was not different at the beginning of the study but was increased significantly (P less than 0.01) after 1 week in the SHR on a high sodium diet; this difference was not apparent at 2, 3 or 4 weeks of the diet. During this same period, the urinary Ca2+ excretion in SHR was enhanced significantly (P less than 0.01) and the urinary calcium/sodium ratio was elevated during the high sodium intake period.

Renal effects of the new calcium channel blocking drug isradipine

The acute effect of a single oral dose of isradipine 5 mg on blood pressure, renal haemodynamics, electrolyte excretion and plasma renin activity was studied in 10 healthy males. Isradipine did not produce a significant change in systolic or diastolic blood pressure, and glomerular filtration rate, renal plasma flow, renal vascular resistance, and urinary albumin excretion remained constant. There was a marked natriuretic and diuretic effect about 1-3 h after isradipine. Plasma renin activity showed a slight, insignificant increase 1 h after dosing. Uric acid clearance and beta 2-microglobulin excretion showed no significant changes, despite an increase in sodium clearance, suggesting an additional mechanism of action other than the proximal tubular natriuretic effect of isradipine in normotensive volunteers.

The use of nifedipine during the postpartum period in patients with severe preeclampsia

Nifedipine is a calcium channel blocker that reduces blood pressure and increases renal blood flow. This double-blind investigation evaluated the effect of nifedipine in postpartum patients with severe preeclampsia. Thirty-one patients were randomized to receive either nifedipine (10 mg) or placebo every 4 hours beginning immediately after delivery. Data analysis revealed a significantly higher urine output in the nifedipine group during the first 24 hours after delivery (3834 versus 2057 ml; p less than 0.05). A significant reduction in mean arterial pressure was also noted in the nifedipine group between 18 and 24 hours postpartum (93.9 versus 100.2 mm Hg; p less than 0.05). There were no significant differences in the systolic or diastolic blood pressures, pulse, laboratory study results, or the need to administer hydralazine to control blood pressure. Nifedipine appears to have a beneficial effect on urinary output and mean arterial pressure during the first 24 hours post partum in patients with severe preeclampsia.

The effects of nicardipine on sodium and calcium metabolism in hypertensive patients: a chronic study

There is evidence in the literature that calcium entry blockers are able to affect calcium-dependent hormone secretion and therefore can influence sodium and calcium metabolism. We have studied in 18 mild to moderate hypertensives (27-65 yrs) the effects of chronic treatment with nicardipine, a dihydropyridine derivative, vs placebo on: 1) renin-angiotensin-aldosterone axis; 2) parathyroid hormone and calcium metabolism; 3) daily sodium and calcium urinary excretion. After a 2-week placebo wash-out when any antihypertensive treatment was withdrawn, patients were kept on a well balanced normocaloric diet without salt intake restriction. Blood pressure, plasma renin and serum aldosterone after a 1-hour standardized walk, serum PTH, serum and 24-hour urinary Na, K, Ca, P, Mg were measured. Thereafter patients were randomly and blindly given nicardipine 20 mg tid or placebo tablet tid for 2 months. At the end of this period the same measurements were repeated. Blood pressure significantly dropped during nicardipine (from 165/96 +/- 19/9 vs 150/88 +/- 16/9 mm Hg P less than .05) without change in heart rate. No change was observed on placebo. Plasma renin, serum aldosterone, serum parathyroid hormone and serum and urinary electrolytes did not change during active and placebo treatment. The results of this study suggest that chronic nicardipine does not affect hormone secretion.

Effects of nifedipine on renal responses to human atrial natriuretic peptide in healthy subjects and normoglycemic patients with type 1 diabetes mellitus

We examined renal responses to a pharmacological dosage of human atrial natriuretic peptide (hANP) and the potential interference of nifedipine administration with the effects of hANP on kidney function in healthy subjects and normoglycemic patients with type 1 diabetes mellitus. Ten healthy volunteers (age, 28 +/- 1 years) and ten patients (age, 33 +/- 2 years; diabetes duration; 14 +/- 3 years; HbAI 7.2% +/- 0.2%) were studied. According to a double-blind, randomized, placebo-controlled trial design, three experiments were performed in each subject using the double-dummy technique: placebo only, hANP only, and nifedipine + hANP. As i.v. bolus injection 100 micrograms hANP was given; nifedipine was applied buccally, at a dose of 10 mg 90 min before and at a dose of 5 mg together with hANP injection. At base-line and in the placebo only experiment, patients did not differ from controls. In the hANP only experiment, in both groups hANP resulted in increased urinary volume and both sodium and chloride excretion (P less than 0.05 vs placebo only experiment). In patients, hANP-induced increase in electrolyte excretion was greater than in controls (P less than 0.05). In the nifedipine + hANP experiment, hANP-induced changes in renal indexes were enhanced in controls (P less than 0.05 vs hANP only experiment) but not in patients. Thus, diuretic response to nifedipine + hANP in patients was decreased in comparison with controls (P less than 0.05). In patients, however, nifedipine administration decreased the hANP-induced increase in urinary albumin excretion (P less than 0.05 vs hANP only experiment). Creatinine clearance was uninfluenced throughout the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular effects of calcium antagonists: implications for hypertension and other risk factors for coronary heart disease

