CROMAKALIM SUPPRESSES HYPERTONIC SALINE-INDUCED RENAL VASOCONSTRICTION IN ANAESTHETIZED DOGS

1. Intrarenal arterial infusion of hypertonic saline (HS) transiently increased and then gradually reduced renal blood flow (RBF) in anaesthetized dogs. Glomerular filtration rate (GFR) but not filtration fraction decreased at the end of the infusion. 2. In the presence of a potassium channel opener cromakalim (0.3 μg/kg per min), HS infusion failed to reduce RBF; the initial increase in RBF was maintained throughout the infusion. Since cromakalim also prevented the decrease in GFR, HS infusion lowered filtration fraction. 3. The results suggest that cromakalim inhibits both pre-and postglomerular vasoconstriction induced by HS infusion.     

Humoral and cellular effects of the K+-channel activator cromakalim in man

Summary The effect of cromakalim, a K⁺-channel activator, on the plasma renin-angiotensin-aldosterone system, catecholamines and -atrial natriuretic peptide, and on the intraerythrocyte concentration and transmembrane fluxes of Na⁺ and K⁺ has been investigated in 18 normal male subjects, in a double-blind parallel study. After a run-in period on placebo for 1 week, the subjects were treated either with placebo (n=6) or cromakalim (n=12) for 1 week.Plasma renin activity was significantly increased during cromakalim. No effect of cromakalim on plasma angiotensin II, aldosterone, adrenaline, noradrenaline and -atrial natriuretic peptide was demonstrated. The intra-erythrocyte K⁺ concentration was decreased during cromakalim administration and Ca²⁺-dependent K⁺-channels in red blood cells were increased.     

Therapeutic potential of potassium channel openers in peripheral vascular disease and asthma

Potassium channel opener's (KCOs) were originally thought of as nonselective smooth muscle relaxants. However, recent investigations in animal models of both peripheral vascular disease (PVD) and asthma have revealed interesting effects of these drugs at unexpectedly low doses. Hemodynamically, KCOs are interesting in PVD since they have little effect on blood supply to normally perfused skeletal muscle, but enhance perfusion to chronically ligated ischemic tissue. In animal PVD models, SDZ PCO-400 and cromakalim have been shown to improve recovery of muscle energy stores from ischemia or to preserve performance under conditions of ischemic contracture. Beneficial effects in rat PVD models were manifest at doses below those affecting systemic blood pressure and may be attributable to a selective dilatation of collateral vessels. With regard to the airways, the apparent efficacy of KCOs as antiasthmatic drugs seems not to be attributable solely to their bronchodilator activity. Although KCOs elicit no antiinflammatory effect in animal models, studies with SDZ PCO-400 in guinea pigs sensitized to antigen or treated with immune complexes have revealed that expression of airway hyperreactivity is significantly inhibited at drug doses exhibiting only modest bronchodilator activity. At least part of this action can be attributed to inhibition at the level of neural innervation of the airways, possibly through attenuation of nonadrenergic noncholinergic (NANC) transmission. Thus, based on results generated in animal models of asthma and PVD, clinical evaluation of the KCOs in these indications would seem warranted, with the hope that (due to their selective actions) beneficial therapeutic effects can be achieved at doses devoid of unwanted systemic actions.     

Nicorandil as a nitrate,and cromakalim as a potassium channel opener,dilate isolated porcine large coronary arteries in an agonist-nonselective manner

