Changes of Macrophages in Rat Corpus Luteum: Immunohistochemical and Transmission Electron Microscopy Studies

Objective: The purpose of this study is to assess morphologically the changes of macrophages during various developmental periods of the corpus luteum in the rat ovary. Methods: The female rats (Sprague-Dawley strain) at age 8 weeks, ovulatory period; 6 days of gestation, early pregnancy period; 19 days of gestation, late pregnancy period; and postpartum 5 days, postpartum period were used. Removed ovaries were dissected and used for TdT-mediated dUTP biotin nick end labelling (TUNEL), macrophages immunohistochemistry, and Transmission Electron Microscopy (TEM). Results: Macrophages were observed in all the developmental periods. The number of apoptotic bodies and macrophages was highest at the ovulatory period, and decreased at postpartum period, early pregnancy period and late pregnancy period in order. The immunoreactivity of macrophages was high at ovulatory period, moderate at late pregnacy and postpartum period, and low at early pregnancy period. In TEM observations, two types of macrophages were observed. One was non-phagocytic macrophage which has slender cell body and long cytoplasmic processes and contained no apoptotic bodies, and the other was phagocytic macrophage which contained apoptotic bodies, phagocytic vacuoles and many lipid droplets and located near the capillaries. Conclusion: In the rat corpus luteum, the number and the degree of immunoreactivity of macrophages changed according to the functional developmental periods of the corpus luteum. The functions of the macrophages were suggested as the elimination of apoptotic bodies at the ovulatory and postpartum periods, and luteotropic action at the early and late pregnancy periods. Ultrastructurally, two types of macrophages, phagocytic and non-phagocytic, were confirmed.