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C R Triggle

Publications and source records attributed to C R Triggle.

At least 19 recordsLinked to original sources
PubMed2001

Endothelin receptor blockade improves endothelial function in human internal mammary arteries.

OBJECTIVE: Endothelial dysfunction, specifically endothelium-derived contracting factors have been implicated in the development of arterial conduit vasospasm. The potent vasoconstrictor endothelin-1 (ET-1) has received much attention in this regard. The present study was designed to evaluate the role of ET-1 in the development of endothelial dysfunction in human internal mammary arteries (IMA). To this aim, we examined the effects of specific and non-specific ET-receptor antagonists on endothelial function (assessed using acetylcholine (ACh)-induced vasodilation) in segments of IMA obtained during coronary artery bypass graft (CABG) surgery. METHODS: Vascular segments of IMA were obtained from 51 patients undergoing elective coronary artery bypass graft (CABG) surgery and in vitro endothelium-dependent and -independent responses to ACh and sodium nitroprusside (SNP) were assessed. Isometric dose response curves (DRC) to ACh and SNP were constructed in pre-contracted rings in the presence and absence of bosentan (ET(A/B) receptor antagonist, 3 microM), BQ-123 (ET(A) antagonist, 1 microM) and BQ-788 (ET(B) antagonist, 1 microM) using the isolated organ bath apparatus. Percent maximum relaxation (%E(max)) and sensitivity (pEC(50)) were compared between interventions. RESULTS: ACh caused dose-dependent endothelium-mediated relaxation in IMA (%E(max) 43+/-4, pEC(50) 6. 74+/-0.12). In the presence of bosentan, BQ-123 and BQ-788 ACh-induced relaxation was significantly augmented (%E(max) bosentan 60+/-3, BQ-123 56+/-4, BQ-788 53+/-5 vs. control 43+/-4, P<0.05) without affecting sensitivity. The effects of these antagonists were endothelium-specific since endothelium-independent responses to SNP remained unaltered. Furthermore, the beneficial effects were independently and maximally mediated by ET(A) and ET(B) receptors (%E(max) BQ-123 56+/-4 vs. BQ-788 53+/-5 vs. bosentan 60+/-3, P>0. 05). CONCLUSIONS: These data uncover, for the first time, beneficial effects of ET receptor blockade on endothelial-dependent vasorelaxation in human IMA.

Acetylcholine↗
PubMed2001

Vasorelaxant effects of a nitric oxide-releasing aspirin derivative in normotensive and hypertensive rats.

1. Nonsteroidal anti-inflammatory drugs have been reported to exacerbate hypertension and to interfere with the effectiveness of some anti-hypertensive therapies. In this study, we tested the effects of a gastric-sparing, nitric oxide-releasing derivative of aspirin (NCX-4016) on hypertension in rats. 2. Hypertension was induced by administering L-NAME in the drinking water (400 mg l(-1)). Groups of rats were treated daily with aspirin, NCX-4016 or vehicle. 3. NCX-4016 significantly reduced blood pressure relative to the aspirin-treated group over the 2-week period of treatment. Aspirin and, to a lesser extent, NCX-4016 suppressed whole blood thromboxane synthesis. 4. In anaesthetized rats, acute intravenous administration of NCX-4016 caused a significant fall in mean arterial pressure in hypertensive rats, but was devoid of such effects in normotensive controls. 5. In vitro, NCX-4016 relaxed phenylephrine-pre-contracted aortic rings obtained from both normotensive and hypertensive rats, and significantly reduced their responsiveness to the contractile effects of phenylephrine. 6. These results suggest that NCX-4016 reduces blood pressure in hypertensive rats, not simply through the direct vasodilatory actions of the nitric oxide released by this compound, but also through possible interference with the effects of endogenous pressor agents. These properties, added to its anti-thrombotic effects, suggest that NCX-4016 may be a safer alternative to aspirin for use by hypertensive patients.

Anesthesia↗
PubMed2001

Vascular smooth muscle relaxation mediated by nitric oxide donors: a comparison with acetylcholine, nitric oxide and nitroxyl ion.

