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J F Wetzels

Publications and source records attributed to J F Wetzels.

At least 73 records · Page 4Linked to original sources
PubMed1996

Cyclosporin does not inhibit the tubular secretion of creatinine.

BACKGROUND: The immunosuppressive drug cyclosporin is known to impair renal function. The degree of renal dysfunction is usually estimated from the clearance of creatinine (CCr). Theoretically however, a fall in CCr can be caused by a decrease of GFR, an inhibition of the tubular secretion of creatinine, or the combination of both. CsA has convincingly been shown to decrease GFR, but detailed information on the effects of CsA on tubular secretion of creatinine is lacking. METHODS: We performed two studies to investigate the influence of CsA on tubular creatinine secretion. In study A we simultaneously measured CCr and GFR (using inulin) immediately before and 4 weeks after cessation of CsA therapy in 17 renal transplant patients. In study B, the rise in serum creatinine after administration of cimetidine, which blocks the tubular secretion of creatinine, was compared in renal transplant patients treated with either CsA (in whom secretion might already be inhibited) or azathioprine. RESULTS: Study A: After cessation of CsA there was an increase of GFR (54+/-15 vs 63+/-16 ml/min/1.73 m2, PCr (71+/-21 vs 82+/-23 ml/min/1.73 m2; PCr and GFR (a measure of the relative contribution of tubular secretion to the clearance of creatinine) did not change significantly (1.33+/-0.21 vs 1. 32+/-0.30). Study B: In nine couples of patients matched for GFR the relative rises in serum creatinine after administration of cimetidine were 26+/-21% and 22+/-7% for CsA and azathioprine treated patients respectively (NS). CONCLUSION: CsA does not substantially inhibit the tubular secretion of creatinine. A rise in serum creatinine after administration of CsA can thus be attributed completely to a fall in GFR.

Adult↗
PubMed1996

Pharmacokinetics and haemodynamic effects of the angiotensin converting enzyme inhibitor cilazapril in hypertensive patients with normal and impaired renal function.

1. The pharmacokinetic and pharmacodynamic properties of the angiotensin converting enzyme (ACE) inhibitor cilazapril were studied in 30 hypertensive patients with various degrees of renal function. 2. After a single oral dose, apparent cilazaprilat clearance was dependent on renal function being 16.0 +/- 3.0, 11.1 +/- 3.0, 8.7 +/- 3.7 and 6.7 +/- 2.1 l h-1 (means +/- s.d.) in patients with creatinine clearances (CLcr) of > 100, 41-100, 21-40, and 8-20 ml min-1, respectively. .3 During 11 weeks of treatment with cilazapril, doses were adjusted to the CLcr and varied from 0.5 to 5.0 mg once daily. At 24 h after drug administration a clear antihypertensive response was seen only in the low clearance groups (CLcr < 40 ml min-1). In contrast, and despite higher once daily dosages, the decline of mean arterial pressure was small and cilazaprilat concentrations after 24 h were lower in the high clearance groups. 4. This study demonstrates that chronic once daily treatment with cilazapril is effective in patients with impaired renal function at dosages adjusted to creatinine clearance. No accumulation was seen. Since cilazaprilat clearance was high in the high creatinine clearance groups, a clear antihypertensive response in these groups was only seen at 3 h after drug administration.

Adult↗
PubMed1996

Rise in cytosolic Ca2+ and collapse of mitochondrial potential in anoxic, but not hypoxic, rat proximal tubules.

