Abstract
It has been shown (Smith 1 ) and confirmed by a number of investigators that the injection of beef A.P. growth preparations, or the daily implantation of rat pituitaries caused a resumption of growth in rats dwarfed by hypophysectomy. Thyroid administration does not cause growth in the absence of the A.P. (Smith, Greenwood, and Foster 2 ). It has been further shown (Flower and Evans 3 ) that the A.P. growth hormone induces growth in rats dwarfed by thyroidectomy, a finding in harmony with the fact that A. P. extracts cause growth in hypophysectomized rats even though they may not repair the atrophied thyroids. It thus seems clear that of these 2 glands the A.P. only is essential for growth.
These findings, however, do not demonstrate that the thyroid may not normally aid the growth action of the pituitary or may not increase the effectiveness of preparations made from it. I have attempted to secure evidence upon this by giving growth hormone∗ with and without concurrent thyroid feeding in a series of rats in which both the hypophysis and thyroid (as well as the parathyroids) had been removed during the active growing period. All members of each series received the same dosage of growth hormone, one member receiving, in addition, thyroid. A dosage of thyroid was administered which did not prevent an increase in weight (100 mg. powder 2-3. times per week). Four series of animals have been treated over a period of several weeks.
In each case the skeletal growth of the rats receiving thyroid in addition to the A.P. extract was distinctly above that of the rats receiving the extract only. In 3, the weight increases were greater also.
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