Vasodilatation of canine cerebral arteries by nicorandil, pinacidil and lemakalim

The vascular effect of glibenclamide: A systematic review

Objective:

To systematically review the vascular effects of glibenclamide.

Background:

Infusion of adenosine triphosphate (ATP)-sensitive potassium (KATP) channel opener (KCO) levcromakalim dilates cranial arteries and induces headache and migraine attacks. Recent data show that levcromakalim-induced vasodilation is associated with headache. Glibenclamide is a KATP channel blocker that may alter the vascular tone and thus has an impact on headache or migraine prevention.

Methods:

A search through PubMed was undertaken for studies investigating the vascular effects of glibenclamide in vitro as well as in vivo published until July 2019.

Results:

We identified 58 articles; 31 in vitro studies, 24 in vivo studies and 3 studies with both. The main findings were that glibenclamide inhibited levcromakalim-induced and other KCOs-induced vasodilation, while the basal vascular tone remained unchanged.

Conclusion:

Glibenclamide could inhibit vasodilation by KCOs, and further studies are needed to clarify the vascular effect of glibenclamide on human cranial arteries.

Role of KATPChannels in the Regulation of Rat Dura and Pia Artery Diameter

The aim of the present study was to examine the effect of KATPchannel openers pinacidil and levcromakalim on rat dural and pial arteries as well as their inhibition by glibenclamide. We used an in-vivo genuine closed cranial window model and an in-vitro organ bath. Glibenclamide alone reduced the dural but not the pial artery diameter compared with controls. Intravenous pinacidil and levcro-makalim induced dural and pial artery dilation that was significantly attenuated by glibenclamide. In the organ bath pinacidil and levcromakalim induced dural and middle cerebral artery relaxation that was significantly attenuated by glibenclamide. In conclusion, KATPchannel openers induce increasing diameter/relaxation of dural and pial arteries after intravenous infusion in vivo and on isolated arteries in vitro. Furthermore, dural arteries were more sensitive to KATPchannel openers than pial arteries.

Characterization of K(ATP)-channels in rat basilar and middle cerebral arteries: studies of vasomotor responses and mRNA expression

Changes in the activity of K+ channels represent a major mechanism that regulates vascular tone. Cerebrovascular adenosine 5'-triphosphate-sensitive K+(K(ATP)) channels were characterized in studies of the molecular expression and vasomotor reactivity to different K(ATP) channel openers in rat basilar and middle cerebral arteries. Both arteries showed strong mRNA expression of the subunits of the pore-forming inward-rectifying K+ channel type 6.1 (Kir6.1), Kir6.2 and the connected sulfonylurea receptor (SUR) subunits, SUR1 and SUR2B, while only weak bands for SUR2A were seen. The K(ATP) channel openers induced relaxation of prostaglalndin F2alpha-precontracted isolated basilar and middle cerebral arteries with the order of potency N-Cyano-N-(1,1-dimethylpropyl)-N''-3pyridylguanidine (P-1075)>levcromakalim>N-(4-Phenylsulfonylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methylpropanamide (ZM226600)>pinacidil>diazoxide. The responses induced by levcromakalim, ZM226600 and diazoxide were significantly more potent in basilar arteries than in middle cerebral arteries, while pinacidil and P-1075 were equipotent. Endothelium removal decreased (P<0.05) the sensitivity (pIC50) of basilar arteries, but not of middle cerebral arteries, to pinacidil, levcromakalim, P-1075 and ZM226600. The maximum relaxant response to P-1075 was stronger (P<0.005) in basilar arteries with endothelium than without endothelium. Correlation of the relaxant potency of K(ATP) channel openers in rat basilar and middle cerebral arteries with historical measurements of affinity obtained in COS-7 cell lines expressing either SUR1, SUR2A or SUR2B showed that vasodilatation by K(ATP) channel openers correlated with binding to either the SUR2A or the SUR2B subunit. Glibenclamide was a blocker of relaxation induced by pinacidil, levcromakalim, P-1075 and ZM226600 in basilar arteries. Only a weak antagonistic effect of glibenclamide on pinacidil-, levcromakalim- and ZM226600-induced relaxations was found in middle cerebral arteries. The subunit profile and the observed pharmacological properties suggest that the K(ATP) channels expressed in rat basilar and middle cerebral artery are likely to be composed of SUR2B co-associated with Kir6.1 or Kir6.2. In basilar arteries, but not in middle cerebral arteries, endothelial K(ATP) channels may be involved.

