Dopaminergic regulation of natriuretic response to acute volume expansion in dogs

Effects of carbidopa, a dopa (3,4-dihydroxyphenylamine) decarboxylase inhibitor, on the renal, haemodynamic and hormonal responses to acute volume expansion were examined in six healthy mongrel dogs which were infused intravenously with 0.9% sodium chloride solution (saline; 30 ml h-1 kg-1) over 2 h. Saline infusion studies were performed in the absence (control) and in the presence of carbidopa given by nasogastric tube in a dose of 1 mg/kg every 8 h beginning 24 h before the infusion. Saline infusion resulted in an increase in renal excretion of dopamine (3,4-dihydroxyphenylethylamine) and a decrease in renal excretion of noradrenaline. Carbidopa treatment decreased urinary sodium excretion and eliminated the increase in renal production of dopamine in response to saline infusion without affecting renal or haemodynamic response to acute vascular volume expansion with saline. Carbidopa treatment obliterated the suppression of aldosterone produced by saline infusion. Thus, dopamine appears to play a significant role in mediating both the natriuretic and aldosterone response to acute volume expansion.