Estrogen reduces total food and carbohydrate intake,but not protein intake,in female rats

Female rats were given simultaneous access to two isocaloric, isocarbohydrate diets that contained 5% or 45% protein. During four consecutive estrous cycles, rats reduced their total food and carbohydrate intake at estrus but maintained protein intake at levels found during the other stages of the estrous cycle. Administration of estradiol benzoate (EB) to ovariectomized rats given the same 5% or 45% protein diet choices also reduced total food and carbohydrate consumption while maintaining protein consumption. By contrast, administration of EB to ovariectomized rats given isocaloric, isonitrogenous diets containing 25% or 70% carbohydrate significantly reduced both total food and carbohydrate intake. The effects of estrogen on food and protein intake reported here are similar to those previously found after administration of drugs that enhance serotoninergic neurotransmission. Thus, the effects of estrogen on nutrient selection may depend, in part, on activation of a serotoninergic mechanism.     

Developmental patterns of macronutrient intake in female and male rats from weaning to maturity

Male and female Sprague-Dawley rats had available pure macronutrient diets, protein, carbohydrate and fat, from birth to day 77 of age. Analyses of their intake of these nitrients, as a function of age, demonstrate that, in both sexes, daily protein intake and preference for this nutrient relative to the other macronutrients rise steadily from weaning and peak precisely at the time of puberty (day 37–44 for females and days 42–49 for males), when there is also a peak in body weight gain. This is in contrast to daily carbohydrate intake, which peaks 2 weeks after puberty in males, and also to the female and male rats' preference for carbohydrate, which remains relatively stable from weaning to maturity. These patterns also differ from those observed for daily fat intake and fat preference for females and males, which are relatively high during the first postweaning week and then decline and remain very low until shortly after puberty (day 54), when there occurs a sharp burst in fat intake. Comparisons between the females and males reveal a significantly stronger preference for carbohydrate in the females, exhibited as early as 23 days of age; a stronger preference for protein and fat in the males, evident after day 28; and greater light-period feeding of carbohydrate and fat by females compared to males, apparent after puberty. Correlational analyses demonstrate that body weight and total kcal intake are closely related to daily protein consumption, more strongly in females compared to males; are strongly related to daily fat intake only in males; and are unrelated to intake of carbohydrate, at any age and in either sex.     

Effects of salinity on food intake and macronutrient selection in European sea bass

Salinity is one of the most relevant environmental parameters in regards to fish physiology, modifying food intake and growth performance in many fish species; however, its possible effects on macronutrient selection are still unknown. The aim of this study was to determine the effects of three salinity levels (25‰, 7‰, and 0‰) on total food intake and encapsulated macronutrient selection in a euryhaline teleost, European sea bass. A total of 40 fish (five per tank) with an average body weight of 52.4 ± 7.1 g were used. Lowering the salinity level from 25‰ to 7‰ and 0‰ reduced food intake by 27% and 42%, respectively. Regarding macronutrient selection, these salinity changes significantly decreased the percentage of CH intake by 31% and 27%, while increasing that of P by 30% and 25%, respectively. Fat selection remained unaltered, with an average value of 22% for all tested salinities. Specific growth rate (SGR) and feed conversion efficiency (FCE) were affected by macronutrient selection pattern, which in turn was salinity-dependent. These results indicate a strong influence of salinity on European sea bass food intake and macronutrient selection.     

Effect of photoperiod on the pineal melatonin rhythm in neonatal rats

Photoperiod already modulates pineal melatonin rhythm in neonatal rats. Pineal melatonin content was about 500 fmol during day and increased up to 2000 and 3000 fmol at night in 8- and 12-day-old rats, respectively. On long photoperiods (LD 14:10) melatonin was increased above 1000 fmol for about 8 h while on short photoperiods (LD 8:16) for 12 to 14 h. Melatonin pattern may thus transduce photoperiodic effects in neonatal rats. However, no differences in plasma LH were found in the rats kept on long and short photoperiods.     

