Oxidative energy metabolism in germ-free and conventional rat liver mitochondria

The ADP:O ratios and State 3 (ADP-stimulated) and State 4 (controlled) rates of succinate, beta-hydroxybutyrate, isocitrate, glutamate, pyruvate + malate, alpha-ketoglutarate, and ascorbate + N,N,N',N'-tetramethylphenylenediamine (TMPD) oxidation were examined in liver mitochondria from germ-free and conventional rats of both Lobund Wistar (100-day-old) and Fisher (120-day-old) strains. The State 3 respiration rates of isolated mitochondria from germ-free and conventional rats were comparable except for the rate of succinate oxidation in the Wistar rats, which was significantly lower (approx. 10%). The State 4 respiration rates were generally lower in mitochondria isolated from germ-free Fisher rats (approx. 8%) and significantly lower (approx. 18%) in germ-free Wistar rats. The ADP:O ratios were similar in germ-free and conventional rats. Serum thyroxine concentrations indicated delayed maturation of thyroid function in young germ-free rats, but adult animals had concentrations similar to those found in conventional rats. The results indicate that, although absence of a microflora results in a 20-30% reduction in metabolic rate, the germ-free state has little influence on the functional respiration or oxidative phosphorylation of mitochondria isolated from the liver of the adult rat.