1164 St Andrew’s COVID Surgery Safety (StACS) Study: Skin Cancer

Background

Skin cancer represents the most common malignancy worldwide and it is imperative that we develop strategies to ensure safe and sustained delivery of cancer care which are resilient to the ongoing impact of COVID-19.

Objective

This study prospectively evaluates the COVID-19 related patient risk and skin cancer management at a single tertiary referral centre, which rapidly implemented national COVID-safety guidelines.

Method

A prospective cohort study was performed in all patients who underwent surgery for elective skin cancer service management, during the UK COVID-19 pandemic peak (April-May 2020). ‘Real-time’ 30-day hospital database deceased data were collected. Random selection was undertaken for patients who either underwent operative (surgery group) management or remained on the waiting list (control group); these groups were also prospectively followed-up within a controlled cohort study design and telephoned at the end of June 2020 for the control group or 30 days post-operatively.

Results

Of the 767 patients who had operations, there were no COVID-19 related deaths. Both the surgery (n = 384) and control (n = 100) groups were matched for age, sex, ethnicity, BMI, presence of comorbidities, smoking and positive COVID-19 contact. There were no differences in post-operative versus any symptom development (1.3%, 5/384 vs. 4%, 4/100, p = 0.093), or proportion of positive tests (8.6%, 33/384 vs. 8%, 8/100; p = 0.849), between the surgery and control groups.

Conclusions

These data support continued and safe service provision, and no increased risk to skin cancer patients who require surgical management, which is vital for continuation of cancer treatment in the context of a pandemic.

Australian Aboriginal techniques for memorization: Translation into a medical and allied health education setting

BACKGROUND

Writing and digital storage have largely replaced organic memory for encoding and retrieval of information in the modern era, with a corresponding decrease in emphasis on memorization in Western education. In health professional training, however, there remains a large corpus of information for which memorization is the most efficient means of ensuring: A) that the trainee has the required information readily available; and B) that a foundation of knowledge is laid, upon which the medical trainee builds multiple, complex layers of detailed information during advanced training. The carefully staged progression in early- to late- years' medical training from broad concepts (e.g. gross anatomy and pharmacology) to in-depth, specialised disciplinary knowledge (e.g. surgical interventions and follow-on care post-operatively) has clear parallels to the progression of training and knowledge exposure that Australian Aboriginal youths undergo in their progression from childhood to adulthood to Tribal Elders.

METHODS

As part of the Rural Health curriculum and the undergraduate Nutrition and Dietetics program in the Monash University Faculty of Medicine, Nursing, and Health Sciences, we tested Australian Aboriginal techniques of memorization for acquisition and recall of novel word lists by first-year medical students (N = 76). We also examined undergraduate student evaluations (N = 49) of the use of the Australian Aboriginal memory technique for classroom study of foundational biomedical knowledge (the tricarboxylic acid cycle) using qualitative and quantitative analytic methods drawing from Bloom's taxonomy for orders of thinking and learning. Acquisition and recall of word lists were assessed without memory training, or after training in either the memory palace technique or the Australian Aboriginal narrative technique.

RESULTS

Both types of memory training improved the number of correctly recalled items and reduced the frequency of specific error types relative to untrained performance. The Australian Aboriginal method resulted in approximately a 3-fold greater probability of improvement to accurate recall of the entire word list (odds ratio = 2.82; 95% c.i. = 1.15-6.90), vs. the memory palace technique (odds ratio = 2.03; 95% c.i. = 0.81-5.06) or no training (odds ratio = 1.5; 95% c.i. = 0.54-4.59) among students who did not correctly recall all list items at baseline. Student responses to learning the Australian Aboriginal memory technique in the context of biomedical science education were overwhelmingly favourable, and students found both the training and the technique enjoyable, interesting, and more useful than rote memorization. Our data indicate that this method has genuine utility and efficacy for study of biomedical sciences and in the foundation years of medical training.

St Andrew's COVID-19 Surgery Safety (StACS) study: Skin cancer

BACKGROUND

Skin cancer represents the most common malignancy worldwide and it is imperative that we develop strategies to ensure safe and sustained delivery of cancer care which are resilient to the ongoing impact of COVID-19.

OBJECTIVE

This study prospectively evaluates the COVID-19 related patient risk and skin cancer management at a single tertiary referral centre, which rapidly implemented national COVID-19 safety guidelines.

METHOD

A prospective cohort study was performed in all patients who underwent surgery for elective skin cancer service management, during the UK COVID-19 pandemic peak (April-May 2020). 'Real-time' 30-day hospital database deceased data were collected. Random selection was undertaken for patients who either underwent operative (surgery group) management or remained on the waiting list (control group); these groups were also prospectively followed-up within a controlled cohort study design and telephoned at the end of June 2020 for the control group or 30 days post-operatively.

RESULTS

Of the 767 patients who had operations, there were no COVID-19 related deaths. Both the surgery (n = 384) and control (n = 100) groups were matched for age, sex, ethnicity, BMI, presence of comorbidities, smoking and positive COVID-19 contact. There were no differences in post-operative versus any symptom development (1.3%, 5/384 vs. 4%, 4/100, p = 0.093), or proportion of positive tests (8.6%, 33/384 vs. 8%, 8/100; p = 0.849), between the surgery and control groups.

CONCLUSION

These data support continued and safe service provision, and no increased risk to skin cancer patients who require surgical management, which is vital for continuation of cancer treatment in the context of a pandemic.

LEVEL OF EVIDENCE

II.

Sulforaphane improves vascular reactivity in mouse and human arteries after "preeclamptic-like" injury

INTRODUCTION

The widespread maternal endothelial dysfunction that underlies the manifestations of preeclampsia is thought to arise from excessive placental production of antiangiogenic factors and enhanced oxidative stress. Therefore, we assessed whether the natural antioxidant sulforaphane could improve vascular function.

METHODS

Cell viability of human umbilical vein endothelial cells (HUVECs) was assessed after 24 or 48 h in normoxia (20% O₂) or hypoxia (1% O₂) with or without sulforaphane. To model vascular dysfunction associated with preeclampsia, mouse mesenteric arteries were incubated in trophoblast conditioned media (TCM), and human omental arteries incubated in preeclamptic explant media (PEM) with or without sulforaphane. Both media are rich in antiangiogenic compounds associated with preeclampsia. TCM was generated from primary cytotrophoblast cells from term placentae of normotensive, while PEM was generated from explants from preeclamptic women. Reactivity was assessed by wire myography. sulforaphane's actions as a vasodilator were also investigated.

RESULTS

Under conditions of hypoxia, sulforaphane improved HUVEC viability. In mouse mesenteric arteries, sulforaphane reduced contraction evoked by potassium (p < 0.001), phenylephrine and endothelin 1 (all p < 0.001). Sulforaphane also inhibited Ca²⁺-induced contraction (p = 0.014). Sulforaphane prevented TCM-induced augmentation of phenylephrine and angiotensin II-mediated contraction of mouse mesenteric arteries. In human omental arteries, sulforaphane induced vasodilation (p < 0.001), and prevented PEM-induced endothelial dysfunction by restoring arterial sensitivity to the endothelium-dependent vasodilator bradykinin (p = 0.008).

DISCUSSION

Sulforaphane causes relaxation in arteries and protects against arterial dysfunction induced by placental-derived antiangiogenic factors, which are known to contribute to the preeclampsia.

Early impact of moderate preterm birth on the structure, function and gene expression of conduit arteries

NEW FINDINGS

What is the central question of this study? What is the immediate impact of moderate preterm birth on the structure and function of major conduit arteries using a pre-clinical sheep model? What is the main finding and its importance? Postnatal changes in conduit arteries, including a significant decrease in collagen within the thoracic aortic wall (predominately males), narrowed carotid arteries, reduced aortic systolic blood flow, and upregulation of the mRNA expression of cell adhesion and inflammatory markers at 2 days of age in preterm lambs compared to controls, may increase the risk of cardiovascular impairment in later life.

