Nitric oxide and sodium nitroprusside-induced relaxation of the human umbilical artery

Fetal sex and the relative reactivity of human umbilical vein and arteries are key determinants in potential beneficial effects of phosphodiesterase inhibitors

Intrauterine growth restriction (IUGR) is a common complication of pregnancy. We previously demonstrated that IUGR is associated with an impaired nitric oxide (NO)-induced relaxation in the human umbilical vein (HUV) of growth-restricted females compared to appropriate for gestational age (AGA) newborns. We found that phosphodiesterase (PDE) inhibition improved NO-induced relaxation in HUV, suggesting that PDEs could represent promising targets for therapeutic intervention. This study aimed to investigate the effects of PDE inhibition on human umbilical arteries (HUAs) compared to HUV. Umbilical vessels were collected in IUGR and AGA term newborns. NO-induced relaxation was studied using isolated vessel tension experiments in the presence or absence of the nonspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX). PDE1B, PDE1C, PDE3A, PDE4B, and PDE5A were investigated by Western blot. NO-induced vasodilation was similar between IUGR and AGA HUAs. In HUAs precontracted with serotonin, IBMX enhanced NO-induced relaxation only in IUGR females, whereas in HUV IBMX increased NO-induced relaxation in all groups except IUGR males. In umbilical vessels preconstricted with the thromboxane A2 analog U46619, IBMX improved NO-induced relaxation in all groups to a greater extent in HUV than HUAs. However, the PDE protein content was higher in HUAs than HUV in all study groups. Therefore, the effects of PDE inhibition depend on the presence of IUGR, fetal sex, vessel type, and vasoconstrictors implicated. Despite a higher PDE protein content, HUAs are less sensitive to IBMX than HUV, which could lead to adverse effects of PDE inhibition in vivo by impairment of the fetoplacental hemodynamics.NEW & NOTEWORTHY The effects of phosphodiesterase inhibition on the umbilical circulation depend on the presence of intrauterine growth restriction, the fetal sex, vessel type, and vasoconstrictors implicated. The human umbilical vascular tone regulation is complex and depends on the amount and activity of specific proteins but also probably on the subcellular organization mediating protein interactions. Therefore, therapeutic interventions using phosphodiesterase inhibitors to improve the placental-fetal circulation should consider fetal sex and both umbilical vein and artery reactivity.

Altered placental ion channel gene expression in preeclamptic high-altitude pregnancies

High-altitude (>2,500 m) residence increases the risk of pregnancy vascular disorders such as fetal growth restriction and preeclampsia, each characterized by impaired placental function. Genetic attributes of highland ancestry confer relative protection against vascular disorders of pregnancy at high altitudes. Although ion channels have been implicated in placental function regulation, neither their expression in high-altitude placentas nor their relationship to high-altitude preeclampsia has been determined. Here, we measured the expression of 26 ion-channel genes in placentas from preeclampsia cases and normotensive controls in La Paz, Bolivia (3,850 m). In addition, we correlated gene transcription to maternal and infant ancestry proportions. Gene expression was assessed by PCR, genetic ancestry evaluated by ADMIXTURE, and ion channel proteins localized by immunofluorescence. In preeclamptic placentas, 11 genes were downregulated (ABCC9, ATP2A2, CACNA1C, KCNE1, KCNJ8, KCNK3, KCNMA1, KCNQ1, KCNQ4, PKD2, and TRPV6) and two were upregulated (KCNQ3 and SCNN1G). KCNE1 expression was positively correlated with high-altitude Amerindian ancestry and negatively correlated with non-high altitude. SCNN1G was negatively correlated with African ancestry, despite minimal African admixture. Most ion channels were localized in syncytiotrophoblasts (Cav1.2, TRPP2, TRPV6, and Kv7.1), whereas expression of Kv7.4 was primarily in microvillous membranes, Kir6.1 in chorionic plate and fetal vessels, and MinK in stromal cells. Our findings suggest a role for differential placental ion channel expression in the development of preeclampsia. Functional studies are needed to determine processes affected by these ion channels in the placenta and whether therapies directed at modulating their activity could influence the onset or severity of preeclampsia.

Evaluation of the bisphenol A-induced vascular toxicity on human umbilical artery

Bisphenol A (BPA) is one of the most widely used synthetic compound in the manufacture of polycarbonate plastics and epoxy resins. Worryingly, BPA is an endocrine disrupting chemical (EDC) with an estrogenic, androgenic, or anti-androgenic activities. However, the vascular implications of BPA exposome in pregnancy is unclear. In this sense, the present work proposed to understand how BPA exposure impair the vasculature of the pregnant women. To elucidate this, ex vivo studies were performed using human umbilical arteries to explore the acute and chronic effects of BPA. The mode of action of BPA was also explored by analysing the activity (by ex vivo studies) and expression (in vitro studies) analysis of Ca²⁺ and K⁺-channels and soluble guanyl cyclase. Moreover, in silico docking simulations were performed to unveil the modes of interactions of BPA with the proteins involved in these signalling pathways. Our study showed that the exposure to BPA may modify the vasorelaxant response of HUA, interfering with NO/sGC/cGMP/PKG pathway by modulation of sGC and activation of BKCa channels. Moreover, our findings suggest that BPA can modulate the HUA reactivity, increasing the L-type Ca²⁺ Channels (LTCC) activity, a common vascular response observed in hypertensive disorders of pregnancy.

Specific dilation pattern in placental circulation and the NO/sGC role in preeclampsia placental vessels

Objective

Endothelial functions in controlling blood flow in placental circulation are still unclear. The present study compares vascular dilations between placental circulation and other vessels, as well as between normal and preeclampsia placental vessels.

Methods

Placental, umbilical, and other vessels (cerebral and mesenteric arteries) were collected from humans, sheep, and rats. Vasodilation was tested by JZ101 and DMT. Q-PCR, Western blot, and Elisa were used for molecular experiments.

Results

Endothelium-dependent/derived vasodilators, including acetylcholine, bradykinin, prostacyclin, and histamine, mediated no or minimal dilation in placental circulation, which was different from that in other vessels in sheep and rats. There were lower mRNA expressions of muscarinic receptors, histamine receptors, bradykinin receptor 2, endothelial nitric oxide synthesis (eNOS), and less nitric oxide (NO) in human umbilical vessels when compared with placental vessels. Exogenous NO donors (sodium nitroprusside, SNP) and soluble guanylate cyclase (sGC) activators (Bay41-2272) decreased the baseline of vessel tone in placental circulation in humans, sheep, and rats, but not in other arteries. The sGC inhibitor ODQ suppressed the reduced baseline caused by the SNP. The decreased baseline by SNP or Bay41-2272 was higher in placental vessels than in umbilical vessels, suggesting that the role of NO/sGC is more important in the placenta. NO concentrations in preeclampsia placental vessels were lower than those in control, while no significant change was found in umbilical plasma between the two groups. eNOS expression was similar between normal and preeclampsia placental vessels, but phosphorylated eNOS levels were significantly lower in preeclampsia. Following serotonin, SNP or Bay41-2272-mediated dilations were weaker in preeclampsia placental vessels. The decreased amplitude of SNP- or Bay41-2272 at baseline was smaller in preeclampsia. The decreased amplitudes of ODQ + SNP were comparable between the two groups. Despite higher beta sGC expression, sGC activity in the preeclampsia placenta was lower.

Conclusion

This study demonstrated that receptor-mediated endothelium-dependent dilation in placental circulation was significantly weaker than other vessels in various species. The results, showed firstly, that exogenous NO played a role in regulating the baseline tone of placental circulation via sGC. Lower NO production and decreased NO/sGC could be one of the reasons for preeclampsia. The findings contribute to understanding specific features of placental circulation and provide information about preeclampsia in placental vessels.

17β-Estradiol Treatment Improves Acetylcholine-Induced Relaxation of Mesenteric Arteries in Ovariectomized UC Davis Type 2 Diabetes Mellitus Rats in Prediabetic State

We recently reported sex differences in mesenteric arterial function of the UC Davis type-2 diabetes mellitus (UCD-T2DM) rats as early as the prediabetic state. We reported that mesenteric arteries (MA) from prediabetic male rats exhibited a greater impairment compared to that in prediabetic females. However, when females became diabetic, they exhibited a greater vascular dysfunction than males. Thus, the aim of this study was to investigate whether the female sex hormone, estrogen preserves mesenteric arterial vasorelaxation in UCD-T2DM female rats at an early prediabetic state. Age-matched female Sprague Dawley and prediabetic (PD) UCD-T2DM rats were ovariectomized (OVX) and subcutaneously implanted with either placebo or 17β-estradiol (E_2, 1.5 mg) pellets for 45 days. We assessed the contribution of endothelium-derived relaxing factors (EDRF) to acetylcholine (ACh)-induced vasorelaxation, using pharmacological inhibitors. Responses to sodium nitroprusside (SNP) and phenylephrine (PE) were also measured. Additionally, metabolic parameters and expression of some targets associated with vascular and insulin signaling were determined. We demonstrated that the responses to ACh and SNP were severely impaired in the prediabetic state (PD OVX) rats, while E₂ treatment restored vasorelaxation in the PD OVX + E₂. Moreover, the responses to PE was significantly enhanced in MA of PD OVX groups, regardless of placebo or E₂ treatment. Overall, our data suggest that 1) the impairment of ACh responses in PD OVX rats may, in part, result from the elevated contractile responses to PE, loss of contribution of endothelium-dependent hyperpolarization (EDH) to vasorelaxation, and a decreased sensitivity of MA to nitric oxide (NO), and 2) the basis for the protective effects of E₂ may be partly attributed to the elevation of the NO contribution to vasorelaxation and its interaction with MA as well as potential improvement of insulin signaling. Here, we provide the first evidence of the role of E₂ in protecting MA from early vascular dysfunction in prediabetic female rats.

