Dilation of Pregnant Rat Uterine Arteries with Phenols from Extra Virgin Olive Oil Is Endothelium-Dependent and Involves Calcium and Potassium Channels

During pregnancy, uterine vasculature undergoes significant circumferential growth to increase uterine blood flow, vital for the growing feto-placental unit. However, this process is often compromised in conditions like maternal high blood pressure, particularly in preeclampsia (PE), leading to fetal growth impairment. Currently, there is no cure for PE, partly due to the adverse effects of anti-hypertensive drugs on maternal and fetal health. This study aimed to investigate the vasodilator effect of extra virgin olive oil (EVOO) phenols on the reproductive vasculature, potentially benefiting both mother and fetus. Isolated uterine arteries (UAs) from pregnant rats were tested with EVOO phenols in a pressurized myograph. To elucidate the underlying mechanisms, additional experiments were conducted with specific inhibitors: L-NAME/L-NNA (10-4 M) for nitric oxide synthases, ODQ (10-5 M) for guanylate cyclase, Verapamil (10-5 M) for the L-type calcium channel, Ryanodine (10-5 M) + 2-APB (3 × 10-5 M) for ryanodine and the inositol triphosphate receptors, respectively, and Paxilline (10-5 M) for the large-conductance calcium-activated potassium channel. The results indicated that EVOO-phenols activate Ca2+ signaling pathways, generating nitric oxide, inducing vasodilation via cGMP and BKCa2+ signals in smooth muscle cells. This study suggests the potential use of EVOO phenols to prevent utero-placental blood flow restriction, offering a promising avenue for managing PE.

The impact of collateral therapeutics on stroke hemodynamics in normotensive and hypertensive rats: a step toward translation

Introduction

Stroke interventions that increase collateral flow have the potential to salvage penumbral tissue and increase the number of patients eligible for reperfusion therapy. We compared the efficacy of two different collateral therapeutics during transient middle cerebral artery occlusion (tMCAO) in normotensive and hypertensive rats.

Methods

The change in collateral and core perfusion was measured using dual laser Doppler in response to either a pressor agent (phenylephrine, 10 mg/kg iv or vehicle) or a collateral vasodilator (TM5441, 5 mg/kg iv or vehicle) given 30 min into tMCAO in male Wistar and spontaneously hypertensive rats (SHRs).

Results

Pressor therapy increased collateral flow in the Wistar rats but was ineffective in the SHRs. The increase in collateral flow in the Wistar rats was associated with impaired cerebral blood flow autoregulation (CBFAR) that was intact in the SHRs. TM5441 caused a decrease in collateral perfusion in the Wistar rats and a modest increase in the SHRs. The pressor therapy reduced early infarction in both groups but increased edema in the SHRs, whereas TM5441 did not have any beneficial effects in either group.

Conclusions

Thus, the pressor therapy was superior to a collateral vasodilator in increasing collateral flow and improving outcomes in the Wistar rats, likely due to pial collaterals that were pressure passive; the lack of CBF response in the SHRs to pressor therapy was likely due to intact CBFAR that limited perfusion. While TM5441 modestly increased CBF in the SHRs but not in the Wistar rats, it did not have a beneficial effect on stroke outcomes. These results suggest that collateral therapies may need to be selected for certain comorbidities.

Optimizing Prepregnancy Cardiovascular Health to Improve Outcomes in Pregnant and Postpartum Individuals and Offspring: A Scientific Statement From the American Heart Association

This scientific statement summarizes the available preclinical, epidemiological, and clinical trial evidence that supports the contributions of prepregnancy (and interpregnancy) cardiovascular health to risk of adverse pregnancy outcomes and cardiovascular disease in birthing individuals and offspring. Unfavorable cardiovascular health, as originally defined by the American Heart Association in 2010 and revised in 2022, is prevalent in reproductive-aged individuals. Significant disparities exist in ideal cardiovascular health by race and ethnicity, socioeconomic status, and geography. Because the biological processes leading to adverse pregnancy outcomes begin before conception, interventions focused only during pregnancy may have limited impact on both the pregnant individual and offspring. Therefore, focused attention on the prepregnancy period as a critical life period for optimization of cardiovascular health is needed. This scientific statement applies a life course and intergenerational framework to measure, modify, and monitor prepregnancy cardiovascular health. All clinicians who interact with pregnancy-capable individuals can emphasize optimization of cardiovascular health beginning early in childhood. Clinical trials are needed to investigate prepregnancy interventions to comprehensively target cardiovascular health. Beyond individual-level interventions, community-level interventions must include and engage key stakeholders (eg, community leaders, birthing individuals, families) and target a broad range of antecedent psychosocial and social determinants. In addition, policy-level changes are needed to dismantle structural racism and to improve equitable and high-quality health care delivery because many reproductive-aged individuals have inadequate, fragmented health care before and after pregnancy and between pregnancies (interpregnancy). Leveraging these opportunities to target cardiovascular health has the potential to improve health across the life course and for subsequent generations.

Abstract TP228: Differential Effect Of Serum From Intracerebral Hemorrhage And Small Vessel Disease Patients On Nonischemic Cerebral Arteries

Introduction: There is evidence that circulating factors disrupt vessel function in the contralateral hemisphere after stroke. However, how different stroke subtypes, that have more severe vascular disruption, affect nonischemic vessels is unknown. Here, we compared circulating factors from human patients with distinct stroke subtypes of cardioembolic (CE), small vessel disease (SVD), and intracerebral hemorrhage (ICH). We hypothesized that serum from ICH patients would cause greater vascular dysfunction of nonischemic arteries than CE, and that serum from SVD patients would have an intermediate effect.

Methods: Serum was obtained 24 hours poststroke from patients with SVD (n=3), ICH (n=4), and CE (n=7) and pooled. All patients had a medical history of hypertension. Only SVD and CE patients received tPA. Pooled serum 20% v/v was perfused into the lumen of 3 rd order posterior cerebral arteries (PCA, CE & ICH n=5, SVD n=6) that were mounted on glass cannulas and pressurized in an arteriograph chamber. Blood brain barrier (BBB) permeability and vascular reactivity was studied to investigate effects on myogenic tone and endothelial function. Data are presented as mean±SEM.

Results: All vessels reacted myogenically at pressures ≥40 mmHg. However, serum from ICH patients caused a significant increase in tone at 20 mmHg vs. CE and SVD groups: 37.5±1.6 vs. 9.0±1.9% and 13.0±4.8% p<0.05. There was no difference in dilation to NS309; however, constriction to nitric oxide synthase (NOS) inhibition with L-NAME was impaired with SVD and ICH serum compared to CE: 14.0±2.3% vs. 4.6±0.8% (p<0.05) and 5.8±2.1% (p=0.09). However, reactivity to sodium nitroprusside, an NO donor, was not different between groups. Serum caused an increase in BBB permeability over time that was not different with the different serums.

Conclusions: Circulating factors from ICH, SVD and CE patients had differing vascular effects on nonischemic cerebral arteries. Serum from ICH patients was vasoconstrictive, potentially due to hemostatic factors, whereas serum from both SVD and ICH patients had impaired NO reactivity demonstrating endothelial dysfunction. These effects of ischemic stroke could affect the contralateral hemisphere and contribute to outcome and therapeutic responses.

Abstract TMP119: Increased Stroke Severity In A Model Of Preeclampsia Is Associated With Poor Collateral Flow, Oxidative Stress, And Elevated Thrombin

Background: Pregnancy is associated with an increased risk of stroke largely driven by the comorbidity of preeclampsia (PE), a hypertensive disorder that complicates 4-8% of all pregnancies. Although stroke treatment has improved in recent years, pregnant women have been excluded from stroke clinical trials and thus little is known about treatment and stroke outcome in this population. We investigated stroke outcome (infarct and hemorrhagic transformation, HT) in normal pregnancy (Preg; n=13) and in a model of preeclampsia (PE; n=6) induced by feeding pregnant Sprague Dawley rats a high cholesterol diet on gestational days 7-21. Nonpregnant (NP; n=7) rats were a control for pregnancy.

