Beginning Of Occlusion Research Articles

A likely protective effect of dimethyl itaconate on cerebral ischemia/reperfusion injury

As a membrane-permeable derivative of itaconate, dimethyl itaconate (DMI) was recently showed to limit inflammatory response of activated macrophages, and to decrease the generation of reactive oxygen species and reduce cardiac ischemia/reperfusion injury. However, the effect of DMI in the context of cerebral ischemia/reperfusion injury remains unclear. Here, we treated the transient middle cerebral artery occlusion (tMCAO) mice with DMI or saline at the beginning of occlusion, and allowed them to recover for 3 days. We found that DMI obviously decreased the neurologic deficit score. Further, DMI significantly inhibited the toxic conversion of the peri-infarct microglia, and decreased the protein level of interleukin 1β. The present findings suggest that DMI might be recognized as a promising candidate for the treatment of ischemic stroke.

Non-invasive detecting human tissue hemoglobin concentrations using near-infrared spectroscopy with in vivo calibration

Human tissue oxygenation status can be completely indicated by its hemoglobin concentrations. To detect them non-invasively using continuous-wave near infrared spectroscopy (NIRS), the ‘in vivo calibration’ algorithm, which was comparing tissue absorption before and after the change of tissue oxygenation, was adopted to obtain its reduced scattering coefficient. The hemoglobin concentrations of forearm muscle of four adults during occlusion, and those of brain cortex of three newborns during oxygen inhalation were detected. For the four adults, the of the forearm muscle were 6.01~7.87 cm–1 under 758 nm, and its total hemoglobin concentration (CtHb) was 37.5 ± 3.1 μM at the beginning of occlusion. For the three newborns, the cerebral were 5.46~8.42 cm–1 under 758 nm, and CtHb was 50.1 ± 6.1 μM at the beginning of oxygen inhalation. All the results were consistent with most recent reports. In summary, the in vivo calibration algorithm is effective to detect human tissue hemoglobin concentrations.

Detrimental Effects of 60 kHz Sonothrombolysis in Rats with Middle Cerebral Artery Occlusion

Recent studies have raised concerns about the safety of low frequency ultrasound in transcranial therapeutic application in cerebral ischemia. This study was designed to evaluate safety aspects and potential deleterious effects of low frequency, 60 kHz ultrasound in treatment of experimental middle cerebral artery occlusion (MCAO) in rats. Forty-five male Wistar rats were submitted to either temporary (90 min; groups I and II) or permanent MCAO (groups III and IV) using the suture technique. All animals received recombinant tissue plasminogen activator (rt-PA) starting 90 min after the beginning of occlusion. Groups I and III were additionally treated with 60 kHz ultrasound (time average acoustic intensity 0.14 W/cm 2, duty cycle 50%). Outcome assessment consisted of magnetic resonance imaging (MRI) and clinical evaluation after 5 and 24 h, and histology (perfusion fixation after 24 h). Overall mortality was higher in animals treated with ultrasound (43% versus 29% in controls). Most animals died during the insonation period (25% in group I, 36% in group III, no animals in the corresponding control groups; p < 0.05). Histology revealed disseminated microscopic intracerebral bleeding and subarachnoid hemorrhage as one possible cause of death. After temporary occlusion, the hemispheric ischemic lesion volume was more than doubled in animals treated with ultrasound (20.3% ± 14.1% versus 8.6% ± 5.1% in controls; p < 0.05). No difference in lesion volume was seen after permanent MCAO. Neurological assessment showed impairment of hearing as an additional specific side effect in ultrasound treated animals (65%, no impairment in controls). Although the results are not directly transferable to the human setting, this study clearly demonstrates the potential limitations of low frequency therapeutic ultrasound and the importance of pre-clinical safety assessment. (E-mail: max.nedelmann@neuro.med.uni-giessen.de)

S-Adenosyl-L-Methionine Ameliorates Ischemic Brain Metabolism in Spontaneously Hypertensive Rats

Effects of S-adenosyl-L-methionine (SAM) on the metabolism in ischemic brain were investigated. The ischemic model employed was an incomplete cerebral ischemia of the spontaneously hypertensive rat (SHR) produced by the occlusion of both common carotid arteries. One hundred mg/kg of SAM was administered (i.p.) 6 times from the beginning of occlusion at 30 min intervals. At 3 hr after the onset of occlusion, animals were killed by microwave irradiation and creatine phosphate (CrP), ATP, glucose, lactate and γ-aminobutyric acid (GABA) contents in the brain were measured. SAM significantly mitigated both the reductions in CrP, ATP and glucose levels and the increase in GABA level due to the cerebral ischemia. In another set of experiments with the same experimental schedule, water content in the brain was examined. SAM significantly suppressed the increase in water content due to the cerebral ischemia. These results indicate ameliorating effects of SAM on the metabolism in ischemic brain.