Calcitonin Gene Related Peptide, Adrenomedullin, and Adrenomedullin 2 Function in Uterine Artery During Human Pregnancy

RATIONALE

Calcitonin gene-related peptide (CGRP) and its family members adrenomedullin (ADM) and adrenomedullin 2 (ADM2; also known as intermedin) support vascular adaptions in rat pregnancy.

OBJECTIVE

This study aimed to assess the relaxation response of uterine artery (UA) for CGRP, ADM, and ADM2 in nonpregnant and pregnant women and identify the involved mechanisms.

FINDINGS

(1) Segments of UA from nonpregnant women that were precontracted with U46619 (1μM) in vitro are insensitive to the hypotensive effects of CGRP, ADM, and ADM2; (2) CGRP, ADM, and ADM2 (0.1-100nM) dose dependently relax UA segments from pregnant women with efficacy for CGRP > ADM = ADM2; (3) the relaxation responses to CGRP, ADM, and ADM2 are differentially affected by the inhibitors of nitric oxide (NO) synthase (L-NAME), adenylyl cyclase (SQ22536), apamin, and charybdotoxin; (4) UA smooth muscle cells (UASMC) express mRNA for calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP)1 and RAMP2 but not RAMP3; (5) receptor heterodimer comprising CRLR/RAMP1 and CRLR/RAMP2 but not CRLR/RAMP3 is present in UA; (6) soluble fms-like tyrosine kinase (sFLT-1) and TNF-α treatment decrease the expression of RAMP1 mRNA (P < 0.05) in UASMC; and (7) sFLT-1 treatment impairs the association of CRLR with all 3 peptides while TNF-α inhibits the interaction of CGRP but not ADM or ADM2 with CRLR in UASMC (P < 0.05).

CONCLUSIONS

Relaxation sensitivity of UA for CGRP, ADM, and ADM2 is increased during pregnancy via peptide-specific involvement of NO system and endothelium-derived hyperpolarizing factors; vascular disruptors such as sFLT-1 and TNFα adversely impact their receptor system in UASMC.

Implications of Endothelial Cell-Mediated Dysfunctions in Vasomotor Tone Regulation

Cardiovascular diseases (CVD) constitute the major cause of death worldwide and show a higher prevalence in the adult population. The human umbilical cord consistsof two arteries and one vein, both composed of three tunics. The tunica intima, lined with endothelial cells, regulates vascular tone through the production/release of vasoregulatory substances. These substances can be vasoactive factors released by endothelial cells (ECs) that cause vasodilation (NO, PGI2, EDHF, and Bradykinin) or vasoconstriction (ET1, TXA2, and Ang II) depending on the cell type (ECs or SMC) that reacts to the stimulus. Vascular studies using ECs are important for the analysis of cardiovascular diseases since endothelial dysfunction is an important CVD risk factor. In this paper, we will address the morphological characteristics of the human umbilical cord and its component vessels. the constitution of the vascular endothelium, and the evolution of human umbilical cord-derived endothelial cells when isolated. Moreover, the role played by the endothelium in the vasomotor tone regulation, and how it may be associated with the existence of CVD, were discussed.

Clinical Importance of the Human Umbilical Artery Potassium Channels

Potassium (K⁺) channels are usually predominant in the membranes of vascular smooth muscle cells (SMCs). These channels play an important role in regulating the membrane potential and vessel contractility-a role that depends on the vascular bed. Thus, the activity of K⁺ channels represents one of the main mechanisms regulating the vascular tone in physiological and pathophysiological conditions. Briefly, the activation of K⁺ channels in SMC leads to hyperpolarization and vasorelaxation, while its inhibition induces depolarization and consequent vascular contraction. Currently, there are four different types of K⁺ channels described in SMCs: voltage-dependent K⁺ (K_V) channels, calcium-activated K⁺ (K_Ca) channels, inward rectifier K⁺ (Kir) channels, and 2-pore domain K⁺ (K_2P) channels. Due to the fundamental role of K⁺ channels in excitable cells, these channels are promising therapeutic targets in clinical practice. Therefore, this review discusses the basic properties of the various types of K⁺ channels, including structure, cellular mechanisms that regulate their activity, and new advances in the development of activators and blockers of these channels. The vascular functions of these channels will be discussed with a focus on vascular SMCs of the human umbilical artery. Then, the clinical importance of K⁺ channels in the treatment and prevention of cardiovascular diseases during pregnancy, such as gestational hypertension and preeclampsia, will be explored.

UV-B Filter Octylmethoxycinnamate Induces Vasorelaxation by Ca2+ Channel Inhibition and Guanylyl Cyclase Activation in Human Umbilical Arteries

Ultraviolet (UV) filters are chemicals widely used in personal care products (PCPs). Due to their effect as endocrine disruptor compounds (EDCs), the toxicity of UV filters is a current concern for human health. EDC exposure may be correlated to cardiovascular diseases (CVD), but to our knowledge, no studies assessed the UV filters effects as human EDCs at the vascular level. Octylmethoxycinnamate (OMC) is the world's most widely used UV-B filter, present in more than 90% of PCPs. Due to its demonstrated multiple hormonal activities in animal models, this substance is also suspected to be a human EDC. The purpose of this study was to assess the rapid/short-term effects of OMC on arterial tonus and analyse its mode of action (MOA). Using human umbilical arteries, the endocrine effects of OMC were evaluated in in vitro (cellular and organ) experiments by planar cell surface area (PCSA) and organ bath, respectively. Our data show that OMC induces a rapid/short-term smooth muscle relaxation acting through an endothelium-independent MOA, which seems to be shared with oestrogens, involving an activation of soluble guanylyl cyclase (sGC) that increases the cyclic guanosine monophosphate (cGMP) intracellular levels and an inhibition of L-type voltage-operated Ca²⁺ channels (L-Type VOCC).

How is the human umbilical artery regulated?

The purpose of this review is to present an update of the main mechanisms involved in the physiological regulation of contraction and relaxation of the human umbilical artery (HUA) smooth muscle cells. A literature review was performed based on the analysis of papers available on PubMed. The most important and relevant studies regarding the regulation of the HUA are presented in this article. The vascular smooth muscle is a highly specialized structure, whose main function is to regulate the vascular tonus. This is controlled by a balance between the cellular signaling pathways that mediate contraction and relaxation. The cells responsible for the contractile property of this muscle are the smooth muscle cells (SMC), and an excellent source of these cells is the HUA, involved in fetoplacental circulation. Since the umbilical blood vessels are not innervated, the HUA tonus is modulated by vasoactive substances that regulate the contractile process. The main vasoactive substances that induce contraction are serotonin, histamine, thromboxane, bradykinin, endothelin 1 and prostaglandin F2α, that are linked to the activation of proteins G_q and G_i/0 . On the other hand, the main vasorelaxation mechanisms are the activation of adenyl and guanil cyclases, potassium channels and the inhibition of calcium channels. The SMC from the HUA allow the study of different cellular mechanisms and their functions. Therefore, these cells are an important tool to study the mechanisms regulating the contractility of this artery, allowing to detect potential therapeutic targets to treat HUA disorders (gestational hypertension and pre-eclampsia).

