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PubMed1984

Effects of starvation and plasma exchange on lecithin: cholesterol acyltransferase activity and cholesterol efflux in cholesterol-fed pigs.

The effects of starvation and of plasma exchange with a cholesterol-free substitute on efflux of tissue cholesterol and on lecithin: cholesterol acyltransferase (LCAT) activity in plasma and peripheral lymph were investigated in two pigs fed a cholesterol diet for 3-4 months. The pigs were labelled with i.v. [14C]cholesterol before plasma exchange or starvation. The cholesterol diet increased plasma total cholesterol concentration and LCAT activity in plasma and lymph, but had little effect on the rate of esterification of cholesterol in plasma or lymph. During cholesterol feeding, and when the animals were fed a normal diet, cholesterol esterification rates in plasma and lymph were much lower than the maximum rates achieved when LCAT was saturated with substrate, suggesting that LCAT in normal pig plasma and lymph is not saturated with substrate. Plasma exchange, carried out when the specific activity of tissue cholesterol exceeded that of plasma cholesterol, was followed by a brief rise in the specific activity of plasma cholesterol to a maximum value between the specific activities of muscle and adipose-tissue cholesterol, reflecting the transfer of radioactive cholesterol from tissue to plasma. During the rise in plasma total cholesterol specific activity there were no differences between the specific activities of low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol in plasma or lymph. Starvation had no effect on the plasma-cholesterol specific-activity curve. From about day 14 after labelling, cholesterol-specific activity decreased in the order: tissues greater than lymph greater than plasma. This suggests that the transfer of cholesterol from tissues to plasma was mediated by lipoproteins in the interstitial fluid.

Animals↗
PubMedDate not supplied

Influence of starvation and total protein deprivation on cardiac mRNA levels.

The effect of starvation and of protein-deprivation on the extractable amount of cardiac mRNA was investigated in male rats. Cardiac mRNA was determined by either (a) isolation of cardiac mRNA by SDS-Phenol/oligo-dT-cellulose, or by (b) hybridization of cardiac mRNA to 3H-Poly(U). During starvation (1-6 days) the extractable amount of cardiac microsomal RNA decreased from 870 micrograms/g heart (controls) to 606 micrograms/g (3 days) and to 547 micrograms/g (6 days), the extractable amount of mRNA fell from 28.6 micrograms/g heart (controls) to 18.7 micrograms/g (3 days) and to 14.5 micrograms/g (6 days). When a normocaloric but protein-deficient diet was fed, the decreases in cardiac microsomal RNA and mRNA were qualitatively similar, but slightly less severe. An analysis of the intracellular distribution of cardiac microsomal RNA and mRNA in the hearts of normal animals and of animals starved or fed a protein-deficient diet indicates that during starvation cardiac mRNA does not accumulate in the cell sap, but gets rapidly degraded. In the refeeding period, mRNA is transported from the nucleus to the cytoplasm and engages in polyribosome formation. The specific mRNA species coding for the major myofibrillar cardiac proteins are affected to a similar extent by these changes during starvation/protein-deprivation and refeeding.

Animals↗
PubMed1989

Time-course of changes in pancreatic size and enzyme composition in rats during starvation.

The effect of starvation for 3, 5, or 7 d on body weight, fat stores, pancreatic weight, and enzyme composition was studied in 300 g rats and was compared with a 3-d fast in 200 g rats. In the 300 g animals, fasting led to a gradual hypotrophy of the pancreas with a marked, continuous decrease in amylase content. Pancreatic lipase, trypsinogen, chymotrypsinogen, proelastase, and secretory trypsin inhibitor contents increased temporarily, but by d 7, they declined to about the initial values. This decline in enzyme levels coincided with the exhaustion of fat stores. The decrease in amylase content could be related to decreases in circulating insulin levels, whereas the temporary increase in lipase content may be owing to changes in plasma free fatty acid concentrations. In 200 g rats, starvation for 3 d led to exhaustion of fat stores that was accompanied by greater losses of pancreatic weight, protein, and amylase contents. In addition, the levels of trypsinogen and chymotrypsinogen decreased and lipase was unchanged. These findings indicate that during starvation, changes in pancreatic secretory enzymes are time-dependent and vary with the age, body weight, and/or adipose tissue mass of the rats.

Adipose Tissue↗
PubMed2006

Dynamics of starvation in humans.

