Acute alveolar hypoxia increases blood-to-tissue albumin transport: role of atrial natriuretic peptide.

Plasma immunoreactive atrial natriuretic peptide (irANP) and blood-to-tissue clearance of 131I-labeled rat serum albumin (CRSA) were examined in anesthetized rats during hypoxic ventilation (n = 5-7/group). Hypoxia (10 min) increased irANP from 211 +/- 29 (room air) to 229 +/- 28 (15% O2, not significant), 911 +/- 205 (10% O2), and 4,374 +/- 961 pg/ml (8% O2), respectively. Graded increases in CRSA were significant at 8% O2 in fat (3.6-fold), ileum (2.2-fold), abdominal muscles (2.0-fold), kidney (1.8-fold), and jejunum (1.4-fold). CRSA was decreased in back skin and testes; heart, brain, and lungs were unaffected. The increases in CRSA were related to irANP and not to arterial PO2. Circulating plasma volume was negatively correlated with whole body CRSA. Graded increases in extravascular water content (EVW) were found in the kidney, left heart, and cerebrum and were positively related to CRSA in the kidney. EVW decreased in gastrointestinal tissues; the magnitude was inversely related to CRSA. We conclude that ANP-induced protein extravasation contributes to plasma volume contraction during acute hypoxia.