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X Remesar

Publications and source records attributed to X Remesar.

At least 109 records · Page 6Linked to original sources
PubMed1993

A radio-enzymatic method for the estimation of L-leucine-specific radioactivity.

A method is presented for the estimation of L-leucine concentration and radioactivity in biological samples. The sample L-leucine is specifically bound to tRNA and its radioactivity estimated in the presence of either added labelled L-leucine or cold L-leucine (in the same proportion), as well as in the presence of a large excess of cold L-leucine. The latter gave the measurement of non-leucine radioactivity present in the sample. The measurements in the presence and absence of labelled/cold L-leucine allowed the estimation of L-leucine levels and radioactivity by using a simple set of calculations and a standard curve built with known cold L-leucine concentrations in the presence of a fixed known amount of [14C]L-leucine.

Alanine↗
PubMed1993

Cooling rates of tissue samples during freezing with liquid nitrogen.

The time-course of temperature changes undergone by tissue samples during freezing in liquid nitrogen has been studied with small thermocouple probes. The specific heat of liver, muscle, adipose tissue and blood has been measured with a calorimeter. Most tissues have lower specific heat values than water. The lower thermal conductance of adipose tissue and fat muscle result in much longer freezing times. It may take an inordinate amount of time for tissue samples to freeze when immersed in liquid nitrogen; in addition, not all tissues behave in the same way, so it takes longer for a muscle sample to freeze than for a piece of liver. These differences between tissues are considerable and may affect the outcome of experiments if not taken into account.

Adipose Tissue↗
PubMed1993

Rates of utilization of intravenous oleylanilide administered chronically to the rat.

The constant injection of [14C]oleylanilide into the vena cava of Wistar rats for 7 days with osmotic minipumps was used to estimate tissue distribution of chronically administered anilides. The largest concentrations of the anilide were found in the brown adipose tissue; all other tissues showed much lower proportions. When anilide distribution was expressed as nmol/g lipid, the high concentration of the compound in the brown adipose tissue contrasted with its very low presence in the white adipose tissue; all other tissues showed intermediate concentrations. Anilide-treated rats consumed more food and lost more weight than did controls; their energy balance showed higher energy inefficiency. The results suggest a possible effect of anilides on the thermogenic pathway of the rat brown adipose tissue. In addition, there was a large individual variability in the proportions of anilide present in all tissues, from as little as 0.3% of the total anilide injected in some animals to 6% in others.

Adipose Tissue↗
PubMed1993

Water balance in Zucker obese rats.

The water balance in Wistar, Zucker obese and Zucker lean rats, aged 60 days, was measured by determining the amount of water they drank, that contained in the solid food eaten, the water lost through urine and droppings, the net water accrued (estimated from the composition of the body and the daily increase in body weight), the measurement of the water vapour lost and the calculation of metabolic water production by means of the measurement of oxygen consumption, carbon dioxide production and protein oxidation in a 24 hr period. 1. Despite widely different body weights, all three groups of animals accrued a similar proportion of their daily water budget (4.3-4.9%, i.e. 1.2-1.4% of the total rat water mass). 2. Wistar and Zucker obese rats had a similar daily water budget despite very different body weights, lean Zucker rats had lower water budgets. 3. Obese and lean Zucker rats produced a more concentrated, and excreted much less urine (the highest urea concentration was found in obese rats) than Wistar rats. 4. The water lost in the droppings was in the same range as that in urine for obese rats, slightly less for lean Zucker rats and much less in Wistar rats. Obese rats produced a higher amount of stool with respect to the amount of food eaten than the lean animals studied. 5. The contribution of metabolic water to the daily water budget was a 23.6% for Zucker obese, 22.5% for Zucker lean and 15.9% for Wistar rats.

Animals↗
PubMed1993

Lipid synthesis: a thermogenic mechanism in cold-exposed Zucker fa/fa rats.

1. The oxygen consumption and carbon dioxide production of Wistar and Zucker lean (Fa/?) and obese (fa/fa) rats was measured at 4, 10, 20 and 30 degrees C. 2. There was a net synthesis of lipid at the expense of carbohydrate in Wistar rats at 20 degrees C, with active lipid oxidation at 4 degrees C, and increasing heat production at lower temperature. Zucker lean rats also showed this trend. 3. Zucker fa/fa rats synthesized lipid at 4, 10 and 20 degrees C, showing a less marked increase in heat production with lowering temperature. 4. It is postulated that Zucker obese rats synthesize lipids as a way to obtain residual metabolic heat to maintain their body temperature. This is part of a process--fully functional in Wistar and Zucker lean rats, and truncated in Zucker obese rats--in which liver lipogenesis can combine with brown adipose tissue lipolysis to generate enough heat to maintain body functions under a cold environment.