A differential equation model describing the dynamics of stored energy in the form of fat mass, lean body mass and ketone body mass during prolonged starvation is developed. The parameters of the model are estimated using available data for 7 days into starvation. A simulation of energy stores for a normal individual with body mass index between 19 and 24 and an obese individual with body mass index over 30 are calculated. The length of time the obese subject can survive during prolonged starvation is estimated using the model.

Body Composition↗
PubMed2000

Enhancement of brush border membrane peptidase activity in rat jejunum induced by starvation.

Conflicting results have been obtained in previous studies concerning the adaptation of intestinal blush border membrane enzymes to starvation. This study was designed to clarity the changes in these enzymes under starvation conditions, using a molecular biological approach. Sprague-Dawley rats were starved or given total parenteral nutrition (TPN) for 5 days. Rats allowed free access to food were used as controls. Changes in the activity and expression of jejunal brush border membrane enzymes were compared between three groups. In the starved group, aminopeptidase N and dipeptidyl peptidase IV activity was significantly elevated to 177% and 166%, respectively, of control values. In contrast, sucrase and maltase activity was significantly decreased. The activity of these peptidases also tended to be increased at the renal brush border membrane. Up-regulation of peptidase activity was not evident in the TPN group. Western and Northern blot analysis revealed that the changes in aminopeptidase N activity were attributable to increases in the protein and mRNA level. The activity and expression of brush border membrane peptidases in rat jejunum is up-regulated during starvation, and these changes are considered to be an effect of whole-body malnourishment, rather than an absence of luminal nutrition.

Aminopeptidases↗
PubMed1984

Effect of starvation on the local and systemic metabolic effects of the lambda-carrageenan wound.

The contribution that starvation makes to the altered glucose metabolism in injured rats was evaluated. Food intake, weight change, nitrogen balance, and muscle tissue concentrations of glycogen, glucose, and the glycolytic intermediates were determined in these animals. This study concluded that the wounded and pair fed control groups presented adequately represent the metabolic states associated with injury and semistarvation in experimental animals, decreased food intake plays a major role in the weight loss and nitrogen balance in this wound model, wounding overrides two of the controlling steps of glycolysis (hexokinase and phosphofructokinase) in skeletal muscle during starvation, the finding of similar pyruvate dehydrogenase activity after wounding and starvation as demonstrated by tissue lactate to pyruvate ratios and lactate and pyruvate concentrations suggest that lactate production in wounded tissue may not be simply a manifestation of an altered redox state secondary to anaerobic conditions.

Animals↗
PubMed1995

Effect of starvation on the activity of the mitochondrial tricarboxylate carrier.

The effect of starvation on the activity of the tricarboxylate carrier has been investigated in intact rat liver mitochondria and in a reconstituted system. In both experimental conditions, the rate of citrate transport, when compared to control, is greatly reduced (35-40%) in starved rats. Similar behaviour is shown by the cytosolic lipogenic enzymes. Kinetic analysis of the carrier activity in intact mitochondria and in the proteoliposomal system has showed that during starvation only the Vmax of this process decreases while there is no change in the Km. No difference in the Arrhenius plot and in the lipid composition has been detected, which indicates that the reduced transport activity in fasted animals is not due to a change in the carrier lipid microenvironment. In starved rats, a reduction of the carrier activity has occurred even after the addition of increasing cardiolipin concentrations to proteoliposomes. These findings thus suggest that starvation-induced decrease of citrate carrier activity could be due to a change of the intrinsic properties of the transport protein.

Acetyl-CoA Carboxylase↗
PubMed1988

Accumulation of phenols and catechols in isolated mouse hepatocytes in starvation or after pretreatment with acetone.

Conditions leading to the accumulation of unconjugated phenols and catechols were investigated in mouse livers. The formation of unconjugated hydroxylated products of added p-nitrophenol and aniline was investigated in isolated hepatocytes prepared from 48 hr fasted or fed mice or from fed mice after acetone pretreatment. 4-Nitrocatechol and p-aminophenol--the hydroxylated products of p-nitrophenol and aniline--were accumulated in cells prepared from fasting animals, while in cells prepared from fed mice these unconjugated derivatives were not detectable. The accumulation of 4-nitrocatechol and p-aminophenol was also shown in isolated hepatocytes prepared from acetone pretreated fed mice. Inhibition of glucuronidation by N6,O2-dibutyryl cAMP or by D-galactosamine increased the accumulation of 4-nitrocatechol upon addition of p-nitrophenol in cells prepared from fasted mice. Both 48 hr starvation and acetone pretreatment enhanced the activity of microsomal p-nitrophenol and aniline hydroxylase by 300% and 600%, respectively, whereas p-nitrophenol conjugation in isolated hepatocytes as well as in hepatocyte homogenates was decreased by about 80% after 48 hr starvation. Acetone pretreatment did not alter the rate of p-nitrophenol conjugation measured in liver homogenates. It is suggested that a shift from conjugation toward hydroxylation in starvation gives rise to the formation of hazardous metabolites.

