Energetic Substrates Research Articles

Changes of carbohydrate metabolism caused by food restriction, as detected by insulin administration

Metabolic changes induced in the rat by food restriction were assessed by administration of insulin (0.025 U/kg BW). The animals subjected to a 2 hr feeding/22 hr fasting schedule during one week have a greater capacity to recover from hypoglycemia even after 4 and 8 hr of fasting, whereas those with free access to food have a far lesser capacity to recover. Food restriction also caused a greater resistance to hepatic glycogen depletion during the hypoglycemic phase. It is likely that the metabolic adaptation during food restriction is important for glucose homeostasis and for rapid mobilization of energetic substrate during prolonged fasting.

Catecholamine-fuel interrelationships during exercise in fasting men.

Adrenergic response to exercise and the relationships between plasma catecholamines and blood energetic substrates were studied in sedentary men after 15 h of fasting. Subjects pedaled a bicycle ergometer until exhaustion at a work load approximating 80% maximal oxygen consumption. Working ability was diminished by the fast (P less than 0.025). Resting plasma norepinephrine level was increased by fasting. During exercise plasma epinephrine (E) and norepinephrine (NE) concentrations were more elevated in fasting subjects than in fed subjects. Plasma catecholamine (CA) levels in fasting men correlated with blood glucose, blood lactate, and plasma glycerol concentrations. There was no significative correlation between CA and plasma free fatty acid (FFA) levels. The increased adrenergic activity in fasting subjects correlated with reduced endurance time. This study emphasizes the role of CA release, probably combined with other hormonal factors, in the mobilization of energy substrates during submaximal exercise.

Diurnal variations of plasma lipoproteins and liver lipids in rats fed starch sucrose or fat.

The incidence of the dietary source of energy on lipid transport and accumulation was investigated over a full nycthemeral cycle in adapted rats fed ad libitum. Starch, sucrose and lard were compared. Lipoprotein composition of the plasma, liver and plasma lipids and insulinemia were analyzed every 3 hours over 24 hours. The pattern of VLDL concentration was dependent on the nature of the energetic substrate. Feeding starch resulted in a remarkable stability of lipoproteins, liver and plasma lipids, despite clearcut diurnal variations in plasma non esterified fatty acids, insulinemia and liver glycogen. In sucrose-fed rats VLDL rose to a sharp maximum in the post prandial period (9-12:00) and were totally cleared by 18:00. In fat-fed rats, HDL were elevated during the night, suggesting a possible stimulation of their synthesis by dietary fat in the intestine. LDL were constantly elevated with peak values at 21:00 while VLDL were very low, even at night, despite elevated levels of non-esterified fatty acids. It is concluded that, in animals adapted to a high fat-diet, a high level of circulating non esterified fatty acids is not sufficient to promote the synthesis of VLDL. The main regulating factor appears to be the intensity of hepatic lipogenesis which is stimulated by sucrose and inhibited by lard. No correlation was found between variations in plasma VLDL and insulinemia.

Dopaminergic stimulation of HGH in diabetes mellitus and in obesity.

The behavior of HGH in basal conditions and after L-Dopa infusion was studied in a group of patients with diabetic retinopathy, in 9 obese and 8 control subjects. In both diabetics and obese subjects, increases found in HGH plasma levels after administration of the drug were slighter than in the controls. On the basis of these results it can be concluded that in diabetics the availability of energetic substrates may modify the HGH response to the L-Dopa stimulus. In obesity, the possibility is considered of a reversible response to the L-Dopa stimulus. In obesity, the possibility is considered of a reversible defect in the sensitivity of the dopaminergic receptors, induced by metabolic and endocrine factors.

Diverses proprietes de l'absorption du citrate du malate et du succinate par les lutoides du latex d' Hevea brasiliensis

Lutoïds from Hevea latex are microvacuoles with lysosomal character. In vitro in a medium free of energetic substrate citrate, malate and succinate are absorbed. The properties of this absorption and the action of some modifiers are discussed.

Time course of regeneration of minced frog muscles estimated by the level of energetic substrates.

1. Gastrocnemius muscles of frogs have been excised, chopped and put back into the leg. 2. The weight of the implanted muscles increases until the 8th day after the operation and then decreases to 1/3 of that of the control by the 30th day. 3. The inulin space is twice as high in regenerating muscle as in the unoperated controls. 4. Adenosine nucleotides are in an enzymatic equilibrium set by the ratio creatine/phosphorylcreatine during regeneration of the muscle. 5. Glycolytic intermediates (hexose monophosphate, fructose-1,6-diphosphate, alpha-glycerophosphate and lactate) have been measured during the course of muscle regeneration up to the 30th day. The results suggest that the glycolysis of regenerating muscle is very active. 6. The total creatine (sum of creatine and phosphorylcreatine) is very low after the operation: 5% of that of the controls; it rises sharply after the 8th day, and reaches 30% of that of the control on the 30th day. 7. The amount of total creatine seems proportional to the progress of the muscle regeneration. It is suggested to use this substance as a biochemical reference for biochemical works on muscle regeneration.

Effect of elevated lactataemia on the rates of lactate turnover and oxidation in rats.

1 The L-Lactate14C(U) priming dose-perfusion technique was used to measure the rates of lactate turnover and oxidation in anesthetized and mechanically ventilated rats. Lactataemia ([L]) was normal (0.5–1mM) or elevated either through moderate hypoxaemia or after lactate loading in normoxic conditions. 2. Lactate turnover and oxidation rates increased linearly with [L] up to 6 mM and the values of the three groups stand on same lines. 3. The slope of the regression line of oxidation rate vs [L] was lower than the turnover one. Thus an increasing part of the lactate flow was oriented to other metabolic pathways in these hyperlactataemic conditions. 4. 15% of the metabolic rate was explained by lactate oxidation in basal condition (50% of the turnover rate oxidized). This participation of [L] to the total energy expenditure increased when [L] rose and reached 45% when [L] is 6 mM. 5. These results are discussed in the light of the physiological role of lactate as metabolic regulator, glucose precursor and energetic substrate.

Biosynthèse des glycoprotéines dans les mitochondries: I. Etude de l'activité mannosyl-transfèrase mitochondriale

Summary Glycoprotein biosynthesis in mitochondria has been approached by studying the mannosyl — transferase activity. This enzyme incorporates mannose, from GDP — mannose, the coenzymic form, onto an endogenous acceptor. Studied on «in vitro acellular systems, the optimal pH is 7,4 and the optimal temperature is 30°C. The affinity constant for the GDP-mannose substrate is 110 nM. The enzyme is inhibited by ADP, GDP and GTP. Mn 2+ and Mg 2+ ions are activators, and maximal activity is reached at 5.10 −3 M concentration of Mn 2+ . Puromycin and cycloheximide have no effect. Introduction of energetic substrates (glutamate, succinate) do not modify the mannosyl-transferase activity. The same is true for inhibitors (rotenone, amytal, antimycin and cyanide) and an uncoupler (2,4-dinitrophenol). Mitochondrial mannosyl-transferase is different from microsomic homologous systems, and its activity is independent from the energetic potentialities of mitochondria.

The effects of tri-hydroxymethyl-aminomethane (TRIS) on plasma levels of insulin, small ions and energetic substrates in the dog.

The effects of tri-hydroxymethyl-aminomethane (TRIS) on plasma levels of insulin, small ions and energetic substrates in the dog.