Regulation of carbohydrate metabolism in lymphoid tissue. Quantitative aspects of [U-14C]glucose oxidation by rat spleen slices.

When washed spleen slices from fed rats are incubated with 3 mm-[U-14C]glucose, the rate of glucose utilization (46.2 mumol/h per g dry wt.) is sufficient to account, theoretically, for 80% of the O2 consumption. Measurement of net lactate production, however, and the fate of the radioactive carbon, indicates that the contribution of glucose to the respiratory fuel of the tissue is only 25-30% whereas 60-70% of the glucose utilized is converted into lactate. At saturating glucose concentrations (above 5 mm) its contribution to the respiratory fuel of the slice is increased to a maximum value of 34-39%. Only 2% of the glucose utilized is metabolized via the oxidative steps of the pentose phosphate pathway. Starvation for 72 h marginally increases both the rate of glucose utilization (by 21%) and its net contribution to the respiratory fuel (by 29%). Insulin, glucagon, adrenaline and adenosine 3':5'-cyclic monophosphate have no significant effect on either the rate of glucose utilization or on the pattern of radioactive isotope distribution. The uptake of glucose is increased by only 20%, whereas the production of lactate doubles when slices are incubated under anaerobic conditions. In assessing the suitability of spleen slices for metabolic studies, the only serious major perturbation, compared with the freeze-clamped organ, is an elevated mitochondrial [NAD+]/[NADH] ratio (connected with increased endogenous NH3 production) that is partially restored to normal values on incubation with glucose. Equal proportions of erythrocytes and leucocytes are found in the washed spleen slice. Metabolic contributions of the constituent cell populations in the washed slice are calculated and it is concluded that lymphocytes account for the major part of the glycolytic metabolism (80-90%), whereas the contribution of erythrocytes is insignificant.     

Modifications by ischemia of carbohydrate and lipid metabolism of the dog heart in situ from circulating and endogenous substrates

The uptake of circulating substrates, lactate, glucose and free fatty acids (FFA) has been investigated concurrently with the tissular contents of these principles and the glycogen and triglyceride stores in the dog heart in situ submitted to incomplete obstruction of left coronary bed. Transmural samples necessary for the repeated determination of tissular substrates were taken from left ventricular wall by means of a total cardiopulmonary by-pass system, then divided to allow the analysis separately in subendocardial and subepicardial layer. A 40 to 70% reduction in coronary blood flow gave rise to decrease or suppression of uptake of all the substrates or even to conversion of uptake into output. The modifications of uptake are chiefly related to the deficiency of breakdown by oxidation, though lessened in the case of FFA by incorporation into triglycerides and enhanced in the case of glucose by glycogenolysis. Glycogenolysis and consequent anaerobic glycolysis appear to be the main process available against the energy cellular defect linked with oxygen lack which affects notably more subendocardial than subepicardial layer.     

Regulation of glycogen metabolism in rat respiratory muscles during exercise

The effect of prolonged exercise on the glycogen level in the respiratory muscles (diaphragm--D, external intercostal--IE and internal--II) has been studied in four groups of rats: 1-control, 2-fasted for 24 h, 3-treated with nicotinic acid and 4-treated with propranolol. There was a sharp reduction in glycogen level in each muscle after 30 min exercise in the control and fasted groups. Exercise till exhaustion further lowered the glycogen level in D in the control group and in IE and II in the fasted group. In the fasted group, the level of glycogen in each muscle, at rest, and after 30 min exercise, and in IE and II muscles after exercise till exhaustion was lower than in the control group. Nicotinic acid did not affect the glycogen level either at rest or during exercise as compared with the control group. Propranolol increased the glycogen level in the muscles at rest and during 30 min exercise. It partially prevented glycogen mobilization in D and IE and fully in II during exercise till exhaustion. In the control group, 24 and 48 h after exercise till exhaustion, the level of glycogen in each muscle exceeded the resting control value. It is concluded that exercise-induced glycogen metabolism in the respiratory muscles differs in some respects from that in the limb or heart muscles.     

The respiratory activity of the liver mitochondria and the viability of rat pups subjected to changes in their carbohydrate metabolism in the prenatal development period]

It is shown that hyperglycemia after insulin introduction to the pregnant rats delays oxidation of pyruvate and malate by liver mitochondria as well as decreases offspring vitality. Digestive hyperglycemia activates utilization of this intermediate by liver mitochondria, that increases the rat vitality.     

Regulation of endogenous proteolysis in rat liver slices.

