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Biomedical subjects

S Moncada

Publications and source records attributed to S Moncada.

At least 487 records · Page 27Linked to original sources
PubMed1978

Prostacyclin (PGI2) induces coronary vasodilatation in anaesthetised dogs.

Prostacyclin (PGI2), the predominant metabolite of arachidonic acid in isolated hearts, relaxes strips of bovine coronary artery and is a potent vasodilator in isolated perfused hearts. We have examined the actions of prostacyclin on coronary blood flow in open chest dogs anaesthetised with chloralose. An electromagnetic flow probe was fitted to the left circumflex artery and phasic coronary flow, mean coronary flow (a measure of coronary volume flow over 4 s intervals), and coronary vascular resistance were recorded together with aortic pressure and heart rate. Intravenous infusion of prostacyclin (0.05 to 1.0 microgram.kg.1.min.1), reduced coronary vascular resistance and aortic pressure according to dose, but had only small effects on phasic coronary flow or mean coronary flow. Both tachycardia and bradycardia occurred during infusion of prostacyclin, but 6-oxo-prostaglandin F1alpha (infused at 10 micrograms.kg-1.min-1), the stable degradation produce of prostacyclin, had no cardiovascular effects. The coronary vasodilator effects of prostacyclin were clear when it was injected into the left circumflex artery via a fine catheter distal to the flow probe. Prostacyclin (0.05 to 0.5 microgram) increased phasic coronary flow and mean coronary flow up to 3 fold and reduced coronary vascular resistance without affecting aortic pressure or heart rate, although higher doses had systemic effects. Prostaglandin E1 (0.1 to 0.5 microgram), which also dilated the coronary vessels, had a longer lasting effect and was 1 to 4 times more potent than prostacyclin. Prostaglandin E2, (0.5 to 4 microgram) was less potent than prostacyclin. In four dogs prostacyclin (20 to 500 micrograms) applied epicardially to the left ventricle caused marked and prolonged coronary vasodilatation. Epicardial application of prostacyclin (10 to 25 micrograms) to the right ventricle increased coronary sinus oxygen content with minimal changes in blood pressure. The endoperoxide prostaglandin H2 was a coronary vasodilator of similar potency to prostacyclin, but its analogue U46619 is a vasoconstrictor. Inhibition of cyclo-oxygenase with indomethacin (5 mg.kg-1 i.v.) or sodium meclofenamate (2 mg.kg-1 i.v.) potentiated the coronary dilator effects of prostacyclin given intravenously or into the coronary artery. Cyclo-oxygenase inhibition did not alter the hypotensive effects and increased the coronary vasodilator potency of prostacyclin relative to prostaglandin E2. Thus the sensitivity of the coronary vascular bed to prostacyclin is enhanced when endogenous biosynthesis of prostaglandin-like substances is inhibited. Although the importance of arachidonic acid metabolites in the coronary circulation still requires validation in vivo, it is clear that prostacyclin, and not prostaglandin E2, is the prostaglandin most likely to be involved.

Animals↗
PubMed1977

Prostacyclin (PGI2) is a weak contractor of coronary arteries of the pig.

The actions of prostacyclin (PGI2), prostaglandin E2 (PGE2), prostaglandin H2 (PGH2) and arachidonic acid have been examined on isolated coronary arteries from pigs. Arachidonate metabolites contracted this tissue, the order of potency being PGH2 greater than PGE2 greater than PGI2 suggesting that the coronary vasoconstrictor effects of PGH2 are limited by metabolism to PGI2. Sodium arachidonate and linoleate weakly relaxed porcine coronary arteries, but the former induced a secondary prolonged contraction: only the contraction was abolished by indomethacin. Thus the relaxation induced by fatty acids does not depend on metabolism to prostaglandin-like substances.

Animals↗
PubMed1977

Diversion of prostaglandin endoperoxide metabolism by selective inhibition of thromboxane A2 biosynthesis in lung, spleen or platelets.

Infusion of arachidonic acid through the guinea pig lung or the cat spleen causes a release of thromboxane A2 and prostaglandins, as measured by bioassay. After incubation of human platelets with arachidonate similar metabolites are formed, as demonstrated chromatographically. Infusion of imidazole (50-75 microgram/ml) through the lung or spleen specifically inhibits thromboxane A2 production and diverts the pathway to the prostaglandins, mainly prostaglandin F2alpha. In human platelets imidazole causes a dose-dependent inhibition of thromboxane A2 formation (ID50 5.5 X 10(-4) M). This inhibition is accompanied by a dose-dependent increase in prostaglandin F2alpha. Since thromboxane A2 induces platelet aggregation and is a potent vasoconstrictor, diversion of pathways to prostaglandins with opposite or less potent action might be of relevance in the treatment of cardiovascular diseases.

Animals↗
PubMed1977

Human arterial and venous tissues generate prostacyclin (prostaglandin x), a potent inhibitor of platelet aggregation.

Fresh rings of arteries and veins obtained from surgical specimens generated an unstable substance, prostacyclin (prostaglandinx, [P.G.X]) WHICH IS A POTENT INHIBITOR OF PLATELET AGGREGATION. The spontaneous generation of prostacyclin as well as its generation from exogenous arachidonic acid was inhibit by incubation of the tissues with a prostaglandin-synthetase inhibitor such as indomethacin, whilst the generation induced by prostaglandin endoperoxides was not. 15-Hydroperoxyarachidonic acid (a lipid hydroperoxide) inhibited the generation of prostacyclin in all three situations. It is postulated that prostacyclin is important for prevention of deposition of platelets on the vessel wall and that the inhibition or prevention of the generation of prostacyclin is important in the genesis of diseases, especially those in which increased lipid peroxidation occurs, such as atherosclerosis.