1. Vasorelaxant properties of three nitric oxide (NO) donor drugs (glyceryl trinitrate, sodium nitroprusside and spermine NONOate) in mouse aorta (phenylephrine pre-contracted) were compared with those of endothelium-derived NO (generated with acetylcholine), NO free radical (NO*; NO gas solution) and nitroxyl ion (NO(-); from Angeli's salt). 2. The soluble guanylate cyclase inhibitor, ODQ (1H-(1,2,4-)oxadiazolo(4,3-a)-quinoxalin-1-one; 0.3, 1 and 10 microM), concentration-dependently inhibited responses to all agents. 10 microM ODQ abolished responses to acetylcholine and glyceryl trinitrate, almost abolished responses to sodium nitroprusside but produced parallel shifts (to a higher concentration range; no depression in maxima) in the concentration-response curves for NO gas solution, Angeli's salt and spermine NONOate. 3. The NO* scavengers, carboxy-PTIO, (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; 100 microM) and hydroxocobalamin (100 microM), both inhibited responses to NO gas solution and to the three NO donor drugs, but not Angeli's salt. Hydroxocobalamin, but not carboxy-PTIO, also inhibited responses to acetylcholine. 4. The NO(-) inhibitor, L-cysteine (3 mM), inhibited responses to Angeli's salt, acetylcholine and the three NO donor drugs, but not NO gas solution. 5. The data suggest that, in mouse aorta, responses to all three NO donors involve (i) activation of soluble guanylate cyclase, but to differing degrees and (ii) generation of both NO* and NO(-). Glyceryl trinitrate and sodium nitroprusside, which generate NO following tissue bioactivation, have profiles resembling the profile of endothelium-derived NO more than that of exogenous NO. Spermine NONOate, which generates NO spontaneously outside the tissue, was the drug that most closely resembled (but was not identical to) exogenous NO.

Acetylcholine↗
PubMed2001

Augmentation of endothelial function by endothelin antagonism in human saphenous vein conduits.

OBJECT: Cerebral revascularization with saphenous vein (SV) conduits is used in the management of hard-to-treat lesions that require deliberate arterial occlusion and in selected patients with occlusive vascular disease. Endothelial dysfunction is thought to contribute to acute perioperative vasospasm and chronic graft atherosclerosis. In the present study the authors examined the contribution of the potent vasoconstrictor endothelin-1 (ET-1) to endothelial dysfunction in human SVs. METHODS: The effects of an ET(A/B) receptor antagonist (bosentan), an ET(A) receptor antagonist (BQ-123), and an ET(B) receptor antagonist (BQ-788) on in vitro endothelium-dependent and -independent responses were studied in human SVs. Vascular segments were obtained in 34 patients who had undergone revascularization procedures, and isometric dose-response curves (DRCs) were constructed using the isolated tissue bath procedure as follows: 1) cumulative DRCs to norepinephrine; and 2) DRCs to acetylcholine (ACh) and sodium nitroprusside in the absence and presence of bosentan, BQ-123, or BQ-788. Maximal vasodilatory responses and sensitivity were compared between groups. In the presence of bosentan (Experiment 1) and BQ-123 or BQ-788 (Experiment 2), ACh responses were significantly augmented (percent maximum relaxation values: 7+/-2 [control] compared with 17+/-3 [bosentan], p < 0.002 [Experiment 1]; and 12+/-2 [control] compared with 29+/-2 [BQ-123] and 25+/-2 [BQ-788], p < 0.003 and p < 0.002, respectively [Experiment 2]). The sensitivity of SVs to ACh was unaffected by treatment. These beneficial effects were specific for the endothelium. CONCLUSIONS: Blockade of ET receptors significantly improves endothelial function in SVs. Furthermore, these effects appear to be independently and maximally mediated by antagonism of either ET(A) or ET(B) receptors. Interventions aimed at improving endothelial function may serve to counter perioperative vasospasm and impede atherosclerosis in SVs used for revascularization procedures.

Aged↗
PubMed2001

Endothelium-derived relaxing factors: a focus on endothelium-derived hyperpolarizing factor(s).

Endothelium-derived hyperpolarizing factor (EDHF) is defined as the non-nitric oxide (NO) and non-prostacyclin (PGI2) substance that mediates endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells (VSMC). Although both NO and PGI2 have been demonstrated to hyperpolarize VSMC by cGMP- and cAMP-dependent mechanisms, respectively, and in the case of NO by cGMP-independent mechanisms, a considerable body of evidence suggests that an additional cellular mechanism must exist that mediates EDH. Despite intensive investigation, there is no agreement as to the nature of the cellular processes that mediates the non-NO/PGI2 mediated hyperpolarization. Epoxyeicosatrienoic acids (EET), an endogenous anandamide, a small increase in the extracellular concentration of K+, and electronic coupling via myoendothelial cell gap junctions have all been hypothesized as contributors to EDH. An attractive hypothesis is that EDH is mediated via both chemical and electrical transmissions, however, the contribution from chemical mediators versus electrical transmission varies in a tissue- and species-dependent manner, suggesting vessel-specific specialization. If this hypothesis proves to be correct then the potential exists for the development of vessel and organ-selective vasodilators. Because endothelium-dependent vasodilatation is dysfunctional in disease states (i.e., atherosclerosis), selective vasodilators may prove to be important therapeutic agents.

