C3Hf (XVII) mice never develop spontaneous mammary
tumors. However, the
transplantation of an isologous pituitary gland under their kidney
capsule is followed by a 10-fold increase in serum and pituitary
prolactin content (180 ng/ml and 20 micrograms/mg of tissue, respectively), concomitant with an increase of
prolactin receptors in mammary glands. Under these conditions, mammary
tumors appear in 90% of the mice. If a racemic brominated
triphenylethylene, i.e.,
broparestrol, is administered, serum and pituitary
prolactin decrease rapidly (10 ng/ml and 4 micrograms/mg of tissue, respectively), and
prolactin receptors in the mammary gland are markedly reduced. This compound also inhibits the development of normal mammary glands, prevents mammary
carcinogenesis, and unexpectedly causes a significant
atrophy of the ovaries. Our study confirms that
prolactin is a key
hormone involved in murine mammary
carcinogenesis and that it can act directly on the mammary gland by stimulaing the level of its own receptor.