Two-hour Occlusion Research Articles

Preventing Hypertension After Ischemic Stroke In The Spontaneously Hypertensive Rat

Over 80% of patients show a transient increase in blood pressure (BP) after ischemic stroke, regardless of their previous blood pressure level. However, whether this increased pressure is necessary to enhance or maintain oxygenation of penumbra tissues remains uncertain. We aimed to determine the impact of treating post‐stroke hypertension in the spontaneously hypertensive (SH) rat model of ischemic stroke.Male SH rats (374±9 g) were instrumented to allow the long‐term recording of BP, intracranial pressure (ICP) and brain tissue oxygen in the penumbra (pO2) via telemetry. After recording a 3‐day baseline on Day 0 an ischemic stroke was induced via a two‐hour occlusion of the middle cerebral artery (MCAo). BP was either Untreated (n= 6) or Treated (n=6) and controlled to baseline levels with the clinically‐indicated adrenergic antagonist, labetalol (0.25 mg/kg/hr sc via osmotic pump). Behavioural testing and neurological scoring (SHIRPA score) were performed on Days 1, 3, 7 and 10 to evaluate the functional recovery from stroke over time, and postmortem stroke infarct size assessed by histology on Day 10.Following a stroke, BP increased rapidly in Untreated SH rats, reaching a peak of 35±3 mmHg above baseline within 24 hours. Treatment with labetalol significantly reduced BP on D0 and D1 (p<0.05), which in combination with a small increase in ICP (3±0.8 mmHg in Untreated; 0.4±0.3 mmHg in Treated; p=0.047) on D0 resulted in a lower cerebral perfusion pressure (CPP=MAP‐ICP) in Treated animals. Penumbra tissue oxygen levels were not reduced with labetalol treatment, with a small but significant elevation in pO2 seen in the treated animals in the 24 hours after stroke. Treated and Untreated rats showed a similar impairment after stroke in terms of neurological score, functional outcome and infarct volume (274±26 mm3 vs Untreated 256±11 mm3).Treating post‐stroke hypertension does not appear to have a major impact on the functional recovery from stroke in rats with pre‐existing hypertension. Future studies will examine the impact of blood pressure lowering in rats already receiving treatment for pre‐existing hypertension, and of treatment to normotensive BP levels in SH rats to mimic the clinical situation of ‘undiagnosed pre‐existing hypertension’.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Epac2-deficiency leads to more severe retinal swelling, glial reactivity and oxidative stress in transient middle cerebral artery occlusion induced ischemic retinopathy.

Ischemia occurs in diabetic retinopathy with neuronal loss, edema, glial cell reactivity and oxidative stress. Epacs, consisting of Epac1 and Epac2, are cAMP mediators playing important roles in maintenance of endothelial barrier and neuronal functions. To investigate the roles of Epacs in the pathogenesis of ischemic retinopathy, transient middle cerebral artery occlusion (tMCAO) was performed on Epac1-deficient (Epac1 (-/-)) mice, Epac2-deficient (Epac2 (-/-)) mice, and their wild type counterparts (Epac1 (+/+) and Epac2 (+/+)). Two-hour occlusion and 22-hour reperfusion were conducted to induce ischemia/reperfusion injury to the retina. After tMCAO, the contralateral retinae displayed similar morphology between different genotypes. Neuronal loss, retinal edema and increase in immunoreactivity for aquaporin 4 (AQP4), glial fibrillary acidic protein (GFAP), peroxiredoxin 6 (Prx6) were observed in ipsilateral retinae. Epac2 (-/-) ipsilateral retinae showed more neuronal loss in retinal ganglion cell layer, increased retinal thickness and stronger immunostaining of AQP4, GFAP, and Prx6 than those of Epac2 (+/+). However, Epac1 (-/-) ipsilateral retinae displayed similar pathology as those in Epac1 (+/+) mice. Our observations suggest that Epac2-deficiency led to more severe ischemic retinopathy after retinal ischemia/reperfusion injury.