Animals↗
PubMed2001

State-dependent block of rabbit vascular smooth muscle delayed rectifier and Kv1.5 channels by inhibitors of cytochrome P450-dependent enzymes.

The effects of the cytochrome P450 inhibitors clotrimazole, ketoconazole, and 1-aminobenzotriazole (1-ABT) on native delayed rectifier (K(DR)) and cloned Kv1.5 (RPV Kv1.5) K+ channels of rabbit portal vein (RPV) myocytes were determined using whole-cell and single channel patch-clamp analysis. Clotrimazole reduced K(DR) and RPV Kv1.5 whole-cell current with respective Kd values of 1.15 +/- 0.39 and 1.99 +/- 0.6 microM. Clotrimazole acted via an open state blocking mechanism based on the following: 1) the early time course of K(DR) current activation was not affected, but inhibition developed with time during depolarizing steps and increased the rate of decay in current amplitude; 2) the inhibition was voltage-dependent, increasing steeply over the voltage range of K(DR) activation; and 3) mean open time of RPV Kv1.5 channels in inside-out patches was decreased significantly. Ketoconazole reduced K(DR) current amplitude with a Kd value of 38 +/- 3.2 microM. However, ketoconazole acted via a closed (resting) state blocking mechanism: 1) K(DR) amplitude was reduced throughout the duration of depolarizing steps and the rate of decay of current was unaffected, 2) there was no voltage dependence to the block by ketoconazole over the K(DR) activation range, and 3) ketoconazole did not affect mean open time of RPV Kv1.5 channels in inside-out membrane patches. 1-ABT between 0.5 and 3 mM did not affect native K(DR) or RPV Kv1.5 current of rabbit portal vein myocytes. Clotrimazole and ketoconazole, but not 1-ABT, suppress vascular K(DR) channels by direct, state-dependent block mechanisms not involving the modulation of cytochrome P450 enzyme activity.

Algorithms↗
PubMed2000

Selective cyclo-oxygenase-2 inhibition with celecoxib elevates blood pressure and promotes leukocyte adherence.

1. Selective inhibitors of cyclo-oxygenase-2 have been shown to be effective anti-inflammatory drugs with reduced gastrointestinal toxicity relative to conventional nonsteroidal anti-inflammatory drugs (NSAIDs). In the present study, we examined the possibility that selective COX-2 inhibition, by blocking prostacyclin synthesis, would increase blood pressure and cause leukocyte adherence and platelet aggregation. 2. Normal rats and rats with hypertension induced by chronic administration of Nomega-nitro-L-arginine methylester were given celecoxib (10 mg kg(-1)) daily for 3 weeks. Celecoxib significantly elevated of blood pressure in both the normal and hypertensive rats (mean increase of >33 mm Hg after 3 weeks). 3. In normal rats, celecoxib had no effect on serum 6-keto prostaglandin (PG)F(1alpha) levels. Hypertensive rats exhibited a significant increase (82%) in serum 6-keto PGF(1alpha) levels, and this was reduced to the levels of normal rats by treatment with celecoxib. 4. Rats treated with celecoxib exhibited significant increases in weight gain (20%), plasma arginine-vasopressin levels (148%) and plasma urea (69%) relative to vehicle-treated controls. Plasma creatinine levels were unaffected by treatment with celecoxib, while plasma renin levels were significantly decreased (30%) relative to controls. 5. Superfusion of mesenteric venules with celecoxib (3 microM) in vivo resulted in significant increases in leukocyte adherence to the endothelium in both normal and hypertensive rats. 6. These studies suggest that suppression of COX-2 significantly influences vascular and/or renal function, leading to elevated blood pressure and leukocyte adherence.

Animals↗
PubMed2000

Comparison of the pharmacological properties of EDHF-mediated vasorelaxation in guinea-pig cerebral and mesenteric resistance vessels.

