Cardiovascular pharmacological studies on JTV-506, a new potassium channel opener. 2nd communication: effects on blood pressure in conscious animals

The effects of JTV-506 ((-)-(3S,4R)-2,2-bis(methoxymethyl)-4-[(1,6-dihydro-1-methyl-6-oxo-3- pyridazinyl)amino]-3-hydroxychroman-6-carbonitrile hemihydrate, CAS 170148-29-5), a novel coronary vasodilator, on blood pressure were evaluated in conscious dogs and rats. In conscious dogs, JTV-506 (0.01-1 mg/kg p.o.), levcromakalim (0.01-1 mg/kg p.o.) and nifedipine (3-30 mg/kg p.o.) elicited an increase in double product, whereas nicorandil (1-10 mg/kg p.o.) did not affect the double product. The JTV-506-induced increase in double product was abolished by a beta-blocker, propranolol, suggesting that this increase in double product may be due to augumentation of heart rate by sympathetic nerves which mediate the baroreflex. The doses at which JTV-506 increased coronary blood flow in a previous study were lower than the doses required to increase the double product. JTV-506 did not have a crucial influence on electrocardiogram. In conscious rats, orally administered JTV-506, levcromakalim, nicorandil and nifedipine reduced blood pressure and increased heart rate dose dependently. These effects were more remarkable in hypertensive rats than in normotensive rats. JTV-506, a new potassium channel opener, seems to be relatively free of any hemodynamic effects.     

Analysis of relaxation and repolarization mechanisms of nicorandil in rat mesenteric artery.

1. The mechanisms by which nicorandil causes relaxation of rat isolated small mesenteric arteries mounted on a Mulvany myograph was investigated by use of a combination of putatively mechanism-specific antagonists. 2. In arteries precontracted by the thromboxane-mimetic, U46619, the EC50 for cromakalim and levcromakalim-induced relaxation curves were raised by 36 and 17 fold by glibenclamide (3 microM) while the EC50 for nicorandil-induced relaxation was unaffected by either glibenclamide or methylene blue (10 microM). A combination of these antagonists raised the EC50 for nicorandil by 8 fold. 3. In U46619-contracted arteries, nifedipine (100 nM) did not affect the cromakalim relaxation curve but it raised the EC50 for nicorandil by 5 fold. The combination of methylene blue, glibenclamide and nifedipine further inhibited the maximum relaxation to nicorandil. 4. In separate experiments, membrane potential (Em) and force responses were measured simultaneously. In arteries depolarized and contracted by U46619 both nicorandil and cromakalim repolarized (delta Em, 35 mV) and relaxed (100%) the vessels. Glibenclamide (3 microM) did not alter the relaxation-concentration curve to nicorandil but reduced the maximum repolarization to delta 10.8 mV. In contrast to Em and relaxation-response curves to cromakalim were shifted to the right by glibenclamide by 30-100 fold. 5. In unstimulated arteries, nicorandil (but not cromakalim) -induced hyperpolarization was significantly antagonized by methylene blue (10 microM) (6.6 fold rightward shift) or nifedipine (100 nM) (2.6 fold). In depolarized arteries (U46619), nifedipine but not methylene blue inhibited the nicorandil-induced hyperpolarization. 6. In arteries precontracted to 50% tissue maximum by either KCl or U46619, nifedipine (100 nM) relaxed the artery but failed to repolarize the Em. Presumably voltage-operated calcium channels (VOCC) were blocked preventing contraction but the artery remained depolarized, presumably through non VOCC mechanisms. 7. These data suggest that nicorandil may relax small arteries through 3 parallel pathways, (i) NO-donor mediated stimulation of guanylate cyclase and increase in cyclic GMP, (ii) K+ATP channel opening, and (iii) nifedipine-sensitive VOCC inhibition. Em data suggest that nicorandil-induced repolarization is caused principally through opening K+ATP channels. Blockade of this hyperpolarization by glibenclamide is not sufficient to alter the relaxation, indicating dissociation of nicorandil-induced changes in membrane potential and relaxation. 8. These results highlight the ''chameleon'' actions of nicorandil where there is no apparent association of Em repolarization with relaxation, in contrast to the parallel responses for cromakalim.     

In vitro pharmacologic profile of the novel beta-adrenoceptor antagonist and vasodilator, carvedilol

