Insulin-induced normoglycemia improves ischemic outcome in hyperglycemic rats

Exogenous Ketone Supplement Administration Abrogated Isoflurane-Anesthesia-Induced Increase in Blood Glucose Level in Female WAG/Rij Rats

It has been demonstrated that isoflurane-induced anesthesia can increase the blood glucose level, leading to hyperglycemia and several adverse effects. The administration of a mix of ketone diester (KE) and medium-chain triglyceride (MCT) oil, named KEMCT, abolished the isoflurane-anesthesia-induced increase in blood glucose level and prolonged the recovery time from isoflurane anesthesia in a male preclinical rodent model, Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. While most preclinical studies use exclusively male animals, our previous study on blood glucose changes in response to KEMCT administration showed that the results can be sex-dependent. Thus, in this study, we investigated female WAG/Rij rats, whether KEMCT gavage (3 g/kg/day for 7 days) can change the isoflurane (3%)-anesthesia-induced increase in blood glucose level and the recovery time from isoflurane-evoked anesthesia using the righting reflex. Moreover, KEMCT-induced ketosis may enhance both the extracellular level of adenosine and the activity of adenosine A1 receptors (A1Rs). To obtain information on the putative A1R mechanism of action, the effects of an A1R antagonist, DPCPX (1,3-dipropyl-8-cyclopentylxanthine; intraperitoneal/i.p. 0.2 mg/kg), on KEMCT-generated influences were also investigated. Our results show that KEMCT supplementation abolished the isoflurane-anesthesia-induced increase in blood glucose level, and this was abrogated by the co-administration of DPCPX. Nevertheless, KEMCT gavage did not change the recovery time from isoflurane-induced anesthesia. We can conclude that intragastric gavage of exogenous ketone supplements (EKSs), such as KEMCT, can abolish the isoflurane-anesthesia-induced increase in blood glucose level in both sexes likely through A1Rs in WAG/Rij rats, while recovery time was not affected in females, unlike in males. These results suggest that the administration of EKSs as an adjuvant therapy may be effective in mitigating metabolic side effects of isoflurane, such as hyperglycemia, in both sexes.

Intranasal insulin attenuates hypoxia-ischemia-induced short-term sensorimotor behavioral disturbances, neuronal apoptosis, and brain damage in neonatal rats

There is a significant need for additional therapy to improve outcomes for newborns with acute Hypoxic-ischemic (HI) encephalopathy (HIE). New evidence suggests that insulin could be neuroprotective. This study aimed to investigate whether intranasal insulin attenuates HI-induced brain damage and neurobehavioral dysfunction in neonatal rats. Postnatal day 10 (P10), Sprague-Dawley rat pups were randomly divided into Sham + Vehicle, Sham + Insulin, HI + Vehicle, and HI + Insulin groups with equal male-to-female ratios. Pups either had HI by permanent ligation of the right common carotid artery followed by 90 min of hypoxia (8% O2) or sham surgery followed by room air exposure. Immediately after HI or Sham, pups were given fluorescence-tagged insulin (Alex-546-insulin)/vehicle, human insulin (25 μg), or vehicle in each nare under anesthesia. Shortly after administration, widespread Alex-546-insulin-binding cells were detected in the brain, primarily co-localized with neuronal nuclei-positive neurons on double-immunostaining. In the hippocampus, phospho-Akt was activated in a subset of Alex-546-insulin double-labeled cells, suggesting activation of the Akt/PI3K pathway in these neurons. Intranasal insulin (InInsulin) reduced HI-induced sensorimotor behavioral disturbances at P11. InInsulin prevented HI-induced increased Fluoro-Jade C+ degenerated neurons, cleaved caspase 3+ neurons, and volume loss in the ipsilateral brain at P11. There was no sex-specific response to HI or insulin. The findings confirm that intranasal insulin provides neuroprotection against HI brain injury in P10 rats associated with activation of intracellular cell survival signaling. If further pre-clinical research shows long-term benefits, intranasal insulin has the potential to be a promising non-invasive therapy to improve outcomes for newborns with HIE.

Prospects for the Use of Intranasally Administered Insulin and Insulin-Like Growth Factor-1 in Cerebral Ischemia

Current approaches to the treatment of stroke have significant limitations, and neuroprotective therapy is ineffective. In view of this, searching for effective neuroprotectors and developing new neuroprotective strategies remain a pressing topic in research of cerebral ischemia. Insulin and insulin-like growth factor-1 (IGF-1) play a key role in the brain functioning by regulating the growth, differentiation, and survival of neurons, neuronal plasticity, food intake, peripheral metabolism, and endocrine functions. Insulin and IGF-1 produce multiple effects in the brain, including neuroprotective action in cerebral ischemia and stroke. Experiments in animals and cell cultures have shown that under hypoxic conditions, insulin and IGF-1 improve energy metabolism in neurons and glial cells, promote blood microcirculation in the brain, restore nerve cell functions and neurotransmission, and produce the anti-inflammatory and antiapoptotic effects on brain cells. The intranasal route of insulin and IGF-1 administration is of particular interest in the clinical practice, since it allows controlled delivery of these hormones directly to the brain, bypassing the blood-brain barrier. Intranasally administered insulin alleviated cognitive impairments in elderly people with neurodegenerative and metabolic disorders; intranasally administered insulin and IGF-1 promoted survival of animals with ischemic stroke. The review discusses the published data and results of our own studies on the mechanisms of neuroprotective action of intranasally administered insulin and IGF-1 in cerebral ischemia, as well as the prospects of using these hormones for normalization of CNS functions and reduction of neurodegenerative changes in this pathology.

Ketone supplementation abolished isoflurane anesthesia-induced elevation in blood glucose level and increased recovery time from anesthesia in Wistar Albino Glaxo Rijswijk rats

BACKGROUND

It has been suggested that administration of exogenous ketone supplements (EKSs) not only increases blood ketone body levels but also decreases blood glucose level and modulates isoflurane-induced anesthesia in different rodents, such as Wistar Albino Glaxo Rijswijk (WAG/Rij) rats. Thus, we investigated whether administration of EKSs can modulate the isoflurane anesthesia-generated increase in blood glucose level and the time required to recover from isoflurane-induced anesthesia.

METHODS

To investigate the effect of EKSs on isoflurane anesthesia-induced changes in blood glucose and R-β-hydroxybutyrate (R-βHB) level as well as recovery time from anesthesia, we used KEMCT (mix of ketone ester/KE and medium chain triglyceride/MCT oil in a 1:1 ratio) in WAG/Rij rats. First, to accustom the animals to the method, water gavage was carried out for 5 days (adaptation period). After adaptation period, rats of first group (group 1) were gavaged by water (3 g/kg), whereas, in the case of second group (group 2), the diet of animals was supplemented by KEMCT (3 g/kg, gavage) once per day for 7 days. One hour after the last gavage, isoflurane (3%) anesthesia was induced for 20 min (group 1 and group 2) and the time required for recovery from anesthesia was measured by using righting reflex. Subsequently, blood levels of both R-βHB and glucose were also evaluated. Changes in blood glucose and R-βHB levels were compared to control, which control glucose and R-βHB levels were measured on the last day of the adaptation period (group 1 and group 2). Time required for recovery from isoflurane anesthesia, which was detected after 7^th KEMCT gavage (group 2), was compared to recovery time measured after 7^th water gavage (group 1).

