Late functional changes in the vasculature of the rat brain after local X-irradiation

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Abstract
The brains of young adult rats were irradiated with doses of 500-4000 rad. At intervals of 3-15 mo. after irradiation regional changes in the functional vasculature were investigated using the iodoantipyrine extraction technique. Modifications in vascular function were restricted to animals locally irradiated with doses of 2000 and 3000 rad. The 1st change was observed 3 mo. after irradiation and was characterized by a reduction in antipyrine extraction in the mid-brain and brain stem of animals irradiated with 2000 rad. At 6 and 9 mo. after exposure to 2000 and 3000 rad significant increases in antipyrine extraction were found in the 4 brain regions examined, although the effect was greatest in the midbrain. These results are compared and contrasted with functional changes reported in other normal tissues; the link between these functional changes in the brain vasculature and the appearance of gross vascular lesions after a latent period of 1 yr is discussed. The increase in iodoantipyrine extraction represents a regulatory reaction by the vasculature of the brain to tissue hypoxia. Focal vascular lesions in the brain occur as a consequence of the failure of this reaction to hypoxia.

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