Are there gender differences in left ventricular remodeling after myocardial infarction in rats?

Amygdalin and exercise training exert a synergistic effect in improving cardiac performance and ameliorating cardiac inflammation and fibrosis in a rat model of myocardial infarction

This study investigated the effects of amygdalin (AMY, a cyanogenic glycoside widely distributed in the fruits and seeds of Rosaceae plants) on cardiac performance and ventricular remodeling in a rat model of myocardial infarction (MI). We also investigated whether the combination of AMY with exercise training (ExT) has a beneficial synergistic effect in treating MI rats. MI was induced by the ligation of the left anterior descending coronary artery in male SD rats. ExT or AMY treatment was started 1 week after MI and continued for 1 week (short-term) or 8 weeks (long-term). Cardiac function was evaluated by echocardiographic and hemodynamic parameters. Heart tissues were harvested and subjected to 2,3,5-triphenyl-tetrazolium chloride, Masson's trichrome, hematoxylin-eosin, and immunohistochemical staining. Gene expression was determined by quantitative polymerase chain reaction. Western blot gave a qualitative assessment of protein levels. AMY or ExT improved cardiac function and reduced infarct size in MI rats. AMY or ExT also suppressed myocardial fibrosis and attenuated inflammation in the infarct border zone of hearts from MI rats, as evidenced by inhibition of collagen deposition, inflammatory cell infiltration, and pro-inflammatory markers (interleukin 1β, interleukin 6, tumor necrosis factor-α, and cyclooxygenase 2). Notably, the effects of AMY combined with ExT were superior to those of AMY alone or ExT alone. Mechanistically, these beneficial functions were correlated with the inhibition of MI-induced activation of the transforming growth factor-β/Smad pathway. Collectively, AMY and ExT exert a synergistic effect on improving cardiac performance and ameliorating cardiac inflammation and fibrosis after MI, and the effects of long-term intervention were better than short-term intervention.

Swimming training attenuates the decrease of calcium responsiveness in female infarcted rats

Aim: To evaluate the influence of swimming training on calcium responsiveness of the myocardium of rats with different infarction sizes (MI).

Method: female Wistar rats, sedentary sham (SS = 14), sedentary moderate MI (SMI = 8) and sedentary large MI (SLI = 10) were compared to trained sham (TS = 16), trained moderate MI (TMI = 9) and trained large MI (TLI = 10). After 4 weeks of MI, the animals swam for 60 min/day, 5 days/week, for additional 8 weeks. Papillary muscles of the left ventricle were subjected to different concentrations of extracellular calcium. Inotropism was evaluated through the developed tension (DT), the maximum positive value of the first temporal derivation (+Td/td) and the time to peak tension (TPT). Lusitropism was evaluated by the maximum negative value of the first temporal derivation (−Td/td) and time to 50% relaxation (50%TR). Statistical significance was determined using multivariate analysis of variance and a Hotelling T2 test for the absolute power values of all four extracellular calcium concentrations (p < 0.05).

Results: MI depressed inotropism (from 17% to 51%) and lusitropism (from 22% to 54%) of the sedentary rats, but exercise attenuated the losses, especially regarding + dT/dt, TPT, −dT/dt and 50%TR. Exercise attenuated the decrease in myocardial responsiveness, proportionally to the size of the MI.

Conclusion: Myocardial calcium responsiveness is favorably affected in animals with moderate and large MI after swimming exercise.

Sex differences in cardiac remodeling post myocardial infarction with acute cigarette smoking

Background

Whether cigarette smoking affects the heart post-myocardial infarction (MI) in a sex-dependent way remains controversial. Using a mouse model, we investigated cardiac remodeling under the influence of acute cigarette smoke (CS) exposure following ischemic injury in both sexes.

Methods

Ten cigarettes were smoked twice daily for 2 weeks followed by MI and then 1 additional week post permanent LAD ligation. Cardiac function, histology, and infarct size were assessed, and inflammatory markers quantified by RT–PCR. Statistical comparisons were performed using an unpaired t test or ANOVA followed by Tukey post hoc test.

