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PubMed1998

Mechanisms of decreased lipoprotein lipase activity in adipocytes of starved rats depend on duration of starvation.

The aim of this study was to delineate the mechanisms by which varying periods of starvation decrease lipoprotein lipase (LPL) activity in rat adipose tissue. LPL mRNA levels and rates of LPL synthesis, degradation and secretion were compared in adipocytes from male rats that had been fed or starved for 1 or 3 d. The decreased LPL activity after 3 d of starvation (-76%) was explained mainly by a 50% decrease in the relative abundance of LPL mRNA levels (P < 0.05) and a parallel 50% decrease in relative rates of LPL biosynthesis (P < 0.05). In contrast, starvation for 1 d decreased total LPL activity by 47% (P < 0.05) but did not affect LPL mRNA levels or relative rates of LPL biosynthesis. Pulse-chase studies demonstrated that 1 d of starvation increased the rate of degradation of newly synthesized LPL (P < 0.05) and markedly decreased its secretion into the medium (P < 0.05). A decrease in overall protein synthesis also contributed to the decreased LPL activity after 1 and 3 d of starvation. We conclude that the relative importance of pre- and post-translational mechanisms in regulating adipose tissue LPL activity depends on the duration of starvation. During short-term starvation, degradation of newly synthesized LPL is an important determinant to its secretion from the adipocyte and hence its functional activity at the capillary endothelium.

Adipocytes↗
PubMed1981

Effect of prolonged starvation on reticuloendothelial function and survival following trauma.

The effects of prolonged starvation on reticuloendothelial system (RE) function and on the survival of animals following trauma were studied. Rats were fasted for 51/2 days (water ad lib) after which a two-cm midline incision was made and the cecum ligated (CL). Food and water were allowed 36 h after CL and survival was measured over 5 days. The mortality rate in these animals was 60% (15/25) compared to 0% (0/15) in CL rats fasted for 24 h. Starvation alone for 7 days did not produce any deaths but after 11 days of starvation mortality was 100%. Another group of animals were fasted for 51/2 days and were used to study RE function 10 h following CL. There was no significant difference in the intravascular clearance rates in injected lipid emulsion in various groups of animals, indicating that total phagocytic function was not changed by prolonged starvation plus CL (SCL). However, emulsion retention in the spleen, expressed as per cent injected dose per gm tissue, decreased by 53% and the lung retention increased by 988% following SLC. Serum GOT levels were not affected by prolonged starvation alone; however, SCL resulted in its elevation (37 vs. 82 IU/ml). Hepatic ATP levels (micromoles/g) decreased from 2.47 to 1.95 following 51/2 days starvation and following SCL, it decreased to 1.75. These results indicate that the increased metabolic demand following trauma (i.e., CL), coupled with prolonged starvation, altered RE function with splenic lipid emulsion uptake decreasing and pulmonary uptake increasing. The relationship of these findings to immune function remains to be determined. Although the precise cause of increased mortality is not known, altered metabolic and RE function may play a role.

Animals↗
PubMed1981

Starvation phase of Physarum polycephalum: characterization of transfer ribonucleic acid.

We have begun a series of studies designed to characterize gene expression during differentiation in the slime mold Physarum polycephalum. This work concerns the starvation phase of the sporulation sequence and describes some of the quantitative changes which occur in plasmodial constituents during the 3-day starvation period and also describes alterations in the transfer ribonucleic acid (tRNA) population. The results show that whereas the plasmodial tRNA content decreased by 75% during starvation, concurrent de novo synthesis of tRNA also occurred, and they also show that overall amino acid acceptor activity of the starvation-phase tRNA population did not differ significantly from that found in the growth phase. Of the 19 starvation-phase tRNA families assayed, however, 6 were found to have consistently lower acceptor activities than did their growth-phase counterparts. Reverse-phase (RPC-5) chromatographic analysis of five of those families failed to reveal any major differences between growth- and starvation-phase isoacceptors. The data suggest that the depletion and resynthesis of tRNA during the starvation phase results in a quantitative alteration in the composition of the tRNA population and that the alteration is tRNA family and not tRNA isoacceptor specific.

