2-Phenylpyridine and 3-phenylpyridine, constituents of tea, are unlikely to cause idiopathic Parkinson's disease.

Idiopathic Parkinson's disease (PD) is likely to be caused by one or more unidentified neurotoxins, present in the environment or formed endogenously, which progressively damage dopaminergic nigrostriatal neurons. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is an experimental neurotoxin which produces biochemical and neuropathological changes in lower primates and mice and in humans inadvertently exposed to it that closely resemble those found in PD. 2-Phenylpyridine (2-PP) and 3-phenylpyridine (3-PP), both of them present in tea, are the only MPTP analogues that are known to be present in the human diet. We exposed C57 black mice, animals very sensitive to the dopaminergic neurotoxicity of MPTP, to prolonged parenteral and oral administration of large doses of 2-PP, and to prolonged parenteral administration of the N-methylated tetrahydro derivatives of 2-PP and 3-PP. The latter are closer chemical analogues of MPTP than are 2-PP and 3-PP themselves. None of these MPTP analogues lowered the contents of dopamine and its metabolites in the striatum of mice. We speculate that the neurotoxins which cause PD are unlikely to resemble MPTP structurally, and we suggest that the search for chemical causes of PD should be directed to a wider variety of compounds encountered by humans.