Effects of erythropoietin, angiotensin II, and angiotensin-converting enzyme inhibitor on erythroid precursors in patients with posttransplantation erythrocytosis

Background. Ansotensin-converting enzyme inhibitors (ACEI) have become the treatment of choice for posttransplantation erythrocytosis (PTE). Yet the p athogenesis of PTE and the mechanisms of action of ACEI remain unclear. The refore, we studied the dose response to erythropoietin (Ep), angiotensin II (AII), and the ACEI enalaprilat on the in vitro proliferation of erythroid progenitors in patients with PTE and in controls. We also evaluated ACE po lymorphism in the two groups. Methods. Twelve patients with PTE and 12 renal transplant patients without PTE were studied. Erythroid burst-forming units (BFU-E) were isolated from peripheral blood using standard methods. Ep sensitivity was determined for four patients with PTE and three control patients, using 0-3 U/ml Ep, AII d ose response was studied in four patients with PTE and five control patient s, using AII concentrations of 0-1000 nM. The effect of enalaprilat was stu died in eight patients with PTE and eight control patients, using drug conc entrations of 0-10 ng/ml, ACE gene insertion/deletion polymorphism was dete rmined by polymerase chain reaction. Results. PTE patients showed a significant shift of the Ep response curve t o the left compared with controls, with 50% maximal growth occurring at a l ower Ep concentration (0.3 U/ml vs. 0.95 U/ml, P<0.025.) However, there was no difference in the number of BFU-E colonies between PTE patients and con trols. AII added to the growth medium produced only minor stimulation in bo th groups. PTE patients showed significant inhibition of BFU-E growth with 10 ng/ml enalaprilat, but controls showed no inhibition of BFU-E growth wit h ACEI, There was no difference in ACE polymorphism between PTE and control s. Conclusions. Our data suggest that PTE is associated with increased erythro id progenitor sensitivity to Ep, The effect of ACEI to decrease hematocrit in patients with PTE may be due to inhibition of red cell precursor growth.