Pre- and post-estrogen administration in global cerebral ischemia reduces blood-brain barrier breakdown in ovariectomized rats.

The aim of present study was to determine the effect of estrogen treatment on blood-brain barrier permeability in rats with induced global cerebral ischemia. The study included six-month-old female Sprague-Dawley rats which were divided into the following groups: Control-Ischemia-Reperfusion (C + I-R); Ovariectomy-Ischemia-Reperfusion (Ovx + I-R); Ovariectomy + Estrogen + Ischemia-Reperfusion (Ovx + E + I-R); Ovariectomy + Ischemia-Reperfusion + Estrogen (Ovx + I-R + E). Ischemia-reperfusion was induced by clamping two carotid arteries, then opening the clamp. Blood-brain barrier permeability was visualized by Evans Blue extravasation and quantified by spectrophotometry. Our results indicate that following ischemia-reperfusion the BBB permeability is increased in ovariectomized rats (Evans Blue extravasation) compared to the control group in the cortex, thalamus, hippocampus, cerebellum and brain stem, while in the midbrain no significant increase was detected. In contrast, BBB permeability in the groups treated with estrogen, administered either before or after ischemia-reperfusion, was significantly lower than in ovariectomized animals. In conclusion, the increase in BBB permeability resulting from experimentally induced cerebral ischemia was prevented by exogenous estrogen treatment. The study results indicate that estrogen may be used for therapeutic purposes in ischemia-reperfusion.

Passage of spermidine across the blood-brain barrier in short recirculation periods following global cerebral ischemia: effects of mild hyperthermia.

Transport of a polyamine (PA), spermidine (SPMD) into rat brain at various early postischemic periods was studied. Rats underwent 20 min of four-vessel occlusion (4VO) followed by 5, 10, 30 and 60 min of recirculation (RC) periods with natural brain temperature. 3H-aminoisobutyricacid (AIB) and 14C-SPMD were utilised to search dual functions of the blood-brain barrier (BBB); barrier and carrier functions, respectively. Unidirectional blood-to-brain transfer constant (Kin) was calculated for AIB and SPMD in four brain regions-parieto-temporal cortex, striatum, hippocampus and cerebellum. Kin for SPMD ranged between 1.2+/-0.3 x 10(3) ml g(-1) min(-1) (for striatum) and 2.2+/-0.4 x 10(3) ml g(-1) min(-1) (for cerebellum) in controls. Kin for AIB showed similar values. At 5 and 10 min RC periods, Kin for both substances increased in a non-specific manner in all brain regions studied. In the cortex, Kin for SPMD at 5 and 10 min RC periods were 3.2+/-0.4 x 10(3) and 2.9+/-0.3 x 10(3) ml g(-1) min(-1), respectively, and found to be maximum with respect to other brain regions studied. 30 and 60 min RC groups showed specific transport for SPMD, whilst there were no changes for Kin for AIB, in all brain regions studied. Hippocampus showed the maximum increase in Kin SPMD at 60 min RC (2.7+/-0.3 x 10(3) ml g(-1) min(-1)), corresponding to a percentage rise of 121%. Intraischemic mild brain hyperthermia (39 degrees C) gave rise to a striking increase in Kin at 60 min postischemia for both substances. These results suggest that there is a specific transport of SPMD into brain at 30 and 60 min RC periods following 20 min of forebrain ischemia. Moreover, dual functions of the BBB were perturbed with intracerebral mild hyperthermia during ischemia.

Chronic nicotine pretreatment protects the blood-brain barrier against nicotine-induced seizures in the rat.

