Rings Of Rabbit Thoracic Aorta Research Articles

Vasorelaxant mechanisms of the antidiabetic anagliptin in rabbit aorta: roles of Kv channels and SERCA pump.

The present study investigated the vasorelaxant mechanisms of an oral antidiabetic drug, anagliptin, using phenylephrine (Phe)-induced pre-contracted rabbit aortic rings. Arterial tone measurement was performed in rabbit thoracic aortic rings. Anagliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the classical voltagedependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly decreased the vasorelaxant effect of anagliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and the large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not attenuate the vasorelaxant effect. Furthermore, the vasorelaxant response of anagliptin was effectively inhibited by pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid. Neither cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) nor cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) reduced the vasorelaxant effect of anagliptin. Similarly, the anagliptin-induced vasorelaxation was independent of the endothelium. Based on these results, we suggest that anagliptin-induced vasorelaxation in rabbit aortic smooth muscle occurs by activating Kv channels and the SERCA pump, independent of other vascular K+ channels, cAMP/PKA- or cGMP/PKG-related signaling pathways, and the endothelium.

Mechanisms underlying the vasodilatory effects of canagliflozin in the rabbit thoracic aorta: Involvement of the SERCA pump and Kv channels

Canagliflozin is an anti-diabetic agent and sodium glucose co-transporter-2 inhibitor. Despite numerous clinical trials demonstrating its beneficial effects on blood pressure, the cellular mechanisms underlying the effects of canagliflozin on vascular reactivity have yet to be clarified. We investigated the vasodilatory effect of canagliflozin on aortic rings isolated from rabbits. We used rabbit thoracic aortic rings and its arterial tone was tested by using wire myography system. Canagliflozin caused concentration-dependent vasodilation in aortic rings pre-constricted with phenylephrine or high K+. However, the degree of canagliflozin-induced vasodilation of the aortic rings pre-constricted with high K+ was less than that of rings pre-constricted with phenylephrine. Application of 4-aminopyridine, a voltage-dependent K+ (Kv) channel inhibitor, reduced canagliflozin-induced vasodilation. However, pre-incubation of an inwardly rectifying K+ channel inhibitor, a large-conductance Ca2+-activated K+ channel inhibitor, and an ATP-sensitive K+ inhibitor did not modulate the vasodilatory effects of canagliflozin. Indeed, canagliflozin increased Kv currents in aortic smooth muscle cells. Pre-treatment with thapsigargin or cyclopiazonic acid, a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors, reduced the vasodilatory effects of canagliflozin. Conversely, pre-treatment with a Ca2+ channel inhibitor, adenylyl cyclase/PKA inhibitors, and guanylyl cyclase/PKG inhibitors did not modulate the vasodilatory effects of canagliflozin. Endothelium removal, and pre-treatment with the nitric oxide synthase inhibitor L-NAME, and small- and intermediate-conductance Ca2+-activated K+ channel inhibitor apamin and TRAM-34, did not diminish the vasodilatory effects of canagliflozin. Our results indicate that canagliflozin induces vasodilation, which is dependent on the robust SERCA activity and Kv channel activation.

The anti-diabetic drug trelagliptin induces vasodilation via activation of Kv channels and SERCA pumps

In this study, we investigated the vasodilatory effects of trelagliptin (a dipeptidyl peptidase-4 inhibitor) and its related mechanisms using rabbit aortic rings. Arterial tone measurement was performed in rabbit thoracic aortic rings. Trelagliptin induced vasodilation in a dose-dependent manner. Pretreatment with the ATP-sensitive K+ channel inhibitor glibenclamide, large-conductance Ca2+-activated K+ channel inhibitor paxilline, and inwardly rectifying K+ channel inhibitor Ba2+ did not affect the vasodilatory effect of trelagliptin. However, pretreatment with the voltage-dependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly attenuated the vasodilatory effect of trelagliptin, suggesting that the vasodilatory effect of trelagliptin is associated with Kv channel activation. Although pretreatment with Kv1.5 and Kv2.1 subtype inhibitors did not affect the response to trelagliptin, pretreatment with a Kv7.X subtype inhibitor effectively reduced the vasodilatory effect of trelagliptin. Furthermore, sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors also significantly attenuated the vasodilatory effect of trelagliptin. These effects, however, were not affected by pretreatment with Ca2+ channel inhibitors, adenylyl cyclase/PKA inhibitors, guanylyl cyclase/PKG inhibitors, or removal of the endothelium. From these results, we concluded that the vasodilatory effect of trelagliptin was associated with the activation of Kv channels (primary the Kv7.X subtype) and SERCA pump regardless of other K+ channels, Ca2+ channels, cAMP/PKA-related or cGMP/PKG-related signaling pathways, and the endothelium. Therefore, caution is required when prescribing trelagliptin to the patients with hypotension and diabetes.

