Effect of HO activity on heme levels in the serum of BALB/c mice.

Twenty-four hours after mice were injected with saline or 1000 μM heme, the levels of heme in the serum were measured using the pyridine hemochromogen assay (thin and thick gray lines, respectively). Delta absorbance between 540 and 557 nm of the spectra correlates with the amount of heme (see “Materials and methods”). The thin black line represents mice pretreated for 24 hours with 20 μM SnMP, an inhibitor of HO activity, followed by treatment with 1000 μM heme for 24 hours. Thus, the inhibition of HO activity results in prolonged presence of heme in the vascular system. Further, the wavelengths of the serum heme spectra do not differ from those of a fresh heme standard (thick black line).