Hours Of Refeeding Research Articles

Abstract 2110: Fasting-refeeding Dynamics Induce Distinct Vascular Responses In Lean And Obese Mice

Background: Intermittent fasting (IF) can improve arterial stiffness, a predictor of cardiovascular disease. However, it is still unclear how many bouts of IF are needed to improve arterial stiffness, and once improvements occur, how long after the fasting period are they maintained. Thus, the primary purpose of this study was to determine how long changes in arterial stiffness are maintained after IF and how many IF cycles are required to alter arterial stiffness in lean and obese animals. Methods: Wild-type (WT) and genetically obese (Ob) mice were randomized to an 11-week protocol to receive either ad libitum control diet (Ad-Lib) or a once weekly 24 hr fast (IF), yielding 4 groups: WT+Ad-Lib; WT+IF; Ob+Ad-Lib; and Ob+IF. Body weight was measured weekly while arterial pulse wave velocity (aPWV) was measured at baseline and at least 24 hrs after fasting at mid- (weeks 5-6), and endpoints (weeks 9-10). To test the persistence of de-stiffening after one week of IF, IF groups were further split only during week 1 of the protocol such that body weight and aPWV were measured immediately after the first 24 hr fast, 1 day after refeeding, or 7 days after refeeding. Results: In WT mice, body weight was reduced by the 24 hr fast (p<0.01) but rebounded after a day of refeeding (p=0.22) when compared to baseline. Interestingly, aPWV was increased after the 24 hr fast (p=0.02) but was restored back to baseline levels within 24 hrs and did not change thereafter. In Ob animals, no significant differences in body weight were found between baseline and any timepoint during the first week. However, compared to baseline, Ob+IF mice had reduced body weight (p<0.01) and aPWV (p<0.01) at the midpoint, and modestly reduced aPWV at the endpoint (p=0.06). Conclusions: A single 24 hr fast increased aPWV in WT mice yet these acute changes returned to baseline within 24 hours of refeeding and did not change thereafter. A single 24 hr fast did not affect aPWV in Ob mice, whereas 5 weeks of IF ameliorated body weight and aPWV, with these vascular improvements being maintained with continued IF for at least another 5 weeks. These data suggest that once weekly 24 hr IF could be a viable dietary strategy to attenuate obesity-induced arterial stiffness.

In Vivo Effects of AICAR and Prodrug 39 (P39) on Anabolic Pathways Following Refeeding in Skeletal Muscle

Exercise training is known to elicit many beneficial adaptations. However, the mechanisms by which this happens are not entirely understood. During muscle contraction, increased intracellular AMP levels mediate many exercise‐induced adaptations by activating AMP‐activated protein kinase (AMPK), among other targets. AMP mimicry may, therefore, be an attractive pharmacological approach to stimulate some of exercise’s benefits. The prodrug AICAR is a well‐established AMPK activator when phosphorylated in the cell to form ZMP, an AMP mimetic. However, it has limited pharmacological potential due to poor pharmacokinetics. Prodrug 39 (P39) uses an alternative approach to deliver ZMP to the cell. The purpose of this study was to compare AMPK and P39 effects on blood glucose levels, AMPK activation, and anabolic signaling in the fasted and refed states. C57BL/6 mice were subjected to a 12 hour fast, followed by 1 hour of refeeding. Following the 12‐hour fast, blood glucose was measured, and mice were injected with saline, AICAR or P39 (400 mg/kg BW). Mice were immediately transferred to cages with food, except for a fasted saline group. After 1 hour of refeeding, food was removed from cages. Blood glucose was measured 25 minutes later, and mice were sacrificed. Gastrocnemius‐plantaris‐soleus complex (GPS) muscles were quick‐frozen for protein analysis. Fasting blood glucose levels were 80 ± 4 mg/dL prior to refeeding and were elevated to 144 ± 8 mg/dL (p<0.0001) after food reintroduction. Both AICAR and P39 caused a significant reduction in blood glucose compared to refed controls (p<0.0001, 54 ± 9, and 56 ± 10 mg/dL, respectively). In GPS muscle, AMPK phosphorylation status was unaffected by any treatment. However, ACC phosphorylation, a downstream target of AMPK, was ~3‐fold higher in AICAR‐treated animals compared to refed controls (p<0.01), with no significant effect of P39. Refeeding induced an increase in anabolic signaling, as indicated by an increase in S6 phosphorylation (~4‐fold, p<0.01) and a trend for increased eIF4E‐binding protein (4E‐BP1) phosphorylation (p = 0.1). This increase was entirely prevented in AICAR and P39‐treated animals. Overall, these results suggest that AICAR and P39 are similarly effective in lowering blood glucose and dampening anabolic signaling following refeeding. However, AICAR was more effective in activating AMPK signaling in skeletal muscle at this dose.

