1
|
Bercea CI, Cottrell GS, Tamagnini F, McNeish AJ. Omega-3 polyunsaturated fatty acids and hypertension: a review of vasodilatory mechanisms of docosahexaenoic acid and eicosapentaenoic acid. Br J Pharmacol 2021; 178:860-877. [PMID: 33283269 DOI: 10.1111/bph.15336] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 11/27/2020] [Accepted: 11/29/2020] [Indexed: 02/06/2023] Open
Abstract
Hypertension is often characterised by impaired vasodilation involving dysfunction of multiple vasodilatory mechanisms. ω-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can reduce blood pressure and vasodilation. In the endothelium, DHA and EPA improve function including increased NO bioavailability. However, animal studies show that DHA- and EPA-mediated vasodilation persists after endothelial removal, indicating a role for vascular smooth muscle cells (VSMCs). The vasodilatory effects of ω-3 PUFAs on VSMCs are mediated via opening of large conductance calcium-activated potassium channels (BKCa ), ATP-sensitive potassium channels (KATP ) and possibly members of the Kv 7 family of voltage-activated potassium channels, resulting in hyperpolarisation and relaxation. ω-3 PUFA actions on BKCa and voltage-gated ion channels involve electrostatic interactions that are dependent on the polyunsaturated acyl tail, cis-geometry of these double bonds and negative charge of the carboxyl headgroup. This suggests structural manipulation of ω-3 PUFA could generate novel, targeted, therapeutic leads.
Collapse
Affiliation(s)
- Cristiana-Ioana Bercea
- Reading School of Pharmacy, School of Chemistry, Food and Pharmacy, The University of Reading, Reading, UK
| | - Graeme S Cottrell
- Reading School of Pharmacy, School of Chemistry, Food and Pharmacy, The University of Reading, Reading, UK
| | - Francesco Tamagnini
- Reading School of Pharmacy, School of Chemistry, Food and Pharmacy, The University of Reading, Reading, UK
| | - Alister J McNeish
- Reading School of Pharmacy, School of Chemistry, Food and Pharmacy, The University of Reading, Reading, UK
| |
Collapse
|
2
|
Aekthammarat D, Pannangpetch P, Tangsucharit P. Moringa oleifera leaf extract induces vasorelaxation via endothelium-dependent hyperpolarization and calcium channel blockade in mesenteric arterial beds isolated from L-NAME hypertensive rats. Clin Exp Hypertens 2020; 42:490-501. [PMID: 31965874 DOI: 10.1080/10641963.2020.1714640] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND An aqueous extract of Moringa oleifera leaves (MOE) is known to cause relaxation of mesenteric resistance arteries of rats in which hypertension has been induced by the administration of L-NAME, but the mechanism(s) of action of MOE remains unclear. The purpose of this study was to investigate these mechanisms in mesenteric arterial beds isolated from L-NAME induced hypertensive rats. Methods: An investigation of vascular reactivity was conducted on isolated mesenteric arterial beds by measuring the changes in perfusion pressure using an in vitro system. RESULTS MOE (0.001-3 mg in 0.1 ml injection volume) caused a dose-dependent relaxation in methoxamine (5 µM) pre-contracted arterial beds, which was partially abolished by endothelium removal. The endothelium-dependent component of vasorelaxation was insensitive to both L-NAME (100 µM) and indomethacin (10 µM), while completely inhibited in high KCl (45 mM)-induced contraction. MOE (1 and 3 mg/ml) showed a dose-dependent inhibitory effect on CaCl2-induced contractions of denuded preparations in Ca2+-free medium containing a high KCl (60 mM) or methoxamine (10 µM). In Ca2+-free medium, MOE (3 mg/ml) also inhibited phenylephrine-induced contractions of denuded preparations. Conclusion: These findings suggest that MOE relaxes mesenteric arterial beds of L-NAME hypertensive rats via both endothelium-dependent and endothelium-independent mechanisms. The endothelium-dependent action occurred via endothelium-derived hyperpolarizing factor-mediated hyperpolarization. The endothelium-independent action was related to blocking the entry of extracellular Ca2+ via voltage-operated and receptor-operated Ca2+ channels, and inhibiting mobilization of sarcolemmal Ca2+ via inositol trisphosphate receptor Ca2+ channels. MOE may be potentially useful as a natural vasodilator against hypertension.