The pharmacologic profile of the novel beta-adrenoceptor antagonist/vasodilator, carvedilol, has been investigated in vitro. Carvedilol produced competitive antagonism of the beta 1-adrenoceptor mediated positive chronotropic response to isoproterenol in guinea pig atria, and the beta 2-adrenoceptor mediated relaxation to isoproterenol in carbachol (1 mumol/l) precontracted guinea pig trachea, with a dissociation constant (KB) for beta 1-adrenoceptors of 0.8 nmol/l and beta 2-adrenoceptors of 1.3 nmol/l. At slightly higher concentrations, carvedilol produced competitive inhibition of the alpha 1-adrenoceptor mediated contractile response to norepinephrine in rabbit aorta with a KB of 11 nmol/l. Carvedilol had no significant effect on the contractile response to angiotensin II in rabbit aorta at concentrations up to 10 mumol/l, thus demonstrating the lack of nonspecific vasodilator actions in arteries. In canine saphenous vein, carvedilol produced noncompetitive blockade of alpha 2-adrenoceptor mediated vasoconstriction, indicative of some additional activity. In estrogen-primed rat uterus precontracted by depolarization with KCl (70 mmol/l), carvedilol produced concentration-dependent relaxation (IC50 of 7.6 mumol/l), consistent with the notion that carvedilol may be a calcium channel antagonist. Support for this hypothesis was obtained in KCl (70 mmol/l) depolarized rabbit aorta where carvediol (10 mumol/l) produced a 10-fold parallel rightward shift in the concentration-response curve to calcium chloride. These studies demonstrate that carvedilol is a potent beta 1-, beta 2- and alpha 1-adrenoceptor antagonist, and a moderately potent calcium channel antagonist. These multiple activities of carvedilol may contribute to the antihypertensive activity of the compound.     

Evidence for mediation by endothelium-derived hyperpolarizing factor of relaxation to bradykinin in the bovine isolated coronary artery independently of voltage-operated Ca2+ channels.

1. The role of endothelium-derived hyperpolarizing factor and voltage-operated Ca2+ channels in mediating endothelium-dependent, NG-nitro-L-arginine (L-NOARG; 100 microM) -resistant relaxations to bradykinin (BK), was examined in isolated rings of endothelium-intact bovine left anterior descending coronary artery. 2. Rings of artery were contracted isometrically to approximately 40% or their respective maximum contraction to 125 mM KCl Krebs solution (KPSSmax) with the thromboxane A2-mimetic, U46619. Relaxations to BK and the endothelium-independent NO donor, S-nitroso-N-acetylpenicillamine (SNAP), were normalized as percentages of reversal of the initial contraction to U46619. All experiments were carried out in the presence of indomethacin (3 microM). 3. BK caused concentration-dependent relaxations [sensitivity (pEC50) 9.88 +/- 0.05; maximum relaxation (Rmax), 103.3 +/- 0.5%] in U46619-contracted rings of bovine coronary artery. L-NOARG (100 microM) caused a significant (P < 0.01) 3 fold reduction in the sensitivity to BK (pEC50, 9.27 +/- 0.11) without affecting the Rmax (101.8 +/- 2.3%). A similar, significant 3 fold reduction in sensitivity to BK with no change in Rmax was observed after treatment with oxyhaemoglobin (20 microM; pEC50, 9.18 +/- 0.13, P < 0.001) or a combination of oxyhaemoglobin (20 microM) and L-NOARG (100 microM; pEC50, 9.08 +/- 0.10, P < 0.001). Oxyhaemoglobin (20 microM) either alone or in combination with L-NOARG (100 microM) caused an approximate 600 fold decrease in the sensitivity to SNAP. 4. The L-type voltage-operated Ca2+ channel inhibitor, nifedipine (0.3 microM-3 microM), reduced the maximum contraction (Fmax) to isotonic 68 mM KCl Krebs solution (103.5 +/- 2.0% KPSSmax) by 85-90% (P < 0.001); yet, the highest concentration of nifedipine (3 microM) caused only a small but significant reduction in both the sensitivity and Fmax to U46619. By contrast, nifedipine (3 microM) had no effect on the relaxation response to BK. Furthermore, a combination of nifedipine (3 microM) and L-NOARG (100 microM) had no further inhibitory effects on relaxations to BK (pEC50, 8.79 +/- 0.10; Rmax, 101.7 +/- 2.4%) than did L-NOARG (100 microM) alone (pEC50, 9.05 +/- 0.12; Rmax, 99.62 +/- 1.19). Also, nifedipine (0.3 microM and 3 microM) had no effect on the maximum relaxation to the K+ channel opener, levcromakalim (0.3 microM). 5. In the presence of nifedipine (0.3 microM to control contractions induced by high KCl) and isotonic 68 mM KCl Krebs solution (to inhibit K+ channel activity), relaxations to BK (pEC50, 9.42 +/- 0.10; Rmax, 93.9 +/- 1.8%) were similar to those observed in normal Krebs solution (pEC50, 9.58 +/- 0.09; Rmax, 98.4 +/- 0.8%). However, in the presence of 68 mM KCl Krebs solution the inhibitory effect of L-NOARG (100 microM) on relaxations to BK (pEC50, 8.53 +/- 0.20; Rmax, 31.0 +/- 11.3%) was markedly greater than that in normal KCl Krebs solution (pEC50, 9.12 +/- 0.08; Rmax, 91.5 +/- 2.0%). Similar treatment with 68 mM KCl Krebs had no effect on relaxations to the NO donor, SNAP, yet abolished the response to the K+ channel opener, levcromakalim (0.3 microM). 6. In summary, this study has shown that (1) NO synthesis in response to BK in bovine coronary artery endothelial cells in situ is likely to be abolished by L-NOARG, (2) NO-independent relaxations to BK are markedly attenuated by 68 mM KCl-containing Krebs, which, in the absence of L-NOARG, had no effect, (3) nifedipine blocked contractions to a maximum-depolarizing stimulus (KCl) yet had no effect on NO-independent relaxations to BK, and (4) maximum relaxations to levcromakalim were abolished by 68 mM KCl Krebs but were not affected by nifedipine. Therefore, we hypothesize that if smooth muscle hyperpolarization is involved in non-NO-, endothelium-dependent relaxation in bovine coronary arteries contracted with U46619, then it can accomplish this via a mechanism which does not i     

