Evidence for a peripheral dopaminergic neural system
In peripheral organs investigated until recently (heart, vas deferens, gut, adrenal gland, etc.) dopamine was present in low concentrations, representing only a few percent of the total catecholamines (Anton and Sayre, 1964; Laverty and Sharman, 1965; Snider et al., 1973). The low concentration, per se, was taken as evidence against a possible neurotransmitter role for dopamine.
In the heart and salivary gland of rat it was possible to block the enzymatic conversion of dopamine to norepinephrine with drugs, thus demonstrating a precursor role for dopamine. Furthermore, inhibition of monoamine oxidase failed to produce a significant increase in the concentration of dopamine (Snider et al., 1973), thus, supporting the notion that peripheral dopamine is solely converted to norepinephrine and is not metabolized by deamination as it is in brain. On the basis of these few studies it was generally assumed that all dopamine in peripheral nerves serves only as a precursor for norepinephrine.
KeywordsAttenuation Dopamine Norepinephrine Epinephrine Catecholamine
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