Compensatory angiogenesis during progressive right ventricular hypertrophy.

We investigated vascular adaptations occurring in progressive right ventricular hypertrophy (RVH) in adult mini pigs. Fourteen mini pigs had progressive RVH induced by implanting an inflatable cuff on the main pulmonary artery for 1-5 months and were compared to a control group (N = 11). RVH animals were divided into two groups, a moderate RVH (MH) that had RV/BW ratio increases of 20%-70% above controls and a severe hypertrophy group (SH) that had RV/BW ratio increase of 70%-117%. We measured coronary blood flow reserve (CBFR) with radiolabelled microspheres at maximal exercise and during adenosine vasodilation. Adenosine vasodilation did not decrease CBFR either regionally or transmurally in both the MH and SH groups. During exercise CBFR showed a small but significant decrease in the SH group. No intervention changed the endo/epi flow ratios. Morphometric studies showed that myocytes increased in cross sectional areas (CSA) in these hypertrophied hearts. The CSA of capillaries and arterioles and their numerical densities increased significantly in the endocardial and epicardial regions in both MH and SH groups. Capillary density showed a small but significant decrease in both MH and SH groups. We measured DNA synthesis in these hearts using tritiated thymidine labelling. We found a high labelling index in endothelial cells and a moderate labelling index in smooth muscle cells in early stages of hypertrophy. These data show that angiogenesis, observed in the morphometric studies and by DNA labelling, prevents CBFR changes during progressive RVH in the pig. Furthermore, angiogenesis is not uniform at different stages of progressive RVH.