Growth hormone has been reported to cause either a depression or a stimulation of the glucose uptake of isolated rat diaphragm. The present paper describes further work on the two effects.
1. Anaerobic conditions during the preparation of the diaphragm for incubation affect the glucose uptake and alter the response of the muscle to growth hormone. By controlling the oxygen tension in the diaphragm immediately after excision, variation of the glucose uptake and the effect of the hormone is reduced.
2. Solutions of growth hormone were found to be extremely labile, but, by rigidly standardizing the method of preparing solutions, consistent results were obtained.
3. The relationship between the concentration of growth hormone and its effect on the glucose uptake of isolated diaphragm was investigated separately for muscle saturated with oxygen and with nitrogen. With oxygenated muscle at high concentrations the hormone stimulates, and at low concentrations depresses, the rate of glucose uptake.
4. The mode of action of growth hormone in vitro and in vivo is discussed.