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Biomedical subjects

A Palou

Publications and source records attributed to A Palou.

At least 73 records · Page 4Linked to original sources
PubMed1995

Decrease of the pool of amino acids adsorbed on blood cell membranes caused by starvation in rats.

The effect of 24 h starvation on the pool of amino acids adsorbed on the blood cell membranes was determined in Wistar rats. Aortic and iliac blood was analysed. 24 h starvation induced a significant decrease in the combined essential amino acids adsorbed on the blood cell membranes, in both arterial and venous blood, without affecting whole-blood levels (adsorbed + non-adsorbed). The same tendency was extended to most of the individual amino acids. This finding indicates that this pool of adsorbed amino acids has a rapid turnover and probably plays a physiological role in a situation of exogenous food deprivation.

Adsorption↗
PubMed1995

Estrogen effects on blood amino acid compartmentation.

The present paper focuses on the study of blood amino acid compartmentation in healthy men (lean and obese) and women, with special emphasis on the estimation of the recently described blood-cell adsorbed amino acid pool. The wide range of changes found in this pool on comparing different physiological situations may be attributable to its proposed characteristic high dynamism on the one hand, but also to the influence of other factors such as hormones. Along these lines, the sex- and obesity-linked variations found here in human blood led to the speculation as to whether these differences could be related to the influence of estrogens. This hypothesis was further tested by chronically treating a group of male rats with estrone and checking their subsequent blood amino acid compartment changes (which yielded a greater difference in the adsorbed pool). From the overall results obtained it may be concluded that the higher production of estrogens in women and obese men affects amino acid availability to the tissues by modulating the blood-cell adsorbed amino acid pool through a mechanism that is, at present, unknown.

Adult↗
PubMed1995

Protein and amino acid intake in cafeteria fed obese rats.

Food selection pattern and portal blood amino acid profile were examined in rats given a cafeteria diet. Compared to standard-diet fed rats, cafeteria-diet fed rats consumed more energy. Increase in energy intake was attributable to an increase in fat intake. Protein intake was slightly higher and carbohydrate intake remained constant and was similar to levels consumed by standard-diet fed rats. The cafeteria rats took up higher quantities of Phenylalanine+Tyrosine, Arginine, Histidine, Lysine, Leucine, Isoleucine, Valine, Threonine, and Glycine, lower quantities of Tryptophan and the same quantity of Methionine+Cysteine vs. control rats. Portal concentrations of Serine, Threonine, Tryptophan and Lysine were significantly higher in cafeteria-diet fed rats than in standard-diet fed rats. This can be interpreted in such a way that, on the whole, the quality of protein ingested by cafeteria and control rats is similar. No statistical differences in the ingestion of individual amino acids were observed between different days of the period of cafeteria diet feeding, thus the idea of a strict control of protein ingestion irrespective of the obese status is reinforced.

Amino Acids↗
PubMed1995

Enzymatic determination of carbon (14C)-labeled glycerol in biological samples.

A method for determination of glycerol-specific-radioactivity in biological samples is presented. It is based on the following steps: (a) enzymatic conversion of glycerol to dihydroxyacetone-phosphate, (b) quantitative trapping of dihydroxyacetone-phosphate in SPE amino (NH2) columns, (c) eluation with HCl 0.5 N of dihydroxyacetone-phosphate followed by radioactivity counting and (d) estimation of the radioactivity thus trapped compared with that of enzymatically untreated aliquots of the same samples. No interferences from other 14C-labeled materials tested such as D-glucose, L-alanine, L-glutamine and D-beta-hydroxybutyrate were observed. This inexpensive and high-speed method can be applied in routine multiple estimations of glycerol-specific-radioactivity in biological samples in tracer metabolic studies.

Animals↗
PubMed1995

In vitro adsorption of amino acids onto isolated rat erythrocyte membranes.

