The effect of two different calcium antagonists on the glomerular haemodynamics in the dog

Renal sympathetic denervation improves pressure-natriuresis relationship in cardiorenal syndrome: insight from studies with Ren-2 transgenic hypertensive rats with volume overload induced using aorto-caval fistula

The aim was to evaluate the effects of renal denervation (RDN) on autoregulation of renal hemodynamics and the pressure-natriuresis relationship in Ren-2 transgenic rats (TGR) with aorto-caval fistula (ACF)-induced heart failure (HF). RDN was performed one week after creation of ACF or sham-operation. Animals were prepared for evaluation of autoregulatory capacity of renal blood flow (RBF) and glomerular filtration rate (GFR), and of the pressure-natriuresis characteristics after stepwise changes in renal arterial pressure (RAP) induced by aortic clamping. Their basal values of blood pressure and renal function were significantly lower than with innervated sham-operated TGR (p < 0.05 in all cases): mean arterial pressure (MAP) (115 ± 2 vs. 160 ± 3 mmHg), RBF (6.91 ± 0.33 vs. 10.87 ± 0.38 ml.min-1.g-1), urine flow (UF) (11.3 ± 1.79 vs. 43.17 ± 3.24 µl.min-1.g-1) and absolute sodium excretion (UNaV) (1.08 ± 0.27 vs, 6.38 ± 0.76 µmol.min-1.g-1). After denervation ACF TGR showed improved autoregulation of RBF: at lowest RAP level (80 mmHg) the value was higher than in innervated ACF TGR (6.92 ± 0.26 vs. 4.54 ± 0.22 ml.min-1.g-1, p < 0.05). Also, the pressure-natriuresis relationship was markedly improved after RDN: at the RAP of 80 mmHg UF equaled 4.31 ± 0.99 vs. 0.26 ± 0.09 µl.min-1.g-1 recorded in innervated ACF TGR, UNaV was 0.31 ± 0.05 vs. 0.04 ± 0.01 µmol min-1.g-1 (p < 0.05 in all cases). In conclusion, in our model of hypertensive rat with ACF-induced HF, RDN improved autoregulatory capacity of RBF and the pressure-natriuresis relationship when measured at the stage of HF decompensation.

How Do Antihypertensive Drugs Work? Insights from Studies of the Renal Regulation of Arterial Blood Pressure

Though antihypertensive drugs have been in use for many decades, the mechanisms by which they act chronically to reduce blood pressure remain unclear. Over long periods, mean arterial blood pressure must match the perfusion pressure necessary for the kidney to achieve its role in eliminating the daily intake of salt and water. It follows that the kidney is the most likely target for the action of most effective antihypertensive agents used chronically in clinical practice today. Here we review the long-term renal actions of antihypertensive agents in human studies and find three different mechanisms of action for the drugs investigated. (i) Selective vasodilatation of the renal afferent arteriole (prazosin, indoramin, clonidine, moxonidine, α-methyldopa, some Ca(++)-channel blockers, angiotensin-receptor blockers, atenolol, metoprolol, bisoprolol, labetolol, hydrochlorothiazide, and furosemide). (ii) Inhibition of tubular solute reabsorption (propranolol, nadolol, oxprenolol, and indapamide). (iii) A combination of these first two mechanisms (amlodipine, nifedipine and ACE-inhibitors). These findings provide insights into the actions of antihypertensive drugs, and challenge misconceptions about the mechanisms underlying the therapeutic efficacy of many of the agents.

Calcium-permeable ion channels in the kidney

Calcium ions (Ca(2+)) are crucial for a variety of cellular functions. The extracellular and intracellular Ca(2+) concentrations are thus tightly regulated to maintain Ca(2+) homeostasis. The kidney, one of the major organs of the excretory system, regulates Ca(2+) homeostasis by filtration and reabsorption. Approximately 60% of the Ca(2+) in plasma is filtered, and 99% of that is reabsorbed by the kidney tubules. Ca(2+) is also a critical signaling molecule in kidney development, in all kidney cellular functions, and in the emergence of kidney diseases. Recently, studies using genetic and molecular biological approaches have identified several Ca(2+)-permeable ion channel families as important regulators of Ca(2+) homeostasis in kidney. These ion channel families include transient receptor potential channels (TRP), voltage-gated calcium channels, and others. In this review, we provide a brief and systematic summary of the expression, function, and pathological contribution for each of these Ca(2+)-permeable ion channels. Moreover, we discuss their potential as future therapeutic targets.