Gene Expression Regulation↗
PubMed1988

Adrenalectomy eliminates both fiber-type differences and starvation effects on denervated muscle.

This report describes changes in muscle mass of innervated and denervated pairs of muscles taken from intact and adrenalectomized 250-g male Sprague-Dawley rats provided with different diets. Diets ranged from a nutritionally complete liquid diet to starvation (water only). In the intact animals, muscles with a more tonic character (soleus) are less sensitive to starvation than are muscles with a more phasic character (extensor digitorum longus), whereas the opposite is true of denervation. In the intact animals, starvation greatly increased the amount of atrophy following denervation. In the adrenalectomized animals, starvation had no effect on the amounts of atrophy following denervation. Furthermore, adrenalectomy virtually eliminated the fiber-type differences in the amount of atrophy following denervation. In addition, a comparison between denervated muscles from intact animals and adrenalectomized animals subjected to starvation demonstrates that all denervated muscles from the adrenalectomized animals atrophy less. Finally, it was observed that although an adrenalectomized animal can tolerate 6 days of starvation, an adrenalectomized-castrated animal cannot tolerate even short periods of starvation. The difference appears to be due to low amounts of corticosterone of testicular origin.

Adrenalectomy↗
PubMed1991

Experimental studies on changes of neuroendocrine functions during starvation and refeeding.

Starvation resulting from famine and malnutrition remains an international concern. Malnutrition also influences the course and outcome of many diseases and when underestimated develops into a cycle of continuing dehabilitation. Thus, studies which contribute to the prevention, amelioration, or rehabilitation of the detrimental effect of starvation are warranted. Although investigations on endocrine changes related to starvation can be traced back to the early 1920s, there has been little work on the hypothalamic-pituitary axis until recently. The traditional line of thought tended to oversimplify the relationship between endocrine gland hypofunction and starvation by concluding that this hypofunction resulted from the inability of hormone production due to cellular damage and/or lack of raw materials and energy. Modern neuroendocrinology has established that neuroendocrine integration plays a major role in the body's homeostasis. The neuroendocrine system is the initial response to stress so that it is reasonable to assume that this system also plays a key role in the pathophysiological changes during starvation. This article presents a brief review of our research on: changes of anterior pituitary hormone secretions during starvation and refeeding; changes of hypothalamic neurotransmitters during starvation; and effects of modulation of central neurotransmitters on anterior pituitary hormone secretion of starved animals.

Adrenocorticotropic Hormone↗
PubMed1992

Effect of starvation and subsequent refeeding on thyroid function and release of hypothalamic thyrotropin-releasing hormone.

Effects of starvation on thyroid function were studied in 5- to 6-week-old (R x U) F1 rats. Starvation lowered plasma TSH in female, but not in male rats. Plasma T4 and T3 levels decreased, whereas the dialysable T4 fraction increased during starvation. Free T4 (FT4) levels decreased rapidly in females, but only after prolonged fasting in male rats. Glucose decreased, and free fatty acid levels increased during starvation. Peripheral TRH levels did not change during food deprivation. Since effects of starvation were most apparent in young female rats, such rats were used to study hypothalamic TRH release during starvation and subsequent refeeding. Basal in vitro hypothalamic TRH secretion was less in starved rats than in control or refed animals. In vitro hypothalamic TRH release in medium with 56 mM KCl increased 3-fold compared to basal release, and in these depolarization conditions TRH release was similar between hypothalami from control, starved and refed rats. In rats starved for 2 days, TRH level in hypophysial portal blood was lower than that of controls. Thus, diminished thyroid function during starvation may at least in part be caused by a reduced hypothalamic TRH release.

Animals↗
PubMedDate not supplied

Serum protein response to surgery and starvation.

