Biochemical Studies on Liver Functions in Primary Cultured Hepatocytes of Adult Rats1: II. Regulation of Protein and Amino Acid Metabolism

The nitrogen balance of adult rat hepatocytes in primary culture was calculated from changes in the concentrations of amino acids, urea and ammonia in the medium. When cells from 3-day cultures were incubated in Hanks' solution they released amino acids, whereas when they were incubated in medium containing amino acids in excess of 0.5 mm they consumed amino acids and formed urea. These catabolic and anabolic states of the cells were stimulated by glucagon and insulin, respectively. Analysis showed that the relative amounts of individual amino acids released in salt solution were very similar to their relative amounts in liver proteins, except that the amounts of alanine, glutamate, aspartate, proline, and arginine released were relatively low. These amino acids were all used for gluconeogenesis, except arginine, which was converted to ornithine. During culture in Williams' medium E, the concentrations of glutamine, alanine, glycine, arginine, and aspartate in the medium decreased greatly; those of histidine, proline, and glutamate did not change; that of ornithine increased; and those of other amino acids decreased moderately. Glucagon markedly stimulated the consumptions of alanine, glutamine, and glycine, whereas dexamethasone stimulated the uptakes of both essential and non-essential amino acids only in Williams' medium E. The uptakes of amino acids exceeded the amounts used for protein synthesis; the excess amounts taken up were metabolized by other pathways, such as glucose formation. These results show that metabolism of proteins in these cells is affected by the amino acids and hormones present in the medium and mimics that in vivo. Thus this system should be useful for comprehensive studies on the control of liver proteins and acid metabolis.