Renal microcirculation and calcium channel subtypes

It has recently been reported that voltage-dependent Ca channel subtypes, e.g., L-, T-, N-, and P/Q-type, are expressed in renal arterioles and renal tubules, and the inhibition of these channels exerts various effects on renal microcirculation. For example, selective blockade of L-type Ca channels with nifedipine preferentially dilates the afferent arteriole and potentially induces glomerular hypertension. On the other hand, recently developed Ca channel blockers (CCBs) such as mibefradil and efonidipine block both T-type and L-type Ca channels and consequently dilate both afferent and efferent arterioles, leading to lowering of intraglomerular pressure. Interestingly, aldosterone has recently been recognized as a factor exacerbating renal diseases, and its secretion from adrenal gland is mediated by T-type Ca channels. Furthermore, T-type CCBs were shown to ameliorate renal dysfunction by suppressing inflammatory processes and renin secretion. On the basis of histological evaluations, N-type Ca channels are present in peripheral nerve terminals innervating both afferent and efferent arterioles. Further, it was suggested that N-type CCBs such as cilnidipine suppress renal arteriolar constriction induced by enhanced sympathetic nerve activity, thereby lowering intraglomerular pressure. Taken together, various Ca channel subtypes are present in the kidney and blockade of selective channels with distinct CCBs exerts diverse effects on renal microcirculation. Inhibition of T-type and N-type Ca channels with CCBs is anticipated to exert pleiotropic effects that would retard the progression of chronic kidney disease through modulation of renal hemodynamic and non-hemodynamic processes.

Effects of T-type calcium channel blockers on renal function and aldosterone in patients with hypertension: a systematic review and meta-analysis

Background

High blood pressure can cause kidney damage, which can increase blood pressure, leading to a vicious cycle. It is not clear whether the protective effects of T-type calcium channel blockers (T-type CCBs) on renal function are better than those of L-type CCBs or renin-angiotensin system (RAS) antagonists in patients with hypertension.

Methods and Findings

PUBMED, MEDLINE, EMBASE, OVID, Web of Science, Cochrane, CNKI, MEDCH, VIP, and WANFANG databases were searched for clinical trials published in English or Chinese from January 1, 1990, to December 31, 2013. The weighted mean difference (WMD) and 95% confidence interval (CI) were calculated and reported. A total of 1494 reports were collected, of which 24 studies with 1,696 participants (including 809 reports comparing T-type CCBs versus L-type CCBs and 887 reports comparing T-type CCB versus RAS antagonists) met the inclusion criteria. Compared with L-type CCBs, T-type CCBs resulted in a significant decline in aldosterone (mean difference = −15.19, 95% CI −19.65–−10.72, p<1×10⁻⁵), proteinuria (mean difference = −0.73, 95% CI −0.88–−0.57, p<1×10⁻⁵), protein to creatinine ratio (mean difference = −0.22, 95% CI −0.41–−0.03, p = 0.02), and urinary albumin to creatinine ratio (mean difference = −55.38, 95% CI −86.67–−24.09, p = 0.0005); no significant difference was noted for systolic blood pressure (SBP) (p = 0.76) and diastolic blood pressure (DBP) (p = 0.16). The effects of T-type CCBs did not significantly differ from those of RAS antagonists for SBP (p = 0.98), DBP (p = 0.86), glomerular filtration rate (p = 0.93), albuminuria (p = 0.97), creatinine clearance rate (p = 0.24), and serum creatinine (p = 0.27) in patients with hypertension.

Conclusion

In a pooled analysis of data from 24 studies measuring the effects of T-type CCBs on renal function and aldosterone, the protective effects of T-type CCBs on renal function were enhanced compared with L-type CCBs but did not differ from RAS antagonists. Their protective effects on renal function were independent of blood pressure.

