[Brain edema initially develops in the periphery of focal cerebral ischemia]

Ischemia causes disturbances of the ionic equilibrium, i.e., Na+ and water influx and K+ efflux. When the ischemic tissue keeps contact with cerebral blood flow, brain tissue equilibrates with systemic circulation and consequently shifts of electrolytes and water are induced. Therefore, brain edema should initiate in the peripheral area of focal cerebral ischemia. To test this hypothesis, we performed the following experiments. Focal ischemia was induced by occlusion of the right common carotid artery in gerbils and by embolization with microspheres in rats. Water and electrolyte content was determined using punched out samples and regional K+ and Ca2+ distribution was visualized by histochemical K+ staining and 45Ca-autoradiography, respectively. Cerebral blood flow and glucose metabolism were evaluated by 14C-iodoantipyrine or 18F-fluoroantipyrine and 14C-deoxyglucose autoradiographies, respectively. Two hours of ischemia in gerbils with definite hemiparesis caused K+ depletion in the ischemic area, often most pronounced in the periphery of the lesion. Water content of cerebral cortex was 79.0 +/- 0.9, 82.0 +/- 1.0, 80.7 +/- 0.9 (%; mean +/- SD) for nonischemic, periphery and center of ischemia, respectively (significantly different with each other). Na+ content was increased and K+ content was decreased most prominently in the periphery of ischemia. Exogenous Ca2+ was also accumulated in the periphery. In the embolized stroke in rats, K+ depletion and Ca2+ accumulation obviously rimmed the ischemic focus. Furthermore the infarcted area was only part of the disturbed area of acute-phase glucose metabolism. Thus water and ionic disturbances were different between in the periphery and in the center of focal cerebral ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)