Background: The presence of lymphatic vessels in the human endometrium is sketchy and is unsettled. Using D2-40 as a marker of lymphatic vessels in the formalin-fixed and paraffin-embedded human endometrium, a reduced density of lymphatic vessels was reported in human functionalis. Normally cycling human endometrium is relatively difficult to study for ethical reasons. 

Objectives: Uteri from menstrual, proliferative, and secretary cycle were collected to study lymphatic vessels compared to blood vessels by immunohistochemical staining for lymphatic vessels in the artificially cycling monkey endometrium. The full thickness of uterus was vertically sectioned and was collected from menstrual, proliferative to secretary cycle in the cycling endometrium. With frozen sections, we studied lymphatic and blood vessels by immunostaining with D2-40 and LYVE-1 for lymphatic vessels and von Willebrand’s factor for blood vessels, respectively. 

Results: There was the consistent presence of lymphatic vessels in myometrium and basalis. Blood vessels supply the growing functionals while lymphatic vessels grew longitudinally from basalis to functionalis with D2-40 and LYVE-1 immunostaining in proliferative phase from lower to middle secretary functionalis in late secretary phase. There were dilated and bursting lymphatic vessels in upper functionalis at menstruation. 

Conclusion: Ample blood vessels supply the entire endometrium while lymphatic vessels do not catch up with the fast-growing blood vessels in the functionalis. The presence of lymphatic vessels in the functionalis during the menstrual period implies the presence of sliver of lymphatic fluid in the menstrual fluid. The less lymphatic vessels in the late secretary functionalis may contribute to extreme interstitial endometrial edema during menstrual shedding.

Blood vessels, D2-40, Immunocytochemistry, Frozen sections, Lymphatic vessels, LYVE-1