Smooth muscle contractile diversity in the control of regional circulations

Each regional circulation has unique requirements for blood flow and thus unique mechanisms by which it is regulated. In this review we consider the role of smooth muscle contractile diversity in determining the unique properties of selected regional circulations and its potential influence on drug targeting in disease. Functionally smooth muscle diversity can be dichotomized into fast versus slow contractile gene programs, giving rise to phasic versus tonic smooth muscle phenotypes, respectively. Large conduit vessel smooth muscle is of the tonic phenotype; in contrast, there is great smooth muscle contractile diversity in the other parts of the vascular system. In the renal circulation, afferent and efferent arterioles are arranged in series and determine glomerular filtration rate. The afferent arteriole has features of phasic smooth muscle, whereas the efferent arteriole has features of tonic smooth muscle. In the splanchnic circulation, the portal vein and hepatic artery are arranged in parallel and supply blood for detoxification and metabolism to the liver. Unique features of this circulation include the hepatic-arterial buffer response to regulate blood flow and the phasic contractile properties of the portal vein. Unique features of the pulmonary circulation include the low vascular resistance and hypoxic pulmonary vasoconstriction, the latter attribute inherent to the smooth muscle cells but the mechanism uncertain. We consider how these unique properties may allow for selective drug targeting of regional circulations for therapeutic benefit and point out gaps in our knowledge and areas in need of further investigation.

Pressure induces intracellular calcium changes in juxtaglomerular cells in perfused afferent arterioles

Calcium (Ca(2+)) has an important role in nearly all types of cellular secretion, with a particularly novel role in the juxtaglomerular (JG) cells in the kidney. In JG cells, Ca(2+) inhibits renin secretion, which is a major regulator of blood pressure and renal hemodynamics. However, whether alterations in afferent arteriolar (Af-Art) pressure change intracellular Ca(2+) concentration ([Ca(2+)](i)) in JG cells and whether [Ca(2+)](i) comes from extracellular or intracellular sources remains unknown. We hypothesize that increases in perfusion pressure in the Af-Art result in elevations in [Ca(2+)](i) in JG cells. We isolated and perfused Af-Art of C57BL6 mice and measured changes in [Ca(2+)](i) in JG cells in response to perfusion pressure changes. The JG cells' [Ca(2+)](i) was 93.3±2.2 nM at 60 mm Hg perfusion pressure and increased to 111.3±13.4, 119.6±7.3, 130.3±2.9 and 140.8±12.1 nM at 80, 100, 120 and 140 mm Hg, respectively. At 120 mm Hg, increases in [Ca(2+)](i) were reduced in mice receiving the following treatments: (1) the mechanosensitive cation channel blocker, gadolinium (94.6±7.5 nM); (2) L-type calcium channel blocker, nifedipine (105.8±7.5 nM); and (3) calcium-free solution plus ethylene glycol tetraacetic acid (96.0±5.8 nM). Meanwhile, the phospholipase C inhibitor, inositol triphosphate receptor inhibitor, T-type calcium channel blocker, N-type calcium channel blocker and Ca(2+)-ATPase inhibitor did not influence changes in [Ca(2+)](i) in JG cells. In summary, JG cell [Ca(2+)](i) rise as perfusion pressure increases; furthermore, the calcium comes from extracellular sources, specifically mechanosensitive cation channels and L-type calcium channels.

