Endothelium-dependent vasodilation induced by Hancornia speciosa in rat superior mesenteric artery

The vasodilator effect of the ethanolic extract of leaves from Hancornia speciosa Gomes (HSE) was evaluated in superior mesenteric artery rings. HSE produced a concentration-dependent vasodilation (IC50 = 10.8 +/- 4.0 microg/mL) in arterial rings pre-contracted with phenylephrine, which was completely abolished in endothelium-denuded vessels. Endothelium-dependent vasodilation induced by HSE was strongly reduced by L-NAME (100 microM), a nitric oxide (NO) synthase inhibitor, but neither by atropine, a muscarinic receptor antagonist (1 microM), nor by indomethacin (10 microM), a cyclooxygenase inhibitor. In rings pre-contracted with 80 mM KCl, the vasodilator effect of HSE was shifted to the right and was completely abolished in the presence of L-NAME (100 microM). Similar effects were obtained in mesenteric rings pre-contracted with phenylephrine in the presence of KCl 25 mM alone or in addition to 100 microM L-NAME. In addition, BaCl2 (1 mM) dramatically reduced the vasodilation induced by HSE. Together, these findings led us to conclude that HSE induces an endothelium-dependent vasodilation in rat mesenteric artery, by a mechanism dependent on NO, on the activation of potassium channels and endothelium-derived hyperpolarizing factor release. Rutin, identified as a major peak in the HPLC fingerprint obtained for HSE, might contribute for the observed vasodilator effect, since it was able to induce an endothelium-dependent vasodilation in rat superior mesenteric arteries.     

糖尿病大鼠肠系膜动脉降钙素基因相关肽释放减少以及一氧化氮的作用

我们以前的工作已表明,内毒素可引起降钙素基因相关肽（ＣＧＲＰ）从大鼠肠系膜动脉床释放,此作用部分是通过一氧化氮介导的。我们在离体肠系膜动脉床研究了内毒素引起糖尿病大鼠ＣＣＲＰ释放的改变以及一氧化氮所起的作用。采用ＣＣＲＰ放射免疫分析法测定灌流液中ＣＣＲＰ含量,ＲＴ－ＰＣＲ法测定背根神经节ＣＧＲＰｍＲＮＡ水平。结果显示：内毒素累积灌流引起ＣＧＲＰ浓度依赖性地释放增多,此作用在糖尿病大鼠系膜动脉术明显     

Idoxifene对人乳内动脉的舒张作用

为了研究idoxifene(吲哚昔酚,一种新型雌激素受体调节剂)对人乳内动脉(human internal mammarya artery,HIMA)的舒张作用及其机制,采用离体血管灌流的方法,观察idoxifene对完整内皮和去内皮HIMA的舒张作用,以及L-NAME和美蓝(metllylene blue,MB)对这一过程的影响,并且和17β雌二醇(17β-estradiol,E2)的舒血管作用进行了比较。实验中观察到保留血管内皮时idoxifenc(0．01～10μmol／L)和E2(0．1～100μmol／I,)可以剂量依赖性地舒张血管,且血管对idoxifene的灵敏度比对E2高15倍左右,而去内皮时则无此作用;NO合成酶阻断剂L-NAME和鸟苷酸环化酶(guanylate cyclasc,GC)的抑制剂MB使idoxifene舒张HIMA的作用完全消失。上述结果表明：idoxifene能够剂量依赖性地舒张HIMA,而且比E2更有效。idoxifene的这种作用是通过NO-GC-cGMP通路实现的。     

Adrenomedullin-induced dilation of human placental arteries is modulated by an endothelium-derived constricting factor

