Rapid effects of MPTP in the mouse colon.

Mechanical responses of the mouse colon to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were measured in vitro. MPTP caused muscle relaxation with an onset time of about 10 s. This relaxation was inhibited by propranolol. Pretreatment of the animals with reserpine significantly reduced the MPTP-induced relaxation. These observations indicate that MPTP liberates a catecholamine (presumably noradrenaline) from nerve terminals in the colon wall. The mechanism underlying this effect is not yet clear but it appears that oxidation to 1-methyl-4-phenyl-pyridinium is not required.