It has been suggested that ischemic renal proximal tubular cell injury is mediated by an increase in cytosolic calcium concentrations ((Ca2+)i). However, measurements of (Ca2+)i in rat or rabbit proximal tubules exposed to hypoxia or anoxia have yielded ambiguous results. This study explored the possibility that the severity of oxygen deprivation and the energy state of the mitochondria are important determinants of (Ca2+)i. To this end, (Ca2+)i (measured with fura-2) and the mitochondrial membrane potential (measured with rhodamine 123) were studied simultaneously in individual rat proximal tubules in hypoxic and anoxic conditions. (Ca2+)i did not change during hypoxia, but increased rapidly during anoxia. Increases in (Ca2+)i were only observed in parallel with a decrease of rhodamine 123 fluorescence, which indicates a collapse of the mitochondrial membrane potential. The increase in (Ca2+)i during anoxia was prevented by incubating the tubules in a low Ca2+ medium, which did not interfere with the collapse of the mitochondrial membrane potential. Both hypoxic and anoxic incubation led to cell death, as assessed by the fluorescent dye propidium iodide. These results clearly demonstrate that the level of oxygen deprivation is critical in determining changes in (Ca2+)i. Because cell damage occurred in both hypoxic and anoxic conditions. It was concluded that an increase in (Ca2+)i is not a necessary prerequisite for the development of ischemic cell injury.

Animals↗
PubMed1996

Decreased HbA1c levels due to sulfonamide-induced hemolysis in two IDDM patients.

Regular measurement of HbA1c (percentage) is an essential component of modern diabetes care. Factors that affect the life span of erythrocytes will also influence HbA1c results. In this study, we describe two patients with IDDM, whose regularly determined HbA1c values were considerably decreased with the concomitant use of two related sulfonamide drugs, sulfasalazine and dapsone. The fall in HbA1c results is explained by increased erythrocytopoiesis as a product of drug-induced hemolysis. Fructosamine concentrations are not affected by hemolysis and reflected glycemic control better. We conclude that under conditions of persistent (subclinical) hemolysis, as occurs during the use of sulfonamides, HbA1c is not a reliable indicator of glycemic control.

Adult↗
PubMed1996

Detailed study of changes in renal function after conversion from cyclosporine to azathioprine.

The renal dysfunction induced by cyclosporine (CsA) has been demonstrated to be at least partially reversible after cessation of CsA therapy. The time course and magnitude of changes in various parameters of renal function after CsA withdrawal have not been studied in detail. We examined 12 renal transplant patients immediately before and 1, 2, and 4 weeks after replacement of CsA by azathioprine at 3 months after transplantation. Nine patients in whom CsA was continued during this period served as a control group. A significant increase in glomerular filtration rate ([GFR] 15 + or - 17%, p <0.01) occurred already in the first week after discontinuation of CsA. From 1 to 4 weeks after conversion, GFR did not significantly increase any further. A fall in serum creatinine (-7 + or - 9%, Ns) paralleled the rise in GFR (r = -0.76, p <0.01), but there was a further decrease of creatinine in the second to fourth week after conversion. Withdrawal of CsA induced a rise in serum magnesium in all patients (0.73 + or - 0.13 vs 0.86 + or - 0.12 mmol/l, p <0.001) as well as a marked decrease in the serum level of urate (0.39 + or - 0.09 vs 0.33 + or - 0.07 mmol/l, p <0.01) within one week. None of the observed changes took place in the control group. In conclusion, a major improvement of GFR occurs within one week after cessation of CsA therapy. Changes in the serum levels of magnesium and urate appear to be the most responsive markers of the renal effects of CsA.

Adult↗
PubMed1995

Protection against hypoxic injury of rat proximal tubules by felodipine via a calcium-independent mechanism.

Most evidence for a key role of calcium entry in hypoxia-induced renal damage stems from studies with calcium channel blockers. In proximal tubules, a primary site of renal ischaemic injury, only phenyl-alkylamines, especially verapamil, have been studied. In the present study the effect of the dihydropyridine felodipine on hypoxic injury in isolated rat proximal tubules was investigated. To discriminate between the block of calcium entry and other effects, the enantiomers and a non-calcium blocking derivative of felodipine (H186/86) were included. Cell membrane injury was assessed by measuring the release of lactate dehydrogenase (LDH). At high concentrations (100 microM) felodipine, H186/86 and the two enantiomers all protected rat proximal tubules against hypoxia-induced injury to the same extent. Absence of extracellular calcium did not offer protection, but rather enhanced hypoxic injury. All dihydropyridines used increased the intracellular potassium concentration during normoxia. Felodipine attenuated the hypoxia-induced loss of cellular potassium. We have tried to mimic the effects of felodipine by using potassium channel blockers. The potassium channel blockers quinidine and glibenclamide afforded some protection against hypoxic injury, although their effects on cellular potassium were equivocal. We conclude that the dihydropyridine calcium channel blocker felodipine protects rat proximal tubules against hypoxic injury via a calcium-independent mechanism. We propose that high levels of intracellular potassium and attenuation of potassium loss during hypoxia are important in this protection.

