Increased Blood–Brain Permeability with Hyperosmolar Mannitol Increases Cerebral O2 Consumption and O2 Supply/Consumption Heterogeneity

Abstract

This study was performed to evaluate whether increasing the permeability of the blood–brain barrier by unilateral intracarotid injection of hyperosmolar mannitol would alter O2 consumption and the O2 supply/consumption balance in the ipsilateral cortex. Rats were anesthetized with 1.4% isoflurane using mechanical ventilation. Retrograde catheterization of a unilateral external carotid artery was performed to administer 25% mannitol at a rate of 0.25 ml/kg/s for 30 s. The blood–brain barrier transfer coefficient ( K of 14C-α aminoisobutyric acid was measured in one group (N = 7) after administering mannitol. Regional cerebral blood flow (rCBF), regional arterial and venous O2 saturation and O2 consumption were measured in another group using a 14C-iodoantipyrine autoradiographic technique and micro-spectrophotometry (N = 7). Vital signs were similar before and after administering mannitol. K i was significantly higher in the ipsilateral cortex (IC) (22.3 ± 8.4 μl/g/min) than in the contralateral cortex (CC) (4.4 ± 1.1). rCBF was similar between the IC (105 ± 21 ml/g/min) and the CC (93 ± 20). Venous O2 saturation was lower in the IC (43 ± 7%) than in the CC (55 ± 4%). The coefficient of variation (100 × SD/mean) of venous O2 saturation was significantly elevated in the IC (32.3) compared with the CC (18.2), indicating increased heterogeneity of O2 supply/consumption balance. O2 consumption was higher in the IC (9.6 ± 3.0 ml O2/100 g/min) than in the CC (6.7 ± 1.5). Our data suggested that increasing permeability of the blood–brain barrier increased cerebral O2 consumption and the heterogeneity of local O2 supply/consumption balance.