Scutellarin protects against vascular endothelial dysfunction and prevents atherosclerosis via antioxidation

Scutellarin is the major constituent responsible for the clinical benefits of Erigeron breviscapus (Vant.) Hand.-Mazz which finds a long history of ethnopharmacological use in Traditional Chinese Medicine. Scutellarin as a pure compound is now under investigation for its protections against various tissue injuries. This study aims to examine the effects of scutellarin on oxidative stress-induced vascular endothelial dysfunction and endothelial cell damage, and then to evaluate the therapeutic efficacy of scutellarin in preventing atherosclerosis in rats. Radical scavenging ability of scutellarin was determined in vitro. Impact of scutellarin on endothelium-dependent relaxation (EDR) of rabbit thoracic aortic rings upon 1, 1-diphenyl-2-picrylhydrazyl (DPPH) challenge was measured. Influences of scutellarin pre-treatment on the levels of reactive oxygen species (ROS), activities of antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase and catalase, and the expression of SOD1 and NADPH oxidase 4 (Nox4) in human umbilical vein endothelial cells (HUVECs) injured by H2O2 were examined. Anti-atherosclerotic effect of scutellarin was evaluated in rats fed with high fat diet (HFD). Scutellarin showed potent antioxidant activity in vitro. Pretreatment of scutellarin retained the EDR of rabbit thoracic aortic rings damaged by DPPH. In H2O2 injured-HUVECs the deleterious alterations in ROS levels and antioxidant enzymes activity were reversed by scutellarin and the mRNA and protein expression of SOD1 and Nox4 were restored also. Oral administration of scutellarin dose-dependently ameliorated hyperlipidemia in HFD-fed rats and alleviated oxidative stress in rat serum, mimicking the effects of reference drug atorvastatin. Scutellarin protects against oxidative stress-induced vascular endothelial dysfunction and endothelial cell damage in vitro and prevents atherosclerosis in vivo through antioxidation. The results rationalize further investigation into the clinical use of scutellarin in cardiovascular diseases.

Mechanisms underlying the antihypertensive properties of Urtica dioica.

BackgroundUrtica dioica has traditionally been used in the management of cardiovascular disorders especially hypertension. The aim of this study was to explore pharmacological base of its use in hypertension.MethodsCrude methanolic extract of U. dioica (Ud.Cr) and its fractions (Ud.EtAc, Ud.nHex, Ud.Chl and Ud.Aq) were tested in vivo on normotensive and hypertensive rats under anesthesia for blood pressure lowering effect. In-vitro experiments on rat and rabbit aortae were employed to probe the vasorelaxation mechanism(s). The responses were measured using pressure and force transducers connected to PowerLab Data Acquisition System.ResultsUd.Cr and fractions were found more effective antihypertensive in hypertensive rats than normotensive with remarkable potency exhibited by the ethyl acetate fraction. The effect was same in the presence of atropine. In isolated rat aortic rings, Ud.Cr and all its fractions exhibited l-NAME sensitive endothelium-dependent vasodilator effect and also inhibit K+ (80 mM)-induced pre-contractions. In isolated rabbit thoracic aortic rings Ud.Cr and its fractions induced relaxation with more potency against K+ (80 mM) than phenylephrine (1 µM) like verapamil, showing Ud.EtAc fraction the most potent one. Pre-incubation of aortic rings with Ud.Cr and its fractions exhibited Ca2+ channel blocking activity comparable with verapamil by shifting Ca2+ concentration response curves to the right. Ud.Cr and its fractions also ablated the intracellular Ca2+ release by suppressing PE peak formation in Ca2+ free medium. When tested on basal tension, the crude extract and all fractions were devoid of any vasoconstrictor effect.ConclusionsThese data indicate that crude methanolic extract and its fractions possess antihypertensive effect. Identification of NO-mediated vasorelaxation and calcium channel blocking effects explain the antihypertensive potential of U. dioica and provide a potential pharmacological base to its medicinal use in the management of hypertension.

