Leptin protects mice from starvation-induced lymphoid atrophy and increases thymic cellularity in ob/ob mice

Thymic atrophy is a prominent feature of malnutrition. Forty-eight hours' starvation of normal mice reduced the total thymocyte count to 13% of that observed in freely fed controls, predominantly because of a diminution in the cortical CD4(+)CD8(+) thymocyte subpopulation. Prevention of the fasting-induced fall in the level of the adipocyte-derived hormone leptin by administering exogenous recombinant leptin protected mice from these starvation-induced thymic changes. The ob/ob mouse, which is unable to produce functional leptin because of a mutation in the obese gene, has impaired cellular immunity together with a marked reduction in the size and cellularity of the thymus. We found that ob/ob mice had a high level of thymocyte apoptosis resulting in a ratio of CD4(+)CD8(+) (cortical) to CD4(-)CD8(-) (precursor) thymocytes that was 4-fold lower than that observed in wild-type mice. Peripheral administration of recombinant leptin to ob/ob mice reduced thymocyte apoptosis and substantially increased both thymic cellularity and the CD4(+)CD8(+)/CD4(-)CD8(-) ratio. In contrast, a comparable weight loss in pair-fed PBS-treated ob/ob mice had no impact on thymocyte number. In vitro, leptin protected thymocytes from dexamethasone-induced apoptosis. These data indicate that reduced circulating leptin concentrations are pivotal in the pathogenesis of starvation-induced lymphoid atrophy.

Starvation: early signals, sensors, and sequelae

To identify the sequences of changes in putative signals, reception of these and responses to starvation, we sampled fed and starved rats at 2- to 6-h intervals after removal of food 2 h before dark. Metabolites, hormones, hypothalamic neuropeptide expression, fat depots, and leptin expression were measured. At 2 h, insulin decreased, and FFA and corticosterone (B) increased; by 4 h, leptin and glucose levels decreased. Neuropeptide Y messenger RNA (mRNA) increased 6 h after food removal and thereafter. Adrenal and plasma B did not follow ACTH and were elevated throughout, with a nadir at the dark-light transition. Leptin correlated inversely with adrenal B. Fat stores decreased during the last 12 h. Leptin mRNA in perirenal and sc fat peaked during the dark period, resembling plasma leptin in fed rats. We conclude that 1) within the first 4 h, hormonal and metabolic signals relay starvation-induced information to the hypothalamus; 2) hypothalamic neuropeptide synthesis responds rapidly to the altered metabolic signals; 3) catabolic activity quickly predominates, reinforced by elevated B, not driven by ACTH, but possibly to a minor extent by leptin, and more by adrenal neural activity; and 4) leptin secretion decreases before leptin mRNA or fat depot weight, showing synthesis-independent regulation.

Decreased densities of intramembranous particles and cytochemically detectable cholesterol in microvilli of starved rat enterocytes

The densities of intramembranous particles (IMPs) and of sterol complexes induced by treatment of filipin were studied by freeze-fracture replication of intact intestine and/or isolated brush border membranes (BBM) of well-fed and starved rats. The density of IMPs and filipin-sterol complexes (FSCs) decrease considerably during starvation. Biochemical estimations show a decrease in the levels of cholesterol and proteins with respect to phospholipids during starvation which is in agreement with morphological findings. It is suggested that these changes may play a role in regulating membrane fluidity which in turn affects absorption of nutrients through BBM.

