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S L Archer

Publications and source records attributed to S L Archer.

At least 73 records · Page 4Linked to original sources
PubMed1994

Inducible nitric oxide synthase mRNA and activity in glomerular mesangial cells.

Previous studies have suggested that glomerular mesangial cells produce nitric oxide (NO), using measurements of the NO decomposition products, NO2- and NO3-. We have now directly measured NO in the headspace above rat mesangial cell cultures, using a chemiluminescence analyzer. In addition, we examined mesangial cell RNA for inducible NO synthase (iNOS). We found no detectable NO in the headspace or iNOS mRNA in unstimulated mesangial cells. However, after four hours of incubation with LPS (10 micrograms/ml), iNOS mRNA was apparent and after six hours, significant increases in NO were detected. Both of these parameters continued to increase for at least 24 hours. Significant increases in NO2-/NO3- in the media and cGMP in the mesangial cells were also detected after 24 hours of incubation with LPS. The induction of iNOS mRNA by LPS was markedly inhibited by actinomycin D and dexamethasone, as was the accumulation of NO2-/NO3- in the media. Cycloheximide significantly inhibited NO2-/NO3- in the media of LPS-treated cells, but had little effect on induction of iNOS mRNA by LPS. We conclude that rat mesangial cells possess an iNOS, with activity and regulation similar to that described in macrophages. Furthermore, we demonstrate the activity of this enzyme by direct measurement of NO and its decomposition products, NO2- and NO3-. We suggest that production of NO by glomerular mesangial cells could occur, even when macrophage infiltration is not present, and could, thereby, modulate glomerular and tubular functions within the kidney.

Amino Acid Oxidoreductases↗
PubMed1994

Increased endothelium-derived NO in hypertensive pulmonary circulation of chronically hypoxic rats.

The hypothesis that the endothelium-derived relaxing factor/nitric oxide (EDNO) activity is elevated in chronic hypoxic pulmonary hypertension (CH-PHT) was tested using isolated Krebs-albumin-perfused rat lungs. Concentration of the EDNO decomposition products (NOx) in the lungs' effluent was measured by a modified chemiluminescence assay. The functional significance of basal EDNO production was studied by measuring the vasoconstrictor response to an EDNO synthesis inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME). Reactivity to the endothelium-dependent vasodilator substance P and to exogenous NO was also studied. More NOx was found in effluent from CH-PHT (22.3 +/- 9.8 nM) than control (0.4 +/- 3.9 nM) lungs. The L-NAME-induced vasoconstriction was greater in CH-PHT than in control rats. The sensitivity, but not the maximal vasodilation, to exogenous NO was elevated in CH-PHT. The substance P-induced vasodilation was potentiated in CH-PHT compared with control rats and blocked by L-NAME in both groups. We conclude that basal and agonist-stimulated pulmonary EDNO activity is enhanced in this model of CH-PHT. The EDNO synthesis may play a counterregulatory role in CH-PHT.

Animals↗
PubMed1994

Diphenyleneiodonium inhibits both potassium and calcium currents in isolated pulmonary artery smooth muscle cells.

Diphenyleneiodonium (DPI) blocks hypoxic vasoconstriction in the pulmonary vasculature. Because one of the actions of DPI is the inhibition of NADPH oxidase, this has led to the suggestion that NADPH oxidase acts as an oxygen tension sensor in pulmonary smooth muscle cells. We investigated the effects of DPI on potassium and calcium currents in freshly isolated pulmonary artery smooth muscle cells by using whole cell patch-clamp recordings, since these ionic currents are known to be involved in hypoxic pulmonary vasoconstriction. DPI (3 and 10 microM) reversibly inhibited potassium currents, and in its presence, residual currents appeared markedly more transient than under control conditions. The actions of DPI could not be reversed by 4.4 mM hydrogen peroxide, the product of NADPH oxidase. Calcium channel currents were also reversibly inhibited by 3 microM DPI. Thus DPI is a nonselective blocker of ionic channels in pulmonary smooth muscle cells, and its mechanism of action does not appear to involve inhibition of hydrogen peroxide formation. The ability of DPI to block calcium currents can explain its inhibition of hypoxic pulmonary vasoconstriction.

Animals↗
PubMed1993

Postischemic oxygen radical production varies with duration of ischemia.