Animals↗
PubMed1995

Familial glomerulonephritis characterized by massive deposits of fibronectin.

In recent years more than 150 cases of glomerulonephritis characterized by deposits of irregularly arranged fibrils have been documented. In the majority of these cases immunoglobulins and complement are the prime constituents of these deposits. We recently made a diagnosis of fibrillary glomerulonephritis without immunoglobulin deposition in two members of a family, a father and a son. In the father, proteinuria was first discovered 18 years ago. In 1985 he was referred to our outpatient clinic because of hypertension and increasing proteinuria. From that time onward he was regularly seen for blood pressure control. Nephrotic-range proteinuria persisted, without hardly any evidence of deterioration of renal function. Renal biopsies were performed in 1985 and 1993. His son underwent a renal biopsy in 1993 because of moderate proteinuria. The biopsies of both patients disclosed a distinct form of fibrillary glomerulonephritis that was characterized by massive deposits of a homogeneous, eosinophilic material in the mesangial and subendothelial areas. Staining for amyloid was negative. Immunofluorescence revealed that the biopsy specimens only stained faintly for immunoglobulins, complement factors C1q and C3, the extracellular matrix proteins, collagen IV, and laminin. However, they strongly stained for fibronectin. Using monoclonal antibodies specific for cell-derived fibronectin (IST-9) and plasma- and cell-derived fibronectin (IST-4), in the biopsy of the son we demonstrated that the fibronectin deposited in the glomeruli was mainly derived from the plasma, and to a lesser extent from resident glomerular cells. In addition, a moderate staining for amyloid P and vitronectin also was present. No or minor enhanced staining for collagen I, III, or V, heparan sulfate proteoglycan or its glycosaminoglycan side chains, tenascin, or thrombospondin could be observed. By electron microscopy the deposits in the mesangium and the subendothelial spaces appeared focally to be composed of irregularly arranged fibrils or microtubules 10 to 12 nm in diameter. Fibrillary glomerulonephritis with massive deposits of fibronectin represents a rare form of familial glomerulonephritis. In our patients the glomerulonephritis has an indolent course with hardly any deterioration of renal function.

Adult↗
PubMed1995

Urinary excretion of beta 2-microglobulin predicts renal outcome in patients with idiopathic membranous nephropathy.

In patients with membranous nephropathy, treatment should be limited to those at risk for disease progression. Urinary beta 2-microglobulin excretion was measured in 30 patients with membranous nephropathy, a nephrotic syndrome, and normal renal function (endogenous creatinine clearance > 80 mL/min), who were subsequently monitored for a median of 48 months. Renal function deteriorated in 11 of the 14 patients with a beta 2-microglobulin excretion > 500 ng/min and in only 2 of the 16 patients with a beta 2-microglobulin excretion < or = 500 ng/min (P < 0.001). The measurement of urinary beta 2-microglobulin excretion thus contributes to the identification of patients with membranous nephropathy at high risk for developing renal insufficiency and may provide guidance for early immunosuppressive treatment.

Adult↗
PubMed1995

Induced alterations in calcium uptake rate in normoxic rate proximal tubules.