Acetone↗
PubMed1995

Induction mechanisms of cytochrome P450 2E1 in liver: interplay between ethanol treatment and starvation.

Chronic ethanol exposure causes marked induction of the ethanol-inducible cytochrome P450 (CYP) 2E1 isozyme in the centrilobular liver region, where alcoholic damage commonly is initiated. In contrast to most other CYP forms, which are ligand-activated at the transcriptional level, ethanol induction of CYP2E1 has been found to be post-translational. However, transcriptional activation of the CYP2E1 gene was recently described in fed animals maintained at very high ethanol levels. To further evaluate mechanisms of ethanol-mediated CYP2E1 induction we compared the effect of short-term heavy-ethanol treatment and fasting on CYP2E1 mRNA, protein and catalytic activity. High blood-ethanol levels (20-70 mM) were maintained for 3 days by regular alcohol intubations to fed or fasted rats. During this period, the amount of liver CYP2E1 apoprotein increased a maximum of 20-fold and catalytic activity 16-fold, both in fed and fasted animals, whereas starvation alone caused only a 4- to 5-fold increase. By comparison, the amount of CYP2E1 mRNA, as assayed both by Northern blot and slot blot, was significantly increased (5- to 6-fold) by ethanol only in fasted rats; this increase was smaller than that observed after fasting alone (8- to 9-fold). Analysis of cell lysates isolated from the periportal and perivenous region revealed that the increase in CYP2E1 mRNA by fasting occurred in the perivenous region. Thus no evidence was obtained for an increased pretranslational CYP2E1 gene expression as a consequence of the continuous presence of ethanol at intoxicating levels for 3 days. CYP2E1 mRNA elevation seems to be strongly associated with starvation while alcohol treatment increases the amount of enzyme, primarily by ligand-dependent stabilization of the synthesized protein. Our results indicate that transcriptional activation of CYP2E1 requires the long-term presence of highly intoxicating ethanol levels. It is conceivable that such activation occurs via indirect physiological responses related to those triggered by starvation.

Animals↗
PubMed1987

Effect of starvation on hypothalamic tyrosine hydroxylase activity in adult male rats.

The activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in norepinephrine synthesis, was determined in the mediobasal hypothalamus of adult male rats during acute and semistarvation. 3,4-Dihydroxyphenylalanine (DOPA) formed by TH was measured using high-performance liquid chromatography (HPLC). Acute starvation, as well as 3 weeks of semistarvation on a high-protein low-carbohydrate diet (CST PR) reduced TH activity significantly. Three weeks of a low-protein high-carbohydrate diet (CST KH) did not affect TH activity. While maximal velocity (Vmax) is significantly diminished in acute starvation and in semistarvation with a high-protein low-carbohydrate diet, Kd-values for tyrosine were not changed. These results suggest that TH activity in the brain contributes to decreased norepinephrine (NE) turnover in starvation.

Acute Disease↗
PubMed1995

Increased oxidation and decreased conjugation of drugs in the liver caused by starvation. Altered metabolism of certain aromatic compounds and acetone.

Starvation causes several changes in the various processes of biotransformation. The focus of this review is on biotransformation of various aromatic and other compounds whose metabolism is catalyzed in phase I by isozymes belonging to the CYP2E1 gene subfamily, while in phase II phenol-UDPGT or conjugation with GSH play a dominant role. The other ways of conjugation are beyond the scope of this review. The reason why this aspect has been chosen is that the capacity of these reactions is profoundly altered by nutritional conditions. There is a balance between the two phases of biotransformation. Therefore, under standard circumstances in a well-fed state the intermediate formed in the course of phase I is converted to a conjugated compound rapidly, as a result of phase II. However, in starvation the pattern of drug metabolism is altered and the balance between the two phases is changed. This alteration of drug metabolism upon starvation is partly connected to the changes of cofactor supplies due to the metabolic state.

Acetone↗
PubMed1988

Nutrition and fetal brain maturation. II. Impact of maternal starvation on changing levels of acetylcholinesterase and enolase in vitro.

