RÔLE OF ESTROGEN IN THE STIMULATION OF MAMMARY LOBULE-ALVEOLAR GROWTH BY PROGESTERONE AND BY THE MAMMOGENIC LOBULE-ALVEOLAR GROWTH FACTOR OF THE ANTERIOR PITUITARY1,2

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Abstract
The ovariectomized virgin [female] mouse was used as the assay animal, the criterion of response being the % of mice showing a minimum amt. of lobule-alveolar growth after 10 daily subcut. injs. of the material to be assayed. The range of estrogen which synergizes well with one mg. progesterone is wide, but approx. 100 I.U. of estrone appears to be optimal. Approx. 6 times as much progesterone is required alone to secure a certain degree of alveolar development as when estrone is simultaneously injected. Similarly, estrone markedly enhanced the ability of pituitary materials to cause such alveolar growth. Large amts. of estrone (2400 I.U.) inhibited the activity of 1 mg. progesterone, but was not able to inhibit the activity of an equivalent amount of a pituitary extract in causing lobule-alveolar growth. Estradiol benzoate and diethylstilbestrol also synergize with progesterone in promoting mammary lobule-alveolar growth. Estrogen may synergize with progesterone and the pituitary mammogenic lobule-alveolar growth factor through its local action on the mammary gland stromal tissue, causing there an increased vascularity and hyperemia, and promoting capillary permeability. This would increase the efficiency of action of the mammary stimulating factor which circulates in the blood.