Methods: Middle cerebral artery occlusion (MCAO) was used to induce focal ischemia for 3 hours with 1 hour of reperfusion. Perfusion deficit in the core MCA and collateral territories were measured using multi-site laser Doppler. Infarction and oxidative stress were determined by cresyl violet and 3-nitrotyrosine staining of fixed brain tissue, respectively. Endothelial oxidative stress and hemostatic factors were measured by ELISA for 8-isoprostane and thrombin.

Results: Perfusion deficit in core MCA was similar between groups; however, collateral flow was significantly impaired in ePE vs. NP and LP: -51±8% vs. -21±15% and -25±13% (p<0.05). Infarct (%) was increased in ePE vs. NP and LP: 33±5% vs. 22±6% and 14±3% (p<0.05). Importantly, the majority of NP animals had HT (4/7), but none of the Preg or ePE suggesting pregnancy was protective of hemorrhage. The increased incidence of HT in NP was associated with increased 3-NT in brain tissue. However, 8-iso was increased in serum of ePE rats vs. NP and LP: 778±16 vs. 208±25 and 274±54 pg/mL (p<0.01), as was plasma thrombin: 6.6±1.2 vs. 0.49±0.01 and 0.56±0.01 pg/mL (p<0.01).

Conclusions: Increased stroke severity in ePE animals was associated with poor collateral flow, oxidative stress and elevated thrombin, all of which could contribute to poor ischemic tolerance and increased infarction. Pregnancy-induced protection of HT may be due to high sex steroids that was present in both LP and ePE groups. Understanding contributors to stroke outcome in this population could help manage these high risk patients.

Worsened Stroke Outcome in a Model of Preeclampsia is Associated With Poor Collateral Flow and Oxidative Stress

BACKGROUND

Preeclampsia increases the incidence of maternal stroke, a devastating condition that is on the rise. We investigated stroke outcome in a model of experimental preeclampsia with and without treatment with clinically relevant doses of magnesium sulfate (experimental preeclampsia+MgSO4) compared to normal late-pregnant and nonpregnant rats.

METHODS

Transient middle cerebral artery occlusion was used to induce focal stroke for either 1.5 or 3 hours. Infarct volume and hemorrhagic transformation were determined as measures of stroke outcome. Changes in core middle cerebral artery and collateral flow were measured by dual laser Doppler. The relationship between middle cerebral artery perfusion deficit and infarction was used as a measure of ischemic tolerance. Oxidative stress and endothelial dysfunction were measured by 3-nitrotyrosine and 8-isoprostane, in brain and serum, respectively.

RESULTS

Late-pregnant animals had robust collateral flow and greater ischemic tolerance of brain tissue, whereas experimental preeclampsia had greater infarction that was related to poor collateral flow, endothelial dysfunction, and oxidative stress. Importantly, pregnancy appeared preventative of hemorrhagic transformation as it occurred only in nonpregnant animals. MgSO4 did not provide benefit to experimental preeclampsia animals for infarction.

CONCLUSIONS

Stroke outcome was worse in a model of preeclampsia. As preeclampsia increases the risk of future stroke and cardiovascular disease, it is worth understanding the influence of preeclampsia on the material brain and factors that might potentiate injury both during the index pregnancy and years postpartum.

Therapeutic Induction of Collateral Flow

Therapeutic induction of collateral flow as a means to salvage tissue and improve outcome from acute ischemic stroke is a promising approach in the era in which endovascular therapy is no longer time-dependent but collateral-dependent. The importance of collateral flow enhancement as a therapeutic for acute ischemic stroke extends beyond those patients with large amounts of salvageable tissue. It also has the potential to extend the time window for reperfusion therapies in patients who are ineligible for endovascular thrombectomy. In addition, collateral enhancement may be an important adjuvant to neuroprotective agents by providing a more robust vascular route for which treatments can gain access to at risk tissue. However, our understanding of collateral hemodynamics, including under comorbid conditions that are highly prevalent in the stroke population, has hindered the efficacy of collateral flow augmentation for improving stroke outcome in the clinical setting. This review will discuss our current understanding of pial collateral function and hemodynamics, including vasoactivity that is critical for enhancing penumbral perfusion. In addition, mechanisms by which collateral flow can be increased during acute ischemic stroke to limit ischemic injury, that may be different depending on the state of the brain and vasculature prior to stroke, will also be reviewed.

Retrospective study of medical student scholarship and career trajectory following a mentored preclinical cardiovascular summer research fellowship

OBJECTIVES

Developing a preclinical training infrastructure for cardiovascular clinician-scientists is an academic workforce priority. The Cardiovascular Research Institute of Vermont developed a cardiovascular summer research fellowship (SRF), wherein medical student awardees were selected by merit-based application and completed mentored research between the first and second years. We aimed to study the impact of the SRF on medical student scholarship and career planning.

DESIGN

Retrospective survey study.

SETTING

Single academic medical centre.

PARTICIPANTS

All SRF participants from 2015 to 2020.

INTERVENTIONS

Not applicable.

PRIMARY AND SECONDARY OUTCOME MEASURES

Prior SRF participants were surveyed to ascertain current position, research engagement and perspectives regarding SRF experience. Comparisons to American Association of Medical Colleges Graduation Questionnaire data from equivalent years were made using χ² tests.

RESULTS

Survey response rate was 87% (20/23), 55% were women. Median time from SRF completion was 2 years (IQR 0.75-2.25), with 75% still enrolled in medical school and 25% in residency. As a result of the first-year summer programme, 45% published a peer-reviewed abstract or manuscript, which was equivalent to the national rate for graduating students (53%, p=0.4). Most respondents (80%) were active in additional research projects during school separate from the SRF, 90% anticipated a career involving research (vs 53% nationally, p<0.001) and 75% planned to pursue a career in cardiovascular medicine.

CONCLUSION

Medical students completing a mentored cardiovascular SRF after their first year have a high rate of academic scholarship, with publication rate already equivalent to national peer graduates. Preclinical SRF students strongly anticipate cardiovascular medicine and research careers.

Treatment with apocynin selectively restores hippocampal arteriole function and seizure-induced hyperemia in a model of preeclampsia

Preeclampsia (PE) is a hypertensive disorder of pregnancy associated with neurovascular dysfunction, cognitive impairment and increased seizure susceptibility. Here, we sought to determine if treatment of experimental PE (ePE) rats with apocynin could prevent hippocampal arteriolar (HA) dysfunction and impaired seizure-induced hyperemia within the hippocampus, a brain region central to cognition and seizure generation. Isolated and pressurized HAs from Sprague Dawley rats that were normal pregnant (Preg; n = 8), ePE (n = 8) or ePE treated with apocynin for 2 weeks of gestation (ePE + apo; n = 8) were compared. Hippocampal blood flow (n = 6/group) was measured using hydrogen clearance before and during seizure. Aorta elastin was quantified using histochemistry. ePE was associated with HA dysfunction including reduced contraction to endothelin-1 and diminished dilation to the endothelium-dependent vasodilator NS309 that was prevented by apocynin. However, apocynin had no effect on ePE-induced impairment of dilation to the nitric oxide donor sodium nitroprusside, but increased myogenic tone and substantially increased HA distensibility. Seizure-induced hyperemia was impaired in ePE rats that was restored by apocynin. Aorta from ePE rats had reduced elastin content, suggesting large artery stiffness, that was unaffected by apocynin. Thus, while apocynin partially prevented HA dysfunction, its restoration of functional hyperemia may be protective of seizure-induced injury during eclampsia.

