Effects of rapamycin on cerebral oxygen supply and consumption during reperfusion after cerebral ischemia.

Activation of the mammalian target of rapamycin (mTOR) leads to cell growth and survival. We tested the hypothesis that inhibition of mTOR would increase infarct size and decrease microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1h and reperfusion for 2h with and without rapamycin (20mg/kg once daily for two days prior to ischemia). Regional cerebral blood flow was determined using a C(14)-iodoantipyrine autoradiographic technique. Regional small-vessel arterial and venous oxygen saturations were determined microspectrophotometrically. The control ischemic-reperfused cortex had a similar blood flow and O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex. Rapamycin significantly increased cerebral O2 consumption and further reduced O2 supply/consumption balance in the reperfused area. This was associated with an increased cortical infarct size (13.5±0.8% control vs. 21.5±0.9% rapamycin). We also found that ischemia-reperfusion increased AKT and S6K1 phosphorylation, while rapamycin decreased this phosphorylation in both the control and ischemic-reperfused cortex. This suggests that mTOR is important for not only cell survival, but also for the control of oxygen balance after cerebral ischemia-reperfusion.

Effects of 17beta-estradiol on blood-brain barrier disruption during focal cerebral ischemia in younger and older rats.

This study was performed to compare the effects of 17beta-estradiol on blood-brain barrier disruption in focal cerebral ischemia between younger and older rats. Younger (three-month-old) and older (24-month-old) ovariectomized female Fischer 344 rats were studied. In one half of each age group, a 500 microg 17beta-estradiol 21-day release pellet and in another half, a vehicle pellet was implanted 21 days before the experiments. One hour after middle cerebral artery occlusion, the transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid and the volume of 3H-dextran distribution were determined to examine the degree of blood-brain barrier disruption. In all four groups, the Ki in the ischemic cortex was higher than in the corresponding contralateral cortex. There was no significant difference in the Ki in both cortices among the groups. The volume of dextran distribution of the ischemic cortex was only greater than in the corresponding contralateral cortex in the older 17beta-estradiol-treated group, and the volume of that group was greater than the younger 17beta-estradiol-treated group (4.00 +/- 1.29 VS. 2.13 +/- 0.88 ml/100 g). After analyzing the difference in Ki between the ischemic cortex and the contralateral cortex in each animal, the difference was significantly greater in the older 17beta-estradiol-treated rats than the older vehicle-treated rats (3.40 +/- 2.10 VS. 1.26 +/- 1.44 microl/g/min). In the younger rats, however, 17beta-estradiol did not significantly affect the difference. Our data showed that 17beta-estradiol treatment failed to attenuate the BBB disruption in the cerebral ischemic cortex in the older or younger Fischer 344 rats. However, our data also suggest the possibility that 17beta-estradiol could aggravate the BBB disruption in older rats.

Effects of 17beta-estradiol on blood-brain barrier disruption in focal ischemia during GABA(A) receptor inhibition.

We performed this study to determine whether gamma-aminobutyric acid (GABA(A)) receptor inhibition could reverse the effect of 17beta-estradiol on blood-brain barrier (BBB) disruption in focal cerebral ischemia. Young ovariectomized rats were implanted with a 500 microg 17beta-estradiol 21-day release pellet or with a vehicle pellet 21 days before the experiments. Forty-five minutes after middle cerebral artery (MCA) occlusion, half of each group was infused with bicuculline (a GABA(A) receptor antagonist) 1 mg/kg/min for 2 min followed by 0.1 mg/kg/min up to the end of experiments. The other half was infused with the same volume of normal saline. The transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid and the volume of 3H-dextran distribution (70,000 Daltons) were determined to measure the degree of BBB disruption one hour after MCA occlusion. In the control vehicle-treated animals, the Ki in the ischemic cortex (7.2 +/- 2.6 microl/g/min) was higher than in the contralateral cortex (2.5 +/- 1.4 microl/g/min). After bicuculline infusion, the Ki in the ischemic cortex increased (10.6 +/- 5.4 microl/g/min) although the increase was not statistically significant. In the 17beta-estradiol treated animals, the Ki in the ischemic cortex (3.8 +/- 1.6 microl/g/min) was lower than control vehicle-treated rats. With bicuculline infusion, the Ki in the ischemic cortex (14.5 +/- 6.8 microl/g/min) was markedly increased. In the non-ischemic cortex, there was no significant difference in Ki among the experimental groups. The volume of dextran distribution was not significantly different between the experimental groups in the ischemic or non-ischemic cortex. Our data suggests that part of the reason for the decreased BBB disruption in the focal ischemic area after 17beta-estradiol treatment could be due to the interaction between GABA(A) receptors and 17beta-estradiol.

