Plasma ANP levels and protein extravasation during graded expansion with equilibrated whole blood

Abstract

The relationship between plasma immunoreactive atrial natriuretic peptide (irANP) and radiolabeled albumin clearance (CBSA) in multiple tissues after graded volume stimuli was examined. To obtain a pure volume 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 equal 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 elevated 1.9- and 4.1-fold above baseline, respectively. Graded increases in CBSA measured between 5 and 35 min post-VE occurred in selective tissues, including intestine, visceral fat, lung, and muscle (P < or = 0.05). In separate animals, the level of VE was maintained after 2% VE by slower administration of an additional 2% VE for the remaining 30 min. This resulted in a more sustained CVP elevation and larger increases in irANP levels and CBSA compared with either 2 or 4% VE. Furthermore, equations derived from previous work in this laboratory involving intravenous administration of ANP predicted the magnitude of CBSA elevation during maintained VE. These findings support a role for ANP in regulating transcapillary protein distribution during acute intravascular expansion.