Voltage-gated potassium channels and NOS contribute to a sustained cutaneous vasodilation elicited by local heating in an interactive manner in young adults

Local skin heating to 42°C causes rapid increases in cutaneous perfusion (initial peak), followed by a brief nadir and subsequent sustained elevation (plateau). Several studies have demonstrated that nitric oxide synthase (NOS) largely contributes to the plateau response during local heating. In this study, we tested the hypothesis that voltage-gated potassium (Kv) channels contribute to the plateau of the cutaneous vasodilation during local heating through NOS-dependent mechanisms. Eleven young males (25±4years) participated in this study wherein cutaneous vascular conductance (CVC) was measured at four intradermal microdialysis sites that were continuously perfused with either 1) lactated Ringer (Control), 2) 10mM 4-aminopyridine (Kv channel blocker), 3) 10mM Nω-Nitro-L-arginine (NOS inhibitor), or 4) a combination of 4-aminopyridine and Nω-Nitro-L-arginine. In comparison to the Control site, the inhibition of Kv channels alone attenuated the increase in CVC observed at the initial peak, nadir, and plateau phases measured during local heating; in contrast, the inhibition of NOS alone attenuated the increase in CVC at the nadir and plateau phases only (e.g., plateau response: Control site: 59±5%max, Kv channel blockade site: 49±8%max, NOS inhibition site: 35±11%max, combined inhibition site: 40±12%max). Further, no effect of Kv channel blockade on CVC was measured at any phase of the local heating response when the modulating influence of NOS was simultaneously removed. We show that Kv channels and NOS contribute to the local heating mediated sustained increase (i.e., plateau) in cutaneous vasodilation in an interactive manner. (243/250 words).

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth

Potassium channels importantly contribute to the regulation of vascular smooth muscle (VSM) contraction and growth. They are the dominant ion conductance of the VSM cell membrane and importantly determine and regulate membrane potential. Membrane potential, in turn, regulates the open-state probability of voltage-gated Ca²⁺ channels (VGCC), Ca²⁺ influx through VGCC, intracellular Ca²⁺, and VSM contraction. Membrane potential also affects release of Ca²⁺ from internal stores and the Ca²⁺ sensitivity of the contractile machinery such that K⁺ channels participate in all aspects of regulation of VSM contraction. Potassium channels also regulate proliferation of VSM cells through membrane potential-dependent and membrane potential-independent mechanisms. VSM cells express multiple isoforms of at least five classes of K⁺ channels that contribute to the regulation of contraction and cell proliferation (growth). This review will examine the structure, expression, and function of large conductance, Ca²⁺-activated K⁺ (BK_Ca) channels, intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels, multiple isoforms of voltage-gated K⁺ (K_V) channels, ATP-sensitive K⁺ (K_ATP) channels, and inward-rectifier K⁺ (K_IR) channels in both contractile and proliferating VSM cells.

Stimulation of calcium-sensing receptors induces endothelium-dependent vasorelaxations via nitric oxide production and activation of IKCa channels

Stimulation of vascular calcium-sensing receptors (CaSRs) is reported to induce both constrictions and relaxations. However, cellular mechanisms involved in these responses remain unclear. The present study investigates the effect of stimulating CaSRs on vascular contractility and focuses on the role of the endothelium, nitric oxide (NO) and K(+) channels in these responses. In wire myography studies, increasing [Ca(2+)]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine pre-contracted rabbit mesenteric arteries. [Ca(2+)]o-induced relaxations were dependent on a functional endothelium, and were inhibited by the negative allosteric CaSR modulator Calhex-231. [Ca(2+)]o-induced relaxations were reduced by inhibitors of endothelial NO synthase, guanylate cyclase, and protein kinase G. CaSR activation also induced NO production in freshly isolated endothelial cells (ECs) in experiments using the fluorescent NO indicator DAF-FM. Pre-treatment with inhibitors of large (BKCa) and intermediate (IKCa) Ca(2+)-activated K(+) channels (iberiotoxin and charybdotoxin), and Kv7 channels (linopirdine) also reduced [Ca(2+)]o-induced vasorelaxations. Increasing [Ca(2+)]o also activated IKCa currents in perforated-patch recordings of isolated mesenteric artery ECs. These findings indicate that stimulation of CaSRs induces endothelium-dependent vasorelaxations which are mediated by two separate pathways involving production of NO and activation of IKCa channels. NO stimulates PKG leading to BKCa activation in vascular smooth muscle cells, whereas IKCa activity contributes to endothelium-derived hyperpolarisations.

Nitric oxide regulation of migrating motor complex: randomized trial of N(G)-monomethyl-L-arginine effects in relation to muscarinic and serotonergic receptor blockade

AIM

The migrating motor complex (MMC) propels contents through the gastrointestinal tract during fasting. Nitric oxide (NO) is an inhibitory neurotransmitter in the gastrointestinal tract. Little is known about how NO regulates the MMC. In this study, the aim was to examine nitrergic inhibition of the MMC in man using N(G)-monomethyl-L-arginine (L-NMMA) in combination with muscarinic receptor antagonist atropine and 5-HT3 receptor antagonist ondansetron.

METHODS

Twenty-six healthy volunteers underwent antroduodenojejunal manometry for 8 h with saline or NO synthase (NOS) inhibitor L-NMMA randomly injected I.V. at 4 h with or without atropine or ondansetron. Plasma ghrelin, motilin and somatostatin were measured by ELISA. Intestinal muscle strip contractions were investigated for NO-dependent mechanisms using L-NMMA and tetrodotoxin. NOS expression was localized by immunohistochemistry.

RESULTS

L-NMMA elicited premature duodenojejunal phase III in all subjects but one, irrespective of atropine or ondansetron. L-NMMA shortened MMC cycle length, suppressed phase I and shifted motility towards phase II. Pre-treatment with atropine extended phase II, while ondansetron had no effect. L-NMMA did not change circulating ghrelin, motilin or somatostatin. Intestinal contractions were stimulated by L-NMMA, insensitive to tetrodotoxin. NOS immunoreactivity was detected in the myenteric plexus but not in smooth muscle cells.

CONCLUSION

Nitric oxide suppresses phase III of MMC independent of muscarinic and 5-HT3 receptors as shown by nitrergic blockade, and acts through a neurocrine disinhibition step resulting in stimulated phase III of MMC independent of cholinergic or 5-HT3 -ergic mechanisms. Furthermore, phase II of MMC is governed by inhibitory nitrergic and excitatory cholinergic, but not 5-HT3 -ergic mechanisms.

Nitrergic neuromuscular transmission in the mouse internal anal sphincter is accomplished by multiple pathways and postjunctional effector cells

The effector cells and second messengers participating in nitrergic neuromuscular transmission (NMT) were investigated in the mouse internal anal sphincter (IAS). Protein expression of guanylate cyclase (GCα, GCβ) and cyclic GMP-dependent protein kinase I (cGKI) were examined in cryostat sections with dual-labeling immunohistochemical techniques in PDGFRα(+) cells, interstitial cells of Cajal (ICC), and smooth muscle cells (SMC). Gene expression levels were determined with quantitative PCR of dispersed cells from Pdgfrα(egfp/+), Kit(copGFP/+), and smMHC(Cre-egfp) mice sorted with FACS. The relative gene and protein expression levels of GCα and GCβ were PDGFRα(+) cells > ICC ≫ SMC. In contrast, cGKI gene expression sequence was SMC = ICC > PDGFRα(+) cells whereas cGKI protein expression sequence was neurons > SMC ≫ ICC = PDGFRα(+) cells. The functional role of cGKI was investigated in cGKI(-/-) mice. Relaxation with 8-bromo (8-Br)-cGMP was greatly reduced in cGKI(-/-) mice whereas responses to sodium nitroprusside (SNP) were partially reduced and forskolin responses were unchanged. A nitrergic relaxation occurred with nerve stimulation (NS, 5 Hz, 60 s) in cGKI(+/+) and cGKI(-/-) mice although there was a small reduction in the cGKI(-/-) mouse. N(ω)-nitro-l-arginine (l-NNA) abolished responses during the first 20-30 s of NS in both animals. The GC inhibitor ODQ greatly reduced or abolished SNP and nitrergic NS responses in both animals. These data confirm an essential role for GC in NO-induced relaxation in the IAS. However, the expression of GC and cGKI by all three cell types suggests that each may participate in coordinating muscular responses to NO. The persistence of nitrergic NMT in the cGKI(-/-) mouse suggests the presence of a significant GC-dependent, cGKI-independent pathway.

Diversity of potassium channels in human umbilical artery smooth muscle cells: a review of their roles in human umbilical artery contraction

Through their control of cell membrane potential, potassium (K(+)) channels are among the best known regulators of vascular tone. This article discusses the expression and function of K(+) channels in human umbilical artery smooth muscle cells (HUASMCs). We review the bibliographic reports and also present single-channel data recorded in freshly isolated cells. Electrophysiological properties of big conductance, voltage- and Ca(2+)-sensitive K(+) channel and voltage-dependent K(+) channels are clearly established in this vessel, where they are involved in contractile state regulation. Their role in the maintenance of membrane potential is an important control mechanism in the determination of the vessel diameter. Additionally, small conductance Ca(2+)-sensitive K(+) channels, 2-pore domains K(+) channels and inward rectifier K(+) channels also appear to be present in HUASMCs, while intermediate conductance Ca(2+)-sensitive K(+) channels and ATP-sensitive K(+) channels could not be identified. In both cases, additional investigation is necessary to reach conclusive evidence of their expression and/or functional role in HUASMCs. Finally, we discuss the role of K(+) channels in pregnancy-related pathologies like gestational diabetes and preeclampsia.

