Histamine H2-receptor antagonism improves conduit artery endothelial function and reduces plasma aldosterone level without lowering arterial blood pressure in angiotensin II-hypertensive mice

Aldosterone through the mineralocorticoid receptor MR has detrimental effects on cardiovascular disease. It reduces the bioavailability of nitric oxide and impairs endothelium-dependent vasodilatation. In resistance arteries, aldosterone impairs the sensitivity of vascular smooth muscle cells to nitric oxide by promoting the local secretion of histamine which activates H2 receptors. The present experiments tested in vivo and ex vivo the hypothesis that systemic H2-receptor antagonism reduces arterial blood pressure and improves vasodilatation in angiotensin II-induced chronic hypertension. Hypertension was induced by intravenous infusion of angiotensin II (60 ng kg-1 min-1) in conscious, unrestrained mice infused concomitantly with the H2-receptor antagonist ranitidine (27.8 µg kg-1 min-1) or vehicle for 24 days. Heart rate and arterial blood pressure were recorded by indwelling arterial catheter. Resistance (mesenteric) and conductance (aortae) arteries were harvested for perfusion myography and isometric tension recordings by wire myography, respectively. Plasma was analyzed for aldosterone concentration. ANGII infusion resulted in elevated arterial blood pressure and while in vivo treatment with ranitidine reduced plasma aldosterone concentration, it did not reduce blood pressure. Ranitidine improved ex vivo endothelial function (acetylcholine 10-9 to 10-6 mol L-1) in mesenteric resistance arteries. This was abolished by ex vivo treatment with aldosterone (10-9 mol L-1, 1 h). In aortic segments, in vivo ranitidine treatment impaired relaxation. Activation of histamine H2 receptors promotes aldosterone secretion, does not affect arterial blood pressure, and protects endothelial function in conduit arteries but promotes endothelial dysfunction in resistance arteries during angiotensin II-mediated hypertension. Aldosterone contributes little to angiotensin II-induced hypertension in mice.

Neuromuscular monitoring of a patient with Charcot-Marie-Tooth disease; which monitoring technique is adequate? - A case report and literature review

BACKGROUND

Charcot-Marie-Tooth disease (CMTD) is a hereditary polyneuropathy associated with a life-threatening risk of pulmonary complications.

CASE

A 61-year-old male with CMTD for 40 years was admitted for the drainage of an abscess in his left ankle. Total intravenous anesthesia was administered, and an electromyography device was attached to the hand for neuromuscular monitoring; however, the response was not measured. Kinemyography and acceleromyography devices were attached to both hands, and responses were obtained. After neuromuscular blockade (NMB) with rocuronium 0.6 mg/kg, the train-of-four (TOF) response on kinemyography was normally measured, but the post-tetanic count on acceleromyography consistently showed 0 during anesthesia. Sugammadex 200 mg was injected to reverse the NMB. After 5 min, the TOF ratios for kinemyography and acceleromyography exceeded 90%. The patient recovered without any complications.

CONCLUSIONS

For CMTD patients, acceleromyography or kinemyography is superior to electromyography, and sugammadex can be used to reverse NMB successfully.