ABSTRACT

The aim of this work was to compare the structure and function of the conduit arteries of moderately preterm and term-born lambs and to determine whether vascular injury-associated genes were upregulated. Time-mated ewes were induced to deliver either preterm (132 ± 1 days of gestation; n = 11 females and n = 10 males) or at term (147 ± 1 days of gestation; n = 10 females and n = 5 males). Two days after birth, ultrasound imaging of the proximal ascending aorta, main, right and left pulmonary arteries, and right and left common carotid arteries was conducted in anaesthetized lambs. Lambs were then killed and segments of the thoracic aorta and left common carotid artery were either snap frozen for real-time PCR analyses or immersion-fixed for histological quantification of collagen, smooth muscle and elastin within the medial layer. Overall there were few differences in vascular structure between moderately preterm and term lambs. However, there was a significant decrease in the proportion of collagen within the thoracic aortic wall (predominantly in males), narrowing of the common carotid arteries and a reduction in peak aortic systolic blood flow in preterm lambs. In addition, there was increased mRNA expression of the cell adhesion marker P-selectin in the thoracic aortic wall and the pro-inflammatory marker IL-1β in the left common carotid artery in preterm lambs, suggestive of postnatal vascular injury. Early postnatal differences in the function and structure of conduit arteries and evidence of vascular injury in moderately preterm offspring may place them at greater risk of cardiovascular impairment later in life.

Relaxin reduces endothelium-derived vasoconstriction in hypertension: Revealing new therapeutic insights

BACKGROUND AND PURPOSE

Endothelium-derived vasoconstriction is a hallmark of vascular dysfunction in hypertension. In some cases, an overproduction of endothelium-derived prostacyclin (PGI₂ ) can cause contraction rather than relaxation. Relaxin is well known for its vasoprotective actions, but the possibility that this peptide could also reverse endothelium-derived vasoconstriction has never been investigated. We tested the hypothesis that short-term relaxin treatment mitigates endothelium-derived vasoconstriction in spontaneously hypertensive rats (SHR).

EXPERIMENTAL APPROACH

Male Wistar Kyoto rats (WKY) and SHR were subcutaneously infused with either vehicle (20 mmol·L^-1 sodium acetate) or relaxin (13.3 μg·kg^-1 ·hr^-1 ) using osmotic minipumps for 3 days. Vascular reactivity to the endothelium-dependent agonist ACh was assessed in vitro by wire myography. Quantitative PCR and LC-MS were used to identify changes in gene expression of prostanoid pathways and PG production, respectively.

KEY RESULTS

Relaxin treatment ameliorated hypertension-induced endothelial dysfunction by increasing NO-dependent relaxation and reducing endothelium-dependent contraction. Notably, short-term relaxin treatment up-regulated mesenteric PGI₂ receptor (IP) expression, permitting PGI₂ -IP-mediated vasorelaxation. In the aorta, reversal of contraction was accompanied by suppression of the hypertension-induced increase in prostanoid-producing enzymes and reduction in PGI₂ -evoked contractions.

CONCLUSIONS AND IMPLICATIONS

Relaxin has region-dependent vasoprotective actions in hypertension. Specifically, relaxin has distinct effects on endothelium-derived contracting factors and their associated vasoconstrictor pathways in mesenteric arteries and the aorta. Taken together, these observations reveal the potential of relaxin as a new therapeutic agent for vascular disorders that are associated with endothelium-derived vasoconstriction including hypertension.

Chronic low alcohol intake during pregnancy programs sex-specific cardiovascular deficits in rats

Background

Exposure to an adverse environment in early life can have lifelong consequences for risk of cardiovascular disease. Maternal alcohol (ethanol) intake is common and associated with a variety of harmful effects to the fetus. However, examining the effects on the cardiovascular system in adult offspring has largely been neglected. The objectives of this study were to investigate the influence of chronic, low ethanol consumption throughout pregnancy on blood pressure, vascular reactivity and wall stiffness, all key determinants of cardiovascular health, in both male and female rat offspring.

Methods

Female Sprague-Dawley rats were fed an ad libitum liquid diet ± 6% vol/vol ethanol throughout pregnancy. Male and female offspring were studied at 12 months of age. Arterial pressure, heart rate and locomotor activity were measured over 7 days via radiotelemetry. Renal lobar arteries were isolated and studied using wire and pressure myography.

Results

Basal mean arterial pressure in female ethanol-exposed rats was reduced by ~ 5–6 mmHg compared to control female offspring, whereas arterial pressure was unaffected in male offspring. Ethanol-exposed offspring had an attenuated pressor response to an acute restraint stress, with this effect most evident in females. Renal artery function was not affected by prenatal ethanol exposure.

Conclusions

We show for the first time that low level chronic maternal alcohol intake during pregnancy influences arterial pressure in adult offspring in the absence of fetal growth restriction.

Electronic supplementary material

The online version of this article (10.1186/s13293-019-0235-9) contains supplementary material, which is available to authorized users.

Uteroplacental insufficiency temporally exacerbates salt-induced hypertension associated with a reduced natriuretic response in male rat offspring

KEY POINTS

Low weight at birth increases the risk of developing chronic diseases in adulthood A diet that is high in salt is known to elevate blood pressure, which is a major risk factor for cardiovascular and kidney diseases The present study demonstrates that growth restricted male rats have a heightened sensitivity to high dietary salt, in the context of raised systolic blood pressure, reduced urinary sodium excretion and stiffer mesenteric resistance vessels Other salt-induced effects, such as kidney hyperfiltration, albuminuria and glomerular damage, were not exacerbated by being born small The present study demonstrates that male offspring born small have an increased cardiovascular susceptibility to high dietary salt, such that that minimizing salt intake is probably of particular benefit to this at-risk population ABSTRACT: Intrauterine growth restriction increases the risk of developing chronic diseases in adulthood. Lifestyle factors, such as poor dietary choices, may elevate this risk. We determined whether being born small increases the sensitivity to a dietary salt challenge, in the context of hypertension, kidney disease and arterial stiffness. Bilateral uterine vessel ligation or sham surgery (offspring termed Restricted and Control, respectively) was performed on 18-day pregnant Wistar Kyoto rats. Male offspring were allocated to receive a diet high in salt (8% sodium chloride) or remain on standard rat chow (0.52% sodium chloride) from 20 to 26 weeks of age for 6 weeks. Systolic blood pressure (tail-cuff), renal function (24 h urine excretions) and vascular stiffness (pressure myography) were assessed. Restricted males were born 15% lighter than Controls and remained smaller throughout the study. Salt-induced hypertension was exacerbated in Restricted offspring, reaching a peak systolic pressure of ∼175 mmHg earlier than normal weight counterparts. The natriuretic response to high dietary salt in Restricted animals was less than in Controls and may explain the early rise in arterial pressure. Growth restricted males allocated to a high salt diet also had increased passive arterial stiffness of mesenteric resistance arteries. Other aspects of renal function, including salt-induced hyperfiltration, albuminuria and glomerular damage, were not exacerbated by uteroplacental insufficiency. The present study demonstrates that male offspring exposed to uteroplacental insufficiency and born small have an increased sensitivity to salt-induced hypertension and arterial remodelling.