RESULTS

The KEMCT maintained the normal glucose level under isoflurane anesthesia-evoked circumstances preventing the glucose level elevating effect of isoflurane. Thus, we demonstrated that administration of KEMCT not only increased blood level of R-βHB but also abolished the isoflurane anesthesia-generated increase in blood glucose level. Moreover, the time required for recovery from isoflurane-evoked anesthesia increased significantly in KEMCT treated animals.

CONCLUSIONS

Putative influence of elevated blood ketone body level on isoflurane-evoked effects, such as modulation of blood glucose level and recovery time from anesthesia, should be considered by anesthesiologists.

Insulin renders diabetic rats resistant to acute ischemic stroke by arresting nitric oxide reaction with superoxide to form peroxynitrite

Background

The functions of free radicals on the effects of insulin that result in protection against cerebral ischemic insult in diabetes remain undefined. This present study aims to explain the contradiction among nitric oxide (NO)/superoxide/peroxynitrite of insulin in amelioration of focal cerebral ischemia–reperfusion (FC I/R) injury in streptozotocin (STZ)-diabetic rats and to delineate the underlying mechanisms. Long-Evans male rats were divided into three groups (age-matched controls, diabetic, and diabetic treated with insulin) with or without being subjected to FC I/R injury.

Results

Hyperglycemia exacerbated microvascular functions, increased cerebral NO production, and aggravated FC I/R-induced cerebral infarction and neurological deficits. Parallel with hypoglycemic effects, insulin improved microvascular functions and attenuated FC I/R injury in STZ-diabetic rats. Diabetes decreased the efficacy of NO and superoxide production, but NO and superoxide easily formed peroxynitrite in diabetic rats after FC I/R injury. Insulin treatment significantly rescued the phenomenon.

Conclusions

These results suggest that insulin renders diabetic rats resistant to acute ischemic stroke by arresting NO reaction with superoxide to form peroxynitrite.

Animal models of stroke: translational potential at present and in 2050

Translation from basic science bench research in ischemic stroke to bedside treatment of patients suffering ischemic stroke remains a difficult challenge. Despite literally hundreds of compounds and interventions that provide benefit in experimental models of cerebral ischemia, efficacy in humans remains to be demonstrated. The reasons for failure to translate the extensive positive basic science findings to successful clinical trials have been the focus of discussion for years. Some attribute the failure to flaws in clinical trial design, others question the predictive value of current animal models and some question the quality of preclinical data. It is likely that a combination of all these shortcomings have ultimately led to the failure. The purpose of this review is to analyze the commonly used animal models used in the field today, provide a framework for understanding the current state of basic science research in the ischemic stroke field and discuss a path forward.

Drug-induced therapeutic hypothermia after asphyxial cardiac arrest in swine

A feasibility study was performed to compare an investigational drug, HBN-1, to forced cooling to induce hypothermia after resuscitation in a translation model of asphyxial cardiac arrest in swine. Serum and cerebral spinal fluid neuron-specific enolase activity (sNSE and csfNSE) were measured after cardiac arrest as surrogate markers of brain injury. In a block design, swine resuscitated from 10 minutes of asphyxial cardiac arrest were infused intravenously with HBN-1 or iced saline vehicle (forced hypothermia [FH]) 5 to 45 minutes after return of spontaneous circulation (ROSC). External cooling in both groups was added 45 minutes after ROSC until hypothermia (T=4°C below baseline) was attained. Esophageal (core) temperature, shivering, cardiopulmonary parameters, and time to hypothermia after ROSC were monitored. sNSE and csfNSE were measured 180 minutes after ROSC. HBN-1 induced hypothermia significantly lowered temperature compared to FH 5-45 minutes after ROSC (p<0.0001). Time to hypothermia was reduced by HBN-1 (93±6 minutes) compared to FH (177±10 minutes) (p<0.0001). HBN-1 sNSE (0.7±1.9 ng/mL) and csfNSE (17.3±1.9 ng/mL) were lower compared to FH (6±1.6 ng/mL) and (49.7±32.0 ng/mL) (p<0.0001, p=0.022, respectively). There was no shivering with HBN-1 cooling while all FH cooled swine shivered (p<0.0001). The time to reach target hypothermia after cardiac arrest was reduced by nearly 50% with HBN-1 compared to the FH method of inducing hypothermia. Moreover, surrogate biomarkers of brain injury were significantly reduced with HBN-1 as compared to FH. While HBN-1-induced hypothermia shows promise for being neuroprotective, survival studies are needed to confirm these preliminary findings.

Hyperglycemia, acute ischemic stroke, and thrombolytic therapy

Ischemic stroke is a leading cause of disability and is considered now the fourth leading cause of death. Many clinical trials have shown that stroke patients with acute elevation in blood glucose at onset of stroke suffer worse functional outcomes, longer in-hospital stay, and higher mortality rates. The only therapeutic hope for these patients is the rapid restoration of blood flow to the ischemic tissue through intravenous administration of the only currently proven effective therapy, tissue plasminogen activator (tPA). However, even this option is associated with the increased risk of intracerebral hemorrhage. Nonetheless, the underlying mechanisms through which hyperglycemia (HG) and tPA worsen the neurovascular injury after stroke are not fully understood. Accordingly, this review summarizes the latest updates and recommendations about the management of HG and coadministration of tPA in a clinical setting while focusing more on the various experimental models studying (1) the effect of HG on stroke outcomes, (2) the potential mechanisms involved in worsening the neurovascular injury, (3) the different therapeutic strategies employed to ameliorate the injury, and finally, (4) the interaction between HG and tPA. Developing therapeutic strategies to reduce the hemorrhage risk with tPA in hyperglycemic setting is of great clinical importance. This can best be achieved by conducting robust preclinical studies evaluating the interaction between tPA and other therapeutics in order to develop potential therapeutic strategies with high translational impact.

Comparative analysis of the neurovascular injury and functional outcomes in experimental stroke models in diabetic Goto-Kakizaki rats

Diabetes worsens functional outcome and is associated with greater hemorrhagic transformation (HT) after ischemic stroke. We have shown that diabetic Goto-Kakizaki (GK) rats develop greater HT and neurological deficit despite smaller infarcts after transient middle cerebral artery occlusion (MCAO) with the suture model. However, the impact of (1) the duration of ischemia/reperfusion (I/R); (2) the method of ischemia; and (3) acute glycemic control on neurovascular injury and functional outcome in diabetic stroke remained unanswered. Wistar and GK rats were subjected to variable MCAO by suture or embolus occlusion. A group of GK rats were treated with insulin or metformin before stroke with suture occlusion. In all groups, infarct size, edema, HT occurrence and severity, and functional outcome were measured. Infarct size at 24h was smaller in GK rats with both suture and embolic MCAO, but expanded with longer reperfusion period. Edema and HT were increased in GK rats after 90min and 3h occlusion with the suture model, but not in the embolic MCAO. Neurological deficit was greater in diabetic rats. These findings suggest that diabetes accelerates the development of HT and amplifies vascular damage in the suture model where blood flow is rapidly reestablished. Acute metformin treatment worsened the infarct size, HT, and behavior outcome, whereas insulin treatment showed a protective effect. These results suggest that the impact of ischemia/reperfusion on neurovascular injury and functional outcome especially in disease models needs to be fully characterized using different models of stroke to model the human condition.

