Distribution of Carbon‐14 Labeled Isoniazid in Brain

Abstract

Autoradiographic and tissue radioassay techniques have revealed that therapeutic levels of C14-labeled isoniazid or its metabolites are distributed in the central nervous system of cats according to a well-defined pattern. The pattern of distribution was compared with local vascularity and showed a positive correlation in such structures as cerebral cortex and medulla, but the relatively more vascular areas such as the geniculate bodies show less radioactivity than does the less vascular hippocampus in which isoniazid is heavily concentrated. Hippocampus was unusual in another respect in that the relative concentration remained high throughout 12 hours, while relative concentration in other areas of brain was falling. It is concluded that factors other than local vascularity condition the distribution of this drug in cat brain, and it is suggested that there is something physiologically different about the relationship of hippocampus to this drug.