Release of atrial natriuretic peptide during hypertonic saline infusion: the importance of posture

It is well known that atrial distension is an important stimulus for atrial natriuretic peptide (ANP) release, but conflicting evidence exists as to whether hyperosmolality also stimulates the release of atrial natriuretic peptide (ANP) in man. As infusion of hypertonic saline causes an increase in both blood volume and plasma osmolality, we have employed this stimulus to investigate: (i) whether hyperosmolality increases plasma ANP concentrations; (ii) the importance of posture in ANP release. Normal male volunteers (n = 6) were infused with hypertonic saline at a rate of 0.06 ml/kg/min for 2 h on two different occasions separated by 1 month. Infusion was performed with subjects in the seated and supine positions in random order. Hypertonic saline infusion induced increases in plasma osmolality (P less than 0.001), plasma sodium (P less than 0.01) and blood volume (P less than 0.001) in both seated and supine position. The increase in plasma osmolality was accompanied by an increase in plasma ANP during the supine infusion (2.7 +/- 1.0 to 9.0 +/- 2.4 pmol/l (mean +/- SEM; P less than 0.01] but no significant change in plasma ANP concentration occurred during the seated infusion. A positive linear correlation was obtained between increase in plasma osmolality and plasma ANP in the supine but not in the seated hypertonic saline infusion. There was a positive linear correlation between estimated increase in blood volume and plasma ANP in the supine but not the seated infusion of hypertonic saline. We suggest that the increase in ANP during hypertonic saline infusion reported by some workers was due to atrial distension, secondary to increased blood volume and is dependent on the position in which the subjects were studied.(ABSTRACT TRUNCATED AT 250 WORDS)