Effect of mild hypothermia on nicorandil-induced vasodilation of pial arterioles in cats

OBJECTIVE

Nicorandil is characterized as hybrid between nitrates and potassium channel activators. Recent evidence suggested that mild hypothermia may alter cerebral vasodilation induced by a nitrate agent and potassium channel opener. However, the effect of mild hypothermia on nicorandil-induced vasodilation is not known. The present study was conducted to investigate whether mild hypothermia could alter nicorandil-induced cerebral vasodilation. In addition, the effects of mild hypothermia on cerebral vasodilation induced by nitroglycerin, a nitrate agent, and cromakalim, a selective adenosine 5'-triphosphate-sensitive potassium channel opener, were assessed in the same model.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-four cats.

INTERVENTIONS

Animals were anesthetized with pentobarbital. The cranial window technique, combined with microscopic video recording, was used to measure small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were assigned randomly to either a normothermic (37 degrees C) or a hypothermic (33 degrees C) group. Nicorandil, nitroglycerin, or cromakalim at concentrations of 10(-8), 10(-6), or 10(-4) mol/L was applied topically in the cranial window, and the diameter of pial arterioles was measured.

MEASUREMENTS AND MAIN RESULTS

Topical administration of nicorandil, nitroglycerin, and cromakalim significantly dilated both small and large pial arterioles in a dose-dependent manner during normothermia. Nicorandil-induced vasodilation of either large or small pial arterioles was not affected by hypothermia. However, hypothermia significantly attenuated nitroglycerine-induced vasodilation in both large and small pial arterioles and enhanced cromakalim-induced vasodilation in both large and small pial arterioles.

CONCLUSIONS

Nicorandil-induced vasodilation of cerebral pial arterioles was not affected by mild hypothermia. By contrast, mild hypothermia significantly attenuated nitroglycerin-induced vasodilation and enhanced cromakalim-induced vasodilation.

Maintained vasodilatory response to cromakalim after inhibition of nitric oxide synthesis

Activation of vascular smooth-muscle adenosine triphosphate-sensitive potassium channels (KATP channels) causes membrane hyperpolarization, reduced entry of Ca2+ through L-type voltage-gated Ca2+ channels, and subsequent smooth-muscle relaxation. Conversely, opening of endothelial KATP channels elicits hyperpolarization but may induce Ca2+ influx and stimulation of endothelium-derived nitric oxide (EDNO) because these cells appear not to possess L-type Ca2+ channels. We therefore hypothesized that EDNO contributes to KATP channel-mediated vasodilation. To test this hypothesis, we examined vasodilatory responses to the KATP channel opener cromakalim in conscious rats, perfused rat tail artery segments, and isolated perfused rat lungs in the presence or absence of the EDNO synthesis inhibitor Nomega-nitro-L-arginine (L-NNA). Additionally, we compared the effect of cromakalim with the EDNO-dependent dilator bradykinin on NO production and intracellular Ca2+ in cultured rat pulmonary artery endothelial cells. Vasodilatory profiles to cromakalim were unaffected by L-NNA in conscious rats, tail arteries, and isolated lungs. Consistent with these results, cromakalim had no apparent effect on either NO synthesis or Ca2+ levels in cultured endothelial cells. These data suggest a lack of a role for EDNO in contributing to KATP-channel-mediated vasodilation in the rat.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

Selectivity of BMS-180448 on myocardial versus brain blood flow in dogs and ferrets

