Stimulation of Adrenal Medulla by Irradiated Insulin. ∗

Abstract

Davis, Luck, and Miller 1 showed that insulin on long exposure to soft X-rays of high intensity loses its characteristic ability to lower the blood-sugar content and, in massive doses, may even produce a slight degree of hyperglycemia. A substantial portion of its phosphate-lowering activity is retained, as well as part of its aminoacid-lowering activity. It was suggested, by way of explanation, that the irradiated insulin, though otherwise inactivated, retains its power to stimulate the adrenal medulla, thus causing the slight hyperglycemia, hypophosphatemia, and hypoaminoacidemia actually observed.

To test this hypothesis we have administered insulin, 7 to 10 units per kilo, irradiated with soft X-rays for 3 hours at an intensity of 3,400 Roentgen units per second, to adreno-demedullated rabbits. Six animals were employed, and in no case was a lowering in blood amino acids observed. In 5 normal animals the irradiated insulin caused quite a pronounced decrease (Table I). Quantitatively the results differ from those obtained by Davis, Luck, and Miller in that no tendency towards hyperglycemia was observed. Indeed, for reasons that are still obscure, we were unable to totally destroy the hypoglycemic activity of the insulin, despite substantial increases in irradiation time and intensity. In the adreno-demedullated rabbits the irradiation product was completely inactive, such hypoglycemia as was observed being confined to the normal animals.

The results clearly indicate that the irradiated insulin, though inactive to a large extent with respect to blood sugar, retains a substantial portion of its activity with respect to blood amino acids. The facts accord with the hypothesis that the irradiation of insulin by soft X-rays does not destroy its ability to stimulate the adrenal medulla.