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 1 – Changes in body weight after 90 days of treatment. Control (C; closed squares, n = 7), animals with food restriction of 50% (R 50 ; closed triangles, n = 7) and animals with alternation between food restriction of 50% and refeeding (RF; open circles, n = 7). Values are means ± SD; * significant at p < 0.05, R 50 vs. C; † p < 0.05, RF vs. R 50 ; # p < 0.05, C vs. RF. Repeated measures two-way ANOVA; post hoc Bonferroni’s test. Source: Research team. 500 400 300 200 Body weight (g) Weeks 0 1 2 3 4 5 6 7 8 9 10 11 12 C R 50 RF # # # # # # # *† *† * *† *† *† *† *† *† *† *† Ca 2+ concentration (5.2 mM); -dL/dt was significantly lower in R 50 than in C group (C: 2.66 ± 0.35 vs. R 50 : 2.18 ± 0.33 ML/s, p < 0.05) (Figure 2E). Isoproterenol stimulation The fasting/refeeding cycles increased +dT/dt, -dT/dt and -dL/dt at the highest isoproterenol concentration (1 µM) compared to those in the R 50 group, indicating a positive inotropic effect in myocytes. In contrast, the RF group promoted a reduction in +dL/dt than the R 50 group at the same isoproterenol concentration (Figure 3F). In addition, the similar effects were noted in +dT/dt and -dT/dt at 1µM isoproterenol of the C group when compared to the R 50 (Figures 3B and C). Furthermore, RF rats presented higher +dL/dt at baseline and isoproterenol concentrations (0.01 µM) in comparison to C group (Figure 3F). There were no significant differences in mechanical data (DT and PS) under inotropic stimulation with isoproterenol among the groups (Figures 3A and D). Myocardial morphology The C group rats showed normal morphological characteristics, with myofibrils filling the entire sarcoplasm, well-defined sarcomeres, mitochondria with lamellar cristae, sarcoplasmic membranes with regular aspect, sarcoplasmic reticulum among myofibrils and nuclei with uncondensed chromatin (Figures 4A and B). The R 50 group presented focal changes, including disorganization or absence of myofibrils, some polymorphic mitochondria with a decreased number of cristae and areas of sarcoplasmic reticulum dilation (Figures 4C, D and E). In RF rats, the only change observed was a loss of mitochondrial cristae in some organelles. Most of the fibers had normal morphology (Figures 4F and G). Discussion Interestingly, little information is available on the relationship between cardiac function and morphology during fasting/refeeding in SHR hypertrophied hearts. Within this context, this dietary regimen has become the subject of Table 3 – Isotonic contraction of groups at baseline condition Groups C R 50 RF PS (%) 19 ± 3 18 ± 3 20 ± 2 -dL/dt (ML/s) 1.89 ± 0.40 1.60 ± 0.36 2.19 ± 0.45 † TPS (ms) 168 ± 26 205 ± 14 * 161 ± 14 † +dL/dt (ML/s) 4.28 ± 1.26 4.13 ± 1.11 4.79 ± 0.86 RT 50 (ms) 58 ± 10 76 ± 12 * 53 ± 9 † 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; PS: percentage of shortening; -dL/dt: maximum shortening velocity; TPS: time to peak shortening; + dL/dt: maximum relaxation velocity; 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. 403