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Biomedical subjects

G M Rubanyi

Publications and source records attributed to G M Rubanyi.

At least 73 records · Page 4Linked to original sources
PubMed1988

Calcium and activation of the release of endothelium-derived relaxing factor.

Indirect and direct experimental evidence demonstrates that both the entry of extracellular calcium and the liberation of calcium from intracellular stores can contribute to an increase in free cytoplasmic calcium concentration in endothelial cells, which seems to be an essential step in the synthesis and/or release of endothelium-derived relaxing factors(s). A variety of Ca2+ transport mechanisms may be involved in the regulation of cytoplasmic calcium in endothelial cells. Ca2+ entry may occur via voltage-operated Ca2+ channels. If they do exist, these channels may have characteristics different from those in underlying vascular smooth muscle cells. Sustained activation of the release of EDRF by various receptor agonists (e.g., acetylcholine, adenine nucleotides, and bradykinin) is also dependent on Ca2+ entry, but it is insensitive to organic Ca2+ channel antagonists. These findings indicate that, when used clinically in various cardiovascular diseases, organic calcium channel antagonists are not expected to interfere with endothelium-dependent relaxation evoked by endogenous vasoactive substances (e.g., ADP, serotonin). Since amiloride and its analogues blocked endothelium-dependent relaxations in different arterial preparations, Na+ transport and Na+/Ca2+ exchange were suggested to play a role in calcium-dependent release of EDRF. The exact nature of Ca2+ transport mechanisms and also the calcium-sensitive cellular processes that lead to the synthesis/release of endothelium derived relaxing factor(s) remain to be determined. However, the available data suggest that calcium handling by the vascular smooth muscle and endothelial cells may be different, allowing potentially selective modulation of Ca2+ activation in these two cell types.

Animals↗
PubMed1988

Endothelium-dependent pressure-induced contraction of isolated canine carotid arteries.

Experiments were conducted in a bioassay system, where a canine coronary artery ring without endothelium (bioassay tissue) was superfused by the effluent from a perfused canine carotid artery segment with endothelium (donor segment). A rapid increase in transmural pressure (from near 0 to 32-38 mmHg) triggered active contraction of the donor segment and simultaneously of the bioassay tissue. These contractions were prevented by removal of the endothelium from the donor segment but not by treatment of the segment with indomethacin. Exposure to elevated pressure depressed basal, acetylcholine-, and flow-induced release of endothelium-derived relaxing factor(s). Methylene blue prevented the pressure-induced contraction of the bioassay ring. These data show that pressure-induced contraction of isolated carotid arteries is endothelium dependent and is mediated by the depression of the synthesis and/or release of endothelium-derived relaxing factor(s).

Acetylcholine↗
PubMed1988

Potassium-induced release of endothelium-derived relaxing factor from canine femoral arteries.

Experiments were designed in a bioassay system to analyze the effect of elevated (from 5.9 mM to 7.5-45.9 mM) extracellular K+ concentration on the release of endothelium-derived relaxing factor. Segments of canine femoral artery with endothelium (donor segment) were mounted in an organ bath and perfused with modified Krebs-Ringer bicarbonate solution; the effluent from the donor segment was used to superfuse a canine coronary artery ring without endothelium (bioassay tissue). Elevation of perfusate K+ concentration by 1.6-15 mM by intraluminal infusion of potassium chloride upstream of the donor segment evoked further contractions of bioassay rings contracted with prostaglandin F2 alpha. In contrast, the bioassay rings progressively relaxed when increasing concentrations of potassium chloride (10-40 mM) were added extraluminally to the organ bath where the perfused segment was mounted. Extraluminal application of phenylephrine or prostaglandin F2 alpha did not evoke relaxations in the bioassay ring. Removal of the endothelium from the donor segment or selective exposure of the segment (but not the bioassay ring) to Ca2+-deficient solution prevented the K+-induced relaxations. Treatment of the donor segment and the bioassay ring with inhibitors of known endogenous vasoactive substances (acetylcholine, norepinephrine, adenine nucleotides, and prostanoids) had no significant effect on the relaxation of the bioassay ring evoked by extraluminal application of potassium chloride. Simultaneous measurements of changes in isometric force in the donor segment and bioassay ring revealed that extraluminal elevation of K+ concentration relaxed the segments as well and that the relaxations could not be prevented by simultaneous intraluminal infusion of potassium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Stereoselective effect of diltiazem on endothelium-dependent relaxations in canine femoral arteries.

