Biomedical subjects

H J Kramer

Publications and source records attributed to H J Kramer.

At least 19 recordsLinked to original sources

PubMed1998

Evaluation of the uncertainty factor for subchronic-to-chronic extrapolation: statistical analysis of toxicity data.

For the extrapolation of a subchronic no-observed-adverse-effect level (NOAEL) to a chronic NOAEL an uncertainty factor of 10 is routinely applied. We evaluated this uncertainty factor by statistically analyzing a database comprising 149 oral NOAEL(subchronic)/NOAEL(chronic) ratios. Since any database forms only a limited sample of all existent chemicals, we believe that estimation errors should be taken into account. Therefore, in addition to the 95th percentile (P95) of the ratio distribution, we calculated the 95% confidence interval (CI) of this percentile. The geometric mean (GM), geometric standard deviation (GSD), P95, and CI were 1.7, 5.6, 29, and 20-46, respectively. These data do not support a lowering of the uncertainty factor as has been suggested by others. Furthermore, we analyzed the LOAEL/NOAEL ratio for subacute, subchronic, and chronic toxicity studies. However, the size of the LOAEL/NOAEL ratio only depends on the spacing between doses of the studies reviewed. Therefore, though the results may be considered supportive for an uncertainty factor of 10, we believe that there is no justification for the use of such a factor. Instead, we recommend the use of dose-response modeling which would make LOAEL-to-NOAEL extrapolation redundant.

Administration, Oral↗

PubMed1998

Effects of urinary ouabain-like factors and vanadium diascorbate on calcium mobilization in porcine inner medullary collecting duct cells: comparison with the effects of ouabain and vasopressin.

It is speculated that ouabain-like factors (OLF) play a role in the pathogenesis of volume-dependent hypertension. In previous studies we isolated a more polar OLF-1 and a more apolar OLF-2 from the urine of healthy subjects after 5 days on a high sodium intake (>400 mmol/day) by gel chromatography (Sephadex G-25 and G-10) and reverse-phase HPLC. We subsequently identified the chemical structure of OLF-2 as vanadium (V(IV)) diascorbate. OLF-1, OLF-2, and vanadium diascorbate inhibited dose-dependently porcine Na-K-ATPase in vitro. Because the inner medullary collecting duct (IMCD) plays a crucial role in the long-term regulation of body fluid volume, in the present study we investigated the effects of urinary OLF-1 and OLF-2, and of vanadium diascorbate in comparison to ouabain and vasopressin (AVP) on calcium mobilization, ie, on free calcium concentration [Ca2+]i, in cultured porcine IMCD cells. [Ca2+]i was determined by the fura-2 method in IMCD cells isolated by hypotonic treatment and density gradient centrifugation from fresh porcine kidneys. Assuming an approximate molecular weight (MW) of 400 for OLF-1 and OLF-2, OLF-1 (10(-4) mol/L) produced a slow increase in [Ca2+]i from 39 +/- 10 to 169 +/- 21 nmol/L (n = 7 ) after 4 min. Similarly, OLF-2 (10(-4) mol/L) resulted in an increase in [Ca2+]i from 74 +/- 20 to 216 +/- 52 nmol/L (n = 7) after 4 min. Vanadium diascorbate (MW 403) dose-dependently increased [Ca2+]i . At a concentration of 10(-6) mol/L it increased [Ca2+]i from 46 +/- 5 to 149 +/- 9 nmol/L (n = 5) after 4 min. A similar slow increase in [Ca2+]i was found with ouabain (10(-6) mol/L), which increased [Ca2+]i from 61 +/- 22 to 180 +/- 29 nmol/L (n = 5) after 4 min in contrast to AVP (10(-7) mol/L), which rapidly increased [Ca2+]i from 48 +/- 10 to 299 +/- 32 nmol/L (n = 4) within 30 sec. Thus, OLF-1, OLF-2, and Vanadium diascorbate, the active component of OLF-2, reveal similar effects as ouabain on IMCD cells, ie, they produce a slow increase in [Ca2+]i as expected from inhibition of Na-K-ATPase. The physiologic or pathologic roles of these and additional OLF in body fluid and blood pressure regulation and in hypertension have yet to be evaluated.

