Acceleration of proteolysis in perfused rat liver by deletion of glucogenic amino acids: Regulatory role of glutamine

Abstract

Glutamine at 1 and 4 times (x) normal plasma concentration (0.74 and 3 mM) suppressed hepatic proteolysis moderately and in proportion to responses of a complete amino acid mixture. The inhibition, however, increased disproportionately between 4 and 10x. Responses at 4x and lower were not associated with alterations in 125 I-asialofetuin uptake whereas higher levels inhibited uptake in a concentration-dependent manner. Thus proteolytic effects below 4x appeared to relate directly to glutamine while those above 4x very likely reflected increased levels of ammonia. The deletion of glutamine from a 1x complete mixture accelerated proteolysis by an amount equal to its inhibitory effect alone. Surprisingly, rates increased dramatically to near-maximum when alanine, glutamate, and glycine were also deleted.