Coronary effects of nicorandil in comparison with nitroglycerin in chronic conscious dogs

The effects of nicorandil (0.2 mg/kg, IV) and nitroglycerin (15 micrograms/kg, IV) on large and small coronary arteries were compared in conscious dogs instrumented with ultrasonic crystals and electromagnetic flow meters in the circumflex coronary artery. Nicorandil dilated the large coronary arteries to the same extent, but with a longer duration of action than nitroglycerin. The small coronary arteries dilated for a very short period of time with nitroglycerin, but dilated markedly with nicorandil. The dilatory action of nicorandil on large coronary arteries persisted after the action on the small coronary artery fell to the control value, indicating that the dilatory action on the large coronary arteries is due to the direct relaxing effect on smooth muscle and is not the result of the flow-dependent effect. The measurement of the plasma concentration of nicorandil after incremental infusions of the agent showed that the dilation of the small coronary artery took place at only a very high level (above 200 ng/ml). On the other hand, the large coronary arteries responded to nicorandil at a much lower concentration (about 100 ng/ml, the clinically effective plasma concentration of nicorandil) than the small coronary resistance arteries. In conclusion, whereas nicorandil possesses a dilatory action on both large and small coronary arteries, in a clinical setting, with a daily dosage of 15-30 mg, part of the beneficial effects of nicorandil may be the result of a dilation of the large coronary arteries and may be due to the fact that a coronary steal phenomenon does not occur after nicorandil administration.     

Role of K+ channels in EDHF-dependent relaxation induced by acetylcholine in canine coronary artery

Summary To identify the K⁺ channels responsible for endothelium-derived hyperpolarizing factor (EDHF)-dependent relaxation, we studied the effects of various K⁺ channel blockers on acetylcholine-induced relaxation, which persists even in the presence of both an inhibitor of nitric oxide synthase and that of cyclooxygenase, in canine coronary artery rings. A nonselective K⁺ channel blocker, tetrabutylammonium (TBA), a large and intermediate conductance Ca²⁺-activated K⁺ channel blocker, charybdotoxin (CTX), and a voltage-dependent K⁺ channel blocker, 4-aminopyridine (4-AP), significantly inhibited this residual relaxation. A combined treatment with CTX and 4-AP almost completely blocked the relaxation. Neither a large (iberiotoxin) nor a small (apamin) conductance Ca²⁺-activated K⁺ channel blocker blocked the relaxation. We also investigated effects of K⁺ channel blockers on basal tone to determine whether or not EDHF is involved in regulating basal tone. TBA and CTX substantially raised basal tone to a greater degree in endothelium-intact preparations than in endothelium-denuded preparations. These results indicate that EDHF may exert its relaxing action through intermediate conductance Ca²⁺-activated and voltage-dependent K⁺ channels in canine coronary arteries. In addition, EDHF may play a role in maintaining basal vascular tone. This study was supported in part by a Grant-in-Aid for Scientific Research (B07457167) from the Ministry of Education, Science and Culture of Japan.     

乙酰胆碱对犬冠状动脉循环和心电活动的影响

本研究对２２条犬，在建立颈总动脉向左冠脉回旋支（ＬＣＸ）供血的模型基础上，进行刺激右侧迷走神经（ＲＶ）。ＬＣＸ内注射乙酰胆硷（Ａｃｈ）、硝酸甘油（ＮＧ）、去甲肾上腺素（ＮＥ）等实验，观察冠脉灌注压（ＣＰＰ）、冠脉平均血流量（ＣＢＦ）及ＥＣＧ的变化。结果表明:刺激ＲＶ和冠脉（ＣＡ）内注射Ａｃｈ对心脏频率、传导和心肌收缩力的抑制作用，随刺激强度和注射剂量的增加而加强；小剂量ＮＧ可直接扩张ＣＡ，使ＣＢＦ增加，大剂量Ａｃｈ可能诱发ＣＡ痉挛和严重心律失常，并使ＣＰＰ和ＣＢＦ降低。     

