Long-term histological effects of high-dose prednisolone administration on the mitral valve in normal Beagle dogs

BACKGROUND: In recent years, left ventricular hypertrophy and cardiac dysfunction have been reported in human and canine patients with hypercortisolism and in dogs treated experimentally with high-dose prednisolone. However, to our knowledge, there have been no reports on the effects of hyperglucocorticism (HGC) on the mitral valve (MV). AIM: This study aimed to compare the MV in dogs treated with high-dose prednisolone with that in healthy dogs to investigate the effects of HGC on the MV. METHODS: We investigated the effects of HGC on the MV by comparing samples obtained from high-dose glucocorticoid (GC)-treated (P) and healthy (C) dogs. The P group included healthy Beagle dogs (n = 6) treated with prednisolone (2 mg/kg, bid, po) for 84 days and the C group included healthy Beagle dogs (n = 6) euthanized for unrelated reasons. The anterior and posterior mitral leaflets (AML and PML, respectively) from both groups were harvested and stained with hematoxylin–eosin, Alcian blue, and Masson trichome. Additionally, adiponectin (ADN) and GC receptor immunohistochemistry were performed. Histological evaluation was performed in the atrialis, spongiosa, fibrosa, and all layers of the proximal, middle, and distal regions of the AML and PML. RESULTS: The proportion of the spongiosa layer thickness to the total thickness was higher in the P than in the C group (proximal and middle AML). However, the proportion of the fibrosa layer thickness to the total thickness was lower in the P than in the C group (middle PML). Areas of acidic sulfated mucosubstance deposition were smaller in the fibrosa layer and all layers (middle AML), while those of collagen deposition were smaller in the spongiosa and total layers (proximal and middle AML), in the P than in the C group. Additionally, ADN expression in the spongiosa layer was higher in the P than in the C group (middle AML). CONCLUSION: These findings suggest that long-term administration of synthetic GCs induces histological changes in the MV. These changes may lead to MV dysfunction in dogs with HGC.