17beta-estradiol prevents blood-brain barrier disruption induced by VEGF.

We performed this study to determine how pretreatment of the ovariectomized rats with 17beta-estradiol could affect blood-brain barrier disruption caused by the vascular endothelial growth factor (VEGF), an important mediator of vascular permeability. Ovariectomized female rats aged twelve to fourteen weeks were used in the study. A 500 micro g 17beta-estradiol 21-day release pellet was implanted in the 17beta-estradiol group, and a vehicle pellet was implanted in the control group 21 days before the experiments. We performed three craniotomies under isoflurane anesthesia to expose cerebral cortices. Normal saline, 10 (- 10)M and 10 (- 9)M VEGF patches were applied on each hole for 30 min. The transfer coefficient (Ki) of (14)C-alpha-amino isobutyric acid and volume of (3)H-dextran (70,000 dalton) distribution were determined to measure the degree of BBB disruption. Ki was increased by 108 % and 138 % with 10 (- 10)M and 10 (- 9)M VEGF respectively after VEGF application in the control group (p < 0.01). However, there was no significant increase in the Ki with the VEGF application in the 17beta-estradiol group, and their values were significantly lower than the corresponding data of the control group (10 (- 10)M: - 55 %, 10 (- 9)M: - 52 %, p <0.05). The volume of dextran distribution in the control group increased by 47 % with VEGF 10 (- 9)M (p < 0.05), whereas there was no significant change in the volume of dextran distribution with VEGF application in the 17beta-estradiol group and the volume was lower than the corresponding volume of the vehicle-treated control group (10 (- 10)M: - 34 %, 10 (- 9)M: -32 %, p < 0.05). In conclusion, our study demonstrated that chronic 17beta-estradiol treatment prevented BBB disruption induced by the VEGF in the ovariectomized rats.

Effects of 17beta-estradiol on blood-brain barrier disruption during focal ischemia in rats.

This study was performed to test whether 17beta-estradiol could attenuate the blood-brain barrier disruption caused by middle cerebral artery occlusion in the ovariectomized rats. Rats aged twelve to fourteen weeks were used in this study. Their ovaries were removed one week prior to the implantation of the pellets. For the 17beta-estradiol group, a 500 microg 17beta-estradiol 21 day-release pellet was implanted and for the control group, a vehicle pellet was implanted 21 days before the experiments. One hour after middle cerebral artery occlusion under isoflurane anesthesia, the transfer coefficient of 14C-alpha-aminoisobutyric acid (104 Daltons) and the volume of 3H-dextran (70,000 Daltons) distribution were determined to represent the degree of blood-brain barrier disruption. Blood pressures and blood gases were similar between controls and 17beta-estradiol-treated rats. In both groups, the transfer coefficient of the ischemic cortex was higher than that of the corresponding contralateral cortex (control: Ischemic Cortex 12.5 +/- 5.9 microl/g/min, Contralateral Cortex 3.0 +/- 1.6, p < 0.001; 17beta-estradiol: Ischemic Cortex 6.7 +/- 3.3 micro l/g/min, Contralateral Cortex 2.2 +/- 0.9, p < 0.01). There was no significant difference in the transfer coefficient of the contralateral cortex between these two groups. However, the transfer coefficient of the Ischemic Cortex of the 17beta-estradiol-treated animals was 46 % lower than that of the control, vehicle-treated rats (p < 0.05). The increase of the volume of 3H-dextran distribution with middle cerebral artery occlusion was significant in the vehicle-treated rats (Ischemic Cortex: 6.4 +/- 2.7 ml/100 g, Contralateral Cortex: 3.8 +/- 0.8, p < 0.01) but not in the 17beta-estradiol-treated animals. Our data suggest that chronic 17beta-estradiol treatment was effective in reducing blood-brain barrier disruption during focal ischemia in the ovariectomized rats.

Effects of mild hypothermia on blood-brain barrier disruption during isoflurane or pentobarbital anesthesia.

