Biomedical subjects

R Busse

Publications and source records attributed to R Busse.

At least 199 records · Page 11Linked to original sources

PubMed1991

Effects of the calmodulin antagonists fendiline and calmidazolium on aggregation, secretion of ATP, and internal calcium in washed human platelets.

Ca2(+)-calmodulin dependent phosphorylation of myosin is essential for the induction of platelet shape change and subsequent reactions. Therefore, we studied the effects of the calmodulin antagonists fendiline and calmidazolium on the thrombin-induced aggregation, secretion of ATP, and increases in the intracellular free calcium concentration ([Ca2+]i) in washed human platelets in the absence and presence of extracellular Ca2+. In Ca2+ free medium, fendiline (10-100 microM) and calmidazolium (3-30 microM) concentration-dependently inhibited aggregation. The effect of fendiline could be partly reversed by extracellular Ca2+ and higher thrombin concentrations. Furthermore, aggregations induced by the calcium ionophore ionomycin and by the protein kinase C-activator 4-beta-phorbol 12-myristate 13-acetate were inhibited by fendiline, although to a smaller degree than the thrombin-induced aggregation. Thrombin-induced secretion of ATP was attenuated by low concentrations of fendiline (1-3 microM) and calmidazolium (1 microM) but enhanced by higher concentrations (10-30 and 3-10 microM, respectively), independently of extracellular Ca2+. Fendiline (1-10 microM) did not affect [Ca2+]i in resting and thrombin-stimulated platelets. At higher concentrations (30-100 microM), it induced increases in [Ca2+]i in unstimulated platelets and attenuated the response to thrombin in Ca2+ free medium, whereas thrombin-induced Ca2+ influx was markedly enhanced. Similar results were obtained with calmidazolium (1-3 microM). These stimulating effects on ATP secretion and on [Ca2+]i of fendiline and calmidazolium may be attributed to interactions with platelet membranes by which the permeability of small cations is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1991

Elevated guanosine 3':5'-cyclic monophosphate mediates the depression of nitrovasodilator reactivity in endothelium-intact blood vessels.

The influence of endothelium-derived nitric oxide (EDNO) on relaxation induced by the nitrovasodilators, sodium nitroprusside and sodium nitrite was assessed in phenylephrine-stimulated hamster thoracic aortas, a preparation that displays significant basal release of EDNO. Removal of the endothelium or treatment with the NO synthase inhibitors, NG-nitro-L-arginine (L-NAG, 10-30 microM) or NG-methyl-L-arginine (L-NMMA; 100 microM) increased the potency and, except for sodium nitroprusside in endothelium-denuded segments, also increased the efficacy of the nitrovasodilators. Removal of the endothelium had no effect on relaxations induced by isoproterenol, an indication that these effects were specific for the nitrovasodilators. Removal of the endothelium, treatment of endothelium-intact preparations with L-NAG or L-NMMA, or exposure of these vessels to the guanylate cyclase inhibitor, methylene blue (10 microM) increased reactivity of the aortas to the guanosine 3':5'-cyclic monophosphate (cGMP) analogue, 8-Br cGMP. Measurement of cGMP revealed that endothelium-intact segments had a 6.5 fold higher level of cGMP than endothelium-denuded preparations and that sodium nitroprusside increased cGMP in both preparations by similar amounts in a concentration-dependent fashion. Exposure of endothelium-denuded or L-NAG-treated segments to sodium nitroprusside, to mimic the effects of basally released EDNO, depressed sodium nitrite and 8-Br cGMP reactivity in a manner similar to endothelium-intact segments. These data indicate that EDNO increases cGMP levels in vascular smooth muscle and that the elevated cGMP levels depress nitrovasodilator and 8-Br cGMP reactivities.

Animals↗

PubMed1991

NG-nitro-L-arginine antagonizes endothelium-dependent dilator responses by inhibiting endothelium-derived relaxing factor release in the isolated rabbit heart.