Adult↗

PubMed1998

Regulation of mitogen-activated protein kinase phosphatase-1 in vascular smooth muscle cells.

Mitogen-activated protein (MAP) kinase cascades are major signaling systems by which cells transduce extracellular cues into intracellular responses. In general, MAP kinases are activated by phosphorylation on tyrosine and threonine residues and inactivated by dephosphorylation. Therefore, MAP kinase phosphatase-1 (MKP-1), a dual-specificity protein tyrosine phosphatase that exhibits catalytic activity toward both regulatory sites on MAP kinases, is suggested to be responsible for the downregulation of extracellular signal-regulated kinase (ERK), stress-activated protein kinase (SAPK), and p38 MAP kinase. In the present study, we examined the role of these MAP kinases in the induction of MKP-1 in vascular smooth muscle cells (VSMCs). Extracellular stimuli such as platelet-derived growth factor (PDGF), 12-O-tetradecanoylphorbol 13-acetate (TPA), and angiotensin II, which activated ERK but not SAPK/p38 MAP kinase, induced a transient induction of MKP-1 mRNA and its intracellular protein. In addition, PD 098059, an antagonist of MEK (MAP kinase/ERK kinase), the upstream kinase of ERK, significantly reduced the PDGF-induced activation of ERK and potently inhibited the expression of MKP-1 after stimulation with PDGF, thereby demonstrating the induction of MKP-1 in response to activation of the ERK signaling cascade. Furthermore, anisomycin, a potent stimulus of SAPK and p38 MAP kinase, also induced MKP-1 mRNA expression. This effect of anisomycin was significantly inhibited in the presence of the p38 MAP kinase antagonist SB 203580. These data suggest the induction of MKP-1, not only after stimulation of the cell growth promoting ERK pathway but also in response to activation of stress-responsive MAP kinase signaling cascades. We suggest that this pattern of MKP-1 induction may be a negative feedback mechanism in the control of MAP kinase activity in VSMCs.

Animals↗

PubMed1997

Effects of erythropoietin on endothelin-1 synthesis and the cellular calcium messenger system in vascular endothelial cells.

A rise in blood pressure is the main side effect of erythropoietin (EPO) treatment in patients with renal anemia. The mechanisms, however, by which EPO may cause hypertension are still unclear. We therefore investigated the effects of EPO on endothelin (ET) synthesis and cytosolic free calcium concentration ([Ca2+]i) in vascular endothelial cells. Porcine endothelial cells were isolated from thoracic aorta, pulmonary artery, and vena cava. Studies were performed with cells of the first subculture. ET concentrations were measured radioimmunologically. Changes in [Ca2+]i were determined with the fluorescent probe fura-2. Cytotoxicity was assessed by sodium 3'-[1-(phenyl-amino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)ben zene sulfonic acid hydrate (XTT) assay. ET synthesis was similar in cells of different vascular origins and was time-dependent, reaching approximately 2 pmol ET/mg protein within 12 h of incubation. EPO (12 to 200 U/mL) stimulated ET release time- and dose-dependently by up to 83.2% (P < .01) within 12 h in the absence of fetal calf serum and heparin. EPO induced an immediate significant rise in [Ca2+]i from 58 +/- 12 nmol/L to 495 +/- 85 nmol/L (P < .01) with a subsequent slow return to 257 +/- 3 nmol/L. During 2 h of incubation, the Ca-ionophore A 23187 (10(-8) mol/L) moderately but significantly stimulated endothelial ET synthesis. However, the Ca-channel blocker verapamil, the intracellular Ca-release blocker TMB-8, and nickel, an unspecific calcium channel blocker, had no consistent effects on [Ca2+]i or ET synthesis. The protein kinase C inhibitor H-7 stimulated basal [Ca2+]i and cellular ET synthesis. The tyrosine kinase inhibitor genistein suppressed the EPO-induced rise in [Ca2+]i and cellular ET synthesis. From these data we conclude that EPO may stimulate ET synthesis in vascular endothelial cells by activation of an EPO-receptor and via intracellular signalling mechanisms that comprise tyrosine kinase activation and a rise in [Ca2+]i. Therefore, the systemic hypertensive effects of EPO may be due at least in part to local stimulation of vascular endothelial ET synthesis via calcium mobilization.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1997

Renal endothelin system in obstructive jaundice: its role in impaired renal function of bile-duct ligated rats.