The essential role of endothelial nitric oxide synthase activation in insulin-mediated neuroprotection against ischemic stroke in diabetes

BACKGROUND

Stroke patients with diabetes have a higher mortality rate, worse neurologic outcome, and more severe disability than those without diabetes. Results from clinical trials comparing the outcomes of stroke seen with intensive glycemic control in diabetic individuals are conflicting. Therefore, the present study was aimed to identify the key factor involved in the neuroprotective action of insulin beyond its hypoglycemic effects in streptozotocin-diabetic rats with ischemic stroke.

METHODS

Long-Evans male rats were divided into three groups (control, diabetes, and diabetes treated with insulin) and subjected to focal cerebral ischemia-reperfusion (FC I/R) injury.

RESULTS

Hyperglycemia aggravated FC I/R injuries with an increase in cerebral infarction and neurologic deficits, inhibition of glucose uptake and membrane-trafficking activity of glucose transporter 1, and reduction of Akt and endothelial nitric oxide synthase (eNOS) phosphorylation in the cerebrum. Insulin treatment alleviated hyperglycemia and the symptoms of diabetes in streptozotocin-diabetic rats. Insulin administration also significantly decreased cerebral infarction and neurologic deficits and increased phosphorylation of Akt and eNOS protein in the cerebrum of FC I/R-injured diabetic rats. However, the glucose uptake and membrane trafficking activity of glucose transporter 1 in the cerebrum were not restored by insulin treatment. Coadministration of the eNOS inhibitor, N-iminoethyl-L-ornithine, with insulin abrogated beneficial effects of insulin on cerebral infarct volume and neurologic deficits in FC I/R-injured diabetic rats without affecting the hypoglycemic action of insulin.

CONCLUSIONS

These results suggest that eNOS activation is required for the neuroprotection of insulin against ischemic stroke in patients with diabetes.

Insulin and glucagon share the same mechanism of neuroprotection in diabetic rats: role of glutamate

In patients with acute ischemic stroke, diabetes and hyperglycemia are associated with increased infarct size, more profound neurologic deficits and higher mortality. Notwithstanding extensive clinical and experimental data, treatment of stroke-associated hyperglycemia with insulin is controversial. In addition to hyperglycemia, diabetes and even early prediabetic insulin resistance are associated with increased levels of amino acids, including the neurotoxic glutamate, in the circulation. The pleiotropic metabolic effects of insulin include a reduction in the concentration of amino acids in the circulation. In this article, we show that in diabetic rats exposed to transient middle cerebral artery occlusion, a decrease of plasma glutamate by insulin or glucagon reduces CSF glutamate, improves brain histology, and preserves neurologic function. The neuroprotective effect of insulin and glucagon was similar, notwithstanding their opposite effects on blood glucose. The therapeutic window of both hormones overlapped with the short duration (~30 min) of elevated brain glutamate following brain trauma in rodents. Similar neuroprotective effects were found after administration of the glutamate scavenger oxaloacetate, which does not affect glucose metabolism. These data indicate that insulin and glucagon exert a neuroprotective effect within a very brief therapeutic window that correlates with their capacity to reduce glutamate, rather than by modifying glucose levels.

Prediction of adverse outcomes by blood glucose level after endovascular therapy for acute ischemic stroke

OBJECT

The authors evaluated the prognostic significance of blood glucose level at admission (BGA) and change in blood glucose at 48 hours from the baseline value (CG48) in nondiabetic and diabetic patients before and after endovascular therapy for acute ischemic stroke (AIS).

METHODS

The BGA and CG48 data were analyzed in 614 patients with AIS who received endovascular therapy at 7 US centers between 2006 and 2009. Data reviewed included demographics, stroke risk factors, diabetic status, National Institutes of Health Stroke Scale (NIHSS) score at presentation, recanalization grade, intracranial hemorrhage (ICH) rate, and 90-day outcomes (mortality rate and modified Rankin Scale score of 3-6 [defined as poor outcome]). Variables with p values < 0.2 in univariate analysis were included in a binary logistic regression model for independent predictors of 90-day outcomes.

RESULTS

The mean patient age was 67.3 years, the median NIHSS score was 16, and 27% of patients had diabetes. In nondiabetic patients, BGA ≥ 116 mg/dl (≥ 6.4 mmol/L) and failure of glucose level to drop > 30 mg/dl (> 1.7 mmol/L) from the admission value were both significant predictors of 90-day poor outcome and death (p < 0.001). In patients with diabetes, BGA ≥ 116 mg/dl (≥ 6.4 mmol/L) was an independent predictor of poor outcome (p = 0.001). The CG48 was not a predictor of outcome in diabetic patients. A simplified 6-point scale including BGA, Thrombolysis in Myocardial Infarction (TIMI) Grade 2-3 Reperfusion, Age, presentation NIHSS score, CG48, and symptomatic ICH (BRANCH) corresponded with poor outcomes at 90 days; the area under the curve value was > 0.79.

CONCLUSIONS

Failure of blood glucose values to decrease in the first 48 hours after AIS intervention correlated with poor 90-day outcomes in nondiabetic patients. The BRANCH scale shows promise as a simple prognostication tool after endovascular therapy for AIS, and it merits prospective validation.

Hyperglycemia, diabetes and stroke: focus on the cerebrovasculature

Acute ischemic stroke (AIS) results from the occlusion of an artery and causes vascular and neuronal damage, both of which affect the extent of ischemic injury and stroke outcome. Despite extensive efforts, there is only one effective treatment for AIS. Given that up to 40% of the AIS patients present with admission hyperglycemia either as a result of diabetes or acute stress response, targets for neuronal and vascular protection under hyperglycemic conditions need to be better defined. Here, we review the impact of diabetes and acute hyperglycemia on experimental stroke with an emphasis on cerebrovasculature structure and function. The relevance to clinical evidence is also discussed.

Insulin activates the PI3K-Akt survival pathway in vulnerable neurons following global brain ischemia

Insulin is neuroprotective following transient global brain ischemia; however, the mechanisms by which insulin exerts its salutary effects remain unclear.

OBJECTIVE

We assessed insulin's effect on the PI3K-Akt survival system and consequent modulation of the pro-apoptotic proteins Bim, Bad and FoxO3a.

METHODS

We utilized rats subjected to 10 minutes of global brain ischemia, with or without insulin administered at the onset of reperfusion.

RESULTS

In sham-operated animals, minimal pAkt immunofluorescence was detected in the CA1. Moreover, at 30 minute reperfusion, there was no change in pAkt in CA1 neurons. Single bolus high-dose insulin treatment resulted in an early increase in pAkt after 30 minutes, preservation of CA1 neurons to 14 days of reperfusion and preservation of spatial learning ability. Insulin treatment increased cytoplasmic and nuclear staining for pAkt in both CA1 and cortex. Insulin-induced Akt phosphorylation was suppressed by the PI3K inhibitor wortmannin. Neither reperfusion nor insulin induced any change in the phosphorylation or subcellular localization of FoxO3a, Bim or Bad. A single bolus of high-dose insulin reduced CA1 neuronal cell death and thus represents a potential therapeutic intervention for global brain ischemia.

