Effects of chlorpromazine on experimental delayed cerebral vasospasm

Differential regulation of intracellular Ca2+ signalling induced by high K+ and endothelin-1 in single smooth muscle cells of intact canine basilar artery: detection by means of confocal laser microscopy

Changes in intracellular calcium concentration ([Ca2+]i) in smooth muscle cells play the key role in regulation of vascular smooth muscle tone and pathogenesis of cerebral vasospasm. In this study, we adopted the confocal laser microscopy to detect the fluorescence signals arising from the individual smooth muscle cells of canine basilar artery. Ring preparations were made, loaded with fluo-3 and changes in fluorescence induced by high K+ and endothelin-1 (ET-1) were measured by confocal laser microscopy. In some unstimulated smooth muscle cells Ca2+ waves arising from discrete region of the cell propagated to the whole cell with a velocity of approximately 10 microm/s. High K+ (80 mmol/L) induced a rapid rise in [Ca2+]i, the peak level being consistently reached approximately 10 s after stimulation. In contrast, the time to peak level of [Ca2+]i induced by ET-1 (0.3 micromol/L) varied widely between 13 and 26 s among individual cells, an indication that the extent of nonuniform coordination of increases in [Ca2+]i in individual cells may be partly responsible for the different time courses of tension development of vascular smooth muscle in response to the vasoactive stimulants. The increase in [Ca2+]i induced by ET-1 was transient but a pronounced and sustained contraction developed further in response to ET-1. Thus ET-1 has a biological property as a potential candidate to elicit cerebral vasospasm. Confocal laser microscopy could be a useful tool to measure the changes in [Ca2+]i in individual smooth muscle cells of cerebral artery.

Mechanisms of cerebral vasospasm in subarachnoid haemorrhage

Cerebrovascular spasm is a slowly developing constriction of the cerebral arteries, which frequently follows subarachnoid haemorrhage and is associated with considerable morbidity and mortality. The condition has been studied by use of models of subarachnoid haemorrhage in the whole animal and examination of isolated blood vessels or vascular smooth muscle cells in culture. The condition probably arises from the action of haemoglobin released from erythrocytes trapped in the subarachnoid clots, although the mechanism of action of haemoglobin remains uncertain. Systemic pharmacotherapy to avert or reverse vasospasm is still experimental.

Changes in Ca(++)-ATPase activity in smooth-muscle cell membranes of the canine basilar artery with experimental subarachnoid hemorrhage

Changes in Ca(++)-adenosine triphosphatase (ATPase) activity in the plasma membrane of smooth-muscle cells in the basilar arteries of dogs with experimental subarachnoid hemorrhage (SAH) were examined. The study methods included electron microscopic histochemistry and bioassay of the enzyme that exports cytoplasmic Ca++ to extracellular spaces. The Ca(++)-ATPase activity in the basilar artery increased significantly in response to the application of vasoconstrictive agents (prostaglandin F2 alpha and a phorbol ester), but decreased significantly 24 hours after experimental SAH, inversely with basilar artery contraction. Dogs that had undergone two arterial blood injections (double SAH) exhibited a further decrease in Ca(++)-ATPase activity as well as persistent contraction of the basilar artery for a longer period (at least 7 days) than was seen in animals with a single arterial blood injection. Bioassay of the enzyme also demonstrated a decrease in vascular Ca(++)-ATPase activity in dogs subjected to double SAH. These findings suggest that the early occurrence of and long-lasting decrease in Ca(++)-ATPase activity in dogs with experimental SAH induces a persistent disturbance of Ca++ homeostasis and indicates that damage to the plasma membrane in the cerebral arterial smooth-muscle cells proceeds to myonecrosis after SAH.