In the presence of L-NNA (100 microM), indomethacin (10 microM) and ODQ (10 microM), acetylcholine induced a concentration-dependent vasorelaxation of guinea-pig mesenteric and middle cerebral arteries precontracted with cirazoline or histamine, but not with high K(+), indicating the contribution of an endothelium-derived hyperpolarizing factor (EDHF). In cerebral arteries, charybdotoxin (ChTX; 0.1 microM) completely inhibited the indomethacin, L-NNA and ODQ-insensitive relaxation; iberiotoxin (IbTX, 0.1 microM), 4-aminopyridine (4-AP, 1 mM), or barium (30 microM) significantly reduced the response; in the mesenteric artery, ChTX and IbTX also reduced this relaxation. Glibenclamide (10 microM) had no affect in either the mesenteric or cerebral artery. Neither clotrimazole (1 microM) nor 7-ethoxyresorufin (3 microM) affected EDHF-mediated relaxation in the mesenteric artery, but abolished or attenuated EDHF-mediated relaxations in the cerebral artery. AM404 (30 microM), a selective anandamide transport inhibitor, did not affect the vasorelaxation response to acetylcholine in the cerebral artery, but in the mesenteric artery potentiated the vasorelaxation response to acetylcholine in an IbTX, and apamin-sensitive, but SR 141816A-insensitive manner. Ouabain (100 microM) almost abolished EDHF-mediated relaxation in the mesenteric artery, but enhanced the relaxation in the cerebral artery whereas the addition of K(+) (5 - 20 mM) to precontracted guinea-pig cerebral or mesenteric artery induced further vasoconstriction. These data suggest that in the guinea-pig mesenteric and cerebral arteries different EDHFs mediate acetylcholine-induced relaxation, however, EDHF is unlikely to be mediated by K(+).

4-Aminopyridine↗
PubMed2000

Lack of involvement of endothelin-1 in angiotensin II-induced contraction of the isolated rat tail artery.

1. The contribution of endothelin-1 (ET-1) to angiotensin II (Ang II)-mediated contraction of the isolated rat tail artery was assessed with measurements of tension, and cytosolic calcium ([Ca(2+)](i)). The distribution of the AT(1) receptor was studied with RT - PCR and immunohistochemistry. 2. Ang II induced an endothelium-independent contraction (pEC(50) 7.95+/-0.06 and E(max): 0.46 g+/-0.05 with endothelium vs 7.81+/-0.02 and 0.41 g+/-0.07 without endothelium; P>0.05). Ang II (0.003 - 0.3 microM)-induced a non-sustained contraction of endothelium-intact preparations which was not antagonized by BQ-123 (1 microM), but was inhibited by losartan (10 nM). In addition, the maximal contraction induced by ET-1 (0.1 microM) could be further increased by the addition of 0.1 microM Ang II. 3. Ang II (0.001 - 0.3 microM) elevated [Ca(2+)](i) in single vascular smooth muscle cells (VSMCs) in a dose-dependent manner (pEC(50) 9.12+/-0.26) and the Ang II-induced increases in [Ca(2+)](i) were not affected by a Ca(2+)-free solution, but were abolished by pretreatment with caffeine (5 mM). Ang II did not increase [Ca(2+)](i) in endothelial cells. ET-1 (0.1 microM) increased [Ca(2+)](i) in single VSMCs in a normal Ca(2+) containing physiological saline solution (PSS), but not in a Ca(2+)-free solution. 4. Ang II-induced contraction was insensitive to inhibition by nifedipine (0.1 microM), an antagonist of L-type voltage-gated Ca(2+) channels, and SK&F96365 (10 microM), which blocks non-selective cation channels, whereas that to ET-1 was inhibited by SK&F69365. 5. RT - PCR data indicate the expression of AT(1A) and AT(1B) on both VSMCs and endothelial cells, but immunohistochemical evidence illustrates that the AT(1) is located primarily on VSMCs. 6. These results indicate that endothelium-derived ET-1 is not involved in the Ang II-mediated vasoconstriction of the rat tail artery and that Ang II- and ET-1-mediated VSM contractions utilize distinct pathways.

Angiotensin II↗
PubMed2000

Tetrahydrobiopterin improves endothelial function in human saphenous veins.