1. Obstructive jaundice predisposes the kidney to acute renal failure. Endothelin (ET), a potent renal vasoconstrictor and modulator of the tubular action of arginine vasopressin, has been suggested to play a pathogenetic role in acute renal failure. In the present study we therefore investigated renal function and the renal ET system in rats on day 4 after bile-duct ligation (BDL) or sham-operation (SO), without (n = 7 in each group) and with treatment with bosentan, a combined ETA/ETB receptor blocker, (n = 5 in each group). 2. On day 4 after BDL, serum bilirubin had increased to 226 +/- 10 mumol/l (SEM) as compared with 6 +/- 2 mumol/l in SO rats. Endogenous creatinine clearance, an index of glomerular filtration rate, was significantly reduced to 0.7 +/0 0.1 ml min-1 g-1 of kidney weight after BDL as compared with 1.1 +/- 0.1 ml min-1 g-1 of kidney weight after SO (P < 0.05). Bosentan prevented the decrease in glomerular filtration rate (1.0 +/- 0.2 ml min-1 g-1 of kidney weight), as well as polyuria and defective concentrating ability, in BDL rats. 3. Plasma ET concentration on day 4 after surgery (28.2 +/- 1.5 pmol/l) was higher (P < 0.01) in BDL than in SO rats (12.9 +/- 1.5 pmol/l) and rose further in bosentan-treated BDL and SO rats (43.4 +/- 5.1 compared with 21.9 +/- 6.6 pmol/l). Urinary ET excretion was significantly higher in BDL rats than in SO rats (1.58 +/- 0.22 compared with 1.28 +/- 0.18 pmol 24 h-1 100 g-1 of body weight; P < 0.05). 4. ET synthesis by glomeruli isolated from BDL rats was lower [81 +/- 19 fmol h-1 (mg of protein)-1] than that from SO-rats [139 +/- 28 fmol h-1 (mg of protein)-1; P < 0.05], whereas papillary ET synthesis was higher in BDL [10 +/- 3 fmol h-1 (mg of protein)-1] than in SO rats [4 +/- 1 fmol h-1 (mg of protein)-1; P < 0.05]. 5. The results indicate that BDL is associated with increased plasma ET concentration and suppression of GFR. Enhanced renal inner medullary collecting-duct ET synthesis, which is reflected by increased urinary ET excretion, may reduce distal tubular water absorption in BDL rats. Increased circulating and renal papillary ET synthesis may thus contribute to renal dysfunction and predispose the kidney to acute renal failure in obstructive jaundice.

Acute Kidney Injury↗

PubMed1997

Comparative effects of the angiotensin II receptor blocker EXP 3174 and of the angiotensin-converting enzyme inhibitor captopril on renal glomerular hemodynamics in the dog.

The effects on glomerular hemodynamics of angiotensin-converting enzyme (ACE) inhibition with captopril and of angiotensin II receptor blockade with EXP 3174, an active metabolite of losartan, either alone or in combination, were compared in anesthetized dogs. Administration of EXP 3174 intrarenally led to an increase in renal blood flow by +14% and in glomerular filtration rate by +7%, thus decreasing the filtration fraction by -5%. Similar changes were observed at the single-nephron level. Water, sodium, potassium, and urea excretion rates rose considerably. A decrease in effective filtration pressure by -27% and an increase in ultrafiltration coefficient, Kf, by +57% were seen. A drop in total arteriolar resistance by -19% was mainly due to a decrease in efferent (-25%) rather than afferent (-14%) resistance. When captopril, an ACE inhibitor, was administered intravenously after and during EXP 3174, an additional increase in renal blood flow, by +8%, with no change in glomerular filtration rate was seen which led to an additional decrease in filtration fraction by -5%; additional increases were observed in water and urea but not in sodium and potassium excretion rates. An additional decrease in total arteriolar resistance, by -14%, was now evenly distributed between the efferent (-6%) and afferent (-8%) arterioles. Almost all of these additional changes disappeared when a bradykinin B2-antagonist, Hoe 140, was infused together with captopril. In conclusion, administration of an ACE inhibitor led to a significantly enhanced vasodilatory response in the kidney as compared with the administration of an angiotensin II-receptor blocker. This enhancement was almost eliminated by the coadministration of Hoe 140, thus rendering the participation of kinins fairly plausible.

