Endothelial function of human gastroepiploic artery in comparison with saphenous vein.

OBJECTIVE: Endothelial function is one of the important determinants of patency rate of a graft material used in coronary revascularisation. The aim of this study was to compare the endothelial reactivity of human gastroepiploic artery versus saphenous vein in response to various vasoactive substances. METHODS: Gastroepiploic artery and saphenous vein rings were mounted in an organ bath containing Krebs-Ringer bicarbonate solution aerated with 95% O2 and 5% CO2 at 37 degrees C. Endothelium dependent responses of acetylcholine, histamine, and bradykinin were examined on the precontracted rings of the vessels. The sensitivity of these two graft materials to the potent vasoconstrictor agent endothelin-1 was also compared. RESULTS: Acetylcholine, histamine, and bradykinin caused dose dependent relaxations in saphenous vein and gastroepiploic artery rings. These agonists were more effective in producing endothelium dependent relaxations in the artery than in the vein. Endothelium removal and pretreatment with nitro-arginine abolished the relaxations completely in saphenous vein but not in gastroepiploic artery, depending on the relaxing agent used. On the other hand, both graft materials showed nearly equal sensitivity to endothelin-1 (EC50 values; 3.5 x 10(-9) M in the vein versus 6.4 x 10(-9) M in the artery, p = NS) which was not affected by endothelium removal. CONCLUSIONS: Gastroepiploic artery exhibited more pronounced relaxation and a different response profile to endogenous vasoactive substances than saphenous vein. The demonstration of higher capacity of the artery to release vasoactive substances in response to various endogenous agents shows that gastroepiploic artery may have a better long term patency rate than saphenous vein.

Nitric oxide production by human umbilical vessels in severe pre-eclampsia.

OBJECTIVE: Pre-eclampsia is characterized by an increased vascular tone which might be related to an abnormal endothelial cell function. As representatives of the fetal circulation, we compared the nitric oxide (NO)-releasing capacity of human umbilical vessels from normal and pre-eclamptic pregnancies. METHODS: Normal and pre-eclamptic umbilical vessels were mounted in parallel in an organ chamber with three perfusion lines superfusing the same detector tissue (rubbed rat aortic ring). In this cascade system the capacity of the umbilical vessels to release NO was measured under basal conditions and after stimulation with histamine, bradykinin or calcium ionophore A23187. RESULTS: Relaxations dependent on basal NO release were found to be significantly higher in pre-eclamptic vessels (especially in veins) than in normal vessels. Conversely, stimulated NO release in response to histamine or bradykinin was significantly decreased in pre-eclamptic umbilical arteries, but not in veins, compared with normal vessels. However, there was no significant difference in the release of NO in response to A23187 between normal and pre-eclamptic vessels. CONCLUSIONS: The NO-releasing and NO-producing capacity in the vessels from fetal circulation is not diminished in pre-eclampsia. However, in pre-eclamptic umbilical arteries the NO release in response to certain stimuli (histamine or bradykinin) is diminished, probably as a result of alterations in the receptor function.

Comparison of antioxidant activities of aminoguanidine, methylguanidine and guanidine by luminol-enhanced chemiluminescence.