Neurologic evaluation in a canine model of single and double subarachnoid hemorrhage

The pathophysiology of cerebral vasospasm is complex and multifactorial. The present study sought to identify the degree of correlation between cerebral vasospasm as observed angiographically and clinical evaluation of an animal's neurologic status in the canine model following a single and double experimental subarachnoid hemorrhage (SAH) protocol. Nineteen mongrel dogs underwent single or double experimental SAH by percutaneous needle puncture of the cisterna magna and placement of a subarachnoid blood clot in the basal cistern on day 1 and day 4, respectively. At 72 h after each experimental SAH, vertebral angiography was performed and compared to control angiography. Basilar artery diameter measured at multiple positions was expressed as percentage of control diameter. Clinical evaluation of the animals was performed every day throughout the experiments. To assess the degree of neurologic impairment we developed a coma scale that efficiently estimated motor ability, eye response and eating habits of the animals. Vasoconstriction after experimental SAH reduced mean basilar artery diameter to 79.1% (+/- 5.4) of control diameter following single SAH and to 69.0% (+/- 2.1) of control diameter following double SAH. No changes were observed in the neurologic behavior of the animals throughout the experiment. Since a principal characteristic of human cerebral vasospasm is the close correlation between arterial constriction and neurological deficit, we believe that the canine model of SAH, although good in creating cerebral arterial vasoconstriction, does not fully represent the best model of human cerebral vasospasm.

The effect of Iloprost on chronic cerebral vasospasm

1. Experimental chronic cerebral vasospasm induced by subarachnoid haemorrhage (SAH) in rabbits was studied in order to evaluate the efficacy of repeated i.v. infusion of Iloprost (ILO). 2. The mean diameter of the basilar artery of intact animals was calculated as 737.5 +/- 52.8 microns while this value was reduced to 237.5 +/- 22.96 microns after SAH. 3. In the ILO treated group the mean diameter of the basilar artery was significantly increased and found to be 593.75 +/- 64.0 microns. 4. No change was observed in intracranial pressure (ICP) except a slight decrease in mean arterial pressure when relatively higher doses of ILO were used. 5. These results were taken as evidence of the high therapeutic value and low side effects of ILO in the treatment of persisting cerebral vasospasm due to SAH.

Transclival approach to rabbit basilar artery for experimental induction of chronic vasospasm

An experimental technique for producing delayed cerebral vasospasm in a rabbit model is described. The basilar artery is punctured via the transclival route and angiographic verification is illustrated.

The effect of hemoglobin on vasodilatory effect of calcium antagonists in the isolated rabbit basilar artery

The effect of hemoglobin on the vasodilatory effect of calcium antagonists was studied in isolated rabbit basilar arteries using an isometric tension measurement method. The ability of nimodipine to relax or inhibit contractions elicited by high K+ depolarization or serotonin (5-hydroxytryptamine, 5-HT) was investigated in control arterial rings and rings pretreated by hemoglobin. Hemoglobin (10(-6) and 10(-5) M) reduced the relaxation induced by nimodipine (10(-10) to 10(-8) M) in the rings contracted by 40 mM KCl. This reduction in relaxation was also observed with 3 x 10(-10) to 3 x 10(-9) M nicardipine, 3 x 10(-8) to 3 x 10(-7) M verapamil, and 10(-7) to 10(-6) M diltiazem. On the other hand, the effect of nimodipine was not influenced by endothelial removal or by pretreatment with 10(-5) M albumin or 10(-6) M prostaglandin F2 alpha. Hemoglobin restored the 10(-10) and 10(-9) M nimodipine-induced inhibition of the contraction elicited by CaCl2 (0.3 to 20 mM) in a K(+)-rich, Ca(++)-free solution. This restoration was greater at higher concentrations of CaCl2. Hemoglobin enhanced both the nimodipine-sensitive tonic phase and the less sensitive phasic phase of contractions produced by 10(-6) M of 5-HT. It abolished the inhibitory effect of 10(-8) and 10(-7) M nimodipine on the phasic contraction. Endothelial removal also enhanced both phases of the contraction, but did not abolish the effect of nimodipine. This study showed that the vasodilatory effect of calcium antagonists, especially nimodipine, on the vasoconstriction induced by other vasoactive substances decreased in the presence of hemoglobin.