Adrenergic beta-Antagonists↗

PubMed1997

Impaired renal function in obstructive jaundice: roles of the thromboxane and endothelin systems.

Patients with intra- or extrahepatic bile-duct obstruction are susceptible to acute renal failure (ARF) especially when undergoing major surgery. We observed in jaundiced rats 4 days after bile-duct ligation (BDL) a decrease in GFR accompanied by polyuria which is associated with increased urinary thromboxane (TX) excretion and glomerular TXB2 synthesis. The TXA2/ PGH2 receptor antagonist daltroban normalized GFR but not urine concentration. There was also a rise in plasma and urinary endothelin (ET-1) with increased papillary ET synthesis. The ETA/ETB receptor blocker bosentan restored GFR and the renal concentrating ability. Since we showed previously that ET-induced decreases in renal perfusion and ultrafiltration coefficient Kf are mediated by other autacoids such as TX, this may explain why both bosentan and daltroban normalized GFR. These results suggest that increased renal glomerular TX and vascular and inner medullary collecting duct ET synthesis contribute to defective GFR and distal tubular function in experimental BDL. Similar alterations may also predispose the human kidney to ARF in patients with obstructive jaundice.

Animals↗

PubMed1997

Cellular mechanisms of cyclosporine A-associated side-effects: role of endothelin.

Immunosuppressive therapy with cyclosporine A (CsA) may be associated with severe side-effects such as nephrotoxicity and arterial hypertension. The partial reversability of these effects suggests that they are at least in part functional. We examined the effects of CsA on cellular signaling in cultured vascular smooth muscle cells from rat aorta. Intracellular free calcium concentrations ([Ca2+]i) were measured using fura-2. Total cell calcium was measured by atomic absorption and cellular endothelin production was estimated by radioimmunoassay. In the presence of CsA the calcium mobilizing effect of angiotensin (Ang) II was significantly enhanced. While the ETA receptor antagonist BQ 123 did not affect Ang II-induced calcium mobilization, the potentiating effect of CsA on [Ca2+]i was blocked by BQ 123. Preincubation of the cells with cyclosporine (10 micrograms/ml) for 30 minutes increased total cell calcium from 2.6 +/- 0.5 to 6.9 +/- 0.3 nmol/mg protein (P < 0.01). Within 24 hours endothelin production was significantly enhanced in the presence of cyclosporine (52.2 +/- 2.5 vs. 65.9 +/- 2.7 fmol/mg protein, P < 0.05). Therefore, the cyclosporine-induced rise of total cell calcium in smooth muscle cells is associated with an enhanced production of endothelin. We speculate that cyclosporine induced changes of Ca(2+)-kinetics may be mediated by endothelin. These results indicate that endothelin may play a major role in cyclosporine-associated side-effects.

Animals↗

PubMed1996

Conversion factors estimating indicative chronic no-observed-adverse-effect levels from short-term toxicity data.

Data on chronic toxicity are generally required to derive a health-based acceptable exposure limit, such as the acceptable daily intake. However, only acute and/or subacute toxicity data are available for many compounds. In this study, we assessed conversion factors (CFs) to estimate a chronic no-observed-adverse-effect-level (NOAELchronic) from these short-term toxicity data. We evaluated distributions of ratios between (sub)acute and chronic toxicity data for 332 compounds. By defining the CF as the upper 95% confidence limit of the 95th percentile for the relevant ratio distribution, both the variation between compounds (95th percentile) and the estimation error (upper 95% confidence limit) could be taken into account. Dividing a NOAELsubacute or LD50 by the corresponding CF results in a conservative estimate of the chronic NOAEL. We assessed a CF of 87 for a NOAELsubacute and a CF of 1.7 x 10(4) for an LD50. We found the NOAELsubacute to be a better predictor of the NOAELchronic than the LD50. Moreover, the added value of an LD50 in estimating a NOAELchronic appeared to be limited when a NOAELsubacute was available.

Animals↗

PubMed1996

Action of endothelin-1 on glomerular haemodynamics in the dog: lack of direct effects on glomerular ultrafiltration coefficient.