Ischemic myocardial cell protection conferred by the opening of ATP-sensitive potassium channels

The responses of the cardiac myocyte to a potentially injurious ischemic stress are multiple. The opening of the ATP-sensitive K⁺ channels may constitute one such response. These channels are present in the plasmalemma at very elevated density and have a large unitary conductance. Consequently, the opening of a small fraction (0.01–0.1%) of these channels during ischemia can help to drive the myocyte into an emergency state, in which its syncytial functions become rapidly downregulated and strategies appropriate to preserving cell viability are implemented. Thus, ATP-sensitive K⁺ channels in cardiac myocytes would appear to be an efficient and apparently redundant natural means of defense against metabolic stress. These channels can undergo physiologic modulation, as occurs during cardiac ischemic preconditioning in several species, including humans. The termcardioprotection refers to an endogenous cardioprotective strategy, whereby the myocardium slows its energy demands, produces fewer toxic glycolytic products, and exhibits reduced injury following a potentially lethal ischemic stress. Openers of cardiac ATP-sensitive K⁺ channels, a class of drugs that includes, in particular, aprikalim and nicorandil, also afford cardioprotection by reducing the functional and biochemical damage produced by ischemia. Hence, these compounds can improve the recovery of cardiac contractility, reduce the extracellular leakage of intracellular enzymes, delay the loss of ATP, and preserve the cell ultrastructure in isolated heart preparations subjected to transient ischemic conditions. Furthermore, when segmental contractility has been strongly depressed by a stunning insult, nicorandil and aprikalim can accelerate recovery at the reperfusion. Finally, nicorandil and aprikalim decrease substantially the size of the necrotic region that results from a prolonged ischemic insult followed by reperfusion. All of these desirable effects of K⁺-channel openers can be abolished by blockers of ATP-sensitive K⁺ channels, such as glibenclamide. The fundamental mechanism of the myocyte viability protection conferred by K⁺-channel openers is not yet clear. It may exploit some of the same pathways that mediate cardiac ischemic preconditioning. If this suggestion holds true, drugs opening cardiac ATP-sensitive K⁺ channels would mimic, exploit, or intensify those cardioprotective means that are naturally available to the cardiac myocyte for overcoming metabolic stress.     

ATP敏感性钾通道对狗的冠状动脉的调节

目的　探讨冠状动脉震颤发生的条件及和ATP敏感性钾通道的关系。方法　用优降糖诱发冠状动脉震颤后分别用尼可的尔、硝酸甘油观察两药对震颤的影响。结果　优降糖 3mg/kg可诱发冠状动脉震颤 ,且此现象在细小的动脉表达得更为强烈 ;震颤不能被硝酸甘油抑制 ,但可被尼可的尔终止。结论　ATP敏感性钾通道的阻滞可发生冠状动脉的震颤 ,且在细小动脉中尤为突出 ,当内皮细胞产生NO减少时震颤也将增强。     

Effect of nicorandil on abnormal coronary flow reserve assessed by exercise201Tl scintigraphy in patients with angina pectoris and nearly normal coronary arteriograms

Summary The purpose of the present study is to assess the effect of nicorandil, a coronary vasodilator with a mechanism of potassium channel opening, on the abnormal myocardial²⁰¹Tl perfusion evoked by exercise. Eleven patients who had a history of typical angina, positive exercise electrocardiograms, positive²⁰¹Tl scintigraphy, nearly normal coronary arteriograms, and negative coronary vasospasm underwent exercise²⁰¹Tl scintigraphies under no medication (baseline test) and administration of nicorandil (nicorandil test).²⁰¹Tl was injected at a matched workload in both tests. Nicorandil did not alter heart rate, blood pressure, or the rate-pressure product at the end of the exercise, but it significantly improved the extent score from 0.37±0.22 to 0.20±0.15 (p<0.05) and the severity score from 33.9±32.2 to 13.5±16.4 (p<0.05), and also significantly hastened the²⁰¹Tl mean washout rate from 30.5±14.8% to 37.4±13.1% (p<0.05). Anginal symptoms disappeared in 3 of 5 cases and ST depression improved in 5 of 7 cases after nicorandil. We conclude that nicorandil augments coronary flow reserve, possibly due to a reduction of vasotone in the small coronary arteries.     

