ATRIAL-NATRIURETIC-PEPTIDE LEVELS AND PLASMA-VOLUME CONTRACTION IN ACUTE ALVEOLAR HYPOXIA

Arterial oxygen tensions (Pa-O2), atrial natriuretic peptide (ANP) con centrations, and circulating plasma volumes (PV) were measured in anes thetized rats ventilated with room air or 15, 10, or 8% O-2 (n = 5-7). After 10 min of ventilation, Pao, values were 80 +/- 3, 46 +/- 1, 32 +/- 1, and 35 +/- 1 Torr and plasma immunoreactive ANP (irANP) levels were 211 +/- 29, 229 +/- 28, 911 +/- 205, and 4,374 +/- 961 pg/ml, res pectively. At PaO2 less than or equal to 40 Torr, irANP responses were more closely related to inspired O-2 (P = 0.014) than to Pa-O2 (P = 0 .168). PV was 36.3 +/- 0.5 mu l/g in controls but 8.5 and 9.9% lower ( P less than or equal to 0.05) for 10 and 8% O-2 respectively. Proporti onal increases in hematocrit were observed in animals with reduced PV; however, plasma protein concentrations were not different from contro l. Between 10 and 50 min of hypoxia, small increases (+40%) in irANP o ccurred in 15% O-2; however, there was no further change in PV, hemato crit, plasma protein, or irANP levels in the lower O-2 groups. Urine o utput tended to fall during hypoxia but was not significantly differen t among groups. These findings are compatible with a role for ANP in m ediating PV contraction during acute alveolar hypoxia.