Adrenomedullin is synthesized and secreted by fetoplacental tissues. Given that the placenta lacks autonomic innervation, we proposed that adrenomedullin acts locally to control blood flow in the placental vasculature through a balance of dilatory and constrictive pathways. Placental stem villous arteries (200 microm) from normotensive human pregnancies were dissected and mounted on a wire myograph. The vessels were preconstricted with the thromboxane A(2) mimetic U46619 (EC(80) concentration), and exposed to cumulative concentrations of adrenomedullin (1 x 10(-9) to 3 x 10(-7) mol/L). Adrenomedullin caused concentration-dependent vasorelaxation which, in endothelium-intact vessels, was attenuated in the presence of the nitric oxide synthase inhibitor L-NMMA. This suggested that the vasodilation was mediated, at least in part, through nitric oxide. However, removal of the endothelium did not similarly alter the response. Nor did L-NMMA have any effect in endothelium-denuded vessels. We hypothesized that adrenomedullin must induce release of both endothelium-derived relaxing (nitric oxide) and constricting factors. When we blocked the two major pathways through which adrenomedullin is known to induce vasodilation, by incubating the vessels with L-NMMA (nitric oxide synthase inhibitor) and Rp-cAMPS (cAMP-dependent protein kinase inhibitor), adrenomedullin induced concentration-dependent vasoconstriction. This was not mediated through endothelin, since addition of the non-specific endothelin receptor antagonist PD142893 failed to alter the response to adrenomedullin. We conclude that, in addition to increasing endothelial nitric oxide biosynthesis in placental stem villous arteries, adrenomedullin induces release of an endothelium-derived constricting factor.     

Nitric oxide-mediated vasorelaxation by Rhizoma Ligustici wallichii in isolated rat thoracic aorta.

The vasorelaxant effect of Rhizoma Ligustici wallichii and its possible mechanism of action on the vasomotor tone of the rat thoracic aortic rings were examined in an organ bath. Chloroform extracts of Rhizoma Ligustici wallichii (Ch1LW) elicited a dose-dependent, transient, relaxing response in endothelium-intact rat aorta contracted with norepinephrine (NE). This relaxant effect was abolished by removal of the endothelium and also by pretreatment with nitric oxide synthase inhibitors. Neither a muscarinic receptor antagonist nor a cyclooxygenase inhibitor altered the Ch1LW-induced relaxation. Tetramethylpyrazine, derived from Rhizoma Ligustici wallichii as a potent vasodilating component, induced a complete relaxation in both endothelium-intact and denuded rat aortas contracted by NE, but nitric oxide synthase inhibitors did not affect the relaxation. Ch1LW-induced endothelium-dependent relaxation was mediated by nitric oxide released from the endothelium, and could be caused by component(s) other than tetramethylpyrazine.     

Involvement of nitric oxide in endothelium-dependent arterial relaxation by leptin

Leptin is a polypeptide, mainly produced in white adipose tissue, and increases sympathetic nerve activity. A few studies investigated leptin's effect on peripheral vessels. We examined the vasorelaxant effects of human leptin on rat arteries. Arterial rings were precontracted with 1 x 10(-6) mol/l of phenylephrine, and leptin was superfused. Leptin relaxed phenylephrine-precontracted arterial rings in a dose-dependent manner. ED50 was calculated to 8.4 microg/ml. Removal of endothelium abolished the effects of leptin. Indomethacin (1 x 10(-5) mol/l) did not affect the vasorelaxation by leptin, whereas 1 x 10(-4) mol/l of N(omega)-nitro-L-arginine methyl ester (L-NAME) completely suppressed it. The inhibition was antagonized by 1 x 10(-4) mol/l of L-arginine. Leptin normally relaxed arterial rings during superfusion of K channel blockers, including 3 x 10(-5) mol/l of glibenclamide, 1 x 10(-6) of mol/l apamin, and 5 x 10(-7) mol/l of charybdotoxin. Low Cl(-) solution (8. 3 mmol/l) inhibited leptin-induced relaxation, but endothelium-independent vasodilatation by nitroprusside was not impaired at low Cl(-) solution. These results suggest that arterial relaxation by leptin is mediated by nitric oxide released from endothelium, and Cl(-) plays an important role in leptin-induced nitric oxide release.     

