Effect of Growth Hormone and Thyroxine on Mammary Gland Growth in the Rat

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Abstract
A study of the possible synergistic effect of bovine and ovine growth hormone (GH) and thyroxine (T4) upon mammary gland growth of the rat, measured by DNA, in both pregnant and ovariectomized rats stimulated by ovarian hormones is presented. Bovine GH alone in pregnant rats had no effect on DNA. Bovine GH plus T4 stimulated a highly significant increase of 29% and ovine GH and T4 stimulated a significant increase of 17% in DNA. Since T4 in a previous study increased DNA 26%, it was concluded that GH had no synergistic effect. In ovariectomized rats, in synergism with ovarian hormones, bovine and ovine GH stimulated nonsignificant increases of DNA of 9 and 5%, respectively. Bovine GH plus T4 stimulated a highly significant increase of 28% over the control group, but not in comparison with T4 alone. Although GH cannot be said to synergize significantly with T4, the 2 groups administered both GH and T4 stimulated mean DNA higher than any previous experimental group.

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