Purpose: An association between activation of the renin-angiotensin system and enhanced erythropoiesis has been observed in patients with several diseases, including congestive heart failure and hypertension. Our goal was to examine whether the renin-angiotensin system is associated with secondary erythrocytosis in patients with chronic obstructive pulmonary disease (COPD).
Subjects and methods: Plasma renin activity, plasma aldosterone concentration, serum erythropoietin level, and serum angiotensin converting enzyme (ACE) activity were measured in 12 patients with COPD and secondary erythrocytosis [mean (+/-SD) hematocrit of 53% +/- 3%] and in 12 matched controls with COPD who did not have erythrocytosis (hematocrit 45% +/- 5%). All patients had chronic hypoxemia (PaO2 <60 mm Hg).
Results: Both plasma renin and aldosterone levels were threefold greater in patients with secondary erythrocytosis compared to controls. No difference in erythropoietin levels was observed between patients with or without secondary erythrocytosis. Renin levels (r = 0.45; P = 0.02) but not erythropoietin levels (r = 0.15; P = 0.47) were correlated with hematocrit in the entire sample. Renin levels and PaO2 were the only variables independently and significantly associated with hematocrit values in a multiple linear regression model.
Conclusion: Activation of the renin-angiotensin system is associated with the development of secondary erythrocytosis in chronically hypoxemic patients with COPD. The exact mechanism is not yet fully understood, but angiotensin II may be responsible for inappropriately sustained erythropoietin secretion or direct stimulation of erythroid progenitors.