Ines Masi

The Influence of Insulin on Carbohydrate Metabolism in the Isolated Diaphragm Muscle of Normal and Alloxan Diabetic Rats

The fate of uniformly labelled 14C glucose in the isolated diaphragm muscle of normal and alloxan diabetic rats has been studied by a quantitative application of the radio paper-chromatographic technique. No significant differences were observed in the metabolism of glucose by muscle from normal and diabetic rats. About 80% of the glucose metabolized by the muscle in the absence and presence of insulin has been accounted for. The extra glucose disappearing from the incubation medium in the presence of insulin was found to be incorporated in oligo- and polysaccharides, the percentage of glucose converted into the other main metabolites (i.e. lactic acid, hexose-phosphate esters and CO2) was shown to be unchanged or decreased by insulin. Insulin markedly accelerated the synthesis of oligo- and polysaccharides. The amount of free glucose in the tissues, which reached a maximum after 15 min of incubation, was uninfluenced by insulin. When the muscle was first incubated with 14C glucose and then in the absence of substrate, there was a sharp decrease in the radioactivity of all the intermediates with the exception of the hexose-phosphate esters which were found to accumulate. Under anaerobic conditions the total glucose metabolism was very reduced, and the greater part of the glucose disappearing from the medium was recovered as free glucose in the tissues. Very little radioactive lactic acid was formed under anaerobic conditions, except when the muscle was first incubated with 14C glucose aerobically and then anaerobically; under these conditions there was a considerable accumulation of radioactive lactic acid. Current theories on the mode of action of insulin have been discussed in reference to the findings reported in the present work.

Fate of uniformly labelled 14C glucose in brain slices

The fate of uniformly labelled 14C glucose in rat-brain slices has been followed by a quantitative application of the radio paper-chromatography technique. After 60 min incubation with brain tissue approximately 60% of the glucose disappearing from the medium was accounted for as lactic acid, about 20% as CO2 and most of the remainder as free amino-acids. Of the total glucose metabolized approximately 9% was converted into glutamic acid, 1.5% alanine, 3% γ-amino-butyric acid and 2.4% aspartic acid. Glutamic acid was the first of the amino-acids to be formed from glucose, and was detectable after 3 min incubation of brain tissue with 14C glucose. Insulin had no effect on glucose metabolism in brain slices. Under anaerobic conditions the total glucose metabolized by brain slices was only about 10% of that found under aerobic conditions; of the total glucose disappearing from the medium anaerobically about 80% was accounted for as lactic acid and the remainder as free unchanged glucose in the tissue cells.

Metabolism of hexoses in rat cerebral cortex slices.

Abstract— 1 The metabolism of two 14C‐labelled hexoses and one hexose analogue, viz. mannose, fructose and glucosamine, has been compared with that of glucose for slices of rat cerebral cortex incubated in vitro. 2 The metabolism of [U‐14C]mannose was essentially identical to that of glucose; oxygen consumption and CO3 production were similar and maximal at a substrate concentration of 2·75 mM. Incorporation of label into lactate, aspartate, glutamate and GABA was similar for the two substrates at 5·5 mM substrate concentration. 3 With [U‐14C]fructose, maximal oxygen consumption and CO3 production were obtained at a substrate concentration of 11 mM. At 5·5 mM, incorporation into lactate was 5 per cent, into glutamate and GABA 30 per cent, into alanine 63 per cent and into aspartate 152 per cent of that from glucose. Increasing substrate concentration to 27·5 mm was without effect on incorporation into amino acids from glucose and raised incorporation from fructose into glutamate, GABA and alanine to a level similar to that found with glucose; at the higher substrate concentration aspartate incorporation from fructose was 200 per cent and lactate 42 per cent of that with glucose. Unlabelled fructose was without effect on incorporation of radioactivity from [3‐14C]pyruvate into CO2 or amino acids; it increased incorporation into lactate by 36 per cent. Unlabelled glucose diminished incorporation into CO2 from [U‐14C]fructose to 35 per cent; incorporation into lactate was stimulated 178 per cent at 5·5 mM fructose; at 27·5 mM it was diminished to 75 per cent. 4 By comparison with [1‐14C]glucose, incorporation of radioactivity from [1‐14C]‐glucosamine into lactate, CO2, alanine, GABA and glutamine was very low; incorporation into aspartate was similar to glucose. Thus the metabolism of glucosamine resembled that of fructose. Glucosamine‐1‐phosphate, glucosamine‐6‐phosphate, and an unidentified metabolite, all accumulated.

BLOOD LIPIDS IN ITALY * Regional Differences

Serum cholesterol and triglyceride levels have been evaluated in samples from fasting males aged 20--59 in Northern (Brisighella), Central (Rome) and Southern (Pozzuoli) Italy. Regularly performed quality controls between laboratories assured comparability of data. A statisitically significant difference of mean serum cholesterol and triglyceride levels was observed for most age-groups in the 3 different areas, lower values being found in the southern population as compared to the central and northern ones. These results support previous findings and the thesis that large differences in blood lipid levels may still exist even within the same country and that they at least in part may be culturally determined in connection with different dietary habits.

The Influence of Glucose on Acetate, Alanine and Pyruvate Metabolism in Rat Cerebral Cortical Slices

The effect of glucose as co-substrate has been studied on the metabolic fate of [U-14C]alanine [2-14C]acetate and [3-14C]pyruvate in brain cortical slices, using the automatic paper radio-chromatographic scanning technique previously described. In comparison to glucose and pyruvate, acetate and alanine were metabolized only to a very small extent by brain cortical tissue. The addition of glucose strongly stimulated the 14CO2 production from acetate, but did not affect 14CO2 production from pyruvate and alanine. The oxygen uptake was stimulated by glucose in presence of all three substances. In addition to CO2 the metabolites formed from pyruvate were aspartate, glutamate, alanine, GABA and lactate. The same metabolites were formed from alanine. The only metabolites, detected with the technique used, formed from acetate, were aspartate and glutamate. The effect of glucose on the metabolites formed from acetate was a marked increase of glutamate, glutamine and GABA and a decrease of aspartate. The effect of glucose on the metabolites formed from alanine was an increase of glutamate, GABA, and lactate, and a decrease of aspartate. The effect of glucose, on the metabolites formed from pyruvate was a very large increase of lactate, and a decrease of all the amino-acids formed except glutamine, the formation of which was stimulated.

The influence of insulin on the specific activities of the hexose phosphate esters and lactate formed from glucose in the isolated rat diaphragm muscle

A microchromatographic technique using ion exchange columns for the separation of glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-diphosphate in extracts of rat diaphragm muscle has been described. Applying this technique it has been shown that when diaphragm muscle was incubated in the presence of uniformly labelled C14-glucose for 2 hr in the absence of insulin the specific activity of the hexose phosphate esters was about half that of the added glucose whereas in the presence of insulin the specific activity of the hexose phosphate esters was equal or approaching to that of the added glucose substrate. Insulin had no influence on the specific activity of lactate formed from glucose. Insulin did not increase the total concentration of glucose-6-phosphate, fructose-6-phosphate, and fructose-1,6-diphosphate present in the muscle at the end of the incubation period.