Autocrine inhibition of Na+/K(+)-ATPase by nitric oxide in mouse proximal tubule epithelial cells.

An inducible nitric oxide synthase has recently been described in proximal tubule epithelium. To investigate the effects of proximal tubule NO on Na+/K(+)-ATPase, we induced NO production in mouse proximal tubule epithelial cells by treatment with lipopolysaccharide (LPS) and interferon-gamma (IFN gamma) followed by determinations of ouabain-sensitive ATPase activity. Na+/K(+)-ATPase activity decreased after 4 h of LPS/IFN gamma treatment, reaching maximal inhibition after 24 h (34% reduction in activity). The inhibition of Na+/K(+)-ATPase activity by LPS/IFN gamma was prevented by simultaneous incubation with N omega-nitro L-arginine and markedly blunted by removal of L-arginine from the medium. The NO donors sodium nitroprusside and SIN-1 also inhibited Na+/K(+)-ATPase activity to a similar extent than LPS/IFN gamma. However, treatment with 8-pCPT-cGMP only modestly reduced Na+/K(+)-ATPase activity. Interestingly, superoxide dismutase prevented the inhibitory effects of NO on Na+/K(+)-ATPase activity, suggesting a role for peroxynitrite in this inhibition. We conclude that NO generated by mouse proximal tubule epithelial cell iNOS inhibits Na/K ATPase activity in an autocrine fashion and that this inhibition is accompanied by a reduction in Na-dependent solute transport.

Ethanol enhances the endothelial nitric oxide synthase response to agonists.

Chronic ethanol consumption is associated with an increased prevalence of hypertension. The mechanisms of this form of hypertension are unknown. Rats fed ethanol for 2 days develop a tolerance to the acute vasoconstrictive effects of ethanol that is believed to be endothelium dependent. We investigated the effects of acute and chronic ethanol exposure on agonist-stimulated nitric oxide synthase activity in bovine pulmonary artery endothelial cells. Exposure of bovine pulmonary artery endothelial cells to ethanol (100 mmol/L) for 20-120 minutes did not change either basal or agonist-stimulated nitric oxide synthase activity measured as the rate of conversion of [3H]L-arginine to [3H]L-citrulline. Chronic exposure of endothelial cells to ethanol (100 mmol/L) for 96 hours significantly increased bradykinin-, adenosine 5'-triphosphate-, and ionomycin-stimulated nitric oxide synthase activity without affecting basal enzyme activity. The ethanol-induced increase in nitric oxide synthase response to agonists was dependent on the duration of ethanol exposure as well as the concentration of ethanol. Moreover, the effect of ethanol was characterized by an increase in the maximal nitric oxide synthase response to adenosine 5'-triphosphate without changes in the EC50. Removal of calcium or addition of N omega-nitro-L-arginine completely abolished agonist-stimulated nitric oxide synthase activity in both control and ethanol-treated cells. Our observations support the hypothesis that ethanol enhances nitric oxide synthase response to agonists during early ethanol exposure and may serve in a protective role against its hypertensive effect.

Hemodialysis central venous catheter tip fracture with embolization into the pulmonary artery.

We describe the first reported case of spontaneous hemodialysis catheter fracture and embolization. We also include a summary of similar cases not previously reported in the literature that appear in the Food and Drug Administration records as medical equipment malfunctions. Our patient presented with a cough and was initially treated for presumptive pneumonia. A chest radiograph indicated that the tip of the catheter had fractured and migrated into a distal branch of the pulmonary artery. The catheter was replaced, but the tip could not be retrieved because of its peripheral location. Possible causes and consequences of this underreported complication are discussed.

Alpha 1-adrenergic receptors in the brain: characterization in astrocytic glial cultures and comparison with neuronal cultures.

Binding of [125I]HEAT to membranes prepared from primary cultures of astrocytic glial cells was time-dependent and 70-85% specific. Various adrenergic agonists and antagonists competed for [125I]HEAT binding according to the potencies of prazosin greater than, yohimbine greater than or equal to, clonidine, norepinephrine (NE), and propranolol. Scatchard analysis showed the Bmax of 209 fmol/mg protein and a Kd of 184 pM for [125I]HEAT binding by astrocytic glial membranes. Pretreatment of astrocytes with NE resulted in a dose-dependent downregulation of [125I]HEAT binding sites with a maximal response observed after 8 h at 100 microM NE. Removal of NE from cultures after pretreatment resulted in a time- and protein synthesis-dependent recovery of binding sites to control levels within 120 h. Incubation of astrocytic glial cultures with NE stimulated phosphoinositide (PI) hydrolysis in a time- and dose-dependent manner with a maximal stimulation of 2-fold observed in 60 min by 100 microM NE. Clonidine expressed differential effects on alpha 1-adrenergic receptors of the neuronal and astrocytic glial cultures. Pretreatment with 10 microM clonidine caused a 40% decrease in the Bmax of [125I]HEAT binding without influencing the Kd value in neuronal cultures. This downregulatory effect of clonidine was associated with a reduction in the ability of NE to stimulate PI hydrolysis in clonidine pretreated cells. In contrast to neuronal cultures, clonidine neither downregulated [125I]HEAT binding sites nor stimulated PI hydrolysis in glial cultures.