Collapse
Affiliation(s)
- Direk Aekthammarat
- Department of Pharmacology, Faculty of Medicine, Khon Kaen University , Khon Kaen, Thailand.,Cardiovascular Research Group, Khon Kaen University , Khon Kaen, Thailand
| | - Patchareewan Pannangpetch
- Department of Pharmacology, Faculty of Medicine, Khon Kaen University , Khon Kaen, Thailand.,Cardiovascular Research Group, Khon Kaen University , Khon Kaen, Thailand
| | - Panot Tangsucharit
- Department of Pharmacology, Faculty of Medicine, Khon Kaen University , Khon Kaen, Thailand.,Cardiovascular Research Group, Khon Kaen University , Khon Kaen, Thailand
| |
Collapse
|
3
|
Zhai R, Xu H, Hu F, Wu J, Kong X, Sun X. Exendin-4, a GLP-1 receptor agonist regulates retinal capillary tone and restores microvascular patency after ischaemia-reperfusion injury. Br J Pharmacol 2020; 177:3389-3402. [PMID: 32232832 PMCID: PMC7348095 DOI: 10.1111/bph.15059] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 03/06/2020] [Accepted: 03/10/2020] [Indexed: 01/02/2023] Open
Abstract
Background and Purpose The aim of this study is to investigate the vasorelaxant effect of exendin‐4, a GLP‐1 receptor agonist on retinal capillaries under normal and ischaemia–reperfusion (I/R) conditions. Experimental Approach Capillary diameters in the whole‐mounted retina were directly observed using infrared differential interference contrast microscopy. A model of retinal I/R was established inraats,using high perfusion pressure in an anterior chamber. To assess the effects of exendin‐4, it was administered through subcutaneous injection, intravitreal injection, or eye drops. The underlying mechanism was explored by immunofluorescence, qPCR, and capillary western blots. Key Results Immunofluorescence staining showed that GLP‐1 receptors were expressed in endothelial cells of retinal capillaries. Exendin‐4 relaxed the capillaries precontracted by noradrenaline, an effect abolished by denuding endothelium with CHAPS and inhibited by GLP‐1 receptor antagonist exendin‐9‐39, endothelial NOS (eNOS) inhibitor l‐NAME, and the guanylate cyclase blocker ODQ but not by a COX inhibitor, indomethacin. Retinal capillaries were constricted in I/R injury, an effect reversed by perfusion of exendin‐4. Expression of PI3K and Akt, phosphorylation level of eNOS and NO production after I/R were lower than that in the normal control group. Administration of exendin‐4 improved the changes. Conclusion and Implications Exendin‐4 can restore injured microvascular patency in I/R. Exendin‐4 may regulate retinal capillaries through the GLP‐1 receptor‐PI3K/Akt‐eNOS/NO‐cGMP pathway. Therefore, exendin‐4 may be an effective treatment for improving tissue perfusion in I/R‐related conditions.
Collapse
Affiliation(s)
- Ruyi Zhai
- Department of Ophthalmology and Visual Science, Eye, Ear, Nose and Throat Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China
| | - Huan Xu
- Department of Ophthalmology and Visual Science, Eye, Ear, Nose and Throat Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China
| | - Fangyuan Hu
- Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China
| | - Jihong Wu
- Department of Ophthalmology and Visual Science, Eye, Ear, Nose and Throat Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China
| | - Xiangmei Kong
- Department of Ophthalmology and Visual Science, Eye, Ear, Nose and Throat Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China
| | - Xinghuai Sun
- Department of Ophthalmology and Visual Science, Eye, Ear, Nose and Throat Hospital, Shanghai Medical College, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai, China.,NHC Key Laboratory of Myopia, Fudan University, Shanghai, China.,Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, China.,State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Fudan University, Shanghai, China
| |
Collapse
|
4
|
Chenopodium ambrosioides induces an endothelium-dependent relaxation of rat isolated aorta. JOURNAL OF INTEGRATIVE MEDICINE-JIM 2019; 17:115-124. [PMID: 30738772 DOI: 10.1016/j.joim.2019.01.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 12/27/2018] [Indexed: 12/30/2022]
Abstract
OBJECTIVE This study aims to evaluate the vasodilatory effect of Chenopodium ambrosioides on the isolated rat aorta, and to explore its mechanism of action. METHODS The vasorelaxant effect and the mode of action of various extracts from the leaves of C. ambrosioides were evaluated on thoracic aortic rings isolated from Wistar rats. In addition, ethyl acetate and methanol fractions were analyzed, using thin-layer chromatography and high-performance liquid chromatography techniques, for their polyphenolic content. RESULTS The various active extracts of C. ambrosioides at four concentrations (10-3, 10-2, 10-1 and 1 mg/mL) relaxed the contraction elicited by phenylephrine, in a concentration-dependent manner. This effect seems to be endothelium-dependent, since the vasodilatory effect was entirely absent in denuded aortic rings. The vasorelaxant effect of the methanol fraction (MF) of C. ambrosioides at 1 mg/mL was also inhibited by atropine and tetraethylammonium. This effect remained unchanged by Nω-nitro-l-arginine methyl ester hydrochloride and glibenclamide. The preliminary phytochemical analysis showed that the leaves of C. ambrosioides are rich in phenolic and flavonoid derivatives. CONCLUSION These results suggest that the MF of C. ambrosioides produces an endothelium-dependent relaxation of the isolated rat aorta, which is thought to be mediated mainly through stimulation of the muscarinic receptors, and probably involving the opening of Ca2+-activated potassium channels.
Collapse
|
5
|
Manicam C, Ginter N, Li H, Xia N, Goloborodko E, Zadeh JK, Musayeva A, Pfeiffer N, Gericke A. Compensatory Vasodilator Mechanisms in the Ophthalmic Artery of Endothelial Nitric Oxide Synthase Gene Knockout Mice. Sci Rep 2017; 7:7111. [PMID: 28769073 PMCID: PMC5541003 DOI: 10.1038/s41598-017-07768-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 06/29/2017] [Indexed: 01/02/2023] Open
Abstract
Nitric oxide (NO) generated by endothelial nitric oxide synthase (eNOS) plays an important role in the maintenance of ocular vascular homeostasis. Therefore, perturbations in vascular NO synthesis have been implicated in the pathogenesis of several ocular diseases. We recently reported that eNOS contributes significantly to vasodilation of the mouse ophthalmic artery. Interestingly, dilatory responses were also retained in eNOS gene-deficient mice (eNOS-/-), indicating inherent endothelial adaptive mechanism(s) that act as back-up systems in chronic absence of eNOS to preserve vasorelaxation. Thus, this study endeavoured to identify the compensatory mechanism(s) in the ophthalmic artery of eNOS-/- mice employing isolated arterial segments and pharmacological inhibitors in vitro. Endothelium removal virtually abolished acetylcholine (ACh)-induced vasodilation, suggesting an obligatory involvement of the endothelium in cholinergic control of vascular tone. However, non-NOS and non-cyclooxygenase components compensate for eNOS deficiency via endothelium-derived hyperpolarizing factors (EDHFs). Notably, arachidonic acid-derived metabolites of the 12-lipoxygenase pathway were key mediators in activating the inwardly rectifying potassium channels to compensate for chronic lack of eNOS. Conclusively, endothelium-dependent cholinergic responses of the ophthalmic artery in the eNOS-/- mice are largely preserved and, this vascular bed has the ability to compensate for the loss of normal vasodilator responses solely via EDHFs.