KATP通道开放剂JTV-506对大鼠心肌梗死范围的影响

目的　探讨ATP敏感性钾通道开放剂JTV-506(JTV)对离体大鼠心功能及心肌梗死范围的影响。方法 用Langerdorff装置，观察JTV对冠脉灌流量及左心室压力的影响。应用离体大鼠双冠脉分别灌流模型，观察药物对心肌梗死面积的影响。结果　JTV在1 μmol.L^-1时明显增加冠脉灌流量，当达10 μmol.L^-1时左室收缩压明显下降，在缺血前加缺血中或缺血时单独应用JTV均可缩小心肌梗死范围，此作用可被格列本脲阻断。结论　JTV有明显扩冠作用，大剂量可降低心脏收缩功能，用不影响心功能的剂量可减小心梗范围，此作用与K_ATP通道开放有关。     

Differential antagonism by glibenclamide of the relaxant effects of cromakalim,pinacidil and nicorandil on canine large coronary arteries

Summary The relaxant mechanisms of action of cromakalim, pinacidil and nicorandil, potassium channel openers, on large epicardial coronary arteries were investigated in isolated canine left circumflex arteries contracted by 10^–7 mol/l U46619, a thromboxane A₂ analogue, or addition of 25 mmol/l KCl in comparison with nitroglycerin.Cromakalim (3 × 10^–8–3 × 10^–5 mol/l), pinacidil (10^–6–10^–4 mol/l), nicorandil (3 × 10^–6–10^–3 mol/l) and nitroglycerin (3 × 10^–8–10^–5 mol/l) all produced a concentration-dependent relaxation in both U46619- or KCl-contracted arteries. At their maximum effects pinacidil, nicorandil and nitroglycerin produced full relaxation in arteries contracted by either means. In contrast, cromakalim produced about a 73% relaxation in KCl-contracted arteries, although it caused full relaxation in U46619-contracted ones. In the presence of glibenclamide the concentration-relaxation curves for cromakalim in U46619- or KCl-contracted arteries underwent rightward parallel shifts. Schild regression had a slope of 1.00 and yielded a pA₂ of 7.47 for glibenclamide in U46619-contracted arteries, and corresponding values obtained in KCl-contracted arteries were 0.86 (not significantly different from unity) and 7.28. The concentration-relaxation curves for pinacidil in U46619-contracted arteries also underwent rightward parallel shifts in the presence of glibenclamide, however, Schild regression had a slope of 0.60. The concentration-relaxation curves for pinacidil in KCl-contracted arteries underwent rightward parallel shifts only to a limited extent in the presence of glibenclamide. The concentration-relaxation curves for nicorandil and nitroglycerin in U46619- or KCl-contracted arteries were not affected by glibenclamide in concentrations which antagonized cromakalim. The concentration-relaxation curves for nicorandil or nitroglycerin in U46619-contracted arteries were shifted by methylene blue (10^–5 mol/l) to the right without suppression of the their maximum effects. Similar curves for cromakalim were not affected at all by this concentration of methylene blue. The concentration-relaxation curves for nicorandil in U46619-contracted arteries determined in the presence of methylene blue (10^–5 mol/l) and glibenclamide (3 × 10^–7, 10^–6 and 3 × 10^–6 mol/l) were not significantly different from those in the presence of methylene blue alone.These results indicate the following: In canine large epicardial coronary arteries (1) cromakalim produced relaxation by the mechanism antagonized by glibenclamide, probably opening ATP-sensitive potassium channels, (2) pinacidil did so by the mechanism shared with cromakalim and by one not antagonized by glibenclamide as well, and (3) nicorandil did so exclusively by the mechanism of action as a nitrate. Send offprint requests to N. Taira at the above address     

