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Biomedical subjects

R W Schrier

Publications and source records attributed to R W Schrier.

At least 19 recordsLinked to original sources
PubMed1996

Inhibitory actions of cyclic adenosine monophosphate and pertussis toxin define two distinct epidermal growth factor-regulated pathways leading to activation of mitogen-activated protein kinase in rat hepatocytes.

Increased intracellular cyclic adenosine monophosphate (cAMP) levels have been shown in some reports to inhibit and in other studies to stimulate growth factor-mediated activation of the mitogen-activated protein kinase (MAP kinase) pathway, depending on the cell type examined. The relationship between cAMP and MAP kinase in hepatocytes has not been examined. In the current study, stimulation of primary cultures of rat hepatocytes with hepatocyte growth factor (HGF) or epidermal growth factor (EGF) increased Ras, Raf, and MAP kinase activity. Incubation of hepatocytes with cAMP-increasing agents blocked activation of Raf by both HGF and EGF, whereas activation of Ras was unaffected. MAP kinase activation by HGF was completely inhibited, whereas EGF-stimulated MAP kinase activity was only slightly reduced. Incubation of hepatocytes with pertussis toxin slightly blunted MAP kinase activation by EGF but not HGF. Increasing cAMP in hepatocytes preincubated with pertussis toxin completely inhibited the activation of MAP kinase by EGF. In conclusion, HGF activates MAP kinase in hepatocytes exclusively through an Raf-dependent pathway and this activation may be completely blocked by increasing cAMP. In contrast, EGF activates MAP kinase in hepatocytes through both Raf-dependent and Raf-independent pathways: the latter pathway probably involves a pertussis toxin-sensitive G protein.

Analysis of Variance↗
PubMed1996

Management of acute renal failure: new perspectives.

Despite major developments in medicine, surgery, and intensive care, acute renal failure (ARF) still remains a common problem affecting approximately 5% of all general hospital patients. Mortality of all forms of ARF continues to be greater than 50%, and this percentage has not decreased significantly over the last 30 years. There are multiple factors, which may explain the persistence of such high mortality; the most important of these is probably the evolution of the disease spectrum underlying the development of ARF. At present, ARF is more often observed in older or more complex patients frequently in association with multiorgan system failure. The annual cost of managing ARF is staggering. This article reviews several of the new strategies and approaches that have been developed to aid in the management and prevention of ARF. For example, the use of biocompatible membranes has been proven to positively influence the course of ARF, which necessitates renal replacement therapy. Although continuous renal replacement therapy has a theoretical advantage compared with intermittent hemodialysis in critically ill and hemodynamically unstable patients, there are no well-controlled clinical studies to support a beneficial effect on mortality. There is, however, good evidence that calcium channel blockers play a positive role in the management of ARF, especially that associated with cadaveric kidney transplantation. Vasoactive agents, such as dopamine, may have the advantage of increasing the urine output in patients with oliguric ARF; however, their efficacy in otherwise altering the course of ARF is not well substantiated. Finally, growth factors and atrial natriuretic peptide appear to have the potential for accelerating renal recovery and decreasing morbidity and mortality from this commonly encountered medical problem. Prospective randomized clinical studies are the key to many of the dilemmas encountered with ARF.

Acute Kidney Injury↗
PubMed1996

Nitric oxide kinetics during hypoxia in proximal tubules: effects of acidosis and glycine.

In the present study, we directly monitored nitric oxide (NO) with an amperometric NO-sensor in suspensions of rat proximal tubules. Hypoxia-stimulated NO generation was characterized by an initial rise and a subsequent sustained increase which preceded cell membrane damage as assessed by lactic dehydrogenase (LDH) release. In contrast, the NO concentration remained unmeasurable in normoxic controls. Nitro-L-arginine-methyl ester (L-NAME) prevented the hypoxia-induced increase in NO in a dose dependent manner in parallel with incremental cytoprotection. The hypoxia-induced elevation in NO and the associated membrane injury were both markedly prevented by extracellular acidosis (pH 6.95). In vitro proximal tubular nitric oxide synthase (NOS) activity (3H-arginine to 3H-citrulline assay) was pH dependent with optimum activity at pH 8.0 and greatly reduced activity at acidic pH even in the presence of calcium and co-factors. However, glycine, a well recognized cytoprotective agent, did not attenuate the NO concentration during hypoxia. The present study therefore provides direct evidence that NO is generated by rat proximal tubules during hypoxia and demonstrates that the protective effect of low pH against hypoxic rat tubular injury is associated with an inhibition of this NO production.

