Carotid Vascular Conductance Research Articles

A simple approach to studying cerebral blood flow during psychological stress.

The purpose of this work was to determine, in the Wistar male rats, the role of the stress system in the control of cerebral hemodynamics induced by emotional stress (air jet). Blood flow rates in the internal carotid arteries have been obtained using chronically implanted Doppler probes. In this investigation, air-jet stress provokes a rapid and substantial elevation of blood pressure combined with hyperemia and vasodilation. Spectral analysis reveals an increase in the variability of carotid blood flow and carotid vascular conductance during stress compared to the baseline state. The coherence between the two carotid blood flow, which provides a linear correlation index in the frequency domain, was calculated before (ordinary coherence) and after mathematical elimination of the influence of blood pressure (partial coherence). The main advantages of the technique are as follows:• It allows the measurement of cerebral blood flow while comparing them with the physiological parameters of the animal such as blood pressure.• Air-jet stress is a psychological rather than physical stress that generates hyperemia in a non-pharmacological way (no side effects) without injuring the animal or damaging the experimental installation during the recording sessions.• A simple method for tracing a kinetic path before and at the moment of stress initiation.• The presence of a catheter facilitates the administration of drug substances if required.• Laboratory-developed software, based on the Lab VIEW 5.1, allows real-time monitoring of blood pressure and carotid flow rates signals using fast Fourier transform.

Carotid Vascular Blood Flow in Individuals with Down Syndrome Following Low Body Negative Pressure Challenge

Individuals with Down Syndrome (DS) exhibit autonomic dysfunction with reduced sympathetic activity, which may cause reduced aerobic capacity and alterations in peripheral blood flow. Carotid vascular function has been considered as a marker of future cardiovascular events. However, changes in carotid blood flow and vascular conductance in response to sympathoexcitation are not well characterized in persons with DS, carotid stiffness responses to exercise differ between individuals with DS and controls.PurposeTo examine the differences in hemodynamics, carotid vascular reactivity and blood flow following sympathoexcitation using lower body negative pressure (LBNP) in individuals with and without DS.Methods13 young (18 < age <40 yrs) individuals with and without DS (DS=6) participated in this study. Changes in hemodynamics and carotid vascular reactivity (BP, carotid diameter, carotid flow and vascular conductance) were measured before, during and after LBNP (−20 mmHg).ResultsBaseline hemodynamics where not different between the group with DS and controls. The group with DS showed an altered response in conductance to LBNP, when compared to controls with large effect size (η2 = 0.138). In addition, carotid blood flow exhibited a large effect size (η2 = 0.242) for a group interaction. During recovery, the group with DS showed an increase in BF, whereas control group exhibited decrease in BF. These changes occurred without differential changes in carotid diameter and blood pressure.ConclusionsOur results demonstrate the tendency of reduced vascular reactivity in individuals with DS to sympathoexcitation, demonstrated by large effects sizes. Our findings indicate altered blood flow control in persons with DS, attributable to autonomic dysfunction. Larger sample sizes will be needed to confirm these findings. DS (N = 6) Control (N = 7) Baseline LBNP (−20mmHg) Recovery Baseline LBNP (−20mmHg) Recovery Carotid SBP (mmHg) 118 ± 5 111 ± 4 119 ± 5 126 ± 5 114 ± 4 121 ± 4 Carotid DBP (mmHg) 69 ± 4 68 ± 3 68 ± 3 76 ± 3 73 ± 2 77 ± 3 Carotid MAP (mmHg) 87 ± 5 84 ± 3 88 ± 4 96 ± 4 90 ± 3 95 ± 4 Carotid Blood Flow (ml/min) 378.0 ± 110.3 394.1 ± 115.3 399.9 ± 112.2 539 4 ± 102.1 552.6 ± 106.8 500.1 ± 103.9 Carotid Vascular Conductance (ml/min/100mmHg) 25.3 ± 3.6 29.0 ± 4.6 28.1 ± 4.0 32.0 ± 3.3 35.1 ± 3.8 30.7 ± 3.6 Mean ± SEM

Asphyxia and therapeutic hypothermia modulate plasma nitrite concentrations and carotid vascular resistance in preterm fetal sheep.

