Meal-fed Rats Research Articles

A Novel Automated System Yields Reproducible Temporal Feeding Patterns in Laboratory Rodents

ABSTRACTBackgroundThe impact of temporal feeding patterns remains a major unanswered question in nutritional science. Progress has been hampered by the absence of a reliable method to impose temporal feeding in laboratory rodents, without the confounding influence of food-hoarding behavior.ObjectiveThe aim of this study was to develop and validate a reliable method for supplying crushed diets to laboratory rodents in consistent, relevant feeding patterns for prolonged periods.MethodsWe programmed our experimental feeding station to deliver a standard diet [StD; Atwater Fuel Energy (AFE) 13.9% fat] or high-fat diet (HFD; AFE 45% fat) during nocturnal grazing [providing 1/24th of the total daily food intake (tdF/I) of ad libitum–fed controls every 30 min] and meal-fed (3 × 1-h periods of ad libitum feeding) patterns in male rats (Sprague-Dawley: 4 wk old, 72–119 g) and mice [C57/Bl6J wild-type (WT): 6 mo old, 29–37 g], and ghrelin-null littermates (Ghr−/−; 27–34 g).ResultsGrazing yielded accurate, consistent feeding events in rats, with an approximately linear rise in nocturnal cumulative food intake [tdF/I (StD): 97.4 ± 1.5% accurate compared with manual measurement; R2 = 0.86; tdF/I (HFD): 99.0 ± 1.4% accurate; R2 = 0.86]. Meal-feeding produced 3 nocturnal meals of equal size and duration in StD-fed rats (tdF/I: 97.4 ± 0.9% accurate; R2 = 0.90), whereas the second meal size increased progressively in HFD-fed rats (44% higher on day 35 than on day 14; P < 0.01). Importantly, cumulative food intake in grazing and meal-fed rats was identical. Similar results were obtained in WT mice except that less restricted grazing induced hyperphagia (compared with meal-fed WT mice; P < 0.05 from day 1). This difference was abolished in Ghr−/− mice, with meal initiation delayed and meal duration enhanced. Neither pattern elevated corticosterone secretion in rats, but meal-feeding aligned ultradian pulses.ConclusionsWe have established a consistent, measurable, researcher-defined, stress-free method for imposing temporal feeding patterns in rats and mice. This approach will facilitate progress in understanding the physiologic impact of feeding patterns.

Avoidance of food effect on oral absorption profile of itraconazole by self-micellizing solid dispersion approach

The present study was aimed to avoid pharmacokinetic transitions of itraconazole (ITZ) evoked by high-fat meal intake by employing a self-micellizing solid dispersion (SMSD) approach. The dissolution behavior of SMSD/ITZ was assessed in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). To evaluate the food effect on the oral absorption profile of ITZ, a pharmacokinetic study was conducted on orally-dosed ITZ samples in fasted and high-fat meal-fed rats. Crystalline ITZ showed a 9.0-fold higher dissolution amount of ITZ in fed-state SGF (FeSSGF) than in fasted-state SGF (FaSSGF), whereas there was no significant difference in the dissolution amount of ITZ in SMSD/ITZ between FeSSGF and FaSSGF. In fed- and fasted-state SIF, SMSD/ITZ exhibited reduced variation of ITZ dissolution, possibly leading to suppression of the food effect on the dissolution behavior of ITZ. After the oral administration of crystalline ITZ to high-fat meal-fed rats, the oral bioavailability of ITZ was 14-fold higher than that in fasted rats. In contrast, orally-dosed SMSD/ITZ in fed rats exhibited limited transition of pharmacokinetic behavior regardless of food intake due to the improvement in the dissolution behavior of ITZ even under fasted conditions. SMSD technology could be an efficacious dosage option for the consistent oral absorption and clinical outcomes of ITZ.

A rat model for determining the postprandial response to foods.

