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Biomedical subjects

A Machado

Publications and source records attributed to A Machado.

At least 145 records · Page 8Linked to original sources
PubMed1991

Involvement of diminution of glutathione, produced by deficiency of methionine in the diet, in the elevation of malic enzyme level in rat liver.

Rats fed on a low protein diet show an increase in the specific activity of malic enzyme and a concomitant decrease of glutathione concentration. We have studied the effect on malic enzyme activity of supplementing of low protein diet with essential amino acids. Only when methionine was excluded from the diet did the specific activity of malic enzyme increase to the same extent as found in rats fed with low protein diet. Immunoprecipitation of malic enzyme indicated that specific activity changes are the result of changes in the amounts of enzyme. Under all dietary conditions studied, the increase in malic enzyme activity is associated with a decrease in the concentration of GSH. To evaluate the possible causative role of GSH in malic enzyme induction, the specific activity of malic enzyme was measured in rats treated with BSO, an inhibitor of GSH biosynthesis. The results show that in BSO-treated rats the decrease of GSH levels is also accompanied by an increase in the activity of malic enzyme.

Amino Acids, Essential↗
PubMed1991

Age-dependent changes in the activity and isoenzymatic pattern of the phosphofructokinase in different areas of the central nervous systems.

Regional activity of phosphofructokinase enzyme and the amount of the isoenzyme C in 7 areas of young, adult and aged rats brain have been studied. The phosphofructokinase activity in substantia nigra decreased in adult and aged rats, but the maximum decrease was found in the septum of aged rats. There is a regional distribution of the isoenzyme C in the different areas studied. There was a general decrease in the amount of this isoenzyme in the areas studied with the exception of the hippocampus and the amygdala. The highest decrease was found in the septal area and in the diagonal band of Broca. These results are discussed in relation to the aging in different regions.

Aging↗
PubMed1991

Effects of neonatal bilateral eye enucleation on postnatal development of the monoamines in posterior thalamus of the rat.

Levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (serotonin, 5-HT) and their metabolites, and the activities of tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH) and monoamine oxidase A and B (MAO-A and MAO-B) have been determined in the rat posterior thalamus after enucleation during postnatal development. DA and 5-HT turnover rate have been measured as 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) accumulation rates after central decarboxylase inhibition by 3-hydroxybenzylhydrazine (NSD-1015). The major changes were an increase in noradrenergic and serotoninergic metabolism in enucleated animals compared with control animals. A decrease of the MAO-A to MAO-B ratio during postnatal development was found.

5-Hydroxytryptophan↗
PubMed1991

Turnover of dopamine and serotonin and their metabolites in the striatum of aged rats.

Turnover of dopamine (DA), serotonin [5-hydroxytryptamine (5-HT)], and their metabolites has been measured in adult and aged rats. Turnover rates of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxy-3-indoleacetic acid (5-HIAA) have been assayed from the disappearance rates after blocking by pargyline inhibition of monoamine oxidase (MAO) and from the accumulation rates by probenecid inhibition of the probenecid-sensitive transport system. DA and 5-HT turnover rates have been measured as accumulation rates of 3,4-dihydroxyphenylalanine and 5-hydroxytryptophan, respectively, after central decarboxylase inhibition by 3-hydroxybenzylhydrazine (NSD-1015) and as accumulation rates of DA and 5-HT after pargyline inhibition of MAO. The DA turnover rate after NSD-1015 was 23.9% lower in aged rats than in adults, whereas after pargyline there was no significant difference between the two age groups. The HVA fractional rate constant and turnover after pargyline were lower in aged rats than in adults, and HVA turnover after probenecid was higher in aged rats than in adults. The DOPAC-HVA pathway seems to be reinforced at the expense of DOPAC conjugation. In aged and adult rats whose 5-HT steady-state levels were not statistically different, the 5-HT turnover rate after pargyline and NSD-1015 treatment was lower in aged rats than in adults. An increase of 5-HIAA levels after pargyline and probenecid treatment in aged rats could be due to the handling stress.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1991

Effects of central epinephrine synthesis inhibition on stress-induced prolactin secretion in male rats.

1. The present study was designed to examine the role of central epinephrine pathways in the control of stress-induced prolactin secretion in male adult Wistar rats. 2. Intracerebroventricular administration of two epinephrine synthesis inhibitors, SKF 64139 (5 and 10 micrograms/rat) and LY 134046 (10 and 20 micrograms/rat), 6 h before the onset of immobilization stress blocked prolactin secretion in a dose-dependent manner. Prolactin values before stress were about 4.0 ng/ml and increased to almost 50 ng/ml in the control group. SKF 64139 injection in the higher dose (10 micrograms/rat) induced a complete blockade of the stress-induced prolactin release, whereas partial blockade was observed after the higher dose (20 micrograms/rat) of LY 134046. 3. Salbutamol pretreatment (10 micrograms/rat) completely restored stress-induced prolactin secretion in animals receiving a central injection of both epinephrine synthesis inhibitors under the same conditions as described above. 4. It is suggested that epinephrine pathways in the brain play an important role in the control of prolactin release occurring during immobilization stress.