Effects of electronic cigarette E-liquid and device wattage on vascular function

Electronic cigarettes (e-cigs) are customizable tobacco products that allow users to select e-liquid composition, flavors, and (in some devices) adjust wattage or heat used to generate e-cig aerosol. This study compared vascular outcomes in a conducting vessel (thoracic aorta) and a resistance artery (middle cerebral artery, MCA) in C57Bl/6 mice exposed to e-cig aerosol generated from either pure vegetable glycerin (VG) or pure propylene glycol (PG) over 60-min (Study 1), and separately the effect of using 5- vs. 30-watt settings with an exposure of 100-min (Study 2). In Study 1, aortic endothelial-dependent-dilation (EDD) was only impaired with PG- exposure (p < 0.05) compared with air. In the MCA, EDD response was impaired by ∼50% in both VG and PG groups compared with air (p < 0.05). In Study 2, the aortic EDD responses were not different for either 5- or 30-watt exposed groups compared with air controls; however, in the MCA, both 5- and 30-watt groups were impaired by 32% and 55%, respectively, compared with air controls (p < 0.05). These pre-clinical data provide evidence that chronic exposure to aerosol produced by either VG or PG, and regardless of the wattage used, leads to vascular dysfunction at multiple levels within the arterial system. For all exposures, we observed greater impairment of arterial reactivity in a resistance artery (i.e. MCA) compared with the aorta. These data could suggest the smaller arteries may be more sensitive or first to be affected, or that different mechanism(s) for impairment may be involved depending on arterial hierarchy.

The angiotensin AT2-receptor agonist compound 21 is an antagonist for the thromboxane TP-receptor - Implications for preclinical studies and future clinical use

Since the AT₂-receptor (AT₂R) agonist C21 has structural similarity to the AT₁-receptor antagonists Irbesartan and Losartan, which are antagonists not only at the AT₁R, but also at thromboxane TP-receptors, we tested the hypothesis that C21 has TP-receptor antagonistic properties as well. Isolated mouse mesenteric arteries from C57BL/6 J and AT₂R-knockout mice (AT₂R^-/y) were mounted in wire myographs, contracted with either phenylephrine or the thromboxane A₂ (TXA₂) analogue U46619, and the relaxing effect of C21 (0.1 nM - 10 µM) was investigated. The effect of C21 on U46619-induced platelet aggregation was measured by an impedance aggregometer. Direct interaction of C21 with TP-receptors was determined by an β-arrestin biosensor assay. C21 caused significant, concentration-dependent relaxations in phenylephrine- and U46619-contracted mesenteric arteries from C57BL/6 J mice. The relaxing effect of C21 was absent in phenylephrine-contracted arteries from AT₂R^-/y mice, whereas it was unchanged in U46619-contracted arteries from AT₂R^-/y mice. C21 inhibited U46619-stimulated aggregation of human platelets, which was not inhibited by the AT₂R-antagonist PD123319. C21 reduced U46619-induced recruitment of β-arrestin to human thromboxane TP-receptors with a calculated K_i of 3.74 µM. We conclude that in addition to AT₂R-agonistic properties, C21 also acts as low-affinity TP-receptor antagonist, and that - depending on the constrictor - both mechanisms can be responsible for C21-induced vasorelaxation. Furthermore, by acting as a TP-receptor antagonist, C21 inhibits platelet aggregation. These findings are important for understanding potential off-target effects of C21 in the preclinical and clinical context and for the interpretation of C21-related myography data in assays with TXA₂-analogues as constrictor.

Viability of ex-vivo myography as a diagnostic tool for rectus abdominis muscle electrical activity collected at Cesarean section within a diamater cohort study

Background

Ex-vivo myography enables the assessment of muscle electrical activity response. This study explored the viability of determining the physiological responses in muscles without tendon, as rectus abdominis muscle (RAM), through ex-vivo myography to assess its potential as a diagnostic tool.

Results

All tested RAM samples (five different samples) show patterns of electrical activity. A positive response was observed in 100% of the programmed stimulation. RAM 3 showed greater weight (0.47 g), length (1.66 cm), and width (0.77 cm) compared to RAM 1, RAM 2, RAM 4 and RAM 5 with more sustained electrical activity over time, a higher percentage of fatigue was analyzed at half the time of the electrical activity. The order of electrical activity (Mn) was RAM 3 > RAM 5 > RAM 1 > RAM 4 > RAM 2. No electrical activity was recorded in the Sham group.

Conclusions

This study shows that it is feasible to assess the physiological responses of striated muscle without tendon as RAM, obtained at C-section, under ex vivo myography. These results could be recorded, properly analyzed, and demonstrated its potential as a diagnostic tool for rectus abdominis muscle electrical activity.