Depletion of acinar secretory granules in the ferret parotid gland: effects of substance P and vasoactive intestinal peptide

The acinar cells of the ferret parotid gland are supplied with parasympathetic nerve fibres containing vasoactive intestinal peptide (VIP) and substance P. In this study intracarotid infusions of the two peptides (0.5-1.0 microgram kg-1 min-1 of each for 40 min) in the pentobarbitone-anaesthetized ferret, treated with atropine and adrenoceptor antagonists, induced a loss of acinar secretory granules from this gland, by 32 % in response to VIP and by 46 % in response to substance P. Stimulation of the parasympathetic auriculo-temporal nerve (40 Hz, in the presence of adrenoceptor antagonists) caused a larger loss of acinar granules from the gland than stimulation of the sympathetic superior cervical ganglion (intermittently, 50 Hz for 1 s every 10th second, in the presence of atropine) over 40 min (52 % versus 10 %). A 27 % granular loss in response to parasympathetic stimulation followed upon atropinization. The parasympathetic response was not further diminished by the tachykinin antagonist Spantide ((d-Arg1, d-Pro2, d-Trp7,9, Leu)-substance P). Thus, despite the large exocytotic response to the infusion of substance P, the parasympathetic non-adrenergic, non-cholinergic secretion of storage granules seemed, under the present experimental conditions, to occur independently of the action of substance P.

Beta-cell mass and proliferation following late fetal and early postnatal malnutrition in the rat

We have recently shown that maternal food restriction during late pregnancy in rats decreased beta-cell mass in the offspring at birth, without altering beta-cell proliferation. The aim of the present work was to determine: 1) whether sustained maternal undernutrition until weaning (R group) more dramatically alters beta-cell mass in the offspring and if normal food supply from weaning until adulthood could reverse the deleterious effects and; 2) if altered beta-cell proliferation was responsible for the decreased beta-cell mass. Beta-cell fraction and proliferative capacity were determined during the suckling period and at adult age after ad libitum feeding from weaning in the R animals and in age-matched controls (C group). At day 21, the offspring born and nursed by food-restricted mothers (R animals) showed a 66% reduction in beta-cell mass and number, which did not increase from birth to weaning, although beta-cell proliferation remained normal. At 3 months of age, R animals had 35% decreased beta-cell fraction, with a 50% decrease in the head of the pancreas. In that area, beta-cell proliferation was similar to that of the controls. In the tail of the pancreas, beta-cell fraction was only slightly impaired but beta-cell proliferation was increased by 37%, as compared with the controls. This increase was associated with a shift in islet size distribution towards medium and large islets compared with the head of pancreas from these R animals. No regional variations of beta-cell fraction, proliferation or islet size distribution were observed in adult control animals. In conclusion, prolonged malnutrition until weaning impairs beta-cell development but not beta-cell proliferation. Subsequent re-nutrition is followed by increased beta-cell proliferation but this is insufficient to fully restore beta-cell mass.

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.

Amaranthin lectin binding in the rat colon: response to dietary manipulation

BACKGROUND

In human colon, binding of the lectin Amaranthus caudatus has been considered to be a marker of cellular proliferation and malignant progression. We studied regional amaranthin binding in rat colon and correlated this with physiologic manipulations of proliferation.

METHODS

Binding of amaranthin in segments of proximal and distal colon was studied in starved, refed, and control Wistar rats and was compared to tritiated thymidine labeling and proliferating cell nuclear-antigen expression.

RESULTS

Amaranthin bound mainly to cells in the lower crypt of distal colon and midcrypt of proximal colon, paralleling the distribution of proliferative markers. Binding occurred in the supranuclear region in distal colon and the pericellular membrane in proximal colon. Starvation/refeeding was associated with a change in amaranthin binding intensity in distal colon, but not in proximal colon.

CONCLUSION

The pattern of amaranthin binding during starvation/refeeding seems to reflect physiologic changes in several areas of the colon.