Involvement of guanylate cyclase and K+ channels in relaxation evoked by ferulate nitrate in rat aorta artery

Vasorelaxant properties of N-2-(ferulamidoethyl)-nitrate (ferulate nitrate, FLNT), a newly synthesized nitrate, were compared with those of isosorbide dinitrate, nicorandil, nitroglycerin, and 8-bromoguanosine 3,5-cyclic monophosphate (8-Br-cGMP) in rat aorta pre-contracted by phenylephrine. FLNT produced vasorelaxation in a concentration-dependent manner (0.1 - 100 µM). The degree of relaxation induced by FLNT was similar to that induced by isosorbide dinitrate. In addition, removal of endothelium did not affect the relaxant effect of FLNT. FLNT caused a rightward shift of the cumulative concentration-response curves of phenylephrine and reduced the maximal efficacy of contraction. 1H-[1,2,4]Oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 µM) and K(+)-channel blockers charybdotoxin (CHT, 0.1 µM) and BaCl(2) (1 µM) reduced the relaxant effect of FLNT in the endothelium-denuded arteries, whereas glibenclamide (1 µM) and 4-aminopyridine (1 mM) failed to influence FLNT-induced vasorelaxation. Furthermore, in the presence of ODQ, both CHT (0.1 µM) and BaCl(2) (1 µM) still significantly reduced the relaxation evoked by FLNT. Pretreatment of vessels with hydroxocobalamin, a nitric oxide scavenger, abolished the FLNT effect. These findings demonstrate that FLNT induces relaxation of the rat aorta rings endothelium-independently. Furthermore, we demonstrated that FLNT-induced vasorelaxation is related to its stimulation of soluble guanylate cyclase and activation of K(+) channels.

The contribution of d-tubocurarine-sensitive and apamin-sensitive K-channels to EDHF-mediated relaxation of mesenteric arteries from eNOS-/- mice

The nature of the potassium channels involved in determining endothelium-derived hyperpolarizing factor-mediated relaxation was investigated in first-order small mesenteric arteries from male endothelial nitric oxide synthase (eNOS-/-)-knockout and control (+/+) mice. Acetylcholine-induced endothelium-dependent relaxation of small mesenteric arteries of eNOS-/- was resistant to N-nitro-L-arginine and indomethacin and the guanylyl cyclase inhibitor, 1H-(1,2,4) oxadiazolo (4,3-a) quinoxalin-1-one. Apamin and the combination of apamin and iberiotoxin or apamin and charybdotoxin induced a transient endothelium-dependent contraction of small mesenteric arteries from both eNOS-/- and +/+ mice. Acetylcholine-induced relaxation in eNOS-/- mice was unaffected by charybdotoxin or apamin alone but significantly inhibited by the combination of these agents. However, the combination of scyllatoxin and iberiotoxin did not mimic the inhibitory effect of the apamin/charybdotoxin combination. Tubocurarine alone completely blocked acetylcholine-induced relaxation in eNOS-/- mice. Single channel analysis of myocytes from small mesenteric arterioles revealed a large conductance calcium-activated potassium channel that was sensitive to iberiotoxin, charybdotoxin, and tetraethylammonium. Tubocurarine blocked this channel from the cytosolic side but not when applied extracellularly. Solutions of nitric oxide (NO) gas also relaxed small mesenteric arteries that had been contracted with cirazoline in a concentration-dependent manner, and the sensitivity to NO was reduced by iberiotoxin and the combination of apamin, scyllatoxin, or tubocurarine with charybdotoxin but not by apamin, charybdotoxin, scyllatoxin, or tubocurarine alone. These data indicate that acetylcholine-induced endothelium-derived hyperpolarizing factor-mediated relaxation in small mesenteric arteries from eNOS-/- involved the activation of tubocurarine and apamin-/charybdotoxin-sensitive K-channels. In eNOS+/+ mice, the acetylcholine-induced response was primarily mediated by NO and was sensitive to iberiotoxin and the combination of apamin and charybdotoxin.

Role of arginase-2 and eNOS in the differential vascular reactivity and hypoxia-induced endothelial response in umbilical arteries and veins

The main vasodilator in the placenta is nitric oxide (NO), which is synthesized by endothelial NO synthase (eNOS). Arginase-2 competes with eNOS for l-arginine, and its activity has been related with vascular dysfunction. Recently, we showed that hypoxia induces arginase-2, and decreases eNOS activity in human umbilical vein endothelial cells (HUVEC). However there is evidence that vascular responses to hypoxia are not similar throughout the placental vascular tree. We studied whether arginase-2 plays a role controlling vascular tone in human umbilical vessels, and the changes in the expression of arginase-2 and eNOS proteins by hypoxia in endothelial cells from umbilical arteries (HUAEC) and veins (HUVEC). In isolated umbilical vessels the presence of eNOS and arginase-2 was determined in the endothelium, and the NO-dependent vasoactive responses in the presence and absence of S-(2-boronoethyl)-L-cysteine (BEC, arginase inhibitor) were studied. Additionally, HUAEC and HUVEC were exposed (0-24 h) to hypoxia (2% O2) or normoxia (5% O2), and protein levels of eNOS (total and phosphorylated at serine-1177) and arginase-2 were determined. In umbilical arteries and veins arginase-2 and eNOS were detected mainly at the endothelium. BEC induced a higher concentration-dependent relaxation in umbilical arteries than veins, and these responses were NOS-dependent. In HUAEC exposed to hypoxia there were no changes in eNOS and arginase-2 levels, however there was a significant increase of p-eNOS. In contrast, HUVEC showed an increase in arginase-2 and a reduction of p-eNOS in response to hypoxia. These results show that arginases have a vascular role in placental vessels counteracting the NOS-dependent relaxation, which is differentially regulated in placental artery and vein endothelial cells.

Endothelial dysfunction in the human umbilical artery due to preeclampsia can be prevented by sildenafil

OBJECTIVES

We aimed to determine the effects of sildenafil in human umbilical artery preparation taken from preeclamptic or normal pregnant women, also to investigate underlying mechanisms in these effects.

STUDY DESIGN

Eighteen pregnant women with preeclampsia and 18 healthy pregnant women were involved. Relaxation responses of sildenafil in presence and absence of nitric oxide (NO) synthase inhibitor, N-[omega]-nitro-L-arginine methyl ester (L-NAME), and soluble guanylyl cyclase inhibitor, 1H-[1,2,4] oxadiazolo [4,3-a]quinoxalin-1-one (ODQ), were compared between the preeclampsia group and control group.

RESULTS

Sildenafil-induced relaxation responses were significantly attenuated in the presence of preeclampsia, L-NAME or ODQ, but not totally abolished. Interestingly, except with ODQ incubation, in all set of experiments maximal relaxation response was achieved by sildenafil.

CONCLUSION

These data indicate that sildenafil might effect vascular responsiveness of human umbilical artery through the involvement of NO/cyclic guanosine monophosphate (cGMP)-dependent and -independent pathways. Further investigations are needed to clarify the exact mechanisms.

Role of nitric oxide in placental vascular development and function

Nitric oxide (NO) is one of the most pleiotropic signaling molecules at systemic and cellular levels, participating in vascular tone regulation, cellular respiration, proliferation, apoptosis and gene expression. Indeed NO actively participates in trophoblast invasion, placental development and represents the main vasodilator in this tissue. Despite the large number of studies addressing the role of NO in the placenta, its participation in placental vascular development and the effect of altered levels of NO on placental function remains to be clarified. This review draws a time-line of the participation of NO throughout placental vascular development, from the differentiation of vascular precursors to the consolidation of vascular function are considered. The influence of NO on cell types involved in the origin of the placental vasculature and the expression and function of the nitric oxide synthases (NOS) throughout pregnancy are described. The developmental processes involved in the placental vascular bed are considered, such as the participation of NO in placental vasculogenesis and angiogenesis through VEGF and Angiopoietin signaling molecules. The role of NO in vascular function once the placental vascular tree has developed, in normal pregnancy as well as in pregnancy-related diseases, is then discussed.