DISCUSSION

These results reveal that proximal elements of a known cell-survival pathway are triggered by high-dose insulin during early reperfusion. Insulin induces robust PI3K-dependent phosphorylation of Akt by 30 minute reperfusion and results in improvement of hippocampal structure and function. However, the Akt substrates FoxO3a, Bim and Bad do not undergo corresponding changes in phosphorylation or subcellular localization in this model of global brain ischemia. The downstream components of insulin-induced Akt survival signaling after transient global brain ischemia remain to be identified.

Optimal blood glucose levels while using insulin to minimize the size of infarction in focal cerebral ischemia

Object. Insulin has been shown to ameliorate cerebral necrosis in global and, more recently, in focal cerebral ischemia. The goal of this study was to determine the relationship between this neuroprotective effect and blood sugar levels in a rat model of focal ischemia.

Methods. Thirty-four rats were subjected to 80 minutes of transient middle cerebral artery occlusion at a mean arterial blood pressure of 60 mm Hg and a temperature of 37°C. Insulin (3.5 IU/kg) was administered 1 hour before (12 rats) and 20 minutes after (12 rats) ischemia; 10 animals served as controls. A quantitative histopathological study conducted after 1 week of survival showed that insulin was not beneficial in reducing the size of the infarction or selective neuronal necrosis in the penumbra when administered before or after ischemia. In addition to infarction, six animals from the insulin-treated groups had bilateral selective neuronal necrosis in the hippocampus or the neocortex. A nonlinear regression analysis in which glucose levels were compared with both cortical necrosis and total infarction yielded a U-shaped curve with a nadir for cerebral necrosis that lay in the 6- to 7-mM blood glucose range. The increased brain damage induced by insulin occurred in animals with very low blood sugar values in the range of 2 to 3 mM.

Conclusions. These results in rats indicate that if insulin is used following ischemia, blood glucose levels should be maintained at approximately 6 to 7 mM. From these data one can infer that hypoglycemia of less than 3 mM should be avoided in situations of focal cerebral ischemia in which insulin is used. Additional animal studies and clinical trials in humans are needed to study the effects of insulin on ischemia.

How Important is Hyperglycemia During Acute Brain Infarction?

BACKGROUND

Although well supported by animal studies, it remains unproven whether lowering hyperglycemia during acute cerebral infarction will improve outcomes. Further support for this therapeutic approach comes from clinical studies in acute myocardial infarction and in ventilated postsurgical patients, where lowering hyperglycemia improved outcomes.

REVIEW SUMMARY

Animal studies support the hypothesis that hyperglycemia during acute brain ischemia augments the brain injury, but only in models with reperfusion. The available human studies to date are all observational and they usually find an association between hyperglycemia during acute cerebral infarction and worse outcome. Also, there is evidence that hyperglycemia during acute cerebral infarction is detrimental only with reperfusion. This association appears to be linear in the glucose ranges tested (normal to high). In addition, there is an association between admission hyperglycemia and hemorrhagic conversion of an acute cerebral infarct when thrombolytics are used.

CONCLUSION

Sufficient evidence has accumulated to proceed to clinical efficacy trials to see if tight glycemic control compared with persistent hyperglycemia during acute cerebral infarction will improve outcomes. If such therapy proves beneficial, the increased cost, effort, and risk associated with tight glycemic control during acute cerebral infarction could be justified. Randomized clinical trials to test this hypothesis are currently in progress.

Severe acidosis caused by starvation and stress

A 1-year-old boy had severe anoxic brain injury owing to a cardiorespiratory arrest. He had an initial metabolic acidosis, but this largely resolved by hospital day 2. He then had a persistent, profound metabolic acidosis. Evaluation on hospital day 6 found that the patient had ketonemia, ketonuria, and a normal serum glucose level; he had received no intravenous dextrose during his hospitalization. The dextrose-free fluids were given initially to protect his brain from the deleterious effects of hyperglycemia after brain injury. Continuation beyond 24 hours was inadvertent. The initiation of dextrose-containing intravenous fluids produced a rapid resolution of his metabolic acidosis. Starvation usually produces a mild metabolic acidosis, but when combined with physiologic stress, starvation may cause a severe metabolic acidosis. Among the few reports of severe starvation ketoacidosis, our case is unique because the patient was monitored closely in an intensive care unit, allowing us to describe the time course of the acidosis in detail.

Critical Care Assessment and Management of Acute Ischemic Stroke

The resuscitation and treatment of patients with an acute stroke has evolved measurably during the past 2 decades. Acute ischemic stroke represents a true emergency where time is crucial and, therefore, evaluation and treatment often proceed simultaneously. Advanced imaging techniques can provide information about the state of brain perfusion, metabolism, and the cerebrovascular anatomy to help identify patients with viable brain tissue who may derive the greatest benefit from available therapies. Currently, several agents are available for rapid restoration of perfusion to ischemic brain. These include intravenous administration of recombinant tissue-type plasminogen activator (tPA), which is effective within a 3-hour period, and intraarterial thrombolytic therapy, which may be effective within 6 hours. In addition, newer agents such as ancrod and abciximab may be effective within the acute time period. Optimal care requires a multidisciplinary approach with attention to a wide variety of therapeutic issues while maintaining adequate brain perfusion to reverse or halt the ischemic process. Herein, the author examines the important therapeutic concerns in the critical care management of ischemic stroke, including the management of elevated intracranial pressure, elevated and low blood pressure, cardiac complications, and potential metabolic disturbances.

Peripheral neuropathy and microangiopathy in rats with insulinoma: association with chronic hyperinsulinemia

BACKGROUND

Hypoglycemia can precipitate or worsen peripheral neuropathy in patients with insulinoma or in diabetic patients on an intensive insulin regimen. It still remains unclear as to whether hyperinsulinemia itself is involved in neuropathic changes in these patients. We, therefore, explored the possible isolated effects of chronic hyperinsulinemia on neuropathic changes in insulinoma-bearing rats (I-rats).

METHODS

I-rats were generated by a combined treatment with nicotinamide and streptozotocin. At 15 months after the treatment, they showed a wide range of the plasma insulin (PI) level with or without a decrease in the blood glucose (BG) level and were divided into three groups on the basis of the presence of hypoglycemia (BG < 2.5 mmol/L) or hyperinsulinemia (PI > 100 mU/L): the first exhibited only hypoglycemia, the second exhibited only hyperinsulinemia, and the third exhibited neither. Peripheral nerve function and structure as well as microvasculature were evaluated among these groups in addition to age-matched untreated control rats (C-rats).

RESULTS

The first group of hypoglycemic I-rats showed a decrease (p < 0.05) in the axon/myelin ratio and an increase (p < 0.0001) in fibers undergoing axonal degeneration compared to C-rats, while the other two groups did not. On the other hand, the second group of hyperinsulinemic I-rats showed a decrease (p < 0.05) in the myelinated axonal size and an increase (all p < 0.05) in the F-wave latency and the densities of myelinated fibers and endoneurial microvessels exhibiting endothelial hyperplasia, vascular wall thickening, or pericytes debris compared to the third group of isoglycemic I-rats without hyperinsulinemia.

