Mechanisms of cGMP-induced cerebral vasodilatation: contractile agonist and developmental age make a difference (original) (raw)
Related papers
General Pharmacology: The Vascular System, 2000
The present study explores the hypothesis that age-related variations in cerebrovascular responses to vasodilators reflect corresponding age-dependent differences in the mechanisms coupling changes in cytosolic cGMP to vasorelaxation. The experiments focused on cGMP's ability to decrease either [Ca 2 + ] i or myofilament Ca 2 + sensitivity, because both effects can contribute to cGMP-induced vasodilation. Use of the cGMP analog 8-pCPT-cGMP minimized problems associated with limited cell permeation or cGMP hydrolysis. In fetal basilars contracted with 10 mM serotonin, the EC 30 for 8-pCPT-cGMP-induced relaxation was 6 mM. In fura-2 loaded ovine basilars, pretreatment with 6 mM 8-pCPT-cGMP significantly depressed the sensitivity of [Ca 2 + ] i to 5HT, and also myofilament sensitivity to calcium, but only in fetal arteries. In fetal basilar arteries contracted with 120 mM potassium, the EC 30 for 8-pCPT-cGMP-induced relaxation was 25 mM. In fura-2 loaded arteries, pretreatment with 25 mM 8-pCPT-cGMP had no effect on the ability of graded concentrations of potassium to elevate [Ca 2 + ] i but reduced potassium's ability to induce contraction and attenuated myofilament calcium sensitivity; these latter effects were significant only in fetal arteries. In a-toxin permeabilized preparations, 25 mM 8-pCPT-cGMP significantly depressed both basal-and agonist-stimulated myofilament calcium sensitivity, only in fetal but not in adult basilars. Together, these results demonstrate that: (1) sensitivity to cGMP is greater in fetal than adult sheep arteries independent of method of contraction; (2) cGMP can reduce [Ca 2 + ] i but only in agonist-contracted and not in potassium-contracted arteries; (3) and cGMP attenuates myofilament calcium sensitivity regardless of method of contraction. Overall, the data demonstrate that variations in the ability of cGMP to produce vasodilatation reflect age-, artery-, and agonist-dependent differences in the combination of mechanisms mediating responses to cGMP. D 0306-3623/01/$ -see front matter D 2001 Elsevier Science Inc. All rights reserved. PII: S 0 3 0 6 -3 6 2 3 ( 0 1 ) 0 0 1 0 0 -8
Mechanism of cGMP contribution to the vasodilator response to NO in rat middle cerebral arteries
American journal of physiology. Heart and circulatory physiology, 2002
This study examined the mechanism by which cGMP contributes to the vasodilator response to nitric oxide (NO) in rat middle cerebral arteries (MCA). Administration of a NO donor, diethylaminodiazen-1-ium-1,2-dioate (DEA-NONOate), or 8-bromo-cGMP (8-BrcGMP) increased the diameter of serotonin-preconstricted MCA by 79 +/- 3%. The response to DEA-NONOate, but not 8-BrcGMP, was attenuated by iberiotoxin (10(-7) M) or a 80 mM high-K(+) media, suggesting that activation of K(+) channels contributes to the vasodilator response to NO but not 8-BrcGMP. The effects of NO and cGMP on the vasoconstrictor response to Ca(2+) were also studied in MCA that were permeabilized with alpha-toxin and ionomycin. Elevations in bath Ca(2+) from 10(-8) to 10(-5) M decreased the diameter of permeabilized MCA by 76 +/- 5%. DEA-NONOate (10(-6) M) and 8-BrcGMP (10(-4) M) blunted this response by 60%. Inhibition of guanylyl cyclase with 1H-[1,2,4]oxadiazole[4,3-a] quinoxalin-1-one (10(-5) M) blocked the inhibitor...
Development affects in vitro vascular tone and calcium sensitivity in ovine cerebral arteries
The Journal of physiology, 2004
We have shown recently that development from neonatal to adult life affects cerebrovascular tone of mouse cerebral arteries through endothelium-derived vasodilatory mechanisms. The current study tested the hypothesis that development from fetal to adult life affects cerebral artery vascular smooth muscle (VSM) [Ca(2+)](i) sensitivity and tone through a mechanism partially dependent upon endothelium-dependent signalling. In pressurized resistance sized cerebral arteries ( approximately 150 microm) from preterm (95 +/- 2 days gestation (95 d)) and near-term (140 +/- 2 days gestation (140 d)) fetuses, and non-pregnant adults, we measured vascular diameter (microm) and [Ca(2+)](i) (nm) as a function of intravascular pressure. We repeated these studies in the presence of inhibition of nitric oxide synthase (NOS; with l-NAME), cyclo-oxygenase (COX; with indomethacin) and endothelium removal (E-). Cerebrovasculature tone (E+) was greater in arteries from 95 d fetuses and adults compared to...
