THE ESTROGEN-STIMULATION OF MAMMARY GROWTH IN OVARIECTOMIZED IMMATURE MICE AND THEIR INHIBITION BY STEROIDS

The mammary growth following the estrogen injection into the ovariectomized immature mice of DS colony was studied using the ductal extension of the third thoracic mammary gland as a criterion. A rapid growth of the gland was achieved by the daily subcutaneous application of estradiol as little as 0.03μg a day for 9days after ovariectomy. A variety of steroids were subcutaneously injected daily along with the estrogen treatment for 9days. 5α-Androstan-17β-ol-3-one and its 2-substituents, dromostanolone propionate, oxymetholone and 17α-methyl dromostanolone, strongly inhibited the estrogen-stimulated mammary duct growth. The reduction of 3-one and/or oxidation of 17β-ol in 5α-androstan-17β-ol-3-one resulted in marked decrease of the inhibitory effect. The introduction of double bond at ring A slightly modified the activity of the parent androstane. On the other hand, potent estrogen antagonists on the uterus, such as 19-nortestosterone, norethisteron, progesterone and MER-25 were almost inactive. These results indicate that there is no direct correlation between the mammary growth inhibiting ability and the androgenic activity or anti-uterotropic activity of a steroid. The biological significance of these estrogen-steroid interactions on the mammary gland development was discussed.