Thyroxine and Mammary Gland Growth in Rat.

Abstract

The effect of mild hyperthyroidism upon mammary gland growth has been studied by injection of exogenous T4 into normal pregnant rats at levels of 2.5, 3.0, and 3.5 [mu]g/100 g BW/day. Normal pregnant rats showed mean total of DNA of 7.63 [plus or minus] .39 mg/100 g BW. Group of 45 pregnant rats injected with T4 showed a mean DNA of 9.07 [plus or minus] .25 mg/100 g BW, an increase of 22%. It is suggested sub-optimal T4 secretion may be one of the limiting factors in attainment of maximum mammary gland proliferation.