Survival outcomes
There was a significant difference in mortality among sham, CLP, and CLP + DIZE groups (P = 0.004; Fig. 1). Compared with the CLP group, the CLP + DIZE group had a lower mortality rate (38.5% versus 61.5%) at 48 hours post-surgery, although this was not statistically significant.
Cardiac functions and myocardial injury
Cardiac function and plasma biomarkers that indicated myocardial injury are shown in Fig. 2. The LVSP, +dp/dtmax, and -dp/dtmax in the CLP group were remarkably lower than those in the sham group at 6, 12, 24, and 48 hours after the surgery (LVSP P = 0.006, 0.013, < 0.001, and 0.002, respectively; +dp/dtmax P < 0.001, P = 0.007, 0.001, and 0.010, respectively; −dp/dtmax P = 0.011, < 0.001, 0.003, and 0.001, respectively). Compared with rats in the CLP group, rats in the CLP + DIZE group had significantly improved LVSP, +dp/dtmax, and -dp/dtmax at 6, 12, and 24 hours (LVSP P = 0.017, 0.002, and < 0.001, respectively; +dp/dtmax P = 0.008, 0.005, and 0.005, respectively; −dp/dtmax P = 0.028, 0.001, and 0.016, respectively). The CLP + DIZE group and the CLP group had no obvious differences in the measurements of LVSP, +dp/dtmax, or -dp/dtmax at 48 hours. Compared with the sham group, the CLP group had significantly higher levels of plasma TnI and BNP at 6, 12, and 24 hours (TNI: P < 0.001, < 0.001, and P = 0.002, respectively; BNP: P = 0.001, < 0.001, and 0.002, respectively). The plasma TnI levels in the CLP + DIZE group were significantly higher than those in the sham group at 6, 12, and 24 hours (P < 0.001, < 0.001, and P = 0.045, respectively), but were lower than those in the CLP group at 6 and 12 hours (P = 0.001 and 0.004, respectively). Meanwhile, the CLP + DIZE group had significantly decreased plasma BNP levels when compared with the CLP group at 6 and 12 hours (P = 0.014 and 0.018, respectively).
Plasma cytokine levels
Comparisons of plasma cytokine levels are shown in Fig. 3. Plasma levels of TNF-α in the CLP group were significantly higher compared to the sham group at 6, 12, and 24 hours (P < 0.001, < 0.001, and < 0.001, respectively). At the same timepoints, plasma TNF-α levels in the CLP + DIZE group were significantly lower than those in the CLP group (P < 0.001, < 0.001, and P = 0.008, respectively). At 6, 12, 24, and 48 hours, the plasma levels of IL-6 in the CLP group were significantly higher compared to the sham group (P = 0.002, < 0.001, = 0.012, and = 0.003 respectively). However, there was no significant difference in the plasma IL-6 levels between the CLP + DIZE group and the CLP group at each time point.
Plasma AngII and Ang-(1–7) levels
Plasma AngII levels in the CLP group and CLP + DIZE group were significantly higher than those in the sham group at 6, 12, and 24 hours (CLP group vs. sham group P = 0.002, 0.007, and 0.021, respectively; CLP + DIZE group vs. sham group P = 0.045, 0.015, and 0.005, respectively; Fig. 4). There was no significant difference in the plasma AngII levels between the CLP + DIZE and CLP groups at each time point.
The plasma Ang-(1–7) levels were significantly higher in the CLP group than in the sham group at 6, 12, and 24 hours (P < 0.001, P = 0.005, and = 0.001, respectively; Fig. 4). Compared with the CLP group, the CLP + DIZE group showed a significant lower plasma Ang-(1–7) level only at 6 hours post-surgery (P = 0.005).
Myocardial Ang-(1–7) levels
There was a significant decrease in myocardial Ang-(1–7) levels in the CLP groups compared to the sham groups between 6 and 24 hours post-surgery (P = 0.004, P = 0.020, and 0.008, respectively; Fig. 5), and this decrease in myocardial Ang-(1–7) levels could be improved by DIZE administration, especially at 12 hours and 24 hours post-operation (P = 0.001 and P < 0.001, respectively).
Myocardial ACE, ACE2, AT1R and MasR expressions
The expression of AT1R and ACE2 in the myocardium of the CLP group were significantly decreased compared to the sham group at 24 hours post-surgery (Fig. 6; AT1R P = 0.047; ACE2 P < 0.001). However, there were no differences between the sham and CLP group in the expression of ACE and MasR. The level of ACE2 was significantly increased in the CLP + DIZE group compared to the CLP group (P < 0.001). The AT1R level was significantly decreased in the CLP + DIZE group compared to the sham group (P = 0.002), but was not different from the CLP group.
Histological examinations
Vacuolar degeneration of myocardial cells, along with few local inflammatory cell infiltration, was observed in tissues from the CLP group at 6 hours post-surgery (Fig. 7). These changes were exaggerated at 12 and 24 hours after the operation when myocyte lysis started to appear. These degenerations were improved at 48 hours post-surgery, although the disorganized structure of the tissue persisted. The CLP + DIZE group had less severe myocardial injuries compared with the CLP group at each timepoint, especially at 12 and 24 hours post-surgery.
Transmission electron microscopy showed that the rats in the CLP group had mitochondrial swelling, decreased electron density, mitochondrial membrane destruction, cristae reduction, and myofibril dissolution at each time point (Fig. 8). Compared to the CLP group, the CLP + DIZE group showed significantly fewer injuries to the mitochondria and myofilaments at each time point between 6 and 24 hours. This protective effect of DIZE on the cellular microstructures was easily observed in the mitochondria.