Abstract
The only physiological action so far established for relaxin 1 is the relaxation of the pelvic ligaments in the guinea pig. This preliminary paper reports observations on the effects of relaxin on mammary gland development in immature rats.
Various combinations of estradiol, progesterone and relaxin were given to ovariectomized immature rats to determine the effects on the growth of mammary glands. The estradiol and progesterone were dissolved in sesame oil and injected once a day. The relaxin was dissolved in distilled water and injected in two equal doses, one in the morning and one at night. All injections were made subcutaneously. The animals used were immature female rats which had been ovariectomized at 30 days after birth. After 6 days of postoperative rest they were injected daily with 0.83 μg estradiol for 13 days. This was the standard pre-treatment given all animals before each of the following experiments. A minimum of 4 animals was used in each group cited below and the reactions within each group were uniform.
Daily injections of estradiol (0.83 μg per 0.05 cc oil), progesterone (1 mg per 0.05 cc oil), and relaxin (25 guinea pig units 2 per 0.5 cc distilled water) produced growth in the mammary glands by the ninth day of treatment (Fig. 1). By the thirteenth day of this treatment the glands had the appearance of mammary glands during late pregnancy in normal animals (Figs. 2 and 3). Daily injections (for 13 days) of estradiol (0.83 μg) and progesterone (1 mg) but without relaxin caused a slight growth by the ninth day (Fig. 4). This was much less than in animals treated with all 3 hormones (compare Fig. 1 and 4) and there was no increase in the size of the glands following the ninth day.
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