Bryce Weir

Changes in endothelial nitric oxide synthase mRNA during vasospasm after subarachnoid hemorrhage in monkeys.

OBJECTIVE We attempt to determine whether changes in messenger ribonucleic acid (mRNA) for nitric oxide synthase (NOS) and soluble guanylate cyclase, enzymes that mediate endothelium-dependent vasodilation in cerebral arteries, occur after subarachnoid hemorrhage (SAH) in monkeys. METHODS Baseline cerebral angiograms were obtained, and right-sided SAH was induced by microsurgically placing autologous blood clot against the right anterior circle of Willis in seven monkeys. Seven days later, angiographic studies were repeated and the animals were killed. Right (vasospastic) and left (control) middle cerebral arteries and underlying cortex were removed. The competitive reverse transcriptase polymerase chain reaction was used to quantify mRNA for soluble guanylate cyclase and two isoforms of constitutive NOS in these tissues. RESULTS Comparison of angiograms at baseline and after 7 days showed a 41 +/- 7% (mean +/- standard error of the mean, P < 0.05, Wilcoxon test) decrease in diameter of the right middle cerebral artery. After the animals were killed, comparison of right and left middle cerebral arteries showed a 56 +/- 11% decrease (P < 0.005, paired t test) in endothelial NOS mRNA. There was a 142 +/- 39% (P < 0.05) increase in right cortex endothelial NOS mRNA compared to the left cortex. There were no significant differences between right and left sides in mRNAs for soluble guanylate cyclase or brain NOS. CONCLUSION Decreased endothelial NOS mRNA in cerebral arteries 7 days after SAH may be caused by endothelial cell damage and could contribute to vasospasm after SAH. Increased endothelial NOS in brain tissue may reflect a compensatory vasodilator mechanism of the brain against the cerebral ischemia associated with vasospasm and SAH.

Pathology and Pathogenesis

This chapter focuses on the cerebral infarction from vasospasm. Infarction involves the death of both neurons and glia. Neuronal necrosis follows cell swelling, mitochondrial damage and dissolution and generalized disruption of internal homeostasis. Membranes lyse and intracellular constituents are released extracellularly which can invoke a local inflammatory reaction. This is characterized by cellular infiltration, edema, and vascular damage. Ischemically induced extreme energy failure in mitochondria is the presumed essential cause of necrosis. Focal cerebral ischemia produces infarction characterized by microvacuolation, ischemic cell change with incrustation, and homogenizing cell change. Ischemia may result not just in neuronal death through these rapid mechanisms. A series of molecular and cellular processes underlie the transition from ischemia to inflammation and ultimate tissue dissolution. These involve polymorphonuclear leukocyte activation and chemotaxis, endothelial cell receptor biology, cytokine synthesis and release, leukocyte transmigration, and tissue invasion and microvascular thrombosis. Ischemia from VSP can be aggravated by coexistent vascular occlusive disease and other factors, such as advanced age, hypertension, diabetes mellitus, smoking, coronary artery disease, and elevated lipids. The infarction is related to the total amount, but it is not the distribution or clearance rate of extravasated blood, which is probably not shared by the majority of investigators.

Increased Expression of Endothelin B Receptor mRNA Following Subarachnoid Hemorrhage in Monkeys

These studies tested the hypothesis that the cerebral vasospasm that follows subarachnoid hemorrhage (SAH) is due to alterations in endothelin (ET) and ET receptor expression. Eight monkeys underwent cerebral angiography and induction of SAH. Angiography was repeated 7 days later to confirm the presence of cerebral vasospasm, and animals were killed. RNA was isolated from right (vasospastic) and left (control) side middle cerebral arteries and surrounding cerebral cortex. The levels of prepro (PP) ET-1 (ppET-1) and ppET-3 and ETA and ETB receptor mRNAs were determined using a quantitative reverse transcriptase polymerase chain reaction-based assay. ET-1 peptide was also measured in CSF at baseline and after 7 days. Specific agonist binding to ETA and ETB receptors in both middle cerebral arteries and in surrounding brain cortex was measured in three animals by autoradiographic binding assays. Levels of ETB receptor mRNA were 3.4 ± 2.2-fold higher in the right than in the left cerebral arteries (p < 0.01). There were no significant differences in the levels of ppET-1, ppET-3, or ETA receptor mRNA in cerebral arteries. ET-1 peptide was not elevated in CSF. Levels of ETA and ETB receptor mRNAs were 2.6 ± 1.1- and 2.1 ± 1.3-fold higher, respectively, in the right than in the left cerebral cortex, while the level of ppET-3 mRNA was 2.1 ± 1.0-fold lower. There were no differences in ppET-1 mRNA levels between right and left cerebral cortex. Binding to ETA and ETB receptors in cerebral arteries and cortex did not differ significantly between right and left sides. These results do not support the hypothesis that overexpression of ET-1 is the principal cause of vasospasm, but rather they suggest that SAH causes complex changes in the ET system that together are responsible for the cellular response to SAH.