Tanshinone IIA attenuates the cerebral ischemic injury-induced increase in levels of GFAP and of caspases-3 and -8

Tanshinone IIA (TSA) is a lipid soluble agent derived from the root of Salvia miltiorrhiza (Danshen). This plant is a traditional Chinese herb, which has been used widely in China especially for enhancing circulation. However mechanisms underlying its efficacy remain poorly understood. The present study was designed to illuminate events that may underlie the apparently neuroprotective effects of TSA following ischemic insult. Adult Sprague–Dawley rats were subjected to transient focal cerebral ischemia by use of a middle cerebral artery occlusion model. They were then randomly divided into a sham-operated control group, and cerebral ischemia/reperfusion groups receiving a two-hour occlusion. Further subsets of groups received the same durations of occlusion or were sham-operated but then received daily i.p. injections of high or low doses of TSA, for seven or 15days. Hematoxylin and eosin staining revealed lesions in the entorhinal cortex of both rats subject to ischemia and to a lesser extent to those receiving TSA after surgery. Levels of glial fibrillary acidic protein (GFAP), caspase-3 and caspase-8, were quantified by both immunohistochemistry and Western blotting. TSA treatment after middle cerebral artery occlusion, markedly reduced infarct size, and reduced the expression of caspase-3 and caspase-8. These changes were considered protective and were generally proportional to the dose of TSA used. These results suggest that TSA may effect neuroprotection by way of reduction of the extent of cell inflammation and death within affected regions.

Selective Over-Expression of Endothelin-1 in Endothelial Cells Exacerbates Inner Retinal Edema and Neuronal Death in Ischemic Retina

The level of endothelin-1 (ET-1), a potent vasoconstrictor, was associated with retinopathy under ischemia. The effects of endothelial endothelin-1 (ET-1) over-expression in a transgenic mouse model using Tie-1 promoter (TET-1 mice) on pathophysiological changes of retinal ischemia were investigated by intraluminal insertion of a microfilament up to middle cerebral artery (MCA) to transiently block the ophthalmic artery. Two-hour occlusion and twenty-two-hour reperfusion were performed in homozygous (Hm) TET-1 mice and their non-transgenic (NTg) littermates. Presence of pyknotic nuclei in ganglion cell layer (GCL) was investigated in paraffin sections of ipsilateral (ischemic) and contralateral (non-ischemic) retinae, followed by measurement of the thickness of inner retinal layer. Moreover, immunocytochemistry of glial fibrillary acidic protein (GFAP), glutamine synthetase (GS) and aquaporin-4 (AQP4) peptides on retinal sections were performed to study glial cell reactivity, glutamate metabolism and water accumulation, respectively after retinal ischemia. Similar morphology was observed in the contralateral retinae of NTg and Hm TET-1 mice, whereas ipsilateral retina of NTg mice showed slight structural and cellular changes compared with the corresponding contralateral retina. Ipsilateral retinae of Hm TET-1 mice showed more significant changes when compared with ipsilateral retina of NTg mice, including more prominent cell death in GCL characterized by the presence of pyknotic nuclei, elevated GS immunoreactivity in Müller cell bodies and processes, increased AQP-4 immunoreactivity in Müller cell processes, and increased inner retinal thickness. Thus, over-expression of endothelial ET-1 in TET-1 mice may contribute to increased glutamate-induced neurotoxicity on neuronal cells and water accumulation in inner retina leading to edema.

Factors Affecting Compliance to Two-Hour Versus Six-Hour Occlusion Therapy Regimens for Treatment of Strabismic Amblyopia

Purpose: To compare the effect of daily occlusion of the sound eye for two hours, without and with near vision exercises, versus six hours without near vision exercises, for the management of strabismic amblyopia and to determine the different factors affecting compliance to each treatment regimen. Methods: Forty five children having unilateral strabismic amblyopia were divided equally into 3 groups. Group A received 2-hour daily occlusion. Group B received 2-hour occlusion combined with near vision exercises. Group C received 6-hour occlusion therapy. Patients were followed up for 6 months. Results: The mean logMAR improvement was -1.03+/-0.57, -0.63+/-0.66 and -0.65+/-0.66, for groups A, B and C, respectively. The difference in mean logMAR improvement was significant (P < .001) in groups A versus B and A versus C, but was insignificant (P =.748) in group B versus C. Factors affecting compliance to each occlusion regimen were related to age, socioeconomic status, life pattern and season of the year.Conclusion: The best outcome was achieved when 2-hour daily patching was combined with near vision activities. Higher compliance to two-hour occlusion with near vision exercises was attained in older, educated children. Six-hour occlusion was more suitable in younger and in uneducated children.

