Variation in glycogen and mucins in the equine uterus related to physiologic and pathologic conditions

Histochemical stains were applied to six equine uterine biopsies representative of the physiologic breeding season, Spring and Fall transition, and Winter anestrus periods. These were compared with uterine biopsies from six mares with intrauterine urine pooling, eight mares used to study the uterine response to indwelling catheterization, and necropsy specimens from four pregnant mares at approximately 60 or 100 d of gestation. Alcian blue staining at pH 2.5 or 1.0 was used to identify the presence of carboxylated and sulfated acid mucins or only suflated acid mucins, respectively. Periodic acid-Schiff staining was used to identify neutral mucosubstances or glycogen, with or without prior diastase digestion. The uterine glands contained glycogen, which was most abundant during the physiologic breeding season. The luminal epithelial cells during the physiologic breeding season and Spring and Fall transition contained predominately carboxylated acid mucins. Carboxylated acid mucin secretion also was stimulated by indwelling catheterization and intrauterine urine pooling. It is hypothesized that secretion of carboxylated acid mucins by the endometrial epithelium may be elicited by hormonal or irritative/inflammatory stimuli, and it may be a protective response.