新钾通道开放剂BPDZ 79对离体主动脉的扩血管作用

AIM: To compare the effect of a novel potassium channel opener 3-(1',2',2'-trimethylpropyl)amine-4H-pyrido (2,3-e)-1,2,4-thiadiazine, 1-dioxide (BPDZ 79), with diazoxide on aorta. METHODS: Muscle tension of rat aorta was compared with adjacent aortic rings without endothelium. One ring was precontracted with KCl 80 mmol.L-1. Three rings were precontracted with KCl 80 mmol.L-1, and two of them were incubated with glibenclamide (0, 1, and 10 mumol.L-1). 86Rb outflow from rat aorta was measured in the presence of glibenclamide 10 mumol.L-1. RESULTS: BPDZ 79 and diazoxide provoked concentration-dependent and endothelium-independent relaxation of the vasoconstriction evoked by KCl 30 mmol.L-1, but not by 80 mmol.L-1. BPDZ 79 showed more potent vasorelaxation and 86Rb outflow than diazoxide. After incubation with glibenclamide (1 and 10 mumol.L-1), an inhibitor of the ATP-sensitive K+ channels, the relaxation induced by BPDZ 79 and diazoxide were decreased with the same pattern. CONCLUSION: BPDZ 79 is a potent vasodilator by opening potassium channels.     

Effects of the potassium channel openers KRN4884 and levcromakalim on the contraction of rat aorta induced by A23187, compared with nifedipine

We examined the different vasodilatory effects of the K⁺ channel openers levcromakalim and 5-amino-N2-[2-(2-chlorophenyl)ethyl]-N-cyano-3-pyridinecarboxamidine (KRN4884), and the Ca²⁺ channel blocker nifedipine in the rat aorta. KRN4884 (10^–10-10^–5 M) and nifedipine (10^–10–10^–5 M) produced concentration-dependent relaxation in the rat aorta precontracted by 25 mM KCl. The K⁺ channel blocker glibenclamide (1 M) inhibited the relaxation induced by KRN4884 but did not influence nifedipine-induced relaxation. KRN 4884 had almost no effect on contraction induced by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl. These results indicate that KRN4884 is a K+ channel opener. We investigated the relaxant effects of KRN4884 (10^–10-10^–5 M), levcromakalim (10^–9-10^–5 M) and nifedipine (10^–9-10^–5 M) on A23187 (1 M)-induced contraction. KRN4884 and levcromakalim had a potent relaxant effect but nifedipine only a weak effect on the smooth muscle contracted by A23187. Glibenclamide (1 M) inhibited the relaxation induced by KRN4884 and levcromakalim, but did not influence the nifedipine-induced relaxation. KRN 4884 (1 M) produced a larger relaxation of A23187-induced contraction but had little effect on the increase in intracellular [Ca²⁺] induced by A23187. These results suggest that KRN4884 is a specific K⁺ channel opener and its vasodilating mechanisms involve not only deactivation of Ca²⁺ channels but also a decrease in the Ca²⁺ sensitivity of contractile elements.     

Potassium channel opening properties of a novel compound, NIP-121, cromakalim and nicorandil in rat aorta and portal vein.

A novel compound, NIP-121, cromakalim and nicorandil caused concentration-dependent relaxation of rat aortas precontracted with 30 mM KCl, with pEC50 (M) values of 8.2, 7.1 and 5.5, respectively. At 60 mM KCl, the vasorelaxation induced by NIP-121 or cromakalim was almost abolished whereas that induced by nicorandil remained. In preparations precontracted with prostaglandin F2 alpha(PGF2 alpha) (10(-5) M), glibenclamide (10(-7) M) and phentolamine (3 x 10(-6), 3 x 10(-5) M) antagonized the relaxation induced by NIP-121 and cromakalim but not that induced by nicorandil. Methylene blue (10(-5) M) showed antagonistic effects against the vasorelaxation induced by nicorandil but not that induced by NIP-121. NIP-121 (10(-7), 10(-6) M) and cromakalim (10(-6), 10(-5) M) significantly increased the 86Rb+ efflux rate in rat aorta. The three compounds inhibited the frequency of spontaneous contractions of the rat portal vein (pIC30; NIP-121 = 8.0, cromakalim = 7.1 and nicorandil = 4.9); glibenclamide and phentolamine antagonized the effects of these compounds. In conclusion, NIP-121 is a more potent K+ channel opener than cromakalim in these tissues. Nicorandil apparently behaves as a K+ channel opener in the rat portal vein, but the vasorelaxation may involve some other mechanisms, such as generation of cyclic GMP.     

Analysis of cromakalim-, pinacidil-, and nicorandil-induced relaxation of the 5-hydroxytryptamine precontracted rat isolated basilar artery

