In vivo distribution of organophosphate antidotes: autoradiography of [14C]HI-6 in the rat.

In order to visualize the distribution of HI-6 in the rat after iv administration, autoradiographic experiments were carried out with [14C]HI-6, labeled at the carbon of the carboxamide moiety. Autoradiography clearly confirms penetration of HI-6 into the central nervous system. Considerable radioactivity was found in the cerebrum, the cerebellum, and the choroid plexus. No significant activity was detected in the pontomedullary region or the spinal cord. Peripherally, [14C]HI-6 is observed in large amounts in kidneys, heart, liver, nose, bladder, testes, and marrow-containing bone. The gastrointestinal tract was largely devoid of any radioactivity. The relative absence of HI-6 in the pontomedullary region renders centrally mediated influences of HI-6 on hemodynamic and respiratory parameters less likely.