Reversible pulmonary trunk banding: Myocardial vascular endothelial growth factor expression in young goats submitted to ventricular retraining

Abstract

Background: Ventricle retraining has been extensively studied by our laboratory. Previous studies have demonstrated that intermittent overload causes a more efficient ventricular hypertrophy. The adaptive mechanisms involved in the ventricle retraining are not completely established. This study assessed vascular endothelial growth factor (VEGF) expression in the ventricles of goats submitted to systolic overload.

Methods: Twenty-one young goats were divided into 3 groups (7 animals each): control, 96-hour continuous systolic overload, and intermittent systolic overload (four 12-hour periods of systolic overload paired with 12-hour resting period). During the 96-hour protocol, systolic overload was adjusted to achieve a right ventricular (RV) / aortic pressure ratio of 0.7. Hemodynamic evaluations were performed daily before and after systolic overload. Echocardiograms were obtained preoperatively and at protocol end to measure cardiac masses thickness. At study end, the animals were killed for morphologic evaluation and immunohistochemical assessment of VEGF expression.

Results: RV-trained groups developed hypertrophy of RV and septal masses, confirmed by increased weight and thickness, as expected. In the study groups, there was a small but significantly increased water content of the RV and septum compared with those in the control group (p<0.002). VEGF expression in the RV myocardium was greater in the intermittent group (2.89% ± 0.41%) than in the continuous (1.80% ± 0.19%) and control (1.43% ± 0.18%) groups (p<0.023).

Conclusions: Intermittent systolic overload promotes greater upregulation of VEGF expression in the subpulmonary ventricle, an adaptation that provides a mechanism for increased myocardial perfusion during the rapid myocardial hypertrophy of young goats.

Fig 1. Photomicrograph of the myocardium from an animal of the Intermittent group, counterstained with Harris hematoxylin.

The perivascular area is indicated manually (red line). Notice the presence of green spots corresponding to the labeled cells after automatic color detection of VEGF labeling in cells of the vessel walls and perivascular region. Objective magnification = 40X. Image Analyzer: AxioVision, software V.4.7.1.0, Carl Zeiss AG.

Fig 2. Right ventricular (RV) to pulmonary artery (PA) systolic pressure gradient (mm Hg) throughout the protocol.

* p <0.001 when compared with respective baseline and control group values; ¤ p<0.001 when compared with 96-hour continuous group. n = 7 in each group.

Fig 3. Weights for the right ventricle (RV), left ventricle (LV), and septum indexed to body weights of the 3 groups.

* p<0.001 when compared to the control group; ¤ p<0.047 when compared to the control group. n = 7 in each group.

Fig 4. Photomicrographs of the myocardium from animals of the three groups submitted to immunohistochemical staining for vascular endothelial growth factor (VEGF).

The panels show the automatic colour detection of vascular and perivascular positive cells in myocardial tissue labeled with anti-VEGF antibody (green color). The area occupied by labeled cells (area fraction) was calculated relative to the total perivascular area, as shown in Fig 1. Panel A shows a control case, while in panels B and C are examples of trained animals (B: Continuous group; C: Intermittent group). Scale bars in all the panels corresponds to 50 micrometers.

Fig 5

Vascular endothelial growth factor (VEGF) expression (% area fraction of immunolabeled histological sections) in the right ventricle (RV), left ventricle (LV), and septum in the 3 groups. * p<0.023 compared to RV of control and continuous groups; ¤ p<0.050 compared to LV myocardium and septum within the same group. n = 7 in each group.