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Biomedical subjects

H Bult

Publications and source records attributed to H Bult.

At least 91 records · Page 5Linked to original sources
PubMed1988

Prostacyclin biosynthesis and reduced 5-HT uptake after complement-induced endothelial injury in the dog isolated lung.

1. Pulmonary prostacyclin (PGI2) biosynthesis was evaluated in relation to endothelial integrity before and after complement activation in isolated plasma-perfused lung lobes of the dog. 2. The plasma was activated with zymosan (ZAP, n = 4), yeast cells (YAP, n = 4) or yeast with 3 microM indomethacin (Indo + YAP, n = 3). Immunoreactive 6-oxo-prostaglandin F1 alpha (i-6-oxo-PGF1 alpha) and thromboxane B2 (iTXB2) were measured to monitor PGI2 and TXA2 biosynthesis. 3. The kinetic parameters Km and Vmax of 5-hydroxytryptamine (5-HT) uptake were calculated on the basis of multiple indicator diffusion data to evaluate endothelial integrity. 4. YAP and ZAP induced a biphasic increase of the arterial perfusion pressure. The immediate pressure peak was partly mediated by TXA2 and the TXB2 was subsequently cleared by the lung. 5. The apparent Vmax of 5-HT uptake remained constant throughout the experiment. Thus, complement activation did not affect the number of endothelial 5-HT carrier sites available to the perfusate. 6. The apparent Km of 5-HT uptake was enhanced in 9 lungs exposed to activated plasma complement for 20 min. This decreased affinity for 5-HT probably reflects endothelial injury. It was transient as the apparent Km had returned to the baseline value after 60 min. 7. PGI2 clearance and biosynthesis were virtually absent in the control period. PGI2 formation increased drastically after infusion of ZAP or YAP and was proportional to the endothelial injury expressed as elevated Km or pulmonary oedema. Thus, PGI2 biosynthesis might be a marker of severe endothelial distress.

Animals↗
PubMed1988

Platelet inhibition by endothelium-derived relaxing factor from the rabbit perfused aorta.

1. The platelet inhibiting activity of endothelium-derived relaxing factor (EDRF) released by the perfused thoracic aorta of the rabbit was investigated. 2. The aortic effluent superfused a ring of the abdominal aorta without endothelium in order to bioassay EDRF. Aliquots of effluent were collected on rabbit washed platelets and aggregation induced by U-46619 was measured after 1 min. Prostacyclin (PGI2) was monitored by radioimmunoassay of 6-oxo-prostaglandin F1 alpha. 3. Acetylcholine (ACh) caused a dose-dependent secretion of EDRF, PGI2 and anti-aggregating activity. Plasma and methylene blue suppressed the platelet inhibition by the effluent. 4. The PGI2 content of the effluent was not sufficient to account for all the anti-aggregating activity. However, the platelet inhibition disappeared when PGI2 formation was blocked with indomethacin. 5. Compression of the thoracic aorta increased the EDRF content in the effluent. A transient secretion of anti-aggregating activity was then observed in aortic effluent in the absence of PGI2. This activity coincided with the presumed EDRF peak in the effluent. 6. Superoxide dismutase enhanced the ACh-induced EDRF content and revealed secretion of an anti-aggregating substance when PGI2 formation was blocked. Pretreatment of the platelets with subthreshold concentrations of PGI2, or the cyclic GMP phosphodiesterase inhibitor RX-RE 56, also revealed the release of a labile platelet inhibitor in response to ACh. 7. The results indicate that EDRF released by fresh aortic endothelium may suppress platelet aggregation, particularly when PGI2 is present.

Acetylcholine↗
PubMed1988

The endothelium inhibits the penetration of serotonin and norepinephrine in the isolated canine saphenous vein.

Serotonin can accumulate in the adrenergic nerves of vascular tissues. We have determined whether in the isolated perfused dog saphenous vein 1) luminal administration of serotonin can result in its accumulation in the adrenergic nerves and 2) endothelium can interfere with the transport of the amine into the vessel wall. Saphenous veins were perfused with medium containing [3H]serotonin, [3H]norepinephrine or [3H]epinephrine; after washout, significant amounts of 3H were detected in the veins. The 3H-accumulation was augmented when the endothelium was removed mechanically; the augmented accumulation was only observed when the [3H]amines reached the tissues from the intimal side. In coronary arteries perfused with [3H]serotonin, similar results were obtained. No increased 3H-accumulation was noted in veins without endothelium perfused in the presence of cocaine. Nerve stimulation of veins labeled with [3H]serotonin caused an augmented release of 3H from the tissues without endothelium. Pargyline augmented the accumulation of [3H]serotonin and [3H]norepinephrine and decreased the difference between tissues with or without endothelium only for norepinephrine. Perfusion of venous segments with platelets, labeled with [3H]serotonin, resulted in a 3H-content which was significantly higher in the veins without endothelium. Our experiments show that serotonin and other amines, applied luminally to perfused blood vessels, can accumulate in the adrenergic nerves and that the endothelium can reduce this accumulation. Serotonin, originating from aggregating platelets, can penetrate the vessel wall much easier at sites of endothelial denudation and this serotonin also can enter the adrenergic nerves.

