Dopaminergic activity and water-sodium handling in the kidneys of essential hypertensive subjects: is renal dopaminergic activity suppressed at the prehypertensive stage?

To investigate whether the suppression of the renal dopaminergic system in hypertension is primary or secondary, renal dopaminergic activity was compared between young healthy normotensive subjects without a family history of hypertension [FH(-)] and those with a family history of hypertension [FH(+)]. A significant decrease in urinary dopamine excretion was recognized, and the responses of urine volume, urinary sodium excretion, fractional excretion of sodium, and urinary kallikrein and kinin activity to infused dopamine were significantly augmented in FH(+) subjects. In addition, a normal level of L-dopa delivery into the kidney and at the renal proximal tubules and a significant reduction of the conversion from L-dopa to dopamine in the kidney were found in FH(+) subjects. These findings suggest that renal dopaminergic activity is already suppressed at the prehypertensive stage, and a reduction in the conversion from L-dopa to dopamine in the proximal tubules may contribute to the attenuation of renal dopaminergic activity in FH(+) subjects.