Cerebral Blood Flow Autoregulation in Offspring From Experimentally Preeclamptic Rats and the Effect of Age

Preeclampsia is a hypertensive disorder of pregnancy that causes significant, long term cardiovascular effects for both the mother and offspring. A previous study demonstrated that middle cerebral arteries in offspring from an experimental rat model of preeclampsia were smaller, stiffer, and did not enlarge over the course of maturation, suggesting potential hemodynamic alterations in these offspring. Here we investigated the effect of experimental preeclampsia on cerebral blood flow autoregulation in juvenile and adult offspring that were born from normal pregnant or experimentally preeclamptic rats. Relative cerebral blood flow was measured using laser Doppler flowmetry, and cerebral blood flow autoregulation curves were constructed by raising blood pressure and controlled hemorrhage to lower blood pressure. Immunohistochemistry was used to assess middle cerebral artery size. Heart rate and blood pressure were measured in awake adult offspring using implanted radiotelemetry. Serum epinephrine was measured using enzyme-linked immunosorbent assay. Offspring from both groups showed maturation of cerebral blood flow autoregulation as offspring aged from juvenile to adulthood as demonstrated by the wider autoregulatory plateau. Experimental preeclampsia did not affect cerebral blood flow autoregulation in juvenile offspring, and it had no effect on cerebral blood flow autoregulation in adult offspring over the lower range of blood pressures. However, experimental preeclampsia caused a right shift in the upper range of blood pressures in adult offspring (compared to normal pregnant). Structurally, middle cerebral arteries from normal pregnant offspring demonstrated growth with aging, while middle cerebral arteries from experimentally preeclamptic offspring did not, and by adulthood normal pregnant offspring had significantly larger middle cerebral arteries. Middle cerebral artery lumen diameters did not significantly change as offspring aged. Serum epinephrine was elevated in juvenile experimentally preeclamptic offspring, and a greater degree of hemorrhage was required to induce hypotension, suggesting increased sympathetic activity. Finally, despite no evidence of increased sympathetic activity, adult experimentally preeclamptic offspring were found to have persistently higher heart rate. These results demonstrate a significant effect of experimental preeclampsia on the upper range of autoregulation and cerebrovascular structure in juvenile and adult offspring that could have an important influence on brain perfusion under conditions of hypo and/or hypertension.

Experimental Preeclampsia Causes Long-Lasting Hippocampal Vascular Dysfunction and Memory Impairment

Preeclampsia (PE) is a hypertensive disorder of pregnancy that is associated with memory impairment, cognitive decline and brain atrophy later in life in women at ages as young as early-to-mid 40 s. PE increases the risk of vascular dementia three-fold, however, long-lasting effects of PE on the vasculature of vulnerable brain regions involved in memory and cognition, such as the hippocampus, remain unknown. Here, we used a rat model of experimental PE (ePE) induced by maintaining rats on a 2% cholesterol diet beginning on day 7 of gestation to investigate hippocampal function later in life. Hippocampal-dependent memory and hippocampal arteriole (HA) function were determined in Sprague Dawley rats 5 months after either a healthy pregnancy or ePE (n = 8/group). Rats that had ePE were hypertensive and had impaired vasoreactivity of HAs to mediators involved in matching neuronal activity with local blood flow (i.e., neurovascular coupling). ePE rats also had impaired long-term memory, but not spatial memory. Thus, this model of ePE mimics some of the long-lasting cardiovascular and cognitive consequences that occur in women who previously had PE. These findings suggest endothelial and vascular smooth muscle dysfunction of HAs were present months after PE that could impair hippocampal neurovascular coupling. This represents a novel vascular mechanism by which PE causes early-onset dementia.

Mechanisms of Flow-Mediated Dilation of Pial Collaterals and the Effect of Hypertension

Leptomeningeal anastomoses are small distal anastomotic vessels also known as pial collaterals in the brain. These vessels redirect blood flow during an occlusion and are important for stroke treatment and outcome. Pial collaterals have unique hemodynamic forces and experience significantly increased luminal flow and shear stress after the onset of ischemic stroke. However, there is limited knowledge of how pial collaterals respond to flow and shear stress, and whether this response is altered in chronic hypertension. Using an in vitro system, pial collaterals from normotensive and hypertensive rats (n=6-8/group) were isolated and luminal flow was induced with intravascular pressure maintained at 40 mm Hg. Collateral lumen diameter was measured following each flow rate in the absence or presence of pharmacological inhibitors and activators. Collaterals from male and female Wistar rats dilated similarly to increased flow (2 µL/minute: 58.4±18.7% versus 67.9±7.4%; P=0.275), and this response was prevented by inhibition of the transient receptor potential vanilloid type 4 channel, as well as inhibitors of nitric oxide and intermediate-conductance calcium-activated potassium channels, suggesting shear stress-induced activation of this pathway was involved. However, the vasodilation was significantly impaired in hypertensive rats (2 µL/minute: 17.7±7.7%), which was restored by inhibitors of reactive oxygen species and mimicked by angiotensin II. Thus, flow- and shear stress-induced vasodilation of pial collaterals appears to be an important stimulus for increasing collateral flow during large vessel occlusion. Impairment of this response during chronic hypertension may be related to poorly engaged pial collaterals during ischemic stroke in hypertensive subjects.

Thomas Willis Lecture: Targeting Brain Arterioles for Acute Stroke Treatment

[Figure: see text].

Hippocampal network dysfunction as a mechanism of early-onset dementia after preeclampsia and eclampsia

Preeclampsia is a hypertensive disorder of pregnancy that can involve dangerous neurological symptoms such as spontaneous seizures (eclampsia). Despite being diseases specific to the pregnant state, preeclampsia and eclampsia have long-lasting neurological consequences later in life, including changes in brain structure and cognitive decline at relatively young ages. However, the effects of preeclampsia on brain regions central to memory and cognition, such as the hippocampus, are unclear. Here, we present a case reporting the progressive and permanent cognitive decline in a woman that had eclamptic seizures in the absence of evidence of brain injury on MRI. We then use rat models of normal pregnancy and preeclampsia to investigate mechanisms by which eclampsia-like seizures may disrupt hippocampal function. We show that experimental preeclampsia causes delayed memory decline in rats and disruption of hippocampal neuroplasticity. Further, seizures in pregnancy and preeclampsia caused acute memory dysfunction and impaired neuroplasticity but did not cause acute neuronal cell death. Importantly, hippocampal dysfunction persisted 5 weeks postpartum, suggesting seizure-induced injury is long lasting and may be permanent. Our data provide the first evidence of a model of preeclampsia that may mimic the cognitive decline of formerly preeclamptic women, and that preeclampsia and eclampsia affect hippocampal network plasticity and impair memory.

Rapamycin Induces an eNOS (Endothelial Nitric Oxide Synthase) Dependent Increase in Brain Collateral Perfusion in Wistar and Spontaneously Hypertensive Rats

BACKGROUND AND PURPOSE

Rapamycin is a clinically approved mammalian target of rapamycin inhibitor that has been shown to be neuroprotective in animal models of stroke. However, the mechanism of rapamycin-induced neuroprotection is still being explored. Our aims were to determine if rapamycin improved leptomeningeal collateral perfusion, to determine if this is through eNOS (endothelial nitric oxide synthase)-mediated vessel dilation and to determine if rapamycin increases immediate postreperfusion blood flow.

METHODS

Wistar and spontaneously hypertensive rats (≈14 weeks old, n=22 and n=15, respectively) were subjected to ischemia by middle cerebral artery occlusion (90 and 120 minutes, respectively) with or without treatment with rapamycin at 30-minute poststroke. Changes in middle cerebral artery and collateral perfusion territories were measured by dual-site laser Doppler. Reactivity to rapamycin was studied using isolated and pressurized leptomeningeal anastomoses. Brain injury was measured histologically or with triphenyltetrazolium chloride staining.

RESULTS

In Wistar rats, rapamycin increased collateral perfusion (43±17%), increased reperfusion cerebral blood flow (16±8%) and significantly reduced infarct volume (35±6 versus 63±8 mm³, P<0.05). Rapamycin dilated leptomeningeal anastomoses by 80±9%, which was abolished by nitric oxide synthase inhibition. In spontaneously hypertensive rats, rapamycin increased collateral perfusion by 32±25%, reperfusion cerebral blood flow by 44±16%, without reducing acute infarct volume 2 hours postreperfusion. Reperfusion cerebral blood flow was a stronger predictor of brain damage than collateral perfusion in both Wistar and spontaneously hypertensive rats.

CONCLUSIONS

Rapamycin increased collateral perfusion and reperfusion cerebral blood flow in both Wistar and comorbid spontaneously hypertensive rats that appeared to be mediated by enhancing eNOS activation. These findings suggest that rapamycin may be an effective acute therapy for increasing collateral flow and as an adjunct therapy to thrombolysis or thrombectomy to improve reperfusion blood flow.

