PubMed Health⌕ Search

Biomedical subjects

G M Rubanyi

Publications and source records attributed to G M Rubanyi.

At least 55 records · Page 3Linked to original sources
PubMed1992

Different mechanisms of hypoxic relaxation in canine coronary arteries and rat abdominal aortas.

Hypoxia causes complex changes in vascular tone of isolated blood vessels. This study was performed in rings with and without endothelium of rat abdominal aortas and canine coronary arteries suspended in organ chambers for isometric tension recording. In both aortic and coronary rings with endothelium precontracted with a half-maximal concentration of phenylephrine or prostaglandin F2 alpha, respectively, hypoxia induced transient relaxations (20 +/- 2 and 15 +/- 3%, respectively); removal of the endothelium prevented the response in aortas, but not coronary arteries. The transient hypoxic relaxation was followed in both preparations by endothelium-dependent contractions (EDCs). Hypoxic relaxations were prevented by indomethacin (10 microM) in canine arteries, but not in rat aortas. The inhibitor of nitric oxide (NO) synthase, N omega-nitro-L-arginine (30 microM), inhibited hypoxic relaxations in intact rat aortas, but left those in coronary arteries unchanged. Similar results were obtained with methylene blue and LY 83583. In preparations without endothelium, sodium nitroprusside (30 nM) elicited a reappearance of hypoxic relaxations in the rat but not the dog coronary artery. Thus, hypoxic relaxation is mediated by a prostaglandin in the dog coronary artery, but by endothelium-derived NO in the rat aorta. As the response was dependent on the level of contraction, this suggests that the release or action of NO decreases with increasing tone.

Aminoquinolines↗
PubMed1991

Cytoprotective function of nitric oxide: inactivation of superoxide radicals produced by human leukocytes.

The oxygen-derived free radical superoxide anion (.O2-) plays an important role in the pathogenesis of various diseases. Recent demonstrations that .O2- inactivates the potent vasodilator endothelium-derived relaxing factor (EDRF) and that EDRF is probably nitric oxide (NO) suggest that EDRF(NO) may act as an endogenous free radical scavenger. This hypothesis was tested in an in vitro system by analyzing the effect of authentic NO (dilutions of a saturated aqueous solution) on .O2- production (detected spectrophotometrically as reduction of cytochrome c) by fMet-Leu-Phe-activated human leukocytes (PMN). NO depressed the rate of reduction of cytochrome c by .O2- released from PMN's or generated from the oxidation of hypoxanthine by xanthine oxidase. This effect was concentration-dependent and occurred at dilutions of the saturated NO solution (1:250 to 1:10) which inhibited platelet aggregation. NO had no direct effect on cytochrome c or on xanthine oxidase. These observations indicate that NO(EDRF) can be regarded as a scavenger of superoxide anion and they suggest that EDRF(NO) may provide a chemical barrier to cytotoxic free radicals (.O2-).

Adenosine Diphosphate↗
PubMed1991

Endothelium-derived relaxing and contracting factors.

Key discoveries in the past decade revealed that the endothelium can modulate the tone of underlying vascular smooth muscle by the synthesis/release of potent vasorelaxant (endothelium-derived relaxing factors; EDRF) and vasoconstrictor substances (endothelium-derived contracting factors; EDCF). It has become evident that the synthesis and release of these substances contribute to the multitude of physiological functions the vascular endothelium performs. Accumulating evidence suggests that at least one of the EDRFs is identical with nitric oxide (NO) or a labile nitroso compound, which is produced from L-arginine by an NADPH- and Ca(2+)-dependent enzyme, arginine oxidase. The existence of more than one chemically distinct EDRF has been proposed, including an endothelium-derived hyperpolarizing factor (EDHF). The target of EDRF (NO) is soluble guanylate cyclase (increase in cyclic GMP) while EDHF appears to activate a K(+)-channel in vascular smooth muscle. Recent data suggest that muscarinic receptor subtypes selectively mediate the release of EDRF(NO) (M2) and EDHF (M1). EDRF(NO) affects not only the underlying vascular smooth muscle, but also platelets, inhibiting their aggregation and adhesion to the endothelium. The antiaggregatory effect of EDRF is synergistic with prostacyclin, so their combined release may represent a physiological mechanism aimed at preventing thrombus formation. An additional proposed biological function of EDRF(NO) is cytoprotection by virtue of scavenging superoxide radicals. The endothelium can also mediate vasoconstriction by the release of a variety of endothelium-derived contracting factors (EDCF). Other than the unique peptide endothelin, the nature of EDCFs has not yet been firmly established. Autoregulation of cerebral and renal blood flow and hypoxic pulmonary vasoconstriction may represent the physiological role of endothelium-dependent vasoconstriction. Growing evidence indicates that the endothelium can serve as a unique mechanoreceptor, sensing and transducing physical stimuli (e.g., shear forces, pressure) into changes in vascular tone by the release of EDRFs or EDCFs. In physiological states, a delicate balance exists between endothelium-derived vasodilators and vasoconstrictors. Alterations in this balance can result in local (vasospasm) and generalized (hypertension) increase in vascular tone and also in facilitated thrombus formation. Endothelial dysfunction may also contribute to the pathophysiology of angiopathies associated with hypercholesterolemia and atherosclerosis.