Magnesium sulfate reverses experimental delayed cerebral vasospasm after subarachnoid hemorrhage in rats

We induced experimental delayed cerebral vasospasm by the intracisternal injection of greater than 0.5 ml blood in 30 rats. Seventy-two hours later the basilar artery was exposed via the transclival approach and photographed at high-power magnification through an operating microscope. We then evaluated the effect of topical (n = 30) and intravenous (n = 20) magnesium sulfate on the spastic artery by computerized image analysis. A greater than 50% reduction in baseline diameter of the basilar artery was observed in the rats subjected to subarachnoid hemorrhage compared with the 10 controls (p less than 0.0001). Intravenous magnesium sulfate dilated the spastic artery to approximately 75% of the baseline diameter in control rats (p less than 0.0001). Topical magnesium sulfate caused dramatic dilation of the basilar artery in both the control and the subarachnoid hemorrhage groups to near 150% of the baseline diameter in the controls (p less than 0.001). All rats receiving intravenous magnesium sulfate reached therapeutic plasma levels of the ion. Hemodynamic effects were mild and immediately reversible upon cessation of magnesium sulfate administration. We suggest that magnesium has a role in the treatment of subarachnoid hemorrhage-induced vasospasm in humans.

Immunomodulators interfere with angiopathy but not vasospasm after subarachnoid haemorrhage in rabbits

The present study deals with the effects of immunomodulators on the morphology of intracerebral arterial walls in rabbits with experimental subarachnoid haemorrhage (SAH). Immunostimulators:thymostimuline and inosine dimethylamino-isopropanol-p-acetamido-benzoate were found to aggravate the angiopathic changes, whereas immunosuppressive drugs-cyclosporine A and azathioprine appeared to prevent the damage. The authors consider the possibility of using immunosuppressive drugs in patients with ruptured intracranial aneurysms.

Effects of ML-9 on experimental delayed cerebral vasospasm

Experimental delayed cerebral vasospasm was produced in a two-hemorrhage canine model. The spastic basilar artery was exposed via the transclival route under a surgical microscope and was dilated by the topical application of 1-(5-chloronaphthalenesulfonyl)-1H-hexa-1,4-diazepine (ML-9), a selective antagonist of myosin light chain kinase. Dilation was dose-dependent, with a median effective dose (+/- standard deviation) of 51.4 +/- 6.9 microM. In addition, 50 microM of ML-9 was injected into the cisterna magna until the intracranial pressure (ICP) reached 200 mm H2O for 30 minutes, including a complete reversal of angiographic delayed vasospasm in three of seven dogs; in contrast, 150 microM of ML-9 was infused at 1.52 ml/min into the vertebral artery for 30 minutes, producing little dilation of the spastic basilar artery. In another study, the intracisternal perfusion of 50 microM of ML-9 at 1.48 ml/min for 30 minutes in dogs with an ICP of less than 200 mm H2O produced no serious electroencephalographic abnormalities, and the mean arterial blood pressure and pulse rate remained normal; no neurological deficits or significant histological abnormalities ascribable to the intracisternal ML-9 were found.

Cerebral vasospasm

Cerebral vasospasm is an important component of pathological entities such as migraine, subarachnoid hemorrhage (SAH), head trauma, post cerebral ischemia and/or hypoxia. The mechanisms underlying cerebral vasospasm in these diseases are not completely understood. Neurochemical and morphological factors involved in the cerebral circulation control are reviewed in this article. The circulatory changes observed after subarachnoid hemorrhage are taken as a model. It is concluded that multiple biochemical, physiological and morphological factors are involved in the cerebral vascular responses after SAH. Possible treatment alternatives for cerebral vasospasm based on its etiology are discussed.

Cerebral resuscitation: pathophysiology and therapy

The interest in the possibility of cerebral resuscitation has been growing exponentially during the last decade. It became clear that pharmacotherapeutic interaction can possibly alter the outcome of cerebral hypoxia/ischemia. The present review is an attempt to provide an organizational framework for a systematic integration of studies specifically dealing with pharmacological treatment post-insult.