CONCLUSION

These results suggest that hypoglycemia is associated with increased myelinated axonal damage, while hyperinsulinemia is associated with increased densities of small myelinated axons and endoneurial microvessels with microangiopathic changes in I-rats. We, therefore, propose that the observed findings may be relevant to the complicated features of neuropathy in diabetic patients with chronic hyperinsulinemia.

Correlation between extracellular glucose and seizure susceptibility in adult rats

In adult diabetic patients, periods of hyperglycemia may be associated with exacerbation of focal seizures. Our objective was to determine in the adult rats the correlation between seizure susceptibility and extracellular glucose concentration in two models of seizures. Male rats were injected with two doses of streptozocin (40 mg/kg IP) on 2 consecutive days to induce diabetic hyperglycemia. Controls either received vehicle or were not injected. After 2 weeks, blood glucose concentration was measured, and the rats were subjected to flurothyl seizure test. Another group of rats received glucose solution (20%, 5 ml IP) 30 minutes before testing to induce nondiabetic hyperglycemia. Thresholds for flurothyl-induced clonic and tonic-clonic seizures were determined. Finally, in vitro epileptiform activity was induced in the entorhinal cortex-hippocampal slices from naive rats by perfusing with magnesium-free medium with various glucose concentrations. In additional slices, paired-pulse paradigm was determined in the perforant path. Susceptibility to clonic and tonic-clonic flurothyl-induced seizures positively correlated with blood glucose concentrations as the increased glucose concentration was associated with proconvulsant effects. Similarly, in the in vitro experiments, epileptiform activity was promoted by increased and suppressed by decreased glucose concentrations. Data indicate that, in the adult rats, high glucose concentrations are associated with proconvulsant effects.

Loss of benefit from estrogen replacement therapy in diabetic ovariectomized female rats subjected to transient forebrain ischemia

In nondiabetic animals, estrogen has been shown to provide significant neuroprotection in focal and transient forebrain ischemia models. However, that neuroprotection may be diminished or lost in the diabetic. In this study, we compared the level of brain damage in intact, ovariectomized (OVX) and 17beta-estradiol (E(2))-treated OVX female rats rendered diabetic and chronically ( approximately 4 weeks) hyperglycemic via streptozotocin (STZ). Rats were subjected to 20 min of unilateral transient forebrain ischemia (reduction in cortical CBF to 20% of baseline). Neurologic function was analyzed daily and brain histopathology (in H&E-stained sections) was evaluated at 72 h of reperfusion. Supplemental histopathologic information was obtained from additional TUNEL-stained sections. When comparing neurologic outcome scores in the three groups, E(2)-treated OVX females displayed the highest degree of dysfunction and intact females the least (OVX rats not treated with E(2) were intermediate), with the difference between the intact and E(2)-treated groups being statistically significant. That same order was often observed with the regional histopathologic analyses of H&E-stained tissue. A significantly higher magnitude of neuronal loss in both OVX groups, when compared to intact females, was observed in the CA4 sector of the hippocampus and in the cortex. In addition, cell loss in the dorsal thalamus of the E(2)-treated group was significantly greater than in the intact females. Those results were generally corroborated by TUNEL-analysis, with 67% of the E(2)-treated, 33% of the control OVX, and only 17% of the intact females displaying TUNEL-positive cells in multiple regions. In conclusion, the present findings strongly suggest that the neuroprotective benefits of estrogen replacement therapy may be lost in the diabetic female rat.

Brain protection during neurosurgery

The initial concept of brain protection during neurosurgery is based on research done in the 1970s-1980 which established the concept that by decreasing cerebral metabolic rate the brain could survive longer periods of ischemia. The first section of this chapter reviews some of this initial research that promoted the use of barbiturates for cerebral protection. The second section reviews current anesthetic drugs and their potential for cerebral protection in addition to the benefits of blood pressure, temperature and glucose control. The final section discusses the "new mechanisms of cerebral protection" and the role old and new drugs may play in the future for brain protection during neurosurgery.

The effects of early insulin treatment combined with thrombolysis in rat embolic stroke

The therapeutic effect of insulin alone or insulin combined with 30 min delayed thrombolytic therapy was investigated in rats embolized in the right hemisphere with a fibrin clot made from autologous blood. Animals were killed seven days after embolization and the infarct volumes were measured in % of the affected hemisphere. Mortality was calculated as the number of animals dying spontaneously before the scheduled euthanasia. The median infarct volume in control animals (n = 12) was 24%. Insulin (3 IU kg(-1)) was given subcutaneously 15 min, 3 h, and 24 h after embolization (n = 12) and reduced median infarct volume to 11%. Human recombinant tissue plasminogen activator, 8 mg kg(-1), was infused intravenously during 45 min starting 30 min after embolization (n = 14), and the median infarct volume was 18% in this group. When the two treatments were combined, the median infarct volume was reduced to 11% (n = 14). The infarct volumes in the treatment groups were not significantly different from controls (p = 0.62, Kruskal Wallis test). Mortality rates increased from 0% among controls to 47% (p = 0.01) in the insulin alone and 38% (p = 0.02) in the combination therapy group. In conclusion, insulin treatment aiming at blood glucose levels around 2-4 mmol l(-1) was detrimental to clinical outcome causing significantly increased mortality.

Protective effect of insulin on ischemic renal injury in diabetes mellitus

BACKGROUND

An exceptional susceptibility to unilateral renal ischemia/reperfusion (I/R) injury resulting in inflammation, fibrosis, atrophy of the kidney, and end-stage renal disease (ESRD) has been demonstrated in the diabetic rat. The aim of this study was to examine whether insulin treatment would reduce I/R injury in diabetic kidneys.

METHODS

Diabetes mellitus (DM) was induced in male Wistar rats by streptozotocin. I/R was achieved by clamping the left renal artery for 30 minutes. Treatment with long acting insulin was started 7 to 14 days before or one day after I/R. Short acting insulin was administrated 2 to 6 hours before the injury. Apoptosis was evaluated six hours after ischemia with the TUNEL-method. Four weeks after the clamping inulin clearance was measured and kidneys were removed for histopathological evaluation.

RESULTS

In DM animals renal I/R caused massive induction of apoptosis in the renal medulla after six hours as well as inflammation, fibrosis, renal atrophy and anuria within four weeks. Treatment with long acting insulin before I/R resulted in decreased cell death and an almost complete protection of both renal function and histomorphology. Treatment with short acting insulin before I/R also decreased the loss of renal function. In contrast, insulin treatment after I/R did not protect the kidney from damage.

CONCLUSIONS

This study shows that insulin treatment with a subsequent improved metabolic control before renal I/R protected kidneys from ESRD.

