Retinoids inhibit prolactin-induced development of the mammary gland in vitro

Mouse mammary gland organ culture technique was utilized to determine the effects of retinoids on the prolactin-induced structural differentiation of the mammary gland. Thoracic glands from BALB/c mice pretreated with steroids differentiate in 6 days into alveolar structures in presence of insulin and prolactin. All-trans-retinoic acid and N-(-4-hydroxyphenyl)retinamide inhibit prolactin-induced structural changes in the glands. Retinyl acetate, which is effective against mammary carcinogenesis in the rat, but is ineffective against mouse mammary carcinogenesis, failed to inhibit such proliferation. These results were correlated with inhibition of [3H]thymidine incorporation into DNA in a dose related manner by retinoids effective in inhibiting mammary development.