Enhancement by L-dopa of the renal action of aldosterone in the rat.

1. The administration of aldosterone to adrenalectomized rats produces an increase in K+ and decrease in Na+ excretion in the urine. The relationship of the post-aldosterone to the pre-aldosterone urinary sodium and potassium excretion is termed the renal response to aldosterone. 2. The administration of L-dopa enhances the renal response to aldosterone. This enhanced renal response does not appear to be due to the enhanced urinary creatinine and sodium excretion also seen with L-dopa. 3. The enhanced response to aldosterone seen in the L-dopa loaded rat is inhibited by spironolactone (an aldosterone antagonist), carbidopa (an inhibitor of the enzyme producing dopamine from L-dopa in the periphery), and haloperidol (a putative dopamine receptor blocker). The action of L-dopa in enhancing the renal response to aldosterone would thus appear to be mediated by dopamine within the kidney. 4. Modification of the renal response to aldosterone may be one role of the high levels of dopamine produced within the kidney.