New technique to assess hypoxia-induced cell injury in individual isolated renal tubules.
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Animals↗
Biomedical subjects
J F Wetzels
Publications and source records attributed to J F Wetzels.
Angiotensin converting enzyme inhibition does not prevent the natriuretic effect of felodipine.
The mechanism of natriuresis with calcium entry blockers such as felodipine is largely unexplained. As these drugs prevent sodium retention following exogenous angiotensin II, the natriuretic effect of felodipine might be due to a similar interaction with endogenous angiotensin II. In such a case, angiotensin converting enzyme inhibition with ramipril should prevent natriuresis with felodipine. We tested this hypothesis in a randomized, double-blind, crossover study in 12 male volunteers by comparing intravenous felodipine after 1 week of oral ramipril with felodipine after placebo and with solvent after ramipril. Ramipril pretreatment reduced ACE activity to 11 +/- 1%, lowered the blood pressure, and increased renal blood flow. However, ramipril pretreatment did not prevent the pronounced increase in natriuresis and diuresis with felodipine. Fractional sodium excretion only tended to increase less during felodipine after ramipril than during felodipine after placebo (absolute changes of + 1.2 +/- 0.2 and + 1.7 +/- 0.2%, respectively; p = 0.07). Ramipril did not influence the felodipine-mediated blood pressure reduction and renal vasodilation. In conclusion, ACE inhibition has no significant effect on the natriuretic and hemodynamic effects of felodipine, suggesting that mechanisms other than interaction with endogenous angiotensin II are involved in these effects of calcium entry blockers.
Adult↗
Glycine protection against hypoxic but not phospholipase A2-induced injury in rat proximal tubules.
We studied the effects of glycine (2 mM) on hypoxia-induced changes in phospholipids and fatty acids in isolated rat proximal tubules. In this preparation, 25 min of hypoxia caused cell injury, as reflected by the release of lactate dehydrogenase (LDH) (13.1 +/- 0.8 vs. 43.5 +/- 3.2%; P < 0.01). Hypoxia caused increases in fatty acids and in lysophospholipids. Glycine prevented the hypoxia-induced cell injury (LDH 13.1 +/- 0.8 vs. 11 +/- 0.7%; not significant) but did not attenuate the increases in fatty acids or lysophospholipids. In additional experiments, the effects of glycine on phospholipid changes and cell injury induced by exogenous phospholipase A2 (PLA2) were studied. PLA2 caused dramatic increases in fatty acids and lysophospholipids and mild cell injury; these effects were not influenced by glycine. In contrast, glycine attenuated increases in LDH release induced by exposing the tubules to exogenous arachidonic acid. In conclusion, glycine does not prevent the phospholipid degradation induced by either exogenous PLA2 or hypoxia in isolated proximal tubules and yet affords protection against hypoxia and exogenous arachidonic acid.
Animals↗
Is the renal dopaminergic system involved in the natriuretic effect of felodipine?
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Adult↗
Calcium modulation and cell injury in isolated rat proximal tubules.
The possible role of an increased calcium influx in mediating hypoxia-induced injury in isolated rat proximal tubules was examined. Reduction of extracellular calcium delayed the development of proximal tubule cell injury as reflected by the release of lactate dehydrogenase (LDH). This protection, as assessed by LDH release, was not associated with improvements of cell ATP or potassium concentrations. The calcium channel blocker verapamil also delayed the development of cell injury due to hypoxia. This protective effect was evident in the presence of normal or low extracellular calcium. Specifically, hypoxic tubules incubated in low calcium medium were further protected by the addition of verapamil. The protection with verapamil was evident not only by diminished LDH release, but also by improvements in cell ATP and potassium concentration. Further experiments demonstrated that verapamil also increased cell potassium levels in control oxygenated tubules incubated in normal calcium medium. Thus, the results demonstrate that low calcium medium delays the onset of cell membrane injury during hypoxia as assessed by LDH release. The protective effects of verapamil can be demonstrated in the presence of normal or low calcium media, and involve not only diminished LDH release but also increased cell ATP and potassium concentrations. Therefore, in addition to any effect on calcium influx, the effect of verapamil appears to involve a protective effect at cell membrane or mitochondria sites.
Adenosine Triphosphate↗
Angiotensin-converting enzyme inhibition and the combination of a beta blocker and a diuretic are equally effective in lowering proteinuria in patients with glomerulonephritis.