OBJECTIVES: Diminished production of nitric oxide has been linked to saphenous vein endothelial dysfunction. Tetrahydrobiopterin is an obligate cofactor for the oxidation of L -arginine by nitric oxide synthase in the production of nitric oxide by endothelial cells. The objective of the present study was to examine whether the exogenous addition of tetrahydrobiopterin improves endothelial function in saphenous veins from patients undergoing coronary artery bypass graft operations. METHODS: Vascular segments of saphenous veins were obtained from 17 patients undergoing elective coronary artery bypass grafting, and in vitro endothelium-dependent and endothelium-independent responses to acetylcholine and sodium nitroprusside were assessed. Isometric dose-response curves were constructed in precontracted rings in the presence and absence of tetrahydrobiopterin (0.1 mmol/L) with the use of the organ bath apparatus. The percentages of maximum relaxation and sensitivity were compared between interventions. RESULTS: Acetylcholine caused dose-dependent endothelium-mediated relaxation in saphenous veins. In the presence of tetrahydrobiopterin, acetylcholine-induced relaxation was significantly augmented (percentage maximum relaxation, 16.8% +/- 2.9% vs control 7.5% +/- 1.8%; P =.003) without an effect on agonist sensitivity. These effects were endothelium-specific because endothelium-independent responses to sodium nitroprusside were preserved. CONCLUSIONS: These data uncover beneficial effects of acute tetrahydrobiopterin addition on endothelial function in human vessels. Because endothelial dysfunction has been implicated in the development of graft failure, studies aimed at chronic delivery of tetrahydrobiopterin would be useful in determining the contribution of this cofactor toward saphenous vein atherosclerosis.

Acetylcholine↗
PubMed2000

Antihypertensive properties of a nitric oxide-releasing naproxen derivative in two-kidney, one-clip rats.

Nonsteroidal anti-inflammatory drugs have been reported to exacerbate hypertension. In this study, we tested the hypothesis that a nitric oxide-releasing derivative of naproxen would ameliorate hypertension in the rat. Hypertension was induced by partially occluding one renal artery (the "2K,1C" model), and 2 wk later the rats started receiving naproxen, the nitric oxide-releasing derivative HCT-3012, or vehicle each day for 2 wk. Naproxen significantly exacerbated the hypertension. HCT-3012 significantly reduced blood pressure relative to both the naproxen- and vehicle-treated groups. Both naproxen and HCT-3012 markedly suppressed whole blood thromboxane B(2) synthesis. In studies of anesthetized rats, naproxen significantly enhanced the late hypertensive response to endothelin-1 and significantly blunted the early hypotensive response. In contrast, HCT-3102 did not affect either response to endothelin-1. In vitro, HCT-3012 significantly reduced the responsiveness of aortic rings to the contractile effects of phenylephrine. These studies suggest that HCT-3012 reduces blood pressure in hypertensive rats, not simply through the vasodilatory actions of the nitric oxide it releases, but through alterations in the responsiveness of the vasculature to endogenous pressor agents.

Animals↗
PubMed1999

Acetylcholine-induced relaxation of peripheral arteries isolated from mice lacking endothelial nitric oxide synthase.

1. Acetycholine-mediated relaxations in phenylephrine-contracted aortas, femoral and mesenteric resistance arteries were studied in vessels from endothelial nitric oxide synthase knock-out (eNOS -/-) and the corresponding wild-type strain (eNOS +/+) C57BL6/SV19 mice. 2. Aortas from eNOS (+/+) mice relaxed to acetylcholine in an endothelium-dependent NG-nitro-L-arginine (L-NOARG) sensitive manner. Aortas from eNOS (-/-) mice did not relax to acetylcholine but demonstrated enhanced sensitivity to both authentic NO and sodium nitroprusside. 3. Relaxation to acetylcholine in femoral arteries was partially inhibited by L-NOARG in vessels from eNOS (+/+) mice, but relaxation in eNOS (-/-) mice was insensitive to a combination of L-NOARG and indomethacin and the guanylyl cyclase inhibitor 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The L-NOARG/ODQ/indomethacin-insensitive relaxation to acetylcholine in femoral arteries was inhibited in the presence of elevated (30 mM) extracellular KCl. 4. In mesenteric resistance vessels from eNOS (+/+) mice, the acetylcholine-mediated relaxation response was completely inhibited by a combination of indomethacin and L-NOARG or by 30 mM KCl alone. In contrast, in mesenteric arteries from eNOS (-/-) mice, the acetylcholine-relaxation response was insensitive to a combination of L-NOARG and indomethacin, but was inhibited in the presence of 30 mM KCl. 5. These data indicate arteries from eNOS (-/-) mice demonstrate a supersensitivity to exogenous NO, and that acetylcholine-induced vasorelaxation of femoral and mesenteric vessels from eNOS (-/-) mice is mediated by an endothelium-derived factor that has properties of an EDHF but is neither NO nor prostacyclin. Furthermore, in mesenteric vessels, there is an upregulation of the role of EDHF in the absence of NO.