Collapse
Affiliation(s)
- Caroline Manicam
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany.
| | - Natalja Ginter
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Huige Li
- Institute of Pharmacology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Ning Xia
- Institute of Pharmacology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Evgeny Goloborodko
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Jenia Kouchek Zadeh
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Aytan Musayeva
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Norbert Pfeiffer
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Adrian Gericke
- Department of Ophthalmology, University Medical Centre of the Johannes Gutenberg University Mainz, Mainz, Germany
| |
Collapse
|
6
|
The Gatekeepers in the Mouse Ophthalmic Artery: Endothelium-Dependent Mechanisms of Cholinergic Vasodilation. Sci Rep 2016; 6:20322. [PMID: 26831940 PMCID: PMC4735817 DOI: 10.1038/srep20322] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 01/04/2016] [Indexed: 01/25/2023] Open
Abstract
Cholinergic regulation of arterial luminal diameter involves intricate network of intercellular communication between the endothelial and smooth muscle cells that is highly dependent on the molecular mediators released by the endothelium. Albeit the well-recognized contribution of nitric oxide (NO) towards vasodilation, the identity of compensatory mechanisms that maintain vasomotor tone when NO synthesis is deranged remain largely unknown in the ophthalmic artery. This is the first study to identify the vasodilatory signalling mechanisms of the ophthalmic artery employing wild type mice. Acetylcholine (ACh)-induced vasodilation was only partially attenuated when NO synthesis was inhibited. Intriguingly, the combined blocking of cytochrome P450 oxygenase (CYP450) and lipoxygenase (LOX), as well as CYP450 and gap junctions, abolished vasodilation; demonstrating that the key compensatory mechanisms comprise arachidonic acid metabolites which, work in concert with gap junctions for downstream signal transmission. Furthermore, the voltage-gated potassium ion channel, Kv1.6, was functionally relevant in mediating vasodilation. Its localization was found exclusively in the smooth muscle. In conclusion, ACh-induced vasodilation of mouse ophthalmic artery is mediated in part by NO and predominantly via arachidonic acid metabolites, with active involvement of gap junctions. Particularly, the Kv1.6 channel represents an attractive therapeutic target in ophthalmopathologies when NO synthesis is compromised.
Collapse
|
7
|
Role of nitric oxide synthase isoforms for ophthalmic artery reactivity in mice. Exp Eye Res 2014; 127:1-8. [PMID: 25017185 DOI: 10.1016/j.exer.2014.06.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2014] [Revised: 06/12/2014] [Accepted: 06/19/2014] [Indexed: 11/23/2022]
Abstract
Nitric oxide synthases (NOS) are involved in regulation of ocular vascular tone and blood flow. While endothelial NOS (eNOS) has recently been shown to mediate endothelium-dependent vasodilation in mouse retinal arterioles, the contribution of individual NOS isoforms to vascular responses is unknown in the retrobulbar vasculature. Moreover, it is unknown whether the lack of a single NOS isoform affects neuron survival in the retina. Thus, the goal of the present study was to examine the hypothesis that the lack of individual nitric oxide synthase (NOS) isoforms affects the reactivity of mouse ophthalmic arteries and neuron density in the retinal ganglion cell (RGC) layer. Mice deficient in one of the three NOS isoforms (nNOS-/-, iNOS-/- and eNOS-/-) were compared to respective wild type controls. Intraocular pressure (IOP) was measured in conscious mice using rebound tonometry. To examine the role of each NOS isoform for mediating vascular responses, ophthalmic arteries were studied in vitro using video microscopy. Neuron density in the RGC layer was calculated from retinal wholemounts stained with cresyl blue. IOP was similar in all NOS-deficient genotypes and respective wild type controls. In ophthalmic arteries, phenylephrine, nitroprusside and acetylcholine evoked concentration-dependent responses that did not differ between individual NOS-deficient genotypes and their respective controls. In all genotypes except eNOS-/- mice, vasodilation to acetylcholine was markedly reduced after incubation with L-NAME, a non-isoform-selective inhibitor of NOS. In contrast, pharmacological inhibition of nNOS and iNOS had no effect on acetylcholine-induced vasodilation in any of the mouse genotypes. Neuron density in the RGC layer was similar in all NOS-deficient genotypes and respective controls. Our findings suggest that eNOS contributes to endothelium-dependent dilation of murine ophthalmic arteries. However, the chronic lack of eNOS is functionally compensated by NOS-independent vasodilator mechanisms. The lack of a single NOS isoform does not appear to affect IOP or neuron density in the RGC layer.