Animals↗
PubMed1991

Endothelins.

The discovery of endothelium-derived relaxing (prostacyclin, EDRF) and contracting factors (EDCF) in the past decade opened up new vistas not only for basic and clinical research, but revolutionized our thinking about regulation and control of the cardiovascular system in health and disease. One of the most exciting developments in recent years was the discovery of a peptidergic EDCF and its isolation and identification as a unique 21-amino-acid peptide, endothelin (ET). This review summarizes the state-of-the-art in some areas of this fast-moving field, including the biosynthesis, tissue-specific expression, and binding of ET isoforms. Recent information about the nature of endothelin-converting enzyme (ECE) and the cloning, sequencing, and expression of ET receptor subtypes will be discussed. Based on current knowledge of the wide variety of biological actions of ETs, working hypotheses are presented about the possible autocrine, paracrine, and humoral actions of ETs and their potential role in modulating cardiovascular functions. In addition, the proposed significance of ETs in human cardiovascular diseases is summarized. In spite of the abundance of studies generated over the past 3 years and the postulated working hypotheses based on these findings, the true significance of ETs in short- and long-term regulation/modulation of tissue function remains to be determined. This will be the task of future investigations, using more sensitive detection methods and selective inhibitors of the biosynthesis and actions of ETs.

Amino Acid Sequence↗
PubMed1991

Smooth muscle cells contain a factor responsible for decreasing big endothelin and endothelin-1 produced by cultured endothelial cells.

The production of big endothelin-1 (big ET-1) and its processing to endothelin (ET-1) were examined in cocultures of bovine pulmonary artery endothelial cells (BPECs) and human bronchiolar smooth muscle cells (HBSMCs). The BPECs produced immunologically reactive ET-1 (ir-ET-1) and big ET-1 (ir-big ET-1) that increased linearly in the cell culture media over a 72 h time course when confluent monolayers were incubated at 37 degrees C in serum-free media. HBSMCs maintained in serum-free media over a 72-h period did not produce any detectable ir-big ET-1 or ir-ET-1. After coculture of these two cell types for 24 h (the monolayers were physically separated), the culture medium contained no detectable ir-big ET-1 or ir-ET-1. When medium conditioned for 24 h with the HBSMCs was transferred to the BPEC monolayers, the accumulation rates of ET-1 and big ET-1 were attenuated 70 and 10%, respectively. When medium conditioned for 24 h with the BPECs was transferred to the HBSM cell monolayers, the amount of ir-ET-1 and ir-big ET-1 in the medium decreased greater than 90% over the next 24 h. Cellular binding and uptake could not account for this decrease as ascertained by quantitation of cellular levels of ET-1 and big ET-1. When conditioned medium from the HBSMCs was added to conditioned medium from the BPECs in a 1:1, 2:1, 3:1, 1:2, or 1:3 ratio (v/v) in the absence of cells, the amount of ET-1 or big ET-1 present in the EC medium did not decrease significantly over the following 24 h. These data imply that HBSMCs contain a factor that is responsible for decreasing the accumulation of ir-big ET-1 and ir-ET-1 in the cell culture media of BPECs. The data also suggest that the most likely mechanism for this effect is a factor that degrades BET-1 and ET-1 at different rates.