Amino acids adsorbed onto blood cell membranes represent about 8% of the total amino acids in blood. The aim of this study was to determine the in vitro adsorption kinetics of different amino acids (L-alanine, glycine, L-glutamate, L-glutamine, L-phenylalanine and L-leucine) onto rat erythrocyte membranes and to assess the effect of 24-hr starvation on these adsorption kinetics. Isolated red cell membranes were incubated at 37 degrees C for 10 sec in the presence of 14C-amino acids--with different specific radioactivity--the radioactivity retained in the membrane fraction measured and kinetic parameters of amino acid adsorption determined. With the exception of glutamate, where the adsorption was negligible, all amino acids studied were adsorbed onto isolated red cell membranes, adhering to simple Michaelis-Menten kinetics. Km' values of glycine, phenylalanine and leucine adsorption in control rats (14.7 +/- 3.8 mM, 8.41 +/- 0.95 mM and 4.65 +/- 0.46 mM respectively, SEM, n = 6-8) decreased in response to 24-hr starvation, giving the following values: 0.792 +/- 0.122 mM, 5.32 +/- 0.82 mM and 3.53 +/- 0.31 mM respectively (SEM, n = 6-8), Vmax' value of glycine adsorption of control rats decreased (from 61.0 +/- 15.5 mmol/mol P/sec to 4.25 +/- 0.70 mmol/mol P/sec, SEM, n = 7) and that of leucine increased (from 13.5 +/- 1.0 mmol/mol P/sec to 18.9 +/- 2.0 mmol/mol P/sec, SEM, n = 7) as an effect of 24-hr starvation. This study shows that alanine, glycine, glutamine, phenylalanine and leucine, but not glutamate, adsorbed onto erythrocyte membranes according to Michaelis-Menten-like kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed1994

Stabilization of the mRNA for the uncoupling protein thermogenin by transcriptional/translational blockade and by noradrenaline in brown adipocytes differentiated in culture: a degradation factor induced by cessation of stimulation?

The stability of the mRNA coding for the uncoupling protein thermogenin was investigated in mouse brown-fat cells differentiated in culture. After 7 days in culture, the cells were stimulated for 24 h with noradrenaline, and a high level of thermogenin mRNA was then observed. If noradrenaline treatment was continued, the mRNA level remained high, but, upon withdrawal of noradrenaline, the level decreased rapidly, with a half-life of only 2.7 h. The presence of transcriptional (actinomycin) or translational (cycloheximide) inhibitors prolonged the apparent half-life by about 50%. The presence of noradrenaline during transcriptional blockade led to a further stabilization of thermogenin mRNA. It was concluded that an induced (or short-lived) gene product is important for thermogenin mRNA degradation. Direct interaction of noradrenaline with the cultured brown adipocytes could apparently not mimic the paradoxical destabilization of thermogenin mRNA in vivo, previously observed in the cold-exposed mouse [Jacobsson, Cannon and Nedergaard (1987) FEBS Lett. 244, 353-356], indicating significant differences between the systems in vitro and in vivo.

Adipocytes↗
PubMed1994

Cold exposure induces different uncoupling-protein thermogenin masking/unmasking processes in brown adipose tissue depending on mitochondrial subtypes.

The effect of cold exposure on thermogenic parameters such as mitochondrial protein content, GDP-binding and uncoupling protein (UCP) levels in different mitochondrial fractions from rat brown adipose tissue has been investigated. Rats were exposed from 12 h to 5 days at 4 degrees C, and three mitochondrial fractions were isolated by differential centrifugation: the M1 fraction (1000 g), the M3 fraction (3000 g) and the M15 fraction (15,000 g). Cytochrome c oxidase activity as an index of mitochondrial mass showed an increase during cold exposure. During the first 24 h of cold exposure UCP was incorporated specifically into the M3 and M15 mitochondrial fractions, and thereafter UCP appeared in the heaviest M1 fraction. However, specific GDP binding was increased during the first 24 h in the same way in all subpopulations, and this increase continued up to 72 h of cold exposure. Results suggest that different molecular events are involved during acute and chronic adaptation to cold: during the first 24 h of cold acclimatization, thermogenic activity is increased by an unmasking process of the UCP binding sites in the M1 mitochondrial fraction as UCP levels were constant and GDP binding increased, but in the M3 and M15 fraction the increase in thermogenic activity was completely due to an increase in GDP binding induced by a specific incorporation of UCP targeted to these mitochondria. Thus thermogenic parameters change in a different way in the brown-fat mitochondrial subpopulations during cold acclimatization.

Acclimatization↗
PubMed1994

Blood cell to plasma gradients of amino acids in arterial and venous blood in fed and fasted rats.

Measurement of amino acid concentrations in blood cells and plasma, and the calculated blood cell to plasma gradients (C/P) from both afferent and efferent vessels to tissues, allowed evaluation of the effect of several tissues (splanchnic bed, skeletal muscle and kidney) on blood amino acid distribution in fed and starved rats. Combined effects of tissues and erythrocyte transport capabilities determined specific C/P values for each amino acid. For amino acids related to the L-system, the high capacity of this erythrocyte transport many buffer some C/P changes as an effect of tissue metabolism. For less permeable amino acids (like Asp and Glu) plasma changes were mainly responsible for changes in C/P values, whereas for other amino acids (such as basic amino acids) blood cells became the main determinants of C/P changes, mainly in starvation. In general, the role of erythrocytes in amino acid transport was enhanced in starvation.