This study was designed to investigate the possible protective actions of nicotine on cerebrovascular permeability in convulsions during nicotine-induced seizures. We have measured the permeability changes in the blood-brain barrier (BBB) macroscopically and spectrophotometrically by using Evans blue dye. Specific gravity measurements were also performed to assess brain edema which develops after blood-brain barrier opening. The experiments were carried out on Wistar rats. Rats were divided into two groups. They received acutely a convulsive dose of nicotine 3, 5, 8 and 9 mg kg(-1)i.p. or pretreated with a low dose of nicotine (0.8 mg kg(-1)i. p.) for 21 days followed by the procedure mentioned in the first group. Acute nicotine injection induced a significant increase in blood pressure and Evans-blue passage, despite a decline in specific gravity values. Low doses of chronic nicotine administration markedly reduced both the leakage of dye, and brain water content. Chronic treatment with low doses of nicotine (0.8 mg kg(-1)day(-1)s. c.) lessened the intensity of tonic-clonic seizures observed with a single dose of 3, 5, 8 or 9 mg kg(-1)nicotine. The data presented here demonstrate that nicotine pretreatment results in decreased sensitivity to nicotine-induced seizures in rats.

Changes in the permeability of the blood-brain barrier in acute hyperammonemia. Effect of dexamethasone.

This study was designed to determine the contribution of elevated plasma ammonia levels to blood-brain barrier (BBB) abnormalities in the presence of intact liver. The permeability changes of the BBB were investigated grossly with Evans blue (EB) and quantitatively by measuring the blood-to-brain transfer content for alpha-aminoisobutyric acid (AIB) in normal rats and rats subjected to sublethal doses of ammonium acetate (NH4OAc) (750 and 600 mg/kg ip; at 30-min intervals). Some rats were pretreated with dexamethasone (DXN). Injection of NH4OAc increased both plasma and brain ammonia concentrations about 16-and 5-fold, respectively, above the control level. In rats receiving NH4OAc injection, the blood-to-brain transfer constant (Ki) for AIB was increased 3- to 11-fold. The elevated Ki values were limited to certain gray matter areas and less pronounced permeability changes were detected in white matter. Extravasation sites of EB were more restricted and were especially observed in thalamus and cerebellum, whereas cortex and white matter were unaffected. Dexamethasone pretreatment for 3 d reduced both leakage of EB and the Ki for AIB in NH4OAc injected animals, whereas acute treatment appeared ineffective. Dexamethasone did not prevent the development of coma but slightly decreased the ammonia concentration in plasma and brain. The results obtained indicate that hyperammonemia may disrupt BBB integrity not only to AIB and EB but also enhance the transport of other solutes.

Hormonal influence on the permeability of the blood-brain barrier: effect of an analog of adrenocorticotropic hormone, beta 1-24 corticotrophin.

Regional unidirectional transport of alpha-aminoisobutyric acid (AIB) (mol. wt.: 104) and sucrose (mol wt.: 342) which have a low permeability across the intact endothelium was investigated in brain of rats either treated with synacthène: an analog of ACTH, tetracosactide retard (beta-1-24 corticotrophin) or in brain of placebo-treated controls. Three days treatment with synacthène, reduced the rate of influx of AIB and sucrose in most of the brain regions studied especially in thalamus, hypothalamus, cortex, and caudate nucleus without affecting the vascular compartment. The brainstem, cerebellum and white matter were less affected. These experimental findings may suggest that ACTH exhibits significant influence on hormonal regulation of blood-brain barrier permeability. Thereby such a regulation may involve the entry of polar compounds into the CNS and may influence the central effects of diffusion-limited drugs.

Age-dependent alteration in regional cerebrovascular permeability during drug-induced epilepsy.