T-type Ca channel blockade as a determinant of kidney protection

Voltage-dependent Ca channels are classified into several subtypes based on the isoform of their α1 subunits. Traditional Ca channels blockers (CCBs), including nifedipine and amlodipine, act predominantly on L-type Ca channels, whereas novel CCBs such as efonidipine, benidipine and azelnidipine inhibit both L-type and T-type Ca channels. Furthermore, cilnidipine blocks L-type and N-type Ca channels. These CCBs exert divergent actions on renal microvessels. L-type CCBs preferentially dilate afferent arterioles, whereas both L-/T-type and L-/N-type CCBs potently dilate afferent and efferent arterioles. The distinct actions of CCBs on the renal microcirculation are reflected by changes in glomerular capillary pressure and subsequent renal injury: L-type CCBs favor an increase in glomerular capillary pressure, whereas L-/T-type and L-/N-type CCBs alleviate glomerular hypertension. The renal protective action of L-/T-type CCBs is also mediated by non-hemodynamic mechanisms, i.e., inhibition of the inflammatory process and inhibition of Rho kinase and aldosterone secretion. Finally, a growing body of evidence indicates that T-type CCBs offer more beneficial action on proteinuria and renal survival rate than L-type CCBs in patients with chronic kidney disease (CKD). Similarly, in CKD patients treated with renin-angiotensin blockers, add-on therapy with N-type CCBs is more potent in reducing proteinuria than that with L-type CCBs, although no difference is found in the subgroup with diabetic nephropathy. Thus, the strategy for hypertension treatment with CCBs has entered a new era: treatment selection depends not only on blood pressure control but also on the subtypes of CCBs.

Ca2+ channel subtypes and pharmacology in the kidney

A large body of evidence has accrued indicating that voltage-gated Ca(2+) channel subtypes, including L-, T-, N-, and P/Q-type, are present within renal vascular and tubular tissues, and the blockade of these Ca(2+) channels produces diverse actions on renal microcirculation. Because nifedipine acts exclusively on L-type Ca(2+) channels, the observation that nifedipine predominantly dilates afferent arterioles implicates intrarenal heterogeneity in the distribution of L-type Ca(2+) channels and suggests that it potentially causes glomerular hypertension. In contrast, recently developed Ca(2+) channel blockers (CCBs), including mibefradil and efonidipine, exert blocking action on L-type and T-type Ca(2+) channels and elicit vasodilation of afferent and efferent arterioles, which suggests the presence of T-type Ca(2+) channels in both arterioles and the distinct impact on intraglomerular pressure. Recently, aldosterone has been established as an aggravating factor in kidney disease, and T-type Ca(2+) channels mediate aldosterone release as well as its effect on renal efferent arteriolar tone. Furthermore, T-type CCBs are reported to exert inhibitory action on inflammatory process and renin secretion. Similarly, N-type Ca(2+) channels are present in nerve terminals, and the inhibition of neurotransmitter release by N-type CCBs (eg, cilnidipine) elicits dilation of afferent and efferent arterioles and reduces glomerular pressure. Collectively, the kidney is endowed with a variety of Ca(2+) channel subtypes, and the inhibition of these channels by their specific CCBs leads to variable impact on renal microcirculation. Furthermore, multifaceted activity of CCBs on T- and N-type Ca(2+) channels may offer additive benefits through nonhemodynamic mechanisms in the progression of chronic kidney disease.

Nitrendipine and amlodipine mimic the acute effects of enalapril on renal haemodynamics and reduce glomerular hyperfiltration in patients with chronic kidney disease

Antihypertensive drugs may have an important effect on glomerular haemodynamics. In chronic nephropathy patients, we compared the effect on glomerular haemodynamics of two second-generation dihydropyridinic agents, nitrendipine and amlodipine, with a first generation dihydropyridinic agent and an ACE-inhibitor, enalapril. In all, 32 patients (pts), divided into four groups, received the different drugs: ENA (enalapril, eight pts), NIF (nifedipine, eight pts), NIT (nitrendipine, eight pts) AML (amlodipine, eight pts). The study assessed the effect on glomerular haemodynamics of a single administration of the test drug in baseline conditions and in glomerular hyperfiltration experimentally induced by amino-acid infusion. The glomerular filtration rate (GFR, measured by inulin clearance), effective renal plasma flow (ERPF, measured by p-aminohippurate clearance), renal vascular resistances (RVR) and filtration fraction (FF) were assessed. Administration of AML and NIT test dose reduced FF, as did ENA, but not NIF, in both baseline (AML: P=0.005; NIT: P=0.02; ENA: P=0.007) and glomerular hyperfiltration conditions (AML: P=0.0003; NIT: P=0.03; ENA: P=0.00006). In baseline conditions, only ENA resulted in a significant drop in the GFR (P=0.008), while NIF, NIT and AML induced a significant increase (P=0.003, 0.03, 0.0001, respectively). However, in hyperfiltration conditions, NIT (0.08) and AML (0.00003) caused a decrease in the GFR, as did ENA (0.0003) but not NIF. In all the experimental conditions, a RVR reduction and an ERPF increase were observed. Single dose of NIT and AML were effective in attenuating the effect of amino-acid infusion on glomerular filtration, similar to ENA; this effect of NIT and AML on the glomerular filtration rate is not observed under basal conditions.

