Effect of starvation on the disposition of free and peptide-linked trimethyllysine in the rat

Free and peptide-linked trimethyllysine were measured in fed and 5-d starved rats. The trimethyllysine content of liver and kidney was significantly increased on d 5 of starvation to two to three times the levels found in fed animals. Skeletal muscle of fed rats contained over six times as much trimethyllysine (19.3 nmol/g) as that found in liver (3.2 nmol/g) or kidney (2.7 nmol/g). Plasma free trimethyllysine significantly increased from 1 nmol/ml in fed rats to 2.2 nmol/ml in 5-d starved rats. During this same period, daily total trimethyllysine excretions averaged approximately 400 nmol/d. Urinary free trimethyllysine was significantly depressed during starvation. Assuming that trimethyllysine in plasma does not exist in a protein-bound form, clearance calculations based on concentrations of plasma and urinary trimethyllysine indicated that this compound is readily reabsorbed by the kidney. As previous studies have indicated that trimethyllysine is not readily absorbed by other tissues, this indicates that the kidney may be the primary regulatory site for the disposition free of free trimethyllysine in plasma and urine. Estimates of the efficiency of entry of trimethyllysine into the carnitine biosynthetic pathway were calculated and ranged from 41% in 3-d starved rats to 80% in fed rats. We conclude that carnitine biosynthesis is limited by the availability of trimethyllysine, which, in the starved rat, is limited by the rate of protein turnover.     

Effect of long-term starvation on the rat liver lysosomes.

The effect of 120- and 240-h starvation on rats hepatocytes ultrastructure and particularly the changes of the lysosomes were studied. Eelectronmicroscopically and cytochemically there have been observed diminution of the number of mitochondria and degranulation and vacuolzation of the ER. At the same time Golgi complex was hypertrophied and the number of lysosomes was much increased, mainly those of the autophagic type. Biochemically was shown, that the activity of some acid hydrolases (beta-glucosidase, alpha- and beta-galactosidases, beta-N-acetylglucosaminidase, beta-glucuronidase and arylsulphatases A and B) in the liver of starved rats was markedly expressed. The sedimentation properties of the lysosomes and the lysosomal membrane stability was damaged as well. The data received have been discussed in the light of the reconstructive role of lysosomes.     

Effect of diet and starvation on hepatic mitochondrial function in the rat

The purpose of the present study was to assess the effect of diet and starvation on mitochondrial function. Diet did not affect hepatic mitochondrial oxidation of lipid or nonlipid substrates when expressed as nanogram atoms of oxygen consumed per minute per milligram mitochondrial protein. Furthermore, diet did not affect mitochondrial palmitoylcarnitine utilization rate, mitochondrial ketoacid production, or mitochondrial carnitine palmitoyltransferase specific activity. When the data for palmitoylcarnitine utilization were expressed per gram liver, the rates were significantly lower in rats fed the high fat diet of Schemmel et al. (J. Nutr. 110: 1041-1048, 1970). DNA content (milligrams/gram) indicated that cell size rather than cell number contributed to greater total liver weight in rats fed the Schemmel high fat diet. In both stock diet-fed controls and rats fed the Schemmel high fat diet, mitochondrial protein per gram liver decreased with duration of starvation. Mitochondrial carnitine palmitoyltransferase was unchanged by diet or starvation. Thus, neither diet nor diet followed by starvation altered hepatic mitochondrial capacity to oxidize lipid substrates.     

Effect of starvation on protein synthesis in neonatal rat liver.

Hepatic protein synthesis was measured in vivo and in vitro (liver slice) in 6- and 19-day-old rats. Fed and 15-hour starved rats were compared in each individual experiment. The study demonstrated that in the 6-day-old rat, hepatic protein synthesis is very sensitive to restrictions in dietary influx. In contrast, no significant differences in protein synthesis were detected when 19-day-old rats were fasted for 15 hours. In the fed state, the protein synthetic activity of the tissue unit was the same irrespective of age. Thus, it appears that it is not the maximal capacity for protein synthesis that changes with age, but rather the extent to which the system can adapt to the changing nutritional environment.     