Sepsis-induced acute kidney injury: A disease of the microcirculation

AKI is a common complication of sepsis and is significantly associated with mortality. Sepsis accounts for more than 50% of the cases of AKI, with a mortality rate of up to 40%. The pathogenesis of septic AKI is complex, but there is emerging evidence that, at least in the first 48 hours, the defects may be functional rather than structural in nature. For example, septic AKI is associated with an absence of histopathological changes, but with microvascular abnormalities and tubular stress. In this context, renal medullary hypoxia due to redistribution of intra-renal perfusion is emerging as a critical mediator of septic AKI. Clinically, vasopressor drugs remain the cornerstone of therapy for maintenance of blood pressure and organ perfusion. However, in septic AKI, there is insensitivity to vasopressors such as norepinephrine, leading to persistent hypotension and organ failure. Vasopressin, angiotensin II, and, paradoxically, α₂ -adrenergic receptor agonists (clonidine and dexmedetomidine) may be feasible adjunct therapies for catecholamine-resistant vasodilatory shock. In this review, we outline the recent progress made in understanding how these drugs may influence the renal microcirculation, which represents a crucial step toward developing better approaches for the circulatory management of patients with septic AKI.

Angiotensin receptor blockade in juvenile male rat offspring: Implications for long-term cardio-renal health

Inhibition of the renin-angiotensin system in early postnatal life is a potential therapeutic approach to prevent long-term cardiovascular and kidney diseases in individuals born small. We determined the long-term effects of juvenile losartan treatment on cardiovascular and kidney function in control male rat offspring and those exposed to uteroplacental insufficiency and born small. Bilateral uterine vessel ligation (Restricted) or sham (Control) surgery was performed in late gestation in Wistar Kyoto rats. At weaning, male offspring were randomly assigned to receive losartan in their drinking water or drinking water alone from 5 to 8 weeks of age, and followed to 26 weeks of age. Systolic blood pressure and kidney function were assessed throughout the study. Pressure myography was used to assess passive mechanical wall properties in mesenteric and femoral arteries from 26-week-old offspring. Losartan treatment for three weeks lowered systolic blood pressure in both Control and Restricted groups but this difference was not sustained after the cessation of treatment. Losartan, irrespective of birth weight, mildly increased renal tubulointerstitial fibrosis when assessed at 26 weeks of age. Mesenteric artery stiffness was increased by the early losartan treatment, and was associated with increased collagen and decreased elastin content. Losartan also exerted long-term increases in fat mass and decreases in skeletal muscle mass. In this study, untreated Restricted offspring did not develop hypertension, vascular dysfunction or kidney changes as anticipated. Regardless, we demonstrate that short-term losartan treatment in the juvenile period negatively affects postnatal growth, and kidney and vascular parameters in adulthood, irrespective of birth weight. The long-term effects of early-life losartan treatment warrant further consideration in settings where the potential benefits may outweigh the risks; i.e. when programmed adulthood diseases are apparent and in childhood cardiovascular and kidney diseases.

Short-term (48 hours) intravenous serelaxin infusion has no effect on myogenic tone or vascular remodeling in rat mesenteric arteries

BACKGROUND

Short-term IV sRLX (recombinant human relaxin-2) infusion enhances endothelium-dependent relaxation in mesenteric arteries. This is initially underpinned by increased NO followed by a transition to prostacyclin. The effects of short-term IV sRLX treatment on pressure-induced myogenic tone and vascular remodeling in these arteries are unknown. Therefore, we investigated the effects of sRLX infusion on pressure-induced myogenic tone and passive mechanical wall properties in mesenteric arteries.

METHODS

Mesenteric artery myogenic tone and passive mechanics were examined after 48-hours and 10-days infusion of sRLX. Potential mechanisms of action were assessed by pressure myography, qPCR, and Western blot analysis.

RESULTS

Neither 48-hours nor 10-days sRLX treatment had significant effects on myogenic tone, passive arterial wall stiffness, volume compliance, or axial lengthening. However, in 48-hours sRLX -treated rats, incubation with the NO synthase blocker L-NAME significantly increased myogenic tone (P<.05 vs placebo), demonstrating an increased contribution of NO to the regulation of myogenic tone. eNOS dimerization, but not phosphorylation, was significantly upregulated in the arteries of sRLX -treated rats.

CONCLUSION

In mesenteric arteries, 48-hours sRLX treatment upregulates the role of NO in the regulation of myogenic tone by enhancing eNOS dimerization, without altering overall myogenic tone or vascular remodeling.

Relaxin Deficiency Leads to Uterine Artery Dysfunction During Pregnancy in Mice

The uterine vasculature undergoes profound adaptations in response to pregnancy. Augmentation of endothelial vasodilator function and reduced smooth muscle reactivity are factors contributing to uterine artery adaptation and are critical for adequate placental perfusion. The peptide hormone relaxin has an important role in mediating the normal maternal renal vascular adaptations during pregnancy through a reduction in myogenic tone and an increase in flow-mediated vasodilation. Little is known however about the influence of endogenous relaxin on the uterine artery during pregnancy. We tested the hypothesis that relaxin deficiency increases myogenic tone and impairs endothelial vasodilator function in uterine arteries of late pregnant relaxin deficient (Rln^−/−) mice. Reactivity of main uterine arteries from non-pregnant and late pregnant wild-type (Rln^+/+) and Rln^−/− mice was studied using pressure and wire myography and changes in gene expression explored using PCR. Myogenic tone was indistinguishable in arteries from non-pregnant mice. In late pregnancy uterine artery myogenic tone was halved in Rln^+/+ mice (P < 0.0001), an adaptation that failed to occur in arteries from pregnant Rln^−/− mice. The role of vasodilator prostanoids in the regulation of myogenic tone was significantly reduced in arteries of pregnant Rln^−/− mice (P = 0.02). Agonist-mediated endothelium-dependent vasodilation was significantly impaired in non-pregnant Rln^−/− mice. With pregnancy, differences in total endothelial vasodilator function were resolved, although there remained an underlying deficiency in the role of vasodilator prostanoids and alterations to the contributions of calcium-activated K⁺ channels. Fetuses of late pregnant Rln^−/− mice were ~10% lighter (P < 0.001) than those of Rln^+/+ mice. In conclusion, relaxin deficiency is associated with failed suppression of uterine artery myogenic tone in pregnancy, which likely contributes to reduced uteroplacental perfusion and fetal growth restriction.

Relaxin treatment reduces angiotensin II-induced vasoconstriction in pregnancy and protects against endothelial dysfunction†

The peptide relaxin has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in cardiovascular disease. In this study, we tested the hypothesis that relaxin treatment alleviates systemic vascular dysfunction characteristic of hypertensive diseases of pregnancy. We investigated vascular effects and mechanisms of relaxin action in (i) pregnant relaxin-deficient (Rln-/-) mice with enhanced responses to angiotensin II (AngII) and (ii) arteries pre-incubated ex vivo in trophoblast conditioned media (TCM) to induce endothelial dysfunction. Pregnant Rln-/- mice received 0.5 μg/h recombinant human H2 relaxin (rhRLX: n = 5) or placebo (20 nM sodium acetate; n = 7) subcutaneously via osmotic minipumps for 5 days prior to gestational day 17.5. This treatment protocol significantly reduced AngII-mediated contraction of mesenteric arteries and increased plasma 6-keto prostaglandin F1α. These vascular effects were endothelium independent and likely involve smooth muscle-derived vasodilator prostanoids. In the second study, mesenteric arteries were incubated ex vivo for 24 h at 37°C in TCM, which contained high levels of soluble Flt-1 (>20 ng/ml) and soluble Eng (>1 ng/ml). TCM incubation caused significant reduction in endothelium-dependent relaxation and increased sensitivity to AngII. Co-incubation of arteries with rhRLX for 24 h (n = 6-16/treatment) prevented endothelial dysfunction but had no effect on AngII-mediated contraction. In conclusion, relaxin treatment prevents and/or reverses vascular dysfunction in mesenteric arteries, but acts through different vascular pathways depending on duration of relaxin treatment and type of vascular dysfunction. Overall, our data suggest that relaxin is a potential therapeutic to alleviate maternal systemic vascular dysfunction associated with hypertensive diseases in pregnant women.

