Biomedical subjects

A Benigni

Publications and source records attributed to A Benigni.

At least 73 records · Page 4Linked to original sources

PubMed1993

Reversible activation defect of the platelet glycoprotein IIb-IIIa complex in patients with uremia.

Patients with chronic renal failure may experience a bleeding tendency and blood loss after surgical procedures or trauma. Altered platelet function has been indicated as the major cause of uremic bleeding, but its pathogenesis remains to be clarified. In two groups of patients with chronic renal disease of various etiology, the receptor function of glycoprotein (GP) Ib and GP IIb-IIIa complex was studied. Glycoprotein Ib was assessed with both 125I-von Willebrand factor (vWF) and 125I-asialo-vWF binding to platelets. Activation-dependent receptor function of the GP IIb-IIIa complex was studied with 125I-fibrinogen and 125I-vWF binding to washed platelets stimulated with adenosine diphosphate plus epinephrine (10 mumol/L each). Flow cytometric analyses on resting and stimulated platelets were performed using an activation-dependent, anti-GP IIb-IIIa monoclonal antibody (PAC1) as well as an activation-independent antibody (LJ-P1). Binding of PAC1 also was assessed in washed and stimulated platelets and in platelet-rich plasma before and after dialysis. We found that the activation-dependent receptor function of the GP IIb-IIIa complex is defective in uremia, as shown by decreased binding of both vWF and fibrinogen to stimulated platelets. Moreover, binding of the activation-dependent anti-GP IIb-IIIa monoclonal antibody, PAC1, was significantly decreased in uremia compared with that of the activation-independent antibody, LJ-P1. Thus, the number of GP IIb-IIIa receptors expressed on the platelet membrane is normal, but their activation is impaired. In contrast to the functional abnormality of GP IIb-IIIa, the vWF-binding activity of GP Ib was normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Calcium channel blockers protect transplant patients from cyclosporine-induced daily renal hypoperfusion.

Renal toxicity, possibly due to vasoconstriction and vascular injury, is the most relevant side-effect of chronic cyclosporine (CsA) therapy given to prevent graft rejection. In kidney transplant recipients each oral dose of CsA is invariably followed by a transient reduction in renal plasma flow (RPF) and glomerular filtration rate (GFR) that results from a form of acute reversible hypoperfusion. We sought to determine whether the Ca2+ channel blocker, lacidipine, prevented CsA-associated renal hypoperfusion in these patients. Parallel studies on CsA pharmacokinetics, renal function parameters (GFR and RPF), as inulin and p-aminohippurate (PAH) clearances, respectively, and urinary excretion of the vasoconstrictor endothelin in 10 consecutive renal transplant patients given CsA as a part of their immunosuppressive therapy were performed. Patients were studied at different time intervals after CsA alone, CsA and lacidipine (4 mg/day), and again seven days after lacidipine withdrawal. In all patients basal RPF and GFR declined on average 51% (139.3 +/- 20.7 ml/min/1.73 m2) and 50% (32.5 +/- 5.8 ml/min/1.73 m2), respectively, two to four hours after maximum blood CsA concentration was reached. As blood levels of CsA returned to trough, both parameters progressively increased to baseline. Lacidipine administration completely prevented the fall in RPF (pre-CsA: 277.1 +/- 23.6; 6 hr post-CsA: 304.5 +/- 31.1 ml/min/1.73 m2) and GFR (pre-CsA: 66.6 +/- 8.1; 6 hr post-CsA: 70.1 +/- 9.8 ml/min/1.73 m2). When lacidipine treatment was discontinued the abnormal RPF and GFR response to CsA administration was again observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

A specific endothelin subtype A receptor antagonist protects against injury in renal disease progression.

We have recently reported that renal preproendothelin-1 gene is up-regulated in rats with renal mass reduction (RMR) and that time-dependent increase in urinary excretion of the corresponding peptide correlates with renal disease progression. Here we evaluated whether a specific endothelin subtype A (ETA) receptor antagonist, FR139317, reduced signs of disease activity in this model. Two groups of rats were given FR139317 or its vehicle (saline) from day 7 to day 60 after the surgical procedure. Sham-operated animals were the control group. Blood pressure, urinary protein excretion and serum creatinine were evaluated at days 0, 7 (before FR139317 or saline administration), 30, 45 and 60. At sacrifice, histological evaluation of renal tissue was performed. The results showed that ETA receptor blocker reduced the abnormal permeability to proteins, limited glomerular injury and prevented renal function deterioration thus confirming the working hypothesis. These findings suggest that this class of compounds may eventually prove useful in the treatment of human progressive nephropathies.