Leukocyte-endothelial cell interactions in diabetic retina after transient retinal ischemia

Diabetes is associated with increased neural damage after transient cerebral ischemia. Recently, leukocytes, which are thought to play a central role in ischemia-reperfusion injury, have been suggested to be involved in exacerbated damage after transient ischemia in diabetic animals. The present study was designed to clarify whether the anticipated worse outcome after transient cerebral ischemia in diabetic animals was due to augmented leukocyte-mediated neural injury. Using rats with streptozotocin-induced diabetes of 4-wk duration, we investigated leukocyte-endothelial cell interactions during reperfusion after a transient 60-min period of retinal ischemia. Unexpectedly, postischemic diabetic retina showed no active leukocyte-endothelial cell interactions during reperfusion. The maximal numbers of rolling and accumulating leukocytes in diabetic retina were reduced by 73.6 and 41.2%, respectively, compared with those in nondiabetic rats. In addition, neither preischemic insulin treatment of diabetic rats nor preischemic glucose infusion of nondiabetic rats significantly influenced leukocyte-endothelial cell interactions during reperfusion. The present study demonstrated that high blood glucose concentration before induction of ischemia did not exacerbate leukocyte involvement in the postischemic retinal injury. Furthermore, diabetic retina showed suppressed leukocyte-endothelial cells interactions after transient ischemia, perhaps due to an adaptive mechanism that developed during the period of induced diabetes.

The effect of intravenous insulin on accumulation of excitotoxic and other amino acids in the ischemic rat cerebral cortex

Insulin has been reported to be neuroprotective during cerebral ischemia/reperfusion. However, it may also increase the sensitivity of cultured cortical neurons to glutamate toxicity. The experiments described here utilized a rat four-vessel occlusion model with cerebral cortical windows to determine the effects of intravenous insulin, alone (I) or combined with glucose (IG) to maintain physiologic blood glucose levels, on the extracellular accumulation of amino acids in superfusates of the cerebral cortex. Aspartate, phosphoethanolamine, taurine and gamma-aminobutyric acid were increased in the I and IG groups and glutamate was increased in the IG group compared to controls during ischemia/reperfusion. Insulin treatment attenuated the rebound in cortical superfusate glucose levels in both groups of animals during reperfusion. The increases in amino acid release during reperfusion may be due to a lack of glycolytically derived energy available for amino acid uptake systems and ionic pumps.

Reproducibility of cerebral cortical infarction in the wistar rat after middle cerebral artery occlusion

Although middle cerebral artery (MCA) occlusion in the rat is often used to study focal cerebral ischemia, the model of ischemia affects the size and reproducibility of infarction. The purpose of this experiment was to methodically examine different preparations to determine the optimum focal cerebral ischemia model to produce a reproducible severe ischemic injury. Eighty-two Wistar rats underwent either 1 hour, 3 hour, or permanent MCA occlusion combined with no, unilateral, or bilateral common carotid artery artery (CCA) occlusion. Three days after ischemia, the animals were prepared for tetrazolium chloride assessment of infarction size. One-hour MCA occlusion produced a coefficient of variation (CV) of 200% with an infarction volume of 20.3+/-10.5 mm(3). Adding unilateral or bilateral CCA occlusion resulted in a CV of 134% and 101%, respectively. Three-hour MCA occlusion combined with bilateral CCA occlusion decreased the CV to 58% with a cortical infarction volume of 82.6+/-12.1 mm(3), P<05, compared with 1-hour MCA occlusion with or without CCA occlusion. Permanent MCA occlusion combined with 3 hours of bilateral CCA occlusion resulted in a CV of 47% with a cortical infarction volume of 89.6+/-16.0 mm(3). These results indicate that 3-hour MCA occlusion combined with bilateral CCA occlusion provide consistently a large infarction volume after temporary focal cerebral ischemia.

Forebrain ischemia: effect on pharmacologically induced seizure thresholds in the rat

Seizures are common after severe cerebral ischemia. To examine the mechanisms underlying these seizures, we determined the impact of prior forebrain ischemia on the seizure thresholds of four convulsants with differing modes of action: lidocaine, pentylenetetrazol (PTZ), N-methyl-D-aspartate (NMDA), and picrotoxin. Anesthetized Sprague-Dawley rats were chronically instrumented with screw electrodes and vascular catheters, and then subjected to 10 min of forebrain ischemia, produced by carotid occlusion and hypotension (mean arterial pressure to 30 mmHg). Animals were then awakened. 6, 24 or 48 h later, groups of awake animals received intravenous infusions of the four drugs. The total dose of drug infused prior to either electrical seizures (lidocaine, PTZ, and picrotoxin) or tonic-clonic convulsions (all drugs) were noted. For each drug, a group of Sham animals (no ischemia) served as controls. There were markedly different patterns of changes in the convulsant thresholds for the drugs. For example, at 6 h post-ischemia, rats treated with lidocaine died before convulsing, while the threshold for PTZ increased by 86%. There was no change in the picrotoxin threshold at 6 h, but the dose of NMDA needed to induce tonic-clonic seizure activity was reduced by 70%. By 48 h, lidocaine and PTZ thresholds had returned to values similar to those in Shams, but the NMDA threshold had now increased to a value 62% greater than Sham. Ten minutes of cerebral ischemia is followed by a complex and changing pattern of susceptibility to chemical convulsants. Finding suggests that early post-ischemic seizures may be related to increased NMDA receptor sensitivity.

Treatment of diving emergencies

Recognition of condition attributable to the environmental changes experienced by divers will facilitate appropriate treatment. The diagnosis of these conditions rarely requires sophisticated imaging or electrophysiologic testing. Divers who have suspected DCI, in addition to general supportive measures, should be administered fluids and oxygen and transported to a recompression chamber. For diving-related conditions, on-line consultation is available from the Divers Alert Network, Durham, NC (919-684-8111).

Cerebral metabolic profile, selective neuron loss, and survival of acute and chronic hyperglycemic rats following cardiac arrest and resuscitation

Cortical metabolites and regional cerebral intracellular pH (pHi) were measured in normoglycemic (NM), acute hyperglycemic (AH), and chronic hyperglycemic (CH, 2 week duration, streptozotocin-induced) Wistar rat brains during cardiac arrest and resuscitation. During total ischemia in AH and CH rats (plasma glucose approximately 30 mM), cortical ATP, PCr, glucose, and glycogen all fell significantly as expected. Lactate levels increased dramatically in association with a concomitant intracellular acidosis. Although lactate reached higher concentrations in AH and CH than NM, pHi was significantly lower only in the AH group. With 5 min of reperfusion, all groups recovered to near baseline in all variables, though lactate remained elevated. In a separate aspect of the study, animals from each experimental group were allowed to recover for 4 days following resuscitation, with outcome being gauged by mortality rate and hippocampal CA1 neuron counts. NM survival rate was significantly better than AH and CH. In particular, no CH rats survived for 4 days despite rapid initial recovery. After 4 days, the AH group had suffered significantly greater CA1 neuron loss than the NM rats. In summary, our research identified differences in intra-ischemic acid-base status in the two hyperglycemic groups, suggesting that chronic hyperglycemia may alter the brain's buffering capacity. These observations may account for differences between acutely and chronically hyperglycemic subjects regarding outcome, and they suggest that factors other than hydrogen ion production during ischemia are responsible for modulating outcome.