Experiments were designed to analyze potential interactions between voltage-dependent calcium channel blockers and endothelium-dependent vascular responses. Rings of canine femoral artery were suspended for isometric force recording in organ chambers and contracted with prostaglandin F2 alpha. Removal of the endothelium had no effect on relaxations induced by d-cis-diltiazem (active stereoisomer), verapamil or nimodipine. When rings with endothelium were first partially relaxed with acetylcholine or the calcium ionophore A23187 the concentration-relaxation curve to d-cis-diltiazem (but not to verapamil or nimodipine) was significantly shifted to the right. Partial relaxation of femoral arterial rings without endothelium by sodium nitroprusside had no effect on relaxations evoked by diltiazem. Pretreatment with diltiazem (10(-6) M) had no effect on endothelium-dependent relaxations to acetylcholine in femoral artery rings. D-cis-Diltiazem partially reversed the relaxation induced by acetylcholine in a bioassay system, in which a ring of canine coronary artery without endothelium was superfused by solution passing through a segment of femoral artery with endothelium. D-cis-Diltiazem relaxed the bioassay ring when infused downstream of the perfused femoral artery with, or upstream of a femoral artery without endothelium. The effect of diltiazem was stereoselective (the less active l-cis-diltiazem had no effect). Verapamil did not reverse the relaxation induced by acetylcholine and did not affect the reversal induced by diltiazem. These findings indicate that diltiazem specifically antagonizes the production and/or the release of endothelium-derived relaxing factor(s) stimulated by acetylcholine or A23187 in canine femoral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Heterogeneity of endothelium-dependent responses to acetylcholine in canine femoral arteries and veins. Separation of the role played by endothelial and smooth muscle cells.

The purpose of this study was to determine whether heterogeneity in endothelium-dependent responses to acetylcholine between canine blood vessels of different anatomical origin reflects variations in endothelial function or in responsiveness of vascular smooth muscle cells. Experiments were conducted in a bioassay system, where segments of femoral artery or vein with endothelium were perfused intraluminally and the perfusate used to superfuse rings of femoral arteries or veins without endothelium. Indomethacin was present in all experiments to prevent the synthesis of prostanoids. The blood vessels were contracted by phenylephrine. Measurement of wall tension in both the perfused segment and bioassay ring allowed simultaneous detection of endothelium-derived relaxing factor(s) released abluminally (segment) and intraluminally (ring). Intraluminal infusion of acetylcholine (ACh) induced relaxations in the perfused artery but not in vein segments. During arterial superfusion ACh induced relaxation in femoral arterial rings but contraction in venous rings. After treatment with atropine the arterial perfusate evoked relaxations in venous rings. Infusion of ACh through the femoral vein evoked only moderate relaxations in arterial rings. These data demonstrate that depressed endothelium-dependent relaxation to ACh in femoral veins compared to femoral arteries is due to a masking effect of the direct stimulating action of ACh and decreased release of the same mediator or the release of a different relaxing factor from venous endothelium.

Acetylcholine↗
PubMed1987

Atrial natriuretic peptide decreases cardiac output independent of coronary vasoconstriction.

Studies were performed in isolated, Langendorff-perfused rat hearts and anesthetized dogs to determine the effects of synthetic atrial natriuretic peptide (ANP 8-33) on the coronary circulation. In vitro studies in the rat examined coronary flow dynamics to ANP 8-33 over a defined range from physiologic to pharmacologic concentrations. No changes in coronary flow or chronotropic and inotropic function of the isolated Langendorff-perfused heart were observed in response to increasing concentrations of ANP 8-33 (10(2) to 10(6) pg/ml). In the dog, a low, nonhypotensive dose of ANP 8-33 (0.05 microgram/kg/min) decreased cardiac output with no change in coronary blood flow or coronary vascular resistance. At a high, hypotensive dose (0.3 microgram/kg/min) ANP 8-33 decreased cardiac output in association with transient coronary vasodilation. Continued infusion resulted in a decrease in coronary blood flow and arterial pressure with no change in coronary vascular resistance. Thus, in vitro physiologic and pharmacologic concentrations of ANP, or in vivo low concentrations of ANP, do not result in an alteration in coronary flow. In vivo ANP 8-33, at both nonhypotensive and hypotensive concentrations, decreased cardiac output in the absence of coronary vasoconstriction.

Animals↗
PubMed1987

Biphasic release of endothelium-derived relaxing factor(s) by acetylcholine from perfused canine femoral arteries. Characterization of muscarinic receptors.