Protein kinase C modulates receptor-independent activation of endothelial nitric oxide synthase.

The intracellular regulation of nitric oxide synthase has been the focus of intense investigation. Bioassay studies using vascular rings have suggested that protein kinase C inhibits endothelium-dependent vascular relaxation. However, information regarding the effects of protein kinase C on the synthesis of nitric oxide in endothelial cells is not available. Therefore, we investigated the effects of protein kinase C to regulate receptor-independent activation of nitric oxide synthase activity in cultured bovine pulmonary artery endothelial cells. Activation of protein kinase C by phorbol 12-myristate 13-acetate or 1,2-dioctanoyl-sn-glycerol inhibited receptor-dependent and receptor-independent nitric oxide synthase activity. The inhibition of nitric oxide synthase by protein kinase C was concentration dependent and markedly blunted by staurosporine. The inhibition of protein kinase C by staurosporine alone enhanced basal nitric oxide synthase activity. Furthermore, depletion of protein kinase C enhanced both basal and agonist-stimulated nitric oxide synthase activity. These studies indicate that protein kinase C modulates the activity of the constitutive Ca2+/calmodulin-dependent endothelial nitric oxide synthase in the basal state and following agonist stimulation through direct inhibition of the enzyme as well as receptor desensitization. These direct regulatory effects of protein kinase C on endothelial nitric oxide synthase activity may have important implications in the physiologic regulation of vascular tone.

Characterization of rat glomerular thromboxane A2 receptors: comparison to rat platelets.

This study was designed to characterize rat glomerular thromboxane A2 (TxA2) receptors and compare them to rat platelet TxA2 receptors. The radioligand binding characteristics of the receptors were characterized using [125I][1S-(1 alpha,2 beta(5Z),3 alpha-(1E,3R*),4 alpha]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo- [2.2.1]heptan-2yl]-5-heptenoic acid ([125I]BOP), a TxA2 agonist. Equilibrium binding with [125I]BOP, as well as competitive binding assays between [125I]BOP and 13-azapinane TxA2 receptors antagonists, were performed in rat glomerular membranes (RGM) and washed rat platelets (WRP). [125I]BOP identified a single class of TxA2 receptor sites in glomerular membranes with a Kd of 318 +/- 55 pM and a Bmax of 260 +/- 62 fmol/mg protein (n = 14). [125I]BOP was displaced by the TxA2 agonist 15S-hydroxy-11 alpha,9 alpha(epoxymethano)-prosta-5Z,13E-dienoic acid (U-46,619) (IC50 = 22 +/- 6 nM, n = 3), the antagonist SQ-29,548 (IC50 = 41 +/- 7 nM, n = 4), and stereoselectively by the antagonists (-)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,925) (IC50 = 0.27 +/- 0.04 nM, n = 3) and (+)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid (L-657,926) (IC50 = 124 +/- 0 nM, n = 2). The ability of six 13-azapinane TxA2 antagonists to compete with [125I]BOP was evaluated. The rank orders for the 13-azapinanes showed no significant correlation between RGM and WRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute renal failure. Prompt diagnosis is key to effective management.

An abrupt decrease in the kidneys' ability to excrete waste products is a common cause of severe morbidity and death in critically ill patients. This complication may result from prerenal, renal parenchymal, or postrenal causes. The authors describe the clinical and laboratory evaluation of acute renal failure and offer an approach to prevention and appropriate management.

Hypertension and kidney disease of diabetes mellitus.

