Evidence in the Hypophysectomized Pigeon of a Synergism Among Prolactin, Growth Hormone, Thyroxine and Prednisone Upon Weight of the Body, Digestive Tract, Kidney and Fat Stores

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Abstract
Various levels of dosage of prolactin and/or growth hormone, alone and in combination with thyroxine and prednisone, were injected daily for 10 days into hypophysectomized pigeons. Adequate doses of prolactin or of growth hormone alone or together increased the weight of the body, liver, pancreas, intestines and kidney. There was no apparent synergism. Greater increases in the weight of these structures were found when the auxiliary solution of thyroxine (10 μg) and prednisone (1 mg) was injected simultaneously. Thyroxine and prednisone together did not increase organ weights but acted as permissive agents when combined with growth hormone and/or prolactin. Synergisms of the order of 50-fold were obtained when all 4 hormones were injected. Twenty μg of prolactin plus 20 μg of growth hormone with the auxiliary solution produced a greater increase in weight of body and of organs than was obtained with 2 mg of growth hormone and prolactin without the auxiliary solution. Prednisone appeared to conserve body fat stores but induced atrophy of the bursa of Fabricius. Changes in organ weights followed the food intake (appetite). The increase of weight of crop sacs with prolactin was not synergized at low levels of dosage by growth hormone, prednisone and T4, but the maximal weight attainable in hypophysectomized pigeons was increased significantly by the mixture of all 4 hormones.