Vasoactive actions of nitroxyl (HNO) are preserved in resistance arteries in diabetes

Endothelial dysfunction is a major risk factor for the vascular complications of diabetes. Increased reactive oxygen species (ROS) generation, a hallmark of diabetes, reduces the bioavailability of endothelial vasodilators, including nitric oxide (NO·). The vascular endothelium also produces the one electron reduced and protonated form of NO·, nitroxyl (HNO). Unlike NO·, HNO is resistant to scavenging by superoxide anions (·O₂^─). The fate of HNO in resistance arteries in diabetes is unknown. We tested the hypothesis that the vasodilator actions of endogenous and exogenous HNO are preserved in resistance arteries in diabetes. We investigated the actions of HNO in small arteries from the mesenteric and femoral beds as they exhibit marked differences in endothelial vasodilator function following 8 weeks of streptozotocin (STZ)-induced diabetes mellitus. Vascular reactivity was assessed using wire myography and ·O₂^─ generation using lucigenin-enhanced chemiluminescence. The HNO donor, Angeli's salt, and the NO· donor, DEA/NO, evoked relaxations in both arteries of control rats, and these responses were unaffected by diabetes. Nox2 oxidase expression and ·O₂^─ generation were upregulated in mesenteric, but unchanged, in femoral arteries of diabetic rats. Acetylcholine-induced endothelium-dependent relaxation was impaired in mesenteric but not femoral arteries in diabetes. The HNO scavenger, L-cysteine, reduced this endothelium-dependent relaxation to a similar extent in femoral and mesenteric arteries from control and diabetic animals. In conclusion, HNO and NO· contribute to the NO synthase (NOS)-sensitive component of endothelium-dependent relaxation in mesenteric and femoral arteries. The role of HNO is sustained in diabetes, serving to maintain endothelium-dependent relaxation.

Nonlinear effects of potassium channel blockers on endothelium-dependent hyperpolarization

In a number of published studies on endothelium-dependent hyperpolarization and relaxation, the results of the effects of K⁺ blockers have been difficult to interpret. When the effects of two blockers have been studied, often either blocker by itself had little effect, whereas the two blockers combined tended to abolish the responses. Explanations suggested in the literature include an unusual pharmacology of the K⁺ channels, and possible blocker binding interactions. In contrast, when we applied the same blockers to segments of small blood vessels under voltage clamp, the blockers reduced the endothelium-dependent K⁺ current in a linearly additive manner. Resolution of these contrasting results is important as endothelium-derived hyperpolarization (EDH) makes its greatest contribution to vasorelaxation in arterioles and small resistance arteries, where it can exert a significant role in tissue perfusion and blood pressure regulation. Furthermore, EDH is impaired in various diseases. Here, we consider why the voltage-clamp results differ from earlier free-running membrane potential and contractility studies. We fitted voltage-clamp-derived current-voltage relationships with mathematical functions and considered theoretically the effects of partial and total block of endothelium-derived K⁺ -currents on the membrane potential of small blood vessels. When the K⁺ -conductance was partially reduced, equivalent to applying a single blocker, the effect on EDH was small. Total block of the endothelium-dependent K⁺ conductance abolished the hyperpolarization, in agreement with various published studies. We conclude that nonlinear summation of the hyperpolarizing response evoked by endothelial stimulation can explain the variable effectiveness of individual K⁺ channel blockers on endothelium-dependent hyperpolarization and resulting relaxation.

Vascular actions of relaxin: nitric oxide and beyond

The peptide hormone relaxin regulates the essential maternal haemodynamic adaptations in early pregnancy through direct actions on the renal and systemic vasculature. These vascular actions of relaxin occur mainly through endothelium-derived NO-mediated vasodilator pathways and improvements in arterial compliance in small resistance-size arteries. This work catalysed a plethora of studies which revealed quite heterogeneous responses across the different regions of the vasculature, and also uncovered NO-independent mechanisms of relaxin action. In this review, we first describe the role of endogenous relaxin in maintaining normal vascular function, largely referring to work in pregnant and male relaxin-deficient animals. We then discuss the diversity of mechanisms mediating relaxin action in different vascular beds, including the involvement of prostanoids, VEGF, endothelium-derived hyperpolarisation and antioxidant activity in addition to the classic NO-mediated vasodilatory pathway. We conclude the review with current perspectives on the vascular remodelling capabilities of relaxin.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Relaxin deficiency attenuates pregnancy-induced adaptation of the mesenteric artery to angiotensin II in mice

Pregnancy is associated with reduced peripheral vascular resistance, underpinned by changes in endothelial and smooth muscle function. Failure of the maternal vasculature to adapt correctly leads to serious pregnancy complications, such as preeclampsia. The peptide hormone relaxin regulates the maternal renal vasculature during pregnancy; however, little is known about its effects in other vascular beds. This study tested the hypothesis that functional adaptation of the mesenteric and uterine arteries during pregnancy will be compromised in relaxin-deficient ( Rln−/−) mice. Smooth muscle and endothelial reactivity were examined in small mesenteric and uterine arteries of nonpregnant (estrus) and late-pregnant ( day 17.5) wild-type ( Rln+/+) and Rln−/− mice using wire myography. Pregnancy per se was associated with significant reductions in contraction to phenylephrine, endothelin-1, and ANG II in small mesenteric arteries, while sensitivity to endothelin-1 was reduced in uterine arteries of Rln+/+ mice. The normal pregnancy-associated attenuation of ANG II-mediated vasoconstriction in mesenteric arteries did not occur in Rln−/− mice. This adaptive failure was endothelium-independent and did not result from altered expression of ANG II receptors or regulator of G protein signaling 5 ( Rgs5) or increases in reactive oxygen species generation. Inhibition of nitric oxide synthase with l-NAME enhanced ANG II-mediated contraction in mesenteric arteries of both genotypes, whereas blockade of prostanoid production with indomethacin only increased ANG II-induced contraction in arteries of pregnant Rln+/+ mice. In conclusion, relaxin deficiency prevents the normal pregnancy-induced attenuation of ANG II-mediated vasoconstriction in small mesenteric arteries. This is associated with reduced smooth muscle-derived vasodilator prostanoids.

Time-dependent activation of prostacyclin and nitric oxide pathways during continuous i.v. infusion of serelaxin (recombinant human H2 relaxin)

BACKGROUND AND PURPOSE

In the RELAX-AHF trial, a 48 h i.v. serelaxin infusion reduced systemic vascular resistance in patients with acute heart failure. Consistent with preclinical studies, serelaxin augments endothelial vasodilator function in rat mesenteric arteries. Little is known about the contribution of endothelium-derived relaxing factors after a longer duration of continuous serelaxin treatment. Here we have assessed vascular reactivity and mechanistic pathways in mesenteric arteries and veins and the aorta after 48 or 72 h continuous i.v. infusion of serelaxin.

EXPERIMENTAL APPROACH

Male rats were infused with either placebo or serelaxin (13.3 μg·kg(-1) ·h(-1) ) via the jugular vein using osmotic minipumps. Vascular function was assessed using wire myography. Changes in gene and protein expression and 6-keto PGF1α levels were determined by quantitative PCR, Western blot and ELISA respectively.

