ANTAGONISM OF PITUITARY ADRENOCORTICOTROPIC HORMONE (ACTH) TO THE ACTION OF GROWTH HORMONE ON THE OSSEOUS SYSTEM OF HYPOPHYSECTOMIZED RATS1

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Abstract
Due to the observation, previously reported, that the body wt. increase of hypophysectomized rats receiving growth hormone was prevented by simultaneous adm. of adrenocorticotrophic hormone, comparisons have been made of the proximal epiphyseal regions of the tibias of hypophysectomized rats, when uninjected, injected with ACTH, with growth hormone or with the combination. ACTH given alone scarcely affected the inactive condition of the epiphysis, except that the cartilage calls in the erosion zone were more irregular. Stasis of bone formation was characteristic, just as in controls. Growth hormone activated the cartilage and caused resumption of formation of delicate, straight trabeculae of bone. As a result of simultaneous adm. of ACTH and growth hormone, the following changes in the typical effects of growth hormone were observed. The proximal epiphyseal cartilage of the tibia was greatly decreased in width. Endochondral bone formation was significantly retarded. Osteoblastic as well as osteoclastic activity was greatly decreased, perhaps accounting for the irregular arrangement of bony trabeculae. The cartilage columns in the erosion zone were also more irregular.