In this study, we tested the hypothesis that cerebral hypoperfusion after asphyxia and induced hypothermia is associated with reduced circulating nitrite levels as an index of nitric oxide synthase (NOS) activity. The preterm fetal sheep at 0.7 gestation (103-104 days, term = 147 days) received 25-minute umbilical cord occlusion, followed by mild whole-body cooling from 30 minutes to 72 hours after occlusion. Occlusion and induced hypothermia were independently associated with reduced carotid vascular conductance (CaVC) from 2 to 72 hours, and with transiently suppressed plasma nitrite levels at 6 hours. There was a significant within-subjects correlation (r(2) = 0.33, P = .002) between CaVC and plasma nitrite values in the first 24 hours after occlusion but not after sham occlusion. These findings suggest that in preterm fetal sheep, changes in NOS activity are an important mediator of changes in carotid vascular tone in the early recovery phase after asphyxia and may help mediate some of the vascular effects of induced hypothermia.

Antiphospholipid antibodies promote leukocyte–endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via β2GPI and apoER2

In antiphospholipid syndrome (APS), antiphospholipid antibodies (aPL) binding to β2 glycoprotein I (β2GPI) induce endothelial cell-leukocyte adhesion and thrombus formation via unknown mechanisms. Here we show that in mice both of these processes are caused by the inhibition of eNOS. In studies of cultured human, bovine, and mouse endothelial cells, the promotion of monocyte adhesion by aPL entailed decreased bioavailable NO, and aPL fully antagonized eNOS activation by diverse agonists. Similarly, NO-dependent, acetylcholine-induced increases in carotid vascular conductance were impaired in aPL-treated mice. The inhibition of eNOS was caused by antibody recognition of domain I of β2GPI and β2GPI dimerization, and it was due to attenuated eNOS S1179 phosphorylation mediated by protein phosphatase 2A (PP2A). Furthermore, LDL receptor family member antagonism with receptor-associated protein (RAP) prevented aPL inhibition of eNOS in cell culture, and ApoER2-/- mice were protected from aPL inhibition of eNOS in vivo. Moreover, both aPL-induced increases in leukocyte-endothelial cell adhesion and thrombus formation were absent in eNOS-/- and in ApoER2-/- mice. Thus, aPL-induced leukocyte-endothelial cell adhesion and thrombosis are caused by eNOS antagonism, which is due to impaired S1179 phosphorylation mediated by β2GPI, apoER2, and PP2A. Our results suggest that novel therapies for APS can now be developed targeting these mechanisms.

Effect of Chronic Hypoxia on Carotid Vascular Responses to Adenosine in Rats

Aim of the work: the present study aims at testing whether chronic hypoxia alters thedilator vascular responses of rat carotid circulation to adenosine-evoked fall inarterial blood pressure (ABP). The arterial blood pressure was lowered to the lowerlimit of cerebral autoregulatory range giving the chance to further study whether thecarotid autoregulatory response to adenosine-evoked fall in ABP is compromised bychronic hypoxia or not. A third aim is to investigate whether the role of tonicallysynthesized nitric oxide (NO) in dilator responses evoked by adenosine in carotidvasculature is different in chronic hypoxic rats. Study Design: the study was doneusing 2 comparable age groups of adult male Wistar rats; the first were breathingnormal 21% O2 (normoxic; N), whereas the second were made chronically hypoxic(CH) by breathing 12% O2 for 3 weeks, while they were growing from 7 to 10 weeks.In anaesthetized rats, the carotid blood flow (CBF) and carotid vascular conductance(CVC) were recorded during a 3 min infusion of adenosine adjusted at a dose aimedat lowering ABP to 60 mm Hg, the lower limit of autoregulatory range before andafter a bolus dose of the nitric oxide synthase inhibitor L-NAME (10mg.kg-1).Results: in chronic hypoxic rats, the adenosine-induced fall in ABP was associatedwith a significant increase in CVC but with no significant increase in CBF in contrastto the significant increase in CBF noticed in N rats. Also, adenosine-evoked increasein baseline CVC was significantly larger in N than in CH rats. Inhibition of nitricoxide synthase produced comparable changes on baseline values in CH as in N rats.In CH rats, L-NAME did not attenuate the increase in CVC evoked by adenosine as itdid in N rats. However, after L-NAME, CBF increased in CH rats. Conclusion: Fromthese results, it could be suggested that exposing rats to chronic hypoxia for 3 weeksdoes not compromise the carotid autoregulatory response to the fall in arterial bloodpressure. However, it seems that adenosine does not exert an active vasodilatation incarotid circulation of CH rats as it does in N rats. Further, it seems that theadenosine-evoked increase in CBF in CH rats is largely nitric oxide-independent.