Openers of adenosine triphosphate (ATP)-sensitive potassium channels relax vascular smooth muscle and protect ischemic myocardium. Cromakalim and BMS-180448 are examples of this class of compounds. They are equipotent in their cardioprotective activity, but cromakalim and related compounds are extremely hypotensive, an activity that limits their use. The effects of cumulative i.v. doses of BMS-180448 or cromakalim on hemodynamics and regional blood flow (radiolabeled microspheres) were evaluated in pentobarbital-anesthetized dogs and ferrets. Both compounds significantly reduced mean arterial blood pressure, cromakalim after 0.03-0.04 mg/kg in both species, and BMS-180448 only after 10 mg/kg in dogs and 30 mg/kg in ferrets. Neither drug affected cardiac output. BMS-180448, like cromakalim, increased blood flow in the heart, with augmented regional left ventricular blood flow occurring more in the subepicardium than in the subendocardium. The effect of BMS-180448 on myocardial blood flow, in both the dog and ferret, occurred at doses that were less hypotensive than those of cromakalim. The most striking difference between the actions of these agents was seen in the brain where cromakalim, but not BMS-180448, increased blood flow in all regions. The results of these studies further demonstrate the myocardium-specific vasodilator activity of BMS-180448. Moreover, the cerebral vasodilator effect of K(ATP) openers, which has been thought responsible for the occurrence of headache in clinical trials, has been found lacking in BMS-180448; this difference may represent a clear advantage in the pharmacologic profile of the agent.

Modulation by the endothelium of the inhibitory effects of pinacidil and nimodipine on endothelin-induced contraction in cerebral arteries

The effects of pinacidil and nimodipine on endothelin-1-induced contractions in isolated cerebral arteries with and without endothelium were compared. The sensitivity to endothelin-1 was increased (0.5 log units) in the rabbit basilar artery after removal of the endothelium. The nitric oxide synthase inhibitor N omega-nitro-L-arginine (0.1 mM) also increased the sensitivity to endothelin-1 (0.6 log units) in basilar arteries with endothelium, whereas N omega-nitro-D-arginine (0.1 mM) and indomethacin (3 microM) had no effect, indicating that withdrawal of endothelium-derived nitric oxide may account for the enhancement of the endothelin-1-induced contraction after endothelial denudation. Pinacidil (1 microM) shifted the concentration-response curve for endothelin-1 to the right without affecting the maximal response in arteries without endothelium, but had no effect on the endothelin-1-induced contraction in vessels with endothelium. Nimodipine (1 microM) reduced the maximal endothelin-1-induced contraction by approximately 50% in both the presence and absence of endothelium, whereas the sensitivity to endothelin-1 was reduced only in vessels without endothelium. Incubation in "calcium-free" medium reduced the maximal endothelin-1-induced contraction by 69% and 80% in vessels with and without endothelium, respectively. In human pial arteries with endothelium, pinacidil did not affect the endothelin-1-induced contraction, whereas nimodipine and exposure to "calcium-free" solution reduced the maximal response by 31% and 74% respectively. The results show that, in the rabbit, pinacidil and to a lesser extent nimodipine preferentially act on cerebral arteries with disrupted endothelium, indicating that vasoactive factors liberated from the endothelium may modify the effect of a vasodilator.

Potassium channels and the cerebral circulation

1. Hyperpolarization of vascular muscle in response to activation of potassium channels is a major mechanism of vasodilatation. 2. In cerebral blood vessels, two potassium channels have received considerable study recently: ATP-sensitive and calcium-dependent potassium channels. Activation of these potassium channels appears to play a major role in the relaxation of cerebral arteries and arterioles in response to diverse stimuli, including receptor-mediated agonists, intracellular second messengers, reactive oxygen species and hypoxia. 3. The functional influence of ATP-sensitive and calcium-dependent potassium channels may be altered in disease states, including hypertension, diabetes and subarachnoid haemorrhage.

Role of potassium channels in cerebral blood vessels

BACKGROUND

Hyperpolarization of vascular muscle in response to activation of potassium channels is a major mechanism of vasodilatation. In cerebral blood vessels, four different potassium channels have been described: ATP-sensitive potassium channels, calcium-activated potassium channels, delayed rectifier potassium channels, and inward rectifier potassium channels.