Animals↗

PubMed1993

Enhanced nitric oxide synthesis in uremia: implications for platelet dysfunction and dialysis hypotension.

Nitric oxide (NO), a potent vasodilator which also inhibits platelet adhesion and aggregation, is generated by endothelial cells and platelets from its precursor L-arginine. Since N-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis, normalizes the prolonged bleeding time of uremic rats, it has been suggested that bleeding associated with uremia was due to an excessive NO formation. With the present study we sought to evaluate whether in patients with chronic renal failure--like in uremic rats--defective platelet aggregation were associated with excessive formation of NO and whether uremic plasma promotes NO synthesis by cultured vascular endothelium. Data indicated that plasma L-arginine was higher in uremics than in controls, uremic platelets generated more NO than control platelets, and intraplatelet levels of cGMP (the NO second messenger) were also higher in uremic than in control platelets. Moreover, uremic plasma potently induced NO synthesis by cultured endothelial cells, a phenomenon which was further amplified by adding to uremic plasma endotoxin and interferon gamma. Increased NO biosynthesis may contribute to platelet dysfunction and possibly other manifestations of uremic syndrome, including hemodialysis hypotension.

Adult↗

PubMed1993

Renal endothelin gene expression is increased in remnant kidney and correlates with disease progression.

We previously demonstrated that urinary endothelin excretion is increased in rats with extensive renal mass reduction, a model of progressive renal disease. Here we explored whether the increased urinary endothelin in this model were due to induction of renal pre-pro-endothelin-1 gene and whether changes in endothelin synthetic pathway correlated with the development of glomerulosclerosis. Four groups of rats with renal mass reduction and four groups of sham-operated control rats were studied 7, 30, 60 and 120 days after the surgical procedure. Urinary protein excretion in renal mass ablation animals did not differ from controls at seven days, but was already significantly elevated (P < 0.01) 30 days after surgery. Then proteinuria progressively increased in rats with remnant kidney at values above 400 mg/day at day 120. Serum creatinine concentration also progressively increased with time in renal mass ablation rats, unlike sham-operated animals, and values were significantly different (P < 0.01) at each of the points considered. Rats with renal mass reduction, unlike sham-operated animals, developed focal glomerulosclerosis that affected 8% of glomeruli at day 30, and 24% of glomeruli at day 120. Seven days after renal mass reduction renal pre-pro-endothelin-1 (pre-pro ET) mRNA was comparable to that of sham-operated rats, while a 2.5-, 5- and fourfold increase in 2.3 Kb pre-proET-1 transcript was observed at 30, 60 and 120 days, respectively. Urinary excretion of endothelin was significantly elevated (P < 0.01) in rats with renal mass reduction with respect to sham-operated rats, starting from 30 days after surgery and increased further thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Urinary excretion of platelet activating factor in patients with immune-mediated glomerulonephritis.

We have investigated whether human immune-mediated glomerulonephritis is associated with changes in platelet activating factor (PAF) biosynthesis. Urinary PAF, taken as a marker of its renal synthesis, was significantly higher in patients with membranous nephropathy (N = 9) than in healthy controls (N = 8). This was not due to a lower degradation of PAF since urinary acetylhydrolase activity was comparable in patients and controls. A significant positive correlation between urinary excretion of PAF and proteinuria was observed. PAF generation was comparable in polymorphonuclear cells isolated from patients with membranous nephropathy and controls. PAF levels in blood from patients with membranous nephropathy were significantly lower than in controls, suggesting that the excessive generation of PAF is confined to the kidney. The results document that signs of renal disease activity in human membranous nephropathy are associated with an excessive renal synthesis of PAF.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1992

Urinary excretion of platelet-activating factor in haemolytic uraemic syndrome.