To investigate the effect of stress on the dynamics of serum protein response during starvation, serum albumin, prealbumin, and transferrin changes were studied in six chair-adapted macaques during two separate 7-day test periods: (1) Starvation--NPO + IV D5/W (100 cc/kg/day), and (2) Surgery/starvation--laparotomy and gastrostomy + NPO + IV D5/W (100 cc/kg/day). During the starvation period, transferrin was the only protein that decreased from baseline values and did so at day 7 of the study period. In contrast, during the period of starvation following surgery, both prealbumin and transferrin were significantly decreased at both day 4 and day 7 of the study period, whereas albumin was only decreased at day 7 of this period. These findings indicate that the addition of a surgical stress to starvation results in a depression of serum protein levels that is not only of greater magnitude, but also more rapid in onset than observed with starvation alone. In addition, the differential response of prealbumin and transferrin to starvation and stress may provide a useful indicator of the presence and/or degree of stress in certain situations. The clinical utility of this finding remains to be ascertained.

Animals↗
PubMed1990

The effect of maternal starvation on plasma insulin-like growth factor I concentrations in the late gestation ovine fetus.

In view of the suggested relationship between substrate availability, fetal growth and circulating fetal IGF-I concentrations, we investigated the effect of maternal starvation on plasma IGF-I levels in the late gestation ovine fetus. Ten fetuses aged 125-130 d gestation were sampled daily from indwelling arterial catheters. Ewes were starved for 72 h. Starvation was terminated with an intravenous infusion of 10% glucose to the ewe. Food was then replaced 4 h later. Fetal IGF-I concentrations fell from 176.1 +/- 15.2 ng/mL before starvation to 124.5 +/- 10.3 ng/mL after 72 h starvation (p less than 0.05, n = 10). The fall in IGF-I concentrations was reversed by 4 h of maternal glucose infusion. In five fetuses, where samples were obtained 24 h after terminating the starvation, fetal IGF-I concentrations were comparable to those seen before starvation (180.0 +/- 37.7 ng/mL). This study demonstrates that acute maternal starvation causes a reversible decrease in fetal plasma IGF-I levels. These studies suggest that nutrient and in particular glucose availability is a significant determinant of fetal IGF-I secretion and support the hypothesis that IGF-I may play a role in the regulation of fetal growth.

Animals↗
PubMed1984

Epinephrine-stimulated glucose production is not diminished by starvation: evidence for an effect on gluconeogenesis.

We infused physiological doses of epinephrine (1.2 microgram/m2 X min) into six healthy obese subjects in the postabsorptive state and after 3-4 days of starvation. During starvation, a reduction in hepatic glycogen stores was demonstrated by the absence of a rise in plasma glucose and glucose production (using [3-3H]glucose) in response to glucagon infusion. The increases in plasma epinephrine and glucose during the epinephrine infusion were comparable before and after starvation. Most importantly, the increase in endogenous glucose production produced by epinephrine was virtually unaffected, i.e. the initial rise in glucose production (59% vs. 49%), the incremental area under the curve (2.6 vs. 3.1 g/m2), and the spike-decline pattern of the response were no different before and after starvation, respectively. Similarly, epinephrine-induced elevations in gluconeogenic precursors (lactate and alanine) were not altered by starvation. However, starvation accentuated the rise in FFA by 200%. We conclude that starvation does not diminish the rise in endogenous glucose production in response to stress-like elevations of epinephrine. This occurs even though the liver fails to respond to high physiological doses of glucagon, possibly because epinephrine enhances the mobilization of gluconeogenic precursors and FFA. These data suggest that epinephrine is a potent stimulator of gluconeogenesis and may be more effective than glucagon in accelerating glucose production in patients with depleted glycogen stores.

Adult↗
PubMed1985

Insulin-like growth factor I and growth hormone in canine starvation.

The roles of plasma insulin-like growth factor I (IGF I) and growth hormone (GH) were studied in 7 beagle dogs before and during starvation and during refeeding. IGF I levels significantly decreased from 75.2 +/- 5.9 ng/ml at 7 days prior to the start of starvation to 9 +/- 1.7 ng/ml at 19 days after the commencement of starvation (mean +/- SEM; P less than 0.0001). During refeeding IGF I significantly rose from 9 +/- 1.7 ng/ml to 55.5 +/- 7.5 ng/ml within 9 days (mean +/- SEM; P less than 0.002). During starvation plasma GH levels significantly increased (P less than 0.05) and these elevated levels returned to normal during refeeding. The dogs' GH secretory capacity significantly increased during starvation (P = 0.012) and became normal again during refeeding. The following conclusions can be drawn from this study: 1) starvation in the dog leads to a significant and drastic reduction of the circulating levels of IGF I, and 2) starvation in the dog, as in man, leads to increased circulating GH levels and to an increased GH-secretory capacity possibly brought about by a lack of a negative feedback normally exerted by IGF I.

