The direction of the chemical reaction of ATP synthetase is reversible. The present study was designed to determine whether mitochondria produce or consume ATP during ischemia. For this purpose, changes in mitochondrial membrane potential were measured in vivo at the site of a direct current (DC) electrode using a potentiometric dye, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1), and a rat model of focal ischemia. Two microL of dye (control group) or dye with oligomycin, an ATP synthetase inhibitor (oligomycin group), was injected into the parietotemporal cortex through the DC electrode. With the initiation of ischemia, a decrease in mitochondrial potential was observed within 20 seconds in the oligomycin group (earlier than the onset of DC deflection, P = 0.02). In contrast, in the control group, mitochondrial potential was maintained at 91 +/- 5% of the preischemia level for 118 +/- 38 seconds before showing full depolarization simultaneously with DC deflection. During the period of ischemia, the mitochondrial potential was higher in the control group (66 +/- 9%) than in the oligomycin group (46 +/- 8%, P = 0.0002), whereas DC potential was lower in the control group (-18 +/- 3) than in the oligomycin group (-15 +/- 2 mV, P = 0.04). These observations suggest that mitochondria consume ATP during ischemia by reversing ATP synthetase activity, which compromises cellular membrane potential by consuming ATP.
In 1961, in Pittsburgh, PA, "cerebral" was added to the cardiopulmonary resuscitation system (CPR --> CPCR). Cerebral recovery is dependent on arrest and cardiopulmonary resuscitation times, and numerous factors related to basic, advanced, and prolonged life support. Postischemic-anoxic encephalopathy (the cerebral postresuscitation disease or syndrome) is complex and multifactorial. The prevention or mitigation of this syndrome requires that there be development and trials of special, multifaceted, combination treatments. The selection of therapies to mitigate the postresuscitation syndrome should continue to be based on mechanistic rationale. Therapy based on a single mechanism, however, is unlikely to be maximally effective. For logistic reasons, the limit for neurologic recovery after 5 mins of arrest must be extended to achieve functionally and histologically normal human brains after 10 to 20 mins of circulatory arrest. This goal has been approached, but not quite reached. Treatment effects on process variables give clues, but long-term outcome evaluation is needed for documentation of efficacy and to improve clinical results. Goals have crystallized for clinically relevant cardiac arrest-intensive care outcome models in large animals. These studies are expensive, but essential, because positive treatment effects cannot always be confirmed in the rat forebrain ischemia model. Except for a still-elusive breakthrough effect, randomized clinical trials of CPCR are limited in their ability to statistically document the effectiveness of treatments found to be beneficial in controlled outcome models in large animals. Clinical studies of feasibility, side effects, and acceptability are essential. Hypertensive reperfusion overcomes multifocal no-reflow and improves outcome. Physical combination treatments, such as mild resuscitative (early postarrest) hypothermia (34 degrees C) plus cerebral blood flow promotion (e.g., with hypertension, hemodilution, and normocapnia), each having multiple beneficial effects, achieved complete functional and near-complete histologic recovery of the dog brain after 11 mins of normothermic, ventricular fibrillation cardiac arrest. Calcium entry blockers appear promising as a treatment for postischemic-anoxic encephalopathy. However, the majority of single or multiple drug treatments explored so far have failed to improve neurologic outcome. Assembling and evaluating combination treatments in further animal studies and determining clinical feasibility inside and outside hospitals are challenges for the near future. Treatments without permanent beneficial effects may at least extend the therapeutic window. All of these investigations will require coordinated efforts by multiple research groups, pursuing systematic, multilevel research--from cell cultures to rats, to large animals, and to clinical trials. There are still many gaps in our knowledge about optimizing extracerebral life support for cerebral outcome.
After ingesting approximately 2 g of amphetamine sulfate, a 21-year-old man was admitted in delirium with a temperature above 108 F. He subsequently developed acute self-limited renal failure and a coagulopathy with intramuscular hemorrhages producing entrapment neuropathies. The association of amphetamines with reversible renal failure has not been previously described. The resemblance of the features in this case to instances of heatstroke is striking and suggests a similar pathophysiology.
Background and Purpose— Darbepoetin alfa is a novel erythropoiesis-stimulating protein developed for treating anemia. In animal models, exogenous recombinant human erythropoietin has been reported to be beneficial in treating experimental cerebral ischemia. In this study, we determined whether darbepoetin alfa would protect in a rat model of transient focal cerebral ischemia. Methods— Rats received 2-hour middle cerebral artery suture-occlusion. The drug (darbepoetin alfa, 10 μg/kg) or vehicle was administered intraperitoneally 2 hours after onset of middle cerebral artery occlusion. Animals were allowed to survive for 3 or 14 days. Behavioral tests were performed sequentially. Infarct volumes and brain swelling were determined. Results— Darbepoetin alfa-treated rats showed improved neuroscores relative to vehicle-treated animals beginning within 1 hour of treatment and persisting throughout the 14-day survival period. Darbepoetin alfa significantly reduced corrected total (cortical + subcortical) infarct volume (56.3±20.6 and 110.8±6.8 mm 3 , respectively) and total infarct areas at multiple levels compared with vehicle in the 14-day survival group. Brain swelling was not affected by treatment. Conclusion— Darbepoetin alfa confers behavioral and histological neuroprotection after focal ischemia in rats.
