Enhanced contractile response of the basilar artery to platelet-derived growth factor in subarachnoid hemorrhage

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.

Skeleton-secreted PDGF-BB mediates arterial stiffening

Evidence links osteoporosis and cardiovascular disease but the cellular and molecular mechanisms are unclear. Here we identify skeleton-secreted platelet-derived growth factor-BB (PDGF-BB) as a key mediator of arterial stiffening in response to aging and metabolic stress. Aged mice and those fed high-fat diet (HFD), relative to young mice and those fed normal chow food diet, respectively, had higher serum PDGF-BB and developed bone loss and arterial stiffening. Bone/bone marrow preosteoclasts in aged mice and HFD mice secrete an excessive amount of PDGF-BB, contributing to the elevated PDGF-BB in blood circulation. Conditioned medium prepared from preosteoclasts stimulated proliferation and migration of the vascular smooth muscle cells. Conditional transgenic mice, in which PDGF-BB is overexpressed in preosteoclasts, had 3-fold higher serum PDGF-BB concentration and developed simultaneous bone loss and arterial stiffening spontaneously at a young age. Conversely, in conditional knockout mice, in which PDGF-BB is deleted selectively in preosteoclasts, HFD did not affect serum PDGF-BB concentration; as a result, HFD-induced bone loss and arterial stiffening were attenuated. These studies confirm that preosteoclasts are a main source of excessive PDGF-BB in blood circulation during aging and metabolic stress and establish the role of skeleton-derived PDGF-BB as an important mediator of vascular stiffening.

Therapeutically Targeting Platelet-Derived Growth Factor-Mediated Signaling Underlying the Pathogenesis of Subarachnoid Hemorrhage-Related Vasospasm

INTRODUCTION

Vasospasm accounts for a large fraction of the morbidity and mortality burden in patients sustaining subarachnoid hemorrhage (SAH). Platelet-derived growth factor (PDGF)-β levels rise following SAH and correlate with incidence and severity of vasospasm.

METHODS

The literature was reviewed for studies investigating the role of PDGF in the pathogenesis of SAH-related vasospasm and efficacy of pharmacological interventions targeting the PDGF pathway in ameliorating the same and improving clinical outcomes.

RESULTS

Release of blood under high pressure into the subarachnoid space activates the complement cascade, which results in release of PDGF. Abluminal contact of blood with cerebral vessels increases their contractile response to PDGF-β and thrombin, with the latter upregulating PDGF-β receptors and augmenting effects of PDGF-β. PDGF-β figures prominently in the early and late phases of post-SAH vasospasm. PDGF-β binding to the PDGF receptor-β results in receptor tyrosine kinase domain activation and consequent stimulation of intracellular signaling pathways, including p38 mitogen-activated protein kinase, phosphatidylinositol-3-kinase, Rho-associated protein kinase, and extracellular regulated kinase 1 and 2. Consequent increases in intracellular calcium and increased expression of genes mediating cellular growth and proliferation mediate PDGF-induced augmentation of vascular smooth muscle cell contractility, hypertrophy, and proliferation.

CONCLUSION

Treatments with statins, serine protease inhibitors, and small molecular pathway inhibitors have demonstrated varying degrees of efficacy in prevention of cerebral vasospasm, which is improved with earlier institution.

PDGF-BB regulates the pulmonary vascular tone: impact of prostaglandins, calcium, MAPK- and PI3K/AKT/mTOR signalling and actin polymerisation in pulmonary veins of guinea pigs

Background

Platelet-derived growth factor (PDGF)-BB and its receptor PDGFR are highly expressed in pulmonary hypertension (PH) and mediate proliferation. Recently, we showed that PDGF-BB contracts pulmonary veins (PVs) and that this contraction is prevented by inhibition of PDGFR-β (imatinib/SU6668). Here, we studied PDGF-BB-induced contraction and downstream-signalling in isolated perfused lungs (IPL) and precision-cut lung slices (PCLS) of guinea pigs (GPs).