BACKGROUND: This study was performed to determine whether mild hypothermia (32 degrees C) could attenuate the degree of blood-brain barrier (BBB) disruption caused by a hyperosmolar solution and whether the degree of disruption would vary depending on anesthetic agents. METHODS: Rats were assigned to one of four groups: normothermic isoflurane, normothermic pentobarbital, hypothermic isoflurane, and hypothermic pentobarbital. During isoflurane (1.4%; normothermic or hypothermic) or pentobarbital (50 mg/kg administered intraperitoneally; normothermic or hypothermic) anesthesia, the external carotid artery and the femoral artery and vein were catheterized. Body temperature was maintained at 37 and 32 degrees C for the normothermic and hypothermic groups, respectively. To open the BBB, 25% mannitol was infused through the right carotid artery at the rate of 0.25 ml x kg(-1) x s(-1) for 30 s. The transfer coefficient of 14C-alpha-aminoisobutyric acid was determined. RESULTS: Blood pressure was similar among the four groups of animals. The degree of the BBB disruption by hyperosmolar mannitol was less with isoflurane than pentobarbital anesthesia in the normothermic groups (transfer coefficient: 29.9 +/- 17.1 and 50.4 +/- 17.5 microl x g(-1) x min(-1) for normothermic isoflurane and pentobarbital, respectively; P < 0.05). Mild hypothermia decreased the BBB disruption during anesthesia with both anesthetic agents (hypothermic isoflurane: 9.8 +/- 8.3 microl x g(-1) x min(-1), P < 0.05 vs. normothermic isoflurane; hypothermic pentobarbital: 30.2 +/- 13.9 microl x g(-1) x min(-1), P < 0.05 vs. normothermic pentobarbital), but the disruption was less during isoflurane anesthesia (hypothermic isoflurane vs. hypothermic pentobarbital, P < 0.005). In the contralateral cortex, there were no significant differences among these four experimental groups. CONCLUSIONS: The data demonstrated that hypothermia was effective in attenuating BBB disruption by hyperosmolar mannitol during isoflurane as well as pentobarbital anesthesia. The degree of disruption appeared smaller during isoflurane than during pentobarbital anesthesia in both the normothermic as well as the hypothermic groups.

Effects of endothelin-1 on blood-brain barrier permeability during focal cerebral ischemia in rats.

The purpose of this study was to determine whether the transport of small hydrophilic molecules across the blood-brain barrier (BBB) during focal cerebral ischemia could be altered by a topical application of endothelin-1 (ET-1) in the ischemic cortex (IC). Forty minutes after middle cerebral artery (MCA) occlusion, patches of 10 nM ET-1 (low-endothelin group), 100 nM ET-1 (high-endothelin group), or normal saline (control group) were placed on the IC of rats for a 20-min period. One hour after MCA occlusion, transfer coefficient (Ki) of [14C-alpha-]aminoisobutyric acid (14C-AIB) or regional cerebral blood flow (rCBF) was determined. Vital signs were not significantly different among the experimental groups. In the control group (n=8), the Ki of the IC was significantly higher than that of the contralateral cortex (CC; 11.9+/-5.8 vs 5.0+/-1.9 microl/g per minute). In the low-endothelin group (n=8), the Ki of the IC was still significantly higher than that of the CC (9.4+/-5.2 vs 5.3+/-2.5 microl/g per minute). However, in the High-endothelin group (n=8), the Ki of the IC was not different from that of the CC (6.9+/-2.1 vs 5.6+/-2.3 microl/g per minute) and 42% lower than that of the control group. The rCBF was not affected by 100 nM of ET-1 [control (n=6): IC 53+/-18 ml/100 g per minute, CC 94+/-23 ml/100 g per minute; high-endothelin (n=6): IC 49+/-15 ml/100 g per minute, CC 98+/-24 ml/100 g per minute]. Our data suggest that the application of endothelin-1 in the IC could reduce the transfer coefficient of small hydrophilic molecules across the BBB during focal ischemia.

Intraoperative mild hypothermia does not increase the plasma concentration of stress hormones during neurosurgery.

