Epidemiological studies have suggested a lower incidence of
arrhythmia-induced
sudden cardiac death in women than in men. 17β-oestradiol (E2) has been reported to have a post-
myocardial infarction antiarrhythmic effect, although the mechanisms have yet to be elucidated. We investigated whether E2-mediated antioxidation regulates macrophage polarization and affects cardiac sympathetic reinnervation in rats after MI. Ovariectomized Wistar rats were randomly assigned to placebo pellets, E2 treatment, or E2 treatment +3-morpholinosydnonimine (a
peroxynitrite generator) and followed for 4 weeks. The
infarct sizes were similar among the infarcted groups. At Day 3 after
infarction, post-
infarction was associated with increased
superoxide levels, which were inhibited by administering E2. E2 significantly increased myocardial IL-10 levels and the percentage of regulatory M2 macrophages compared with the ovariectomized infarcted alone group as assessed by immunohistochemical staining, Western blot and RT-PCR.
Nerve growth factor colocalized with both M1 and M2 macrophages at the magnitude significantly higher in M1 compared with M2. At Day 28 after
infarction, E2 was associated with attenuated myocardial
norepinephrine levels and sympathetic hyperinnervation. These effects of E2 were functionally translated in inhibiting fatal arrhythmias. The beneficial effect of E2 on macrophage polarization and sympathetic hyperinnervation was abolished by 3-morpholinosydnonimine. Our results indicated that E2 polarized macrophages into the M2 phenotype by inhibiting the
superoxide pathway, leading to attenuated
nerve growth factor-induced sympathetic hyperinnervation after
myocardial infarction.