Age-related changes in carotid vascular responses to adenosine and nitric oxide in the rat: in vitro and in vivo studies

We investigated how the ability of adenosine to release nitric oxide (NO) from carotid artery in vitro, and dilator responses evoked in carotid circulation in vivo by systemic infusion of adenosine, change with age in rats of 4-5, 10-12, and 42-44 wk (juvenile, mature, and middle aged). A secondary aim was to follow age-related changes in carotid/cerebral autoregulation. In opened carotid artery, graded doses of adenosine evoked graded increases in NO output measured with a NO sensor that were greater in mature and middle-aged than juvenile rats. Infusion of adenosine to reduce mean arterial pressure (ABP) to approximately 60 mmHg increased carotid vascular conductance (CVC) in all groups, but the increase was larger in mature rats; carotid blood flow (CBF) was unchanged in juvenile, increased in mature, but fell in 4/8 middle-aged rats. The NO synthase inhibitor nitro l-arginine methyl ester (l-NAME; 10 mg/kg iv) increased baseline ABP in all groups but caused larger percentage reductions in baseline CVC and CBF in mature and middle-aged than juvenile rats. Thereafter, the adenosine-evoked increase in CVC was unchanged in juvenile and middle-aged rats, yet CBF remained constant in juvenile but increased in middle-aged rats. In mature rats, the evoked increases in CVC and CBF were attenuated and further attenuated by l-NAME at 30 mg/kg. We propose that the ability of adenosine to release NO and cause vasodilation in the carotid artery and its circulation is greater in mature, than juvenile or middle-aged rats, but NO has greater tonic dilator influence in carotid circulation of mature and middle-aged than juvenile rats. By middle age, the lower limit of cerebral autoregulation has increased such that the tonic dilator influence of NO on ABP and CVC limits autoregulation of CBF to depressor responses. However, partial NO synthase inhibition overcomes this impairment, raising baseline ABP and allowing adenosine-evoked increases in CVC to increase CBF.

Age-related changes in the sympathetic innervation of cerebral vessels and in carotid vascular responses to norepinephrine in the rat: in vitro and in vivo studies

We hypothesized that the density of sympathetic noradrenergic innervation of cerebral arteries and vasoconstrictor responses evoked in carotid circulation by norepinephrine (NE) increase with maturation and age. In rats of 4-5, 10-12, and 42-44 wk of age (juvenile, mature, middle aged), glyoxylic acid applied to stretch preparations showed the density of noradrenergic nerves in basilar and middle cerebral arteries was greater in mature than juvenile or middle-aged rats. In anesthetized rats, infusion of NE (2.5 mug/kg iv) increased mean arterial pressure (ABP) to approximately 180 mmHg in mature and middle-aged but to only approximately 150 mmHg in juveniles rats. Concomitantly, carotid blood flow (CBF) decreased in mature and middle-aged rats but remained constant in juveniles because carotid vascular conductance (CVC) decreased more in mature and middle-aged than juvenile rats. We also hypothesized that nitric oxide (NO) blunts cerebral vasoconstrictor responses to NE. Inhibition of NO synthase with l-NAME (10 mg/kg iv) induced similar increases in baseline ABP in each group, but larger decreases in CVC and CBF in mature and middle-aged than juvenile rats. Thereafter, the NE-evoked increase in ABP was similar in juvenile and mature but accentuated in middle-aged rats. Concomitantly, NE decreased CVC in juvenile and mature, but not middle-aged rats; in them, CBF increased. Thus, in juvenile rats, sparse noradrenergic innervation of cerebral arteries is associated with weak NE-evoked pressor responses and weak carotid vasoconstriction that allows autoregulation of CBF. Cerebral artery innervation density increases with maturation but lessens by middle age. Meanwhile, NE-evoked pressor responses and carotid vasoconstriction are stronger in mature and middle-aged rats, such that CBF falls despite the evoked increase in ABP. We propose that in juvenile and mature rats, NO does not modulate NE-evoked pressor responses, cerebral vasoconstriction, or CBF autoregulation, but by middle age, NO limits pressor responses and prevents breakthrough of CBF in the upper part of the autoregulatory range.

Antiphospholipid Antibodies Promote Leukocyte-Endothelial Cell Adhesion by Antagonizing Endothelial NO Synthase Via b2GPI and ApoER2.

