Blood pressure response to acute changes in dietary sodium in young Zimbabwean men

OBJECTIVE: The primary objective of this study was to determine the effect of acute alterations in sodium intake upon the blood pressure and hormone levels of young Zimbabwean men. DESIGN: Blood pressure, 24-h urinary electrolyte excretion and plasma concentrations of angiotensin II, aldosterone, and atrial natriuretic peptide were measured in normotensive black medical students. Three sets of measurements were taken: (1) during free access to sodium (baseline); (2) after 4 days on a low-sodium diet (10 mmol/day); and (3) after 4 days on a high-sodium diet (800 mmol/day). METHODS: Blood pressure was measured by random zero sphygmomanometry, hormone levels by radioimmunoassay, and urinary electrolytes by flame photometry. RESULTS: The low-sodium diet caused the range of pulse pressure to narrow, with a decrease in systolic blood pressure (SBP) and an increase in diastolic blood pressure (DBP). With the introduction of the high-sodium diet, SBP increased and DBP decreased. Mean arterial pressure did not change. At the same time, angiotensin II and aldosterone decreased. Plasma atrial natriuretic peptide did not change. A subgroup of the men on the high-sodium diet also received 100 mmol potassium/day. The increase in SBP associated with high sodium was significantly attenuated by the presence of added potassium. CONCLUSIONS: SBP of young black Zimbabwean men is lowered by dietary sodium restriction and rises with a large increase in dietary sodium for a short duration, but mean arterial pressure does not change due to the opposing decreases in DBP.