Sucrose-induced hyperphagia and obesity in rats fed a macronutrient self-selection diet

Adult female rats were allowed to self-select their diet from separate sources of fat, protein, and carbohydrate (starch). Other rats were fed a composite diet that matched the nutrient composition chosen by the self-selecting rats (50% fat, 28% protein, 22% carbohydrate) or a low-fat, high-carbohydrate chow diet. Half of the rats in each diet condition were given access to a 32% sucrose solution for 30 days. Sucrose availability increased total caloric intake (approximately 20%) and body weight gain in all three groups compared to control groups not fed the sucrose solution. The selection animals compensated for their sucrose intake by reducing their fat intake, and to a lesser degree, their starch intake; protein intake was the least affected by sucrose availability. The selection rats consumed less sucrose than the chow-fed rats and displayed a smaller increase in weight, relative to controls, than the chow-fed rats. These differences were attributed to the high-fat intake of the selection animals since similar results were obtained with the rats fed the composite diet. In particular, both the selection and composite diets produced mild obesity in the absence of sucrose. The results demonstrate that sucrose-induced overeating and overweight is not an artifact of restraining the diet choices of rats to a pure sugar and a nutritionally complete diet.     

Effects of dietary protein on food and water intake in spontaneously hypertensive rats

We have been studying the development of hypertension in spontaneously hypertensive rats (SHR) fed a low protein diet. The effects of a low protein diet upon food and water intake were examined. Body weight gain, food and water intake were measured in three to twenty-three week-old SHR and Wistar Kyoto rats (WKY) fed diets containing 8%, 15% or 25% casein. Body weights of SHR and WKY fed an 8% casein diet were significantly lower at 23 weeks than rats on the higher protein diets, although both groups on the 8% diet consumed more food and water per g of body weight. In addition, SHR fed an 8% casein diet drank less water per gram of food than WKY or SHR fed 15% and 25% casein diets. These results indicate that changes in food and water intake, as a consequence of low protein diets, should be an additional consideration when examining the effects of dietary protein on the development of hypertension.     

Early postnatal protein malnutrition changes the development of social play in rats

Early protein malnutrition produces structural and functional alterations in the brain and changes the organism-environment interactions. Rats from 26 to 76 days of age were used to study the effects of early postnatal protein malnutrition on the development of social play. During lactation phase the litters were fed diet containing 16% protein (well-nourished) or 6% protein (malnourished). From weaning to the end of behavioral tests well-nourished animals were fed a commercial lab chow diet (well-nourished--W) and the malnourished rats were divided into 2 groups: one was maintained on 6% protein diet (malnourished--M) and the other was fed a commercial lab chow diet (previously malnourished--PM). Pairs of male rats of same diet conditions were tested, at different ages, for three consecutive days. During sessions the following behaviors were recorded: pinning, wrestling, walk-over and rear. The frequency of wrestling and walk-over was significantly higher in malnourished as compared to well-nourished animals (p<0.05). Early protein malnutrition also changed the ontogeny of play behaviors (pinning and wrestling) with developmental retards in M and PM as compared with W animals, especially at 46 and 56 days of age. These results suggest that early protein malnutrition can affect the development of neural mechanisms underlying social play in rats.     

The Effects of Age and Hindlimb Supension on the Levels of Expression of the Myogenic Regulatory Factors Myod and Myogenin in Rat Fast and Slow Skeletal Muscles

