Influence of hormones on liver. I. Effects of steroids and thyroxine on pyridine nucleotide-linked dehydrogenases

Modification of the endocrine milieu intérieur by administration or withdrawal of hormones considerably influenced the concentration in liver of lactic dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconic dehydrogenase. Hormones effective in this regard are thyroxine, estradiol-17β, dihydrotestosterone, and 3α-hydroxysteroids in the androstane series. These hormonal effects are both organ-selective and, in liver, enzyme-selective. Thyroxine and steroids are not equivalent in their influence on the 3 hepatic dehydrogenases. Thyroxine was preeminent in this regard among hormones investigated in the present experiments. Each of the pyridine nucleotide-linked dehydrogenases in liver had an individually characteristic response to the administration of various hormones which was reflected in its hepatic level. The concentration in liver of lactic dehydrogenase was profoundly raised or lowered, respectively, by the administration of thyroxine or by thyroidectomy, and injection of steroids had small influence on its level. The levels of glucose-6-phosphate dehydrogenase and of 6-phosphogluconic dehydrogenase were considerably influenced by injection of thyroxine, estradiol-17β, or testosterone. Sex steroids did not increase the levels of these enzymes in hypophysectomized or thyroidectomized rats unless thyroxine was administered concurrently. Under designated conditions, it was found that the concentration of 6-phosphogluconic dehydrogenase was increased by hormonal methods which did not elevate the concentration of glucose-6-phosphate dehydrogenase. But high levels of glucose-6-phosphate dehydrogenase were not achieved without a considerable elevation of 6-phosphogluconic dehydrogenase as well.

The histochemical demonstration of glyceraldehyde-3-phosphate dehydrogenase activity

A histochemical method for demonstration of glyceraldehyde-3-phosphate dehydrogenation by tissues is described. The method utilizes Nitro BT as an indicator, glyceraldehyde-3-phosphate obtained from hydrolysis of commercially obtainable glyceraldehyde-3-phosphate diethylacetal (monobarium salt) as substrate, and (ethylenediamine)tetraacetic acid acid disodium as an activating agent in a medium buffered to pH 7.2 by 0.2 M sodium phosphate. The heat lability, substrate and coenzyme specificity, and sulfhydryl and phosphate dependence of the tissue component catalyzing this reaction indicate that glyceraldehyde-3-phosphate dehydrogenase activity is being demonstrated. The disparity between the known pH optimum of this enzyme and that determined histochemically, and the anomalous histochemical localization to mitochondria of this enzyme which has been found in the soluble fraction by differential centrifugation, are thought to result from the diaphorase dependence of the tetrazolium methods and to emphasize the need for caution in the interpretation of histochemically determined intracellular localization of dehydrogenating enzymes. The evidence gathered by previous workers concerning the feasibility of demonstrating specific dehydrogenases with Nitro BT, and the correspondence of the distribution of glyceraldehyde-3-phosphate dehydrogenase determined histochemically with available quantitative data, suggest that at the cellular level the histochemical results accurately reflect the distribution of this enzyme.