Atrial natriuretic factor in normal man: effects of tilt, posture, exercise and haemorrhage.

Low-pressure atrial baroreceptors are important in the regulation of plasma volume. Plasma atrial natriuretic factor (ANF) increases with volume loading, and may therefore be influenced by manoeuvres which affect venous return and right atrial pressure. Plasma ANF was measured in six normal subjects following head-up and head-down tilt, changes in posture, severe exercise and haemorrhage. Plasma ANF concentrations were similar while the subjects were supine, sitting, standing or tilted head-up. Plasma ANF rose from 6.9 +/- 0.8 pmol/l while supine to 11.8 +/- 1.9 pmol/l while tilted head-down (P less than 0.05) and to 27.2 +/- 1.3 pmol/l following severe exercise (P less than 0.05). There was no significant change in plasma ANF following haemorrhage of up to 1000 ml. The effects of posture and blood loss are small, and may be largely discounted when blood is drawn for measurement of plasma ANF concentration in normal man. Our results suggest that in normal man the basal secretion of ANF is low, and is not further suppressed by manoeuvres which decrease the right atrial pressure or volume. In contrast, manoeuvres which increase the right atrial pressure or volume are associated with a rapid increase in ANF release from the heart.