双环醇减轻超氧阴离子诱导的大鼠胸主动脉舒张功能损伤

目的：探讨双环醇（bicyclol）对超氧阴离子（O2）诱导的血管舒张功能损伤的影响。方法：采用离体器官灌流技术,观察bicyclol对离体大鼠胸主动脉环张力的影响。采用焦酚（O2的供体）建立O2损伤模型,观察bicyclol预孵育对氧化应激损伤后血管内皮依赖性舒张功能的改善作用。结果：bicyclol（10-8~10-5mol/L）对由苯肾上腺素预收缩的内皮完整主动脉环产生舒张作用,该作用可被NO合酶抑制剂L-NAME和环氧化酶抑制剂吲哚美辛阻断。500μmol/L焦酚可引起乙酰胆碱诱导的主动脉环内皮依赖性舒张反应减弱,bicyclol（10-5mol/L）预孵育45 min可减轻焦酚的损伤作用。对于吲哚美辛处理的主动脉环,bicyclol（10-5mol/L）可抑制焦酚所致的血管舒张反应降低,但这一效应未见于L-NAME处理的主动脉环。结论：bicyclol具有内皮依赖性舒血管作用,并能对抗O2引起的血管舒张功能损伤,该作用通过NO途径介导。     

Mechanisms of the renal vasodilation caused by insulin in anesthetized pigs

The present study was planned to determine the mechanisms involved in the renal vasodilation caused by insulin. Changes in flow caused by the intravenous infusion of 0.004 IU/kg/min of insulin at constant heart rate, aortic blood pressure, left ventricular contractility and blood levels of glucose and potassium in the left renal artery were assessed using an electromagnetic flowmeter. In ten pigs, infusion of insulin caused an increase in renal blood flow which averaged 12.8% of the control values. After hemodynamic variables had returned to control values, insulin infusion was repeated in five pigs following blockade of alpha-adrenergic receptors with injection of phentolamine into the renal artery and in the other five pigs following blockade of nitric oxide formation with injection in the same artery of Nomega-nitro-L-arginine methyl ester (L-NAME). After blockade of alpha-adrenergic receptors, insulin infusion caused an increase in renal blood flow which averaged 18.1% of the control values, being significantly enhanced with respect to the increase previously obtained in the same pigs. On the contrary, after blockade of nitric oxide formation insulin infusion caused a decrease in renal blood flow which averaged 6.5% of the control values. These responses were respectively abolished by the subsequent injection into the renal artery of L-NAME and phentolamine. The present study showed that the renal vasodilation caused by insulin in the anesthetized pig was the result of two opposite effects which involved a predominant vasodilation mediated by the release of nitric oxide from the endothelium and a sympathetic vasoconstrictor mechanism mediated by alpha-adrenergic receptors.     

Analysis of responses to hAmylin, hCGRP, and hADM in isolated resistance arteries from the mesenteric vascular bed of the rat

Responses to human calcitonin gene-related peptide (hCGRP) and human adrenomedullin (hADM) hAmylin were investigated in isolated mesenteric resistance arteries from the rat. The results of the present investigation show that hCGRP, hAmylin, and hADM induce dose-related vasodilator responses in isolated resistance arteries from the rat mesenteric vascular bed. Vasodilator responses to hCGRP and hAmylin were not altered after denuding the vascular endothelium, after administration of the nitric oxide synthase inhibitor L-NA, or after administration of the soluble guanylate cyclase inhibitor ODQ, suggesting that vasodilator responses to hCGRP and hAmylin are not mediated by the release of nitric oxide from the vascular endothelium and the subsequent increase in cGMP. Vasodilator responses to hCGRP, hAmylin, and hADM were not altered by the vascular selective K+(ATP) channel antagonist U-37883A. The role of the CGRP1 receptor was investigated and responses to hCGRP and hAmylin, but not hADM, were significantly reduced following administration of hCGRP-(8-37). Moreover, vasodilator responses to hCGRP and hAmylin, but not hADM, were significantly reduced by hAmylin-(8-37), suggesting that an hAmylin-(8-37)-sensitive receptor mediates responses to hCGRP and hAmylin in the rat mesenteric artery. These data suggest that hCGRP and hAmylin have direct vasodilator effects in the isolated mesenteric resistance artery that are mediated by hAmylin-(8-37)- and hCGRP-(8-37)-sensitive receptors.     