Postmortem investigations on winter stranded sperm whales from the coasts of Belgium and The Netherlands

During winter 1994-95, four and three sperm whales (Physeter macrocephalus) were stranded along the Belgian and the Dutch coasts, respectively. Necropsies and tissue samplings were collected 24 hrs post mortem. Lesions on several whales included round and linear skin scars, ventral skin abrasions, acute skin ulcers, acute ulcerative stomatitides, acute to chronic external otitides, and passive visceral congestion. In addition, these sperm whales appeared to be debilitated with severe weight deficit, had blubber thickness reduction, the absence of abdominal fat, and the intestinal tracts were almost empty. Three categories of lesions and their possible relation with the stranding were evaluated. Cutaneous scars observed on the seven whales appeared to have no relation with the stranding. The poor body condition and acute integument ulcerative lesions were present before the stranding. Ventral skin abrasions and visceral passive congestion were caused by the strandings. Absence of food in the alimentary tracts, evidence of weight loss and blubber thickness reduction were compatible with an extended presence of the sperm whales in the North Sea, where adequate food is not available. This might lead to progressive weakness, predisposing the animals to secondary pathogens such as viral diseases. Finally, the coastal configuration of the southern North Sea makes it a trap for sperm whales which have entered the area during their wanderings.

Decreased interleukin-2 production from cultured peripheral blood mononuclear cells in human acute starvation

Depressed cell-mediated immunity and decreased insulin-like growth factor I (IGF-I) are observed in malnourished humans. To study the interaction among nutrition, IGF-I, and cytokines, healthy volunteers (six men and four women, aged 21-38 yr, weighing 93-124% of ideal body weight) were subjected to a 7-day fast (mineral water only). Fasting steadily decreased serum IGF-I from 247 +/- 29 (prefast) to 87 +/- 10 ng/mL (postfast; P < 0.0001), total T cells (CD3+) from 1499 +/- 68 to 1308 +/- 70 x 10(9) (P < 0.0001), and T helper cells (CD4+) from 997 +/- 62 to 856 +/- 55 x 10(9) (P < 0.001). Peripheral blood mononuclear cells were isolated and cultured in serum-free RPMI 1640 for 24 h. Fasting attenuated peripheral blood mononuclear cell production of interleukin-2 in response to various concentrations of phytohemagglutinin P [PHA-P; 347 +/- 48 (prefast) vs. 135 +/- 52 pg/mL (postfast) when challenged with 3 micrograms/mL PHA-P; P < 0.005 when comparing dose-response curves (1-100 micrograms/mL PHA-P)]. Although the approximately 3-fold suppression of interleukin-2 and IGF-I in subjects fasted for 1 week is not likely to affect immune function significantly, our results with this short term model of nutrient restriction provide insight into possible mechanisms for immune suppression in chronic starvation.

Effects of OP 2507, a stable analogue of prostaglandin I2, on carbon tetrachloride-induced liver damage in starved rats

It has been reported that vasodilatory prostaglandins have cytoprotective effects against various types of liver damage. We investigated the effects OP 2507, a stable analogue of prostaglandin I2, on carbon tetrachloride-induced liver damage in starved rats. Intraperitoneal administration of OP 2507 at 1,500 micrograms/kg lessened both an increase in serum alanine aminotransferase activity and an inhibition of starvation ketosis, both of which were induced by carbon tetrachloride. At lower doses, however, OP 2507 not only failed to ameliorate the carbon tetrachloride-induced changes, but it actually exaggerated them. Although the deterioration of carbon tetrachloride-induced liver damage by lower doses of OP 2507 was not statistically significant, it seems possible that OP 2507 has dual effects on carbon tetrachloride-induced liver damage. While none of the three agents cimetidine, reduced glutathione and deferoxamine, prevented increase in serum alanine aminotransferase activity induced with lower dose OP 2507, allopurinol had a tendency to prevent the increase, indicating that lower doses of OP 2507 may promote a reaction catalyzed by xanthine oxidase. We propose that both the co-administration of prostaglandins and other potentially hepatotoxic drugs, and the administration of prostaglandins to patients with drug-induced liver damage should be done carefully.