KEY RESULTS

Continuous i.v. serelaxin infusion augmented endothelium-dependent relaxation in arteries (mesenteric and aorta) but not in mesenteric veins. In mesenteric arteries, 48 h i.v. serelaxin infusion increased basal NOS activity, associated with increased endothelial NOS (eNOS) expression. Interestingly, phosphorylated-eNOS(Ser1177) , eNOS and basal NOS activity were reduced in mesenteric arteries following 72 h serelaxin treatment. At 72 h, serelaxin treatment improved bradykinin-mediated relaxation through COX2-derived PGI2 production.

CONCLUSIONS AND IMPLICATIONS

Continuous i.v. serelaxin infusion enhanced endothelial vasodilator function in arteries but not in veins. The underlying mediator at 48 h was NO but there was a transition to PGI2 by 72 h. Activation of the PGI2 -dependent pathway is key to the prolonged vascular response to serelaxin treatment.

Accelerated age-related decline in renal and vascular function in female rats following early-life growth restriction

Many studies report sexual dimorphism in the fetal programming of adult disease. We hypothesized that there would be differences in the age-related decline in renal function between male and female intrauterine growth-restricted rats. Early-life growth restriction was induced in rat offspring by administering a low-protein diet (LPD; 8.7% casein) to dams during pregnancy and lactation. Control dams were fed a normal-protein diet (NPD; 20% casein). Mean arterial pressure (MAP) and renal structure and function were assessed in 32- and 100-wk-old offspring. Mesenteric artery function was examined at 100 wk using myography. At 3 days of age, body weight was ∼24% lower ( P < 0.0001) in LPD offspring; this difference was still apparent at 32 wk but not at 100 wk of age. MAP was not different between the male NPD and LPD groups at either age. However, MAP was greater in LPD females compared with NPD females at 100 wk of age (∼10 mmHg; P < 0.001). Glomerular filtration rate declined with age in the NPD male, LPD male and LPD female offspring (∼45%, all P < 0.05), but not in NPD female offspring. Mesenteric arteries in the aged LPD females had reduced sensitivity to nitric oxide donors compared with their NPD counterparts, suggesting that vascular dysfunction may contribute to the increased risk of disease in aged females. In conclusion, females growth-restricted in early life were no longer protected from an age-related decline in renal and arterial function, and this was associated with increased arterial pressure without evidence of renal structural damage.

Differential effects of relaxin deficiency on vascular aging in arteries of male mice

Exogenous treatment with the naturally occurring peptide relaxin increases arterial compliance and reduces vascular stiffness. In contrast, relaxin deficiency reduces the passive compliance of small renal arteries through geometric and compositional vascular remodeling. The role of endogenous relaxin on passive mechanical wall properties in other vascular beds is unknown. Importantly, no studies have investigated the effects of aging in arteries of relaxin-deficient mice. Therefore, we tested the hypothesis that mesenteric and femoral arteries stiffen with aging, and this is exacerbated with relaxin deficiency. Male wild-type (Rln (+/+)) and relaxin knockout (Rln (-/-)) mice were aged to 3, 6, 12, 18, and 23 months. Passive mechanical wall properties were assessed by pressure myography. In both genotypes, there was a significant increase in circumferential stiffening in mesenteric arteries with aging, whereas in the femoral artery, aging reduced volume compliance. This was associated with a reduced ability of the artery to lengthen with aging. The predominant phenotype observed in Rln (-/-) mice was reduced volume compliance in young mice in both mesenteric and femoral arteries. In summary, aging induces circumferential stiffening in mesenteric arteries and axial stiffening in femoral arteries. Passive mechanical wall properties of Rln (-/-) mouse arteries predominantly differ at younger ages compared with Rln (+/+) mice, suggesting that a lack of endogenous relaxin only has a minor effect on vascular aging.

M2 macrophage accumulation in the aortic wall during angiotensin II infusion in mice is associated with fibrosis, elastin loss, and elevated blood pressure

Macrophages accumulate in blood vessels during hypertension. However, their contribution to vessel remodeling is unknown. In the present study, we examined the polarization state of macrophages (M1/M2) in aortas of mice during hypertension and investigated whether antagonism of chemokine receptors involved in macrophage accumulation reduces vessel remodeling and blood pressure (BP). Mice treated with ANG II (0.7 mg·kg(-1)·day(-1), 14 days) had elevated systolic BP (158 ± 3 mmHg) compared with saline-treated animals (122 ± 3 mmHg). Flow cytometry revealed that ANG II infusion increased numbers of CD45(+)CD11b(+)Ly6C(hi) monocytes and CD45(+)CD11b(+)F4/80(+) macrophages by 10- and 2-fold, respectively. The majority of macrophages were positive for the M2 marker CD206 but negative for the M1 marker inducible nitric oxide synthase. Expression of other M2 genes (arginase-1, Fc receptor-like S scavenger receptor, and receptor-1) was elevated in aortas from ANG II-treated mice, whereas M1 genes [TNF and chemokine (C-X-C motif) ligand 2] were unaltered. A PCR array to identify chemokine receptor targets for intervention revealed chemokine (C-C motif) receptor 2 (CCR2) to be upregulated in aortas from ANG II-treated mice, while flow cytometry identified Ly6C(hi) monocytes as the main CCR2-expressing cell type. Intervention with a CCR2 antagonist (INCB3344; 30 mg·kg(-1)·day(-1)), 7 days after the commencement of ANG II infusion, reduced aortic macrophage numbers. INCB334 also reduced aortic collagen deposition, elastin loss, and BP in ANG II-treated mice. Thus, ANG II-dependent hypertension in mice is associated with Ly6C(hi) monocyte and M2 macrophage accumulation in the aorta. Inhibition of macrophage accumulation with a CCR2 antagonist prevents ANG II-induced vessel fibrosis and elevated BP, highlighting this as a promising approach for the future treatment of vessel remodeling/stiffening in hypertension.

Regulator of G protein signaling 5 is a determinant of gestational hypertension and preeclampsia

Preeclampsia is a systemic vascular disorder of pregnancy and is associated with increased sensitivity to angiotensin II (AngII) and hypertension. The cause of preeclampsia remains unknown. We identified the role of regulator of G protein (heterotrimeric guanine nucleotide–binding protein) signaling 5 (RGS5) in blood pressure regulation during pregnancy and preeclampsia. RGS5 expression in human myometrial vessels is markedly suppressed in gestational hypertension and/or preeclampsia. In pregnant RGS5-deficient mice, reduced vascular RGS5 expression causes gestational hypertension by enhancing vascular sensitivity to AngII. Further challenge by increasing AngII results in preeclampsia-like symptoms, namely, more severe hypertension, proteinuria, placental pathology, and reduced birth weight. In pregnant heterozygote null mice, treatment with peroxisome proliferator–activated receptor (PPAR) agonists normalizes vascular function and blood pressure through effects on RGS5. These findings highlight a key role of RGS5 at the interface between AngII and PPAR signaling. Because preeclampsia is refractory to current standard therapies, our study opens an unrecognized and urgently needed opportunity for treatment of gestational hypertension and preeclampsia.

Renal dysfunction is associated with a reduced contribution of nitric oxide and enhanced vasoconstriction after a congenital renal mass reduction in sheep

BACKGROUND

Children born with reduced congenital renal mass have an increased risk of hypertension and chronic kidney disease in adulthood, although the mechanisms are poorly understood. Similar sequelae occur after fetal uninephrectomy (uni-x) in sheep, leading to a 30% nephron deficit. We hypothesized that renal dysfunction is underpinned by a reduced contribution of nitric oxide (NO) and vascular dysfunction in uni-x sheep.