Similar long-term cardiovascular effects of propofol or isoflurane anesthesia during ischemia/ reperfusion in dogs.

To compare the long-term functional and metabolic effects of propofol or isoflurane general anesthesia in a canine model of ischemia/reperfusion. Using magnetic resonance (MR) techniques, we monitored both regional metabolism ((31)P MR spectroscopy) and systolic function of the heart ((1)H MR imaging) throughout a two-hour occlusion of the left anterior descending coronary artery and ten days of reperfusion. Twenty-two beagles were randomized into isoflurane and propofol general anesthesia groups (n = 10, n = 12 respectively). Contrast-enhanced MR imaging was used to measure infarct size (% of left ventricle that was necrotic) and coronary blood flow was determined using radioactively labelled microspheres. Cardiac metabolism, as monitored by intracellular pH and high-energy phosphate ratios, was not significantly different between the two groups throughout the protocol. Relative to propofol, isoflurane reduced the depression of left ventricular ejection fraction (EF) during the ischemic period [isoflurane 68.5% +/- 4.2%, propofol 58.3% +/- 2.0% of baseline (B); P = 0.04], propofol increased the recovery of EF at day three (isoflurane 63.9% +/- 4.3%, propofol 74.0% +/- 2.5% of B; P = 0.05). By day ten, EF in both groups was similar. Infarct sizes were also similar at day ten (isoflurane 15.7% +/- 3.0%, propofol 13.2% +/- 2.2%). Normalizing these by the region at risk (volume of tissue with low blood flow during the occlusion) to assess infarct ratios was also not significant (isoflurane 0.58% +/- 0.08%, propofol 0.54% +/- 0.07%). There were no significant differences between the two anesthetic groups at day ten, suggesting that any apparent dissimilarities in early cardiovascular effects were short-term only. These results indicate that isoflurane and propofol produce equivalent long-term cardiovascular effects following ischemia/reperfusion.

EX-VIVO LIVER PERFUSION SYSTEM FOR HEPATIC FAILURE PENDING LIVER REGENERATION OR LIVER TRANSPLANTATION

215 There is a well recognised need for a system capable of providing effective support for patients with hepatic failure pending liver regeneration or liver transplantation. Recent attempts of using bioartificial liver containing capsulated porcine hepatocytes, the practice of emergency whole liver or hepatocyte transplantation are complex and not consistently successful. The technique of ex-vivo hepatic perfusion developed and used clinically by Abouna in the 1970s, has now been redesigned in a perfusion circuitry which mimics the physiological conditions of a normal liver. Prior to clinical application of this system, a preclinical trial was carried out in dogs with induced hepatic failure. Methods: Acute hepatic failure was induced in dogs by an end-to-side portacaval shunt followed 24 hours later, by a two-hour occlusion of the hepatic and gastroduodenal arteries. All animals (n=20) were medically supported and were divided into two groups. In the control group (n=6), only medical support was used. In the experimental group (n=14), the animals were connected to the ex-vivo liver support apparatus during acute hepatic failure via an AV shunt using a dog liver (n=6) or calf liver (n=8). In the latter group, a temporary extracorporeal bovine kidney transplant was first carried out for one hour prior to liver perfusion to remove preformed xeno antibody. Hepatic perfusion was carried out at 37°C through the hepatic artery and portal vein at physiologic pressures and blood flow rate for 6-8 hours. Results: All control animals died in hepatic failure at 14-19 hours after clamping of the hepatic artery. The animals treated with ex-vivo liver showed remarkable clinical and biochemical improvement. Six animals survived for 36-60 hours and another eight recovered completely and became long-term survivors with biochemical and histological evidence of regeneration of their own liver. Biopsy of ex-vivo allogeneic livers at end of perfusion showed some interstitial edema. Biopsy of exenogeneic calf livers showed only mild and delayed xenograft rejection as a result of significant reduction of preformed xeno antibody (from 1:512 to 1:4) following temporary transplantation of the calf kidney prior to liver perfusion. Conclusions: The observations and results obtained in this trial strongly confirm that extracorporeal perfusion through a whole liver, using the system described, is very successful and cost effective for the treatment of acute, but reversible hepatic failure, as well as serving as a bridge to liver transplantation. The time has come for this form of liver support technology to be reintroduced and widely used.

