HYPOXIA-INDUCED BRAIN ANGIOGENESIS IN THE ADULT-RAT

1. Prolonged hypoxia increases the brain vascularity. Here ave studied the protein and deoxyribonucleic acid (DNA) content of isolated cereb ral microvessels in hypoxic and control rats. 2. Adult male Wistar rat s that were subjected to hypobaric hypoxia at 50.5 kPa (0.5 atm) for p eriods of 1, 2 or 3 weeks and normoxic littermate controls were used. Cerebral microvessels were harvested by bulk isolation from the pooled cortical mantles of three to six rats in each group. The isolated mic rovessels were assayed for their protein and DNA content. 3. Microvess el protein yield increased from 0.31 to 0.45 mg of microvessel protein (g wet wt)(-1) of cerebral cortex after 1 week of hypoxia, but did no t increase further during up to 3 weeks of hypoxia. In contrast, micro vessel DNA yield did not increase during the first week of hypoxia, bu t increased significantly after 2 weeks of hypoxia and continued to in crease up to 56 mu g of microvessel DNA (g cerebral cortex)(-1) at 3 w eeks of hypoxia (normoxic mean was 32 mu g DNA g(-1)). 4. The cell siz e index (mg protein : mg DNA) of isolated cerebral microvessels increa sed after 1 week of hypoxia, suggesting microvascular hypertrophy, but returned to control by the second week of hypoxia and decreased to be low control levels by the third week of hypoxia, suggesting microvascu lar hyperplasia. These results indicate that the increased vascularity of the brain in hypobaric hypoxia progresses from an early phase of m icrovascular hypertrophy to later microvascular hyperplasia.