Summary The effects of the K⁺ channel activators cromakalim, pinacidil, and nicorandil were investigated in endothelium intact, 5-hydroxytryptamine (5-HT) precontracted rat isolated basilar artery. Cromakalim, pinacidil, and nicorandil produced concentration-dependent relaxation of rat isolated basilar artery precontracted with 5-HT with a rank order of potency of cromakalim > pinacidil > nicorandil. All compounds produced full or nearly full relaxation. The calculated Hill coefficients for cromakalim-, pinacidil-, and nicorandil-induced relaxation of 5-HT-precontracted rat isolated basilar artery were 2.20 ± 0.36, 1.30 ± 0.07, and 1.00 ± 0.01, respectively. Under conditions of increased tone produced by 50 mmol/1 KCl (which inhibits cromakalim-induced relaxation) pinacidil and nicorandil produced marked reversal of spasm, with pinacidil being more potent than nicorandil. In arteries precontracted with 5-HT, preincubation with glibenclamide (0.1–1 mol/1) produced concentration-related inhibition of relaxation with calculated mean pA ₂ values (and slopes of Schild regression) ± SEM of 6.84 ± 0.20 (1.1 ± 0.20) against cromakalim, 6.60 ± 0.14 (0.95 ± 0.23) against nicorandil,and6.57 ± 0.26(1.04 ± 0.18) against pinacidil. For cromakalim, pinacidil, and nicorandil the slopes of Schild regression were not significantly different from unity. Tolbutamide 10 mol/l was without effect against the cromakalim-, pinacidil-, or nicorandil-induced relaxation. Tetraethylammonium (TEA; 1–10 mmol/l) produced noncompetitive inhibition of the cromakalim-induced relaxation, but appeared to produce competitive inhibition of the pinacidil- and nicorandil-induced relaxations. We conclude that cromakalim, pinacidil, and nicorandil produce relaxation of the 5-HT precontracted rat basilar artery by similar mechanisms to those identified in other peripheral vascular and visceral smooth muscle. Furthermore, pinacidil and nicorandil differ from cromakalim in possessing marked spasmolytic activity in 50 mmol/l KCl precontracted arteries. Send offprint requests to M. Wahl at the above address     

The effects of calcium channel antagonists on coronary nitrite outflow in isolated rat heart

The aim of the study was to compare the effects of Ca2+ channel antagonists on coronary endothelial L-arginine/NO system in isolated rat heart. The hearts of male Wistar albino rats (n = 36, age 8 weeks, body mass 180-200 g) were perfused according to Langendorff technique at gradually increased coronary perfusion pressure (CPP) which induced flow-dependent NO release (nitrite outflow). The experiments were performed during control condition or in the presence of different Ca2+ channel antagonists: nifedipine (CAS 21829-25-4, 30 nmol/l), diltiazem (CAS 42399-41-7, 3 mumol/l), verapamil (CAS 52-53-9, 0.4 mumol/l) or amlodipine (CAS 88150-42-9, 100 nmol/l) were administered separately. Also, nifedipine or amlodipine were administered in combination with an inhibitor of nitric oxide synthase (NOS), L-NAME (NG-nitro-L-arginine-methylester, 30 mumol/l). Coronary flow (CF) varied in autoregulatory range from 3.93 +/- 0.25 ml/min/g wt at 50 cmH2O to 4.49 +/- 0.31 ml/min/g wt at 90 cmH2O. In autoregulatory range nitrite outflow varied from 1.80 +/- 0.22 nmol/min/g wt at 50 cmH2O to 2.21 +/- 0.25 nmol/min/g wt at 90 cmH2O and was strictly parallel with the CPP-CF (coronary perfusion pressure/coronary flow) curve. The autoregulatory range of CF was significantly extended (40-100 cmH2O) under the influence of nifedipine. Hemodynamic effects were accompanied by significant changes in nitrite outflow in all groups except for the verapamil group. Nifedipine and diltiazem induced statistically significant increases of nitrite outflow in coronary venous effluent, strictly parallel with the CPP-CF curve, from 58% at 120 cmH2O to 190% at 40 cmH2O and from 74% at 120 cmH2O to 166% at 40 cmH2O, respectively. On the contrary, amlodipine induced significant reduction of nitrite outflow which was stronger at the lower value of CPP (44-46% at 40-80 cmH2O), compared to the higher value of CPP (32-37% at 100-120 cmH2O). When L-NAME was applied in combination with nifedipine or amlodipine, CF was significantly reduced with parallel changes in nitrite outflow. The results show that Ca2+ channel antagonists (verapamil, diltiazem, nifedipine and amlodipine) strongly influence the coronary endothelial L-arginine/NO system in isolated rat heart leading to the difference in nitrite outflow.     

Vasodilator effects of KRN2391, levcromakalim and 3-morpholino-sydnonimin in human pial and omental arteries

