Platelets and prostacyclin in arterial bypasses: implications for coronary artery surgery.

BACKGROUND: We investigated effects of platelets and prostacyclin formation in human internal mammary (IMA) and radial (RA) arteries. METHODS: IMA and RA segments were suspended in organ bath with increasing concentrations of platelets. Experiments were applied with and without ketanserin, a 5HT2 receptor antagonist, or U3405, a TXA2 receptor antagonist. The release of prostacyclin (PGI2) was assessed by enzyme immunoassay in vessels without endothelium, before and after contraction with angiotensin (AT) I-II. RESULTS: In IMA and RA with endothelium, platelets caused contractions, significantly enhanced in arteries without endothelium. Contractions to platelets were higher in RA than in IMA. U3405 reduced the platelet induced contractions in RA but not in IMA. Ketanserin inhibited the platelet induced contractions in IMA and RA. The basal release of PGI2 was more important in IMA than in RA. Addition of AT/I-II significantly reduced the release of PGI2 in IMA but not in RA. CONCLUSIONS: The RA responds more powerfully to platelets than IMA. Protective system with PGI2 seems to be more powerless in RA than in IMA. This accentuates the importance of antispastic and antiplatelet drugs when arteries are used for coronary artery bypass surgery.

Synthesis and biological evaluation of new tetrahydronaphthalene derivatives as thromboxane receptor antagonists.

New polysubstituted tetrahydronaphthalene derivatives were prepared as thromboxane receptor (TP-receptor) antagonists. Within this series of compounds S 18886 has been identified as an orally active, highly potent antagonist with a very long duration of action in different species.

New tetrahydronaphthalene derivatives as combined thromboxane receptor antagonists and thromboxane synthase inhibitors.

A pyridine group was linked to the tetrahydronaphthalene moiety of the derivatives described in the preceding paper, to afford new combined thromboxane receptor (TP-receptor) antagonists and synthase inhibitors. The most interesting compound 2f inhibits TXA2 synthase with an IC50 value of 0.64 microM and the aggregation of human platelets with an IC50 value of 0.063 microM and shows a long duration of action in different species after oral administration.

(S)-spiro[(1,3-diazacyclopent-1-ene)-5,2'-(7'-methyl-1',2',3',4'- tetrahydronaphthalene)]: resolution, stereospecific synthesis, and preliminary pharmacological characterization as a partial alpha-adrenergic agonist.

Recently, we reported on the design, synthesis, and structure-activity relationships of a series of spiroimidazolines endowed with alpha-adrenergic agonist activities. Among the compounds described, (R,S)-spiro(1,3-diazacyclopent-1-ene)-[5,2'](7'-methyl-1'2',3', 4',-tetrahydronaphthalene) fumarate (5RS) was chosen for further development as a venotonic agent. The resolution of this compound, as well as the pharmacological characterization of the enantiomers, stereospecific synthesis of eutomer (5S, S 18149), and determination of absolute configuration by single-crystal X-ray diffraction analysis, are described.

Regulation of nitric oxide-like activity by prostanoids in smooth muscle of the canine saphenous vein.

