Tatsuo Mima

Endothelin acts in feline and canine cerebral arteries from the adventitial side.

We investigated the in vivo vasoconstrictor effect of endothelin, a recently characterized vasoconstrictor peptide from vascular endothelium, in the basilar arteries of five cats and five dogs. Basilar artery caliber was angiographically measured under anesthesia before (control) and after either vertebral artery infusion or cisternal injection of the peptide. In cats, 5-500 pmol endothelin induced a dose-dependent basilar artery contraction in vivo when injected intracisternally; within 3 minutes after injection of 500 pmol endothelin, basilar artery caliber was decreased by 73 +/- 4% compared with control diameter before injection. The vasoconstriction was extremely long-lasting; no significant recovery of basilar artery caliber was observed for up to 2 hours after injection. In contrast, infusion of up to 3,000 pmol endothelin into the vertebral artery had no appreciable effect on basilar artery caliber. Similar results were obtained in dogs; vasoconstriction was maintained for as long as 12 hours. Our observations suggest that endothelin acts in cerebral vessels from the adventitial side, not from the luminal side, possibly due to the presence of the blood-arterial wall barrier. The long-lasting nature of endothelin-induced constriction of the cerebral arteries in vivo suggests that the peptide might be involved in the pathogenesis of cerebral vasospasm.

Endothelins: vasoconstrictor effects and localization in canine cerebral arteries

1 The vascular effects of endothelin and localization of endothelin‐like immunoreactivity were characterized in isolated cerebral arteries of dogs. 2 Endothelin‐like immunoreactivity was detected in a few populations of endothelial cells of dog basilar artery. 3 Endothelin‐1, endothelin‐2 and endothelin‐3 contracted isolated ring preparations of cerebral arteries in a dose‐dependent manner independently of the presence of endothelium. The ED50 values (and 95% confidence intervals) for the contraction were 411 pm (242–697 pm) and 478 pm (295–776 pm) for endothelin‐1 and endothelin‐2, respectively. Endothelin‐3 induced vascular contraction at a higher concentration (ED50 = 26.5 nm, 95% confidence interval = 15.7–45.7 nm). 4 The increases in tone induced by endothelin‐1 and endothelin‐2 did not return to the resting level after repeated washings, while a rinse with Krebs solution reversed the vasoconstrictor response to endothelin‐3. The endothelins did not cause any vasodilator response in arteries precontracted with uridine 5′‐triphosphate even in the presence of intact endothelial cells. 5 NiCl2 (1 mm) attenuated the contractions induced by endothelin‐3 (10–300 nm) and those to relatively low doses (1 nm) but not higher doses (10–100 nm) of endothelin‐1 and endothelin‐2. The contractions in response to endothelin‐1, endothelin‐2 and endothelin‐3 were greatly attenuated in Ca2+‐free solutions although high concentrations of endothelin‐1 and endothelin‐2 still evoked contractions. 6 These results suggest that the vasoconstriction induced by endothelin‐3 and lower doses of endothelin‐1 and endothelin‐2, largely depends on the influx of Ca2+ ions. The apparent insensitivity to Ni2+ shows that additional distinct mechanisms also operate in the vasoconstrictor responses to high concentrations of endothelin‐1 and endothelin‐2. 7 The presence of endothelin‐like immunoreactivity in endothelial cells suggests that endothelin is a potential endogenous spasmogen.

Intraventricular Hemorrhage after Carotid Stenting

Purpose: To report an important complication related to carotid stenting. Methods and Results: A 71-year-old man with symptomatic subtotal occlusion of the left internal carotid artery had a 30-mm lesion treated percutaneously with implantation of 2 stents. Although the procedure was completed satisfactorily, left intraventricular hemorrhage occurred 4 hours later, possibly related to hyperperfusion injury. The patient expired 30 days after the stent procedure. Preoperative single-photon emission computed tomography revealed severely reduced vasoreactivity in the affected territory after acetazolamide challenge. Conclusions: The risk of hyperperfusion injury must be considered and minimized in patients with significant restriction of regional vasoreactivity. We recommend that cerebral hemodynamic status be determined prior to carotid stenting.

