Sodium elimination rate and blood pressure during normal and high salt intake in subjects with and without familial predisposition to hypertension.

We have assessed the elimination rate of 22Na (ER-22Na), total exchangeable sodium (NaE), blood pressure, plasma volume (PV), haematocrit, urinary noradrenaline (U-NA) and urinary 3-methoxy-4-hydroxymandelic acid (U-VMA) in normotensive men with (n = 17) and without (n = 15) familial predisposition to hypertension. All measurements were done during habitual salt intake and after four weeks of increased salt intake (ordinary intake + 12 g NaCl/daily). On ordinary salt intake, ER-22Na, NaE, blood pressure, PV, haematocrit, U-NA and U-VMA did not differ between the groups thus indicating a normal sodium turnover in both groups and a comparable activity of the sympathetic nervous system. After 10 days of high salt intake those without familial predisposition showed signs of volume expansion and decreased sympathetic activity and those with such predisposition showed insignificant changes in the same direction. After four weeks of increased salt intake, ER-22Na had increased significantly and equally in both groups, while blood pressure and NaE remained unchanged. This indicates that the predisposed individuals had a normal ability to cope with a prolonged increase in salt intake.