1. Organ bath experiments and measurements of prostanoids were performed to investigate the presence of nitric oxide synthase in venous smooth muscle and its interaction with cyclo-oxygenase. 2. In rings of canine saphenous vein without endothelium, the inhibitor of cyclo-oxygenase, indomethacin (10 microM), induced contraction. NG-nitro-L-arginine (100 microM) (L-NOARG), an inhibitor of nitric oxide synthase did not affect the tone of rings of canine saphenous vein when administered alone. However, in the presence of indomethacin L-NOARG (100 microM) induced further contraction. 3. Similar results were obtained in response to NG-monomethyl-L-arginine (L-NMMA)(300 microM or NG-nitro-L-arginine methylester (L-NAME)(100 microM). 4. When rings of canine saphenous vein without endothelium were contracted with phenylephrine (1 microM) instead of indomethacin, neither L-NOARG or L-NMMA induced further contraction. 5. When rings of canine saphenous vein without endothelium were contracted with noradrenaline (0.3 microM) in the presence of indomethacin (10 microM) plus L-NOARG (100 microM), a relaxation to L-arginine was observed. Transient relaxations to superoxide dismutase (150 u ml-1) were observed in all rings. 6. When rings of saphenous vein without endothelium were incubated with lipopolysaccharide (LPS) (100 micrograms ml-1) or interleukin-1 beta (10 u ml-1) the concentration-contraction curve to noradrenaline was not affected. 7. Rings without endothelium released prostaglandin E2 and prostaglandin I2, as measured by radioimmunoassay. The basal production was abolished by indomethacin and not affected by L-NOARG. 8. These results suggest that when cyclo-oxygenase is inhibited, a nitric oxide synthase activity is revealed in rings of canine saphenous vein without endothelium.

Design, synthesis, and structure-activity relationships of a new series of alpha-adrenergic agonists: spiro[(1,3-diazacyclopent-1-ene)-5,2'-(1',2',3',4'- tetrahydronaphthalene)].

The contractions induced by a partial alpha 1-adrenoceptor agonist in cutaneous veins, such as the saphenous vein, show a particular sensitivity to changes in local temperature: the contractility to a partial alpha 1-adrenoceptor agonist increases when the temperature is raised, a response that contrasts to that noted with full alpha 1- and alpha 2-adrenoceptor agonists. This observation may be of importance for the treatment of the symptoms of venous insuffiency, favored during warm summer days. A new series of full and partial alpha-adrenergic agonists was designed and synthesized, the spiro[(1,3-diazacyclopent-1-ene)-5,2'-(1',2',3',4'- tetrahydronaphthalene)] 7a-kk or spiro-imidazolines. Using in vitro (femoral artery and saphenous vein) and in vivo (pithed rat) biological evaluations, structure-activity relationships could be defined which allowed the discovery of a full alpha 2-agonist (34b), a full alpha 1-agonist (7s), and a nonselective partial alpha 1/alpha 2-agonist (7aa) endowed with an outstanding veinotonic selectivity as compared to its effect on mean arterial pressure. The latter compound is presently undergoing extensive pharmacological and toxicological evaluations, as a clinical candidate.

S 17162 is a novel selective inhibitor of big ET-1 responses in the rat.

Endothelin-1 (ET-1) is a powerful renal vasoconstrictor peptide that may be implicated in acute renal failure. The aim of the present study was to test the effects of the novel endothelin-converting enzyme inhibitor S 17162 (N-(2,3 dihydroxy propyl phosphonyl)-(S)-Leu-(S)-Trp-OH, disodium salt) on pressor responses to ET-1 and its precursor, big ET-1, in isolated perfused rat kidneys and in pithed rats. In both models, phosphoramidon selectively inhibited the pressor responses to big ET-1 without influencing those to ET-1, angiotensins (AT-I and AT-II) or norepinephrine. S 17162 was active against big ET-1 in both test systems. It selectively inhibited the pressor responses to big ET-1 with ID50 values of 160 micrograms/kg/min (phosphoramidon: 120 micrograms/kg/min) in the spinal rat and 6 microM (phosphoramidon: 5 microM) in the perfused rat kidney. In the nonanesthetized rat, S 17162 at 20 mg/kg p.o. inhibited the pressor responses to big ET-1, demonstrating its oral bioavailability. Therefore, S 17162 is a potential candidate for development as an orally active anti-endothelin drug.

[Vaso-reactive properties of radial and internal mammary arteries: application to coronary bypass surgery]. / Propriétés vasoréactives des artères radiale et mammaire interne; application à la chirurgie coronaire.