Animals↗
PubMed1988

Influence of starvation on hormonal control of hypophyseal secretion in rats.

The reduction of hypophyseal hormone secretion during starvation is not completely understood. A previous study showed that the concomitant reduction of plasma TSH and T3 may be related to an increased sensitivity of the thyrotrope cell to T3. This suggests that regulation of hypophyseal secretion by peripheral hormones may be altered in starved rats. As GH and PRL secretion are under the control of thyroid and steroid hormones, the aim of the present study was to investigate the modification of feed-back control by T3 or E2 on hypophyseal secretion during starvation. For this purpose, pituitary GH, PRL and TSH contents and their plasma responses to TRH injection were measured in euthyroid, thyroidectomized (Tx), T3-supplemented Tx and E2-treated male Wistar rats before and after a 3-day starvation. TRH (0.25 micrograms/100 g) was injected iv through a chronically-implanted catheter. Our results show that GH content and GH plasma response to TRH are dramatically increased in T3-treated Tx starved rats, suggesting that starvation also increases the effectiveness of T3 influence on somatotrope cell secretion. By contrast, effects of T3 on PRL secretion remain unchanged during starvation. Furthermore, starvation in E2-treated rats is associated with a marked rise in the PRL and GH responsiveness to TRH without any significant change of hormonal pituitary content. This suggests that, in starved rats, E2 increases the effects of TRH on lactotrope and somatotrope secretion. No significant effect on TSH secretion could be demonstrated. Thus, starvation seems to act differentially on the feed-back mechanisms controlling the hormonal secretion of the three adenohypophyseal target cells to TRH.

Animals↗
PubMed2004

Quantitative trait loci affecting starvation resistance in Drosophila melanogaster.

The ability to withstand periods of scarce food resources is an important fitness trait. Starvation resistance is a quantitative trait controlled by multiple interacting genes and exhibits considerable genetic variation in natural populations. This genetic variation could be maintained in the face of strong selection due to a trade-off in resource allocation between reproductive activity and individual survival. Knowledge of the genes affecting starvation tolerance and the subset of genes that affect variation in starvation resistance in natural populations would enable us to evaluate this hypothesis from a quantitative genetic perspective. We screened 933 co-isogenic P-element insertion lines to identify candidate genes affecting starvation tolerance. A total of 383 P-element insertions induced highly significant and often sex-specific mutational variance in starvation resistance. We also used deficiency complementation mapping followed by complementation to mutations to identify 12 genes contributing to variation in starvation resistance between two wild-type strains. The genes we identified are involved in oogenesis, metabolism, and feeding behaviors, indicating a possible link to reproduction and survival. However, we also found genes with cell fate specification and cell proliferation phenotypes, which implies that resource allocation during development and at the cellular level may also influence the phenotypic response to starvation.

Analysis of Variance↗
PubMed1995

Starvation-induced changes in the hypothalamic content of prothyrotrophin-releasing hormone (proTRH) mRNA and the hypothalamic release of proTRH-derived peptides: role of the adrenal gland.