The feeding microstructure of male and female mice.

The feeding pattern and control of energy intake in mice housed in groups are poorly understood. Here, we determined and quantified the normal feeding microstructure of social male and female mice of the C57BL/6J genetic background fed a chow diet. Mice at 10w, 20w and 30w of age showed the expected increase in lean and fat mass, being the latter more pronounced and variable in males than in females. Under ad libitum conditions, 20w and 30w old females housed in groups showed significantly increased daily energy intake when adjusted to body weight relative to age-matched males. This was the combined result of small increases in energy intake during the nocturnal and diurnal photoperiods of the day without major changes in the circadian pattern of energy intake or spontaneous ambulatory activity. The analysis of the feeding microstructure suggests sex- and age-related contributions of meal size, meal frequency and intermeal interval to the control of energy intake under stable energy balance, but not under negative energy balance imposed by prolonged fasting. During the night, 10-20w old females ate less frequently bigger meals and spent more time eating them resulting in reduced net energy intake relative to age-matched males. In addition, male and female mice at all ages tested significantly shortened the intermeal interval during the first hours of re-feeding in response to fasting without affecting meal size. Further, 20-30w old males lengthened their intermeal interval as re-feeding time increased to reach fed-levels faster than age-matched females. Collectively, our results suggest that the physiological mechanisms controlling meal size (satiation) and the non-eating time spent between meals (satiety) during stable or negative energy balance are regulated in a sex- and age-dependent manner in social mice.

Homeostatic versus hedonic control of carbohydrate selection.

Macronutrient intake is associated with cardiometabolic health, ageing and longevity, but the mechanisms underlying its regulation have remained unclear. Most rodents increase carbohydrate selection under certain physiological and pathological conditions such as fasting. When presented with a choice between a basally preferable high-fat diet (HFD) and a high-carbohydrate diet (HCD) such as a high-sucrose diet, fasted mice first eat the HFD and then switch to the HCD during the first few hours of refeeding and continue to eat the HCD up to 24h in the two-diet choice approach. Such consumption of an HCD after fasting reverses the fasting-induced increase in the plasma concentration of ketone bodies more rapidly than does refeeding with an HFD alone. 5'-AMP-activated protein kinase (AMPK)-regulated neurons in the paraventricular nucleus of the hypothalamus (PVH) that express corticotropin-releasing hormone (CRH) are necessary and sufficient for the fasting-induced selection of carbohydrate over an HFD in mice. These neurons appear to contribute to a fasting-induced increase in the positive valence of carbohydrate without affecting the preference for more palatable and energy-dense diets such as an HFD. Identification of the neural circuits in which AMPK-regulated CRH neurons in the PVH of mice are embedded should shed new light on the physiological and molecular mechanisms responsible for macronutrient selection.

β-Cell Control of Insulin Production During Starvation-Refeeding in Male Rats.

Mammalian metabolism has evolved to adapt to changes in nutrient status. Insulin, the key anabolic hormone, facilitates intracellular storage of nutrient fuels and plays a pivotal role in the transition away from catabolism upon refeeding. Although circulating insulin relative to nutrient levels has been well characterized during fasting and refeeding, how pancreatic β-cell biology caters to acute changes in insulin demand has not been sufficiently addressed. Here, we examined the dynamics of (pro)insulin production and associated changes in β-cell ultrastructure during refeeding after a 72-hour fast in male rats. We found that fasted β-cells had marked degranulation, which inversely coordinated with the upregulation of autophagolysomal and lysosomal organelles. There was also expanded Golgi that correlated with enhanced (pro)insulin biosynthetic capacity but, conversely, blunted in vivo insulin secretion. Within 4 to 6 hours of refeeding, proinsulin biosynthesis, cellular ultrastructure, in vivo insulin secretion, and glucose tolerance normalized to levels near those of fed control animals, indicating a rapid replenishment of normal insulin secretory capacity. Thus, during a prolonged fast, the β-cell protects against hypoglycemia by markedly reducing insulin secretory capacity in vivo but is simultaneously poised to efficiently increase (pro)insulin production upon refeeding to effectively return normal insulin secretory capacity within hours.

