Figure 1. Age-dependent changes in polyamine metabolism and effect of spermidine on cardiac aging in rats. (A) Representative immunoblot bands for ODC and SSAT and quantification of protein levels in the myocardium of 3-month-old (Young) and 24-month-old (Old) rats. GAPDH was used as loading control. (B) Polyamine content, including putrescine (PU), spermidine (SPD), and spermine (SP) in the myocardium of young, old, and SPD-treated old rats (SPD group) evaluated by high-performance liquid chromatography. (C) Representative immunoblot bands for p21 and p16 and quantification of protein levels. GAPDH was used as loading control. (D) Positive area of senescence-associated β-galactosidase (SA-β-gal) staining. Scale bars: 20 μm. (E) Representative transmission electron microscopy images showing ultrastructural changes in the myocardia. Quantification of the area of cells occupied by mitochondria (%); Magnification: ×10,000. n = 6 for each group. # P < 0.05 vs. young control, ## P < 0.01 vs. young control, * P < 0.05 vs. old.