The purpose of this study was to investigate the mechanisms involved in the reduced thyroid function in starved, young female rats. Food deprivation for 3 days reduced the hypothalamic content of prothyrotrophin-releasing hormone (proTRH) mRNA, the amount of proTRH-derived peptides (TRH and proTRH160-169) in the paraventricular nucleus, the release of proTRH-derived peptides into hypophysial portal blood and the pituitary levels of TSH beta mRNA. Plasma TSH was either not affected or slightly reduced by starvation, but food deprivation induced marked increases in plasma corticosterone and decreases in plasma thyroid hormones. Refeeding after starvation normalized these parameters. Since the molar ratio of TRH and proTRH160-169 in hypophysial portal blood was not affected by food deprivation, it seems unlikely that proTRH processing is altered by starvation. The median eminence content of pGlu-His-Pro-Gly (TRH-Gly, a presumed immediate precursor of TRH), proTRH160-169 or TRH were not affected by food deprivation. Since median eminence TRH-Gly levels were very low compared with other proTRH-derived peptides it is unlikely that alpha-amidation is a rate-limiting step in hypothalamic TRH synthesis. Possible negative effects of the increased corticosterone levels during starvation on proTRH and TSH synthesis were studied in adrenalectomized rats which were treated with corticosterone in their drinking water (0.2 mg/ml). In this way, the starvation-induced increase in plasma corticosterone could be prevented. Although plasma levels of thyroid hormones remained reduced, food deprivation no longer had negative effects on hypothalamic proTRH mRNA, pituitary TSH beta mRNA and plasma TSH in starved adrenalectomized rats. Thus, high levels of corticosteroids seem to exert negative effects on the synthesis and release of proTRH and TSH. This conclusion is corroborated by the observation that TRH release into hypophysial portal blood became reduced after administration of the synthetic glucocorticosteroid dexamethasone. On the basis of these results, it is suggested that the reduced thyroid function during starvation is due to a reduced synthesis and release of TRH and TSH. Furthermore, the reduced TRH and TSH synthesis during food deprivation are probably caused by the starvation-induced enhanced adrenal secretion of corticosterone.

Adrenal Glands↗
PubMed2001

Effect of starvation on branched-chain alpha-keto acid dehydrogenase activity in rat heart and skeletal muscle.

The aim of the present study was to investigate changes in the activity of branched-chain alpha-keto acid dehydrogenase (BCKAD) in skeletal muscle and the heart during brief and prolonged starvation. Fed control rats and rats starved for 2, 4 and 6 days were anesthetized with pentobarbital sodium before heart and hindlimb muscles were frozen in situ by liquid nitrogen. Basal (an estimate of in vivo activity) and total (an estimate of enzyme amount) BCKAD activities were determined by measuring the release of 14CO2 from alpha-keto[1-(14)C]isocaproate. The activity state of BCKAD complex was calculated as basal activity in percentages of total activity. Both basal and total activities and the activity state of the BCKAD were lower in skeletal muscles than in the heart. In both tissues, starvation for 2 or 4 days caused a decrease in the basal activity and activity state of BCKAD. On the contrary, in the heart and muscles of animals starved for 6 days a marked increase in basal activity and activity state of BCKAD was observed. The total BCKAD activity was increasing gradually during starvation both in muscles and the heart. The increase was significant in muscles on the 4th and 6th day of starvation. The demonstrated changes in BCKAD activity indicate significant alterations in branched-chain amino acid (BCAA) and protein metabolism during starvation. The decreased BCKAD activity in skeletal muscle and heart observed on the 2nd and 4th day of starvation prevents the loss of essential BCAA and is an important factor involved in protein sparing. The increased activity of BCKAD on the 6th day of starvation indicates activated oxidation of BCAA and accelerated protein breakdown.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1986

Comparison between starvation and consumption of a high protein diet: plasma insulin and glucagon and hepatic activities of gluconeogenic enzymes during the first 24 hours.

Plasma insulin, glucagon, glucose, free fatty acids and glycerol, hepatic cyclic AMP and glycogen, and liver phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-bisphosphatase (FBPase), glucose 6-phosphatase (G6Pase) and alanine amino transferase (AAT) activities were examined in adult rats during the first 24 h of either starvation or consumption of a high protein, carbohydrate-free (HP) diet. Under both nutritional conditions, plasma insulin fell within 12 h and remained constant thereafter. Glucagon increased 12 h after the start of the experiment and peaked between 18-24 h. The insulin: glucagon ratio was lower during the last 12 h of the experiment. In both experimental groups, liver cyclic AMP increased progressively and peaked between 15-24 h, but it increase was higher on HP diet than on starvation. Whereas plasma glucose remained low on starvation for 24 h, it returned to normal on consumption of the HP diet. In both groups, liver glycogen fell within 12 h and remained low until the end of experiment. FBPase, G6Pase and AAT did not change on starvation, while they increased toward the end of 1 d HP consumption. During starvation or consumption of the HP diet, PEPCK increased progressively and peaked between 15-24 h, but the increase was greater with the HP diet than with starvation. These findings suggest that in the first 24 hours, the adaptative response of hepatic gluconeogenesis is higher with a HP diet than upon starvation.