The use of small animal models for studying postprandial changes in circulating nutrients, hormones and metabolic biomarkers is hampered by the limited quantity of blood that can be withdrawn for analysis. Here, we describe the development of an unrestrained, meal-fed rat model, having a permanent or temporary vascular cannula that permits repeated blood sampling. The applicability and performance of the model were evaluated in a series of experiments on acute glycaemic and insulinaemic responses to carbohydrate-based test meals. A test food containing 0.4 g carbohydrate raised blood glucose by 1.5 mmol L-1 . Postprandial blood glucose levels peaked at 15 min and returned to baseline at 180 min, whereas they remained elevated for longer when the test meal contained 1.25 g carbohydrate. The glycaemic response tended (P = 0.063) to be higher when the meal tolerance test was conducted at the start rather than the end of the dark period, but the insulinaemic response was unaffected. The magnitude of the glycaemic response was less for blood collected from the caudal vein compared to that from the jugular vein. Both cannulation strategies were equally effective in enabling return of red blood cells, thus preserving blood volume. This improved small animal model affords new opportunities to screen foods for nutrient bioavailability and explore metabolic mechanisms mediating responses to food consumption. © 2016 Society of Chemical Industry.

Meal feeding improves oral glucose tolerance in male rats and causes adaptations in postprandial islet hormone secretion that are independent of plasma incretins or glycemia.

Meal-fed (MF) rats with access to food for only 4 consecutive hours during the light cycle learn to eat large meals to maintain energy balance. MF animals develop behavioral and endocrine changes that permit glucose tolerance despite increased meal size. We hypothesized that enhanced activity of the enteroinsular axis mediates glucose homeostasis during MF. Cohorts of rats were allocated to MF or ad libitum (AL) regimens for 2-4 wk. Insulin secretion and glucose tolerance were determined after oral carbohydrate and intraperitoneal (ip) and intravenous (iv) glucose. MF rats ate less than AL in the first week but maintained a comparable weight trajectory thereafter. MF rats had decreased glucose excursions after a liquid mixed meal (AUC: MF 75 ± 7, AL 461 ± 28 mmol·l⁻¹·min, P < 0.001), with left-shifted insulin secretion (AUC(0-15): MF 31.0 ± 4.9, AL 9.6 ± 4.4 pM·min, P < 0.02), which peaked before a significant rise in blood glucose. Both groups had comparable fasting glucagon levels, but postprandial responses were lower with MF. However, neither intestinal expression of proGIP and proglucagon mRNA nor plasma incretin levels differed between MF and AL groups. There were no differences in the insulin response to ip or iv glucose between MF and AL rats. These findings demonstrate that MF improves oral glucose tolerance and is associated with significant changes in postprandial islet hormone secretion. Because MF enhanced β-cell function during oral but not parenteral carbohydrate administration, and was not accounted for by changes in circulating incretins, these results support a neural mechanism of adaptive insulin secretion.

Meal-Anticipatory Glucagon-Like Peptide-1 Secretion in Rats

Animals anticipating a meal initiate a series of responses enabling them to better cope with the meal's metabolic impact. These responses, such as cephalic insulin, occur prior to the onset of ingestion and are especially evident in animals maintained on a meal-feeding schedule with limited but predictable access to food each day. We tested the hypothesis that meal-fed rats secrete the incretin hormone glucagon-like peptide-1 (GLP-1) cephalically when anticipating a large meal. Male Long-Evans rats were fed ad libitum (controls) or adapted to a schedule on which food was available for the same 4-h period each day (meal fed animals). Plasma GLP-1 increased in meal-fed rats over an interval from 75 to 60 min prior to feeding time, from a baseline of 10 to around 40 pm, and then returned to baseline prior to food presentation. Controls had steady plasma GLP-1 levels (10-15 pm) over the same span. Meal-fed rats also secreted cephalic insulin starting around 15 min prior to food presentation. Administration of the selective GLP-1 receptor antagonist exendin-4[desHis-1,Glu-9] prior to the premeal spike of GLP-1 caused meal-fed rats to eat significantly less food than normal, whereas administration of the antagonist after the GLP-1 spike but prior to food presentation resulted in a significant increase in food consumption. These findings document for the first time a cephalic increase of plasma GLP-1 and suggest that it functions to facilitate consumption of a large meal.