Acidosis, Renal Tubular↗
PubMed1996

Arachidonic acid protects against hypoxic injury in rat proximal tubules.

Free fatty acids (FFA) and lysophospholipids accumulate during hypoxia (H) in rat proximal tubular epithelial cells partly as a result of increased phospholipase A2 (PLA2) activity. The role of FFA in mediating hypoxic injury and modulating PLA2 activity is not clear. In the present study, the effect of several FFA including arachidonic acid (AA, 20:4) on hypoxia-induced injury and PLA2 activity was assessed in freshly isolated rat proximal tubules. Hypoxia (H) was induced in the presence of either an unsaturated free fatty acid (uFFA) [AA or linoleic acid (LA, 18:2)] or a saturated FFA (sFFA) [palmitic (PA, 16:0) or myristic acid (MA, 14:0)]. Cell membrane injury was assessed by measuring lactate dehydrogenase release (LDH). AA markedly reduced LDH release during hypoxia in a dose dependent manner, while sFFA had no protective effect. LA showed similar protection to that observed with AA. AA did not affect buffer calcium concentration, buffer pH, intracellular pH or intracellular calcium concentration. Neither inhibiting the cyclooxygenase pathway with indomethacin, nor the lipoxygenase pathway with nordihydroguaiaretic acid (NDGA) had any effect on the AA observed cytoprotection. In vitro PLA2 activity in the control tubular extracts was compared to that following addition of AA or PA. PLA2 activity decreased significantly with AA but not with PA in a dose dependent manner. These data suggest that: (1) AA protects against hypoxic injury in rat proximal tubules. (2) This cytoprotection is not specific for AA and other uFFA have a similar effect. (3) AA significantly inhibits PLA2 activity, (4) AA induced cytoprotection may be related to a negative feedback inhibition of PLA2 activity.

Animals↗
PubMed1996

Upregulation of endothelial constitutive NOS: a major role in the increased NO production in cirrhotic rats.

Nitric oxide (NO) is postulated to mediate the peripheral arterial vasodilation in cirrhosis. However, it is not known which isoform of the nitric oxide synthase (NOS) is involved in the increased production of NO. This study was therefore undertaken to examine the expression of the NOS isoforms in arteries of cirrhotic rats compared with controls. Cirrhosis was induced by CCl4, and vessels were harvested for immunoblots using antibodies against inducible NOS (iNOS) and endothelial constitutive NOS (ecNOS). Endothelial cells were used as controls for ecNOS, and vascular smooth muscle cells treated with lipopolysaccharide or septic rats were used for iNOS controls. The results demonstrated an upregulation of ecNOS in both the aortas and mesenteric arteries of cirrhotic compared with control rats. Chronic inhibition of NOS decreased ecNOS in cirrhotic vessels. Although iNOS mRNA was found by reverse transcription-polymerase chain reaction in arteries of cirrhotic rats, iNOS protein was not detectable by immunoblotting compared with septic rats, suggesting a low vascular level of this isoform. In conclusion, the ecNOS seems to play a major role in the increased NO production in cirrhotic rats, whereas the role of iNOS remains elusive.

Animals↗
PubMed1996

Effect of risk factors on exercise capacity in NIDDM.