In this study we compared the antihypertensive and antiproteinuric efficacies of an angiotensin-converting enzyme inhibitor and of conventional treatment consisting of a beta blocker and a diuretic in 13 patients with biopsy-proven glomerulonephritis and a proteinuria of more than 2 g/24 h. Ten of these 13 patients were normotensive. None had diabetes mellitus. In a randomized cross-over design with two treatment periods of 6 weeks, each preceded by a washout period of 4 weeks, patients were treated with benazepril (20 mg o.d.) and the combination of metoprolol (200 mg o.d.) and chlorthalidone (25 mg o.d.). At the end of the treatment periods with benazepril or metoprolol/chlorthalidone mean arterial pressure was lowered to a similar degree by 7.4 (mean, 95% confidence interval 2.0-12.7) and 9.7 (5.7-13.7) mmHg respectively. Both treatment modalities caused similar reductions in proteinuria, being 3.4 g/24 h (mean, 95% confidence interval 2.1-4.8) on benazepril and 3.2 (1.2-5.1) g/24 h on metoprolol/chlorthalidone. Glomerular filtration rate and renal plasma flow were slightly less during metoprolol/chlorthalidone treatment. Subgroup analysis of normotensive patients gave similar results. In conclusion, in these patients with glomerular disease angiotensin-converting enzyme inhibition was not more effective than the conventional treatment with the combination of a beta blocker and a diuretic in reducing blood pressure and proteinuria. Both treatments reduced proteinuria not only in hypertensive, but also in normotensive patients.
Adult↗
Infusion of glycine does not attenuate in vivo ischemic acute renal failure in the rat.
Recent in vitro studies have demonstrated that the amino acid glycine affords profound protection against hypoxic injury in isolated rat proximal tubules and the isolated perfused rat kidney. In the present study we have examined the in vivo effect of glycine in a rat model of ischemic acute renal failure. Acute renal failure was induced in rats by right uninephrectomy and clamping of the left renal artery for 45 or 60 minutes. Glycine infusion was initiated 60 minutes before renal artery clamping at a rate to increase serum glycine levels above 2.0 mmol/L. Control rats received a 5% dextrose infusion. In the control rats, both 45 minutes and 60 minutes of clamping resulted in reversible acute renal failure and a serum creatinine level after 24 hours averaging 2.1 +/- 0.3 mg/dl (mean +/- SEM) and 3.3 +/- 0.4 mg/dl, respectively. Glycine treatment did not attenuate the decrease of renal function in the 45-minute and 60-minute models, with serum creatinine averaging 2.1 +/- 0.4 mg/dl and 3.4 +/- 0.5 mg/dl, respectively. Histologic examination also did not reveal any differences between control and glycine-treated rats. Therefore, we conclude that infusion of glycine does not afford in vivo protection against acute ischemic renal injury in the rat. The in vitro protective effects of glycine therefore cannot be extrapolated to the in vivo situation.
Acute Kidney Injury↗
Captopril acutely lowers albuminuria in normotensive patients with diabetic nephropathy.
Angiotensin-converting enzyme (ACE) inhibitors decrease albuminuria in patients with diabetic nephropathy. To study the change in albuminuria in relation to changes in systemic and renal hemodynamics, nine normotensive patients with type 1 (insulin-dependent) diabetes mellitus and persistent proteinuria were given a single oral dose of 25 mg of the ACE inhibitor captopril. Blood pressure, glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and albumin excretion rate (AER) were measured in two periods of 40 minutes before and in four periods of 40 minutes after administration of captopril. A constant water diuresis was maintained. Blood pressure did not decrease significantly (130/79 +/- 4/3 v 124/74 +/- 4/3 mm Hg; mean +/- SEM), median AER decreased from 403 (interquartile range [IQR], 812) micrograms/min to 333 (707) micrograms/min (P < 0.01). GFR did not change (123 +/- 13 v 117 +/- 14 mL/min), but ERPF increased significantly from 609 +/- 56 to 714 +/- 55 mL/min (P < 0.01). Consequently, the filtration fraction (FF; quotient of GFR and ERPF) decreased from 0.20 +/- 0.014 to 0.17 +/- 0.014 (P < 0.01). A strong correlation was found between the decrease of AER and the decrease of FF (rs = 0.75; P < 0.02). No correlation was found between the decrease in AER and changes in GFR or blood pressure. In the normotensive patient with diabetic nephropathy, captopril causes an acute reduction of AER, which is probably mediated by a lowering of the intraglomerular pressure.
