THE EFFECT OF GROWTH HORMONE ON MUSCLE POTASSIUM AND ON EXTRACELLULAR FLUID1

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Abstract
Because of the known ability of growth hormone (GH) to cause Na, Cl, and K retention, the body thiocyanate space, plasma volume and muscle Na and K were measured in normal, hypophysectomized and GH treated-hypophysectomized animals. In 7 series of 13-22 animals each, hypophysectomy produced no change in the thiocyanate space (normal = 34.2% of body weight (BW), hypophysectomized = 33.2% of BW,) but giving 1 mg of GH for 2-10 days elevated the SCN space to values as high as 42.5% of BW. Moreover, in 4 series of 8-19 animals each, GH in the same dosage elevated the plasma volume 0.3-0.5% of the BW. Plasma Na and K were unchanged. Muscle K concentration was lowered significantly following hypophysectomy in 10 of 11 series (average: NC 104.7 meq/kg and hypophysectom-ized 98.6 meq/kg). Giving GH at 1 mg/day for at least 10 days restored the muscle K concentration toward normal (average-104.5). Muscle Na and N concentrations were unchanged. To determine whether these effects are specific for GH, similar experiments were carried out using ACTH, Pitressin, thyroxine, and testosterone propionate. None of these agents produced the effects observed with GH. Moreover, gonadectomy did not alter the response to GH. Also restriction of the food intake of normal animals did not cause reduction of muscle K concentration as seen in the hypophysectomized controls. It is therefore concluded that GH causes an expansion of the extracellular fluid space, which explains the previously observed Na and Cl retention. Also GH plays some role in maintaining the muscle K.