Plasma Dopamine Beta Hydroxylase (D.B.H.) activity in Parkinsonian patients under L-dopa, and 2-Bromo-alpha-ergocriptine loading

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Abstract
Dopamine-Beta-Hydroxylase (D.B.H.)-activity was measured in the plasma of untreated Parkinsonian patients, after treatment 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<0.02) in the control group. After 2-Bromo-alpha-ergocriptine loading the decrease in D.B.H.-activity was 32.6±4.4% in the Parkinsonian patients, and 158±4.9% (p<0.02) in the control group. This reduced D.B.H.-activity after L-dopa loading may reflect an impairment, in the Parkinsonian patients' ability to metabolize 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.