Biodistribution of N-isopropyl-p-iodoamphetamine in the rat brain.

The biodistribution of N-isopropyl-p-iodoamphetamine (IMP) was studied in the rat brain. 131I-labelled IMP was injected intravenously in awake animals. Activities in the brain of Sprague-Dawley rats were 2.68-3.22 (% dose/g) in the cortex and 0.59-0.66 (% dose/g) in the white matter at 1 min p.i. Activities in the cortex were slightly increased at 60 min p.i., while activities in the white matter increased markedly at 60 min and 6 h p.i. Therefore, the cerebral cortex-to-white matter ratio decreased from 5 to 1 within 60 min after injection. Autoradiograms of the rat brain at 1-10 min p.i. showed high contrasts. Activities were high in the cortex and low in the white matter, but homogeneous at 60 min-6 h. IMP seems to be a useful agent for cerebral perfusion imaging in the early phase after injection. Knowledge of biodistribution of this agent is considered to be indispensable for the interpretation of images.