1. The aim of the present study was to assess the effects of hypercapnia or hypoxia on plasma concentrations of atrial natriuretic factor (ANF) in conscious unrestrained dogs.
2. For this purpose, chronically instrumented dogs were exposed in a random order to either room air, or to an atmosphere containing 21% O2/10% CO2/69% N2 to produce hypercapnia, or 10% O2/3% CO2/87% N2 to produce hypoxia without respiratory alkalosis.
3. Plasma concentrations of ANF did not change significantly during hypoxia.
4. In contrast, during hypercapnia, plasma concentrations of ANF increased by more than 100% and returned to baseline at the end of hypercapnia.
5. Hypercapnia, but not hypoxia, induced an increase in left atrial and central venous pressures.
6. We conclude that hypercapnia increases plasma ANF concentration, and that this increase may be secondary to an increase of the left and right atrial pressures. These phenomena may explain the increase in diuresis and natriuresis which has been described during hypercapnia.