A primer for measuring cGMP signaling and cGMP-mediated vascular relaxation

Soluble guanylyl cyclase (sGC, also called GC1) is the main receptor for nitric oxide (NO) that catalyzes the production of the second messenger molecule, 3'5' cyclic guanosine monophosphate (cGMP) leading to vasorelaxation, and inhibition of leukocyte recruitment and platelet aggregation. Enhancing cGMP levels, through sGC agonism or inhibition of cGMP breakdown via phosphodiesterase inhibition, has yielded FDA approval for several cGMP modifier therapies for treatment of cardiovascular and pulmonary diseases. While basic research continues to improve our understanding of cGMP signaling and as new therapies evolve to elevate cGMP levels, we provide a short methodological primer for measuring cGMP and cGMP-mediated vascular relaxation for investigators.

Neurotoxicity of Olindias sambaquiensis and Chiropsalmus quadrumanus extracts in sympathetic nervous system

Cnidarians are equipped with nematocysts, which are specialized organelles used to inoculate venom during prey capturing and defense. Their venoms are rich in toxins and a potential source of bioactive compounds, however, poorly explored so far. In this work, the activity of the methanolic extracts from the hydromedusa Olindias sambaquiensis and the cubozoan jellyfish Chiropsalmus quadrumanus were studied in sympathetic neurotransmission. For that, bisected rat vas deferens - a classic model of sympathetic neurotransmission - were incubated with the extracts for further myographic and histopathological analysis. The O. sambaquiensis extract, at 0.1 μg/mL, facilitated the neurogenic contractions of the noradrenergic-rich epididymal portion, while reducing the noradrenaline (NA) potency, which suggests an interaction with postsynaptic α₁-adrenoceptors. On the other hand, a higher concentration (1 μg/mL) leads to time- and frequency-dependent blockade of nerve-evoked contractions without significantly changing the response to exogenous NA. In turn, the C. quadrumanus extract at 0.1 μg/mL induced blockade of nerve-evoked noradrenergic contractions while reducing the potency to exogenous NA. Both extracts did not affect the purinergic neurotransmission or induce muscle damages. Our results demonstrate that O. sambaquiensis and C. quadrumanus extracts significantly interfere with the noradrenergic neurotransmission without altering purinergic response or smooth muscle structure on rat vas deferens. Such results bring to light the pharmacological potential of O. sambaquiensis and C. quadrumanus molecules for therapeutics focusing on noradrenergic neurotransmission.

Estrogen receptors α, β and GPER in the CNS and trigeminal system - molecular and functional aspects

BACKGROUND

Migraine occurs 2-3 times more often in females than in males and is in many females associated with the onset of menstruation. The steroid hormone, 17β-estradiol (estrogen, E2), exerts its effects by binding and activating several estrogen receptors (ERs). Calcitonin gene-related peptide (CGRP) has a strong position in migraine pathophysiology, and interaction with CGRP has resulted in several successful drugs for acute and prophylactic treatment of migraine, effective in all age groups and in both sexes.

METHODS

Immunohistochemistry was used for detection and localization of proteins, release of CGRP and PACAP investigated by ELISA and myography/perfusion arteriography was performed on rat and human arterial segments.

RESULTS

ERα was found throughout the whole brain, and in several migraine related structures. ERβ was mainly found in the hippocampus and the cerebellum. In trigeminal ganglion (TG), ERα was found in the nuclei of neurons; these neurons expressed CGRP or the CGRP receptor in the cytoplasm. G-protein ER (GPER) was observed in the cell membrane and cytoplasm in most TG neurons. We compared TG from males and females, and females expressed more ER receptors. For neuropeptide release, the only observable difference was a baseline CGRP release being higher in the pro-estrous state as compared to estrous state. In the middle cerebral artery (MCA), we observed similar dilatory ER-responses between males and females, except for vasodilatory ERβ which we observed only in female arteries.