SUMMARY OF REVIEW

Activation of ATP-sensitive and calcium activated potassium channels appears to play a major role in relaxation of cerebral arteries and arterioles in response to diverse stimuli, including receptor-mediated agonists, intracellular second messengers, and hypoxia. Both calcium-activated and delayed rectifier potassium channels may contribute to a negative feedback system that regulates tone in large cerebral arteries. The influence of ATP-sensitive and calcium-activated potassium channels is altered in disease states such as hypertension, diabetes, and atherosclerosis.

CONCLUSIONS

Activation of potassium channels is a major mechanism of cerebral vasodilatation. Alteration of activity of potassium channels and impairment of vasodilatation may contribute to the development or maintenance of cerebral ischemia or vasospasm.

Effects of potassium channel activators on isolated cerebral arteries of large and small diameter in the cat

The smooth-muscle relaxant action of adenosine 5'-triphosphate (ATP)-sensitive potassium (KATP) channels in cerebral arteries of large diameter has been confirmed in a number of in vitro studies, but there is still debate about the presence of KATP channels in small cerebral arteries. In the present study, the authors compare the effects of cromakalim and bimakalim, two putative KATP channel activators, in different parts of the feline isolated middle cerebral artery (MCA) designated proximal, intermediate, and distal. The latter corresponds to those small pial arteries that are usually studied in vivo. In ring segments precontracted with 10(-5) M of uridine-5-triphosphate (UTP), both cromakalim and bimakalim induced concentration-related relaxation, with bimakalim being more potent than cromakalim, and no significant differences noted among segments obtained from the different regions of the MCA. In vessels precontracted by adding 30 mM KCl the potency of cromakalim and bimakalim was reduced compared with that obtained after UTP precontraction. In the presence of 10(-6) M glibenclamide, an antagonist of KATP channel activators, the concentration-effect curve to bimakalim was shifted to the right in the proximal and distal MCA, indicating a similar route of action for bimakalim and cromakalim in these arteries. The present study therefore indicates the presence of KATP channels in isolated small cerebral arteries according to results obtained in vivo. Activators of KATP channesl may prove helpful in the treatment of vasospasm, which may occur in large and small cerebral arteries after subarachnoid hemorrhage.

K+ channel openers relax longitudinal muscle of guinea pig ileum

The plexus-free longitudinal muscle was used to investigate the muscle-relaxing effects of the known K+ channel openers, cromakalim, pinacidil and nicorandil, and compared with other known muscle relaxants, calcitonin gene-related peptide (CGRP) and isoprenaline. The three K+ channel openers all decreased basal tension and inhibited the tonic tension evoked by 30 mM KCl, 0.5 microM histamine or 0.1 microM oxotremorine in a dose-dependent manner. The order of potency is cromakalim > pinacidil > nicorandil in KCl or oxotremorine-precontracted muscle strip and nicorandil > cromakalim > pinacidil in histamine-precontracted muscle strip. Inhibition by cromakalim was completely reversed by glibenclamide, a blocker of ATP-sensitive K+ channels, while inhibition by nicorandil or pinacidil was only partially antagonized. The tonic tension evoked by KCl, histamine or oxotremorine was relaxed by CGRP or isoprenaline. Inhibition by neither of these compounds was relieved by glibenclamide. These results suggest that while ATP-sensitive K+ channels may be present in the longitudinal muscle cells, they may not be involved in the actions of CGRP or isoprenaline on the longitudinal muscle.

Cerebral vascular smooth muscle potassium channels and their possible role in the management of vasospasm

One of the promising therapeutic uses of the potassium channel openers is in the management of cerebral vasospasm, a prolonged vasoconstriction of major cerebral arteries which follows aneurysmal subarachnoid haemorrhage. In this review, we first summarize the properties of potassium channels in cerebral vascular smooth muscle. Calcium-activated and ATP-dependent potassium channels are the major potassium channels identified in the cerebrovascular smooth muscle and both are believed to play a role in the regulation of cerebrovascular smooth muscle tone. The calcium-activated potassium channels can be activated by depolarization, by elevation of internal calcium and by some vasodilators. Some neuropeptides and potassium channel openers open the ATP-dependent potassium channels and produce vasodilation. We then review the effects of both synthetic and endogenous potassium channel openers in the cerebrovascular system, discuss their efficacy in the management of models of cerebrovascular spasm, and outline the clinical promise of these agents.