Neuronal connections of the central amygdalar nucleus with refeeding-activated brain areas in rats

Following fasting, satiety is accompanied by neuronal activation in brain areas including the central amygdalar nucleus (CEA). Since CEA is known to inhibit food intake, we hypothesized that CEA contributes to the termination of meal during refeeding. To better understand the organization of this satiety-related circuit, the interconnections of the CEA with refeeding-activated neuronal groups were elucidated using retrograde (cholera toxin-β subunit, CTB) and anterograde (phaseolus vulgaris leucoagglutinin, PHA-L) tracers in male rats. C-Fos-immunoreactivity was used as marker of neuronal activation. The refeeding-activated input of the CEA primarily originated from the paraventricular thalamic, parasubthalamic and parabrachial nuclei. Few CTB-c-Fos double-labeled neurons were detected in the prefrontal cortex, lateral hypothalamic area, nucleus of the solitary tract (NTS) and the bed nuclei of the stria terminalis (BNST). Only few refeeding-activated proopiomelanocortin-producing neurons of the arcuate nucleus projected to the CEA. Anterograde tract tracing revealed a high density of PHAL-labeled axons contacted with refeeding-activated neurons in the BNST, lateral hypothalamic area, parasubthalamic, paraventricular thalamic and parabrachial nuclei and NTS; a low density of labeled axons was found in the paraventricular hypothalamic nucleus. Chemogenetic activation of the medial CEA (CEAm) inhibited food intake during the first hour of refeeding, while activation of lateral CEA had no effect. These data demonstrate the existence of reciprocal connections between the CEA and distinct refeeding-activated hypothalamic, thalamic and brainstem nuclei, suggesting the importance of short feedback loops in the regulation of satiety and importance of the CEAm in the regulation of food intake during refeeding.

Dietary macronutrient composition affects hypothalamic appetite regulation in chicks

Objective: The objective was to determine the effects of high-protein and high-fat diets, and fasting and refeeding, on appetite regulation in chicks.Methods: Day of hatch chicks were fed one of four diets: basal, high protein (25% crude protein), and 15 and 30% high fat (15 and 30% metabolizable energy derived from soybean oil, respectively), and assigned to one of three treatments at 4 days: (1) access to feed, (2) 3 hours of fasting, or (3) fasting followed by 1 hour of refeeding. The hypothalamus was collected, total RNA isolated, and mRNA abundance measured.Results: Food intake was reduced in chicks fed the high-protein and high-fat diets. Agouti-related peptide, neuropeptide Y (NPY), NPY receptors 1, 2, and 5, melanocortin receptors 3 and 4 (MC3R and 4R, respectively), mesotocin, corticotropin-releasing factor (CRF), and CRF receptor sub-type 2 (CRFR2) mRNAs were greatest in chicks that consumed the basal diet. Refeeding was associated with increased MC3R mRNA in the high-protein diet group. CRFR2 mRNA was increased by fasting and refeeding in chicks that consumed the high-protein diet.Discussion: Food intake and hypothalamic gene expression of some important appetite-associated factors were reduced in chicks fed the high-protein or high-fat diets. Fasting and refeeding accentuated several differences and results suggest that the CRF and melanocortin pathways are involved.