Animals↗
PubMed1993

Intestinal and hepatic nitrogen balance in the rat after the administration of an oral protein load.

The fate of a small oral dose of protein given to overnight-starved rats was studied. After 3 h, 62% of the protein amino acids had been absorbed. Most of the absorbed N went into the bloodstream through the portal in the form of amino acids, but urea and ammonia were also present. About one-quarter of all absorbed N was carried as lymph amino acids. The liver was able to take all portal free ammonia and a large proportion of portal amino acids, releasing urea. The hepatic N balance was negative, indicating active proteolysis and net loss of liver protein.

Amino Acids↗
PubMed1993

Methodological evaluation of indirect calorimetry data in lean and obese rats.

1. The applicability of current indirect calorimetry formulae to the study of energy and substrate balances on obese rats has been evaluated. The energy consumption of series of 60-day rats of Wistar, lean and obese Zucker stock were studied by means of direct and indirect calorimetry, and by establishing their energy balance through measurement of food intake and retention. Calorimetric studies encompassed a 24 h period, with gas and heat output measurements every 2 or 5 min, respectively, for direct and indirect calorimetry. 2. The analysis of fat composition (diet, whole rat, and synthesized and oxidized fat) showed only small variations that had only a limited effect on the overall energy equation parameters. 3. A gap in the nitrogen balance, which represents a urinary N excretion lower than the actual protein oxidized, resulted in significant deviations in the estimation of carbohydrate and lipid oxidized when using the equations currently available for indirect calorimetry. 4. Analysis of the amino acid composition of diet and rat protein as well as of the portion actually oxidized, and correcting for the nitrogen gap allowed the establishment of a set of equations that gave better coincidence of the calculated data with the measured substrate balance. 5. The measured heat output of all rats was lower than the estimated values calculated by means of either indirect calorimetry of direct energy balance measurement; the difference corresponded to the energy lost in water evaporation, and was in the range of one-fifth of total energy produced in the three rat stocks. 6. Wistar rats showed a biphasic circadian rhythm of substrate utilization, with alternate lipid synthesis/degradation that reversed that of carbohydrate, concordant with nocturnal feeding habits. Zucker rats did not show this rhythm; obese rats synthesized large amounts of fat during most of the light period, consuming fat at the end of the dark period, which suggests more diurnal feeding habits. Lean Zucker rats showed a similar, but less marked pattern. 7. The results obtained indicate that lean and obese rats can be studied using the same indirect calorimetry formulae provided that there is an adequate measure of protein oxidation and the composition of diet does not differ.

Amino Acids↗
PubMed1993

Short-term oscillations of aortic core temperature and thermogenic organ blood flow in the rat.

Core and organ temperatures in the rat have been found to be subject to regular periodic oscillations (with a frequency of ca 12 cycles per day, i.e. 143 mu Hz) within set limits, by using a chronic thermocouple implant procedure. These cycles consisted of consecutive warming (the temperature increased steadily) and cooling periods (the temperature decreased regularly). There were sustained temperature differences between several tissues and that of the aortic blood (core temperature), higher for brown adipose tissue, kidney and liver, and lower for muscle, white adipose tissue and skin. Organ blood flows and cardiac output were measured by a radioactive microsphere retention method applied to unanaesthetized rats. Blood flow measurements were done on unaware rats (see Methods), during either the warming or cooling phases. During the warming phases, there was a higher blood flow across the brown adipose tissue, kidney and skin, with a cardiac output about twice that found in the cooling periods. The haemodynamic changes observed, as well as the organ temperature differences observed with respect to the blood, suggest that periodic changes in blood flow are an essential part of the operation of the thermogenic system.

Activity Cycles↗
PubMed1993

Dietary amino acid balances in young Wistar rats fed a cafeteria diet.

