Osamu Gotoh

Ischemic brain edema following occlusion of the middle cerebral artery in the rat. I: The time courses of the brain water, sodium and potassium contents and blood-brain barrier permeability to 125I-albumin.

The present study was undertaken to analyze the roles of brain cations and of the blood-brain barrier (BBB) to albumin in the development of ischemic brain edema. Using the rat middle cerebral artery (MCA) occlusion model, changes in the brain water, sodium, and potassium contents were followed for a period of seven days. The permeability of the BBB to proteins was also followed by 125I-albumin transfer from the blood into the brain. A significant edema developed as early as three hours after MCA occlusion. This progressed rapidly to reach a maximum on the third day, gradually regressing thereafter. The increase in the brain water contents showed a parallel time course to the increase in the sodium and decrease in the potassium contents. A significant increase in the BBB permeability to albumin occurred 72 hours after MCA occlusion. However, there was no correlation between the brain water content and BBB permeability to albumin in the hemispheres studied 72 hours after MCA occlusion. The correlation between the brain water and sodium contents was not clear during the first six hours, but became highly significant thereafter. The data suggest that an increase in the BBB permeability to sodium occurred 12-48 hours after MCA occlusion, which, together with an antecedent intracellular shift of sodium, resulted in a massive influx of water and sodium into the brain. The BBB permeability change to sodium, not to proteins, seems to play a predominant role in the pathogenesis underlying ischemic brain edema.

Ischemic brain edema following occlusion of the middle cerebral artery in the rat. II: Alteration of the eicosanoid synthesis profile of brain microvessels.

Using the rat middle cerebral artery occlusion model, alterations in the eicosanoid synthetic capacity of brain microvessels following ischemia were studied by radiochromatography. Brain microvessels of normal rats predominantly produced hydroxyacids with relatively small amounts of PGD2 and PGE2 from exogenous arachidonic acid. Confirmation that hydroxyacids and prostaglandins were products respectively of lipoxygenase(s) and cyclooxygenase was obtained by experiments using indomethacin and eicosatetraynoic acid. The eicosanoid synthetic capacity of the brain microvessel, especially of hydroxyacids, was significantly enhanced 24 and 72 hours after the onset of ischemia. Because this is the phase of maximum edema in the present model, enhanced eicosanoid production in the brain microvessel may be involved in the mechanisms that underly ischemic brain edema.

Alterations of the eicosanoid synthetic capacity of rat brain microvessels following ischemia relevance to ischemic brain edema

To know the mechanism underlying ischemic brain edema, a time‐course analysis of the eicosanoid synthetic capacity of brain microvessels was carried out using unilateral, middle cerebral artery (MCA)‐occluded rats. Concomitant with the development of brain edema the synthetic capacity of all products, including cyclooxygenase and lipoxygenase products, increased significantly. Next the effects of 15‐hydroperoxyarachidonic acid (15‐HPAA) on the synthetic capacity of microvessels were examined. The drug caused a generalized increase of each product, the profile of which was similar to that obtained with ischemic hemispheres, although the ratios of each product differed somewhat among them. The enhanced synthesis of eicosanoids by 15‐HPAA was markedly suppressed by radical scavengers such as α‐tocopherol, hydroquinone, and 1,2‐bis(nicotineamide)‐propane. Furthermore, the evolution of brain edema was virtually suppressed by the systemic administration of 1,2‐bis(nicotineamide)‐propane. The above result suggests that the enzyme activity of the arachidonic acid (AA) cascade of microvessels is stimulated by its own products. Such a mechanism will form a vicious cycle that accelerates the accumulation of free radicals within microvessels and thus may play a role in the progressing disruption of the blood‐brain barrier (BBB) following ischemia.

The role of free radicals and eicosanoids in the pathogenetic mechanism underlying ischemic brain edema

Results of our consecutive study on the pathogenic mechanism underlying ischemic brain edema are summarized in this paper. Pertinent findings are as follows: (1) there is a close correlation between the influxes of water and sodium following ischemia; (2) the edema fluid can be regarded as the ultrafiltrate of serum; (3) there is a significant increase in the brain content of HETEs following ischemia; (4) the lipoxygenase activity of brain microvessels is increased following ischemia; (5) the lipoxygenase activity as well as the Na+, K+-ATPase activity of brain microvessels are enhanced by a hydroperoxide, 15-HPETE; (6) inhibition of Na+, K+-ATPase of brain microvessels by intraarterial infusion of ouabain resulted in a significant decrease in edema formation; and (7) not the cyclooxygenase, but the lipoxygenase pathway seems to be involved in the enhancement of microvessel Na+, K+-ATPase. Lipoxygenase(s) and Na+-K+-ATPase of brain microvessels, the activities of which are enhanced by an increased level of free radicals and/or hydroperoxides, may play a significant role in the occurrence of ischemic brain edema.

Fine structures in denaturation curves of bacteriophage lambda DNA. Their relation to the intramolecular heterogeneity in base composition

Precise recording of polyphasic optical melting curves was carried out for three kinds of bacteriophage lambda DNA differing in length (lambdac1857s7, lambdacIb2 and lambdacIb2b5). Each of denaturation steps in melting profiles was characterized by two parameters, the melting temperature and the relative size. Any difference in fine structures in melting profiles was not recognized between the intact lambdacI857s7DNA and the DNA fragmented into halves. The change in fine structures in melting profiles caused by the deletions of the b2 and b5 region agreed qualitatively well with the prediction based on the physical and the genetical maps of phage lambda chromosome. The combined results indicate that, first, the well-known linear relationship between melting temperature and G+C content may apply also to each of denaturation steps in polyphasic melting curves due to heterogeneity of nucleotide distribution in a single DNA species, and, second, the effect of molecular ends on melting fine structures can be neglected at moderate salt concentration (0.01 M less than or equal to Na+ less than or equal to 0.2 M) for such a high molecular weight DNA. The heterogeneous distribution of nucleotides was derived for lambdaDNA and for its b2 and b5 regions.

A Model to Study Ischemic Brain Edema in Rats and the Influence of Drugs

We have recently reported that middle cerebral artery (MCA) occlusion in rats produces a uniform pattern of cerebral infarction13. Development of edema in this model was further studied using exogenous and endogenous protein tracers. It was found that vasogenic edema developed several hours after MCA occlusion3. The purpose of the present study was to find out whether progression of edema can be quantitatively evaluated in this model of focal cerebral ischemia. The effect of dexamethasone and of a nicotinamide derivative (AVS: 1,2-Bis(nicotinamido)propane) in the time-course of edema were studied in addition. The therapeutic effect of steroids on ischemic brain edema is still a controversial subject. AVS is a scavenger of hydroxyl radicals (OH). Since involvement of free radicals is considered in ischemic brain edema, treatment with AVS was compared with that of dexamethasone.

Ischemic Brain Edema and the Glutathione System

Recent studies have suggested the possible role of free radical formation and the resultant lipid peroxidation in the pathogenesis of ischemic brain edema. If this is true, the dynamics of naturally occurring radical scavengers such as the glutathione system may also be influenced. The present study was undertaken to examine the evolution of brain edema and the concomitant changes in the dynamics of the glutathione system in focal cerebral ischemia.