This study is well-oxygenated, freshly isolated rat proximal tubules (RPT), examined the effects of several drugs that alter the transmembrane K+ and Na+ gradients across cell membranes, including valinomycin (VAL), amphotericin B (AMPHO), and ouabain (OUAB). The effects of high extracellular potassium chloride (KCl) concentrations (45 mM) and low extracellular sodium concentration (100mM) were also studied. After 10 min of drug exposure Ca2+ uptake rate (nmol/mg/min) increased from 2.7 to 3.8 with VAL (p < .02), from 2.9 to 3.7 with AMPHO (p < .05), from 3.6 to 4.1 with OUAB (p < .05), and from 3.2 to 4.8 with 45 mM KCl (p < .001). Ca2+ uptake rate was sustained at these high levels at 20 min in all treated RPT except those exposed to OUAB. LDH release averaged less than 15% in control tubules and did not increase significantly except in RPT treated with VAL, where LDH release at 10 min was 48% and at 20 min was 57% (both p < .001). Of importance, only in VAL-treated RPT did ATP decrease to low levels (6.7 nmol/mg in control to 2.0 +/- 0.3 nmol/mg in VAL, p < .001). Treatment with verapamil reduced Ca2+ uptake rates at 10 min in VAL-treated RPT (from 3.8 to 3.1, p < .02, in AMPHO-treated RPT (from 3.8 to 3.1 p < .001), in OUAB-treated tubules (from 4.0 to 3.4, p < .01), and in KCl-treated RPT (from 3.7 to 3.2, p < .01). These results indicate that acute changes in the transmembrane ion gradient in RPT are accompanied by increased Ca2+ uptake rates. Ca2+ uptake rates are also increased during O2 deprivation in RPT, a situation in which the transmembrane ion gradient is likewise altered. The increased Ca2+ uptake rate observed in the present study and during hypoxia may have a common basis, that is, altered transmembrane ion gradients or some function thereof.

Adenosine Triphosphate↗
PubMed1995

Cyclosporin A reduces albuminuria in experimental anti-GBM nephritis independently from changes in GFR.

Cyclosporin A (CsA) can reduce proteinuria in various forms of human and experimental glomerulonephritis. This antiproteinuric effect of CsA may be the consequence of diminution of immunological damage, a drug-induced decrease of GFR, or changes in permselectivity of the glomerular basement membrane (GBM). We studied the antiproteinuric effect of CsA in the heterologous phase of a passively induced anti-GBM nephritis in the mouse. This passive model is characterized by acute exudative glomerular lesions and a dose-dependent albuminuria. Rabbit anti-mouse GBM antibodies were administered intravenously in C57B110 mice at day 4, after 3 days of pretreatment with either CsA (75 mg/kg body weight) (n = 15) or olive oil (OO, controls, n = 15) orally. CsA did not influence the severity of the histological lesions. Albuminuria was substantially reduced by CsA (CsA 1.6 +/- 1.8; OO 5.6 +/- 3.2 mg/18 h; P < 0.002). There was a considerable concomitant reduction of the GFR by CsA, as measured with a 51Cr-EDTA single-shot plasma clearance technique before (day-1) and during treatment (day 4): GFR ratio day 4/day-1 for CsA, 0.4 +/- 0.1; for OO controls, 1.1 +/- 0.6; P < 0.01. This drug-induced decrease of GFR was prevented by simultaneous treatment with phenoxybenzamine (PB) twice daily 45 micrograms orally for 4 days (GFR ratio day 4/day-1 for PB and CsA, 0.9 +/- 0.4; controls (PB and OO), 1.0 +/- 0.4; P = NS). Although the CsA-induced GFR reduction was prevented, CsA still reduced albuminuria significantly (PB and CsA, 2.2 +/- 1.8; controls (PB and OO), 5.6 +/- 1.8 mg/18 h; P = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Albuminuria↗
PubMed1994

Preserving renal function in patients with membranous nephropathy: daily oral chlorambucil compared with intermittent monthly pulses of cyclophosphamide.