Impact of Acute and Chronic Hypertension on Changes in Pial Collateral Tone In Vivo During Transient Ischemia

We investigated vasoconstrictive responses of pial collaterals in vivo at baseline and during transient middle cerebral artery occlusion during chronic hypertension. A cranial window was used to measure diameter of leptomeningeal anastomoses (pial collaterals) in male Wistar (n=8) and spontaneously hypertensive rats (SHRs; n=8) using video dimensional analysis. Middle cerebral artery occlusion was induced by remote filament for 2 hours with 2 hours reperfusion. Phenylephrine was infused during ischemia as a pressor therapy. Active diameters of pial collaterals were significantly smaller in SHRs versus Wistar (14.1±1.5 versus 21.6±2.8 µm; P<0.01); however, passive diameters were similar (25.0±2.9 versus 25.0±2.6 µm; P>0.05). Basal tone of pial collaterals before occlusion was 42±5% in SHRs versus 15±4% in Wistar (P<0.01). Tone decreased in both Wistar and SHRs during occlusion but remained higher in SHRs (9±2% versus 29±4%; P<0.05). Phenylephrine increased blood pressure in both groups but had little effect on leptomeningeal anastomoses diameters. Reperfusion caused vasoconstriction of pial collaterals, increasing tone from 8±1% to 20±5% in Wistar and 29±5% to 44±5% in SHRs (P<0.01). Higher tone in pial collaterals from SHRs basally and during occlusion/reperfusion could limit flow to the penumbra and promote evolution of infarction. Sustained elevated tone of pial collaterals from SHRs with phenylephrine suggests pressor therapy may not be appropriate during chronic hypertension.

ACE (Angiotensin-Converting Enzyme) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals in Chronic Hypertension

Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and important for stroke outcome. We previously showed LMAs from SHRs (spontaneously hypertensive rats) were vasoconstricted compared with normotensive Wistar rats. Here, we investigated mechanisms by which hypertension causes LMA vasoconstriction. SHRs were treated with the ACE (angiotensin-converting enzyme) inhibitor captopril, an Ang II (angiotensin II)-independent antihypertensive agent hydralazine, or vehicle for 5 weeks in drinking water (n=8/group). A group of Wistar rats (n=8) had regular drinking water served as controls. Blood pressure was measured twice weekly by tail-cuff. LMAs were isolated and studied under pressurized conditions. Vasoreactivity of LMAs, including myogenic responses, reactivity to Rho-kinase inhibitor Y-27632, and nitric oxide were measured. Both captopril and hydralazine lowered blood pressure in SHRs similar to Wistar. However, only captopril normalized LMA increased tone compared with untreated SHRs (15±2% versus 50±3%; P<0.01) that was similar to Wistar (16±2%) but not hydralazine (38±6%; P>0.05). Vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared with Wistar (28±3% versus 81±4%; P<0.01) that was restored by captopril (84±5%; P<0.01) and partially hydralazine (59±4%). LMAs from all groups constricted similarly to NOS (NO synthase) inhibition; however, the vasodilatory response of LMAs to the nitric oxide donor sodium nitroprusside was impaired in SHRs compared with Wistar rats (29±4% versus 80±2%; P<0.01) that was restored by captopril (84±4%; P<0.01), not hydralazine (38±8%; P>0.05). These results suggest that ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs that could improve stroke outcome by increasing collateral perfusion.

Memory impairment in spontaneously hypertensive rats is associated with hippocampal hypoperfusion and hippocampal vascular dysfunction

We investigated the effect of chronic hypertension on hippocampal arterioles (HippAs) and hippocampal perfusion as underlying mechanisms of memory impairment, and how large artery stiffness relates to HippA remodeling. Using male spontaneously hypertensive rats (SHR) and normotensive Wistar rats (n = 12/group), long-term (LTM) and spatial memory were tested using object recognition and spontaneous alternation tasks. Hippocampal blood flow was measured via hydrogen clearance basally and during hypercapnia. Reactivity of isolated and pressurized HippAs to pressure and pharmacological activators and inhibitors was investigated. To determine large artery stiffness, distensibility and elastin content were measured in thoracic aorta. SHR had impaired LTM and spatial memory associated with decreased basal blood flow (68 ± 12 mL/100 g/min) vs. Wistar (111 ± 28 mL/100 g/min, p < 0.01) that increased during hypercapnia similarly between groups. Compared to Wistar, HippAs from SHR had increased tone at 60 mmHg (58 ± 9% vs. 37 ± 7%, p < 0.01), and decreased reactivity to small- and intermediate-conductance calcium-activated potassium (SK/IK) channel activation. HippAs in both groups were unaffected by NOS inhibition. Decreased elastin content correlated with increased stiffness in aorta of SHR that was associated with increased stiffness and hypertrophic remodeling of HippAs. Hippocampal vascular dysfunction during hypertension could potentiate memory deficits and may provide a therapeutic target to limit vascular cognitive impairment.

Abstract 138: Angiotensin Converting Enzyme (ACE) Inhibition Reverses Vasoconstriction and Impaired Dilation of Pial Collaterals During Chronic Hypertension

Introduction: Leptomeningeal anastomoses (LMAs) are pial collaterals that perfuse the penumbra and are important for stroke outcome. In the current study, we investigated mechanisms by which hypertension causes LMA vasoconstriction that is known to limit the amount of salvageable tissue when stroke occurs during chronic hypertension. We hypothesized that increased vasoreactivity of LMAs from hypertensive rats is angiotensin II (Ang II)-dependent.

Methods: Spontaneously hypertensive rats (SHRs, n=8/group) were treated with the ACE inhibitor captopril, hydralazine to lower blood pressure (BP) independent of AngII, or vehicle for 5 weeks in drinking water. A group of normotensive Wistar rats (n=8) had regular drinking water served as controls. BP was measured twice weekly by tail cuff. LMAs were isolated and studied in pressurized conditions. Vasoactivity of LMAs, including myogenic responses, reactivity to the Rho-kinase inhibitor Y-27632 and nitric oxide (NO) were measured.

Results: Both captopril and hydralazine lowered BP in SHRs similar to Wistar rats. LMAs from untreated SHRs had increased myogenic tone vs. Wistar that was normalized by captopril but not hydralazine (Fig. 1A). LMAs from all groups constricted similarly to NO synthase inhibition; however, the vasodilatory response of LMAs to the NO donor sodium nitroprusside, was impaired in SHRs vs. Wistar rats that was restored by captopril and not hydralazine (Fig. 1B). Maximum vasodilatory response of LMAs to Y-27632 was impaired in SHRs compared to Wistar rats (28±3% vs. 81±4%, p<0.01) that was restored by captopril (84±5%) and partially by hydralazine (59±4%) treatment.

Conclusions: ACE inhibition during chronic hypertension reversed vascular dysfunction and hyperconstriction of LMAs, an effect that could improve stroke outcome by increasing collateral perfusion. In addition, lowering BP alone without inhibition of Ang II, may not provide the same protective effect on pial collaterals.

Perinatal stroke

Perinatal stroke is a heterogeneous syndrome resulting from brain injury of vascular origin that occurs between 20 weeks of gestation and 28 days of postnatal life. The incidence of perinatal stroke is estimated to be between 1:1600 and 1:3000 live births (approximately 2500 children per year in the United States), though its actual incidence is difficult to estimate because it is likely underdiagnosed. Perinatal arterial ischemic stroke (PAIS) accounts for approximately 70% of cases of perinatal stroke. Cerebral sinovenous thrombosis, while less common, also accounts for a large proportion of the morbidity and mortality seen with perinatal stroke. Hemorrhagic stroke leads to disruption of neurologic function due to intracerebral hemorrhage that is nontraumatic in origin. While most cases of PAIS fall into one of these three categories, other patterns of injury should also be considered perinatal stroke. In some cases, the etiology of PAIS is not known but is idiopathic. This chapter will review the classification, risk factors, pathogenesis, clinical presentation, management, and long-term sequelae of perinatal stroke.