Animals↗
PubMed1986

Inhibition of rabbit platelet activation by lipoxygenase products of arachidonic and linoleic acid.

The hydroperoxy fatty acids, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), 13-hydroperoxy and 9-hydroperoxyoctadecadienoic acid (13- and 9-HPODE) and the corresponding hydroxy compounds (15-HETE and 13-HODE) were synthesized and purified. Washed rabbit platelets were incubated with these fatty acid derivatives before aggregation was induced. Arachidonic acid-induced aggregation, as well as the secretion of ATP and the formation of thromboxane B2 (TXB2) were dose-dependently inhibited by these compounds. Low thrombin-, collagen- and ADP-induced aggregations were also suppressed by 15-HPETE. Platelet activation induced by the calcium ionophore A23187 and by high thrombin concentrations were not affected by 15-HPETE. In addition, doses of 15-HPETE which were inactive by themselves, potentiated the anti-aggregating activity of prostacyclin (PGI2). It is suggested that the hydroperoxy and hydroxy compounds suppress platelet activation by interference with the rise in cytoplasmic calcium in addition to the inhibition of cyclo-oxygenase.

Adenosine Triphosphate↗
PubMed1986

Modulation of prostacyclin biosynthesis by calcium entry blockers and extracellular calcium.

The influence of variations in the availability of extracellular Ca2+ and of Ca2+-entry blockers on prostacyclin production by mesothelial cells in culture was studied. The Ca2+-entry blockers nifedipine and verapamil suppressed the basal, as well as the thrombin-, bradykinin-, and ionophore A23187-stimulated biosynthesis by about 50-60%, but high concentrations were required and the inhibition was never complete. Basal prostacyclin formation was unaffected by a Ca2+-poor buffer, but showed 50% reduction in the Ca2+-free buffer. Although the thrombin-stimulated prostacyclin formation was not significantly influenced by a Ca2+-poor or a Ca2+-free buffer, prostacyclin release stimulated by A23187 and bradykinin was diminished in the presence of these modified incubation media; the reduction of bradykinin stimulated biosynthesis was rather small (30%). These results suggest that the Ca2+ from intracellular stores is sufficient for half maximal stimulation of the phospholipases involved in the biosynthetic pathway of prostacyclin and that--depending on the nature of the stimulus--different phospholipases are activated with varying requirements for free Ca2+.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Dexamethasone and prostacyclin biosynthesis by serosal membranes of the rabbit peritoneal cavity.

The effect of 2.5 microM dexamethasone on prostacyclin biosynthesis in isolated peritoneal serosa of the rabbit was studied. Pretreatment with dexamethasone for 90 min or more led to suppression of the subsequent prostacyclin biosynthesis in the absence of dexamethasone. This inhibition and the formation of extracellular non dialysable inhibitors were dependent on protein biosynthesis. These results indicate that glucocorticoids can partly suppress prostacyclin biosynthesis, probably via formation of lipocortin-like activity.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Effects of dexamethasone on prostacyclin biosynthesis in rabbit mesothelial cells.

We investigated whether glucocorticoids reduce the formation of arachidonic acid metabolites in a non myeloid cell type, the mesothelial cell, which is functionally and embryologically related to the vascular endothelial cell and which forms almost exclusively prostacyclin from arachidonic acid. Preincubation of rabbit mesothelial cells with 2.5 microM dexamethasone suppressed basal as well as bradykinin- or thrombin-stimulated prostacyclin biosynthesis. In further experiments bradykinin was selected as stimulus. The inhibition by dexamethasone was dose-dependent between 0.025 and 2.5 microM. The minimum contact period required for expression of this effect was 30 min and after a contact period of 60 to 120 min the inhibition reached a maximum, but was never complete. After 240 min, sufficient activity was secreted in the extracellular medium for inhibition of the prostacyclin formation in untreated cells. Experiments with cycloheximide were somewhat confused by its direct effects on prostacyclin biosynthesis, but still suggested that the anti-prostacyclin effect of dexamethasone required de novo protein biosynthesis. Our experiments indicate that glucocorticoids induce the formation of lipocortin-like factor(s) in non-phagocytic mesothelial cells, thereby suppressing the formation of prostacyclin, their main arachidonic metabolite.