식이급여형태가 고지방식이를 급여한 흰쥐 지방조직의 지방합성 및 지방합성 효소활성에 미치는 영향

본 연구는 식이급여형태를 달리하면서 고지방식이를 급여한 흰쥐의 부고환지방조직과 장간막지방조직의 지방조직 부위별 지방합성량, 지방합성에 관여하는 주된 효소인 ME, G6PDH 및 6PGDH 활성 및 지방축적의 주된 효소인 LPL 활성에 미치는 영향을 구명하였다. Sprague-Dawley 계통 수컷 흰쥐 16마리를 체중에 따라 2군으로 나누어 4주간 실시하였고, ad libitum군은 실험 식이를 무제한 급여하였으며, meal-fed군은 1일 1회 3시간씩 제한 급여하였다. 지방조직의 지방합성량은 포도당이 총지방으로 변하는 양으로 측정하였고, 지방조직의 G6PDH, 6PGDH 및 ME 활성은 NADPH 생성량으로 측정하였다. 또한 지방조직의 LPL 활성과 혈청지단백질, 중성지방 및 insulin 함량도 측정하였다. Mealfed군이 ad libitum군에 비해 식이섭취량 저하로 인한 증체량 및 부고환지방조직과 장간막지방조직의 무게가 유의하게 저하되었다. 혈청 총콜레스테롤, HDL-콜레스테롤 및 LDL-콜레스테롤 함량은 식이급여형태에 따른 유의차가 없었으나, 혈청 중성지방 함량은 meal-fed군이 ad libitum군에 비해 유의하게 증가하였고, insulin 함량은 저하되었다. 지방합성량 및 G6PDH과 6PGDH 활성은 부고환지방조직과 장간막지방조직 모두 meal-fed군이 ad libitum군에 비해 증가하였으나, ME 활성은 식이급여형태에 따른 유의차가 없었다. 지방조직의 HR-LPL과 TE-LPL 활성은 meal-fed군이 ad libitum군에 비해 유의하게 높았다. 지방조직 부위에 따른 차이는 지방함량, 지방합성량 및 G6PDH와 LPL 활성은 부고환지방조직에 비해 장간막지방조직에서 낮은 경향이었다. 이와 같이 meal feeding시 섭취한 에너지를 체지방 형태로 더 많이 보유하도록 지방조직내 지방합성량과 지방합성 관련 효소들의 활성을 증가시켜 체내 대사에 영향을 미치는 것으로 사료된다. 또한 지방조직 부위에 따라 지방대사에 미치는 영향이 다르다는 것을 알 수 있었다.

Effects of a Fixed Meal Pattern on Ghrelin Secretion: Evidence for a Learned Response Independent of Nutrient Status

Circulating levels of the orexigenic peptide ghrelin increase during fasting and decrease with refeeding. Exogenous ghrelin administration is a potent stimulus for food intake in rodents and humans. In subjects on fixed feeding schedules, ghrelin increases before each meal, raising the possibility that anticipation of meals, in addition to effects of fasting and feeding, contributes to ghrelin secretion. To distinguish among these regulatory influences, plasma ghrelin profiles were generated in freely fed rats and in meal-fed rats trained to consume their daily calories over a 4-h period in the light phase. In freely feeding rats, plasma ghrelin levels increased to a peak of 778 +/- 95 pg/ml just before the onset of the dark. Similarly, in meal-fed rats anticipating a large meal of either chow or Ensure at their usual feeding time, plasma ghrelin increased steadily over the 2 h preceding the meal to peaks of 2192 +/- 218 and 2075 +/- 92 pg/ml, respectively. When freely fed rats were food deprived for a time equivalent to meal-fed rats, there was no peak of plasma ghrelin. In addition, eating-induced suppression of the ghrelin response differed significantly between meal-fed rats and ad libitum-fed rats receiving meals of similar size. These findings indicate that anticipation of eating, as well as fasting/feeding status, influences pre- and postprandial plasma ghrelin levels in rats. Together, these data are consistent with a role for ghrelin in the regulation of anticipatory processes involved in food intake and nutrient disposition.

Effect of the GH secretagogue L-163,255 and restricted feeding time on GH pulsatility in the rat.