Satisfactory results were obtained with the radial artery used as a conduit for coronary artery bypass. However, spasm of this conduit was observed. Human radial and internal mammary artery ring segments were studied in organ chambers. Potassium chloride, norepinephrine, serotonin and thromboxane A2 mimetic were used to obtain dose-response curves, permitting assessment of force of contraction and sensitivity. The radial artery presents stronger contractions than the internal mammary artery. The two vessels have equal sensitivity to the vasoconstrictors used. These data emphasize the hyperreactivity of the radial artery and the need for prevention of vasospasm when this vessel is used as a conduit for coronary artery bypass.

[Comparative vasoreactivity of the radial, internal mammary and gastroepiploic arteries. Implications in coronary surgery]. / Vasoréactivité comparative des artères radiale, mammaire interne et gastro-épiploïque. Implications en chirurgie coronaire.

Recently, satisfactory results were obtained in a series of patients in whom the radial artery was used as a conduit for coronary artery bypass. However, spasm of this conduit was observed in four percent of patients. The aim of this study was to analyze the vasoreactive properties of the radial artery and to compare them to those of the internal mammary and the gastroepiploic arteries. Human radial (56 from n = 15 patients), internal mammary (77 from n = 20 patients) and gastroepiploic (41 from n = 12 patients) arteries ring segments were mounted on a strain gauge in oxygenated, normothermic, Krebs solution at optimal resting tension. With potassium chloride (100 mM) serving as the control, the dose response curves to norepinephrine, serotonin and thromboxane A2 mimetic were obtained, hence permitting to assess force of contraction and sensitivity. Functional endothelium was assessed by acetylcholine. Smooth muscle-dependent relaxation was assessed by sodium nitroprusside. The radial artery had stronger contractions to potassium chloride than the other vessels. The radial and the gastroepiploic arteries with endothelium presented a higher contraction force than the internal mammary artery in response to norepinephrine and serotonin. The gastroepiploic artery had a lower sensitivity to thromboxane A2 mimetic compared to the two other vessels. This increased reactivity of the radial artery explains its propensity to spasm and emphasizes the need for antispastic drugs and platelet inhibitors when the radial artery is used for coronary artery bypass.

Vasoreactivity of the radial artery. Comparison with the internal mammary and gastroepiploic arteries with implications for coronary artery surgery.

BACKGROUND: Recently, satisfactory results were obtained in a series of patients in whom the radial artery was used as a conduit for coronary artery bypass. However, spasm of this conduit was observed in 4% of patients. The aim of this study was to analyze the vasoreactive properties of the radial artery and to compare them with those of the internal mammary and the gastroepiploic arteries. METHODS AND RESULTS: Human radial (56 from 15 patients), internal mammary (77 from 20 patients), and gastroepiploic (41 from 12 patients) artery ring segments were mounted on a strain gauge in oxygenated, normothermic Krebs' solution at optimal resting tension. With KCl (100 mM) serving as the control, the dose-response curves to norepinephrine, serotonin, and thromboxane A2 mimetic were obtained, permitting assessment of force of contraction and sensitivity. Functional endothelium was assessed with acetylcholine. Smooth muscle-dependent relaxation was assessed with sodium nitroprusside. The radial artery had stronger contractions to KCl than the other vessels. The radial and the gastroepiploic arteries with endothelium presented a higher contraction force than the internal mammary artery in response to norepinephrine and serotonin. The three vessels had equal sensitivities to norepinephrine and serotonin. The gastroepiploic artery had a lower sensitivity to thromboxane A2 mimetic than the two other vessels. CONCLUSIONS: This increased reactivity of the radial artery explains its propensity to spasm and emphasizes the need for antispastic drugs and platelet inhibitors when the radial artery is used for coronary artery bypass.

Endothelial thromboxane production plays a role in the contraction caused by 5-hydroxytryptamine in rat basilar arteries.