PURPOSE: To determine how mild hypothermia (34 degrees C) affects the hemodynamic and the stress hormonal responses intraoperatively and during extubation in patients undergoing cerebral aneurysm surgery. METHODS: After induction, anesthesia was maintained with 1.2% isoflurane and 50% nitrous oxide. For the normothermia and the hypothermia groups, the body temperature was maintained at 36.9 +/- 0.3 degrees C and 34.2 +/- 0.2 degrees C respectively up to the recovery room. Hemodynamic changes were recorded continuously. Stress hormones comprising epinephrine, norepinephrine, ADH, ACTH, and cortisol were measured at the awake control, intraoperative, and extubation periods. RESULTS: Vital signs of the intraoperative and postextubation time periods were not significantly different between the normothermia and hypothermia groups except for a statistically lower pulse rate intraoperatively in the hypothermia group (P <0.05). In the control awake state, all five hormonal concentrations were similar between the two groups. Intraoperatively, all of the hormonal levels tended to be lower in the hypothermia group compared to the normothermia group, but only the epinephrine level decreased sufficiently to reach statistical significance (P <0.05). During extubation, all stress hormone concentrations, except norepinephrine, were lower in the hypothermia group (epinephrine: P <0.05; ADH: P <0.05; ACTH: P <0.05; cortisol: P <0.05). CONCLUSIONS: Our data suggest that intraoperative mild hypothermia neither significantly affects the blood pressure response nor increases the concentrations of stress hormones intraoperatively. Furthermore, mild hypothermia significantly decreased the plasma concentrations of stress hormones during the extubation period.

Effect of AMPA on cerebral cortical oxygen balance of ischemic rat brain.

We tested the hypothesis that the excitatory neurotransmitter receptor agonist, alpha amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), would worsen cerebral cortical oxygen supply/consumption balance during focal ischemia. In this study, we compared regional cerebral blood flow, arterial and venous O2 saturation, O2 extraction and oxygen consumption of ischemic and AMPA treated ischemic and control regions of rat brain. Ischemia was induced by middle cerebral artery (MCA) occlusion in isoflurane (1.4%) anesthetized Wistar rats. Twenty minutes after MCA occlusion, 10(-5) M AMPA was applied to the ischemic cortex (IC) for a period of 40 min; the fluid was changed every 10 min. After 1 hr of ischemia, animals were sacrificed and regional cerebral blood flow (rCBF) was determined using the C14-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined microspectrophotometrically. In control, the cerebral blood flow and oxygen consumption of the IC were significantly lower than the contralateral cortex (rCBF: 46 +/- 20 vs. 81 +/- 39 ml/min/100g, O2 consumption: 2.8 +/- 1.4 vs. 3.6 +/- 1.4 ml O2/min/100g). 10(-5) M AMPA did not significantly alter regional cerebral blood flow and oxygen consumption of the IC, but did decrease the average venous O2 saturation of the IC from 50.2 +/- 3.9% to 46.7 +/- 1.6%. AMPA also significantly increased the frequency of small veins with less than 45% O2 saturation in the IC (8 out of 56 veins in IC vs. 18 out of 56 veins in AMPA treated IC). Thus, topical application of 10(-5) M AMPA to the ischemic area worsens cerebral O2 balance and suggests that excitatory amino acids contribute to the degree of cerebral ischemia.

The effects of morphine on blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats.

UNLABELLED: This study was performed to evaluate whether morphine could alter the degree of disruption of the blood-brain barrier (BBB) caused by hyperosmolar mannitol. Under isoflurane anesthesia, rats in a control group were infused with 25% mannitol into the internal carotid artery before measuring the transfer coefficient (Ki) of (14)C-alpha-aminoisobutyric acid. Infusion of morphine 3 mg/kg in the small-dose morphine group and 10 mg/kg in the large-dose morphine group was completed, 10 min before administering mannitol. There were no statistical differences in systemic blood pressures between these three groups of animals. In the control group, the Ki of the ipsilateral cortex where mannitol was injected, increased to 4.6 times that of the contralateral cortex (19.5 +/- 8.5 vs 4.2 +/- 1.2 microL. g(-1). min(-1), P < 0.002). The Ki of the ipsilateral cortex of the small-dose morphine group was 13.5 +/- 7.6 microL. g(-1). min(-1). The Ki of the ipsilateral cortex of the large-dose morphine group was 9.2 +/- 4.5 microL. g(-1). min(-1) and was smaller than that of control animals (P < 0.05). There was no significant difference in the Ki of the contralateral cortex among the three groups. In conclusion, morphine attenuated BBB disruption induced by hyperosmolar solution without significant effects on systemic blood pressure. IMPLICATIONS: Our study suggests that morphine may be effective in reducing the blood-brain barrier disruption by hyperosmolar mannitol without significant effects on systemic blood pressure.