1. Although numerous studies have demonstrated the potent vasoconstrictor effect of endothelin-1 on the renal vasculature, it is difficult to differentiate in vivo between indirect and direct actions of endothelin. 2. In the present study we therefore performed micropuncture experiments in 14 anaesthetized dogs after the administration of endothelin-1 into the renal artery (i.r.a.) for 15 min at a dose of 2.78 ng min-1 kg-1 which did not affect blood pressure or contralateral kidney function. 3. In seven dogs on a 'normal' sodium diet (3.5 mmol of NaCl day-1 kg-1) endothelin-1 resulted in decreases in renal blood flow and glomerular filtration rate with a rise in filtration fraction from 0.24 +/- 0.01 to 0.35 +/- 0.01. Similar changes were seen at the single-nephron level. An increase from 0.11 +/- 0.01 to 0.23 +/- 0.02 (+109 +/- 11%) in efferent, and from 0.15 +/- 0.01 to 0.24 +/- 0.02 mmHg min-1 microliter-1 (+58 +/- 4%) in afferent arteriolar resistance was observed. The ultrafiltration coefficient, Kf, decreased from 4.75 +/- 0.14 to 3.67 +/- 0.14 microliter min-1 mmHg-1 (P < 0.01). 4. In another group of seven dogs, the same endothelin-1 infusion was given after an administration into the renal artery of a 'cocktail' designed to block the receptors of alpha- and beta-adrenergic agonists, thromboxane A2, leukotrienes and angiotensin II together with intravenous cyclo-oxygenase inhibition. Under these conditions, the vasoconstrictor action of endothelin-1 was reduced by more than 30%. The increase in vascular resistance was now relatively similar in both arterioles, i.e. +44 +/- 5% in the afferent and 66 +/- 6% in the efferent arterioles (no significant difference). No change in Kf was seen after the 'cocktail'-blockade (9.4 +/- 0.4 versus 10.1 +/- 0.1 microliter min-1 mmHg-1). 5. In conclusion, in anaesthetized dogs on a 'normal' salt diet, the vasoconstrictor effect of endothelin-1 is more pronounced on the efferent than on the afferent arteriole. This is accompanied by decreases in glomerular filtration rate and water, urea and electrolyte excretion. Part of the vasoconstrictor action of endothelin seems to be mediated by other autacoids. Endothelin-1 itself contributes only partly to pre- and post-glomerular vasoconstriction and has no direct effect on the glomerular ultrafiltration coefficient Kf.

Adrenergic alpha-Antagonists↗

PubMed1996

Calcium entry and 5-HT2 receptor blockade in oliguric ischaemic acute renal failure: effects of levemopamil in conscious rats.

1. Unilateral left renal artery occlusion for 1 h in a group of 8 untreated female Sprague-Dawley rats resulted in oliguric acute renal failure (ARF) persisting for more than 6 h after reflow, i.e. after reperfusion of the kidney by removal of the arterial clamp. In a second group of 8 rats with left unilateral ARF the effects of levemopamil (L), a calcium entry blocker with 5-hydroxytryptamine2 (5-HT2) receptor antagonistic properties, were studied. Rats received L as a continuous infusion (6 mg kg-1 h-1) from 1 h before ischaemia until 6 h after reflow. 2. Endogenous creatinine clearance, an estimate of glomerular filtration rate (GFR), of left ischaemic kidneys of untreated rats was almost completely abolished and urine flow was 0.05 +/- 0.02 and 0.03 +/- 0.01 ml h-1 100 g-1 body weight (body wt.) at 2 and at 6 h of reflow, respectively. In contrast, left ischaemic kidneys of L-treated rats revealed significantly higher GFR (0.10 +/- 0.02 and 0.03 +/- 0.01 ml min-1 g-1 kidney weight (k.wt.); P < 0.01) and urine flow (0.51 +/- 0.05 and 0.15 +/- 0.04 ml h-1 100 g-1 body wt.; P < 0.05) at 2 and 6 h of reflow, respectively. 3. At 6 h of reflow, mitochondria from the cortex of left ischaemic kidneys of untreated rats showed significantly reduced ATP synthesis when compared to right intact kidneys (0.06 +/- 0.02 vs 0.26 +/- 0.02 mumol ATP mg-1 protein min-1 (P < 0.01)). In contrast, in L-treated rats, ATP synthesis of left ischaemic kidneys was largely preserved (0.17 +/- 0.01 mumol ATP mg-1 protein min-1). 4. Ischaemia of left kidneys resulted in a significant decrease in medullary Na-K-ATPase activity to 9.6 +/- 2.4 as compared to 20.4 +/- 3.7 mumol P(i) h-1 mg-1 protein in the intact right kidneys which was not prevented by L (9.4 +/- 2.4 mumol P(i) h-1 mg-1 protein). 5. In untreated rats the calcium content in cortical mitochondria from left ischaemic kidneys had risen 2 fold to 23.0 +/- 1.8 at 6 h of reflow as compared to 12.2 +/- 0.3 nmol mg-1 protein in right intact kidneys (P < 0.01). This rise in mitochondrial calcium was not significantly attenuated by treatment with L (19.9 +/- 1.7 nmol mg-1 protein). 6. The results show that L transiently converted oliguria into non-oliguria during the early phase after reflow in ischaemic ARF, i.e. after reperfusion following 1 h of complete interruption of renal perfusion. The present data suggest indirectly that the 5-HT2-antagonistic properties of L rather than its calcium channel blocking action maintains GFR at low level and protects mitochondrial function early after reflow in this model of ischaemic ARF.