The Temporal Pattern of cfos Activation in Hypothalamic, Cortical, and Brainstem Nuclei in Response to Fasting and Refeeding in Male Mice

In this study we examined fasted and refed cfos activation in cortical, brainstem, and hypothalamic brain regions associated with appetite regulation. We examined a number of time points during refeeding to gain insight into the temporal pattern of neuronal activation and changes in endocrine parameters associated with fasting and refeeding. In response to refeeding, blood glucose and plasma insulin returned to basal levels within 30 minutes, whereas plasma nonesterified fatty acids and leptin returned to basal levels after 1 and 2 hours, respectively. Within the hypothalamic arcuate nucleus (ARC), fasting increased cfos activation in ∼25% of neuropeptide Y neurons, which was terminated 1 hour after refeeding. Fasting had no effect on cfos activation in pro-opiomelanocortin neurons; however, 1 and 2 hours of refeeding significantly activated ∼20% of ARC pro-opiomelanocortin neurons. Acute refeeding (30, 60, and 120 minutes), but not fasting, increased cfos activation in the nucleus accumbens, the cingulate cortex (but not the insular cortex), the medial and lateral parabrachial nucleus, the nucleus of the solitary tract, the area postrema, the dorsal raphe, and the ventromedial nucleus of the hypothalamus. After 6 hours of refeeding, cfos activity was reduced in the majority of these regions compared with that at earlier time points. Our data indicate that acute refeeding, rather than long-term fasting, activates cortical, brainstem, and hypothalamic neural circuits associated with appetite regulation and reward processing. Although the hypothalamic ARC remains a critical sensory node detecting changes in the metabolic state and feedback during fasting and acute refeeding, our results also reveal the temporal pattern in cfos activation in cortical and brainstem areas implicated in the control of appetite and body weight regulation.

Catabolic Signaling Pathways, Atrogenes, and Ubiquitinated Proteins Are Regulated by the Nutritional Status in the Muscle of the Fine Flounder

A description of the intracellular mechanisms that modulate skeletal muscle atrophy in early vertebrates is still lacking. In this context, we used the fine flounder, a unique and intriguing fish model, which exhibits remarkably slow growth due to low production of muscle-derived IGF-I, a key growth factor that has been widely acknowledged to prevent and revert muscle atrophy. Key components of the atrophy system were examined in this species using a detailed time-course of sampling points, including two contrasting nutritional periods. Under basal conditions high amounts of the atrogenes MuRF-1 and Atrogin-1 were observed. During fasting, the activation of the P38/MAPK and Akt/FoxO signaling pathways decreased; whereas, the activation of the IκBα/NFκB pathway increased. These changes in signal transduction activation were concomitant with a strong increase in MuRF-1, Atrogin-1, and protein ubiquitination. During short-term refeeding, the P38/MAPK and Akt/FoxO signaling pathways were strongly activated, whereas the activation of the IκBα/NFκB pathway decreased significantly. The expression of both atrogenes, as well as the ubiquitination of proteins, dropped significantly during the first hour of refeeding, indicating a strong anti-atrophic condition during the onset of refeeding. During long-term refeeding, Akt remained activated at higher than basal levels until the end of refeeding, and Atrogin-1 expression remained significantly lower during this period. This study shows that the components of the atrophy system in skeletal muscle appeared early in the evolution of vertebrates and some mechanisms have been conserved, whereas others have not. These results represent an important achievement for the area of fish muscle physiology, showing an integrative view of the atrophy system in a non-mammalian species and contributing to novel insights on the molecular basis of muscle growth regulation in earlier vertebrates.

PCSK2-null mice exhibit delayed intestinal motility, reduced refeeding response and altered plasma levels of several regulatory peptides

AimsTo examine the effects of global lack of proprotein convertase subtilisin/kexin 2 (PCSK2) in mouse on intestinal motility, post-fast refeeding response and levels of several PCSK-generated peptides known to regulate food intake and processing. Main methodsUsing male and female PCSK2 knockout (KO) and wild-type (WT) mice, intestinal motility was assessed by determining the percent of intestinal length travelled by a charcoal-dyed meal following an oral gavage; the refeeding response by measuring the amount of meal consumed following an overnight fast; the levels of the regulatory peptides by enzyme immunoassays or immunoblotting. Key findingsRelative to same-gender WT mice, KO mice exhibited delayed intestinal transit (P<0.001 in females; P<0.05 in males). Their post-fast feeding response was reduced in females during the first hour of refeeding (P<0.05). The circulating level of substance P (SP) was lower (P<0.001 in females; P<0.05 in males); it was higher for somatostatin (SS) (P<0.001 in females; P<0.05 in males) and GLP-1 (P<0.001 in females; P<0.01 in males) and GLP-2 (P<0.001 in both genders); it was higher for peptide YY (PYY) in female mice only (P<0.01). Processing of brain proneuropeptide Y was impaired in both genders. SignificanceThe alterations in intestinal motility and post-fast refeeding response observed in PCSK2-KO mice correlate with changes in the circulating and tissue levels of the regulatory peptides tested, suggesting that PCSK2 is needed for normal food intake and processing.

