Effect of adrenalectomy and of growth hormone on enzymes concerned with urea synthesis in rat liver

Abstract

The activities of enzymes of the urea cycle (carbamoyl phosphate synthetase, ornithine transcarbamoylase, arginine synthetase, argininosuccinase and arginase) have been measured in control, adrenalectomized, cortisone-treated and growth-hormone-treated rats. In addition measurements have been made of glutamic dehydrogenase and glutamic-oxaloacetic transaminase. Adrenalectomy caused a reduction in the activity of all five enzymes of the urea cycle and of glutamic dehydrogenase. The most striking changes were in the activity of the rate-limiting enzyme of the urea cycle, the condensing enzyme of the arginine-synthetase system, and in liver arginase, both of which fell to about 40% of the pair-fed control values. The effect of cortisone acetate on the activities of the three enzymes of the urea cycle located in the soluble fraction of the cell (arginine synthetase, argininosuccinase and arginase) was studied. In normal rats, treatment with this hormone raised the total liver-enzyme activities of all three enzymes well above control values. In adrenalectomized rats cortisone acetate restored the activities of these enzymes towards normal; arginase showed the most rapid response. The most striking change in the growth-hormone-treated animals was the reduction in the activity of the arginine-synthetase system.