Since some of the features of haemolytic uraemic syndrome (HUS), such as platelet activation and glomerular injury, could be brought about by platelet-activating factor (PAF), we have studied the urinary excretion of PAF in 10 children with HUS and in 10 healthy age-matched controls. Urinary PAF concentrations, measured by radioimmunoassay, were significantly higher in acute-phase HUS patients than in controls (mean 2.04 [SD 1.66] vs 0.72 [0.43] ng/mg creatinine, p less than 0.05) but were similar to those in controls in samples taken after recovery. High PAF concentrations during the acute phase of HUS may reflect platelet activation and glomerular injury; the lower values after recovery suggest that urinary PAF may be a marker of disease activity.

Child↗

PubMed1992

Renal prostacyclin biosynthesis is reduced in children with hemolytic-uremic syndrome in the context of systemic platelet activation.

Previous studies have reported various abnormalities in prostacyclin (PGI2) synthesis and metabolism in hemolytic-uremic syndrome (HUS). However, the conclusions of most of these studies are based on in vitro or ex vivo experiments that only give an indirect estimate of the actual biosynthesis in vivo. We studied the urinary excretion of PGI2 metabolites, taken as a marker of the actual biosynthesis, in six children with HUS during the acute phase of the disease and again when remission was achieved. Eight age- and sex-matched healthy children were studied as controls. Since HUS is also associated with platelet activation and consumption, we also studied the urinary excretion of thromboxane A2 (TxA2) metabolites. Urinary PGI2 and TxA2 metabolites were assessed by radioimmunoassay after high-performance liquid chromatography (HPLC) purification. Urinary excretion of the PGI2 hydrolysis product, 6-keto-PGF1 alpha, was significantly reduced in children with acute HUS as compared with controls, indicating a defective renal synthesis of PGI2. A significant inverse correlation was found between urinary 6-keto-PGF1 alpha and blood urea nitrogen (BUN), as well as plasma creatinine. At remission, urinary 6-keto-PGF1 alpha levels increased to values higher than those of controls. By contrast, the urinary excretion of the major PGI2 beta-oxidation product, 2,3-dinor-6-keto-PGF1 alpha, was comparable to controls, indicating normal systemic PGI2 biosynthesis. The urinary excretion of both TxA2 hydrolysis product, TxB2, and the major beta-oxidation metabolite, 2,3-dinor-TxB2, were lower than normal in the acute phase of HUS if expressed as absolute values.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗

PubMed1992

Methylprednisolone dosage effects on peripheral lymphocyte subpopulations and eicosanoid synthesis.

Glucocorticoids have a major role in the treatment of glomerular diseases. Despite recent advances in understanding of their mechanism of action, very few studies have addressed the relative advantage of the wide range of different dose regimens employed in clinical practice. We studied the effects of methylprednisolone given intravenously for three consecutive days at the doses of 1 mg/kg (group 1, N = 7; group 2, N = 5), 5 mg/kg (group 3, N = 5) or 15 mg/kg (group 4, N = 6) on total blood peripheral leukocytes and on lymphocyte subsets in patients with glomerular diseases, and investigated whether such effects were a function of the drug concentration in the blood. Since glucocorticoids have an inhibitory effect on the formation of eicosanoids in different cells, we also investigated in the same patients the effect of 1 and 15 mg/kg methylprednisolone on systemic and renal eicosanoid synthesis. Results of pharmacokinetic study showed that the three different doses of methylprednisolone we used resulted in major differences in patient's exposure to the drug, and within the same dose there was a great individual variability. By contrast the three different doses of methylprednisolone induced a comparable drop in the absolute number of lymphocytes six hours after the first injection of methylprednisolone, while 24 hours later blood lymphocyte counts returned to the pre-injection values in all patients. Analysis of lymphocyte subsets showed a selective decrease in the number of circulating CD4+ and CD8+ cells six hours after methylprednisolone which was comparable in the four groups of patients studied. As for the effect of methylprednisolone on systemic and renal eicosanoid synthesis in patients with glomerular diseases, 1 and 15 mg/kg were equally unable to reduce thromboxane A2 (TxA2) and prostaglandin E2 (PGE2) release by circulating polimorphonuclear cells (PMNs). By contrast, methylprednisolone partially inhibited eicosanoid synthesis by PMNs in vitro. Consistent with the data on PMNs, urinary excretion of TxA2 and prostacyclin (PGI2) metabolites were unaltered by the different doses of methylprednisolone. By contrast urinary PGE2 was markedly and significantly reduced in patients given 15 but not 1 mg/kg. We conclude that 1 mg/kg methylprednisolone given to patients with glomerular diseases has the same effect on peripheral total blood leukocyte count and lymphocyte subsets than 5 and 15 mg/kg. The same is true for eicosanoid synthesis by PMNs. Renal synthesis of PGE2 is inhibited by 15 mg/kg but not by 1 mg/kg.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed1992

Daily renal hypoperfusion induced by cyclosporine in patients with renal transplantation.

