Effect of enalapril on exaggerated erythropoietin response to phlebotomy in erythrocytosic renal transplant patients

Background. Exaggerated erythropoietin (EPO) response to phlebotomy regardless of the baseline EPO levels have been shown in patients with post-transplant erythrocytosis (PTE) and administration of angiotensin-converting enzyme inhibitors (ACE-I) seems to be effective in controlling PTE. However, the mechanism of this ACE-I induced reduction in haematocrit (Hct) is not well known. Although some authors have suggested that ACE-I may reduce EPO secretion, this is still controversial. The aim of the present study was to assess the effect of a single dose ACE-I on exaggerated EPO response to phlebotomy. Methods. In this study, we compared serum EPO and renin (PRA) levels of 10 PTE patients, 10 non-PTE patients and 10 healthy blood donors before and after phlebotomy. The effects of a single dose of ACE-I (enalapril, 5 mg p.o.) in PTE patients were also evaluated in the second phlebotomy. Results. While the mean basal serum EPO level was significantly higher in the PTE group than the other two groups (P < 0.01), the mean basal PRA levels did not differ significantly between these groups. Serum EPO and PRA levels increased significantly after the phlebotomy (P < 0.001) and exaggerated EPO response to phlebotomy was suppressed by single dose enalapril (P < 0.001) in the PTE patients. Conclusion. The present study has shown that the renin-angiotensin system plays an important role in EPO formation and the Hct lowering effect of the ACE-I is through reduction of EPO in PTE patients.