Peripheral origin of plasma dopamine

To clarify the peripheral origin of plasma dopamine (DA), we studied the changes in plasma levels of free and conjugated catecholamines after nephrectomy, adrenalectomy, chemical sympathectomy and renal denervation. Nephrectomy markedly increased conjugated DA levels, indicating that plasma DA is rapidly excreted through the kidney and originates outside the kidney. Adrenalectomy reduced plasma total epinephrine (E) to undetectable limits, whereas total norepinephrine (NE) and DA levels remained unchanged. In addition, the subsequent immobilization stress significantly increased both total NE and DA, but not E. Chemical sympathectomy with 6-hydroxydopamine decreased both NE and DA by 66% and 72%, respectively. E level, however, was not affected by sympathectomy. Although the following immobilization stress significantly increased all catecholamines levels, the magnitude of increase in concentrations of NE and DA were much less than that of E. These results suggest that plasma DA is mainly derived from the peripheral sympathetic nerve terminals. However, the renal nerve, one of the sympathetic nerves, did not serve as a source of plasma DA because renal denervation had no effect on plasma DA levels in spite of the marked depletion of free DA in the kidney.