The effects of a recently described inhibitor of endothelial NO synthesis, NG-nitro-L-arginine (L-NNA), on the vasomotor responses to endothelium-dependent and independent vasodilators, and on the release of endothelium-derived relaxing factor (EDRF), were studied in the isolated saline-perfused rabbit heart. Infusion of L-NNA (30 microM) resulted in a 52 +/- 12% increase in basal coronary perfusion pressure. The vasomotor responses to 1 microM acetylcholine (ACh) and serotonin after L-NNA became biphasic, showing a small transient dilation followed by a pronounced vasoconstriction. In contrast, the dilation observed with sodium nitroprusside was not affected by L-NNA. None of the above-mentioned effects was elicited by the stereo-isomer D-NNA. Similarly, an increase in the basal coronary perfusion pressure by endothelin-1 (0.3 nM) to the same level as observed with L-NNA did not alter the vasomotor responses to ACh and sodium nitroprusside. The increase in cyclic GMP (cGMP) in platelets passing through the coronary vascular bed was used as an index of EDRF release. Platelet cGMP amounted to 0.50 +/- 0.10 pmol/mg protein after passage through the coronary bed of the unstimulated heart. When platelets were injected during an ACh infusion (1 microM), a 2.7 fold increase in cGMP was observed (P less than 0.01). After a 30-min infusion with L-NNA, the cGMP content of platelets passing through the unstimulated heart was reduced by 62%. Likewise, the ACh-induced increase in platelet cGMP was totally blocked. These results show that L-NNA inhibits EDRF release, and is thus a potent and selective inhibitor of EDRF-mediated dilation in the isolated rabbit heart.

Acetylcholine↗

PubMed1991

Rhythmic smooth muscle activity in hamster aortas is mediated by continuous release of NO from the endothelium.

Hamster aortas display endothelium-dependent, agonist-induced rhythmic contractions. However, the mechanism responsible for these oscillations is not known. Therefore, we investigated the possible role of nitric oxide (NO) on phenylephrine-induced rhythmicity in rings and segments of thoracic aortas of the hamster. We found that hamster aortas release NO, as detected by activation of purified soluble guanylate cyclase. The release of NO was abolished by mechanical removal of the endothelium or by exposure of the vessels to NG-nitro-L-arginine (NAG), a stereospecific selective inhibitor of NO synthesis. Correlated with the tonic release of NO was an elevation in guanosine 3',5'-cyclic monophosphate (cGMP) content in the vessels that could also be abolished by removal of the endothelium or treatment with NAG. The same procedures inhibited phenylephrine-induced isometric tension or diameter oscillations. Rhythmicity could be restored by exposure to the nitrovasodilator sodium nitroprusside, which increased cGMP levels in the aortas, or by exposure to the permeant analogue of cGMP, 8-BrcGMP. The beta-adrenergic agonist isoproterenol, as well as the cAMP analogue dibutyryl cAMP, failed to produce rhythmic contractions in either preparation. These data indicate that endothelium-derived NO, which stimulates the production of cGMP in the vascular smooth muscle, is the signal that leads to the observed rhythmic oscillations in smooth muscle mechanical activity.

Animals↗

PubMed1991

Potent effects of AP3A and AP4A on coronary resistance and autacoid release of intact rabbit hearts.

We investigated effects of platelet-derived dinucleotides diadenosine 5',5"'-P1,P3-triphosphate (AP3A) and diadenosine 5',5"'-P1,P4-tetraphosphate (AP4A) on coronary vasculature. In isolated rabbit hearts, saline perfused at constant flow (36 +/- 3 ml/min), AP3A and AP4A induced dose-dependent decreases in coronary perfusion pressure. Dose-effect curves of AP3A [-log M mean effective concentration (EC50) 6.2 +/- 0.1] and AP4A (EC50 6.4 +/- 0.2) were identical and not significantly different from those of adenosine, ADP, and ATP (n = 4-8). There were, however, distinct differences between both dinucleotides: pretreatment with endothelium-derived relaxing factor (EDRF)-inhibitors oxyhemoglobin (6 microM, n = 6) and NG-nitro-L-arginine (30 microM, n = 6) significantly reduced AP4A-induced dilation by 44 and 42% but did not affect vasomotor effects of AP3A or of sodium nitroprusside, adenosine, ATP, and ADP. Concentration of the stable hydrolysis product of prostaglandin (PG)I2, 6-keto-PGF1 alpha, increased by 173 +/- 25% in coronary effluent (n = 23) during infusion of AP3A (1 microM). This increase was significantly higher than during infusion of equimolar concentrations of AP4A (38 +/- 10%), ATP (23 +/- 5%), adenosine (20 +/- 10%), or an equimolar combination of AMP and ADP (52 +/- 25%), the hydrolysis products of AP3A. Luminometric and high-performance liquid chromatography analysis showed a nearly complete (94 +/- 3%) degradation of ATP during passage through the coronary bed while significant amounts of AP3A (31 +/- 5%) and AP4A (33 +/- 6%) remained uncleaved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1991

