Pharmacological actions of dopamine sulfoconjugate on cardiovascular system

Pharmacological actions of dopamine 4-sulfate on the cardiovascular systems were examined and compared with those of dopamine. Dopamine 4-sulfate, used in the present study, was minimally contaminated with dopamine (less than 0.02%). Dopamine 4-sulfate at doses ranging from 0.1 to 1 mumol/kg did not elicit any appreciable changes in systemic blood pressure and heart rate of anesthetized rabbits. Contractile activity and heart rate of isolated perfused rat heart were also unaffected by the agent. Dopamine 4-sulfate at concentrations of 1 and 0.3 mM, reduced a significant contraction of isolated rabbit renal and femoral arteries, respectively, but not in the aorta. The extent of the increase in tension development induced by 1 mM dopamine 4-sulfate in the femoral artery, was almost similar to that induced by 3 microM dopamine. The maximal tension development induced by 1 mM dopamine 4-sulfate in the femoral artery occurred more slowly than that induced by 3 microM dopamine. Furthermore, dopamine 4-sulfate-induced increase in tension development, like that of dopamine itself, was inhibited by 0.3 microM phentolamine and 0.1 microM haloperidol. Any appreciable conversion of dopamine 4-sulfate into dopamine was not seen in the medium of the organ bath in vitro during the experiment. The results suggest that dopamine sulfoconjugate exerts little effect on the cardiovascular system and, if any, induces a constriction of some vascular beds without conversion into dopamine.