CONCLUSION

These data reveal significant differences in ER receptor expression between male and female rats. This contrasts to CGRP and PACAP release where we did not observe discernable difference between the sexes. Together, this points to a hypothesis where estrogen could have a modulatory role on the trigeminal neuron function in general rather than on the acute CGRP release mechanisms and vasomotor responses.

Endothelial lipase increases eNOS activating capacity of high-density lipoprotein

Endothelial lipase (EL) changes structural and functional properties of high-density lipoprotein (HDL). HDL is a relevant modulator of endothelial nitric oxide synthase (eNOS) activity, but the effect of EL on HDL induced eNOS-activation has not yet been investigated. Here, we examined the impact of EL-modified HDL (EL-HDL) on eNOS activity, subcellular trafficking, and eNOS- dependent vasorelaxation. EL-HDL and empty virus (EV)-HDL as control were isolated from human serum incubated with EL-overexpressing or EV infected HepG2 cells. EL-HDL exhibited higher capacity to induce eNOS phosphorylation at Ser1177 and eNOS activity in EA.hy 926 cells, as well as eNOS-dependent vasorelaxation of mouse aortic rings compared to control HDL. As revealed by confocal and structured illumination-microscopy EL-HDL-driven induction of eNOS was accompanied by an increased eNOS-GFP targeting to the plasma membrane and a lower eNOS-GFP colocalization with Golgi and mitochondria. Widefield microscopy of filipin stained cells revealed that EL-HDL lowered cellular free cholesterol (FC) and as found by thin-layer chromatography increased cellular cholesterol ester (CE) content. Additionally, cholesterol efflux capacity, acyl-coenzyme A: cholesterol acyltransferase activity, and HDL particle uptake were comparable between EL-HDL and control HDL. In conclusion, EL increases eNOS activating capacity of HDL, a phenomenon accompanied by an enrichment of the plasma membrane eNOS pool, a decreased cell membrane FC and increased cellular CE content.

Endothelin-1 induces a strong pressor effect in ball pythons (Python regius)

Endothelin-1 (ET-1) is a very potent vasoactive peptide released from endothelial cells, and ET-1 plays an important role in the maintenance and regulation of blood pressure in mammals. ET-1 signaling is mediated by two receptors: ET_A and ET_B. In mammals, ET_A receptors are located on vascular smooth muscle where they mediate vasoconstriction. ET_B receptors located on the endothelium mediate vasodilatation through the release of nitric oxide, whereas stimulation of ET_B receptors placed on vascular smooth muscle leads to vasoconstriction. Less is known about ET-1 signaling in reptiles. In anaesthetized alligators, ET-1 elicits a biphasic blood pressure with a long-lasting initial decrease followed by a smaller increase in systemic blood pressure. In anaesthetized freshwater turtles, ET-1 causes a dose-dependent systemic vasodilatation mediated through ET_B receptors. In the present study, we investigated the cardiovascular effects of ET-1 on the systemic and pulmonary vasculature of pythons. The presence of ET_A and ET_B receptors in the vasculature of pythons was verified by means of immunoblotting. Myography on isolated vessels revealed a dose-dependent vasoconstrictory response to ET-1 in both mesenteric and pulmonary arteries. Pressure measurements in recovered specimens revealed an ET-1-induced rise in systemic blood pressure supporting our in vitro findings. In conclusion, our study shows that ET-1 induces a strong pressor effect in the systemic circulation.

Acute experimental venous thrombosis impairs venous relaxation but not contraction

OBJECTIVE

Venous thrombosis (VT) damages the vein wall, both physically by prolonged distension and from inflammation. These factors contribute to post-thrombotic syndrome (PTS). Interleukin (IL)-6 might play a role in experimental PTS and vein wall responses. Previous assessments of post-thrombotic vein wall injury used static measures such as histologic examination and immunologic assays. The purpose of the present study was to use myography to quantify the changes in contraction and relaxation of murine vessels exposed to an acute VT.

