Role of Relaxin in Stimulating Mammary Gland Growth in Mice.

Abstract

Using DNA as index of mammary gland lobule-alveolar growth in intact and castrate male mice, it was shown that daily injection of 0.75 ug estradiol benzoate and 2.5 GPU of relaxin for 10 days stimulated increases in DNA equal to that produced by the same level of estrogen and 0.75 mg progesterone. Therefore, relaxin no longer need be considered merely a synergist of estrogen and progesterone in mammary gland growth. Estrogen and relaxin at above levels were without effect upon mammary alveolar growth in hypophysectomized mice. Relaxin, therefore, is not comparable to pituitary mammogen as a stimulator of mammary gland growth. It is suggested estrogen and progesterone stimulate endogenous secretion of relaxin and relaxin, in turn, stimulates increased secretion of mammogen by the pituitary.