Nineteen rhesus monkeys received single exposures to carbon monoxide (CO) sufficient to produce consistent neuropathologic lesions. Inhalation of 0.2% CO led to stable plateau levels of blood carboxyhemoglobin, which averaged 76%. The mean arterial blood oxygen content of these animals declined to 4.2 ml/100 ml. The arterial oxygen pressure remained normal. The jugular venous oxygen content exceeded that of the central venous blood during and following the intoxication. Arterial hypotension and metabolic acidosis evolved consistently though to a variable extent. The central venous pressure remained unaltered. Severe respiratory depression occurred only rarely, whereas cardiac arrhythmias constituted a major risk to life during the actual exposure. Ventricular fibrillation occurred in four animals and was fatal in two but could be largely prevented by the use of lidocaine prophylactically. Arterial hypotension led to the death of two animals.
We have recently shown that high-dose human serum albumin (HSA) therapy confers marked histological protection in experimental middle cerebral artery occlusion. Thus, the purpose of this study was to determine whether treatment with high-dose HSA would protect in a rat model of traumatic brain injury (TBI). Twenty-four hours prior to TBI, the fluid percussion interface was positioned parasagittally over the right cerebral cortex. On the following day, fasted rats were anesthetized with 3% halothane, 70% nitrous oxide, and 30% oxygen and received right parieto-occipital parasagittal fluid-percussion injury (1.5–2.0 atm). Cranial and rectal temperatures were monitored throughout the experiment and held at normothermic levels (36.5–37.5°C) by a warming lamp above the animal's head. The agent (25% human serum albumin, HSA) or vehicle (sodium chloride 0.9%) was administered i.v. (1% of body weight) 15 min after trauma. Behavioral function was evaluated in all rats before and after TBI (at 2 h, 24 h, 48 h, 72 h, and 7 days). Neurological function was graded on a scale of 0–12 (normal score = 0; maximal score = 12). Seven days after TBI, brains were perfusion-fixed, coronal sections at various levels were digitized, and contusion areas in the superficial, middle and deep layers of cortex and in the underlying fimbria were measured. HSA significantly improved the neurological score compared to saline at 24 h, 72 h, and 7 days after TBI (6.0 ± 0.6 [albumin] versus 8.4 ± 0.5 [saline]; 3.6 ± 0.7 versus 6.8 ± 1.0; and 2.6 ± 0.6 versus 5.7 ± 0.8, respectively; p < 0.05). HSA therapy also significantly reduced total contusion area (0.89 ± 0.2 versus 1.82 ± 0.3 mm2; p = 0.02). Our findings document that high-concentration albumin therapy instituted 15 min after trauma significantly improves the neurological score and reduces histological damage. We believe that this pharmacological agent may have promising potential for the clinical treatment of brain injury.
We have previously demonstrated that elevated intraischemic glutamate levels are insufficient, of themselves, to engender ischemic damage. Glycine and γ-aminobutyric acid (GABA), which modulate glutamatergic activity, may also play a significant role. We compared ischemia-induced changes in glutamate, glycine, and GABA release in a selectively vulnerable region (dorsolateral striatum) to the changes occurring in a region, although rendered ischemic, is usually spared with 20 min ischemia (anterior thalamus). Regional extracellular neurotransmitter levels were measured by microdialysis before, during, and after 20 min of global ischemia induced by 2-vessel occlusion plus systemic hypotension in the rat (n = 5). Similar ischemia-induced increases in glutamate, GABA, and glycine were observed in both striatum and thalamus (19–25 fold, 43–52 fold, and 3–4 fold, respectively). During recirculation, both glutamate and GABA returned to baseline in both regions by 30 min of reperfusion. Glycine levels remained two-fold higher than baseline in the striatum but fell to baseline in the thalamus. To derive a quantitative descriptor reflecting the composite magnitude of aminoacid neurotransmitter changes with ischemia, we defined the 'excitotoxic index' as: [glutamate] × [glycine]/[GABA]. While increases in the excitotoxic index during ischemia were similar for striatum and thalamus, a marked and highly significant increase was found in the striatum compared to the thalamus at early (1 h = 91.5 ± 27.4 and 25.1 ± 6.3, P < 0.01, ANOVA) as well as later recirculation times (2 h = 111.3 ± 30.9 and 20.9 ± 3.6, P < 0.01). Thus, the excitotoxic index, which reflects the composite neurotransmitter response, appears to be a reliable biochemical marker of selective neuronal vulnerability.
The concept of altering the body temperature to achieve a therapeutic result in an injured brain is not new. Much has been written, both in the experimental and clinical literature, on therapeutic hypo- and hyperthermia. The protective effect of profound hypothermia (30°C or less) has been well established during cardiac and intracranial surgical procedures necessitating interruption of blood flow to the brain. Hypothermia has also been and continues to be used in the head-injured patient for the control of increased intracranial pressure that is refractory to hyperventilation, ventricular drainage, osmotherapy, and barbiturates. Conversely, the adjunctive chemotherapeutic effect of selective brain tumor hyperthermia remains under intense investigation.
