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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Our findings indicate that protein synthesis is enhanced in weanling rats with hypothalamic obesity, that this enhancement is not dependent on increased amino acid transport into cells, and that muscle protein breakdown is also enhanced in these rats. The mechanisms of these changes are yet to be discovered. Finally, muscle protein has been demonstrated to be a probable source of the amino acids required to support enhanced gluconeogenesis in these rats.
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PMID:Protein metabolism in weanling rats with hypothalamic obesity. 125 Aug 41

Obese and lean Zucker rats were made diabetic by intracardiac injections of alloxan (65-72 mg/kg body weight) and then given daily injections of protamine zinc insulin [1.25 U/(100 g/d)] for 6, 9 and 12 d. Body weight, food intake, plasma glucose and immunoreactive insulin concentrations were not different for lean and obese diabetic rats of similar ages. Rates of increase in carcass protein, mixed muscle protein and myofibrillar protein were less in obese than in lean rats. However, rates of increase for the sarcoplasmic fraction were not different. Fractional rates of synthesis of total muscle protein and myofibrillar protein, as determined by continuous intravenous infusion of [14C]tyrosine, were comparable in the two genotypes. Fractional rate of myofibrillar protein degradation, as determined by urinary 3-methylhistidine excretion, was higher in obese than in lean rats. Differences in calculated absolute rates between genotypes did not parallel differences in the fractional rates, due mainly to a smaller protein mass in obese rats. As a consequence, absolute synthetic rates were lower in obese rats, while absolute degradation rates were similar in the two genotypes. In contrast, rates of liver protein synthesis were similar in obese and lean rats, whether expressed as fractional or absolute rates. These results indicate that decreased protein deposition in the obese animal is a consequence of both an absolute decrease in protein synthesis in muscle as well as a disproportionately elevated protein degradation in muscle. Hyperinsulinemia normally seen in obese rats may be an adaptive response to minimize the impaired balance between protein synthesis and degradation.
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PMID:Protein turnover in insulin-treated, alloxan-diabetic lean and obese Zucker rats. 389 2

Obese Zucker rats exhibit marked hyperphagia when compared to lean littermates but deposit a smaller percentage of total dietary energy as body protein. This study was designed to determine the roles of skeletal muscle protein synthesis, protein degradation, RNA, or DNA in producing the lower muscle mass of obese rats. At 44 days, 3 hindlimb muscles, the extensor digitorum longus (EDL), the gastrocnemius and the plantaris were significantly smaller in the obese animals. At 72 days, the differences in weights of these muscles were more pronounced. Protein synthesis and degradation were determined in the soleus at 44 days of age using an in vitro whole muscle incubation technique. Protein synthesis rate was significantly decreased in the obese animals. These changes were accompanied by reductions in both RNA and DNA levels. Significant changes in nucleic acid levels were observed in both the red and white portions of the gastrocnemius muscle. These changes in the anabolic process of protein accretion appear to be sufficient to account for the reduced muscle mass in the obese Zucker rat.
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PMID:Skeletal muscle growth in lean and obese Zucker rats. 619 56

The effects of prolonged fasting on the composition of weight loss and the rates of muscle protein synthesis and degradation were compared in obese and nonobese (lean) rats. Lean rats weighting 400 g could survive 60 days of fasting whereas obese rats weighing 550 g could survive 60 days. Weight loss was similar in both phenotypes over the first 10 days of fasting (15 g/day), but the composition of weight loss differed. Obese rats lost nearly twice as much lipid but only one-fifth as much body protein as lean rats. The fasting metabolic rate [kilocalories/(day . kilograms 0.75)] was similar in both phenotypes. This finding indicates a slower decline in metabolic rate during fasting in obese rats, since maintenance requirements are greater in lean rats. In fed rats, the fractional rates of muscle protein synthesis (FRS) and breakdown (FRB) were slightly higher in obese rats. Fasting reduced muscle protein synthesis in both phenotypes. In obese rats, however, the FRS declined more slowly than in lean rats. On the other hand, FRB decreased in fasted obese rats but greatly increased in fasted lean rats. It was concluded that the better protein retention and slower decline in metabolic rate in fasted obese rats were related to their different regulation of muscle protein synthesis and breakdown during fasting.
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PMID:Effects of fasting on muscle protein turnover, the composition of weight loss, and energy balance of obese and nonobese Zucker rats. 711 91