OBJECTIVE: To compare oral chlorambucil and intravenous cyclophosphamide-based drug regimens in the treatment of patients with membranous nephropathy and deteriorating renal function. DESIGN: Randomized study. SETTING: University hospital and teaching hospitals. PATIENTS: 18 patients with membranous nephropathy, a nephrotic syndrome, and deteriorating renal function. INTERVENTION: Chlorambucil (0.15 mg/kg body weight per day orally in months 2, 4, and 6) and prednisone (three intravenous pulses of 1 g of methylprednisolone followed by oral prednisone at 0.5 mg/kg per day in months 1, 3, and 5) or intravenous cyclophosphamide (750 mg/m2 body surface area once every month for 6 months) and methylprednisolone (three intravenous 1-g pulses in months 1, 3, and 5). MEASUREMENTS: Serum creatinine, serum cholesterol, serum albumin, and urinary protein levels. RESULTS: Before treatment, no statistical differences were found between the treatment groups. Six months after treatment was started, serum creatinine levels had decreased in the group treated with chlorambucil, methylprednisolone, and prednisone from a mean of 260 +/- 112 mumol/L to 186 +/- 74 mumol/L (P = 0.003) and had increased in the group treated with intravenous cyclophosphamide and methylprednisolone from 218 +/- 85 mumol/L to 297 +/- 143 mumol/L (P = 0.02; difference between both groups, P < 0.001). Serum albumin levels increased in both groups by 9 and 6 g/L, respectively, and the urinary protein/creatinine ratio decreased by 2.6 and 3.1 g/10 mmol, respectively. At the end of follow-up (median, 15 months; range, 6 to 36 months), one patient in the chlorambucil group and four patients in the cyclophosphamide group had reached end-stage renal failure after 36, 12, 12, 18, and 18 months of therapy, respectively. One patient in the intravenous cyclophosphamide group died after 6 months of therapy. CONCLUSIONS: Thus far, both oral chlorambucil and oral cyclophosphamide have been shown to be effective in the treatment of patients with membranous nephropathy and deteriorating renal function. Our study shows that intermittent monthly pulses of low-dose cyclophosphamide are ineffective in preserving renal function in such patients.

Administration, Oral↗
PubMed1994

Captopril and atenolol are equally effective in retarding progression of diabetic nephropathy. Results of a 2-year prospective, randomized study.

The progression of diabetic nephropathy can be positively influenced by maintaining a low blood pressure level. This has been shown in studies with conventional antihypertensive treatment as well as with ACE inhibitors. Whether the latter group of drugs is more effective remains to be proven and was the aim of our study. In a prospective randomized study we compared the effects of ACE inhibition and beta-blockade on retarding progression of renal function in IDDM patients with an early stage of overt diabetic nephropathy. Twenty-nine patients were studied for 2 years, 15 were randomized for treatment with captopril and 14 for atenolol. Every 6 weeks blood pressure and urinary albumin and total protein excretion were measured. GFR was measured every 6 months as 51Cr-EDTA clearance. Baseline values for blood pressure, renal function and albuminuria were identical in the two groups. The effect of both drugs on blood pressure was not significantly different. In the captopril-treated patients MAP before and after 2 years was 110 +/- 3 (SEM) and 100 +/- 2 mm Hg, respectively and in the atenolol-treated patients 105 +/- 2 vs 101 +/- 2 mm Hg. Both drugs reduced albuminuria and total proteinuria to the same extent. With captopril albuminuria decreased from 1549 (989-2399) to 851 (537-1380) mg/24 h and proteinuria from 2.5 (1.6-3.8) to 1.2 (0.8-1.8) g/24 h. With atenolol albuminuria decreased from 933 (603-1445) to 676 (437-1047) mg/24 h and proteinuria from 1.5 (1.0-2.4) to 0.9 (0.6-1.5) g/24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Acute effects of nifedipine in renal transplant recipients treated with cyclosporine or azathioprine.

