Hp sequestration of Hb. Guinea pigs were infused with stroma-free Hb (peak plasma Hb concentration, 150μM heme) and, after 10 minutes, a treatment group of animals was infused with human plasma–derived Hp to match an equimolar Hb:Hp concentration. (A) Mean arterial blood pressure response before and after Hp treatment. (B) Unbound plasma Hb (red) before and after Hp administration. The left shift in the chromatogram indicates the large molecular size Hb:Hp complex with approximately 90% Hp bound and 10% unbound Hb. (C) Hemoglobinuria after Hb infusion (150μM heme) without (−Hp, left) and with Hp (+Hp, right). (D) Iron deposition (brown staining) in normal kidney renal cortex (left), Hb infusion (middle), and Hb infusion plus Hp (right). (E) HO-1 expression in kidneys after 24 hours after Hb exposure with and without Hp infusion (left). Densitometry is shown to the right of the HO-1 Western blot. All data are presented as means ± SEM.