Abstract
Dietary protein-carbohydrate ratio affected the change in rat hepatic threonine de-hydratase (TDH) activity: 7% casein-85.5% carbohydrate, 0.ll; 20% casein-72.5% carbohydrate, 7.07; 40% casein-52.5% carbohydrate, 26.71; 90% casein-2.5% carbohydrate, 63.71 μ mole α-ketobutyric acid/min/g liver. The variation of TDH activity thus covering a wide range exceeded that due to the regulation by gluco-corticoid alone observed previously by us in the case of disorder in dietary amino acid balance. Alloxan-diabetic rats showed enormously high TDH activity. Insulin was effective in lowering the TDH activity which had been elevated by feeding 20% casein diet. Insulin also had a suppressing effect on the elevation of TDH activity by feeding higher protein diet. The function of adrenals measured by adrenal glucose-6-phosphate dehydrogenase activity did not show so wide variation throughout these studies. Effects of adrenalectomy, alloxan treatment and/or cortisone treatment on TDH activity were as follows: adrenalectomy, 2.33; adrenalectomy-alloxan, 3.92; adrenalectomy-cortisone, 10.98; adrenalectomy-cortisone-alloxan, 32.57 μ mole α-ketobutyric acid/min/g liver. These results indicate that the depression of insulin secretion is independent of the increase in TDH activity, but gives rise to the increase in the TDH activity through the lowering of counteraction of insulin against gluco-corticoid. Actinomycin S3 treatment on rats disclosed that the change in TDH activity based on insulin related to de novo synthesis of this enzyme via transcriptional step.