Effect of starvation on degradation of rat liver nuclear proteins

Starvation is characterized by rapid loss in liver weight and proteins. The loss in liver protein is reflected in loss of protein in most organelles including mitochondria, microsomes, and cytosol, with the exception of nuclei. The nuclear proteins increase per unit weight of liver during starvation and this holds true for both histone and non-histone fractions. Comparison of degradation pattern of histone and non-histone fractions with microsomal fraction indicates a significantly different profile. The nuclear proteins reflect a pattern of decreased degradation during starvation. The increase in the activity of lysosomal enzyme cathepsin D measured during this period was indicative of general increase in catabolic processes. However, the nuclear protease activity decreased during this period, suggesting an organelle compartmentation of degradation process.     

Effect of prolonged starvation on substrate uptake in the isolated perfused rat heart

The pattern of substrate uptake by the heart in prolonged starvation, when lipid reserves are approaching depletion, has been examined. The classical Langendorff perfused heart preparation was employed to determine substrate uptakes in male rats fed ad libitum or starved for 7 days. Levels of metabolites in "arterial" and "venous" perfusion media and in heart tissue were determined by fluoroenzymatic assays, with the exception of palmitic acid which was analyzed by gas chromatography. It was found that glucose is the principal fuel of oxidation in perfused hearts of ad libitum-fed rats, whereas palmitate (FFA) is the major fuel of oxidation in perfused hearts of starved rats, followed by lactate, glucose, beta-hydroxybutyrate, pyruvate and alanine. Such changes might be related to some of the alterations in the metabolic pathway (e.g., glycolytic inhibition) in prolonged starvation.     

Effect of prolonged starvation on glycogen synthase and glycogen synthase phosphatase activity in rat heart

Rats were fasted 24, 48 or 72 hours to determine the effect of several days without food on glycogen synthase and synthase phosphatase activity in heart. The basal percentage of synthase I decreased gradually from approximately 20% in fed animals to approximately 6% in rats starved for 72 hours. Glycogen increased progressively from 4.6 mg/g wet weight in fed rats to 7.6 mg/g wet weight in 72-hour starved rats. Thus, there was an inverse relationship between the glycogen concentration and the basal percentage of synthase I. The total synthase phosphatase activity measured at a standardized glycogen concentration decreased 50% by 24 hours of starvation and then was unchanged up to 72 hours. The 50% decrease in phosphatase activity correlated directly with insulin concentration in rats fasted 24-72 hours. The rapid stimulatory effect of insulin on synthase activity observed in fed rats was delayed in rats starved 24 and 48 hours. This correlated with a progressively slower synthase phosphatase response to insulin. The stimulatory effect of insulin was lost completely in 72-hour fasted rats. The proposed mechanism for the delayed response in rats starved 24 and 48 hours and lack of response in rats starved 72 hours is insulin resistance. The mechanism remains to be elucidated.     

Effect of starvation and diet composition on two pathways of L-serine metabolism in isolated rat hepatocytes

This study examined the effects of starvation and of feeding to rats diets that contain varying protein, carbohydrate and fat levels on serine metabolism in isolated hepatocytes. The conversion of [14C]serine and [14C]lactate to 14CO2 and [14C]glucose was measured in the presence and absence of 5 mM quinolinic acid (QA) or 1 mM 3-mercaptopicolinic acid (MPA), inhibitors of phosphoenolpyruvate carboxykinase. Inclusion of MPA eliminated the contribution of the serine dehydratase-mediated pathway of serine metabolism to glucose production, allowing estimation of serine aminotransferase-mediated metabolism. Addition of MPA reduced [14C]glucose formation from [14C]serine to between 3 and 47% of control values in all dietary treatments. Addition of 10 mM threonine or 10 mM pyruvate depressed [14C]glucose production in hepatocytes from the groups fed 80% protein. Differences in serine metabolism were observed within each protein group, depending on the carbohydrate and fat ratio of the diet. These results suggest the following: 1) MPA is a more potent gluconeogenic inhibitor than QA, permitting estimation of relative flux through two pathways of serine metabolism; 2) serine metabolism occurs primarily via serine dehydratase, although the contribution of serine aminotransferase varies depending upon the nutritional state of the rat, and 3) changing a single dietary component at the expense of another may mask the intricacies of metabolic homeostasis.     

Effects of prolonged starvation on cardiac energy metabolism in the rat.

