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Figure 2 Immunohistochemistry for Myoglobin, Neutrophils, and iNOS in Hearts From Mice at Day 1 and 28 After MI

(A, C) Low- and high-power (respectively) magnifications of a wild-type (WT) mouse heart on post-myocardial infarction (MI) day 1 double-immunostained for myoglobin (brown) and neutrophils (purple). (B, D) Low- and high-power (respectively) serial sections from the same mouse heart immunostained for inducible nitric oxide synthase (iNOS) (brown). The iNOS immunoreactivity in panel D is most abundant in the swath of cardiomyocytes located within the black oval. Comparison with panel C reveals that the same swath of cardiomyocytes contains little myoglobin and is largely nonviable. (E, F) Sections from WT mouse hearts on post-MI day 28 immunostained for iNOS. (E) iNOS in cardiomyocytes bordering scar tissue (arrows). (F) iNOS in cardiomyocytes bordering mature scar and in granulation tissue (arrows). (G) Graph of plasma nitrite/nitrate (NOx) concentrations over time after MI in WT and iNOS knockout (KO) mice. Significant elevations were observed at days 1 and 28 after MI in WT mice, whereas NOx levels were unchanged in iNOS KO mice. Error bars represent SEM. *p < 0.05 versus same group before MI.