Effect of upregulation of AMPA glutamate receptors on cerebral O(2) consumption and blood flow in rat.

AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate) receptors, in cerebral cortex, underwent upregulation (35% increase) following chronic blockade with a non-competitive AMPA receptor antagonist, GYKI 52466 (1-(aminophenyl)-4-methyl-7, 8-methylenedioxy-5H-2,3-benzodiazepine). Such upregulation did not alter basal cerebrocortical blood flow or O(2) consumption. There was a much higher increase in blood flow and O(2) consumption in the upregulated, agonist (AMPA) stimulated cortices of anesthetized rats.

The effects of propranolol on heterogeneity of rat cerebral small vein oxygen saturation.

UNLABELLED: beta-Adrenergic receptors are involved in altering cerebral metabolism and blood flow. This study was performed to determine whether propranolol would alter the microregional O2 balance in the brain. Rats were anesthetized with 1.4% isoflurane. Isotonic sodium chloride solution (control group), propranolol 2 mg/kg (low propranolol group) or propranolol 20 mg/kg (high propranolol group) was administered IV to the rats. Twenty minutes later, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Small (diameter <70 microm) arterial and venous oxygen saturation (SaO2 and SvO2, respectively) was determined using microspectrophotometry in the alternate slices of the tissue sections used to measure rCBF. In both the low and high propranolol groups, average cortical rCBF was 35% lower than that in the control group. The average O2 consumption of the cortex of the propranolol groups was significantly lower than control (low propranolol: -41%, high propranolol: -49%). In all groups, SaO2 was almost identi-cal. The heterogeneity of the microregional SvO2 expressed as the coefficient of variation (CV = 100 x sD/mean) was significantly lower in the propranolol groups (low propranolol: 8.0+/-2.3, high propranolol: 7.3 +/- 2.9) than in the control group (13.4 +/- 3.5). The proportion of cortical veins with Svo2 <55% was significantly smaller in the low and high propranolol groups (4 of 60 and 3 of 60, respectively) than that in the control group (15 of 60). In the other brain regions, the data followed a similar pattern. Our data demonstrated that propranolol is effective in decreasing O2 consumption, improving microregional O2 balance, and reducing its heterogeneity in the brain. IMPLICATIONS: Our data suggest that the linkage of O2 supply and consumption is not tightly coupled under isoflurane anesthesia. beta-Adrenergic blockers may tighten this linkage and reduce the number of low O2-saturated microregions.

Effects of cyclic GMP on microvascular permeability of the cerebral cortex.

This study was performed to test the hypothesis that a direct application of cyclic guanosine monophosphate (cGMP) to the cortex would increase blood-brain barrier (BBB) permeability. Rats were anesthetized with 1.4% isoflurane and were mechanically ventilated. Two cranial windows (3 mm in diameter) were made on each side of the rat's skull (a total of four windows on each rat) to expose the cerebral cortex. A patch of normal saline, 10(-5) M, 10(-4) M, or 10(-3) M 8-bromo-cGMP was applied to each cranial window. The patches were changed every 5 min. Ten minutes after applying the patches, BBB permeability was determined by measuring the transfer coefficient (Ki) of [alpha-14C]aminoisobutyric acid. Vital signs were not changed after applying 8-bromo-cGMP. Blood gases were within normal limits. In the cortex, 10(-5) M 8-bromo-cGMP did not significantly affect the Ki; 10(-4) M 8-bromo-cGMP increased the Ki by 115%; 10(-3) M 8-bromo-cGMP increased the Ki by 124%. However, there was no statistical difference in the Ki between the doses of 10(-4) M and 10(-3) M 8-bromo-cGMP. In the pons where no patch was applied, the Ki was similar to that of the cortical area where a normal saline patch was applied. Our data demonstrated that a direct application of cGMP to the cerebral cortex significantly increased the permeability of the BBB.

A nonNMDA antagonist, GYKI 52466 improves microscopic O2 balance in the cortex during focal cerebral ischemia.