Age-related response of the small intestine to severe starvation and refeeding in rats

The impact of severe starvation and refeeding on the intestinal mucosa of rats of different ages has been studied in a diet-controlled model. Structural and functional alterations of the small intestinal mucosa were assessed by standard parameters including mucosal protein, DNA content as well as maltase, sucrase and leucine aminopeptidase enzymatic activities. Decreases in mucosal mass, DNA, protein and leucine aminopeptidase activity in both the jejunum and ileum caused by starvation, diminished with age. The depression of disaccharidase activities increased with age in the jejunum but not in the ileum. Except for jejunal protein and leucine aminopeptidase activity, the recovery from starvation, after refeeding, was complete for the other parameters studied, regardless of age.

Protein synthesis in the heart in vivo, its measurement and patho-physiological alterations

Changes in cardiac protein composition occur in a variety of patho-physiological situations and are usually accompanied by modifications in protein synthesis. Although adjustments in protein synthesis during starvation may be adaptive, the alterations in protein synthesis seen in response to ethanol ingestion may be pathological and an important step in the genesis of alcoholic heart muscle disease. The alterations in heart muscle in hypertension are initially adaptive but in the long term they are deleterious, and involve both transcription and translation. While adequate methods exist for quantifying the amount of mRNA for contractile and non-contractile proteins, such studies of gene-expression provide no dynamic information on the rate at which tissue proteins are lost or accrued. This can only be determined by measuring the rate of protein turnover, i.e. either protein synthesis or protein breakdown. Techniques for directly determining the rates of protein breakdown are limited or involve surgical procedures. Methods for measuring the rate of protein synthesis are described, and are illustrated by their application to the investigation of starvation and ethanol toxicity. In particular, attention is focused on the fact that reliable rates of protein synthesis are obtained only if the specific radioactivity of the precursor at the site of protein synthesis (aminoacyl-tRNA) is assessed.

Influence of casein and casein hydrolysate diets on nutritional recovery of starved rats

BACKGROUND

The aim of this study was to compare the effects of two diets, which differed in their protein source (casein and casein hydrolysate), on the nutritional recovery and intestinal repair of undernourished rats at weaning after a 3-day fasting period. Profound alterations in gut structure and signs of malnutrition appeared after the starvation period.

METHODS

The casein hydrolysate was prepared by enzymatic hydrolysis and ultrafiltration. Rats were refed the casein-based or the casein hydrolysate-based diet for 96 hours. Normal-fed male Wistar rats at weaning were given the casein diet for 7 days and were used as controls. Liver acetylcholinesterase, glutamate dehydrogenase activities, serum amino acid profiles, jejunal oligosaccharidases, alkaline phosphatase, and leucine aminopeptidase activities were studied. Intestinal permeability to intact proteins was also tested by using ovalbumin and measuring its concentration in serum.

RESULTS

Intestinal and liver enzyme activities and serum amino acid profiles reached normal values after 96 hours of refeeding, regardless of the diet used. Glutamate dehydrogenase activity remained higher in both diet groups. Intestinal permeability to ovalbumin remained significantly increased only in the group refed the casein diet.

CONCLUSIONS

Our results show that 4 days of refeeding are sufficient for complete intestinal recovery after fasting, provided the dietary protein source is a casein hydrolysate. We suggest that patients with malnutrition or malabsorption syndrome should be fed formula composed of enzymatic protein hydrolysates (because of their low antigenicity) rather than enteral formulas composed of intact proteins.

Sister chromatid exchange frequency is elevated and cell proliferation is delayed in bone marrow cells of starved and marginally malnourished rats

The frequency of sister chromatid exchanges (SCE) and the cell proliferation kinetic were analyzed in bone marrow (BM) cells of Wistar rats subjected to starvation and marginal malnutrition (MN) after 24h of 5-bromodeoxyuridine (BdUr) implantation. SCE were analyzed in a minimum of 18 consecutive second division metaphases and for cell proliferation, 100 consecutive metaphases were analyzed and classified into the first, second and third or subsequent replication cycles. Rats subjected to starvation and MN exhibited significantly higher mean SCE per lymphocyte in bone marrow than the well nourished rats. Further, they also showed a longer proliferation kinetic in BM cells. These observations indicate that starvation and MN per se resulted in greater SCE and prolongation of the cell cycle in experimental animals. On rehabilitation, the cells with high SCE frequency and prolonged cell cycle in both starved and MN rats were comparable to control groups.

