It was stated in preliminary reports (1, '2) that the hexokinase reaction, glucose + adenosine triphosphate -+ glucoseB-phosphate + adenosine diphosphate, in muscle extracts from rats made diabetic with alloxan was markedly inhibited by the addition of adrenal cortex extract, while no inhibition was observed when adrenal cortex was added to extracts of normal rat muscle. Hexokinase preparations (muscle, brain) of normal animals could be inhibited, however, by the addition of certain protein

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... tions of the anterior pituitary, particularly in the presence of adrenal cortex extract, and this inhibition, like that observed in diabetic extracts, could be counteracted by insulin. Other experiments indicated that insulin was not an accelerator of the reaction, since it did not exert an effect unless the system was inhibited by adrenal cortex alone in diabetic extracts and by pituitary plus adrenal cortex in normal extracts. This raised the question whether the diabetic extracts contained an inhibitory factor similar to that prepared from the anterior pituitary. On the assumption that the phenomena are related, the experiments with extracts of diabetic rat muscle and the preparation of inhibitory pituitary fractions will be described in this paper. EXPERIMENTAL Hexokinase in Muscle Extracts of Diabetic Rats--In some of the early experiments rats were injected intraperitoneally with 200 mg. of alloxan per kilo; the degree of glycosuria varied considerably in the different animals and there were a number of fatalities. More uniform results were obtained when the procedure of Kass and Waisbren (3) was adopted, which consists in fasting the animals for 48 hours before injecting the above dose of alloxan subcutaneously. After the injection the animals were given food ad libifum and the urine was collected in individual metabolism cages. The animals showing marked glycosuria were killed about 2 days after the injection. About 10 gm. of leg muscle were rapidly excised and minced