Phosphodiesterase inhibitors and cerebral vasospasm

Systemic administration of phosphodiesterase V inhibitor, sildenafil citrate, for attenuation of cerebral vasospasm after experimental subarachnoid hemorrhage

OBJECTIVE

One of the phosphodiesterase isoenzymes, Type V (PDE V), specifically hydrolyzes cyclic guanosine monophosphate to cause vasoconstriction. This study analyses the effect of PDE V inhibition with sildenafil citrate (SC) on cerebral vasospasm and its effect on apoptotic changes of the vascular endothelium.

METHODS

Twenty-four rabbits were divided into four groups. The first group was composed of sham-surgery animals. The second group was the subarachnoid hemorrhage (SAH) group, in which cerebral vasospasm was induced. In the third group, sham-surgery rabbits were treated with SC. In the fourth group, animals were treated with SC after SAH. SC was administered for 48 hours, 0.7 mg/kg, three times per day in Groups 3 and 4. Basilar artery lumen circumferences were measured in all groups by computerized image analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method was used to evaluate the rate of apoptosis between SAH and SC-treated SAH groups. Results were compared by analysis of variance and paired t tests, and P values less than 0.05 were considered significant.

RESULTS

Basilar artery circumferences between groups were significantly different (P < 0.001). SC (0.7 mg/kg, three times per d) significantly dilated the basilar arteries in both the sham-surgery group (2370 +/- 233 microm; P = 0.039) and the SAH group (2142 +/- 195 microm; P = 0.006) after 48 hours of treatment. The TUNEL method for apoptosis revealed that actual numbers of the apoptotic endothelial cells per cross section after SAH in the control (no treatment) (73 +/- 2) and SC-treated (0.7 mg/kg) groups(76 +/- 3) were not significantly different (P > 0.05).

CONCLUSION

The vasodilatory effect of SC was observed to be significant on normal cerebral vessels and after SAH-induced vasospasm. SC did not prevent apoptosis of the endothelium in our study, which suggests that prevention of apoptosis is not necessary in the treatment of cerebral vasospasm.

Enhancement of endogenous excitatory amino acids by theophylline does not modify the behavioral and histological consequences of forebrain ischemia

The neuroprotective role of endogenous adenosine during forebrain ischemia elicited by 4-vessel occlusion in rats was assessed using the adenosine antagonist, theophylline (32 mg/kg). Despite an increase in the release of glutamate in the hippocampus during ischemia, theophylline did not alter the neurological and histological outcomes. These results indicate that endogenous adenosine does not act as an endogenous neuroprotector by modulating glutamate release in this model.

Acute syphilitic blindness in AIDS

To our knowledge, bilateral syphilitic optic neuritis has not been reported in conjunction with AIDS. We document a case of a bisexual man with AIDS whose vision deteriorated overnight from 20/20 in both eyes to total bilateral blindness as a result of syphilitic retrobulbar neuritis. The implications and management of leutic disease in immunocompromised individuals are discussed.

Functional arterial changes in chronic cerebrovasospasm in monkeys: an in vitro assessment of the contribution to arterial narrowing

Cerebral arteries from monkeys with chronic cerebral vasospasm arising from experimental subarachnoid hemorrhage produced 5-6 days previously were examined for changes in their functional properties in an attempt to understand the basis of the narrowing. Hemorrhage was caused by puncture of the internal carotid artery just proximal to the circle of Willis. Segments taken close to the origins of the anterior and middle cerebral arteries consistently showed decreased distensibility. In addition, they exhibited large, prolonged, spontaneous increases in muscle tone. Other alterations observed include a marked reduction in the capacity of the vessel wall to contract, reduction in constrictor and dilator nerve influences on vascular tone, and some increased sensitivity to serotonin. Small pial arteries (150-200 micron o.d.) from the side of the injury showed large spontaneous irregular increases in tone. It is proposed that 5-6 days after experimental subarachnoid hemorrhage in monkeys the change most responsible for persistent narrowing in the larger arteries is an increased rigidity of the vessel wall. This is probably caused by an inflammatory response. In the smaller arteries, abnormal spontaneous contractile activity is a major factor in narrowing. This activity is not stretch-dependent. We suggest that the initial cause of the arterial narrowing after hemorrhage is the action of vasoactive substances released in the close vicinity of the arterial wall, which lead to tissue damage, abnormal tone, and an inflammatory response with fibrosis.

