Recrystallization from ether causes unusual changes in the convulsant activity of pentylenetetrazol.

The convulsant activity of commercial pentylenetetrazol (PTZ) and that of pentylenetetrazol recrystallized from ether (PTZE) were compared in the waking rabbit by means of recording the electrical activity of the brain. In addition, the interaction between the two substances was studied. When given in slow intravenous infusion, PTZE proved only half as effective as PTZ (threshold doses: 23.18 +/- 1.8 mg/kg and 12.40 +/- 0.7 mg/kg, respectively). One single infusion of PTZE 5-10 days prior to the administration of PTZ decreased the latter's convulsant activity to half of the original, while PTZ pretreatment left the activity of PTZE unaltered. Previous physico-chemical investigations suggested that, after recrystallization from ether the molecule might be present in dimer form at the phase-boundaries. Such a process, if taking place also at the cell membrane surface might account for the diminished convulsant activity of the recrystallized molecule.