Age-related changes in blood-brain barrier permeability were investigated during pentylenetetrazol-induced seizures in rats aged from 15 days to 120 days. Tracers such as [14C]sucrose and [3H]inulin which diffuse very slowly across the intact endothelium were simultaneously injected i.v. in rats treated with pentylenetetrazol (PTZ) or in control animals. Permeability-surface area products (PA) were determined in 9 brain regions. Pentylenetetrazol-induced seizures caused a significant increase in PA for both sucrose and inulin in all brain regions studied. Blood-brain barrier dysfunction was present only in animals in which the mean arterial blood pressure rose at seizure onset. Although increased blood-brain barrier permeability was found partly in similar areas in both young and adult rat brains, in adults the increase was the highest in the preoptic area, septum, colliculus inferior, hypothalamus and in the cerebellum while the increase was comparatively much smaller in the same areas of young brains. The increase in blood-brain barrier permeability was extremely high in the hippocampus, hypothalamus and cerebellum of 15-day-old rat brain and, was least affected in the corpus striatum and cerebral cortex in contrast to older rats. From the results obtained it may be concluded that the increased cerebrovascular permeability induced by pentylenetetrazol differs markedly in localization in young and adult rats. The age-dependent increased blood-brain barrier integrity is not over all dependent on variations in the blood pressure, but rather on progressive maturation of capillaries and changes in their internal structure, and local phenomena in neuronal activity during the seizures.

Blood-brain barrier permeability: regional alterations after acute and chronic administration of ethinyl estradiol.

In this study we measured the effect of acute and chronic estrogen treatment on cerebrovascular permeability to sucrose and inulin. Animals were subcutaneously injected once with 0.1 micrograms/rat of ethinyl estradiol or injected daily with the same drug dose for 3 weeks. Control rats received the same amount of arachis oil vehicle. Three weeks treatment but not the single injection of ethinyl estradiol produced significant increases in the cerebrovascular permeability-surface area product for sucrose and inulin in almost all brain regions.

Regional alterations in blood-to-brain transfer of alpha-aminoisobutyric acid and sucrose, after chronic administration and withdrawal of dexamethasone.

The effect of dexamethasone administration and withdrawal was studied with respect to blood-brain barrier function. The tracers alpha-[3H]aminoisobutyric acid (AIB) (MW 104) and [14C]sucrose (MW 342), which have a low permeability across the intact endothelium, were simultaneously injected intravenously in rats treated with dexamethasone and placebo-treated control animals or in rats in which dexamethasone treatment was discontinued 3 days before the experiment. Unidirectional transfer constants (Ki) were determined in discrete brain regions. Steroid administration reduced the rate of influx of AIB and sucrose, whereas discontinuation of drug resulted in an increased permeability. These findings suggest that when exposure to glucocorticoids is prolonged, the efficiency of medical treatment of CNS diseases may decrease due to reduction of drug delivery to CNS. Thus, these experimental findings may have particular importance in the clinical setting of drug administration when considering the combination of steroids with other drugs, and may aid in understanding better the pathogenesis of some types of brain edema seen in patients from whom corticosteroid therapy has been withdrawn.

Age-related changes in regional patterns of blood-brain barrier breakdown during epileptiform seizures induced by pentylenetetrazol.

Age related changes in blood-brain barrier (BBB) permeability to macromolecules were investigated during seizures induced by pentylenetetrazol in rats aged from 6 to 120 days. Evans blue was used as a visual indicator of BBB integrity. BBB leakage due to seizures was present only in animals in which the mean arterial blood pressure (BP) rose with the seizure onset. Although considerable BBB damage was found partly in similar areas in young and adult rat brains, in adults the leakage of Evans blue was most intense in preoptic area, colliculus inferior, hypothalamus and cerebellum whereas the BBB opening was comparatively rare, in the same areas of young brains. In 6- and 15-day-old rats which did not differ in BP changes from the adults, the leakage was extremely intense in hypothalamus and hippocampus and in contrast to 30- or 120-day-old rats there was no leakage of Evans blue in preoptic area and cerebral cortex. From the results obtained, the conclusion may be drawn that the brain regions which are vulnerable to seizures induced by pentylenetetrazol differ markedly in developing and adult rats. On the other hand, in adult animals, either certain brain areas are more vulnerable to pentylenetetrazol or the BBB has an increased fragility particular to seizure activity. These results indicate that the sensitivity of BBB mechanisms may depend on proliferation of capillaries and changes in their internal structure and may emphasize it.

Effect of dexamethasone on transport of alpha-aminoisobutyric acid and sucrose across the blood-brain barrier.

