ABC | Volume 111, Nº3, September 2018

Original Article Pinotti et al Fasting/refeeding cycles and myocardial remodeling Arq Bras Cardiol. 2018; 111(3):400-409 Figure 2 – Effects of increased extracellular calcium on myocardial isotonic and isometric parameters in papillary muscles from control (C = black bars), animals with food restriction of 50% (R 50 = gray bars) and animals with alternation between food restriction of 50% and refeeding (RF = white bars). Extracellular calcium experiment: 7 animals each group. Isometric parameters: A: DT (peak developed tension normalized per cross-sectional area); B: +dT/dt (peak isometric tension development rate normalized per cross-sectional area); C: -dT/dt, g/mm 2 /s (maximum tension decline rate normalized per cross-sectional area). Isotonic parameters: D: PS (percentage of shortening); E: -dL/dT (maximum shortening velocity); F: +dL/dT (maximum relaxation velocity). L max : muscle length at peak DT. Values are means ± SD; * significant at p < 0.05 vs. C; † p < 0.05 vs. R 50 . Repeated measures two-way ANOVA and post hoc Tukey’s test. Source: Research team. A B D E F C 10 8 6 4 2 0 DT (g/mm 2 ) +dT/dt (g/mm 2 /s) –dT/dt (g/mm 2 /s) PS (%) –dL/dT (ML/s) +dL/dT (ML/s) 200 100 150 50 0 50 40 30 20 10 0 30 20 10 0 4 3 2 1 0 8 6 4 2 0 0.625 1.25 2.5 5.2 0.625 1.25 2.5 5.2 0.625 1.25 2.5 5.2 0.625 1.25 2.5 5.2 0.625 1.25 2.5 5.2 0.625 1.25 2.5 5.2 calcium concentration (mM) calcium concentration (mM) calcium concentration (mM) calcium concentration (mM) calcium concentration (mM) calcium concentration (mM) C R 50 RF † † † † † * † † † considerable scientific interest for weight loss and improving cardiometabolic health. Thus, the main finding of this study was that fasting/refeeding attenuated the damage caused by CR. The results reveal that fasting/refeeding showed increased isotonic and isometric parameters at baseline, as well as improved the myocardial inotropic response to calcium and isoproterenol. In addition, fasting/refeeding prevented cardiac atrophy and morphological injuries. Less body weight gain was observed in the RF group than in the C group (Table 1, Figure 1), but more body weight gain than in the R 50 group. According to literature, body weight reduces approximately 13% when the animals are submitted Table 4 – Isometric contraction of groups at baseline condition Groups C R 50 RF DT (g/mm 2 ) 6.17 ± 1.24 6.37 ± 1.14 7.18 ± 1.20 RT (g/mm 2 ) 1.06 ± 0.12 1.12 ± 0.31 1.07 ± 0.17 +dT/dt (g/mm 2 /s) 77 ± 17 63 ± 13 93 ± 18 † TPT (ms) 146 ± 27 184 ± 19 * 128 ± 25 † -dT/dt (g/mm 2 /s) 29 ± 5 22 ± 4 33 ± 9 † RT 50 (ms) 174 ± 40 224 ± 32 * 171 ± 21 † CSA (mm 2 ) 0.95 ± 0.22 0.85 ± 0.17 0.91 ± 0.18 C: control group; R 50: animals with food restriction of 50%; RF: animals with alternation between food restriction of 50% and refeeding; DT: peak developed tension; RT: resting tension; TPT: time to peak tension; +dT/dt: maximum tension development rate; -dT/dt: maximum tension decline rate; RT 50: time from peak tension to 50% relaxation; CSA: muscle cross-sectional area. Values are means ± SD (n = 7) at basal calcium concentration (1.25 mM); * significant at p < 0.05 vs. C; † p < 0.05 vs. R 50 . One-way ANOVA and post hoc Tukey’s test. 404