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Biomedical subjects

F Mayor

Publications and source records attributed to F Mayor.

At least 73 records · Page 4Linked to original sources
PubMed1982

[Effect of neonatal anoxia on bilirubin levels in rat brain].

Neonatal anoxia induces a remarkable rise in brain bilirubin levels in the rat. The percentage of rats affected and the bilirubin levels reached are higher between the 3rd and 6th day after the anoxic episode. The accumulation of bilirubin in the brain could reflect the incidence of intracerebral hemorraghes (of different size and localization) caused by anoxia, and can plan an important role in the ethiology of the bilirubin encephalopathy and the neurological damage due to perinatal asphyxia.

Animals↗
PubMed1981

Glycine transport into plasma-membrane vesicles derived from rat brain synaptosomes.

1. Transport of glycine has been demonstrated in membrane vesicles isolated from rat brain, using artificially imposed ion gradients as the sole energy source. 2. The uptake of glycine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a C1- gradient (out greater than in) when the other essential ion is present. 3. The uptake of glycine is stimulated by a membrane potential (interior negative), as demonstrated by the effects of the ionophores valinomycin and carbonyl cyanide m-chlorophenylhydrazone and anions of different permeabilities. 4. The kinetic analysis shows that glycine is accumulated by two systems with different affinities. 5. The presence of ouabain, an inhibitor (Na+ + K+)-activated ATPase, does not affect glycine transport. 6. The existence of a high-affinity, Na+-dependent glycine-uptake system in membrane vesicles derived from rat brain suggests that this amino acid may have a transmitter role in some areas of the rat brain.

Animals↗
PubMed1981

Tyrosine transport by membrane vesicles isolated from rat brain.

Tyrosine uptake by membrane vesicles derived from rat brain has been investigated. The uptake is dependent on an Na+ gradient ([Na+]outside greater than [Na+]inside). The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of the ionophores valinomycin and carbonyl cyanide m-chlorophenylhydrazone and anions with different permeabilities. Kinetic data show that tyrosine is accumulated by two systems with different affinities. Tyrosine uptake is inhibited by the presence of phenylalanine and tryptophan.

Animals↗
PubMed1981

L-Aspartate transport into plasma membrane vesicles derived from rat brain synaptosomes.

Aspartate uptake by membrane vesicles derived from rat brain was investigated. The uptake is dependent on a Na+ gradient ([Na+] outside greater than [Na+] inside). Active transport of aspartate is strictly dependent upon the presence of sodium and maximal extent of transport is reached when both Na+ and Cl- ions are present. The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The uptake of aspartate is stimulated by a membrane potential (negative inside), as demonstrated by the effect of the ionophore carbonyl cyanide m-chlorophenylhydrazone and anions with different permeabilities. The presence of ouabain, an inhibitor of (Na+ + K+)-ATPase, does not affect aspartate transport. The kinetic analysis shows that aspartate is accumulated by two systems with different affinities, showing Km and Vmax values of similar order to those found in slightly "cruder" preparations. Inhibition of the L-aspartate uptake by D-aspartate and D- and L-glutamate indicates that a common carrier is involved in the process, this being stereospecific for the D- and L-glutamate stereoisomers.

Animals↗
PubMed1980

Prematurity in the rat. I. Fuels and gluconeogenic enzymes.

Changes in liver glycogen, plasma glucose, lactate, alanine and glycerol concentrations during the first 2 h after delivery by cesarean section in term and preterm rats were studied. Liver glycogenolysis initiated in both groups just after delivery, the rates of glycogenolysis being about 50 mumol/h/g wet weight. Glycogen breakdown came along with very low plasma glucose concentrations suggesting that glycogenolysis could be promoted by neonatal hypoglycemia. Plasma alanine concentrations decreased in both groups at similar rates suggesting that alanine utilization was enhanced during the first 2 h of extrauterine life. The plasma glycerol concentration increased in preterm rats but no changes were observed in term rats. The plasma lactate concentration progressively decreased during the first 2 h in term rats. However, preterm rats showed no changes in plasma lactate concentrations during the first hour, then decreased during the second hour at similar rates to those observed in term rats. These results suggest that preterm rats showed a transient resistence to lactate utilization at delivery which was overcome during the first hour of extrauterine life.

Alanine↗
PubMed1979

Effects of galactose, glucose and fructose on carbohydrate-lipid metabolism.

Doses of glucose, galactose and fructose were administered orally and intravenously, while monitoring the levels of blood glucose, serum insulin, free fatty acids, cholesterol and triglycerides. Blood glucose increases when glucose is administered orally or intravenously, but does not vary significantly with any other sugar. The increase in insulinemia only with oral and intravenous glucose and with oral galactose is in agreement with the participation of intestinal factors in the determination of insulin secretion. The results obtained for free fatty acids with the various sugars may be due to the metabolic properties of each sugar. We found no significant variations in the levels of cholesterol and triglycerides, perhaps because of the short duration of the experiment.

Administration, Oral↗
PubMed1978

Stimulation of ketogénesis after glycogen depletion by nicotinic acid in perfused rat liver.

Treatment with nicotinic acid produced an enhancement of ketone bodies production from endogenous, substrates, either oleate or octanotate. The enhancement was accounted for by an increase of acetoacetate synthesis. These results suggest that the increase of acetoacetate production may be due to the enhancement of extramitochondrial ketogenesis as a consequence of the inhibition of lipogenesis.

