Figure 2. Administration of metformin decreased the endoplasmic reticulum (ER) stress in aged mouse hearts. Compared to 3 mo., the contents of the cleaved ATF6 (A) and CHOP (B) were significantly increased in 24 mo., supporting the presence of increased ER stress in aged hearts. The contents of cleaved ATF6 and CHOP were markedly decreased in metformin-treated 24 mo. hearts compared to vehicle, supporting that metformin treatment decreased the ER stress present in aged hearts. Metformin treatment did not alter the ER stress in 3 mo. hearts. Mean ± SEM. *p<0.05 vs. 3 mo. vehicle, †p<0.05 vs. 24 mo. vehicle. n=4 in each group.