Oral administration of alpha-ketoisovaleric acid or valine in humans: blood kinetics and biochemical effects.

alpha-Ketoisovaleric acid levels increase from 10.6 +/- 0.8 to 121 +/- 20 mumol/L, and valine levels increase from 175 +/- 14 to 940 +/- 50 mumol/L after oral administration of an isomolar (62.5 mg/kg) bolus of alpha-ketoisovaleric acid or valine to healthy human subjects. alpha-Ketoisovaleric acid levels have a different time course relative to valine. alpha-Ketoisovaleric acid and valine affect various other amino and keto acids, and some of these effects are qualitatively different. alpha-Ketoisovaleric acid enhances alpha-ketoisocaproic acid and alpha-keto-beta-methyl-n-valeric acid, but diminishes the corresponding amino acids, and causes an early decline of ornithine along with a late augmentation of plasma arginine. Valine does the opposite. The data suggest that in humans, overall capacity for alpha-ketoisovaleric acid decarboxylation appears greater than the capacity for valine transamination, and that all branched-chain amino acids and branched-chain keto acids seem to be interconvertible by reversible transaminations.