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Biomedical subjects

A Conforto

Publications and source records attributed to A Conforto.

11 recordsLinked to original sources
PubMed1995

Inhibition of endothelial nitric oxide synthase by cytochrome P-450 reductase inhibitors.

Nitric oxide synthase (NOS) shows similarities to cytochrome P-450 reductase. The two enzymes catalyze the oxidation of N-omega-hydroxy-L-arginine by NADPH and oxygen to nitric oxide (NO) and citrulline. Nitric oxide synthase activity is inhibited by L-arginine analogs like N-omega-nitro-L-arginine, which does not affect cytochrome P-450 reductase. Dihydroergotamine, miconazole, and troleandomycin are classical inhibitors of cytochrome. The present study shows the concentration-dependent inhibitory effect of these compounds and of L- but not D-N-omega-nitro-arginine on the activity of constitutive nitric oxide synthase from bovine aortic endothelial cells. Activity of nitric oxide synthase was estimated by measurement of conversion of [3H]arginine to [3H]citrulline. The tested cytochrome P-450 inhibitors are likely to interfere with heme of nitric oxide synthase. The data confirms a similarity as well as functional differences between the enzymes.

Amino Acid Oxidoreductases↗
PubMed1994

Inducible nitric oxide synthase activity in myocardium after myocardial infarction in rabbit.

The activity of nitric oxide synthase (NOS) in infarcted and noninfarcted rabbit myocardium was determined. NOS activity, as measured by conversion of [14C]arginine to [14C]citrulline, was significantly higher in the infarcted area of myocardium (22.7 +/- 3.7 fmol/mg as compared to 7.67 +/- 1.0 in noninfarcted area). NOS activity within the area of risk remained on control level. Increased inducible NOS activity was observed on the first postoperative day and persisted for at least 14 days; it declined 3 weeks after infarction. Citrulline formation was inhibited by N-omega-nitro-L-arginine and N-omega-monomethyl-L-arginine The localization of NOS by monoclonal anti-NOS antibody indicates mononuclear cells/macrophages as the likely source of the enzyme. The concentrations of tumor necrosis factor-alpha and interleukin-1 beta were not increased in peripheral blood or myocardium.

Amino Acid Oxidoreductases↗
PubMed1994

The production of nitric oxide in endothelial cells by amphiphiles.

Lysophosphatidylcholine, an endogenous detergent is an endothelium-dependent smooth muscle relaxant, which acts through the release of nitric oxide. It is known to activate a number of membrane-bound enzymes. Because of the relationship between detergent action, relaxation of endothelium-intact rabbit aortic strips and the release of nitric oxide, we considered the possibility that other amphiphiles also produce nitric oxide from endothelial cells. We therefore investigated the effect of digitonin on relaxation of precontracted rabbit aortic strips and the release of nitric oxide from freshly harvested bovine endothelial cells as determined by chemiluminescence. We found that both digitonin and LPC release nitric oxide and that this process is inhibited by the NO synthase inhibitor N omega-Nitro-L-Arginine Methyl Ester (L-NNAME).

Animals↗
PubMed1994

Effect of amphiphiles on nitric oxide synthase in endothelial cells.

Amphiphiles are known to modulate the activity of ATPase, phospholipase A2, adenylate and guanylate cyclase amongst others and relax vascular smooth muscle. The effect of two amphiphiles, lysophosphatidylcholine (LPC) and digitonin on the activity of nitric oxide synthase (NOS), as measured by conversion of radiolabeled L-arginine to L-citrulline, has been studied. Neither digitonin (0.01 mmol/l) nor LPC (0.01 mmol/l) influenced NOS activity in endothelial cell homogenates. Digitonin but not LPC stimulated NOS in intact endothelial cells. NOS activity was markedly inhibited by L- but not by D-omega-nitroarginine (D-NNA, 0.1 mmol/l). L-NNA or D-NNA data demonstrate no effect of amphiphiles on isolated NOS. NOS activation may occur as a result of detergent action on the membrane.

Amino Acid Oxidoreductases↗
PubMed1993

Synthesis of leukotrienes by freshly harvested endothelial cells.