Cyclosporine (CsA) impairs renal function, probably by preglomerular vasoconstriction. Vasodilating substances may therefore be of benefit to ameliorate CsA-induced renal dysfunction. We studied the acute effects on blood pressure and renal function of the dihydropyridine calcium antagonist nifedipine (10 mg orally) in 20 CsA-treated renal transplant patients. In addition, we compared the effects of nifedipine when given immediately before and 4 weeks after elective conversion from CsA to azathioprine. Compared with placebo (n = 14), administration of nifedipine led to a significant decrease in blood pressure and a strong natriuretic and diuretic response. Despite the reduction in blood pressure, glomerular filtration rate improved from 60 +/- 20 (mean +/- SD) to 69 +/- 24 mL/min/1.73 m2 (P < 0.001) and renal plasma flow (RPF) increased from 260 +/- 87 to 338 +/- 120 mL/min/1.73 m2 (P < 0.001). The combination of a decreased blood pressure with an increased RPF was reflected in a sharp decrease in renal vascular resistance (0.34 +/- 0.18 units v 0.23 +/- 0.10 units; P < 0.001). The conversion from CsA to azathioprine by itself led to significant increases in glomerular filtration rate (62 +/- 15 mL/min/1.73 m2 v 76 +/- 18 mL/min/1.73 m2; P < 0.05) and RPF (280 +/- 86 mL/min/1.73 m2 v 334 +/- 66 mL/min/1.73 m2; P < 0.05). During treatment with azathioprine an effect of nifedipine on glomerular filtration rate and RPF was no longer observed, although the natriuretic effect was similar on both occasions. The decrease in renal vascular resistance was larger during treatment with CsA than during treatment with azathioprine (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Azathioprine↗
PubMed1994

Ca2+ uptake, fatty acid, and LDH release during proximal tubule hypoxia: effects of mepacrine and dibucaine.

In freshly isolated hypoxic rat proximal tubules, Ca2+ uptake rate increases promptly, within 1 min, and remains significantly elevated throughout a 20-min period of hypoxia. Lactate dehydrogenase (LDH) release, a sign of membrane injury, increases only after 5 min of hypoxia and thereafter rises progressively. The potential effect of increased Ca2+ uptake rate to activate phospholipases, which would then initiate membrane injury, was evaluated by treating hypoxic tubules with three dissimilar phospholipase inhibitors, i.e., mepacrine, dibucaine, or p-bromophenacyl bromide (PBPB). LDH release averaged 11.9 and 13.8% after 10 and 20 min of normoxia, respectively. With 10 or 20 min of hypoxia LDH release increased to 46.0 and 65.2%, respectively (P < 0.01), and Ca2+ uptake rate increased from 2.56 in normoxia to 4.71 nmol.mg-1 x min-1 at 10 min of hypoxia (P < 0.01) and from 2.82 in normoxia to 3.76 nmol/mg at 20 min of hypoxia (P < 0.05). In a separate series of tubules, after 10 min of hypoxia LDH release was reduced by pretreatment with 50 microM mepacrine (66.1 to 47.3%, P < 0.01) or 50 microM dibucaine (53.1 to 38.5%, P < 0.02). The increase in Ca2+ uptake rate also was significantly reduced. After 20 min of hypoxia neither mepacrine nor dibucaine reduced Ca2+ uptake rate; LDH release was modestly reduced by dibucaine but not mepacrine. Higher doses of mepacrine (500 microM) and dibucaine (250 microM) also reduced cell injury at 10 min of hypoxia as assessed by LDH release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Exogenous aldosterone antagonizes distal tubular effects of calcium entry blocker felodipine.