Increased carbohydrate intake as a function of insulin administration in rats

Patterns of dietary self-selection were examined in male rats following subcutaneous injections of NPH insulin. Self-selection animals received separate dietary sources of protein, carbohydrate and fat, while single diet animals received ground Purina Rodent Chow. Food intakes and body weights were measured daily. In comparison to non-injected animals, both self-selection and single-diet animals displayed similar increases in caloric intakes and body weights in response to insulin administration. In animals maintained on the self-selection regime, the increase in caloric intake was solely a function of an increase in carbohydrate intake. Neither protein intake nor fat intake varied as a function of insulin administration. While fat intake remained stable in insulin-injected animals, non-injected self-selection animals gradually increased fat consumption throughout the experiment. Termination of insulin administration for all animals led to decreases in caloric intake below the levels of non-injected animals. Again, modification in caloric intakes in selecting animals were primarily a consequence of altered carbohydrate intake. Patterns of dietary self-selection in insulin-injected animals are contrasted to patterns of selection in other forms of experimental obesity.     

Metabolic consequences of food restriction in rats

Some aspects of carbohydrate metabolism were studied in rats subjected to food restriction (single daily meal offered during two hours, either diurnal or nocturnal) for a week. Nocturnal preference for the nocturnal meal was patent in spite of food restriction, inasmuch as the rats fed from 8:00 to 10:00 p.m. ingested significantly more than those fed from 8:00 to 10:00 a.m. The amount of food ingested by rats of both groups was lower than that ingested by the animals with free access to food (as evaluated in 24 hours); nevertheless, both food-restricted groups did not lose weight for the duration of the experiments. The more prominent carbohydrate metabolic adaptations to food-restriction were: (1) high hepatic glycogen concentration during the intermeal periods; (2) hyperglycemia in the 12, 14 and 16 hour intermeal periods; (3) insulinemia was lower than in rats having free access to food all day long; (4) gastric emptying was delayed.     

Self-selecting albino rats exhibit differential preferences for pure macronutrient diets: Characterization of three subpopulations

Analyses of natural feeding behavior in albino male Sprague-Dawley rats demonstrate that, when allowed to self-select from pure macronutrient diets (protein, carbohydrate and fat), these rats of the same genetic strain can be categorized into 3 subpopulations according to either their 24-h or their 12-h nocturnal patterns of nutrient intake. A majority of the animals (HC for high carbohydrate, 50% of the total population) consumed a diet rich in carbohydrate relative to protein or fat, while a smaller population of rats (HF, 30%) preferred the fat diet, and an even smaller population (HP, 20%) chose a high-protein diet. These 3 subpopulations, after a few weeks of maintenance on the diets, differed in their body weight, with the HF rats having a higher body weight than the HP animals, who tended to weigh more than the lightest HC rats. Whereas all subgroups exhibited a similar bimodal distribution of feeding during the nocturnal cycle, with peaks during the early and late dark periods, they were distinguishable on the basis of their nutrient consumption during specific phases of the dark cycle. This difference was most apparent in the early dark phase, when the 3 subgroups exhibited exaggerated preferences for the specific nutrient that was generally preferred over the 24-h cycle. This is in contrast to the middle dark phase, when diet preferences were attenuated or lost, and the late dark phase, when most rats were similar in showing an increased preference for protein and fat and a decreased preference for carbohydrate. The HF group was further distinguished by an unusually strong burst of feeding during the first 2 h of the dark period and an extra peak of feeding in the middle dark period (7th h), both of which were relatively high in fat content.     