Methods

In IPLs, PDGF-BB was perfused after or without pre-treatment with imatinib (perfused/nebulised), the effects on the pulmonary arterial pressure (P_PA), the left atrial pressure (P_LA) and the capillary pressure (P_cap) were studied and the precapillary (R_pre) and postcapillary resistance (R_post) were calculated. Perfusate samples were analysed (ELISA) to detect the PDGF-BB-induced release of prostaglandin metabolites (TXA₂/PGI₂). In PCLS, the contractile effect of PDGF-BB was evaluated in pulmonary arteries (PAs) and PVs. In PVs, PDGF-BB-induced contraction was studied after inhibition of PDGFR-α/β, L-Type Ca²⁺-channels, ROCK/PKC, prostaglandin receptors, MAP2K, p38-MAPK, PI3K-α/γ, AKT/PKB, actin polymerisation, adenyl cyclase and NO. Changes of the vascular tone were measured by videomicroscopy. In PVs, intracellular cAMP was measured by ELISA.

Results

In IPLs, PDGF-BB increased P_PA, P_cap and R_post. In contrast, PDGF-BB had no effect if lungs were pre-treated with imatinib (perfused/nebulised). In PCLS, PDGF-BB significantly contracted PVs/PAs which was blocked by the PDGFR-β antagonist SU6668. In PVs, inhibition of actin polymerisation and inhibition of L-Type Ca²⁺-channels reduced PDGF-BB-induced contraction, whereas inhibition of ROCK/PKC had no effect. Blocking of EP_1/3- and TP-receptors or inhibition of MAP2K-, p38-MAPK-, PI3K-α/γ- and AKT/PKB-signalling prevented PDGF-BB-induced contraction, whereas inhibition of EP₄ only slightly reduced it. Accordingly, PDGF-BB increased TXA₂ in the perfusate, whereas PGI₂ was increased in all groups after 120 min and inhibition of IP-receptors did not enhance PDGF-BB-induced contraction. Moreover, PDGF-BB increased cAMP in PVs and inhibition of adenyl cyclase enhanced PDGF-BB-induced contraction, whereas inhibition of NO-formation only slightly increased it.

Conclusions

PDGF-BB/PDGFR regulates the pulmonary vascular tone by the generation of prostaglandins, the increase of calcium, the activation of MAPK- or PI3K/AKT/mTOR signalling and actin remodelling. More insights in PDGF-BB downstream-signalling may contribute to develop new therapeutics for PH.

Involvement of platelet-derived growth factor ligands and receptors in tumorigenesis

Platelet-derived growth factor (PDGF) isoforms and their receptors have important roles during embryogenesis, particularly in the development of various mesenchymal cell types in different organs. In the adult, PDGF stimulates wound healing and regulates tissue homeostasis. However, overactivity of PDGF signalling is associated with malignancies and other diseases characterized by excessive cell proliferation, such as fibrotic conditions and atherosclerosis. In certain tumours, genetic or epigenetic alterations of the genes for PDGF ligands and receptors drive tumour cell proliferation and survival. Examples include the rare skin tumour dermatofibrosarcoma protuberance, which is driven by autocrine PDGF stimulation due to translocation of a PDGF gene, and certain gastrointestinal stromal tumours and leukaemias, which are driven by constitute activation of PDGF receptors due to point mutations and formation of fusion proteins of the receptors, respectively. Moreover, PDGF stimulates cells in tumour stroma and promotes angiogenesis as well as the development of cancer-associated fibroblasts, both of which promote tumour progression. Inhibitors of PDGF signalling may thus be of clinical usefulness in the treatment of certain tumours.

The Role of Platelet-Derived Growth Factor Receptor in Early Brain Injury Following Subarachnoid Hemorrhage

OBJECTIVE

This study aims to observe encephaledema and cell apoptosis in rats following subarachnoid hemorrhage (SAH) and to explore the mechanism of platelet-derived growth factor receptor (PDGFR) in the development of early brain injury (EBI).

METHODS

Adult and male Sprague-Dawley rats were randomly divided into 4 groups: sham operation, SAH, SAH + imatinib, and SAH + platelet-derived growth factor-BB (PDGF-BB). SAH model was established using intravascular silk puncture of the internal carotid artery crotch. The SAH + imatinib group was treated with intraperitoneal injection of imatinib 1 hour before establishing the model. The SAH + PDGF-BB group was administered with intracerebroventricular injection of PDGF-BB 1 hour before establishing the model. The mortality, encephaledema, and nerve functional scoring were observed after 24 hours in all groups. The expression of caspase-3 in hippocampus was tested by reverse transcription polymerase chain reaction and Western blotting.