The impact of maternal starvation during Days 17-20 of gestation was examined in 20-day fetal rat brain tissue cultured for 6 days in MEM and 10% adult rat serum. Acetylcholinesterase (AChE) activities were consistently greater in fetal brain cell cultures from starved mothers. When fetal tissues from starved mothers were continuously exposed to 72-h fasted serum, AChE activities increased from 1.03 +/- 0.14 to 1.59 +/- 0.21 mumol/h/mg protein (P less than 0.001). In fetal tissues from fed mothers, lower AChE activities were increased from 0.78 +/- 0.09 to 1.04 +/- 0.07 mumol/h/mg protein (P less than 0.05) when 72-h fasted serum was used to replace the fed serum during incubation. When fetal brain cell cultures from fed mothers were exposed for 6 days to graded concentrations of fed serum (2.5-15%), the activities of AChE fell reciprocally from 1.34 +/- 0.10 to 0.82 +/- 0.12 mumol/h/mg protein (P less than 0.05). The levels of AChE activity in tissues exposed to fasted serum were consistently greater, but fell similarly from 1.62 +/- 0.10 to 0.97 +/- 14 mumol/h/mg protein (P less than 0.01), when serum concentrations were increased from 2.5 to 15%. AChE activities were 30% higher in tissues incubated with cycloheximide 10(-3) M (P less than 0.02). Unlike AChE, fetal brain enolase activities were unaffected by maternal starvation. In fetal brain cell cultures from fed mothers, enolase fell from 1.85 +/- 0.10 to 1.37 +/- 0.12 mumol/min/mg protein following exposure to fasted instead of fed serum (P less than 0.02). In fetal cultures from starved mothers, enolase activities were depressed similarly from 1.76 +/- 0.08 to 1.41 +/- 0.09 mumol/min/mg protein when fasted replaced fed serum (P less than 0.02). Thus, the fetal brain cell cultures appear to maintain enzymatic realignments imposed by maternal starvation for at least 6 days. In addition, serum from fasted animals has significant growth inhibiting properties manifested by heightened activities of AChE and lower activities of enolase.

Acetylcholinesterase↗
PubMed1988

Regulation of polypeptide-chain initiation in rat skeletal muscle. Starvation does not alter the activity or phosphorylation state of initiation factor eIF-2.

In rats, 48-h starvation causes a decrease in the rate of protein synthesis in skeletal (e.g. gastrocnemius) muscle, due largely to impairment of peptide-chain initiation. In other cell types inhibition of initiation is associated with decreased activity and recycling of initiation factor eIF-2, and increased phosphorylation of its alpha-subunit. However, 48-h starvation has no effect on the activity or recycling of eIF-2 measured in extracts of gastrocnemius muscle, or on the level of alpha-subunit phosphorylation. The effects of starvation on peptide-chain initiation in skeletal muscle must therefore involve alterations in other components of the translational machinery.

Animals↗
PubMed1992

Effect of starvation on glucose transport and membrane fluidity in rat intestinal epithelial cells.

Studies on the surface area of microvilli (MV), fluidity of brush border membranes (BBM) and D-glucose uptake were carried out in rat intestinal epithelial cells (IEC) during progressive starvation and under re-feed conditions. The surface area of MV, fluidity of BBM and D-glucose transport through IEC membranes showed an increase during starvation when compared to well-fed controls. Re-feeding experiments restored the control values of all the three parameters within a short time. The results showed that the increase in D-glucose transport through IEC membranes during starvation is due to increased surface area of MV and increased fluidity of BBM.

Alkaline Phosphatase↗
PubMed1988

Effects of starvation, refeeding, and insulin on energy-linked metabolic processes in catfish (Rhamdia hilarii) adapted to a carbohydrate-rich diet.

The effects of starvation and of a short period of refeeding on energy-linked metabolic processes, as well as the effects of insulin administration, were investigated in an omnivorous fish (catfish, Rhamdia hilarii) previously adapted to a carbohydrate-rich diet. Following food deprivation blood sugar levels declined progressively to about 50% of fed values after 30 days. During the same period plasma free fatty acid (FFA) concentration increased twofold. Starvation resulted in reduced concentrations of lipid and glycogen in the liver and of glycogen, lipid, and protein in white muscle. However, taking into account the initial and final concentrations of tissue constituents, the liver weight, and the large fractions of body weight represented by muscle, it could be estimated that most of the energy utilized during starvation derived from the catabolism of muscle lipid and protein. Refeeding starved fishes for 48 hr induced several-fold increases in the rates of in vivo and in vitro incorporation of [14C]glucose into liver and muscle lipid and of [14C]glycine into liver and muscle protein. Incorporation of [14C]glucose into liver glycogen was also increased. However; refeeding did not affect the incorporation of labeled glucose into muscle glycogen, neither in vivo nor in vitro. Administration of pharmacological doses of insulin to normally fed catfishes resulted in marked increases in the in vivo incorporation of 14C from glucose into lipid and protein in both liver and muscle. In contrast, labeled glucose incorporation into muscle glycogen was not affected by insulin and label incorporation into liver glycogen was actually lower than that in noninjected controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1989

The effect of severe starvation and captivity stress on plasma thyroxine and triiodothyronine concentrations in an antarctic bird (emperor penguin).