Combined argatroban and edaravone caused additive neuroprotection against 15 min of forebrain ischemia in gerbils.

We investigated whether or not a combination of the selective thrombin inhibitor, argatroban, and the free radical scavenger, edaravone (MCI-186), ameliorates postischemic hypoperfusion and decreases mortality after 15 min of forebrain ischemia in the gerbil. Argatroban or edaravone alone significantly increased postischemic cerebral blood flow and attenuated brain edema after reperfusion. However, only the combination increased the survival ratio (P<0.05 by Mantel-Cox) and protected the damage of neuronal cells. The present study indicates that anticoagulants and free radical scavengers reciprocally function to inhibit the progression of ischemic cell damage and that a combination of these types of drugs will help to improve the outcomes after cerebral ischemia.

EARLY DECREASE OF P-GLYCOPROTEIN IN THE ENDOTHELIUM OF THE RAT BRAIN CAPILLARIES AFTER MODERATE DOSE OF IRRADIATION

In this study, we examined the degree of disruption of blood-brain barrier (BBB) in irradiated rat brains using P-glycoprotein, one of the functional molecules of BBB, as a marker. In the animal experiments, disruption of BBB has been mainly studied at the acute stage of brain edema caused by a lethal dose of irradiation. However, they do not mimic the clinical situation of radiotherapy for malignant brain tumors. Therefore, we examined effects of a clinically compatible dose of radiation on BBB. The rat hemisphere received a single application of 25 Gy of X-rays, and P-glycoprotein was analyzed 5 days later by immunohistochemistry and Western blotting. Immunoreactivity of P-glycoprotein was found to be strong in endothelial cells of the brain of the nonirradiated rat as well as in the nonirradiated hemisphere of the irradiated rat. In contrast, very weak or no immunoreactivity was observed in the majority of endothelial cells in the irradiated hemisphere. Western blotting quantitatively showed that P-glycoprotein in the irradiated hemisphere decreased to nearly 60% that of the controls. The present study indicated that even a clinically applicable dose of radiation causes early disruption of BBB in the rat model.

Prostaglandin profiles in relation to local circulatory changes following focal cerebral ischemia in cats

We explored the temporal and topographic relations between local cerebral blood flow and regional brain prostaglandin profile following prolonged or transient occlusion of the middle cerebral artery in cats. Each experimental group was subjected to a sham operation, prolonged ischemia, or recirculation. Local cerebral blood flow was measured by the hydrogen clearance method. Following in situ freezing, cortical samples were obtained from each gyrus for determination of prostaglandin (PG) F2 alpha, PGE2, 6-keto-PGF1 alpha, and thromboxane (TX) B2 concentrations by radioimmunoassay. During prolonged ischemia, the concentrations of PGF2 alpha and PGE2 within the middle cerebral artery territory were significantly increased. Immediately after recirculation, there was a prominent but transient increase in PGF2 alpha and PGE2 in gyri that had been exposed to moderate ischemia (perifocal area). By contrast, the increases in these prostaglandins were slow and less prominent in gyri that had been exposed to severe ischemia (the focal area). The concentration of 6-keto-PGF1 alpha did not change during prolonged ischemia but transiently increased following recirculation in both the focal and perifocal areas. The TXB2 concentration did not change in any experimental group. Our study revealed a homogeneous increase in the regional brain content of PGE2 or PGF2 alpha in spite of the heterogeneous reduction of local cerebral blood flow during prolonged ischemia. Following recirculation, the focal and perifocal areas exhibited different patterns of prostanoid content. No correlation was found between local cerebral blood flow and the regional concentration of any prostaglandin examined.

Aberrant Expression of Neurotrophic Factors in the Ventricular Progenitor Cells of Infant Congenitally Hydrocephalic Rats.

