alpha-Aminoisobutyric acid transport in liver slices from rats fed low protein meals

The effect of low protein intake on alpha-aminioisobutyric acid (AIB) transport has been examined in liver slices from meal-fed rats. Treatments (force-feeding casein or gelatin hydrolysates, glycine, or potassium chloride; injecting glucagon, or preincubating liver slices with cyclic AMP) which stimulated transport in control rat fed 3-hour meals containing 18% casein were less effective in rats fed 6% casein meals for 8 days. Responses of protein-depleted rats to glucagon or cyclic AMP had become essentially normal after they had consumed 18% casein meals for 2 days, whereas between 6 to 10 days were required for complete recovery of the response to casein hydrolysate. Stimulation of AIB transport by casein hydrolysate was also normal in depleted rats after they had consumed 40% casein meals for 2 days. Basal, non-stimulated transport of AIB was not significantly depressed in rats fed the low protein diet. Casein hydrolysate-induced increases in hepatic cyclic AMP concentrations were smaller in rats fed low protein meals. The results show that, although various stimuli of hepatic AIB transport become less effective in the protein-deprived rat, relatively rapid recovery of the response can occur upon refeeding adequate or high levels of protein.