1. We measured urinary excretion rates of dopamine (3,4-dihydroxyphenethylamine) and dopa (3,4-dihydroxyphenylalanine) and the spillover rate of dopa into arterial blood during dietary salt loading in conscious Dahl salt-sensitive and salt-resistant rats with intact or denervated kidneys.
2. Dopa spillover was calculated from the steady-state clearance of intravenously infused l-[3H]dopa and arterial levels of endogenous dopa.
3. Daily excretion rates of dopa and dopamine increased by about sixfold during salt loading in both rat strains. Bilateral renal denervation delayed these increases and the natriuretic responses.
4. During dietary salt loading, dopa spillover increased to approximately the same extent as simultaneously measured dopamine excretion.
5. The results suggest that increases in urinary excretion of dopamine during dietary salt loading can be accounted for by increases in the release of dopa into the bloodstream and that the renal nerves contribute to the dopa and dopamine excretory responses.