Effect of T-type selective calcium antagonist on renal microcirculation: studies in the isolated perfused hydronephrotic kidney

Although calcium antagonists exert preferential vasodilation of renal afferent arterioles, we have recently demonstrated that nilvadipine and efonidipine, possessing both L-type and T-type calcium channel blocking action, reverse the angiotensin (Ang) II-induced afferent and efferent arteriolar constriction. In the present study, we investigated the role of T-type calcium channels in mediating the Ang II-induced efferent arteriolar tone using the selective T-type calcium channel blocker mibefradil. Isolated perfused hydronephrotic rat kidneys were used for direct visualization of renal microcirculation. Administration of Ang II (0.3 nmol/L) caused marked constriction of afferent (from 13.5+/-0.6 to 9.2+/-0.6 microm, P<0.01, n=6) and efferent (from 11.5+/-1.0 to 7.4+/-0.7 microm, P<0.01, n=5) arterioles. Mibefradil (1 micromol/L) dilated both vessels, with 82+/-11% and 72+/-7% reversal of afferent and efferent arterioles, respectively. Similarly, nickel chloride (100 micromol/L) caused dilation of both arterioles, similar in magnitude in afferent (68+/-10%, n=7) and efferent (80+/-7%, n=7) arterioles. To eliminate the possibility that the mibefradil-induced dilation was mediated by L-type channel blockade, mibefradil was administered in the presence of nifedipine (1 micromol/L). Thus, nifedipine caused modest efferent arteriolar dilation (30+/-6% reversal, n=9), and subsequent addition of mibefradil elicited further dilation of this vessel (80+/-4%, P<0.01 versus nifedipine). Furthermore, mibefradil reversed the Ang II-induced efferent arteriolar constriction even in the presence of nifedipine and phentolamine. These findings demonstrate that T-type calcium antagonists markedly dilate the Ang II-induced efferent arteriolar constriction, but the action is not mediated by inhibition of catecholamine release. This potent activity would contribute to the efferent arteriolar response to nilvadipine and efonidipine and may offer benefit in light of glomerular hemodynamics.

Heterogeneous activation mechanisms in the renal microvasculature

Vascular smooth muscle cells in different renal microvascular segments utilize different activation mechanisms to respond to mechanical and vasoactive stimuli. L-type Ca2+ channel blockers vasodilate primarily the preglomerular vascular resistance component responsible for autoregulation. Local interstitial infiltration of Ca2+ channel blockers increases glomerular pressure and markedly reduces vascular responsiveness of the tubuloglomerular feedback mechanism. Ca2+ channel blockers selectively attenuate the afferent vasoconstrictor responses to increases in perfusion pressure. Although both afferent and efferent arterioles constrict in response to angiotensin II (Ang II), afferent but not efferent constriction requires Ca2+ influx through L-type Ca2+ channels. Sensitivity of the preglomerular arterioles to Ang II is also heterogeneous with the greatest sensitivity in glomerulus-near, terminal segments. Adenosine triphosphate (ATP) is a vasoconstrictor agonist that selectively activates Ca2+ entry pathways in afferent arterioles but has no effect on efferent arterioles. In isolated preglomerular smooth muscle cells, increasing extracellular [KCl] increases intracellular Ca2+ by stimulating voltage-dependent Ca2+ influx. Ang II, norepinephrine, and ATP also elicit similar increases in intracellular Ca2+. Mechanical and agonist-induced voltage-dependent Ca2+ influx is thus a primary pathway in the control of cytosolic Ca2+ in afferent arterioles. Efferent arterioles, however, rely primarily on intracellular Ca2+ mobilization and other Ca2+ influx pathways.