METHODS

Wild-type (WT) C57BL/6 mice were used to determine the baseline vein wall passive tension on a DMT 610m myograph (DMT-USA, Inc., Ann Arbor, Mich), including dosing concentrations of phenylephrine (Phe) and acetylcholine (Ach). WT and IL-6^-/- mice underwent VT using inferior vena cava (IVC) ligation (complete stasis) and stenosis (partial stasis), with no-surgery mice used as controls. The mice were harvested at 2 days (2D) and analyzed using a myograph. The vessels were stimulated with Phe and Ach to stimulate a contraction and relaxation response. The endothelial responses to VT were quantified by CD31 immunohistochemistry, Greiss assay, polymerase chain reaction, and Evans blue assay.

RESULTS

Optimal passive tension was determined to be 2 mN, with an optimal concentration of Phe and Ach of 7E-3M and 1E-5M, respectively. No significant differences were found in the contractions when exposed to Phe between the WT control, WT 2D ligation, and WT 2D stenosis IVC segments and the IL-6^-/- mice with and without thrombus (P > .05 for all). When treated with Ach, significantly more relaxation was found in the nonthrombosed control IVC segments than in those IVC segments that had had a 2D thrombus from either ligation- or stenosis-derived thrombotic mechanisms in both WT and IL-6^-/- mice. CD31 staining showed ∼20% less luminal endothelium after stasis thrombosis (P ≤ .01) but no loss in the controls (P > .05). Evans blue staining showed a trend toward increased leakiness in post-thrombotic vein walls. No significant difference in the endothelial gene markers or nitric oxide production was found.

CONCLUSIONS

Compared with the controls, acute thrombosis in the total or partial stasis models did not impair IVC contractile responses, suggesting no effect on the medial vascular smooth muscle response. The relaxation response was significantly reduced in the post-thrombotic groups, likely from direct endothelial injury. These findings suggest, at acute points, that VT impairs the endothelial function of a vein wall while retaining the vascular smooth muscle cell function and might be a mechanism that promotes PTS.

Preparation of Pulmonary Artery Myocytes and Rings to Study Vasoactive GPCRs

G protein-coupled receptors (GPCR) are crucial transducers of extracellular signals into changes in vascular tone. Vasoactive GPCR stimulation in the pulmonary circuit may be elicited by agonists released in acute tissue hypoxia or inflammation, as well as chronic disease. Acute responses involve activation of smooth muscle contraction or relaxation machinery causing changes in actomyosin interaction, thereby altering lumen diameter. Chronic responses may typically include activation of proliferation or fibrosis. Using pulmonary artery myocytes and pulmonary artery rings, we describe a general strategy for quantification of vasoconstrictor or vasodilator GPCR responses, and for comparison of signaling pathways in cultured cells and in contracted vessels using immunohistochemistry of contracting vessels.

Simultaneous Measurements of Tension and Free H2S in Mesenteric Arteries

Hydrogen sulfide (H₂S), in addition to nitric oxide and carbon monoxide, is the third gasotransmitter and known to cause relaxation in peripheral arteries. Here we describe a method that allows simultaneous measurement of contractility in arteries mounted in an isometric wire myograph and the concentration of free H₂S in the lumen of the artery as well as in the organ bath. This method can be used to directly correlate how much free H₂S is needed to cause relaxation, which previously has been difficult to answer as H₂S can be found in many different forms.

Vascular Myography to Examine Functional Responses of Isolated Blood Vessels

Vascular myography is an in vitro technique used to examine functional responses of isolated blood vessels. This classical pharmacological technique has been in use for over a century. The assay technique studies changes in isometric tone of large and small vessels, arteries and veins, and tissues from genetic or disease models. This chapter describes the apparatus required, tissue collection methods, and the mounting of the tissues in the chambers of both large organ baths and the small vessel myograph. Considerations of the experimental conditions and design are discussed as well as the analysis of the collected data.