Results

We observed that cigarette smoking exacerbated both left and right ventricular remodeling only in males at an early stage of post-MI. Females did not display a significant structural and/or functional alteration within 7 days of cardiac remodeling post-MI upon CS exposure. Worsened right ventricular remodeling in males was independent of pulmonary congestion. CS-exposed males exhibited enhanced increases in left ventricular end systolic and diastolic volumes, as well as reductions in ejection fraction and fractional area changes of left ventricular base. At day 7, infarct size was increased by cigarette smoking in males only, which was accompanied by enhanced collagen deposition in both the infarcted and peri-infarcted areas. Both IL-6 and TNF-α mRNA expression significantly increased in CS-exposed MI male group only at day 7 post-MI suggestive of prolonged inflammation.

Conclusions

These findings indicate that CS exposure worsens the progression of cardiac remodeling post-MI in male sex in a significant manner compared to female sex at least at early stages.

Comparison between Radionuclide Ventriculography and Echocardiography for Quantification of Left Ventricular Systolic Function in Rats Exposed to Doxorubicin

Background

Radionuclide ventriculography (RV) is a validated method to evaluate the left ventricular systolic function (LVSF) in small rodents. However, no prior study has compared the results of RV with those obtained by other imaging methods in this context.

Objectives

To compare the results of LVSF obtained by RV and echocardiography (ECHO) in an experimental model of cardiotoxicity due to doxorubicin (DXR) in rats.

Methods

Adult male Wistar rats serving as controls (n = 7) or receiving DXR (n = 22) in accumulated doses of 8, 12, and 16 mg/kg were evaluated with ECHO performed with a Sonos 5500 Philips equipment (12-MHz transducer) and RV obtained with an Orbiter-Siemens gamma camera using a pinhole collimator with a 4-mm aperture. Histopathological quantification of myocardial fibrosis was performed after euthanasia.

Results

The control animals showed comparable results in the LVSF analysis obtained with ECHO and RV (83.5 ± 5% and 82.8 ± 2.8%, respectively, p > 0.05). The animals that received DXR presented lower LVSF values when compared with controls (p < 0.05); however, the LVSF values obtained by RV (60.6 ± 12.5%) were lower than those obtained by ECHO (71.8 ± 10.1%, p = 0.0004) in this group. An analysis of the correlation between the LVSF and myocardial fibrosis showed a moderate correlation when the LVSF was assessed by ECHO (r = -0.69, p = 0.0002) and a stronger correlation when it was assessed by RV (r = -0.79, p < 0.0001). On multiple regression analysis, only RV correlated independently with myocardial fibrosis.

Conclusion

RV is an alternative method to assess the left ventricular function in small rodents in vivo. When compared with ECHO, RV showed a better correlation with the degree of myocardial injury in a model of DXR-induced cardiotoxicity.

Low-Level Laser Application in the Early Myocardial Infarction Stage Has No Beneficial Role in Heart Failure

Low-level laser therapy (LLLT) has been targeted as a promising approach that can mitigate post-infarction cardiac remodeling. There is some interesting evidence showing that the beneficial role of the LLLT could persist long-term even after the end of the application, but it remains to be systematically evaluated. Therefore, the present study aimed to test the hypothesis that LLLT beneficial effects in the early post-infarction cardiac remodeling could remain in overt heart failure even with the disruption of irradiations. Female Wistar rats were subjected to the coronary occlusion to induce myocardial infarction or Sham operation. A single LLLT application was carried out after 60 s and 3 days post-coronary occlusion, respectively. Echocardiography was performed 3 days and at the end of the experiment (5 weeks) to evaluate cardiac function. After the last echocardiographic examination, LV hemodynamic evaluation was performed at baseline and on sudden afterload increases. Compared with the Sham group, infarcted rats showed increased systolic and diastolic internal diameter as well as a depressed shortening fraction of LV. The only benefit of the LLLT was a higher shortening fraction after 3 days of infarction. However, treated-LLLT rats show a lower shortening fraction in the 5th week of study when compared with Sham and non-irradiated rats. A worsening of cardiac function was confirmed in the hemodynamic analysis as evidenced by the higher LV end-diastolic pressure and lower +dP/dt and −dP/dt with five weeks of study. Cardiac functional reserve was also impaired by infarction as evidenced by an attenuated response of stroke work index and cardiac output to a sudden afterload stress, without LLLT repercussions. No significant differences were found in the myocardial expression of Akt₁/VEGF pathway. Collectively, these findings illustrate that LLLT improves LV systolic function in the early post-infarction cardiac remodeling. However, this beneficial effect may be dependent on the maintenance of phototherapy. Long-term studies with LLLT application are needed to establish whether these effects ultimately translate into improved cardiac remodeling.