Animals↗
PubMed1977

Experimental phenylketonuria: metabolic studies in rat liver.

The "in vivo" effects of L-phenylalanine on the gluconeogenic pathway in the liver of fasted rats with experimentally induced phenylketonuria-like characteristics have been investigated. Significant increases of the fructose 6-phosphate, glucose 6-phosphate and glucose concentrations were observed. The study of the effect of L-phenylalanine on the cytoplasmic and mitochondrial redox state and energy charge showed an increase in the mitochondrial NAD+/NADH ratio while the energy charge was virtually unchanged. The effects of phenylalanine and its metabolic derivatives (phenylacetate, phenylethylamine, phenyl-lactate, o-hydroxyphenylacetate and phenylpyruvate) on the activity of lactate dehydrogenase (EC 1.1.1.27), malate dehydrogenase (EC 1.1.1.37) and 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) in rat liver have been also investigated. Phenylpyruvate inhibited the lactate dehydrogenase activity with a Ki of 5.3 mM. Phenylpyruvate also inhibited both the mitochondrial (Ki = 4 mM) and cytoplasmic (Ki = 5 mM) malate dehydrogenase activities. Phenylpyruvate, phenylacetate and o-hydroxyphenylacetate inhibited the 3-hydroxybutyrate dehydrogenase activity with Ki values of 0.7, 6.0 and 9.5 mM respectively.

Animals↗
PubMed1976

Pyruvate kinase activity and gluconeogenesis in rat liver after glycogen depletion with nicotinic acid.

Nicotinic acid administration, which depletes liver glycogen, leads to an increase of both pyruvate kinase L and phosphoenolypyruvate carboxykinase in liver by a factor of nearly two. The former is not prevented by either cycloheximide or actinomycin D. L-Cysteine, an allosteric inhibitor of pyruvate kinase L, favors gluconeogenesis from lactate in both nicotinic acid treated and starved animals.

Animals↗
PubMed1976

Effect of phenylalanine metabolites on the activities of enzymes of ketone-body utilization in brain of suckling rats.

1. The effects of phenylalanine and its metabolites (phenylacetate, phenethylamine, phenyl-lactate, o-hydroxyphenylacetate and phenylpyruvate) on the activity of 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) 3-oxo acid CoA-transferase (EC 2.8.3.5) and acetoacetyl-CoA thiolase (EC 2.3.1.9) in brain of suckling rats were investigated. 2. The 3-hydroxybutyrate dehydrogenase from the brain of suckling rats had a Km for 3-hydroxybutyrate of 1.2 mM. Phenylpyruvate, phenylacetate and o-hydroxyphenylacetate inhibited the enzyme activity with Ki values of 0.5, 1.3 and 4.7 mM respectively. 3. The suckling-rat brain 3-oxo acid CoA-transferase activity had a Km for acetoacetate of 0.665 mM and for succinyl (3-carboxypropionyl)-CoA of 0.038 mM. The enzyme was inhibited with respect to acetoacetate by phenylpyruvate (Ki equals 1.3 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). The reaction in the direction of acetoacetate was also inhibited by phenylpyruvate (Ki equals 1.6 mM) and o-hydroxyphenylacetate (Ki equals 4.5 mM). 4. Phenylpyruvate inhibited with respect to acetoacetyl-CoA both the mitochondrial (Ki equals 3.2 mM) and cytoplasmic (Ki equals 5.2 mM) acetoacetyl-CoA thiolase activities. 5. The results suggest that inhibition of 3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase activities may impair ketone-body utilization and hence lipid synthesis in the developing brain. This suggestion is discussed with reference to the pathogenesis of mental retardation in phenylketonuria.

Acetyl-CoA C-Acetyltransferase↗
PubMed1976

Regulation of the level of yeasts citrate synthase by oxygen availability.

The activity of yeasts citrate synthase in cells grown under different hypoxic conditions has been investigated. A linear relationship between the citrate synthase activity and the respiratory capacity of the cells has been found. When Saccharomyces cerevisiae was grown on fermentable substrates the activity decreased as the concentration of sugars in the medium increased. The enzyme of the yeast Rhodoturula showed a high activity in spite of the existence of high sugar concentration in the culture medium. Neither feed-back repression by glutamate nor feed-forward induction by ammonia has been found in bakers' yeast. The results suggest that the regulation of the enzyme by oxygen availability takes place by the ""de novo'' synthesis of the enzyme.

Acetates↗
PubMed1975

Isocitrate dehydrogenases and oxoglutarate dehydrogenase activities of baker's yeast grown in a variety of hypoxic conditions.

The activities of isocitrate dehydrogenase (NAD), isocitrate dehydrogenase (NADP) and oxoglutarate dehydrogenase have been investigated in Saccharomyces cerevisiae grown in a variety of aerobic and hypoxic conditions, the latter including oxygen deprivation, high glucose concentration, addition of inhibitors of mitochondrial protein synthesis, respiratory inhibition by azide, and impaired respiration mutants. All hypoxic conditions led to a marked decrease of oxoglutarate dehydrogenase and significant decreases of the two isocitrate dehydrogenases. According to its kinetic properties, the NAD-isocitrate dehydrogenase will not be operative in hypoxia "in vivo". From these and other related facts it is concluded that hypoxic conditions in yeast generally lead to a splitting of the tricarboxylic acid cycle and that glutamate synthesis in these conditions takes place through the coupling of the NADP-linked isocitrate and glutamate dehydrogenases.

Aerobiosis↗