Endothelial cells produce endothelin, a powerful vasoconstrictor. We report the release of additional vasoconstrictor material in conditional filtrate from freshly harvested cells, which we identified as leukotrienes by radioimmunoassay (RIA) and by high pressure liquid chromatography (HPLC). The material was collected in cell free filtrates by superfusion of freshly harvested bovine endothelial cells attached to cytodex-3 microcarrier beads. Cells and beads form a dense network on filter paper permitting collection of cell free filtrate. The amount of leukotrienes in conditioned filtrate was 158 +/- 21 picograms/million cells. The calcium ionophore A23187 stimulated the release of leukotrienes (392.0 +/- 47.6). The peak of leukotriene production occurred within an hour after incubation of cells slowly declining thereafter. Conditioned filtrate to which indomethacin had been added caused coronary vasoconstriction in the perfused rat heart preparation, as did synthetic leukotrienes C4, D4 and E4. It was found by RIA and HPLC that some of the constrictor effect of conditioned filtrate derived from leukotrienes.

Animals↗
PubMed1993

Membrane function and vascular reactivity.

This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates sialyltransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.

Animals↗
PubMed1993

Vascular smooth muscle and nitric oxide.

Experiments were performed to investigate the production of endothelium-derived relaxing factor (EDRF or nitric oxide; NO) by vascular smooth muscle cells. The lumen of bovine pulmonary arteries were filled with Krebs-Henseleit solution (incubates). Both endothelium-intact and endothelium-deprived vessels were used. Incubate solutions from the lumen of generator vessels contained a significant amount of nitric oxide (NO). Although the NO concentration was higher in incubates from endothelium-intact vessels, endothelium-deprived vessels also produced NO. The length of incubation did not influence the amount of nitric oxide released. Endothelium-deprived pulmonary arteries also generated NO as detected by chemiluminescence. The amount produced however was not sufficient to relax endothelium-deprived detector vessels in superfusion bioassay experiments. Samples from Krebs-Henseleit (K-H) solution surrounding the preparation (bathing solution) contained NO values which were also significantly higher than the control. Nitric oxide found in the bathing solution also appeared to originate from endothelium and vascular smooth muscle. Oxyhemoglobin attenuated NO signals. The results demonstrate that nitric oxide is released by vascular smooth muscle cells as well as by endothelium. However, the amount of NO released by muscle is insufficient to relax endothelium-deprived vascular preparations.

Animals↗
PubMed1993

The production of coronary vasoconstrictor substances by freshly harvested endothelial cells.

The effects of cell free superfusates from freshly harvested bovine endothelial cells attached to microcarrier beads on the isolated rabbit and rat heart and on superfused rabbit jugular veins were observed. Cell free conditioned filtrates from freshly harvested cells caused marked diminution in coronary flow and cardiac output in the isolated rabbit heart; in the perfused rat heart an increase in coronary perfusion pressure and a decline in left ventricular systolic tension and maximal left ventricular contractility (dP/dt) were recorded. Marked differences were found between changes induced by conditioned filtrate as compared to synthetic endothelin. Endothelin as present in conditioned filtrate could not account for the pronounced effect on coronary perfusion pressure, dp/dt and cardiac output induced by conditioned filtrate; more than one hundred times that of synthetic endothelin was needed to achieve comparable cardiodynamic effects. This suggested that additional non-prostanoid vasoconstrictor substance or substances are produced by freshly harvested endothelial cells. This conclusion was supported by the observation that BQ-123, a specific inhibitor of endothelin A (ETA) receptor significantly prevented contractions by endothelin, while failing to inhibit those induced by freshly harvested endothelial cells. These constrictor substances may be leukotrienes.

Animals↗
PubMed1993

Lysophosphatidylcholine-induced vascular relaxation and production of cGMP are mediated by endothelium-derived relaxing factor.

Endothelial cells produce powerful vasorelaxant substances, among them an endothelium-derived relaxing factor that is believed to be nitric oxide. It relaxes vascular smooth muscle via activation of guanylate cyclase and a subsequent rise in cyclic GMP level. Lysophosphatidylcholine is a potent endothelium-dependent vascular smooth muscle relaxant. Its action, similar to that of endothelium-derived relaxing factor, mediates an increase of cGMP in smooth muscle cells. The experiments reported here demonstrate that inhibitors of nitric oxide formation, such as N-omega-nitro-L-arginine and its methyl ester, inhibit relaxation and cyclic GMP formation by lysophosphatidylcholine in bovine pulmonary artery strips with intact endothelium in a dose-dependent manner. N-omega-Nitro-D-arginine methyl ester does not inhibit relaxation; L-arginine, but not D-arginine, reverses the effect of N-omega-nitro-L-arginine and its methyl ester. It is concluded that lysophosphatidylcholine-induced endothelium-dependent vasorelaxation is endothelium-derived relaxing factor-mediated.

Animals↗