Lydia Johns

Emboli Enter Penetrating Arteries of Monkey Brain in Relation to Their Size

BACKGROUND AND PURPOSE Controversy exists regarding whether lacunar infarction is due to embolism or whether it is always due to lipohyalinosis of small penetrating arteries. We hypothesized that emboli can enter penetrating arteries in relation to the blood flow to these arteries and to the diameter of the emboli. METHODS We injected agarose spheres of three different mean diameters (31 +/- 4, 68 +/- 14, and 92 +/- 28 microns [n = 50 for each]) into one internal carotid artery of 3 monkeys for each sphere size (total, n = 9 monkeys). After injection of spheres, monkeys were killed, the brains were removed and fixed in formalin, and serial hematoxylin and eosin sections of three coronal sections of the cerebrum were examined by light microscopy. Sphere diameter (n = 25 for each territory and sphere size) and distribution in circumferential and penetrating artery territories were measured with the use of an image analyzer. Corrections were made for shrinkage of spheres during fixation and for the effect of random sampling of 10-microns sections through spheres of different diameter. RESULTS Mean numbers of spheres for each size were significantly higher in circumferential than penetrating artery territories (P < .05, t test). When correction was made for the volume of brain supplied by each territory, there was no significant difference in the number of spheres in circumferential versus penetrating artery territories for the two smaller sphere sizes. For spheres of mean diameter of 92 microns, significantly more spheres entered circumferential rather than penetrating artery territories (P < .05, t test). The percentage of the total number of spheres that entered penetrating artery territories was 5%, 6%, and 1.4% for beads of 31 +/- 4, 68 +/- 14, and 92 +/- 28 microns mean diameter, respectively. CONCLUSIONS Small emboli can enter penetrating arteries and could therefore produce lacunar infarction. The majority of emboli, however, enter circumferential arteries. The larger the emboli, the more likely that they will enter circumferential arteries rather than penetrating arteries.

Papaverine-sensitive vasospasm and arterial contractility and compliance after subarachnoid hemorrhage in dogs.

This study examined the relationship between papaverine-sensitive and -insensitive components of vasospasm, arterial contractility and compliance, and time after subarachnoid hemorrhage (SAH) in dogs. Eighteen dogs underwent angiography and then two intracisternal injections of blood. Angiography was repeated 4 (n = 5), 7 (n = 4), 10 (n = 4), or 14 (n = 5) days later. Papaverine, 100 to 200 mg, was infused into the basilar artery, and angiography was repeated. Four additional dogs had cerebral angiography only and served as controls. The basilar arteries were removed and studied pharmacologically. Significant vasospasm of the basilar artery was observed each time after SAH. Papaverine significantly reversed vasospasm at 4 and 7 days (88 +/- 6% and 63 +/- 11% of vasospasm reversed; analysis of variance, P < 0.05). The papaverine-insensitive component of vasospasm increased significantly with increasing time after SAH and with increasing severity of vasospasm. Arterial contractility and compliance decreased significantly with increasing time after SAH and were significantly related to the degree of papaverine-insensitive vasospasm but not to the severity of vasospasm. In conclusion, the majority of vasospasm early after SAH in dogs was caused by reversible vasoconstriction. The ability of papaverine to reverse vasospasm depended on the time after SAH and on the severity of vasospasm, a finding that may be important to the use of papaverine in humans. The pathological and biochemical basis for the association between papaverine-insensitive vasospasm and reduced arterial wall contractility and compliance remains to be determined.

Randomized Comparison of Guglielmi Detachable Coils and Cellulose Acetate Polymer for Treatment of Aneurysms in Dogs