Animals↗
PubMed1991

Phorbol dibutyrate stimulates the release of diffusible endothelium-derived vasoconstrictor factor(s) from canine femoral arteries.

The purpose of this study was to analyze the effect of the tumor-promoting phorbol ester 12,13-dibutyrate (PDBu) on the synthesis/release of nonprostanoid endothelium-derived vasoactive factors. In bioassay experiments (in the presence of 10(-5) M indomethacin), infusion of PDBu (10(-9)-10(-7) M) through a femoral artery (donor) segment with endothelium evoked further, concentration-dependent contraction of superfused canine coronary artery bioassay rings without endothelium (already contracted with 10(-7) M PDBu). Removal of the endothelium from the donor segment abolished further contractions of the bioassay ring to 10(-9) M PDBu and significantly depressed the contractile responses to 10(-9) and 10(-7) M PDBu infused through the donor segment. The inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate had no effect on vascular preparations mounted in the bioassay system. Selective exposure of the bioassay tissue to 10(-7) M PDBu completely inhibited its responsiveness to basally released endothelium-derived relaxing factor. These data indicate that PDBu stimulates the release of a diffusible and bioassayable vasoconstrictor mediator(s) from the endothelium of canine femoral arteries.

Acetylcholine↗
PubMed1991

Ionic mechanisms involved in the flow- and pressure-sensor function of the endothelium.

Changes in hemodynamic forces (shear stress and pressure) modulate the tone of blood vessels. Recent evidence suggests that the endothelium plays an important role in these responses. Cascade bioassay experiments with various blood vessels demonstrated that increases in shear stress stimulated, and elevated transmural pressure suppressed the synthesis/release of endothelium-derived relaxing factor (EDRF). Studying the potential mechanisms of stimulus-response coupling in endothelial cells, it was shown that shear stress hyperpolarizes and pressure depolarizes the membrane of endothelial cells. Using whole-cell patch-clamping and various inhibitors of ion channels, it was demonstrated that modulation of the inward rectifying K(+)-channel may be the initial step in stimulus-response coupling: shear stress activates and pressure inactivates this channel, respectively. Since membrane potential is the main determinant of Ca(2+)-entry into endothelial cells, this still hypothetical mechanism may explain the opposing effects of shear stress (increased Ca(2+)-entry) and pressure (decreased Ca(2+)-entry) on the synthesis/release of EDRF.

Acetylcholine↗
PubMed1990

Membrane potential and Na(+)-K+ pump activity modulate resting and bradykinin-stimulated changes in cytosolic free calcium in cultured endothelial cells from bovine atria.

The effects of membrane potential on resting and bradykinin-stimulated changes in [Ca2+]i were measured in fura-2 loaded cultured endothelial cells from bovine atria by spectrofluorimetry. The basal and bradykinin-stimulated release of endothelium-derived relaxing factor, monitored by bioassay methods, were dependent on extracellular Ca2+. Similarly, the plateau phase of the biphasic [Ca2+]i response to bradykinin stimulation exhibited a dependence on extracellular Ca2+, whereas the initial transient [Ca2+]i peak was refractory to the removal of extracellular Ca2+. The effect of membrane depolarization on the plateau phase of the bradykinin-induced change in [Ca2+]i was determined by varying [K+]o. The resting membrane potential measured under current clamp conditions was positively correlated with the extracellular [K+] (52 mV change/10-fold change in [K+]o). The observed decrease in resting and bradykinin-stimulated changes in [Ca2+]i upon depolarization is consistent with an ion transport mechanism where the influx is linearly related to the electrochemical gradient for Ca2+ entry (Em - ECa). The inhibition of bradykinin-stimulated Ca2+ entry by isotonic K+ was not due to the absence of extracellular Na+ since Li+ substitution did not inhibit the agonist-induced Ca2+ entry. In K(+)-free solutions and in the presence of ouabain, bradykinin evoked synchronized oscillations in [Ca2+]i in confluent endothelial cell monolayers. These [Ca2+]i oscillations between the plateau and resting [Ca2+]i levels were dependent on extracellular Ca2+ and K+ concentrations. Although the mechanism(s) underlying [Ca2+]i oscillations in vascular endothelial cells is unclear, these results suggest a role of the membrane conductance.