Abstract 3039Poster Board II-1015The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of antiphospholipid antibodies (aPL), with pathogenic aPL directed primarily against the cell surface protein β2 glycoprotein I (β2GPI), increased risk for thrombosis and cardiovascular events, and pregnancy morbidity. The endothelium is a critical direct target of aPL, which upregulate adhesion molecule expression and procoagulant activity. However, the molecular basis for aPL actions on endothelium is unknown. Nitric oxide (NO) generated by endothelial NO synthase (eNOS) has potent antiadhesive and antithrombotic properties. In this study we determined if aPL-induced alterations in endothelial cell phenotype are mediated by aPL actions on eNOS. Normal human IgG (NHIgG) and polyclonal aPL were obtained from healthy adults and APS patients, respectively. We found that aPL prevented acetylcholine (Ach)- or VEGF-mediated attenuation of monocyte adhesion to cultured endothelial cells and this was reversed by an NO donor, indicating a role for eNOS antagonism. In contrast, NHIgG did not affect adhesion. Whereas NHIgG did not alter eNOS activation, stimulation of eNOS by VEGF and other agonists was fully antagonized by aPL. In mice, NO-dependent, Ach-induced increases in carotid vascular conductance were unaffected by NHIgG but impaired by aPL, indicating that these processes are operative in vivo. Additional studies in culture showed that aPL attenuates eNOS activation by inhibiting Ser1179 phosphorylation, deprivation of β2GPI prevented aPL inhibition of eNOS, and monoclonal antibody against β2GPI mimicked the effects of aPL. Furthermore, receptor-associated protein (RAP) antagonism of LDL receptors, which are known to bind dimerized β2GPI, prevented aPL inhibition of eNOS in culture, and mice null for the LDL receptor apolipoprotein receptor 2 (apoER2) were protected from aPL inhibition of eNOS in vivo. Moreover, aPL-stimulated increases in leukocyte-endothelial adhesion were absent in both eNOS-/- and apoER2-/- mice. Thus, aPL-induced increases in leukocyte-endothelial adhesion are caused by eNOS antagonism, which is due to impaired S1179 phosphorylation mediated by β2GPI and apoER2. Novel therapies for APS can now be developed targeting these mechanisms. DisclosuresThomas:NIcox Research Institute: Research Funding. Thorpe:Peregrine Pharm.: Consultancy, sponsored research agreement.

EFFECT OF CHRONIC HYPOXIA ON CAROTID VASCULAR RESPONSES TO NORADRENALINE IN RATS

Aim: The aim of the present study was to examine whether chronic hypoxia would alter the noradrenaline (NA)-evoked vascular responses in carotid circulation in rats. Furthermore, whether the carotid autoregulatory response to NA-evoked rise in arterial blood pressure (ABP) is compromised by chronic hypoxia or not. Also, the role of tonically synthesised nitric oxide (NO) in these responses was investigated. Methods: the study was done using two comparable age groups of adult Wistar rats; the first were breathing normal 21% O2 (normoxic; N), whereas the second were made chronically hypoxic (CH) by breathing 12% O2 for 3 weeks, while they were growing from 7 to 10 weeks. In anaesthetised rats, the carotid blood flow (CBF) and carotid vascular conductance (CVC) were recorded during a 3 min infusion of NA at a dose 2.5 μg kg -1 to induce an acute rise in ABP to 150 mm Hg, the upper limit of autoregulatory range, before and after a bolus dose of the nitric oxide synthase inhibitor, L-NAME (10mg kg -1 ). Results: the NA-evoked rise in ABP was comparable in N and CH rats, but the increase in heart rate was more significant in CH rats. In CH rats, the NA-evoked rise in ABP was associated with a significant reduction in CVC but with no change in CBF, whereas in N rats the reduction in CVC was accompanied with a significant reduction in CBF (p<0.05). In both groups, L-NAME did not accentuate the rise in ABP induced by NA. However, in CH rats the reduction in CBF became more significant after L-NAME. Conclusion: the carotid vasculature in CH rats is less sensitive to vasopressor effect of NA, when compared to N rats. However, the carotid autoregulatory response to NA-induced rise in ABP was not compromised by chronic hypoxia. Further, it seems that NO does not play a role in the blunted carotid vasoconstrictor responses to NA in CH rats. Keywords: Chronic hypoxia, carotid circulation, noradrenalin, nitric oxide

Advantages of a selective β-isoform phosphoinositide 3-kinase antagonist, an anti-thrombotic agent devoid of other cardiovascular actions in the rat

Phosphoinositide 3-kinase (PI3K) β has been shown to play a critical role in shear-induced arterial thrombosis. The anti-thrombotic effects of a β isoform selective PI3K inhibitor, TGX221, were compared to the effects of non-selective PI3K inhibitors (LY294002 and wortmannin) and a PI3K δ inhibitor (IC87114) in the rat. TGX221 (2.5 mg/kg i.v.) abolished cyclic flow reductions in a Folts-like carotid artery stenosis preparation of thrombosis while not changing bleeding time, heart rate, blood pressure or carotid vascular conductance. In contrast, the PI3K non-selective isoform inhibitor, wortmannin (5 mg/kg i.v.) was as effective in abolishing cyclic flow reductions, but caused marked hypotension and carotid vasodilatation. In isolated mesenteric arteries, wortmannin was the most potent relaxant of K +-precontracted vessels (pEC 50 = 6.6), while LY294002 and TGX221 were 40–60 fold less potent and IC87114 was without effect. These findings suggest that of the subclass of PI3K isoforms, the β isoform is critical for the selective development of arterial thrombosis in vivo. The multiple actions of wortmannin are consistent with inhibition of the PI3K-C2α and β isoforms and possibly other actions. Thus, a selective inhibitor of the β isoform of PI3K offers advantages as a potential therapeutic target for the treatment of thrombosis without unwanted extension of bleeding time or adverse cardiovascular sequelae.