Effects of streptozotocin-induced hyperglycemia on brain damage following transient ischemia

Hyperglycemia is known to aggravate ischemic brain damage. The present experiments were undertaken to explore whether hyperglycemia caused by streptozotocin-induced diabetes exacerbates brain damage following transient brain ischemia as it does in animals acutely infused with glucose. Experimental diabetes was induced by injection of streptozotocin in rats which were subjected to 10 min of forebrain ischemia either 1 week (1-wk) or 4 weeks (4-wk) after the induction of diabetes. Normoglycemic rats exposed to the same duration of ischemia and sham-operated diabetic rats served as controls. The animals underwent evaluation of clinical outcome and histopathological analysis of brain damage. Postischemic seizures developed in 35.3 and 42.1% of 1-wk and 4-wk diabetic hyperglycemic animals, respectively. The incidence of seizure was not different between the two groups. None of the diabetic animals with plasma glucose concentrations below 12 mM exhibited seizure activity. The extent and distribution of brain damage were similar between 1-and 4-wk diabetic animals. In the CA1 and in the subicular regions of hippocampus, both diabetic hyperglycemic and normoglycemic animals showed 70-80% cell death. Diabetic hyperglycemic animals had more severe neuronal necrosis in the parietal cortex than normoglycemic animals. In diabetic hyperglycemic animals, neuronal damage involved additional brain structures, e.g., cingulate cortex, thalamus nuclei, substantia nigra, pars reticulata, and the hippocampal CA3 sector, i.e., structures in which neurons were not affected in normoglycemic ischemic subjects at this duration of ischemia. These findings demonstrate that diabetic hyperglycemic animals frequently develop postischemic seizures and that streptozotocin-induced hyperglycemia results exacerbated postischemic brain damage of the same density and distribution as in acutely glucose-infused animals.

The neurologic implications of diabetic hyperglycemia during surgical procedures at increased risk for brain ischemia

The neurologic implications of diabetic hyperglycemia depend on whether the ischemic insult is permanent or temporary. Laboratory studies show that following permanent focal ischemia, a situation analogous to stroke, diabetic hyperglycemia is protective in the penumbral region, whereas it may slightly increase infarct size. In addition, clinical studies cannot unequivocally attribute poor outcome in diabetic stroke patients to hyperglycemia. Thus, both laboratory and clinical studies have been unable to define a cause and effect relationship between diabetic hyperglycemia and neurologic outcome following stroke. On the other hand, diabetic hyperglycemia is an important determinant of neurologic outcome following temporary focal ischemia (analogous to temporary occlusion of a cerebral vessel) and global ischemia (analogous to circulatory arrest). Based on laboratory studies, aggressive insulin-based blood glucose management with the goal of euglycemia is imperative prior to temporary ischemia. However, intraoperative ischemic events are overwhelmingly of a permanent focal nature, and the neurologic implications of diabetic hyperglycemia for the vast majority of surgical procedures at increased risk for brain ischemia are minimal. It is only in circumstances where temporary focal or global ischemia are used as part of the surgical procedure that aggressive insulin-based blood glucose management is warranted.

Phenytoin-induced hyperglycaemia may confound rat cerebroprotection models

1. The anticonvulsant phenytoin (PHT) has been used with variable success in animal models of cerebral ischaemia. Although PHT has been reported to alter glucose regulation in man, this potential effect has been largely ignored in animals. Because hyperglycaemia strongly influences the outcome of cerebral ischaemia, we sought to systematically delineate the effects of PHT on serum glucose in several rat strains. 2. We studied the PHT dose-response curve for serum PHT and glucose concentrations and several physiological variables. Phenytoin induces a significant, concentration-dependent hyperglycaemia, even in the ranges commonly used for humans and in animal models. 3. Hypothermia of several degrees was observed during PHT administration, but no hypotension or bradycardia was found. 4. Both hyperglycaemia and hypothermia must be considered when PHT is studied as a neuroprotective agent in animal models.

Vertebrobasilar thrombosis: diagnosis, management, and the use of intra-arterial thrombolytics

OBJECTIVES

To review the diagnosis and management of vertebrobasilar thrombosis and to discuss the use of thrombolytics in the treatment of this disease.

DATA SOURCES

Selected references discussing epidemiology, anatomy, pathophysiology, diagnosis, therapy, and rehabilitation of vertebrobasilar occlusive disease.

STUDY SELECTION

Studies addressing acute intervention and outcome in the therapy of vertebrobasilar thrombosis were reviewed.

DATA EXTRACTION

Only those studies with angiographic documentation of arterial thrombosis and, in the case of thrombolysis, recanalization, were considered valid.

DATA SYNTHESIS

Thrombosis of the vertebrobasilar system is a highly fatal disease and should be treated as a neurologic emergency. The key to effective management depends on early recognition of the symptom complex and a thorough understanding of the anatomy and pathophysiology of the disease process.

CONCLUSIONS

A timely, integrated, multidisciplinary approach to the patient with vertebrobasilar thrombosis can improve outcome. The use of thrombolytics in the treatment of vertebrobasilar occlusion holds promise but the benefits have not yet been proven in a controlled, randomized study.

Glucose modulation of ischemic brain injury: review and clinical recommendations

Ischemic brain injury is the third-leading cause of death among Americans and the leading cause of serious disability. Based on studies of animal models, a substantial amount of experimental evidence shows that hyperglycemia at the onset of brain ischemia worsens postischemic neurologic outcome. Consistent with these observations, hyperglycemia also is associated with a worsening of postischemic brain injury in humans. In humans, however, data are often difficult to interpret because of problems in determining the timing of hyperglycemia relative to a critical ischemic event and in elucidating the effect of coexisting pathophysiologic processes (for example, a stress response) on outcome. Glucose modulation of neurologic injury is observed when ischemia is either global (for example, that accompanying cardiac arrest or severe systemic hypotension) or focal (for example, that accompanying thrombotic or embolic stroke). Toxicity is probably the result of an intracellular lactic acidosis. Specifically, the associated hydrogen ions are injurious to neurons and glia. On the basis of these factors, we recommend diligent monitoring of blood glucose concentrations in patients who are at increased risk for new-onset, ongoing, or recurring cerebral ischemia. In such patients, the use of fluid infusions, corticosteroid drugs, and insulin, as well as stress management, should be tailored to treat preexisting hyperglycemia and prevent new-onset hyperglycemia. Maintenance of normoglycemia is recommended. When one attempts to treat preexisting hyperglycemia, care should be taken to avoid rapid fluid shifts, electrolyte abnormalities, and hypoglycemia, all of which can be detrimental to the brain.

Cerebrovascular disorders in patients with diabetes mellitus

Diabetes mellitus is a risk factor for ischemic, but not hemorrhagic stroke. The frequency of transient ischemic attacks is not increased in patients with diabetes compared to the general population. Diabetes mellitus is associated with higher mortality, worse functional outcome, more severe disability after stroke and a higher frequency of recurrent stroke. Diabetes is not associated with an increased size of cerebral infarction. Controversy exists regarding whether hyperglycemia adversely affects stroke outcome or primarily reflects stroke severity. Cerebral blood flow disturbances, impaired cerebrovascular reactivity, and damage to large and small extra- and intracranial cerebral vessels have been found in humans and animals with diabetes. Combinations of some or all of these factors may underlie the high incidence and worse outcome of stroke in patients with diabetes. Knowledge of these pathophysiologic factors will assist in the design of future intervention strategies.

