Effect of low normal and high normal sodium intake on hormonal and metabolic responses to ACTH, angiotensin II and an acute salt load in normal subjects.

Five healthy male volunteers were subjected successively to the extremes of normal sodium intake (100 mEq and 225 mEq per day). They were infused for 4 h on different days with (1) 0.25 mg and (2) 1 mg alpha 1-24 adrenocorticotrophin (ACTH), (3) angiotensin II to raise mean blood pressure by 15 mm Hg and (4) 21 of 0.9% NaCl. There was no change in the response of cortisol to ACTH on either regimen of sodium intake. Plasma renin activity increased after ACTH infusion only on the lower sodium intake. Blood pressure response to angiotensin II was greater on the higher sodium intake. Plasma ACTH and cortisol concentrations did not rise during angiotensin II infusion on either diet. Kaliuresis was increased on the day of the 4-h infusion of angiotensin II on the higher sodium intake but no significant changes were apparent during the administration of angiotensin II. Urinary kallikrein excretion was significantly lower on the higher sodium intake. During angiotensin II infusion, urinary kallikrein excretion and plasma aldosterone became dissociated. Urinary kallikrein excretion correlated with the urinary volume. After salt loading, natriuresis was appropriately exaggerated under the higher sodium intake. The hormonal and electrolyte changes that result from large variations in sodium intake in man are also found when small changes in sodium intake, within the usual range of North American Society are investigated. These changes may have a role to play in the consequences of excess sodium intake on body fluid homeostasis and blood pressure.