Lymphatics of the rat mammary gland during virgin, pregnant, lactating andpost-weaning periods

The distribution and ultrastructure of the lymphatics of the rat mammary gl and in virgin, pregnant, lactating and post-weaning periods were examined b y enzyme-histochemistry for 5'-nucleotidase (5'-Nase) and transmission elec tron microscopy. Enzyme-histochemistry for 5'-Nase stained lymphatics in da rk brown. In the lactating period, lymphatics abounded in the interlobular connective tissues, but in other periods they were few. The interlobular ly mphatics drained into collecting lymphatics running along the mammary ducts . Gaps between lymphatic endothelial cells were significantly wider in lact ating period than in other periods, while both number and area of vesicles in the lymphatic endothelial cells were significantly larger in the virgin period than in other periods. In the pregnant and lactating period, the lym phatics contained many lymphocytes and lipid droplets. The results show tha t during lactating period, the interlobular lymphatics increase and that ga ps between lymphatic endothelial cells serve as a major route through which tissue fluids and particulate matters enter the lymphatics, while vesicles seem to be main trans-endothelial transport route during the virgin period . The results will provide basic information for our next investigation on lymphangiogenesis in association with breast cancer.