1. The objective of this study was to investigate the ability of aminoguanidine, methylguanidine and guanidine to inhibit free radicals or metabolites generated by either stimulated human leucocytes or cell-free systems using luminol-enhanced chemiluminescence (CL). 2. Aminoguanidine (0.1 microM-10 mM), methylguanidine (10 microM-10 mM) and guanidine (10 microM-10 mM) produced concentration-dependent inhibition (96+/-0.1%, n=7, 59+/-1.3%, n=6, and 62+/-3%, n=6, P<0.05 at 10 mM, respectively) in FMLP-stimulated leucocytes CL. 3. In cell-free experiments, hydrogen peroxide (H2O2), hypochlorous acid (HOCl), hydroxyl radical and peroxynitrite-induced CL responses were initiated by hydrogen peroxide (3.5 mM), NaOCl (50 microM), FeSO4 (40 nM) and peroxynitrite (20 nM), respectively. Aminoguanidine, methylguanidine and guanidine produced concentration-dependent inhibition in H2O2-(69+/-0.7%, n=7, 26+/-1%, n=6, and 15+/-0.5%, n=6, at 1 mM, respectively) and HOCl-(84+/-0.3%, n=6, 50+/-1%, n=6, and 29+/-1%, n=7, at 1 mM, respectively) induced luminol CL. Peroxynitrite-induced CL was markedly attenuated in a concentration-dependent manner by aminoguanidine (99+/-0.1%, n=6, at 10 mM), methylguanidine (5+/-0.2%, n=6, at 10 mM) and guanidine (27+/-0.4%, n=7, at 10 mM). However, inhibition with aminoguanidine was found to be more marked than with methylguanidine and guanidine. Aminoguanidine (95+/-0.5%, n=6, at 1 mM) and methylguanidine (25+/-1%, n=6, at 1 mM), but not guanidine (2+/-1%, n=6, at 1 mM), significantly decreased ferrous iron-induced CL. 4. Collectively, these data suggest that aminoguanidine and a high concentration (> or = 0.1 mM) of methylguanidine have direct scavenging activities against H2O2, HOCl, hydroxyl radical and peroxynitrite. Guanidine, at a high concentration (> or = 0.1 mM), scavenges H2O2, HOCl and peroxynitrite, but not the hydroxyl radical. These direct scavenging properties may contribute to inhibitory effects of these compounds on human leucocyte CL.

Evidence for the involvement of peroxynitrite in ischaemic preconditioning in rat isolated hearts.

1. The aim of this study was to investigate the involvement of peroxynitrite, reactive metabolite originating from nitric oxide and superoxide, in preconditioning of the ischaemic myocardium in rat isolated hearts. 2. Isolated hearts perfused with Krebs-Henseleit solution were preconditioned either by 3 min of coronary artery occlusion (CAO) or by peroxynitrite administration at three different concentrations (0.1, 1, 10 microM) for 3 min, followed by 10 min reperfusion and 30 min of CAO. Peroxynitrite, at 1 microM concentration, decreased the incidence of VT from 100% (n=14) to 62% (n=13) and abolished the occurrence of VF (50% in the control group). 3. N-2-mercaptopropionylglycine (MPG, 1 microM - 10 mM) produced a concentration-dependent inhibition of peroxynitrite signals in luminol chemiluminescence and 67+/-1% inhibition was observed at 100 microM (n=7). MPG (at 300 microM, n=7) added to the perfusate 10 min prior to ischaemic preconditioning or peroxynitrite infusion and maintained until CAO, significantly reversed the beneficial effects of the ischaemic and peroxynitrite-treated groups. MPG administration in the peroxynitrite-treated group increased the incidence of VT from 62% (n=13) to 100% (n=10) and total VF from 0% (n=0) to 67% (n=10). Similarly, MPG elevated the incidence of VT from 50% (n=10) to 100% (n=8) in the ischaemic preconditioned group. On its own, MPG did not affect the severity of cardiac arrhythmias. 4. These results suggest that endogenously produced peroxynitrite plays a significant role in the antiarrhythmic effect of ischaemic preconditioning in the rat isolated hearts.

Involvement of prostanoids in the pulmonary pressor effect of histamine.

The role of prostanoids in the pulmonary actions of histamine(HA) was investigated using various antagonists and assay organs in superfusion cascade. Intraarterial injection of HA to the perfused lung caused contractions of rabbit aorta, rat stomach strips, guinea pig trachea, but contraction followed by relaxation of bovine coronary artery, superfused with lung effluent. Lung effluent produced no significant changes in resting tensions of guinea pig ileum or rat colon. The thromboxane synthetase inhibitor, UK 38485, reduced and the thromboxane/prostaglandin receptor antagonist, SQ 29548 abolished HA-induced contractions of all superfused assay tissues. Both contractile and relaxant responses of bovine coronary artery were completely inhibited by indomethacin. The pulmonary pressor effect of HA was also significantly inhibited by all of these antagonists. Our results indicate that HA releases thromboxane A2, prostaglandin endoperoxides, and prostacyclin but not leukotriene and prostaglandin E2- like substances from the guinea pig lung.

