The isolation and characterization of Ca++-accumulating subcellular membrane fractions from cerebral arteries

Oxalate-induced encephalitis after infusions of sugar surrogates

The case of a 55-year-old female with oxalate-induced lethal encephalitis following infusions of sugar surrogates is reported. Renal failure and subsequent central coma developed following the use of xylitol, fructose and sorbitol above the recommended dosages. The patient died due to raised intracranial pressure. Cerebral damage was caused by encephalitis due to calcium oxalate crystals. Oxalosis induced by sugar surrogates may be explained either by dose-dependent toxic effects or genetically fixed intolerance.

Efficacy and mechanism of action of a calcium channel blocker after global cerebral ischemia in rats

Dihydropyridine calcium channel blockers such as nicardipine are under evaluation for treating acute cerebral ischemia because they may increase cerebral blood flow by causing vasodilation and because they may be cytoprotective in part by limiting production of arachidonic acid metabolites. We demonstrated in a previous study that nicardipine improves postischemic neuronal function, as measured by somatosensory evoked potentials, without reducing the extent of light-microscopic CA-1 hippocampal histologic damage. To characterize further the effect of nicardipine on global ischemic injury, we administered the drug beginning 24 hours before 30 minutes of four-vessel ischemia in Wistar rats. We then measured hippocampal ATP, phosphocreatine, and glucose contents immediately and 2 hours after ischemia, and measured learning ability (working and reference errors) on an eight-arm radial maze beginning 30 days after ischemia. To gain insight into the possible mechanism of action, we measured production of arachidonic acid metabolites (eicosanoids: TXB2 and 6-keto-PGF1 alpha) and hemispheric and hippocampal cerebral blood flow by the [14C]butanol indicator fractionation technique immediately and 2 hours after ischemia. Nicardipine was associated with fewer working errors (p less than 0.02) but no difference in reference errors. The drug had no effect on energy metabolites, cerebral blood flow, or eicosanoids immediately after ischemia, but ATP, phosphocreatine, and cerebral blood flow all returned to normal levels significantly more rapidly during reperfusion in treated rats. Nicardipine improves behavioral, electrophysiologic, and mitochondrial function after ischemia without preventing cellular damage and improves postischemic reperfusion. The drug's positive effect appears to occur during reperfusion.

The effects of an intracellular calcium antagonist HA 1077 on delayed cerebral vasospasm in dogs

The effectiveness of calcium antagonists on a chronic cerebral vasospasm after an SAH is still under debate. Calcium channel blockers such as nimodipine, nifedipine etc. can dilate spastic arteries by intrathecal administration, but not by systemic (iv or po) use. HA 1077 is a novel and potent calcium antagonist vasodilator which is considered to act by employing different mechanisms from the usual calcium channel blockers since it inhibits 1. calcium ionophore A 23187 induced contraction in arterial strips and 2. phenylephrine induced contraction in calcium free media, suggesting that its site of action is in the intracellular space. HA 1077 is water soluble and relatively stable in light. In the present study, the efficacy of HA 1077 was evaluated on dogs by using the spiral arterial strips in vitro and by angiography in vivo. In the arterial strips from the control dogs, a 50% relaxation of KCl (15 mM) induced contraction was obtained by a 10(-6) M HA 1077 for the "intracranial" basilar and middle cerebral arteries, while a 10(-5) M was needed to obtain the same effect for the "extracranial" common carotid and vertebral arteries, indicating that HA 1077 is more effective for the intracranial arteries. A vasospasm was produced by the "two haemorrhage" model of Varsos et al. The average angiographic diameter of the basilar artery was reduced to 60% of the control on SAH day 7. Intravenous infusion of HA 1077 (0.5-3 mg/kg/30 min) significantly dilated the spastic basilar artery (up to 20-30%), for over 2 hours. A fall in the systemic BP remained less than 20% during this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nimodipine on mitochondrial respiration in different rat brain areas after subarachnoid haemorrhage

The mitochondrial respiration was evaluated in three different rat brain areas (cerebral cortex, hippocampus and brain stem) after experimental subarachnoid haemorrhage (SAH). The haemorrhage was induced by injecting 0.35 ml of autologous arterial blood into cisterna magna. Intravenous administration of Nimodipine (2 micrograms/kg/min for 30 minutes) was started immediately after the haemorrhage induction. At the set time (1 hour after SAH procedure), animals were sacrificed and non-synaptic mitochondria from the above mentioned areas were isolated. The following respiratory parameters were evaluated utilizing glutamate plus malate and succinate plus rotenone as substrates: state 3, state 4, uncoupled state, respiratory control ratio (RCR) and ADP/O ratio. SAH significantly influences respiratory parameters, mainly RCR; the cerebral cortex and brain stem seem to be more sensitive during the acute phase of vasospasm which follows SAH procedure. Nimodipine treatment significantly ameliorates mitochondrial respiratory conditions.