This study was performed to test whether GYKI 52466, a nonNMDA receptor antagonist, would improve microregional oxygen supply and consumption balance in the focal cerebral ischemic area. Rats were anesthetized with 1.4% isoflurane. For the GYKI Group (n = 8), 10 min before middle cerebral artery (MCA) occlusion, a bolus of 5 mg kg-1 of GYKI 52466 i.v. was administered and was followed by an infusion of 5 mg kg-1 h-1. For the Control Group (n = 8), the same volume of the vehicle was administered. One hour after MCA occlusion, regional cerebral blood flow (rCBF) was measured using the 14C-iodoantipyrine autoradiographic technique. Microscopic arterial and venous oxygen saturations were determined using microspectrophotometry. In the cortex contralateral to MCA occlusion, the average rCBF and the average O2 consumption were lower in the GYKI Group than in the Control Group (rCBF: GYKI 65.5 +/- 24.1 ml 100 g-1 min-1, Control 97.7 +/- 33.4 ml 100 g-1 min-1; O2 consumption: GYKI 3.9 +/- 1.2 ml O2 100 g-1 min-1, Control 6.2 +/- 2.5 ml O2 100 g-1 min-1) without a significant difference in the number of veins with SvO2 < 50%. In the ischemic cortex, the number of veins with SvO2 < 50% was significantly smaller in the GYKI Group (21 veins out of 63) than in the Control Group (45 out of 59) without a significant difference in the average rCBF (GYKI 44.9 +/- 17.7, Control 29.7 +/- 10.4) or regional O2 consumption between these two groups (GYKI 3.3 +/- 1.4, Control 2.7 +/- 1.2). Our data demonstrated that GYKI 52466 was effective in improving microscopic O2 balance in the focal ischemic cortical area of the brain and it decreased O2 consumption in the non-ischemic cortex.

The effects of pentobarbital on blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats.

UNLABELLED: This study was performed to evaluate both the effects of pentobarbital on disruption of the blood-brain barrier (BBB) by hyperosmolar mannitol and the relationship between its effect on blood pressure and the integrity of the BBB. Under isoflurane anesthesia, rats in the control group were infused with 25% mannitol into the internal carotid artery before measuring the transfer coefficient (Ki) of 14C alpha-aminoisobutyric acid. Ten minutes before the administration of mannitol, rats received an infusion of pentobarbital: 20 mg/kg in the small-dose group and 50 mg/kg in the large-dose group. In another group of animals (hydralazine group), hydralazine was administered to maintain the mean arterial blood pressure (MAP) at 65 mm Hg during the experimental period. The MAP of the control group (113 +/- 14 mm Hg) was significantly higher (P < 0.002) than that of the small-dose pentobarbital group (78 +/- 13 mm Hg) or the large-dose pentobarbital group (68 +/- 14 mm Hg). In the control group, the Ki of the cortex ipsilateral to the mannitol injection was increased to 4.5 times that of the contralateral cortex (14.5 +/- 7.7 vs 3.2 +/- 0.6 microL x g(-1) x min(-1); P < 0.002). The Ki of the ipsilateral cortex of the small-dose pentobarbital group was 9.7 +/- 5.6 microL x g(-1) x min(-1). The Ki of the ipsilateral cortex of the large-dose pentobarbital group was 5.5 +/- 2.9 microL x g(-1) x min(-1), and lower (-9.0 microL x g(-1) x min(-1)) than that of the control animals (P < 0.05). There was no significant difference in the Ki of the contralateral cortex among any of the three groups of animals. At the same MAP, the Ki of the ipsilateral cortex of the large-dose pentobarbital group was lower (-4.3 microL x g(-1) x min(-1)) than that of the hydralazine group (9.8 +/- 4.6 microL x g(-1) x min(-1)) (P < 0.05). Pentobarbital attenuated the BBB disruption induced by hyperosmolar mannitol. This may be attributed, at least in part, to the blood pressure effect of pentobarbital. IMPLICATIONS: When the blood-brain barrier (BBB) was disrupted by a hyperosmolar solution, pentobarbital attenuated the degree of leakage of the BBB. Systemic hypotension caused by pentobarbital played a significant role in decreasing the leakage. Our study suggests that when the BBB is disrupted, pentobarbital may be effective in protecting the BBB. Furthermore, systemic blood pressure plays an important role in determining the degree of disruption.

Effects of isoproterenol on blood-brain barrier permeability in rats.

