Influence of respiratory stress and hypertension upon the blood-brain barrier

The effects of acute hypertension and respiratory stress induced by Aramine (metaraminol bitartrate) upon blood-brain barrier (BBB) permeability to horseradish peroxidase (HRP) were studied in adult inbred white rats. The BBB permeability was quantitated by slicing the brain of each animal into 500-mu thick sections, incubating the sections using the Reese-Karnovsky method, and counting all observed HRP perivascular exudates. No evidence of BBB compromise or significant elevation of blood pressure (BP) was observed in the following experimental groups: 1) control group of five animals; 2) hyperventilated group of five animals (final mean arterial blood gases; pO2, 104.2 mm Hg; pCO2, 24.8 mm Hg; pH, 7.53); 3) anoxic-stress group of five animals (final mean arterial blood gases; pO2, 31.4 mm Hg; pCO2, 58.2 mm Hg; pH 7.21). However, in a group of 15 animals subjected to anoxic stress followed by hyperventilation, in addition to extreme changes in the levels of arterial blood gases, a significant BP increase occurred (mean BP increase per second, 3.43 +/- 0.25 mm Hg; final mean BP, 163.3 +/- 3.18 mm Hg); as well as significant BBB opening (mean number of HRP exudates per animal, 12.2 +/- 0.85). Likewise, a final group of 10 animals given intravenous Aramine displayed a significant systemic BP elevation (mean BP increase per second, 6.9 +/- 0.38 mm Hg; final mean BP, 165.8 +/- 3.16 mm Hg), accompanied by BBB opening (mean number of exudates per animal, 51.5 +/- 5.95). The variable most strongly associated with the degree of barrier opening was the rate of BP rise (correlation coefficient = +0.84).