Animals↗
PubMed1985

Modification of endotoxin-induced haemodynamic and haematological changes in the rabbit by methylprednisolone, F(ab')2 fragments and rosmarinic acid.

The effects of methylprednisolone, F(ab')2 fragments of human gamma globulins and rosmarinic acid, an inhibitor of complement activation, were tested on endotoxin-induced haemodynamic and haematological changes in the rabbit. Their effects were compared with complement depletion by cobra venom factor (CVF) pretreatment. The results provide further evidence for the role of complement activation and the concomitant triggering of the arachidonic acid cascade in the early phase of shock. The formation of vasoactive prostanoids (prostacyclin and thromboxane A2), the arterial hypotension and the thrombocytopenia were largely dependent on the presence of the intact complement system. F(ab')2 fragments (150 mg kg-1, i.v.) diminished the second fall in blood pressure to some extent but failed to alter any of the other endotoxin-induced changes. Methylprednisolone (40 mg kg-1, i.v.) given 10 min before endotoxin significantly reduced the activation of complement, the second rise of prostacyclin and the secondary hypotension, but was without effect on the early thromboxane peak of the haematological features of endotoxin shock. Rosmarinic acid (20 mg kg-1, i.v.) may be of potential interest for treatment of septic shock, since the drug suppressed the endotoxin-induced activation of complement, the formation of prostacyclin, both hypotensive phases, the thrombocytopenia and the concomitant release of thromboxane A2. The role of leukocytes and their arachidonic acid metabolites in plasma exudation deserves further investigation, because leukopenia and pulmonary oedema were not complement-dependent and were not affected by any of the treatments. Our results indicate that drugs, interfering with complement activation and/or prostaglandin biosynthesis, may be beneficial in endotoxin shock, provided that they are administered at an early stage.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Formation of prostanoids during intravascular complement activation in the rabbit.

Plasma concentrations of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha) and thromboxane B2 (TXB2) were measured by radioimmunoassay in arterial blood before and after injections of the complement activator, cobra venom factor (CVF). During the control period, the concentration of 6-oxo-PGF1 alpha, which gives the sum of prostacyclin plus 6-oxo-PGF1 alpha, and TXB2 were, respectively, less than 20 pg ml-1 and 70 +/- 15 pg ml-1. Intravenous injections of CVF induced dose-dependent, reversible elevations in the plasma levels of both prostanoids. The time courses for the increases of 6-oxo-PGF1 alpha and TXB2 paralleled the arterial hypotension and thrombocytopenia, suggesting the existence of a causal relationship between these parameters. The results further support our hypothesis that complement-dependent formation of arachidonic acid metabolites contributes to some of the haemodynamic and haematological changes occurring during endotoxin shock.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

Complement derived factors and prostacyclin formation by rabbit isolated peritoneum and cultured mesothelial cells.

Activation of rabbit or human serum complement led to the generation of factors which stimulated prostacyclin biosynthesis by isolated rabbit peritoneal tissue. Their formation was proportional to the degree of complement activation, measured as consumption of total hemolytic activity or immunoreactive C3. The stimulation of prostacyclin biosynthesis was mimicked by fragments obtained by trypsinisation of C3 (C3f) and C5 (C5f). Peritoneal macrophages, which could stimulate peritoneal prostacyclin biosynthesis through release of chemical mediators in response to C3f or C5f, were not essential, since the C3f and C5f also stimulated prostacyclin biosynthesis in monolayers of cultured mesothelial cells. Of the putative mediators, platelet activating factor (PAF) was inactive as a stimulator of peritoneal PGI2 biosynthesis. The finding that activated complement components stimulate prostacyclin biosynthesis forms an explanation for the endotoxin-induced rise in rabbit arterial blood levels of prostacyclin and may have wider implications for the understanding of inflammatory reactions.

Animals↗
PubMed1984

Prostacyclin biosynthesis and hypotension in relation to complement activation in rabbit endotoxic shock.

Intravenous endotoxin injection in rabbits led to complement activation, a biphasic hypotension and elevated arterial levels of prostacyclin and/or 6-oxo-prostaglandin F1 alpha. Primary hypotension and stimulation of prostacyclin biosynthesis were completely dependent on complement activation whereas the secondary changes of these parameters were partly complement dependent, as indicated by experiments with cobra venom factor pretreated rabbits. Prostacyclin, which was never detectable in arterial blood, contributed to the development of hypotension in rabbit endotoxic shock.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Influence of endotoxin on arachidonate metabolism in isolated rabbit peritoneum.