The role of tyrosine kinase in hypoxic constriction of sheep pulmonary artery rings.

Complex and incompletely understood mechanisms underline the vascular responses to hypoxia. Recent studies showed that the tyrosine kinase pathway is involved in vasoconstriction of vascular smooth muscle. Therefore, the aim of this study was to determine the tyrosine kinase pathway for the hypoxic contraction in large-diameter sheep pulmonary artery rings in vitro by studying the effects of selective inhibitors of tyrosine kinase and of a protein tyrosine kinase inhibitor. Lowering the pO2 from 96 to 5 mm Hg caused a contraction in arteries precontracted with 5-hydroxytryptamine (5-HT) but not under resting force. Preincubation of arteries with the tyrosine kinase inhibitors, genistein and tyrphostin, abolished the hypoxic contraction without affecting 5-HT contractions. Inhibition of tyrosine phosphatase activity by sodium orthovanadate increased the hypoxic vasoconstriction in 5-HT-precontracted arteries. These results suggest that the tyrosine kinase pathway is involved in hypoxic pulmonary vasoconstriction in sheep isolated pulmonary artery rings.

Epithelium-dependent responses of serotonin in a co-axial bioassay system.

Serotonin (10(-6) - 10(-4) M) produced relaxations in a concentration-dependent (at 10(-6) and 10(-5) M concentrations) manner followed by a contraction (at 10(-4) M concentration) in a co-axial system, which consisted of guinea-pig trachea as a donor organ for epithelial derived-relaxing factor(s) and phenylephrine-precontracted rat anococcygeus muscle as assay tissue. Serotonin produced a concentration-dependent contraction only in precontracted rat anococcygeus muscle mounted alone or mounted co-axially within epithelium-denuded trachea. Indomethacin (10(-6) M) significantly inhibited the initial relaxations (from 25.1 +/- 7.8 to 7.8 +/- 5.0% and from 35.6 +/- 8.7 to 10.4 +/- 8.3% at 10(-6) and 10(-5) M concentrations of serotonin), but did not affect the contraction. Imipramine (10(-8) M) and hydrocortisone (3 x 10(-5) M) reduced the initial relaxations (from 20.5 +/- 1.6 to 3.8 +/- 1.5% and from 32.1 +/- 6.4 to 18.9 +/- 3.9% at 10(-6) M and 10(-5) M concentrations of serotonin, respectively) and also converted the serotonin (10(-4) M)-induced contraction to a relaxation. In the co-axial system with trachea from guinea-pigs previously sensitized with i.p. injected egg-ovalbumin, the serotonin-induced biphasic response was converted to a contractile response only after ovalbumin challenge. Histopathologic changes were observed in the epithelium of challenged tracheas taken from sensitized guinea-pigs and alterations of serotonin-induced epithelium-dependent responses were attributed to the morphological and/or functional damage of tracheal epithelium caused by ovalbumin challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

The beneficial effects of peroxynitrite on ischaemia-reperfusion arrhythmias in rat isolated hearts.

The simultaneous production of nitric oxide (NO) and superoxide leads to the formation of a potent toxic metabolite peroxynitrite (ONOO(-)). However, ONOO(-) at low concentrations has been found to exert cardioprotective effects. The purpose of the present study was to investigate the effects of exogenous ONOO(-) on ischaemia-reperfusion arrhythmias. We studied the concentration-response effects of ONOO(-) (0.4, 4, 40 microM ml(-1) min(-1) for 20 min) in rat isolated hearts perfused with Krebs-Henseleit solution. The 0.4 microM concentration of ONOO(-) was selected for further experiments since it did not affect the sinus rhythm. In the hearts subjected to 10 min of ischaemia followed by 10 min of reperfusion during 0.4 microM ml(-1) min(-1) ONOO(-) infusion, the incidence of ventricular fibrillation was decreased significantly from 93% to 38% (n=8) and none of the hearts had an irreversible ventricular fibrillation. Urate, a ONOO(-) scavenger (at 1 mM, n=7), added to the perfusate 5 min prior to the coronary artery occlusion and maintained throughout the experimental period, did not significantly modify the beneficial effects of ONOO(-). Although L-N(G)-nitroarginine methylester (L-NAME) (100 microM, n=8) had no effect, superoxide dismutase (10 U ml(-1))+catalase (100 U ml(-1)) increased the number of ventricular ectopic beats from 91+/-32 to 286+/-83 (n=5) and augmented the incidence of irreversible ventricular fibrillation from 0% to 60%. There were no marked changes in the time of onset of the first arrhythmias in any group. These results suggest that ONOO(-) at a low concentration may exert beneficial effects on ischaemia-reperfusion-induced arrhythmias in rat isolated hearts.

