Histopathological changes of pulmonary vascular remodeling in dogs affected with pulmonary hypertension secondary to degenerative mitral valve disease

Introduction/objectives: Pulmonary hypertension (PH) can cause pul-monary arterial remodeling. Medial remodeling is a structural change of the pul-monary artery seen with PH. Hyperplasia and hypertrophy of pulmonary arterial smooth muscle cells (SMCs) are suggested as causes of medial remodeling. To de-monstrate the histopathological changes of the pulmonary artery in dogs affected with PH secondary to degenerative mitral valve disease (DMVD) compared with DMVD without PH and control dogs. Animals: Lung samples obtained from the carcasses of 19 older small-breed dogs (Control, n = 5; DMVD, n = 7; DMVD + PH, n = 7). Materials and methods: Lung tissue sections were stained with hematoxylin and eo-sin, Masson's trichrome, and proliferating cell nuclear antigen (PCNA) immunohisto-chemistry. Results: The internal diameters of the pulmonary artery in the three groups were not different. Masson's trichrome staining revealed no collagen deposition in the in -timal layer of the pulmonary artery in all dogs. The external diameter, percentage of medial thickness (%MT), percentage of SMC layer and collagen deposition areas, average number of SMCs, and the percentage of PCNA positive cells (%PCNA) of the pulmonary artery were increased in the DMVD and DMVD + PH groups compared with the control group. The %PCNA in the DMVD thorn PH group was significantly decreased when compared with the DMVD group. Conclusions: Medial remodeling was found in left-sided heart failure DMVD dogs with and without PH. The medial remodeling in DMVD dogs with and without PH is related to SMC hyperplasia, hypertrophy, and collagen deposition, leading to an increased medial layer thickness of the pulmonary artery. 2021 Elsevier B.V. All rights reserved.