Albuterol↗
PubMed1991

Pharmacologic characterization of GABAA/benzodiazepine receptor in rat hippocampus during aging.

We have characterized the pharmacologic properties of the gamma-aminobutyric acid (GABAA)/benzodiazepine receptor complex in hippocampal membranes from 3-month- and 24-month-old Wistar rats. No major changes were found in [3H]flunitrazepam or [3H]muscimol binding parameters. Neither the dissociation constant(s) nor the Bmax for either ligand seemed to be modified during aging in hippocampus. Furthermore, the allosteric interaction between the barbiturates binding site and the GABA binding site, determined by pentobarbital stimulation of [3H] muscimol binding, remained unaltered. However, there was a significant increase with aging in the efficacy of the GABA-enhancement of [3H]flunitrazepam binding. On the other hand, we have also detected a significant increase in the proportion of type I benzodiazepine receptor in 24-month-old hippocampal membranes. We propose that the age-related increase in the efficacy of GABA-enhancement of [3H]flunitrazepam binding could be correlated with the increase in the proportion of type I benzodiazepine receptor. Based on these results it is tempting to speculate that the age-dependent modifications on the GABAA/benzodiazepine receptor might reflect an age-dependent neuronal degeneration of the hippocampus or the hippocampal formation.

Aging↗
PubMed1990

Effects of enucleation on postnatal development of catecholamines and serotonin metabolism in the superior colliculus of the rat.

We have measured the level of catecholamines and serotonin and their principal metabolites, and the activities of tyrosine hydroxylase, tryptophan hydroxylase and monoamine oxidase-A and -B in the rat superior colliculus during postnatal development after bilateral removal of the eyes. The visual deprivation has different effects on the catecholamines and serotonin metabolism. The major changes in both amines were at day 15. Tyrosine hydroxylase and tryptophan hydroxylase activities increased during postnatal development but this increase was higher in enucleated compared with controls. An increase of the MAO-B to MAO-A ratio during postnatal development was found. The significance of these changes has been discussed.

Aging↗
PubMed1990

Possible involvement of NADPH requirement in regulation of glucose-6-phosphate and 6-phosphogluconate dehydrogenase levels in rat liver.

Previous studies examining regulation of synthesis of Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase in rat liver have focussed on the induction of these enzymes by different diets and some hormones. However, the precise mechanism regulating increases in the activities of these enzymes is unknown and the factors involved remain unidentified. Considering that many of these metabolic conditions occur simultaneously with the increase of some NADPH consuming pathway, in particular fatty acid synthesis, we suggest that the activities of Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase could be regulated through a mechanism involving changes in the NADPH requirement. Here, we have studied the effect of changes in the flux through different NADPH consuming pathways on the NADPH/NADP ratio and on Glucose-6-Phosphate and 6-Phosphogluconate levels. The results show that: i) an increase in consumption of NADPH, caused by activation of fatty acid synthesis or the detoxification system which consumes NADPH, is paralleled by an increase in levels of these enzymes; ii) when increase in consumption of NADPH is prevented, Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase levels do not change.

Animals↗
PubMed1990

Determination of levels of biogenic amines and their metabolites and both forms of monoamine oxidase in prefrontal cortex of aged rats.

Levels of dopamine, noradrenaline and serotonin and their metabolites and the activities of monoamine oxidase A and B, have been determined in the prefrontal cortex of the rat during ageing. Serotonin turnover rate has been measured as 5-hydroxytryptophan accumulation rate after central decarboxylase inhibition. The major changes were an increase of dopamine and noradrenaline levels and a decrease of serotonin in aged animals compared with control animals. A decrease of the MAO-A to MAO-B ratio was found in aged rats.

Aging↗
PubMed1990

Desipramine blocks stress-induced prolactin release in rats: role of central beta-2 adrenoceptors.

1. The present study was designed to examine the relationship between beta-adrenoceptors and the enhanced, sustained prolactin secretion induced by immobilization stress in rats. 2. Chronic administration of desipramine (15 mg kg-1 day-1, intraperitoneally) for 7 days, a procedure that desensitizes central beta-adrenoceptors, partially inhibits stress-induced prolactin release. 3. Intracerebroventricular administration of the beta-2 adrenoceptor agonist salbutamol (1 microgram/rat) to rats pretreated with desipramine for 7 days, 15 min before immobilization, significantly relieved the inhibition by desipramine 5 and 10 min after the initiation of stress but the effect was not demonstrable after 20 and 40 min. 4. We conclude that beta-2 adrenoceptors play a role in the control of prolactin release in response to stress.

Albuterol↗
PubMed1989

Implication of lysine residues in the loss of enzymatic activity in rat liver 6-phosphogluconate dehydrogenase found in aging.