Sex-related differences in intrinsic myocardial properties influence cardiac function in middle-aged rats during infarction-induced left ventricular remodeling

We previously determined that residual left ventricular (LV) myocardium of middle-aged rats had sex-related differences in regional tissue properties 4 weeks after a large myocardial infarction (MI). However, the impact of such differences on cardiac performance remained unclear. Therefore, our current study aimed to elucidate whether sex-related changes in MI-induced myocardial remodeling can influence cardiac function. A similar-sized MI was induced in 12-month-old male (M-MI) and female (F-MI) Sprague-Dawley rats by ligation of the left coronary artery. The cardiac function was monitored for 2 months after MI and then various LV parameters were compared between sexes. We found that although two sex groups had a similar pattern of MI-induced decline in LV function, F-MI rats had greater cardiac performance compared to M-MI rats, considering the higher values of EF (39.9 ± 3.4% vs. 26.7 ± 7.7%, P < 0.05), SW index (40.4 ± 2.1 mmHg • mL/kg vs. 20.2 ± 3.3 mmHg • mL/kg, P < 0.001), and CI (139.2 ± 7.9 mL/min/kg vs. 74.9 ± 14.7 mL/min/kg, P < 0.01). The poorer pumping capacity in M-MI hearts was associated with markedly reduced LV compliance and prolonged relaxation. On the tissue level, F-MI rats revealed a higher, than in M-MI rats, density of cardiac myocytes in the LV free wall (2383.8 ± 242.6 cells/mm(2) vs. 1785.7 ± 55.9 cells/mm(2), P < 0.05). The latter finding correlated with a lower density of apoptotic cardiac myocytes in residual LV myocardium of F-MI rats (0.18 ± 0.08 cells/mm(2) vs. 0.91 ± 0.30 cells/mm(2) in males, P < 0.01). Thus, our data suggested that F-MI rats had markedly attenuated decline in cardiac performance compared to males due to ability of female rats to better retain functionally favorable intrinsic myocardial properties.

Previous exercise training increases levels of PPAR-α in long-term post-myocardial infarction in rats, which is correlated with better inflammatory response

OBJECTIVE

Exercise is a protective factor for cardiovascular morbidity and mortality, with unclear mechanisms. Changing the myocardial metabolism causes harmful consequences for heart function and exercise contributes to metabolic adjustment modulation. Peroxisome proliferator-activated receptors (PPARs) are also myocardium metabolism regulators capable of decreasing the inflammatory response. We hypothesized that PPAR-α is involved in the beneficial effects of previous exercise on myocardial infarction (MI) and cardiac function, changing the expression of metabolic and inflammatory response regulators and reducing myocardial apoptosis, which partially explains the better outcome.

METHODS AND RESULTS

Exercised rats engaged in swimming sessions for 60 min/day, 5 days/week, for 8 weeks. Both the exercised rats and sedentary rats were randomized to MI surgery and followed for 1 week (EI1 or SI1) or 4 weeks (EI4 or SI4) of healing or to sham groups. Echocardiography was employed to detect left ventricular function and the infarct size. Additionally, the TUNEL technique was used to assess apoptosis and immunohistochemistry was used to quantitatively analyze the PPAR-α, TNF-α and NF-κB antigens in the infarcted and non-infarcted myocardium. MI-related mortality was higher in SI4 than in EI4 (25% vs 12%), without a difference in MI size. SI4 exhibited a lower shortening fraction than EI4 did (24% vs 35%) and a higher apoptosis/area rate (3.97±0.61 vs 1.90±1.82) in infarcted areas (both p=0.001). Immunohistochemistry also revealed higher TNF-α levels in SI1 than in EI1 (9.59 vs 4.09, p<0.001) in infarcted areas. In non-infarcted areas, EI4 showed higher levels of TNF-α and positive correlations between PPAR-α and NF-κB (r=0.75, p=0.02), in contrast to SI4 (r=0.05, p=0.87).

CONCLUSION

Previously exercised animals had better long-term ventricular function post-MI, in addition to lower levels of local inflammatory markers and less myocardial apoptosis, which seemed to be related to the presence of PPAR-α.