Influence of diets with different levels of protein and energy on liver albumin content in the rat.

ABSTRACT

The influence of protein ingestion on liver albumin synthesis and albumin content was investigated in rats fed protein as a meal (90% casein) given apart from the other dietary components provided ad libitum. In this condition, protein ingestion rapidly stimulates liver total protein synthesis. Separately fed rats were studied 6 and 20 h after the protein meal. Control rats fed mixed diets containing 13 or 80% casein were killed either during the absorptive (night) or postabsorptive (light) periods. The ratio of hepatic albumin synthesis to total protein synthesis remained fairly constant (12-15%) in all groups, indicating that albumin synthesis paralleled total protein synthesis. Liver albumin content measured in microsomes by immunonephelometry was significantly higher in separately fed rats killed 6 h postmeal than in those killed after 20 h. In rats fed 13% casein, the liver albumin content remained high regardless of the time of killing. In rats fed 80% casein, the albumin content was higher during the absorptive period than during the postabsorptive period. Immunoperoxidase staining of the hepatocyte organelles involved in albumin synthesis, especially the Golgi apparatus, was more intense for separately fed rats killed 6 h postmeal than for those killed after 20 h. Livers of rats fed 13% casein also exhibited a pattern indicative of high hepatocyte albumin content, whereas livers of rats fed 80% casein contained less. These results show that, in separate feeding, wide circadian variations of albumin synthesis run parallel to changes in liver albumin content.