Acetylcholine↗
PubMed1999

Endothelium-derived hyperpolarizing factor(s): species and tissue heterogeneity.

1. Endothelium-derived relaxing factor is almost universally considered to be synonymous with nitric oxide (NO); however, it is now well established that at least two other chemically distinct species (prostacyclin (PGI2) and a hyperpolarizing factor) may also contribute to endothelium-dependent relaxation. 2. Only relatively few studies have provided definitive evidence that an endothelium-derived hyperpolarizing factor (EDHF), which is neither NO nor PGI2, exists as a chemical mediator. 3. There is a lack of agreement as to the likely chemical identity of this putative factor. Some evidence suggests that EDHF may be a cytochrome P450-derived arachidonic acid product, possibly an epoxyeicosatrienoic acid (EET); conflicting evidence supports an endogenous cannabinoid as the mediator and still other studies infer an unknown mediator that is neither a cytochrome P450 nor a cannabinoid. 4. Data from our laboratory with a rabbit carotid artery 'sandwich' preparation have provided evidence that a mediator that meets the pharmacological expectations of a cytochrome P450 product is an EDHF. 5. Data from guinea-pig mesenteric arterioles suggest that EDHF is not a cytochrome P450 product, whereas in guinea-pig middle cerebral arteries, relaxation mediated by the NO/PGI2-independent mediator(s) is sensitive to cytochrome P450 inhibitors. In addition, in the rabbit middle cerebral artery, it is likely that endothelium-dependent hyperpolarization is mediated by both NO and PGI2. 6. In conclusion, these data indicate that EDHF is unlikely to be a single factor and that considerable tissue and species differences exist for the nature and cellular targets of the hyperpolarizing factors.

Animals↗
PubMed1998

Involvement of nitrosothiols, nitric oxide and voltage-gated K+ channels in photorelaxation of vascular smooth muscle.

The effects of nitrosothiol depleting compounds (p-hydroxymercuribenzoate, iodacetamide and ethacrynic acid), a guanylyl cyclase inhibitor (1H[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) and nitric oxide (NO) scavenger agents (xanthine/xanthine oxidase and 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; carboxy-PTIO) on light-induced photorelaxation in rat thoracic aorta were investigated. Photorelaxation responses were decreased in the presence of nitrosothiol depleting compounds suggesting S-nitrosothiols as the tissue source of the NO, whereas reduction in photorelaxation by the guanylyl cyclase inhibitor and NO scavenger agents indicates involvement of both NO and cGMP in photorelaxation. In addition the sensitivity of photorelaxation to the voltage-gated potassium channel (KV) inhibitor, 4-aminopyridine, indicates that photorelaxation is mediated via a NO/cGMP-dependent, and, perhaps, direct light, activation of KV channels.

Benzoates↗
PubMed1998

h1- and h2-calponins are not essential for norepinephrine- or sodium fluoride-induced contraction of rat aortic smooth muscle.

To investigate the controversial issue concerning the role of calponin in smooth muscle contraction, this study examined the relationship between smooth muscle calponin and the contraction of aortic rings from different strains of rats: Sprague-Dawley (SD), Wistar, and Wistar Kyoto (WKY). Western blot analysis demonstrated that h1- and h2-calponins are present in aortic smooth muscle from adult SD rats but not Wistar or WKY rats. Nevertheless, h1-calponin is detectable in stomach from Wistar rats, although at a much lower level compared with that in the SD rat stomach. This suggests that a repressed expression of the gene, instead of a simple null mutation, may have caused its absence from the aortic smooth muscle. Despite the presence or absence of calponin, the aortic smooth muscles from the different strains of rats all develop contractions in response to the physiological agonist norepinephrine (NE) and following activation with the plasma membrane receptor-independent NaF induction. The data indicate that h1- and h2-calponins are not essential for NE- and NaF-induced contractions in aortic smooth muscle. The calponin-positive adult SD rat aorta was found to be more sensitive in contractile response to NE and NaF inductions compared with the calponin-negative rat aortae. This may imply a potential modulator function of calponin in the contraction of smooth muscle, whereas other contractile protein isoform differences between these rat strains may also play a role.

