Vasoconstrictor responses of isolated pig coronary arteries

In helical strips of pig coronary arteries, histamine, serotonin, acetylcholine and a stable analogue of thromboxane A2 (9, 11-epithio-11, 12-methano TXA2: s-TXA2) produced a dose-dependent contraction. The histamine-induced contraction was suppressed by treatment with chlorpheniramine, suggesting an involvement of H1 receptors. Contractile responses to serotonin were attenuated by not only ketanserin, an S2 antagonist, but also by cinanserin and methysergide. Relaxation induced by serotonin in preparations treated with high concentrations of ketanserin were inhibited by cinanserin and methysergide. Norepinephrine contracted coronary arteries treated with propranolol. Contractile responses to norepinephrine were reversed to relaxations by prazosin, which were abolished by treatment with yohimbine. Contractile responses to histamine were potentiated by treatment with low concentrations of serotonin or s-TXA2. Contractile responses to serotonin were also potentiated by low concentrations of histamine or s-TXA2. Removal of the endothelium from pig coronary arterial strips potentiated contractions induced by serotonin, histamine and norepinephrine. These results suggest that, in addition to damaged endothelium, integrating action of endogenous vasoconstrictors, including histamine, serotonin, TXA2 and norepinephrine, may play an important role in producing coronary vasospasm.     

Vasomotor effect of histamine on pig and cattle coronary artery in vitro.

Vasomotor effects of histamine were examined in isolated coronary arteries from pigs and cattle. Histamine produced a concentration-dependent contraction in these arteries. These contractile responses were dose-dependently inhibited by diphenhydramine. The slopes of the Schild plots, however, were significantly lower than unity in both species. Cimetidine potentiated the histamine-induced contractions at relatively high doses of histamine (larger than 10(-5) M) in pig coronary arteries, but did not show a significant effect in cattle arteries. After the removal of endothelium, the Schild plot of diphenhydramine against histamine gave a straight line with a pA2 value of 7.80 and slope of 1.00 in pigs, confirming the competitive nature of the antagonism. In cattle, the slope was significantly lower than unity; however, in the presence of cimetidine, it was not significantly different from unity. Dimaprit did not contract the cattle coronary arteries with endothelium, but contracted them after the removal of endothelium. These results suggest that histamine-induced vasoconstriction in pig and cattle coronary arteries is mainly dependent on the H1-receptors in the smooth muscle cells, and that H1- and H2-receptors in the endothelial cells of pigs and H2-receptors in the smooth muscle cells of cattle modify the histamine-induced vasoconstrictions.     

Iloprost (ZK 36374) enhances recovery of regional myocardial function during reperfusion after coronary artery occlusion in the pig.

Ligation of the left anterior descending coronary artery in open-chest pigs for 20 min caused a complete loss of regional myocardial function, which did not recover during the first two hours of reperfusion. Infusion of the stable prostacyclin analogue Iloprost (100 ng kg-1 min-1) did not prevent the loss of systolic wall function during ischaemia. Recovery of regional myocardial function during the first two hours of reperfusion was enhanced to 40% of baseline by Iloprost. This effect of Iloprost cannot be explained by a decreased O2-demand during ischaemia or an enhanced recovery of myocardial ATP content.     

Mechanisms of bradykinin-induced relaxation in pig coronary arteries.