This study was performed to examine whether the direct topical application of isoproterenol to the cerebral cortex could modify the blood-brain barrier (BBB) permeability and whether this effect could be blocked by Timolol, a beta-adrenergic receptor antagonist without a membrane stabilizing effect. After a craniotomy in each animal, a low-dose (10(-4) M, n = 6) or a high-dose (10(-3) M, n = 6) isoproterenol patch was placed on one cortex (Ipsilateral Cortex: IC) and a normal saline patch was placed on the other cortex (Control Cortex: CC). Another 6 animals were pretreated with Timolol 1.5 mg kg(-1) i.v. before the placement of high dose isoproterenol patches. The BBB transfer coefficient (Ki) was determined using 14C-alpha-aminoisobutyric acid. Mean arterial blood pressure decreased after low- and high-dose isoproterenol patches. The low- and high-dose of isoproterenol increased Ki by 58% (IC: 5.94+/-2.02, CC: 3.77+/-1.75 microl g min(-1)) and 66% (IC: 6.97+/-3.66, CC: 4.19+/-2.48 microl g min(-1)) respectively when compared to that of the corresponding CC. Pretreatment with Timolol prevented the increase of the Ki by a high-dose of isoproterenol (IC: 5.33+/-1.88, CC: 5.66+/-1.72 microl g min(-1)). Our data demonstrate that a direct application of a beta-adrenergic receptor agonist to the brain parenchyma increased the permeability of the BBB, and that this effect could be prevented with a beta-adrenoceptor antagonist.

Effects of topical N-methyl-D-aspartate on blood-brain barrier permeability in the cerebral cortex of normotensive and hypertensive rats.

This study was performed to examine if blood-brain barrier (BBB) permeability could be increased by N-methyl-D-aspartate (NMDA) in the cerebral cortex, and to compare the degree of alteration of BBB permeability in normotensive and in chronic hypertensive rats. Twenty- to 22-week-old spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were anesthetized with isoflurane. After craniotomy in 7 animals in each group (SHR and WKY group), an NMDA patch (10 mM) was placed on one cortex (ipsilateral cortex: IC), and a normal saline patch was placed on the other cortex (control cortex: CC). The other 7 rats in each group were pretreated with MK-801 before placing NMDA and normal saline patches (SHR.MK-801 and WKY.MK-801 group). The BBB transfer coefficient (Ki) was determined using 14C-alpha-aminoisobutyric acid. The mean arterial pressures of the SHR and the SHR.MK-801 group were about 65% higher than those of the WKY and the WKY.MK-801 groups. In the WKY group, the Ki of the IC was significantly higher than that of the CC (IC: 10.0 +/- 2.7, CC: 6.2 +/- 2.4 microliters g-1 min-1). In the WKY.MK-801 group, the Ki was similar in both cortices (IC: 8.6 +/- 4.0, CC: 8.2 +/- 3.3). In the SHR group, the Ki of the IC was significantly higher than that of the CC (IC: 9.5 +/- 3.7, CC: 6.5 +/- 3.4), and the Ki of each cortex was similar to that of the corresponding cortex of the WKY group. In the SHR.MK-801 group, the Ki was similar in both cortices (IC: 7.2 +/- 1.5, CC: 7.1 +/- 2.7), and was also similar to those of the WKY.MK-801 group. Our data suggest that NMDA is involved in increasing BBB permeability. In chronic hypertension, the response of the BBB to NMDA is not altered when compared with normotension.

Effects of nitric oxide on blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats.

We performed this study to evaluate the effects of changing the level of nitric oxide (NO) on disruption of the blood-brain barrier (BBB) by hyperosmolar mannitol. Under isoflurane anesthesia, control rats (control group, n = 6) were given infusions with 25% mannitol into the internal carotid artery before measuring the transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid (14C-AIB). In the CAS group (n = 6), [3-(cis-2,6-dimethyl piperidino)-sydnonimine] (CAS 754), a NO donor, was injected to decrease the mean arterial pressure (MAP) to 55 mm Hg and in the L-NAME group (n = 6), NG-nitro-L-arginine methyl ester (L-NAME), a NO synthase inhibitor, was injected before administering mannitol. In additional control animals (control + P group, n = 6) and additional CAS 754-treated animals (CAS + P group, n = 6), phenylephrine was infused to keep MAP at 130 mm Hg during the experimental period. In the control group, with mannitol injection, the Ki of the ipsilateral cortex (IC) where mannitol was injected increased to 4.3 times that of the contralateral cortex (CC) (17.2 +/- 2.9 vs 4.0 +/- 2.6 microliters.g-1.min.1). Without blood pressure control, the Ki of the IC of the CAS group (7.0 +/- 4.5) was lower and that of the L-NAME group (26.2 +/- 12.7) was higher than that of the control animals. At the same MAP, the Ki of the IC of the CAS + P group (9.6 +/- 3.1) was significantly lower than that of the control + P group (21.3 +/- 14.5) or that of the L-NAME group. There was no significant difference in the Ki of the IC between the control + P and the L-NAME groups. In conclusion, L-NAME worsened BBB disruption induced by hyperosmolar solution, which may be due to the pressure effect of L-NAME. CAS 754 was effective in attenuating disruption of the BBB caused by hyperosmolar mannitol. This effect is apparently not due to decreased MAP.