Experiments were carried out on two series of adult male rats (ad libitum-fed control and starved) for 7 days, at the end of which time components of the glycolytic, citric acid cycle, and associated metabolic pathways in the heart were examined. Levels of myocardial and arterial plasma metabolites in vivo were determined by fluoroenzymatic assays. Activities of enzymes in heart extracts and isolated mitochondria were measured in vitro spectrophotometrically. In starved rats, decreases were observed in heart tissue glucose, fructose-1,6-diphosphate, lactate, alanine, glutamate, and ADP; increases occurred in fructose-6-phosphate, beta-hydroxybutyrate, acetoacetate, and ATP. Slight to moderate elevations were noted in citric acid cycle metabolites. States of marked hypoglycemia, hyperketonemia, and hypocitricemia also developed. Evidence indicates that flux through the glycolytic pathway is diminished in prolonged starvation as a result of PFK inhibition. Elevated ATP and decreased AMP are suggested as possible factors in PFK inhibition; citrate is believed to have little effect. It is also postulated that amino acid utilization in the heart increases and that dependence on lipids as fuels of oxidation decreases. The latter occurs despite the high levels of circulating ketone bodies. There is little indication from a profile of citric acid cycle metabolites and analyses of mitochondrial enzyme activities that regulation of cycle activity is significantly altered.     

Influence of starvation on sucrase regulation by dietary sucrose in the rat

We have studied the action of sucrose on jejunal sucrase activity. Rats (175 g) were first starved or fed a digestible carbohydrate-free diet for 60 h and then fed a high sucrose diet for varying times up to 84 h. 1) Rats starved for 60 h showed mucosal atrophy with a decrease in protein content/10 cm (18.00 +/- 1.4 versus 40.1 +/- 3 mg (controls p less than 0.001) and in villus height (357 +/- 18 versus 526 +/- 5 microns, p less than 0.001) which was fully repaired only after 60 h on the sucrose diet (528 +/- 11 microns). Rats on digestible carbohydrate-free diet showed no mucosal atrophy. 2) Starved rats had a delayed (60 h) sucrase activity response to sucrose (53 +/- 7 versus 122 +/- 4 microns/mg protein, p less than 0.001). Maximum activity was obtained after 12 h on sucrose diet in rats maintained on the carbohydrate-free diet: 38 +/- 1 versus 108 +/- 2.3 microns/mg protein, p less than 0.001. 3) Villus and crypt cell analysis after starvation and 12 h on a high sucrose diet localized the increase in sucrase activity to the villus-crypt junction. No change occurred in the upper villus. The increase was complete all along the villus by 36 h. In contrast, after the carbohydrate-free diet, sucrase activity increased maximally at all levels of the villus by 12 h on the high sucrose diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

海洋胶原肽对剖宫产大鼠伤口愈合促进作用

目的 观察海洋胶原肽对大鼠剖宫产术后恢复的促进作用.方法 将96只SD孕鼠在孕19 d时进行剖宫产手术,随机分为4组,3个剂量组术后每天给予0.13,0.38,1.15 μg/(kg.bw)剂量的海洋胶原肽灌胃,空白对照组等体积生理盐水灌胃;在术后7,14,21 d每组分别处死8只大鼠,观察切口愈合情况,测定皮肤切口和子宫切口的抗张力强度、羟脯氨酸含量.结果 给予海洋胶原肽1.15 μg/(kg.bw)组大鼠皮肤伤口中羟脯氨酸含量在3个时间点上均高于对照组,差异有统计学意义(P<0.05);在7,21 d时,给予海洋胶原肽1.15 μg/(kg.bw)组大鼠皮肤张力为(354.45±200.45),(978.23±20.40)g/mm²,子宫压力为(874.63±293.51),(818.20±227.52)mmHg,均大于空白对照组的(165.44±29.82),(379.21±171.46)g/mm²和(684.52±220.16),(511.92±86.48)mmHg,差异有统计学意义(P<0.05);21 d时,给予海洋胶原肽0.38g/(kg.bw)组大鼠的皮肤张力为(936.59±56.27)g/mm²,大于空白对照组,差异有统计学意义(P<0.05).结论 海洋胶原肽能够促进伤口胶原蛋白合成,促进大鼠剖宫产术后伤口的愈合.     