BACKGROUND AND PURPOSE Endovascular treatments for aneurysms are being used more frequently in patients in the absence of a large body of information on their histopathological effects. This study determined the efficacy and histopathological effects of treatment of experimental aneurysms with Guglielmi detachable coils (GDC) or cellulose acetate polymer (CAP). METHODS Fourteen dogs had 13 terminal and 30 sidewall aneurysms created with venous pouches sutured to the cervical carotid arteries. Two weeks later, dogs had angiography followed by randomization to no treatment (n=2) or to aneurysm occlusion with GDC (n=4) or CAP (n=6). Two months later, angiography was repeated, animals were killed, and aneurysms were excised, fixed, photographed, and examined by light and electron microscopy. RESULTS Two dogs were excluded because of common carotid artery occlusion at 2-week angiography. There were 11 terminal and 16 sidewall aneurysms available for treatment. The rate of spontaneous thrombosis of untreated aneurysms was 0% (0/5). Treatment with GDC showed complete terminal and sidewall aneurysm obliteration rates of 33% (1/3) and 80% (4/5), respectively. Greater than 90% occlusion occurred in the remaining cases. There were no parent or branch artery occlusions. Treatment with CAP showed complete terminal and sidewall aneurysm obliteration rates of 20% (1/5) and 0% (0/5), respectively, and incomplete sidewall aneurysm obliteration in 1 of 5 cases. Aneurysms reformed at 2 months in 2 of 5 terminal and 1 of 5 sidewall cases. There were parent or branch artery occlusions with CAP in 2 and 4 cases, respectively. The rate of aneurysm occlusion was significantly lower and the rate of arterial occlusion significantly higher with CAP than with GDC (P<.05). Histopathology showed complete endothelialization across the orifice of the aneurysm successfully treated with CAP, whereas aneurysms treated with GDC were significantly more likely to show fresh or organizing thrombus without complete endothelialization (P<.05). CONCLUSIONS It is concluded that both treatments have limitations. Complete packing of aneurysms with GDC obliterates the aneurysm, but endothelialization does not always occur within 2 months. There are substantial problems with CAP. It is thrombogenic and carries a higher risk of causing arterial thrombosis. Even if an aneurysm is successfully obliterated initially with CAP, the CAP may disappear, leaving the aneurysm completely untreated.

Effect of adenovirus-mediated nitric oxide synthase gene transfer on vasospasm after experimental subarachnoid hemorrhage.

OBJECTIVE Evidence indicates that vasospasm after subarachnoid hemorrhage (SAH) is caused in part by a decrease in the vasodilator nitric oxide (NO), which is produced mainly in endothelial cells. This study tested whether intracisternal injection of adenovirus-expressing endothelial NO synthase (eNOS) would decrease vasospasm in dogs. METHODS In 12 dogs, baseline cerebral angiography was performed, and then SAH was produced by two injections of blood into the cisterna magna. The dogs were randomized (n = 6/group) to intracisternal injection of adenovirus-expressing lacZ (Ad327beta-Gal) or eNOS (AdCD8-NOS), administered immediately after the first blood injection. Angiography was repeated on Day 7, and then L-arginine (50 mg) was administered intracisternally, and angiography was repeated. Cerebrospinal fluid aspirated from the cisterna magna on Days 2 and 7 was analyzed for levels of NO metabolites. The dogs were killed, and their basilar arteries were removed and studied pharmacologically. Four control dogs underwent angiography on Day 0, followed by virus injection (n = 2/group). Angiography was repeated on Day 7, and the control dogs were killed. Transgene expression was detected in tissue removed on Day 7 by histochemical staining for lacZ, by polymerase chain reaction for messenger ribonucleic acid for eNOS, and by measurement of NO metabolites in cerebrospinal fluid. RESULTS Angiography showed significant vasospasm in each group (Ad327beta-Gal, -54 +/- 7% reduction in basilar artery diameter; AdCD8-NOS, -53 +/- 7%), with no significant difference between groups. Injection of L-arginine caused an insignificant increase in arterial diameter in each group. In dogs without SAH, Ad327beta-Gal caused a reduction in basilar artery diameter (-13 +/- 10%, P = 0.42; paired t test), whereas injection of AdCD8-NOS caused an increase in diameter (14 +/- 16%, P = 0.77; paired t test). Histological examination and beta-galactosidase staining of dogs given injections of Ad327beta-Gal showed staining in inflammatory cells in the subarachnoid space, in the adventitia of the cerebral vessels, and in the liver and lungs. Messenger ribonucleic acid for eNOS was detected in the leptomeninges of dogs given injections of AdCD8-NOS. Under isometric tension, basilar arteries from each group demonstrated similar relaxation to L-arginine, but arteries exposed to eNOS demonstrated significantly greater relaxation to L-arginine plus tetrahydrobiopterin than arteries exposed to lacZ. Cerebrospinal fluid levels of NO and its metabolites were significantly higher in dogs treated with AdCD8-NOS than those treated with Ad327beta-Gal 2 days after SAH. CONCLUSION These results demonstrate that adenovirus vectors can be used to transfer genes to cells in the subarachnoid space of dogs. Enough NO can be produced in the absence of SAH to dilate the basilar artery. After SAH, however, NO plus a cofactor can dilate arteries in vitro, but not enough NO is generated in the subarachnoid space to prevent vasospasm, perhaps owing to the scavenging of NO by hemoglobin.

Heme oxygenase-1 and ferritin are increased in cerebral arteries after subarachnoid hemorrhage in monkeys.