Inhibition of periarterial nerve stimulation-induced vasodilation of the mesenteric arterial bed by CGRP (8-37) and CGRP receptor desensitization

We provide the first functional evidence that calcitonin gene-related peptide (8-37) induces a direct vasoconstriction and reversibly antagonizes vasodilation of the mesenteric arterial bed induced by calcitonin gene-related peptide (CGRP) suggesting that CGRP (8-37) is a competitive antagonist of vascular CGRP receptors. Vasodilation induced by periarterial nerve stimulation was inhibited both by CGRP (8-37) and by desensitization of CGRP receptors. These results further support the evidence that the periarterial nerve stimulation-induced nonadrenergic noncholinergic vasodilation of the mesenteric vasculature is mediated by endogenous CGRP and its receptors.     

Chronic hypoxia attenuates cGMP-dependent pulmonary vasodilation

Chronic hypoxia (CH) augments endothelium-derived nitric oxide (NO)-dependent pulmonary vasodilation; however, responses to exogenous NO are reduced following CH in female rats. We hypothesized that CH-induced attenuation of NO-dependent pulmonary vasodilation is mediated by downregulation of vascular smooth muscle (VSM) soluble guanylyl cyclase (sGC) expression and/or activity, increased cGMP degradation by phosphodiesterase type 5 (PDE5), or decreased VSM sensitivity to cGMP. Experiments demonstrated attenuated vasodilatory responsiveness to the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate and to arterial boluses of dissolved NO solutions in isolated, saline-perfused lungs from CH vs. normoxic female rats. In additional experiments, the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, blocked vasodilation to NO donors in lungs from each group. However, CH was not associated with decreased pulmonary sGC expression or activity as assessed by Western blotting and cGMP radioimmunoassay, respectively. Consistent with our hypothesis, the selective PDE5 inhibitors dipyridamole and T-1032 augmented NO-dependent reactivity in lungs from CH rats, while having little effect in lungs from normoxic rats. However, the attenuated vasodilatory response to NO in CH lungs persisted after PDE5 inhibition. Furthermore, CH similarly inhibited vasodilatory responses to 8-bromoguanosine 3'5'-cyclic monophosphate. We conclude that attenuated NO-dependent pulmonary vasodilation after CH is not likely mediated by decreased sGC expression, but rather by increased cGMP degradation by PDE5 and decreased pulmonary VSM reactivity to cGMP.     

Influence of NG-monomethyl-L-arginine on endothelium-dependent relaxations in the perfused mesenteric vascular bed of the rat

Endothelium-dependent relaxation mediated by the formation of nitric oxide (NO) from L-arginine, is prevented by the arginine analog NG-monomethyl L-arginine (L-NMMA) (Palmer et al., Biochem. Biophys. Res. Comm. 153:1251-1256 (1988)). In the rat mesenteric arterial bed, incubation with L-NMMA did not prevent acetylcholine-induced relaxation, which, however, was reversed when L-NMMA was added during its maximum effect. A similar profile of action was observed with methylene blue, an inhibitor of guanylate cyclase. Methylene blue, but not L-NMMA, increased basal perfusion pressure. These data indicate that in the mesenteric arterial bed, NO formation via the L-NMMA-sensitive pathway occurs during stimulation with acetylcholine, but not under basal conditions.     

Dilazep-induced vasodilation is mediated through adenosine receptors

Administration of dilazep, an inhibitor of adenosine uptake, significantly reduced systemic arterial blood pressure and increased superior mesenteric arterial conductance without affecting the plasma adenosine levels of femoral arterial or portal venous blood. Administration of a bolus dose of 8-phenyltheophylline (8-PT), an antagonist of adenosine receptors, blocked adenosine-mediated autoregulation of the superior mesenteric artery. After the blockade of adenosine receptors by 8-PT, dilazep did not produce vasodilation. These data suggest that dilazep has a vasodilating effect in vivo that is mediated by adenosine.     

Effect of alpha-lipoic acid on vascular responses and nociception in diabetic rats.