A variety of side effects are associated with the use of cyclosporine, the most relevant of which remains the renal toxicity. We did parallel studies on cyclosporine pharmacokinetics and renal function in patients who had a recent kidney transplant and were given cyclosporine as a part of their immunosuppressive therapy. Seven consecutive renal transplant patients were studied at the end of a month of treatment while on different oral cyclosporine doses (5, 3.5, 2.5, or 1.5 mg/kg, twice a day, respectively). Cyclosporine pharmacokinetics profiles and renal function parameters (GFR and renal plasma flow [RPF], as inulin and p-amino hippurate clearances, respectively) were determined before and over a 12-hr period after each single dose of cyclosporine. Plasma levels and urinary excretion rate of endothelin were also studied before and after the highest cyclosporine dose (5 mg/kg). Mean trough levels, area under the curve values, and maximum concentration of blood cyclosporine were comparable after 5 and 3.5 mg/kg cyclosporine and decreased in a dose-dependent manner after the lower doses (2.5 and 1.5 mg/kg). In the same patients GFR declined on average 63%, 53%, 35%, and 18%, 2-4 hr after maximum cyclosporine concentration was reached. As blood levels of cyclosporine returned to trough, GFR progressively increased to baseline. Similar results were found for RPF; 5 mg/kg cyclosporine did not modify endothelin plasma levels. By contrast, urinary excretion of the peptide increased significantly (P less than 0.01) in the 6 hr that followed cyclosporine administration and returned within the normal range in the subsequent 6 hr. Following each oral administration of cyclosporine, 2-4 hr after peak blood concentration was reached, patients showed renal hypoperfusion, transient and rapidly reversible. This was associated with an increased urinary endothelin excretion rate that was also transient. It is speculated that an excessive renal synthesis of endothelin is the cause of the daily renal hypoperfusion observed in patients with renal transplants given cyclosporine.

Adult↗

PubMed1992

The acute effect of FK506 and cyclosporine on endothelial cell function and renal vascular resistance.

We have previously documented that cyclosporine exerts a direct cytotoxic effect on endothelial cells and causes an increase in renal vascular resistance (RVR) in the rat. In the present study we investigated whether FK506, a novel immunosuppressive agent thought to be less nephrotoxic than CsA, impairs endothelial cell function in vitro and affects RVR in vivo. In vitro eicosanoid release and endothelin release were measured in bovine aortic endothelial cells in culture exposed for 1, 6, and 24 hr to increasing concentrations of FK506 (1 nM to 10 microM) or CsA (0.5, 10 microM). No significant changes in TxB2 and 6-keto-PGF1 alpha (the stable breakdown products of TxA2 and PGI2, respectively) and endothelin release were found after 1 and 6 hr of incubation with all the concentrations of FK506 and CsA considered. FK506 did not affect endothelin release even after 24 hr of incubation. In contrast, cell exposure to CsA was associated with a dose-dependent increase in TxB2, 6-keto-PGF1 alpha, and endothelin release that reached statistical significance after incubation with 10 microM CsA. FK506 did not induce cell detachment or lysis at any concentration and time considered, while 10 microM CsA induced a significant reduction in cell count accompanied by cell lysis. In vivo studies showed that a single i.v. injection of FK506 to rats within a broad range of doses (28 ng/kg to 2.8 micrograms/kg) did not modify RVR. This was true even for a dose as high as 20 mg/kg, while 20 mg/kg CsA caused a dramatic increase in RVR. We conclude that FK506, unlike CsA, does not induce endothelial cell injury in vitro. Whether this explains the differences in renovascular resistance observed in vivo after acute injection of FK506 and CsA is an attractive possibility that needs to be further explored.