Salvianolic acid B possesses vasodilation potential through NO and its related signals in rabbit thoracic aortic rings

Salviae miltiorrhizae, a traditional Chinese medicine, is widely used in the treatment of cardiovascular and cerebrovascular diseases. Salvianolic acid B is identified as one of the most important water-soluble active ingredients in Salviae miltiorrhizae and associated with the activation of Ca(2+) channel of cytomembrane. But the further mechanism of action was not very clearly. In our study, we investigated the vasodilation activity of salvianolic acid B using the isolated thoracic aortic rings from Japanese white rabbit. Salvianolic acid B significantly released the contraction of the isolated thoracic aortic rings induced by phenylephrine and CaCl(2) while had no effects on the aortic rings with KCl stimulated. Different with Di-ao-xin-xue-kang capsule, salvianolic acid B caused an increase of Ca(2+) in cytoplasm from not only activation of Ca(2+) channel in cytomembrane but also release of endogenous Ca(2+). Then, a series of endogenous Ca(2+) inhibitors were pretreated to explore the mechanism of salvianolic acid B, and the results provided further evidences that salvianolic acid B causes intracellular calcium release in ryanodine receptors-dependent manners. Moreover, combining l-arginine (l-Arg) with salvianolic acid B promoted the vasodilation activity suggesting a relationship with nitric oxide (NO). To further investigated its mechanism, both guanylate cyclase (GC) inhibitor and NO Synthase inhibitor were used and demonstrated to block vasodilation activity of the aortic rings. Our findings reveal a NO-sGC-cGMP signals dependence mechanism of salvianolic acid B on its vasodilation activity which provide an evidence for its subsequent application in clinic.

Apamin-sensitive K+ currents mediate arachidonic acid-induced relaxations of rabbit aorta.

Arachidonic acid induces an endothelium-dependent relaxation of the rabbit aorta that is blocked by lipoxygenase inhibitors. The cellular vasodilatory mechanisms activated by arachidonic acid metabolites remain undefined. In rabbit thoracic aortic rings pretreated with indomethacin (10 micromol/L) and contracted with phenylephrine, arachidonic acid (0.1 to 100 micromol/L) induced concentration-dependent relaxations. Maximal relaxations averaged 45+/-3% and were inhibited by increasing extracellular K+ (30 mmol/L, 15+/-5%; P<0.001) or incubation with apamin (100 nmol/L, 26+/-7%; P<0.05) but not incubation with charybdotoxin (100 nmol/L, 41+/-5%). In aortic strips with an intact endothelium that were treated with phenylephrine, arachidonic acid (10 micromol/L) increased the membrane potential from -28.7+/-1.3 to -37.8+/-3.0 mV (P<0.01). Preincubation with apamin did not alter basal membrane potential but inhibited arachidonic acid-induced hyperpolarization (-31.5+/-1.5 mV). Incubation of rabbit aortic segments with apamin or charybdotoxin did not alter [14C]arachidonic acid metabolism. Whole-cell outward K+ currents from isolated rabbit aortic smooth muscle cells averaged 43.0+/-4.8 pA/pF at 60 mV and were significantly decreased to 35.7+/-4.2 pA/pF by apamin (P<0.001). Subsequent addition of charybdotoxin further decreased maximal currents to 14.4+/-2.3 pA/pF. Addition of 11,12,15-trihydroxyeicosatrienoic acid increased the outward whole-cell K+ current. In inside-out patches of aortic smooth muscle, apamin inhibited the calcium activation (100 to 300 nmol/L; P<0.001) of a small-conductance K+ channel (approximately 24 pS). These results suggest that arachidonic acid induces endothelium-dependent hyperpolarization and relaxation of rabbit aorta through activation of smooth muscle, apamin-sensitive K+ currents.