In this study we tested the hypothesis that, compared to young adult rats, senescent rats have a reduced ability to respond to muscle unloading. Unloading of the muscles was induced by hindlimb suspension (HS) of young adult and senescent rats for 21 days. Plantaris muscles from young adult rats had significantly higher levels of myogenin mRNA and protein (890 % and 314 %, respectively, P < 0.05) than plantaris muscles from senescent rats and also a higher MyoD mRNA level (280 %, P < 0.05), but ageing did not increase MyoD protein levels. Although HS did not increase plantaris mRNA or protein levels of myogenin or MyoD in senescent rats (P = 0.22), myogenin mRNA and protein levels increased by 850 % and 580 % respectively, and MyoD mRNA and protein levels by 235 % and 1600 %, respectively in young adult rats (P < 0.05). Soleus muscles from senescent rats had 150 % and 85 % greater myogenin and MyoD mRNA levels, respectively (P < 0.05), than soleus muscles from young adult rats, whereas protein levels of myogenin were similar (P > 0.05) and MyoD protein levels were 60 % lower in the muscle of senescent rats (P < 0.05). In young rats, soleus muscle mRNA levels of myogenin and MyoD were not altered by HS but myogenin protein levels decreased by 57 % (P < 0.05) whereas MyoD protein levels increased by 187 % (P < 0.05). In senescent rats, HS decreased soleus muscle myogenin mRNA and protein levels by 42 % and 26 % respectively (P < 0.05), but MyoD protein and mRNA levels were not changed. MRF4 levels were not affected by ageing in either muscle. These data suggest that ageing reduces the ability of fast muscles to increase myogenin protein levels, and prevents both fast and slow muscles from increasing MyoD protein levels during muscle unloading. Experimental Physiology (2001) 86.4, 509-517.     

Reflex-elicited increases in female rat parotid protein synthesis involving parasympathetic non-adrenergic, non-cholinergic mechanisms

Normal rats or rats parasympathetically denervated on one side by cutting the auriculo-temporal nerve were maintained on a liquid diet for 1 week. After fasting overnight, experimental rats were then offered hard, pelleted food over a period of 2 h, while unfed animals served as controls. The reflex-induced increase in the [3H]leucine incorporation into trichloroacetic acid-insoluble material of the parotid glands following intake of the food in the presence of the muscarinic blocker atropine and alpha- and beta-adrenoceptor antagonists was greater (104%) than in the absence of the blockers (75%) in normal rats. The picture was the same when the innervated glands of rats subjected to unilateral parasympathetic denervation were examined. In this case, the protein synthesis increased by 108% in the presence of the blockers and by 63% in their absence. Analysis of the parasympathetically denervated and contralateral innervated glands revealed no support for a cholinergic or adrenergic contribution to this response. The increase in protein synthesis in the innervated glands was 86% in the rats treated with atropine, whilst it was 76% in those treated with alpha- and beta-adrenoceptor antagonists. The protein synthesis in the denervated glands increased by 57% in the absence of receptor blockade. Neither atropine (51%), nor a- and b-adrenoceptor antagonists (52%), nor a combination of the three blockers (55%) affected the response of the denervated glands. A large part of the response in the presence of the traditional autonomic receptor blockers was thus dependent on the parasympathetic auriculo-temporal nerve. Under natural feeding conditions, the parasympathetic non-adrenergic, non-cholinergic (NANC) mechanisms are likely to contribute to the synthesis of secretory proteins.     

Ethanol effects on protein synthesis in nonparenchymal liver cells, hepatocytes, and density populations of hepatocytes

Rats were given ethanol chronically (20-30% of the energy) in a nutritionally sufficient diet regimen. Controls received lipid as an isoenergetic substitute for ethanol. Protein synthesis in hepatocytes isolated from ethanol-fed rats was decreased compared with controls, but not in isolated nonparenchymal liver cells. Ethanol added in vitro inhibited protein synthesis in hepatocytes by 30%, but not in nonparenchymal cells for both ethanol-fed and control rats. Protein export and protein degradation in isolated hepatocytes were not affected by long-term ethanol treatment. Isolated hepatocytes were separated according to their buoyant density in linear metrizamide gradients. They were distributed in a bell-shaped manner regardless of donor rat treatment. Cells of low density contained three times as much lipid as high density cells. They were probably enriched in periportal cells, since histologic examination indicated a predominantly periportal localization of cells containing lipid droplets. Distribution of the intra-acinar marker alanine aminotransferase supported this conclusion. Protein synthesis was similar in the low-density hepatocyte populations of the respective groups of rats, whereas it was inhibited in a high-density population of ethanol-treated rats compared to the controls. Inhibition of protein synthesis by 80 mM ethanol was lower in the low-density hepatocytes of ethanol-fed rats.     

