THE ACTION OF RELAXIN ON MAMMARY GLAND GROWTH IN THE RAT1

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Abstract
SMALL doses of progesterone injected simultaneously with estrogens produce optimal lobulo-alveolar growth in the mammary glands in the mouse (Mixner and Turner, 1940) or rabbit (Lyons and McGinty, 1941), while in the rat relatively larger doses of progesterone are required to elicit a comparable reaction (Curtiss, 1949). Hamolsky and Sparrow (1943) first showed that relaxin, injected simultaneously with small doses of estradiol and progesterone, resulted in good lobulo-alveolar growth in immature, estradiol- primed, ovariectomized rats. Administration of a combination of any two of these hormones in the dosage used yields negative results. There was little or no mammary response to any combination in the ovariectomized, hypophysectomized rat. This paper is a further investigation into the effects of relaxin on the mammary glands of the rat. MATERIAL AND METHODS Relaxin made up in normal saline was injected subcutaneously twice daily. The steroids were also injected subcutaneously every day using a concentration of 20 μg. of estradiol per ml. of oil and 20 mg.