Summary Nicorandil is an antianginal vasodilator having a hybrid property between nitrates and potassium channel openers, and cromakalim is a relatively specific potassium channel opener. We investigated whether or not the vasorelaxant actions of the two drugs would be selective for certain vasoconstrictor agonists (simplyagonists hereafter), and the underlying mechanisms in isolated porcine large coronary arteries. Both nicorandil and cromakalim produced a complete relaxation in the arteries precontracted with seven agonists, i.e., Bay-K-8644, endothelin, histamine, 5-hydroxy-tryptamine (5-HT), phenylephrine, PGF₂, and U 46619. The EC₅₀ values (–log M) of nicorandil and cromakalim were 5.20–5.44 and 6.43–6.87, respectively, toward the seven agonists, indicating that the vasorelaxant actions of the two drugs were agonist nonselective. In the arteries precontracted with Bay-K-8644, endothelin, 5-HT, and U 46619, the vasorelaxant action of cromakalim was antagonized by glibenclamide, an antagonist of potassium channel openers, and Schild analysis of these antagonisms yielded pA₂ values of 7.10–7.41 for glibenclamide. The vasorelaxant actions of nicorandil in the arteries precontracted with the four agonists each were not antagonized by glibenclamide. Instead, the vasorelaxant action of nicorandil was antagonized by methylene blue (10 µM), an inhibitor of guanylate cyclase, and slightly potentiated by M&B 22,948 (10 µM), an inhibitor of cyclic-GMP phosphodiesterase, in the arteries precontracted with U 46619. These results indicate that the vasorelaxant actions of nicorandil and cromakalim in the porcine large coronary artery are agonist nonselective and that nicorandil exerts such an action entirely as a nitrate, whereas cromakalim does so entirely as a potassium channel opener.     

色满卡林对自发性高血压大鼠血管平滑肌细胞凋亡的影响

目的：观察色满卡林对自发性高血压大鼠(SHR)血管平滑肌细胞(VSMCs)凋亡的影响。方法：30只12 wk龄SHR,随机分为高血压组、色满卡林组,另设正常对照组。色满卡林组给予色满卡林0.6 mg·kg~(-1)·d~(-1),分2次灌胃；另2组每日给予等量的生理盐水,共16 wk。监测尾动脉收缩压。用免疫组化法检测Bcl-2,Bax和PCNA蛋白表达。荧光标记TUNEL法检测VSMCs凋亡,计算VSMCs凋亡指数(SMAI)。结果：高血压组与正常对照组比较,收缩压明显增高(P＜0.05)；VSMCs中的Bcl-2,PCNA蛋白表达明显增强(P＜0.05)；SMAI明显减少(P＜0.01)；Bax蛋白表达2组间差异无显著意义(P＞0.05)。与高血压组比较,色满卡林组尾动脉收缩压呈降低趋势,但差别无显著意义(P＞0.05)；VSMCs的Bcl-2和PCNA蛋白的表达减少(P＜0.05),Bcl-2/Bax比值下降；SMAI增加(P＜0.05)。结论：色满卡林促进了SHR的VSMCs凋亡,可能机制是通过调节VSMCs的Bcl-2/Bax蛋白表达平衡。     

Effects of ATP-sensitive K+ channel openers and tolterodine on involuntary bladder contractions in a pig model of partial bladder outlet obstruction

AIMS: To compare in vivo the efficacy, potency, and bladder-vascular selectivity of ATP-sensitive potassium channel openers (KCOs), YM934 and (-)-cromakalim to a muscarinic antagonist, tolterodine in a novel partial outlet obstructed pig model. METHODS: Partially obstructed female Landrace pigs were implanted with telemetry transmitters to allow the continuous measurement of intravesical, abdominal and arterial pressures. A subcutaneous port catheter was used to adjust bladder volume. Bladder and arterial pressure were simultaneously monitored under isoflurane anesthesia before and after increasing i.v. doses of test compounds. RESULTS: Under anesthesia, voiding was completely inhibited, but spontaneous, nonvoiding bladder contractions were observed with mean amplitude of 16 +/- 1 cm H(2)O, duration of 35 +/- 2 seconds, and intercontraction interval of 43 +/- 4 seconds (n = 25). YM934 and (-)-cromakalim both caused dose-dependent decreases in bladder contraction area under the curve (AUC) with effective doses to inhibit AUC by 35% of 3.6 and 14.9 nmol/kg, i.v., respectively. However, concomitant reductions in mean arterial pressure of 12 and 13% were also observed. Tolterodine did not inhibit spontaneous bladder contractions at doses up to 100 nmol/kg, i.v. corresponding to plasma concentrations up to 41 ng/mL. CONCLUSIONS: The superior efficacy of KCOs to inhibit spontaneous bladder contractions relative to tolterodine support the hypothesis that KCOs may provide an alternate therapeutic mechanism to treat symptoms of overactive bladder if bladder-vascular selectivity can be sufficiently improved. The minimally invasive model described herein appears useful in the preclinical evaluation of potential therapeutics targeted to treat the overactive bladder.     

