Chronic and acute volume expansion in normal man: effect on atrial diameter and plasma atrial natriuretic peptide

Plasma levels of immunoreactive alpha human atrial natriuretic peptide (IR-ANP) and left atrial diameter were measured in 6 normal subjects before and after 6 days of sodium loading using salt supplements and 9-alpha-fluorohydrocortisone. During chronic sodium loading, which increased mean body weight by 1.5 kg and markedly reduced plasma renin and aldosterone levels, plasma IR-ANP increased from 21 +/- 3 to 36 +/- 7 pmol/l (P less than 0.02). Increase in atrial diameter correlated with gains in body weight (r = 0.93, P less than 0.01) but not with increase in plasma IR-ANP. After chronic sodium loading for 6 days, further volume expansion (2 litres of saline infused over 2 hours) significantly increased left atrial diameter but did not affect plasma IR-ANP levels. We conclude that chronic sodium loads increase plasma IR-ANP. However, the failure of further acute atrial distension to increase hormone levels suggests that factors in addition to atrial stretch are important in regulating atrial peptide secretion in man.