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R Parrilla

Publications and source records attributed to R Parrilla.

At least 91 records · Page 5Linked to original sources
PubMed1977

Preparation and metabolic characterization of isolated rat lung cells.

Collagenase digestion of minced lung tissue yielded isolated cells, functionally viable as judged by several metabolic and morphological criteria, representative of all the cell species normally present in the tissue. The efficiency of the isolation procedure was about 25 per cent. Aerobic metabolism was not affected by most of the substrates tested except by succinate which increased oxygen utilization, and glucose, fructose and octanoate which significantly decreased oxygen uptake. Since no significant changes have been observed in the cellular adenine nucleotide content during glucose depression of aerobic metabolism it is concluded that the glycolytic flux had to be sufficient as to account for the decrease in the mitochondrial energy production. The mechanism responsible for these effects as well as their physiological significance are discussed herewith.

Adenosine Diphosphate↗
PubMed1977

Metabolic features of isolated rat lung cells. I. Factors controlling glucose utilization.

Isolated rat lung cell suspensions were prepared by collagenase digestion of the lung stroma. These cells were functionally competent as judged, among other criteria, by their constant rates of oxygen uptake and glucose utilization. An important metabolic feature of these cells is that they display very high glycolytic rates. At least 60% of the glucose utilized was converted to lactate, regardless of the glucose concentration in the medium. The state of reduction of the nicotinamide system, as indicated by the lactate-to-pyruvate ratio, was normal, thus indicating that the high glycolytic fluxes are not related to poor oxygenation of the preparation. Utilization of glucose displayed Michaelis-Menten saturation type kinetics with a Vmax of 331 nmol/10(6) cells per h and an apparent Km of 2.4 mM. These values were not affected by the presence of ouabain (0.1 mM), mannoheptulose (5 mM), or insulin (1 mU/ml), whereas phloridzin produced a drastic inhibition of glucose utilzation showing an apparent Ki of 0.4 mM. The substitution of sodium by K+ or Li+ as the predominant cations in the incubation medium does not alter rates of glucose utilization. Optimal pH for glucose utilization was within the physiological range with a more pronounced inhibitory effect at alkaline pH's. The intracellular concentration glucose was found to be low. This finding, in conjunction with a Q10 (27-37 degrees C) for glucose utilization above 2.0 and the differential effects of D- and L-glucose on production, seems to indicate that a stereospecific glucose transport system exists in lung cells. Several findings point to glucose transport into the lung cells as a probable rate-limiting step for its metabolism:1) the activity of the glycolytic enzymes largely exceeded the observed rate of glucose utilization;2) the decrease in enzyme activity during starvation was not accompanied by a decreased glycolytic flux, suggesting that factors other than enzyme activity, perhaps the supply of fuel, are rate limiting in the overall process of glucose breakdown;3) fructose was able to increase lactate production in the presence of saturating concentrations of glucose. These additive effects of glucose and fructose seem to support the point of view that it is not the glycolytic machinery but the supply of fuel which is rate limiting for glucose utilization by isolated rat lung cells.

Animals↗
PubMed1976

Role of glucagon on the control of hepatic protein synthesis and degradation in the rat in vivo.

The effect of glucagon on hepatic protein systhesis and proteolysis has been investigated. The intraperitoneal administration of 200 mug of glucagon produced an increase of the polypeptide chains completion time which was maximal 5 min after its administration and approached control values at 20 min. The increase of the polypeptides chains completion time observed at 5 min after the hormone administration represents a 38% inhibition of the hepatic protein synthetic rate. When glucagon was continuously supplied by intravascular infusion, maximal inhibition was attained throughout the experiment. This inhibition of protein synthesis brought about by glucagon was accompanied by an increase in the polyribosomal state of aggregation, indicating that the hormone acts mainly if not exclusively, on the elongation or termination step, or both. The administration of glucagon produced also a progressive increase in the hepatic valine concentration. This increase could not be accounted for the the decrease in plasma valine levels, suggesting that the rise in haptic valine concentration is an expression of hepatic proteolysis rather than the result of an accelerated transport of amino acids across the hepatocyte plasma membrane. The different time sequence in the glucagon-induced effects of protein synthesis and proteolysis suggests that both effects are independent and probably mediated by different mechanisms.

Animals↗
PubMed1976

Use of endogenous triglycerides to support gluconeogenesis in the perfused isolated rat liver.

The carbon balances in isolated perfused rat liver during gluconeogenesis from L-alanine and sodium L-lactate indicate that assuming the substrate unaccounted for were fully oxidized the energy yielded was not sufficient to support the observed rates of glucose synthesis. This observation indicates that endogenous substrates must also be oxidized. The possibility that endogenous fatty acid oxidation was the source of the energy needed to support glucose synthesis was investigated by measuring the rate of 14CO2 formation from tracer quantities of added [U-14C] palmitate. Short pulses of L-alanine or sodium L-lactate infusion produced an increased rate of 14CO2 production paralleled by increases in oxygen uptake indicating that more endogenous fuel is being mobilized. That the rate of 14CO2 output is an expression of fatty acid mobilization was supported by experiments demonstrating that the addition of octanoate to dilute the fatty acid pool produced an immediate fall in the rate of 14CO2 output. On the other hand, the administration of glucose produced no changes in oxygen uptake or 14CO2 output. However, lactate even in the presence of glucose induced a rise in 14CO2 production which occurred in parallel with the enhancement in oxygen uptake. It is concluded that mobilization of hepatic endogenous fatty acid is a metabolic event intimately associated with enhancement of gluconeogenesis. Consequently the control of the different steps of this process may indirectly control gluconeogenesis.

