Sodium and blood pressure. Studies in young and middle-aged men with a positive family history of hypertension.

To study the relationship between family history of hypertension and the response to increased salt intake, normotensive 50-year-old men with (n = 11) and without (n = 26) and younger men (mean age 30 years) with (n = 17) and without (n = 15) a family history of hypertension were studied on habitual and increased salt intake (ordinary intake + 12 g NaCl/day for four weeks). No difference in blood pressure was seen in either age group between the familial groups during habitual salt intake. The older group increased blood pressure and weight during high salt intake, whilst the younger group did not, indicating that age is important for the handling of sodium. Family history had no impact on the changes in blood pressure. Echocardiography in the younger group showed no haemodynamic differences between the familial groups during habitual salt but after three days of high salt an increased cardiac output and a decreased total peripheral resistance was seen in the group with a family history of hypertension while the control group showed no such changes. This difference disappeared during the course of the study. Plethysmography in the younger group showed no structural vascular changes in the familially predisposed group. At rest they had however an increased resistance and vascular tone indicating a higher contractile state in their calf muscle resistance vessels. Increased salt intake did not influence any of these variables in neither group. Both the younger and older familially predisposed men had higher levels of intraerythrocyte sodium during habitual salt intake compared to the control groups. In the younger group this increase was probably due to a significant decrease in the sodium efflux rate constant. During high salt the intraerythrocyte sodium decreased in the familially predisposed groups, and the efflux rate constant in the younger group increased significantly, the initial difference between the familial groups thereby disappeared. These findings do not support the existence of a circulating sodium transport inhibitor. No difference in catecholamine excretion was seen between the familial groups during habitual salt intake. An increase in urine catecholamines was seen during increased salt intake in the older group whilst a slight decrease was seen in the younger groups mainly during the first 10 days. The reason for this discrepancy is not clear. During ordinary salt intake a higher plasma renin activity was noted in the younger familially predisposed group.(ABSTRACT TRUNCATED AT 400 WORDS)