The amino acid composition of the diet ingested by reference and cafeteria diet-fed rats has been analyzed in Wistar rats from day 30 to 60 after birth. Body protein amino acid composition and the urinary and faecal losses were also measured. Cafeteria diet resulted in a higher proportion of amino acids extracted from the diet, although this diet had a very similar amino acid composition to that of the standard reference diet. The net rates of amino acid accretion into body protein were similar for cafeteria and reference diet-fed rats, resulting in a comparable net overall accumulation of protein. Urinary losses of amino acids were small, but higher for reference diet-fed rats. Cafeteria feeding leads to an essentially equal amino acid intake pattern to that resulting from the reference diet. In addition, cafeteria-feeding resulted in a similar amino acid nitrogen intake and practically equal amino acid availability, which is translated into higher net protein accrual and lower nitrogen losses in cafeteria-fed rats. It is postulated that the lower protein-energy proportion of the cafeteria diet--and not its amount in absolute terms--could trigger a series of amino acid-sparing mechanisms that eventually result in even higher amino acid availability, which leads to increased net protein deposition and a wider nitrogen gap.

Amino Acids↗
PubMed1993

Effect of chronic intravenous injection of steroid hormones on body weight and composition of female rats.

The effects of the constant infusion with mini-osmotic pumps of several steroid hormones on body weight, energy balance and protein/lipid/water composition in young female rats has been studied for a period of 15 days. Despite unchanged food consumption, progesterone strongly induced fat deposition, with higher protein accrual efficiency coupled with lowered energy losses through thermogenesis. Estrogens lowered body weight but maintained higher protein levels and protein accrual rates; beta-estradiol induced the loss of lipid and diminished food intake. Heat production was unchanged or lower in all estrogen-treated animals; beta-estradiol had a more marked effect on body weight (through food intake, heat production and lipid mobilization/storage combined) than estrone. Testosterone and 5-androstenediol increased the proportion of protein, but none of them had a significant effect on lipid deposition or heat production. Nortestosterone, increased energy expenditure, fuelled in part by a higher food ingestion, a trait shared by 4-androstenedione, but not by the other androgens. The effect of androgens on body weight may thus be a combination of their actions on a) food intake, b) efficiency of protein deposition and c) activation of heat production or of lipid (energy) storage. Practically all increased the efficiency of protein deposition. Nortestosterone increased heat production. Androstenedione increased lipid storage. Dehydroepiandrosterone did not decrease body weight or metabolic rate. Cortisol depressed heat production and food intake, with a net loss of weight. Cortisol and cortisone did not increase protein deposition, but corticosterone did; deoxycorticosterone showed a high efficiency of protein deposition and increased the size of fat stores, also increasing the metabolic rate by a mean 26% versus controls, compared with a reduction of about the same magnitude induced by cortisol. The data presented suggest that cortisol-cortisone and corticosterone may represent two distinct groups of glucocorticoids.

Androgens↗
PubMed1992

Fatty acid utilization by young Wistar rats fed a cafeteria diet.

The content and accretion of fatty acids in 30, 45 and 60-day old Wistar rats fed either reference chow or a cafeteria diet has been studied, together with their actual fatty acid intake during that period. Diet had a small overall effect on the pattern of deposition of fatty acids, but the deposition of fat was much higher in cafeteria rats. The fat-rich cafeteria diet allowed the direct incorporation of most fatty acids into lipid storage, whilst chow-feeding activated lipogenesis and the deposition of a shorter chain and more saturated type of fatty acids. During the second month of the rat's life, the elongation pathway as well as delta 9-desaturase became functional, thus helping to shape the pattern of fatty acids actually accrued. The 60-day rats showed a relative impairment in the operation of delta 5-desaturase, since their lipids had a higher C20:4/C20:3 ratio than those of the diet ingested. Cafeteria-diet feeding minimized this effect since the large supply of dietary polyunsaturated fatty acids made the operation of the elongation-desaturase pathways practically unnecessary.

Aging↗
PubMed1992

Changes in alanine and glutamine transport during rat red blood cell maturation.

Alanine and glutamine transport have been studied during red blood cell maturation in the rat. Kinetic parameters of Na(+)-dependent L-alanine transport were: Km 0.43 and 1.88 mM and Vmax 158 and 45 nmoles/ml ICW/min for reticulocytes and erythrocytes, respectively. During red cell maturation in the rat there is a loss of capacity and affinity of the system ASC for L-alanine transport. The values for Na(+)-dependent L-glutamine transport in reticulocytes were Km 0.51 mM and Vmax 157 nmoles/ml ICW/min. On the other hand, a total loss of L-glutamine transport mediated by both N and ASC systems is demonstrated in mature red cells. This seems to indicate that during rat red cell maturation the system N disappears. Furthermore, the system ASC specificity in mature cells changes, and glutamine enters the red cell by non-mediated diffusion processes.

Alanine↗
PubMed1992

Membrane vesicles from brown adipose tissue: a tool for the study of amino acid transport. The case of L-alanine.