The goal of the present study was to characterize the role of the endothelium in the 5-hydroxytryptamine (5-HT)-induced contraction of the rat basilar artery. Rat basilar artery segments were mounted in myographs to study their isometric tension development. 5-HT caused dose-dependent contractions that were minimally affected by endothelium removal. The dose-response curve obtained with the 5-HT1 receptor agonist, 5-carboxamidotryptamine (5-CT), was biphasic in arteries with endothelium; removal of the endothelium eliminated the first phase of the contraction. The 5-HT2 receptor antagonist, ketanserin (30 nM), shifted the dose-response curve to 5-HT to the right; in arteries with endothelium, the curve became biphasic. Ketanserin inhibited the second phase of the dose-response curve to 5-CT. The mixed 5-HT1/5-HT2 receptor antagonist, metergoline (30 nM), shifted the dose-response curve to 5-HT non-competitively to the right and depressed both phases of the dose-response curve to 5-CT. In basilar arteries with endothelium and treated with ketanserin, the thromboxane A2 receptor antagonist, ICI 192605 (1 microM), significantly decreased the responsiveness to 5-HT and the dose-response curve for 5-HT became monophasic. ICI 192605 and the thromboxane A2 synthase inhibitor, ridogrel (10 microM), both suppressed the first phase of the dose-response curve to 5-CT. These data indicate that both endothelial 5-HT1 and smooth muscle 5-HT2 receptors participate in the contractions caused by 5-HT in the rat basilar artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoxia causes an abnormal contractile response in the atherosclerotic rabbit aorta. Implication of reduced nitric oxide and cGMP production.

Both atherosclerotic lesions and hypoxia alter the contractile properties of the arterial wall and, in particular, may interfere with the relaxation mechanisms dependent or not on the endothelium. The present study was designed to test the effect of severe hypoxia on the contractile behavior of the atherosclerotic rabbit aorta. Segments of aortas obtained from control, cholesterol-fed, or Watanabe hereditary hyperlipidemic rabbits were mounted in organ chambers for isometric tension recording. A change of the bath PO2 from "normoxic" conditions (95% O2-5% CO2) to "hypoxic" conditions (95% N2-5% CO2) caused relaxation in the precontracted control aortas (by approximately 85%) but a transient contraction (approximately 20% of the maximal contraction obtained with 30 mM KCl) followed by a relaxation in the precontracted atherosclerotic aortas. Both types of responses were observed in aortas contracted with aggregating platelets, 5-hydroxytryptamine (5-HT), norepinephrine, endothelin, and prostaglandin F2 alpha. The hypoxic contractions in atherosclerosis were not dependent on the presence of an intact endothelium. They could not be antagonized by blockers of alpha-adrenoceptors, 5-HT2 receptors, histamine receptors, thromboxane receptors, and muscarinic cholinoreceptors. Inhibitors of cyclooxygenase, lipoxygenase, Na+, K(+)-ATPase, and free radical scavengers or an activator of endothelium-derived relaxing factor did not significantly affect the hypoxic contraction; the absence of effect of some inhibitors of protein synthesis seems to rule out the involvement of endothelin, angiotensin II, and bradykinin. The hypoxic contraction was not influenced by omission of Ca2+ from the medium or by inhibition of Ca2+ influx but was prevented by blockade of intracellular Ca2+. The inhibitor of nitric oxide synthase (nitro-L-arginine, 100 microM) and the guanylyl cyclase inhibitor (methylene blue, 10 microM) both enhanced the initial contractile responses to 5-HT to a similar extent as hypoxia and completely prevented the hypoxic contraction in the atherosclerotic tissues. The cyclic nucleotide analogues 8-bromo-cGMP and dibutyryl cAMP also inhibited the hypoxic contraction in the atherosclerotic aorta. The cGMP levels were markedly decreased and the cAMP levels were moderately decreased in the aortas of the cholesterol-fed rabbits as compared with the control aortas. Hypoxia further decreased cGMP but not the cAMP levels in atherosclerotic aortas with and without endothelium. Our data thus demonstrate the occurrence of an unusual vasoconstrictor response in atherosclerotic arteries; this constrictor response depends on the availability of intracellular Ca2+ and seems to be due to the further inhibition of an already impaired cGMP production.(ABSTRACT TRUNCATED AT 400 WORDS)

Alpha-adrenoceptor antagonistic and calcium antagonistic effects of nicergoline in the rat isolated aorta.