METHODS AND RESULTS

In 5-year-old female uni-x and sham sheep, mean arterial pressure, glomerular filtration rate, and renal blood flow were measured before and during NO inhibition (N(ω)-nitro-l-arginine methyl ester [L-NAME]). Reactivity was assessed in resistance arteries, including renal lobar and arcuate arteries. Basal mean arterial pressure was 15 mm Hg higher and glomerular filtration rate and renal blood flow were ≈30% lower (P<0.001) in uni-x animals. L-NAME increased mean arterial pressure by ≈17 mm Hg in both groups, whereas glomerular filtration rate and renal blood flow were decreased less in uni-x sheep (PInteraction<0.01). Endothelial NO synthase and Ser-1177-phosphorylated endothelial NO synthase protein levels were upregulated in renal cortex of uni-x sheep (P<0.05). Lobar arteries of uni-x sheep had enhanced responsiveness to phenylephrine and nitrotyrosine staining and reduced sensitivity to endothelial stimulation. Vasodilator prostanoid contribution to endothelium-dependent relaxation was reduced in lobar arteries of uni-x sheep, accompanied by reduced cyclooxygenase-1 and -2 gene expression (P<0.05). Neurovascular constriction was enhanced ≈1.5-fold in renal arteries of uni-x sheep (P<0.05).

CONCLUSIONS

Renal dysfunction after congenital renal mass reduction is associated with impaired regulation of renal hemodynamics by NO. Reductions in renal blood flow and glomerular filtration rate are underpinned by impaired basal NO contribution, endothelial dysfunction, and enhanced vascular responsiveness to sympathetic nerve stimulation.

A vasoactive role for endogenous relaxin in mesenteric arteries of male mice

The peptide hormone relaxin has striking effects on the vascular system. Specifically, endogenous relaxin treatment reduces myogenic reactivity through nitric oxide (NO)-mediated vasorelaxation and increases arterial compliance in small resistance arteries. However, less is known about the vascular roles of endogenous relaxin, particularly in males. Therefore, we used male wild-type (Rln^+/+) and relaxin knockout (Rln^−/−) mice to test the hypothesis that passive wall properties and vascular reactivity in mesenteric arteries would be compromised in Rln^−/− mice. Passive compliance was determined in arteries (n = 8–9) mounted on a pressure myograph and in Ca²⁺-free Krebs containing 2 mM EGTA. Passive volume compliance was significantly (P = 0.01) decreased in the mesenteric arteries of Rln^−/− mice. Vascular reactivity was assessed using wire myography. In mesenteric arteries (n = 5) of Rln^−/− mice, there was a significant (P<0.03) increase in sensitivity to the vasoconstrictors phenylephrine and thromboxane-mimetic U41669. This enhanced responsiveness to vasoconstrictors was abolished by endothelial denudation, and attributed to impaired NO and prostanoid pathways in Rln^−/− mice. Sensitivity to the endothelial agonist acetylcholine was significantly (n = 7–9, P≤0.03) decreased, and this was abolished in the presence of the cyclooxygenase inhibitor, indomethacin (2 µM). This indicates that prostanoid vasoconstrictor pathways were upregulated in the mesenteric arteries of Rln^−/− mice. In summary, we demonstrate endothelial dysfunction and impaired arterial wall remodeling in male mice deficient in relaxin. Thus, our results highlight a role for endogenous relaxin in the maintenance of normal mesenteric artery structure and function in males.

Maternal alcohol consumption in pregnancy enhances arterial stiffness and alters vasodilator function that varies between vascular beds in fetal sheep

While the impact of alcohol consumption by pregnant women on fetal neurodevelopment has received much attention, the effects on the cardiovascular system are not well understood. We hypothesised that repeated exposure to alcohol (ethanol) in utero would alter fetal arterial reactivity and wall stiffness, key mechanisms leading to cardiovascular disease in adulthood. Ethanol (0.75 g (kg body weight)(-1)) was infused intravenously into ewes over 1 h daily for 39 days in late pregnancy (days 95-133 of pregnancy, term ∼147 days). Maternal and fetal plasma ethanol concentrations at the end of the hour were ∼115 mg dl(-1), and then declined to apparent zero over 8 h. At necropsy (day 134), fetal body weight and fetal brain-body weight ratio were not affected by alcohol infusion. Small arteries (250-300 μm outside diameter) from coronary, renal, mesenteric, femoral (psoas) and cerebral beds were isolated. Endothelium-dependent vasodilatation sensitivity was reduced 10-fold in coronary resistance arteries, associated with a reduction in endothelial nitric oxide synthase mRNA (P = 0.008). Conversely, vasodilatation sensitivity was enhanced 10-fold in mesenteric and renal resistance arteries. Arterial stiffness was markedly increased (P = 0.0001) in all five vascular beds associated with an increase in elastic modulus and, in cerebral vessels, with an increase in collagen Iα mRNA. Thus, we show for the first time that fetal arteries undergo marked and regionally variable adaptations as a consequence of repeated alcohol exposure. These alcohol-induced vascular effects occurred in the apparent absence of fetal physical abnormalities or fetal growth restriction.

Maternal melatonin administration mitigates coronary stiffness and endothelial dysfunction, and improves heart resilience to insult in growth restricted lambs

Intrauterine growth restriction (IUGR) is associated with impaired cardiac function in childhood and is linked to short- and long-term morbidities. Placental dysfunction underlies most IUGR, and causes fetal oxidative stress which may impact on cardiac development. Accordingly, we investigated whether antenatal melatonin treatment, which possesses antioxidant properties, may afford cardiovascular protection in these vulnerable fetuses. IUGR was induced in sheep fetuses using single umbilical artery ligation on day 105-110 of pregnancy (term 147). Study 1: melatonin (2 mg h(-1)) was administered i.v. to ewes on days 5 and 6 after surgery. On day 7 fetal heart function was assessed using a Langendorff apparatus. Study 2: a lower dose of melatonin (0.25 mg h(-1)) was administered continuously following IUGR induction and the ewes gave birth normally at term. Lambs were killed when 24 h old and coronary vessels studied. Melatonin significantly improved fetal oxygenation in vivo. Contractile function in the right ventricle and coronary flow were enhanced by melatonin. Ischaemia-reperfusion-induced infarct area was 3-fold greater in IUGR hearts than in controls and this increase was prevented by melatonin. In isolated neonatal coronary arteries, endothelium-dependent nitric oxide (NO) bioavailability was reduced in IUGR, and was rescued by modest melatonin treatment. Melatonin exposure also induced the emergence of an indomethacin-sensitive vasodilation. IUGR caused marked stiffening of the coronary artery and this was prevented by melatonin. Maternal melatonin treatment reduces fetal hypoxaemia, improves heart function and coronary blood flow and rescues cardio-coronary deficit induced by IUGR.

Acute intravenous injection of serelaxin (recombinant human relaxin-2) causes rapid and sustained bradykinin-mediated vasorelaxation

Background

A recent clinical trial (RELAXin in Acute Heart Failure [RELAX‐AHF]) demonstrated that 48 hours of continuous intravenous infusion of the vasorelaxant peptide serelaxin (recombinant human relaxin‐2) to patients with acute heart failure reduced cardiovascular mortality at 180 days. The persistence of a vasorelaxant response as a potential mechanism for this long‐term benefit and the vascular effects of a bolus intravenous injection of serelaxin have not been examined. This study investigates changes in resistance artery reactivity and passive mechanical wall properties following an intravenous serelaxin injection and whether these vascular effects persist in the absence of detectable circulating serelaxin.