Nitric oxide-induced biphasic mechanism of vascular relaxation via dephosphorylation of CPI-17 and MYPT1

Nitric oxide (NO) from endothelium is a major mediator of vasodilatation through cGMP/PKG signals that lead to a decrease in Ca(2+) concentration. In addition, NO-mediated signals trigger an increase in myosin light chain phosphatase (MLCP) activity. To evaluate the mechanism of NO-induced relaxation through MLCP deinhibition, we compared time-dependent changes in Ca(2+), myosin light chain (MLC) phosphorylation and contraction to changes in phosphorylation levels of CPI-17 at Thr38, RhoA at Ser188, and MYPT1 at Ser695, Thr696 and Thr853 in response to sodium nitroprusside (SNP)-induced relaxation in denuded rabbit femoral artery. During phenylephrine (PE)-induced contraction, SNP reduced CPI-17 phosphorylation to a minimal value within 15 s, in parallel with decreases in Ca(2+) and MLC phosphorylation, followed by a reduction of contractile force having a latency period of about 15 s. MYPT1 phosphorylation at Ser695, the PKG-target site, increased concurrently with relaxation. Phosphorylation of RhoA, MYPT1 Thr696 and Thr853 differed significantly at 5 min but not within 1 min of SNP exposure. Inhibition of Ca(2+) release delayed SNP-induced relaxation while inhibition of Ca(2+) channel, BK(Ca) channel or phosphodiesterase-5 did not. Pretreatment of resting artery with SNP suppressed an increase in Ca(2+), contractile force and phosphorylation of MLC, CPI-17, MYPT1 Thr696 and Thr853 at 10 s after PE stimulation, but had no effect on phorbol ester-induced CPI-17 phosphorylation. Together, these results suggest that NO production suppresses Ca(2+) release, which causes an inactivation of PKC and rapid CPI-17 dephosphorylation as well as MLCK inactivation, resulting in rapid MLC dephosphorylation and relaxation.

In vitro assessment of mouse uterine and fetoplacental vascular function

Adequate blood flow provision through alterations in maternal vascular function is essential during pregnancy for optimal fetal development. Abnormal uterine vasculature adaptation, resulting in aberrant blood flow to the placenta, has been implicated as a possible cause of fetal growth restriction (FGR). Our study aimed to develop strategies to evaluate murine vascular function in pregnancy using wire myography. Main uterine artery loop and branch vessels isolated from near-term pregnant mice showed significant contraction to phenylephrine (PE). Endothelial-dependent relaxation was noted with acetylcholine (ACH). U46619 elicited significant contraction of umbilical arteries and veins, but relaxation was only demonstrable with the nitric oxide (NO) donor sodium nitroprusside (SNP). In conclusion, our data suggest that murine uteroplacental and fetoplacental arteries show distinct responses to vasoactive agents. Furthermore, this study indicates that wire myography represents a robust technique for the assessment of murine uteroplacental and fetoplacental vascular function, which will aid evaluation of mouse genetic models of FGR.

Umbilical artery tone in maternal obesity

BACKGROUND

The increasing prevalence of obesity constitutes a major health problem in obstetrics with implications for feto-maternal growth and wellbeing. This study investigated and compared the contractile properties of umbilical arteries excised from obese women, with those excised from women with a normal body mass index (BMI).

METHODS

Sections of umbilical artery were obtained from umbilical cord samples immediately after delivery and mounted for isometric recording in organ tissue baths under physiological conditions. Cumulative additions of 5-Hydroxytryptamine (5-HT) and Prostaglandin F-2alpha (PgF2alpha) were added in the concentration range of 1 nmol/L to 10 micromol/L. Control vessels were exposed to Krebs physiological salt solution (PSS) only. The resultant effects of each drug addition were measured using the Powerlab hardware unit.

RESULTS

5-HT exerted a significant effect on human umbilical artery tone at concentrations of 100 nmol/L, 1 micromol/L, and 10 micromol/L in normal (n = 5; P < 0.05) and obese (n = 5; P < 0.05) women. The contractile effect was significantly greater in vessels from obese women {Mean Maximum Tension (MMT) = 4.2532 g} than in those from women of normal BMI (MMT = 2.97 g; P < 0.05). PgF2alpha exerted a significant contractile effect on vessels at 1 micromol/L and 10 micromol/L concentrations when compared with controls (n = 5; P < 0.05). There was a non-significant trend towards an enhanced tone response in vessels from obese women (MMT = 3.02 g; n = 5), in comparison to vessels from women of a normal BMI (MMT = 2.358 g; n = 5; P > 0.05).

CONCLUSION

These findings support the hypothesis that endogenous regulation of umbilical artery tone is altered in association with maternal obesity. This may be linked to the cardiovascular effects of secretory products of adipose tissue, with implications for the feto-maternal circulation.

Role of voltage-dependent potassium channels and myo-endothelial gap junctions in 4-aminopyridine-induced inhibition of acetylcholine relaxation in rat carotid artery

The present study examined the role of voltage-gated potassium (K(v)) channels and myo-endothelial gap junctions in 4-aminopyridine-induced inhibition of acetylcholine-evoked endothelium-dependent relaxation and NO release in the rat carotid artery. The acetylcholine-induced relaxation was drastically inhibited by 94% and 82%, respectively in the presence of either 100 microM N(G)-nitro-l-arginine methyl ester (L-NAME) or 10 microM 1H-[1,2,4]oxadiazolo[4,3,a]quinoxalin-1-one (ODQ), while it was abolished following endothelium removal. 4-aminopyridine (1 mM), a preferential blocker of the K(v) channels significantly decreased the vasodilator potency, as well as efficacy of acetylcholine (pD(2) 5.7+/-0.09, R(max) 86.1+/-3.5% versus control 6.7+/-0.10 R(max) 106+/-3.5%, n=6), but had no effect on the relaxations elicited by either sodium nitroprusside (SNP) or 8-bromo-cyclic guanosine monophosphate (8-Br-cGMP). 4-AP (1 mM) also inhibited acetylcholine (3 microM)-stimulated nitrite release in the carotid artery segments (99.4+/-4.93 pmol/mg tissue weight wt; n=6 versus control 123.8+/-7.43 pmol/mg tissue weight wt, n=6). 18alpha-glycyrrhetinic acid (18alpha-GA, 5 microM), a gap junction blocker, completely prevented the inhibition of acetylcholine-induced relaxation, as well as nitrite release by 4-AP. In the pulmonary artery, however antagonism of acetylcholine-evoked relaxation by 4-AP was not reversed by 18alpha-GA. These results suggest that 4-AP-induced inhibition of endothelium-dependent relaxation and NO release involves electrical coupling between vascular smooth muscle and endothelial cells via myo-endothelial gap junctions in the rat carotid artery, but not in the pulmonary artery. Further, direct activation of 4-AP-sensitive vascular K(v) channels by endothelium-derived NO is not evident in the carotid blood vessel, while this appears to be an important mechanism of acetylcholine-induced relaxation in the pulmonary artery.

Voltage-dependent K+ channels regulate the duration of reactive hyperemia in the canine coronary circulation

We previously demonstrated a role for voltage-dependent K(+) (K(V)) channels in coronary vasodilation elicited by myocardial metabolism and exogenous H(2)O(2), as responses were attenuated by the K(V) channel blocker 4-aminopyridine (4-AP). Here we tested the hypothesis that K(V) channels participate in coronary reactive hyperemia and examined the role of K(V) channels in responses to nitric oxide (NO) and adenosine, two putative mediators. Reactive hyperemia (30-s occlusion) was measured in open-chest dogs before and during 4-AP treatment [intracoronary (ic), plasma concentration 0.3 mM]. 4-AP reduced baseline flow 34 +/- 5% and inhibited hyperemic volume 32 +/- 5%. Administration of 8-phenyltheophylline (8-PT; 0.3 mM ic or 5 mg/kg iv) or N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mg/min ic) inhibited early and late portions of hyperemic flow, supporting roles for adenosine and NO. 4-AP further inhibited hyperemia in the presence of 8-PT or L-NAME. Adenosine-induced blood flow responses were attenuated by 4-AP (52 +/- 6% block at 9 microg/min). Dilation of arterioles to adenosine was attenuated by 0.3 mM 4-AP and 1 microM correolide, a selective K(V)1 antagonist (76 +/- 7% and 47 +/- 2% block, respectively, at 1 microM). Dilation in response to sodium nitroprusside, an NO donor, was attenuated by 4-AP in vivo (41 +/- 6% block at 10 microg/min) and by correolide in vitro (29 +/- 4% block at 1 microM). K(V) current in smooth muscle cells was inhibited by 4-AP (IC(50) 1.1 +/- 0.1 mM) and virtually eliminated by correolide. Expression of mRNA for K(V)1 family members was detected in coronary arteries. Our data indicate that K(V) channels play an important role in regulating resting coronary blood flow, determining duration of reactive hyperemia, and mediating adenosine- and NO-induced vasodilation.

