Intracellular cGMP and cAMP levels in human erythroid progenitor cells. (A) Intracellular cGMP and cAMP levels in erythroid progenitor cells (left y-axis). Hydroxyurea (HU) dose-dependently inhibits erythroid cells growth after 24 and 48 hours of incubation (right y-axis). (B) Hydroxyurea (30 μM) and DEANONOate (50 μM) increased cGMP levels during 4 hours of incubation of human erythroid progenitor cells at day 4 of phase II liquid culture. (C) Hydroxyurea (30 μM) and DEANONOate (50 μM) increases and inhibits, respectively, cAMP levels during 4 hours of incubation of human erythroid progenitor cells at day 4 of phase II liquid culture (n = 3). Values are means (± SEM).