Kidney disease is a primary cause of morbidity and mortality in diabetic patients. Factors that predetermine development of nephropathy remain unknown. Poor glycemic control, insulin requirement, duration of diabetes and family history of hypertension appear to be associated with an increased risk. Arterial hypertension, which is twice as common in diabetic patients as in the normal population, accelerates the progression of diabetic nephropathy. The pathophysiologic mechanisms responsible for hypertension appear to be different in IDDM and NIDDM. In IDDM, hypertension occurs usually as a consequence of diabetic renal disease. Conversely, the pathogenesis in NIDDM appears to be multifactorial. In either condition, aggressive blood pressure control is the single most important intervention proven to retard the progression of nephropathy. A stepped-care approach similar to that for essential hypertension with slight modifications is indicated in the treatment of the hypertensive diabetic patient with nephropathy. Nonpharmacological therapy, including dietary protein restriction, should be used as first step. Selection of the ideal antihypertensive must be based not only on efficacy but also on its side effect profile. Angiotensin converting enzyme inhibitors and calcium antagonists have a low incidence of side effects and do not induce metabolic disturbances. Therefore, they are the agents of choice for patients who do not respond to nonpharmacological therapy alone. Thiazide diuretics and beta-blockers should be used as first line therapy only for specific indications. Antihypertensive therapy combined with good glycemic control and dietary protein restriction constitute the standard of care for diabetic patients with hypertension and renal disease.

Regulation of inositol transport by glucose and protein kinase C in mesangial cells.

Since inositol (Ins) depletion appears to be an important mechanism of cell injury in diabetic glomerulopathy, we studied Ins transport in cultured rat mesangial cells during hyperglycemia. High glucose stimulated [3H]-Ins uptake by 50 to 90% within 24 hours in a dose dependent manner. This effect was characterized by an increase in the Vmax of a Na(+)-dependent Ins transporter (10.3 +/- 0.2 vs. 16.4 +/- 0.4 pmol/mg/min, P less than 0.005). Since high glucose also induced activation of protein kinase C (PKC) in permeabilized mesangial cells, we examined the potential role of this enzyme in the stimulation of Ins transport by glucose. Both PKC inhibition with H7 and staurosporine, and down regulation of PKC by prolonged PMA (1.6 microM) treatment inhibited the stimulatory effect of glucose on Ins transport. In conclusion, high glucose stimulates Na(+)-dependent Ins transport in mesangial cells by a mechanism mediated by PKC. This process may represent an important adaptive response of mesangial cells to hyperglycemia.

Malignant hypertension and hypertensive emergencies.

Hypertensive emergencies and urgencies are important causes of morbidity and mortality. Malignant hypertension is a hypertensive urgency characterized by grade III/IV retinopathy and widespread endothelial damage. Control of BP is essential in the treatment of these disorders. The effects of hypertension on target organ function need to be balanced against the risks of excessive BP lowering. In hypertensive emergencies, BP should be lowered within minutes with parenteral agents to prevent critical end-organ damage. In hypertensive urgencies, BP can be lowered more slowly over several hours, often with oral agents, to avoid a detrimental fall in BP. The absolute indications for treatment and the optimal therapy depend on the underlying condition.

A non-nucleotide-bridged DNA decoy inhibits renal epithelial nitric oxide synthase expression.

UNLABELLED: A non-nucleotide-bridged DNA decoy inhibits renal epithelial nitric oxide synthase expression. BACKGROUND: The expression of inducible nitric oxide synthase (iNOS) is subject to strict tissue-specific transcriptional control. In mouse renal epithelium, an interferon-gamma (IFN-gamma)-induced signaling protein, IFN-gamma regulatory factor 1 (IRF-1), appears to mediate the induction of iNOS expression by cytokines and bacterial lipopolysaccharide (LPS). METHODS: We used a novel technique, namely, blockade of cytosolic IRF-1 activity with a triethyleneglycol-bridged decoy DNA oligonucleotide (ODN) containing the IRF-1 consensus binding sequences present in the iNOS promoter to inhibit iNOS gene expression. Cultured mouse renal epithelial cells were treated with a combination of LPS (1 microg/mL) and IFN (100 U/mL) in the absence or presence of IRF-1 decoy ODN followed by determinations of NO production and iNOS protein and mRNA expression. RESULTS: Treatment with IRF-1 decoy ODN resulted in concentration-dependent inhibition of NO production and a marked reduction in iNOS protein and mRNA levels. A scrambled ODN failed to affect LPS/IFN-stimulated NO production or iNOS protein and mRNA levels. Transcriptional assays showed that the IRF-1 decoy ODN inhibited transcriptional activity of an iNOS promoter-CAT gene construct. CONCLUSIONS: Decoy ODN-based techniques effectively inhibit iNOS expression in renal epithelium and represent a potentially useful approach for selective blockade of this enzyme in pathologic conditions associated with excessive NO production.

Guanosine triphosphate cyclohydrolase I regulates nitric oxide synthesis in renal proximal tubules.