PDE4 and PDE5 regulate cyclic nucleotides relaxing effects in human umbilical arteries

Cyclic nucleotides (cAMP and cGMP) are the main second messengers linked to vasodilatation. They are synthesized by cyclases and degraded by different types of phosphodiesterases (PDE). The effect of PDE inhibition and cyclases stimulation on 5-hydroxytryptamine (5-HT; 1 microM) and histamine (10 microM) contracted arteries was analysed. Stimulation of guanylate cyclase or adenylate cyclase relaxed the histamine- and 5-HT-induced contractions indicating that intracellular increase of cyclic nucleotides leads to vasodilatation of the human umbilical artery. We investigated the role of different PDE families in the regulation of this effect. The presence of the different PDE types in human umbilical artery smooth muscle was analysed by RT-PCR and the expression of PDE1B, PDE3A, PDE3B, PDE4C, PDE4D and PDE5A was detected. The unspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX; 50 microM) relaxed histamine-contracted human umbilical artery on 47.4+/-7.2%. This effect seems to be due to PDE4 and PDE5 inhibition because among the selective PDE inhibitors used only the PDE4 inhibitor (rolipram; 1 microM) and the PDE5 inhibitors (dipyridamole and T0156; 3 microM and 1 microM respectively) induced significant relaxation (39.0+/-8.7, 30.4+/-6.0 and 36.3+/-2.8 respectively). IBMX, dipyridamole and T0156 produced similar relaxation on 5-HT-induced contraction. After forskolin, the addition of IBMX or rolipram increased the effect of the adenylate cyclase stimulator and almost completely relaxed the human umbilical artery contracted by histamine (92.5+/-4.9 and 90.9+/-4.7 respectively), suggesting a main role of PDE4. The data obtained with 5-HT contracted arteries confirmed this, because only rolipram and IBMX significantly increased the forskolin vasodilator effect. The administration of dipyridamole and T0156 after sodium nitroprusside (SNP) induced a significant increase of the SNP relaxant effect on histamine-contracted arteries, but PDE1 and PDE3 inhibition did not increase the effect of the guanylate cyclase stimulator. Similar effects were obtained in 5-HT contracted arteries, the SNP induced relaxation was increased by the PDE5 inhibition, but not by PDE1 or PDE3 inhibition. In summary, our results demonstrate that: 1) the increase of cAMP and/or cGMP levels induces relaxation of the human umbilical vascular smooth muscle; 2) four families of PDE are expressed in this smooth muscle: PDE1, PDE3, PDE4 and PDE5; 3) between these families, PDE4 and PDE5 are the key enzymes involved in the regulation of the relaxation associated to cAMP and cGMP, respectively.

Influence of physical preconditioning on the responsiveness of rat pulmonary artery after pulmonary ischemia/reperfusion

The aim of this work was to evaluate the effect of physical preconditioning in the responsiveness of rat pulmonary rings submitted to lung ischemia/reperfusion (IR). Wistar rats were divided into three groups: Sedentary sham-operated (SD/SHAM); sedentary submitted to ischemia/reperfusion (SD/IR) and trained submitted to ischemia/reperfusion (TR/IR) animals. Exercise training consisted in sessions of 60 min/day running sessions, 5 days/week for 8 weeks. Left pulmonary IR was performed by occluding for 90 min and reperfusing for 120 min. After that, pulmonary arteries were isolated and concentration-response curves to acetylcholine (ACh), histamine (HIST), sodium nitroprusside (SNP), phenylephrine and U46619 were obtained. Neither potency (-log EC(50)) nor maximal responses (E(max)) were modified for ACh and HIST in all groups. On the other hand, the potency for SNP was significantly increased in TR/IR group (8.23+/-0.06) compared to SD/IR group (7.85+/-0.04). Contractile responses mediated by a-adrenergic receptor were markedly decreased in IR groups (SD/IR: 6.75+/-0.06 and TR/IR: 6.62+/-0.04) compared to SD/SHAM (7.33+/-0.05). No changes were seen for the U46619 in all groups. In conclusion, the present study shows that exercise training has no protective actions in the local blood vessel where the IR process takes place.

Vasodilating mechanisms of levosimendan: involvement of K+ channels

Levosimendan, a novel agent developed for the treatment of acute and decompensated heart failure, exerts potent positive inotropic action and peripheral vasodilatory effects. The mechanism of vasodilation by levosimendan may involve reduction of Ca2+ sensitivity of contractile proteins in vascular smooth muscle, the lowering of intracellular free Ca2+, the potential inhibition of phosphodiesterase (PDE) III, and an opening of K+ channels. Although the importance and relative contribution of each of these mechanisms of vasorelaxation is unclear and may be different in various vessels and dependent on the dose of levosimendan, the important roles of K+-channel opening and Ca2+ desensitization in vascular smooth muscle are obvious, whereas the role of PDE inhibition remains to be defined. This review article briefly discusses the current research data on the mechanism of levosimendan-induced vasodilation with an emphasis on the types of the blood vessels and the K+ channels. It also summarizes the current experimental and clinical knowledge of the use of levosimedan in the treatment of heart failure.

Characterization of the mechanisms of action and nitric oxide species involved in the relaxation induced by the ruthenium complex

Nitric oxide (NO) plays an important role in the control of vascular tone. NO donors have therapeutic use and the most used NO donors, nitroglycerin and sodium nitroprusside have problems in their use. Thus, new NO donors have been synthesized to minimize these undesirable effects. Nytrosil ruthenium complexes have been studied as a new class of NO donors. trans-[RuCl([15]aneN(4))NO](2+), induces vasorelaxation only in presence of reducing agent. In this study, we characterized the mechanisms of vasorelaxation of trans-[RuCl([15]aneN(4))NO](2+) in denuded rat aorta and identified which NO forms are involved in this relaxation. We also evaluated the effect of this NO donor in decreasing the cytosolic Ca(2+) concentration ([Ca(2+)]c) of the vascular smooth muscle cells. Vasorelaxation to trans-[RuCl([15]aneN(4))NO](2+) (E(max): 101.8 +/- 2.3%, pEC(50): 5.03 +/- 0.15) was almost abolished in the presence of the NO* scavenger hydroxocobalamin (E(max): 4.0 +/- 0.4%; P < 0.001) and it was partially inhibited by the NO(-) scavenger L-cysteine (E(max): 79.9 +/- 6.9%, pEC(50): 4.41 +/- 0.06; P < 0.05). The guanylyl cyclase inhibitor ODQ reduced the E(max) (57.7 +/- 4.0%, P < 0.001) and pEC(50) (4.21 +/- 0.42, P < 0.01) and the combination of ODQ and TEA abolished the response to trans-[RuCl([15]aneN(4))NO](2+). The blockade of voltage-dependent (K(v)), ATP-sensitive (K(ATP)), and Ca(2+)-activated (K(Ca) K(+) channels reduced the vasorelaxation induced by trans-[RuCl([15]aneN(4))NO](2+). This compound significantly reduced [Ca(2+)]c (from 100% to 85.9 +/- 3.5%, n = 4). In conclusion, our data demonstrate that this NO donor induces vascular relaxation involving NO* and NO(-) species, that is associated to a decrease in [Ca(2+)]c. The mechanisms of vasorelaxation involve guanylyl cyclase activation, cGMP production and K(+) channels activation.

Properties of the Human Umbilical Vein as a Living Scaffold for a Tissue-Engineered Vessel Graft

Umbilical cords are usually discarded after delivery, even though they contain a set of functional vessels. We investigated whether the human umbilical vein (HUV) is suitable as a storable scaffold for the tissue engineering of small-caliber vessel grafts. Isolated HUVs were cryopreserved by freezing or vitrification. The reaction of the vessels to vasoactive compounds and the mechanical properties were determined in an organ bath. Mitochondrial metabolism, release of antithrombotic compounds, and platelet adhesion were measured on the luminal vessel surface. Seeding with endothelial cells was tested on denuded HUVs. The vessels showed a weak response to norepinephrine but were readily contracted by serotonin and by the thromboxane A2 mimetic U46619. Endothelium-dependent vasorelaxation was weak, reaching significance only for histamine. However, the vessels relaxed to sodium nitroprusside, and to acetylcholine if sandwiched with human saphenous vein. Cryopreservation did not change the mechanical properties in the relevant tension range. Vasoconstriction to potassium chloride and serotonin were reduced after freezing (22.9+/-7.6%, 27.7+/-10.2%) and after vitrification (2.6+/-5.8%, 4.3+/-7.1%). The mitochondrial metabolism was also attenuated after freezing (57.9+/-25.9%) and after vitrification (21.7+/-6.7%). Prostacyclin release was elevated after both cryopreservation procedures (4.0-fold, 3.9-fold), whereas there was no significant change in the adhesion of platelets. Denuded HUVs could readily be seeded with isolated endothelial cells before and after freezing. We conclude that HUV is suitable as a storable living scaffold with antithrombogenic properties.

