Inhibition of Mammary Tumorigenesis by Ergot Alkaloids and Promotion of Mammary Tumorigenesis by Pituitary Isografts in Adreno-Ovariectomized Mice

Abstract

The effect of ergocornine or 2-bromo-α-ergocryptine (CB-154) in intact C3H/He virgin mice and the effect of pituitary isografts in adreno-ovariectomized mice on spontaneous mammary tumor incidence were investigated to clarify the importance of prolactin on mammary tumorigenesis. At the end of 8 months after the experiment began, mammary tumor incidences were 23.5 and 16.7% in mice with subcutaneous pellet implants of ergocornine and CB-154, respectively, whereas the incidence in control mice was 73.7%. Mammary tumor incidence was significantly inhibited by these ergot alkaloids undoubtedly through their suppression of pituitary prolactin secretion. Mammary tumor incidence was 51.3% at the end of 8 months after 3 pituitaries were grafted in adreno-ovariectomized mice, while no tumors appeared in the adreno-ovariectomized controls; this indicated that prolactin secreted continuously by the grafted pituitaries promoted the development of spontaneous mammary tumors in the apparent absence of adrenal and ovarian hormones. These results demonstrated that prolactin is a primary hormonal factor in spontaneous mammary tumorigenesis in mice.