Blood pressure, intraerythrocyte content, and transmembrane fluxes of sodium during normal and high salt intake in subjects with and without a family history of hypertension: evidence against a sodium transport inhibitor.

Seventeen young normotensive men with a family history of hypertension in two generations (H) and 15 age-matched control subjects (C) were studied with respect to blood pressure (BP), intraerythrocyte sodium content (IeNa), sodium influx, and rate of sodium efflux. The investigations were done during normal salt intake and after 4 weeks of ordinary intake plus 12 g NaCl daily. BP did not increase significantly in either of the two groups during increased salt intake. During normal salt intake H had a significantly (p less than 0.01) higher IeNa (9.5 +/- 1.5 mmol/L) compared with C (8.2 +/- 1.4 mmol/L). During high salt intake IeNa in H decreased significantly to 8.1 +/- 1.2 mmol/L, the difference from C (7.6 +/- 1.2 mmol/L) not being significant. While the Na influx was similar in the two groups, the rate constant for Na efflux was significantly lower during normal salt intake in H (0.23 +/- 0.08 vs 0.29 +/- 0.1 h-1, p less than 0.05). Salt intake increased the efflux rate constant significantly in H (0.28 +/- 0.08 h-1, p less than 0.05), while it did not change significantly in C (0.32 +/- 0.08 h-1) compared with the value for normal salt intake. Our results suggest that young men with a hereditary predisposition to hypertension have a higher IeNa secondary to a lower rate of Na efflux, while a normal Na influx indicates normal cell permeability to Na. The findings in H during high Na intake--a decreased IeNa and an increased efflux rate of Na--do not favor the existence of a sodium transport inhibitor, in subjects predisposed to hypertension, increasing during high salt intake and volume expansion and acting through inhibition of the Na efflux.