Animals↗
PubMed1976

Cellular metabolite distribution and the control of gluconeogenesis in the perfused isolated rat liver.

Glucose production was measured in isolated rat livers perfused with 100 ml of blood-free recirculating medium. The gluconeogenic rate using L-alanine as substrate was only 55% of that obtained with L-lactate. The steady-state concentration of gluconeogenic and tricarboxylic acid cycle intermediates were measured in freeze clamped biopsies. Livers perfused with L-lactate displayed higher concentrations of malate, alpha-glycerophosphate and beta-hydroxybutyrate probably as a result of a higher state of reduction of the nicotinamide system. Hexose-phosphate intermediates were also increased when L-lactate was the substrate. Phosphoenolpyruvate and 3-phosphoglycerate were considerably elevated when L-alanine was the glucose precursor. Livers perfused with L-lactate displayed higher cytosolic concentration of all the tricarboxylic acid cycle intermediates except oxaloacetate while glutamate was slightly and aspartate considerably higher when alanine was the substrate. In the mitochondrial compartment the pattern of distribution tended to be the opposite; that is, livers perfused with L-lactate showed lower concentrations of all the intermediates except alpha-ketoglutarate. The mitochondrial: cytosolic metabolite gradients of all the intermediates whose distribution was studied were higher in livers perfused with L-alanine. The relevance of these findings to the observed differences in the gluconeogenic fluxes are discussed.

Alanine↗
PubMed1975

Glucagon and insulin control of gluconeogenesis in the perfused isolated rat liver. Effects on cellular metabolite distribution.

The metabolic effects of glucagon and glucagon plus insulin on the isolated rat livers perfused with 10 mM sodium L-lactate as substrate were studied. Glucagon stimulated gluconeogenesis, ketogenesis and ureogenesis at the concentration used of 2.1 nM. The addition of insulin to give a glucagon-to-insulin ratio of 0.2 reversed all the glucagon effects. The glucagon enhancement of gluconeogenesis was accompanied by a rise in cytosolic and mitochondrial state of reduction of the NAD system and a fall in the [ATP]/[ADP] ratio. The analysis of the intermediary metabolite concentrations suggested, as possible sites of glucagon action, the steps between pyruvate and phosphoenolpyruvate as well as the reactions catalyzed by phosphofructokinase and/or fructose bisphosphatase. All the changes in metabolite contents were abolished when insulin was present. Glucagon increased the intramitochondrial concentration of all the metabolites, whose intracellular distribution was calculated. The finding of a significant rise in the calculated intramitochondrial concentration of oxaloacetate points to pyruvate carboxylation as an important site of glucagon interaction with the gluconeogenic pathway. A primary event in the glucagon action redistributing intracellular metabolites seems to be the mitochondrial entry of malate. The possibility is discussed that the changes in metabolite cellular distribution were brought about by the increased cellular state of reduction caused by the hormone.

Animals↗
PubMed1975

Control of hepatic protein synthesis. Differential effects of ATP levels on the initiation and elongation steps.

The effect of nucleotide energy levels in vivo on the different steps of protein synthesis has been studied. Hepatic anoxia was induced by interrupting the blood portal-vein flow. At 5 min of anoxia ATP fell to 59% of the control values and the amino acid incorporation into protein was inhibited by more than 70%. This strong inhibition was not paralleled by polyribosomal breakdown. On the contrary, when fasted rats were used, at 5 min of anoxia the ribosomal state of aggregation was found to increase. Longer periods of anoxia resulted in a further decrease in triphosphonucleoside content and polyribosomal breakdown. Based on these results and other reports from the literature it is concluded that the Km for the GTP of the peptide-chain-elongation mechanism must be higher than the Km of the initiation step. This finding implies that variations of nucleotide levels in vivo within the physiological range may control protein synthesis at the elongation step without apparent changes in the polyribosomal profiles.

Adenine Nucleotides↗
PubMed1974

Nitrogen metabolism in the isolated perfused rat liver. Nitrogen balance, redox state and rates of proteolysis.

Nitrogen balances were measured in isolated perfused rat livers in the presence and absence of nitrogen donors. In all instances the balance apparently was incomplete. The expression [alanine][alpha-oxoglutarate]/[pyruvate][glutamate] remained fairly constant under the metabolic conditions studied, indicating that it may be at near-equilibrium. The source of the extra nitrogen seems to be derived from increased hepatic proteolysis. The addition of a nitrogen donor to the perfusate arrested proteolysis, as did the addition of pyruvate. The free mitochondrial [NAD(+)]/[NADH] ratio, calculated from the glutamate dehydrogenase and beta-hydroxybutyrate dehydrogenase reactants, showed similar values and exhibited parallel changes under most metabolic situations studied. These results suggest that, under the reported experimental conditions, both dehydrogenases share a common mitochondrial NAD pool. Glutamate dehydrogenase plays an important role in hepatic nitrogen metabolism in vivo.

Alanine↗