531. Lyve-1 AND Vegfr-3 POSITIVE LYMPHATIC VESSELS ARE LARGELY RESTRICTED TO THE MYOMETRIUM IN THE MOUSE UTERUS

The human endometrium contains a distinct population of lymphatic vessels, with reduced numbers of vessel profiles in the functionalis relative to the basalis and underlying myometrium. The mechanisms restricting lymphatic vessel development within the functionalis and the consequences of this distribution for endometrial function have not been investigated. To determine how the distribution of endometrial lymphatics is regulated, an in vivo animal model is required for mechanistic studies. As an initial step, we described the distribution of lymphatic vessels and the expression of Vegf-C and Vegf-D within the mouse uterus using immunohistochemistry. Uterine tissues were collected from mice during the oestrus cycle (diestrus, proestrus and oestrus, n=7–9 per group), during early pregnancy (days 1-4, n = 4–5 per group), and from ovariectomised mice treated with vehicle, estradiol-17β or progesterone treatment (n=7–8 per group). Uterine sections were immunostained with antibodies against Lyve-1, Vegfr3, Vegf-C and Vegf-D. Lyve-1 positive lymphatic vessels were almost exclusively observed in the connective tissue between the longitudinal and circular muscle layers of the myometrium. Lymphatic vessel profiles were rare within the endometrium and were only observed on 24 % of the sections examined. The Vegfr3 immunostaining was less robust than Lyve-1 with considerable variation in non-lymphatic staining among the different sections (which did not relate to a particular reproductive state or treatment group). Despite the variability, the pattern of lymphatic vessels was as seen with the Lyve-1 antibody. Vegf-C and Vegf-D immunostaining was present in all uterine compartments (epithelium, stroma, myometrium), however, only minimal changes were noted in expression across the oestrus cycle, during early pregnancy, or in hormone treated mice. In conclusion, despite the presence of the key lymphangiogenic growth factors Vegf-C and Vegf-D, there are minimal lymphatic vessels present within the mouse endometrium. This implicates other factors in the mechanism restricting endometrial lymphatic vessel growth.