All calcium antagonists (CAs) so far developed are vasodilators, and this property is a most important component of their therapeutic potency in hypertension and angina pectoris. At a cellular level, the specific interaction of CAs with transmembranous calcium fluxes involves both potential and receptor-operated channels, respectively. Both alpha 2 and alpha 1 adrenoceptors when activated with an appropriate agonist can trigger the calcium influx through receptor-operated CA channels, alpha 2 adrenoceptors probably more readily so than alpha 1. More recently, angiotensin II receptors have also been demonstrated to be involved, although moderately, in the influx of calcium ions from the extracellular space. The hemodynamic profile of CAs is characterized by a particular specificity for the resistance vessels and for the coronary arterial system, as a useful basis for their therapeutic effect in hypertension and in angina pectoris. The weak natriuretic activity of CAs, probably the result of a tubular effect in the kidney, counteracts the fluid retention to be expected for vasodilator drugs. Interesting ancillary properties of CAs are their potentially favorable effects on the myocardial and vascular hypertrophy associated with long-standing hypertension, as well as their antiatherogenic activity that so far has only been demonstrated in animal models. Such additional properties are of potential benefit and deserve further research, since most large-scale hypertension trials have shown that vasodilatation and the reduction of elevated blood pressure as such, are probably not sufficient to adequately protect hypertensive patients against coronary events.

Isradipine in essential hypertension: the Belgian General Practitioners' Study

Over 200 hypertensive patients were recruited by 37 general practitioners into a single-blind 12-week study to assess the efficacy, tolerability, and safety of isradipine as an antihypertensive, alone and in combination with guanfacine. A total of 212 patients were given isradipine at doses of 1.25 and 2.5 mg twice daily. Twelve hours after the last dose, diastolic blood pressure was reduced to no more than 90 mm Hg in 52.6 percent of patients treated with isradipine alone. After eight weeks of treatment, 30 percent of patients were also given guanfacine 1 mg daily. By Week 12, 67.6 percent of the patients had attained normotension. Compared with placebo, side-effect frequency was higher for flushing and edema with isradipine, and dry mouth was more frequent with added guanfacine. Electrocardiographic examinations and routine laboratory determinations showed no clinically relevant changes. These data indicate that isradipine as monotherapy and in combination with guanfacine is an effective antihypertensive agent. Most patients will continue to participate in a two-year follow-up involving bimonthly clinical visits and half-yearly electrocardiographic examinations and laboratory determinations.

Calcium-channel blockers and sodium intake: a controlled study in patients with essential hypertension

Thirteen patients with mild to moderate essential hypertension and whose average supine blood pressure with no treatment was 165/104 mmHg were studied as inpatients for 3 consecutive one-week periods on different sodium intakes. On the last day of each dietary period, they received a single, 20-mg nitrendipine tablet and blood pressure was monitored every 10 minutes for 2 hours after drug administration. Nitrendipine significantly lowered blood pressure independently of the level of sodium intake, and the maximum blood-pressure lowering effect was achieved approximately 1 hour after the dose. The blood-pressure lowering effect of nitrendipine was greater on high sodium intake as compared to low sodium intake (p less than 0.02), and it was also greater with higher initial blood pressures. However, the sodium-related effect on blood pressure was, at least in part, independent of the pretreatment blood pressure. These results suggest that calcium antagonists, such as nitrendipine, are effective in reducing blood pressure in patients with essential hypertension and could be drugs of choice in those who are unable to restrict their salt intake.

The acute renal haemodynamic and endocrine response to felodipine in normal man

Felodipine (0.075 mg/kg p.o.), a calcium antagonist, was given to 9 male volunteers, with and without indomethacin pretreatment. Diuresis and natriuresis occurred after felodipine without significant change in effective renal plasma flow or glomerular filtration rate. There was no significant change in urinary 6 keto PGF 1 alpha or urinary kallikrein excretion and indomethacin did not inhibit the natriuretic or diuretic response to felodipine. The felodipine induced diuresis and natriuresis appears most likely to be mediated by an action of the drug on renal tubules.

Repetitive natriuresis and blood pressure. Long-term calcium entry blockade with isradipine

The long-term effects (3.5 months) of a new calcium entry blocker of the 1-4-dihydropyridine class, isradipine (PN 200-110), on renal hemodynamics and excretional parameters were investigated in 10 essential hypertensive subjects (World Health Organization Classes I and II). Blood pressure and renal vascular resistance fell significantly (p less than 0.001), and a slight increase in glomerular filtration rate and renal plasma flow was seen (p less than 0.05). Output of fluid from the proximal tubules, measured as clearance of lithium and uric acid, increased significantly (p less than 0.01 and p less than 0.05, respectively), and a compensatory increase in absolute reabsorption of sodium beyond the proximal tubular level accompanied by an increase in clearance of potassium was noted. A 40% increase in the resultant clearance of sodium (p less than 0.01) and an increase in diuresis (p less than 0.05) followed the morning dose of isradipine after 3.5 months of treatment. Changes in blood pressure were significantly correlated with changes in absolute proximal reabsorption of sodium (r = 0.81), excretion of sodium (r = -0.64), and diuresis (r = -0.80). Thus, the natriuretic properties of calcium entry blockers may be more important for the long-term antihypertensive effect than the vasodilator effect per se. A model for renal sodium handling following treatment with calcium entry blockers was proposed. Although a causal relationship is not implied, isradipine induced a sustained, repetitive postdose effect on proximal fluid output, net natriuresis, and diuresis, that was intimately related to the long-term blood pressure-regulating response.