Oxidative stress contributes to the vascular and neurological complications of diabetes mellitus. The aim was to evaluate the effects of treatment with the radical scavenger and transition metal chelator, alpha-lipoic acid, on endothelium-dependent relaxation of the mesenteric vasculature and on superior cervical ganglion blood flow in 8 week streptozotocin-induced diabetic rats. alpha-Lipoic acid effects on small nerve fiber-mediated nociception were also monitored. For the in vitro phenylephrine-precontracted mesenteric vascular bed, diabetes caused a 31% deficit in maximum endothelium-dependent relaxation to acetylcholine, and a 4-fold reduction in sensitivity. alpha-Lipoic acid gave 85% protection against these defects. Acetylcholine responses are mediated by nitric oxide and endothelium-derived hyperpolarizing factor: isolation of the latter by nitric oxide synthase blockade revealed a 74% diabetic deficit that was halved by alpha-lipoic acid. Superior cervical ganglion blood flow, 52% reduced by diabetes, was dose-dependently restored by alpha-lipoic acid (ED(50), 44 mg/kg/d). Diabetic rats exhibited mechanical and thermal hyperalgesia, which were abolished by alpha-lipoic acid treatment. Thus, diabetes impairs nitric oxide and endothelium-derived hyperpolarizing factor-mediated vasodilation. This contributes to reduced neural perfusion, and may be responsible for altered nociceptive function. The effect of alpha-lipoic acid strongly implicates oxidative stress in these events and suggests a potential therapeutic approach.     

Vascular smooth muscle relaxation by a lectin from Pisum arvense: evidences of endothelial NOS pathway

The vasorelaxant effect of the lectin of Pisum arvense (PAL) seeds was investigated in rat aorta. PAL (10-100 μg/ml) was applied on aorta rings, with or without endothelium, pre-contracted with phenylephrine (Phe; 0.1 μM). Participation of endothelium derived relaxant factors was evaluated incubating the tissue with indomethacin (10 μM), L-nitro arginine methyl ester (L-NAME, 100 μM) and tetraethylammonium (TEA, 5 mM) before addition of PAL. The role of the lectin domain was investigated by addition of PAL into tissue in presence of glucose (3x 10?? M), or N-acetyl Dglucosamine (GlcNAc; 3 x 10?? M). The importance of extracellular calcium (Ca2?e) or interaction with muscarinic receptors in the relaxant effect was evaluated by addition of PAL into aorta rings containing calcium free solution (OCa) and atropine (1 μ M), respectively. PAL induced concentration-dependent relaxation in endothelized aorta (IC50 =58.38 ± 1.87 μg/ml), which was reversed by L-NAME and glucose. The lectin effect was totally inhibited when the preparation was inserted in OCa, but not in presence of atropine. Summarizing, our data showed a relaxant effect of PAL in isolated rat aorta rings in presence of endothelium, suggestive of interaction between the lectin carbohydrate binding sites with specific receptors located in vascular endothelial cells leading to nitric oxide synthase activation. This effect seems to require Ca2?e but is independent on muscarinic receptors interaction.     

Maternal vasodilation in pregnancy: the emerging role of relaxin

Pregnancy is a unique physiological condition of profound maternal renal and systemic vasodilation. Our goal has been to unveil the reproductive hormones mediating this remarkable vasodilatory state and the underlying molecular mechanisms. In addition to advancing our knowledge of pregnancy physiology, reaching this goal may translate into therapeutics for pregnancy pathologies such as preeclampsia and for diseases associated with vasoconstriction and arterial stiffness in nonpregnant women and men. An emerging player is the 6 kDa corpus luteal hormone relaxin, which circulates during pregnancy. Relaxin administration to rats and humans induces systemic and renal vasodilation regardless of sex, thus mimicking the pregnant condition. Immunoneutralization or elimination of the source of circulating relaxin prevents renal and systemic vasodilation in midterm pregnant rats. Infertile women who become pregnant by donor eggs (IVF with embryo transfer) lack a corpus luteum and circulating relaxin, and they show a markedly subdued gestational increase in glomerular filtration rate. These data implicate relaxin as one of the vasodilatory reproductive hormones of pregnancy. There are different molecular mechanisms underlying the so-called rapid and sustained vasodilatory actions of relaxin. The former is mediated by Gα(i/o) protein coupling to phosphatidylinositol-3 kinase/Akt (protein kinase B)-dependent phosphorylation and activation of endothelial nitric oxide synthase, the latter by vascular endothelial and placental growth factors, and increases in arterial gelatinase(s) activity. The gelatinases, in turn, hydrolyze big endothelin (ET) at a gly-leu bond to form ET(1-32), which activates the endothelial ET(B) receptor/nitric oxide vasodilatory pathway.     