The vasodilator action of KRN2391 (10 nM-10 microM), a combined ATP-sensitive potassium channel (KATP) opener and organic nitrate, was investigated in human pial and omental arteries. Previous animal studies have suggested that opening of KATP and activation of guanylate cyclase may contribute to varying extents to the vasodilator action of KRN2391, depending on the origin and size of the vascular preparation. Vasodilator responses were studied in isolated vascular segments (diameter 0.4-0.8 mm) pre-contracted with endothelin-1 in the presence or absence of glibenclamide (inhibitor of KATP), LY83583 (inhibitor of guanylate cyclase), zaprinast (inhibitor of cyclic GMP phosphodiesterase V) and NG-nitro-L-arginine (inhibitor of nitric oxide synthase). KRN2391 induced concentration-dependent vasodilator responses of similar potency in arteries from the two vascular regions. While glibenclamide (1 microM) had no effect in omental arteries, this compound produced a tenfold rightwards shift of the concentration-response curve for KRN2391 in pial arteries without affecting the maximal response (Emax). LY83583 (10 microM), zaprinast (10 microM) and NG-nitro-L-arginine (0.1 mM) all failed to affect the vasodilator responses to KRN2391 significantly in either artery. However, in ring segments of rat aorta LY83583 displaced the concentration-response curve for the nitric oxide donor 3-morpholino-sydnonimin (10 nM-0.1 mM) to the right, while zaprinast produced a leftwards shift. The prototype KATP opener levcromakalim (0.01-10 microM) elicited a larger relaxation in pial (Emax 80+/-6%) than in omental (Emax 47+/-13%) arteries, whereas 3-morpholino-sydnonimin produced a smaller relaxation in pial (Emax 50+/-18%) than in omental (Emax 90+/-4%) arteries. These results suggest that the vasodilator response to KRN2391 is mediated by KATP in human cerebral arteries, but dependent on neither KATP nor guanylate cyclase in human omental arteries. The results with levcromakalim and 3-morpholino-sydnonimin indicate that opening of KATP may be a more effective mechanism of vasodilatation in pial than in omental arteries from man, whereas the reverse appears to be true for guanylate cyclase activation.     

Cardioprotective effects of nicorandil in rabbits anaesthetized with halothane: potentiation of ischaemic preconditioning via KATP channels

1. The roles of ATP-sensitive K+ channels (KATP channels) in ischaemic or pharmacological preconditioning in the rabbit heart remain unclear. Infarct limitation by ischaemic preconditioning was abolished by the KATP channel blocker glibenclamide under ketamine/xylazine anaesthesia, but not under anaesthesia induced by pentobarbital. Infarct limitation by the KATP channel opener pinacidil was detected under ketamine/xylazine anaesthesia, but not under pentobarbital anaesthesia. Thus, these effects appear to be anaesthetic dependent. 2. In the present study, we examined whether nicorandil (a KATP channel opener nitrate) exhibits cardioprotective actions under halothane anaesthesia, another commonly used volatile anaesthetic. Control animals were subjected to 40 min coronary occlusion and 120 min reperfusion. Before 40 min ischaemia, the nicorandil group received nicorandil (100 microg/kg per min, i.v., for 10 min), the 5' preconditioning (PC) group received 5 min ischaemia/20 min reperfusion, the 2.5'PC group received 2.5 min preconditioning ischaemia/20 min reperfusion, the nicorandil +2.5'PC group received both nicorandil and 2.5 min ischaemia/20 min reperfusion, the nicorandil +2.5'PC + 5-hydroxydecanoate (5HD) group received both nicorandil and 2.5 min ischaemia/20 min reperfusion in the presence of 5-hydroxydecanoate (5HD; a KATP blocker) and the 5HD group received 5 mg/kg, i.v., 5HD alone. Myocardial infarct size in control (n = 7), nicorandil (n = 5), 5'PC (n = 8), 2.5'PC (n = 5), nicorandil + 2.5'PC (n = 5), nicorandil + 2.5'PC + 5HD (n = 5) and 5HD (n = 4) groups averaged 44.4 +/- 3.6, 41.7 +/- 5.7, 17.8 +/- 3.2,* 34.1 +/- 4.8, 21.3 +/- 4.2,* 39.1 +/- 5.6 and 38.9 +/- 5.0% of the area at risk, respectively (*P <0.05 vs control). 3. Thus, nicorandil alone did not have an infarct size-limiting effect in halothane-anaesthetized rabbits. However, the results suggest that even when nicorandil alone does not demonstrate a direct cardioprotective effect, it may enhance ischaemic preconditioning via KATP channels. Key words: ATP-sensitive K+ (KATP) channel, ischaemic preconditioning, myocardial infarction, nicorandil, rabbit.     

Depolarization of membrane potential and the smooth muscle contraction by isothiocyanatobenzyl imidazoline in guinea-pig stomach circular muscle