Animals↗

PubMed1992

Evidence against a pathogenetic role for endothelin in pre-eclampsia.

OBJECTIVE: To assess whether increased placental or systemic endothelin synthesis has a pathogenic role in pre-eclampsia (gestational proteinuric hypertension). DESIGN: Prospective observations study. SUBJECTS: 19 women with pre-eclampsia and 10 healthy pregnant women were studies. All were in the last trimester. MAIN OUTCOME MEASURES: Preproendothelin-1 gene expression by Northern blot analysis and generation of endothelin-1 precursor, big-endothelin-1, and endothelin isoforms, namely endothelin-1, 2 and 3, were assessed by specific radio-immunoassays, in placental tissue. Plasma endothelin-1 levels and urinary excretion of big-endothelin-1 and endothelin-1 were measured. RESULTS: Placental preproendothelin-1 gene expression and immunoreactive big-endothelin-1 and endothelin-1, 2 and 3, were comparable in placental tissue from pre-eclamptic and normal pregnant women. Plasma levels of endothelin-1 did not differ between pre-eclamptic and normal pregnancies. In contrast, urinary excretion of endothelin-1, which is likely to reflect the renal synthesis of the peptide, was significantly decreased in pre-eclamptic, as compared with normal pregnant women. This was not due to a decreased renal generation of endothelin-1 precursor, since urinary excretion of big-endothelin-1 did not differ between pre-eclamptic and normal pregnancies. These data suggest an increased renal endothelin-1 breakdown in pre-eclampsia. CONCLUSIONS: Endothelin is unlikely to play a role in the pathogenesis of pre-eclampsia. Instead, an increased renal breakdown may have a role in limiting the negative effects of other vasoactive factors on the renal circulation.

Adult↗

PubMed1992

Atrial natriuretic peptide and prostacyclin synergistically mediate hyperfiltration and hyperperfusion of diabetic rats.

The relative contribution of atrial natriuretic peptide (ANP) and vasodilatory prostaglandins to hyperfiltration in Wistar rats with experimental diabetes was studied 6-8 wk after streptozocin injection. Plasma levels of immunoreactive ANP were significantly higher (P less than 0.01) in hyperglycemic diabetic (72.9 +/- 11.7 pg/ml) than in normoglycemic diabetic (44.8 +/- 8.6 pg/ml) or nondiabetic (40.0 +/- 6.8 pg/ml) rats. Blocking endogenous ANP by specific ANP-antiserum infusion reduced significantly (P less than 0.01) glomerular filtration rate (GFR) and renal plasma flow (RPF) of hyperglycemic rats compared with preinfusion values (1.23 +/- 0.06-1.02 +/- 0.04; 2.87 +/- 0.25-2.40 +/- 0.10 ml.min-1.100 g-1, respectively). However, correction of hyperfiltration and hyperperfusion was only partial (nondiabetic rats GFR 0.85 +/- 0.07; RPF 2.27 +/- 0.13 ml.min-1.100 g-1). Because diabetic rats with hyperglycemia also had an increased urinary excretion of prostacyclin metabolite 6-keto-prostaglandin F1 alpha (220.6 +/- 62.8 ng/24 h) compared with nondiabetic rats (51.2 +/- 2.7 ng/24 h), we wondered whether excessive prostacyclin formation contributed to hyperfiltration and hyperperfusion in this setting. Indomethacin infusion partially reduced GFR (1.25 +/- 0.07 to 1.06 +/- 0.07 ml.min-1.100 g-1, P less than 0.05) and RPF (2.85 +/- 0.11 to 2.46 +/- 0.12 ml.min-1.100 g-1, P less than 0.01) in diabetic rats. The combined infusion of ANP antiserum and indomethacin normalized GFR and RPF in diabetic rats with hyperglycemia (1.27 +/- 0.05 to 0.88 +/- 0.05 and 2.84 +/- 0.10 to 2.22 +/- 0.06 ml.min-1.100 g-1, respectively; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Human placenta expresses endothelin gene and corresponding protein is excreted in urine in increasing amounts during normal pregnancy.