Regulation of nitric oxide production by stimulated rat Kupffer cells.

Macrophages have been described to release nitric oxide (NO) as a cytotoxic radical. This highly unstable substance is as well known as endothelium-derived relaxing factor produced by vascular endothelial cells. Because of its cytotoxic activity the synthesis of NO by rat Kupffer cells, the liver macrophages, upon stimulation with endotoxin (lipopolysaccharide; LPS) and tumor necrosis factor-alpha (TNF-alpha) in combination with prostaglandin E2 (PGE2) and dibutyryl cAMP (dBcAMP) was studied. Kupffer cells were stimulated after 48 h of primary culture. NO was quantified as NO2- in the cell medium 24 h after stimulation. LPS stimulated NO generation 5- to 10-fold over the basal level. This increase could be further enhanced by PGE2 and dBcAMP, especially when added 1 h after LPS. NO generation after stimulation with LPS or LPS + PGE2 depended on the simultaneous production of PGE2 by the stimulated Kupffer cells. It could be partly inhibited by anti-PGE2 antibody or acetylsalicylic acid. While murine TNF-alpha did not stimulate NO synthesis significantly, added PGE2 raised NO synthesis about 6-fold. The addition of dBcAMP to TNF-alpha in the same concentration as with LPS, however, had no effect. Thus, stimulation by LPS + PGE2 equals that of LPS + dBcAMP whereas TNF-alpha + PGE2 does not equal TNF-alpha + dBcAMP, indicating differences in the mode of action of PGE2 on LPS- or TNF-alpha-treated Kupffer cells.

Animals↗

PubMed1991

Ramiprilat enhances endothelial autacoid formation by inhibiting breakdown of endothelium-derived bradykinin.

We studied whether inhibition of angiotensin converting enzyme stimulates the formation of nitric oxide and prostacyclin in cultured human and bovine endothelial cells by an enhanced accumulation of endothelium-derived bradykinin. Nitric oxide formation was assessed in terms of intracellular cyclic GMP accumulation, prostacyclin release by a specific radioimmunoassay. Inhibition of angiotensin converting enzyme by ramiprilat dose- and time-dependently increased the formation of nitric oxide and prostacyclin. These increases, peaking within 10 minutes, were maintained for at least 60 minutes. The ramiprilat-induced cyclic GMP increase was completely abolished by the stereospecific inhibitor of nitric oxide synthase, NG-nitro-L-arginine. The B2-kinin receptor antagonist, Hoe 140 (0.1 microM), markedly attenuated the cyclic GMP accumulation and abolished the increase in prostacyclin release. The supernatant of endothelial cells, incubated with ramiprilat (0.3 microM) for 15 minutes, elicited a significant nitric oxide release (as assessed by a guanylyl cyclase assay) in untreated endothelial cells used as detector tissue. Preincubation of the detector cells with Hoe 140 completely abolished this nitric oxide release. These data indicate that cultured endothelial cells from different species are capable of producing and releasing bradykinin into the extracellular space in amounts that lead to a sustained stimulation of nitric oxide and prostacyclin formation, provided that bradykinin degradation is prevented by angiotensin converting enzyme inhibition. Thus, the protective effect of angiotensin converting enzyme inhibitors observed on endothelial vasomotor function in hypertension may be explained by the local accumulation of endothelium-derived bradykinin that acts in an autocrine and paracrine manner as potent stimulus for endothelial autacoid formation.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1991

Endothelial cells modulate renin secretion from isolated mouse juxtaglomerular cells.

