Thyroid Hormone and Mammary Gland Growth in the Rat.

Abstract

The effect of mild hyperthyroidism upon mammary gland growth has been studied in adult ovariectomized rats treated with estradiol benzoate (EB) and progesterone (P) for 19 days. Using total deoxyribonucleic acid (DNA) as index of mammary growth, glands of animals receiving daily injections of 1 [mu]g EB, 3 mg P and 3 or 6 [mu]g/100 g thyroxine did not differ from that of controls. Upon doubling EB and P levels, a significant increase in total DNA was observed. It is suggested that thyroid hormone may be a limiting factor in mammary gland growth when estrogen (E) and P secretions are adequate, but when TSR is optimal, E and P secretion may limit growth.