The serous membranes of the rabbit peritoneal cavity are tissues in which cyclo-oxygenase and lipoxygenase pathways of arachidonate metabolism can be studied simultaneously. After elaboration of the optimum conditions, the metabolism of two concentrations of arachidonic acid (AA) was studied in the presence and absence of endotoxin lipopolysaccharide (LPS) from E. coli O127:B8 (0.1 and 1.0 mg/ml). LPS suppressed the formation of radiolabelled cyclo-oxygenase products (predominantly prostacyclin) at the lower concentration of exogenous AA (0.8 microM), but not at the higher substrate concentration (34.5 microM). The biosynthesis of lipoxygenase metabolites, i.e. monohydroxyeicosatetra-enoic acids (HETEs), was not influenced by LPS. These findings can be explained by an enhanced release of endogenous AA in the prostacyclin forming mesothelial cells in the presence of LPS. Measurements of the endogenous biosynthesis of prostacyclin supported this assumption.

Animals↗
PubMed1983

Relationship between prostacyclin biosynthesis and cyclic AMP in cultured rabbit mesothelial cells.

Calcium ionophore A23187 (10 microM) as well as thrombin (10 U/ml) stimulated the biosynthesis of prostacyclin in cultured rabbit mesothelial cells; in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (Mix, 1 mM) the cyclic AMP (cAMP) content was also elevated. Both effects were inhibited by indomethacin (28 microM). Exogenous prostacyclin elicited by itself a clear enhancement of intracellular cAMP. An increased cAMP content was also obtained with isoproterenol (10 microM), whose activity was antagonized by propranolol (10 microM). These two products however, had no effect on the prostacyclin release. In all these experiments, inhibition of phosphodiesterase with Mix, was necessary to obtain detectable cAMP levels. In the presence of Mix, the stimulation of prostacyclin production by A23187 and thrombin was significantly lower as compared to the stimulation in the absence of Mix. Our results suggest that increased prostacyclin biosynthesis results in adenylate cyclase stimulation. This rise in intracellular cAMP in the presence of Mix, is accompanied by a downward regulation of further prostacyclin production.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Activated complement and anaphylatoxins increase the in vitro production of prostacyclin by rabbit aorta endothelium.

The effect of activated human serum complement and highly purified anaphylatoxins on the production of prostacyclin (PGI2) by endothelium of the isolated rabbit aorta was investigated. The results indicated that complement activation with endotoxin (LPS) or cobra venom factor (CVF) led to the generation of principles that stimulated PGI2 formation. A similar effect was seen with tryptic cleavage products of complement factors C5 and C3, suggesting the possible involvement of anaphylatoxins. Indeed, on molar base purified porcine C5a and C5a des Arg were at least 1000 times more potent than other vasoactive inflammatory mediators, as stimulators of vascular PGI2 release. Therefore we suggest that complement-mediated stimulation of vascular PGI2 production contributes to the decreased peripheral vascular resistance during endotoxic shock in rabbits. We further propose that C5a-dependent stimulation of PGI2 formation may dilatate resistance vessels, thereby increasing local blood flow. Together with the vascular permeability effects of C5a, this may provide a local regulatory mechanism for histamine- and bradykinin-independent oedema formation during inflammatory reactions.

Anaphylatoxins↗
PubMed1983

Mechanism of complement-induced stimulation of prostacyclin production by isolated rabbit peritoneum.

The interaction between the complement system and prostaglandin synthesis has not thoroughly been explored, although both mediators are known to be involved in inflammatory reactions and endotoxic shock. When rabbit peritoneum, a rich source of prostacyclin forming activity was incubated in serum in which the complement system was activated (CVF, LPS, zymosan), the tissue produced significantly more PGI2, when compared with appropriate controls, indicating that by activation of the complement, factors were generated that stimulated PGI2 biosynthesis. Further results indicated that tryptic cleavage products of complement factor C3 and C5 also led to the appearance of PGI2 releasing principles with a molecular weight of about 7000-11000. The stimulation of PGI2 biosynthesis was explained by enhanced release of AA, and not due to increased activity of cyclo-oxygenase or PGI2 synthetase. Our results suggest that complement-derived products may promote the supply of prostaglandins at the site of inflammation.

6-Ketoprostaglandin F1 alpha↗