Characterisation of a modified approach to the study of sympathetic neurotransmission and its presynaptic modulation in the isolated rabbit thoracic aorta

The quantification of [(3)H]noradrenaline spillover from electrically stimulated, sympathetic nerves is a widely used method to study presynaptic effects of hormones, transmitters and drugs. Although a straightforward approach, the execution of the experiments is not trivial. This holds true mainly for a reliable control of the experimental conditions, a major pitfall of the commonly used superfusion setup, and problems concerning the sampling of the tritium containing probes. These difficulties prompted us to develop a variant of this method, which is based on a classical organ bath setup. Rabbit thoracic aortic rings were incubated with [(3)H]-labeled noradrenaline. Instead of being constantly washed away by superfusion, the [(3)H]noradrenaline is allowed to accumulate in the medium. Electrical field stimulation (EFS) (2 Hz, 3 ms, 150 mA) caused a significant increase of [(3)H]noradrenaline outflow by approximately a factor 4.2 (P<.05). The fractional release of noradrenaline during consecutive periods of stimulation remained unaltered (FR(2)/FR(1) 0.99+/-0.03). The EFS-evoked release could be nearly abolished by the selective sodium channel blocker tetrodotoxin (1 microM) (FR(2)/FR(1) 0.06+/-0.03, P<.05). The N-type calcium antagonist omega-conotoxin GVIA (0.3 microM) abolished the stimulation-evoked outflow (FR(2)/FR(1) 0.01+/-0.06, P<.05), whereas the antisympathotonic agent guanethidine (10 microM) attenuated the EFS-evoked noradrenaline outflow by approximately a factor 2 (FR(2)/FR(1) 0.46+/-0.07, P<.05). Angiotensin II (0.1 and 1 nM) enhanced the EFS-evoked [(3)H]noradrenaline outflow by nearly a factor 1.5 and 2, respectively (FR(2)/FR(1) of 1.43+/-0.11 (0.1 nM) and 2.03+/-0.11 (1 nM); n=6-8, P<.05). All agents failed to influence basal outflow. Our modified experimental approach appears to be suitable to study presynaptic influences on sympathetic transmission in the rabbit thoracic aorta. In addition to optimal control of the experimental conditions, the method offers the advantage of a safe and reliable sampling.

Paradoxical cholinergic and purinergic vascular reactivity of rabbit thoracic aorta cold-stored in University of Wisconsin solution.

Endothelial dysfunction has been reported in donor blood vessels destined for organ transplantation following cold-storage preservation with University of Wisconsin solution (UW). This was investigated in the present work. Segments of rabbit thoracic aorta were mounted on isometric fine-wire myographs at 37 degrees C and gassed with 95% O2/5% CO2. Concentration-dependent vasodilatations to acetylcholine and adenosine-5'-triphosphate (ATP) were obtained in freshly-harvested rabbit aortic rings, with and without the endothelium, and after 8 days of cold-storage, at 4 degrees C, in either UW, Krebs-Bülbring buffer (KBB) or saline. The action of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) (100 microM) was evaluated upon the concentration-response curves to determine whether nitric oxide (NO) exerted any modulatory actions. Endothelium-dependent, NO-mediated responses to acetylcholine were unaltered after eight days of storage in UW, reduced after storage in KBB and absent after removal of the vascular endothelium, saline storage or after testing in the presence of L-NAME, suggesting improved NO-mediated endothelial function with the use of UW. Structural preservation was also confirmed using scanning electron microscopy. In contrast, endothelium-dependent responses to ATP were unchanged after eight days of storage in KBB but were reduced after storage in UW and saline, suggesting purinergic (ATP) endothelial dysfunction after storage in UW. L-NAME markedly reduced vasodilatation to ATP in freshly harvested rings and after eight days of storage in KBB. This reduction was statistically significant (P < 0.05, Student's two tailed, unpaired t-test) at -log (M) ATP concentrations of 5.5, 5.0, 4.5, 4.0 and 3.5. NO-dependent vasodilatation to ATP was not attenuated by L-NAME in UW-stored rings. Eight days' UW-storage of rabbit thoracic aortic rings appeared to have differential and paradoxical effects upon NO-dependent vasodilatation to acetylcholine and ATP. Morphological observations using electron microscopy suggested that UW preserved the vascular endothelium and this was verified by retained vascular reactivity of endothelium-dependent vasodilatations to acetylcholine. UW-storage however, significantly reduced endothelium-dependent relaxation to ATP thereby suggesting that P2Y-purinoceptors, which are located on the vascular endothelium, may be more susceptible to biodegradation than cholinergic receptors and may be responsible for endothelial dysfunction following transplantation.