Effect of nimodipine on arachidonic acid metabolites after subarachnoid hemorrhage

Arachidonic acid metabolites are under investigation as possible vasoactive agents involved in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage. Prostaglandins, as well as other vasoactive compounds, activate contractile proteins through utilization of extracellular bound Ca++ to the intracytoplasmic free fraction. Recently, calcium-antagonists, mainly Nimodipine, have been proposed for the prophylaxis and/or reversal of the ischemic damage caused by vasospasm. Nimodipine failed to reduce vasospasm incidence in a series of 30 patients admitted with diagnosis of subarachnoid hemorrhage from ruptured intracranial aneurysm. Nimodipine failed to reduce level of four arachidonate metabolites measured (prostaglandin D2, prostacyclin, thromboxane B2 and leukotriene C4) in lumbar and cisternal CSF. After subarachnoid hemorrhage there is a significant increase of CSF levels of arachidonate metabolites; in perianeurysmic cisterns level of prostaglandin D2, thromboxane B2 and leukotriene C4 are significantly higher than lumbar CSF levels. Moreover, cisternal CSF level of prostaglandin D2 and leukotriene C4 are significantly higher in patients with symptomatic vasospasm. Nimodipine did not significantly modify CFS level of arachidonate metabolites: this suggests that Nimodipine treatment, which definitely improves long-term results of patients for intracranial aneurysms, could exert its pharmacological action reducing Ca++ intake from the extracellular compartment and preventing a direct toxic effect of calcium, without a direct action against the release of vasoactive compounds.

Effects of calcium antagonists on isolated bovine cerebral arteries: inhibition of constriction and calcium-45 uptake induced by potassium or serotonin

The purpose of this study was to determine the mechanisms by which organic calcium channel blockers inhibit cerebral vasoconstriction. Isolated bovine middle cerebral arteries were cut into rings to measure contractility or into strips to measure radioactive calcium (45Ca) influx and efflux. Calcium channel blockers (10(-5) M verapamil or 3.3 X 10(-7) M nifedipine) and calcium-deficient solutions all produced near-maximal inhibition of both potassium- and serotonin-induced constriction. In calcium-deficient solutions containing potassium or serotonin, verapamil and nifedipine each blocked subsequent calcium-induced constriction in a competitive manner. Potassium and serotonin significantly increased 45Ca uptake into cerebral artery strips during 5 minutes of 45Ca loading; for potassium 45Ca uptake increased from 62 to 188 nmol/g, and for serotonin from 65 to 102 nmol/g. Verapamil or nifedipine had no effect on basal 45Ca uptake but significantly blocked the increase in 45Ca uptake induced by potassium or serotonin. Potassium, and to a lesser extent serotonin, each induced a brief increase in the rate of 45Ca efflux into calcium-deficient solutions. Verapamil or nifedipine had no effect on basal or potassium-stimulated 45Ca efflux. The results demonstrate that verapamil and nifedipine block 45Ca uptake through both potential-operated (potassium) and receptor-operated (serotonin) channels in bovine middle cerebral arteries.

Brain extraction of a calcium channel blocker

Dihydropyridine calcium channel blockers may be effective treatment for acute cerebral ischemia, but the uptake of these drugs into the brain is unknown. A 0.2-ml bolus of [14C]nicardipine hydrochloride and [3H]water was injected into the common carotid arteries of 7 normal and 7 ischemic rats. The corrected first-pass extraction of nicardipine, compared to water, was calculated to be 30.7% into the hemispheres and 42.3% into the hippocampi. The uptake was greater into the ischemic hemispheres (p less than 0.001). These data suggest that dihydropyridines are available to binding sites and calcium channels in neurons.

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.