Inhibition of PAI (Plasminogen Activator Inhibitor)-1 Improves Brain Collateral Perfusion and Injury After Acute Ischemic Stroke in Aged Hypertensive Rats

Background and Purpose- Aging and hypertension, comorbidities prevalent in the stroke population, are associated with poor collateral status and worsened stroke outcome. However, underlying mechanisms by which these conditions affect stroke outcome are not clear. We studied the role of PAI (plasminogen activator inhibitor)-1 that is increased in aging and hypertension on brain and vascular expression of inflammatory factors and perfusion that may contribute to worse stroke outcomes. Methods- Aged (≈50 weeks) and young (≈18 weeks) spontaneously hypertensive rats (SHR) were subjected to ischemia by middle cerebral artery occlusion (2 hours) and reperfusion (2 hours) with or without treatment with the PAI-1 inhibitor TM5441. Changes in middle cerebral artery and collateral perfusion territories were measured by multisite laser Doppler. Reactivity to TM5441 was studied using isolated and pressurized leptomeningeal anastomotic arterioles. Brain injury was determined by 2,3,5-triphenyltetrazolium staining and quantitative immunohistochemistry of amyloid-β-42, PAI-1, and hemoglobin. Circulating inflammatory factors were measured by ELISA. Results- Changes in cerebral blood flow during middle cerebral artery occlusion were similar between groups, with both having poor collateral perfusion and incomplete reperfusion. However, aged SHR had greater brain injury versus young (41±2 versus 23±2%, P<0.05) as well as increased brain deposition of amyloid-β-42 and circulating oxLDL (oxidized low-density lipoprotein). Erythrocyte aggregation and hemorrhage within the injured brain was observed in 50% of aged but no young SHR, with increased circulating PAI-1 in this subgroup of aged SHR (16±3 versus 6±2 ng/mL, P<0.05). PAI-1 inhibition with TM5441 improved brain injury but did not affect hemorrhage. TM5441 increased collateral perfusion by 38±7% and dilated leptomeningeal anastomotic arterioles by 44±10%, which was abolished by nitric oxide synthase inhibition. Conclusions- Increased injury in aged SHR seemed to be related to poor collateral perfusion, hemorrhagic transformation, increased amyloid-β-42, and oxidative stress. PAI-1 inhibition reduced infarction in both groups of SHR that possibly due, in part, to increased collateral perfusion.

Posterior reversible encephalopathy syndrome in stroke-prone spontaneously hypertensive rats on high-salt diet

Stroke-prone spontaneously hypertensive rats (SHRSP) on high-salt diet are characterized by extremely high arterial pressures, and have been endorsed as a model for hypertensive small vessel disease and vascular cognitive impairment. However, rapidly developing malignant hypertension is a well-known cause of posterior reversible encephalopathy syndrome (PRES) in humans, associated with acute neurological deficits, seizures, vasogenic cerebral edema and microhemorrhages. In this study, we aimed to examine the overlap between human PRES and SHRSP on high-salt diet. In SHRSP, arterial blood pressure progressively increased after the onset of high-salt diet and seizure-like signs emerged within three to five weeks. MRI revealed progressive T2-hyperintense lesions suggestive of vasogenic edema predominantly in the cortical watershed and white matter regions. Histopathology confirmed severe blood-brain barrier disruption, white matter vacuolization and microbleeds that were more severe posteriorly. Hematological data suggested a thrombotic microangiopathy as a potential underlying mechanism. Unilateral common carotid artery occlusion protected the ipsilateral hemisphere from neuropathological abnormalities. Notably, all MRI and histopathological abnormalities were acutely reversible upon switching to regular diet and starting antihypertensive treatment. Altogether our data suggest that SHRSP on high-salt diet recapitulates the neurological, histopathological and imaging features of human PRES rather than chronic progressive small vessel disease.

Transient receptor potential vanilloid-4 channels are involved in diminished myogenic tone in brain parenchymal arterioles in response to chronic hypoperfusion in mice

AIM

Adaptive responses of brain parenchymal arterioles (PAs), a target for cerebral small vessel disease, to chronic cerebral hypoperfusion are largely unknown. Previous evidence suggested that transient receptor potential vanilloid 4 channels may be involved in the regulation of cerebrovascular tone. Therefore, we investigated the role of TRPV4 in adaptations of PAs in a mouse model of chronic hypoperfusion.

METHODS

TRPV4 knockout (^-/- ) and wild-type (WT) mice were subjected to unilateral common carotid artery occlusion (UCCAo) for 28 days. Function and structure of PAs ipsilateral to UCCAo were studied isolated and pressurized in an arteriograph.

RESULTS

Basal tone of PAs was similar between WT and TRPV4^-/- mice (22 ± 3 vs 23 ± 5%). After UCCAo, active inner diameters of PAs from WT mice were larger than control (41 ± 2 vs 26 ± 5 μm, P < 0.05) that was due to decreased tone (8 ± 2 vs 23 ± 5%, P < 0.05), increased passive inner diameters (46 ± 3 vs 34 ± 2 μm, P < 0.05), and decreased wall-to-lumen ratio (0.104 ± 0.01 vs 0.137 ± 0.01, P < 0.05). However, UCCAo did not affect vasodilation to a small- and intermediate-conductance calcium-activated potassium channel agonist NS309, the nitric oxide (NO) donor sodium nitroprusside, or constriction to a NO synthase inhibitor L-NNA. Wall thickness and distensibility in PAs from WT mice were unaffected. In TRPV4^-/- mice, UCCAo had no effect on active inner diameters or tone and only increased passive inner diameters (53 ± 2 vs 43 ± 3 μm, P < 0.05).

CONCLUSION

Adaptive response of PAs to chronic cerebral hypoperfusion includes myogenic tone reduction and outward remodelling. TRPV4 channels were involved in tone reduction but not outward remodelling in response to UCCAo.

The importance of comorbidities in ischemic stroke: Impact of hypertension on the cerebral circulation

Comorbidities are a hallmark of stroke that both increase the incidence of stroke and worsen outcome. Hypertension is prevalent in the stroke population and the most important modifiable risk factor for stroke. Hypertensive disorders promote stroke through increased shear stress, endothelial dysfunction, and large artery stiffness that transmits pulsatile flow to the cerebral microcirculation. Hypertension also promotes cerebral small vessel disease through several mechanisms, including hypoperfusion, diminished autoregulatory capacity and localized increase in blood-brain barrier permeability. Preeclampsia, a hypertensive disorder of pregnancy, also increases the risk of stroke 4-5-fold compared to normal pregnancy that predisposes women to early-onset cognitive impairment. In this review, we highlight how comorbidities and concomitant disorders are not only risk factors for ischemic stroke, but alter the response to acute ischemia. We focus on hypertension as a comorbidity and its effects on the cerebral circulation that alters the pathophysiology of ischemic stroke and should be considered in guiding future therapeutic strategies.

Implications for understanding ischemic stroke as a sexually dimorphic disease: the role of pial collateral circulations

We investigated structural and functional differences in primary and pial collateral circulations in adult normotensive male and female Wistar rats. Male ( n = 10) and female ( n = 7) rats were subjected to middle cerebral artery (MCA) occlusion and changes in relative cerebral blood flow in MCA and pial collateral territories were measured by multisite laser-Doppler flowmetry. Rats were then transcardially perfused with a mixture of carbon black and latex, perfusion fixed, and imaged to compare primary and pial collateral structure between male ( n = 4) and female ( n = 3) rats, including lumen diameters and number. To study pial collateral function, leptomeningeal anastomoses (LMAs) were isolated and pressurized from male ( n = 7) and female ( n = 6) rats. Myogenic tone and reactivity to pressure, vascular function to pharmacological activator, or inhibitor of ion channels was measured and compared. There was no difference between relative cerebral blood flow in both MCA and pial collateral territories during occlusion and reperfusion between groups. Compared with male LMAs, female LMAs had similar myogenic tone (24.0 ± 7.3% vs. 16.0 ± 3.7%, P > 0.05) and reactivity to increased pressure and similar vascular responses to vasoconstrictive and vasodilatory stimuli. Additionally, compared with female LMAs, male LMAs had similar numbers (21 ± 1 vs. 20 ± 2, P > 0.05) and diameters (30.5 ± 2.0 vs. 26.2 ± 0.6 μm, P > 0.05), and no sex difference was detected in the diameter of arterial segments of circle of Willis. Together, our data establish no sex difference of cerebral collateral structure or function, suggesting that the reduced severity of stroke outcome in female rats is not likely due to differences in the cerebral collateral circulation. NEW & NOTEWORTHY Our work compared the function of leptomeningeal anastomoses between male and female adult normotensive rats with no sex difference found. We also confirmed no sex difference in primary and pial collateral structure in Wistar rats. Our findings suggest that the reduced severity of stroke in premenopausal women and reproductively intact female rodents is not likely due to improved primary and pial collateral circulations.