Systemic and renal hemodyanmic changes in normal pregnancy have been attributed in part to altered vascular synthesis of vasodilatory prostaglandins. Besides vasodilatory substances, endothelium also generates vasoconstrictors, including endothelin. We evaluated the capacity of placental tissue from normal pregnant women to express endothelin gene and to generate endothelin. Placental tissue expressed a single 2.3 kb preproendothelin messenger ribonucleic acid and produced comparable amounts of endothelin 3, Big endothelin 1, and endothelin 1 and a minor quantity of endothelin 2. To investigate the possible influence of placental endothelin production on plasma levels of the peptide, plasma endothelin concentrations were measured in normal pregnant women at delivery and were found to be numerically higher than those measured in nonpregnant subjects. Urinary excretion of endothelin, taken as a marker of the renal synthesis of the peptide, tended to increase, although not significantly, in the first 14 weeks of pregnancy. This trend continued throughout pregnancy, resulting in a significant increase from the second trimester to delivery.

Adult↗

PubMed1991

Recombinant human erythropoietin to correct uremic bleeding.

Recombinant human erythropoietin may improve hemostasis of uremic patients by correcting anemia. However, a complete correction of renal anemia carries the risk of hypertension, encephalopathy, thrombosis, and hyperkalemia. Our aim was to establish the minimum level of packed cell volume (PCV) achieved with recombinant human erythropoietin that corrects the prolonged bleeding time in uremia. Twenty patients with chronic renal failure, anemia, and very prolonged bleeding time (greater than or equal to 15 minutes) were randomly allocated to erythropoietin or no specific treatment. The initial dose of erythropoietin was 50 U/kg intravenously (IV) three times a week. Every 4 weeks, the dose was increased by 25 U/kg until a normalization of bleeding time was achieved. Erythropoietin at a dose ranging from 150 to 300 U/kg/wk induced an increase in PCV to a range of 27% to 32% in all patients but one, and normalized bleeding time in all patients. A significant negative correlation (r = 0.898, P less than 0.001) was found between PCV and bleeding time measurements. Erythropoietin also significantly (P less than 0.01) increased values for red blood cell (RBC) distribution width (basal, 11.3 +/- 0.6; 12 weeks, 13.1 +/- 1.3). Platelet count and platelet function parameters did not significantly change. In untreated patients, no changes were recorded in all the parameters considered. These results establish in a controlled fashion that erythropoietin shortens bleeding time of uremic patients and indicate that a partial correction of renal anemia is enough to normalize bleeding time.

Adult↗

PubMed1991

Increased renal endothelin production in rats with reduced renal mass.

Renal endothelin (ET) production was investigated in rats after renal mass ablation, a model of progressive renal disease characterized by glomerular hemodynamic alterations and capillary thrombosis, and in sham-operated animals. Thrombin stimulation of renal cortical tissue from rats with renal mass reduction, 45 but not 7 days after surgery, generated significantly (P less than 0.01) more ET than tissue from sham-operated animals. Exposure to thrombin of isolated glomeruli from remnant but not sham kidneys also significantly (P less than 0.01) increased ET production compared with unstimulated glomeruli. At day 45, in rats with renal mass ablation ET plasma levels were numerically lower, whereas urinary excretion rate of ET was significantly (P less than 0.01) increased compared with sham-operated animals. After a 50-min intravenous infusion of 125I-ET to normal rats and animals with renal mass ablation, less than 0.3% and 0.03%, respectively, of total infused radioactivity was recovered in urine. These results indicate that thrombin-stimulated ET production by renal cortical tissues is increased in rats with renal mass reduction. Despite normal or low-normal plasma ET levels, urinary excretion of the peptide is markedly increased in this model. The exogenously labeled ET added to circulation is not excreted by the kidney, suggesting that enhanced urinary excretion rate would reflect an increased renal production of the peptide in rats with remnant kidney.

Animals↗

PubMed1991

Endothelin induces diuresis and natriuresis in the rat by acting on proximal tubular cells through a mechanism mediated by lipoxygenase products.