Losartan Reduces the Vasorelaxant Effect of Atrial Natriuretic Peptide on Basal Tone in Aorta

The Ca2+-and receptor-dependencies of the basal tone seen in angiotensin II (Ang II)-conditioned rabbit thoracic aortic rings were investigated. Ca2+-free Krebs significantly and partially reversibly reduced basal tone in aortic rings that had recovered from an earlier challenge with Ang II; rings not previously exposed to Ang II were unaffected. The effect of Ca2+-free Krebs was similar to the reduction in basal tone evoked by atrial natriuretic

Role of oxidative metabolism on endothelium-dependent vascular relaxation of isolated vessels.

The obligatory role of endothelium in mediating vasodilator response to numerous humoral agents has been definitely accepted. However, the chemical identity of endothelium-derived relaxing factor(s) (EDRF) and the mechanisms underlying its synthesis and release remain unclear. Much evidence suggests a compartmentalization of ATP into cells, such that ATP derived from glycolysis or from oxidative metabolism is used for different cellular functions. To investigate which energy source (i.e. oxidative v glycolytic metabolism) is preferentially used for the biosynthesis and/or release of EDRF, rings of rabbit thoracic aorta were studied in organ chambers. After preconstriction with PGF2 alpha, inhibition of glycolysis with either iodoacetate (300 microM) (n = 6) or 2-deoxyglucose (20 mM) (n = 6) did not affect concentration-response curve to the endothelium-dependent agent acetylcholine. In contrast, inhibition of oxidative metabolism with either 1 mM amytal or 5 microM rotenone markedly impaired relaxation to acetylcholine. In fact, maximal relaxation was 75 +/- 5% in control rings (n = 6), and 42 +/- 7% (P < 0.01) in amytal-treated rings (n = 6), whereas rotenone converted acetylcholine relaxation into constriction (n = 6; P < 0.001). The effect of amytal on endothelium-dependent relaxation was reversible, suggesting that endothelial cells were not damaged by the inhibitor. Amytal also markedly reduced endothelium-mediated relaxation to ADP (37 +/- 6%; P < 0.05; n = 5), as well as to the calcium ionophore A23187. Neither mitochondrial inhibitor affected relaxation to nitroglycerin, an endothelium-independent agent. Finally, amytal did not affect relaxation to S-nitrosocysteine (a recently proposed EDRF) (n = 5), suggesting that the effects on acetylcholine and ADP responses were not due to non-specific interferences with EDRF once released from endothelial cells. In conclusion, our data demonstrate that the active process of biosynthesis and/or release of EDRF requires energy derived mainly from mitochondrial oxidative metabolism.

Complement-induced endothelial dysfunction in rabbits: mechanisms, recovery, and gender differences.