Feeding pattern after intraperitoneal capsaicin desensitization in rats

Event Abstract Back to Event Feeding pattern after intraperitoneal capsaicin desensitization in rats Peter Cseplo1, Andras Garami1, Margit Solymár1, Marta Balasko1, Erika Petervari1 and Miklos Szekely1* 1 University of Pecs, Department of Pathophysiology and Gerontology, Hungary In regulation of satiety and hunger, similarly as in the regulation of postprandial hypermetabolism or fasting hypometabolism there may be a role for neural information from the abdominal cavity. Capsaicin-sensitive afferent abdominal vagal fibers may influence both onset and cessation of feeding, i.e. the feeding pattern, besides influencing the total amount of food consumed. In the present experiments strictly the local (abdominal) afferent fibers were desensitized by intraperitoneal (IP) application of small dose capsaicin. For this purpose, 4-months-old male Wistar rats were injected IP with 2+3 mg/kg capsaicin a few days after IP implantation of telemetric sensors of body temperature, heart rate and spontaneous activity. The animals were placed into the biotelemetric system to record these signals along with feeding frequency (FF) and feeding duration (FD) registered by the infrared Feeding monitor. The amount of consumed food was measured manually. One week after the desensitization a 5-days-long fasting followed to check the usually defective hypometabolic adaptation to fasting in desensitized animals (enhanced tendency for hyperthermic periods), then the food was returned and FD, FF and the food consumption were analyzed. During the first hour of re-feeding, the desensitized rats ate significantly more than the controls and the difference was sustained for well over 3 hours. As expected, in desensitized rats the FD was longer in some fractions of the first hour, but FF was also higher. Besides, the elevation of these parameters was more prolonged. Apparently, IP neural signals influence feeding behavior. Support: OTKA 49321 Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Homeostatic regulatory mechanisms Citation: Cseplo P, Garami A, Solymár M, Balasko M, Petervari E and Szekely M (2009). Feeding pattern after intraperitoneal capsaicin desensitization in rats. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.006 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Mar 2009; Published Online: 02 Mar 2009. * Correspondence: Miklos Szekely, University of Pecs, Department of Pathophysiology and Gerontology, Pecs, Hungary, miklos.szekely@aok.pte.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Peter Cseplo Andras Garami Margit Solymár Marta Balasko Erika Petervari Miklos Szekely Google Peter Cseplo Andras Garami Margit Solymár Marta Balasko Erika Petervari Miklos Szekely Google Scholar Peter Cseplo Andras Garami Margit Solymár Marta Balasko Erika Petervari Miklos Szekely PubMed Peter Cseplo Andras Garami Margit Solymár Marta Balasko Erika Petervari Miklos Szekely Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Ghrelin and body weight regulation in the obese Zucker rat in relation to feeding state and dark/light cycle.

Ghrelin is a new orexigenic peptide primarily produced by the stomach but also present in the hypothalamus. It has adipogenic effects when it is chronically injected in rodents but in obese humans, its plasma concentration is decreased. It can reverse the anorectic effects of leptin when it is co-injected with this peptide in the brain ventricles. The Zucker fa/fa rat is a genetic model of obesity related to a default in the leptin receptor. It is characterized by a large dysregulation of numerous hypothalamic peptides but the ghrelin status of this rat has not yet been determined. Through several experiments, we determine in lean and obese Zucker rats its circulating form in the plasma, its tissue levels and/or expression, and studied the influence of different feeding conditions and its light/dark variations. Ghrelin expression was higher in the obese stomach and hypothalamus (P < 0.05 and P < 0.02, respectively). The ratio of [Octanoyl-Ser3]-ghrelin (active form) to [Des-Octanoyl-Ser3]-ghrelin (inactive form) was approximately 1:1 in the stomach and 2:1 in the plasma in lean and obese rats (no differences). After fasting, plasma ghrelin concentrations increased significantly in lean (+ 64%; P < 0.001) and obese (+ 60%; P < 0.02) rats. After 24 hours of refeeding, they returned to their initial ad lib levels. Ghrelin concentrations were higher in obese rats by 69% (P < 0.005), 65% (P < 0.02), and 73% (P < 0.005) in the ad libitum, fast, and refed states respectively. These results indicate that the obese Zucker rat is characterized by increases in the stomach mRNA expression and in peptide release in the circulation. They clearly support a role for ghrelin in the development of obesity in the absence of leptin signaling.