Oxygen radicals have been implicated in the pathogenesis of myocardial injury. Enhanced chemiluminescence is a sensitive technique for continuous nondestructive measurement of oxygen radical generation. Using an isolated perfused rat heart model, we studied the effect of variable durations of ischemia on oxygen radical generation and postischemic myocardial function. Peak postischemic oxygen radical generation was higher with an intermediate period of ischemia (11.5 min; 528 +/- 53 counts/s) than with either a shorter period (5 min; 328 +/- 21 counts/s) or a prolonged period (40.8 min; 286 +/- 53 counts/s). The magnitude of oxygen radical generation did not correlate with postischemic mechanical function, although it was related to the duration of ischemia with regard to brief and intermediate periods of ischemia (both associated with limited mechanical damage). The increased reperfusion chemiluminescence seen with the intermediate versus the brief ischemic insults can be explained by time-dependent enhancement of the mechanisms present during ischemia that serve to increase oxygen radical generation during reperfusion. In contrast, the longer period of ischemia, resulting in severe mechanical dysfunction, was associated with lower levels of chemiluminescence than observed with an intermediate ischemic duration. This most likely results from the irreversible myocardial injury associated with prolonged ischemia and the consequent inability to generate oxygen radicals. We conclude that, although reperfusion-associated enhancement of myocardial free radical generation may be related to mild to moderate postischemic mechanical dysfunction (stunning), this mechanism may not be of importance in the generation of irreversible reperfusion myocardial injury.

Animals↗
PubMed1993

Chronic EDRF inhibition and hypoxia: effects on pulmonary circulation and systemic blood pressure.

It has been suggested that chronic hypoxic pulmonary hypertension results from chronic hypoxic inhibition of endothelium-derived relaxing factor (EDRF) synthesis. We tested this hypothesis by studying whether chronic EDRF inhibition by N omega-nitro-L-arginine methyl ester (L-NAME) would induce pulmonary hypertension similar to that found in chronic hypoxia. L-NAME (1.85 mM) was given for 3 wk in drinking water to rats living in normoxia or hypoxia. Unlike chronic hypoxia, chronic L-NAME treatment did not increase pulmonary arterial pressure. Cardiac output was reduced and mean systemic arterial pressure was increased by chronic L-NAME treatment. The vascular pressure-flow relationship in isolated lungs was shifted toward higher pressures by chronic hypoxia and, to a lesser degree, by L-NAME intake. In isolated lungs, vasoconstriction in response to angiotensin II and acute hypoxia and vasodilation in response to sodium nitroprusside were increased by chronic L-NAME treatment in normoxia and chronic hypoxia. Chronic hypoxia, but not L-NAME, induced hypertensive pulmonary vascular remodeling. Chronic supplementation with the EDRF precursor L-arginine did not have any significant effect on chronic hypoxic pulmonary hypertension. We conclude that the chronic EDRF deficiency state, induced by L-NAME, does not mimic chronic hypoxic pulmonary hypertension in our model. In addition, EDRF proved to be less important for basal tone regulation in the pulmonary than in the systemic circulation.

Animals↗
PubMed1993

A redox-based O2 sensor in rat pulmonary vasculature.

The effector mechanism of hypoxic pulmonary vasoconstriction (HPV) involves K+ channel inhibition with subsequent membrane depolarization. It remains uncertain how hypoxia modulates K+ channel activity. The similar effects of hypoxia and mitochondrial electron transport chain (ETC) inhibitors on metabolism and vascular tone suggest a common mechanism of action. ETC inhibitors and hypoxia may alter cell redox status by causing an accumulation of electron donors from the Krebs cycle and by decreasing the production of activated O2 species (AOS) by the ETC. We hypothesized that this shift toward a more reduced redox state elicits vasoconstriction by inhibition of K+ channels. Pulmonary artery pressure and AOS, measured simultaneously using enhanced chemiluminescence, were studied in isolated perfused rat lungs during exposure to hypoxia, proximal ETC inhibitors (rotenone and antimycin A), and a distal ETC inhibitor (cyanide). Patch-clamp measurements of whole-cell K+ currents were made on freshly isolated rat pulmonary vascular smooth muscle cells during exposure to hypoxia and ETC inhibitors. Hypoxia, rotenone, and antimycin A decreased lung chemiluminescence (-62 +/- 12, -46 +/- 7, and -148 +/- 36 counts/0.1 s, respectively) and subsequently increased pulmonary artery pressure (+14 +/- 2, +13 +/- 3, and +21 +/- 3 mm Hg, respectively). These agents reversibly inhibited an outward, ATP-independent, K+ current in pulmonary vascular smooth muscle cells. Antimycin A and rotenone abolished subsequent HPV. In contrast, cyanide increased AOS and did not alter K+ currents or inhibit HPV. The initial effect of rotenone, antimycin A, and hypoxia was a change in redox status (evident as a decrease in production of AOS). This was associated with the reversible inhibition of an ATP-independent K+ channel and vasoconstriction. These findings are consistent with the existence of a redox-based O2 sensor in the pulmonary vasculature.