A further study of the vasodilator and negative inotropic mechanisms of action of nicorandil and its congeners in the canine heart

Summary The vasodilator and negative inotropic mechanisms of action of nicorandil and its congeners (SG-209, SG-103, and SG-86) were investigated in isolated canine papillary muscle preparations cross-circulated through the anterior septal artery with support dogs. SG-209, SG-103, and SG-86 were obtained by replacement of the nitroxyl group of nicorandil by acetoxyl, nicotinoyloxyl, and hydroxyl groups, respectively. Nicorandil (0.03–10 µmol), SG-209 (0.1–10 µmol), SG-103 (1–30 µmol), and SG-86 (3–100 µmol) all produced an increase in coronary blood flow through the anterior septal artery. Both nicorandil and SG-209 produced a near-maximal increase in coronary blood flow, the latter being about 5.5 times less potent than the former. SG-103 and SG-86 were far less potent than SG-209 in that order. The vasodilator actions of nicorandil and SG-209 were antagonized by glibenclamide given IV to support dogs, but those of SG-103 and SG-86 were not. The pK_B values of glibenclamide were 6.34 toward nicorandil and 6.49 toward SG-209. Developed tension of the papillary muscle was reduced by nicorandil, SG-209, and SG-103, but not by SG-86. In this respect SG-209 was about 4.7 times less potent than nicorandil, and SG-103 was much less potent than SG-209. The negative inotropic effects of nicorandil and SG-209 were antagonized by glibenclamide, but that of SG-103 was not. These results indicate that both nicorandil and SG-209 act as K-channel openers in coronary resistance vessels and in ventricular myocardium, and that the nitroxyl and the acetoxyl group at C2 of the parent structure of nicorandil and its congeners, i.e., N-ethylnicotinamide, play a pivotal role in making these compounds act as K-channel openers. In this respect, the nitroxyl group is about five times more potent than the acetoxyl group.     

Diameter of coronary arteries in 36 species of mammalian from mouse to giraffe

Summary Systematic quantitative investigations were performed in the coronary arteries of 102 hearts of 36 mammal species with an overall more than tenthousandfold difference of their heart weight. After postmortem coronary angiography with a filling pressure of 100 mm Hg x-rays were taken, and the widest diameters of the coronary artery stems were determined. We found a nearly linear correlation between diameter of a standardized coronary artery and virtual diameter of heart, but the increase in diameter of coronary arteries exceeded somewhat that of the diameter of heart especially for heart weights surmounting 100 g. Perhaps relative enlargement of coronary arteries in the bigger hearts contributes to the prevention of large increase of blood flow velocity.This study was supported by a research grant of the Deutsche Forschungsgemeinschaft 282/8     

Hydrogen peroxide-induced vascular relaxation in porcine coronary arteries is mediated by Ca2+-activated K+ channels

Summary Hydrogen peroxide (H₂O₂) elicited concentration-dependent relaxation of endothelium-denuded rings of porcine coronary arteries. The relaxation induced by the H₂O₂ was markedly attenuated by 10μM 1H-[1,2,4]oxadiazolo [4,3,a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase, or by 100nM charybdotoxin, an inhibitor of large-conductance Ca²⁺-activated K⁺ (K_Ca) channels. A combination of the ODQ and charybdotoxin abolished the H₂O₂-induced relaxation. Pretreatment with 25 μM of an Rp stereoisomer of adenosine-3′,5′-cyclic monophosphothioate (Rp-cAMPS), 20μM glibenclamide, or 1mM 4-aminopyridine did not affect the vascular response to H₂O₂. The presence of catalase at 1000U/ml significantly attenuated the H₂O₂-induced relaxation. Exposure of cultured smooth muscle cells to H₂O₂ activated K_Ca channels in a concentration-dependent manner in cell-attached patches. Pretreatment with catalase significantly inhibited the activation of K_Ca channels. Rp-cAMPS did not inhibit the H₂O₂-induced activation of K_Ca channels. The activation of K_Ca channels by H₂O₂ was markedly decreased in the presence of ODQ. However, even in the presence of ODQ, H₂O₂ activated K_Ca channels in a concentration-dependent manner. In inside-out patches, H₂O₂ significantly activated K_Ca channels through a process independent of cyclic guanosine 3′,5′-monophosphate (cGMP). In conclusion, H₂O₂ elicits vascular relaxation due to activation of K_Ca channels, which is mediated partly by a direct action on the channel and partly by activation of soluble guanylate cyclase, resulting in the generation of cGMP.     