Neuronal activation and corticotropin-releasing hormone expression in the brain of obese (fa/fa) and lean (fa/?) Zucker rats in response to refeeding.

The present study was conducted to investigate the pattern of neuronal activation and corticotropin-releasing hormone (CRH) expression in fed, food deprived and refed lean (Fa/?) and obese (fa/fa) Zucker rats. The pattern of neuronal activation was studied by measuring the expression of the immediate-early gene c-fos. Expression of c-fos and CRH mRNA was determined by in situ hybridization histochemistry. In both lean and obese rats, one hour of refeeding led to a transient increase in c-fos mRNA levels which was detected in the paraventricular hypothalamic nucleus (PVH), the dorsomedial hypothalamic nucleus, the supraoptic nucleus, the paraventricular thalamic nucleus, the central nucleus of amygdala (CeA), the lateral and medial parabrachial nuclei, the nucleus of the solitary tract, and the area postrema. In addition, refeeding led to strong activation of the arginine-vasopressin neurons located in the magnocellular part of the PVH. Following 24 h of food deprivation, CRH expression in the parvocellular division of the PVH was significantly higher in obese rats compared to lean animals. During refeeding, PVH CRH mRNA levels in obese rats decreased to reach control values. The decrease in CRH expression in obese rats was accompanied by the alleviation of the hypercorticosteronemia that characterized obese Zucker rats. CRH mRNA levels in the central nucleus of the amygdala were significantly higher in lean rats than in obese animals, when the rats were fed ad libitum During food deprivation, CeA CRH mRNA levels decreased in lean rats and gradually returned to predeprivation values during refeeding. In refed obese rats, CeA levels of CRH mRNA were higher than those of ad libitum fed or food-deprived obese mutants. In the perifornical region of the lateral hypothalamic area (LHA), the expression of CRH mRNA rose significantly in response to refeeding in lean rats, but not in obese animals. Following the first hour of refeeding, the number of neurons expressing CRH mRNA in the LHA in lean rats almost doubled. The present results demonstrate that refeeding has a stimulating effect in obese Zucker rats in a pattern of activation similar to that seen in lean Fa/? rats. They also demonstrate differences in CRH expression between Fa/? and fa/fa rats after refeeding. The most apparent of these differences was seen in the lateral hypothalamus in which refeeding failed to up-regulate CRH expression in obese rats.

The influence of fasting/refeeding on the lipoprotein lipase activity of adipose tissue and muscle.

Lipoprotein lipase activity in adipose tissue and muscle is modulated by changes in the pattern of food intake. We have measured total lipoprotein lipase activity in adipose tissue and muscle of male Wistar rats (N = 6-10), weighing 200-250 g (~12 weeks), during the refeeding/fasting state following 24 h of fasting. Lipoprotein lipase activity in tissue homogenates was evaluated using a [3H]-triolein-containing substrate, and released [3H]-free fatty acids were extracted and quantified by liquid scintillation. Adipose tissue lipoprotein lipase activity did not completely recover within 2 h of refeeding (60% of refed ad libitum values). Cardiac lipoprotein lipase activity remained increased even 2 h after refeeding (100% of refed ad libitum values), whereas no significant changes were observed in the soleus and diaphragm muscles. Adipose tissue lipoprotein lipase activities were consistently higher than the highest skeletal muscle or heart values. It is therefore likely that adipose tissue, rather than muscle makes the major contribution to triacylglycerol clearance. There was concomitant relatively high lipoprotein lipase activity in both adipose tissue and cardiac muscle during the first few hours of refeeding, therefore cardiac muscle may contribute significantly to triacylglycerol clearance during this period. The results suggest that during fasting, increased lipoprotein lipase activity provides a complementary source of free fatty acids from circulating triacylglycerol, allowing the heart to maintain its continuous, high-energy expenditure.