RESULTS

Mortality and encephaledema were the highest in the SAH + PDGF-BB group, which were alleviated when the rats were injected with imatinib (P < .01).

CONCLUSION

PDGFR may participate in the pathogenesis of EBI following SAH. The antagonist of PDGFR, imatinib, can reduce brain damage to some degree.

Mechanisms underlying increased vascular smooth muscle contractility in the rabbit basilar artery following subarachnoid hemorrhage

Increased vascular contractility plays an important role in the development of cerebral vasospasm following subarachnoid hemorrhage (SAH). Here, we summarize our current knowledge regarding molecular mechanisms that contribute to increased smooth muscle contractility of rabbit basilar artery following SAH. Our studies demonstrated that upregulation of receptor expression, impairment of feedback regulation of receptor activity, and enhancement of myofilament Ca²⁺ sensitization might lead to increased smooth muscle contractility following SAH.

The role of rosiglitazone in the proliferation of vascular smooth muscle cells after experimental subarachnoid hemorrhage

BACKGROUND

Recent evidence has demonstrated that rosiglitazone can attenuate cerebral vasospasm following subarachnoid hemorrhage (SAH). Some studies have shown that rosiglitazone can suppress inflammation and immune responses after SAH. However, the precise molecular mechanisms by which cerebral vasospasm is attenuated is not clear.

METHODS

In this study, SAH was created using a "double hemorrhage" injection rat model. Rats were randomly divided into three groups and treated with saline (control group), untreated (SAH group), or treated with rosiglitazone. Using immunocytochemistry, hematoxylin and eosin (HE) staining, and measurement of the basilar artery, we investigated the formation of pathologic changes in the basilar artery, measured the expression of caveolin-1 and proliferating cell nuclear antigen (PCNA), and investigated the role of rosiglitazone in vascular smooth muscle cell (VSMC) proliferation in the basilar artery after SAH.

RESULTS

In this study, we observed significant pathologic changes in the basilar artery after experimental SAH. The level of vasospasm gradually increased with time during the 1st week, peaked on day 7, and almost recovered on day 14. After rosiglitazone treatment, the level of vasospasm was significantly attenuated in comparison with the SAH group. Immunocytochemistry staining showed that caveolin-1 expression was significantly increased in the rosiglitazone group, compared with the SAH group. Inversely, the expression of PCNA showed a notable decrease after rosiglitazone treatment.

CONCLUSIONS

The results indicate that rosiglitazone can attenuate cerebral vasospasm following SAH. Up-regulation of caveolin-1 by rosiglitazone may be a new molecular mechanism for this response, which is to inhibit proliferation of VSMCs after SAH, and this study may provide a novel insight to prevent delayed cerebral vasospasm (DCVS).

Intraventricular tissue plasminogen activator for the prevention of vasospasm and hydrocephalus after aneurysmal subarachnoid hemorrhage

BACKGROUND

The sequelae of aneurysmal subarachnoid hemorrhage (SAH) include vasospasm and hydrocephalus.

OBJECTIVE

To assess whether intraventricular tissue plasminogen activator (tPA) results in less vasospasm, fewer angioplasties, or fewer cerebrospinal fluid shunting procedures.

METHODS

41 patients (tPA group, Hunt and Hess 3, 4, 5) from 2007 to 2008 received intraventricular tPA and lumbar drainage for a minimum of 5 days (range 5-7 days) and were compared to a matched group of 35 patients from 2006 to 2007 (Control, HH 3, 4, 5). Statistical comparison was done by t test analysis or Fisher exact tests and data are expressed as average+/-standard error of the mean.

RESULTS

There were no significant differences in demographic data, although the tPA group had a trend toward more surgical patients. The tPA group of patients had a significantly higher modified Fisher grade than controls (P<.001) and had a significantly better Hunt and Hess grade than controls (P<.03). The angioplasty rate was significantly lower among the tPA patients (15.0%+/-5.6) than controls (40.0%+/-8.5, P=.019). The number of days spent in severe vasospasm normalized over the 14-day monitoring period by transcranial Doppler was significantly lower in the tPA group (0.09+/-0.02) than controls (0.17+/-0.03). The shunt rate was significantly lower among tPA patients (17.5%+/-6.0) than controls (42.8%+/-8.6). There were 2 clinically silent tract hemorrhages in the tPA group (4.8%).