Cerebral protection

Cerebral protection from an ischemic/hypoxic insult implies that tissue injury can be controlled or even prevented by certain therapeutic maneuvers. For example, physiological thresholds may be altered so that tissue vulnerability to the insult is reduced, or the intensity of an insult may be blunted by enhancing brain homeostasis. Such a therapeutic maneuver is carotid endarterectomy to improve blood flow in the disordered hemisphere. Alternatively, drugs with protective properties can be used before or even after the insult to "stabilize" injured tissue and prevent the harmful secondary effects that often follow. Various past and present approaches to cerebral protection employing physiological, pharmacological, and surgical intervention are reviewed. The mechanisms by which each allegedly protects the brain from ischemia and hypoxia are discussed briefly. Promising, but not always successful, approaches used in the past have pointed the way for new and more rational therapies. Truly effective protection of the brain from ischemia and hypoxia depends directly upon our capability to explore basic mechanisms of injury and our willingness to measure accurately and objectively the outcome of newly developed protective measures.

The effects of HA compound calcium antagonists on delayed cerebral vasospasm in dogs

The authors have examined the effects of the HA compounds HA1004(N-(2-guanidinoethyl)-5-isoquinolinesulfonamide) and HA 1077(1-(5-isoquinolinesulfonyl)homopiperazine), which are intracellular calcium antagonists, on delayed cerebral vasospasm from subarachnoid hemorrhage (SAH). The modes of action of these compounds were compared with those of the more commonly used calcium entry blockers. Calcium ionophore A23187 (4.8 X 10(-6) M)-induced contraction of a canine basilar artery strip was completely antagonized by the HA compounds (10(-5) M) but not by the entry-blocking calcium antagonists nicardipine, diltiazem, and verapamil (10(-5) M), suggesting that the HA compounds act differently. Delayed cerebral vasospasm was induced by a "two-hemorrhage" canine model. The magnitude of the vasospasm and the effects of the HA compounds were determined angiographically. On SAH Day 7, a significant vasospasm was observed in every dog. The diameter of the basilar artery had diminished to 59% +/- 2% (mean +/- standard error) of the control value obtained before SAH (on Day 1). The intravenous administration of HA 1004 caused a mild dilation of the basilar artery of 10% and 11% at doses of 3 and 10 mg/kg, respectively; however, HA 1077 produced a more marked dilation of 19% and 27%, respectively, at the same doses. Both of these drugs lowered mean arterial blood pressure to about 80% and 50% at doses of 3 and 10 mg/kg, respectively. Intracisternal administration of the HA compounds (6 mg) completely reversed cerebral vasospasm without much effect on the blood pressure. The intracellular calcium antagonists of the HA compound group appear to be promising agents for the treatment of intractable cerebral vasospasm.

Cerebral vasospasm following aneurysmal subarachnoid hemorrhage

Cerebral vasospasm following aneurysmal subarachnoid hemorrhage is one of the most important causes of cerebral ischemia, and is the leading cause of death and disability after aneurysm rupture. There are two definitions of cerebral vasospasm: angiographic and clinical. Care must be exercised to be certain that it is clear which entity is being addressed. The diagnosis of the clinical syndrome is one of exclusion and can rarely be made with absolute certainty. The pathogenesis of cerebral vasospasm is poorly understood. Most current theories focus on the release of factors from the subarachnoid clot. More attention must be given to the role of endothelial damage and alterations in the blood-arterial wall barrier. The application of modern techniques for studying vascular smooth muscle which have been developed as a result of research in the areas of hypertension and atherosclerosis must be applied to the problem of cerebral vasospasm. A stress test to select patients with angiographic arterial narrowing who have adequate cerebral vascular reserve to undergo surgery should be developed. The optimal treatment of vasospasm awaits development of agents for blocking or inactivating spasmogenic substances or blocking arterial smooth muscle contraction. Rheological or hemodynamic manipulations to prevent or reverse ischemic consequences of vasospasm are relatively effective, but complicated and hazardous, and should be viewed principally as interim measures awaiting development of more specific therapies for the arterial narrowing.