To determine the effect of repeated treatments with the growth hormone secretagogue (GHS) L-163,255 on the pulsatile release of GH when administered in meal-fed rats before and after feeding. The first group of rats (AL, n=6) had food available ad libitum. The second (restricted, R, n=6), third (GHSB, n=6), and fourth (GHSA, n=6) groups were fed from 1100 to 1400 h. Groups GHSB and GHSA were given GHS by gavage, 3.0 mg/kg L-163,255, at 1000 h (before feeding, B) and at 1500 h (after feeding, A) respectively. Three weeks after the initiation of the treatment, blood samples were collected at 10-min intervals over 6 h, and GH levels were determined. In group R, the concentrations of GH were higher before feeding (17.6+/-2.4 ng/ml) than during feeding (11.2+/-1.2 ng/ml), P<0.05. The average concentrations of the peak in response to GHS were higher when GHS was administered before (121.70+/-33.68 ng/ml) than after (49.67+/-17.87 ng/ml) feeding. The mass of GH, as calculated by deconvolution analysis was also higher in the GHSB group than in the GHSA group (251.6+/-64.1 ng/ml per min vs 85.3+/-22.9 ng/ml per min respectively, P<0.05). L-163,255 is effective in inducing GH release after repeated oral administration in rats. The effectiveness is greater when GHS is administered before rather than after feeding in meal-fed animals.

Effects of voluntary resistance exercise on heme biosynthesis in rats given glucocorticoid-injections.

To identify the effects of a tower-climbing exercise on bone marrow heme biosynthesis and hematological status in rats given glucocorticoid-injections as a model of aging, 29 male Sprague-Dawley rats, 10 weeks of age, were assigned to three groups: a saline control (C, n = 9), a glucocorticoid-sedentary (GS, n = 10) group, and a glucocorticoid-exercise (GE, n = 10) group. The GS and GE groups were given 2 mg/kg prednisolone daily, and the C group was given 2 ml of saline daily, subcutaneously. Each group was meal-fed commercial rat chow isoenergetically and given free access to water for 8 weeks. The GE group were allowed to climb a 200-cm tower to drink water from a bottle set at the top of it. Weight gain during the 8-week experimental period was greater in the C group than in the GS and GE groups. The gastrocnemius and tibialis anterior muscles were heavier in the C group than in other groups. The hematological parameters were not influenced by glucocorticoid administration with or without climbing exercise. Bone marrow delta-aminolevulinic acid dehydratase activity was significantly higher in the GE group than in the C group. These results suggest that 8 weeks of climbing exercise increases heme biosynthesis without alteration of hematological status in rats given glucocorticoid-injections. Resistance exercise may be a preventive therapy for iron-deficiency anemia associated with aging.

Opioid and Cholecystokinin Antagonists Alleviate Gastric Inhibition of Food Intake by Premeal Loads of Casein in Meal-Fed Rats

This study was undertaken to determine whether casein, compared with its constituent amino acids, given at the onset of a meal, would influence intake due to cholecystokinin (CCK) or opioid activity. Male Sprague-Dawley rats (n = 80; 225 g) were given either premeal loads of casein or its constituent amino acids and treated with opioid or CCK antagonists in a 2 x 4 factorially designed experiment. During a 21-d period, rats were meal-fed by restricting access to food to 5 h/d. The rats were fed the AIN-93 diet with soy isolate substituted for casein as the dietary protein source. On d 7-21, rats were given oral premeal loads of 5 mL of a 50 g/L casein or constituent amino acid solution before meal-feeding. On d 14-21, 20 rats were injected intraperitoneally with one of the following treatments: saline, naltrexone (l mg/kg), naloxone methiodide (5 mg/kg) or lorglumide (1 mg/kg) before the premeal load and feeding. Antagonist treatments increased intake (P < 0.05) by 15.3% compared with saline treatment (7.82 vs. 9.02 g/d) in rats given premeal loads of casein. Intake of rats given premeal loads of amino acids was not influenced by antagonists. At 2 h after feeding on d 21, the rats were killed, bled and eviscerated. Effects of antagonists on stomach and intestinal mass, digesta contents and fecal output were also dependent on the type of premeal load, indicating that gastric retention of digesta due to casein was mediated by CCK and opioids. Body weight accretion, liver, and epididymal fat mass and blood concentrations of specific amino acids changed in the same manner as intake (P < 0.05). Serum insulin was greater (P < 0.05) in casein-treated rats and reduced (P < 0.01) by opioid antagonists. Satiety associated with premeal loads of casein is related to changes in gastrointestinal function of meal-fed animals and involves both opioid and CCK regulation.