A density gradient method is used to isolate membrane vesicles from brown adipose tissue. These respond to changes in osmolarity and show the classical overshoot pattern when L-alanine uptake is assayed. Transport is shown to be effected by two components: a linear (Kd = 0.498 min-1) and Na(+)-dependent saturable component (Km = 2.3 mM) and a Vmax = 19.9 pmol/micrograms protein.min). This pattern is similar to that shown by cells isolated from brown adipose tissue.

5'-Nucleotidase↗
PubMed1992

An enzymatic method for the estimation of L-leucine in rat blood.

A specific enzymatic method for the routine measurement of L-leucine in blood samples is presented. The method uses a commercial preparation of tRNAs and amino acetyl-tRNA synthetases for the specific loading of L-leucine into the tRNA(Leu) present, competing with carrier-free L-[U-14C]leucine. The radioimmunoassay-like plot of radioactivity found in the acid-insoluble (tRNA) fraction was used to determine the amount of unlabelled L-leucine of the samples when compared against a standard curve. The interference of L-isoleucine, L-valine and L-alanine was very low.

Alanine↗
PubMed1992

Nitrogen balances of lean and obese Zucker rats subjected to a cafeteria diet.

The effects of a cafeteria diet on nitrogen balance in lean (Fa/?) and obese Zucker rats (fa/fa) was studied for two consecutive 15 day periods after weaning. Obese rats were able to absorb a lower proportion of dietary nitrogen than the lean controls. Cafeteria diet increased the retention of dietary nitrogen, and lowered urinary nitrogen losses in both obese and lean rats. Urea constituted practically the only product of urinary nitrogen excretion in obese rats, whereas it accounted for only about 75% of that eliminated by Fa/? rats. Nitrogen accretion in the body was highest for the younger animals, and again increased with cafeteria feeding. Obese fa/fa rats showed a lower percentage of body nitrogen retention than their lean counterparts; obese rats were able, however, to accumulate large amounts of nitrogen and fat, in part because of their higher intake. A significant part of the absorbed nitrogen was not found in either the body or the urine; the cafeteria diet markedly increased the weight of this fraction of nitrogen unaccounted for. In conclusion, the effects of cafeteria feeding on weight and nitrogen handling were comparable in lean and obese rats, i.e. the effects of genetic and dietary obesity seem to be additive with regard to nitrogen extraction and excretion for Zucker rats.

Absorption↗
PubMed1992

Deposition of dietary fatty acids in young Zucker rats fed a cafeteria diet.

The content and accretion of fatty acids in 30, 45 and 60-day-old Zucker lean Fa/? and obese fa/fa rats fed either reference chow or a cafeteria diet has been studied, together with their actual fatty acid intake during each period. Diet had little overall effect on the pattern of deposition of fatty acids, but quantitatively the deposition of fat was much higher in cafeteria-fed rats. The fat-rich cafeteria diet allowed the direct incorporation of most fatty acids into the rat lipids, whilst chow feeding activated lipogenesis and the deposition of a shorter chain and more saturated pattern of fatty acids. Genetic, obesity induced a significant expansion of net lipogenesis when compared with lean controls. Cafeteria-fed obese rats accrued a high proportion of fatty acids, which was close to that ingested, but nevertheless showed a net de novo synthesis of fatty acids. It is postulated that the combined effects of genetic obesity and a fat-rich diet result in high rates of fat accretion with limited net lipogenesis. Lean Zucker rats show a progressive impairment of their delta 5-desaturase system, a situation also observed in obese rats fed a reference diet. In Zucker obese rats, cafeteria feeding resulted in an alteration of the conversion of C18:2 into C20:3. The cafeteria diet fully compensated for these drawbacks by supplying very high amounts of polyunsaturated fatty acids.

Animals↗
PubMed1992

Nitrogen balance discrepancy in Wistar rats fed a cafeteria diet.

The nitrogen balance of Wistar rats aged 30-45 and 45-60 days fed either control or cafeteria diet has been determined by measuring the intake fecal and urinary excretion and nitrogen deposition in the body. The efficiency of extraction of dietary nitrogen was higher for cafeteria diet-fed rats, which showed a lower nitrogen excretion and higher body nitrogen accretion than controls. The accurate measurement of nitrogen intake, excretion and deposition showed a consistent proportion of nitrogen unaccounted for (10-26% of net intake) in the studied fractions, which proportion was higher in the youngest cafeteria diet-fed rats.

Animals↗