Effect of starvation and refeeding on activity of a Ca2+-dependent protease in rat skeletal muscle

The effects of starving, refeeding, and restarving rats for different periods on content of sarcoplasmic and contractile proteins and on activity of the Ca2+-dependent proteinase (CAF) in skeletal muscle was determined. Groups of five to six male rats, 8 to 11 weeks old, were starved up to 8 days, refed up to 6 days, and in two experiments, restarved up to 10 days. CAF activity was assayed in P 0-45 crude CAF fractions prepared so as to remove a protein inhibitor of CAF; the assays were demonstrated to be specific for CAF. Sarcoplasmic protein content of rat skeletal muscle changed little until after 6 days of restarvation when it decreased to 68-89% of control level (P less than 0.05). Contractile protein content decreased to 65% of control level (P less than 0.01) after 8 days of starvation, remained at this level for 4 days of refeeding, then increased to approximately 80% of control level after 6 days of refeeding, remained at this level for 2 days of restarvation, and then decreased to approximately 65% of control level (P less than 0.01) after 6 and 8 days of restarvation. Muscle CAF activity did not change during the first 8 days of starvation but increased to 113% above control level (P less than 0.01) after 6 days refeeding and then decreased to only 29% of control level (P less than 0.01) after 8 days of restarvation. These changes in muscle CAF activity are consistent with the proposed role for CAF in initiating metabolic turnover of contractile proteins, but because actual measurements of myofibrillar protein were not made and because in vivo CAF activity is difficult to assess, they do not prove this role for CAF nor do they exclude participation of other proteinases.     

Effect of linkage disequilibrium between markers in linkage and association analyses

Contributions to Group 17 of the Genetic Analysis Workshop 15 considered dense markers in linkage disequilibrium (LD) in the context of either linkage or association analysis. Three contributions reported on methods for modeling LD or selecting a subset of markers in linkage equilibrium to perform linkage analysis. When all markers were used without modeling LD, inflated evidence for linkage was observed when parental genotypes were missing. All methods for handling LD led to some decreased linkage evidence. Two groups performed a genome-wide association scan using either mixed models to account for known or unknown relatedness between individuals, trend tests or combination statistics. All methods failed to detect four of the eight simulated loci because of low LD in some regions. Three groups performed association analysis using simulated dense markers on chromosome 6, where a simulated HLA-DRB1 locus played a major role in disease susceptibility along with two additional loci of smaller effect. The overall conditional genotype method correctly identified both additional loci while a novel transmission disequilibrium test-statistic to combine studies with non-overlapping markers identified one HLA locus after stratifying on the parental HLA-DRB1 genotypes; LD mapping using the Malécot model mapped two loci in this region, even when using greatly reduced marker density. While LD between markers appears to be a nuisance that may cause spurious linkage results with missing parental genotypes in linkage analysis, association analysis thrives on LD, and disease genes fail to be detected in regions of low LD.     

Effect of linkage disequilibrium on the identification of functional variants

We summarize the contributions of Group 9 of Genetic Analysis Workshop 17. This group addressed the problems of linkage disequilibrium and other longer range forms of allelic association when evaluating the effects of genotypes on phenotypes. Issues raised by long-range associations, whether a result of selection, stratification, possible technical errors, or chance, were less expected but proved to be important. Most contributors focused on regression methods of various types to illustrate problematic issues or to develop adaptations for dealing with high-density genotype assays. Study design was also considered, as was graphical modeling. Although no method emerged as uniformly successful, most succeeded in reducing false-positive results either by considering clusters of loci within genes or by applying smoothing metrics that required results from adjacent loci to be similar. Two unexpected results that questioned our assumptions of what is required to model linkage disequilibrium were observed. The first was that correlations between loci separated by large genetic distances can greatly inflate single-locus test statistics, and, whether the result of selection, stratification, possible technical errors, or chance, these correlations seem overabundant. The second unexpected result was that applying principal components analysis to genome-wide genotype data can apparently control not only for population structure but also for linkage disequilibrium.     

The effects of starvation and refeeding on muscle protein synthesis and catabolism in the young rat

We studied the effects of acute starvation and refeeding on muscle protein synthesis and degradation in young rats. As measures of synthesis, we determined muscle RNA concentration and the rate of incorporation of [14C]leucine into skeletal muscle protein (Sm). As an estimate of nitrogen retention we measured urea production (UrP). Starvation reduced these variables significantly. One refeeding period returned Sm to control values, only partially restored RNA concentration, and increased UrP. We determined the urinary excretion rate of 3-methylhistidine (3-MH) as a measure of the rate of myofibrillar protein degradation. Excretion of 3-MH was lowest in control and highest in starved rats. Refeeding decreased 3-MH excretion to a level midway between control and starved animals. Growth was attended by high rates of synthesis and low rates of degradation. Starvation depressed synthesis and increased degradation. With refeeding, synthesis increased and degradation decreased, compared with the starved state.