Utilizing cocultures of mouse renal juxtaglomerular cells with bovine microvascular endothelial cells, we have examined whether endothelial cells exert direct influence on renin secretion from renal juxtaglomerular cells. In the presence of endothelial cells both spontaneous and forskolin (10 microM) or isoproterenol (10 microM) stimulated renin release were markedly attenuated. The stimulatory effect of the calmodulin antagonist calmidazolium (10 microM) on renin secretion was not altered by endothelial cells, whereas the stimulatory effect of ethylisopropylamiloride (50 microM) an inhibitor of sodium-proton exchange was enhanced in the presence of endothelial cells. Indomethacin (10 microM) and NG-monomethyl-l-arginine (NMMA) (1 mM) used to inhibit cyclooxygenase activity and production of endothelium-derived relaxing factor (EDRF) decreased spontaneous renin release in the presence of endothelial cells only, but had no effect on forskolin stimulated renin secretion. Endothelin (1 microM) inhibited cAMP stimulated renin release both in the absence and in the presence of endothelial cells. ATP (10 microM) which acts on both endothelial and juxtaglomerular cells via purinergic P2 receptors inhibited cAMP stimulated renin release only in the absence but not in the presence of endothelial cells. This modulatory effect of endothelial cells was no altered by indomethacin nor by NMMA. Taken together, our findings provide first evidence for a local control function of the endothelium on cAMP stimulated renin secretion from renal juxtaglomerular cells, which could in part be mediated by endothelin.

1-Methyl-3-isobutylxanthine↗

PubMed1990

Refilling of endothelial calcium stores without bypassing the cytosol.

The present study was undertaken to define the route of Ca2+ used for refilling of intracellular Ca2+ stores in endothelial cells. Ca2+ stores, after emptying with bradykinin in Ca2+ free solution and termination of the stimulation with the bradykinin antagonist, Hoe 140, were allowed to refill by addition of Ca2+. Refilling was prevented by 2,5-di(tert-butyl)-1,4-benzohydroquinone (BuBHQ), an inhibitor of microsomal Ca2+ sequestration. BuBHQ induced large increases in the cytosolic Ca2+ concentration during the refilling phase. This finding is not compatible with a model proposing Ca2+ uptake into the stores directly from the extracellular space but provides evidence for uptake from the cytosolic compartment.

Animals↗

PubMed1990

Induction of nitric oxide synthase by cytokines in vascular smooth muscle cells.

We investigated the mechanisms by which cytokines lead to a diminished responsiveness of vascular smooth muscle to vasoconstrictors. The attenuation of noradrenaline-induced contraction by 6 to 24 h incubations with the cytokines, tumor necrosis factor and interleukin-1, in endothelium-denuded rabbit aorta was associated with an increase in intracellular cyclic GMP level. This increase was abolished by the stereoselective inhibitor of nitric oxide-synthase, NG-nitro-L-arginine and by cycloheximide. Formation of nitric oxide was detected in the cytosol of cytokine-treated native and cultured smooth muscle cells by activation of purified soluble guanylate cyclase, and depended on tetrahydrobiopterin, but not on Ca2(+)-calmodulin. The results indicate that cytokines induce a nitric oxide-synthase of the macrophage-type in vascular smooth muscle.

Amino Acid Oxidoreductases↗

PubMed1990

Induction and activity of NO synthase in bone-marrow-derived macrophages are independent of Ca2+.

