Significance of Plasma Dopamine β-Hydroxylase Activity as an Index of Sympathetic Neuronal Function

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Abstract
Plasma norepinephrine and dopamine .beta.-hydroxylase (EC 1.14.17.1) activity were measured in rats. Adrenergic neuron blockade with bretylium for 4 h and ganglion blockade with chlorisondamine for 72 h lowered plasma norepinephrine. Neither treatment altered plasma dopamine .beta.-hydroxylase activity. Phenoxybenzamine for up to 48 h markedly raised plasma norepinephrine and transiently lowered plasma dopamine .beta.-hydroxylase at 24 h. Prolonged pharmacological modification of sympathetic nervous activity and plasma norepinephrine were not attended by parallel changes in circulating dopamine .beta.-hydroxylase activity. Plasma dopamine .beta.-hydroxylase activity does not appear to be a sensitive index of prolonged alterations in sympathetic neural activity. Norepinephrine in plasma appears to reflect sensitively and accurately the rate of neurotransmitter release.