Deficiency of dietary EAA preferentially inhibits mRNA translation of ribosomal proteins in liver of meal-fed rats.

The goal of these studies was to investigate the mechanisms by which amino acid supply regulates global rates of protein synthesis as well as the translation of ribosomal protein (rp) mRNAs in liver. In the experiments conducted, male weanling rats were trained over a 2-wk period to consume their daily food intake within 3 h. On day 14, rats were fed the control diet or an isocaloric, isonitrogenous diet lacking glycine, tryptophan, leucine, or the branched-chain amino acids (BCAA) for 1 h. Feeding Trp-, Leu-, or BCAA-deficient diets resulted in significant reductions in serum insulin, hepatic protein synthesis, eukaryotic initiation factor 2B (eIF2B) activity, and phosphorylation of eIF4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase (S6K1). Phosphorylation of eIF2alpha was inversely related to eIF2B activity under all conditions. Alterations in the hepatic synthesis of rp were assessed by changes in the distribution of rp (S4, S8, L26) mRNAs across sucrose density gradients and compared with non-rp (beta-actin, albumin) mRNAs. In all dietary treatments, non-rp mRNAs were mostly polysome associated. Conversely, the proportion of rp mRNAs residing in polysomes was two- to fivefold less in rats fed diets lacking tryptophan, leucine, or BCAA compared with rats fed the control diet. Total hepatic abundance of all mRNAs examined did not differ among treatment groups. For all parameters examined, there were no differences between rats fed the glycine-deficient diet and rats fed the control diet. The data suggest that essential amino acid (EAA) deficiency inhibits global rates of liver protein synthesis via a block in translation initiation. Additionally, the translation of rp mRNAs is preferentially repressed in association with decreased S6K1 phosphorylation.

Nutritional response of rats to faba beans (Vicia faba L. minor black 'Kalimattar') and its fractions

The investigations on protein quality of raw faba bean seed meal (Vicia faba L. minor) and its fractions were carried out using rats in two experiments. Two varieties of faba seeds were used, locally grown faba bean 'Kalimattar' or 'black' (KSM) (492 g/kg diet) and its exotic counterpart Vicia faba L. minor 'White' (VFW) obtained from International Centre for Agricultural Research in the Dry Areas (ICARDA) (540g/kg diet). The pulverized cotyledons of 'Kalimattar' (KMC; 438 g/kg diet), hull (KMH; 78 g/kg diet) as well as cotyledons of 'White' faba bean (VFWC; 470g/kg diet) and hull (VFWH; 82 g/kg diet) fractions were tested. All diets were made isocaloric and isonitrogenous, however, without addition of individual amino acids to the target requirements. Performance of rats fed on both locally grown KSM and exotic FBW meal-fed rats were found to be inferior to those obtained from the rats fed on standard protein diet. The net protein utilization (NPU) of the rats fed on this seed meal was comparatively better than those obtained from the VFW. Replacement of standard protein with cotyledons from the either of the seed (KMC and VFWC) depressed food intake and protein utilization. This was due, in part, to the excretion of comparatively higher amount of nitrogen in faeces. Inclusion of KMH in the diet had no adverse effects on any variable studies as compared to the VFWH, which was found to impose severe restriction on the absorption of standard protein added to this diet. As a result, body weight gain, and NPU value were significantly lower than those obtained from the KMH. We conclude that the locally grown faba bean 'Kalimattar' is better than those of exotic 'White' cultivar and may contain less antinutritional substances. However, this warrants further investigations.