Bradykinin (BK) induced endothelium- and concentration-dependent relaxations in segments of porcine posterior descending coronary arteries submaximally precontracted with the thromboxane A2 mimetic, U-46619. The effects of BK were reduced by L-NG-monomethylarginine (L-NMMA) and 6-anilinoquinoline-5,8-quinone (LY-83583), respective inhibitors of nitric oxide (NO) synthase and guanylate cyclase, but were unaffected by the cytochrome P450 monoxygenase blocker, thiopentone sodium; however, BK effects were slightly reduced by dimethyl sulfoxide (DMSO), an hydroxyl radical scavenger. Relaxant responses were reduced markedly by ouabain, a sodium pump inhibitor but only slightly by tetraethylammonium (TEA) and charybdotoxin, respective blockers of Ca-activated (KCa) and large-conductance (BKCa) K+ channels. However, BK responses were practically abolished by TEA + L-NMMA + ouabain while unaffected by apamin, 4-aminopyridine and glibenclamide, blockers of small-conductance KCa voltage-sensitive and ATP-sensitive K+ channels, respectively. In segments submaximally precontracted with K+, BK-induced relaxation was lower than that of those precontracted with U-46619, and was further reduced by L-NMMA, LY-83583 and especially, ouabain; L-NMMA + ouabain + TEA abolished the effect. Precontraction of segments with higher K+ concentrations almost abolished the relaxation. These results suggest that the relaxation to BK is mediated: 1) by endothelial NO release which activates guanylate cyclase of smooth muscle cells; 2) by hydroxyl radicals; and 3) by an endothelial hyperpolarizing factor, that does not seem to be a metabolite derived from cytochrome P450 monoxygenases and that relaxes activating K+ channels (mainly BKCa), and especially, the sodium pump.     

Vasomotor responses of isolated human coronary arteries to magnesium, nitroglycerin and verapamil: a comparison with coronary arteries from cat and rat

The vasomotor responses in vitro to magnesium, nitroglycerin and verapamil were investigated in human coronary arteries. In order to examine possible species differences in reactivity to these agents, experiments were performed also on cat and rat coronary arteries. Potassium (124 mM) regularly produced stable contractions suitable for experiments with dilator agents. The order of potency for eliciting relaxation was the same in all three species; verapamil greater than nitroglycerin greater than magnesium. Maximum relaxation induced by nitroglycerin or magnesium was significantly lower in arteries from cat as compared to that obtained in coronary artery segments from man and rat. Spontaneous rhytmic activity was often present in human coronary arteries but never in arterial segments from cat or rat. The rhytmic activity was frequently enhanced by the addition of prostaglandin F2 alpha (3 microM) to the tissue bath, on the other hand the rhythmic activity was depressed, or even abolished, by potassium (124 mM), magnesium (1.2-13.2 mM), nitroglycerin (2.2 X 10(-5) M) or verapamil (10(-8)-10(-7) M). The magnitude of the vasomotor response of feline coronary arteries to nitroglycerin or verapamil was dependent on the extracellular concentration of magnesium; in the presence of a high concentration of magnesium (4.4 mM) the dilator effect of nitroglycerin was enhanced while that of verapamil was slightly depressed. The dilator activity of the two agents was not changed by incubation of the vessel segments in a magnesium-free medium as compared to that obtained in the standard (1.2 mM Mg) buffer solution.     

The beta-adrenoceptors in the smooth muscle of pig coronary arteries

An attempt has been made to classify the coronary vascular β-adrenoceptors as ‘β₁’ or ‘β₂’ by studying the effect of 3 different β-blocking agents on the isoprenaline-induced relaxation of isolated strips of pig coronary arteries. The study includes propranolol as a potent blocker of both cardiac and peripheral vascular β-adrenoceptors, H 93/26, 1-isopropylamino-3-[4-(2-methoxyethyl)-phenoxyl]-2-propanol, as a ‘cardioselective’ β-blocker, and H 35/25, 2-isopropylamino-1-(4-methylphenyl)- 1-propanol, as a blocker with predominant action on the peripheral adrenoceptors. The differential influence of the latter 2 substances is illustrated by experiments on isolated rat atria and rat portal veins. The coronary artery strips resembled the atrial effectors in their sensitivity to all 3 blockers but they differed from the venous smooth muscle. It is suggested that the β-adrenoceptors of the coronary arteries should be placed in the β₁ category.     

