Production of Sugar by Surviving Liver.

Abstract

That the liver can form carbohydrate from certain metabolites, and, in particular, lactic acid, is a view widely accepted. Examination of the experimental evidence nevertheless reveals a large number of contradictory results.

Mandel and Lusk 1 showed that lactic acid when given to the diabetic organism was excreted as glucose. This transformation they suggested occurred in the liver. Jannsen and Jost 2 could not show that intravenous injection of lactic acid led to the formation of sugar in the muscles. They supposed the change occurred in the liver. Meyerhof and Lohmann 3 and Takane 4 claim that liver slices bring about a synthesis of carbohydrate when respiring in Ringer solution containing lactic acid. Abramson and Eggleston 5 find, however, that the intact anesthetized dog does not demonstrably synthesize glycogen (in the liver) from sodium r-lactate. Finally, Burn and Marks 6 by perfusing livers previously rendered glycogen free found that there was a production of sugar which was not derived from either lactic acid or from protein. The following results were obtained in some work planned to investigate lactic acid, carbohydrate relationships in normal and abnormal tissues.

Rabbits were starved for 36-48 hours. The animals were stunned by a sharp blow on the head and rapidly bled to death. The liver was excised, chopped with scissors into pieces only fine enough to allow of good sampling (the tissue was not made into a brei), and samples weighed out, fairly accurately, but rapidly. The tissue to be incubated was placed in flasks containing 20 cc. phosphate-Ringer solution—pH 7.4—and the air in the flasks was displaced by oxygen. The tissue was incubated at 37° C. for 3 hours, the flasks being gently shaken all the time. The control samples were placed in either ice-cold 95% alcohol (for glycogen, soluble sugar and lactic acid determinations) or in ice-cold 4% HCl (for the total sugar content). Glycogen was estimated by Pflugers' method; soluble sugars were extracted in 66% alcohol and, after removal of the alcohol, the aqueous mixtures were cleared by the use of the HgNO₃ reagent of Patein and Durfan. After removal of excess mercury by H₂S and blowing off of the H2S crystal clear solutions were obtained. To insure that there was no sugar in the tissue which escaped detection in these methods, samples were also hydrolyzed with 4% HCl for 3½ hours. After removal of proteins by NaOH and ZnSO₄ these solutions were also cleared with HgNO₃. The method of Hagedorn and Jensen was employed for the estimation of sugar.