A Linoleic Acid Enriched Diet Increases Serum Cholesterol Esterification by Lecithin:Cholesterol Acyltransferase in Meal-Fed Rats

Dietary fats are known to influence the fatty acid profile of plasma lipids, including phospholipids which are substrates of lecithin:cholesterol acyltransferase (LCAT; EC 2.3.1.43), an important enzyme in lipoprotein metabolism. We tested whether the dietary fatty acid profile has an effect on LCAT activity in an animal model. Rats were conditioned to eat two meals per day, which were enriched in either palmitic, oleic or linoleic acids, for 10 weeks. Serum was isolated from blood samples taken prior to the meal. The LCAT activity was determined in two ways: (1) by measuring serum cholesterol esterification rates, which are an estimate of LCAT action on endogenous lipoproteins, and (2) by measuring serum LCAT activity levels with excess exogenous substrates, an estimate of LCAT mass. Animals receiving the linoleic acid diet had lower serum concentrations of unesterified cholesterol and triglycerides, if compared with animals fed oleic acid or palmitic acid diets (p < 0.05). Serum LCAT activity levels (measured with excess exogenous substrates) were not different, but both the absolute and fractional rates of cholesterol esterification were highest on the linoleic acid rich diet (p < 0.01), showing that LCAT action on endogenous lipoproteins is improved. No differences were found in serum apolipoprotein B and A-IV concentrations between the dietary groups. Apolipoprotein A-I levels were lowest in the palmitic acid group (oleic and linoleic > palmitic; p < 0.05), and apolipoprotein E levels were highest in the palmitic acid group (palmitic > oleic and linoleic; p < 0.05). It is concluded that a linoleic acid rich diet may cause increased metabolism of serum cholesterol by LCAT in rats. This effect is not due to elevated serum concentrations of LCAT or of its apolipoprotein activators, but most likely to changes in the chemical composition of endogenous lipoprotein substrates. It remains to be established whether the serum cholesterol esterification rates measured in vitro are related to in vivo rates of reverse cholesterol transport.

Changes in the Microstructure of Feeding After Administration of Enterostatin into the Paraventricular Nucleus and the Amygdala

Ling, L. and D. A. York. Changes in the microstructure of feeding after administration of enterostatin into the paraventricular nucleus and the amygdala. Peptides 19(3) 557–562, 1998.—The effects of enterostatin (ENT) injected into the paraventricular nucleus (PVN) and the amygdala (AMYG) on the microstructure of feeding was studied by using an automated feeding apparatus. In rats adapted to a 6-h meal feeding regime, ENT reduced the size and duration of the first meal after injection in both the PVN and the AMYG. Similar effects were observed when ENT was given at the beginning of the dark cycle in rats fed ad libitum although the onset of feeding was also delayed in this situation. The number of meals and the size of subsequent meals was unaffected by ENT but the eating rate within the first meal was reduced after ENT injection into the AMYG of meal-fed rats. Enterostatin injected into the AMYG at a dose that suppressed feeding did not produce a conditioned taste aversion. ENT given centrally therefore appears to reduce food intake by delaying the initiation of feeding and/or advancing meal termination suggesting that it affects both appetite and satiation mechanisms.

Are Physiological Changes in Meal-Fed Rats Determined by the Amount of Food Ingested in the Last Meal or Due to Feeding Schedule?

Batista, M. R., M. Ferraz and R. B. Bazotte. Are physiological changes in meal-fed rats determined by the amount of food ingested in the last meal or due to feeding schedule? Physiol Behav 62(2) 249–253, 1997.—Rats trained to eat a single meal from 0800 to 1000 AM, (MF rats), increased food intake from the 1st (7.0 g) to the 13th (16.1 g) day and showed higher hepatic glycogen concentration and glycemia during fasting. To verify if these changes were determined by the higher food intake or due to the disciplining condition we compared rats at the 1st (MF 1st day-5 g group) and 13th day (MF 13th day-5 g group) of training, refed with a fixed amount of food (5 g). In addition, a third group (MF 13th day-12 g group) composed by trained meal-fed rats, refed on day 13 with approximately 75% of food ingested by MF rats on day 13 (12 g) of feeding training was included. The experiments with these 3 groups were performed at zero (1000 h), 6 (1600 h), 13 (2300 h), 18 (0400 h) and 22 (0800 h) h after meal. Our results demonstrated that part of the physiological changes of MF rats is consequence of feeding training (increased food intake during the fixed meal time and spontaneous elevation of glycemia 13 h after meal) and part of the differences (hepatic glycogen concentration, gastric and intestinal emptying) correlate well with effective time of fasting. In addition, hepatic gluconeogenesis from L-lactate and glycerol was influenced by both factors.

