A functional role for renal dopaminergic nerves in the dog

1. Efferent renal nerve stimulation at 5 Hz causes secretion of both dopamine (DA) and noradrenaline (NA) into renal venous plasma. DA comprises about 8% of the total catecholamine overflow; by contrast, DA efflux into femoral venous plasma following stimulation of the lumbar sympathetic nerves is 1% or less of total catecholamine. 2. Intact, but not denervated, kidneys of volume-loaded dogs also secrete both dopamine (DA) and noradrenaline (NA) into renal venous blood at rest, but the DA:NA ratio is considerably higher than that evoked by nerve stimulation. 3. Acute animal treatment with 6-hydroxydopamine (6-OHDA) abolishes stimulus-evoked catecholamine overflow and the usual fall in glomerular filtration and sodium and water excretion that accompanies renal nerve activation. 4. When 6-OHDA is administered in the presence of a selective inhibitor of UptakeDA (GBR 12909), stimulus-evoked DA overflow is selectively protected against the effect of 6-OHDA. Under these circumstances, nerve stimulation increases glomerular filtration and excretion of water, but not of sodium. These effects are abolished by DA1 receptor blockade. 5. These data indicate that DA is released from intrarenal dopaminergic nerve terminals in vivo, both in response to direct nerve stimulation and tonically under conditions of volume expansion. The main effects of dopaminergic nerve activation are juxtaglomerular vasodilatation and inhibition of distal tubular water reabsorption.