Influence of nutrient preload on encapsulated macronutrient selection in European sea bass

The sea bass is a teleost that is able to regulate its energy intake by selecting from pure macronutrient sources, although the regulatory mechanisms involved in this selection are unknown. Nutrient preloads are known to reduce food intake and modify macronutrient selection patterns in mammals, but no information is available on its effects in fish. The aim of the present work was to determine the effect of orally administered macronutrient preloads of protein (P), fat (F) or carbohydrate (CH) on the subsequent macronutrient selection, using for the purpose feed consisting of CH, P or F packaged separately in gelatin capsules. The macronutrient preloads left the total food intake unaltered, but caused differential changes in the pattern of macronutrient selection. The CH preload increased the selection of CH (39%) and decreased that of P (20%), independently of the fish's previous nutritional preferences. The F preload induced an F increase (32%) and a P decrease (18%) in P-preferring fish, but not in F-preferring fish in which the macronutrient selection pattern remained unaffected. The P preload stimulated F selection by 42% in P-preferring fish, but left the macronutrient selection pattern unchanged in F-preferring fish. In conclusion, oral macronutrient preloads affected the pattern of macronutrient selection in fish, acting by post-ingestive mechanisms. The effect was influenced by the fish's previous nutritional preference and/or status, which could depend on its metabolic capacity.     

Different diurnal rhythms of protein and non-protein energy intake by rats

Rats allowed to self-select dietary constitutents control their intake of protein and energy (calories) independently. Although absolute protein consumption per meal remains almost constant, meal size increases progressively from the mid-light period through the dark period by selective increases in the non-protein content. Hence the composition of selected meals follows a daily rhythm with protein concentration decreasing from light to dark meals. The consistency of these feeding rhythms indicates separate short-term regulation of protein and energy intakes.     

Carbohydrate metabolism and food intake in food restricted rats: effects of an unexpected meal

Rats subjected to a daily single-meal feeding schedule were presented with an unexpected meal at three different times of the day and the effects on the carbohydrate metabolic patterns were determined. The results indicate that it is the actual metabolic moment of the organism, rather than the duration of the inter-meal period and the degree of gastric emptying, that determines the amount of food ingested.     

结肠炎大鼠结肠免疫功能的改变和褪黑素调节

目的:研究褪黑素(MT)对免疫性结肠炎大鼠结肠局部免疫功能的影响。方法:利用三硝基苯磺酸和乙醇复制大鼠免疫性结肠炎模型,设正常对照组、模型对照组、5-氨基水杨酸给药组(5-ASA,100mg·kg~(-1))和MT给药组(2.5,5.0,10.0mg·kg~(-1)),每天灌肠给药1次,从复制模型7d后开始至实验结束共21d。检测大鼠结肠组织白细胞介素(IL-1、IL-2)、肿瘤坏死因子(TNF-α)、一氧化氮(NO)、髓过氧化物酶(MPO)和丙二醛(MDA)水平;另制备模型对照组大鼠炎症结肠匀浆并加入脂多糖LPS,设阴性对照组、模型对照组、5-ASA给药组(终浓度为100μmol/L)和MT给药组(终浓度为0.01,0.1,1.0mmol/L)。取上清测IL-1、IL-2、TNF-α、NO、乳酸脱氢酶(LDH)、MPO和MDA水平。结果:模型对照组大鼠结肠中IL-1、IL-2、TNF-α、NO、MPO和MDA含量增多,MT可呈不同程度的抑制作用;模型对照组大鼠炎症结肠匀浆中IL-1、IL-2、TNF-α、NO、LDH、MPO和MDA含量显著增加,预先加入MT可明显降低IL-1、TNF-α、LDH、MPO和MDA含量,1.0mmol/LMT可明显抑制NO产生。结论:三硝基苯磺酸引起的结肠炎大鼠结肠存在明显免疫功能紊乱,MT可从不同水平调节结肠异常免疫功能减轻大鼠结肠炎症状。     

