Oxygen administration increases plasma digoxin-like substance and renal sodium excretion in chronic hypoxic patients

Despite the absence of cardiac or renal pathologies, edema and mild hyponatremia may often occur in patients affected by chronic obstructive pulmonary disease (COPD). Therefore, it has been suggested that hypoxia may influence the release of different hormones regulating renal sodium handling. To evaluate the effect of hyperoxia and O2 removal on plasma digitalis-like substance (DLS) levels, 9 patients affected by COPD and 7 normal subjects were studied. After 1 h in supine position, O2 was administered for 3 h by a tight-fitting face-mask. Blood samples for plasma DLS were taken at time 0, 60, 180 min and then for 3 h after O2 removal. In normal subjects, plasma DLS did not vary after O2 administration (from basal values of 162.25 +/- 8.59 to 107.75 +/- 6.65 pg/ml at 180 min; NS), and O2 removal (143.7 +/- 16.87 pg/ml after 3 h from O2 removal; NS). On the contrary, in patients affected by COPD, plasma DLS levels increased during O2 administration (from basal values of 138.98 +/- 8.31 to 202.14 +/- 8.21 pg/ml at 180 min; p < 0.05), and returned to baseline levels (142.59 +/- 8.28 pg/ml) 3 h after O2 removal. In the same patients, DLS increase was accompanied by a rise in Na+ excretion (from 0.08 +/- 0.01 at time 0 to 0.16 +/- 0.02 mEq/min after 3 h of O2 administration; p < 0.05). In conclusion, our findings showed an oxygen-related increase in plasma DLS levels and in urinary Na+ excretion in patients affected by COPD. This phenomenon could promote Na+ urinary loss during prolonged O2 therapy in these patients and should be taken into account in their management.