Functional development of the visual system in normal and protein deprived rats

During an investigation focused on development of visual evoked responses (VER) in normal and protein deprived rats indications of persisting latency differences were found. Since such differences are in variance with previous reports special attention was paid to compare control and protein deprived adult rats. Protein deprivation was induced by feeding rats a diet with 50% reduction in protein content compared with control rat diet from two weeks before onset of gestation until examination. Dependence on experimental variables of latencies and complexity of the VER illustrated the need of a well defined experimental situation. Adult protein deprived rats showed significantly longer latencies to onset and to the first three peaks of the VER and an altered complexity of the response. It is suggested that the observed alterations result from effects of the protein deprivation on early brain development since this and previous studies have shown similar alterations in developing young rats. The divergence in findings between the present and previous reports may be explained by differences in degree of malnutrition and in other experimental conditions.     

Control of protein intake in the young rat

Both adult and weanling rats are able to control their dietary intake of protein. The purposes of the current study were to determine: the precision of this ability in the weanling rat and when this ability makes its ontogenic appearance. We studied three overlapping age groups spanning the third, fourth and fifth postnatal weeks. Animals chose between two isocaloric liquid diets, one protein-free and the other composed of 50% protein. The intake volume of each diet was measured daily. Three days after introduction to the diets, pups were subjected to short-term tests designed to determine their ability to distinguish between the two diets. All three age groups responded to the protein conditions. However, the youngest group displayed comparatively weaker responses characterized by a prolonged period of reduced protein intake and weaker responses to the protein conditions of the short-term test. We conclude that young rats control protein intake by the end of the third postnatal week and that this ability strengthens throughout the remainder of the weaning period.     

Functional development of the visual system in normal and protein deprived rats. I. Persistent changes in light-induced cortical evoked response

During an investigation focused on development of visual evoked responses (VER) in normal and protein deprived rats indications of persisting latency differences were found. Since such differences are in variance with previous reports special attention was paid to compare control and protein deprived adult rats. Protein deprivation was induced by feeding rats a diet with 50% reduction in protein content compared with control rat diet from two weeks before onset of gestation until examination. Dependence on experimental variables of latencies and complexity of the VER illustrated the need of a well defined experimental situation. Adult protein deprived rats showed significantly longer latencies to onset and to the first three peaks of the VER and an altered complexity of the response. It is suggested that the observed alterations result from effects of the protein deprivation on early brain development since this and previous studies have shown similar alterations in developing young rats. The divergence in findings between the present and previous reports may be explained by differences in degree of malnutrition and in other experimental conditions.     

Identification of three extended antibody-binding segments in recombinant human muscle acetylcholine receptor alpha subunit extracellular domain 1-210.

The duplicated alpha subunits account for 40% of the total protein of the nicotinic acetylcholine receptor of muscle, and are implicated as targets for pathogenic autoantibodies in the neuromuscular disease myasthenia gravis (MG). This study reports some of the specificities of antibodies induced by a myasthenogenic recombinant protein (rH alpha 1-210) corresponding to the proposed extracellular domain of the alpha subunit of human acetylcholine receptor, residues 1-210. Antisera produced by immunizing rats, rabbits, and mice were tested with a panel of overlapping synthetic peptides (each 16 amino acids) comprising residues 1-216 of the human alpha subunit. IgG antibodies produced in all three species bound only to peptides that were clustered in three segments: segment I (residues 9-24); segment II (57-96 in rats, 57-88 in rabbits, and 57-80 in mice); and segment III (137-184 in rats, 145-184 in rabbits and mice). Monoclonal antibodies were produced by 41 independent hybridomas derived from three rats immunized with rH alpha 1-210; 12 reacted only with the recombinant or native protein, and 29 reacted additionally with peptides in segments II or III. Four mAbs bound to native human receptor; of these, three bound to peptides 57-72/65-80, 81-96, or 153-168, and one lacked peptide-binding activity. Lack of mAb reactivity with rat receptor precluded correlation of peptide reactivity with myasthenogenicity. Nevertheless, the data indicate that the human acetylcholine receptor's alpha subunit contains multiple sites in its extracellular domain that are potentially stimulatory for B cells.     

Reduced cerebrospinal fluid levels of alpha-secretase-cleaved amyloid precursor protein in aged rats: correlation with spatial memory deficits.

