Influence of graded thyroxin levels on mammary gland growth

Abstract

The effect of graded thyroxin (T-4) doses on mammary growth in hypothyroid-ovariectomized rats treated with 2 µg estradiol benzoate and 6 mg progesterone was determined using deoxyribonucleic acid (DNA) content of the abdominal-inguinal glands as an index of the degree of cellular proliferation. Concomitant injection of estradiol benzoate, progesterone, and 1–2 µg T-4/100 g for 19 days resulted in an increase in mammary DNA. No significant difference in DNA was evident between rats receiving estradiol benzoate, plus progesterone plu 0.5 µg T-4/100 g and those treated with only estradiol benzoate and progesterone. Pituitary lactogen concentration was 28–143% greater in animals receiving T-4 than in those injected with only estradiol and progesterone. In another experiment a single injection of 2.5 or 5.0 µg T-4/100 g into lactating rats lowered the pituitary lactogen content 33–38% when compared with a control value of 1.78 µg/mg pituitary. Pituitary lactogen of rats receiving a single injection of 10 or 20 µg T-4/100 g did not differ from the controls. Thyroxin apparently influences production and secretion of lactogenic hormone, and enhancement of mammary growth resulting from thyroxin administration may be due, in part, to increased secretion of lactogen.