The aim of the present study was to analyse whether an increase in the intracellular free Ca2+ concentration ([Ca2+]i) plays a role as a signal mediating synthesis of nitric oxide (NO) in bone-marrow-derived macrophages, either by stimulating induction of NO synthase or by regulating the activity of the enzyme. Therefore we compared the effects of various synthetic analogues of bacterial lipopeptide and of lipopolysaccharide (LPS) on NO production (assessed as nitrite formation during an incubation for 24 h) and on [Ca2+]i [measured with the fluorescent probe indo-1 (1-[2-amino-5-(6-carboxyindol-2-yl)phenoxy]-2- 2-(2'-amino-5'-methylphenoxy)ethane-NNN'N'-tetra-acetic acid)]. Strongly dissociating effects were evoked on nitrite formation and on [Ca2+]i by the stimuli. LPS was preferentially effective on nitrite formation, whereas the Ca2+ ionophore ionomycin and AlF3 induced increases only in [Ca2+]i. The lipopeptides N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)-(2RS)- propyl]-(R)-cysteinylalanylglycine, N-palmitoyl-(S)-[2,3-bis(palmitoyloxy)- (2RS)-propyl]-(R)-cysteinylseryl-lysyl-lysyl-lysine and (S)-(1,2- dicarboxyhexadecyl)ethyl-N-palmitoylcysteinylseryl-lysyl-lys yl-lysine stimulated both parameters, but the maximal effects on nitrite formation and the shape of the dose-response curves did not parallel the effects on [Ca2+]i. Reduction of extracellular Ca2+ with EGTA significantly inhibited increases in [Ca2+]i, but did not change nitrite formation. Furthermore, NO synthesis in the cytosolic fraction of stimulated macrophages was not affected by Ca2+ over the concentration range 10 nM-2 microM. We conclude that increases in [Ca2+]i are not required for NO production in bone-marrow-derived macrophages. Thus the cellular regulation of NO production strikingly differs from that in the vascular endothelium, brain and adrenal gland.

Aluminum↗

PubMed1990

Calcium-dependent nitric oxide synthesis in endothelial cytosol is mediated by calmodulin.

We investigated whether calmodulin mediates the stimulating effect of Ca2+ on nitric oxide synthase in the cytosol of porcine aortic endothelial cells. Nitric oxide was quantified by activation of a purified soluble guanylate cyclase. The Ca2(+)-sensitivity of nitric oxide synthase was lost after anion exchange chromatography of the endothelial cytosol and could only be reconstituted by addition of calmodulin or heat-denatured endothelial cytosol. The Ca2(+)-dependent activation of nitric oxide synthase in the cytosol was inhibited by the calmodulin-binding peptides/proteins melittin, mastoparan, and calcineurin (IC50 450, 350 and 60 nM, respectively), but not by the calmodulin antagonist, calmidazolium. In contrast, Ca2(+)-calmodulin-reconstituted nitric oxide synthase was inhibited with similar potency by melittin and calmidazolium. The results suggest that the Ca2(+)-dependent activation of nitric oxide synthase in endothelial cells is mediated by calmodulin.

Amino Acid Oxidoreductases↗

PubMed1990

Activators of potassium channels enhance calcium influx into endothelial cells as a consequence of potassium currents.

Ca2+ influx into stimulated endothelial cells is attenuated by depolarization. We hypothesized that Ca2+ influx is driven by the membrane potential and may be enhanced by hyperpolarizing drugs like activators of K+ channels. Therefore we studied the effects of pinacidil, cromakalim, and cicletanine on membrane currents and on the intracellular free calcium concentration ([Ca2+]i) in cultured endothelial cells from porcine aorta. In patch-clamped cells, pinacidil (1 mumol/l) and cromakalim (1 mumol/l) elicited outward currents carried by K+ and significantly prolonged the Ca2(+)-dependent K+ currents induced by bradykinin and ATP. Peak currents in response to bradykinin were not affected. In cells loaded with the fluorescent Ca2+ indicator indo-1 and prestimulated with thimerosal, pinacidil (0.1-1 mumol/l elicited long-lasting increases in [Ca2+]i from 100 +/- 10 to 550 +/- 110 nmol/l. These effects were completely abolished in a medium containing 90 mmol/l K+. Similar results were obtained with cromakalim. Likewise, in cells stimulated with bradykinin, pinacidil raised [Ca2+]i when applied during the decline of [Ca2+]i after the initial peak. Cicletanine elicited K+ currents in resting and attenuated K+ currents in bradykinin-stimulated cells. It elevated [Ca2+]i even in the absence of extracellular Ca2+ and in K(+)-rich medium. Hence, the effects of cicletanine cannot be explained by direct actions on K+ channels. However, our studies demonstrate that pinacidil and cromakalim elevate [Ca2+]i secondary to their activation of K+ channels by inducing hyperpolarization and augmenting the driving force for potential-dependent Ca2+ influx. In this way, the two drugs may promote Ca2(+)-dependent formation of endothelium-derived relaxing factor.