Methods and Results

Male rats were injected with 13.3 μg/kg serelaxin into the tail vein; mesenteric arteries were assessed 3 and 24 hours after treatment by using wire‐myography. Serelaxin increased basal nitric oxide synthase activity and reduced maximal contraction to endothelin‐1 at 3 hours after administration. Serelaxin treatment also selectively enhanced bradykinin‐mediated endothelium‐dependent relaxation. This effect was sustained for 24 hours in the absence of circulating serelaxin. Serelaxin‐mediated augmentation of bradykinin‐evoked relaxation involved endothelium‐derived hyperpolarization after 3 hours and prostacyclin‐mediated relaxation after 24 hours. Furthermore, upregulation of inducible nitric oxide synthase, phosphorylation of protein kinase B at Ser473 and endothelial nitric oxide synthase at Ser1177 was observed at 24 hours after serelaxin injection. There were no effects of serelaxin on passive arterial wall stiffness.

Conclusion

Our data show that a bolus intravenous injection of serelaxin modulates endothelial vasodilator function 3 hours after administration, an effect that was sustained for 24 hours. The prolonged bradykinin‐mediated vasorelaxation is principally mediated through prostacyclin.

Loss of a kidney during fetal life: long-term consequences and lessons learned

Epidemiological studies reveal that children born with a solitary functioning kidney (SFK) have a greater predisposition to develop renal insufficiency and hypertension in early adulthood. A congenital SFK is present in patients with unilateral renal agenesis or unilateral multicystic kidney dysplasia, leading to both structural and functional adaptations in the remaining kidney, which act to mitigate the reductions in glomerular filtration rate and sodium excretion that would otherwise ensue. To understand the mechanisms underlying the early development of renal insufficiency in children born with a SFK, we established a model of fetal uninephrectomy (uni-x) in sheep, a species that similar to humans complete nephrogenesis before birth. This model results in a 30% reduction in nephron number rather than 50%, due to compensatory nephrogenesis in the remaining kidney. Similar to children with a congenital SFK, uni-x sheep demonstrate a progressive increase in arterial pressure and a loss of renal function with aging. This review summarizes the compensatory changes in renal hemodynamics and tubular sodium handling that drive impairments in renal function and highlights the existence of sex differences in the functional adaptations following the loss of a kidney during fetal life.

Hypotensive and vascular relaxant effects of phospholipase A2 toxins from Papuan taipan (Oxyuranus scutellatus) venom

Phospholipase A2 (PLA2) toxins are common and abundant components of Australasian elapid venoms. These toxins are associated with a range of activities including neurotoxicity, myotoxicity and coagulation disturbances. We have recently reported that sudden cardiovascular collapse induced by Papuan taipan (Oxyuranus scutellatus) venom involves a combination of the release of dilator autacoids and a direct effect on the smooth muscle. In this study, we aimed to isolate PLA2 components from Papuan taipan venom and investigate their contribution to the hypotensive action of this venom. O. scutellatus venom was fractionated using size-exclusion high performance liquid chromatography (HPLC), and fractions screened for activity in anaesthetized rats. Fraction three from O. scutellatus venom (i.e. OSC3, 14.2±1.0% of whole venom) produced a 64% decrease in mean arterial pressure. Reverse-phase HPLC indicated that OSC3 consisted of two major components (i.e. OSC3a and OSC3b). OSC3a and OSC3b produced a significant hypotensive response in anaesthetized rats which were attenuated by prior administration of indomethacin or the combination of mepyramine and heparin. N-terminal analysis indicated that OSC3a and b displayed sequence homology to PLA2 toxins isolated from coastal taipan (O. scutellatus scutellatus) venom. These findings indicate that PLA2 components may play an important role in the development of hypotension and vascular relaxation which may contribute to the effects observed after envenoming by these Australasian elapids.

Enhanced contractility in pregnancy is associated with augmented TRPC3, L-type, and T-type voltage-dependent calcium channel function in rat uterine radial artery

In pregnancy, α-adrenoceptor-mediated vasoconstriction is augmented in uterine radial arteries and is accompanied by underlying changes in smooth muscle (SM) Ca2+ activity. This study aims to determine the Ca2+ entry channels associated with altered vasoconstriction in pregnancy, with the hypothesis that augmented vasoconstriction involves transient receptor potential canonical type-3 (TRPC3) and L- and T-type voltage-dependent Ca2+ channels. Immunohistochemistry showed TRPC3, L-type Cav1.2 (as the α1C subunit), T-type Cav3.1 (α1G), and Cav3.2 (α1H) localization to the uterine radial artery SM. Fluorescence intensity of TRPC3, Cav1.2, and Cav3.2 was increased, and Cav3.1 decreased in radial artery SM from pregnant rats. Western blot analysis confirmed increased TRPC3 protein expression in the radial artery from pregnant rats. Pressure myography incorporating pharmacological intervention to examine the role of these channels in uterine radial arteries showed an attenuation of phenylephrine (PE)-induced constriction with Pyr3 {1-[4-[(2,3,3-trichloro-1-oxo-2-propen-1-yl)amino]phenyl]-5-(trifluoromethyl)-1 H-pyrazole-4-carboxylic acid}-mediated TRPC3 inhibition or with nifedipine-mediated L-type channel block alone in vessels from pregnant rats; both effects of which were diminished in radial arteries from nonpregnant rats. Combined TRPC3 and L-type inhibition attenuated PE-induced constriction in radial arteries, and the residual vasoconstriction was reduced and abolished with T-type channel block with NNC 55-0396 in arteries from nonpregnant and pregnant rats, respectively. With SM Ca2+ stores depleted and in the presence of PE, nifedipine, and NNC 55-0396, blockade of TRPC3 reversed PE-induced constriction. These data suggest that TRPC3 channels act synergistically with L- and T-type channels to modulate radial artery vasoconstriction, with the mechanism being augmented in pregnancy.

Localization of relaxin receptors in arteries and veins, and region-specific increases in compliance and bradykinin-mediated relaxation after in vivo serelaxin treatment

Relaxin is a potent vasodilator of small resistance arteries and modifies arterial compliance in some systemic vascular beds, yet receptors for relaxin, such as RXFP1, have only been localized to vascular smooth muscle. This study first aimed to localize RXFP1 in rat arteries and veins from different organ beds and determine whether receptors are present in endothelial cells. We then tested the hypothesis that region-specific vascular effects of relaxin may be influenced by the cellular localization of RXFP1 within different blood vessels. The aorta, vena cava, mesenteric artery, and vein had significantly higher (P<0.05) RXFP1 immunostaining in endothelial cells compared with vascular smooth muscle, whereas the femoral artery and vein and small pulmonary arteries had higher (P<0.01) RXFP1 immunostaining in the vascular smooth muscle. Male rats were treated subcutaneously with recombinant human relaxin-2 (serelaxin; 4 μg/h) for 5 d; vasodilation and compliance in mesenteric and femoral arteries and veins were compared with placebo controls. Serelaxin significantly (P=0.04) reduced wall stiffness and increased volume compliance in mesenteric arteries but not in the other vessels examined. This was associated with changes in geometrical properties, and not compositional changes in the extracellular matrix. Serelaxin treatment had no effect on acetylcholine-mediated relaxation but significantly (P<0.001) enhanced bradykinin (BK)-mediated relaxation in mesenteric arteries, involving enhanced nitric oxide but not endothelium-derived hyperpolarization or vasodilatory prostanoids. In conclusion, there is differential distribution of RXFP1 on endothelial and smooth muscle across the vasculature. In rats, mesenteric arteries exhibit the greatest functional response to chronic serelaxin treatment.