In Vitro Action of Insulin on Erythrocyte Sodium Transport Mechanisms: Its Possible Role in the Pathogenesis of Arterial Hypertension

The effects of insulin on sodium and potassium metabolism have been well known for many years; clinical observation and laboratory experience showed different results about the insulin effect on the sodium-potassium pump. Moreover, studies about the insulin effect on the sodium-potassium cotransport are not available. Therefore, the effects of insulin on Na,⁺K⁺ pump and Na⁺,K⁺ cotransport were evaluated. Results show that insulin inhibits Na⁺, K⁺ pump, while Na⁺, K⁺ cotransport is markedly activated. The possible link between pathogenesis of arterial hypertension in hyperinsulinemic subjects and present data is examined.     

Regulation of large coronary vessels by adrenergic mechanisms in conscious dogs

Summary The effects of and adrenergic stimulation were examined in conscious dogs on measurements of left circumflex coronary blood flow and coronary arterial diameter and on calculations of mean coronary resistance (MCR) and left circumflex coronary internal cross-sectional area (CSA). Methoxamine (50 g/kg/min), after transiently increasing left circumflex coronary dimensions, induced sustained reductions in left circumflex coronary diameter (9±2%) and CSA (27±5%) at a time when mean arterial pressure rose by 65±5%, left ventricular (LV) dP/dt had decreased only slightly, and heart rate and mean coronary blood flow were at control levels. Isoproterenol, (0.1 g/kg/min), increased heart rate by 66±8%, LV dP/dt by 58±5%, and CSA by 17±3%, while it decreased mean arterial pressure by 12±1% and MCR by 44±5%. After ₁ adrenergic receptor blockade and with heart rate held constant, isoproterenol did not increase LV dP/dt but decreased mean arterial pressure similarly (13±2%) and induced attenuated increases in CSA (6±1%), and decreases in MCR (17±3%). After combined ₁ and ₂ adrenergic receptor blockades isoproterenol induced no significant effects.Thus, in the conscious dog, large coronary vessels not only react passively to changes in aortic pressure but also undergo substantial active changes. Alpha adrenergic stimulation is sufficiently powerful to reduce CSA, despite the opposing elevation of distending pressure. Moreover, large vessels appear to be regulated by ₁ adrenergic mediated increase in myocardial metabolic demands, as well as by ₂ adrenergic mediated vasodilation.Supported in Part by USPHS Grants HL 15416 and HL 17459     

Sequential dissection of multiple ionic currents in single cardiac myocytes under action potential-clamp

The cardiac action potential (AP) is shaped by myriad ionic currents. In this study, we develop an innovative AP-clamp Sequential Dissection technique to enable the recording of multiple ionic currents in the single cell under AP-clamp. This new technique presents a significant step beyond the traditional way of recording only one current in any one cell. The ability to measure many currents in a single cell has revealed two hitherto unknown characteristics of the ionic currents in cardiac cells: coordination of currents within a cell and large variation of currents between cells. Hence, the AP-clamp Sequential Dissection method provides a unique and powerful tool for studying individual cell electrophysiology.     