CONCLUSION

Intraventricular tPA is a safe and effective treatment for reducing both angioplasty and shunting rates in patients with SAH H&H Grades 3 to 5. A randomized trial is indicated.

Targeting the PDGF signaling pathway in the treatment of non-malignant diseases

Platelet-derived growth factor (PDGF) is a family of mesenchymal mitogens with important functions during the embryonal development and in the control of tissue homeostasis in the adult. The PDGF isoforms exert their effects by binding to α-and β-tyrosine kinase receptors. Overactivity of PDGF signaling has been linked to the development of certain malignant and non-malignant diseases, including atherosclerosis and various fibrotic diseases. Different types of PDGF antagonists have been developed, including inhibitory monoclonal antibodies and DNA aptamers against PDGF isoforms and receptors, and receptor tyrosine kinase inhibitors. Beneficial effects have been recorded using such inhibitors in preclinical models and in patients with certain malignant as well as non-malignant diseases. The present communication summarizes the use of PDGF antagonists in the treatment of non-malignant diseases.

Suppression of the Rho/Rho-kinase pathway and prevention of cerebral vasospasm by combination treatment with statin and fasudil after subarachnoid hemorrhage in rabbit

The Rho/Rho-kinase pathway is considered important in the pathogenesis of sustained smooth muscle cell contraction during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The aims of this study were to investigate whether combination treatment, with pitavastatin as an inhibitor of RhoA and fasudil as an inhibitor of Rho-kinase, prevents the cerebral vasospasm. SAH was simulated using the double-hemorrhage rabbit model, and pitavastatin, or fasudil, or both (combination treatment) were administrated. The basilar artery (BA) cross-sectional area only in the combination treatment group was statistically larger than in the SAH group (p < 0.05). BA Rho-kinase, as measured by ELISA, was statistically reduced only in the combination treatment group compared with the SAH group (p < 0.05). In the other two treatment groups, pitavastatin or fasudil treatment group showed larger BA cross-sectional areas and lower value for BA Rho-kinase, but there were no statistically significant differences compared with the SAH group. The expression of endothelial nitric oxide synthase (eNOS), evaluated by immunohistochemistry in the pitavastatin group and the combination group, was higher than in the SAH group. Results indicate that combination treatment could extensively prevent cerebral vasospasm due to the synergic effect of combining pitavastatin and fasudil on the Rho/Rho-kinase pathway and on eNOS.

Role of platelet-derived growth factor in cerebral vasospasm after subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

The role of platelet-derived growth factor (PDGF) remains unknown in cerebral vasospasm after subarachnoid hemorrhage (SAH). In this study, we examined the effects of PDGF receptor (PDGFR) inactivation on cerebral vasospasm in the endovascular perforation model of SAH in rats.

METHODS

Rats were assigned to sham, SAH plus vehicle, and SAH plus imatinib mesylate (imatinib) groups (n = 4 per group). Imatinib (50 mg/kg body weight), an inhibitor of the tyrosine kinases of PDGFR, or vehicle was administered intraperitoneally 30 min post-SAH. Vasospasm was evaluated in the left (perforation-sided) internal carotid artery by means of neurobehavioral tests, India ink angiography, and immunohistochemistry at 24 h after SAH.

RESULTS

Imatinib significantly inhibited post-SAH PDGFR activation in the left internal carotid artery, in which vasospasm was significantly prevented. Animal's neurobehavior also showed a tendency to improve by imatinib treatment.

CONCLUSIONS

PDGF may play an important role in the pathogenesis of vasospasm after SAH.

A novel intravital method to evaluate cerebral vasospasm in rat models of subarachnoid hemorrhage: a study with synchrotron radiation angiography

Precise in vivo evaluation of cerebral vasospasm caused by subarachnoid hemorrhage has remained a critical but unsolved issue in experimental small animal models. In this study, we used synchrotron radiation angiography to study the vasospasm of anterior circulation arteries in two subarachnoid hemorrhage models in rats. Synchrotron radiation angiography, laser Doppler flowmetry-cerebral blood flow measurement, [¹²⁵I]N-isopropyl-p-iodoamphetamine cerebral blood flow measurement and terminal examinations were applied to evaluate the changes of anterior circulation arteries in two subarachnoid hemorrhage models made by blood injection into cisterna magna and prechiasmatic cistern. Using synchrotron radiation angiography technique, we detected cerebral vasospasm in subarachnoid hemorrhage rats compared to the controls (p<0.05). We also identified two interesting findings: 1) both middle cerebral artery and anterior cerebral artery shrunk the most at day 3 after subarachnoid hemorrhage; 2) the diameter of anterior cerebral artery in the prechiasmatic cistern injection group was smaller than that in the cisterna magna injection group (p<0.05), but not for middle cerebral artery. We concluded that synchrotron radiation angiography provided a novel technique, which could directly evaluate cerebral vasospasm in small animal experimental subarachnoid hemorrhage models. The courses of vasospasm in these two injection models are similar; however, the model produced by prechiasmatic cistern injection is more suitable for study of anterior circulation vasospasm.