Peroxynitrite produces relaxations on the rat anococcygeus muscle.

Effects of peroxynitrite (ONOO-), its stable product 3-nitrotyrosine (NT) and sodium nitroprusside (SNP) on isolated rat anococcygeus muscle were investigated. Administration of 0.1-1.0 mM ONOO- or 0.01-100.0 microM SNP produced concentration-dependent relaxations on the phenylephrine (2 microM)-precontracted muscle. Time courses of these relaxations to ONOO- and SNP were not similar and decomposed ONOO- caused a biphasic response composed of an initial contraction followed by a relaxation. NT (0.01-0.1 mM) either incubated for 20 min prior to precontraction or given during precontraction plateau did not attenuate precontraction or ONOO(-)-induced relaxations. Results of the present study demonstrate that ONOO- relaxes rat anococcygeus muscle specifically while its stable metabolite NT has no effect.

The comparison of vascular reactivities of arterial and venous grafts to vasodilators: management of graft spasm.

Graft spasm in the perioperative or postoperative period increases the risk of morbidity and mortality after coronary revascularization and hence necessitates urgent treatment. We have studied the effects of various vasodilators against noradrenaline- and endothelin-1-induced spasms in saphenous vein, internal mammary artery and gastroepiploic artery. In internal mammary and gastroepiploic arteries, the nitrovasodilators, sodium nitroprusside and glyceryl trinitrate, effectively reversed the spasms induced either with noradrenaline (for sodium nitroprusside; internal mammary artery: 101.07% +/- 1.63%; gastroepiploic artery: 94.10% +/- 2.07%) or endothelin-1 (for sodium nitroprusside; internal mammary artery: 97.67% +/- 4.94%; gastroepiploic artery: 90.69% +/- 2.61%). However, in saphenous vein contracted with endothelin-1, the responsiveness to nitrovasodilators was significantly blunted (for sodium nitroprusside: 52.33% +/- 5.19%) than that of rings contracted with noradrenaline (for sodium nitroprusside: 95.04% +/- 1.94%). Both arterial and venous grafts exhibited moderate beta-receptor function in response to isoproterenol. Isoproterenol was less effective in inhibiting the contractions of endothelin-1 in saphenous vein and gastroepiploic artery but not in internal mammary artery. On the other hand, nifedipine and papaverine were fully effective in reversing all the spasms in three of the graft materials. From these results, it can be deduced that saphenous vein is refractory against cyclic guanidine monophosphate (cGMP)-dependent and beta-receptor mediated relaxations when endothelin-1 was used as the spasmogenic agent. Internal mammary artery is the most responsive graft material to the vasodilators regardless of the nature of spasmogenic stimulus. Gastroepiploic artery exhibits functional similarity with internal mammary artery, with the exception of beta-receptor responsiveness.

Antinociceptive effect of some amaryllidaceae plants in mice.

The antinociceptive effects of ethanolic extracts of Pancratium maritimum L., Narcissus tazetta subspecies tazetta and Leucojum aestivum L. bulbs have been investigated in mice using the p-benzoquinone-induced abdominal constriction and hot-plate tests. In the p-benzoquinone-induced abdominal constriction test the ethanolic extracts of P. maritimum (300, 600 or 1200 mg kg-1, s.c.) and N. tazetta subsp. tazetta (5, 50, 100 or 200 mg kg-1, s.c.) caused dose-dependent inhibition of abdominal constrictions whereas a fluctuating response was obtained from ethanolic extracts of L aestivum (2.5-500 mg kg-1, s.c.). In the hot-plate test P. maritimum and L. aestivum caused a significant increase of latency only at the highest concentrations used (1200 mg kg-1 and 500 mg kg-1, i.p., respectively). However, at these concentrations they also caused significant toxic effects. In contrast with P. maritimum and L. aestivum, N. tazetta subsp. tazetta (5-500 mg kg-1, i.p.) extracts had no antinociceptive effect in this test. These findings indicate that the antinociceptive effect of Amaryllidaceae plants differs depending on the model of nociception investigated.