Exercise capacity has been used as a noninvasive parameter for predicting cardiovascular events. It is known that diabetic patients have an impaired exercise capacity when compared with nondiabetic age-matched control subjects, but the risk factors associated with this impairment have not been thoroughly analyzed. A total of 453 male and female NIDDM patients who underwent graded exercise testing with expired gas analysis were studied to determine the possible influences of demographic and cardiac risk factors on exercise capacity. Univariate and multiple linear regression analyses were performed on baseline patient characteristics with respect to peak oxygen consumption (VO2). In the regression analyses, African-American race was strongly associated with a decrease in peak VO2; the difference in means between African-Americans and other subjects for men was -2.50 ml.kg-1.min-1 (-4.28, -0.07, 95% CI) (P < 0.006) and for women was -2.96 ml.kg-1.min-1 (-4.45, -1.47) (P < 0.0002). Univariate analyses revealed that African-American subjects had increased prevalence, longer duration, and higher systolic and diastolic hypertension than the non-Hispanic and Hispanic whites. Other independent predictors of peak VO2 (reported as change in peak VO2 in milliliters per kilogram per minute) were BMI (men: -0.39 kg/m2 [-0.52, -0.29], P < 0.0001; women: -0.39 kg/m2 [-0.48, -0.31], P < 0.0001), age (men: -0.16/year [-0.23, -0.09], P < 0.0001; women: -0.17/year [-0.24, -0.11], P < 0.0001), baseline resting systolic blood pressure (men: -0.03/mmHg [-0.06, -0.01], P < 0.05; women: -0.03/mmHg (-0.06, -0.01)f1p4< 0.05), and pack-years smoking (men: -0.04/pack-years [-0.04, -0.01], P < 0.01; women: -0.04/pack-years [-0.07, -0.01], P < 0.0001). Thus, in this large NIDDM study, weight loss, smoking cessation, and aggressive blood pressure control, particularly in African-Americans with NIDDM, would appear to be important in improving exercise capacity and potentially improving the increased cardiovascular mortality associated with an impaired exercise capacity.

Adult↗
PubMed1995

The role of cysteine proteases in hypoxia-induced rat renal proximal tubular injury.

The role of the lysosomal proteases cathepsins B and L and the calcium-dependent cytosolic protease calpain in hypoxia-induced renal proximal tubular injury was investigated. As compared to normoxic tubules, cathepsin B and L activity, evaluated by the specific fluorescent substrate benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methylcoumarin, was not increased in hypoxic tubules or the medium used for incubation of hypoxic tubules in spite of high lactate dehydrogenase (LDH) release into the medium during hypoxia. These data in rat proximal tubules suggest that cathepsins are not released from lysosomes and do not gain access to the medium during hypoxia. An assay for calpain activity in isolated proximal tubules using the fluorescent substrate N-succinyl-Leu-Tyr-7-amido-4-methylcoumarin was developed. The calcium ionophore ionomycin induced a dose-dependent increase in calpain activity. This increase in calpain activity occurred prior to cell membrane damage as assessed by LDH release. Tubular calpain activity increased significantly by 7.5 min of hypoxia, before there was significant LDH release, and further increased during 20 min of hypoxia. The cysteine protease inhibitor N-benzyloxycarbonyl-Val-Phe methyl ester (CBZ) markedly decreased LDH release after 20 min of hypoxia and completely prevented the increase in calpain activity during hypoxia. The increase in calpain activity during hypoxia and the inhibitor studies with CBZ therefore supported a role for calpain as a mediator of hypoxia-induced proximal tubular injury.

Animals↗
PubMed1995

Normalization of nitric oxide production corrects arterial vasodilation and hyperdynamic circulation in cirrhotic rats.

BACKGROUND & AIMS: Recent studies suggest that production of nitric oxide is increased in cirrhosis. This study determines to what extent this increased production contributes to arterial vasodilation and hyperdynamic circulation in cirrhosis. METHODS: Mean arterial pressure (MAP), cardiac index, and systemic vascular resistance (SVR) were determined in cirrhotic rats with ascites undergoing long-term treatment with different doses of the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (3 mg or 0.5 mg.kg-1.day-1). Untreated cirrhotic rats with ascites and controls were also studied. The vascular production of NO was estimated by the aortic concentration of guanosine 3',5'-cyclic monophosphate (cGMP). RESULTS: Untreated cirrhotic rats had significantly lower MAP and SVR and higher cardiac index and aortic cGMP concentration than controls. When administrated to cirrhotic rats, an L-NAME dose of 3 mg.kg-1.day-1 induced a reduction of cGMP concentration less than normal levels. In these rats, MAP and SVR increased to greater than and cardiac index decreased to less than values in controls. By contrast, cirrhotic rats treated with 0.5 mg.kg-1.day-1 L-NAME had similar aortic cGMP concentrations as controls, suggesting a normalization of NO production. This was associated with a normalization of MAP, cardiac index, and SVR and a reduction in the elevated plasma renin activity and vasopressin concentration. CONCLUSIONS: Normalization of vascular NO production corrects systemic hemodynamic abnormalities in cirrhotic rats with ascites.

Animals↗
PubMed1995

Clinical factors associated with urinary albumin excretion in type II diabetes.