The hepatocellular uptake of free fatty acids is selectively preserved during starvation

BACKGROUND/AIMS

The liver loses protein during fasting. This study sought to determine if hepatic protein loss during fasting selectively preserves functions important to survival such as uptake of fatty acids, which are major energy substrates in that condition.

METHODS

Initial [3H]oleate uptake and efflux rates in hepatocytes from starved (for 48 hours) and fed male rats were measured in media containing 250 mumol/L albumin at oleate/albumin ratios of 0.2:1-2:1. Uptake rates of sulfobromophthalein, taurocholate, and glucose were also determined.

RESULTS

Initial oleate uptake rate was saturable with respect to unbound oleate concentration. Maximum initial velocity expressed per cell number did not differ between fasted and fed animals, but measured cell volume and estimated surface area were decreased in starved vs. fed hepatocytes (921 +/- 21 vs. 1623 +/- 58 microns2, respectively; P < 0.001). Consequently, when expressed per surface area, maximum initial velocity was greater in starved cells (17 +/- 3 vs. 10 +/- 2 [pmol.min-1.micron2] x 10(-7); P < 0.02). Expressed similarly, oleate efflux was also greater from starved hepatocytes and was inhibited by an antibody to plasma membrane fatty acid binding protein (FABPpm). FABPpm concentration per unit area of plasma membrane also increased in starved hepatocytes (P < 0.05). By contrast, uptake rates of sulfobromophthalein, taurocholate, and glucose by starved hepatocytes were decreased when expressed per cell number and unchanged per unit area.

CONCLUSIONS

During fasting, the hepatocellular uptake mechanism for oleate is selectively preserved compared with those for sulfobromophthalein, taurocholate, or glucose.

31P magnetic resonance spectroscopy demonstrates expansion of the extracellular space in the skeletal muscle of starved rats

Starvation significantly alters the distribution of body water. To study the effects of starvation on cellular energetics and water distribution in skeletal muscle, a novel 31P magnetic resonance technique (31P MRS) was developed to measure water compartments. After 31P MRS-visible water space markers which distribute in total body water (dimethyl methylphosphonate, DMMP) and extracellular water (phenylphosphonate, PPA) were infused intravenously, 31P MRS spectra were obtained from the gastrocnemius muscle of male virus-free Wistar rats at baseline and after starvation or ad libitum feeding for 4 days. Muscle water spaces were also measured using the chloride method and Nernst's equation. Muscle water contents as determined by drying were equivalent in the two groups. In vivo measurements of changes in DMMP relative to all of the MRS visible phosphates also demonstrated that the total water space was similar in control and starved rats. However, starvation significantly increased the ratio of PPA/DMMP (0.67 +/- 0.05 vs 0.87 +/- 0.04, Control vs Starvation; P < 0.001), and therefore the ratio of extracellular water to total water in the gastrocnemius. Furthermore, because muscle water contents were comparable between the groups, this expansion of the extracellular space was accompanied by contraction of the intracellular compartment in starved animals. Equivalent changes were detected in vitro using the chloride method. Lastly, phosphocreatine/ATP ratios, which measured changes in high-energy phosphate stores, decreased after starvation (4.09 +/- 0.06 vs 3.61 +/- 0.06; P < 0.001) and were inversely related to changes in PPA/DMMP (r = -0.61; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of gastric lesions and hypoglycemic response by food deprivation in streptozotocin-diabetic rats