Intracranial vascular complications of choriocarcinoma.

Choriocarcinoma is the most malignant of the tumors of chorionic tissue that (most commonly) arise from fetal tissues and invade the maternal vasculature. Two cases of choriocarcinoma are presented. One patient had a suprasellar mass in conjunction with a neoplastic carotid-cavernous fistula. The mass and the fistula disappeared after apparently successful radiation therapy and chemotherapy. The second patient had a ruptured arterial aneurysm associated with an intracerebral hematoma treated by evacuation of the hematoma and resection of the aneurysm. The vascular complications of this tumor are reviewed, and a management plan is suggested.

Attempted experimental modification of the postlaminectomy membrane by local instillation of recombinant tissue-plasminogen activator gel.

A prospective, randomized, blinded trial involving 25 adult mongrel dogs was performed to evaluate whether placement of a fat graft or local instillation of recombinant tissue-plasminogen activator gel [rt-PA] could modify the development of a postlaminectomy membrane. One component of the study involved the performance of a lumbar laminectomy and placement of gel rt-PA, free fat, or no tissue placement over the exposed dura mater. Three months later the animals were killed and sections of spine were removed en bloc, decalcified, and examined histologically. No significant differences were found in the degree of cellular fibrosis or heavy collagen production. A similar laminectomy at another lumbar level was also followed by gel rt-PA, free fat, or no tissue placement. Three months after surgery, surgery was performed again at this level immediately before death. There were no differences in the adhesiveness of the laminectomy membrane to dura mater or roots It was concluded that the local Instillation of gel rt-PA aftar laminectomy d id not inhibit scar formation or scar adherence to the dura mater.

Electron microscopy of simian cerebral arteries after subarachnoid hemorrhage and after the injection of horseradish peroxidase.

A large unilateral subarachnoid hemorrhage (SAH) was created in 21 monkeys, and horseradish peroxidase (HRP) was injected into the cisterna magna or left internal carotid artery in 3 others (normals). Cerebral fixation was performed on Day 14 after SAH or 15 minutes after HRP injection. The major cerebral arteries from both the nonclot (control) and clot sides and the normal animals were examined with scanning and transmission electron microscopy (SEM and TEM). SEM of the adventitial surfaces of control and normal arteries revealed tunnel-like structures along the longitudinal axis. No vasa vasorum were seen, but adventitial rounded openings were observed, 10 to 35 micron in diameter in vessels of the anterior circulation and up to 80 micron in diameter in the basilar arteries. The stomas, numbering 5 to 10/mm of specimen, appeared to connect the subarachnoid and intraadventitial spaces or pathways. In SAH arteries, the tunica adventitia was coated with cellular remnants of hematoma or dense, well-organized blood clots, the removal of which revealed blocked stomas. TEM showed HRP in the vessel walls after injection into the cisterna magna, but not after injection into the carotid artery. TEM of control arteries revealed Virchow-Robin (intraadventitial) spaces lined by simple planar epithelium-like cells; Virchow-Robin spaces contained sparse nerve fiber bundles and connective tissue fibers. In SAH arteries, these spaces were almost filled with strands of connective tissue and fibroblasts; no nerve fibers were detected. Vasogenic substances probably reach smooth muscle cells via the adventitial stomas. SAH occluding the stomas may block the cerebrospinal fluid circulation, disturbing nutrition of the arterial wall or removal of wastes from it, thereby aggravating vasospasm.

Effects of various intracranial fluids on smooth muscle.

