IC50 Value: 53uM（inhibited the nerve-evoked twitches of phrenic nerve-hemidiaphragm preparations from ICR mice） . MPTP HCl (Sigma-Chem.) induced reduction in the DOPAC HVA/dopamine (DA) ratio and increase in striatal ascorbate (AS) oxidation in rats [1]. in vitro: MPTP inhibited the nerve-evoked twitches of phrenic nerve-hemidiaphragm preparations from ICR mice (20-30 g). PP 50 uM, but not PA 50 uM or TP 50 uM, potentiated the inhibitory effect of MPTP. PP 100 uM itself had an inhibitory action on twitch amplitude. The IC50 values for twitch inhibition by MPTP, TC and PP were 53, 0.7 and 123 uM, respectively. Pretreatment with PP 50 uM reduced the IC50 values of MPTP and TC to 18 and 0.3 uM, respectively[2]. in vivo: MPTP was examined in 12 squirrel monkeys (2 mg/kg every 2 hr for 4 doses) and human addicts self-administering varying doses with varying dosage patterns. In other experiments, 6 squirrel monkeys (0.6-1.0 kg) received MPTP (2 mg/kg every 2 hr for 4 doses). Some animals were pretreated with pargyline. These were killed 1 or 12 hr after the last MPTP dose while the others were killed up to 72 hr after that lase dose. Brain concentrations of MPGP/MPP were determined by GC/MS on a regional basis [3]. Clinical trial: Treatment of Levodopa Induced Dyskinesia in Patients With Parkinson's Disease. Phase II.