The effect of protein intake on the potential activity of the lysosomal vacuolar system in the cat.

1. Experiments were conducted to examine the relationship between protein intake and protein degradation in the liver of cats. 2. The cats were fed either a low protein/high carbohydrate diet (LP) or a high protein diet devoid of carbohydrate (HP). 3. The potential proteolytic activity of the lysosomal vacuolar system in the liver was assessed by both indirect (osmotic fragility of hepatic lysosomes) and direct (stereological measurement of lysosomal volume) methods. 4. The results from both tests indicated a significantly lower autophagic activity of the lysosomal system in the LP fed animals than in the HP fed cats. 5. This suppression of lysosomal protein degradation may represent an important mechanism for the conservation of proteins by the cat when low protein diets are fed.