Animals↗
PubMed1990

Lack of biological activity of preproendothelin [110-130] in several endothelin assays.

A 21 amino acid peptide containing the prepropendothelin sequence from amino acids 110 to 130 and two intrachain disulfide bonds was synthesized and tested for biological activity in the following endothelin assays: 1.) a competition binding assay using [125I]ET-1 and dog heart membranes, 2.) three RIA's using 125I-ET-1, -2 and -3 and the respective anti-ET rabbit antisera; and 3.) a contractile activity bioassay using hamster aortic rings. The synthetic peptide which has been referred to as the "endothelin-like" peptide occurs 36 amino acids C-terminal to endothelin in the prepro-protein sequence. It contains only 40% sequence homology to the three endothelin isoforms, but has the same sequence and cyclization pattern of cysteines at positions 1, 3, 11 and 15. Despite the overall similarity in secondary structure to the three isoforms of endothelin and sarafotoxin S6b, preproendothelin [110-130] had no activity in any of the assays when tested at concentrations of 10(-10)M to 10(-5)M.

Amino Acid Sequence↗
PubMed1990

Mechanoreception by the endothelium: mediators and mechanisms of pressure- and flow-induced vascular responses.

Mechanoreception, a widely distributed sensory modality, has been shown to be present in certain blood vessels. Changes in physical forces, like sudden increase of transmural pressure or flow velocity (shear stress), trigger changes in blood vessel diameter; the former reduces it while the latter increases vessel caliber. These changes in diameter, which are the result of contraction and relaxation of vascular smooth muscle in the blood vessel media, can serve the purpose of physiological regulation of blood flow (autoregulation) and protection of the intima against damages from high shear forces. The precise location of mechanosensor(s) and the mechanism of mechanoreception and signal transduction are poorly understood. Accumulating evidence suggests that the endothelium may be a site of mechanoreception and that changes in the synthesis/release of endothelium-derived relaxing (EDRF, EDHF, PGI2) and contracting factors (EDCF) result in altered vascular smooth muscle tone and vessel caliber. Increased shear stress stimulates the release of EDRF and PGI2 probably via activation of a K+ channel (inward rectifier) in endothelial cell membrane. Endothelium-dependent vascular contraction evoked by increased transmural pressure may be the result of (1) reduced release of EDRF (canine carotid artery) and (2) stimulation of the release of a still unidentified EDCF(s) (feline cerebral artery). Thus the endothelium can serve as pressure and flow sensor and is capable of transducing changes in mechanical forces into changes of vascular smooth muscle tone by modulating the release of endothelium-derived vasoactive factors. The physiological importance of the mechanoreception by endothelial cells in the intact circulation remains to be determined.

Animals↗
PubMed1990

Endothelium-derived relaxing factor released from canine femoral artery by acetylcholine cannot be identified as free nitric oxide by electron paramagnetic resonance spectroscopy.

Recent studies using chemiluminescence and spectrophotometry have shown that cultured and native endothelial cells release nitric oxide (NO). Pharmacological and biochemical evidence argue for and against the proposal that endothelium-derived relaxing factor (EDRF) is identical with free NO. In an attempt to identify EDRF as free NO, a bioassay technique was combined with an NO trap (hemoglobin bound to agarose; Ag-Hb), and electron paramagnetic resonance (EPR) spectroscopy was used to detect the resultant nitrosylhemoglobin (NO-Hb). Canine femoral arteries with or without endothelium were perfused with physiological saline solution containing superoxide dismutase and ibuprofen and were stimulated with acetylcholine. The relaxing activity of the effluent was monitored in canine coronary artery rings without endothelium (bioassay tissue) half-maximally contracted with U46619. Acetylcholine stimulated the release of EDRF from intact femoral arteries (but not from segments without endothelium), which relaxed the bioassay tissue by 63 +/- 5%. NO (approximately 1 and approximately 10 nM) infused directly over the bioassay tissue produced 34 +/- 8% and 96 +/- 3% relaxation, respectively (ED50, approximately 2 nM). Effluents were collected under vacuum in the absence of oxygen through a column containing Ag-Hb, and the samples were assayed for NO-Hb by EPR. Samples containing NO produced the triplet EPR signal characteristic of NO-Hb, but the effluent containing EDRF did not. Infusion of NO through the donor tissue in the presence of acetylcholine gave an EPR signal similar to that observed when NO had no contact with the tissue. Nitrite anion (up to 2.7 x 10(-2) M) produced no detectable NO-Hb in analogous experiments. Thus, EDRF released from the native endothelium of canine femoral artery cannot be identified as free NO. The present findings support a concept that EDRF may be a labile precursor of NO.