Anticoagulants↗
PubMed1977

Effects of prostacyclin (PGX) on cyclic AMP concentrations in human platelets.

Prostacyclin (PGX) strikingly increases cyclic AMP concentrations in human platelets. Prostacyclin is approximately 10 times more active than PGD2, 30 times more active than PGE1 and more than 1000 times more active than its stable end product, 6-oxo-PGF1alpha. These results correlate well with the anti-aggregating activity of prostacyclin, compared with PGE1 and PGD2.

Arachidonic Acids↗
PubMed1977

Prostacyclin (PGX) is the endogenous metabolite responsible for relaxation of coronary arteries induced by arachindonic acid.

The actions of prostacyclin (PGX) and several other derivatives of arachidonic acid were examined on spiral-strips of bovine coronary artery. The strips were contracted by PGE2 and thromboxane A2. Although PGH2 usually cause a transient contraction followed by a relaxation, a few strips were only contracted whilst others were only relaxed. Prostacyclin invariably relaxed coronary artery strips. Sodium arachidonate usually relaxed the strips but occasionally had no effect. Indomethacin increased the resting tone and abolished or substantially reduced the relaxation induced by sodium arachidonate. 15-hydroperoxy arachidonic acid (15-HPAA), a specific inhibitor of prostacyclin synthetase, also increased the resting tone, abolished the effects of sodium arachidonate and the relaxation component of the PGH2 response, but did not greatly modify the relaxation induced by exogenous prostacyclin. These results strongly suggest that prostacyclin mediates the relaxation induced by arachidonic acid in bovine coronary artery strips. As PGH2 is avidly converted into prostacyclin by the vascular tissue of several species including man, prostacyclin is probably involved in the local regulation of the coronary vascular bed.

Animals↗
PubMed1977

Enzymatic preparation of prostaglandin endoperoxides.

A simple and reliable method is described for the preparation of the endoperoxide intermediates (PGG2 and PGH2) in the biosynthesis of prostaglandins. The endoperoxides are thermolabile and easily decomposed by water (t 1/2 congruent to 5 min at 37 degrees C). Because of this, special precautions must be taken to work at low temperature and to minimize contact with moisture. Milligram quantities of PGG2 and PGH2 were obtained by running several reactions successively and pooling the extracts before chromatographic fractionation. The method is now being developed further to scale up the procedure.

Animals↗
PubMed1977

The effects of prostacyclin (PGI2) on tissues which detect prostaglandins (PG'S).

The effects of prostacyclin (PGI2) and its stable metabolite 6-oxo-PGF1alpha on various bioassay tissues are compared with those of PGE2 and PGF2alpha, using the cascade superfusion method. On vascular smooth muscle, PGI2 caused relaxation of all tissues tested except the rabbit aorta. PGE2 relaxed rabbit coeliac and mesenteric artery but contracted bovine coronary artery and had no effect on rabbit aorta. 6-oxo-PGF1alpha was ineffective at the concentrations tested. On gastro-intestinal smooth muscle, PGI2 contracted strips of rat and hamster stomach and the chick rectum. It was less potent than PGE2 or PGF2alpha. None of these substances contracted the cat terminal ileum. 6-oxo-PGF1alpha was inactive on these tissues at the doses tested. PGI2 was less active than PGE2 or PGF2alpha in contracting guinea-pig trachea and rat uterus; 6-oxo-PGF1alpha was active only on the rat uterus. Thus, PGI2 can be distinguished from the other stable prostaglandins using the cascade method of superfusion.

Animals↗
PubMed1977

Imidazole: a selective inhibitor of thromboxane synthetase.

Imidazole inhibits the enzymic conversion of the endoperoxides (PGG2 and PGH2) to thromboxane A2 by platelet microsomes (IC50: 22 MICRONG/ML; DETERMINED BY BIOASSAY). The inhibitor is selective, for prostaglandin cyclo-oxygenase is only affected at high doses. Radiochemical data confirms that imidazole blocks the formation of 14C-thromboxane B2 from 14C-PGH2. Several imidazole analogues and other substances were tested but only 1-methyl-imidazole was more potent than imidazole itself. The use of imidazole to inhibit thromboxane formation could help to elucidate the role of thromboxanes in physiology or pathophysiology.

Animals↗
PubMed1977

Synthesis of 6-keto-PGF1alpha by ram seminal vesicle microsomes.

At low substrate/enzyme ratios, and in the absence of reduced glutathione (GSH), the major prostaglandin (PG) biosynthesised by the ram seminal vesicle cyclo-oxygenase from arachidonic acid was 6-keto-PGF1alpha. The addition of nanomolar amounts of reduced GSH suppressed biosynthesis of this product and stimulated the formation of PGE2; 1-epinephrine enhanced the conversion of the substrate but had no effect on the type of product formed. 15-Hydroperoxy arachidonic acid selectively inhibited formation of 6-keto-PGF1alpha (IC50 100 muM) but blocked synthesis of all cyclo-oxygenase products at concentrations greater than 1 mM. At substrate concentrations of muM or greater, synthesis of 6-keto-PGF1alpha was inhibited and PGE2 and PGF2alpha were the main products formed.

Animals↗