Urinary dopamine and noradrenaline outputs during oral salt loading in healthy Chinese subjects with a family history of hypertension.

1. Increased salt sensitivity has been reported in first-degree relatives of hypertensive patients. To determine if the enhanced effect of oral salt intake on blood pressure in such individuals is related to abnormal renal dopamine (DA) or sympathetic nervous system responses, we studied the effects of two different sodium intakes (20 mmol/day followed by 220 mmol/day each given for 5 days) on mean arterial pressure (MAP) and urinary excretion of sodium, free DA and noradrenaline (NA) in seven normotensive Chinese subjects with a family history of hypertension. We compared these results with those we have reported previously for normotensive subjects without a family history of hypertension. 2. There was a seven- to ten-fold increase in sodium excretion (P < 0.02). MAP increased from 80.1 +/- 2.5 to 83.1 +/- 2.1 mmHg (P < 0.05). A 23% increase in urine DA (P < 0.02) was seen on day 1. From day 2 to day 5, the increase in urine DA (12-15%) became attenuated and reached statistical significance only on days 2 and 5. There was no significant change in urinary NA output. 3. As in healthy Chinese subjects without a family history of hypertension, those with a family history showed an early but unsustained rise in urine DA during oral sodium loading. Such an increase was rather small compared to the increase in urine sodium, suggesting that renal DA only contributes partly to the natriuretic response. Unlike those with no family history, subjects with a family history showed an increase in blood pressure after oral salt loading, possibly because of inadequate suppression of sympathetic nervous system activity.