Relationship between the degree of endometrial periglandular fibrosis and the presence of angiotensin-converting enzyme in the equine endometrium.

Endometrial periglandular fibrosis (EPF) has been proposed as a possible aetiology for equine embryonic and fetal loss. However, the pathophysiology of EPF is not well understood. Angiotensin-converting enzyme (ACE) is found in macrophages, endothelium (during angiogenesis) and myofibroblasts at sites of fibrosis in the heart, kidneys, liver and skin in several species. An increase in local tissue ACE-binding activity appears to be a critical event in the initiation and progression of fibrosis in these tissues. The aim of this study was to investigate the correlation between ACE activity in the equine endometrium and the degree of EPF, as determined by histological evaluation and morphometry based on a collagen-specific stain. ACE-binding activity values were significantly higher in the endometrial samples with moderate EPF (modified Kenney EPF category IIB) compared with endometria in all other categories. Ultrastructurally, the fibroblasts surrounding the glandular basal laminae in modified Kenney EPF category IIB and III endometria were undergoing myofibroblastic transformation-like changes. These observations indicate a possible link between ACE activity and the onset of EPF in mares.