Effect of rhatannin on glutamine metabolism in rat liver.

Abstract

The present investigation was undertaken to evaluate the effect of rhatannin (condensed tannin purified form Rhei rhizoma) on transamination from glutamine by measuring the individual amino acids formed from α-keto analogues of amino acids with glutamine or glutamane or glutamate in the supernate of rat liver homogenate. Increased glycine formation was observed 2 to 4h after the intraperitoneal administration of rhatannin (12.5mg/kg body weight). Glutamate (derived from glutamine via glutaminase) may not participate in the rhatannin-induced elevation of glyoxylate amination by glutamine. This effect by rhatannin was completely abolished by cycloheximide treatment 30 min prior to rhatannin treatment, while actinomycin D had no effect. With 20 mM glutamine as the amino-donor, the order of effectiveness of 20 mM keto analogues of amino acids was glyoxylate>pyruvate>hydroxypyruvate>phenylpyruvate>α-ketoisocaproate, and little activity was observed with α-ketoisovalerate. Phenylalanine and leucine production rates were enhanced with either glutamine or glutamate in rhatannin-treated rats.The results of the present investigation suggest that the hepatic glutamine transaminase pathway might be enhanced in rhatannin-treated rats. This enhancement might be associated with a protein synthesis process.