The effect of subarachnoid hemorrhage on mechanisms of vasodilation mediated by cyclic adenosine monophosphate

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: Experimental-Clinical Disconnect and the Unmet Need

BACKGROUND

Delayed cerebral ischemia (DCI) is among the most dreaded complications following aneurysmal subarachnoid hemorrhage (SAH). Despite advances in neurocritical care, DCI remains a significant cause of morbidity and mortality, prolonged intensive care unit and hospital stay, and high healthcare costs. Large artery vasospasm has classically been thought to lead to DCI. However, recent failure of clinical trials targeting vasospasm to improve outcomes has underscored the disconnect between large artery vasospasm and DCI. Therefore, interest has shifted onto other potential mechanisms such as microvascular dysfunction and spreading depolarizations. Animal models can be instrumental in dissecting pathophysiology, but clinical relevance can be difficult to establish.

METHODS

Here, we performed a systematic review of the literature on animal models of SAH, focusing specifically on DCI and neurological deficits.

RESULTS

We find that dog, rabbit and rodent models do not consistently lead to DCI, although some degree of delayed vascular dysfunction is common. Primate models reliably recapitulate delayed neurological deficits and ischemic brain injury; however, ethical issues and cost limit their translational utility.

CONCLUSIONS

To facilitate translation, clinically relevant animal models that reproduce the pathophysiology and cardinal features of DCI after SAH are urgently needed.

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

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

Time-dependent alterations in functional and pharmacological arteriolar reactivity after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Disturbances in cerebral arteriolar function, in addition to large vessel vasospasm, may be responsible for ischemia after subarachnoid hemorrhage. The purpose of this study was to test the hypothesis that subarachnoid hemorrhage alters cerebral microvascular reactivity.

METHODS

An endovascular filament model was used to induce subarachnoid hemorrhage in halothane-anesthetized male Sprague-Dawley rats. We evaluated pial arteriolar responses to sciatic nerve stimulation, topically applied vasoactive agents (adenosine or sodium nitroprusside), and CO(2) inhalation in rats subjected to subarachnoid hemorrhage at 1 to 5 days after insult.

RESULTS

In sham-operated rats, sciatic nerve stimulation evoked a 23.5+/-1.8% increase in arteriolar diameter, which was significantly attenuated to 13.7+/-0.9%, 12.8+/-2.5%, and 18.8+/-2.9% at 24, 48, and 72 hours after subarachnoid hemorrhage, respectively (P<0.05; n> or =7). At 96 and 120 hours after subarachnoid hemorrhage, sciatic nerve stimulation-induced dilation recovered to sham levels. Somatosensory-evoked potentials were unaltered by subarachnoid hemorrhage. Pial vasodilatation to adenosine (10 micromol/L) and sodium nitroprusside (1 micromol/L) were significantly impaired, by 47% and 41%, respectively, at 48 hours after subarachnoid hemorrhage (P<0.05; n=7). In contrast, CO(2) reactivity was unaffected by subarachnoid hemorrhage.

CONCLUSIONS

Pial arteriolar responses to cortical activation may be decreased in the initial 2 to 3 days after experimental subarachnoid hemorrhage.

The cerebrovascular dilatation effects of olprinone, a phosphodiesterase III inhibitor, in comparison with acetazolamide—a pliot study

To examine the effects of olprinone, a phosphodiesterase III inhibitor, on cerebral blood flow (CBF), we compared the effects of olprinone on CBF to that of acetazolamide. Using technetium-99m-ethyl cysteinate dimer (99mTc-ECD) brain SPECT, we measured regional CBF (rCBF) at 33 sites, including 16 right and left pairs of non-infarct cerebral cortexes, in seven stroke patients (66.0+/-3.2 years) in a resting state and 15 min after the administration of acetazolamide. Within 1 week, rCBF at each site was measured 15 min after the initiation of olprinone infusion. Resting rCBF showed a significant negative correlation with the change in rCBF (DeltaCBF) during olprinone infusion (r = -0.43, P=0.013), but no significant correlation was seen following acetazolamide administration. The difference in rCBF between the right and left cortex increased more following acetazolamide administration (14.1+/-10.9 ml/(min 100 g)) than during olprinone infusion (5.4+/-4.8 ml/(min 100 g), P=0.013). The rCBF at four regions of interest (ROI) with low-resting CBF (< 49 ml/(min 100 g)) further decreased following the administration of acetazolamide. The vasodilatory effects of olprinone are dependent on resting CBF instead of on the intracerebral steal phenomenon that occurs with acetazolamide.