The synthesis of nitric oxide by proximal tubule-inducible nitric oxide synthase requires tetrahydrobiopterin as a cofactor. To determine whether tetrahydrobiopterin synthesis is required for nitric oxide production, nitrite release by mouse proximal tubule cells treated with 2,4-diamino-6-hydroxypyrimidine, an inhibitor of the rate-limiting enzyme in the de novo synthesis of tetrahydrobiopterin from guanosine triphosphate, guanosine triphosphate cyclohydrolase I, was measured. Treatment with lipopolysaccharide (0.1 micrograms/mL) and interferon-gamma (100 U/mL) for 12 h increased nitrite production from 2.7 +/- 0.2 to 25.4 +/- 1.3 nmol/mg of protein (P < 0.001; N = 9). 2,4-Diamino-6-hydroxypyrimidine (6 mM) reduced lipopolysaccharide/interferon-gamma-induced nitrite production by 53.1 +/- 3.4%. Sepiapterin, a substrate for tetrahydrobiopterin synthesis via the dihydrofolate reductase-dependent pterin salvage pathway, prevented the inhibition by 2,4-diamino-6-hydroxypyrimidine, an effect that was blocked by methotrexate. In conclusion, guanosine triphosphate cyclohydrolase I activity is required for cytokine-induced nitric oxide production by proximal tubular epithelium. The inhibition of guanosine triphosphate cyclohydrolase I could prove useful in the treatment of nitric oxide-mediated renal disorders.

Effects of glucose on receptor-mediated phosphoinositide hydrolysis and second messenger generation in rat glomerular mesangial cells.

The phosphoinositide system plays a critical role in mesangial cell contraction. myo-Inositol depletion occurs in glomeruli from diabetic animals and may result in mesangial cell dysfunction. The hypothesis that mesangial cell exposure to high concentrations of glucose could lead to abnormalities in phosphoinositide metabolism and receptor-mediated inositol phosphate release was tested. When compared with controls (5 mM glucose), inositol phosphate release in mesangial cells exposed to 28 mM glucose was decreased by 27% after maximal stimulation with angiotensin II, by 41% after arginine vasopressin, and by 63% after the thromboxane A2 analog, U46619. Increasing the concentration of glucose to 50 mM caused a further reduction (from 27 to 54%) in maximal angiotensin II stimulation of inositol phosphate release. High glucose decreased incorporation of myo-inositol into phospholipids but did not change phosphoinositide mass. High glucose also resulted in increased de novo synthesis of diacylglycerol which was associated with membrane translocation of protein kinase C. myo-inositol supplementation prevented the reduction in phosphoinositide hydrolysis whereas sorbinil did not. It was concluded that high concentrations of glucose cause abnormalities in myo-inositol metabolism in mesangial cells which lead to reduced receptor-mediated phosphoinositide hydrolysis. These abnormalities appear to be related to desensitization of receptor-mediated phosphoinositide responses due to negative feedback by protein kinase C which becomes activated as a result of enhanced de novo diacylglycerol formation from glucose. These changes are unrelated to the polyol pathway and can be prevented by myo-inositol supplementation.

Nitric oxide inhibits bafilomycin-sensitive H(+)-ATPase activity in rat cortical collecting duct.

Nitric oxide (NO) is a messenger molecule that is produced from L-arginine by NO synthase (NOS). Some NOS isoforms are present in cells constitutively, whereas others can be induced by cytokines. Recent evidence suggests that NO inhibits intracellular pH regulation by the vacuolar H(+)-adenosinetriphosphatase (ATPase) in macrophages, which contain an inducible form of NOS. The vacuolar H(+)-ATPase is involved in proton secretion in intercalated cells in the collecting duct. We have therefore examined the effect of NO on bafilomycin-sensitive H(+)-ATPase activity in individual cortical collecting ducts (CCD) microdissected from collagenase-treated kidneys of normal rats using a fluorometric microassay. Incubation of CCD with the NO donors, sodium nitroprusside (0.1 and 1 mM) or 3-morpholino-sydnonimine hydrochloride (SIN-1, 30 microM), caused a dose-dependent decrease in H(+)-ATPase activity. Incubation of CCD with lipopolysaccharide (LPS) and interferon-gamma, which induces NOS in macrophages, decreased H(+)-ATPase activity by 85%. This effect was prevented by simultaneous incubation with N omega-nitro-L-arginine, a competitive inhibitor of NOS, indicating that the decrease in H(+)-ATPase activity was caused by NO production. Incubation with 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP) also inhibited H(+)-ATPase activity, suggesting that NO may exert its effect in the CCD via activation of guanylyl cyclase and production of cGMP. Immunohistochemistry using antibodies to the macrophage-type NOS revealed strong labeling of intercalated cells in the CCD, confirming the presence of NOS in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnesium and zinc potentiate ethanol inhibition of N-methyl-D-aspartate-stimulated nitric oxide synthase in cortical neurons.