Collapse
|
8
|
|
9
|
Riva CE, Schmetterer L. Microcirculation of the Ocular Fundus. Microcirculation 2008. [DOI: 10.1016/b978-0-12-374530-9.00018-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
|
10
|
Stirrat A, Nelli S, Dowell FJ, Martin W. Flow-induced enhancement of vasoconstriction and blockade of endothelium-derived hyperpolarizing factor (EDHF) by ascorbate in the rat mesentery. Br J Pharmacol 2007; 153:1162-8. [PMID: 17922023 DOI: 10.1038/sj.bjp.0707499] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE We previously reported that ascorbate inhibits flow- and agonist-induced, EDHF-mediated vasodilatation in the bovine ciliary circulation. This study examined whether ascorbate had similar actions in the rat mesenteric vasculature. EXPERIMENTAL APPROACH The effects of ascorbate were examined both in rat second order mesenteric arterial rings suspended in a static wire myograph and the rat mesentery perfused at different rates of flow. KEY RESULTS Ascorbate (50 microM) had no effect on U46619-induced tone or acetylcholine-induced, EDHF-mediated vasodilatation in either rings of mesenteric artery or the perfused mesentery at rates of flow below 10 ml min(-1). At higher rates of flow, ascorbate produced two distinct effects in the rat mesentery: a rapid and maintained enhancement of vasoconstrictor tone and a slow (max at 3 h) inhibition of acetylcholine-induced, EDHF-mediated vasodilatation. The enhancement of vasoconstrictor tone appeared to be due to inhibition of flow-induced EDHF-like activity, since it was endothelium-dependent, but could be elicited during blockade of nitric oxide synthase and cyclooxygenase. Despite this, the classical inhibitors of EDHF, apamin and charybdotoxin, failed to affect the ascorbate-induced enhancement of tone, although they inhibited acetylcholine-induced vasodilatation. CONCLUSIONS AND IMPLICATIONS Ascorbate inhibits both flow- and agonist-induced EDHF in the rat mesentery. The strikingly different timecourses of these two effects, together with their differential sensitivity to apamin and charybdotoxin, suggest that the flow- and agonist-induced EDHFs in the rat mesenteric vasculature may either be different entities or operate by different mechanisms.
Collapse
Affiliation(s)
- A Stirrat
- Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, UK
| | | | | | | |
Collapse
|
11
|
Delaey C, Boussery K, Breyne J, Vanheel B, Van de Voorde J. The endothelium-derived hyperpolarising factor (EDHF) in isolated bovine choroidal arteries. Exp Eye Res 2007; 84:1067-73. [PMID: 17418119 DOI: 10.1016/j.exer.2007.02.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 01/17/2007] [Accepted: 02/03/2007] [Indexed: 11/15/2022]
Abstract
The present study reports of an endothelium-dependent and NO- and prostanoid-independent relaxation in isolated choroidal arteries, and evaluates the hypothesis of an endothelium-derived hyperpolarising factor (EDHF) playing a role in the choroidal circulation. Choroidal arteries were isolated from bovine eyes and mounted in a small vessel wire-myograph for isometric tension recording. Concentration-response curves for acetylcholine (0.1nM-10microM) were constructed in isolated choroidal arteries contracted with 10microM norepinephrine. Acetylcholine induced a concentration-dependent relaxation in the choroidal arteries. The presence of the NO-synthase inhibitor L-NA and the cyclo-oxygenase inhibitor indomethacin only had a limited effect on this relaxation. All further experiments were performed in the presence of L-NA and indomethacin, in order to study the NO- and prostanoid-independent part of the acetylcholine-relaxations. Both removal of the vascular endothelium or the presence of an increased K(+) concentration in the organ bath abolished the NO- and prostanoid-independent part of the acetylcholine-relaxations. The presence of TEA, a rather non-specific K(+) channel blocker, significantly reduced the acetylcholine-relaxations. Simultaneous application of apamin (an inhibitor of small-conductance Ca(2+)-activated K(+) channels) and charybdotoxin (an inhibitor of intermediate- and large-conductance Ca(2+)-activated K(+) channels) abolished the acetylcholine-induced relaxation and even resulted in a concentration-dependent contraction. Transmembrane potential recordings in isolated choroidal arteries revealed a clear membrane hyperpolarisation in the vascular smooth muscle cells of isolated choroidal arteries. It was therefore concluded that the acetylcholine-induced relaxation of choroidal arteries in the presence of NO-synthase and cyclo-oxygenase inhibitors is mediated by an endothelium-derived hyperpolarising factor. This EDHF seems to be of more importance than endothelium-derived NO or prostanoids.