Olprinone: a phosphodiesterase III inhibitor with positive inotropic and vasodilator effects

Olprinone is a newly developed phosphodiesterase III inhibitor characterized by several properties. First, olprinone has positive inotropic and vasodilator actions and improves myocardial mechanical efficiency. Second, olprinone augments cerebral blood flow by a direct vasodilatory effect on cerebral arteries. The cerebrovascular reactivity to olprinone is marked in patients with impaired cerebral circulation. Third, olprinone selectively improves carotid artery distensibility, which may be attributable to differences in the arterial structural components or the reactivity of smooth muscle cells to olprinone. Fourth, olprinone improves inadequate redistribution of brain perfusion and may prevent cerebral metabolic abnormalities in heart failure.

Resolution of cerebral vasospasm with trapidil; an animal model

Cerebral vasospasm and rebleeding are important clinical phenomena associated with a high mortality rate. Therefore, any promising finding in the laboratory deserves assessment in clinical practice. The present study was designed to examine the possible effects of trapidil on the basilar artery of the rabbit through a cerebral vasospasm model. This experimental study was carried out on 26 adult New Zealand albino rabbits of both sexes weighing 2.5-3.0 kg. A transclival exposure was performed. Vasospasm was produced by an intracisternal injection of autologous blood. After observation of the vasospasm, trapidil was locally applied in increasing concentrations (10(-5)-10(-4) M). The effect of each concentration was measured independently after 10 minutes for each application and was extended to three hours. Trapidil was shown to have a clear spasmolytic effect on the rabbit's basilar artery. These data suggest that trapidil can have a potential use in the treatment of patients suffering from cerebral vasospasm.

Heat shock protein expression in cerebral vessels after subarachnoid hemorrhage

OBJECTIVE

The mechanisms of cerebral vasospasm after subarachnoid hemorrhage (SAH) remain controversial. Recent data have implicated two small heat shock proteins (HSPs), namely HSP20 and HSP27, in the regulation of vascular tone. Increases in the phosphorylation of HSP20 are associated with vasorelaxation, and increases in the phosphorylation of HSP27 are associated with impaired vasorelaxation. Therefore, we hypothesized that alterations in the expression and/or phosphorylation of these two small HSPs might play a role in cerebral vasospasm after SAH.

METHODS

A rat model of endovascular perforation was used to induce SAH. Middle cerebral arteries were harvested from control animals, sham-treated animals, and animals with SAH, 48 hours after SAH induction. Dose-response curves for endothelium-independent (sodium nitroprusside, 10(-8) to 10(-4) mol/L) and endothelium-dependent (bradykinin, 10(-10) to 10(-5) mol/L) relaxing agents were recorded ex vivo. Physiological responses were correlated with the expression and phosphorylation of HSP20 and HSP27 by using one- and two-dimensional immunoblots.

RESULTS

There was impaired endothelium-independent and endothelium-dependent relaxation in cerebral vessels after SAH. These changes were associated with decreased expression of both total and phosphorylated HSP20 and increases in the amount of phosphorylated HSP27.

CONCLUSION

In this model, impaired relaxation of cerebral vessels after SAH was associated with increases in the amount of phosphorylated HSP27 and decreases in the expression and phosphorylation of HSP20. These data are consistent with alterations in the expression and phosphorylation of these small HSPs in other models of vasospasm.

Impaired intracellular signal transduction via cyclic AMP contributes to cerebral vasospasm in rats with subarachnoid hemorrhage

No drug can completely prevent vasospasm after subarachnoid hemorrhage. Impaired intracellular signal transduction by cyclic nucleotides might be involved. We investigated effects of intravenous isoproterenol and NKH477 on cerebral blood flow in rats with or without intracisternal injection of autologous blood one week previously. In controls without hemorrhage, isoproterenol at 0.01, 0.1, 1, and 10 mg kg(-1) min(-1) increased cerebral blood flow by 1.2%+/-9.5%, 19.7%+/-12.8%, 46.8%+/-23.5%, and 63.8%+/-32.9% respectively; 10mg kg(-1) min(-1) of isoproterenol increased systemic blood pressure by 66.6%+/-58.1%, while other doses decreased blood pressure. In the subarachnoid hemorrhage group, isoproterenol increased cerebral blood flow by -20.0%+/-6.5%, -7.6%+/-8.7%, 8.2%+/-8.8%, and 35.9%+/-83.1% respectively; 10 mg kg(-1) min(-1) of isoproterenol increased systemic blood pressure by 68.8%+/-79.5%, while other doses decreased blood pressure. In controls, NKH477 at 3, 10, and 30 mg kg(-1) increased cerebral blood flow by 2.3%+/-3.6%, 14.4%+/-7.0%, and 50.7%+/-14.6%, respectively; in the subarachnoid hemorrhage group, NKH477 changed cerebral blood flow by -1.3%+/-2.4%, 4.6%+/-2.8%, and -12.6%+/-10.8% (not significant difference from controls). NKH477 at 30 mg kg(-1) min(-1) decreased systemic blood pressure in both groups, but the effect in the hemorrhage group was greater. Either isoproterenol or NKH477 at appropriate doses can increase cerebral blood flow in vasospasm following subarachnoid hemorrhage without decreasing blood pressure.