Long-acting coronary vasodilatory action of the molsidomine metabolite Sin I: a quantitative angiographic study

The vasodilatory action of molsidomine was studied by intracoronaryinjection of its active metabolite, Sin 1. In 10 patients repeatcoronary angiography in multiple projections was performed beforeand 2 minutes after administration of 1 mg of Sin 1, and beforeand after a second injection 60 minutes later. Contours of obstructedand non-obstructed segments of the left coronary artery werequantitatively analysed with a computer-based angiography analysissystem. Immediately after its administration, Sin I increasedthe mean diameters of 44 normal coronary segments by 12% (P<000I).Significant vasodilation (8%) was still observed after 60 minutes.At that time, repeated administration of Sin I increased thevasodilation by an additional 14% with respect to the controlsituation. An increase in obstruction diameter was observedin6 out of 8 obstructed segments. Mean increase in the minimalobstruction diameter was still 10% after 60 minutes.     

Effects of endothelin-1 on epicardial coronary tone,coronary blood flow,ECG-ST change and regional wall motion in anesthetized dogs

Summary The effects of intracoronaryadministrated endothelin-1 on coronary hemodynamics and regional myocardial function were studied in anesthetized open-chest dogs. Epicardial coronary diameter (CoD) and coronary blood flow (CBF) were measured by a sonomicrometer of 10 MHz piezoelectric crystals and an electromagnetic flow probe on the left circumflex coronary artery (LCX). Regional wall motion was sonomicrometrically measured at regions supplied by the LCX and left anterior descending artery (LAD) and electrocardiograms were recorded. Endothelin-1, administered as a bolus injections into the LCX via an intracoronary cannula, in a dose-dependent manner reduced COD and CBF. The extent of the reduction of COD and CBF at a dose of 300 pmol was 12.3±1.5% (P<0.01) and 86±5% (p<0.01), respectively, of the control. The extent of CBF reduction and deterioration of systolic wall motion were linearly related with the dosage of endothelin-1. ST-elevation (lead II) and fatal ECG abnormalities, including complete atrioventricular block or ventricular fibrillation, were observed with doses above 60 and 100 pmol, respectively. Coronary angiography revealed that filling defects of dye were propagated from the third or distal branches to those of more proximal arteries when the doses of endothelin-1 were cumulatively infused into the LCX. Accordingly, lethal myocardial ischemia induced by endothelin-1 is produced by critical obstruction of rather small coronary vessels.Part of the study was supported by Grants-in-Aid for Scientific Research (Nos. 02454259, 02404045) from the Ministry of Education, Science, and Culture, Japan, and a Research Grant for Cardiovascular Disease (1S-1) from the Ministry of Health and Welfare, Japan.     

Comparative study on the effects of intracoronary nicorandil and nitroglycerin in ischaemic, reperfused porcine hearts

The direct cardioprotective properties of nitroglycerin andnicorandil were compared in regionally ischaemic (45 min), reperfused(24 h) porcine hearts. Intracoronary treatments, which werestarted 15 min prior to occlusion of the distal left anteriordescending coronary artery (LAD), were continuously administeredfor 105min. The following equi-hypotensive drug dosages wereused in nine pigs each; nitroglycerin 6 fig. kg^–1 x minbefore ischaemia and during 45 min of reperfusion, 0.6 µg.kg^–1x min during ischaemia; nicorandil 5 fig. kg^–1x min before ischaemia and during 45 min of reperfusion, and0.5 fig. kg^–1 x min during ischaemia. Nine control animalswere treated with isotonic sodium hydrochloride solution (1ml. min^–1). Despite comparable effects on blood pressure, intracoronarynicorandil, in contrast to intracoronary nitroglycerin, didnot increase heart rate. Although neither drug affected coronaryblood flow significantly, nicorandil substantially reduced regionalmyocardial oxygen consumption before coronary artery occlusion( – 37±22%, P=0003 vs control group, P=0.01 vsnitroglycerin treatment). Infarct sizes (tetrazolium method)after 45 min of ischaemia and 24 h of reperfusion were significantlydecreased by nicorandil (control group 76.9 ± 19%, nicorandilgroup 49.3 ± 24%, P=0.012)whereas nitroglycerin exhibiteda borderline effect (62.5 ± 15%, P=0.054). Both treatmentsresulted in improved regional systolic shortening of the reperfusedsegment at the end of the experiments but this was not significant.At these drug dosages the direct cardioprotective action ofnicorandil is slightly superior to nitroglycerin. This may beascribed to its K-channel opening property associated with reducedregional myocardial oxygen consumption before the onset of ischaemia.     