S-adenosyl-L-methionine ameliorates ischemic brain metabolism in spontaneously hypertensive rats.

Effects of S-adenosyl-L-methionine (SAM) on the metabolism in ischemic brain were investigated. The ischemic model employed was an incomplete cerebral ischemia of the spontaneously hypertensive rat (SHR) produced by the occlusion of both common carotid arteries. One hundred mg/kg of SAM was administered (i.p.) 6 times from the beginning of occlusion at 30 min intervals. At 3 hr after the onset of occlusion, animals were killed by microwave irradiation and creatine phosphate (CrP), ATP, glucose, lactate and gamma-aminobutyric acid (GABA) contents in the brain were measured. SAM significantly mitigated both the reductions in CrP, ATP and glucose levels and the increase in GABA level due to the cerebral ischemia. In another set of experiments with the same experimental schedule, water content in the brain was examined. SAM significantly suppressed the increase in water content due to the cerebral ischemia. These results indicate ameliorating effects of SAM on the metabolism in ischemic brain.

Inotropic Response of the Salvaged Myocardium after Acute Coronary Occlusion

We determined the response of the reperfused myocardium to inotropic stimulation with dobutamine hydrochloride. The middle part of the left anterior descending coronary artery (LAD) was occluded in 15 greyhounds for 3 hours. Group 1 (N = 8) was reperfused for 3 hours in the beating, working heart. Group 2 ( N = 7) was put on cardiopulmonary bypass (CPB) for 1 hour, received 500 ml of potassium cardioplegia in the aortic root and in the area of ischemia through an internal mammary–LAD graft, and the LAD was reperfused off CPB for 3 hours. After 3 hours of reperfusion, dobutamine was given at 10 μg/kg/min for 20 minutes. Regional myocardial function was determined with subendocardial ultrasonic crystals in the area of ischemia and in the base of the heart; segmental contractility was determined from the ratio of peak left ventricular pressure to end-systolic segment length; and global contractility was determined by the slope of the ventricular pressure wave at a developed pressure of 40 mm Hg. Measurements were made prior to LAD occlusion (control), at the end of 3 hours of reperfusion (6 hours from the beginning of occlusion), and after 20 minutes of dobutamine infusion. Dobutamine infusion improved segmental function in all animals compared with 3 hours of reperfusion. The study shows that the reperfused myocardium responds favorably to inotropic stimulation after 3 hours of occlusion and 3 hours of reperfusion, and that the contractile response both to reperfusion and to inotropic stimulation is greatly affected by the method of reperfusion.

Very weak luminescence of blood plasma in experimental embolism of the main limb arteries

Changes in the level of chemiluminescence of the blood plasma, initiated by hydrogen peroxide and bivalent iron, were studied in 15 dogs with experimental embolism of the bifurcation of the aorta. After occlusion of the artery the level of chemiluminescence initiated by iron fell. Meanwhile, the level of chemiluminescence initiated by hydrogen peroxide rose to reach a maximum 6 h after the beginning of occlusion, followed by a tendency to fall. A statistically significant increase in luminescence initiated by hydrogen peroxide can be used to judge the duration of the disease. After restoration of the blood flow to the limb there was a decrease in chemiluminescence initiated by hydrogen peroxide together with a further decrease in chemiluminescence initiated by iron.

Effect of reperfusion on myocardial infarct, and the accuracy of estimating infarct size from serum creatine phosphokinase in the dog.

