Blood flow changes in response to 20 Gy 137Cs whole brain irradiation were measured with quantitative autoradiography of [14C}iodoantipyrine} (IAP) in intracerebral grafts of the 36B-10 rat glioma, the brain around tumor (BAT), the contralateral corpus callosum, and the contralateral cerebral cortex. Irradiations were delivered on Day 14 post-transplantation, and measurements of flow (F) were performed with IAP on Day 15 or Day 16. Mean values of F were determined in individual tumors and in treatment groups. In 15- and 16-day-old unirradiated control tumors, the group mean F was 0.31 ml · g−1 · min−1. In both 15- and 16-day-old tumor groups irradiated on Day 14 (Day 1 and 2 postirradiation tumors) the mean F for each day's group was 0.52 ml · g−1 · min−1, 68% higher than the control (P < 0.01). Flow in the BAT and the contralateral corpus callosum similarly was increased at these times (P < 0.01). Flow in the contralateral cerebral cortex was 1.1, 1.5, and 1.3 ml · g−1 · min−1 in the control, 1 day postirradiated, and 2 day postirradiated groups, respectively, but these increases were not significantly different from the control. These data indicate that flow increases in the intracerebral gliomas as well as in normal brain regions during the 2 days following 20 Gy irradiation. Changes such as these following radiotherapy may have important effects on the bioavailability of chemotherapeutic drugs.

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