Acetylcholine↗
PubMed1990

Endothelium-dependent modulation of endothelin-induced vasoconstriction and membrane depolarization in cat cerebral arteries.

Effects of endothelin, the newly discovered, endothelium-derived vasoactive peptide, were examined on isolated, pressurized cat arteries. Responses to increasing concentrations of porcine endothelin (10(-12) to 10(-8) M) were compared in endothelium intact and denuded vessel segments utilizing diameter and membrane potential measurements. Endothelin produced a concentration-dependent contraction in arteries with intact endothelium with a maximal response of 26 +/- 2.8% of the initial diameter in physiological saline solution at 100 mm Hg of intraluminal pressure. Removal of the endothelium sensitized the smooth muscle to endothelin and increased the maximal response to 48 +/- 2.3% of the initial diameter. After incubation of the intact vessels with 10(-5) M indomethacin, the endothelin response was potentiated to the maximal value of 66 +/- 1.26% of the initial diameter of the intact vessels, and to 61 +/- 2.6% of the denuded arteries. The arterial smooth muscle cells were depolarized by 6 +/- 0.45 mV after administration of endothelin to the vessels, and by 10 +/- 0.8 mV in the denuded vessels. This depolarization was not altered by indomethacin. Our data suggest that endothelin has a direct effect on the smooth muscle of cat cerebral vascular tissue, and the sensitivity of these vessels to endothelin may be modulated by the release of dilatory cyclooxygenase products derived from the intact endothelium.

Animals↗
PubMed1989

Endothelin-1 stimulates phosphatidylinositol hydrolysis and calcium uptake in isolated canine coronary arteries.

The effects of synthetic endothelin-1 (ET-1) (10(-10)-3 x 10(-7) M) on isometric force, 45Ca2+ uptake, and phosphatidylinositol (PI) hydrolysis were determined in isolated canine coronary artery rings. ET-1 caused contraction and stimulated 45Ca2+ uptake and PI hydrolysis (determined as inositol monophosphate accumulation) in a concentration-dependent manner with EC50 values of 6.3 x 10(-9), 2 x 10(-9), and 3 x 10(-9) M, respectively. Maximal responses were obtained with 3 x 10(-8) M ET-1 for all three parameters. At the maximally effective concentration, ET-1 caused a 1.8-fold increase in the rate of 45Ca2+ uptake following a 1-min exposure (the shortest time point tested) while the contractile response reached maximum only after 6 min. ET-1 (3 x 10(-8) M) stimulated a biphasic accumulation of inositol monophosphate with an initial rapid 1.4-fold increase detectable between 30 and 60 s followed by a secondary 11.9-fold increase at 30 min. These data show that PI hydrolysis and Ca2+ uptake are early events in the action of ET-1 on coronary artery vascular smooth muscle that precede the maximal contractile response. It is suggested that all of these responses are triggered by the interaction of ET-1 with a cell-surface receptor.

Animals↗
PubMed1989

Pressure releases a transferable endothelial contractile factor in cat cerebral arteries.