Audiogenic seizures following global ischemia induced by chest compression in Long-Evans rats

Transient global ischemia was used to produce a rat model of generalized tonic-clonic epilepsy. Controlled chest compression in ketamine-anesthesized Long-Evans rats produced transient global ischemia by mechanically preventing the heart from pumping blood. Circulation was restored by standard cardiopulmonary resuscitation techniques. With a temporal muscle (skull) temperature of 35 +/- 0.4 degrees C, 75% (76/102) of the rats survived 7 min of chest compression. Generalized seizures could be evoked in 78% (59/76) of the surviving rats by a 60 s exposure to a loud sound (bell, 110 dB) beginning 24 h after the ischemic episode. The seizure patterns seen resembled those described by Maresceaux (1987) for genetically seizure-prone Wistar rats. Susceptibility to sound-induced seizures declined with time, with wide variations in recovery rate between individuals; one rat showed a daily sound-induced seizure for over 5 months. Seizures were attenuated or blocked by treatment with carbamazepine or sodium valproate. This model is similar to the great vessel occlusion model used by Kawai et al. (1995), but is less invasive. We believe it will be useful in the evaluation of therapies for acquired generalized (grand mal) seizures.

Glucose regulation and cognitive functions: relation to Alzheimer's disease and diabetes

Glucose has been found to improve memory in animals and humans. Animal research has revealed that glucose may improve memory through a facilitation of acetylcholine (ACh) synthesis and release in the brain. This glucose-related memory improvement has prompted research in elderly humans. These studies have shown that the memory-improving action of glucose depends on each individuals' blood glucose regulation. Based on these data, researchers have evaluated the effect of glucose on memory in patients with Alzheimer's disease (AD). Results demonstrated that glucose could improve memory in a subset of patients that had abnormalities in their blood glucose regulation. Interestingly, these alterations in blood glucose regulation were believed to depend on the severity of the disease process. Another line of investigation has focused on alterations in brain glucose metabolism. Both animal models and studies with Type II diabetic elderly patients have shown that altered glucose regulation impairs learning and memory processes. It is possible that in AD patients, hyperglycemia exerts a deleterious effect by potentiating the neuronal death produced by other pathological processes taking place such as amyloid deposition. Based on these data, it appears important to find the prevalence of altered glucoregulation at various stages of AD. Secondly, it may be of interest to determine prospectively whether altered glucoregulation is linked to a faster progression of the disease. Finally, if such a relationship is observed, the next logical step would be to determine whether AD patients could benefit from treatments aimed at normalizing blood glucose regulation and improving insulin sensitivity.

Con: glucose priming solutions should not be used for cardiopulmonary bypass

In conclusion, the advantage of glucose-containing CPB priming solutions are quite modest. In contrast, the weight of current evidence strongly supports the notion that hyperglycemia is far more likely to be detrimental than beneficial to a brain challenged by ischemia, especially when there is reperfusion (hypotension or circulatory arrest) or when the brain is normothermic. Because neurologic complications pose such a serious threat to cardiac surgery patients, avoidance of hyperglycemia during surgery and CPB seems prudent at this time. Hence, CPB priming solutions should not contain glucose.

The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders

For some considerable time, there has been a growing awareness that defective essential fatty acid metabolism plays a causal role in the pathogenesis of both schizophrenia and non-insulin-dependent diabetes mellitus (NIDDM) but the influence of defective essential fatty acid metabolism in the pathogenesis of rheumatoid arthritis and cancer is less well appreciated. An EFA deficiency, or defective EFA metabolism, negatively influences prostaglandin synthesis and glucose regulation and transport. Moreover, defective EFA metabolism negatively influences estrogen availability which contributes to the observed gender bias some of these illnesses manifest. While fluctuations of estrogen are known to contribute to the pathogenesis of these conditions, so also do fluctuations of IGF-II and there is some suggestion that IGF-II and insulin may well be inversely regulated. In addition, insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, and schizophrenia are thought to be autoimmune disorders, while cancer is associated with immune system failure. Consequently, this paper aims to examine the pathophysiological similarities and differences between mental illness, diabetes, rheumatoid arthritis and cancer in respect of which the causal relationship that obtains between essential fatty acids, estrogen, IGF-II, glucose regulation and autoimmunity will be addressed.

Poor hemodynamic and metabolic recovery after global incomplete cerebral ischemia associated with short-term diabetes in dogs

We determined the effect of 4-5 weeks of diabetes on ATP recovery following global incomplete cerebral ischemia. 31P magnetic resonance spectra of ATP, intracellular pH (pHi), and CBF (radiolabeled microspheres) were measured in three groups of anesthetized dogs (n = 8/group): chronic hyperglycemic diabetes (pancreatectomy followed by blood glucose of > 10 mM for 4-5 weeks); acute hyperglycemia (blood glucose of > 10 mM) during ischemia and reperfusion in nondiabetic dogs; and normoglycemic controls. Twenty minutes of incomplete ischemia was produced by ventricular fluid infusion to keep cerebral perfusion pressure (CPP) at 10 mm Hg during spontaneous variations in MABP. Intracranial pressure was increased initially to similar levels, resulting in a similar Cushing response among the groups. However, during the final 8 min of ischemia, MABP decreased to a greater extent in diabetic (86 +/- 42 mm Hg) than in hyperglycemic (162 +/- 30 mm Hg) and normoglycemic (135 +/- 54 mm Hg) groups and remained lower throughout 3 h of reperfusion. CPP was kept constant during ischemia, but was lower throughout reperfusion in diabetic dogs. During ischemia CBF was reduced similarly among groups: 5 +/- 3 ml.min-1 x 100 g-1 in hyperglycemic and normoglycemic and 4 +/- 3 ml.min-1 x 100 g-1 in diabetic dogs. During reperfusion early hyperemia was attenuated and delayed hypoperfusion was augmented (7 +/- 17 ml.min-1 x 100 g-1 by 180 min) as a result of low perfusion pressure in diabetics. However, medullary blood flow was similar among groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraventricular administration of insulin and IGF-1 in transient forebrain ischemia

A beneficial effect of insulin in reducing cerebral ischemic damage has been recently demonstrated, and a direct central mechanism of insulin action in cerebral ischemia has been proposed. To test the hypothesis that one of the neuroprotective mechanisms of insulin action involves a direct interaction with CNS tissue via a growth factor effect, a continuous intraventricular infusion of two doses of insulin and of insulin-like growth factor 1 (IGF-1) was given to fed Wistar rats subjected to 10 min, 15 s of transient forebrain ischemia. Quantitative neuropathology after 1-week survival showed that low-dose insulin (7 IU/rat/day; n = 10) reduced selective necrosis in the striatum (p = 0.015) and one level of the hippocampus (p = 0.023) as compared with animals infused with phosphate-buffered saline (200 microliters/rat/day; n = 8). IGF-1 (50 micrograms/rat/day; n = 8) significantly ameliorated hippocampal damage in four of the six hippocampal levels (p < 0.05). High-dose insulin infusion (23 IU/rat/day; n = 8) produced a robust reduction in cortical (p = 0.0108), striatal (p = 0.003), and hippocampal (p < 0.05) necrosis at all coronal levels. However, this high-dose insulin reduced the blood sugar significantly (p < 0.01), from 11.8 to 7.8 mM, probably by virtue of centrally administered insulin reaching the periphery. We conclude that insulin and IGF-1 offer a moderate, centrally mediated, neuroprotective effect, likely mediated at least in part via a growth factor mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)