Animals↗
PubMed1993

Chronic hypoxic pulmonary hypertension. Is thrombin involved?

Thrombin contracts vascular smooth muscle and stimulates its proliferation. Using a specific thrombin inhibitor, hirudin, we studied whether thrombin contributes to the pulmonary vasoconstriction and vascular proliferation that occurs in pulmonary hypertension. Hirudin was infused intravenously (0.2 mg/h/kg) by minipumps in nine rats during a 3-wk exposure to hypobaric hypoxia (HH). Vehicle (normal saline) was infused in eight hypoxic control (HC) and seven normoxic control (NC) rats. Sufficient hirudin delivery was confirmed by a failure of undiluted plasma from HH, but not from NC and HC, to clot in response to thrombin. When the plasma samples were diluted 1:10, the thrombin time was significantly prolonged in HH when compared with that in both NC and HC. Although hirudin slightly reduced mean pulmonary arterial pressure in open-chest rats, there was no significant difference between the hypoxic groups in total pulmonary resistance, right ventricle weight, morphologic remodeling of lung vessels, or the perfusion pressure-flow relationship in isolated lungs. Vasoconstrictor responses of isolated lungs to angiotensin II and acute hypoxic challenges were not affected by hirudin treatment. We conclude that hirudin, in a dose sufficient to reduce thrombin's catalytic effect on fibrinogen, does not significantly prevent the development of chronic hypoxic pulmonary hypertension.

Animals↗
PubMed1993

Diagnosis of pulmonary vein varix by transesophageal echocardiography.

A pulmonary vein varix is a localized dilatation of a pulmonary vein that usually is asymptomatic, presenting as a mass on a chest roentgenogram. Pulmonary angiography has been the mainstay of diagnosis. This case is the first in which transesophageal echocardiography was used to diagnose pulmonary vein varix.

Aged↗
PubMed1992

NG-monomethyl-L-arginine causes nitric oxide synthesis in isolated arterial rings: trouble in paradise.

Arginine analogs are commonly used as inhibitors of the synthesis of endothelium-derived relaxing factor, nitric oxide. However, their effect on nitric oxide levels is rarely measured. Using a chemiluminescence assay for nitric oxide, we found that NG-monomethyl-L-arginine enhanced, rather than reduced, nitric oxide synthesis in pulmonary arterial and aortic rings. NG-monomethyl-L-arginine inhibited relaxation to the endothelium-dependent vasodilator A23187 in aortic but not pulmonary arterial rings. In contrast, N omega-nitro-L-arginine did not stimulate nitric oxide synthesis and it inhibited relaxation to A23187 in all rings. We conclude that NG-monomethyl-L-arginine is a partial agonist for nitric oxide synthesis.

Animals↗
PubMed1992

Direct role for potassium channel inhibition in hypoxic pulmonary vasoconstriction.

Cellular mechanisms responsible for hypoxic pulmonary vasoconstriction were investigated in pulmonary arterial cells, isolated perfused lung, and pulmonary artery rings. Three K+ channel antagonists, Leiurus quinquestriatus venom, tetraethylammonium, and 4-aminopyridine, mimicked the effects of hypoxia in isolated lung and arterial rings by increasing pulmonary artery pressure and tension and also inhibited whole cell K+ currents in isolated pulmonary arterial cells. Reduction of oxygen tension from normoxic to hypoxic levels directly inhibited K+ currents and caused membrane depolarization in isolated canine pulmonary arterial smooth muscle cells but not in canine renal arterial smooth muscle cells. Nisoldipine or high buffering of intracellular Ca2+ concentration with [1,2-bis(2)aminophenoxy] ethane-N,N,N',N'-tetraacetic acid prevented hypoxic inhibition of K+ current, suggesting that a Ca(2+)-sensitive K+ channel may be responsible for the hypoxic response. These results indicate that K+ channel inhibition may be a key event that links hypoxia to pulmonary vasoconstriction by causing membrane depolarization and subsequent Ca2+ entry.

Animals↗
PubMed1992

H2O2 injury causes Ca(2+)-dependent and -independent hydrolysis of phosphatidylcholine in alveolar epithelial cells.