Acute Kidney Injury↗

PubMed1996

Losartan protects the rat kidney from ischemic injury.

Administration of losartan (L), an angiotensin II receptor antagonist, at a daily dose of 3 mg/kg body wt, lowered systolic blood pressure (SBP) in both the Prague hypertensive rat and the Prague normotensive rat (PNR). Proteinuria was markedly reduced in both strains by L. Seven days after kidney ischemia due to bilateral clamping of both renal arteries for 45 minutes, the renal function (endogenous creatinine clearance, sodium, potassium, and urea excretion rates) was completely normal in L-treated PHR and PNR, whereas distinct deterioration was observed in untreated animals. The survival rate after kidney ischemia was significantly improved by L in both PHR and PNR. Thus, L had a significant blood pressure-lowering action in both strains and exerted a distinct renal protective effect from kidney ischemia.

Animals↗

PubMed1995

Vanadium-diascorbates are strong candidates for endogenous ouabain-like factors in human urine: effects on Na-K-ATPase enzyme kinetics.

Recently, we isolated from the urine of salt-loaded healthy subjects a more polar ouabain-like factor OLF-1 and a more apolar OLF-2, the latter cross-reacted with a digoxin anti-body. They were purified to single compounds with dose-dependent Na-K-ATPase inhibition. Mass-spectroscopy (MS) showed a Mr of around 400 and 1H-NMR- and IR-spectroscopy suggested diascorbic acid salts, i.e., vanadium (V) diascorbates (Mr 403) with similar elution times from RP-HPLC as OLFs. IC50 was 9 x 10(-5)M for VIV-diascorbate as compared to 2 x 10(-6)M for Vv-diascorbate. Enzyme inhibition was non-competitive with respect to sodium and Mg-ATP; p-NPPase assay showed strong inhibition in its E2-configuration. We suggest that V-diascorbates represent endogenous OLFs excreted in human urine.

4-Nitrophenylphosphatase↗

PubMed1995

The exercise-induced increase in plasma levels of endothelin-1 is enhanced in patients with atherosclerotic coronary artery disease. Modulation by pentaerithrityltetranitrat (PETN).