Comparison of the mechanisms underlying the relaxation induced by two nitric oxide donors: sodium nitroprusside and a new ruthenium complex

We studied the mechanisms involved in the relaxation induced by nitric oxide (NO) donors, ruthenium complex ([Ru(terpy)(bdq)NO(+)](3+)-TERPY) and sodium nitroprusside (SNP) in denuded rat aorta. Both NO donors induced vascular relaxation independent of the agonist used in the pre-contraction. [Ru(terpy)(bdq)NO(+)](3+) and SNP activated guanylyl cyclase (GC) and K(+) channels. The production of cGMP induced by [Ru(terpy)(bdq)NO(+)](3+) - was higher than that obtained with SNP. The combination of GC inhibitor with K(+)channels blocker almost abolished the relaxation induced by the NO donors. The extracellular NO scavenger oxyhemoglobin reduced the potency without changing the maximum effect (Emax) of both NO donors. By using specific NO species scavengers, hydroxocobalamin and l-cysteine, we have identified the contribution of free radical NO (NO()) and nytroxil anion (NO(-)), respectively, to the rat aorta relaxation induced by both NO donors. The selective scavengers for NO() and NO(-) reduced the potency but not the Emax of [Ru(terpy)(bdq)NO(+)](3+). However, the NO(-) scavenger had no effect on the relaxation induced by SNP and NO() scavenger reduced only the potency to SNP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduced only the potency of SNP without effect on the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+). Our results demonstrate that both NO donors induce relaxation by activating the GC and K(+) channels. The NO() is the unique NO specie involved in the SNP-relaxation. On the other hand, the relaxant effect of [Ru(terpy)(bdq)NO(+)](3+) involves both NO() and NO(-), that produce higher concentration of cGMP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduces the relaxation induced by SNP but it did not alter the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+).

Potassium channels in the vasodilating action of levosimendan on the human umbilical artery

OBJECTIVE

Levosimendan is a calcium-sensitizing agent and inodilator working via potassium channels, which is under current investigation in the treatment of heart failure. We investigated the type of potassium channels that play a role on the dilatating effect of levosimendan on the contractile tones of the isolated human umbilical artery (HUA).

METHODS

The response in the HUA was recorded isometrically by a force displacement transducer in isolated organ baths. Levosimendan was added to organ baths after precontraction with serotonin (5-HT, 1 microM). Levosimendan-induced relaxations were tested in the presence of the large conductance Ca2+-activated K+ channel inhibitor tetraethylammonium (TEA, 1 mM), the adenosine triphosphate (ATP)-sensitive K+ channel inhibitor glibenclamide (GLI, 10 microM), and the voltage-sensitive K+ channel inhibitor 4-aminopyridine (4-AP, 1 mM). All experiments were performed in solutions containing the cyclooxygenase inhibitor indomethacin (10 microM) and the nitric oxide synthase inhibitor L-NAME (100 microM).

RESULTS

Levosimendan (10 nM to 3 microM) produced potent relaxation in the HUA. Vehicle had no significant relaxant effect. The relaxation to levosimendan was not affected by the K+ channel inhibitor, GLI. However, 4-AP (1 mM) and TEA (1 mM) inhibited levosimendan-induced relaxation significantly (P <.05).

CONCLUSION

These results show that levosimendan effectively and directly decreases the tone of the HUA. The mechanism of this levosimendan-induced relaxation in the HUA appears in part to be due to voltage-gated and large conductance Ca2+-activated K+ channel opening action.

Effect of propofol and etomidate on normoxic and chronically hypoxic pulmonary artery

Background

Chronic alveolar hypoxia results in sustained arterial constriction, and increase in pulmonary vascular resistance leading to pulmonary artery hypertension (PAHT). The aim of this study was to investigate the effect of propofol and etomidate on pulmonary artery (PA) reactivity in chronically hypoxic (CH) rats, a model of pulmonary arterial hypertension (PAHT), in normoxic animals, and human PA.

Methods

CH rats were maintained 14 days at 380 mmHg pressure in a hypobaric chamber. Human tissue was retrieved from histological lung pieces from patients undergoing resection for carcinoma. Cumulative concentrations of anaesthetics were tested on isolated vascular rings precontracted with phenylephrine (PHE) or 100 mM KCl. Statistical comparisons were done by ANOVA, followed, when needed, by Student t tests with Bonferroni correction as post-hoc tests.

Results

In normoxic rat PA, maximal relaxation (R_max) induced by etomidate and propofol was 101.3 ± 0.8% and 94.0 ± 2.3%, respectively, in KCl-precontracted rings, and 63.3 ± 9.7% and 46.1 ± 9.1%, respectively, in PHE-precontracted rings (n = 7). In KCl-precontracted human PA, R_max was 84.7 ± 8.6 % and 66.5 ± 11.8%, for etomidate and propofol, respectively, and 154.2 ± 22.4 % and 51.6 ± 15.1 %, respectively, in PHE-precontracted human PA (n = 7). In CH rat PA, the relaxant effect of both anaesthetics was increased in PHE-precontracted and, for etomidate only, in KCl-precontracted PA. In aorta, CH induced no change in the relaxant effect of anaesthetics.

Conclusion

Propofol and etomidate have relaxant properties in PA from human and normoxic rat. The relaxant effect is specifically accentuated in PA from CH rat, mainly via an effect on the pharmacomechanical coupling. Etomidate appears to be more efficient than propofol at identical concentration, but, taking into account clinical concentrations, etomidate is less potent than propofol, which effect was in the range of clinical doses. Although these findings provide experimental support for the preferential use of etomidate for haemodynamic stability in patients suffering from PAHT, the clinical relevance of the observations requires further investigation.

Expression and function of potassium channels in the human placental vasculature

In the placental vasculature, where oxygenation may be an important regulator of vascular reactivity, there is a paucity of data on the expression of potassium (K) channels, which are important mediators of vascular smooth muscle tone. We therefore addressed the expression and function of several K channel subtypes in human placentas. The expression of voltage-gated (Kv)2.1, KV9.3, large-conductance Ca2+-activated K channel (BKCa), inward-rectified K+ channel (KIR)6.1, and two-pore domain inwardly rectifying potassium channel-related acid-sensitive K channels (TASK)1 in chorionic plate arteries, veins, and placental homogenate was assessed by RT-PCR and Western blot analysis. Functional activity of K channels was assessed pharmacologically in small chorionic plate arteries and veins by wire myography using 4-aminopyridine, iberiotoxin, pinacidil, and anandamide. Experiments were performed at 20, 7, and 2% oxygen to assess the effect of oxygenation on the efficacy of K channel modulators. KV2.1, KV9.3, BKCa, KIR6.1, and TASK1 channels were all demonstrated to be expressed at the message level. KV2.1, BKCa, KIR6.1, and TASK1 were all demonstrated at the protein level. Pharmacological manipulation of voltage-gated and ATP-sensitive channels produced the most marked modifications in vascular tone, in both arteries and veins. We conclude that K channels play an important role in controlling placental vascular function.

Dual impact of a nitric oxide donor, GEA 3175, in human pulmonary smooth muscle

Nitric oxide (NO) donors could constitute an alternative to inhaled NO as treatment in some patients with pulmonary hypertension. Therefore, the present study investigated the relaxation mechanisms of a novel NO donor, 3-(3-chloro-2-methylphenyl)-5-[[4-methylphenyl)sulphonyl]amino]-)hydroxide (GEA 3175) in segments of human pulmonary arteries and bronchioles, which were mounted in microvascular myographs. GEA 3175 induced concentration-dependent relaxations and was more potent in pulmonary arteries than in bronchioles. A blocker of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), and iberiotoxin, a blocker of large-conductance calcium-activated K channels, both reduced relaxations induced by GEA 3175 in pulmonary arteries and bronchioles. Combining of ODQ and iberiotoxin did not produce additional inhibition. GEA 3175 relaxation is mediated through guanylyl cyclase-dependent mechanisms followed by activation of large-conductance calcium-activated K(+) channels. The dilatation of both pulmonary small arteries and airways by GEA 3175 seems advantageous, if it is considered administered as inhalation therapy for pulmonary hypertension.

Nitric oxide-dependent modulation of the delayed rectifier K+ current and the L-type Ca2+ current by ginsenoside Re, an ingredient of Panax ginseng, in guinea-pig cardiomyocytes

1 Ginsenoside Re, a major ingredient of Panax ginseng, protects the heart against ischemia-reperfusion injury by shortening action potential duration (APD) and thereby prohibiting influx of excessive Ca2+. Ginsenoside Re enhances the slowly activating component of the delayed rectifier K+ current (IKs) and suppresses the L-type Ca2+ current (I(Ca,L)), which may account for APD shortening. 2 We used perforated configuration of patch-clamp technique to define the mechanism of enhancement of IKs and suppression of I(Ca,L) by ginsenoside Re in guinea-pig ventricular myocytes. 3 S-Methylisothiourea (SMT, 1 microm), an inhibitor of nitric oxide (NO) synthase (NOS), and N-acetyl-L-cystein (LNAC, 1 mm), an NO scavenger, inhibited IKs enhancement. Application of an NO donor, sodium nitroprusside (SNP, 1 mm), enhanced IKs with a magnitude similar to that by a maximum dose (20 microm) of ginseonside Re, and subsequent application of ginsenoside Re failed to enhance IKs. Conversely, after IKs had been enhanced by ginsenoside Re (20 microm), subsequently applied SNP failed to further enhance IKs. 4 An inhibitor of guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microm), barely suppressed IKs enhancement, while a thiol-alkylating reagent, N-ethylmaleimide (NEM, 0.5 mm), clearly suppressed it. A reducing reagent, di-thiothreitol (DTT, 5 mm), reversed both ginsenoside Re- and SNP-induced IKs enhancement. 5 I(Ca,L) suppression by ginsenoside Re (3 microm) was abolished by SMT (1 microm) or LNAC (1 mm). NEM (0.5 mm) did not suppress I(Ca,L) inhibition and DTT (5 mm) did not reverse I(Ca,L) inhibition, whereas in the presence of ODQ (10 microm), ginsenoside Re (3 microm) failed to suppress I(Ca,L). 6 These results indicate that ginsenoside Re-induced IKs enhancement and I(Ca,L) suppression involve NO actions. Direct S-nitrosylation of channel protein appears to be the main mechanism for IKs enhancement, while a cGMP-dependent pathway is responsible for I(Ca,L) inhibition.

