In previous studies of normal renin essential hypertension two subsets were identified. One subset showed salt-sensitivity of blood pressure, subnormal stimulation of plasma renin activity, normal urinary dopamine, supranormal cumulative sodium retention and no change in plasma norepinephrine during a high sodium intake. The other subset showed salt-insensitivity of blood pressure, normal stimulation of plasma renin activity, supranormal urinary dopamine, normal cumulative sodium retention and a significant decrease in plasma norepinephrine during a high sodium intake. Since mean urinary dopamine correlated inversely with both cumulative sodium retention and the percent change in plasma norepinephrine, the differences between these two subsets appeared to be attributable, in part, to differences in dopaminergic activity. Results of similar studies of normal subjects indicate that some, like the hypertensives, show the phenomenon of salt-sensitivity of blood pressure. Compared to the salt-resistant normal subjects the salt-sensitive normal subjects had a lower stimulated plasma renin activity, lower urinary dopamine, greater cumulative sodium retention and a higher plasma norepinephrine that showed a smaller change in response to a high sodium intake. These initial findings suggest that salt-sensitive normal subjects are qualitatively similar to patients with salt-sensitive hypertension in many respects and many represent the population at risk for development of salt-sensitive essential hypertension. The results also suggest that many features that characterize the salt-sensitive hypertensive subjects represent modifications of normal physiology and do not appear to be acquired as a consequence of the hypertensive process.