The effect of glucocorticoids on the blood-brain barrier (BBB) was studied in rats following a single injection or 3 days of dexamethasone administration. Tracers with a low permeability across the intact endothelium, [14C]sucrose and alpha-[3H]aminoisobutyric acid ([3H]AIB), were simultaneously injected intravenously in untreated rats or in rats treated with dexamethasone. Unidirectional blood-to-brain transfer constants (Ki) in 14 regions of the rat brain were determined. In regions of control brain, average Ki values for AIB and sucrose were approximately 0.0020 and 0.00060 ml g-1 min-1, respectively. The lowest transfer constants were found in caudate nucleus, hippocampus, white matter, and cerebellum. In dexamethasone-treated animals, Ki values for both sucrose and AIB markedly decreased by 30-50% in almost all brain regions. These results indicate that a single injection or 3 days of treatment with dexamethasone causes an apparent reduction in the normal BBB permeability, and dexamethasone may greatly interfere with drug delivery into brain. These observations may have an importance for the administration of drugs in brain disease in the presence of steroids.

Kinetics and distribution volumes for tracers of different sizes in the brain plasma space.

Regional brain and plasma concentrations were determined for a series of radiotracers that differ in molecular weight and size in pentobarbital-anesthetized rats at 1, 5 and 30 min after i.v. injection. The tracers, [3H]inulin (mol. wt. 5000 Da, radius 1.5 nm), 5 [3H]dextrans (10,000-200,000 Da, 2.3-9.5 nm) and [51Cr]transferrin (79,000 Da, 3.8 nm), are not taken up into erythrocytes and do not measurably cross the blood-brain barrier in 30 min. Results were expressed as a brain distribution volume, defined as (dpm/g brain)/(dpm/ml plasma). Within 1 min after injection, all tracers attained an initial distribution volume which varied regionally from 0.4 to 1.6 X 10(-2) ml/g. The volumes remained constant between 1 and 30 min for tracers with radii greater than or equal to 3.8 nm, whereas the volumes increased up to 90% for tracers with radii less than or equal to 3.1 nm. Rates of equilibration for tracers with radii less than or equal to 3.1 nm were size dependent with smaller tracers equilibrating before larger tracers. These results indicate that the brain distribution volume for plasma tracers consists of two compartments: one which is quickly filled (less than or equal to 1 min) by all tracers and comprises approximately 60% of the total volume, and one which allows only tracers with radii less than or equal to 3.1 nm and comprises 40% of the total volume. The inverse relation between the rate of equilibration in the second compartment and molecular size may indicate a diffusion limitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dimethyl sulfoxide on blood-to-brain transfer of alpha-aminoisobutyric acid: examination of regional blood-brain barrier function.

The effect of dimethyl sulfoxide (DMSO) on brain capillary permeability has been controversial. We have studied the effect of DMSO on unidirectional transport of alpha-aminoisobutyric acid (AIB) across the blood-brain barrier (BBB) in rats. Rats were treated with 15% DMSO intraperitoneally (i.p.), intravenously (i.v.) or by an i.p. injection in combination with an i.v. injection, or in some cases intra-arterially by rapid infusion into left external carotid artery. The unidirectional blood-to-brain transfer constant (Ki) for AIB was measured in each group after the animals were killed. DMSO administration did not significantly increase Ki as compared to control Kj. These results show that it is unlikely that DMSO increases the permeability of BBB and therefore do not support the proposal that DMSO can act as a carrier at the BBB for compounds with restricted vascular permeability.

Water and electrolyte content of rabbit brain after opening the blood-brain barrier by acute hypertension.

Changes in water and electrolyte content of the brain and edema formation after acute, drug-induced hypertension were studied in albino rabbits. Blood-brain and blood-cerebrospinal fluid (CSF) barriers opened to Evans blue-albumin when systemic blood pressure was elevated abruptly to more than 160 mm Hg by i.v. injection of Aramin. No statistically significant changes in sodium and potassium content of brain, muscle, and CSF were observed. Measurable brain edema did not develop. The results suggest that short-lasting hypertensive barrier opening does not cause brain edema, but may enhance a tendency for brain edema.

