On the pathogenesis of regional cerebral ischemia in intracranial hemorrhage: a causal influence of potassium?

Cerebral ischemia and intracranial hemorrhage are the most important causes of perinatal brain damage and their pathogenesis seems to be interrelated. Several components in blood have been shown to cause contraction of cerebral blood vessels. In the present study we examined the changes with time of the concentration of standard electrolytes in a mixture of blood and mock cerebrospinal fluid, whether these changes may affect cerebrovascular tone, and if calcium blockers could influence such an effect. Extracellular K+ increased to about 23 mM 4 days after mixing when half of the mixture consisted of blood, and remained nearly constant for at least 8 days thereafter. Using isometric recording of circular tension in a controlled tissue bath it was found that isolated human pial arterioles, small arteries, and feline middle cerebral arteries contracted markedly when K+ exceeded 10 and 20 mM, respectively. It is concluded that neonatal perihemorrhagic ischemia may be, at least partly, due to leakage of K+ from the erythrocytes. The contractile effect of extracellular K+ is effectively counteracted by Ca++ entry blockers, which therefore may have a role in the prevention of perihemorrhagic ischemia in neonates.