Studies on the vascular effects of the fractions and phenolic compounds isolated from Viscum album ssp. album.

Viscum album L. has been used in the indigenous system of medicine for treatment of various diseases such as atherosclerosis and hypertension. In the literature, phenylpropan and flavonoid derivatives were suggested to play a role in the inhibition of cyclic adenosine monophosphate (cAMP)-phosphodiesterase (PDE) and a correlation was proposed between the in vitro inhibition of PDE and in vivo pharmacological activity. The vascular effects of the phenolic compounds and subfractions isolated from n-butanolic fraction of V. album ssp. album were studied on noradrenaline-contracted rat aortic rings. Isolated phenolic compounds (Syringin (VA-1), Coniferin (VA-9), 5, 7-dimethoxy-flavanone-4'-O-[beta-D-apiofuranosyl(1-->2)]-beta-D-gl uco pyranoside (VA-4)) produced concentration-dependent contractions in rat aortic rings. Only one compound (Kalopanaxin D (VA-15)) displayed very slight relaxant response. The weak concentration-dependent relaxing effect of the subfractions gave the idea that vasodilator activity were observed in the less polar subfractions. In addition, there was no clear correlation between the weak relaxant effects of subfractions and an inhibitory effect on cAMP-PDE.

Hypoglycaemic effect of Momordica charantia extracts in normoglycaemic or cyproheptadine-induced hyperglycaemic mice.

The hypoglycaemic effect of orally administered extracts of Momordica charantia L. fruits was examined in normoglycaemic or cyproheptadine-induced hyperglycaemic mice. The aqueous extract reduced the fasting glucose levels of hyperglycaemic or normoglycaemic mice. However, the ethanol extract did not affect the fasting or nonfasting glucose levels significantly in both groups of mice. There was no significant difference between the glucose-loaded and glucose-loaded plus aqueous extract given group. On the other hand, oral glucose-loading of the cyproheptadine-induced hyperglycaemic animals reduced the fasting glucose levels significantly. These results showed that aqueous extract of M. charantia fruits has a hypoglycaemic activity without improving the tolerance to glucose in cyproheptadine-induced diabetic mice.

Inhibitory effects of streptomycin on bronchoconstrictor, hypotensive and inflammatory responses to bradykinin and histamine.

Streptomycin inhibits significantly the bronchoconstrictor effects of bradykinin and histamine. This effect of streptomycin is probably through the relaxation of bronchiolar smooth muscle. The hypotensive and inflammatory responses to bradykinin and histamine are also significantly suppressed with streptomycin. This is thought to be due to the decreased vascular permeability to streptomycin.

Effects of vitamin K3 on the hypotensive and bronchoconstrictor responses to bradykinin and histamine in the guinea pig.

Vitamin K3 significantly inhibits the bradykinin-induced bronchoconstriction in the guinea pig lungs in vivo. On the other hand, the bronchoconstrictor responses to histamine are significantly potentiated with vitamin K3. Vitamin K3 does not significantly alter the hypotensive responses to either brandykinin or histamine.

Non-competitive inhibition of bradykinin, acetylcholine and histamine on guinea-pig ileum with streptomycin and vitamin K3.

Streptomycin and vitamin K3 were studied on the guinea-pig ileum for their effects on the cumulative dose-response curves of bradykinin, acetylcholine and histamine. Streptomycin and vitamin K3 antagonized each of these agonists non-competitively. The comparison of the non-competitive affinities of the antagonists indicate that all of these agonists antagonized by a common mechanism.

Effects of WEB 2086 on the protective role of preconditioning against arrhythmias in rats.