When exposed to an increasing transmural pressure, middle cerebral arteries of the cat exhibit reduction of internal diameter which is mediated by vascular muscle cell depolarization. This laboratory has recently demonstrated that this "pressure-induced" activation is dependent upon the presence of an intact endothelium. The present studies were undertaken to determine if this phenomenon is due to inhibition of tonically released endothelium-derived relaxing factors (EDRF) or release of a contractile substance. When cerebral arterial segments were pressurized to between 40 and 160 mm Hg there was 13.2% reduction in internal diameter accompanied by significant muscle cell depolarization from -53 +/- 2.7 to -22 +/- 1.4 mV. There was a significant positive correlation between the delta Em and step increases in transmural pressure. These excitatory responses were lost and vessels dilated to pressure when the endothelium was removed. Upon exposing the denuded vessel to a pressurized intact donor, the denuded vessel recovered its ability to contract and depolarize suggesting that a contractile substance might be released from the vascular endothelium upon pressurization. The EDRF antagonist oxyhemoglobin did not alter the excitatory response to pressure in these isolated cerebral arteries further suggesting that the reduction in diameter and muscle cell depolarization results from the release of a contractile substance from the vascular endothelium and not inhibition of EDRF.

Animals↗
PubMed1989

Phorbol dibutyrate inhibits release and action of endothelium-derived relaxing factor(s) in canine blood vessels.

The effects of phorbol esters on endothelium-dependent relaxations evoked by ACh and the calcium ionophore A23187 were analyzed in isolated canine femoral and coronary arteries mounted in organ chambers or in a bioassay system. In rings of femoral and coronary arteries, phorbol 12,13-dibutyrate (PDBu) (10(-7) M) evoked contraction (ED50 2.9 x 10(-8) M) and depressed endothelium-dependent relaxations to ACh (4-fold increase in ED50 and 72% depression of maximal response). PDBu depressed maximal relaxations to A23187 by 50% but had no effect on ED50. The inactive phorbol ester 4-alpha-phorbol didecanoate (10(-7) M) did not evoke contractions and had no effect on endothelium-dependent relaxations to ACh or A23187. Endothelium-independent relaxations to sodium nitroprusside were not effected by PDBu (10(-7) M) in femoral or coronary arteries. In bioassay experiments, selective treatment of perfused femoral artery segments with PDBu (10(-8)-10(-6) M) caused concentration-dependent inhibition of basal and ACh- (10(-6) M) and A23187-(10(-6) M) induced release of endothelium-derived relaxing factor (EDRF) (as assessed by relaxation of superfused bioassay coronary artery rings without endothelium). PDBu inhibited these responses with different potency: basal (10(-8) M) greater than ACh (10(-7) M) much greater than A23187 (only partial inhibition at 10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1988

Potassium-free solution prevents the action but not the release of endothelium-derived relaxing factor.

Exposure to a K+-free solution reversibly inhibited the acetylcholine-induced relaxation in perfused canine femoral artery segments with endothelium and in superfused bioassay femoral artery rings without endothelium. Infusion of 6.7 mM K+ into the K+-free perfusate downstream of the perfused artery restored the acetylcholine-induced relaxation in the bioassay ring, whereas no relaxation was observed in the perfused segment still exposed to the K+-free solution. These data demonstrate that the K+-free solution depresses the endothelium-dependent relaxation to acetylcholine in femoral arteries by preventing the action, but not the production, of endothelium-derived relaxing factor.

Acetylcholine↗
PubMed1988

Vascular effects of oxygen-derived free radicals.

This review attempts to summarize the available data regarding the vascular actions of free oxygen radicals. Studies on blood vessels in situ and in vitro demonstrate that free oxygen radicals can evoke both vasodilation and vasoconstriction. Free oxygen radicals can modulate the tone of vascular smooth muscle by acting directly on the smooth muscle cells, and also via indirect mechanisms by changes in the production or biological activity of vasoactive mediators. The individual oxygen radicals may have different (sometimes opposite) vascular effects. Superoxide anion inactivates endothelium-derived relaxing factor and the adrenergic neurotransmitter norepinephrine. Hydrogen peroxide and the hydroxyl radical evoke vasodilation by acting directly on vascular smooth muscle and also by stimulating the synthesis/release of endothelium-derived relaxing factor. In acute arterial hypertension or experimental brain injury oxygen radicals are important mediators of vascular damage. Production of oxygen-derived free radicals by activated neutrophils may be responsible for vasodilation and increased permeability of capillary membrane during the acute inflammatory process. Free oxygen radicals also play an important role in reperfusion injury of various organs, and vascular actions of the free radicals may contribute to the damage of parenchymal tissues.

Animals↗