Effect of changes in hormonal and dietary status of rats and mice on the activity of their liver glutamic dehydrogenases

Abstract

Summary Glutamic dehydrogenase was measured spectrophotometrically in extracts of mouse and rat liver and mouse brain following a variety of treatments of the animals in vivo . Determinations were carried out separately of the loosely bound (extract A) and tightly bound (extract B) isoenzymic forms and related to the total nitrogen content of the extracts. Starvation of mice up to 120 hr caused no significant decrease in the glutamic dehydrogenases of liver. The lactic dehydrogenase activity was also unaffected, but glucose-6-phosphate dehydrogenase decreased appreciably on a protein basis. Since the weight of liver per mouse was considerably lower in the starved animals, an overall diminution of all three enzymes per mouse was obtained. In brain extracts, glutamic and lactic dehydrogenases decreased with prolonged starvation. Repeated injections of nicotinamide into mice caused the expected rise in the diphosphopyridine nucleotide concentration in the liver, but had no effect on the activities of the pyridine nucleotide-dependent glutamic dehydrogenases, lactic dehydrogenase, or glucose-6-phosphate dehdrogenase in liver extracts. Chronic administration in vivo of diethylstilbestrol, which in vitro is a potent inhibitor of both glutamic dehydrogenases, brought about a gradual decrease in the enzyme activity in both extracts of the liver. A higher dose of the hormone was more effective than a lower dose. Adrenalectomy of young or mature rats was followed by a gradual diminution of the glutamic dehydrogenase activity of both extracts of the liver, particularly in the second week following extirpation of the adrenal glands. None of the treatments examined in this series of experiments had any consistent differential effects on the two isoenzymic forms of glutamic dehydrogenase.