In previous studies of patients with normal renin essential hypertension those that were salt-resistant were shown to have higher urinary dopamine than those that were salt-sensitive. The salt-resistant patients also suppressed their plasma norepinephrine in response to a high-sodium intake whereas the salt-sensitive patients did not. Similar studies performed in normal subjects indicate that when sodium intake was increased from 9 to 249 mEq/d, sodium retention was only slightly less than that in the salt-resistant but significantly less than that in the salt-sensitive patients. Urinary dopamine did not differ from that in the salt-sensitive but was significantly lower than that in the salt-resistant patients. Plasma norepinephrine also did not differ from that in the salt-sensitive but was significantly higher than that in the salt-resistant patients who suppressed plasma norepinephrine in response to high-salt intake. These results suggest that during a high-salt intake supranormal renal dopaminergic activity in the salt-resistant hypertensives prevents supranormal sodium retention; the dopaminergic nervous system may also mediate the supranormal decrease in plasma norepinephrine in these patients. Supranormal sodium retention that does not suppress plasma norepinephrine may mediate, in part, the increase in blood pressure that occurs during a high-sodium intake in the salt-sensitive hypertensives.