Adult↗
Is increased erythrocyte sodium-lithium countertransport a useful marker for diabetic nephropathy?
Genetic predisposition to essential hypertension has been proposed as a risk factor for the development of diabetic nephropathy in type 1 (insulin-dependent) diabetes mellitus. An increased sodium-lithium countertransport activity (NaLiCT) has been suggested as a genetic marker for essential hypertension. We therefore evaluated NaLiCT in diabetic patients with (N = 39) or without (N = 23) diabetic nephropathy (DNP), patients with non-diabetic renal diseases (N = 42) and in healthy controls (N = 24). The NaLiCT was elevated in both diabetic patient groups compared to healthy controls (median 244; range 134 to 390 mumol.liter cells-1.hr-1), but was not different in patients with DNP (median 314; range 162 to 676), without DNP (median 325; range 189 to 627) and patients with non-diabetic renal disease (median 300; range 142 to 655). The genetic predisposition to DNP is illustrated by the fact that diabetic sibs of probands with DNP showed a higher occurrence of DNP than diabetic sibs of patients without DNP. We analyzed whether familial DNP clustered with an increased NaLiCT. The NaLiCT in sibs concordant for the presence of DNP (N = 10; median 307; range 217 to 428 mumol.liter cells-1.hr-1) was not significantly different from that in sibs concordant for absence of DNP (N = 15; median 279; range 189 to 442). We conclude that erythrocyte sodium-lithium countertransport activity cannot be used as a marker to identify patients at risk for the development of diabetic nephropathy.
Adult↗
Acute phosphate depletion and in vitro rat proximal tubule injury: protection by glycine and acidosis.
The effects of phosphate (PO4) removal from Krebs Henseleit buffer on freshly isolated rat proximal tubules (rPT) were assessed by measuring Ca2+ uptake (nmol/mg protein), cellular adenosine triphosphate (ATP) (nmol/mg), tissue K+ content (nmol/mg) and lactate dehydrogenase (LDH) as an index of cell integrity. Ca2+ uptake increased by 50% in rPT incubated in zero PO4 medium as compared to control (2.6 +/- 0.1 vs. 3.9 +/- 0.19, P less than 0.001) and LDH release increased 2.5-fold from 14.2 +/- 0.6 to 31.6 +/- 1.6%, P less than 0.001. Neither verapamil (200 microM) nor mepacrine (50 microM) reduced Ca2+ uptake or decreased LDH release suggesting that the increased Ca2+ uptake was not occurring through potential operated channels and that phospholipase-induced cell injury was not the cause of increased LDH release. Either glycine (2 mM) or extracellular fluid acidosis (pH 7.06), however, significantly diminished rPT injury and Ca2+ uptake. Specifically, as compared to the increased LDH released in untreated. PO4-depleted rPT, LDH release was diminished significantly by glycine treatment (31.0 +/- 0.9 vs. 15.5 +/- 1.6%, P less than 0.001) or acidosis (30.3 +/- 0.04 vs. 19.2 +/- 0.9%, P less than 0.01). Ca2+ uptake did not increase in glycine treated tubules (2.6 +/- 0.1 vs. 2.8 +/- 0.2 nmol/mg, NS) or in the presence of acidosis (2.6 +/- 0.1 vs. 2.97 +/- 0.17 nmol/mg, NS). ATP concentrations were markedly reduced by PO4 depletion (2.8 +/- 0.2 vs. 4.8 +/- 0.3 nmol/mg, P less than 0.001) and remained at low levels during either acidosis or glycine-induced protection.(ABSTRACT TRUNCATED AT 250 WORDS)
Acidosis↗
Evidence for renal vasodilation in pre-dialysis patients during correction of anemia by erythropoietin.
