Effect of dietary GABA and protein on growth, food intake and GABA metabolism in the rat

Abstract

GABA, when present as 4.5% of a 6% casein diet, decreased food intake and almost completely suppressed growth in young rats. Growth and food intake increased as dietary protein content increased; growth of rats receiving a 60% casein diet+GABA was 86% of that in the absence of GABA. Plasma, liver and kidney concentrations of GABA became lower as dietary protein content increased; brain GABA levels were unaltered by dietary GABA. GABA transaminase (GABA-T; E.C. 2.6.1.19) activity per mg tissue protein increased 2–3 fold in liver as dietary protein content increased but activity in brain and kidney did not change. Total hepatic enzyme activity in rats fed 80% casein was about 7 fold greater than in rats fed a protein-free diet. Rats fed 20% or 60% casein converted in 6 hrs about twice as much 14C-GABA to 14CO 2 as did rats fed 6% casein. Urinary excretion of 14C-GABA was not altered by changes in dietary protein content. Relationships between the suppression of food intake and growth by dietary GABA and its neurotransmitter functions are not clear.