Oxidants may play a central role in the pathogenesis of adult respiratory distress syndrome, and phospholipase activation is a potential mechanism of oxidant-induced injury of alveolar epithelial cells. Studies were performed in rat alveolar type II epithelial cells (RAEC) after 3 days in culture. As measured by 51Cr and lactate dehydrogenase release, H2O2 caused time- and dose-dependent cytotoxicity to RAEC. RAEC phospholipids labeled with [14C]-stearic acid ([14C]SA) and [3H]arachidonic acid ([3H]AA) released free fatty acids in response to H2O2 in a manner that closely paralleled the cytotoxicity indexes. Analysis of phospholipid subclasses indicated that phosphatidylcholine was preferentially affected. Analysis for putative products of phospholipase activity revealed significant increases in diacylglycerol and phosphorylcholine, expected products of phospholipase C, as well as significant increases in L-alpha-lysophosphatidylcholine and L-alpha-glycerophosphocholine, expected products of phospholipase A2. Increases in phospholipase D activity were not detected. To determine whether H2O2-stimulated phospholipase activity might be Ca2+ stimulated, RAEC were loaded with fura-2/AM, and changes in intracellular Ca2+ concentrations ([Ca2+]i) were monitored by epifluorescent microscopy. Exposure to H2O2 caused elevations in [Ca2+]i, and the time and dose relationships were consistent with the hypothesis that the release of [14C]SA and [3H]AA is related to changes in cellular Ca2+ concentrations. Additionally, pretreatment with MAPTAM, an intracellular chelator of calcium, partially blocked H2O2-mediated [3H]AA liberation. However, experiments in saponin-permeabilized RAEC, in which [Ca2+]i was strongly buffered by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, indicate that H2O2-induced phospholipase activity also has a Ca(2+)-independent component.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Measurement of endothelial cytosolic calcium concentration and nitric oxide production reveals discrete mechanisms of endothelium-dependent pulmonary vasodilatation.

Nitric oxide is an endothelium-derived relaxing factor. Conversion of L-arginine to nitric oxide follows mediator-induced elevation of endothelial cytosolic calcium concentration. However, not all endothelium-dependent vasodilatation is caused by endothelium-derived relaxing factor, and few studies have correlated changes in vascular tone with measurement of free cytosolic calcium concentration or nitric oxide. The effects of three endothelium-dependent vasodilators (acetylcholine, bradykinin, and A23187) on vascular tone and nitric oxide production were studied in proximal rat pulmonary artery rings. Changes in free cytosolic calcium concentration and nitric oxide production were also studied in bovine pulmonary artery endothelial cells. A23187 and bradykinin caused pulmonary vasodilatation, nitric oxide production, and elevation of endothelial calcium concentrations. Although acetylcholine caused endothelium-dependent vasodilatation, it reduced free cytosolic calcium concentration and failed to increase nitric oxide levels. Acetylcholine-induced dilatation was partially inhibited by meclofenamate but was unaffected by ouabain. Acetylcholine, unlike bradykinin and A23187, does not act through a nitric oxide-dependent mechanism in the rat pulmonary vasculature.

Animals↗
PubMed1990

Comparison of the hemodynamic effects of nitric oxide and endothelium-dependent vasodilators in intact lungs.

The effects of endothelium-dependent vasodilation on pulmonary vascular hemodynamics were evaluated in a variety of in vivo and in vitro models to determine 1) the comparability of the hemodynamic effects of acetylcholine (ACh), bradykinin (BK), nitric oxide (NO), and 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP), 2) whether methylene blue is a useful inhibitor of endothelium-dependent relaxing factor (EDRF) activity in vivo, and 3) the effect of monocrotaline-induced pulmonary hypertension on the responsiveness of the pulmonary vasculature to ACh. In isolated rat lungs, which were preconstricted with hypoxia, ACh, BK, NO, and 8-bromo-cGMP caused pulmonary vasodilation, which was not inhibited by maximum tolerable doses of methylene blue. Methylene blue did not inhibit EDRF activity in any model, despite causing increased pulmonary vascular tone and responsiveness to various constrictor agents. There were significant differences in the hemodynamic characteristics of ACh, BK, and NO. In the isolated lung, BK and NO caused transient decreases of hypoxic vasoconstriction, whereas ACh caused more prolonged vasodilation. Pretreatment of these lungs with NO did not significantly inhibit ACh-induced vasodilation but caused BK to produce vasoconstriction. Tachyphylaxis, which was agonist specific, developed with repeated administration of ACh or BK but not NO. Tachyphylaxis probably resulted from inhibition of the endothelium-dependent vasodilation pathway proximal to NO synthesis, because it could be overcome by exogenous NO. Pretreatment with 8-bromo-cGMP decreased hypoxic pulmonary vasoconstriction and, even when the hypoxic pressor response had largely recovered, subsequent doses of ACh and NO failed to cause vasodilation, although BK produced vasoconstriction. These findings are compatible with the existence of feedback inhibition of the endothelium-dependent relaxation by elevation of cGMP levels. Responsiveness to ACh was retained in lungs with severe monocrotaline-induced pulmonary hypertension. Many of these findings would not have been predicted based on in vitro studies and illustrate the importance for expanding studies of EDRF to in vivo and ex vivo models.