Effect of theophylline on ischemically induced hippocampal damage in Mongolian gerbils: a behavioral and histopathological study

We investigated the influence of the adenosine antagonist theophylline on the degree of hippocampal cell damage in the Mongolian gerbil following brief periods of forebrain ischemia. Male gerbils were randomly divided into nine groups. Ten minutes before surgery, four groups, which were later subjected to 1, 2, 3, or 5 min of bilateral carotid occlusion under halothane anesthesia, received theophylline (30 mg/kg, p.o.). Four groups served as nontreated ischemic controls; the ninth group was used to measure theophylline serum concentration. Neurological symptoms were classified by using a behavioral score. Fourteen days after ischemia, the brains were removed, and the hippocampus was histologically examined "blind" for the degree of cell damage in the CA1 sector, which was expressed as a semiquantitative histopathological score. There were no behavioral or histological abnormalities in either the control or theophylline group with 1 min of ischemia. With increasing duration of ischemia, the neurological symptoms worsened and the number of necrotic pyramidal cells increased significantly. The pretreatment with theophylline only moderately aggravated the neurological symptoms, whereas it enhanced the ischemic cell damage significantly. The results are discussed with respect to recent findings that theophylline may block putatively protective effects of endogenous adenosine, whose concentration in the brain is known to rise significantly during ischemia.

Observations on the perioperative management of aneurysmal subarachnoid hemorrhage

Thirty-two patients with aneurysmal subarachnoid hemorrhage (SAH) were managed according to a protocol based on pain control and hemodynamic manipulation, monitored by an arterial line and Swan-Ganz catheter. Hemodynamic parameters were adjusted to four clinical situations. 1) For the unoperated patient with no neurological deficit, the regimen aims to maintain pulmonary wedge pressure (PWP) at 10 to 12 mm Hg, and the cardiac index (CI) and blood pressure (BP) at normal levels. 2) For the unoperated patient presenting with or developing neurological deficit, the PWP is increased until the deficit is reversed or the CI falls; the CI is high, and the BP normal. 3) For the postoperative patient with no neurological deficit, the PWP is maintained at 12 to 14 mm Hg, the CI is a high normal, and the BP is normal. 4) For the postoperative patient developing neurological deficit but showing no surgical complication on the computerized tomography scan, the PWP is increased until the deficit is reversed or the CI falls; the CI is high and the BP is increased with vasopressors if necessary. Fourteen patients developed neurological deficits either preoperatively, postoperatively, or both. Neurological deficits were repeatedly reversed by increasing the PWP, as measured hourly. In several patients an optimal wedge pressure was determined, below which deficits would reappear. In one patient whose neurological deficit was reversed on several occasions by increasing the PWP, the optimal PWP rose after each episode until it reached 22 mm Hg. Detailed event-related analysis of these patients' course illustrates these phenomena well. The optimal PWP varied from patient to patient, but ranged most frequently from 14 to 16 mm Hg. Meticulous monitoring of the patients' neurological status coupled with prompt correction of low PWP (assuming an adequate CI) has proven to be an effective way to prevent and reverse neurological deficits following aneurysmal SAH.

Experimental chronic cerebrovascular spasm in the monkey: an assessment of the functional changes in the cerebral arteries and their protection by diltiazem

The structure and function of cerebral arteries obtained from a monkey model of chronic cerebral vascular spasm 5 days after hemorrhage have been examined. Narrowing of the larger cerebral arteries demonstrated by angiography at all sites of measurement seems to be due primarily to an increased wall rigidity associated with cellular damage, the resultant inflammatory response and large, long-lasting spontaneous increases in muscle tone. Changes in agonist sensitivity were extremely variable. The reduction of contractility of the vessel wall to a mean of 30% of control diminished the consequence of any changes in active tone characteristics. Neurogenic control on the side of the lesion was remarkably depressed. When treated with diltiazem, beginning 1 day before induction of hemorrhage and continuing to the time of sacrifice, arterial diameter was reduced at only 1 of the 6 standard sites of measurement and then by only a small amount. Neurologic effects invariably seen in the untreated monkeys were prevented by diltiazem. Many of the changes in the artery wall, including structural alterations, were diminished by the drug. Abnormal spontaneous myogenic tone was present but was less in the diltiazem-treated group; however, nerve damage and its functional consequences were not prevented. It is concluded that diltiazem, presumably by preventing the accumulation of intracellular calcium within the cell, prevents the initial events in the evolution of chronic cerebrovasospasm or narrowing. This is probably achieved by a diminishing of the direct vasoconstrictor effects and the toxicity of putative spasmogens released from blood clots, nerves and the brain on the vascular smooth muscle, thus interrupting the sequence leading to pathologic change.