Calcium entry blockers, such as felodipine, increase natriuresis without increasing kaliuresis. Since these drugs acutely increase plasma renin activity without a concomitant change of aldosterone, inhibition of such stimulated aldosterone release might explain the absence of kaliuresis. In a randomized crossover study in 12 male volunteers, we compared the effects of simultaneously administered exogenous aldosterone and felodipine with the effects of either felodipine or aldosterone alone. Felodipine infusion decreased blood pressure, increased renal plasma flow, and induced natriuresis without kaliuresis. Aldosterone alone reduced sodium excretion and increased potassium excretion without influencing hemodynamics. Addition of aldosterone to felodipine attenuated its natriuretic effect and induced a kaliuresis, which clearly exceeded the rise of potassium excretion during aldosterone alone [delta% fractional excretion of K+ +42 +/- 12 with felodipine+aldosterone and +7 +/- 8% with aldosterone alone; means +/- SE, P < 0.02]. Our data suggest that felodipine-mediated inhibition of stimulated aldosterone release is essential for the absence of kaliuresis with felodipine. In addition, the pronounced kaliuresis with aldosterone during felodipine is in keeping with increased distal sodium delivery due to a proximal tubular action of felodipine.

Adult↗
PubMed1994

Metoclopramide stimulates kaliuresis during felodipine without affecting its natriuresis.

Calcium entry blockers such as felodipine induce natriuresis without a parallel rise of potassium excretion. Previous studies with exogenous aldosterone and felodipine have suggested that the absence of kaliuresis might be explained by a felodipine-induced inhibition of aldosterone release. The natriuresis with calcium entry blockers could not be attributed to a similar mechanism but might be due to the stimulation of intrarenal natriuretic systems such as the dopaminergic system. We studied whether the aselective dopamine antagonist metoclopramide prevents the natriuresis with low and therapeutic felodipine doses and whether metoclopramide-induced aldosterone release promotes kaliuresis with felodipine. Twelve healthy male volunteers participated in a randomized, placebo-controlled, crossover study comparing felodipine infusion during metoclopramide with felodipine alone. Metoclopramide had no significant influence on the pronounced and dose-dependent increases of renal plasma flow and urinary sodium excretion with felodipine. Metoclopramide increased plasma aldosterone concentration from 0.17 +/- 0.03 to 0.60 +/- 0.14 nmol/L, and subsequent felodipine infusion clearly increased urinary potassium excretion by 23 +/- 6 and 35 +/- 8 mumol/min (low and therapeutic doses, respectively). In contrast, potassium excretion remained stable with felodipine alone (+5 +/- 4 and +7 +/- 5 mumol/min, respectively). In conclusion, the natriuretic action of calcium entry blockers cannot be blocked by the aselective dopamine antagonist metoclopramide. This natriuresis is accompanied by kaliuresis only in the presence of elevated endogenous aldosterone concentrations. The ability of calcium entry blockers to prevent a rise of plasma aldosterone thus seems essential for the prevention of urinary potassium losses.

Adult↗
PubMed1994

Evidence for role of cytosolic free calcium in hypoxia-induced proximal tubule injury.

The role of cytosolic free Ca2+ ([Ca2+]i) in hypoxic injury was investigated in rat proximal tubules. [Ca2+]i was measured using fura-2 and cell injury was estimated with propidium iodide (PI) in individual tubules using video imaging fluorescence microscopy. [Ca2+]i increased from approximately 170 to approximately 390 nM during 5 min of hypoxia. This increase preceded detectable cell injury as assessed by PI and was reversible with reoxygenation. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; 100 microM) reduced [Ca2+]i under basal conditions (approximately 80 nM) and during hypoxia (approximately 120 nM) and significantly attenuated hypoxic injury. When [Ca2+]i and hypoxic cell injury were studied concurrently in the same individual tubules, the 10 min [Ca2+]i rise correlated significantly with subsequent cell damage observed at 20 min. 2 mM glycine did not block the rise in [Ca2+]i, yet protected the tubules from hypoxic injury. These results indicate that in rat proximal tubules, hypoxia induces an increase of [Ca2+]i which occurs before cell damage. The protective effect of BAPTA supports a role for [Ca2+]i in the initiation of hypoxic proximal tubule injury. The glycine results, however, implicate calcium-independent mechanisms of injury and/or blockade of calcium-mediated processes of injury such as activation of phospholipases or proteases.

Adenosine Triphosphate↗