Blood-brain barrier permeability to sucrose and dextran after osmotic opening.

Regional cerebrovascular permeability-surface area (PA) products were calculated for two nonelectrolyte tracers differing considerably in molecular weight and size [( 14C]sucrose: mol wt 340 daltons, radius 5 A; and [3H]dextran: mol wt approximately 79,000 daltons, radius approximately 65 A) in control (uninfused) rats and in rats 6, 35, and 55 min after the blood-brain barrier was opened by a 30-s infusion of 1.8 molal L(+)-arabinose into a carotid artery. In control brain regions, mean PA for [14C]sucrose was 10(-5) s-1, whereas PA was not measurable for [3H]dextran. Six minutes after arabinose infusion, PA for both substances increased dramatically to 10(-4) s-1 or more; PA then declined at 35 and 55 min after arabinose infusion, but more markedly for [3H]dextran than for [14C]sucrose. The results demonstrate a size-dependent, differential rate of closure of the blood-brain barrier after osmotic opening. This is shown to be consistent with a pore model with bulk flow for blood-brain barrier permeability after osmotic opening.

Pathophysiology of the opening of the blood-brain and blood-cerebrospinal fluid barriers in acute hypertension.

Acute hypertension, produced by i.v. Aramine injection, opened the blood-brain and blood-cerebrospinal fluid (CSF) barriers to Evans blue-albumin. In rabbits the threshold for blood-brain barrier (B-BB) opening was approximately 160 mm Hg and for blood--CSF barrier opening 150 mm Hg. The blood-brain and blood-CSF barriers were not opened by blood pressure elevations less than 80 mm Hg. Multiple blue spots (1- to 10-mm diameter) which show Evans blue-albumin extravasation, were seen throughout the cerebral cortex, occasionally in the medulla-pons, and cerebellum. Diffuse extravasation was not seen and the extravasation was nearly symmetrical in the two hemispheres. The barrier permeability was increased when systemic blood pressure was elevated rapidly rather than gradually to the threshold level. Endothelial or epithelial cell destruction was never observed in light and electron microscopic studies. Arterial blood and CSF PCO2, PO2 and pH remained constant, which is indicative of the lack of significant metabolic effect caused by hypertension. Barrier opening in acute hypertension is postulated to be due primarily to the direct mechanical effect of increased intraluminal pressure in cerebral vessels, which may cause widening of the tight junctions between endothelial cells.

Differential blood-brain barrier permeabilities to [14C]sucrose and [3H]inulin after osmotic opening in the rat.

The blood-brain barrier (B-BB) in 3-month-old rats was opened unilaterally by infusing 1.8 m L(+)arabinose in water into the internal carotid artery through a catheter in the external carotid. Two poorly penetrating uncharged test radiotracers of differing molecular weight and size, [14C]sucrose (340 daltons, radius 5 A) and [3H]inulin (5500 daltons, radius 15 A), were simultaneously injected i.v. in untreated rats, or rats at 1, 30, or 50 min after infusion of hypertonic arabinose solution. Evans-blue solution was injected 5 min prior to osmotic treatment as a visual indicator of barrier integrity. In regions of uninfused control brains, the [14C]sucrose permeability-surface area (PA) product approximated 10(-5) s-1, whereas PA was not measurable for [3H]inulin. In arabinose-infused animals, PA products on the ipsilateral hemisphere for both [14C]sucrose and [3H]inulin were markedly elevated 6 min after infusion, but decreased by 35 and 55 min. In nearly all regions, statistically significant differences were not found between 6-min [14C]sucrose- and [3H]inulin-PA values (P greater than 0.05). However, at 35 and 55 min in most regions, the PA for [3H]inulin was significantly lower (P less than 0.05) than PA for [14C]sucrose. The results indicated that the B-BB closed more rapidly to larger than to smaller molecules after osmotic treatment and were consistent with a pore model for osmotic B-BB opening.