Samples of cerebrospinal fluid (CSF) drawn from patients with subarachnoid hemorrhage, subdural hemorrhage, or brain tumor, as well as control samples from patients without a known cerebral pathological condition, were tested for their ability to contract smooth muscle. Canine middle cerebral artery, canine basilar artery, and rat stomach fundus were used, and contractions were expressed as the percentage of the contraction elicited by a standard dose of 5-hydroxytryptamine. All samples that contained blood produced contractions of the smooth muscle preparations, and despite a large sample no significant differences were observed in the magnitude of the contractions either between preparations or between samples from different groups of patients. Control samples were generally without significant effect. Neither methysergide, a 5-hydroxytryptamine antagonist, nor indomethacin, an inhibitor of prostaglandin synthesis, significantly diminished the contractions induced by bloody CSF, although the calcium antagonist D600 successfully antagonized the response in all groups. D600 was a better antagonist of the action of blood-containing CSF on cerebral artery than on stomach fundus. Samples obtained from patients with angiographic evidence of vasospasm were significantly more active than those obtained from patients without vasospasm, but the latter retained considerable activity.

Morphometric Analysis of Monkey Cerebral Arteries Exposed in vivo to Whole Blood, Oxyhemoglobin, Methemoglobin, and Bilirubin

Whether vasospasm results from smooth muscle contraction or from arterial wall infiltration by cells and other material is subject to debate. Computer-assisted image analysis was used to measure lumen area, total wall area, and area of tunica media plus tunica intima of cross-sections of monkey right middle cerebral arteries (MCAs), exposed in vivo for 6 days to whole blood (n = 4), oxyhemoglobin (OxyHb, n = 5), methemoglobin (MetHb, n = 5), bilirubin (n = 5), mock cerebrospinal fluid (CSF, n = 6), and supernatant fluid from an incubated mixture of autologous blood and mock CSF (n = 5). Five control (left) MCAs from each group and 4 MCAs contracted in vitro with potassium chloride were measured. Significant angiographic vasospasm occurred in groups receiving whole blood, supernatant fluid, and OxyHb (p less than 0.05). There was significant correlation (r = 0.58, p less than 0.05) between right MCA diameter on angiography and diameter calculated from lumen area. When compared to effects of mock CSF, OxyHb significantly increased total wall area. When right and left MCAs were compared within groups, total wall area increased in every group with significant increases in groups exposed to mock CSF, OxyHb, and bilirubin (p less than 0.05). No changes developed in area of tunica media plus tunica intima, whether comparing right versus left MCAs within groups or right MCAs between groups. Contraction in vitro did not significantly increase total wall area or area of tunica media plus tunica intima. Light microscopy demonstrated inflammatory debris in the tunica adventitia of arteries from every group. This study shows that whole blood, OxyHb, and supernatant fluid, which contains OxyHb, cause vasospasm. Increases in total wall area are not sufficient to account for luminal narrowing, and therefore, changes such as cell proliferation and arterial wall fibrosis in the intima or media apparently do not contribute primarily to arterial narrowing of vasospasm but could be related to persistence of narrowing. Vessel wall thickening, which does occur, is caused by increased tunica adventitia area only and is nonspecific in that it develops after injection of substances not associated with vasospasm. The data are consistent with the hypothesis that oxyHb causes vasospasm (both angiographic and morphologic) by inducing muscle contraction in the media.

Trends in blood pressure, osmolality and electrolytes after subarachnoid hemorrhage from aneurysms

Daily trends in blood pressure, osmolality and electrolytes were analyzed in a series of 173 operated aneurysm cases who had subarachnoid hemorrhage (SAH) and were admitted within 4 days of the ictus. High blood pressure was associated with a greater risk of mortality and the development of clinically significant vasospasm (VSP). High osmolality shortly after admission was related to mortality but not VSP. Changes in sodium and potassium had no obvious relationship to mortality or VSP.

Ventricular Size and Cerebral Blood Flow Following Subarachnoid Hemorrhage

The relationship among ventricular size on computed tomography (CT), the clinical status of the patient, and cerebral blood flow alterations in subarachnoid hemorrhage is examined. Fifty patients with subarachnoid hemorrhage underwent a total of 71 cerebral blood flow measurements and 115 CT scans. Flow was measured noninvasively using 133Xe inhalation. It is demonstrated that increasing ventricular size is accompanied by clinical deterioration and also by a reduced flow. The effects of the various lesions (as demonstrated by CT) on cerebral perfusion are examined. Of the 23 patients scanned 5 days or less after hemorrhage, 12 had subarachnoid blood visible on the scan. These 12 had flows that averaged 20% lower than the other 11 when examined 6 to 17 days after the hemorrhage. Ventricular enlargement is more prevalent in the first week after the hemorrhage than in the second. Also, blood flow is maximally reduced at the end of the first week following hemorrhage.