Tissue Distribution and Excretion of Alpha-aminoisobutyric Acid in the Rat: I. Effect of Dietary Protein Level and Composition

Abstract

The nature of the diet fed to rats greatly influenced the distribution ratio of injected 1-C14-α-aminoisobutyric acid (AIB) between tissues and serum, as well as its pattern of urinary excretion. An increased concentration of AIB was observed in the liver of animals maintained with deficient diets while at the same time the non-hepatic tissues showed a decreased concentrative capacity. The levels of dietary protein ranging from a protein-free diet to as high as 54% casein, affected very significantly the pattern of urinary excretion and the net AIB retention, but did not affect to any great extent, the relative tissue distribution. At high protein levels the urinary loss of AIB was greatly enhanced. The large amount of stored AIB in the tissues of rats fed low protein diets over an extended period was immediately mobilized and excreted when the protein content of the diet was suddenly increased. The importance of taking into account the nature, as well as the amount, of the diet consumed during studies on amino acid distribution is stressed.