Isothiocyanatobenzyl imidazoline (IBI) produces characteristic slowly developing contraction of many smooth muscle preparations including the circular smooth muscle of the guinea-pig stomach. Changes in the membrane potential were recorded intracellularly, and the muscle contraction induced by IBI was investigated. IBI at 100 micromol/l slowly produced a sustained depolarization of the membrane with a maximum change of approximately 15 mV. This depolarization could not be blocked by 1-hyoscyamine, 100 nmol/l. An imidazoline analogue, oxymetazoline at 1 micromol/l, did not change the resting membrane potential as observed after IBI. Significant membrane depolarization after IBI still occurred in Ca2+-free medium. During IBI-induced depolarization, sudden reduction of Na+ to 30 mmol/l in the medium reduced the depolarization slightly. IBI-induced depolarization was additive with that produced by 20 mmol/l K+ in the medium. In the presence of tetraethylammonium chloride or levcromakalim or nifedipine, IBI continued to depolarize the membrane although functional pharmacological experiments showed that the contractile effects of IBI were significantly inhibited by 30 micromol/l levcromakalim and abolished by 100 nmol/l nifedipine. At 100 micromol/l phentolamine (reported by others as an inhibitor of ATP-sensitive potassium channels) completely blocked IBI-induced contraction. Phentolamine (30 micromol/l) blocked the contractile effects of IBI by 50%. On the other hand, S(-)-Bay K 8644, a voltage-dependent calcium channel activator, was additive with the contractile response of IBI. These results indicated that IBI produced membrane depolarization and contraction of the guinea-pig stomach circular muscle, by a mechanism not involving muscarinic receptors or alpha-adrenoceptors. Even though levcromakalim, an ATP-sensitive potassium channel opener, could not inhibit IBI-induced depolarization, the ATP-sensitive potassium channel and the voltage-dependent calcium channel may be intrinsically linked with the action of IBI.     

Comparison of the effects of KRN2391 and other coronary dilators on porcine isolated coronary arteries of different sizes

Abstract— The present study was performed to determine whether KRN2391 (N-cyano-N′-(2-nitroxyethyl)-3-pyridinecarboximidamide monomethanesulphonate), a novel vasodilator, shows different effects on porcine isolated coronary arteries of different sizes. The vasodilating effects of KRN2391 on porcine large (2·5–3·0 mm outer diam.) and small (0·8–1·0 mm) coronary arteries were also compared with those of cromakalim, nicorandil, nifedipine, nitroglycerin and adenosine. The relaxant effects of these drugs were examined in coronary arteries contracted by 25 Mm KCl. Nitroglycerin caused greater relaxation in large vessels than in small vessels. In contrast, adenosine, nifedipine and cromakalim caused greater relaxation in small vessels. However, there was no difference between large and small vessels in the relaxing effects of KRN2391 and nicorandil. These unique features of KRN2391 and nicorandil appear to be beneficial in ischaemic heart disease.     

Relaxant effect of levcromakalim in isolated human small subcutaneous arteries

The effect of levcromakalim, an ATP-sensitive K⁺ channel opener, on isolated subcutaneous arteries from mammary tissues obtained from female patients undergoing reconstructive breast surgery was investigated. The small arteries were preserved in the University of Wisconsin (UW) solution. The contractile responses to K⁺ and 9,11-dideoxy-11,9-epoxy-methano-prostaglandin F₂ (U46619) and the relaxant responses to levcromakalim and to the endothelium-dependent vasodilator, methacholine, in these arteries remained fully intact after preservation in UW solution for at least 5 days. The pD₂ value and maximal relaxation obtained from the concentration-response curve of levcromakalim (n = 7) were 5.78 ± 0.23 and 81 ± 6%, respectively. The vasodilator effect of levcromakalim was significantly antagonised by the ATP-sensitive K⁺ channel blocker, glibenclamide (1 and 3 μM). In conclusion, isolated human arteries contain ATP-sensitive K⁺ channels, which can be modulated by K⁺ channel openers and blockers. Subcutaneous small arteries, as used in our experiments, appear to be very suitable for pharmacological experiments.     

Vasorelaxant mechanism of KRN2391 and nicorandil in porcine coronary arteries of different sizes.

1. The relaxant mechanisms of action of KRN2391, a novel vasodilator, and nicorandil on epimyocardial coronary artery (2.5- 3.0 mm outer diameter) and mid-myocardial coronary artery (0.8-1.0 mm outer diameter) were investigated in porcine isolated coronary arteries. In addition, the vasorelaxant responses of KRN2391 and nicorandil were compared with those of nitroglycerin and cromakalim, a K+ channel opener, in epi- and mid-myocardial coronary arteries. 2. Nitroglycerin showed a more potent relaxant effect on epi-myocardial coronary arteries than on mid-myocardial coronary arteries, whereas cromakalim produced greater relaxation responses in mid-myocardial coronary arteries. There was no difference between epi- and mid-myocardial coronary arteries in terms of the relaxant effect of KRN2391 and nicorandil. 3. Relaxation induced by KRN2391 in epi- and mid-myocardial coronary arteries was inhibited by oxyhaemoglobin, a pharmacological antagonist of nitrovasodilators, and glibenclamide, a pharmacological antagonist of K+ channel opening drugs. However, the inhibitory effect of glibenclamide on KRN2391-induced relaxation was greater in mid-myocardial coronary artery than in epi-myocardial coronary artery. 4. Relaxation induced by nicorandil was inhibited by oxyhaemoglobin alone in epi-myocardial coronary arteries and by both oxyhaemoglobin and glibenclamide in mid-myocardial coronary arteries. 5. In epi- and mid-myocardial coronary arteries, relaxation induced by cromakalim was inhibited by glibenclamide but not by oxyhaemoglobin, whereas relaxation induced by nitroglycerin was inhibited by oxyhaemoglobin but not by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiovascular pharmacological studies on JTV-506, a new potassium channel opener. 1st communication: effects on myocardium and vasculature