Experiments were designed to compare the release of endothelium-derived relaxing factor(s) in response to various muscarinic receptor agonists from canine femoral arteries mounted in organ chambers or perfused in a bioassay system. In rings of femoral arteries, suspended for isometric tension recording in organ chambers, acetylcholine induced endothelium-dependent relaxations during contractions evoked by prostaglandin F2 alpha. Atropine and pirenzepine antagonized these relaxations in a competitive manner, atropine with a higher affinity (KB = 1.9 X 10(-9) M) than pirenzepine (KB = 5.4 X 10(-7) M). Carbachol and McN-A-343 also evoked endothelium-dependent relaxations, and pirenzepine inhibited these responses with a similar low potency. The order of relative potency of the agonists in organ chamber studies was acetylcholine = carbachol much greater than McN-A-343. Isolated segments of femoral arteries with endothelium were perfused (2 ml/min) with modified Krebs-Ringer-bicarbonate solution containing indomethacin; the perfusate was bioassayed for endothelium-derived relaxing factor(s) by means of a ring of coronary artery without endothelium. When infused above but not below the femoral artery, low concentrations (10(-8)-10(-7) M) of acetylcholine caused transient relaxations of the bioassay ring contracted with prostaglandin F2 alpha; higher concentrations of acetylcholine caused sustained decreases in tension. Atropine inhibited the two phases of the concentration-relaxation curve with similar potencies. Pirenzepine inhibited both phases in a competitive manner but exhibited significantly higher potency against the first- (ED50, 1.9 X 10(-9) M) than against the second-phase responses (ED50, 2.1 X 10(-7) M). Compound McN-A-343 induced only transient decreases in tension, whereas carbachol caused sustained relaxations.(ABSTRACT TRUNCATED AT 250 WORDS)

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1987

Nature of endothelium-derived relaxing factor: are there two relaxing mediators?

The role of arachidonic acid in forming endothelium-derived relaxing factor remains controversial. This controversy may be explained if more than one factor exists. To test this hypothesis, the effects of various inhibitors of arachidonic acid metabolism were studied. The perfusate from canine femoral arteries with endothelium was bioassayed with coronary artery rings without endothelium. Treatment of the perfused segment (but not the bioassay ring) with inhibitors of phospholipase A2 (quinacrine) or cytochrome P450 (metyrapone) had no effect on the basal relaxing activity of the effluent; treatment with the inhibitor of lipoxygenase, nordihydroguaiaretic acid, significantly depressed it. With increasing concentrations of acetylcholine, a biphasic concentration-relaxation curve was obtained; the enzyme inhibitors depressed or prevented the first phase but did not affect the second phase. Infusion of arachidonic acid or soybean lipoxidase directly on the bioassay ring did not cause relaxation; together, they evoked concentration-dependent relaxations. These data suggest that acetylcholine can trigger the release of two chemically different relaxing mediators from the endothelium of the canine femoral artery. One factor may be a product of lipoxygenase (or epoxigenase). The second factor is not a metabolite of arachidonic acid and may be released under basal conditions. The existence of two (or more) chemically different endothelium-derived mediators may help to explain the controversial data regarding the nature of the factor(s).

Acetylcholine↗
PubMed1986

Oxygen-derived free radicals, endothelium, and responsiveness of vascular smooth muscle.

Experiments were designed to determine the role of oxygen-derived free radicals in modulating contractions of vascular smooth muscle and endothelium-mediated relaxations to acetylcholine. The effects of generating or scavenging these radicals were studied in rings of canine coronary arteries suspended for isometric tension recording. Xanthine oxidase plus xanthine caused relaxations, which were greater in rings with endothelium than in rings without endothelium; the relaxations were not affected by superoxide dismutase or mannitol, but could be prevented by catalase. Xanthine oxidase plus xanthine depressed endothelium-mediated relaxations to acetylcholine; this effect was prevented by superoxide dismutase, but was not affected by catalase or mannitol. Exogenous hydrogen peroxide induced catalase-sensitive relaxations, which were depressed by the removal of the endothelium. Superoxide dismutase evoked catalase-sensitive relaxations only in rings with endothelium. Endothelium-mediated relaxations to acetylcholine were slightly depressed by superoxide dismutase or catalase alone; the combination of the two enzymes or mannitol caused a major shift to the right of the concentration-response curve to acetylcholine. In rings without endothelium, relaxations caused by sodium nitroprusside were not affected by the scavengers (alone or in combination) but were augmented by xanthine oxidase plus xanthine. These data suggest that the endothelium-derived relaxing factor released by acetylcholine is not likely to be an oxygen-derived free radical; hydrogen peroxide has a direct inhibitory action on coronary arterial smooth muscle and triggers endothelium-dependent relaxations; and superoxide anions depress and hydroxyl radicals facilitate endothelium-dependent relaxations caused by activation of muscarinic receptors.