Involvement of the medial preoptic area in the anorectic action of estrogens.

The implication of the medial preoptic area (MPOA) as a site for estrogen in the regulation of energy balance was investigated. Food intake, O2 consumption (VO2), and CO2 production were measured in ovariectomized rats injected with estradiol (E2) in the medial preoptic nucleus (MPN). Moreover, knowing the potential for corticotropin-releasing factor (CRF) in the anorectic effects of estrogens, we identified estrogen receptors (ER) colocalized in CRF-containing cells of the MPOA and how MPN injections of CRF compared with estrogen injections with respect to VO2 and the VO2-to-CO2 production ratio (respiratory quotient RQ). These energy balance measurements after the injections of four different doses of E2 or CRF were carried out in meal-fed rats chronically implanted with a guide cannula targeted to the MPN. The identification of cells colocalizing ER and CRF was determined using a double-immunostaining procedure revealing ER and CRF immunoreactivities with two different couplers. The injection of E2 into the MPN induced a dose-dependent reduction in food intake, whereas it did not affect VO2 or RQ. Conversely, the injection of CRF into the MPN had no effect on food intake but increased VO2 and decreased RQ. The colocalization of ER and CRF immunoreactivities was found in the MPOA and adjacent regions of the bed nucleus of the stria terminalis. In conclusion, the results of this study provide evidence that the MPOA may represent a potential site for the anorectic effects of E2. Furthermore, the presence of ER and CRF in neurons of the MPOA and adjacent areas suggests a direct interaction between estrogens and the CRF system in the MPOA that is consistent with a role for CRF in the anorectic effects of estrogens. Finally, the results of this study indicate that the effects of a CRF injection into the MPOA differ from those of estrogens, suggesting that if CRF neurons are involved in the anorectic effect of estrogens they likely exert their action outside the MPOA.

Interleukin-1 beta-induced anorexia and pyrexia in rat: relationship to hypothalamic neuropeptide Y.

We investigated the effect of recombinant human interleukin-1 beta (rhIL-1 beta)-induced anorexia and pyrexia on the hypothalamic neuropeptide Y (NPY)-ergic system, which stimulates feeding and reduces thermogenesis. In meal-fed rats, food intake decreased by 83%, 90 min after IL-1 beta treatment (1.3 micrograms/100 g ip; n - 8) vs. controls. NPY concentrations were significantly higher in the medial preoptic area (MPO), paraventricular (PVN), ventromedial (VMN), and dorsomedial (DMN) nuclei but unchanged in the arcuate nucleus (ARC) in both IL-1 beta-treated and pair-fed groups. Indomethacin (0.25 mg/100 g ip) reduced IL-1 beta-induced anorexia and tended to normalize NPY concentrations. In study 2, IL-1 beta increased core temperature by 1.1 degrees C above preinjection values (P < 0.001) and significantly raised NPY concentrations in the MPO, PVN, VMN, and DMN compared with controls, 60 min postinjection. Indomethacin prevented the pyrexia and normalized hypothalamic NPY levels. As NPY concentrations were not increased in the ARC (the hypothalamic site of synthesis), we suggest that the increased NPY levels may result from blocked release, which would be in accord with the known experimental effects of NPY.