N-acetylcysteine-induced vasodilation involves voltage-gated potassium channels in rat aorta

AimsN-acetylcysteine (NAC) has a protective effect against vascular dysfunction by decreasing the level of reactive oxygen species (ROS) in experimental and human hypertension. This study was designed to examine whether NAC would relax vascular rings in vitro via nitric oxide–cyclic guanosine monophosphate (NO–cGMP) pathway, extracellular Ca²⁺ and/or K⁺ channels.Main methodsRat aortic arteries were mounted in an organ bath, contracted with 0.1, 0.5 or 1 µmol/L phenylephrine to plateau, and the vasodilatory effect of NAC was examined in the absence or presence of ROS scavengers, inhibitors of NO–cGMP pathway or K⁺ channels. Vascular smooth muscle cells (VSMCs) were loaded with a calcium sensitive fluorescent dye fluo-3 AM, and [Ca²⁺]_i was determined with laser-scanning confocal microscopy.Key findingsNAC (0.1–4 mmol/L) dose-dependently relaxed rat aorta pre-contracted with phenylephrine. Endothelium removal, endothelial nitric oxide synthase inhibitor N^ω-Nitro-l-arginine (L-NNA) (100 µmol/L) or soluble guanylyl cyclase (sGC) inhibitor (ODQ) (10 µmol/L) did not affect NAC-induced vasodilation. In contrast, NAC-induced vasodilation was blunted after extracellular calcium was removed and calcium imaging showed that 4 mmol/L NAC quickly decreased [Ca²⁺]_i in fluo-3 AM loaded VSMCs. NAC-induced vasodilation was significantly reduced in the presence of voltage-gated K⁺ channels (Kv) inhibitor 4-aminopyridine (4-AP).SignificanceThe vasodilatory effect of NAC may be explained at least partly by activation of voltage-gated K⁺ channels.     

乙酰胆碱不依赖NO的释放引起耳蜗螺旋动脉平滑肌细胞的超极化

目的：乙酰胆碱（ACh）不仅是神经递质,也是一种有效的血管舒张物质参与许多血管床的调节活动。本实验观察ACh引起耳蜗螺旋动脉平滑肌细胞超极化的离子机制以及NO在超极化反应中的可能作用。方法：在豚鼠离体耳蜗螺旋动脉标本上,运用细胞内微电极技术记录外源性的ACh引起的反应。结果：在保持灌流液中含有5mmol／L K^＋以及最小纵向张力的情况下,ACh（0．1—10μmol／L）引起低静息膜电位细胞明显的超极化反应,而引起高静息膜电位细胞明显的去极化反应。ACh引起的平滑肌细胞超极化反应是浓度依赖性的（ACh的浓度是1μmol／L和10／μmol／L时,分别引起超极化的幅度是22和30mV,n=7）。ACh引起的超极化反应能被阿托品（atropine,0．1～1μmol／L,n=6）或DAMP（50～100nmol／L,n=6,一种选择性的地受体的拮抗剂）所阻断,同时也可被BAPTA—AM（10μmol／L,n=7,一种可通过细胞膜的Ca^2＋螯合剂）或eharybdotoxin＋apamin（50-100nmol／L,n=4,两种Ca^2＋激活K^＋通道的阻断剂）所阻断,但是Nω-nitro-L-arginine methyl ester（L-NAME,300μmol／L,n=8,一种NO合成酶的完全抑制剂,n≥5）或glipizide（10μmol／L,ATP敏感性的K^＋通道阻断剂,n=4）或indomethacin（10μmol／L,环氧合酶的抑制剂,n=4）不能阻断ACh引起的超极化反应。结论：ACh通过激活内皮细胞的M3受体,开放钙依赖的钾通道．进而引起耳蜗螺旋动脉平滑肌细胞产生超极化反应,并且这一超极化反应与内皮细胞NO的产生和释放无关。     

