Dopamine receptor blockade does not affect the natriuresis accompanying sodium chloride infusion in dogs

Intravenous (IV) saline infusions cause parallel increments in urinary excretion of dopamine (DA) and sodium. Exogenous administration of DA exerts a natriuretic effect by action on DA receptors. The possibility that DA mediates the natriuretic response to saline infusion was studied by infusing 0.9% saline solution IV (60 ml/kg) in conscious dogs with and without selective blockade of DA1 and DA2 receptors. With no antagonist, the total increase in sodium excretion during the 120-minute saline infusion and the 60 minutes after the saline infusion was 99.5 +/- 7.6 mmol. The increase in total sodium excretion was not affected by IV infusion of the selective DA1 antagonist SCH 23390 in doses of 0.5 micrograms/kg/min and 5 micrograms/kg/min. The total increment in sodium excretion produced by saline was also unaltered by large doses (1 micrograms/kg/min and 10 micrograms/kg/min) of the selective DA2 antagonist domperidone. Our results do not support a role of DA as a mediator of saline-induced natriuresis in the dog.