Abstract
Galactose bears a close resemblance to glucose in the molecular structure. It is stereochemically interesting to compare the changes of metabolites during galactose tolerance test with the those during GTT. We carried out 40g oral and intravenous galactose tolerance tests in the normal, diabetic and hepatopathic subjects. In the normal subjects, the galactose led to a slight and transient elevation in blood glucose concentration, whereas in the diabetic and hepatopathic cases, it produced a persistent elevation in the blood glucose level. At that time increases of the glucose excretion in urine were observed at 2 hours after the administration without the significant elevations over the threshold value of blood glucose. The monosaccharide transports in the kidney have been reported to be related to the stereospecificity of molecular structures. Following the interaction between glucose and galactose, galactose was absorbed through the membrane in preference to glucose, and then glucose was excreted in urine. Plasma NEFA concentrations, on the other hand, diminished markedly after the administration irrespective of the levels of the blood galactose retention. However the decreases of the blood NEFA levels at 2 hours after the loading was more dominant in GTT than in the galactose tolerance test. No significant increases in the blood IRI levels were observed in either the oral or the intravenous galactose tolerance tests.
The galactose tolerance test is considered, in other words, to indicate the degree of hepatic dysfunction at the redox state. The redox potentials in the cytoplasma of hepatic cells has been described to have the significant influence upon the metabolism of galactose. According to our studies, the transient significant elevations in the blood lactate and pyruvate levels were observed after the administration in the normal group of the galactose tolerance tests. In abnormal groups, however, the elevation in the blood lactate and pyruvate levels were not so significant. During the galactose loading the significant positive correlations between the changes in the blood lactate and pyruvate levels were found in the normal subjects and diabetics, but no correlation in the hepatic disorders. While the significant negative correlations between the changes in blood lactate and NEFA levels were recognized only in the abnormal groups of the galactose tolerance tests. The fact that the abnormality in galactose tolerance was noted not only in cases of hepatic disorder but also in cases of diabetes suggests a possible involvement of NADH metabolism. As shown in our studies, the lactate-pyruvate system will be considered to play an important part in the conversion of the redox state, and when the regulation by this system was disturbed, the other system concerning the fatty acid metabolism might be connected with the regulation of them.
