Interrelationship between pituitary and ovarian hormones in normal and neoplastic growth of mammary glands of mice.

While prolactin is a key hormone for normal and neoplastic mammary gland growth, the participation of ovarian estrogen and progesterone is essential for these processes under the normal physiological conditions. Prolactin exerts its influence directly to the glands and indirectly through its luteotropic effects by stimulation of ovarian progesterone secretion. Furthermore, the action of prolactin, whether in promoting normal growth and function or enhancing the progression of neoplastic foci, depends upon the circulating levels of other mammotropic hormones as well as the level of prolactin itself. Presence of estrogen and prolactin is essential for manifestation of progesterone effects on mammary gland growth. Estrogen acts on the mammary glands directly by modulating mammary cell responsiveness to prolactin and indirectly by stimulating pituitary prolactin secretion. While data have been accumulated on the effects of growth hormone on mammary gland growth, the significance of these findings is still unknown. Neoplastic potential of mammary cells is largely dependent upon the susceptibility of the cells to mammotropic hormones.