Effects of glutathione S-transferase inhibitors on nitroglycerin action in pig isolated coronary arteries

1. The present study was designed to clarify the role of glutathione S-transferase (GST) in the vasorelaxation response and development of tolerance to nitroglycerin (GTN) using GST inhibitors. 2. In pig isolated coronary arteries, GST activity was significantly changed to 77 and 82, or 69% of the control level (100%) following treatment with bromosulphophthalein (BSP; 10-3 and 10-4 mol/L) or ethacrynic acid (ETA; 10-4 mol/L), both GST inhibitors, respectively, but not following treatment with 10-3 and 10-4 mol/L GTN (GST activity 97 and 98% of control, respectively). 3. In KCl-contracted coronary artery strips pre-incubated with 10-5 and 10-4 mol/L GTN, 10-4 and 10-3 mol/L BSP or 10-4 mol/L ETA, concentration-dependent relaxations produced by GTN were significantly decreased compared with control. 4. 8-Bromo cGMP (8-Br-cGMP), a membrane-permeable cGMP analogue, produced concentration-dependent relaxations in GTN-pretreated arterial strips that were identical to control responses. However, there was weak but significant decrease in concentration-dependent relaxations in response to 8-Br-cGMP in BSP- and ETA-pretreated arteries. 5. The cGMP content in coronary arteries was significantly increased with GTN, GTN + BSP or GTN + ETA to similar high levels compared with control. 6. The results of the present study show that BSP and ETA decrease GTN- and 8-Br-cGMP-induced vasorelaxation, but have no effect on the GTN-induced increase in cGMP content in coronary arteries, suggesting a possibility that the GST inhibitors may have depressant actions on GTN- and 8-Br-cGMP-induced vasorelaxation through direct inhibition of the vasorelaxation of vascular smooth muscle themselves, in addition to having inhibitory effects GST activity.     

Regional myocardial blood flow during nicotine infusion after chronic coronary artery occlusion: effect of beta-adrenergic blockade

In eight dogs a portion of the left ventricular free wall (LVFW) was rendered collateral-dependent (CD) by gradual occlusion of the left anterior descending coronary artery with a surgically implanted Ameroid constrictor. Six to 8 weeks later, the dogs were anesthetized and regional myocardial blood flow was measured with 7-10-micron radioactive microspheres during (a) control conditions, (b) nicotine alone (24 micrograms/kg/min i.v.), and (c) nicotine (24 micrograms/kg/min i.v.) after beta-adrenergic blockade with propranolol. During control conditions, mean transmural flow was similar in CD, border, and normal regions of the LVFW. Nicotine alone increased flow in all regions of the LVFW, with normal (+ 104%) greater than CD (+ 56%). These changes in flow were accompanied by increases in mean arterial pressure (+ 34%) and mean aortic flow (+ 54%). Nicotine after beta-adrenergic blockade appreciably raised mean arterial pressure (+ 83%) and mean left atrial pressure (+ 307%), but caused no increase in flow to any region of the LVFW. The results indicate (a) that the nicotine-induced increase in flow is blunted in a CD region, and that (b) beta-adrenergic blockade unmasks coronary vasoconstrictor mechanisms during nicotine infusion which prevent increases in flow to either normal or CD regions despite increased perfusion pressure and augmented myocardial oxygen demands.     

多支冠状动脉完全闭塞132例介入治疗体会

目的 分析探讨多支冠状动脉闭塞(MTO)的最佳治疗方案。方法 2684例经冠状动脉造影(CAG)检查发现MTO132例(4．9％),其中35例急性心肌梗死(AMI)发病12h内对罪犯血管行直接经皮冠状动脉介入治疗术(PCI),术后10～14d对其余病变血管作第二次PCI;97例不稳定性心绞痛(UAP)首次及术后第7d两次行PCI。手术前后常规给氯吡格雷、阿斯匹林,AMI予低分子肝素,心绞痛同时予硝酸盐类药物,心力衰竭同时予狄高辛、速尿或武都力等治疗。AMI伴低血压、心源性休克18例,术前予主动脉内气囊反搏术(IABP)。24例伴缓慢性心律失常术前先行右心室心内膜临时起搏治疗。结果 AMI35例首次PCI成功率100％,二次成功率81％,术后死亡3例,治愈率91.2％;97例PCI首次PCI成功97支(95．8％),二次成功率86．6％。结论 MTO血管闭塞时间短,PCI成功率高;根据病情对心力衰竭、心源性休克、心律失常患进行干预后再选择PCI或冠状动脉搭桥术(CABG)。     

The preservation of functional activity of smooth muscle and endothelium in pig coronary arteries after storage at -190 degrees C