Effects of olprinone, a phosphodiesterase 3 inhibitor, on regional cerebral blood flow of cerebral cortex in stroke patients

The effects of olprinone (0.2 microg/kg per minute, i.v.) on cerebral blood flow were examined using technetium-99m-ethyl cysteinate dimer (99mTc-ECD) brain single-photon emission computed tomography in 14 stroke patients (69.0 +/- 5.6 years) and 12 normal subjects (68.1 +/- 6.2 years). The regional cerebral blood flow of the cerebral cortex was measured at six sites for each stroke patient (stroke group: n = 68, excluding 16 infarct areas confirmed on computed tomography image) and for each normal subject (normal group: n = 72). 99mTc-ECD brain single-photon emission computed tomography was repeated as the baseline 7 days after olprinone treatment study. The percent increment of the rCBF was 14.4 +/- 9.8% in the normal group and 10.7 +/- 11.7% in the stroke group (p = 0.002). The baseline value of the regional cerebral blood flow had a significant negative correlation with the increase of the regional cerebral blood flow in the normal group (r = -0.73, p < 0.0001) and in the stroke group (r = -0.43, p < 0.001). Although olprinone could dilate the cerebral vessels of stroke patients as well as those of normal subjects, smooth muscle dysfunction of the cerebral vessels due to advanced arteriosclerosis may reduce this effect.

Adenylate cyclase and potassium channels are involved in forskolin- and 1,9-dideoxyforskolin-induced inhibition of pregnant rat uterus contractility

OBJECTIVE

We sought to study the contribution of potassium channels in the effect of forskolin and 1,9-dideoxyforskolin on uterine contractility in the pregnant rat.

STUDY DESIGN

Rings taken from the middle portions of uterine horns from rats at 16 days of gestation were positioned in organ chambers containing physiologic salt solution bubbled with 5% carbon dioxide in air (37 degrees C, pH approximately 7.4) for isometric tension recording under 2 g passive tension. The effects of cumulative concentrations of forskolin and 1,9-dideoxyforskolin in the absence or presence of an adenylate cyclase inhibitor (MDL-12,330A, 10(-5) mol/L), a nonselective potassium channel blocker (tetrabutylammonium, 10(-4) mol/L), or an adenosine triphosphate-dependent potassium channel blocker (glibenclamide 10(-5) mol/L) were studied.

RESULTS

Both forskolin and, to a lesser extent, 1,9-dideoxyforskolin inhibit uterine contractions. Tetrabutylammonium, glibenclamide, and MDL-12, 330A attenuated the effects of forskolin, whereas glibenclamide was less effective against 1,9-dideoxyforskolin.

CONCLUSION

Activation of adenylate cyclases, as well as adenosine triphosphate-dependent potassium channels and, to a greater extent, calcium-dependent potassium channels, is involved in the inhibitory effect of forskolin in uterine rings from rats at 16 days of gestation. Inhibition of uterine contractions by 1,9-dideoxyforskolin is less than that by forskolin and involves activation of adenylate cyclase and calcium-dependent potassium channels. Whether activation of guanylate cyclase is involved in the effect of the agents on calcium-dependent potassium channels needs further investigation. 1, 9-Dideoxyforskolin is not an inactive isomer of forskolin in rat uterine rings.

