Synthesis of C-labeled imipramine and its biodistribution in mice: a potential tracer for positron emission tomography.

A tricyclic antidepressant, C-labeled imipramine was synthesized by N-methylation of desipramine with 11CH3I to assist in the imaging of the human imipramine receptor by positron emission tomography. The radiochemical yield after purification of 11C-imipramine by high performance liquid chromatography was 28-63% at a specific activity of 26-53 Ci/mmol. The time required for synthesis, including purification was 30 min from the end of 11CH3I trapping. The organ distribution of 11C-imipramine was investigated in mice at various times after i.v. injection. The main accumulation of radioactivity was in the kidney, followed by the lung and the heart. In the brain, the radioactivity levels in the hypothalamus and striatum were the highest and remained constant, differentiating them from other portions of the brain. Furthermore, the result of a binding assay with 3H-labeled imipramine suggested that the regional distribution of 11C-imipramine in the same mouse brain correlated to that of the high affinity imipramine binding site.