Hypertension, 2006
Decreases in intrinsic NO cause cerebral vasospasms because of the dysregulation of cGMP formation by NO-mediated pathways. Because 5-cyclopropyl-2-{1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl}pyrimidin-4-ylamine (BAY 41-2272) is a potent soluble guanylyl cyclase (sGC) stimulator in an NO-independent manner, this study aimed to investigate the mechanisms underlying the relaxant effects of BAY 41-2272 in the rat basilar artery. BAY 41-2272 (0.0001 to 1 μmol/L) induced relaxations in a concentration-dependent manner, with pEC 50 values of 8.13±0.03 and 7.63±0.05 in intact and denuded rings, respectively. The sGC inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) markedly displaced the curve for BAY 41-2272 to the right in intact or denuded rings (&10-fold). The NO synthesis inhibitor N G -nitro- l -arginine methyl ester caused a rightward shift in the curve for BAY 41-2272 (4-fold), whereas the phosphodiesterase type 5 inhibitor sildenafil enhanced BAY 41-2272–induce...
American Journal of Physiology-Heart and Circulatory Physiology, 2007
The present study tests the hypothesis that age-related changes in patterns of agonist-induced myofilament Ca2+sensitization involve corresponding differences in the relative contributions of thick- and thin-filament regulation to overall myofilament Ca2+sensitivity. Posterior communicating cerebral arteries from term fetal and nonpregnant adult sheep were used in measurements of cytosolic Ca2+, myosin light chain (MLC) phosphorylation, and contractile tensions induced by varying concentrations of K+or serotonin [5-hydroxytryptamine (5-HT)]. The results were used to assess the relative contributions of the relationships between cytosolic Ca2+and MLC phosphorylation (thick-filament reactivity), along with the relationships between MLC phosphorylation and contractile tension (thin-filament reactivity), to overall myofilament Ca2+sensitivity. For K+-induced contractions, both fetal and adult arteries exhibited similar basal myofilament Ca2+sensitivity. Despite this similarity, thick-fi...
Journal of Applied Physiology, 2005
The present study tests the hypothesis that age-related differences in contractility of cerebral arteries from hypoxic animals involve changes in myofilament Ca2+sensitivity. Basilar arteries from term fetal and nonpregnant adult sheep maintained 110 days at 3,820 m were used in measurements of cytosolic calcium concentration ([Ca2+]i), myosin light chain phosphorylation, and contractile tensions induced by graded concentrations of K+or serotonin (5-HT). Slopes relating [Ca2+]ito tension were similar in fetal (0.83 ± 0.07) and adult (1.02 ± 0.08) arteries for K+contractions but were significantly greater for fetal (3.77 ± 0.64) than adult (2.00 ± 0.13) arteries for 5-HT contractions. For both K+and 5-HT contractions, these relations were left shifted in fetal compared with adult arteries, indicating greater Ca2+sensitivity in fetal arteries. In contrast, slopes relating [Ca2+]iand %myosin phosphorylation for K+contractions were less in fetal (0.37 ± 0.08) than adult (0.81 ± 0.07) ar...
Cephalalgia, 1995
The functional role of the trigeminal system has been addressed in experiments on the cortical surface of alpha-chloralose anaesthetized cats. Application of calcitonin gene-related peptide (CGRP) caused a concentration-dependent increase in arteriolar calibre by 38 & 5% (n = 8) with an IC,, of 2 nM. Cerebral veins did not relax upon CGRP administration (n = 12). Substance P (SP) was less potent but showed dilatation of both arterioles (2 1 k 4%) and veins (16 k 4%). The cerebrovascular trigeminal system was investigated after chronic (1 4 days) surgical lesion of the trigeminal nerve with the concomitant disappearance of perivascular CGRP/SP immunoreactive nerves. The cortical arteriolar responses to subarachnoid microinjections of acidic (pH 6.8) and basic CSF (p H 7.6) as well as noradrenaline M), neuropeptide Y (lo-' M), prostaglandin F,, (M), and autologous blood (5 PI) were examined in anaesthetized cats with lesions of the trigeminal nerve, and were compared with their effects in sham-operated animals. The magnitude of the vasodilator and vasoconstrictor responses to these agents was unaffected by trigeminal lesions. However, duration of the vasoconstriction produced by basic CSF, but not the vasodilatation to acidic CSF, was markedly prolonged by trigeminal lesions (from 0.8 0.1 min to 2.2 k 0.3 min, p < 0.01). Also, the vasoconstrictor responses to noradrenaline, prostaglandin F,,, barium chloride, and autologous blood were significantly prolonged, while the maximum contractile effect to each agent was similar in lesioned as in sham-operated controls. The effects of CGRP, SP, and neurokinin A (NKA) have been examined on isolated cerebral arteries in vitro. Different CGRP analogues induced a strong relaxation with no difference in I , , , (85-96%) or pD, values (8.65-9.12). NKA induced a stronger relaxation than SP (Imax: 33% and 13%, respectively). SP was more potent than NKA (pD,: 8.7 and 7.7, respectively). Capsaicin, a substance which selectively causes the release of stored sensory neuropeptides (CGRP, SP, NKA), caused in vitro relaxation of precontracted arteries. This relaxation was not affected by the neurokinin blocker spantide, but shifted towards higher capsaicin concentrations by the CGRP antagonist CGRP,-,,. Thus, in this preparation CGRP rather than a neurokinin (SP/NKA) is responsible for the capsaicin-induced dilatations. 0 Calcitonin gene-related peptide, cerebral arteries and veins, neurokinin A, substance P, vasomotor reactivity in situ, vasomotor responses in vitro