Oral-pharyngeal-esophageal and gastric cues contribute to meal-induced c-fos expression

We recently demonstrated that a meal induces c-fos immunoreactivity in the dorsal motor nucleus of the vagus (DMV), the nucleus of the tractus solitarius (NTS), and the area postrema (AP) of the rat brain stem. This response was not eliminated by the cholecystokinin A (CCK-A) antagonist L-364,718, a finding suggesting that feeding induces c-fos immunoreactivity by a pathway that is largely independent of CCK-A receptor activation. Consequently, the role of alternative gastrointestinal cues in the induction of c-fos was investigated. The induction of c-fos after oral-pharyngeal and esophageal stimuli was examined by use of a sham-feeding procedure via a gastric fistula. Gastric fistula-closed and fed rats displayed c-fos immunoreactivity similar to that of meal-fed rats seen previously. Fistula-open and fed rats showed the same degree of staining in the more rostral section of NTS examined as fistula-closed and fed rats, but fewer c-fos-positive nuclei in the more caudal level of the NTS. The potential for gastric distension to induce c-fos was assessed after the inflation of a gastric balloon. Physiological inflation of the balloon produced marked c-fos induction primarily in the medial NTS.

LY226936 Administered Orally and Centrally to Obese Zucker Rats Suppresses Food Intake and Body Weight Gain

LY226936, methylcarbamothoic acid-S-(4,5-dihydro-2-thiazolyl) ester, is a new compound that, when administered to obese Zucker rats, caused reduced food intake. LY226936 reduced the food consumption after a single oral dose of 50 and 100 mg/kg. On chronic oral administration to meal-fed obese (5 to 35 mg/kg. once daily) and to fed obese and lean (15 mg/kg. twice daily) Zucker rats, LY226936 reduced food intake and body weight gain for periods ranging from 40 to 48 days. The effect on both parameters was statistically significant. There is no evidence in our studies that tolerance to the actions of LY226936 developed. LY226936 decreased the consumption of both high carbohydrate and high fat diets. Food consumption of meal-fed obese Zucker rats was reduced significantly each time a single dose of 10 ugm LY226936 per rat was infused intracerebroventricularly. None of the receptors studied (mu and kappa opioid, CCK, serotonin, neuropeptide Y, galinin, N-methyl-D-aspartic acid) appeared to bind LY226936 and therefore, appear not to be involved in the depression of food intake by the obese Zucker rat.

The effects of two acylcoenzyme a: Cholesterol acyltransferase (ACAT) inhibitors, cyclandelate and a non-hydrolysable ether analogue, benzyl3,3,5-trimethylcyclohexanol on low density lipoprotein metabolism in macrophages and hepatocytes

Cyclandelate (3,3,5,-trimethylcyclohexanylmandelate) caused a dose-dependent decrease in the metabolism of radioiodinated low density lipoprotein [ 125I-LDL] by J774 mouse macrophages. This was probably an indirect effect dur to the inhibition of cholesterol esterification by the cells rather than a direct one one the interaction of LDL with its receptor, since no inhibition was seen in cells which had been cholesterol-depleted by prior incubation with lipoprotein-depleted serum for 48 hr. Cyclandelate also inhibited immediately de novo synthesis of cholesterol from [1- 14C]acetate in J774 cells, suggesting a direct action of the drug on an enzyme of the cholesterol biosynthetic pathway. The drug was an efficient inhibitor of hamster and rat intestinal acylcoenzyme A: cholesterol acyltransferase (ACAT) activity in vitro with an ic 50 of 20 μM. Addition of cyclandelate to the diet of meal-fed rats caused a marked inhibition of the rate of appearance of dietary [4- 14C]cholesterol in the plasma. A nonhydrolysable ether analogue of cyclandelate, benzyl3,3,5-trimethylcyclohexanol, was prepared to compare hepatic and extrahepatic actions of the two molecules. The analogue inhibited cholesterol esterification in J774 cells, transformed human macrophages U937 and human umbilical vein endothelial cells with an ic 50 of 20 μM and had effects similar to those of cyclandelate on 125I-LDL metabolism in J774 cells. Differences between the analogue and cyclandelate were seen in hepatocytes and hepatic microsomal fractions, where preincubation with the analogue inhibited cholesterol esterification in both systems while cyclandelate had no inhibitory action in either. Consequently, preincubation of rat hepatocytes with benzyl3,3,5-trimethylcyclohexanol for 17 hr caused a marked decrease in the binding of 125I-LDL to the cells, whereas binding to cells preincubated with cyclandelate was the same as to control cells.