Amino Acids↗
PubMed1994

Amino acid distribution in human blood. A significant pool of amino acids is adsorbed onto blood cell membranes.

The recently published existence of a pool of amino acids absorbed onto the blood cell membranes in the rat has provided a new insight into the role of the blood cell amino acid pools, in the context of tissue-blood amino acid transport and their metabolic relationships. In the present study, this pool has been measured in a large (n = 40) representative healthy human population. This pool represents 9% of the blood cell amino acids, which is somewhat lower but in the same order as that previously measured in the rat. The inside-erythrocyte and plasma pools have also been quantified, giving an inside to outside ratio of 1.32 for the combined total amino acids. Statistically significant age related changes in the different blood compartments were detected for some amino acids (aspartate, asparagine, glutamine, tyrosine, methionine, phenylalanine, tryptophan and lysine) as well as for the ratio of tryptophan to the large neutral amino acids. The results obtained emphasize the importance of the amino acid red blood cell pool and assign to it the same order as the plasma pool. The results also feature the membrane-attached pool of some specific amino acids, ie taurine, glutamine, glutamate, aspartate and valine.

Adult↗
PubMed1994

Brown and white adipose tissue adaptive enzymatic changes on amino acid metabolism in persistent dietary-obese rats.

The objective was to determine the effects of persistent obesity on amino acid enzymes in white (WAT) and brown (BAT) adipose tissues. Dietary obesity was induced by feeding a cafeteria diet ad libitum for 3 months, then it was removed and the obese animals received the same diet as controls for 5 months. Dietary-induced obesity was persistent as obese rats showed a stable, higher body weight than controls (26%). Key enzymes of alpha-amino nitrogen metabolism were studied and results showed reduced activities in obese rats: glutamine synthetase (45%), AMP deaminase (52%), alanine aminotransferase (66%) and glutamate dehydrogenase (68%) in BAT, whereas WAT of obese animals only showed lower aspartate aminotransferase activity (47%) with respect to the controls. We can conclude that these adaptations in amino acid metabolism were exclusively dependent on the obese status as they were observed in an obesity model in which obese rats eat the same diet as controls.

AMP Deaminase↗
PubMed1994

Blood amino acid compartmentation in obese rats is specifically altered in the iliac vein.

Amino acid concentration in blood cells and plasma and the calculated blood cell to plasma gradients (C/P) were measured in different blood vessels (aortic artery and portal, hepatic, iliac and renal veins) from both control and cafeteria diet obese rats. Essential amino acids are increased in plasma in all blood vessels in obese rats. The iliac vein was the only vessel in which cell concentration of amino acids, and mainly the mean of the combined non-essential amino acids, was affected by obesity. Only in the iliac vein were C/P values of the combined amino acids, including both essential and non-essential, significantly lower in obese versus control rats. These results also show that there are differences between sampling sites which should be noted in the design of physiological studies of amino acid metabolism.

Amino Acids↗
PubMed1993

Combined enzymic and chromatographic techniques to determine specific radioactivity in free and triglyceride fatty acid plasma fractions.

A reliable method to determine both free and triglyceride fatty acids and simultaneously to determine the specific radioactivity in each fraction has been developed. The procedure can be used to analyse a large number of samples. Lipoprotein lipase was used to hydrolyse triglyceride fatty acids, and a Carbopack B column was used to isolate free fatty acids. The radiolabeled fatty acids were determined by liquid scintillation counting, and individual fatty acid levels in each fraction were determined by gas chromatography. Free and triglyceride fatty acids were eluted in different fractions from the Carbopack B column. No interferences from other compounds were significant.

Amino Acids↗
PubMed1993

"In vivo" glutamic acid metabolism in late pregnant rats.

Glutamic acid metabolism in 24-hour starved 20-day pregnant and control non-pregnant rats, following intravenously administered [14C]-glutamic acid has been studied. The utilization of glutamate as a gluconeogenic precursor is not increased in late pregnancy under 24-hour starvation and it is regulated by the lower blood substrate availability. In addition, the steady state levels of glutamate, glutamine, aspartate, protein and glucose in blood, liver and skeletal muscle, together with tissue glycogen and lipids and metabolite composition pools, are given for both non-pregnant and pregnant rats.

Animals↗
PubMed1993

Opposite response to starvation of Trp/LNAA ratio in lean and obese Zucker rats.

Total blood and plasma free amino acids and plasma urea levels were studied in fed and 24 h fasted Zucker rats. In fed animals there were no differences between obese and lean rats in the overall essential and non essential blood free amino acids. However, starvation reduced blood amino acid levels in the obese animals compared to the lean group, mainly due to changes in the plasma compartment. The reduction of available amino acids from plasma in the obese rats during starvation affected most of the amino acids, including the branched chain amino acids, which showed higher levels in the fed situation than in lean rats. Of particular interest is the opposite response to starvation in lean and obese Zucker rats concerning the plasma ratio of tryptophan (Trp) to the large neutral amino acids (LNAA) which could be implicated in the alteration of food intake and energy expenditure characteristic of obesity.