During aging, there is a decrease in the activity of the 6-phosphogluconate dehydrogenase enzyme in rat liver. The "old" 6-phosphogluconate dehydrogenase enzyme is about 26% less active than the "young" enzyme. In this paper, some biochemical and chemical properties of this enzyme are studied. 2,4,6-Trinitro-benzenesulfonic acid measurements indicate that the old enzyme has 11 lysine residues less than the young enzyme. The proteolysis with trypsin produces more peptides in the young enzyme than in the old one. However, similar numbers of peptides were produced when endoproteinase Arg-C was used on both enzymes. Moreover, the treatment of the young enzyme with ascorbate for 15 min produces the loss of 8 lysine residues. These results suggest that during aging there is a modification of the lysine residue, and this could be involved in the loss of its enzymatic activity.

Aging↗
PubMed1989

Inhibition of fatty acid biosynthesis by bezafibrate in different rat cells.

Bezafibrate is one of the main drugs used in the treatment of human hyperlipemic diseases. Its action on the biosynthesis of fatty acids has been studied and the following conclusions have been drawn: (1) Lipogenesis from glucose is inhibited in hepatocytes and adipocytes isolated from "refed" rats previously treated with bezafibrate. (2) Lipogenesis from glucose is inhibited by bezafibrate in hepatocytes and adipocytes isolated from "refed" rats. (3) Lipogenesis from glucose is also inhibited by bezafibrate in acini isolated from lactating rats. These results show that bezafibrate is an inhibitor of fatty acid synthesis.

Adipose Tissue↗
PubMed1989

Determination of monoamines and both forms of monoamine oxidase in the rat's substantia nigra during postnatal development.

Changes in biogenic amine content in the substantia nigra and in both forms of monoamine oxidase in substantia nigra and striatum of the rat during postnatal development (15-180 days) have been studied. Dopamine and serotonin had the same levels at day 15, however, each monoamine showed a different developmental profile. Dopamine levels and their metabolites (except 3-methoxytyramine) decreased during postnatal development. Serotonin levels and their main metabolite, 5-hydroxyindolacetic acid, underwent an increase during all stages studied. There were no statistically significant changes in noradrenaline levels until day 180 when they increased with respect to day 15. The highest activity of the monoamine oxidase-A in substantia nigra coincided with the highest 5-hydroxyindolacetic acid:serotonin ratio. Monoamine oxidase-A in the striatum did not change contrary to that which happened in substantia nigra. The monoamine oxidase-B:monoamine oxidase-A ratio increased during development both in the substantia nigra and the striatum. The significance of these changes is discussed.

Aging↗
PubMed1989

Age-related changes of catecholamines and their metabolites content in the visual system of the rat.

The changes in the content of the catecholamines in each structure of the geniculate and extrageniculate visual system of the rat during the aging period (6-30 months) have been studied. Dopamine was found at lower levels than noradrenaline in all the structures. The dopamine and noradrenaline showed different developmental profiles. Dopamine and its metabolite levels decreased in the lateral geniculate and visual cortex and increased in superior colliculus and posterior thalamus. Noradrenaline and its metabolites increased in all structures during the aging period. However, 3-methoxy-4-hydroxyphenylglycol/noradrenaline and normetanephrine/noradrenaline ratios decreased in all structures except in superior colliculus. These results suggest age-related changes in the catecholamines in the visual system of the rat.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Operant conditioning of behavioral variability using a percentile reinforcement schedule.

The present investigation developed and tested a new percentile reinforcement schedule suited to study pattern variability, whose main feature was the relative dissociation it provided between the variability requirement defining criterional responses and overall probability of reinforcement. In a discrete-trials procedure, pigeons produced patterns of four pecks on two response keys. If the pattern emitted on the current trial differed from the N preceding patterns, reinforcement was delivered with probability mu. The schedule continuously adjusted the criterion N such that the probability of a criterional response, estimated from the subject's recent behavior, was always constant. In these circumstances, the criterion corresponded to an invariant percentile in the distribution of recent responses. Using a between-subjects design, Experiment 1 manipulated the variability requirement--the percentile--while keeping overall reinforcement probability constant. The degree of variability varied directly with the requirement. In addition, an inverse relationship existed between the requirement and within-group variance. Experiment 2 manipulated probability of reinforcement while maintaining the variability requirement constant. No consistent relationship was found between variability and reinforcement probability. A tentative hypothesis was advanced ascribing the operant conditioning of behavioral variability to a process of probability-dependent selection.

Animals↗
PubMed1988

Possible involvement of histidine residues in the loss of enzymatic activity of rat liver malic enzyme during aging.

During aging there is a decrease in activity of the malic enzyme in rat liver. The "old" malic enzyme is about 36% less active than the "young" enzyme. Some properties and modifications of amino acid residues are studied here (--SH, arginine, methionine, histidine, lysine) to try and check on the existence of any relationship between them and the loss of enzymatic activity during aging. Diethyl pyrocarbonate measurements indicate that the old enzyme has 1 histidine residue less than the young enzyme. Moreover, the treatment of the young enzyme with ascorbate for 15 min produces the loss of 36% of the enzymatic activity and the loss of 1.2 histidine residues. These results suggest that during aging the modification of the histidine residue could be involved in the loss of its enzymatic activity.

Aging↗