The objective of this study was to evaluate whether renal excretion of
sodium is impaired and whether tubular reabsorption of sodium is incr
eased in normotensive white men with a familial predisposition to deve
lop essential hypertension. We compared 11 normotensive sons of two hy
pertensive parents (SOHT) with 11 normotensive sons of two normotensiv
e parents (SONT); renal sodium handling was assessed after 1 week of l
ow-sodium diet (10 mmol/d) and after 1 week of high-sodium diet (200 m
mol/d). The SOHT were on average 5.5 years older than the SONT (46.9 /- 5.2 [SD] vs 41.4 +/- 4.1, P = .012). On the sixth day of each diet,
mean urinary sodium excretion did not differ between the two groups (
12.9 +/- 6.3 vs 12.7 +/- 6.7 mmol/d on low-sodium diet, P = .930; 197
+/- 25 vs 200 +/- 27 mmol/d on high-sodium diet, P = .817). On the sev
enth day of each diet, baseline means for filtered load of sodium, abs
olute excretion of sodium, fractional excretion of sodium (an index of
total tubular sodium reabsorption), and fractional excretion of lithi
um (an inverse index of proximal tubular sodium reabsorption) also did
not differ between the groups. To assess renal sodium handling under
non-steady-state conditions, we infused 2 L normal saline intravenousl
y over a 2-hour period. The means for absolute excretion of sodium, fr
actional excretion of sodium, and fractional excretion of lithium incr
eased from baseline, but the increases did not differ in magnitude bet
ween the groups. With both diets, mean blood pressure was 7 mm Hg grea
ter in the SOHT than in the SONT (P = .046) and did not change signifi
cantly during saline infusion. These results provide no evidence that
renal excretion of sodium is impaired or that tubular reabsorption of
sodium is increased in normotensive white men who have a familial pred
isposition to develop essential hypertension. If such alterations are
underlying characteristics of the familial predisposition to develop e
ssential hypertension, then higher blood pressure in the offspring of
hypertensive parents may have compensatory renal effects that restore
renal sodium handling to normal.