Feeding status and bacterial LPS-induced cytokine and neuropeptide gene expression in hypothalamus.

This study determined the effects of feeding status on basal and lipopolysaccharide (LPS)-stimulated cytokine and neuropeptide gene expression in the hypothalamus. With the use of RNase protection assays, we measured mRNA levels of interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1RA), IL-1 receptor type I (IL-1RI), IL-1R accessory proteins (AcP I and II), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta1 (TGF-beta1), glycoprotein 130 (Gp 130), leptin receptor (OB-R), neuropeptide Y (NPY), preprodynorphin, and proopiomelanocortin (POMC). Analyses were done in ad libitum-fed, fasted, and fasted and refed rats treated with the intracerebroventricular administration of physiological saline or LPS. The data show that food deprivation increases the basal mRNA expression of IL-1beta, IL-1RA, TNF-alpha, IL-1RI, and IL-1R AcP I, whereas mRNA levels of POMC showed a decrease. Five hours of refeeding returned cytokine levels to those observed in the ad libitum-fed group. LPS administration induced a robust upregulation of IL-1beta, TNF-alpha, and IL-1RI during all three feeding conditions. Acute food deprivation did not modulate LPS-induced changes in hypothalamic cytokine mRNA profiles. These findings show that 1) cytokine modulation occurs as an adaptive response to the stress of acute fasting and 2) acute fasting does not affect LPS-induced cytokine mRNA modulation in the hypothalamus. The data have implications to gram-negative infections associated with acute anorexia.

Neuropeptide Y Y1 receptor antisense oligodeoxynucleotides enhance food intake in energy-deprived rats

In the literature, conflicting data on the effect of NPY Y1 antisense oligodeoxynucleotides (ODNs) on food intake have been reported, describing either an increase or a decrease in feeding in antisense-treated animals. In the present studies antisense oligodeoxynucleotides targeted to the Y1 receptor (Y1 antisense ODNs) were used to re-investigate the functional importance of this receptor subtype in vivo in the regulation of feeding in rats. We used phosphothioate-terminal protected derivatives of two ODN sequences used in previous reports. In addition, as one of these sequences was not tested in vitro, we demonstrated its efficacy in LMTK-cells transfected with the Y1 receptor subtype. In vivo, repeated intracerebroventricular (i.c.v.) injections of Y1 antisense ODNs did not affect basal food intake or the increase in food intake after i.c.v. injection of neuropeptide Y (NPY, 300 pmol). Y1 antisense ODNs given intracerebroventricularly enhanced food intake in energy-deprived rats (+175% and +60% vs. control scrambled and sense sequences, respectively after 2 h of refeeding). Analysis of the structure of feeding behaviour revealed that Y1 antisense ODNs enhanced fasting-induced food intake during the first hour of refeeding by inducing increases in meal size (+143% and +155% vs. sense and scrambled ODNs) but not meal duration. These data suggest that the NPY Y1 receptor is not directly implicated in feeding in the rat when calorie intake is normal but might be specifically activated during energy deprivation.

Recovery of gut-associated lymphoid tissue and upper respiratory tract immunity after parenteral nutrition.