Energy density and weight of food effect short-term caloric compensation in men

OBJECTIVE: The purpose of the study was to examine the effect of energy density and food weight (volume) on subsequent intake. DESIGN: Sixteen lean men were each studied four times during a 2-d protocol at the Rowett's Human Nutrition Unit. On day 1, subjects were fed a mandatory diet at 1.6 x resting metabolic rate (RMR). On day 2, during the mandatory morning period (08.30-12.30) subjects consumed a fixed breakfast (08.30) plus a snack (10.30) in one of four treatments [with values in weight (kg), ED (kJ/100g), Energy (MJ)]: (i) zero intake, 0:0:0 (ii) low energy density (LED), 0.615: 400: 2.46; (iii) high energy density (HED), 0.615: 800: 4.92; (iv) 2 x LED, 1.225: 400: 4.91. From 12.30, throughout the remainder of the day, subjects had ad libitum access to 15 high-protein, 15 high-fat and 15 high-carbohydrate foods. Motivation to eat was tracked hourly using 100 mm line scales. RESULTS: ANOVA showed subjects were hungrier after the zero and LED treatments in the mandatory period (p<0.001). Lunch time EI was 5.0, 3.1, 4.2 and 3.2 MJ on the zero, HED, LED and 2 x LED treatments, respectively (p<0.001). Total ad libitum EI was 11.7, 9.6, 10.3 and 9.5 MJ/d, respectively (p=0.033). Total ad libitum plus mandatory intakes amounted to 11.7, 14.5, 12.6 and 14.4 MJ/d, respectively (p=0.001). Corresponding food intakes were 2.18, 2.39, 2.51 and 3.06 kg/d, respectively (p<0.001). CONCLUSIONS: The present study showed that subjects respond to both the amount of food eaten in the morning and to the energy density of those foods. However, compensation was only partial and short-term. Subjects only compensated EI by approximately 40% and that compensation only occurred at the next meal.     

Metformin and melatonin improve histopathological outcome of NMU-induced mammary tumors in rats

Objective

Numerous reports showed inhibition of carcinogenesis after metformin (MF) and melatonin (MEL) administration. However, most in vivo studies used standard diet type, with relatively low fat content. As increase in fat intake may have a considerable impact on malignant transformation, we evaluated the effects of these two substances in a model of mammary carcinogenesis in rats fed a high-fat diet (10%).

Effect of deprivation and time of refeeding on food intake.

The amount of food eaten in a two hour trial by male Sprague Dawley rats was recorded after periods of food deprivation up to 42 hr in length. Rats ate 50-78% more when refed during the dark phase than when refed during the light phase. This occurred even when light fed animals were fasted for longer periods than the dark fed animals. Rats eat in a rhythmic pattern after deprivation. These data are in good agreement with data previously reported and extend it by increasing the number of observations, increasing the length of deprivation, and comparing different age groups.     

Suppressive effects of naloxone on food and water intake in vagotomized rats

Rats were (1) sham operated and ad lib fed, (2) given bilateral subdiaphragmatic vagotomies or (3) sham operated and pair fed to the vagotomized group. At the start of the dark period, following a 24 hr fast, the animals were tested for the ability of naloxone (0.5, 1.5, 3.0 and 5.0 mg/kg body weight) to suppress food and water consumption. In comparison to saline control injections the data indicated that naloxone was equally effective in suppressing food intake, over a two hour period, in all groups. Similarly naloxone effectively decreased water consumption of all groups in comparison to their saline trials. When the post naloxone data were calculated as a percentage of saline baseline this suppression was, at times, slightly greater in the vagotomized group than in the other groups. However, this may be an artifact of the low baseline intake of the vagotomized group. The results are discussed with relevance to the recent findings of others concerning this subject.     

Ghrelin stimulates growth hormone secretion and food intake in aged rats

Age-related decreases in energy expenditure have been associated with the loss of skeletal muscle and decline of food intake, possibly through a mechanism involving changes of growth hormone (GH) secretion and feeding behavior. Age-related declines of growth hormone secretion and food intake have been termed the somatopause and anorexia of ageing, respectively. Ghrelin, a 28-amino-acid peptide, was isolated from human and rat stomachs as an endogenous ligand of growth hormone secretagogue receptor. Ghrelin stimulates growth hormone release and food intake when peripherally administered to rodents and humans. Here, we investigate the relationship between age-related decline of growth hormone secretion and/or food intake and ghrelin function. Ghrelin (10 nmol/kg body weight) was administered intravenously to male 3-, 12-, 24-and 27-month-old Long-Evans rats, after which growth hormone concentrations and 2 h food intake were measured. An intravenous administration of ghrelin to rats increased food intake in all generations. In addition, to orexigenic effect by ghrelin, intravenous administration of ghrelin elicited a marked increase in plasma GH levels, with the peak occurring 15 min after administration. These findings suggest that the aged rats maintain the reactivity to administered exogenous ghrelin.     

