Paracrine control by immune cells on the expression of gonadal function

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It can be taken that ovulation and luteinization are a local inflamatory reaction and succeeding trauma formation, respectively. At ovulation, macrophages invade into and stay in corpora lutea after luteinization. However, their function is not yet clear. To clarify the function, rats were splenectomized on different days of cycle, and the effect on ovulation was examined. Rats splenectomized in the morning of metestrus showed delay of ovulation by one day. On the day of diestrus their blood concentrations of progesterone and 20alpha-dihydroprogesterone were higher and lower than those in normally cycling rats, respectively. As high progesterone concentrations in the morning of diestrus prolong the appearance of LH surge which induces ovulation, the delay of ovulation after splenectomy may be caused by this high progesterone level.This delay of ovulation by splenectomy on the day of metestrus is overcome by grafting of spleens from metestrous rats. These results suggest that splenocytes which invade into corpora lutea promote luteolysis. In rats, prolactin inhibits the regression of luteal function by inhibition of the activity of 20alpha-hydroxysteroid dehydrogenase in corpora lutea. This luteotropic actitivity of prolactin has not been confirmed in vitro. We examined this prolactin action by culturing luteal cells with macrophages. When luteal cells from pseudopregnant rats were cultured for 48 h with macrophages from metestrous rats, the inhibition of 20 -hydroxysteroid dehydrogenase by prolactin was observed. All these data suggest that function of luteal cells are under paracrine control of splenocytes including macrophages.