The effect of carbidopa administration on urinary sodium excretion in man. Is dopamine an intrarenal natriuretic hormone?

1 Carbidopa, a known inhibitor of the peripheral conversion of dopa to dopamine, was given to six normal volunteers to examine the effect of interference with dopamine synthesis on urinary sodium excretion. 2 On the first day of administration, carbidopa caused a significant fall not only in urinary dopamine excretion (P less than 0.01) but also in urinary sodium excretion (P less than 0.05). 3 A highly significant correlation was also found between mean sodium excretion and mean dopamine excretion in the days prior to and during carbidopa administration (r = 0.617, P less than 0.001; 4 = 0.764, P less than 0.001 respectively). 4 The significance of these findings is discussed and it is proposed that dopamine may be an important intrarenal natriuretic hormone.