Figure 7. Aging mice present high circulating ET-1 levels, loss of muscle strength, fibrosis and senescence in gastrocnemius and tibialis anterior muscles. Animals were kept on a 12:12h light-dark cycle, at 24°C, and food and water were available ad libitum. Male C57Bl6 mice from 5, 18, and 24 month-old were used, 10 animals per group. (A) Serum ET-1 levels was measured by ELISA. (B) Muscle force was registered using the 4 limb grip test and data were corrected by body weight of each mouse. Values are the mean±SEM of 10 mice, *p<0.05 vs. 5-month-old; **p<0.05 vs 18 month-old. Mice of 5-month-old (Young-closed bars) and 24-month-old (Old-stripped bars) were used to measure Sirius red staining in sections of the gastrocnemius (GNM) and the tibialis anterior muscles to visualize fibrosis (C), to analyze FN protein expression by Western blot (D) and to assess senescence by measuring p16 protein content by Western blot (E) in those muscles of the same mice. (C) Sirius red staining (20x) is shown with the mean ± standard error below pictures. (D, E) A representative Western blot was shown above with the densitometric analysis below. Values are the mean±SEM of 20 mice, *p<0.05 vs. young mice. (F) Graphs of correlations based on data from young (5-month-old) and old (24-month-old) mice were shown: ET-1 levels and grip force (Spearman r= -0.5669, p= 0.0091), ET-1 levels and Sirius red in GNM (Spearman r= 0.7787, p= 0.0002), ET-1 levels and p16 expression in GNM (Spearman r= 0.6548, p= 0.0043), grip force and Sirius red in GNM (Spearman r= -0.7028, p= 0.0011) and grip force and p16 expression in GNM (Spearman r= -0.5789, p= 0.0118).