Collapse
Affiliation(s)
- Christophe Delaey
- Department of Physiology and Pathophysiology, Ghent University, De Pintelaan 185, Blok B, B-9000 Ghent, Belgium
| | | | | | | | | |
Collapse
|
12
|
Goseki T, Ishikawa H, Nishimoto H, Mashimo K, Uga S, Yoshitomi T, Shimizu K. Pharmacological vascular reactivity in isolated diabetic rabbit ciliary artery. Exp Eye Res 2006; 83:1317-24. [PMID: 16979623 DOI: 10.1016/j.exer.2006.06.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 05/13/2006] [Accepted: 06/04/2006] [Indexed: 10/24/2022]
Abstract
Impairment of the ocular circulation induced by diabetes mellitus has not been fully defined, but is thought to be related to hemodynamic changes in the ocular circulation. The purpose of the present study is to investigate the functional and morphological changes occurring in the ciliary artery wall of rabbits with alloxan-induced diabetes mellitus. A single intravenous bolus injection of alloxan (100 mg/kg) was given to each of 26 10-week-old rabbits and 16 sham-injected control rabbits. Twenty weeks later, control rabbits and diabetic rabbits were sacrificed, and their ciliary arteries were mounted in a myograph system. The responses of these arteries to high K+ solution (K-Krebs solution), phenylephrine and carbachol were investigated using isometric tension recording. L-NAME (NG-nitro-l-arginine methyl ester; 100 microM) and indomethacin (1 microM) were also used to test the mechanism causing the carbachol induced relaxation. The arteries were also examined morphologically. The maximum tensions induced by K-Krebs solution in this tissue were not significantly different: 17.2+/-0.8 mN (n=16) in the control rabbits and 17.6+/-0.8 mN (n=23) in the diabetic rabbits (P=0.36). Phenylephrine caused dose-dependent contraction with EC50 values of 1.3+/-0.4 microM (n=6) in the control and 5.1+/-2.3 microM (n=6) in the diabetic rabbits, but there was no significant difference between the two (P=0.36). Carbachol induced dose-dependent relaxations in segments precontracted with K-Krebs solution. These relaxations were significantly reduced in the diabetic rabbits. The maximum relaxation induced by carbachol was 77.0+/-2.4% (10 microM) and 66.4+/-2.5% (100 microM) in the control and diabetic rabbits, respectively. These values were significantly different (P=0.0076). The IC(50) value for carbachol was 396.3+/-58.4 nM (n=16) in the control, and 443.6+/-141.1 nM (n=23) in the diabetic rabbit (P=0.87). Application of a 100 microM nitric oxide synthase inhibitor, L-NAME, significantly inhibited the amplitude of relaxations evoked by carbachol (P=0.0066). However, these relaxations were not inhibited by pretreatment with 1 microM indomethacin (P=0.60). Histologically, the frequency of invaginations was less in the diabetic arterioles with a flattening of the lamina in the diabetic rabbits than in the controls. The cytoplasm of endothelial cells contained large vacuoles, indicating weak adhesion to the lamina. Some endothelial cells even showed vacuolar degeneration due to breakdown of the cell membranes. However, the smooth muscle cells were well preserved in the diabetic rabbit. These results suggest that the mechanism of impairment of ocular circulation induced by diabetes mellitus is mainly the reduction of NO synthase due to endothelial cell dysfunction. Furthermore, the characteristics of rabbits with alloxan-induced diabetes mellitus probably make them a useful model for investigating ocular complications induced by diabetic mellitus.
Collapse
Affiliation(s)
- Toshiaki Goseki
- Department of Ophthalmology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa, Japan.
| | | | | | | | | | | | | |
Collapse
|
13
|
Stirrat A, Nelli S, McGuckin A, Ho VWM, Wilson WS, Martin W. Ascorbate elevates perfusion pressure in the bovine extraocular long posterior ciliary artery: role of endothelium-derived hyperpolarizing factor (EDHF). Eur J Pharmacol 2006; 534:152-8. [PMID: 16612841 DOI: 10.1016/j.ejphar.2006.01.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Ascorbate blocks agonist-induced, endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine perfused ciliary artery and this is associated with a rise in perfusion pressure. We now report the origins of this ascorbate-induced rise in perfusion pressure. In segments of ciliary artery perfused at 2.5 ml/min, the addition of ascorbate (10-150 microM) enhanced U46619-induced perfusion pressure. Ascorbate produced no enhancement in the absence of U46619, suggesting that its effects resulted not from a constrictor action but through removal of a tonic vasodilator influence. Experiments revealed the endothelial source of this vasodilator influence, and EDHF, but not nitric oxide or prostanoids, appeared to be involved. The ascorbate-induced enhancement of vasoconstrictor tone was not seen in a static myograph or in segments perfused at low rates of flow, but was seen at flow rates of 2.5 ml(-1) and above. We conclude that ascorbate augments vasoconstrictor tone through inhibition of flow-induced EDHF activity.
Collapse
Affiliation(s)
- Alison Stirrat
- Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
| | | | | | | | | | | |
Collapse
|
14
|
Overend J, Wilson WS, Martin W. Biphasic neurogenic vasodilatation in the bovine intraocular long posterior ciliary artery: involvement of nitric oxide and an additional unidentified neurotransmitter. Br J Pharmacol 2006; 145:1001-8. [PMID: 15912133 PMCID: PMC1576216 DOI: 10.1038/sj.bjp.0706264] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We have investigated the neurogenic factors inducing relaxation in the intraocular segment of the bovine long posterior ciliary artery. In precontracted vessels, electrical field stimulation (EFS, 0.5-128 Hz, 10 s trains) in the presence of guanethidine (30 microM) evoked biphasic relaxation: optimal relaxation for the first and second components occurred at 10 and 50 s, respectively. The first component, but not the second, was abolished by L-NAME (100 microM) or ODQ (3 microM). Relaxation to exogenous CGRP (0.1-300 nM) was inhibited by the CGRP antagonist, CGRP(8-37) (1-5 microM), but neither component of neurogenic relaxation was affected. Preincubation with the sensory nerve excitotoxin, capsaicin (1 microM), had no effect on either the first or second components of neurogenic relaxation. Substance P (0.1 nM-0.1 microM) induced relaxation, but rapid and complete desensitisation occurred within minutes. Neither desensitisation to substance P (0.1 microM) nor incubation with the NK(1) antagonist, L-733,060 (0.3 microM), had any effect on the first or second components of neurogenic relaxation.VIP (0.1 nM-0.3 microM) induced relaxation and this was followed by substantial desensitisation. Neither desensitisation to VIP (0.6 microM) nor treatment with the protease, alpha-chymotrypsin (10 U ml(-1)), had any effect on the first or second components of neurogenic relaxation. The results indicate that nitric oxide mediates the first component of neurogenic relaxation in the bovine intraocular ciliary artery. The neurotransmitter mediating the second component remains to be determined but is unlikely to be CGRP, substance P or VIP.