Advanced glycation end products alter steroidogenic gene expression by granulosa cells: an effect partially reversible by vitamin D

STUDY QUESTION

Does vitamin D attenuate the adverse effects of advanced glycation end products (AGEs) on steroidogenesis by human granulosa cells (GCs)?

SUMMARY ANSWER

AGEs alter the expression of genes important in steroidogenesis while 1,25-dihydroxyvitamin D3 (vit D3) in vitro attenuates some of the actions of AGEs on steroidogenic gene expression, possibly by downregulating the expression of the pro-inflammatory cell membrane receptor for AGEs (RAGE).

WHAT IS KNOWN ALREADY

Vitamin D attenuates the pro-inflammatory effects of AGEs in non-ovarian tissues.

STUDY DESIGN, SIZE, DURATION

Women who were undergoing IVF were enrolled. Follicular fluid samples (n = 71) were collected and cumulus GCs (n = 12) were treated in culture.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicular fluid levels of the anti-inflammatory soluble RAGE (sRAGE), AGEs and 25-hydroxyvitamin D (25-OHD) were quantified for possible correlations. GCs of each participant were split equally and treated with either media alone (control) or with human glycated albumin (HGA as a precursor for AGEs) with or without vit D3 after which RT-PCR and immunofluorescence were performed and cell culture media estradiol (E2) levels were compared.

MAIN RESULTS AND THE ROLE OF CHANCE

In follicular fluid, sRAGE levels were positively correlated with 25-OHD levels. HGA treatment (i) increased CYP11A1 (by 48%), 3β-HSD (by 38%), StAR (by 42%), CYP17A1 (by 30%) and LHR (by 37%) mRNA expression levels (P < 0.05 for all) but did not alter CYP19A1 or FSHR mRNA expression levels; and (ii) increased E2 release in cell culture media (P = 0.02). Vit D3 treatment (i) downregulated RAGE mRNA expression by 33% and RAGE protein levels by 44% (P < 0.05); (ii) inhibited the HGA-induced increase in CYP11A1, StAR, CYP17A1 and LHR mRNA levels, but not the increase in 3β-HSD mRNA levels; and (iii) did not inhibit the HGA-induced E2 release in cell culture media.

LIMITATIONS REASONS FOR CAUTION

This study used luteinized GCs that were collected from women who received gonadotropins thus the results obtained may not fully extrapolate to non-luteinized GCs in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests that there is a relationship between AGEs and their receptors (RAGE and sRAGE) with vitamin D. Understanding the interaction between AGEs and vitamin D in ovarian physiology could lead to a more targeted therapy for the treatment of ovarian dysfunction.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was received from NIH (R01 NS045940), American Society for Reproductive Medicine, Ferring Pharmaceuticals Inc., and University of Vermont College of Medicine Bridge Funds. All authors have nothing to disclose.

Pharmacologically increasing collateral perfusion during acute stroke using a carboxyhemoglobin gas transfer agent (Sanguinate™) in spontaneously hypertensive rats

Similar to patients with chronic hypertension, spontaneously hypertensive rats (SHR) develop fast core progression during middle cerebral artery occlusion (MCAO) resulting in large final infarct volumes. We investigated the effect of Sanguinate™ (SG), a PEGylated carboxyhemoglobin (COHb) gas transfer agent, on changes in collateral and reperfusion cerebral blood flow and brain injury in SHR during 2 h of MCAO. SG (8 mL/kg) or vehicle ( n = 6-8/group) was infused i.v. after 30 or 90 min of ischemia with 2 h reperfusion. Multi-site laser Doppler probes simultaneously measured changes in core MCA and collateral flow during ischemia and reperfusion using a validated method. Brain injury was measured using TTC. Animals were anesthetized with choral hydrate. Collateral flow changed little in vehicle-treated SHR during ischemia (-8 ± 9% vs. prior to infusion) whereas flow increased in SG-treated animals (29 ± 10%; p < 0.05). In addition, SG improved reperfusion regardless of time of treatment; however, brain injury was smaller only with early treatment in SHR vs. vehicle (28.8 ± 3.2% vs. 18.8 ± 2.3%; p < 0.05). Limited collateral flow in SHR during MCAO is consistent with small penumbra and large infarction. The ability to increase collateral flow in SHR with SG suggests that this compound may be useful as an adjunct to endovascular therapy and extend the time window for treatment.

Impaired function of cerebral parenchymal arterioles in experimental preeclampsia

Preeclampsia (PE), a dangerous hypertensive complication of pregnancy, is associated with widespread maternal vascular dysfunction. However, the effect of PE on the cerebral vasculature that can lead to stroke and cognitive decline is not well understood. We hypothesized that function of cortical parenchymal arterioles (PAs) would be impaired during PE. Using a high cholesterol diet to induce experimental PE in rats (ePE), we studied the function and structure of isolated and pressurized PAs supplying frontoparietal white matter (WM) tracts and cortex and compared to normal pregnant (Preg) and nonpregnant (Nonpreg) Sprague Dawley rats (n = 8/group). Myogenic reactivity and tone were similar between groups; however, constriction to intermediate-conductance calcium-activated potassium (IK) channel inhibition was diminished and dilation to inward-rectifying K⁺ (K_IR) channel activation was impaired in PAs from ePE rats, suggesting altered ion channel function. Conducted vasodilation was significantly delayed in response to 12 mM KCl, but not 10 μM adenosine, in PAs from ePE rats versus Preg and Nonpreg rats (940 ± 300 ms vs. 70 ± 50 ms and 370 ± 90 ms; p < 0.05). Overall, dysfunction of PAs supplying frontoparietal WM and gray matter was present in ePE. If persistent these changes could potentiate neuronal injury that over time could contribute to WM lesions and early-onset cognitive decline.

Abstract WP407: Function and Reactivity of Pial Collaterals In Vivo in Normotensive and Hypertensive Rats: Response to Ischemia and Reperfusion

Background: Collateral therapeutics is an emerging treatment for acute ischemic stroke. However, whether pial collaterals have tone in vivo and thus the ability to vasodilate is not clear. We investigated the function of pial collaterals in vivo during ischemia and reperfusion in normotensive and hypertensive rats that are known to have poor collaterals. We hypothesized that pial collaterals from spontaneously hypertensive rats (SHR) would have greater basal tone during ischemia and reperfusion than normotensive Wistar rats that could contribute to decreased collateral perfusion.

Methods: A cranial window was performed in SHR (n=4) and Wistar (n=4) rats prior to remote middle cerebral artery occlusion (MCAo) under pentobarbital anesthesia. Video microscopy was used to measure changes in diameter of leptomeningeal anastomoses (LMAs) during MCAo for 2 hrs and 2 hrs reperfusion (Figure, top). After reperfusion, the brain surface was exposed to physiological saline solution with EDTA (67 mmol/L) to measure fully relaxed diameters and calculate basal tone. Blood pressure was measured via arterial catheter and animals were mechanically ventilated to control blood gases.

Results: Blood pressure was significantly elevated in SHR vs. Wistar rats (157±9 vs. 107±7; p<0.01). LMAs (~15-20 μm diameters) had basal tone that was higher in SHR vs. Wistar (15.4±9% vs. 8.4±4.9%; n.s.). After 5 min MCAo, tone in LMAs from Wistar rats decreased to 2.7±1.5% but increased to 17.2±9.7% in SHR. Reperfusion caused vasoconstriction of LMAs from both groups and increased tone to 18.7±5.3% in Wistar and to 29.5±9.7% in SHR (p<0.01 vs. basal for both; Figure, bottom).

Conclusions: These data demonstrate functional pial collaterals in normotensive and hypertensive rats. While increased tone of LMAs during MCAo in SHR could limit perfusion to the penumbra, vasoconstriction of LMAs from both groups suggests therapeutic intervention to increase diameter and salvage at risk tissue is possible.

Abstract 79: Chronic and Acute Hypertension in Ischemic Stroke Are Distinct Markers of Impaired Collateral Circulation

Background: Acute blood pressure (BP) elevation in acute ischemic stroke (AIS) is common, yet the link with collateral circulation remains elusive due to lack of longitudinal data on premorbid hypertension (HTN) and serial BP changes within an individual. Precision medicine for AIS and management of HTN requires an understanding of collateral circulation.