Fetal cardiovascular, metabolic and endocrine responses to acute hypoxaemia during and following maternal treatment with dexamethasone in sheep

In sheep, direct fetal treatment with dexamethasone alters basal cardiovascular function and the cardiovascular response to acute hypoxaemia. However, in human clinical practice, dexamethasone is administered to the mother, not to the fetus. Hence, this study investigated physiological responses to acute hypoxaemia in fetal sheep during and following maternal treatment with dexamethasone in doses and at dose intervals used in human clinical practice. Under anaesthesia, 18 fetal sheep were instrumented with vascular and amniotic catheters, a carotid flow probe and a femoral flow probe at 118 days gestation (term ca 145 days). Following 6 days recovery at 124 days gestation, 10 ewes received dexamethasone (2 x 12 mg daily i.m. injections in saline). The remaining animals were saline-injected as age-matched controls. Two episodes of hypoxaemia (H) were induced in all animals by reducing the maternal F(IO2)for 1 h (H1, 8 h after the second injection; H2, 3 days after the second injection). In fetuses whose mothers received saline, hypoxaemia induced significant increases in fetal arterial blood pressure, carotid blood flow and carotid vascular conductance and femoral vascular resistance, significant falls in femoral blood flow and femoral vascular conductance and transient bradycardia. These cardiovascular responses were accompanied by a fall in arterial pH, increases in blood glucose and blood lactate concentrations and increased plasma concentrations of catecholamines. In fetuses whose mothers were treated with dexamethasone, bradycardia persisted throughout hypoxaemia, the magnitude of the femoral vasoconstriction, the glycaemic, lactacidaemic and acidaemic responses and the plasma concentration of neuropeptide Y (NPY) were all enhanced during H1. However, during H2, all of these physiological responses were similar to saline controls. In dexamethasone fetuses, the increase in plasma adrenaline was attenuated during H1 and the increase in carotid vascular conductance during hypoxaemia failed to reach statistical significance both during H1 and during H2. These data show that maternal treatment with dexamethasone in doses and intervals used in human obstetric practice modified the fetal cardiovascular, metabolic and endocrine defence responses to acute hypoxaemia. Furthermore, dexamethasone-induced alterations to these defences depended on whether the hypoxaemic challenge occurred during or following maternal dexamethasone treatment.

Magnesium Sulphate Reverses the Carotid Vasoconstriction Caused by Endothelin-1, Angiotensin II and Neuropeptide-Y, but Not That Caused by NG-nitro-l-Arginine Methyl Ester, in Conscious Rats

1. Magnesium sulphate (MgSO4) has been used for many years in the prevention of eclamptic seizures, but its mechanism of action has never been elucidated. Recent studies suggest that cerebral vasospasm is an important feature of eclampsia and we have developed and tested the hypothesis that MgSO4 can reverse cerebral vasoconstriction. 2. Studies were performed in conscious, male Long Evans rats with pulsed Doppler probes sutured around both common carotid arteries after the external carotid artery had been ligated on the left, thus allowing simultaneous measurement of changes in common and internal carotid blood flow. Intravascular catheters were placed in the abdominal aorta for measurement of systemic blood pressure and in the right jugular vein for administration of drugs. Mean arterial blood pressure and mean Doppler shift signals were used to calculate percentage changes in common and internal carotid vascular conductance. 3. After a period of recovery the animals were infused with endothelin-1, angiotensin II, neuropeptide-Y or NG-nitro-L-arginine methyl ester alone or in combination, and MgSO4 in low or high dose was infused when the effects of the vasoconstrictors had become established. 4. MgSO4 itself, at the low dose, had no effect on carotid vascular conductance. Endothelin-1, angiotensin II and neuropeptide-Y all reduced common and internal carotid vascular conductance and this effect was significantly attenuated by low dose MgSO4. The carotid vasoconstrictor action of endothelin-1 was completely abolished by high dose MgSO4.(ABSTRACT TRUNCATED AT 250 WORDS)