EFFECT OF SYMPATHETIC-STIMULATION ON PERMEABILITY OF THE BLOOD-BRAIN-BARRIER TO ALBUMIN DURING ACUTE HYPERTENSION IN CATS

Most studies concerning effects of neural stimuli on the cerebral circulation have focused on changes in cerebral blood flow (CBF). The purpose of this study was to examine effects of sympathetic nerves on permeability of the blood-brain barrier (BBB) to albumin, using a quantitative method, and to relate changes in blood flow to changes in permeability of the BBB. Permeability of the BBB was evaluated by measuring the accumulation of 131I-labeled serum albumin (RISA) in brain. RISA was injected intravenously, and the ratio of brain RISA to blood RISA was used as an index of permeability of the BBB. In normotensive cats, the BBB index in the cerebellum was 0.12±0.04% (mean ± SE. During acute hypertension produced by intravenous norepinephrine, the BBB index in the cerebrum increased to 0.91±0.20% (P<0.05). Sympathetic stimulation during hypertension attenuated the increase in BBB index: the BBB index was 0.38±0.10% and 1.01±0.26% on the stimulated and unstimulated sides of the cerebrum, respectively (P<0.05). CBF increased more than threefold during severe hypertension; sympathetic stimulation attenuated the increase in flow. Increases in flow and disruption of the BBB were most marked in cortical gray matter, and responses to sympathetic stimulation were also largest in cortical grey matter. Disruption of the BBB during hypertension was minimal in subcortical grey and white matter, and sympathetic stimulation had no detectable effect in these areas. In summary, these studies provide the first quantitative evidence that acute hypertension increases the permeability of the BBB to albumin and that sympathetic stimulation reduces disruption of the barrier. The regions of the brain that were most susceptible to disruption of the BBB were most responsive to the protective effect of sympathetic stimulation.