[Evaluation of 3H-paroxetine as a radiopharmaceutical for lung function].

The potential of 3H-paroxetine as a radiotracer for in vivo study of the function in mouse lung was examined. A high accumulation of radioactivity in the mouse lung was observed after intravenous administration of 3H-paroxetine. However, the distributions of radioactivity in the mouse lung were not significantly decreased by treatment with paroxetine or other monoamine uptake inhibitors (6-nitroquipazine, desipramine and GBR 12909). It was found that the radioactivity in the mouse lung at 1 hr after intravenous administration of 3H-paroxetine was due to unmetabolized 3H-paroxetine from TLC and HPLC analyses. Furthermore, 3H-paroxetine exhibits both saturable and high affinity binding sites in mouse lung with a maximal number of binding sites (Bmax) of 303 fmoles/mg protein and a dissociation constant (Kd) of 92.2 pM. These results suggest that 3H-paroxetine would be a suitable radiopharmaceutical for in vivo study of the function of lung as a metabolic organ of serotonin.