The effect of 60-min constant iv infusions of alpha-human atrial natriuretic peptide (alpha hANP; 200 micrograms), sufficient to increase the steady state venous plasma alpha hANP concentration to levels found in patients with some circulatory disorders, was studied in six normal men equilibrated on a high sodium diet (200 mmol daily) and again when equilibrated on a low sodium intake (10 mmol daily). In each instance, the responses to alpha hANP were compared to those to control infusions given on the preceding day. The mean steady state plasma immunoreactive ANP concentration during the infusions was 320 pmol/liter and was the same during both diets. Thus, the MCR of alpha hANP was unaffected by major changes in sodium intake. Compared to control day observations, infusions of alpha hANP induced a more than 3-fold increase in sodium excretion and at least a 2-fold increase in urine volume and calcium and magnesium excretion in subjects ingesting 200 mmol sodium daily. During the low sodium diet, alpha hANP was still diuretic and induced comparable magnesium excretion, but the natriuresis was only 11% of that during the high salt diet. No significant changes in blood pressure or heart rate occurred during alpha hANP infusions during either diet, although during both diets there was a significant rise in plasma norepinephrine (P less than 0.02), which persisted well beyond the disappearance of immunoreactive ANP from plasma. Despite this sympathetic activation, renin and aldosterone production was reduced by alpha hANP. During low salt intake, alpha hANP significantly decreased PRA (mean pretreatment, 1.79; posttreatment, 1.25 nmol/liter/h; P less than 0.03), angiotensin II (mean pretreatment, 49; posttreatment, 28 pmol/liter; P less than 0.008), and plasma aldosterone (mean pretreatment, 554; posttreatment 307 pmol/liter; P less than 0.007), whereas values during control infusions did not change. Similar percent decreases in PRA and aldosterone also occurred during the high salt diet. Plasma cortisol and arginine vasopressin did not change during the alpha hANP infusions on either diet. We conclude that steady state levels of alpha hANP in plasma, similar to those in patients with some circulatory disorders, significantly increase sodium excretion and inhibit all elements of the renin-angiotensin-aldosterone system. The natriuretic, but not the hormonal or chronotropic, effects of alpha hANP are reduced by sodium depletion in normal man.
Cuneo et al. (Wed,) studied this question.