Acetylcholine↗
PubMed1986

Superoxide anions and hyperoxia inactivate endothelium-derived relaxing factor.

Experiments were designed to determine the effects of oxygen-derived free radicals on the production and biological activity of endothelium-derived relaxing factor or factors released by acetylcholine. Rings of canine coronary arteries without endothelium (bioassay rings) were superfused with solution passing through a canine femoral artery with endothelium. Superoxide dismutase caused maximal relaxation of the bioassay ring when infused upstream, but not downstream, of the femoral artery; this effect of superoxide dismutase was inhibited by catalase. Infusion of acetylcholine relaxed the bioassay rings because it released a labile relaxing factor (or factors) from the endothelium. When infused below the femoral artery, superoxide dismutase and, to a lesser extent, catalase augmented the relaxations to acetylcholine. Superoxide dismutase, but not catalase, doubled the half-life of the endothelium-derived relaxing factor(s). This protective effect of the enzyme was augmented fivefold by lowering the oxygen content of the perfusate from 95 to 10%. These data demonstrate that: superoxide anions inactivate the relaxing factor(s) released by acetylcholine from endothelial cells and hyperoxia favors the inactivation of endothelium-derived relaxing factor(s).

Acetylcholine↗
PubMed1986

Flow-induced release of endothelium-derived relaxing factor.

To analyze the potential mediator(s) involved in flow-induced endothelium-dependent vasodilation, we measured the wall tension of intraluminally perfused canine femoral artery segments and compared the content of 6-ketoprostaglandin F1 alpha (determined by radioimmunoassay) and the relaxing activity of the effluent (determined by bioassay on canine coronary artery rings). During perfusion at a steady flow of 2 ml/min the effluent contained 6-keto-prostaglandin F1 alpha and relaxed the bioassay rings. Sudden increase in steady flow rate to 4 ml/min, or the introduction of pulsatile flow, increased the release of 6-keto-prostaglandin F1 alpha and induced further relaxations of the bioassay ring. No relaxations were observed with the effluent passing through a femoral artery segment without endothelium. Indomethacin significantly depressed the release of 6-keto-prostaglandin F1 alpha during increases in flow but had no significant effect on the relaxing activity of the effluent. In the presence of indomethacin, increases in flow produced significant relaxation in the perfused femoral artery segments with endothelium. Superoxide dismutase restored the relaxing activity of the effluent during increases in flow at a transit time of 30 seconds. These data demonstrate that in addition to prostacyclin, flow triggers the release of another relaxing substance (or substances) from vascular endothelial cells that has characteristics similar to the endothelium-derived relaxing factor released by acetylcholine.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Effects of naftidrofuryl on adrenergic nerves, endothelium and smooth muscle in isolated canine blood vessels.

Experiments were designed to determine the effects of the vasoactive drug naftidrofuryl on vascular smooth muscle, endothelial cells and adrenergic nerves in isolated canine blood vessels. Naftidrofuryl inhibited contractions of basilar arteries (in a decreasing order of potency), evoked by 5-hydroxytryptamine greater than KCl = anoxia (in rings with endothelium) greater than prostaglandin F2 alpha = uridine-5'-triphosphate. Naftidrofuryl antagonized competitively the contractions evoked by 5-hydroxytryptamine in the femoral artery and the saphenous vein. Naftidrofuryl caused the release of an endothelium-derived relaxing factor(s) from the endothelium of femoral arteries. The compound depressed contractions of saphenous veins evoked by electrical stimulation of the adrenergic nerve endings, but not those caused by the indirect sympathomimetic amine tyramine or exogenous norepinephrine. In saphenous veins incubated previously with [3H]norepinephrine, the drug inhibited the contractions and the release of transmitter evoked by electrical stimulation. Thus, naftidrofuryl acts at different levels in the blood vessel wall to cause: release of endothelium-derived relaxing factor(s); inhibition of S2-serotonergic receptors on vascular smooth muscle; prejunctional inhibition of adrenergic neurotransmission; and nonselective inhibition of the contractile process in vascular smooth muscle, which is particularly pronounced in cerebral arteries.

Adrenergic Fibers↗
PubMed1986

Serotonin reduces coronary flow in the isolated heart of the spontaneously hypertensive rat.