BACKGROUND AND OBJECTIVE: Previous studies have suggested that endothelin (ET)-1 with its marked vasoconstrictive potency may play a role in the induction of coronary artery spasms. Furthermore, it was demonstrated using in-vitro vessel preparations that the secretion of ET-1 by the vascular endothelium is enhanced in the presence of atherosclerotic alterations. The objective of the present study was to investigate a) the effects of ergometric exercise on ET-1 plasma concentrations in 10 patients with coronary artery disease (CAD) as compared to an age and sex matched control group and b) the modulatory role of the orally administered organic nitrate, pentaerithrityltetranitrat (PETN), in patients with CAD. PATIENTS AND METHODS: 10 male patients with CAD confirmed by coronarography and 10 male healthy controls underwent a bicycle ergometry according to the WHO-standards upt to 125 watts. Venous blood samples for determination of ANP and ET-1 plasma concentrations were drawn in supine position directly before and 5 min after ergometric exercise. Subsequently, patients were randomized and treated for 3 days in a crossover design either with placebo or PETN (150 mg b.i.d.). RESULTS: Basal plasma levels of ET-1 were 6.1 +/- 0.7 pg/ml (patients) and 5.5 +/- 0.6 pg/ml (controls), resp. (n.s.). After ergometric exercise ET-1 plasma concentrations rose significantly (7.3 +/- 0.9 pg/ml; p < 0.05) in the placebo-treated patient group, whereas they remained constant (5.5 +/- 0.7 pg/ml) in the PETN-treated patient group. Blood pressure and heart rate were not modified by the PETN-treatment. ET-1 plasma levels remained unaffected by ergometric exercise in controls. DISCUSSION: In contrast to healthy controls ergometric exercise induced an increase in ET-1 plasma concentrations in patients with CAD that may be potentially harmful by promoting coronary vasospasms. The almost complete blunting of the ET-1-increase in the presence of PETN-therapy may result from local-hemodynamic effects of the organic nitrate; it may be hypothesized that the nitrate-induced rise in local NO-concentrations counteracts ET-secretion. The findings of the present study are in accordance with the beneficial clinical effects of organic nitrates in patients with CAD.

Administration, Oral↗

PubMed1995

Endothelin synthesis by porcine inner medullary collecting duct cells. Effects of hormonal and osmotic stimuli.

Previously, we have shown in porcine inner medullary collecting duct (IMCD) cells that endothelin (ET), probably in an autocrine fashion, suppresses arginine vasopressin (AVP)-induced synthesis of cAMP and thereby, may modify the action of AVP on IMCD fluid transport. In the present study we investigated the effects of various stimuli including extracellular tonicity on ET synthesis in porcine IMCD cells in culture. IMCD cells produced ET in a saturationlike time-dependent manner over a period of 24 h. Neither AVP (10(-7) mol/L), bradykinin (10(-7) mol/L), nor atrial natriuretic peptide (10(-7) mol/L) affected basal ET synthesis of IMCD cells at extracellular isotonicity (323 mOsm/kg H2O). The calcium ionophore A23187 (10(-7) mol/L) increased ET production by 38% within 2 h (P < .05). Preincubation for 48 h with increased osmolality in the incubation media from 323 to 600 mOsm/kg H2O by raising the concentrations of 1) NaCl (n = 6), 2) urea (n = 6), or 3) NaCl+urea (n = 6) increased ET synthesis from a control value of 225 +/- 25 pg/mg cell protein/2 h in isotonic medium to 1) 555 +/- 13 pg/mg cell protein/2 h (P < .01), 2) 354 +/- 18 pg/mg cell protein/2 h (P < .05), and 3) 448 +/- 22 pg/mg cell protein/2 h (P < .05), respectively, in hypertonic media. These data suggest that increases in papillary osmolality are associated with enhanced ET synthesis possibly involving a calcium-dependent process and attenuating AVP-dependent fluid absorption in a short-loop feedback fashion.

Animals↗

PubMed1995

Endogenous sodium pump inhibitors in human urine. Further identification of inhibitors of Na-K-ATPase.

We investigated the presence of endogenous Na-K-ATPase inhibitor(s), ie, ouabain-like factors (OLFs), in the urine of salt-loaded healthy subjects. For this purpose 24-h urine was collected on days 3, 4, and 5 of high sodium intake (> 30 g NaCl/day). The samples then were lyophilized. Redissolved urine concentrates were acidified (pH 3.5) and subjected to gelchromatography on a Sephadex G-25 column where the OLFs eluted in the post-salt fraction IV. When lyophilized fraction IV was rechromatographed on Sephadex G-10, OLFs with molecular mass (M(r) of approximately 400 eluted in a late fraction IV/8 separate from added ouabain, ouabagenin (or digoxin), which eluted shortly after void volume. With the subsequent reverse-phase HPLC of fraction IV/8 a polar OLF-1 eluted in fraction IV/8a after the void volume in the water phase and a more apolar OLF-2 eluted at 20% acetonitrile in fraction IV/8d. Only the more apolar OLF-2 cross-reacted with a digoxin antibody. By preparative thin-layer chromatography OLF-1 and OLF-2 were purified as single compounds with potent dose-dependent Na-K-ATPase inhibition and Ki-values approximating 1.5 x 10(-5) mol/L and 1.5 x 10(-4) mol/L, respectively. Mass-spectroscopy (MS) showed M(r) of 391 and 1H-NMR characterized the endogenous urinary apolar OLF-2 as a compound that is structurally totally unrelated to ouabain; infrared (IR) spectroscopy of OLF-1 and OLF-2 also revealed no similarity with ouabain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Impaired renal function in obstructive jaundice: enhanced glomerular thromboxane synthesis and effects of thromboxane receptor blockade in bile duct-ligated rats.