A Simple Method for Normalization of Aortic Contractility

Vascular contractile function changes in proliferative vascular diseases, e.g. atherosclerosis, and is documented using isolated blood vessels; yet, many laboratories differ in their approach to quantification. Some use raw values (e.g., mg, mN); others use a "percentage of control agonist" approach; and others normalize by blood vessel characteristic, e.g. length, mass, etc. A lack of uniformity limits direct comparison of contractility outcomes. To address this limitation, we developed a simple 2-step normalization method: (1) measure blood vessel segment length (mm), area (mm2) and calculate volume (mm3); then, (2) normalize isometric contraction (mN) by segment length and volume. Normalized aortic contractions but not raw values were statistically different between normal chow and high-fat diet-fed mice, supporting the practical utility and general applicability of normalization. It is recommended that aortic contractions be normalized to segment length and/or volume to reduce variability, enhance efficiency, and to foster universal comparisons across isometric myography platforms, laboratories, and experimental settings.

Uterine electrical activity, oxytocin and labor: translating electrical into mechanical

PURPOSE

Uterine activity plays a crucial role in labor, especially when utero-tonic materials are administered. We aimed to determine the electrical responsiveness of the uterine musculature to labor augmentation with oxytocin using electrical uterine myography (EUM) technology, and to assess whether the kinetics of the EUM device may serve as a predictor for successful vaginal delivery.

METHODS

EUM prospectively measured electrical uterine activity in women with singleton gestations at term (≥ 37 + 0 weeks) undergoing labor augmentation by oxytocin administration. The results were reported as the EUM index, which represented the mean electrical activity in 10-min intervals and measured in units of microwatt per second (mW/s). Measurements were performed at least 30 min before oxytocin initiation and until at least four contractions per 10 min were recorded by standard tocodynamometry. The delta EUM index was defined as the difference between the mean EUM index before and after the initiation of oxytocin.

RESULTS

The mean EUM index increased significantly during oxytocin augmentation in all the parturients (P < 0.001). Mean and minimum (but not maximum) uterine electrical activity during oxytocin infusion correlated with the baseline uterine activity. The delta EUM index was not significantly affected by demographic or obstetric parameters. There was no correlation between the delta EUM index and time to delivery or the mean EUM index during oxytocin administration and time to delivery.

CONCLUSIONS

Uterine electrical activity as evaluated by EUM is significantly intensified following oxytocin administration, regardless of obstetrical characteristics, and is correlated with the baseline uterine electrical activity prior to oxytocin infusion.

A Toll-Like Receptor 1/2 Agonist Augments Contractility in Rat Corpus Cavernosum

INTRODUCTION

Activation of the innate immune Toll-like receptor 2 (TLR2) initiates inflammation and has been implicated in vascular dysfunction. Increased contraction and decreased relaxation responses in the penile vasculature lead to erectile dysfunction, a condition associated with inflammation. However, whether TLR2 activation plays a role in penile vascular function has not been established.

AIM

We hypothesized that activation of the TLR 1/2 heterodimer (TLR1/2) augments contractile and impairs relaxation responses of corpus cavernosum and that these perturbations of vascular function are mediated by low nitric oxide (NO) availability and enhanced activity of the RhoA/Rho-kinase pathway.

METHODS

Contraction and relaxation responses were measured in rat cavernosal strips using a myograph after incubation with a TLR1/2-activating ligand Pam3 CSK4 (Pam3), the TLR1/2 inhibitor CuCPT 22 (CuCPT), and inhibitors of NO synthase (LNAME) and Rho-kinase (Y27632). TLR2 protein expression was assessed by immunohistochemistry.

MAIN OUTCOME MEASURES

Cumulative concentration response curves, sensitivity (pEC50), and maximal response (Emax ) of cavernosal strips to vasodilatory and vasocontractile agonists were compared between treatments.

