Adrenergic and dopaminergic properties of dopamine sulfoconjugates

The 3- and 4-sulfate esters of dopamine (DA-3-SO4 and DA-4-SO4, respectively), the two main metabolites of DA, were evaluated for potential intrinsic or indirect catecholaminergic activities. Both compounds lacked any appreciable affinities for alpha 1, alpha 2, beta 1, beta 2 and DA-2 receptors. In the superfused [3H]norepinephrine-preloaded dog saphenous vein, both dopamine sulfates were devoid of any intrinsic inhibitory activity such as observed with dopamine pre- and postsynaptically. In addition, they did not displace the labeled vesicular neurotransmitter as did dopamine. In anesthetized dogs the two compounds failed to stimulate either the dopaminergic receptors (DA-1) of mesenteric vascular beds or the adrenergic receptors mediating the vasodilatory and pressor responses to dopamine.

In our experimental conditions DA-3-SO4 and DA-4-SO4, the products of dopamine sulfoconjugation, lacked any demonstrable intrinsic affinity and/or efficacy on the dopaminergic and adrenergic receptors directly or indirectly through their metabolic transformation or through displacement of endogenous neurotransmitter.