Clinical factors associated with urinary albumin excretion (UAE) in type II diabetes are less well known than in type I diabetes. To examine the factors associated with UAE in type II diabetes, 933 Appropriate Blood Pressure Control in Diabetes Trial patients were classified according to UAE status: normoalbuminuria (< 20 micrograms/min), microalbuminuria (20 to 200 micrograms/min), and macroalbuminuria (> 200 micrograms/min). The class of UAE was then correlated with various clinical factors. Using univariate analyses, Hispanic ethnicity, African-American race, male gender, poor glycemic control, insulin use, long duration of diabetes, dyslipidemia, diastolic and systolic hypertension, smoking, and obesity were significantly correlated with microalbuminuria and macroalbuminuria. Using multivariate logistic regression analyses controlling for diabetes duration, glycosylated hemoglobin, gender, and race, the most significant predictors of microalbuminuria and macroalbuminuria were systolic hypertension, body mass index, high-density lipoprotein cholesterol, insulin use, and smoking pack-years. Of these factors, several are potentially reversible with aggressive intervention.

Albuminuria↗
PubMed1995

Arginine vasopressin gene expression in rats with puromycin-induced nephrotic syndrome.

Nephrotic syndrome is characterized by water and sodium retention, which leads to edema formation. The nonosmotic stimulation of arginine vasopressin (AVP) release from the pituitary gland has been implicated to be one of the important factors of abnormal water retention in patients with nephrotic syndrome. It is not known, however, whether nephrotic syndrome is associated with stimulation of hypothalamic vasopressin gene expression. Puromycin aminonucleoside is known to cause altered glomerular permeability, which results in experimental nephrotic syndrome in rats. In the present study, therefore, AVP gene expression has been studied in the hypothalamus of rats with puromycin aminonucleoside-induced nephrotic syndrome (PNS). Nephrotic syndrome was induced by a single intravenous injection of puromycin aminonucleoside (50 mg/kg body weight). Nephrotic syndrome was confirmed by urinary protein excretion (control 20.8 +/- 3.5 mg/24 hr v PNS 273.9 +/- 41.4 mg/24 hr; P < 0.0001, n = 6) and serum albumin concentrations (control 4.52 +/- 0.07 g/dL v PNS 2.96 +/- 0.22 g/dL; P < 0.001, n = 6). In PNS rats, plasma AVP was significantly higher than in control rats (control 0.77 +/- 0.10 pg/mL v PNS 2.13 +/- 0.42 pg/mL; P < 0.005, n = 12), even though there were no differences in plasma osmolality (control 292.0 +/- 2.0 mOsm/kg H2O v PNS 290.3 +/- 2.5 mOsm/kg H2O; P = NS, n = 12) or serum sodium concentration (control 142.7 +/- 0.7 v PNS 142.1 +/- 1.1; PNS, n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Inhibition of MAP kinase by prostaglandin E2 and forskolin in rat renal mesangial cells.

Activation of the mitogen-activated protein (MAP) kinase pathway is believed to play a critical role in normal and pathophysiological proliferation of mesangial cells. Recent studies have shown that MAP kinase activation by growth factors in other cell types involves activation of the low-molecular-weight G protein Ras and the protooncogene serine kinase c-Raf-1. In this study, the role of this pathway in rat renal mesangial cells was assessed. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), as well as phorbol esters (PMA) rapidly activated MAP kinase three- to fourfold in these cells. PDGF and EGF, but not PMA, were able to activate c-Raf-1 and Ras activity. Stimulation of mesangial cells with the inflammatory mediator prostaglandin E2 (PGE2) or elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) by treatment with forskolin markedly blunted activation of MAP kinase induced by PDGF and EGF, but not by PMA. Consistent with this observation, PGE2 abolished growth factor-induced activation of c-Raf-1. However, Ras activation induced by growth factors was not affected by PGE2 and forskolin. These results suggest that MAP kinase activation can occur by at least two separate pathways in mesangial cells. Tyrosine kinase receptors activate MAP kinase through activation of Ras and Raf. This pathway can be blocked by PGE2 and elevation of cAMP, presumably by interfering with the ability of Ras to activate Raf. In addition, activation of protein kinase C by phorbol esters can activate MAP kinase in a Ras/Raf-independent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Hypoxia induces changes in phospholipase A2 in rat proximal tubules: evidence for multiple forms.