Animals↗
PubMed1998

Roles of calcium-activated and voltage-gated delayed rectifier potassium channels in endothelium-dependent vasorelaxation of the rabbit middle cerebral artery.

1. The cellular mechanism(s) of action of endothelium-derived vasodilator substances in the rabbit middle cerebral artery (RMCA) were investigated. Specifically, the subtypes of potassium channels involved in the effects of endothelium-derived relaxing factors (EDRFs) in acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in this vessel were systematically compared. 2. In the endothelium-intact RMCA precontracted with histamine (3 microM), ACh induced a concentration-dependent vasorelaxation, which was sensitive to indomethacin (10 microM) or N(G)-nitro-L-arginine (L-NOARG; 100 microM); pD2 values 8.36 vs 7.40 and 6.38, P < 0.01 for both, n = 6 and abolished by a combination of both agents. ACh caused relaxation in the presence of high K+ PSS (40 mM KCl), which was not affected by indomethacin, but abolished by L-NOARG and a combination of indomethacin and L-NOARG. 3. In the presence of indomethacin, relaxation to ACh in the endothelium-intact RMCA precontracted with histamine was unaffected by either glibenclamide (10 microM), an ATP-sensitive K+ channel (K[ATP]) blocker, 4-aminopyridine (4-AP, 1 mM) or dendrotoxin (DTX, 0.1 microM), delayed rectifier K channel (Kv) blockers. However, relaxation responses to ACh were significantly inhibited by either LY83583 (10 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM), guanylyl cyclase inhibitors, or charybdotoxin (CTX; 0.1 microM), iberiotoxin (ITX, 0.1 microM) and apamin (APA, 0.1 microM), large conductance Ca2+-activated K+ channels (BK[Ca]) blocker and small conductance Ca2+-activated K+ channel (SK[Ca]) blocker, respectively. 4. In the presence of L-NOARG, relaxation to ACh was unaffected by glibenclamide or the cytochrome P450 mono-oxygenase inhibitor, clotrimazole (1 microM), but was significantly inhibited by either 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536, 10 microM) and 2',3'-dideoxyadenosine (2',3'-DDA, 30 microM), adenylyl cyclase inhibitors, or 4-AP, DTX, CTX, ITX and APA. 5. In the endothelium-denuded RMCA precontracted with histamine, authentic NO-induced relaxation was unaffected by glibenclamide, 4-AP and DTX, but significantly reduced by ODQ, ITX and APA. Authentic prostaglandin I2 (PGI2)-induced relaxation was unaffected by glibenclamide, but significantly reduced by 2',3'-DDA, 4-AP, DTX, ITX and APA. Forskolin-induced relaxation was significantly inhibited by high K+, CTX and 4-AP. 6. These results indicate that: (1) in the RMCA the EDRFs released by ACh are NO and a prostanoid (presumably PGI2), and there is no evidence for the release of a non-NO/PGI2 endothelium-derived hyperpolarizing factor (EDHF), (2) K(Ca) channels are involved in NO-mediated relaxation of the RMCA but both K(Ca) and Kv channels are involved in PGI2-mediated relaxation.

Acetylcholine↗
PubMed1998

Dual endothelium-dependent vascular activities of proteinase-activated receptor-2-activating peptides: evidence for receptor heterogeneity.

