In Vivo activation by diets and in vitro activation by hormones are additive for urea synthesis in the rat liver

Abstract

The basal rate of urea or glucose synthesis, set in vivo by different diets, was challenged by addition of hormones to isolated hepatocytes. Basal rate of urea synthesis ranged from 7.1 to 23.5 and 27.8 nmol/mg wet weight cells/hr in hepatocytes prepared from rats with a protein free diet or with two distinct but complete protein diets. Maximum difference in the basal rate of glucose synthesis from lactate was only 26.7% for the same diets. Depending on the basal rate of urea synthesis fixed in vivo by the diets, significant in vivo activations superimposed on these, either low or high, basal rates with a remarkable constancy: 2.4-fold with glucagon, 1.9-fold with epinephrine and 1.4-to 1.8-fold with adenosine. Likewise, the basal rate of glucose synthesis from lactate, established by these diets, superimposed 3.7-fold with glucagon, 2.4-fold with epinephrine, 2.1-to 2.4-fold with adenosine and 2.0-to 2.5-fold with inosine. The stimulation of hepatocytes in vivo showed a direct relationship in the increased rates of urea and glucose synthesis. The short-term activation in urea and glucose synthesis superimposed in proportion to the long-term status of urea or glucose formation set in the liver by the diet.