Effect of glucagon and dibutyryl cyclic AMP on the tissue distribution of [14-C] alpha-aminoisobutyric acid in rats

Amino acid transport in isolated rat hepatocytes

Improvements in the collagenase perfusion techniques have made isolated rat hepatocytes a popular model in which to study hepatic function. Our knowledge of hepatic amino acid transport has been advanced as a result of this methodology. Translocation across the hepatocyte plasma membrane can, in some instances, represent the rate-limiting step in the overall metabolism of certain amino acids. Furthermore, regulation of amino acid uptake by hepatocytes appears to play a role in diabetes, and perhaps in malignant transformation. Comparisons between normal adult hepatocytes and several hepatoma cell lines show basic differences in amino acid transport. There are at least eight distinct systems in normal hepatocytes for transport of the hormones. Systems A and N exhibit enhanced uptake rates after the cells have been maintained in the absence of extracellular amino acids, a phenomenon termed adaptive control. Further studies using isolated hepatocytes will increase our basic understanding of membrane transport processes and their regulation.

Food and protein intake, glucagon, and distribution of alpha-aminoisobutyrate in the rat

Distribution of alpha-aminoisobutyric acid (AIB) in the rat was modified by food, dietary protein, and glucagon. In rats last fed 24 h before AIB injection, AIB clearance from plasma and uptake into liver were greater in rats fed a high-protein diet (60% casein) than in rats fed the control diet (18% casein); AIB clearance from plasma and uptake into muscle were lowered by a low-protein diet (6% casein). Feeding rats lowered clearance of AIB from plasma in low- and high-protein groups. Distribution ratios (AIB concentration in tissue water/AIB in plasma) were low in all tissues but liver during the first 7 h after feeding high protein when compared to the control values; ratios were low in muscle, heart, and kidney after feeding low protein. Maximum ratios occurred at different times for different tissues; the time was delayed by the high-protein diet in all tissues but liver. Glucagon increased all ratios in rats fed the control or low-protein diets, with the smallest changes occurring in liver and muscle from low-protein rats.