Effect of long-term L-threo-3,4-dihydroxyphenylserine administration on alpha 2-adrenergic receptors in platelet membranes in neurologic disorders.

The effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS), an unnatural norepinephrine precursor, on alpha 2-adrenergic receptors in platelet membranes were investigated in a patient with familial amyloidotic polyneuropathy, two patients with multiple system atrophy, and two patients with Parkinson's disease. Each patient was treated for at least six months. While L-threo-DOPS alone, or in combination with decarboxylase inhibitor benserazide hydrochloride, produced sustained increase in plasma norepinephrine and clinical improvement, it did not induce a change in the number of alpha 2-adrenergic receptors in platelet membranes.