Hydroxyethyl starch solution attenuates blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats.

This study was performed to investigate whether a fraction of hydroxyethyl starch macromolecules, prepared from pentastarch and known as "Hes-Pz," with molecular weights of 100,000-1,000,000, protects against blood-brain barrier (BBB) disruption due to intracarotid injection of hyperosmolar mannitol. Rats were anesthetized with isoflurane, and retrograde catheterization of a unilateral eternal carotid artery was performed. Except for the Control group (n = 8), hemodilution was performed using lactated Ringer's solution LR group, n = 7), 6% hetastarch (HES group, n = 7), or 6% HES-Pz (HES-Pz group, n = 8) to reduce the hematocrit to about 23%. The BBB transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid was determined after a unilateral intracarotid injection of 25% mannitol. Blood pressure and hematocrit were similar in all groups. In the control group, Ki was increased significantly in the ipsilateral cortex (IC) where mannitol was injected (16.3 +/- 6.1 vs 4.1 +/- 1.4 microL.min-1) when compared with the contralateral cortex (CC). Ki was similar in the CC in all four groups. The Ki in the IC was significantly lower in the HES-Pz(6.4 +/- 3.5 microL.g-1.min-1) than in the Control, HES, or LR group (16.3 +/- 6.1, 19.0 +/- 12.9, 17.9 +/- 10.8 microL.g-1.min-1, respectively). Our data suggest that HES-Pz significantly attenuates disruption of the BBB caused by an injection of hyperosmolar mannitol.

Cerebral microregional oxygen balance during chronic versus acute hypertension in middle cerebral artery occluded rats.

This study was performed to compare microregional 0(2) supply and consumption balance in spontaneously hypertensive rats (SHR), normotensive Wistar Kyoto rats (WKY), and in phenylephrine-induced acutely hypertensive WKY (WKY + ph) rats. Under isoflurane anesthesia, a middle cerebral artery (MCA) of SHR (n = 7) and WKY (n = 14) rats was occluded. Seven of the WKY rats were infused with phenylephrine (WKY + ph) to keep the mean arterial pressure (MAP) at the same level as that of the SHR. In all animals, 1 h after MCA occlusion, regional cerebral blood flow (rCBF) was determined using an autoradiographic technique, and microregional arterial and venous 02 saturations were determined using microspectrophotometry. MAP was 76 +/- 4 (SD), 136 +/- 15, and 132 +/- 12 mm Hg for the WKY, WKY + ph, and SHR groups, respectively. All variables describing regional O2 balance and rCBF were similar between the SHR and the WKY groups in the ischemic cortex as well as in the contralateral cortex. With phenylephrine infusion, rCBF of both the ischemic cortex and the contralateral cortex were increased in the WKY group. The average 02 supply-to-consumption ratio in the ischemic cortex was higher in the WKY + ph than in the WKY or SHR group. In the ischemic cortex, heterogeneity of venous 02 saturation (SvO2), expressed as a coefficient of variation (CV = 100 X SD/mean), was significantly lower in the WKY + ph (18.3 +/- 2.4) group than in the SHR (30.5 +/- 11.8) or in the WKY (31.3 +/- 9.0) group. The number of veins with low 02 saturation (SvO2 < 40%) in the ischemic cortex was significantly lower in the WKY + ph than in the SHR or in the WKY group. Our data suggest that in chronically hypertensive animals, cerebrovascular adaptations enable the microregional 02 balance in focal ischemia to be maintained at a level similar to that of normotensive animals. However, in normotensive animals with focal cerebral ischemia, an acute increase of MAP improves microregional O2 balance.