MIDDLE CEREBRAL-ARTERY OCCLUSION INCREASES CEREBRAL CAPILLARY-PERMEABILITY

One hour after middle cerebral artery occlusion, the regional blood to brain transfer coefficient of alpha-aminoisobutyric acid was determin ed in eight barbiturate anaesthetized rats, The transfer coefficient ( mul/min-1/g-1) was significantly higher in the ischaemic cortex (10.6 +/- 2.3) than in the contralateral cortex (6.5 +/- 1.0). Cerebral regi onal capillary surface area was determined in another group of twelve rats using an alkaline phosphatase stain for the total capillary bed a nd fluorescein isothiocyanate-dextran to visualize the perfused capill aries. Perfused capillary surface area (cm2/cm3) was lower in the isch aemic cortex (141 +/- 31) than in the contralateral cortex (426 +/- 32 ). Using these values for the transfer coefficient, surface area and o ur previously published data of regional cerebral blood flow after mid dle cerebral artery occlusion, we calculated the extraction fraction o f alpha-aminoisobutyric acid, the permeability-surface area product an d the permeability of cerebral regional capillary beds. Although, ther e are numerous reports of permeability-surface area product of brain c apillaries, to our knowledge, the permeability has never been determin ed before. The calculated extraction fraction ratio for alpha-aminoiso butyric acid for ischaemic cortex/contralateral cortex was 3.1. Simila r ratios for permeability-surface area product and capillary permeabil ity were 1.6 and 4.4, respectively. Thus, there was a more than four f old increase in capillary permeability to small molecules in the ischa emic cortex one hour after middle cerebral artery occlusion.