Immunohistochemical staining of von Willebrand factor in human endometrium during normal menstrual cycle

Endometrial biopsies were obtained from 73 normal women throughout the menstrual cycle. Using a polyclonal antibody and a streptavidin-biotin-peroxidase method, formalin-fixed paraffin sections of the tissue were stained for von Willebrand factor (vWF). Both subjective scoring and objective quantitative colour image analysis were used to assess the staining intensity, and the results obtained by the two methods were in concordance with each other. Positive staining was observed at all stages of the menstrual cycle. Specific staining was confined to the vascular endothelium and showed cyclical changes. The staining intensity was the weakest during the menstrual phase and was significantly (P < 0.02) reduced from all other stages of the cycle, except late secretory phase. This was followed by a rapid increase in the early proliferative phase to reach a peak in the mid cycle before gradually falling off towards the end of the cycle. The staining intensity in the late secretory phase was significantly reduced (P < 0.05) from other stages except menstrual, early proliferative and mid secretory phase. Vascular staining for vWF was heterogeneous with some vessels devoid of any positive staining.