Serotonin may cause vasodilatation or vasoconstriction. In hypertension the vasoconstrictor effects of serotonin predominate. Experiments were designed to study the effects of serotonin on coronary flow in isolated hearts of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. The hearts were paced at constant rate and perfused by the Langendorff technique at constant pressure (75 cmH2O). In WKY rats serotonin (10-9 to 10-5 mol/l) caused concentration-dependent increases in coronary flow and a decrease in cardiac performance. In SHR, the monoamine caused concentration-dependent, partially reversible decreases in coronary flow, and a marked decrease in cardiac performance. The inhibitor of cyclo-oxygenase indomethacin prevented the decrease in coronary flow and cardiac performance caused by serotonin in SHR, but did not affect the increase in coronary flow in WKY rats. These experiments suggest that in the coronary circulation of SHR the response to serotonin is shifted from vasodilatation to vasoconstriction. The mediator of this vasoconstriction is probably a product of cyclo-oxygenase.

Animals↗
PubMed1986

Autoregulation and vascular reserve in the coronary circulation of the spontaneously hypertensive rat.

Hypertension causes structural and functioning changes in blood vessels. Experiments were performed in isolated hearts of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats perfused by the Langendorff technique. Spontaneously hypertensive rats had significantly higher left heart to body weight ratios than WKY rats, indicating left ventricular hypertrophy. Coronary flow per unit cardiac mass was lower and vascular resistance was higher at 75 cm H2O perfusion pressure in SHR. This difference was maintained during maximal vasodilatation. In WKY rats, but not in SHR, autoregulation of flow was observed in the pressure range 75-150 cm H2O due to an increase in coronary vascular resistance. After maximal vasodilatation the pressure-flow relationship was linear in SHR and WKY rats, but less steep and shifted to the right in SHR. We conclude that structural adaptations of the coronary circulation in SHR lead to decreased coronary vascular reserve and a loss of autoregulation in the normal blood pressure range.

Animals↗
PubMed1985

Hypoxia releases a vasoconstrictor substance from the canine vascular endothelium.

Experiments were designed to determine the role of the endothelium in the facilitation by anoxia of contractile responses of isolated coronary arteries. Rings and strips of canine coronary arteries, with or without endothelium, were suspended for isometric tension recording in modified Krebs-Ringer bicarbonate solution. To determine the release of a vasoactive substance(s) from the endothelial cells, strips without endothelium were layered with strips containing endothelium. In rings and in layered preparations with endothelium, anoxia (95% N2-5% CO2) augmented contractile responses to prostaglandin F2 alpha. Hypoxia (10 or 5% O2) caused contractions in the presence of indomethacin. Removal of the endothelium abolished the anoxic facilitation, and the hypoxic contractions. Inhibitors of cyclo-oxygenase, lipoxygenase or phospholipase A2 or of adrenergic, serotonergic and histaminergic receptors did not prevent the response to anoxia. Likewise, inhibitors of the endothelium-derived factor(s) (quinacrine, phenidone and methylene blue) did not affect the anoxic facilitation. Hypoxia and anoxia caused contraction of coronary arteries without endothelium when layered with femoral arteries and veins with endothelium. Anoxic facilitation was observed in femoral arteries, but not in femoral veins, with endothelium. These experiments indicate that hypoxia and anoxia cause the release of a diffusible vasoconstrictor substance(s) from endothelial cells. The sensitivity of smooth muscle of different anatomical origin to the facilitatory mediator(s) varies.

Acetylcholine↗
PubMed1985

Bioassay of endothelium-derived relaxing factor(s): inactivation by catecholamines.

A bioassay technique was developed to analyze the effect of vasoactive substance(s) released from endothelial cells. Canine femoral arteries with or without endothelium were perfused with physiological salt solution at 37 degrees C. The perfusate was bioassayed with a ring of coronary artery without endothelium. A substance(s) released by the endothelial cells under basal conditions caused relaxation of unstimulated coronary arteries or relaxation of those contracted with prostaglandin F2 alpha. The release of the relaxing substance(s) was augmented by acetylcholine. The relaxation induced by acetylcholine was biphasic: an initial rapid phase followed by a partial recovery and a slowly developing prolonged relaxation; the half-life of the substance(s) causing the initial phase averaged 6.3 s. Norepinephrine, epinephrine, and ascorbic acid, given downstream of the femoral artery, reversibly prevented the second phase but only attenuated the initial relaxation. These observations indicate that an endothelium-derived relaxing substance(s) is released into the lumen of the femoral artery under basal conditions and during stimulation with acetylcholine. Catecholamines can inactivate the relaxing substance(s) but do not prevent either its production by endothelial cells or its action on vascular smooth muscle.

Acetylcholine↗