维拉帕米、福司考林和克罗马卡林对高K~ 及去甲肾上腺素预收缩血管舒张作用的比较

目的：比较３个作用机理不同的舒血管药在不同激动剂所致预收缩血管中的作用特点。方法：以高Ｋ＋及去甲肾上腺素预收缩家兔主动脉条，观察维拉帕米、福司考林和克罗马卡林的舒血管特点。结果：维拉帕米对高Ｋ＋收缩的舒张明显大于其对去甲肾上腺素预收缩血管的舒张作用，相反福司考林和克罗马卡林对去甲肾上腺素收缩的舒张远较其对高Ｋ＋收缩的舒张作用为大。克罗马卡林对高Ｋ＋预收缩血管的舒张作用比福司考林微弱得多。结论：维拉帕米、福司考林、克罗马卡林的舒血管效应各有其不同特点。为研究未知扩血管药的作用原理提供参考。     

Beneficial hemodynamic effects of nicorandil in a canine model of acute congestive heart failure: Comparison with nitroglycerin and cromakalim

Summary— Comparative hemodynamic effects of nicorandil (NCR), nitroglycerin (NTG) and cromakalim (CRM) were examined in a canine model of acute congestive heart failure (CHF). CHF was produced by injections of saponin into coronary arteries of anesthetized dogs followed by volume loading and continuous iv infusion of methoxamine. After the treatment, aortic blood flow (AoF), left ventricular d P /d t and myocardial segment shortening (SS) markedly decreased, while the left ventricular end-diastolic pressure (LVEDP), the right atrial pressure (RAP) and the systemic vascular resistance (SVR) increased. NCR ( n = 6), NTG ( n = 6) and CRM ( n = 8), which were administered iv after production of CHF, caused a comparable reduction in LVEDP. NCR and CRM profoundly increased AoF and SS but NTG did only slightly. On the other hand, NTG and NCR but not CRM significantly reduced RAP. Intracoronary NCR ( n = 8) exerted no or similar effects on SS as well as systemic hemodynamic indices to those observed with iv NCR despite distinct coronary vasodilation. These results indicate that NCR may exert beneficial hemodynamic effects in an experimental CHF mainly due to lessening both afterload and preload rather than the coronary vasodilating effect.     

Ca2+ flux through voltage-gated channels with flow cessation in pulmonary microvascular endothelial cells

Objective: To investigate the role of voltage-gated Ca2+ channels in Ca2+ influx with flow cessation in flow-adapted rat pulmonary microvascular endothelial cells. Methods: Cells were evaluated for mRNA and protein levels for major components of the voltage-gated Ca2+ channels. Ca2+ influx with flow cessation and cell membrane potential were measured in real time with fluorescent dyes. Mibefradil and nifedipine were used as inhibitors of Ca2+ channel activity. Results: Voltage-gated Ca2+ channel protein and mRNA for the T-type channel were expressed at a relatively low level in endothelial cells cultured under static conditions and expression was induced significantly during flow adaptation. Flow-adapted but not control cells showed Ca2+ influx during flow cessation that was blocked by mibefradil but not by nifedipine. Ca2+ influx also was blocked by cromakalim, a KATP channel agonist. Cell membrane depolarization with flow cessation was unaffected by mibefradil. Conclusions: Rat pulmonary microvascular endothelial cells express T-type voltage-gated Ca2+ channels that are induced during adaptation to flow and are responsible for Ca2+ influx that occurs as a result of flow cessation-mediated membrane depolarization.