Pig coronary arteries have been investigated in-vitro using fresh tissue or after storage at -190 C in foetal calf serum containing 1.8 M dimethyl sulphoxide. Attention was paid to modulation of contractile activity and endothelium-dependent relaxation. After cryopreservation of the arteries maximal contractile responses to both 5-hydroxytryptamine (5-HT) and prostaglandin F2 alpha (PGF2 alpha) were markedly reduced and the pD2 values for both agonists were slightly, but significantly, diminished. Nevertheless, 5-HT antagonism by ketanserin and pizotifen was unchanged. Endothelium-independent relaxant responses of precontracted arteries to isoprenaline, forskolin, 3-isobutyl-1-methylxanthine, nitroprusside, atriopeptin III and cromakalim were generally unchanged after storage. Mechanical removal of the endothelium by rubbing enhanced the contractile response to PGF2 alpha in both fresh and stored arteries to a similar extent. In addition, endothelium-dependent relaxant responses to both 5-HT and substance P were well maintained, suggesting release of endothelium-derived relaxing factor by the stored arteries. The evidence suggests that after cryopreservation of pig coronary arteries at -190 degrees C mechanisms of relaxation, in particular those which are endothelium-dependent, are well maintained.     

Enhanced response of pig coronary arteries to endothelin-1 after ischemia-reperfusion. Role of endothelin receptors, nitric oxide and prostanoids

To analyse the coronary effects of endothelin-1 after ischemia-reperfusion, the left anterior descending coronary artery of anesthetized pigs was subjected to 30-min occlusion followed by 60-min reperfusion. Then, rings distal (ischemic arteries) and proximal (control arteries) to the occlusion were taken from this artery and prepared for isometric tension recording. The sensitivity of the contraction in response to endothelin-1 (3 x 10(-10)-3 x 10(-7) M) and the endothelin ET(B) receptor agonist IRL-1620 (3 x 10(-10)-3 x 10(-7) M) was greater in ischemic vessels. The endothelin ET(A) receptor antagonist BQ-123 (10(-7)-3 x 10(-6) M) decreased the sensitivity of the response to endothelin-1 similarly in ischemic and control arteries. The endothelin ET(B) receptor antagonist BQ-788 (10(-6) M), endothelium removal or the inhibitor of nitric oxide synthesis N(omega)-nitro-L-arginine methyl ester (L-NAME 10(-4) M) potentiated the response to endothelin-1 and IRL-1620 in control arteries only. The cyclooxygenase inhibitor meclofenamate (10(-5) M) augmented the maximal response to endothelin-1 in control arteries, and reduced it in ischemic arteries. In precontracted arteries, IRL-1620 (3 x 10(-11)-3 x 10(-10) M) relaxed control but not ischemic arteries, and L-NAME or meclofenamate abolished this relaxation. Therefore, ischemia-reperfusion increases the coronary vasoconstriction in response to endothelin-1 probably due to impairment of endothelin ET(B) receptor-induced release of nitric oxide and prostacyclin, augmentation of the contractile response to activation of endothelin ET(B) receptors, and increased release of vasoconstrictor prostanoids.     

Antifibrillatory properties of alinidine after coronary artery occlusion in rats

Ligation of the left anterior descending coronary artery was performed in open-chest anaesthetized rats and mortality as well as changes in ECG were evaluated for 30 min thereafter. Saline or drugs were administered 15 min prior to ligation. In the control group, following a 4 min lag period ventricular arrhythmias as single ectopic beats, ventricular tachycardia and ventricular fibrillation (VF) appeared, reaching a maximum between 10 and 20 min and disappearing after 30 min. Mortality (40% in the control group) coincided with the period of maximal arrhythmias, with VF more common in animals that died than in those surviving. Alinidine, a drug which reduces sino-atrial rate specifically but has no conventional antiarrhythmic properties, reduced mortality and VF. By means of order statistics the quantity ‘risk of death’ was used for evaluation of drug effects, considering incidence of death and VF as well as duration of VF. This quantity was reduced in correlation with the dose of alinidine (1–6 mg/kg i.v.) and in correlation with the reduction of heart rate. Mexiletine, an antiarrhythmic drug with membrane-depressant properties, also reduced the ‘risk of death’ dose dependently (1–10 mg/kg i.v.), but there was no correlation with a decrease in heart rate. It is suggested that alinidine reduced ‘risk of death’ by means of a reduced oxygen demand due to a decrease in heart rate.     

