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Effect of Growth Hormone and Thyroxine on Mammary Gland Growth in the Rat¹

Department of Dairy Husbandry, University of Missouri, Columbia

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 two groups administered both GH and T₄ stimulated mean DNA higher than any previous experimental group.

¹ Contribution from Missouri Agricultural Experiment Station Journal Series No. 2761. Approved by the Director. Aided in part by research grants from P.H.S.

² Kindly supplied by NIH.