The purpose of the present study was to investigate a possible role of platelet activating factor (PAF) in ischaemic preconditioning (PC). Since both PC and PAF act through protein kinase C (PKC), PAF could play a role in PC. To test this hypothesis, anaesthetized, open-chest male rats were subjected to four different protocols. Group I was subjected to 30 min of left coronary artery occlusion. In Group II, WEB 2086 (10 mg kg-1 i.v. bolus+1 mg kg-1 h-1 i.v. infusion) a selective PAF antagonist was given to non-preconditioned rats 23 min before the 30-min occlusion period. In Group III and IV ischaemic PC was elicited by one cycle of 3 min occlusion and 5 min reperfusion and also in Group IV, WEB 2086 (10 mg kg-1 i.v. bolus+1 mg kg-1 h-1 i.v. infusion) was given 23 min before the 30 min occlusion period. Ventricular ectopic beats (VEB), ventricular tachycardia (VT), and ventricular fibrillation (VF) that occurred during 30 min occlusion were determined. WEB 2086 administration or PC reduced the VEBs significantly. Incidence of VT and VF were not affected by WEB 2086 compared with control values, although PC decreased the incidence of VT and VF. WEB 2086 administration did not attenuate PC-induced improvement of arrhythmia parameters. These data demonstrated that a specific PAF antagonist, WEB 2086 did not abolish PC-induced protection against arrhythmias.

Biphasic effect of histamine on spontaneously beating rat atria.

1. Effect of histamine (HA) (10(-4)-10(-2) M) on spontaneously beating rat atrium was investigated. HA produced a biphasic effect which is composed of an initial negative chronotropy followed by a positive chronotropic phase, at each single dose. 2. At a submaximal dose of HA (3 x 10(-3) M) we have investigated the effects of some antagonists on the biphasic effect profile. 3. Propranolol (10(-7) M) depressed the secondary phase by abolishing the biphasic pattern of the effect of HA leading it to a monophasic one (negative chronotropy). 4. On the other hand, combination with atropine (10(-7) M) was shown to reduce the negative inotropic effect (in the secondary phase) which was produced by HA in the presence of propranolol. 5. The initial negative chronotropic phase was significantly enhanced by propranolol and reduced by pheniramine (10(-6) M). 6. Pheniramine also potentiated the positive chronotropy at the secondary phase of the response, but cimetidine (10(-4) M) has no significant effect on both phases. 7. Theophylline (10(-4) M) abolished the initial negative chronotropic phase, but did not influence the secondary phase. Dipyridamole (10(-5) M) did not affect the secondary phase of the response of HA, but increased the initial negative chronotropic effect.

Hypochlorous acid-induced responses in sheep isolated pulmonary artery rings.

The formation of reactive oxygen species (ROS) appears to play a significant role in many pathological states including cystic fibrosis and asthma. Although stimulated inflammatory cells represent a major source of oxygen metabolites and these cells are able to generate the potent oxidant hypochlorous acid (HOCl) effects of HOCl on arteries are not known. HOCl at low concentrations (10(-7)to 10(-4)m) did not affect the resting force or have an action in precontracted sheep pulmonary arteries. HOCl at 10(-4) m concentration reduced histamine-induced relaxations in endothelium intact preparations. However, at high concentrations (10(-2) to 1 m) HOCl led to constriction under resting conditions and caused vasodilation in endothelium intact and denuded serotonin (10 microm) precontracted arteries. These effects of HOCl were significantly reduced by pretreatment of l -arginine (10(-3)m), sodium nitroprusside (SNP, 10(-5) m) and N -acetyl-l-cysteine (NAC, 10(-4) m). The effects of SNP and NAC on HOCl-induced responses were due to direct interaction since only these compounds markedly diminished the HOCl-induced luminol chemiluminescence (CL). Lack of contraction with KCl after high concentrations of HOCl showed that HOCl causes irreversible tissue damage. These results suggest that HOCl produce vasoconstriction under resting force and cause vasodilation when the pulmonary arteries precontracted. HOCl may interact with endothelium-derived mediators and contribute to tissue injury and vascular dysfunction seen in disease states.