Besides being a potent renal vasoconstrictor, endothelin causes diuresis and natriuresis. At which site along the nephron and how endothelin alters water and sodium handling in the tubule remain to be clarified. It was found that endothelin (75 pmol) given as an i.v. infusion in vivo to rats caused diuresis and urinary sodium excretion to double but did not affect glomerular filtration rate and renal plasma flow. On raising the dose of endothelin to 150 pmol, a further increase in diuresis and natriuresis was found, whereas glomerular filtration rate fell 33% and renal plasma flow fell 36%; 300 pmol of endothelin reduced glomerular filtration rate by 73% and renal plasma flow by 77% but did not significantly affect diuresis and absolute sodium excretion. It did, however, increase fractional sodium excretion eightfold. Lithium clearance studies of changes in tubular handling of water and sodium indicated that infusion of 150 pmol of endothelin to rats caused a reduction in absolute (pre, 84.7 +/- 5.9; post, 47.9 +/- 6.1 microEq/min/100 g) and fractional (pre, 85.7 +/- 3.0; post, 64.7 +/- 6.4%) proximal reabsorption of sodium. Endothelin infusion (150 pmol) was not associated with any significant change in plasma atrial natriuretic peptide levels, which on average remained comparable to those in rats given the vehicle alone (49.7 +/- 8.4 versus 46.3 +/- 5.6 pg/mL). In the isolated perfused rat kidney preparation, exposure to 150 pmol of endothelin significantly increased fractional sodium excretion over preinjection values (pre, 2.2 +/- 0.2; post, 7.3 +/- 1.0%) despite a marked decrease in glomerular filtration rate and renal perfusate flow. Additional in vivo experiments showed that oral administration of the specific 5-lipoxygenase inhibitor L-651,392 to rats prevented the increase in urine flow rate (pre, 5.7 +/- 0.1; post, 6.6 +/- 0.8 microL/min), and in absolute (pre, 0.33 +/- 0.04; post, 0.37 +/- 0.05 microEq/min) and fractional (pre, 0.10 +/- 0.02; post, 0.11 +/- 0.03%) sodium excretion caused by bolus i.v. infusion of endothelin (150 pmol). Similarly, a specific leukotriene C4/D4 receptor antagonist, L-649,923, also prevented the diuretic and natriuretic effect of 150 pmol of endothelin i.v. infusion. These findings show that (1) endothelin has a diuretic and natriuretic effect that is independent of its action on renal hemodynamics; (2) this effect depends on a direct action on the proximal tubules; (3) atrial natriuretic peptide does not appear to be involved in this effect; and (4) the diuretic and natriuretic responses to endothelin are mediated by 5-lipoxygenase products.

Animals↗

PubMed1991

Constitutive expression of endothelin gene in cultured human mesangial cells and its modulation by transforming growth factor-beta, thrombin, and a thromboxane A2 analogue.

The present study was designed to assess whether human glomerular mesangial cells in culture express preproendothelin gene and whether endothelin gene expression in the mesangium is regulated by factors potentially released by inflammatory cells and platelets infiltrating the glomerular tuft during the course of various types of glomerulonephritis. For this purpose mesangial cells were incubated for 6 hours in the presence of absence of interleukin 1 beta (IL-1 beta), transforming growth factor-beta (TBF-beta), the thromboxane A2 analogue U-46619, and thrombin. Resting mesangial cells expressed a 2.3-kilobase mRNA on blot hybridization analysis with a human cDNA preproendothelin probe, indicating that this type of cells, in addition to glomerular endothelial cells, constitutively expresses endothelin gene. IL-1 beta did not change endothelin mRNA levels in respect to unstimulated mesangial cells. At variance, TGF-beta, U-46619, and thrombin had a marked effect on endothelin mRNA, stimulating a 3- to 8-fold increase over basal levels. Quantification of actin mRNA and analysis of the autoradiographic signals provided validation of the difference in the endothelin mRNA levels. Expression of preproendothelin mRNA in either resting or stimulated mesangial cells was associated with synthesis and release of the corresponding peptide in the cell supernatant as determined by a specific radioimmunoassay for endothelin. Endothelin production from IL-1 beta stimulated mesangial cells was not different from that of unstimulated cells, whereas a significant (p less than 0.01) increase in endothelin production was observed after cell stimulation with TGF-beta, U-46619, and thrombin. The demonstration that mesangial cells constitutively express mRNA for preproendothelin and release endothelin into culture medium, together with the finding that endothelin gene expression and production in mesangial cells are regulated by molecules potentially released at glomerular level during an inflammatory reaction may suggest that endothelin participates in the complex process of glomerular disease progression.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