Brain extracellular space in monkey fetuses subjected to prolonged partial asphyxia

Abstract

Rhesus monkey fetuses, closely approaching term, were subjected to episodes of prolonged partial asphyxia while still in utero. Maternal blood presure was gradually decreased by increasing the concentration of inspired fluothane until a moderate degree of fetal compromise, indicated by a pH of 6.9–7.1 and a Po 2 of 15–18 mm Hg was sustained for 3–4 hr. Immediately after delivery by cesarian section, specimens of fetal cerebral cortex were frozen in liquid Freon-22, pre-chilled to —78C for 10 days. Electron micrographs of these specimens were prepared from which the relative volume of extracellular space was estimated stereometrically. A mean extracellular space of 4.1% in fetal animals subjected to prolonged partial asphyxia differed significantly from an extracellular space of 9.1% found in cerebral cortex from normal fetuses, similarly delivered. Additionally, mitochondria from asphyxiated fetuses were swollen and characterized by a dispersed, dilute-appearing matrix. These data suggested that the brain swelling concomitant with prolonged partial asphyxia is associated with a translocation of extracellular fluid, which appears to depend upon an altered mitochondrial metabolism and which results in a reduced volume of extracellular space.