Amino Acids↗
PubMed1992

Induction and degradation of the uncoupling protein thermogenin in brown adipocytes in vitro and in vivo. Evidence for a rapidly degradable pool.

The induction and degradation of the brown-fat-specific uncoupling protein thermogenin in brown fat cell cultures was investigated. Cultures were initiated with undifferentiated precursor cells from young mice and the amount of thermogenin was determined by immunoblotting. High levels of thermogenin could be induced by noradrenaline treatment in cells grown for more than 5 days in culture, and in such cell cultures continuously stimulated with noradrenaline, the thermogenin level continued to increase for at least a further 5 days. In cell cultures stimulated for only 24 h, the induced thermogenin was subsequently specifically and rapidly degraded, with a half-life of 20 h. As the half-life was prolonged by cycloheximide treatment, the degradation was apparently due to the induction of specific proteins after cessation of adrenergic stimulation. In cell cultures continuously stimulated with noradrenaline for 5 days, the induced thermogenin was degraded much more slowly after noradrenaline removal, with a half-life of 70 h. This half-life was unchanged by cycloheximide treatment, and the degradation after cycloheximide was in parallel with the degradation of protein in general, and was therefore non-specific. The prolongation of the half-life of thermogenin after the chronic treatment may be related to mitochondrial incorporation of thermogenin and consequent stabilization of the protein. The half-life of thermogenin in an in vivo situation of similar experimental design (the reacclimation of mice to warm after 5 days in the cold), was also long (about 7 days), and the loss was also non-specific, as it paralleled the loss of protein. Thus different molecular events are involved in thermogenin degradation when the protein is found in different functional pools.

Adaptation, Physiological↗
PubMed1992

Thermogenic actions of tryptophan in the rat are mediated independently of 5-HT.

Serotonin (5-HT) has been implicated in the central control of energy balance, via inhibition of food intake and stimulation of thermogenesis. Its rate of synthesis in brain is dependent on the availability of its precursor amino acid, tryptophan. The objective of the present study was therefore to investigate the thermogenic actions of tryptophan and to determine whether these actions are mediated by 5-HT. Central or peripheral injections of 5-HT (i.c.v.; 0.5-40 micrograms), 5-hydroxytryptophan (5-HTP) (i.c.v.; 20 micrograms) or tryptophan (i.p.; 20 mg/kg, i.c.v.; 12-60 micrograms) significantly increased resting oxygen consumption (VO2 by approximately 15-20%) in conscious rats, without apparent effects on physical activity. Small increases (5-7%) in VO2 were also observed following peripheral injections of aspartate or glycine (20 mg/kg) but not taurine, whilst central injections of tyrosine or leucine (15-18 micrograms) significantly increased VO2 by 15%. We have previously reported that the thermogenic and anorexic actions of 5-HT are mediated by corticotropin-releasing factor (CRF). In the present study, the thermogenic actions of 5-HTP, like those of 5-HT, were significantly reduced by pretreatment (5 min before) with the CRF antagonist alpha-helical CRF9-41 (25 micrograms, i.c.v.) or a polyclonal antibody to CRF. However, the thermogenic actions of tryptophan were not significantly modified by pretreatment with either the 5-HT antagonist, methysergide (20 micrograms, i.c.v.) or with the CRF antagonist or antibody and thus appear to act through different mechanisms to 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptophan↗
PubMed1992

Metabolic utilization of muscular L-proline in 24-hr starved rats.

1. The aim of this paper was to study the in vivo skeletal muscle L-proline related to its destination to other key tissues such as liver and intestine as well as to give some insight into the role of blood cells in proline handling. 2. L-U-[14C]Proline was injected intramuscularly and following by sampling of blood, liver, intestine and contralateral muscle at 20 and 30 min after injection. 3. The distribution of radioactivity between blood cells and plasma and in total and individual amino acids, protein and glycogen fractions was determined in the above tissues. 4. The pattern of well fed rats was compared with those submitted to 24-hr complete starvation. 5. During starvation a minor degree of proline oxidation occurs. 6. The main destruction of proline in the liver seem to be the synthesis of proteins. 7. The radioactivity recovered in the blood proline fraction of starved rats is twice that of the fed rats and that it could be attributed mainly to plasma protein. 8. We have obtained in vivo evidence for the role of erythrocyte in the interorgan proline transport.

Animals↗