Abstract 538: Prolonged Functional Sympathetic Efferent Denervation Following Ablation of the Renal Nerves in SHR

Renal denervation (RDN) has been shown to be an effective and safe treatment for human resistant hypertension and is considered one of the most promising advances in the field of hypertension. However, the mechanisms mediating the sustained decrease in arterial pressure in response to RDN in humans are unknown. This issue is particularly perplexing, given reports that the depressor effect of RDN in animal models is short lived. The current dogma in the literature is that overtime the efferent sympathetic nerves regrow and so the longevity of the depressor effect of RDN in humans cannot be ascribed to the absence of efferent renal sympathetic nerve activity. We hypothesize that the renal sympathetic nerves regenerate following RDN, and arrive at the target tissues, but the functional response is not fully restored and this contributes to the long-term depressor effect of RDN. Our aim was to examine mean arterial pressure (MAP) and vascular function in spontaneously hypertensive rats (SHR) following RDN. In 10 week old male SHR radiotelemetry probes were implanted to measure MAP. At 12 weeks of age, following 3 days basal MAP recording, sham (n=5) or bilateral RDN (n=5) surgery was performed. MAP was recorded until 24 weeks of age (12 weeks post-RDN). Renal lobar arteries were mounted on a myograph and membrane potential and tension responses to perivascular nerve stimulation assessed. Perivascular nerve stimulation with single pulses at increasing voltage evoked excitatory junction potentials (Ejps) of increasing amplitude in SHR-sham. Ejp amplitude was markedly reduced in arteries from SHR-RDN (P<0.01). Repetitive stimulation (1-8Hz, 5s) evoked slow depolarisation and contraction. At 5Hz 5s, slow depolarisation was 12±2 mV in SHR-shams and 7±2 mV in SHR-RDN (P<0.01), and contractions were smaller than SHR-sham (10 ± 3% vs 22 ± 2% HiK; P<0.01). In conclusion, smaller Ejps suggest that close contacting neuroeffector junctions are not reformed and blunted vasoconstrictor responses indicate neuro-vascular function has only partially returned 12 weeks post-RDN (Fig. 2). Our finding of continued ‘functional’ denervation is compatible with our data that RDN causes a sustained decrease in arterial pressure in SHR.

Regulator of G-protein signaling 5 controls blood pressure homeostasis and vessel wall remodeling

RATIONALE

Regulator of G-protein signaling 5 (RGS5) modulates G-protein-coupled receptor signaling and is prominently expressed in arterial smooth muscle cells. Our group first reported that RGS5 is important in vascular remodeling during tumor angiogenesis. We hypothesized that RGS5 may play an important role in vessel wall remodeling and blood pressure regulation.

OBJECTIVE

To demonstrate that RGS5 has a unique and nonredundant role in the pathogenesis of hypertension and to identify crucial RGS5-regulated signaling pathways.

METHODS AND RESULTS

We observed that arterial RGS5 expression is downregulated with chronically elevated blood pressure after angiotensin II infusion. Using a knockout mouse model, radiotelemetry, and pharmacological inhibition, we subsequently showed that loss of RGS5 results in profound hypertension. RGS5 signaling is linked to the renin-angiotensin system and directly controls vascular resistance, vessel contractility, and remodeling. RGS5 deficiency aggravates pathophysiological features of hypertension, such as medial hypertrophy and fibrosis. Moreover, we demonstrate that protein kinase C, mitogen-activated protein kinase/extracellular signal-regulated kinase, and Rho kinase signaling pathways are major effectors of RGS5-mediated hypertension.

CONCLUSIONS

Loss of RGS5 results in hypertension. Loss of RGS5 signaling also correlates with hyper-responsiveness to vasoconstrictors and vascular stiffening. This establishes a significant, distinct, and causal role of RGS5 in vascular homeostasis. RGS5 modulates signaling through the angiotensin II receptor 1 and major Gαq-coupled downstream pathways, including Rho kinase. So far, activation of RhoA/Rho kinase has not been associated with RGS molecules. Thus, RGS5 is a crucial regulator of blood pressure homeostasis with significant clinical implications for vascular pathologies, such as hypertension.

Myoendothelial contacts, gap junctions, and microdomains: anatomical links to function?

In several species and in many vascular beds, ultrastructural studies describe close contact sites between the endothelium and smooth muscle of <∼20nm. Such sites are thought to facilitate the local action of signaling molecules and/or the passage of current, as metabolic and electrical coupling conduits between the arterial endothelium and smooth muscle. These sites have the potential for bidirectional communication between the endothelium and smooth muscle, as a key pathway for coordinating vascular function. The aim of this brief review is to summarize the literature on the ultrastructural anatomy and distribution of key components of MECC sites in arteries. In addition to their traditional role of facilitating electrical coupling between the two cell layers, data on the role of MECC sites in arteries, as signaling microdomains involving a spatial localization of channels, receptors and calcium stores are highlighted. Diversity in the density and specific characteristics of MECC sites as signaling microdomains suggests considerable potential for functional diversity within and between arteries in health and disease.

In vivo and in vitro cardiovascular effects of Papuan taipan (Oxyuranus scutellatus) venom: Exploring "sudden collapse"

'Sudden collapse' following envenoming by some Australasian elapids is a poorly understood cause of mortality. We have previously shown that Oxyuranus scutellatus venom causes cardiovascular collapse in anaesthetized rats. Prior administration of a sub lethal dose of venom attenuated the response to subsequent administration of higher (lethal) venom doses. In this study, we investigated the possible mechanisms mediating this 'protective effect'. Papuan taipan venom (5μg/kg, i.v.) produced a small transient hypotension in anaesthetized rats, while 10μg/kg resulted in a 73±12% decrease in arterial pressure. Venom (20μg/kg or 50μg/kg) produced cardiovascular collapse in all animals tested (n=12). Cardiovascular collapse by 50μg/kg venom was prevented by prior administration of 'priming' doses of venom (5, 10 and 20μg/kg). Also, prior administration of indomethacin (30mg/kg, i.v.) or heparin (300units/kg, i.v.) prevented sudden collapse induced by venom (20μg/kg). Venom was without effect in isolated hearts indicating that a direct cardiac effect was unlikely to be responsible for 'sudden collapse'. Venom induced endothelium-dependent and -independent relaxation in pre-contracted rat mesenteric artery rings which was inhibited by indomethacin, IbTx and Rp-8-CPT-cAMPs. This relaxation was markedly reduced upon second exposure. Our results indicate that cardiovascular collapse induced by O. scutellatus venom may be due to a combination of release of dilator autacoids and to direct relaxation of vascular smooth muscle involving the cAMP/protein kinase A cascade. Further work will involve identification of the venom component(s) responsible for this action and may provide insight into the management of envenomed patients.

Relaxin mediates uterine artery compliance during pregnancy and increases uterine blood flow

Normal pregnancy involves dramatic remodeling of the uterine vasculature, with abnormal vascular adaptations contributing to pregnancy diseases such as preeclampsia. The peptide hormone relaxin is important for the renal and systemic hemodynamic adaptations to pregnancy, and has been shown to increase arterial compliance and outward hypertrophic remodeling. Therefore, we investigated the possibility that relaxin acts on its receptor, RXFP1, to mediate uterine artery compliance in late pregnancy and increase uterine blood flow velocity in rats. RXFP1 was predominantly localized to the tunica media vascular smooth muscle cells in the uterine artery, although receptors were also detected in endothelial cells. Highest expression of Rxfp1 in the uterine artery occurred in estrus and early pregnancy. Isolated uterine arteries from late pregnant rats treated with a monoclonal antibody against circulating relaxin (MCA1) had significantly increased vessel wall stiffness compared with controls, with no reduction in wall thickness. Chronic infusion of relaxin (4 μg/h, osmotic minipump) for 5 d in nonpregnant rats significantly increased uterine artery blood flow velocity. Overall, these data demonstrate a functional role for relaxin in mediating uterine artery compliance in pregnant rats, which may be necessary to maintain adequate uterine blood flow to the uterus and placenta.