Biomedical subjects

I Rafecas

Publications and source records attributed to I Rafecas.

33 records · Page 2Linked to original sources

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

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↗

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

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

Rat intestinal amino acid balances after the administration of an oral protein load.

The intestinal amino acid balances in rats given an oral load of protein were measured three hours after the gavage. During that period, about one half of the nitrogen from the protein given appeared as net balance in the portal blood. The release of amino acids was not a continuous process, since two peaks of maximal intestinal efflux were found at 1 and 2.5 hours after gavage. This pattern followed that of portal blood flow with a 30 minute delay. Under prandial conditions, the intestine showed a net uptake of glutamine, aspartate, serine, threonine, phenylalanine, tyrosine, leucine, isoleucine and valine. It also showed a net production of alanine, glutamate, ornithine skeleton (arginine + citrulline + ornithine) and ammonia. There was also a surge of taurine, attributed to reabsorption of secreted taurine conjugates. There was a net unchanged absorption of glycine, proline, lysine and histidine, with respect to their proportions in the protein administered. The results suggest that the amino acid metabolism in the intestine under prandial conditions is much less passive than is generally assumed. The intestinal action upon the luminal amino acids is not limited to absorption, but is directly implied in their transformation to complement the ensuing homeostatic action of the liver upon them.

Amino Acids↗

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↗

PubMed1991

Plasma amino acids of lean and obese Zucker rats subjected to a cafeteria diet after weaning.

Plasma amino acids of Zucker obese (fa/fa) and lean (Fa/?) rats fed either a reference nonpurified pellet or a cafeteria diet have been studied from 30 to 60 days after birth. Obese rats showed higher plasma branched chain amino acid levels but similar total amino acids, urea and glucose concentrations. The ingestion of a cafeteria diet induced higher levels in many amino acids, as well as in the composite figure in lean rats, but failed to alter total 2-amino nitrogen concentrations in obese rats, despite high levels in several non-essential amino acids and lower values in essential amino acids; urea levels were much lower in rats fed the cafeteria diet. The results are consistent with an impairment of amino acid nitrogen elimination via urea cycle in cafeteria diet-fed rats. This is independent of the hyperinsulinemia-driven plasma accumulation of several essential amino acids induced by genetic obesity. The effects were, then additive.

Amino Acids↗

PubMed1991

Rat liver amino acid balances after the administration of an oral protein load.

The hepatic balances of amino acids, ammonia and urea have been measured in rats for three hours after receiving a protein load. The liver took up practically all of the portal ammonium. Alanine was retained to a large extent during all three hours. Other portal amino acids, mainly essential amino acids, were largely retained in about one hour after the gavage, to be released in a similar proportion thereafter. The other amino acids were also retained and then released, but to a lower extent. These amino acids were used in part by the liver for the synthesis and release of urea, which appearance in hepatic vein peaked at two hours after the protein administration.

Administration, Oral↗

PubMed1990

Rat splanchnic net oxygen consumption, energy implications.

1. The blood flow, PO2, pH and PCO2 have been estimated in portal and suprahepatic veins as well as in hepatic artery of fed and overnight starved rats given an oral glucose load. From these data the net intestinal, hepatic and splanchnic balances for oxygen and bicarbonate were calculated. The oxygen consumption of the intact animal has also been measured under comparable conditions. 2. The direct utilization of oxygen balances as energy equivalents when establishing the contribution of energy metabolism of liver and intestine to the overall energy expenses of the rat, has been found to be incorrect, since it incorporates the intrinsic error of interorgan proton transfer through bicarbonate. Liver and intestine produced high net bicarbonate balances in all situations tested, implying the elimination (by means of oxidative pathways, i.e. consuming additional oxygen) of high amounts of H+ generated with bicarbonate. The equivalence in energy output of the oxygen balances was then corrected for bicarbonate production to 11-54% lower values. 3. Intestine and liver consume a high proportion of available oxygen, about one-half in basal (fed or starved) conditions and about one-third after gavage, the intestine consumption being about 15% in all situations tested and the liver decreasing its oxygen consumption with gavage.

Animals↗

PubMed1988

A sensitive direct calorimeter for small mammals.

A sensitive direct calorimeter for small animals is presented. Its principle is based on the measurement of the heat transfer from the animal chamber to a heat sink. The system gives repetitive measurements with a high efficiency and allows a detailed time-related measurement of the heat production by the whole animal. Its low response time can be advantageously used for the study of post-prandial heat generation and diet-induced thermogenesis. Data on the heat production by Wistar and lean and obese Zucker rats is also included.

Animals↗

PubMedDate not supplied

Dietary sucrose supplementation fails to modify fat deposition in lean or obese rats.

The effects of sucrose supplementation on body composition and heat production were studied in lean, dietary (cafeteria diet) and genetically (Zucker fa/fa) obese adult (60 days) rats. Sucrose supplement (29 kJ) for 10 days did not result in significant changes in the pattern of energy (fat) deposition or carcass composition. There were no alterations, either, in heat production measured by direct calorimetry. Under the conditions studied, sucrose intake did not affect lipid deposition or thermogenesis.

Adipose Tissue↗

PubMedDate not supplied

Analysis of ultradian heat production and aortic core temperature rhythms in the rat.

The rhythms of aortic core temperature and overall heat production in Wistar rats was analyzed by using long series of recordings of temperature obtained from implanted thermocouple probes and heat release values from a chamber calorimeter. There was a very high degree of repetitiveness in the presentation of actual heat rhythms, with high cross-correlation values ascertained wit paired periodograms. No differences were observed between heat production between male and female adult rats. The cross-correlation for temperature gave similar figures. The cross-correlation study between heat production and aortic core temperature in the same animals was significant and showed a displacement of about 30 minutes between heat release and aortic core temperature. The analysis of heat production showed a strong predominance of rhythms with periods of 24 hours (frequencies < 11.6 microHz) or more; other rhythms detected (of roughly the same relative importance) had periods of 8 or 2.2 hours (35 or 126 microHz, respectively). The analysis of aortic core temperature showed a smaller quantitative contribution of the 8 or 2.2 hours (35 or 126 microHz) rhythms, with other harmonic rhythms interspersed (5.1 and 4.0 hours, i.e. 54 and 69 microHz). The proportion of 'noise' or cycles lower than 30 minutes (< 550 microHz) was higher in internal temperature than in the actual release of heat. The results are in agreement with the existence of a basic period of about 130 minutes (126 microHz) of warming/cooling of the blood, with a number of other harmonic rhythms superimposed upon the basic circadian rhythm.

Activity Cycles↗