Platelet-derived growth factor (PDGF)-BB produces NO-mediated relaxation and PDGF receptor β-dependent tonic contraction in murine iliac lymph vessels

We studied the effects of PDGF-BB on changes in the diameters of murine lymph vessels with or without intact endothelium. PDGF-BB induced dilation of the lymph vessels with endothelium. Pretreatment with l-NAME or removal of the endothelium caused a significant attenuation in the PDGF-BB-induced dilation. PDGF-BB also produced dose-related reduction of the diameters of the lymph vessels without endothelium. To evaluate intracellular signal transduction and Ca(2+) -dependence of the PDGF-BB-induced tonic contraction, we investigated the effects of imatinib, GW5074 (an inhibitor of Raf-1 kinase), U-73122 (an inhibitor of phospholipase C), and xestospongin C on the PDGF-BB-induced reduction responses. All of these inhibitors caused a significant attenuation in the PDGF-BB-induced reduction response that was significantly decreased by treatment with Ca(2+) -free Krebs-bicarbonate solution or nifedipine. Higher concentrations of PDGF-BB produced a marked reduction of lymph vessel diameter within both high K(+) Krebs-bicarbonate solution and Ca(2+) -free high K(+) Krebs solution containing 1mM EGTA. These findings suggest that PDGF-BB induced endothelium-dependent NO-mediated relaxation of lymphatic smooth muscles in murine lymph vessels. PDGF receptor β-mediated tonic contraction of the muscles through increased Ca(2+) influx through the membrane and the release of membrane-bound and intracellular Ca(2+) .

Unfractionated heparin: multitargeted therapy for delayed neurological deficits induced by subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is associated with numerous "delayed neurological deficits" (DNDs) that have been attributed to multiple pathophysiological mechanisms, including ischemia, microthrombosis, free radical damage, inflammation, and vascular remodeling. To date, effective prophylactic therapy for SAH-induced DNDs has been elusive, due perhaps to the multiplicity of mechanisms involved that render typical, single-agent therapy seemingly futile. We hypothesized that heparin, which has multiple underappreciated salutary effects, might be useful as a multitargeted prophylactic agent against SAH-induced DNDs. We performed a comprehensive review of the literature to evaluate the potential utility of heparin in targeting the multiple pathophysiological mechanisms that have been identified as contributing to SAH-induced DNDs. Our literature review revealed that unfractionated heparin can potentially antagonize essentially all of the pathophysiological mechanisms known to be activated following SAH. Heparin binds >100 proteins, including plasma proteins, proteins released from platelets, cytokines, and chemokines. Also, heparin complexes with oxyhemoglobin, blocks the activity of free radicals including reactive oxygen species, antagonizes endothelin-mediated vasoconstriction, smooth muscle depolarization, and inflammatory, growth and fibrogenic responses. Our review suggests that the use of prophylactic heparin following SAH may warrant formal study.

Current perspective on the role of the thrombin receptor in cerebral vasospasm after subarachnoid hemorrhage

Cerebral vasospasm is a persistent arterial narrowing typically observed during the 3 - 14 days after subarachnoid hemorrhage (SAH). Vasospasm is frequently associated with ischemic neurological deficits or even death, resulting in a poor prognosis for patients with SAH. However, the mechanism underlying cerebral vasospasm remains elusive, and no effective therapeutic strategies have been established. A large amount of thrombin is produced during SAH. Recent investigations have uncovered a key role of the thrombin receptor in the pathogenesis of cerebral vasospasm. Thrombin has little contractile effect in the normal cerebral artery, but it induces an enhanced and prolonged contraction after SAH, owing to the up-regulation of thrombin receptor PAR(1) (proteinase-activated receptor 1) and the impairment of receptor desensitization in arterial smooth muscle. Thrombin-mediated activation of PAR(1) is an irreversible process, as it is initiated by the proteolytic removal of the N-terminal region. Since the mechanism of receptor desensitization is impaired after SAH, the thrombin-induced contraction irreversibly persists even after terminating thrombin stimulation. Intrathecal administration of a PAR(1) antagonist prevents the PAR(1) up-regulation and the increased reactivity to thrombin. PAR(1) is suggested to play a key role in cerebral vasospasm and may be useful as a therapeutic target for prevention and treatment of cerebral vasospasm.