Intact regulation of protein intake during the development of hypothalamic or genetic obesity in rats

Adult female rats made hyperphagic with bilateral lesions of the medial hypothalamus as well as spontaneously hyperphagic adult female rats of the Zucker strain were studied for their abilities to regulate dietary protein and energy intakes. This was accomplished by permitting both models of animal obesity to select freely between two isocaloric diets containing 10% vs 60% by weight casein (protein) for at least one month. Compared to appropriate control groups, both experimental groups became obese by consuming more of the low protein diet and less of the high protein diet. The overall effect of this selection pattern was an excessive intake of energy in the form of carbohydrate and fat while maintaining control levels of protein intake. These data imply that the stimulus for hyperphagia in both animal models of obesity is some physiological and/or behavioral error in energy regulation but not protein regulation.     

Taste, intake rate, and food choice in rats

The contribution of taste to the food choices of foraging rats was examined. Rats in a laboratory foraging paradigm searched for sequential opportunities to eat at two feeders containing chow-based food pellets that were plain or flavored with saccharin or citric acid. Pellets cost the same number of bar presses at both feeders. Saccharin adulteration had no effect on intake parameters. Citric-acid-flavored pellets were eaten more slowly and in smaller meals. If there was no alternative food, daily intake was slightly reduced. When the alternative food was plain, fewer meals and fewer pellets were taken of the citric-acid-flavored than plain pellets. When we gradually increased the price of the plain pellets at one feeder, while the price at the alternative feeder (which contained either plain or citric-acid-flavored pellets) remained low, the rate of eating (profitability) decreased at the higher-price feeder, and the rats shifted their intake toward the less-costly, more profitable pellets. We compared the relationship between the relative eating rate at each feeder and the relative meal size (or daily intake) at each feeder when the low-priced food was plain and when it was flavored with citric acid, and found no differences. This indicates that taste may influence choice via its effect on rate of intake.     

Energy intake and macronutrient selection in sharpsnout seabream (Diplodus puntazzo) challenged with fat dilution and fat deprivation using encapsulated diets

Sharpsnout seabream fed pure macronutrient capsules were challenged to fat dilution and fat deprivation in order to investigate the effects of fat level on energy intake regulation and macronutrient selection by fish, as they lack oropharyngeal chemosensory information from the diet. During the control phase, the fish were fed three individually encapsulated macronutrients, from which they composed a diet containing 67.36% protein (P), 19.08% carbohydrates (CH) and 13.57% fat (F), in terms of macronutrient weight intake percentage. During the second phase of the experiment, a lipid content reduction in F capsules from 55.0% to 13.4% did not significantly modify this selection pattern, energy ingestion or the number of capsules ingested of each macronutrient. During the third phase, in which they were subjected to fat deprivation, starting on almost the first day, the fish increased their total energy intake and total ingested number of capsules. These results reveal that fish are capable of distinguishing and selecting each of the three macronutrients contained in gelatine capsules, and that fish selection of a balanced diet from pure macronutrients is remarkably stable. Fish are capable of sustaining their macronutrient selection pattern and energy intake with very low amounts of fat in their diets (Phase 2). A certain instability in the initial P, CH and energy intake was only observed when fat was totally deprived (Phase 3), which resulted in higher values than those observed in Phase 1. In order to examine any possible effects of diet encapsulation, digestibility assays were performed in a second experiment. The fish were divided into two experimental groups and fed the same complete commercial diet, the only difference being the way it was presented to each group (pelleted or encapsulated). No statistical differences between the experimental groups were found with regards to both apparent digestibility coefficients and fish growth.