This study was designed to determine the effect of coronary reperfusion on (1) myocardial infarct size and (2) the accuracy of previously reported methods for estimation of infarct size serum creatine phosphokinase (CPK) values. Thirty mongrel dogs, chronically prepared, were studied in the awake state, and were divided into four groups according to the period or left circumflex coronary artery (LCCA) occlusion. Group 1: permanent occlusion (24 h) in nine dogs; group 2: 45 min occlusion (eight dogs); group 3: 1 h occlusion (five dogs); and group 4: 3 h occlusion (eight dogs). Serial blood samples were drawn for 24 h following the beginning of occlusion and were used to determine total and isoenzyme levels of CPK, and lactic dehydrogenase isoenzymes. All dogs were sacrified 24 h after the beginning of occlusion and were anatomically examined. The extent of anatomical myocardial infarction was determined and compared with the extent of myocardial infarction as estimated from serial serum CPK values. Total serum CPK increased significantly in all groups and was associated with the appearance of CPK-MB isoenzyme and an increase in LDH1,2 (LDH1 greater than LDH2) in most dogs. Total serum CPK increased within an hour after reperfusion and the mean values in groups 2, 3, and 4 were significantly high (P less than 0.05) than serum CPK values in group 1 in the period from 110 min to 4 after occlusion. These data demonstrate that reperfusion after 45 min to 3 h of coronary occlusion results in an earlier appearance of total serum CPK. The anatomical infarction in group 1 averaged 28% +/- 3% (SEM) of the total heart and was significantly larger than infarct size in all groups with reperfusion. In contrast, estimated infarction calculated from total CPK in group 1 was not significantly different from the reperfused groups. Although there was correlation between estimated and anatomical infarction, the data in each group showed that anatomical infarct size could not be accurately estimated from total serum CPK.

THE RESUSCITATION OF THE CENTRAL NERVOUS SYSTEM OF MAMMALS

The cerebral circulation was interrupted for periods of three to eighty-one minutes by ligation of the innominate and left subclavian arteries proximal to the origin of the vertebral, in ninety-three cats. Eleven dogs were used in the earlier experiments. The eye reflexes disappear very quickly and a period of high blood pressure follows the occlusion immediately; vagus inhibition causes cardiac slowing and a fall in blood pressure, followed by a second rise after the vagus center succumbs to anaemia. Respiration stops temporarily (twenty to sixty seconds) after the beginning of occlusion, and then follows a series of strong gasps of the Cheyne-Stokes type, after which it stops until some time after the restoration of the cerebral circulation. The respiratory and vagus centers lose their power of functioning at approximately the same time. Asphyxial slowing of the heart may occur without the agency of the vagus center. The blood pressure slowly falls to a level which is maintained throughout the remainder of the period of occlusion. The anterior part of the cord and the encephalon lose all function; no reflexes are obtainable. The reflexes of the posterior part of the cord persist; the intravenous injection of strychnine does not affect the anterior part of the cord during the period of occlusion; but does affect the posterior portion of the cord. There is no secretion of tears or saliva, and the intra-ocular pressure is reduced. The blood pressure falls still more after release of the cerebra arteries, but soon begins to rise. The respiration returns suddenly, two to sixty minutes after restoration of the cerebral circulation, the first gasp being a strong one. The rate gradually increases until rapid enough for natural respiration. The eye reflexes and intra-ocular tension return more gradually, ten minutes to three hours after restoration of the cerebral circulation. The anterior part of the cord recovers its functions gradually. The first reflexes occur only on the same side as the stimulus, crossing of reflexes, to involve the other side, not occurring till later. As a rule, all reflexes return, and a short period of quiet follows. The anterior part of the cord again becomes irritable to strychnine, but succumbs to its action before the normal part. Spasms, of tonic, clonic, or mixed type, then appear, terminating in (a) death, (b) partial or (c) complete recovery. In partial recovery, disturbances of locomotion, such as walking in a circle, paralysis, dementia, loss of sight, hearing, and general intelligence, characterize the post-convulsive period. After complete recovery, there is a return to normal deportment. No gross lesions of the nervous system, other than a congested appearance of the previously anaemic area, were observed. Transection of the spinal cord stops the spasms below the level of section. Hemisection of the cord stops the spasms on the same side, below the level of section. Death, without any return of the reflexes after release of the cerebral arteries, has followed an occlusion of seven and one-half minutes. Respiration has returned after an occlusion of one hour. Five animals have recovered completely after an occlusion of seven minutes or more. Only one animal has recovered completely after an occlusion of fifteen minutes. No animal has recovered completely after an occlusion of twenty minutes. In Herzen's (26) resuscitation of an animal after several hours of cerebral anaemia, there must have been some anastomotic channels to the brain. Mayer's (27) limit of ten to fifteen minutes of cerebral anaemia, beyond which resuscitation is not practicable, is close to the correct one. It appears to us that, in cases of resuscitation two hours after cessation of the heart-beat, (Prus., loc.cit.) the auricles must have kept up a slow but, in some degree, an efficient movement of the blood through the brain. The truth of this suggestion might be tested by introducing some easily recognized, non-diffusible substance into a vein after the heart-beat ceases to affect a manometer, and later searching for it in the brain and other parts of the body. But, whatever the reason, cerebral anaemia in these cases must have been less complete than in our experiments. The histological alterations of the cord and brain are now being studied. The results will be published later.