Results from animal experiments have suggested that treatment with recombinant human erythropoietin (rHuEPO) causes changes in renal hemodynamics which are detrimental to renal function. Therefore, the effects of correction of the anemia by rHuEPO on glomerular filtration rate (GFR; inulin clearance) and effective renal plasma flow (ERPF; PAH clearance) were studied in eight pre-dialysis patients. The studies were done before (Hct 0.24 +/- 0.05 liter/liter) and at 89 +/- 19 days after the start of rHuEPO therapy (Hct 0.39 +/- 0.03 liter/liter). To further evaluate the effects of ACE inhibition, 25 mg of captopril was given orally after baseline values had been obtained. Baseline GFR, renal blood flow (RBF) and filtration fraction (FF) did not change during rHuEPO therapy. At low hematocrit (Hct) captopril induced a significant increase in ERPF and RBF, and a decrease in MAP. After correction of the hematocrit the blood pressure lowering effect of captopril remained unchanged. However, captopril no longer induced changes in ERPF and RBF. We conclude that the increase in hematocrit had no adverse effects on GFR. The results suggest that changes in hematocrit may influence the effects of ACE inhibition on efferent vascular resistance. Therefore, the hematocrit should be taken into account when evaluating studies on the effects of ACE inhibition in the progression of chronic renal failure.
Adult↗
Prevention and attenuation of acute renal failure.
Recent progress in our understanding of the pathogenetic processes involved in ischemic acute renal failure is considerable. Blockade of the production of endothelium-derived relaxing factor may markedly improve survival in patients with septic shock. Atrial natriuretic peptide and growth factors enhance renal recovery in animal models of acute renal failure, even when administered well after the ischemic insult. Aminoglycosides and radiocontrast agents are the most common causes of drug-induced acute renal failure. Once-daily administration of aminoglycosides is an effective treatment modality that may limit the occurrence of nephrotoxicity. Awareness of the patient's volume status has decreased the incidence of radiocontrast-induced acute renal failure. The new, expensive, nonionic, low-osmolar radiocontrast agents do not offer apparent benefits in patients with normal or slightly decreased renal function. However, use of such agents may decrease the incidence of radiocontrast-induced renal failure in diabetic patients with severe renal failure. The prognosis for patients with renal vasculitis has improved greatly in the past decade. The discovery of antibodies directed against antigenic targets in the cytoplasm of neutrophils has facilitated the diagnosis of renal vasculitides, has improved our knowledge of the pathogenesis of these diseases, and may guide rational treatment.
Acute Kidney Injury↗
Calcium channel blockers: protective effects in ischemic acute renal failure.
Studies in heart, liver, and kidney have provided evidence that calcium is an important factor in cell injury. Calcium channel blockers are used with increasing frequency in ischemic and toxic renal failure. In this review the available data on the effects of calcium channel blockers in animal models of ischemic renal failure are presented and possible mechanisms of protective actions are discussed.
Acute Kidney Injury↗
Is natriuresis on felodipine due to reversal of the renal effects of angiotensin II?
Felodipine induces natriuresis, possibly by renal hemodynamic and/or tubular effects. Theoretically, reversal of the sodium-retaining effect of angiotensin II (Ang II) could be involved. Therefore, we administered felodipine during Ang II infusion and during suppression of endogenous Ang II production in two double-blind studies in healthy volunteers. First, a gradually increasing dose of Ang II was infused during felodipine or solvent infusion. Before starting Ang II, felodipine had lowered renal vascular resistance (RVR) and filtration fraction (FF), and simultaneously increased CNa. The Ang II induced rise of mean arterial pressure (MAP) and renal vasoconstriction was partly antagonized and the falls in glomerular filtration rate (GFR) and CNa completely abolished by felodipine. The combination of felodipine and 3.0 ng/kg/min Ang II even enhanced natriuresis. Second, felodipine or solvent was infused after one week of pretreatment with placebo or the angiotensin converting enzyme (ACE) inhibitor ramipril, which reduced MAP and induced renal vasodilatation. Ramipril pretreatment did not influence significantly the blood pressure reduction, renal vasodilatation, and natriuresis caused by felodipine. In conclusion, it seems unlikely that the natriuretic effect of felodipine is due to interference with renal effects of endogenous Ang II. The fact that felodipine reverses sodium retention on exogenous Ang II may be explained by interference with systemic and renal hemodynamic effects of exogenous Ang II.
Adult↗
Removal of interleukin-1 beta and tumor necrosis factor from human plasma by in vitro dialysis with polyacrylonitrile membranes.