Collapse
Affiliation(s)
- Jill Overend
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, Scotland
| | - William S Wilson
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, Scotland
| | - William Martin
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, Scotland
- Author for correspondence:
| |
Collapse
|
15
|
Shahidullah M, Yap M, To CH. Cyclic GMP, sodium nitroprusside and sodium azide reduce aqueous humour formation in the isolated arterially perfused pig eye. Br J Pharmacol 2005; 145:84-92. [PMID: 15711584 PMCID: PMC1576120 DOI: 10.1038/sj.bjp.0706156] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The effect of nitric oxide (NO) on aqueous humour formation (AHF) and intraocular pressure (IOP) was studied using NO donors, sodium azide (AZ) and sodium nitroprusside (SNP). Using the porcine arterially perfused eye preparation, drug effects on AHF and IOP were measured by fluorescein dilution and manometry, respectively. Perfusion pressure of the ocular vasculature was also monitored using digital pressure transducer and pen recorder. L-Arginine (1.0 mM), a precursor of NO, but not D-arginine (1.0 mM), the inactive analogue, produced a significant reduction in AHF (28.5%) and IOP (21.1%). L-NAME (L-nitro-L-arginine) (10-100 microM), an NO synthase inhibitor, had no effect on AHF and IOP. However, L-NAME (100 microM) completely reversed L-arginine's effect. AZ and SNP reduced the AHF and IOP dose-dependently. AZ at 100 nM, 1 and 10 microM reduced AHF by 26.0, 39.7 and 51.7% and IOP by 10.8, 17.3 and 24.0%, respectively. SNP at 1, 10 and 100 microM reduced the AHF by 6.0, 24.2 and 35.4% and IOP by 3.5, 9.5 and 15.5%, respectively. 8-pCPT-cGMP (8-para-chlorophenyl-thioguanosine-3',5'-cyclic guanosine monophosphate, 10 microM), a cGMP analogue, also reduced the AHF (34.9%) and IOP (15.9%). The effects of AZ and SNP on the AHF and IOP were blocked by a soluble guanylate cyclase inhibitor ODQ (10 microM), whereas ODQ alone or combined with 8-pCPT-cGMP had no effect on the AHF and IOP. None of the drugs had any significant effect on ocular vasculature. The reduction of the AHF and IOP in the arterially perfused pig eye by nitrovasodilators is likely to involve the NO-cGMP pathway.
Collapse
Affiliation(s)
- Mohammad Shahidullah
- The Laboratory of Experimental Optometry, Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
- Author for correspondence:
| | - Maurice Yap
- The Laboratory of Experimental Optometry, Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
| | - Chi-ho To
- The Laboratory of Experimental Optometry, Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
| |
Collapse
|
16
|
Cleary C, Buckley CH, Henry E, McLoughlin P, O'Brien C, Hadoke PWF. Enhanced endothelium derived hyperpolarising factor activity in resistance arteries from normal pressure glaucoma patients: implications for vascular function in the eye. Br J Ophthalmol 2005; 89:223-8. [PMID: 15665357 PMCID: PMC1772531 DOI: 10.1136/bjo.2004.044446] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
BACKGROUND/AIMS Endothelial cell dysfunction in the ocular circulation may contribute to normal pressure glaucoma (NPG). This study aimed to investigate the contributions made by endothelium derived relaxing factors to relaxation of (1) subcutaneous resistance arteries from patients with NPG, and (2) porcine ciliary arteries. METHODS Human gluteal resistance arteries were isolated from seven patients with NPG and matched controls. Human and porcine arteries produced endothelium dependent relaxation when exposed to acetylcholine (ACh) (10(-9)-3 x 10(-5)M) or bradykinin (10(-10)-3 x 10(-6)M). Pharmacological agents were used to inhibit the nitric oxide pathway (l-arginine analogues, soluble guanylate cyclase inhibitor), endothelium derived hyperpolarising factor (EDHF) activity (potassium channel antagonists), and prostaglandin synthesis (cyclo-oxygenase inhibitors). RESULTS In all arteries, endothelium dependent relaxation was attenuated by nitric oxide (NO) inhibition or potassium channel blockade, but not by cyclo-oxygenase inhibition. Inhibition of ACh mediated relaxation by potassium channel antagonists was greater (p<0.05) in patients with NPG (Emax, 55.4% (SD 8.16%) relaxation, n = 4) than controls (Emax, 81.8% (6.0%), n = 5). In contrast, combined inhibition of NO synthase (NOS) and cyclo-oxygenase produced similar inhibition of ACh mediated relaxation in both groups. CONCLUSIONS The enhanced contribution of EDHF to ACh mediated relaxation in systemic resistance arteries from NPG patients may contribute to the maintained endothelium mediated relaxation in these vessels. EDHF also contributes significantly to bradykinin mediated relaxation in porcine ocular ciliary arteries. Therefore, similar changes in the balance of relaxing factors in the ocular circulation could influence the response of the eye to vascular endothelial dysfunction in NPG.
