Histochemical Studies on the Nervous and Humoral Regulation of Lipids and Carbohydrate Metabolism

The purpose of the present study is to reveal the precise mechanism of nervous and humoral regulations of lipid and carbohydrate metabolisms in the adipose tissues. Histochemical and biochemical observations were made on the innervated and denervated interscapular brown adipose tissues and partly on the liver and adrenal cortex of male mice during starvation with or without carbohydrate introduction with special consideration to the changes of the lipid and glycogen contents and to the activities of several important enzymes as well as to pH values in the tissues. In a state of absolute starvation, the animals died in a few days showing a gradual discharge of stored lipids from the innervated brown adipose tissues, while in the denervated tissues the stored lipids increased gradually even in a state of slight or moderate starvation as well as in the cases of normally fed animals. The increase of lipids continued before the stage of severe starvation and the stored lipids being rapidly discharged became nil at the terminal stage of life. Introduction of glucose into starved animals caused also a more marked deposition of glycogen in the denervated than in the innervated tissues in proportion to the degree of starvation, although it did not cause the deposition in both tissues at the terminal stage of life. These facts represent that the nervous regulation is essential for the mobilization of lipids and carbohydrates from this tissue. Adrenalectomy also caused the death of animals within a few days with a gradual decrease of depot lipids. In this case denervation likewise caused a marked depositon of lipids in the brown adipose tissues, showing a sudden escape of lipids at the end of life. Experiments on transplanted adipose tissues taken from the animals at the terminal stage of starvation, proved that the tissue cells retain the ability to deposit lipids until the end of life. Chemical estimation elucidated that the serum glucose and lipids fall markedly at the terminal stage of life. The innervated tissues showed increased activities of succinic dehydrogenase, alkaline phosphatase, ATPase and lipase during starvation with a gradual discharge of lipids. Glucose injection increased the degree of the activities of all these enzymes, though in the terminal stage of starvation the ATPase activity declined again. The activity of total cholinesterase declined slightly in severe starvation. The pH value fell gradually with the progress of starvation. On the other hand, in the denervated tissues the activity of succinic dehydrogenase fell with an increased deposition of lipids, though in the final stage of starvation the activity rose with the discharge of lipids; while the activities of phosphatase, ATPase and lipase rose during starvation and total, unspecific and specific cholinesterase activities declined slightly. The pH value in the denervated tissues rose slightly during mild starvation and fell markedly in severe starvation. Observations proved that the activities Df these enzymes and pH, which are under the control of the autonomic nervous system, have close relationships to the deposition and the discharge of lipids and glycogen from the adipose tissues, and that the rapid discharge of lipids from the denervated tissue at the terminal stage of life is an expression of the onesided progress of oxidative process which may mean a complete loss of regulation of metabolism.