Differential effect of L-threo-3,4-dihydroxyphenylserine in pure autonomic failure and multiple system atrophy with autonomic failure.

Treatment with L-threo-3,4-dihydroxyphenylserine (L-threo-dops), a synthetic precursor of norepinephrine, significantly increased upright blood pressure in patients with multiple system atrophy but had no effect on the upright blood pressure of patients with pure autonomic failure. These results suggest that the site of action of L-threo-dops is central and that its pressor effect requires intact peripheral sympathetic neurons.