The authors characterize the recovery of parenteral nutrition-induced changes in gut-associated lymphoid tissue (GALT) and upper respiratory tract immunity with enteral nutrition and provide further information defining the effects of enteral feeding on mucosal immunity. The small intestine plays a prominent role in development and maintenance of mucosal immunity, both intestinal and extraintestinal, primarily through immunoglobulin A (IgA)-mediated mechanisms. Prior research has shown that mice fed total parenteral nutrition (TPN) have reduced GALT T and B cells, the cells responsible for IgA production, as well as impaired upper respiratory tract immunity to viral challenge of previously immunized animals. The recovery of TPN-induced changes in GALT and upper respiratory tract immunity after enteral refeeding is studied. Male institute of Cancer Research mice received 5 days of TPN followed by 0 to 4 days of chow. Small intestinal GALT was characterized by flow cytometry. In a second experiment, animals were immunized intranasally with moused-adapted influenza virus. Three weeks later, one group received a 5-day course of TPN followed by enteral refeeding for 5 days. A second group received TPN alone. Both groups were challenged with intranasal virus and killed 40 hours postchallenge to determine viral shedding from the upper respiratory tract. Animals fed TPN only had significantly fewer GALT lymphocytes compared with those chow-fed control subjects. Peyer's patch counts increased after a single day of refeeding, returning to normal levels by 48 hours. Lamina propria counts remained significantly depressed after 24 hours of refeeding, but also returned to normal after 48 hours of refeeding. The T-cell and B-cell populations mimicked total cell patterns. Lamina propria CD4+/CD8+ ratio returned to normal only after 72 hours of refeeding. None of the 9 animals refed enterally for 5 days were positive for viral shedding, compared with 8 of 12 matched TPN-fed animals. Enteral refeeding after TPN is associated with rapid repletion of GALT cellularity, initially within Peyer's patches and subsequently within the lamina propria. Refeeding corrects the impairment of IgA-mediated upper respiratory tract antiviral immunity occurring with TPN administration. This work further enhances the authors' knowledge of the underlying immunologic differences influenced by routes of nutrition.

Thyroid hormones homeostasis in rats refed after short-term and prolonged fasting.

Effects of starvation on thyroid hormone homeostasis were usually determined after 2 or more days of fasting, however, both in man and in rodents, natural feeding cycles comprise far shorter fasting periods. Therefore serum levels of T4, FT4, T3, FT3 and rT3 were measured in rats refed chow diet for 1, 4, 8 or 24 hours after 14 or 48 hours of starvation. Both short-term (14 h) and long-term fasting (48 h) decreased body weight and serum glucose level. Short-term fast decreased serum FT3 and did not change serum levels of T4, FT4, T3 and rT3. Total T3 and reverse T3 increased after one and 4 hours, free T3 after 4 hours and total T4 after 4 and 8 hours of refeeding. Percent of FT3 did not change after short-term fast, declined after 1 and 4 hours of refeeding, and normalised thereafter. Prolonged starvation (48 h) decreased serum T4, T3, FT3 and % FT3 with no changes in FT4 and rT3. After 24 hours of refeeding only FT3 and % FT3 returned to control levels while total T4 and total T3 were still diminished, and reverse T3 levels did not change. The results suggest that the length of preceding fasting period may strongly influence thyroid hormone homeostasis during fasted-to-fed transition.

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

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. 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. 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. 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.

Insulin-independent and extremely rapid switch in the partitioning of hepatic fatty acids from oxidation to esterification in starved-refed diabetic rats. Possible roles for changes in cell pH and volume.

The requirement for a normal insulin response in mediating the starved-to-refed transition, with respect to the partitioning of hepatic fatty acids between beta-oxidation and esterification to glycerol, was studied. Diabetic rats were starved for 24 h and refed ad libitum for various periods of time. There was no increase in plasma insulin in response to the meal. However, the fatty acid oxidation:esterification ratio was very rapidly decreased from the starved to the fed value, most of the transition being achieved within the first hour of refeeding. There was a 2 h lag in the response of hepatic malonyl-CoA concentration, such that this rapid switch from oxidation to esterification could not be explained on the basis of changes in the absolute concentration of this inhibitor of carnitine palmitoyltransferase I (CPT I). Hepatic pyruvate and lactate concentrations both increased by several-fold upon refeeding and peaked after 1 h and 3 h, respectively. The hepatic lactate:pyruvate ratio increased 3.2-fold during the first 3 h of refeeding, suggesting that the cytosolic NAD(+)-NADH couple became much more highly reduced during the lag-period between the onset of inhibition of flux of fatty acids towards oxidation and the rise in malonyl-CoA concentration. This may be indicative of a lowering of intracellular pH, which would amplify greatly the sensitivity of CPT I to the inhibitor. In view of the very rapid and high food intake by these diabetic rats, the possibility is also considered that portal concentrations of amino acids and other metabolites could give rise to an increase in liver cell-volume that would inhibit CPT I acutely by an as yet unknown mechanism [M. Guzman, G. Velasco, J. Castro and V. A. Zammit (1994) FEBS Lett. 344, 239-241].