Effect of prostacyclin and adenosine triphosphate on vasospasm of canine basilar artery

Cerebral vasospasm is one of the most important factors influencing morbidity and mortality of intracranial operations or diseases. Platelet aggregation and adhesion is increased in spastic vessels. Degradation of platelets liberates mediators, which in turn increase vasospasm, thus creating a vicious cycle. Healthy vessels cope with this by increasing the synthesis of prostacyclin. The purpose of this study was to increase experimentally the levels of arterial prostacyclin and adenosine triphosphate (ATP) in animals through intraarterial injection of these substances because they are lower in spastic vessels. Prostacyclin promotes antiaggregation and dilatation, increases blood flow, inhibits thromboxane A2, and prevents synthesis of angiotensin II. Most of these effects were done by increasing cyclic adenosine monophosphate (cAMP). After injecting autogenous blood into the cisterna magna of male dogs, both the acute and chronic phases of vasospasm and the degenerative changes in the arterial wall were observed. Injecting ATP increased the severity of vasospasm. During vasospasm it was found that when prostacyclin is used intraarterially, vasodilatation began, but degeneration of the arterial wall could not be prevented. In the group of animals in which both ATP and prostacyclin were used, there was no degeneration of the arterial wall and the basilar artery was seen to be normal when viewed under the electron microscope.

Cyclic nucleotides in stroke and related cerebrovascular disorders

Evidence has steadily accumulated to indicate that the rapid fluctuations in cyclic nucleotides during primary and secondary stroke are more than epiphenomena of the disease. During acute phases of ischemia, anoxia or hypoxia cyclic AMP rapidly accumulates in cerebral tissue, cerebrospinal fluid (CSF) and venous plasma, while cyclic GMP either remains unchanged or declines. The massive release of transmitters (catecholamines and adenosine) or ionic fluxes (Na+ and K+) may account for these observations. If reflow is established through a previously occluded vessel cyclic AMP content rises even higher in conjunction with a sharp rise in cyclic GMP. It is during this reflow period subsequent to longer term stroke (30-60 min) that the synaptic membrane enzyme, adenylate cyclase, is especially vulnerable. Presumably the cause of injury to cell membrane systems results from excess lactic acid accumulation and/or Ca++ entry through the damaged blood-brain barrier. The latter initiates breakdown of membrane phospholipids with resultant synthesis of vasoactive prostaglandins and formation of free radicals causing further insult to membrane phospholipids. Thus drugs acting to inhibit formation of prostaglandins, scavenge free radicals, reduce lactate formation, inhibit Ca++ entry or stabilize cell membranes have been shown to possess varying degrees of protective action toward adenylate cyclase. Moreover, cyclic AMP has been found to reverse stroke-induced vasospasm in central vessels. Reduced cyclic AMP content in CSF has been used to monitor the severity of coma, whereas clinical improvement was associated with predictable increases in the cyclic nucleotide. Therefore, cyclic nucleotides and related membrane enzyme systems might be used as target molecules in which to develop future therapeutic strategies for prevention or treatment of stroke.

Cerebral vasospasm after subarachnoid hemorrhage: an update

Symptomatic vasospasm, or delayed cerebral ischemia associated with arteriographic evidence of arterial constriction, is currently the most important cause of morbidity after acute subarachnoid hemorrhage. The development of vasospasm is directly correlated with the presence of thick blood clots in the basal subarachnoid cisterns, which can be detected by an early computed tomographic scan. Symptomatic vasospasm usually develops between 4 and 12 days after subarachnoid hemorrhage. The onset is gradual, occurring over hours or days. There is typically a gradual deterioration of the level of consciousness, accompanied by focal neurological deficits that are determined by the arterial territories involved. Hyponatremia frequently occurs and may exacerbate the symptoms. The patients are usually volume depleted, and therefore many authorities now treat them with replenishment and expansion of their intravascular volume with colloid and blood. Volume expansion, together with elevation of the systemic blood pressure and reduction of the intracranial pressure when elevated, constitute the only currently available effective therapy for symptomatic vasospasm. The cause of vasospasm remains obscure. Mechanisms of smooth muscle cell contraction and relaxation and experimental efforts to elucidate the nature of vasospasm are reviewed.