Molecular keys to the problems of cerebral vasospasm

The mechanisms responsible for subarachnoid hemorrhage (SAH)-induced vasospasm are under intense investigation but remain incompletely understood. A consequence of SAH-induced vasospasm, cerebral infarction, produces a nonrecoverable ischemic tissue core surrounded by a potentially amenable penumbra. However, successful treatment has been inconsistent. In this review, we summarize the basic molecular biology of cerebrovascular regulation, describe recent developments in molecular biology to elucidate the mechanisms of SAH-induced vasospasm, and discuss the potential contribution of cerebral microcirculation regulation to the control of ischemia. Our understanding of the pathogenesis of SAH-induced vasospasm remains a major scientific challenge; however, molecular biological techniques are beginning to uncover the intracellular mechanisms involved in vascular regulation and its failure. Recent findings of microvascular regulatory mechanisms and their failure after SAH suggest a role in the development and size of the ischemia. Progress is being made in identifying the various components in the blood that cause SAH-induced vasospasm. Thus, our evolving understanding of the underlying molecular mechanism may provide the basis for improved treatment after SAH-induced vasospasm, especially at the level of the microcirculation.

Impaired cerebral vasodilator responses to NO and PDE V inhibition after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is associated with impaired nitric oxide (NO)-mediated cerebral vasodilatation. We tested the hypothesis that SAH causes alterations in the production of, hydrolysis of, or responsiveness to cGMP in the rat basilar artery in vivo. Rats were injected with saline or autologous blood into the cisterna magna. Two days later, effects of vasoactive drugs on basilar artery diameter were examined using a cranial window preparation. Vasodilator responses to ACh, sodium nitroprusside (SNP), and low concentrations (</=10(-5) M) of zaprinast, an inhibitor of phosphodiesterase V (PDE V), were impaired in SAH rats (P < 0.05). In contrast, vasodilator responses to adenosine and 8-BrcGMP were similar in control and SAH rats. Vasoconstrictor responses to 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, were unaffected by SAH. In the presence of zaprinast (10(-5)-10(-4) M), responses to ACh and SNP were equivalent in control and SAH rats. Thus an increased rate of cGMP hydrolysis by PDE V may be a major factor contributing to the impairment of NO-mediated cerebral vasodilatation after SAH.

Subarachnoid haemorrhage

A high percentage of the population has aneurysms of the cerebral vessels, which are detected only by chance or after spontaneous rupture. Subarachnoid haemorrhage is still a problem because of high morbidity and mortality. Many patients do not fully recover neurologically and suffer from physical and psychosocial symptoms. The aims of treatment are to prevent the patient from rebleeding and to prevent secondary neurological damage. Whereas in former times, clipping of the aneurysm was often delayed for days or weeks, early operative intervention is the rule today, if the patient is not moribund and if there is no significant cerebral oedema. The anaesthetist can support the neurosurgeon with a spectrum of different methods of anaesthesia and monitoring, individually tailored to the needs of the patient. Most important, however, is a stable haemodynamic status, stable and normal intracranial pressure and a sufficient cerebral perfusion pressure. Vasospasm is still the main problem, as is early rebleeding. To treat this, nimodipine is the drug of choice combined with volume therapy, a slightly elevated cardiac output and a modestly elevated blood pressure.

Hypotension dilates pial arteries by KATP and kca channel activation

Hypotension induced pial artery dilation is prostaglandin-dependent in the newborn pig. Prostaglandins, in turn, elicit vasodilation through cGMP and cAMP dependent mechanisms and K+ channel activation contributes to cyclic nucleotide induced vasodilation. The present study was designed to characterize the role of ATP sensitive (KATP) and calcium sensitive (Kca) channel activation in hypotension induced pial artery dilation in newborn pigs equipped with a closed cranial window. Glibenclamide and iberiotoxin, KATP and Kca channel antagonists, attenuated hypotension induced dilation (36+/-1 vs. 14+/-2% before and after iberiotoxin). Combined administration of these K+ channel antagonists eliminated the vascular response. Hypotension induced dilation was associated with elevated cerebrospinal fluid (CSF) cAMP but not cGMP concentration (1023+/-29 vs. 1566+/-39 fmol/ml for cAMP). L-NNA, a nitric oxide (NO) synthase inhibitor, and Rp 8-Br cGMPs, a protein kinase G inhibitor, had no effect but Rp 8-Br cAMPs, a protein kinase A inhibitor, attenuated hypotensive dilation (35+/-1 vs. 16+/-2% before and after Rp 8-Br cAMPs). Dilation by the cAMP analogue 8-Bromo cAMP (10(-8), 10(-6) M) was attenuated by glibenclamide and iberiotoxin (8+/-1 and 17+/-1 vs. 4+/-1 and 9+/-1% before and after glibenclamide). These data show that both KATP and Kca channel activation contribute to hypotension induced dilation. These data suggest that dilation during hypotension results from the sequential release of prostaglandins and cAMP, which, in turn, activates both the KATP and Kca channel.