The effects of JTV-506 ((-)-(3S,4R)-2,2-bis(methoxymethyl)-4-[(1,6-dihydro-1-methyl-6-oxo-3- pyridazinyl)amino]-3-hydroxychroman-6-carbonitrile hemihydrate, CAS 170148-29-5), a novel coronary vasodilator, on hemodynamics, cardiac function and cardiac oxygen consumption were evaluated in anesthetized dogs. In anesthetized, open-chest dogs, JTV-506 (0.3-10 micrograms/kg i.v.) induced a marked increase in coronary blood flow in a dose dependent manner, while at these doses it had smaller effects on vertebral and mesenteric blood flow and almost no effect on renal blood flow. JTV-506 (1-10 micrograms/kg i.v.) showed a tendency to decrease oxygen consumption of the heart and elevate myocardial oxygen pressure without cardiac suppression. Effects of JTV-506 on hemodynamics and the respiratory system following i.v. administration (0.3-300 micrograms/kg) were investigated in spontaneously breathing anesthetized dogs. The effective dose to induce hemodynamic changes was more than 3 micrograms/kg. JTV-506 did not have a crucial influence on electrocardiogram. JTV-506 caused marked increase in coronary blood flow and myocardial oxygen pressure with slight change in blood pressure. It is concluded that JTV-506 is a potent vasodilator, with particularly pronounced effect on vasculature of the heart. These results suggest that JTV-506 may be useful in the treatment of angina pectoris.     

Effects of nonsteroidal antiestrogens in the in vitro rat uterus.

We have studied the effect of nonsteroidal antiestrogens on rat uterine contractions induced by oxytocin (8 nmol/l), methacholine (10 mumol/l), prostaglandin F2 alpha (1 mumol/l), KCl (60 mmol/l) and CaCl2 (6 mmol/l). In a concentration-dependent way, the antiestrogens tamoxifen, clomiphene, nafoxidine and ethamoxytriphetol inhibited the amplitude and frequency of the oxytocin-induced contractions and the contraction produced by CaCl2. At a concentration of 30 mumol/l the four drugs inhibited the contractions induced by methacholine and prostaglandin F2 alpha. They also relaxed the tonic contraction to KCl in a concentration-dependent way. This action was partially counteracted by CaCl2 (0.1-10 mmol/l). Bay k 8644 (0.3 nmol/l to 3 mumol/l) only partially reversed the inhibition by ethamoxytriphetol (0.1 mmol/l) of CaCl2 (6 mmol/l)-induced contractions. The steroidal antiestrogen, ICI 164,384, which lacks agonist activity, had an inhibitory effect (44 +/- 4%, n = 7) on KCl-induced contractions only at a concentration of 0.1 mmol/l. However, the quaternary analogue of tamoxifen (tamoxifen ethyl bromide) produced 86 +/- 3% relaxation of the KCl-induced contracture (IC50 1.52 +/- 0.1 mumol/l, n = 10) and this effect was counteracted by addition of CaCl2. Taken together the results indicate that the inhibitory effects of nonsteroidal antiestrogens on rat uterine contractions could be mediated by an action to block Ca2+ entry through an agonist action on extracellular estrogen receptors.     

Nicorandil prevents epinephrine-induced arrhythmias in halothane-anesthetized rats by nitric oxide-dependent mechanism

The effect of opening ATP-sensitive K(+) channels on the genesis of arrhythmias is still controversial. We investigated the effect of nicorandil, an ATP-sensitive K(+) channel opener, on the genesis of halothane-epinephrine arrhythmias in rats. We also clarified the involvement of nitric oxide in the effect of nicorandil. Furthermore, we studied the effect of levcromakalim, another ATP-sensitive K(+) channel opener, for comparison. Nicorandil and levcromakalim significantly increased the arrhythmogenic thresholds of epinephrine in a dose-dependent manner. On the other hand, nitroprusside, a potent vasodilator (5.0 micro g/kg per min), did not exert antiarrhythmic action significantly. Both glibenclamide (non-specific ATP-sensitive K(+) channel blocker) and 5-hydroxydecanoate (mitochondrial ATP-sensitive K(+) channel blocker) inhibited the antiarrhythmic action of nicorandil. Although pretreatment with N-omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, did not modulate the genesis of halothane-epinephrine arrhythmias in the absence of nicorandil, it completely abolished the antiarrhythmic action of nicorandil, but not the effect of levcromakalim. We concluded that nicorandil dose-dependently inhibited halothane-epinephrine arrhythmias through mitochondrial ATP-sensitive K(+) channels and nitric oxide is required for the antiarrhythmic effect of nicorandil.