Delayed cerebral vasospasm is not reversible by aminophylline, nifedipine, or papaverine in a "two-hemorrhage" canine model

Angiographic spasm of cerebral arteries was produced in dogs by successive injections of cisternal blood 48 hours apart. Angiograms were taken before and after each cisternal injection. There was progressively greater angiographic vasospasm of the basilar artery. Intravenous aminophylline, 10 mg/kg/hr, reversed vessel constriction on the 1st and 3rd day after one injection of cisternal blood. On the 5th day after two blood injections (on Day 1 and Day 3), intravenous aminophylline, nifedipine (1 mg/kg), and intra-arterial bolus injection of 2 mg/kg papaverine failed to reverse the constriction. The intractable constriction produced in this model resembles that found in patients. The calcium antagonist, nifedipine, is as ineffective as the more traditional vasodilators in reversing vasospasm in this model.

Medical management of patients following a ruptured cerebral aneurysm, with epsilon-aminocaproic acid, kanamycin, and reserpine

Patients suffering from a subarachnoid hemorrhage who were admitted to the Neurosurgical Unit of the Royal Perth Hospital during the period 1971 to 1979 were assessed with regard to the effectiveness of preoperative treatment with epsilon-aminocaproic acid, kanamycin, and reserpine. Forty-two patients who were treated with epsilon-aminocaproic acid had a rebleed rate of 2.3% compared to 1 9.7% rebleed rate in appropriately selected controls. Patients treated with kanamycin and reserpine had a preoperative cerebral vasospasm rate of 32% compared to a 26% rate in controls; however, kanamycin and reserpine were found useful for decreasing the postoperative complications of cerebral vasospasm.

Effect of aminophylline and isoproterenol on spinal cord blood flow after impact injury

A study of the effects of spinal cord injury upon spinal cord blood flow was carried out in cats. A 400 mg-cm impact produced an overall reduction in spinal cord blood flow of 24% in the white matter and 30% in the gray matter, as determined by 14C-antipyrine autoradiography. At the level of the injury, white-matter flow was 8.1 ml/100 gm/min, a reduction of 49%, and in the gray matter, 12.5 ml/100 gm/min, a reduction of 76%. Treatment with aminophylline and isoproterenol improved the overall blood flow in the spinal cord. At the level of the injury, white-matter flow after this treatment was no longer significantly different from control values. The gray-matter flow remained decreased to 26.2 ml/100 gm/min, a reduction of only 47%. It is proposed that aminophylline and isoproterenol may increase cyclic adenosine monophosphate (AMP) and prevent platelet aggregation along the endothelial surfaces of the microcirculation, and may thereby help to maintain improved perfusion of the injured spinal cord.

Cerebral vasospasm following aneurysm rupture. A protocol for therapy and prophylaxis

A retrospective study was made of 195 patients who had ruptured intracranial aneurysms without significant intracerebral hematomas and who recovered to at least Grade III by Hunt and Hess' classification. The first 121 patients underwent aneurysm surgery 10 days to 2 weeks after subarachnoid hemorrhage (SAH) without repeat preoperative angiography and without special attention to volume replacement or avoidance of hypotension. Vasospasm resulted in cerebral ischemia in 15% of this group, more than half of these postoperatively, and was treated successfully in half the patients with a combination of aminophylline and isoproterenol. The later 74 patients were managed with aggressive maintenance of normal circulating blood volume and preoperative angiography at 2 weeks following SAH. If significant vasospasm persisted on angiography, surgery was delayed an additional week and, if spasm was still present then, aminophylline and isoproterenol was added prophylactically to aggressive volume replacement before surgery. In this second group of patients, the incidence of clinical vasospasm was essentially unchanged; however, it was almost completely limited to the preoperative period, and was more effectively treated with aminophylline and isoproterenol. Postoperative vasospasm was almost completely eliminated from the second group of patients.