1. Patients with obstructive jaundice are especially susceptible to acute renal failure. We have previously observed that in rats with bile duct ligation impaired renal function is associated with increased urinary thromboxane excretion. 2. In the present study we therefore investigated, in rats with bile duct ligation, renal function, urinary thromboxane excretion and thromboxane B2 synthesis by isolated glomeruli as well as the effects of the thromboxane A2/prostaglandin H2 receptor antagonist Daltroban on renal function in rats with bile duct ligation as compared with sham-operated rats. 3. On the fourth day after bile duct ligation (n = 7 rats) endogenous creatinine clearance as an estimate of glomerular filtration rate was significantly reduced to 0.74 +/- 0.05 (SEM) as compared with 1.06 +/- 0.09 ml min-1 g-1 kidney weight in sham-operated rats (n = 7, P < 0.01). In rats with bile duct ligation, urine volume was slightly increased, whereas urinary sodium (Na+) (P < 0.001) and potassium (K+) (P < 0.01) excretion as well as urine osmolarity (P < 0.05) were significantly reduced and lower than in sham-operated rats. 4. Urinary thromboxane excretion was significantly higher in rats with bile duct ligation than in sham-operated rats: 116.6 +/- 22.3 versus 56.8 +/- 10.2 pmol 24 h-1 100 g-1 body weight (P < 0.05). Thromboxane B2 synthesis in glomeruli isolated from rats with bile duct ligation was also significantly higher than in sham-operated rats: 12.6 +/- 2.0 versus 6.4 +/- 0.9 pmol h-1 mg-1 protein (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗

PubMed1995

Differential influence of arachidonic vs. eicosapentaenoic acid on experimental pulmonary hypertension.

The impact of the 2- and 3-series prostanoid precursors arachidonic acid (AA) and eicosapentaenoic acid (EPA) on experimental pulmonary hypertension was investigated. The model of buffer-perfused rabbit lungs was stimulated by infusion of Escherichia coli hemolysin (HlyA), which is known to provoke sustained thromboxane (Tx)-mediated pulmonary hypertension. Release of di- and trienoic Tx into the recirculating perfusate was quantified by a post-high-performance liquid chromatography enzyme-linked immunosorbent assay technique. HlyA at 0.08 hemolytic unit/ml caused a sustained rise in pulmonary arterial pressure (PAP; maximum increase 14 +/- 2 mmHg) accompanied by progressive TxB2 liberation (maximum perfusate concn 33 +/- 4 pg/ml, baseline < 2 pg/ml). Between 5 and 30 nM, AA provoked a transient monophasic rise in PAP (maximum pressor response 1.5-15 mmHg) and concomitant TxB2 release (peak concn 2-30 pg/ml). Simultaneous administration of HlyA and AA exhibited additive effects with regard to mediator release and pressor responses. EPA at 200-2,000 nM caused a transient rise in PAP similar to that provoked by 5-30 nM AA (maximum pressor response 3-18 mmHg). This was accompanied by liberation of TxB2 (peak concn 16 +/- 5 and 28 +/- 4 pg/ml after 1,000 and 2,000 nM EPA) and TxB3 (peak concn 9 +/- 4 and 30 +/- 3 pg/ml). Combined application of HlyA and EPA resulted in approximate addition of the TxB2 release reaction to each single compound, and TxB3 liberation more than doubled (maximum concn 59 +/- 12 pg/ml). The pressor responses to HlyA-EPA (200-2,000 nM) did not, however, surpass those to HlyA-AA (5-30 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

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