Progesterone and estrogen receptor distribution in the endometrium of the mare

An immunoperoxidase staining technique was used to localize receptors for progesterone and estrogen in the uterus of the mare. Specific staining for receptors was limited to cell nuclei. During estrus, stromal cells tended to stain more intensely for both receptor types than myometrial cells or luminal and glandular epithelial cells. During diestrus, staining intensities in stromal and myometrial cells tended to decrease. Staining intensities of epithelial cells were not affected by the cycle stage. Early pregnancy did not markedly affect the staining intensities of pregnant mares compared with the nonpregnant mares on Day 14 of diestrus. In mares susceptible to endometritis from which samples were taken during diestrus, stromal and myometrial staining for estrogen receptors was more intense than in endometrium from genitally-normal mares.