Integrating multiple paracrine regulators of renal microvascular dynamics

There has been tremendous growth in our knowledge about the multiple interacting mechanisms that regulate renal microvascular function. Paracrine signals originating from endothelial and epithelial cells exert profound influences on the basal tone and reactivity of the pre- and postglomerular arterioles. Selective responsiveness of these arterioles to various stimuli is possible because of differential activating mechanisms in vascular smooth muscle cells of afferent and efferent arterioles. Afferent arterioles rely predominantly on voltage-dependent calcium channels, while efferent arterioles utilize other mechanisms for calcium entry as well as intracellular calcium mobilization. The autoregulatory responses of preglomerular arterioles exemplify the selectivity of these complex control mechanisms. The myogenic mechanism responds to increases in renal perfusion pressure through "stretch-activated" cation channels that lead to depolarization, calcium entry, and vascular contraction. Autoregulatory efficiency is enhanced by the tubuloglomerular feedback (TGF) mechanism which responds to flow-dependent changes in tubular fluid composition at the level of the macula densa and transmits signals to the afferent arterioles to alter the activation state of voltage-dependent calcium channels. Recent studies have implicated extracellular ATP as one paracrine factor mediating TGF and autoregulatory related signals to the afferent arterioles. Other paracrine agents including nitric oxide, angiotensin II, adenosine, and arachidonic acid metabolites modulate vascular responsiveness in order to maintain an optimal balance between the metabolically determined reabsorptive capabilities of the tubules and the hemodynamically dependent filtered load.

Renal effects of the calcium channel blocker aranidipine and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats

The purpose of this study was to investigate the renal effects of aranidipine, a novel calcium channel blocker of the dihydropyridine type, and its active metabolite in anesthetized dogs and conscious spontaneously hypertensive rats (SHRs). When infused into the renal artery in anesthetized dogs, aranidipine (0.03 microg/kg/min) induced sustained increases in urine volume and urinary excretion of sodium and of potassium. This effect was greater than that elicited by nifedipine (0.1 microg/kg/min). The aranidipine metabolite, M-1 (0.1 microg/kg/min), also caused diuresis and natriuresis almost equal to those of nifedipine. The stop-flow experiment using the anesthetized dog showed that intrarenal infusion of aranidipine (0.03 microg/kg/min), as well as nifedipine (0.1 microg/kg/min), produced natriuresis at the distal tubular site rather than at the proximal site. Aranidipine (0.3, 1, and 3 mg/kg), when administered orally, dose-dependently increased urine volume and urinary excretion of electrolytes in conscious saline-loaded SHRs. M-1 (10 mg/kg, p.o.) also showed diuretic and natriuretic effects comparable to those of nifedipine (10 mg/kg) in SHRs. In addition, after repeated oral administration of aranidipine for 7 days, short-term tolerance was not found for its diuretic and natriuretic effects in SHRs. These results suggest that, apart from antihypertensive efficiency, aranidipine may offer a therapeutic advantage by producing diuresis and natriuresis in hypertensive patients. The metabolite of aranidipine may contribute, in part, to the diuretic, natriuretic, and antihypertensive effects of aranidipine.

Nifedipine attenuates systemic and renal vasoconstriction during nitric oxide inhibition in humans