Activation of complement and attenuation of endothelium-dependent relaxation occur in a number of pathophysiological conditions. The aim of this study was to investigate the mechanisms of human complement activation and loss of endothelium-dependent relaxation in rabbit tissue, the duration of this loss, and the effects of gender and serum concentration. In rabbit thoracic aortic rings precontracted with phenylephrine, human serum (HS) concentration dependently induced a loss of endothelium-dependent relaxation to the receptor-dependent vasodilator acetylcholine (ACh) and receptor-independent vasodilator calcium ionophore A23187. Serum-induced loss of ACh-dependent relaxation was decreased when rings were bathed in 1) HS depleted of factor B, C2, or C8, 2) heat-inactivated HS, or 3) HS with complement inhibitor sCR1 or sCR1[desLHR-A]. Superoxide dismutase had no effect on serum-induced loss of ACh-dependent relaxation. Serum-induced loss of ACh-dependent relaxation returned to control values after removal of HS. Serum-induced loss of ACh-dependent relaxation was greater in male than in female aortic rings. These results suggest that 1) complement activation directly attenuates endothelium-dependent relaxation via the classical and alternative pathways independent of superoxide anion formation, 2) this attenuation is concentration dependent, reversible, and dependent on formation of C5b-9, and 3) endothelial tissue from males is more susceptible than that from females to the acute effects of complement activation.

979-34 Adriamycin May Impair Vascular Smooth Muscle Relaxation via a Nitric Oxide-Related Mechanism

The free radical-dependent cardiac toxicity of adriamycin (ADR) is well known. Recently we observed that ADR is also able to affect vascular function, reducing endothelium-dependent relaxation. Moreover, endotheliumindependent relaxation to nitroglycerin (NTG) was also impaired. Therefore, we wanted to investigate the mechanism through which ADR induces impairment of vascular smooth muscle function. In isolated rings of rabbit thoracic aorta preconstricted with 1 μM phenylephrine, maximal relaxation to NTG was decreased after 1 h incubation with ADR is a dose-dependent manner. In 6 experiments relaxation to NTG was 103 ± 3% in control rings, and was reduced to 97 ± 5% (p = NS), 85 ± 8 (p = NS) and 77 ± 8% (p &lt; 0.05) in presence of 30 μM, 90 M and 150 μM ADR. As a consequence, ED 50 increased from -7.93 ± 0.11 Log Mol NTG in controls to -7.81 ± 0.11 (p = NS). -7.20 ± 0.15 (p &lt; 0.05) and -6.99 ± 0.25 Log Mol NTG (p &lt; 0.01) with increasing concentrations of ADR. Similar results were observed with two other endothelium-independent vasodilators, SIN-l (which activates guanylate cyclase) and isoproterenol (which activates adenylate cyclase). However, the inhibitory effect of ADR on NTG relaxation was much less pronounced if endothelium was absent. In fact, in denuded rings control maximal relaxation to NTG was 101 ± 3% and after 150 μM ADR it was 89 ± 4% (n = 6; P = NS). with no significant changes in ED 50 . Furthermore, when nitric oxide synthesis in rings with endothelium was inhibited by 300 μM L-NAME, maximal relaxation to NTG was not significantly affected, being 100 ± 42% before and 85 ± 44% after 150 μM ADR incubation (n = 6; p = NS). Thus, ADR may acutely impair smooth muscle relaxation. This impairment is dependent on the presence of normal endothelium. Formation of toxic peroxynitrite, via interaction of nitric oxide with ADR-formed free radicals, might mediate this phenomenon.

Effect of captopril on acetylcholine-induced relaxation in the presence of nitroglycerin tolerance in isolated rabbit aorta.

We investigated the effects of angiotensin converting enzyme inhibitors on acetylcholine-induced endothelium-dependent vasodilation in the presence of nitroglycerin tolerance in rings of rabbit thoracic aorta mounted in tissue baths and precontracted with 10(-6) M norepinephrine. The vasorelaxant effects of acetylcholine were measured before and after 1 h treatment with 5 x 10(-4) M nitroglycerin. The acetylcholine dose-response curve shifted to the right after the induction of nitroglycerin tolerance. Pretreatment with captopril (a sulfhydryl angiotensin converting enzyme inhibitor), but not with M-1 (a metabolite of delapril and a nonsulfhydryl angiotensin converting enzyme inhibitor) restored acetylcholine-induced relaxation. Pretreatment with N-acetylcysteine also restored reduced acetylcholine-induced relaxation. These results suggest that the sulfhydryl group plays a major role in restoration of reduced acetylcholine-induced vasodilation in the presence of nitroglycerin tolerance.