Animals↗

PubMed1990

Calcium influx into endothelial cells and formation of endothelium-derived relaxing factor is controlled by the membrane potential.

We studied the role of the membrane potential in the control of the intracellular free calcium concentration ([Ca2+]i) and release of the two autacoids endothelium-derived relaxing factor (EDRF = nitric oxide) and prostaglandin I2 in endothelial cells. ATP (3 mumol/l) and bradykinin (1 nmol/l) evoked rapid increases (sixfold) in [Ca2+]i in cultured endothelial cells. [Ca2+]i remained elevated over several minutes. When the cells were depolarized, either by K+ (70-90 mmol/l) or by preincubation with the blocker of K+ channels tetraethylammonium (3 mmol/l), the initial peak of [Ca2+]i remained unaffected but [Ca2+]i returned significantly faster to resting levels, indicating a reduction in Ca2+ influx. In native, freshly isolated endothelial cells, K+ abolished increases in [Ca2+]i induced by acetylcholine (3 mumol/l). Release of EDRF in response to bradykinin (cultured cells) and acetylcholine (native cells) was inhibited by K+ (by 70%), whereas release of prostaglandin I2 was not significantly reduced. Preincubation of cultured endothelial cells with the receptor-independent stimulus thimerosal (5 mumol/l, 40 min) evoked a long-lasting release of EDRF and small elevations of [Ca2+]i (twofold) after washout of the drug. Depolarization with K+ decreased thimerosal-induced EDRF release and [Ca2+]i in a reversible manner. In patch-clamped endothelial cells, bradykinin (1 nmol/l) induced transient hyperpolarizations that were significantly prolonged by BRL 34915 (1 mumol/l), an activator of K+ channels. BRL 34915 also elicited increases in [Ca2+]i, particularly in thimerosal-stimulated endothelial cells. These effects were abolished by K+. We conclude that the initial rise in [Ca2+]i in response to receptor-binding agonists, caused by mobilization of Ca2+ from intracellular stores, activates K+ channels, thereby inducing hyperpolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1990

Interaction of granulocytes and endothelial cells upon stimulation with tumor necrosis factor-alpha: an ultrastructural study.

By the production of microbicidal agents, such as reactive oxygen species, activated PMN are capable of inducing tissue damage in the host. TNF-alpha was recently shown to be a potent activator of PMN oxidative metabolism. To further evaluate the interaction between activated PMN with physiological target cells, the effect of human PMN on cultured bovine aortic and human umbilical vein endothelial cells (EC) upon stimulation with human TNF-alpha was investigated by ultrastructural techniques: Scanning and transmission electron microscopy (SEM and TEM resp.) and ultrastructural detection of H2O2 production. When isolated PMN were added to EC in the presence of recombinant human TNF-alpha (10(3) U/ml) the EC-monolayer was disrupted within 4 h and EC changed their shape by exhibiting a spindle-like structure. PMN were seen in the intercellular spaces. Release of H2O2 was observed at the surface of the PMN plasma membrane, the luminal part of the small intracytoplasmic vacuoles in the PMN as well as in the contact zone between PMN and EC, but not within the EC. Scavengers of reactive oxygen species, such as superoxide dismutase and catalase or D-mannitol failed to block the effect of TNF-alpha-stimulated PMN on EC. In contrast, addition of NaN3 (0.1 mM), an inhibitor of myeloperoxidase activity, almost completely inhibited the disruption of EC-monolayers. Subsequent addition of NaN3-insensitive horseradish peroxidase reconstituted the effect. The results obtained suggest that TNF-alpha-stimulated PMN effectively cause the disruption of EC monolayers by an adherence-dependent mechanism which is mediated by the release of myeloperoxidase. The results may be of major importance for the pathogenesis of inflammatory vascular reactions.

Animals↗

PubMed1990

Endothelium-dependent modulation of vascular tone and platelet function.