The activity of the alpha-adrenoceptor antagonist nicergoline, a molecule composed of two constituent parts, ergoline and bromonicotinic acid, was investigated in the rat isolated aorta. Nicergoline (10 nM-0.1 microM) displaced concentration-effect curves elicited by noradrenaline and phenylephrine to the right and inhibited maximal responses elicited by both alpha-adrenoceptor agonists without significantly affecting prostaglandin F2 alpha-induced contractions. Higher concentrations of nicergoline (1 microM-50 microM) displaced to the right the concentration-effect curves elicited by calcium in a depolarizing medium. This calcium antagonist activity was not shared by either of the constituent parts. Nicergoline 100 microM abolished the 45Ca influx induced into rat aorta by 100 mM K+-containing physiological solution. The selectivity of nicergoline for alpha 1-adrenoceptors seen in binding experiments also depends on the presence of the bromonicotinic moiety of the molecule. It is concluded that nicergoline, but not its substituent parts, displays both alpha 1-adrenoceptor and calcium antagonism. The latter property may account for some of the observed effects of this compound.

Diphenylalkylamine calcium antagonists interact with alpha-adrenoceptor binding sites in aortic membranes.

Some interactions of calcium antagonists with [3H]prazosin and [3H]yohimbine binding sites were investigated in bovine aorta membranes. Diphenylalkylamines (flunarizine, cinnarizine and bepridil) acted as competitors of the two ligands with Ki values in the microM range. With the exception of verapamil, reference compounds (nifedipine, Bay-K 8644, diltiazem) and the peripheral benzodiazepine receptor antagonist PK 11195 did not displace the ligands. The apparent affinity of the diphenylalkylamines for alpha-adrenoceptor was consistent with the concentrations producing vasodilatation.

Characterization of two distinct alpha-adrenoceptor binding sites in smooth muscle cell membranes from rat and bovine aorta.

In order to characterize postjunctional alpha adrenoceptor binding sites of aortic smooth muscle, the specific binding of (3H)prazosin and (3H)yohimbine to membranes prepared from the medial layers of rat and bovine thoracic aorta was investigated. Binding of (125I)-BE 2254 (2-[B-(4-hydroxyphenyl)-ethylaminomethyl] tetralone) and (3H)RX 781094 (idazoxan) was also examined in bovine membranes. Each of the ligands displayed saturable, specific binding to a single population of sites; the KD values of the respective ligands were similar in the two animal species. The number of (3H)prazosin and (125I)BE 2254 binding sites (160-190 fmol X mg protein-1 in the two species) was higher than the number of (3H)yohimbine and (3H)RX 781094 binding sites (110-120 fmol X mg protein-1 in the bovine and 50 fmol X mg protein-1 in the rat). Alpha-adrenoceptor ligands inhibited binding of the ligands with the following orders of potency:prazosin greater than BE 2254 greater than yohimbine greater than RX 781094 greater than clonidine in the case of (3H)-prazosin, and yohimbine greater than RX 781094 greater than clonidine greater than prazosin in the case of (3H)yohimbine. Methoxamine, in concentrations up to 10 microM, was without effect on the binding of either ligand. The absence or presence of Na+, K+ or Ca2+ added at physiological concentrations did not change the order of potency of displacing ligands whereas Ca2+ reduced by 50% the numbers of (3H)prazosin and (3H)-yohimbine sites and Na+ increased by 3-fold the affinity of (3H)yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)