The coupling of calcium mobilizing receptors to nitric oxide (NO) formation was examined in cerebral cortical cultures. Of the various agents tested, only glutamate, depolarization with KCl and the calcium ionophore ionomycin stimulated nitric oxide synthase (NOS) activity. Characterization of the glutamate response revealed that the ionotropic glutamate receptor agonists N-methyl-D-aspartate (NMDA), kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic all stimulated NOS activity with a relative maximal efficacy of NMDA > kainate > alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic. Ethanol, Mg++ and Zn++ produced a concentration-dependent inhibition of NMDA stimulation of NOS. The Mg++ inhibition was reversed by increasing concentrations of NMDA, whereas Zn++ inhibition was not. Ethanol (100 mM) produced an apparent competitive type inhibition as seen by a parallel right-shift in the NMDA concentration-response curve. However, ethanol inhibition was dependent upon the presence of Mg++ and/or Zn++ in a concentration-related manner. Whereas 100 mM ethanol did not significantly inhibit NMDA stimulation of NOS activity in the absence of Mg++ and Zn++, inclusion of a combination of these cations increased the sensitivity to ethanol such that the NMDA response was completely blocked by 100 mM ethanol (IC50 approximately 30 mM). The potency for inhibition of NMDA stimulation of NOS by several short-chain alcohols followed their hydrophobicity profile and showed a similar dependency upon Mg++ for inhibition, alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic, but not kainate, stimulation of NOS was also inhibited by ethanol (100 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

NF-kappa B and transcriptional control of renal epithelial-inducible nitric oxide synthase.

Expression of the inducible isoform of nitric oxide synthase (iNOS) is subject to strict tissue specific transcriptional control. Recently, the NF-kappa B/Rel family of transcription factors, and particularly c-rel, was shown to mediate bacterial lipopolysaccharide (LPS) induction of iNOS in macrophages. Since LPS is only a weak inducer of iNOS in most nonimmune cells, we investigated the role of NF-kappa B in the regulation of iNOS expression in mouse renal epithelial cells. We report that LPS activates NF-kappa B in renal epithelium, but that this is not sufficient for induction of iNOS activity. The NF-kappa B complexes activated by LPS in renal epithelium differ from those in macrophages in that they lack c-rel, which may explain the absence of iNOS induction in renal epithelium. Conversely, LPS and interferon-gamma (IFN) synergize to induce renal epithelial iNOS. Functional iNOS promoter analysis indicate that this synergistic induction requires NF-kappa B. We conclude that NF-kappa B is necessary but not sufficient for the induction of renal epithelial iNOS expression, and that in contrast to macrophages, c-rel does not appear to play a major role in the regulation of renal epithelial iNOS.

Na+, K+, and BP homeostasis in man during furosemide: effects of prazosin and captopril.

Furosemide increases sodium (Na+) and potassium (K+) excretion but if dietary salt is provided, a compensatory reduction in Na+ and K+ excretion follows which restores neutral balances within 18 to 24 hours. This compensation is not interrupted by blockade of the renin-angiotensin-aldosterone system (RAA) alone with captopril. Since plasma norepinephrine concentration increases after furosemide and alpha 1 adrenoreceptors can mediate enhanced Na+ reabsorption, we administered prazosin (2 mg 6 hr-1) to six normal volunteers consuming a daily intake of 270 mmol of Na+ and 75 mmol of K+, and added captopril (25 mg 6 hr-1) for an additional day to block the RAA system concurrently. Furosemide (40 mg day-1) was given for the last four days. Prazosin given alone before the diuretic reduced (P less than 0.05) BP and plasma angiotensin II (AII) concentration and increased body weight and heart rate. However, when given with furosemide, neither prazosin nor prazosin with captopril modified the short-term natriuretic or kaliuretic responses to furosemide, or the ensuing compensatory reductions in Na+ and K+ excretion. Accordingly, cumulative balances for Na+ and K+ remained neutral over four days of diuretic administration. Neither drug altered the renal responsiveness to the diuretic which was assessed from the relationship between renal Na+ and K+ excretion and diuretic elimination. Although the BP was maintained when furosemide was given alone, when given with prazosin and captopril, the mean BP fell by 13 +/- 5 mm Hg (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)