The effect of confinement and severe starvation on the plasma thyroxine (T4) and triiodothyronine (T3) concentrations was determined in emperor penguins (Aptenodytes forsteri). During their annual cycle, emperor penguins fast freely for periods of up to 4 months and may thus represent a unique subject to study endocrine adaptations to fasting. Plasma T4 concentrations progressively decreased following capture and confinement of naturally fasting penguins, and within 15-20 days stabilized at levels three times lower than in free-living penguins. A transient fourfold increase in plasma T3 concentration developed within the day following confinement in parallel with a rise in daily body mass loss. Both plasma T3 concentration and mass loss subsided to normal levels within 15 days. The decrease in plasma T4 concentration is in accordance with the well-known inhibitory effect of stress on thyroid function in birds and mammals, whereas the transient increase in plasma T3 concentration seems related to enhancement of energy expenditure as a consequence of restlessness. Starvation severe enough to exhaust fat stores and to activate protein catabolism induced a 6- and 5 to 10-fold fall in plasma T4 and T3, respectively. This is in marked contrast with maintenance of plasma thyroid levels during long-term natural fasting associated with protein sparing (R. Groscolas and J. Leloup (1986) Gen. Comp. Endocrinol. 63, 264-274). Surprisingly, there was a final reincrease in plasma T4 concentration in very lean penguins. These results suggest that the effect of starvation on plasma thyroid hormones seems to depend on how much protein catabolism is activated and demonstrate the acute sensitivity of thyroid hormone balance to stress in penguins.

Animals↗
PubMed1987

Protein synthesis in skeletal muscle of rats following starvation and refeeding.

Determination of protein synthesis in individual tissues is important to understand the changes in protein metabolism during catabolic states. Three methods based on different underlying assumptions were compared in assessing muscle protein synthesis during nutritional manipulation. Rats were nonstarved, starved for 1 or 3 days, or refed for 2 days after 3 days of starvation. The extensor digitorum longus (EDL) muscles from the two hindlegs were used for analysis. In one EDL muscle the concentration and size distribution of ribosomes as well as the incorporation of [14C]leucine into protein in a cell-free system were determined. The other EDL muscle was incubated as such and the incorporation of [14C]phenylalanine into protein was measured. The total ribosome concentration per milligram of DNA decreased to 65% on the third day of starvation and remained low after refeeding. The amount of polyribosomes in the percentage of total ribosomes fell to 90% on the first day of starvation, regained the initial level on the third day, and reached 110% upon refeeding. During refeeding amino acid incorporation into protein in a cell-free system decreased to 40% and that in intact muscle to 64% of the prestarvation level. Upon refeeding, the activity increased to or above the original values. The use of several different techniques in parallel to assess protein synthesis in skeletal muscle is recommended since it gives information about the factors involved in regulation of the translational process in intact mammalian tissues.

Animals↗
PubMed1986

Starvation-induced changes in rat brain corticotropin-releasing factor (CRF) and pituitary-adrenocortical response.

Starvation-induced changes in CRF concentration in major brain regions and abnormalities in the pituitary-adrenal axis were examined in rats using rat CRF radioimmunoassay. The CRF concentrations in the hypothalamus and cerebellum were significantly reduced in the completely starved rats, while those in the midbrain, thalamus and neurointermediate lobe of the pituitary were significantly increased in the semi-starved or completely starved rats. No significant changes in the CRF concentrations were found in the pons, medulla oblongata and cerebral cortex. In the completely starved rats, the serum ACTH level was significantly reduced, whereas the serum corticosterone level was markedly elevated. These observations suggest that starvation may stimulate the CRF-ACTH-corticosterone system and that not only hypothalamic CRF but also extrahypothalamic CRF may be discretely related to feeding behavior or starvation. The reduced serum ACTH level in starved rats may be ascribed to the negative feedback effect of the elevated serum corticosterone.

Adrenocorticotropic Hormone↗