Hemoglobin is a key factor in the production of cerebral vasospasm. Metabolism of hemoglobin involves breakdown of heme by heme oxygenase (HO) and sequestration of the released iron in ferritin. We determined whether subarachnoid hemorrhage induces these proteins in cerebral arteries and, if so, in which cells they are produced. Whether the changes correlated with vasospasm also was investigated. Subarachnoid hemorrhage was created in monkeys, and vasospasm was assessed by angiography in cohorts of animals killed 3, 7, or 14 days after the hemorrhage. Ferritin and HO-1 messenger ribonucleic acid (mRNA) and protein were measured by competitive reverse transcription-polymerase chain reaction and Western blotting in hemorrhage-side and control-side cerebral arteries and brain tissue. The location of these proteins was determined by immunohistochemistry. There was significant vasospasm 3 and 7 days but not 14 days after subarachnoid hemorrhage. There were no significant changes in mRNA for HO-1 or ferritin in cerebral arteries or brain tissue at any time. There was a significant increase in HO-1 and ferritin protein in hemorrhage-side compared with control-side cerebral arteries at 3, 7, and 14 days. The increase in HO-1 protein was maximal at 3 days, whereas the increase in ferritin protein was maximal at 7 days. There was no detectable increase in HO-1 or ferritin protein in brain tissue at any time. Immunohistochemistry localized HO-1 protein and ferritin to cells in the adventitia of the arterial wall. We show that subarachnoid hemorrhage is associated with a significant increase in HO-1 and ferritin proteins in cerebral arteries that begins at least as early as 3 days after the hemorrhage and that persists for up to 14 days.

Blood Supply to the Spinal Cord: Anatomic and Physiologic Correlations

Although the subject has been studied for many years, the clinicians understanding of the blood supply to the spinal cord is complicated by both confusing nomenclature and conflicting data. This review attempts to clarify prevailing thoughts on the arterial and venous structures in this clinically important area.

Vasospasm in Monkeys Resolves Because of Loss of and Encasement of Subarachnoid Blood Clot

Background and Purpose— We studied in monkeys why vasospasm resolves after subarachnoid hemorrhage (SAH). Methods— Monkeys underwent angiography and right (n=17) or bilateral (n=8) SAH. Animals with bilateral SAH underwent angiography 1, 3, 5, and 7 days later. Animals with right SAH underwent angiography 7 days later. The clot was then not removed (n=5), removed and replaced with fresh clot (n=7), or removed and not replaced (n=5). At the same time on day 7, the removed clot (n=12) or fresh clot (n=5) was placed on the left side. Angiography was repeated every 2 days until day 14. Results— SAH caused significant vasospasm on day 7 that resolved by day 14. Removal of clot on day 7 resulted in more rapid resolution of vasospasm. Placement of fresh clot onto arteries that had already been exposed to clot for 7 days produced vasospasm that persisted without resolving for an additional 7 days. Placement of 7-day-old clot from the right onto previously unexposed left arteries or of clot from blood removed from an animal 7 days after SAH caused significantly more rapid onset of vasospasm compared with de novo vasospasm. Microscopic examination of the clots showed they were surrounded by macrophages 7 days after SAH. Arterial compliance and contractility were reduced in relation to duration of the exposure of arteries to clot. Conclusions— Vasospasm resolves because of loss of subarachnoid blood clot. We hypothesize that reduced spasmogen release from the clot contributes to resolution of vasospasm. There was no response in the cerebral arteries that rendered them less responsive to the subarachnoid clot.

Effect of BQ-123 and Tissue Plasminogen Activator on Vasospasm After Subarachnoid Hemorrhage in Monkeys

BACKGROUND AND PURPOSE We aimed to determine the effect of intracisternal administration of an endothelin-A receptor antagonist (BQ-123) against vasospasm in a monkey model and to determine whether this drug would have adverse interactions with intracisternal tissue plasminogen activator (TPA). METHODS Thirty-three monkeys were randomly allocated to undergo baseline cerebral angiography, creation of right subarachnoid hemorrhage (SAH), and intracisternal delivery of (1) placebo (n = 10); (2) low-dose BQ-123 (5 mg/kg per day, n = 7); (3) high-dose BQ-123 (10 mg/kg per day, n = 9); or (4) BQ-123 10 mg/kg per day plus TPA 1 mg every 12 hours for three doses (n = 7). Angiography was repeated after 7 days, and animals were killed. Vasospasm was assessed by comparisons of angiograms within groups across time by paired t test and by comparisons across groups at each time by ANOVA. RESULTS Significant clot remained in the basal cisterns in all groups except those receiving TPA, in whom complete clot clearance was noted. Comparisons of angiograms at baseline and after 7 days showed significant vasospasm of the right middle cerebral artery in animals receiving placebo (mean +/- SEM reduction in diameter, 36 +/- 7%; P < .05) and low- and high-dose BQ-123 (16 +/- 4% and 18 +/- 7%, respectively). Animals that received TPA did not develop significant right cerebral artery vasospasm. Comparisons of arterial diameters at day 7 revealed significant variance in right middle cerebral artery diameter, with animals in the placebo group having significantly more and animals in the TPA group having significantly less vasospasm than the BQ-123 groups. Histopathological examination of the brains did not show inflammation or pathological change in animals that received BQ-123 or BQ-123 plus TPA. CONCLUSIONS Intracisternal TPA was efficacious against vasospasm in monkeys. Combination therapy with TPA and BQ-123 was not associated with reduction in efficacy of either drug or with evidence of toxicity.