NO- activates soluble guanylate cyclase and Kv channels to vasodilate resistance arteries

Nitric oxide (NO) plays an important role in the control of vascular tone. Traditionally, its vasorelaxant activity has been attributed to the free radical form of NO (NO*), yet the reduced form of NO (NO-) is also produced endogenously and is a potent vasodilator of large conduit arteries. The effects of NO- in the resistance vasculature remain unknown. This study examines the activity of NO- in rat small isolated mesenteric resistance-like arteries and characterizes its mechanism(s) of action. With the use of standard myographic techniques, the vasorelaxant properties of NO* (NO gas solution), NO- (Angeli's salt), and the NO donor sodium nitroprusside were compared. Relaxation responses to Angeli's salt (pEC50=7.51+/-0.13, Rmax=95.5+/-1.5%) were unchanged in the presence of carboxy-PTIO (NO* scavenger) but those to NO* and sodium nitroprusside were inhibited. l-Cysteine (NO- scavenger) decreased the sensitivity to Angeli's salt (P<0.01) and sodium nitroprusside (P<0.01) but not to NO*. The soluble guanylate cyclase inhibitor ODQ (3 and 10 micromol/L) concentration-dependently inhibited relaxation responses to Angeli's salt (41.0+/-6.0% versus control 93.4+/-1.9% at 10 micromol/L). The voltage-dependent K+ channel inhibitor 4-aminopyridine (1 mmol/L) caused a 9-fold (P<0.01) decrease in sensitivity to Angeli's salt, whereas glibenclamide, iberiotoxin, charybdotoxin, and apamin were without effect. In combination, ODQ and 4-aminopyridine abolished the response to Angeli's salt. In conclusion, NO- functions as a potent vasodilator of resistance arteries, mediating its response independently of NO* and through the activation of soluble guanylate cyclase and voltage-dependent K+ channels. NO- donors may represent a novel class of nitrovasodilator relevant for the treatment of cardiovascular disorders such as angina.

The effects of propofol and etomidate on airway contractility in chronically hypoxic rats

We investigated the effect of two IV anesthetics, propofol and etomidate, on airway responsiveness in a rat model of chronic hypoxia (CH) in comparison with normoxic rats. CH rats were obtained using a hypobaric chamber (14 days at a barometric pressure of 380 mm Hg). The ability of both anesthetics to relax and prevent agonist-induced contraction was assessed in isolated tracheal rings precontracted with the muscarinic agonist carbachol (CCh) and the depolarizing agent KCl. Cumulative concentrations of both compounds relaxed tracheal rings precontracted with CCh or KCl with a similar amplitude in CH and normoxic rats. In tracheal rings precontracted with CCh, the negative logarithm of anesthetics that reduced the maximal contraction by 30%, i.e., -log half-maximal inhibitory concentration, for propofol and etomidate were 4.10 +/- 0.09 and 4.12 +/- 0.15 in normoxic rats and 4.20 +/- 0.22 and 3.61 +/- 0.19 in CH rats, respectively. At a fixed concentration, propofol (3 x 10(-4) M) or etomidate (10(-4) M) also inhibited CH tracheal rings contraction in response to cumulative concentrations of CCh and KCl. However, in contrast with the equivalent relaxant effect of both anesthetics, etomidate was two-fold less effective than propofol for inhibiting the subsequent contraction to CCh and KCl. These results indicate that propofol and etomidate retain their relaxant properties in CH rat airways by acting on the pharmaco- and electromechanical coupling.

IMPLICATIONS

Anesthesia may cause airway constriction or bronchospasm in patients with normal or pathological airways. This study investigated the ability of propofol and etomidate to both reverse precontraction and inhibit contraction of tracheal rings isolated from chronically hypoxic rats.

Smooth muscle membrane potential modulates endothelium-dependent relaxation of rat basilar artery via myo-endothelial gap junctions

The release of endothelium-derived relaxing factors, such as nitric oxide (NO), is dependent on an increase in intracellular calcium levels ([Ca(2+)](i)) within endothelial cells. Endothelial cell membrane potential plays a critical role in the regulation of [Ca(2+)](i) in that calcium influx from the extracellular space is dependent on membrane hyperpolarization. In this study, the effect of inhibition of vascular smooth muscle delayed rectifier K(+) (K(DR)) channels by 4-aminopyridine (4-AP) on endothelium-dependent relaxation of rat basilar artery to acetylcholine (ACh) was assessed. ACh-evoked endothelium-dependent relaxations were inhibited by N-(Omega)-nitro-L-arginine (L-NNA) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), confirming a role for NO and guanylyl cyclase. 4-AP (300 microM) also suppressed ACh-induced relaxation, with the maximal response reduced from approximately 92 to approximately 33 % (n = 11; P < 0.01). However, relaxations in response to exogenous NO, applied in the form of authentic NO, sodium nitroprusside or diethylamineNONOate (DEANONOate), were not affected by 4-AP treatment (n = 3-11). These data are not consistent with the view that 4-AP-sensitive K(DR) channels are mediators of vascular hyperpolarization and relaxation in response to endothelium-derived NO. Inhibition of ACh-evoked relaxation by 4-AP was reversed by pinacidil (0.5-1 microM; n = 5) or 18beta-glycyrrhetinic acid (18betaGA; 5 microM; n = 5), indicating that depolarization and electrical coupling of the smooth muscle to the endothelium were involved. 4-AP caused depolarization of both endothelial and vascular smooth muscle cells of isolated segments of basilar artery (mean change 11 +/- 1 and 9 +/- 2 mV, respectively; n = 15). Significantly, 18betaGA almost completely prevented the depolarization of endothelial cells (n = 6), but not smooth muscle cells (n = 6) by 4-AP. ACh-induced hyperpolarization of endothelium and smooth muscle cells was also reduced by 4-AP, but this inhibition was not observed in the combined presence of 4-AP and 18betaGA. These data indicate that 4-AP can induce an indirect inhibition of endothelium-dependent relaxation in the rat basilar artery by electrical coupling of smooth muscle membrane depolarization to the endothelium via myo-endothelial gap junctions.

Sildenafil (Viagra) augments sodium nitroprusside-induced but not nitroglycerin-induced hypotension in dogs

We investigated whether sildenafil citrate (Viagra) may reduce the dose of nitrovasodilators to induce deliberate hypotension. Ten mongrel dogs were acutely instrumented with a femoral artery catheter and a pulmonary artery catheter. Sodium nitroprusside (SNP; 1-16 microg. kg(-1). min(-1)) or nitroglycerin (NTG; 2-32 microg. kg(-1). min(-1)) was IV given to induce hypotension. The study consisted of two occasions, in a random order, in each animal: one with sildenafil pretreatment (1 mg/kg IV followed by 0.3 mg. kg(-1). h(-1)) and the other without to serve as a control. Hemodynamic variables were continuously monitored. Plasma cyclic guanosine monophosphate (cGMP) concentrations were measured by radioimmunoassay. Both SNP and NTG produced dose-dependent decreases in mean arterial blood pressure without affecting the heart rate in the presence as well as in the absence of sildenafil. Systemic vascular resistance index and mean pulmonary arterial pressure were also decreased. The magnitude of mean arterial blood pressure and systemic vascular resistance index reductions caused by SNP was augmented by sildenafil, whereas that caused by NTG was not affected. Neither SNP nor NTG alone altered the plasma cGMP concentrations. Sildenafil increased the plasma cGMP concentration, which was further increased by SNP but not affected by NTG. These results indicate that sildenafil may reduce the dose of SNP in producing deliberate hypotension in the dog. The potentiation of SNP-induced hypotension by sildenafil may be related to an augmented accumulation of cGMP.

IMPLICATIONS

Sildenafil may reduce the dose of sodium nitroprusside required to induce deliberate hypotension and hence the potential for cyanide toxicity.