Adaptation, Physiological↗
PubMed1983

Dopamine excretion during natriuresis of starvation.

Five obese subjects were studied when they were on a 3.35 MJ (800 kcal)-diet, 1.67 MJ (400 kcal) diet and during total starvation. Urine excretion of sodium and dopamine and plasma renin activity (PRA) and plasma aldosterone levels were measured. Urine sodium excretion increased from 88 +/- 9.8 mmol/d before starvation to 150 +/- 15.7 mmol/d on day 4 of starvation. Dopamine excretion increased from 0.92 +/- 0.23 mumol/d before starvation to 1.56 +/- 0.24 mumol/d on day 1 of starvation (P less than 0.01). These results suggest that dopamine excretion is increased in early starvation and may play a role in the natriuresis of starvation.

Adult↗
PubMed2000

Carbohydrate metabolism during starvation in the silkworm Bombyx mori.

The effect of starvation on carbohydrate metabolism in the last instar larvae of the silkworm Bombyx mori was examined. Trehalose concentration in the hemolymph increased slightly during the first 6 h of starvation and decreased thereafter, whereas glucose concentration decreased rapidly immediately after diet deprivation. Starvation-induced hypertrehalosemia was completely inhibited by neck ligation, suggesting that starvation stimulates the release of a hypertrehalosemic factor(s) from the head. The percentage of active glycogen phosphorylase in the fat body increased within 3 h of starvation and its glycogen content decreased gradually. These observations suggest that production of trehalose from glycogen is enhanced in starved larvae. However, hypertrehalosemia during starvation cannot be explained by the increased supply of trehalose into hemolymph alone, as similar changes in phosphorylase activity and glycogen content in the fat body were observed in neck-ligated larvae, in which hemolymph trehalose concentration did not increase but decreased gradually. When injected into larvae, trehalose disappeared from hemolymph at a rate about 40% lower in starved larvae than neck-ligated larvae. The hemolymph lipid concentration increased during starvation, suggesting that an increased supply of lipids to tissues suppresses the consumption of hemolymph trehalose and this is an important factor in hypertrehalosemia.

Animals↗
PubMed2006

Proteome signatures for stress and starvation in Bacillus subtilis as revealed by a 2-D gel image color coding approach.

In this paper we have defined proteome signatures of Bacillus subtilis in response to heat, salt, peroxide, and superoxide stress as well as after starvation for ammonium, tryptophan, glucose, and phosphate using the 2-D gel-based approach. In total, 79 stress-induced and 155 starvation-induced marker proteins were identified including 50% that are not expressed in the vegetative proteome. Fused proteome maps and a color coding approach have been used to define stress-specific regulons that are involved in specific adaptative functions (HrcA for heat, PerR and Fur for oxidative stress, RecA for peroxide, CymR and S-box for superoxide stress). In addition, starvation-specific regulons are defined that are involved in the uptake or utilization of alternative nutrient sources (TnrA, sigmaL/BkdR for ammonium; tryptophan-activated RNA-binding attenuation protein for tryptophan; CcpA, CcpN, sigmaL/AcoR for glucose; PhoPR for phosphate starvation). The general stress or starvation proteome signatures include the CtsR, Spx, sigmaL/RocR, sigmaB, sigmaH, CodY, sigmaF, and sigmaE regulons. Among these, the Spx-dependent oxidase NfrA was induced by all stress conditions indicating stress-induced protein damages. Finally, a subset of sigmaH-dependent proteins (sporulation response regulator, YvyD, YtxH, YisK, YuxI, YpiB) and the CodY-dependent aspartyl phosphatase RapA were defined as general starvation proteins that indicate the transition to stationary phase caused by starvation.

Bacillus subtilis↗