Isoproterenol treatment of visual symptoms in migraine

Six patients with transient or permanent visual loss associated with migraine are presented. In 3 patients with monocular and one patient with binocular episodes of transient visual loss subsequent visual episodes were relieved by prompt inhalation of isoproterenol. The authors review the possible mechanisms of action of isoproterenol in migraine and present evidence to support the prophylactic use of isoproterenol to prevent transient and possible persistent visual loss in patients with migraine.

Effect of aminophylline on cerebral infarction in the Mongolian gerbil

The effects of aminophylline in Mongolian gerbils subjected to unilateral carotid ligation were studied. The drug was given in varying intraperitoneal doses at varying postoperative intervals and the animals observed for 5 days for clinical signs of stroke. Doses of 100 mg per kg caused early death and were discontinued. Doses of 50 mg per kg had no significant effect on morbidity, mortality, time until death, stroke incidence or lesion size, as compared to saline given as a control. Doses of 80 mg per kg caused a higher mortality, higher morbidity, and a shorter interval to death, but a smaller infarct. Thus, aminophylline did not have a protective effect against stroke in gerbils and was actually detrimental during the first 16 hours following the carotid ligation.

Experimental head injury in the rat. Part 3: Cerebral blood flow and oxygen consumption after concussive impact acceleration

Cerebral blood flow (CBF) and oxygen consumption (CMRO2) were determined during timmediate posttraumatic period in rats subjected to concussive impact acceleration. According to previous studies an impact of 9 m/sec velocity elicited typical and marked symptoms of experimental concussion and often a prolonged comatose state, accompanied by cerebral metabolic signs of energy failure. During the immediate concussive response there was an increase of the CBF, followed within the next few minutes by a decrease to about one-third of normal flow, and then by a tendency toward normalization of flow 20 to 40 minutes posttrauma. Simultaneous measurements of cerebral oxygen extraction indicated an increase of the CMRO2 during the first minute. During the ischemic phase oxygen extraction increased but the lowest CBF values were only partially compensated for, and normal oxygen availability could not be maintained. The combined data, including cerebrospinal fluid pressure measurements, indicated primary cerebrovascular effects of the concussive trauma. These vasomotor effects may induce critical cerebral ischemia and thus profoundly influence posttraumatic cerebral function, and cause irreversible damage.

Dibutyryl cyclic adenosine monophosphate effects in the ischemic-hypoxic cat

The effects of dibutyryl cyclic adenosine monophosphate (dB-cAMP) were studied in fifty cats, twenty anesthetized with pentobarbital and thirty with halothane. Nasopharyngeal temperature and Paco2 were maintained at normal values. Somatosensory evoked response was monitored and used as an indicator of cerebral cortical function. Ischemic hypoxic injury was produced by an orthopedic tourniquet snugly applied around the animal's neck and inflated for a period of fifteen minutes. This method produces a reliable and reproducible injury. Times for recovery of the evoked response to 10% of control value, as well as immediate and long-term animal survival, were noted. The dBcAMP was administered at the end of the hypoxic insult. Treated animals recovered the evoked response earlier than the untreated controls and had better immediate and long-term survival rates.

Reserpine and cerebral vasospasm

Cerebral vasospasm was produced in the dog basilar artery by topically applied five-day-old clotted autologous blood, but not by freshly drawn blood. The spasm was reversed by methysergide, an antiserotonin agent. However, vasospasm was not produced by five-day-old clotted autologous blood from dogs pretreated with reserpine. This suggests platelet serotonin or a similar, unidentified substance as the vasospastic element in dog blood responsible for experimental vasospasm from topically applied whole blood. Other experimental data support these findings.

A theory of the mechanism of cerebral vasospasm and its reversal, the role of calcium and cyclic AMP

It is proposed that the basic mechanism of vasospasm which sometimes follows subarachnoid hemorrhage is dependent on increased free intracellular calcium ion produced by spasmogens from closely applied extravasated blood. Relaxation of this spasm occurs when the intracellular cyclic AMP levels are raised, resulting in sequestration of calcium ion by the vascular smooth muscle cell sarcoplasmic reticulum.