Kinetic characterization of adenosine A 2 receptor-mediated relaxation in isolated rabbit aorta

Previous studies in our laboratory (Wiener et al., 1991, Soc. Neurosci. Abstr. 17, 989) have addressed aspects of the functional antagonism between the responses mediated by activated adenosine A2 receptors and alpha 1-adrenoceptors in adventitia- and endothelium-denuded rabbit thoracic aortic rings by steady-state protocols which ignore the time course of response generation. In the present communication we describe aspects of the time-dependent kinetics of relaxation responses to adenosine A2 receptor agonists in tissues pre-contracted with the alpha 1-adrenoceptor agonist phenylephrine. The results were analyzed by application of the model originally developed by Keitz et al. (1990, J. Pharmacol. Exp. Ther. 255, 650) to describe the relaxation response, to a beta-adrenoceptor agonist, as a first-order exponential decrease in tissue tension over time to estimate the apparent rate constant for relaxation (krel) and the magnitude of relaxation at equilibrium. The magnitude of the relaxation responses to adenosine, N6-cyclohexyladenosine, N6-methyladenosine, 5'-N-ethylcarboxamidoadenosine, and R(-)-N6-(2-phenylisopropyl)adenosine were agonist concentration-dependent and saturable, as were the apparent rate constants for relaxation. In addition, the magnitude of the apparent rate constants for relaxation and the relaxation responses were inversely proportional to the fractional occupancy of the alpha 1-adrenoceptor. The hypothesis put forth by Keitz et al. that the maximal value of the apparent rate constant for relaxation may serve as the kinetic definition of agonist efficacy was also tested and found to be invalid for the adenosine A2 receptor. We propose that this pair of activated receptors and tissue preparation is a good model to study quantitative aspects of functional antagonism by kinetic paradigms.

1,1-Dinitroethyl substituted furoxans: a new class of vasodilators and inhibitors of platelet aggregation

Abstract The synthesis and structural characterization of a series of 1,1-dinitroethyl substituted furoxans are described. Their vasodilatory properties, evaluated on isolated rings of rabbit thoracic aorta precontracted with noradrenaline, as well as their ability to inhibit the collagen induced aggregation in human platelet-rich plasma, are reported. The most active derivative of the series is 3-(1,1-dinitroethyl)-4-phenylfuroxan 7b . Its vasodilatory property is similar to that of glyceryl trinitrate. In addition, this compound is a more potent platelet aggregation inhibitor than sodium nitroprusside.

Effects of vanadate on vascular contractility and membrane potential in the rabbit aorta.

Isolated rabbit aortic ring with intact endothelial cell preparations precontracted with NE (10(-7) M) were relaxed by vanadate in a dose dependent manner (from 0.2 to 2 mM). Application of vanadate and ACh during the tonic phase of high K+(100 mM)-induced contraction showed a slight relaxation in contrast to that in NE-induced contraction, but sodium nitroprusside (10 microM) more effectively relaxed the aortic ring preparations in high K+ contraction than that of vanadate. Vanadate-induced relaxation in NE-contracted aortic rings was reversed by application of BaCl2 (50 microM) or glibenclamide (10 microM). Furthermore, Vanadate hyperpolarized membrane potential of smooth muscle cells in endothelium-intact aortic strips and this effect was abolished by application of glibenclamide. The above results suggest that vanadate release EDHF (Endothelium-Derived Hyperpolarizing Factor), in addition to EDRF (Endothelium-Derived Relaxing Factor) from endothelial cell. This EDHF hyperpolarize the smooth muscle cell membrane potential via opening of the ATP-sensitive K+ channel and close a voltage dependent Ca++ channel. So it is suggested that the vanadate-induced relaxation of rabbit thoracic aortic rings may be due to the combined effects of EDRF and EDHF.