Methods: The Interventional Management of Stroke III angiography core lab prospectively evaluated collateral circulation utilizing the ASITN scale prior to endovascular therapy. We used these data to discern the relationship of clinical and imaging markers of premorbid HTN with acute, serial BP measures and collaterals.

Results: Collaterals at angiography were graded in 276/331 (83%) subjects. Higher initial BP was associated with impaired collateral status, driven by diastolic BP (ASITN 0-1: mean 88.9 ± 23.5 mmHg (n=70); 2: 82.7 ± 18.5 mmHg (n=106); 3-4: 79.4 ± 15.0 mmHg (n=95); p=0.002) but not systolic BP (ASITN 0-1: mean 153.7 ± 31.5 mmHg (n=71); 2: 147.8 ± 29.0 mmHg (n=107); 3-4: 146.8 ± 28.3 mmHg (n=95); p=0.153). Premorbid HTN was linked with worse collaterals (ASITN 0-1: 88.9% (64/72); 2: 78.7% (85/108); 3-4: 64.2% (61/95); p=0.001). Admission anti-hypertensive medications were tied to worse collaterals (ASITN 0-1: 76.4% (55/72); 2: 64.8% (70/108); 3-4: 57.3% (55/96); p=0.036). Prior infarction on baseline imaging was also a marker of worse collaterals (ASITN 0-1: 33.3% (24/72); 2: 24.3% (26/107); 3-4: 19.1% (18/94); p=0.039). Serial BP from pre-randomization to post-tPA, however, was unrelated to collateral status. Multivariate modeling to predict collateral grade revealed that history of HTN (OR 0.29 95%CI (0.13, 0.64); p=0.002) and diastolic BP measured post-stroke but pre-randomization (per 10 mm Hg) (OR 0.80 95%CI (0.69, 0.93); p=0.004) were both distinct markers of impaired collaterals. The poorest collaterals were seen in those with both history of HTN and acutely elevated BP.

Conclusions: Chronic and acute HTN are both potent predictors of impaired collaterals in AIS. Understanding how HTN affects the structure and function of collaterals and response to acute BP changes is critical for future hypertensive management and collateral augmentation.

Inhibition of blood-brain barrier efflux transporters promotes seizure in pregnant rats: Role of circulating factors

Seizure-provoking factors circulate late in gestation during normal pregnancy, but do not readily gain access to the brain due to the protective nature of the blood-brain barrier. In particular, efflux transporters are powerful ATP-driven pumps that actively prevent unwanted compounds from entering the brain. We hypothesized that acute inhibition of efflux transporters at the blood-brain barrier would result in spontaneous seizures in pregnant rats. We further hypothesized that the blood-brain barrier protects the maternal brain from seizure by increasing expression and/or activity of p-glycoprotein (P-gp), a major efflux transporter. Main blood-brain barrier efflux transporters were inhibited in-vivo in nonpregnant (Nonpreg) and pregnant (Preg; d19) Sprague Dawley rats (n=8/group). Seizures were monitored in conscious animals for 8h via chronically implanted electroencephalography (EEG) electrodes in the hippocampus and motor cortex and time-synced video. P-gp activity was measured via a calcein accumulation assay in freshly isolated cortical and hippocampal capillaries from Preg (d20) and Nonpreg rats (n=8-16/group), to assess regional susceptibility to transporter inhibition. P-gp expression, capillary density, and microglial activation as a measure of neuroinflammation were quantified using immunohistochemistry (n=4-6/group). Efflux transporter inhibition elicited hippocampal seizures within 1h in 100% of Preg rats that was not associated with neuroinflammation or elevated tumor necrosis factor alpha (TNFα) or vascular endothelial growth factor (VEGF), but negatively correlated with levels of estradiol. Hippocampal seizures were considerably less prevalent in Nonpreg rats. However, behavioral seizures in the motor cortex developed of similar severity in both groups of rats, demonstrating regional heterogeneity in response to efflux transporter inhibition. Basal P-gp activity was similar between groups, however, exposure to serum from Preg rats significantly decreased P-gp activity in the hippocampus, but not cortex, compared to serum from Nonpreg rats (0.29±0.1units/s in Preg vs. 0.06±0.02units/s in Nonpreg rats; p<0.05) that was not associated with elevated TNFα or VEGF. Thus, pregnancy differentially increased the susceptibility of the hippocampus to seizures in response to blood-brain barrier efflux transporter inhibition that may be due to the inhibitory effect of circulating factors in pregnancy on P-gp activity in the hippocampus.

Treatment with low dose fasudil for acute ischemic stroke in chronic hypertension

We investigated the effect of Rho kinase inhibition on changes in cerebral blood flow (CBF), brain injury and vascular function after ischemic stroke in spontaneously hypertensive rats (SHR). Changes in core MCA and collateral perfusion were measured by a validated laser Doppler method. Animals underwent 2 h tMCAO and 2 h reperfusion. Fasudil (0.1 mg/kg, i.v.) or vehicle was given at 30 min ischemia (n = 9/group; mean (SD)). Brain injury was determined by 2,3,5-triphenyltetrazolium chloride staining. To determine the effect of fasudil on vascular function, fasudil was given 10 min before reperfusion and parenchymal arterioles studied isolated (n = 6/group; mean(SD)). Collateral perfusion was low in vehicle-treated SHR (-8(32)%) that changed minimally with fasudil (6(24)%, p > 0.05, effect size: 0.47;95% CI-0.49-1.39). Reperfusion CBF was below baseline in vehicle (-27(26)%) and fasudil (-32(25)%, p > 0.05, effect size: 0.19; 95% CI-0.74-1.11) groups, suggesting incomplete reperfusion in both groups. Fasudil had little effect on brain injury volume (28(13)% vs. 36(7)% in vehicle, p > 0.05, effect size: 0.75; 95% CI-0.24-1.66). In isolated parenchymal arterioles, myogenic tone was similar between groups (37(6)% vs. 38(10)% in vehicle, p > 0.05, effect size: 0.09; 95% CI-1.05-1.21). There were no differences with fasudil treatment vs. vehicle in perfusion, brain injury and vascular function that may be related to the low dose that had minimal blood pressure lowering effect.

Altered hippocampal arteriole structure and function in a rat model of preeclampsia: Potential role in impaired seizure-induced hyperemia

We investigated the effect of experimental preeclampsia on hyperemia during seizure in the hippocampus and vascular function and structure of hippocampal arterioles using Sprague Dawley rats (n = 14/group) that were nonpregnant, pregnant (d20), or had experimental preeclampsia (induced by a high cholesterol diet d7-20). Hyperemia was measured via hydrogen clearance basally and during pentylenetetrazol-induced seizure (40-130 mg/kg i.v.). Reactivity of isolated and pressurized hippocampal arterioles to KCl, nitric oxide synthase inhibition with NG-nitro-L-arginine methyl ester and the nitric oxide donor sodium nitroprusside were investigated. Capillary density was quantified via immunohistochemistry. Cerebral blood flow increased during seizure vs. baseline in pregnant (118 ± 14 vs. 87 ± 9 mL/100 g/min; p < 0.05) and nonpregnant rats (106 ± 9 vs. 82 ± 9 mL/100 g/min; p < 0.05) but was unchanged in preeclamptic rats (79 ± 16 vs. 91 ± 4 mL/100 g/min; p > 0.05), suggesting impaired seizure-induced hyperemia in preeclampsia. Hippocampal arterioles from preeclamptic rats had less basal tone, and dilated less to 15 mM KCl (9 ± 8%) vs. pregnant (61 ± 27%) and nonpregnant rats (20 ± 11%). L-NAME had no effect on hippocampal arterioles in any group, but dilation to sodium nitroprusside was similar. Structurally, hippocampal arterioles from preeclamptic rats underwent inward hypotrophic remodeling and capillary rarefaction. Impaired seizure-induced hyperemia, vascular dysfunction, and limited vasodilatory reserve of hippocampal arterioles could potentiate hippocampal injury in preeclampsia especially during eclampsia.

