Regional blood‐to‐tissue transport in ethylnitrosourea‐induced brain tumors

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Abstract
Regional blood-to-tissue transport, expressed as a unidirectional transfer rate constant (K), was measureed in experimental brain tumors using alpha-aminoisobutyric acid (AIB) labeled with carbon 14 and quantitative autoradiography. A total of sixteen oligodendrogliomas, four mixed gliomas, three astrocytomas, two diffuse gliomatoses, one anaplastic astrocytoma, one ependymoma and four malignant schwannomas were studied in 9 rats. The mean Ks for all glioma classifications were similar, averaging 2.6 ± 0.4 (standard error of the mean) ml · kg−1 min−1, and were only slightly higher than those for nontumorous parietal cortex (2.1 ml · kg−1 · min−1), corpus callosum (0.9 ml · kg−1 min−1), and a comparable region of brain tissue in the contralateral hemisphere (1.3 ml · kg−1 · min−1). Values of K varied minimally in the intracerebral gliomas and were marginally correlated with tumor cell morphology in only two tumors. In some (but not all) of the larger gliomas, increased vascularity, with or without endothelial proliferation, was associated with a 3-to 15-fold increase in K. Regional K values in malignant schwannomas were highly variable (4 to 207 ml · kg−1 · min−1) and generally were not correlated with specific histological features of the tumor, except in some regions with increased vascularity. Estimates of the average fractional extraction of AIB by the intracranial gliomas and malignant schwannomas were 0.01 and 0.2, respectively; average fractional extractions for nontumorous brain were approximately 0.003.

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