We studied the suitability of in vitro dialysis with polyacrylonitrile (PAN) membranes to remove small amounts of interleukin-1 beta (IL-1 beta) and tumor necrosis factor (TNF) from plasma to be used as diluent for the standards in radioimmunoassays (RIA). Incubation of PAN membrane fragments with radiolabeled IL-1 beta or TNF yielded a significant binding of both cytokines to the membrane (percentage of membrane-bound cytokine after incubation in saline or plasma was 14-17% and 23-46%, respectively). Dialysis of plasma (containing radiolabeled cytokine) against plasma (initially devoid of cytokine) resulted in a binding percentage of IL-1 beta and TNF to the PAN membranes of 44 and 28%, respectively. When plasma was dialyzed against saline the percentage of membrane-bound IL-1 beta and TNF was 63 and 37%, respectively. After dialysis of plasma against either plasma or saline the percentage IL-1 beta recovered from the dialysate was approximately 16% in contrast with 1-2% TNF. The results confirm the capacity of in vitro dialysis with PAN membranes to remove IL-1 beta and to a lesser extent TNF from plasma. Removal is most marked in the first minutes of dialysis (suggesting saturation of the membrane) and less effective for TNF due to its low diffusion across the membrane.
Acrylic Resins↗
Acute renal effects of felodipine in hypertensive patients with kidney disease.
In contrast to other types of directly acting vasodilators, calcium antagonists promote sodium excretion. It is not well established, however, whether these drugs also induce natriuresis in hypertensive patients with renal disease. Therefore, we studied the acute effects of the dihydropyridine calcium antagonist felodipine in nine such patients (CCr 68 +/- 19 ml/min) and 12 healthy normotensive subjects. In both the hypertensive patients and the normotensive subjects total and fractional sodium excretion rose during the first 40 minutes of intravenous felodipine infusion; in the hypertensive patients this rise of sodium excretion was positively correlated to the initial glomerular filtration rate (GFR) (r = 0.87, P less than 0.01). In the patients, during ongoing felodipine infusion, natriuresis was attenuated in the setting of a large continuing decrease of blood pressure. In contrast, in the normotensive subjects, in whom blood pressure did not fall any further, a steady rise of sodium excretion was observed. In both the hypertensive patients and the normotensive subjects GFR remained unchanged and renal vascular resistance decreased, whereas renal plasma flow increased only in the latter group. Changes in sodium excretion were not correlated to changes in renal hemodynamic parameters. It is concluded, that also in hypertensive patients with diminished renal function felodipine exerts a potentially advantageous natriuretic effect. However, this natriuretic effect is possibly less at lower GFR and seems to be attenuated by blood pressure reduction. The mechanism of this natriuretic effect as well as its contribution to the antihypertensive effect of felodipine still has to be clarified.
Adult↗
Time-dependent protective effects of calcium channel blockers on anoxia- and hypoxia-induced proximal tubule injury.
The effects of anoxia or hypoxia on Ca++ uptake and lactic dehydrogenase (LDH) release were examined in freshly isolated rat proximal tubules (rPT). Both Ca++ uptake and LDH release were increased above control after only 10 min of either anoxia or hypoxia in rPT. The increase in Ca++ uptake was through voltage-sensitive, slow Ca++ channels, because pretreatment with chemically dissimilar calcium channel blockers (CCB), either verapamil or flunarizine, prevented the increased Ca++ uptake and reduced the LDH release from the anoxic and hypoxic rPT. After 20 min of hypoxia, however, verapamil pretreatment did not significantly reduce the high Ca++ uptake rate, thus, suggesting that this increase in Ca++ permeability was occurring through pathways other than the slow Ca++ channels. The increase in LDH release was only slightly decreased by verapamil after 20 min of hypoxia. After 20 min of anoxia in rPT, Ca++ uptake was no longer increased, but the increased LDH release persisted. These effects of anoxia were unaltered by verapamil. These results, thus, suggest that early membrane injury to isolated rPT in suspension, which is associated with 10 min of either anoxia or hypoxia, involves increased cellular Ca++ uptake through voltage-sensitive Ca++ channels and protection is afforded by CCB. In contrast, after 20 min of anoxia or hypoxia, rPT membrane damage persisted and was only partially reversed by CCB. The rPT injury induced by 20 min of O2 deprivation, thus, involves factors independent of voltage-sensitive Ca++ channels.
Animals↗
Evaluation of a closed perfusion chamber for single cell fluorescence measurements.
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Cytological Techniques↗