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 Table 2 – General characteristics of rats Parameters Groups C R 50 RF IBW (g) 247 ± 15 248 ± 12 249 ± 13 FBW (g) 366 ± 14 236 ± 17 * 342 ± 21 *† FC (g/week) 159 ± 23 77 ± 4 * 130 ± 55 † SBP initial (mmHg) 177 ± 8 177 ± 5 181 ± 7 SBP final (mmHg) 163 ± 13 157 ± 15 156 ± 5 LVW (g) 0.99 ± 0.04 0.51 ± 0.01 * 0.87 ± 0.08 *† RVW (g) 0.21 ± 0.02 0.11 ± 0.01 * 0.17 ± 0.02 *† LVW/FBW (mg/g) 2.71 ± 0.05 2.19 ± 0.16 * 2.53 ± 0.08 *† RVW/FBW (mg/g) 0.58 ± 0.04 0.47 ± 0.05 * 0.51 ± 0.05 * C: control group; R 50: animals with food restriction of 50%; RF: animals with alternation between food restriction of 50% and refeeding; IBW: initial body weight; FBW: final body weight; FC: food consumption; SBP: systolic blood pressure; LVW: left ventricle weight; RVW: right ventricle weight. Values are means ± SD (n = 7). * significant at p < 0.05 vs. C; † p < 0.05 vs. R 50 . One-way ANOVA and post hoc Tukey’s test. myocardial function at baseline condition were reported as means ± standard deviation (SD). Comparisons between groups were performed using one-way analysis of variance (ANOVA) for independent samples. A repeated-measures two‑way ANOVA was utilized to evaluate the body weight evolution and the positive and negative inotropic effects on myocardial function. When significant differences were found (p < 0.05), post hoc Tukey’s or Bonferroni’s test for multiple comparisons was carried out. The level of significance considered was 5%. The sample size (n) was performed using the equation: n = 1 + [2C * (s/d) 2 ], where C (z score α + z score β ) 2 is dependent on the values chosen for statistical power of the test (90%; type II error) and level of significance (0.05; type I error); the standard deviation value (s) adopted was 0.25, and the minimal difference between groups (d) was 0.5. The sample size needed to detect a significant difference between groups is 6.25 rats per group; however, we decided to use 7 animals per group for most of the analyses. Results General and morphological characteristics of rats Significantly higher values of FBW, LVW, RVW, LVW/FBW and RVW/FBW were found in C compared to R 50 and RF rats (Table 2). After 12 weeks, fasting/refeeding cycles promoted a substantial elevation of FBW and food consumption that were significantly greater than those in the R 50 group. In relation to cardiac parameters, the RF and R 50 groups presented different behavior. Specifically, the LVW (RF: 12.12% and R 50 : 48.5%; p < 0.05), RVW (RF: 19.04% and R 50 : 47.62%; p < 0.05), LVW/FBW (RF: 6.64% and R 50 : 19.2%; p < 0.05) and RVW/ FBW (RF: 12.06% and R 50 : 18.96%; p < 0.05) were reduced in percentage in the RF and R 50 rats as compared to C rats. Nevertheless, the fasting/refeeding cycles presented lower cardiac atrophy than R 50 rats in relation to C rats. In addition, C rats experienced increasing weight gain, while R 50 rats maintained their IBW after 12 weeks of experimental protocol (Figure 1). On the other hand, RF rats gained weight dependent on food intake, with body weight increasing and decreasing during refeeding and fasting, respectively (Figure 1). Isolated muscle performance Fasting/refeeding cycles did not cause functional impairment (Tables 3 and 4). Nevertheless, the isotonic [-dL/dt, TPS, and RT 50 )] and isometric parameters (TPT, +dT/dt, -dT/ dt, RT 50 ) were significantly elevated in RF rats compared to those in the R 50 group, indicating that fasting/refeeding cycles preserves the contraction and relaxation phase of cardiac function. Furthermore, the R 50 rats presented cardiac damage in relation to the C group for isotonic and isometric variables. In addition, the papillary muscle CSA showed no difference among groups. Calcium stimulation After baseline condition, the increases in extracellular Ca 2+ concentrations from 0.625 to 5.2 mM resulted in a positive inotropic effect in myocytes from all groups (Figures 2A-F). However, the results shown in Figures 2B, C and E indicate that extracellular Ca 2+ (1.25 and 2.5 mM) induced a greater response in +dT/dt (RF: 99.1 ± 23.6; 132.1 ± 36.2 g/mm 2 /s vs. R 50 : 63.2 ± 12.8; 91.5 ± 22.0 g/mm 2 /s; p < 0.05, respectively), -dT/dt (RF: 30.6 ± 5.9; 35.9 ± 5.8 g/mm 2 /s vs. R 50 : 22.0 ± 4.4; 28.5 ± 6.1 g/mm 2 /s; p < 0.05, respectively) and -dL/dt (RF: 2.19 ± 0.45; 2.77 ± 0.51 ML/s vs. R 50 : 1.47 ± 0.24; 1.99 ± 0.31 ML/s; p < 0.05, respectively) in the RF rats than in the R 50 rats. In addition, -dT/dt and -dL/dt were significantly diminished in the R 50 myocardium at Ca 2+ concentration of 5.2 mM when compared to those in the RF group. When submitted to inotropic maneuvers, DT, PS and +dL/dt were similar between RF and R 50 . In relation to the cardiac function of C rats after Ca 2+ stimulation, the fasting/refeeding cycles presented similar behavior (Figures 2A-F). The only significant result between C and R 50 was noted in the highest 402