Effect of hypertension and peroxynitrite decomposition with FeTMPyP on CBF and stroke outcome

We investigated the effect of peroxynitrite decomposition catalyst FeTMPyP treatment on perfusion deficit, vascular function and stroke outcome in Wistar ( n = 26) and spontaneously hypertensive rats stroke-prone (SHRSP; n = 26) that underwent tMCAO for 2 h or Sham operation. Peri-infarct CBF was measured by hydrogen clearance in the absence or presence of FeTMPyP (10 mg/kg, i.v.) or vehicle 10 min before reperfusion. Myogenic tone of parenchymal arterioles (PAs) was measured as an indication of small vessel resistance (SVR). Baseline CBF was similar between Wistar and SHRSP (114 ± 12 vs. 132 ± 9 mL/100 g/min); however, MCAO caused greater perfusion deficit in SHRSP (24 ± 6 vs. 7 ± 1 mL/100 g/min; p < 0.05) and increased infarct volume by TTC (12 ± 6 vs. 32 ± 2%; p < 0.05). Reperfusion CBF was decreased from baseline in both SHRSP and Wistar (54 ± 16 and 46 ± 19 mL/100 g/min; p < 0.05), suggesting increased infarction in SHRSP was related to greater perfusion deficit. PAs from SHRSP had increased tone vs. Wistar that was enhanced after tMCAO. FeTMPyP treatment did not affect CBF during ischemia or reperfusion, or tone of PAs, but decreased the incidence of hemorrhage in SHRSP by 50%. Thus, increased tone in PAs from SHRSP could increase perfusion deficit during MCAO that was not alleviated by FeTMPyP.

Improving Reperfusion Therapies in the Era of Mechanical Thrombectomy

Recent positive clinical trials using mechanical thrombectomy proved that endovascular recanalization is an effective treatment for patients with acute stroke secondary to large vessel occlusions. The trials offer definite evidence that in acute ischemia recanalization is a powerful predictor of good outcome. However, even in the era of rapid and effective recanalization using endovascular approaches, the percentage of patients with good outcomes varies between 33 and 71 %. In addition, the number of patients who are eligible for endovascular thrombectomy is small and usually based on having salvageable tissue on imaging. There is therefore room for improvement to both enhance the effectiveness of current practice and expand treatment to a larger subset of stroke patients. In this review, we highlight some of the most promising approaches to improve endovascular therapy by combining with strategies to enhance collateral perfusion and vascular protection.

Effects of Early Post-Ischemic Reperfusion and tPA on Cerebrovascular Function and Nitrosative Stress in Female Rats

Stroke is a major health issue in women. Our previous studies in male rats showed decreased myogenic tone in middle cerebral arteries (MCAs) after ischemia and reperfusion (I/R), while tone in parenchymal arterioles (PAs) was increased. This vascular response may aggravate stroke damage in males by limiting reperfusion; however, the effect in females is not known. The current study investigated the effect of I/R and tissue plasminogen activator (tPA) on myogenic tone and reactivity of MCAs and PAs in female rats. Nitrosative stress by peroxynitrite and recruitment of inflammatory neutrophils to the microvasculature were also studied. Female rats were subjected to 2-h MCA filament occlusion (n = 16) or sham surgery (n = 17) and given tPA (1 mg/kg, i.v) or vehicle followed by 30-min reperfusion. Myogenic tone and reactivity were measured in isolated and pressurized MCAs and PAs from the same animals. Cerebrovascular F-actin, 3-nitrotyrosine (3-NT, peroxynitrite marker), and intravascular neutrophils were quantified. Myogenic tone and constriction to the nitric oxide synthase inhibitor Nω-nitro-L-arginine were decreased in MCAs but unchanged in PAs after I/R with no effect of tPA. F-actin and 3-NT expression were unaffected by I/R or tPA. Our study showed that MCAs from females, similar to what has been seen in males, are dilated after I/R and have decreased myogenic tone while tone in PAs was unchanged. Increased small vessel resistance may contribute to decreased reperfusion and worse outcome after stroke.

Pial Collateral Reactivity During Hypertension and Aging: Understanding the Function of Collaterals for Stroke Therapy

Supplemental Digital Content is available in the text.

Background and Purpose—

We investigated vasoactive properties of leptomeningeal arterioles (LMAs) under normotensive conditions and during hypertension and aging that are known to have poor collateral flow and little salvageable tissue.

Methods—

LMAs, identified as distal anastomotic arterioles connecting middle and anterior cerebral arteries, were studied isolated and pressurized from young (18 weeks) or aged (48 weeks) normotensive Wistar Kyoto (WKY18, n=14; WKY48, n=6) rats and spontaneously hypertensive rats (SHR18, n=16; SHR48, n=6). Myogenic tone and vasoactive responses to pressure as well as endothelial function and ion channel activity were measured.

Results—

LMAs from WKY18 had little myogenic tone at 40 mm Hg (8±3%) that increased in aged WKY48 (30±6%). However, LMAs from both WKY groups dilated to increased pressure and demonstrated little myogenic reactivity, a response that would be conducive to collateral flow. In contrast, LMAs from both SHR18 and SHR48 displayed considerable myogenic tone (56±8% and 43±7%; P<0.01 versus WKY) and constricted to increased pressure. LMAs from both WKY and SHR groups had similar basal endothelial nitric oxide and IK channel activity that opposed tone. However, dilation to sodium nitroprusside, diltiazem and 15 mmol/L KCl was impaired in LMAs from SHR18.

Conclusions—

This study shows for the first time that LMAs from young and aged SHR are vasoconstricted and have impaired vasodilatory responses that may contribute to greater perfusion deficit and little penumbral tissue. These results also suggest that therapeutic opening of pial collaterals is possible during middle cerebral artery occlusion to create penumbral tissue and prevent infarct expansion.

The Importance of Considering Sex Differences in Translational Stroke Research

Stroke is the second leading cause of death worldwide, and differences between men and women have been documented in incidence, prevalence, and outcome. Here, we reviewed the literature on sex differences in stroke severity, mortality, functional outcome, and response to therapies after ischemic stroke. Many of the sex differences in stroke severity and mortality are explained by differences in baseline demographics such as older age in women. However, women account for more stroke deaths, consistently suffer from worse stroke outcomes, and are more often institutionalized and permanently disabled than men. These sex differences in functional outcome are equalized after treatment with tissue plasminogen activator (tPA) and women may benefit more from treatment than men. However, this may depend on race, as African-American women have less of a response to tPA than other groups. Regarding endovascular treatments, the few existing studies that have investigated sex differences in stroke outcome point to equal benefit in both sexes; however, many clinical trials are relatively underpowered to detect sex differences. Further, we considered sex-specific effects in animal models of stroke and present recommendations for the performance of stroke studies in female animals. The male-biased use of research animals is distinguished from the clinical situation where there is a disproportionate and growing female stroke population. Stroke in women is greatly understudied, and including both sexes is especially important in both preclinical and clinical studies that evaluate potential stroke therapies.

Effects of Acute Stroke Serum on Non-Ischemic Cerebral and Mesenteric Vascular Function

We investigated the effects of circulating factors in serum obtained from patients in the acute phase of different subtypes of ischemic stroke on non-ischemic cerebral and mesenteric arteries, as a potential mechanism involved in influencing regional perfusion and thus clinical evolution. Posterior cerebral arteries (PCAs) and mesentery arteries (MAs) isolated from Wistar Kyoto rats were perfused with serum from acute stroke patients with large vessel disease without (LVD) or with hypertension (LVD + HTN), cardioembolism with hypertension (CE + HTN), or physiologic saline as controls. Myogenic activity and nitric oxide-dependent vasorelaxation were assessed after 2 h of intraluminal exposure to serum. Vascular function was differentially affected by sera. Exposure to LVD serum increased myogenic tone and produced endothelial dysfunction in both PCAs and MAs. However, CE + HTN serum increased tone and decreased smooth muscle sensitivity to NO in vessels from both vascular beds. LVD + HTN serum was associated with reduced smooth muscle sensitivity to NO in vessels from both vascular beds but increased tone only in PCAs. Inflammation and oxidative stress, determined by measurement of high sensitivity C-reactive protein, uric acid, and free 8-isoprostane, were enhanced in all the serum groups. These results demonstrate vasoactive properties of acute stroke serum related to stroke subtypes that could potentially contribute to the pathogenesis of early hemodynamic-based clinical events.