Flow stimulates endothelial cells to release a nitrovasodilator that is potentiated by reduced thiol

We designed a novel system to study flow-mediated endothelium-dependent vasodilation. Vascular rings of rabbit thoracic aorta were mounted for isometric tension recording in a flow chamber filled with physiological saline solution. The flow chamber contained a stir bar and was mounted on a magnetic stirrer to induce vortical flow. Norepinephrine (NE, 10(-6) M) induced contraction of the vascular rings. Bovine endothelial cells on microcarrier beads added to the chamber had little effect on contraction to NE in the absence of flow. Flow induced endothelium-dependent relaxation of the vascular rings that was dependent on the flow rate. Relaxations were annulled or reversed to a contraction with methylene blue, bovine hemoglobin, or N-monomethyl-L-arginine. Conversely, N-acetyl-L-cysteine augmented the flow-mediated relaxation. Furthermore, in the presence of N-acetyl-L-cysteine, the half-life of the endothelium-dependent relaxing factor was increased. In conclusion, the stimulus of flow induces the release by endothelial cells of a diffusible, short-lived factor with the attributes of a nitrovasodilator. The action of this endogenous vasodilator is augmented by the reduced thiol N-acetyl-L-cysteine.

Vascular smooth muscle influences the release of endothelium-derived relaxing factor

Conditioned medium was collected from vascular smooth-muscle cells grown in culture to determine if these cells synthesize vasoactive substances. The medium caused a short-acting endothelium-independent constriction of rat aorta, followed by a prolonged, endothelium-dependent relaxation. This relaxation was mediated through the release of endothelium-derived relaxing factor (EDRF) as it was abolished by the addition of methylene blue (5 x 10(-6) M), haemoglobin (10(-6) M) or methyl arginine, but was not affected by indomethacin (10(-5) M). Smooth-muscle medium stimulated the production of EDRF from both rat and rabbit thoracic aortic rings as well as from cultured bovine pulmonary artery endothelial cells. The prolonged stimulation of EDRF by smooth-muscle medium was not mimicked by known physiological stimuli to EDRF release; EDRF-stimulating activity was not affected when smooth-muscle cells were grown in the presence of indomethacin (10(-5) M), although serum in the medium was required. The EDRF-stimulating substance(s) in the smooth-muscle medium was heat stable and associated with a high molecular mass (30,000 greater than Mr greater than 3500) water-soluble species that is as yet unidentified.

Release of a neutrophil‐derived vascoconstrictor agent which augments platelet‐induced contractions of blood vessels in vitro

1. The effects of neutrophil-derived products on vascular tone in vitro were examined by adding purified rabbit neutrophils to siliconized organ baths containing rings of rabbit thoracic aorta. 2. Neutrophil-derived products induced a concentration-dependent contraction of the blood vessels generating 3.9 +/- 0.2 g of tension at a cell concentration of 2 X 10(6) ml-1. This contractile response was not dependent on an intact endothelium and was not ameliorated by treatment of the neutrophils with inhibitors of lipoxygenase or cyclo-oxygenase enzymes, by free radical scavengers or by the use of end organ antagonists to angiotensin II, desArg9-bradykinin, histamine, catecholamines or acetylcholine. 3. Neutrophils stimulated with phorbol myristate acetate, formyl methionyl-leucyl-phenylalanine or calcium ionophore A23187 released a contractile factor into the supernatant which produced qualitatively similar contractions compared to those elicited by incubation with intact unstimulated neutrophils. 4. Ten to twenty times more platelets were required to evoke equivalent contractions to those observed with neutrophils. However, neutrophil supernates significantly augmented platelet-mediated contractions (P less than 0.001). 5. Contractions elicited by neutrophils and supernates derived from activated neutrophils were partially antagonized by 5-hydroxytryptamine (5-HT) receptor antagonists, methysergide and ketanserin. However, the inhibition of exogenous 5-HT-induced contractions on rabbit aorta and rat stomach strips by both antagonists was greater than the inhibition of contractions produced by neutrophils and neutrophil-derived supernates. 6. Extraction of the biologically active material from supernatants of activated neutrophils into acetone, but not chloroform-methanol or ethyl acetate, suggests the contractile factor may be a protein/peptide. Partial purification on a Sephadex G100 column yields a contractile factor with a molecular weight of less than 4,000 daltons. 7. This factor may augment vascular tone, either directly or by interactions with platelets, in pathophysiological states associated with neutrophil activation and accumulation.