PLASMA ANP LEVELS AND PROTEIN EXTRAVASATION DURING GRADED EXPANSION WITH EQUILIBRATED WHOLE-BLOOD

The relationship between plasma immunoreactive atrial natriuretic pept ide (irANP) and radio-labeled albumin clearance (C-BSA) in multiple ti ssues after graded volume stimuli was examined. To obtain a pure volum e stimulus, pentobarbital sodium-anesthetized rats (5 or 6 per group) were equilibrated with a reservoir of blood by a femoral arteriovenous shunt, and volume expansion (VE) was produced by adjusting reservoir outflow. Peak increases in central venous pressure (CVP) during VE equ al to 2 and 4% of the body weight over 5 min were 3.6+/-0.2 and 7.0+/- 0.3 mmHg, and plasma irANP levels measured at 40 min post-VE were elev ated 1.9- and 4.1-fold above baseline, respectively. Graded increases in C-BSA measured between 5 and 35 min post-VE occurred in selective t issues, including intestine, visceral fat, lung, and muscle (P less th an or equal to 0.05). In separate animals, the level of VE was maintai ned after 2% VE by slower administration of an additional 2% VE for th e remaining 30 min. This resulted in a more sustained CVP elevation an d larger increases in irANP levels and C-BSA compared with either 2 or 4% VE. Furthermore, equations derived from previous work in this labo ratory involving intravenous administration of ANP predicted the magni tude of C-BSA elevation during maintained VE. These findings support a role for ANP in regulating transcapillary protein distribution during acute intravascular expansion.