Summary of progesterone receptor isoform expression and regulation in normal and PCOS women. PRA and PRB are both expressed in the epithelial and stromal cells of the human endometrium, and the levels of PRA and PRB expression fluctuate in the cycling endometrium in an isoform-specific and cell-specific manner. Several studies have shown that the endometrial PR expression is altered in women with PCOS. See text for details. The normal endometrium is stained with hematoxylin and eosin. PR, progesterone receptor; Epi, epithelial cells; Str, stromal cells. See text for details.