Plasma dopamine beta hydroxylase (D.B.H.) activity in Parkinsonian patients under L-dopa, and 2-bromo-alpha-ergocriptine loading.

Dopamine-Beta-Hydroxylase (D.B.H.)-activity was measured in the plasma of untreated Parkinsonian patients, after tretment with L-dopa and 2-Bromo-alpha-ergocriptine. The findings were compared to the D.B.H.-activity of a matched healthy control group. After L-dopa loading D.B.H.-activity decreased in the Parkinsonian patients by 27.6 +/- 3.1% compared to 16.2 +/- 3.3% (p less than 0.02) in the control group. After 2-Bromo-alpha-ergocriptine laoding the decrease in D.B.H.-activity was 32.6 +/- 4.4% in the parkinsonian patients, and 158 +/- 4.9% (p less than 0.02) in the control group. This reduced D.H.B.-activity after L-dopa loading may reflect an impairment, in the Parkinsonian patients' ability to metaoblize L-dopa. The reduced D.B.H.-activity after treatment with 2-Bromo-alpha-ergocriptine may be explained by a pronounced antagonistic influence of 2-Bromo-alpha-ergocriptine on the presynaptic dopamine receptors, suggesting that presynaptic dopaminergic receptors are involved in Parkinson's disease.