The amyloid precursor protein undergoes proteolysis at several sites to yield a number of functionally relevant peptides, including beta-amyloid and the soluble amyloid precursor protein derivatives alpha-soluble amyloid precursor protein and beta-soluble amyloid precursor protein. beta-Amyloid is the primary constituent of senile plaques associated with Alzheimer's disease, while a-soluble amyloid precursor protein promotes synaptogenesis and plays a role in neuroprotective processes. We tested for age-related alterations in these amyloid precursor protein proteolytically derived peptides by measuring the levels of alpha-soluble amyloid precursor protein, total soluble amyloid precursor proteins (alpha- and beta-soluble amyloid precursor protein combined) and beta-amyloid in cerebrospinal fluid from three-, 13- and 23-month-old Fischer-344 rats. Western blot analysis using selective antibodies revealed 50% less total soluble amyloid precursor protein and a-soluble amyloid precursor protein in cisternal cerebrospinal fluid from 23-month-old rats compared with three- and 13-month-old animals. Mass spectrometric analysis indicated, however, that beta-amyloid in cerebrospinal fluid was not different between the three age groups. In a second group of young (five to six months of age) and aged (24-25 months of age) rats, spatial working and reference memory were assessed in a water maze followed by collection of cerebrospinal fluid. As a group, the aged rats consistently performed below the young rats in both working and reference memory tests. The aged rats also had 49% less cerebrospinal fluid alpha-soluble amyloid precursor protein than did their younger counterparts. There was a positive correlation (r= 0.52-0.57, P < 0.001) between performance in spatial memory tasks and cerebrospinal fluid alpha-soluble amyloid precursor protein in these young and aged rats. These results suggest that there is a positive association between cerebrospinal fluid levels of alpha-soluble amyloid precursor protein and cognitive performance in rats, and that alpha-soluble amyloid precursor protein may be involved in the spatial learning and memory changes that accompany ageing.     

Postnatal protein malnutrition affects play behavior and other social interactions in juvenile rats

The effects of postnatal protein malnutrition on juvenile social behaviors were investigated in male and female Wistar rats. During the lactation period (21 days), each litter (six male and two female pups) was provided with 16% (control) or 6% (low protein) casein diets. At weaning, the control group (W) continued to receive the 16% protein diet and the malnourished group was divided into two groups: one continuing to receive a 6% protein diet (malnourished group - M) and the other shifted to a 16% protein diet (previously malnourished group - PM). These conditions lasted until 38 days of age when the behavioral tests ended. To assess social interaction, pairs of rats of the same nutritional condition and same gender were placed in a familiar arena for 3 consecutive days. Playful social behavior (pin), nonplayful social behavior (anogenital sniff, walk-over, side-mount and allogroom) and nonsocial behavior (rear) were recorded in three 10-min sessions. Postnatal protein malnutrition significantly decreased playful social behavior, nonsocial behavior (rear) and nonplayful social behaviors such as side-mount and walk-over. Anogenital sniff and allogroom were increased by early malnutrition. Nutritional rehabilitation from weaning reversed the changes produced by protein malnutrition in nonplayful (side-mount, walk-over, anogenital sniff and allogroom) and nonsocial behaviors (rear) but increased playful social behavior (pin). Gender effects were observed only on side-mount (higher incidence in males) and walk-over (higher incidence in females) indicating that playful behavior and nonsocial behavior were not affected by sex. The present results suggest that behavioral differences described in adulthood may result from changes in social behaviors of juvenile rats induced by early protein malnutrition.     

Effect of type of protein on food intake of rats fed high protein diets

The effects of type of protein on intake of a high protein diet after adapting rats to a low protein diet were examined in rats trained to eat a 5.2% (N X 6.25) protein diet containing a mixture of casein, lactalbumin, egg white and soy protein, in a single 3-hour period per day. Food intake was measured from 0-15, 15-30, 30-90, and 90-180 minutes. After a 2-week adjustment period, rats were presented with a 40% (N X 6.25) protein purified diet containing only one of the 4 proteins mentioned above or a mixture of these 4 proteins. During the first 15-minute interval, rats eating diets containing protein mixture, lactalbumin, egg white or soy protein depressed their intake significantly compared with the average intake of the 3-day pre-test period, whereas rats eating casein diet increased their intake. During the last 90-minute interval of the first day, all rats depressed their intake, those rats eating casein the least and those rats eating egg white the most. On the second day, rats offered lactalbumin depressed their intake 52.5% for the 3-hour period and rats offered casein depressed their intake 34.3%. Rats eating soy protein, egg white and protein mixture increased their intake from day 1 to day 2. These experiments show that type of protein affects rats' initial intake when they are offered a high protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary protein and captopril on glomerular permselectivity in rats with unilateral nephrectomy