Abstract Objects: This study was conducted to investigate the roles of neurotrophic factors in the development of hydrocephalus in HTX rats. Methods: Expressions of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and fibroblast growth factor (FGF)-1 were examined immunohistochemically in the cerebral cortex and ventricular zone of 6-day-old rats with congenital hydrocephalus (HTX rats). In the ventricular zone of hydrocephalic rats, potent BDNF-like immunoreactivity (-LI) and weak but significant signals for NT-3- and FGF-1-LIs were observed. However, no significant signals were detected in non-HTX rats. A small subpopulation of ventricular cells was positive for microtubule-associated protein 2 in HTX and non-HTX rats. The positive cells in the HTX rats had neurites much longer than those in the non-HTX animals, suggesting that some ventricular cells of the hydrocephalics had ectopically differentiated into mature neurons. Conclusions: This abnormal differentiation may have been responsible for the aberrant expressions of neurotrophic factors. In contrast, the cerebral neuronal layers did not show such prominent alterations in neurotrophic factor expression.

Doxorubicin, an RNA synthesis inhibitor, prevents vasoconstriction and inhibits aberrant expression of endothelin-1 in the cerebral vasospasm model of the rat

A vasoconstrictor peptide, endothelin-1 (ET-1), has been identified as one of the causative substances in cerebral vasospasm after subarachnoid hemorrhage. We investigated whether doxorubicin, an RNA synthesis inhibitor, effectively suppresses induction of ET-1 in the rat vasospasm model. Blood was injected around the right femoral artery and the left one was used as an internal control. Seven days later (day 7), diameters of the right femoral arteries narrowed to about 60% and this vasoconstriction was prevented by clinical dose (0.6 mg/kg) or one third of its dose of doxorubicin injected on day 1. Reverse transcriptase-polymerase chain reaction analysis demonstrated that expression of ET-1 mRNA in the vasospastic artery was not detected in doxorubicin-treated rats. It is concluded that doxorubicin effectively inhibits aberrant expression of ET-1 in the vasospasm-destined artery in the rat.

Studies on DNA fragmentation and disruption of the blood-brain barrier in delayed radiation injuries in the rat brain

Delayed effect of radiation injury to the central nervous system often results in improper prognosis for the patients with malignant brain tumors. Two types of cell, the endothelial cell and the oligodendrocyte, are considered to be causative lesions for delayed radiation injury. Recently, morphological studies with both light and electron microscope have also indicated involvement of apoptosis at the acute stage of radiation injury. In the rat radiation injury model, we first examined the capillary endothelial cells when they were damaged after irradiation, using immunohistochemical analysis of endothelial blood antigen (EBA) as one of the indicators of normal function of the blood‐brain barrier (BBB). Secondly, we examined the types and location of DNA‐fragmented cells using in situ end‐labeling using the TUNEL (terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick end labeling) method. A single dose of 10, 20 or 30 Gy was irradiated to the hemispheres and the brains were analyzed at 3, 6 and 12 months later. Although damage of endothelial cells was seen in the brains at 6 months after 20 Gy irradiation, disruption of BBB, as indicated by no immunoreactivity of EBA, occurred only in the brains at 12 months after 30 Gy irradiation. DNA fragmentation, indicated by TUNEL positive cells, were shown in the oligodendrocyte, astrocytes and endothelial cells in the brains at 6 months after 20 Gy irradiation. The results suggest that both disruption of BBB and apoptosis in the glial cells and endothelial cells are involved in the delayed radiation injury in the rat brain.

Aniracetam ameliorated behavioral abnormality at chronic stage after 10 min forebrain ischemia in the gerbil

Behavioral abnormality detected in an open-field test at chronic stage following 10 min forebrain ischemia in the gerbil may mimic the abnormal behavior “wandering’ often seen in senile dementia. We examined whether aniracetam. I-anisoyl-2-pyrrolidinone, which has been reported to be clinically effective in the treatment of “wandering”. ameliorates this behavioral abnormality in the ischemia-insulted gerbils. Three months after 10 min forebrain ischemia the gerbils were treated with aniracetam (30 mgkg i.p.) for 3 consecutive days. On the next day and the 14th day of the foal drug administration, an open-field test was conducted. The severity of the behavioral abnormality was graded as O-3 (O= normal: 3= most severely abnormal). Severity of behavioral abnormality was significantly attenuated by aniracetam compared to the vehicle-injected group (p<O.Ol). and returned to the pre-treatment condition 14 days after discontinuation of the drug. The present study may provide experimental evidence for the clinical effect of aniracetam on “wandering” in senile dementia.