Effect of Various Hormones on Mammary Gland Growth of Pregnant Rats1

Abstract

A study of the effect of several hormones alone and in combination upon mammary gland growth, body and litter weight of pregnant rats is reported. The mean DNA of 49 control rats was 7. 41 mg/100 g body weight (bw). Growth hormone (GH) stimulated an increase in DNA of the mammary gland of 13%, insulin plus thyroxine (L-T4) of 19%, GH plus L-T4 of 37%, GH plus L-T4, plus insulin of 41%, and GH plus insulin of 62%. In this study, L-T4 and insulin alone were ineffective. It is suggested that these hormone combinations synergize with estrogen and progesterone secreted during pregnancy to stimulate increased mammary lobulo-alveolar growth, as measured by DNA, and contribute to the number of normal pregnant rats with DNA above the mean. The combination of bovine GH plus L-T4 plus insulin increased the mean body weight gain 34%, compared to mean initial body weight. GH plus insulin increased the body weight gain by 32%; GH alone, 27%; GH plus L-T4, 24%; insulin, 19%; insulin plus L-T4 15%; and L-T4 alone, 9%. The combination of GH plus L-T4 increased the mean pup weight about 8% over the controls. L-T4 and insulin increased pup weight 7% and 3%, respectively. GH and insulin increased mean pup weight 1% each. Insulin plus L-T4 decreased pup weight 6%, and GH plus L-T4 plus insulin about 9%.