Increased free fatty release during hypoxia is believed to contribute to cell injury. This phenomenon is likely to be mediated through activation of specific isoforms of phospholipase A2 (PLA2). In this study, PLA2 enzymatic activity was measured in cell-free extracts prepared from rat renal proximal tubules. Both soluble and membrane-associated PLA2 activity were detected. All PLA2 activity detected during normoxia was Ca2+ dependent. Fractionation of cytosolic extracts by gel filtration revealed three peaks of PLA2 activity. Exposure of tubules to hypoxia resulted in stable activation of soluble PLA2 activity, which correlated with disappearance of the highest molecular mass form (> 100 kDa) and appearance of a low-molecular-mass form (approximately 15 kDa) of PLA2. Hypoxia also resulted in release of a low-molecular-mass form of PLA2 into the extracellular medium. Pretreatment of tubules with glycine before hypoxia blocked this release of PLA2 but not activation of soluble PLA2 activity. These studies provide direct evidence for PLA2 activation during hypoxia and suggest that multiple mechanisms regulate free fatty acid release associated with hypoxia injury.

Animals↗
PubMed1995

Expression and preferential inhibition of inducible nitric oxide synthase in aortas of endotoxemic rats.

Septic shock is associated with high mortality. There is in vitro evidence that the induction of nitric oxide synthase (iNOS) in vascular smooth muscle cells may be an important mediator of the systemic vasodilation and hypotension associated with sepsis. In this study, an in vivo murine model of sepsis was used to further examine this important question. Lipopolysaccharide (LPS), the major wall component of gram-negative bacteria, was administered to rats. By the use of a selective cDNA probe for iNOS, mRNA for iNOS was demonstrated in the aortas of these rats. The functional significance of this iNOS was then examined with aminoguanidine, a preferential inhibitor of iNOS. Aminoguanidine reversed the blunted phenylephrine-evoked contraction of endothelium-denuded aortic rings from LPS-treated rats or rings exposed to LPS in vitro. Aminoguanidine did not impair the relaxation of aortic rings with endothelium to acetylcholine, a known stimulator of endothelial NOS. The reversal of LPS-induced vascular hyporesponsiveness by aminoguanidine therefore strongly supports the functional importance of iNOS mRNA expression in the aorta of endotoxemic rats. Future clinical trials in treating septic shock should therefore consider the preferential inhibition of iNOS while maintaining the integrity of endothelial NOS.

Animals↗
PubMed1995

Nitric oxide synthase inhibition and acute renal ischemia: effect on systemic hemodynamics and mortality.

This study was designed to examine if acute systemic blockade of nitric oxide (NO) production by inhibition of nitric oxide synthase (NOS) with N-omega-nitro-L-arginine methyl ester (L-NAME) would worsen the severity of ischemic acute renal failure (ARF). Initially three groups of rats, were studied: 45 min of bilateral renal ischemia (I) alone, Group I; L-NAME (L; 10 mg/kg BW, i.v.) alone, Group L; and L-NAME administered 15 min before renal ischemia, Group L+I. We observed, however, a 60% mortality in Group I+L during the first 4 h of reflow. Captopril, administered acutely 15 min before L-NAME in an attempt to offset any detrimental effects of increased angiotensin II generation in response to renal ischemia, failed to obviate the mortality because 67% of rats in this group (Group C+L+I) also died. Therefore, additional studies were performed in rats instrumented for cardiovascular studies to evaluate the acute hemodynamic responses during the first 90 min of reperfusion following renal ischemia in rats pretreated with L-NAME. As expected, L-NAME injection was accompanied by a 25-30 mm Hg increase in mean systemic arterial pressure (SAP) (p < 0.05), a bradycardia (p < 0.02), and a decrease in cardiac output (CO) (p < 0.02). The increase in SAP was due exclusively to an increase in systemic vascular resistance (SVR) (p < 0.01). Ischemia and reflow in the L-NAME-treated rats were attended by a progressive increase in SVR and a progressive decrease in CO such that by the end of 45 min of reperfusion SVR had increased 10-fold and CO had decreased to one third of its initial rate (both p < 0.02). Pulmonary artery pressure (PAP) increased promptly following L-NAME injection. Total pulmonary resistance (PRT) increased significantly by the end of reperfusion. L-NAME in combination with renal ischemia and reflow induces a large increase in both SVR and PRT, and is accompanied by a 70% reduction in CO and substantial mortality.

Acute Kidney Injury↗
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↗