Collapse
Affiliation(s)
- C Cleary
- Department of Ophthalmology, Conway Institute, University College Dublin, Ireland
| | | | | | | | | | | |
Collapse
|
17
|
Kernohan AFB, Spiers A, Sattar N, Hillier C, Cleland SJ, Small M, Lumsden MA, McConnell J, Petrie JR. Effects of low-dose continuous combined HRT on vascular function in women with type 2 diabetes. Diab Vasc Dis Res 2004; 1:82-8. [PMID: 16302646 DOI: 10.3132/dvdr.2004.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Improvement in vascular endothelial function is widley cited as a beneficial effect of hormone replacement therapy (HRT). Women with type 2 diabetes (T2DM) are at increased cardiovascular risk and have impaired endothelial function. Any benefits of HRT on endothelial function in this group are of particular interest. OBJECTIVES We assessed effects on vascular function of oral 17beta oestradiol (1 mg) and norethisterone (0.5 mg) in postmenopausal women with T2DM. DESIGN Double-blind, randomised, placebo-controlled trial. ASSESSMENTS Twenty-eight women had pulse wave velocity (PWV) and adhesion molecules VCAM-1 and ICAM-1 assessed before and after three months' treatment. Twenty-four women also had gluteal fat biopsy for assessment of resistance vessel function (using wire myography). RESULTS HRT did not affect PWV, VCAM-1, ICAM-1 or carbachol response. Effects of L-NAME and indomethacin on carbachol sensitivity were similar in both groups. CONCLUSIONS This HRT preparation had no detectable effect on these measures of endothelial function in women with T2DM.
Collapse
Affiliation(s)
- Andrew F B Kernohan
- Division of Cardiovascular and Medical Sciences, University of Glasgow, 36 Church St, Glasgow, G11 6NT, UK.
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Nelli S, Dowell FJ, Wilson WS, Stirrat A, Martin W. Requirement for flow in the blockade of endothelium-derived hyperpolarizing factor (EDHF) by ascorbate in the bovine ciliary artery. Br J Pharmacol 2004; 142:1081-90. [PMID: 15237098 PMCID: PMC1575176 DOI: 10.1038/sj.bjp.0705816] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We previously reported that ascorbate inhibits endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine perfused ciliary circulation and rat perfused mesentery, but not in rings of bovine or porcine coronary artery. In this study, we have compared the ability of ascorbate to inhibit EDHF-mediated vasodilatation in a single vessel, the bovine long posterior ciliary artery, when perfused and when mounted as rings in a myograph. Both in segments perfused at a flow rate of 2.5 ml min(-1) and in rings mounted in a myograph, bradykinin and acetylcholine each induced vasodilator responses that were mediated jointly by EDHF and nitric oxide, as revealed by their respective blocking agents, apamin/charybdotoxin, and L-NAME. Ascorbate (50 and 150 microm) induced a time (max at 2-3 h)-dependent inhibition of the EDHF-mediated component of vasodilatation to bradykinin or acetylcholine in perfused segments, but not in rings. Ascorbate (50 microm) failed to inhibit bradykinin-induced vasodilatation at a flow rate of 1.25 ml min(-1) or below, but produced graded blockade at the higher flow rates of 2.5 and 5 ml min(-1). Furthermore, using a pressure myograph where pressure and flow were independently controlled, it was confirmed that the inhibitory action of ascorbate (150 microm) was directly related to flow per se and not any associated changes in pressure. Thus, we have shown in the bovine ciliary artery that ascorbate inhibits EDHF-mediated vasodilatation under conditions of flow but not in a static myograph. The mechanism by which flow renders EDHF susceptible to inhibition by ascorbate remains to be determined.
Collapse
Affiliation(s)
- Silvia Nelli
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow, G12 8QQ, Scotland
| | - Fiona J Dowell
- Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow, G61 1QH, Scotland
| | - William S Wilson
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow, G12 8QQ, Scotland
| | - Alison Stirrat
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow, G12 8QQ, Scotland
| | - William Martin
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow, G12 8QQ, Scotland
- Author for correspondence:
| |
Collapse
|
19
|
Crane GJ, Garland CJ. Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery. Br J Pharmacol 2004; 142:43-50. [PMID: 15051624 PMCID: PMC1574933 DOI: 10.1038/sj.bjp.0705756] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The possibility that thromboxane (TXA(2)) receptor stimulation causes differential block of the SK(Ca) and IK(Ca) channels which underlie EDHF-mediated vascular smooth muscle hyperpolarization and relaxation was investigated in the rat isolated mesenteric artery. 2. Acetylcholine (30 nm-3 microm ACh) or cyclopiazonic acid (10 microm CPA, SERCA inhibitor) were used to stimulate EDHF-evoked smooth muscle hyperpolarization. In each case, this led to maximal hyperpolarization of around 20 mV, which was sensitive to block with 50 nm apamin and abolished by repeated stimulation of mesenteric arteries with the thromboxane mimetic, U46619 (30 nm-0.1 microm), but not the alpha(1)-adrenoceptor agonist phenylephrine (PE). 3. The ability of U46619 to abolish EDHF-evoked smooth muscle hyperpolarization was prevented by prior exposure of mesenteric arteries to the TXA(2) receptor antagonist 1 microm SQ29548. 4. Similar-sized smooth muscle hyperpolarization evoked with the SK(Ca) activator 100 microm riluzole was also abolished by prior stimulation with U46619, while direct muscle hyperpolarization in response to either levcromakalim (1 microm, K(ATP) activator) or NS1619 (40 microm, BK(Ca) activator) was unaffected. 5. During smooth muscle contraction and depolarization to either PE or U46619, ACh evoked concentration-dependent hyperpolarization (to -67 mV) and complete relaxation. These responses were well maintained during repeated stimulation with PE, but with U46619 there was a progressive decline, so that during a third exposure to U46619 maximum hyperpolarization only reached -52 mV and relaxation was reduced by 20%. This relaxation could now be blocked with charybdotoxin alone. The latter responses could be mimicked with 300 microm 1-EBIO (IK(Ca) activator), an action not modified by exposure to U46619. 6. An early consequence of TXA(2) receptor stimulation is a reduction in the arterial hyperpolarization and relaxation attributed to EDHF. This effect appears to reflect a loss of SK(Ca) activity.