European Journal of Neuroscience, 1990
In this study we describe the localization of formaldehyde-fixed cGMP-immunoreactivity (cGMP-IR) in rat cerebellar tissue slices incubated in vitro. In the absence of phosphodiesterase inhibition, cGMPimmunofluorescence was of low intensity in tissue slices prepared from immature cerebella. Addition of isobutylmethylxanthine (IBMX) to the incubation medium resulted in the appearance of cGMP-IR in clusters of astrocytes in the internal granular layer. Addition of N-methyl-D-aspartate (NMDA), kainic acid, atrial natriuretic factor (ANF), or sodium nitroprusside (SNP) gave an intense cGMP-IR in Bergmann fibres, Bergmann cell bodies, and astrocytes in the internal granular layer. Astrocytes in the white matter showed cGMP-IR after incubation of the slice in the presence of ANF or nitroprusside, but not after NMDA or kainic acid. In addition, after SNP stimulation of cGMP production, cGMP-IR was found in fibres which were not positive for glial fibrillary acidic protein (GFAP). In the adult cerebellar slice, intense basal cGMPimmunostaining was observed in Bergmann fibres, Bergmann cell bodies, and astrocytes in the granular layer. No cGMP-IR was observed in Purkinje cells. Stimulation of the cGMP-content in the glial structures by NMDA, ANF, or SNP, was suggested by the immunocytochemical results. However, when measured biochemically, only the effect of SNP was statistically significant, and immunocytochemistry showed that SNP clearly stimulated cGMP synthesis in neuronal cell structures. In the cerebellum of the aged rat a reduced cGMP-IR was found compared to the adult, in the same structures which showed cGMP-IR in the adult. Basal cGMP-immunostaining was reduced in the presence of haemoglobin, methylene blue, by inhibiting nitric oxide synthesis with NG-monomethyl-L-arginine (NGMAr), or by depletion of external Ca2+. Also the stimulatory effect of NMDA and of ANF (partly) on the cGMP-IR was inhibited by these compounds. cGMP-IR after stimulation of guanylate cyclase by SNP was reduced by the concomitant presence of haemoglobin or methylene blue, but not by NGMAr, or by omission of Ca2+. Our results point to an important role for cGMP in the functioning of glial tissue in the cerebellum and also suggest a role for nitric oxide as an intercellular mediator in the functioning of glutamate and ANF in the cerebellum.
Pharmacology & Toxicology, 1995
It is considered that cyclic guanosine monophosphate (cGMP) plays a pivotal role in mediating the relaxation of vascular and nonvascular smooth muscles. cGMP steady state levels are regulated by guanylyl cyclase, cGMP phosphodiesterases and its flux from cells. The present study examines the possible relation between cerebrovascular vasodilator agents and generation of cGMP in guinea pig cerebral vessels. Acetylcholine, substance P, nitroglycerine and sodium nitroprusside significantly increased the generation of cGMF! The application of acetylcholine, substance P, nitroglycerine and sodium nitroprusside elicited concentration-dependent relaxation of basilar artery segments.
The Role of L- and T-type Ca2+ Channels in Rat Cerebral Arteries
2013
This thesis work would not have been possible without the help, support and encouragement of many wonderful people. I would like to express my sincere gratitude to my interim supervisor, Dr. Gary Kargacin, whose expertise, and patience, added considerably to my graduate experience. I thank him for always being available when I needed him the most. I am forever grateful to Dr. Meg Kargacin and Dr. Michael Walsh for their invaluable guidance, help in editing my thesis, and encouragement. It is a pleasure to thank those who made this thesis possible, and I owe my deepest gratitude to my supervisory committee members, Dr. Michael Walsh, and Dr. William C. Cole, who have provided me with valuable feedback and insight for my projects, my thesis and their tremendous input and many stimulating discussions, whom without their help, I could not proceed with this journey. All of my appreciation goes to Dr. Andy Braun for his great help and support to make this thesis come together. Special thanks go to Dr. Ray Turner and his technician Mirna Kruskic for their great help and support in teaching me and answering my questions. I would like to extend my warm gratitude to my friend and colleague Dr. Rania Mufti for her great support, advice and guidance. I also would like to thank my past and present colleagues Dr.