SERINE METABOLISM IN RAT LIVER SLICES

[The role of carbonic acid in the regulation of nitrogen metabolism in the animal body. 1. Effect of changes in CO2 concentration in tissues on the processes of NH+ metabolism in rabbits]

In two groups of rabbits of 24 animals each the dependence of NH4+-utilisation on the level of carbonic acid in the organism was investigates. The rabbits of the second group received injections into the abdominal cavity of 8 ml/kg body weight of a 5% NaHCO3-solution (enriched with CO2, pH 7.35) for the purpose of increasing the concentration of carbonic acid in the blood (pCO2: HCO3) and for the purpose of decreasing it an amount of NaCl-solution, which, in its content of Na+, was equivalent to the NaHCO3-dose. The difference in the concentration of carbonic acid in the blood between the two groups under the conditions of the experiment was between 30 and 35%, the pH-value was approximately the same. In order to investigate the NH4+-metabolism the animals of both groups received injections of 2 ml/kg body weight of a 1% (NH4)2HPO4-solution, their protein metabolism was studied after the intravenous injection of 2-14C-glycine. Together with the increase or decrease resp. of the level of carbonic acid in the organism, the keto acid concentration increases or decreases simultaneously. Due to the NH4-load the keto acid concentration in all animals decreases. it remains, however, higher in the animals with a higher HCO-3-level than in the control animals. The alpha-ketoglutarate concentration in the liver tissue of the animals with a higher HCO-3-level is, despite the NH4+-load, 87%, p less than 0.05, higher than in the control animals. The intensity of a removal of an NH4+-excess from the animal organism is directly dependent on the concentration of carbonic acid in the tissues. One hour after the NH4+-load the NH4+-concentration in the blood of the rabbits with a higher level of carbonic acid is normal again, whereas it is still 36% (p less than 0.05) higher than the original value in the control animals. In the liver and kidney tissues of the animals with an increased HCO-3-concentration 30 minutes after the (NH4)2HPO4-injection is by 16 and 14.5% (p greater than 0,05) resp. lower than that of the control animals. This is caused by the increased supply with NH4+-fixing substrates which are either formed directly or through intermediate stages by CO2-fixing reactions: oxaloacetate (the pyruvate concentration in the liver and kidney tissues compared to the control group was by 58%, p less than 0.05 lower), alpha-ketoglutarate, aspartate.(ABSTRACT TRUNCATED AT 400 WORDS)