An Evaluation of Streptokinase Therapy in Early Coronary Reperfusion in a Primate Model

Efficacy of streptokinase (SK) administered beyond the period of coronary occlusion with regard to ultimate infarct size and the extent of hemorrhagic infarction was assessed in primates. Eleven macaques underwent coronary occlusion for two hours and were then reperfused. Five of them were given a 2,000 U IV bolus of SK followed by a 10,000 U IV infusion over ninety minutes. The remaining 6 served as controls. Macaques were sacrificed seven days postocclusion. The left ventricle was sectioned parallel to the minor axis, and these were examined histologically for infarct size and hemorrhage. Multiplying the planimetric values by the thickness of the sections yielded the total volumes of left ventricle, infarction, and hemorrhage. The mean percentage of left ventricle involved in infarction in the treated group was not significantly different from the controls (14.06 +/- 6.35 versus 16.50 +/- 4.67, P > 0.10). SK-treated animals had a significantly greater volume of infarct involved with hemorrhage as compared with controls (27.1 +/- 10.8 versus 4.0 +/- 1.4, P < 0.05). SK infusions done concurrently with reperfusion following a two-hour occlusion did not result in a significant reduction or increase in the size of infarct. However, SK infusions resulted in a significant increase in the amount of hemorrhagic infarction.

Free Radicals in Reperfusion Injury After Acute Aortic Occlusion

This investigation aims to evaluate the role of free radicals and the influence of radical scavengers in reperfusion injury of the skeletal muscle in male Wistar rats. Various parameters, including tissue blood flow, serum and calf muscle tissue levels of thiobarbituric acid (TBA) reactants, and the water content of calf muscles, were measured in the experimental setting, where infrarenal abdominal aorta was occluded for two hours followed by reperfusion with and without intraperitoneal administration of radical scavengers (superoxide dismutase or catalase). The rats were divided into four groups: group A: single laparotomy; group B: two-hour occlusion; group C: two-hour occlusion with superoxide dismutase; group D: two-hour occlusion with catalase. The increases in both serum and calf muscle tissue levels of TBA reactants following reperfusion were diminished in groups C and D as compared with those in group B. The water content of calf muscles showed a significant increase after reperfusion in group B, whereas it did not change in group D. The calf muscle tissue blood flow after reperfusion was significantly lower in group C than that in group B. These results indicate that oxygen-derived free radicals may be responsible for reperfusion injury in the lower extremity and that the attenuated blood flow during reperfusion produced by these scavengers seems to play an important role in reducing lipid peroxidation . In a clinical setting, limiting the rate of reperfusion blood flow may reduce the reperfusion injury in skeletal muscle.

The effects of a high dose of ascorbate on ischemia-reperfusion-induced mitochondrial dysfunction in canine hearts.

The cardioprotective effects of a high dose of ascorbate on ischemia-reperfusion-induced myocardial damage were investigated using open chest anesthetized dogs. Two-hour occlusion of the left anterior descending coronary artery (LAD) induced mitochondrial dysfunction with a depletion of mitochondrial glutathione (GSH) concentration. Two-hour LAD occlusion followed by 1-h reperfusion worsened the ischemia-induced mitochondrial dysfunction together with a marked depletion of mitochondrial GSH concentration. Ascorbate reduced the mitochondrial dysfunction and prevented the depletion of mitochondrial GSH concentration after 2-h LAD occlusion and 1-h reperfusion. Activities of mitochondrial glutathione peroxidase and glutathione reductase did not change significantly in each group. Administration of ascorbate also prevented reperfusion arrhythmias without affecting blood pressure or heart rate. These results suggest that coronary reperfusion induces mitochondrial dysfunction and a depletion of mitochondrial GSH concentration, and that a high dose of ascorbate prevents reperfusion damage.