Collapse
Affiliation(s)
- G J Crane
- Department of Pharmacy & Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY
| | - C J Garland
- Department of Pharmacy & Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY
- Author for correspondence:
| |
Collapse
|
20
|
McNeish AJ, Nelli S, Wilson WS, Dowell FJ, Martin W. Differential effects of ascorbate on endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine ciliary vascular bed and coronary artery. Br J Pharmacol 2003; 138:1172-80. [PMID: 12684274 PMCID: PMC1573753 DOI: 10.1038/sj.bjp.0705143] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The ability of ascorbate to inhibit endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation was compared in the bovine perfused ciliary vascular bed and isolated rings of coronary artery. 2. Acetylcholine-induced, EDHF-mediated vasodilatation of the ciliary circulation was blocked following inclusion of ascorbate (50 micro M, 120 min) in the perfusion fluid. The blockade was highly selective since ascorbate had no effect on the vasodilator actions of the K(ATP) channel opener, levcromakalim, nor on the tonic vasodepressor action of basally released nitric oxide. 3. The possibility that concentration of ascorbate by the ciliary body was a prerequisite for blockade to occur was ruled out, since EDHF was still blocked when the anterior and posterior chambers were continuously flushed with Krebs solution or when both the aqueous and vitreous humour were drained. 4. Ascorbate at 50 micro M failed to affect bradykinin- or acetylcholine-induced, EDHF-mediated vasodilatation in rings of bovine coronary artery. Raising the concentration to 3 mM did produce blockade of EDHF, but this was nonselective, since vasodilator responses to endothelium-derived nitric oxide were also inhibited. 5. Thus, ascorbate (50 micro M) is not a universal blocker of EDHF. Whether its ability to block in the bovine ciliary circulation, but not in the coronary artery, is due to differences in the nature of EDHF at the two sites, differences in vessel size (resistance arterioles versus conduit artery), the presence or absence of flow, or to some other factor remains to be determined.
Collapse
Affiliation(s)
- Alister J McNeish
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, U.K
| | - Silvia Nelli
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, U.K
| | - William S Wilson
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, U.K
| | - Fiona J Dowell
- Institute of Comparative Medicine, University of Glasgow Veterinary School, Bearsden Road, Glasgow, G61 1QH, U.K
| | - William Martin
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, U.K
- Author for correspondence:
| |
Collapse
|
21
|
McNeish AJ, Wilson WS, Martin W. Ascorbate blocks endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine ciliary vascular bed and rat mesentery. Br J Pharmacol 2002; 135:1801-9. [PMID: 11934822 PMCID: PMC1573289 DOI: 10.1038/sj.bjp.0704623] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effects of ascorbate were assessed on vasodilatation mediated by endothelium-derived hyperpolarizing factor (EDHF) in the ciliary vascular bed of the bovine isolated perfused eye and in the rat isolated perfused mesenteric arterial bed. 2. In the bovine eye, EDHF-mediated vasodilator responses induced by acetylcholine or bradykinin were powerfully blocked when ascorbate (50 microM) was included in the perfusion medium for at least 120 min; with acetylcholine a normally-masked muscarinic vasoconstrictor response was also uncovered. 3. The blockade of EDHF-mediated vasodilatation by ascorbate was time-dependent (maximum blockade at 120 min) and concentration-dependent (10 - 150 microM). 4. Ascorbate (50 microM) also blocked acetylcholine-induced, EDHF-mediated vasodilator responses in the rat mesenteric arterial bed in a time-dependent manner (maximum blockade at 180 min). 5. The ability of ascorbate to block EDHF-mediated vasodilatation is likely to result from its reducing properties, since this action was mimicked in the bovine eye by two other reducing agents, namely, N-acetyl-L-cysteine (1 mM) and dithiothreitol (100 microM), but not by the redox-inactive analogue, dehydroascorbate (50 microM). 6. In conclusion, concentrations of ascorbate present in normal plasma block EDHF-mediated vasodilator responses in the bovine eye and rat mesentery. The mechanism and physiological consequences of this blockade remain to be determined.
Collapse
Affiliation(s)
- Alister J McNeish
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ
| | - William S Wilson
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ
| | - William Martin
- Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ
- Author for correspondence:
| |
Collapse
|