Acetylcholine↗
PubMed1990

Enhanced chemiluminescence as a measure of oxygen-derived free radical generation during ischemia and reperfusion.

It has been suggested that oxygen-derived free radicals may contribute to the myocardial injury associated with ischemia and reperfusion. As the presence of enhanced free radical generation is a prerequisite for such damage, several techniques have been used to provide evidence of increased oxygen free radical production during reperfusion; however, all such techniques have substantial limitations. In this study, we used enhanced chemiluminescence to evaluate oxygen free radical generation during ischemia and reperfusion in the isolated Langendorff-perfused rat heart. The chemiluminescent technique, which has high sensitivity and can monitor radical generation continuously, avoids some of the limitations of earlier methods. Chemiluminescence (expressed as counts per second) decreased from 219 +/- 11 at baseline to 142 +/- 9 during ischemia and markedly increased to a peak of 476 +/- 36 during the first 3-5 minutes of reperfusion. This was followed by a slow decline over 11-16 minutes to a steady-state level of 253 +/- 14 (each sequential change in chemiluminescence was highly significant; p less than 0.001). Superoxide dismutase (2,000 units/min) significantly decreased peak reperfusion chemiluminescence to 316 +/- 17 (p less than 0.01). Hearts subjected to a second period of ischemia and reperfusion had a higher peak chemiluminescence (626 +/- 62), which also was significantly attenuated by 1,000 units/min superoxide dismutase (398 +/- 16; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Hypoxic pulmonary vasoconstriction is enhanced by inhibition of the synthesis of an endothelium derived relaxing factor.

Inhibition of the synthesis of endothelium derived relaxing factor by NG-monomethyl-L-arginine, a competitive inhibitor of the synthesis of nitric oxide from L-arginine, enhances hypoxic pulmonary vasoconstriction in pulmonary artery rings and isolated, Krebs albumin perfused rat lungs. L-arginine rapidly reduces hypoxic vasoconstriction, particularly in lungs treated with NG-monomethyl-L-arginine. Following administration of NG-monomethyl-L-arginine, bradykinin-induced vasodilatation is inhibited (p less than 0.01) and a bradykinin-induced vasoconstriction develops (p less than 0.001). NG-monomethyl-L-arginine does not significantly diminish acetylcholine-induced vasodilatation in the isolated lung. NG-monomethyl-L-arginine causes an endothelium-dependent vasoconstriction in pulmonary artery rings.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

Hydroxylamine is a vasorelaxant and a possible intermediate in the oxidative conversion of L-arginine to nitric oxide.

Our objective was to determine whether hydroxylamine is a possible intermediate in the oxidative conversion of L-arginine to nitric oxide. Vasorelaxation by hydroxylamine is known to be mediated by nitric oxide. The vasorelaxant properties of hydroxylamine were examined using rat aortic rings and an isolated rat lung perfusion model. Hydroxylamine and acetylcholine were equally effective in relaxing norepinephrine-contracted intact aortic rings, whereas only hydroxylamine relaxed aortic rings with endothelium removed. This endothelium-independent vasorelaxation by hydroxylamine indicated that the hydroxylamine-converting enzyme is not localized solely within endothelial cells. Catalase, an enzyme known to oxidize hydroxylamine to nitric oxide, was present in homogenates of intact and endothelium-denuded rings. Cyanamide, another catalase substrate and a known precursor of nitroxyl (HNO), was not a vasorelaxant of aortic rings or of isolated, hypoxia-constricted lungs. These results suggest that free nitroxyl is not an intermediate in the oxidation of hydroxylamine to nitric oxide. An overall pathway for the oxidative conversion of L-arginine through an hydroxylamine intermediate to nitric oxide is proposed.

Acetylcholine↗