Intracisternal Sodium Nitroprusside Fails to Prevent Vasospasm in Nonhuman Primates

OBJECTIVE Hemoglobin contributes to vasospasm after subarachnoid hemorrhage. One mechanism may involve binding of nitric oxide, destruction of nitric oxide, or both. Support for this mechanism would be evidence that nitric oxide donors prevent vasospasm. This study attempted to provide such evidence. METHODS A randomized, blinded study was conducted in which 13 monkeys underwent cerebral angiography and creation of a right subarachnoid hemorrhage. Subcutaneous osmotic pumps were implanted to deliver sodium nitroprusside (n = 7) or vehicle (n = 6) via catheters into the right basal cisterns. Seven days later, angiography was repeated, and the animals were humanely killed. Levels of cyclic nucleotides, hemoglobins, and thiocyanate were measured. RESULTS Significant vasospasm of the right middle cerebral artery was present in animals treated with sodium nitroprusside (35 ± 22% reduction in diameter, P < 0.05, paired t test) and placebo (28 ± 20% reduction, P < 0.05, not significantly different from nitroprusside group by unpaired t test). Adequate delivery of sodium nitroprusside was supported by the finding of a significant increase in cyclic guanosine monophosphate levels in the cerebral arteries of treated animals compared with placebo (P < 0.05, unpaired t test). Thiocyanate was not present in significantly increased amounts in animals treated with nitroprusside, although this group did display elevated concentrations of nitrosyl hemoglobin (measured by electron paramagnetic resonance spectroscopy) and cyanomethemoglobin (measured by spectrophotometry) in the cerebrospinal fluid on Day 7. CONCLUSION The lack of effect of sodium nitroprusside was not the result of inadequate drug delivery because cyclic guanosine monophosphate levels were significantly increased in vasospastic arteries. Vasospasm may not have been prevented because of a toxic effect of sodium nitroprusside metabolites, involvement of smooth muscle relaxation or contraction processes downstream of cyclic guanosine monophosphate, or both.

U74389G Prevents Vasospasm after Subarachnoid Hemorrhage in Dogs

OBJECTIVE Oxygen-derived free radicals may contribute to vasospasm after the rupture of an intracranial aneurysm through direct vasoconstricting effects occurring within the arterial wall or, secondarily, by causing lipid peroxidation in the subarachnoid erythrocytes with secondary induction of vasoconstriction. U74389G is a potent inhibitor of lipid peroxidation and a scavenger of oxygen-derived free radicals. This study determined the relative contributions of oxygen-derived free radicals and lipid peroxidation to vasospasm in the double-hemorrhage dog model. METHODS Sixteen dogs underwent baseline (Day 0) cerebral angiography and induction of subarachnoid hemorrhage by two injections of blood into the cisterna magna 2 days apart. They were randomized to receive drug vehicle (n=8) or U74389G (n=8, 3 mg/kg of body weight/d) intravenously. Drug administration and end point analysis were blinded. The end points were angiographic vasospasm, as assessed by comparison of angiograms obtained before and 7 days after subarachnoid hemorrhage, and the levels of malondialdehyde and salicylate hydroxylation products (dihydroxybenzoic acids) in cerebrospinal fluid and of malondialdehyde in subarachnoid blood clots and basilar arteries 7 days after hemorrhage. RESULTS Comparisons within groups of Day 0 and Day 7 angiograms and between groups of angiograms obtained at Day 7, showed significant vasospasm in animals in the vehicle group (mean+/-standard error, 51%+/-4) but not in the U74389G group (25%+/-11, P < 0.05, unpaired t test). High-pressure liquid chromatographic assays of malondialdehyde and dihydroxybenzoic acids in cerebrospinal fluid, subarachnoid blood clots, and basilar arteries showed no significant differences between groups. CONCLUSION The significant prevention of vasospasm by U74389G without change in levels of indicators of free radical reactions suggests that the effect of the drug is related to other processes occurring in the arterial wall and that cerebrospinal fluid levels of oxygen radicals and lipid peroxides are not useful markers of vasospasm.