Effect of posture on clearance of atrial natriuretic peptide from plasma

The effect of posture on plasma atrial natriuretic peptide (ANP) levels during a constant iv infusion of the 28-amino acid polypeptide was investigated in 8 normal men. alpha-Human ANP was infused at a constant rate of 0.5 micrograms/min (162 pmol/min) while the men were supine, then erect, and finally when supine again. Plasma ANP levels rose from 10.9 +/- 1.6 (+/- SEM) to 33.3 +/- 2.4 pmol/L after 60 min of constant infusion with the men in the supine position. On standing, plasma ANP increased further to 40.6 +/- 3.4 pmol/L, then fell to 32.2 +/- 2.7 pmol/L with resumption of supine posture. The calculated MCR of ANP fell from a mean of 7.7 to 5.7 L/min on standing, but rose again to 7.6 L/min upon lying down. We conclude that body posture has a significant effect on the rate of clearance of ANP from plasma.