Methodological difficulties limit studies on cell protein catabolism both in intact animals and in vitro. We have studied the rate of protein degradation by measuring in vitro the release of acid-soluble radioactivity from rat liver slices and tested some factors that control the process. We found a rate of protein degradation of 6.5, or 2% per hr after 1 or 15 hrs of labelling in vivo during the first 90 min. These results indicate that a correlation exists between the rate of production of acid-soluble radioactivity by liver slices and the fast-or slow-turnover rate of the liver proteins. Cyanide and fluoride greatly inhibit the production of acid-soluble radioactivity from both slow- and fast-turnover proteins. Glucagon increases this production while insulin shows an opposite effect. Our preliminary investigations show that liver slices are a suitable surviving medium to study protein catabolism and its modifications under physiological and pathological stimuli.     

Oxidative metabolism of funicular tissue. I. Effect of exogenous substrates on oxygen consumption of funicular tissue in vitro]

Umbilical cord slices were incubated with various concentrations of either glucose, pyruvate or succinate. Furthermore the conversion of pyruvate to AcCoA and the oxidation of the latter were assessed respectively by measuring labelled CO2 evolved from 14C-pyruvate labelled on C1 or C2. The results suggest that 1) ADP stores are low since glucose induces a Crabtree effect; 2) the "succinoxidase" complex is far from being saturated and cannot account for the low oxidations observed under basal conditions; and 3) that the limiting step should be looked for either in Krebs' cycle or at the level of Complex I of the electron transport chain.     

Electrophoretic separation of rat spleen and thymus leukocytes and their reactions to mitogens in vitro]

Electrophoretic mobility (EPM) of lymphocytes from the thymus and spleen of August and Wistar rats as well as capacity of lymphocytes with different surface hemagglutinin (PHA) and concanavalin A (Con A) were studied by the method of free flow electrophoresis. Lymphocytes of the rat spleen were shown, depending on the surface charge, to divide into two groups during cultivation: cells with high and low electrophoretic mobility. At separation the lymphocytes consisted of 8--10 fractions with different EPM. There was a relationship between the surface charge of the lymphocytes and their stimulation rate by mitogens. Increased thymidine-3H uptake was recorded at mitogenic exposure of lymphocytes from the spleen with high EPM. Low mobile lymphoid elements of the spleen did not respond to mitogenic stimulation. A subpopulation of thymocytes with low EPM was resistant to Con A stimulation. The thymocytes of rats did not virtually respond to PHA irrespective of EPM.     

Regulation by auxin of carbohydrate metabolism involved in cell wall synthesis by pea stem tissue

Promotion of cell wall synthesis (from glucose) in pea (Pisum sativum) stem segments by indoleacetic acid (IAA) develops over a period of 1 to 2 hours and is comprised of a promotion of glucose uptake plus a promotion of the utilization of absorbed glucose. The effect of IAA resembles, in these and other respects, its effect on cell wall synthesis in oat coleoptile segments, but the pea system differs in not being inhibited by galactose or mannose, in involving considerably more isotope dilution by endogenous substrates, and in certain other respects.     

Enzymes of carbohydrate metabolism ofCotugnia digonopora and their activity in the presence of anthelmintics,in vitro

Cotugnia digonopora, a fowl cycllophyllidean cestode, was found to possess most of the enzymes, associated with the glycolytic sequence and phosphoenolpyruvate branch point, in the cytosol fraction. Enzymes of malate metabolism were predominantly mitrochondrial. Anthelmintic agents inhibited hexokinase, phosphofructokinase, glucose-6-phosphate dehydrogenase, malate dehydrogenase, fumarate reductase, and malic enzyme. In intact worms this effect was significantly reduced. However, the activities of glycogen Phosphorylase and pyruvate kinase were significantly enhanced. Communication No. 4113 from CDRI, Lucknow.     

Pathways of carbohydrate metabolism in peripheral nervous tissue. I. The contribution of alternative routes of glucose utilization in peripheral nerve and brain

The activities of enzymes of the glycolytic route, the pentose phosphate pathway, the tricarboxylic acid cycle and lipogenesis have been measured in rat sciatic nerve and brain. Parallel studies have been made of the utilization of 14 C-labelled glucose and pyruvate in these two tissues. Comparison of the enzyme profiles and flux through alternative routes was based on activity relative to the rate of glucose phosphorylation as measured by the rate of formation of 3H2O from [2-3H]glucose. The contributions of the pentose phosphate pathway and lipogenesis to glucose utilization were substantially higher in sciatic nerve than brain. The relatively high activity of transketolase (EC 2.2.1.1) and transaldolase (EC 2.2.1.2) suggested a special role for these enzymes in sciatic nerve.