Nebivolol-induced vasodilation of renal afferent arterioles involves β3-adrenergic receptor and nitric oxide synthase activation

Nebivolol is a β(1)-adrenergic blocker that also elicits renal vasodilation and increases the glomerular filtration rate (GFR). However, its direct actions on the renal microvasculature and vasodilator mechanism have not been established. We used the in vitro blood-perfused juxtamedullary nephron technique to determine the vasodilator effects of nebivolol and to test the hypothesis that nebivolol induces vasodilation of renal afferent arterioles via an nitric oxide synthase (NOS)/nitric oxide (NO)/soluble guanylate cyclase (sGC)/cGMP pathway and the afferent arteriolar vasodilation effect may be mediated through the release of NO by activation of NOS via a β(3)-adrenoceptor-dependent mechanism. Juxtamedullary nephrons were superfused with nebivolol either alone or combined with the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or the NOS inhibitor N(ω)-nitro-l-arginine (l-NNA) or the β-blockers metoprolol (β(1)), butoxamine (β(2)), and SR59230A (β(3)). Nebivolol (100 μmol/l) markedly increased afferent and efferent arteriolar diameters by 18.9 ± 3.0 and 15.8 ± 1.8%. Pretreatment with l-NNA (1,000 μmol/l) or ODQ (10 μmol/l) decreased afferent vasodilator diameters and prevented the vasodilator effects of nebivolol (2.0 ± 0.2 and 2.4 ± 0.6%). Metoprolol did not elicit significant changes in afferent vasodilator diameters and did not prevent the effects of nebivolol to vasodilate afferent arterioles. However, treatment with SR59230A, but not butoxamine, markedly attenuated the vasodilation responses to nebivolol. Using a monoclonal antibody to β(3)-receptors revealed predominant immunostaining on vascular and glomerular endothelial cells. These data indicate that nebivolol vasodilates both afferent and efferent arterioles and that the afferent vasodilator effect is via a mechanism that is independent of β(1)-receptors but is predominantly mediated via a NOS/NO/sGC/cGMP-dependent mechanisms initiated by activation of endothelial β(3)-receptors.     

Characteristics of myogenic reactivity in isolated rat mesenteric veins

Mechanisms of mechanically induced venous tone and its interaction with the endothelium and key vasoactive neurohormones are not well established. We investigated the contribution of the endothelium, l-type voltage-operated calcium channels (L-VOCCs), and PKC and Rho kinase to myogenic reactivity in mesenteric vessels exposed to increasing transmural pressure. The interaction of myogenic reactivity with norepinephrine (NE) and endothelin-1 (ET-1) was also investigated. Pressure myography was used to study isolated, cannulated, third-order rat mesenteric small veins and arteries. NE and ET-1 concentration response curves were constructed at low, intermediate, and high transmural pressures. Myogenic reactivity was not altered by nitric oxide synthase inhibition with N(ω)-nitro-L-arginine (L-NNA; 100 μM) or endothelium removal in both vessels. L-VOCCs blockade (nifedipine, 1 μM) completely abolished arterial tone, while only partially reducing venous tone. PKC (chelerythrine, 2.5 μM) and Rho kinase (Y27632, 3 μM) inhibitors largely abolished venous and arterial myogenic reactivity. There was no significant difference in the sensitivity of NE or ET-1-induced contractions within vessels. However, veins were more sensitive to NE and ET-1 when compared with corresponding arteries at low, intermediate, and high transmural pressures, respectively. These results suggest that 1) myogenic factors are important contributors to net venous tone in mesenteric veins; 2) PKC and Rho activation are important in myogenic reactivity in both vessels, while l-VOCCs play a limited role in the veins vs. the arteries, and the endothelium does not appear to modulate myogenic reactivity in either vessel type; and 3) mesenteric veins maintain an enhanced sensitivity to NE and ET-1 compared with the arteries when studied under conditions of changing transmural distending pressure.