Age-related morphometrical changes of arteries of uterine wall in mares

To investigate the morphological changes of uterine wall arteries associated with the progression of age in Thoroughbred broodmares, uterine wall arteries from 13 mares, aged 2 to 31 years, were studied by routine histomorphometry. The ratio of intimal thickness to external diameter increased due to hyperplasia of elastic fibers and was significantly correlated with age (r = 0.95, P < 0.001). The ratio of medial thickness to external diameter decreased and was also significantly correlated with age (r = -0.84, P < 0.001). Using electron microscopy, it was determined that the cross-sectional area of the tunica media occupied by smooth muscle cells gradually decreased with increasing age. These results demonstrate that in arteries of the uterine wall in mares, hyperplasia of intimal elastic fiber and thinning of the medial smooth muscular layer is associated with aging, suggesting that aging may influence endometrial pathology.