RESULTS

Pam3-treated cavernosal strips exhibited greater pEC50 and higher Emax to phenylephrine (PE) than control tissues. Inhibition of NO synthase increased Emax to PE in Pam3-treated cavernosal strips. Pam3 treatment reduced relaxation to Y27632 compared with control tissues. Inhibition of TLR1/2 activation with CuCPT returned the augmented contraction to PE and the decreased relaxation to Y27632 of Pam3-treated cavernosal strips to control values.

CONCLUSIONS

The TLR1/2 heterodimer mediates augmented contraction and reduced relaxation in rat cavernosal strips. Thus, TLR1/2 activation antagonizes vascular responses crucial for normal erectile function and implicates immune activation in vasculogenic erectile dysfunction. Immune signaling via TLR2 may offer novel targets for treating inflammation-mediated vascular dysfunction in the penis.

Analysis of the ghrelin receptor-independent vascular actions of ulimorelin

Ulimorelin (TZP101) is a ghrelin receptor agonist that stimulates intestinal motility, but also reduces blood pressure in rodents and humans and dilates blood vessels. It has been proposed as a treatment for intestinal motility disorders. Here we investigated the mechanisms through which ulimorelin affects vascular diameter. Actions of ulimorelin on wall tension of rodent arteries were investigated and compared with other ghrelin receptor agonists. Saphenous, mesenteric and basilar arteries were obtained from Sprague-Dawley rats (male, 8 weeks) and saphenous arteries were obtained from wild type or ghrelin receptor null mice. These were mounted in myography chambers to record artery wall tension. Ulimorelin (0.03-30µM) inhibited phenylephrine-induced contractions of rat saphenous (IC50=0.6µM; Imax=66±5%; n=3-6) and mesenteric arteries (IC50=5µM, Imax=113±16%; n=3-4), but not those contracted by U46619, ET-1 or 60mM [K(+)]. Relaxation of phenylephrine-constricted arteries was not observed with ghrelin receptor agonists TZP102, capromorelin or AZP-531. In rat saphenous and basilar arteries, ulimorelin (10-100µM) and TZP102 (10-100µM) constricted arteries (EC50=9.9µM; Emax=50±7% and EC50=8µM; Emax=99±16% respectively), an effect not attenuated by the ghrelin receptor antagonist YIL 781 3µM or mimicked by capromorelin or AZP-531. In mesenteric arteries, ulimorelin, 1-10µM, caused a surmountable rightward shift in the response to phenylephrine (0.01-1000µM; pA2=5.7; n=3-4). Ulimorelin had similar actions in mouse saphenous artery from both wild type and ghrelin receptor null mice. We conclude that ulimorelin causes vasorelaxation through competitive antagonist action at α1-adrenoceptors and a constrictor action not mediated via the ghrelin receptor.

How ubiquitous is endothelial NOS?

The ability to regulate vascular tone is an essential cardiovascular control mechanism, with nitric oxide (NO) assumed to be a ubiquitous smooth muscle relaxant. However, the literature contains reports of vasoconstrictor, vasodilator and no response to nitroergic stimulation in non-mammalian vertebrates. We examined functional (branchial artery myography), structural (immunohistochemistry of skeletal muscle), proteomic (Western analysis) and genomic (RT-PCR, sequence orthologues, syntenic analysis) evidence for endothelial NO synthase (NOS3) in model and non-model fish species. A variety of nitrodilators failed to elicit any changes in vascular tone, although a dilatation to exogenous cyclic GMP was noted. NOS3 antibody staining does not localise to endothelial markers in cryosections, and gives rise to non-specific staining of Western blots. Abundant NOS2 mRNA was found in all species but NOS3 was not found in any fish, while putative orthologues are not flanked by similar genes to NOS3 in humans. We conclude that NOS3 does not exist in fish, and that previous reports of its presence may reflect use of antibodies raised against mammalian epitopes.