Clinical states associated with nitric oxide deficiency are often accompanied by vasoconstriction. We studied the effects of prolonged infusion of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) on systemic and renal hemodynamics in humans and the reversibility of the established vasoconstriction by calcium channel blockade with nifedipine. Seven healthy men underwent three 7-hour clearance studies. During one study, L-NMMA (3 mg/kg priming dose plus 3 mg.kg-1.h-1) was infused during hours 2 through 5, and during another study, nifedipine (0.015 mg/kg priming dose plus 0.015 mg.kg-1.h-1) was coinfused during hours 4 and 5. A third study served as time control. L-NMMA elicited reproducible systemic and renal vasoconstriction that was stable during the 4 hours of infusion. Systemic vascular resistance index, calculated from bioimpedance-derived cardiac index, increased from 22 +/- 1 to 29 +/- 2 mm Hg.min.m2.L-1 (P < .05). Mean arterial pressure rose by 4 +/- 1 mm Hg (P < .05), and heart rate, stroke index, and cardiac index decreased. Renal blood flow, calculated from renal plasma flow, decreased from 1182 +/- 101 to 785 +/- 53 mL/min, and renal vascular resistance increased from 73 +/- 5 to 115 +/- 6 mm Hg.min.L-1 (P < .05). Glomerular filtration rate decreased from 114 +/- 6 to 104 +/- 6 mL/min (P < .05), and filtration fraction increased. Sodium excretion fell from 89 +/- 9 to 32 +/- 7 mumol/min (P < .05). Nifedipine completely reversed systemic vasoconstriction. Nifedipine caused partial restoration of renal vascular resistance and complete normalization of glomerular filtration rate and sodium excretion but left the elevated filtration fraction unaltered. We conclude that sustained nitric oxide deficiency in humans is accompanied by strong systemic and renal vasoconstriction, decreased glomerular filtration rate, and sodium retention. Nifedipine can reverse most of these effects, suggesting a role for calcium channel blockade in pathological states of impaired nitric oxide activity.

Protection from hypoxemic renal dysfunction by verapamil and manganese in the rabbit

The ability of calcium channel blockers to prevent and/or to reverse the hypoxemia-induced renal dysfunction was studied in anesthetized and mechanically-ventilated rabbits. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by para-aminohippuric acid and inulin clearance, respectively. Each animal was considered as its own control. In 9 rabbits (group 1), verapamil infusion, 1 microgram.kg-1.min-1, did not change basal renal hemodynamics. In a second group (n = 9), hypoxemia induced marked significant decreases in GFR, RBF and urine flow rate (-22 +/- 5%, -18 +/- 6% and -34 +/- 7% respectively). The administration of verapamil partially reversed the hypoxemia-induced renal dysfunction. Likewise, hypoxemia did not induce any change in renal function in verapamil pretreated rabbits (n = 8). This study shows that verapamil is able to prevent and to partially reverse the adverse effects of hypoxemia on renal hemodynamics. The intrarenal infusion of manganese chloride, another calcium channel blocker, was also effective in blunting the hypoxemia-induced changes in the left infused kidney, but not in the contralateral kidney. The overall results demonstrate that a significant protection from hypoxemic renal dysfunction can be achieved by inhibitors of calcium ion transport.

Effect of nifedipine and captopril on glomerular hyperfiltration in normotensive man

Glomerular hyperfiltration and hypertension induced by extensive loss of renal parenchyma are suspected to accelerate progression of renal failure. Amino acid infusion or protein ingestion also modify renal hemodynamics and increase glomerular filtration rate (GFR). This phenomenon was used to study the influence of two commonly used antihypertensive agents, captopril and nifedipine, on renal hemodynamics at rest and during glomerular hyperfiltration. Thirteen healthy volunteers were studied on three separate days (days A, B, and C) in random sequence: inulin and p-amino hippurate (PAH) clearance were measured first under glucose infusion and afterwards under stimulation by amino acid infusion (0.35 mmol/kg/min; 4 mg/kg/min). Day A served as a control, where no medication was given. On day B, 10 mg nifedipine, and on day C, 25 mg captopril, were administered orally before study. Without premedication (= day A, control) GFR increased from 108.0 +/- 6.9 mL/min (SEM) to 131.7 +/- 7.0 mL/min (P less than 0.05). On day B (nifedipine), GFR before stimulation by amino acids was already elevated to 121.8 +/- 4.2 mL/min (P less than 0.05 compared with day A) and increased to 132.6 +/- 6.3 mL/min with infusion of amino acids, thus to the same range as on day A without medication. On day C, after captopril, GFR did not increase with infusion of amino acids (from 112.5 +/- 7.2 to 117.3 +/- 6.3 mL/min). Our results indicate the calcium channel antagonist nifedipine and the angiotensin-converting enzyme (ACE) inhibitor captopril differ in their effect on intrarenal hemodynamic parameters. Nifedipine induces hyperfiltration at rest and allows maximal hyperfiltration to develop under amino acid infusion.(ABSTRACT TRUNCATED AT 250 WORDS)