Mechanisms of vasodilation of cerebral vessels induced by the potassium channel opener nicorandil in canine in vivo experiments

BACKGROUND AND PURPOSE

Nicorandil, a potent antianginal agent characterized as a potassium channel opener, could produce cerebrovascular dilation in in vitro studies. Our aim was to investigate the pharmacologic response to the topical application of nicorandil on the vasomotor tone of pial vessels in vivo. To elucidate its mechanism, we also studied the inhibitory action of methylene blue and glibenclamide against nicorandil-induced vasodilation.

METHODS

In 14 dogs prepared with a parietal cranial window, we administered five different concentrations of nicorandil solution (10(-7), 10(-6), 10(-5), 10(-4), and 10(-3) mol/L) under the window and measured pial arterial and venular diameters. After pretreating pial vessels with either 10(-5) mol/L methylene blue or 10(-5) mol/L glibenclamide, we examined inhibitory action after the application of 10(-5) mol/L nicorandil. In additional experiments with 9 dogs, we evaluated the effects of nitroglycerin and cromakalim on pial vessels in the absence or presence of 10(-5) mol/L methylene blue and 10(-5) mol/L glibenclamide, respectively.

RESULTS

Nicorandil produced significant, concentration-dependent dilation of pial vessels (P < .05). Methylene blue blocked nicorandil-induced dilation, whereas glibenclamide only attenuated such action of nicorandil. Nitroglycerin and cromakalim also produced a concentration-dependent increase in pial arteriolar and venular diameters (P < .05), and those effects were blocked in the presence of methylene blue or glibenclamide, respectively.

CONCLUSIONS

Our in vivo study demonstrates that topical application of nicorandil dilates both pial arterioles and venules in a concentration-dependent manner and suggests that the mechanisms of such actions are most likely due to both cyclic GMP-mediated vascular smooth muscle dilation and the regulation of K+ flux.

Effects of nicorandil on human isolated corpus cavernosum and cavernous artery

Nitric oxide (NO) released from nonadrenergic-noncholinergic (NANC) nerves seems to be a principal mediator of the relaxation of penile erectile tissue necessary for erection, and drugs acting by release of NO have been shown to produce erection when injected intracorporeally into impotent patients. By producing hyperpolarization, K+ channel openers are effective in relaxing isolated penile erectile tissue from rabbit and man, and can produce tumescence and erection when injected intracorporeally into animals. Nicorandil is classified as a K+ channel opener, but it also acts as a donor of NO. In the present study, the effects of nicorandil on isolated preparations from human corpus cavernosum (CC) and deep cavernous artery (Acc) were compared with those of cromakalim (K+ channel opener) and SIN-1 (NO donor). Nicorandil produced a concentration-dependent relaxation of CC and Acc preparations. The relaxations obtained at the highest nicorandil concentration used (10(-4) M.) were 75 +/- 3% and 66 +/- 4% in CC preparations contracted by noradrenaline and endothelin-1, respectively. The corresponding effects in Acc preparations were 70 +/- 14% and 73 +/- 5%. Glibenclamide (blocking ATP-dependent K+ channels) significantly reduced the nicorandil-induced relaxation in CC, but not in Acc. Methylene blue (believed to block soluble guanylate cyclase) reduced nicorandil's relaxant effect in CC, although statistical significance was not obtained. NG-nitro-L-arginine 10(-4) M. (NO synthase inhibitor) did not significantly influence the effect of nicorandil on precontracted preparations in either tissue. In CC preparations contracted by electrical field stimulation, nicorandil and cromakalim concentration dependently inhibited the responses. This effect was significantly counteracted by glibenclamide. It is concluded that nicorandil is effective in relaxing human CC chiefly by its K+ channel opening action, and to some extent by its ability to release NO. For nicorandil's relaxing effect on Acc, ATP dependent K+ channels seem to be of limited importance. If effective in impotent patients, the drug may represent a new, interesting approach to the treatment of erectile dysfunction.