Mechanism of hCG-induced spermiation in the toad Rhinella arenarum (Amphibia, Anura)

In Rhinella arenarum spermiation occurs as a consequence of LH/FSH increase during the amplexus or by a single dose of hCG, among other gonadotropins. The present study employs an in vitro system to study the mechanism of action of hCG in the spermiation of R. arenarum. Testicular fragments were incubated for 2 h at 28 °C in the presence or absence of 20 IU hCG with or without different PKA/PKC inhibitors and activators as well as ouabain and amiloride as Na⁺/K⁺ ATPase and transcellular Na⁺ transport inhibitors, respectively. Ouabain did not induce spermiation in absence of hCG and inhibited hCG-induced spermiation in a dose-dependent manner, reaching 90% inhibition with the higher concentration. In contrast, amiloride neither affected spermiation nor steroidogenesis. Activation of PKA with 8Br-cAMP induced spermiation in the absence of hCG while its inhibition with H89 blocked hCG action. On the other hand, PKC inhibition with Bi or STP did not affect hCG-induced spermiation although PKC activation significantly decreased hCG-dependent sperm release. These results suggest that PKC inhibits spermiation but also that the inhibition exerted by the kinase could be blocked by hCG. Taken together, these observations could indicate that PKA is involved in the mechanism of the gonadotropin action, mechanism also requiring the activation of a non-pumping Na⁺/K⁺ ATPase pathway.     

In vitro insulin action on different ATPases of erythrocyte membranes in normal and diabetic rats

Summary Thein vitro effect of porcine insulin on Na⁺+K⁺-, Ca²⁺- and Mg²⁺-ATPases of the rat erythrocyte membrane of normal and alloxan-induced diabetic rats was investigated. Na⁺+K⁺- and Ca²⁺-stimulated enzyme activities were significantly decreased in diabetic rats in comparison to normal animals. The specific activities of both these ATPases in the latter group were markedly reduced on pre-incubating the ghosts with insulin. Similar treatment of the erythrocyte membranes of diabetic animals, however, resulted in a significant increase of these activities. These qualitatively different effects of the hormone in the two groups increased progressively with hormone concentration and duration of pre-incubation. Mg²⁺-stimulated ATPase activity was not significantly affected in diabetes or by insulin.     

急性实验性冠状动脉狭窄时血栓和微血栓的形成

目的:探讨急性冠状动脉狭窄与血栓和微血栓的关系。方法: 将实验犬用微米缩窄器造成冠脉左回旋支定量狭窄,形成心电图ST段下移组（A组）与ST段抬高组（B组）,经60 min缺血后观察冠脉血流量变化和冠状窦内血管活性物质的变化,并做血管组织病理学检查。结果: A组冠脉血流量轻度下降,B组冠脉血流量严重下降;A、B两组的血小板聚集功能、乳酸和血栓素B2(TXB2)增加,血小板生长因子1α(PGF1α)、纤维连接蛋白和纤维蛋白原减少;两组间上述指标无明显差异;病理组织学检查揭示,冠脉急性狭窄后出现血管内皮细胞的损伤、血小板的聚集、附壁血栓的形成以及微循环内以红色血栓与白色血栓组成微血栓形成。A、B两组的上述病理改变无显著差异。结论: 实验性急性冠脉狭窄可以引起心电图ST段下移和抬高不同变化,并造成冠脉内皮的损伤、血栓和微血栓的形成,这在不稳定心绞痛发病机制中起了重要作用。