Overnight fasting causes hemorrhagic lesions in the stomach of streptozotocin (STZ)-induced diabetic rats, but the pathogenetic mechanism remains unknown. The present study was performed to investigate the pathogenesis of such lesions developed in STZ-diabetic rats after starvation, mainly in relation to blood glucose changes. A single injection of STZ (70 mg/kg, intraperitoneally) induced hyperglycemic conditions one week after the administration, and high blood glucose levels (BGL: > 350 mg%) remained up to three weeks later. The STZ-diabetic rats developed gastric lesions with the marked reduction of BGL after 18 hr of fasting, depending upon the duration of diabetes; the lesion score and delta BGL reduction in the 3-week-old STZ rats were 32.0 +/- 7.8 mm and > 250 mg/100 ml, respectively. Acid secretion in the pylorus-ligated rats was not significantly changed in the STZ-induced diabetic conditions for the initial two weeks but slightly decreased at three weeks when compared with normal rats. Fasting of normal rats for 18 hr did not cause either BGL reduction or any lesion in the stomach. In the 3-week-old STZ animals, the severity of gastric lesions increased with the duration of fasting (4-18 hr) and was again closely associated with the degree of delta BGL reduction. These lesions induced by 18 hr of starvation in 3-week-old STZ rats were significantly inhibited by pretreatment with insulin (4 units/rat/day) for the last one week to maintain BGL within normal ranges or by intravenous infusion of 25% glucose during fasting period. Both of these treatments significantly prevented BGL reduction in response to fasting.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of emaciation in relation to threat to life in anorexia nervosa

Twenty patients with anorexia nervosa and a body weight below 60% of the standard weight were studied. One died of starvation; the others survived. Four patients, including the deceased, had such severe weakness that they could not sit up without support, and another five could sit up only from a lateral position. Serum albumin or hemoglobin levels at the beginning of therapy could not be used for nutritional assessment because of dehydration, while increased blood urea nitrogen was associated with acute illness. The present results together with data from previous studies of fatal anorexia indicate that the risk of mortality may be quite low when body weight is above 60% of the standard. We suggest that gross muscle weakness in addition to body weight for height can be a valuable indicator to assess the criticalness in anorexia nervosa.

Ultrastructural alterations of the rat intestinal epithelium fed with polymeric, oligopeptidic or elementary full diet, following starvation

In this study the ultrastructure of rat jejunal epithelial cells was examined, following a starvation period of 72 hours and an enteral refeeding period of 12 days, with either Nutrison, Pepti 2000, or Nutri 2000. Most changes occurred in the animals examined immediately after the 72-hour starvation period; these mainly included a significant decrease in microvilli population, occasional cell membrane disintegration, and a usual microvesicular appearance and degranulation of the rough endoplasmic reticulum. No alterations were found in the normally-fed animals (control group). This was also practically the same for the Pepti 2000 group. In the Nutrison group, a small amount of changes were found, while in the Nutri 2000 group many alterations were detected, which nevertheless were fewer than in the starved animals. The results demonstrate that the micromorphological alterations of the intestinal epithelium caused by starvation improve faster when an oligopeptidic formula is provided, which consequently results in faster and better absorption of the nutrients.

Chromosomal abnormalities in starved and marginally malnourished rats and in utero upon rehabilitation

The effects of starvation and marginal malnutrition (MN) on the lymphocytes of rats were evaluated by chromosomal analysis before and after rehabilitation. The effect of parental starvation or malnutrition on chromosomal aberrations in the foetus was also studied. Wistar rats, 30-35 days old, were starved for 5 days or fed a minimally restricted or a severely restricted diet for three weeks. At the end of the period of starvation or malnutrition, lymphocytes were isolated and chromosomal analysis was performed. Starved and severely restricted rats showed significantly higher mean chromosomal aberrations than the controls. These aberrations returned to a normal level when the experimental groups were rehabilitated for a month, indicating that the damage was transient. A chromosomal aberration study done on foetal cells from rehabilitated rats which had previously been starved or fed a severely restricted diet showed significantly increased values, indicating that some damage was permanent. A low number of implantations was also recorded in these experimental groups. These observations clearly indicate that young animals exposed to conditions like starvation or chronic malnutrition are prone to permanent damage of the genetic system.