Adult obese (ob/ob) and lean male mice were fed severely-restricted amounts (approximately 20 to 30 per cent of ad-libitum intake) of either a high-carbohydrate, high-fat or high-protein diet for three weeks. All mice were fed an equal amount of metabolizable energy. Total body fat, total body nitrogen and skeletal-muscle nitrogen were measured in separate groups of mice initially and following three weeks of energy restriction. Obese mice lost 38 to 75 per cent more body energy than did lean mice. Fat accounted for most of the total energy lost (80 to 95 per cent). Obese mice lost more fat, but less protein, than lean mice. Of the total body protein lost by lean mice, 40 to 50 per cent was from skeletal muscle; but obese mice lost very little skeletal-muscle protein. Composition of the diet fed did not significantly affect losses of body weight, fat or protein in either obese or lean mice; mice fed the high-protein diet had heavier livers and kidneys. These results suggest that adult obese mice expend more total energy than lean mice. In addition, loss of body protein during restricted energy intake may be more closely related to remaining body fat stores than to composition of the diet.
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PMID:Changes in body composition of adult obese (ob/ob) and lean mice fed restricted levels of diets high in carbohydrate, fat or protein. 739 Jul 2

A mixture of [U-14C]amino acids was injected intraperitoneally into fed obese and non-obese Zucker rats that were either growing (8 weeks of age) or at maintenance (17 weeks of age). The metabolic fate of the dietary amino acid pool was determined from the distribution of 14C into carcass lean tissue, carcass lipid, CO2 and urine. In a second experiment, urinary and skeletal muscle 3-methylhistidine content was used to compare the rate of muscle protein breakdown between phenotypes at 8 weeks of age. The obese rat deposited a smaller proportion of its dietary amino acid pool in lean tissue compared with its non-obese control during growth and at maintenance. Obese rats incorporated a greater proportion of dietary amino acids into body lipid at both ages and metabolized a greater proportion of dietary amino acid carbon to CO2 during growth. At 8 weeks of age, the obese rat had a higher fractional rate of muscle protein breakdown and was less efficient at retaining amino acids that had been incorporated into muscle. These latter differences were major factors in producing the variation in dietary amino acid utilization and protein accretion between growing obese and non-obese rats. At maintenance, the variation in dietary amino acid utilization between phenotypes was due principally to the smaller body protein mass of the obese animals.
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PMID:Comparative amino acid and protein metabolism in obese and non-obese Zucker rats. 741 Dec 43

Obese Zucker (fa/fa) rat skeletal muscle is characterized by a reduced rate of muscle protein deposition possibly due to alterations in amino acid transport. The purpose of the present study was to investigate alanine transport in plasma membrane vesicles from skeletal muscle of lean and obese Zucker rats, facilitating the study of alanine transport independent of cellular metabolism. Initial rates of alanine transport were measured in the presence and absence of Na using a rapid filtration technique, and the properties of membranes from control and maximally insulin-treated lean and obese Zucker rats were studied. For lean rats, the maximal stimulation (Vmax) for Na-dependent alanine transport was 207 pmol.mg-1.s-1, and the half-maximal affinity constant (K1/2) was 2.3 mM. Insulin treatment increased the Vmax to 387 pmol.mg-1.s-1 with no changes in K1/2. For the obese rats, the Vmax for Na-dependent alanine transport was 248 pmol.mg-1.s-1, and the K1/2 was 2.8 mM. These values were not changed by insulin treatment. Thus Na-dependent alanine transport in obese rat skeletal muscle is resistant to stimulation by insulin; this alteration may contribute to the abnormal muscle protein metabolism observed in these animals.
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PMID:Insulin and Na-dependent alanine transport in skeletal muscle of obese Zucker (fa/fa) rats. 781 Jul 71

Adult male Sprague-Dawley rats (> or = 180 days old) develop an obesity-exacerbated insulin resistance in contrast with female animals of the same strain. Given the fact the maintenance of muscle mass requires an adequate supply of insulin and active insulin receptors, we postulated that gender differences might exist in both protein content and metabolic properties of skeletal and cardiac muscle in adult Sprague-Dawley rats. Therefore, to test this hypothesis, we examined activities of bioenergetic enzymes and total protein content in the diaphragm, the heart and the plantaris muscle in 12-month-old male and female animals. Mean (+/- SD) body weights of male animals were significantly (P < 0.05) greater than female animals (598 +/- 8 vs. 362 +/- 19 g) and the diaphragm weight/body weight ratio was significantly lower in males compared to females (2.36 +/- 0.05 vs. 3.02 +/- 0.13 mg/g). The activities of isocitrate dehydrogenase (NADP-specific) and succinate dehydrogenase were significantly lower (P < 0.05) in male animals compared to females in both the crural and costal regions of the diaphragm, the heart, and the plantaris muscle. In contrast, no gender differences (P > 0.05) existed in lactate dehydrogenase activity in any of the muscles studied. Finally, muscle protein concentration was significantly higher in female animals when compared to males (P < 0.05) in all muscles studied except the heart. These data support the hypothesis that gender differences exist for adult Sprague-Dawley rats in general and specific protein content of the diaphragm, locomotor muscles, and the heart.
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PMID:Gender differences in diaphragmatic metabolic properties of the adult Sprague-Dawley rat. 797 31