Endothelial cells exert potent effects on vascular tone and platelet activity by the release of autacoids. One of the functionally most important autacoids is the endothelium-derived relaxant factor (EDRF). It inhibits platelet and vascular smooth muscle activation by cGMP-dependent attenuation of the agonist-induced rise of intracellular free Ca2+. Recent experiments suggest that EDRF has a physiologic role in the control of the vascular tone of large arteries and resistance vessels. Furthermore, there is evidence that an impairment of EDRF release may be a significant pathophysiologic factor in myocardial ischaemia. Coronary vascular tone might be also affected by the endothelium-derived vasoconstrictor peptide, endothelin, but its significance for the control of coronary blood flow remains to be elucidated.

Endothelins↗

PubMed1990

cAMP attenuates autacoid release from endothelial cells: relation to internal calcium.

The effects of elevated levels of adenosine 3',5'-cyclic monophosphate (cAMP), in cultured endothelial cells from bovine aorta, on the ATP-induced increases in the intracellular free calcium concentration [( Ca2+]i) and the release of prostaglandin I2 (PGI2) and endothelium-derived relaxant factor (EDRF) were investigated. Endothelial cAMP production was assessed in terms of cAMP release in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine; this release was increased fivefold by isoproterenol (1 microM), 1.6-fold by isoproterenol (0.1 microM), and 1.5-fold by the stable PGI2 analogue iloprost (10 microM). [Ca2+]i, measured with the fluorescent probe indo-1, was increased by ATP (1 microM) from 150 +/- 20 (SE) to 410 +/- 50 nM. Neither isoproterenol nor iloprost changed [Ca2+]i in unstimulated cells, but they significantly reduced [Ca2+]i levels in the presence of ATP. Similar inhibitions of increases in [Ca2+]i as by iloprost and isoproterenol (0.1 microM) were evoked by dibutyryl-cAMP (100 microM). Release of PGI2 was enhanced from 3.9 +/- 0.5 to 34.6 +/- 6 ng.min-1.5 x 10(6) cells-1 by ATP (3 microM); in the presence of isoproterenol, the ATP-stimulated release was reversibly reduced to 18.1 +/- 4.9 ng/min. Release of EDRF was assayed in terms of its stimulatory action on purified soluble guanylate cyclase. EDRF release in the first minute after stimulation with ATP (10 microM) was significantly attenuated by isoproterenol from 32.3 +/- 4.8 to 23.0 +/- 4.6 nmol.min-1.mg-1 (activity of soluble guanylate cyclase).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1990

Oxidized low density lipoproteins potentiate vasoconstrictions to various agonists by direct interaction with vascular smooth muscle.

In hypercholesterolemia, low density lipoproteins (LDLs) may be oxidized by monocytes/macrophages in the arterial wall. Therefore, we investigated the effect of LDL and its oxidative derivatives (ox-LDL) on vascular tone in isolated perfused rabbit femoral arteries. Perfusion of endothelium-intact and endothelium-denuded segments with ox-LDL (80 micrograms protein/ml) caused no or only weak vasoconstrictions in the absence of contractile agonists. However, in the presence of ox-LDL, vasoconstrictions to threshold concentrations of norepinephrine, serotonin, phenylephrine, or potassium were significantly enhanced. This enhancement correlated with the degree of oxidation. When ox-LDL was administered at higher concentrations (greater than 200 micrograms protein/ml), it evoked moderate vasoconstrictions even in the absence of contractile agonists. Native LDL had no effect on vascular tone. Preincubation with verapamil, diltiazem, and nitrendipine inhibited vasoconstrictions evoked by ox-LDL, both in the presence and in the absence of a contractile agonist. The contractile responses to ox-LDL were significantly greater in endothelium-denuded segments than in endothelium-intact segments. At the above concentrations, ox-LDL had no influence on endothelium-derived relaxing factor-mediated vasodilations. These data indicate that ox-LDL enhances agonist-induced vasoconstrictions by a direct effect on the vascular smooth muscle. We therefore suggest that ox-LDL is an important factor that may increase the risk of inappropriate vasoconstriction in hypercholesterolemia, independent of its putative cytotoxic effect on the endothelium.

Animals↗