Impaired feedback regulation of the receptor activity and the myofilament Ca2+ sensitivity contributes to increased vascular reactiveness after subarachnoid hemorrhage

Cerebral vasospasm determines the prognosis of subarachnoid hemorrhage (SAH). The increased vascular reactiveness has an important role in the development of cerebral vasospasm. This study analyzed the roles of the receptor-mediated signaling and the myofilament Ca(2+) sensitivity in the increased vascular reactiveness in SAH, using the basilar artery of a rabbit SAH model. Endothelin-1, thrombin, and phenylephrine induced transient increases in [Ca(2+)](i), myosin light chain phosphorylation, and contraction in the controls. All these responses were not only enhanced but also became sustained in SAH. In the sequential stimulation of thrombin receptor or alpha(1)-adrenoceptor, the second response was substantially attenuated in the controls, whereas it was maintained in SAH. The thrombin-induced contraction in SAH irreversibly persisted even after terminating the thrombin stimulation. This contraction was completely reversed by trypsin and a Galpha(q) inhibitor YM254890, thus suggesting the sustained receptor activity during the sustained contraction. YM254890 also inhibited the endothelin-1- and phenylephrine-induced sustained contraction. Furthermore, the GTPgammaS-induced transient contraction in the control alpha-toxin-permeabilized strips was converted to a sustained contraction in SAH. The results provide the first evidence that the feedback inactivation of the receptor activity and the myofilament Ca(2+) sensitivity was impaired in SAH, thus contributing to the increased vascular reactiveness.

Platelet-derived growth factor-induced severe and chronic vasoconstriction of cerebral arteries: proposed growth factor explanation of cerebral vasospasm

OBJECTIVE

After subarachnoid hemorrhage (SAH), platelet-derived growth factor-BB (PDGF-BB) is secreted in and around the cerebral arteries. To clarify the role of PDGF-BB in the development of vasospasm after SAH, we determined whether PDGF-BB alone can cause long-lasting vasoconstriction of a severity similar to that of vasospasm. In addition, the anti-vasospastic effect of trapidil, an antagonist of PDGF-BB function, was investigated.

METHODS

We infused recombinant PDGF-BB (10 microg/mL saline as the vehicle) (n = 14) into the subarachnoid space of rabbits and analyzed alterations in the caliber of the basilar artery using repeated angiography. To study the role of PDGF-BB on the development of vasospasm, trapidil was administered continuously starting 1 hour after SAH, on day 0 (0.63-1.25 mg/kg /h or vehicle) for 47 hours (n = 24), or after the full development of cerebral vasospasm on day 2 (3.0 mg/kg/h or vehicle) for 0.5 hours (n = 17), and alterations in the caliber of the basilar artery were monitored.

RESULTS

PDGF-BB caused long-lasting vasoconstriction, with maximum constriction of 56% (P < .001) of the control value (= 100%) on day 2, resembling vasospasm seen after SAH. Prolonged administration of intravenous trapidil, starting soon after SAH, prevented the development of vasospasm in a dose-dependent manner (P < .05, .01, or .001). Intravenous or intra-arterial administration of trapidil significantly dilated vasospasm (P < .01) on day 2, at least transiently.

CONCLUSION

PDGF-BB, a growth factor synthesized in the subarachnoid space after SAH, can cause severe and long-lasting vasoconstriction. Significant prevention and resolution of vasospasm can be achieved by the PDGF-BB antagonist trapidil. We propose that excessive production of PDGF-BB, essentially aiming to repair injured arteries, causes cerebral vasospasm. Although the half-life of trapidil in serum may be shorter than that of PDGFG-BB-derived spasmogenic signaling, trapidil is a candidate drug for constructing a new therapeutic modality for preventing and resolving vasospasm.