Recent reports describe poor growth in treated children with phenylketonuria (PKU). That poor growth is not a concomitant of the disorder and need not result from therapy is demonstrated by data from the U.S.A. PKU Collaborative Study and from recent data from the U.S.A. In these studies, sufficient protein equivalent was supplied by medical food containing either a low phenylalanine (Phe) casein hydrolysate or Phe-free L-amino acids. Protein and energy intakes of infants and children with PKU who grew well are compared to intakes of normal North American children. Factors that influence nitrogen (N) requirements include: state of health, energy intake, the form in which N is administered and the size of the dose. Failure to prevent poor growth in childhood may lead to a stunted adult [13] who is at risk for obesity. The use of actual body weight as a basis for calculating protein and energy requirements is appropriate only when the child is growing normally. Based on experience with PKU in the U.S.A., the following are recommended: (1) a protocol that prescribes a range for Phe, protein, and energy for infants and children should be developed; (2) adequate protein equivalent to cover N losses due to poor utilization of amino acids and protein hydrolysates should be prescribed; (3) medical food should be administered in several doses throughout the day; (4) a source of Phe should be fed with the medical food; (5) adequate energy should be prescribed to prevent excess use of amino acid for energy purposes; (6) nutrition support during illness should be appropriate to help prevent muscle protein catabolism with attendant elevated plasma Phe.
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PMID:Recommendations for protein and energy intakes by patients with phenylketonuria. 882 26

Many types of drugs are used by athletes to improve performance. This paper reviews the literature on 3 categories of drugs: those that enhance performance as stimulants (amphetamines, ephedrine, and cocaine), those that are used to reduce tremor and heart rate (beta-blockers) and those involved in bodyweight gain or loss (anabolic-androgenic steroids, growth hormone, beta 2-agonists, and diuretics). Limitations of research on these drugs as they relate to performance enhancement are also discussed. The numerous studies that have assessed the effects of amphetamines on performance report equivocal results. This may be due to the large interindividual variability in the response to the drug and the small sample sizes used. Most studies, however, show that some individuals do improve exercise performance when taking amphetamines, which may be attributed to their role in masking fatigue. As a stimulant, ephedrine has not been found to improve performance in the few studies available. More recently, ephedrine has been purported to be effective as a fat burner and used by athletes to maintain or improve muscle mass. Although research on individuals with obesity supports the use of ephedrine for fat loss, no studies have been done on athletes. The few studies of cocaine and exercise suggest that little to no performance gains are incurred from cocaine use. Moreover, the sense of euphoria may provide the illusion of better performance when, in actuality, performance was not improved or was impaired. beta-Blockers have been found to reduce heart rate and tremor and to improve performance in sports that are not physiologically challenging but require accuracy (e.g. pistol shooting). However, there is evidence that some individuals may be high responders to beta-blockers to the extent that their heart rate response is so blunted as to impair performance. Although equivocal, several studies have reported that anabolic-androgenic steroids increase muscle size and strength. However, most studies are not well controlled and use insufficient drug doses. One recent well controlled study did find an increase in muscle mass and strength with supraphysiological doses, and the improvements were greater in participants who were also resistance training. There is little information available on the effects of growth hormone on muscle mass or performance in athletes, although data suggest that growth hormone administration does not increase muscle protein synthesis. beta 2-Agonists, such as clenbuterol and salbutamol, when administered orally appear to improve muscular strength due to their potential role in increasing muscle mass. However, studies have not been done using athletes. Diuretics results in a loss of body water and hence bodyweight that can be advantageous for sports with strict bodyweight classifications. There is insufficient evidence on possible performance decrements in the field that could result from dehydration induced by the diuretics. Overall, the most significant concern in studies of drug use is the large inter-individual variability in responses to a drug. Further studies are needed to understand why some individuals are more responsive than others and to assess whether the responses are consistent for a given individual. Most studies of drug effectiveness have not used athletes. The effectiveness of many drugs may be reduced in highly trained athletes because there is a lower margin for improvement.
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PMID:Drugs and sport. Research findings and limitations. 942 62


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