1. The vascular actions of the proteinase-activated receptor-2-activating peptides (PAR2APs), SLIGRL-NH2 (SL-NH2) and SLIGKV-NH2 (KV-NH2) as well as the reverse-sequence peptide, LSIGRL-NH2 (LS-NH2) and an N-acylated PAR2AP derivative, trans-cinnamoyl-LIGRLO-NH2 (tcLI-NH2), were studied in rat intact and endothelium-denuded artery ring preparations, primarily from the pulmonary artery (RPA). 2. In RPA rings with but not without a functional endothelium, SL-NH2 (but not LS-NH2) caused either an endothelium-dependent relaxation (at concentrations: < 10 microM) or (at higher concentrations: > 10 microM), an endothelium-dependent contraction. No contractile response was observed in endothelium-denuded preparations, that otherwise contracted in response to the PAR1AP, TFLLR-NH2. 3. The endothelium-dependent contractile response to SL-NH2 was not blocked by the alpha-adrenoceptor antagonist prazosin, the endothelin antagonist BQ123, the angiotensin II antagonist DuP753, by tetrodotoxin; nor by the enzyme inhibitors, N(omega)-nitro-L-arginine-methylester (NO-synthase), indomethacin (cyclo-oxygenase), SKF-525A (epoxygenase) and MK886 (leukotriene synthesis inhibitor). 4. In the relaxation assay, KV-NH2 was 5 fold less potent than SL-NH2, whereas in the contractile assay KV-NH2 was about equipotent with SL-NH2. However, the maximal contractile response to KV-NH2 was lower than that of SL-NH2. 5. The PAR2AP analogue, tcLI-NH2, was as active as SL-NH2 in the relaxation assay but was inactive as a contractile agonist in the endothelium-intact RPA. 6. The relaxant responses caused by SL-NH2 and trypsin, as well as the contractile response caused by SL-NH2, did not desensitize in the course of repeated exposures of the tissue to agonist; whereas the contractile response to trypsin, only observed at concentrations greater than 30 u ml(-1), was desensitized by previous exposure of the tissue to either thrombin or trypsin. 7. In a contractile assay, where the tissue was desensitized to a concentration of trypsin that would otherwise cause a relaxant response, the preparation still contracted in response to SL-NH2. However, the trypsin-desensitized preparations were no longer contracted by thrombin. 8. From the cross-desensitization by thrombin of the contractile response to trypsin (and vice versa), we concluded that the contractile effect of trypsin was due to activation of the thrombin receptor and not PAR2. 9. We concluded that the endothelium-dependent contraction caused by high concentrations of SL-NH2 is due to an as yet unidentified contracting factor; whereas the endothelium-dependent relaxation response observed at low concentrations of SL-NH2 (< or = 10 microM) is mediated by nitric oxide. 10. The distinct structure activity profiles for the contractile response (potency of KV-NH2 < or = SL-NH2) compared with the relaxant response (potency of KV-NH2 << SL-NH2); the contractile responsiveness to SL-NH2 of an endothelium-intact RPA preparation, that did not contract in response to trypsin; and the lack of contractile activity of the PAR2AP analogue tcLI-NH2, that was as active as SL-NH2 in the relaxation assay all argue in favour of receptor heterogeneity in the vasculature for the PAR2APs. It remains to be determined if the distinct endothelial receptor responsible for the contractile action of SL-NH2 can be proteolytically activated, like PAR1 and PAR2.

Animals↗
PubMed1998

Cyclic GMP-dependent and cyclic GMP-independent actions of nitric oxide on the renal afferent arteriole.

1. The effects of exogenous NO and endothelial-derived NO (EDNO) on the afferent arteriole were investigated in the in vitro perfused hydronephrotic rat kidney. Vessels were pre-constricted with angiotensin II (0.1-0.3 nM) or KCl (30 mM). NO was infused directly into the renal artery at concentrations ranging from 30-9000 nM. ODQ (10, 30 microM) was administered to examine the effects of guanylyl cyclase inhibition. Kidneys were treated with ibuprofen (10 microM) to avoid actions of prostaglandins. 2. During angiotensin II-induced vasoconstriction, NO elicited vasodilation at concentrations of 30 900 nM (EC50=200 nM) and ODQ caused a 10 fold shift in NO-sensitivity (EC50 1600 nM). During KCl-induced vasoconstriction, NO elicited a maximal dilation of 82+9% at 9000 nM (EC50 2000 nM) and ODQ had no effect. Thus in the presence of ODQ, the NO concentration-response curves for KCI- and angiotensin II-induced vasoconstriction were identical (P>0.2). 3. To assess the possible role of cyclic GMP-independent mechanisms in the actions of EDNO, we compared the effects of L-NAME, ODQ and ODQ+L-NAME on acetylcholine-induced vasodilation. Angiotensin II reduced afferent arteriolar diameters from 16.7+/-0.5 to 8.1+/-0.8 microns and acetylcholine fully reversed this effect (16.9+/-0.5 microns). ODQ restored the angiotensin II response in the presence of acetylcholine (7.1+/-0.6 microns) and the subsequent addition of L-NAME had no further effect (6.8+/-0.7 microns). Similarly, L-NAME alone, fully reversed the actions of acetylcholine. 4. Our findings indicate that exogenous NO is capable of eliciting renal afferent arteriolar vasodilation through both cyclic GMP-dependent and cyclic GMP-independent mechanisms. The cyclic GMP-independent action of NO did not require K+ channel activation, as it could be elicited in the presence of 30 mM KCl. Finally, although cyclic GMP-independent effects of exogenous NO could be demonstrated in our model, EDNO appears to act exclusively through cyclic GMP.

Animals↗