Mechanisms involved in relaxation induced by exogenous nitric oxide in pig coronary arteries.

The aim of the present study was to analyze the mechanisms involved in the vasodilator responses elicited by nitric oxide (NO) in segments of porcine posterior descending coronary artery. Exogenous NO (0.1-30 microM) induced concentration-dependent relaxations in segments precontracted with a concentration of the thromboxane A2 mimetic, U-46619 (30-300 nM) that produced a contraction 70% (submaximal contraction) of that elicited by 75 mM K+ (maximal contraction). The relaxations were almost abolished by 6-anilinoquinoline-5,8-quinone (LY-83583, 10 microM), an inhibitor of guanylate cyclase, and with precontraction with 40 or 60 mM K+. Relaxations were reduced by 5 mM tetraethylammonium (TEA), a blocker of Ca(2+)-activated K+ channels (Kca channels) and unaltered by ouabain (500 microM), 4-aminopyridine (1 mM), glibenclamide (10 microM), apamin (1 microM) and charybdotoxin (0.3 microM), inhibitors of sodium pump, voltage-sensitive, ATP-sensitive, small-conductance Kca and large-conductance KcaK+ channels, respectively. These results suggest that the relaxation caused by exogenous NO is mediated by guanylate cyclase activation, with only a slight participation of a hyperpolarizing mechanism mediated by activation of Kca channels.     

On the contractile function of protein phosphatases in isolated human coronary arteries

It is unknown whether protein phosphatases types 1 and 2A are present in and can regulate the tone of human vascular tissue. The expression and possible function of serine/threonine protein phosphatases (PP) type 1 (PP1) and type 2A (PP2A) were studied in isolated human coronary arteries. Catalytic subunits of PPI and PP2A were identified by means of phosphatase activity measurement in tissue homogenates, by separation of enriched extracts through affinity column chromatography, by immunoblotting with specific antibodies, by hybridization of mRNA with specific DNA probes and PCR of reverse transcribed mRNA. Based on these methods, the catalytic subunits of PP1(alpha,beta,gamma) and PP2A(alpha,beta) were identified. Appropriately, cantharidin, an inhibitor of PP1 and PP2A, increased basal tone of human isolated coronary artery rings with an EC50 of about 16 micromol/l by increasing the phosphorylation state of the regulatory light chains of myosin. In summary, PP1 and PP2A are expressed in human coronary arteries and they can alter vascular tone.     

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.     

Prostacyclin releases endothelium-derived relaxing factor and potentiates its action in coronary arteries of the pig.

1. The possible interactions between prostacyclin and endothelium-derived relaxing factor were examined, in isolated coronary arteries of the pig treated with indomethacin (10(-5) M). 2. In organ chamber experiments, prostacyclin caused relaxations, which were potentiated in the presence of the endothelium; the potentiation was abolished by oxyhaemoglobin. 3. In bioassay experiments, prostacyclin caused minimal relaxations of bioassay rings without endothelium; these relaxations were potentiated when the bioassay ring was exposed to basally-released endothelium-derived relaxing factor (interaction between prostacyclin and basal endothelium-derived relaxing factor) and further augmented when the endothelial cells were exposed to the prostanoid (stimulated release of endothelium-derived relaxing factor). The endothelium-dependent, but not the direct effects of prostacyclin were augmented by superoxide dismutase plus catalase and abolished by oxyhaemoglobin. 4. Forskolin, a direct activator of adenylate cyclase, caused relaxations of rings without endothelium, which were augmented by the presence of the endothelium. 5. The relaxations induced by prostacyclin or forskolin also had an endothelium-dependent component in basilar and femoral arteries and in jugular veins of the pig. 6. The endothelium-dependent actions of prostacyclin probably reflect activation of adenylate cyclase.