ATRIAL PLASMA ANP AND NH2-TERMINAL PROANP DURING RIGHT ATRIAL PRESSURE INCREASE IN HUMANS

To compare plasma NT-proANP, a stable and biologically inactive N-term inal portion of ANP prohormone. with the known plasma ANP response to increased right atrial pressure a Swan-Ganz catheter was inserted into the right atrium or five normal healthy male volunteers. The elevatio n of right atrial pressure was produced by a head-down tilt after a hy pertonic saline infusion. Blood samples were drawn from the lumen of t he right atrium. After 5 min of starring the tilt the right atrial pre ssure had increased from 7.0+/-1.0 to 11.6+/-0.9 mmHg (P < 0.05) and t hen began to normalize in spite of the constant tilt. Atrial plasma AN P increased in relation to the pressure increase and peaked at 15 min after the start of the tilt. The change was from 27.9+/-6.5 to 53.9+/- 9.7 pmol L(-1) (P < 0.05). Atrial plasma NT-proANP increased significa ntly from 357+/-91.2 to 529.1+/-116.13 pmol L(-1) (P < 0.05) at 10 min and remained high throughout the experiment. The molar ratio of NT-pr oANP to ANP varied in atrial plasma from 9.5+/-1.2 to 13.9+/-2.7 showi ng that the plasma clearance of ANP from plasma was much higher than t hat of NT-proANP.