Proteinuria and progressive glomerulosclerosis are commonly associated with nephron loss. We studied the pathogenesis of these lesions by examining the role of changes in specific glomerular capillary wall permeability properties in uninephrectomized rats. The development of altered capillary permselectivity to macromolecules and loss of glomerular basement membrane anionic charge were measured by the dextran fractional clearance and ferritin tracer probe methods, respectively. In addition, the protective effect of dietary protein restriction and an angiotensin I-converting enzyme inhibitor (captopril) were studied in eight groups of male Sprague-Dawley rats. Four groups of rats underwent sham-nephrectomy or left nephrectomy and were fed an 8.5% protein diet (sham-nephrectomy and low protein, nephrectomy and low protein) or a 30% protein diet, respectively (sham-nephrectomy and high protein, nephrectomy a high protein). Four other groups of rats underwent sham-nephrectomy or left nephrectomy and were treated with captopril (50 mg/kg/day) while receiving a 8.5% protein diet (sham-nephrectomy, low protein and captopril, nephrectomy, low protein and captopril) or a 30% protein diet, respectively (sham-nephrectomy, high protein and captopril, nephrectomy, high protein and captopril). Rats were nephrectomized at 21 days of age and were functionally tested and sacrificed at 7 months of age. The nephrectomy and high protein rats had significantly greater proteinuria and higher fractional clearance of neutral dextrans in the 30 to 42 A range compared with that of sham-nephrectomy and high protein, nephrectomy and low protein, and nephrectomy, high protein and captopril rats. The nephrectomy and high protein rats also had a significantly lower labeling of the glomerular basement membrane with cationic ferritin tracer molecules compared with the nephrectomy and low protein and nephrectomy, high protein and captopril rats. Of the eight treatment groups, the nephrectomy and high protein rats had the most severe glomerular lesions. In general, nephrectomized rats fed low dietary protein and nephrectomized rats treated with captopril had significantly less proteinuria, glomerular lesions, and milder changes in the glomerular capillary wall porosity and glomerular basement membrane anionic charge.(ABSTRACT TRUNCATED AT 400 WORDS)     

绿色荧光蛋白转基因小鼠骨髓间充质干细胞干预重症急性胰腺炎大鼠后在多脏器的分布*

背景：利用绿色荧光蛋白转基因小鼠间充质干细胞自身携带荧光性的特点,干预重症急性胰腺炎大鼠后,便于动物体内跟踪观察。 目的：观察绿色荧光蛋白转基因小鼠骨髓间充质干细胞在重症胰腺炎大鼠体内各脏器的分布情况。 方法：直接贴壁法分离培养绿色荧光蛋白转基因小鼠骨髓间充质干细胞,90%融合后消化传代扩增。传至第3代后行CD29+、CD90+、CD34-、CD45-细胞免疫表型鉴定。显微镜下逆行胰胆管注射5%牛黄胆酸钠制造SD大鼠重症急性胰腺炎模型。1 h后,按2×106/只尾静脉注入重症急性胰腺炎SD大鼠体内。分别于6,12,24 h取肝、肾、脑、肺、胰、肠脏器送普通病理检查,观察胰腺病理变化及骨髓间充质干细胞干预重症急性胰腺炎SD大鼠后在各脏器干细胞分布情况及灰度值测定。 结果与结论：胰腺破坏随时间延长而加强,24 h破坏最严重;GFP小鼠CD29阳性细胞91.1%,CD90阳性细胞93.5%,CD34阳性细胞0.82%,CD45阳性细胞2.22%;注射干细胞SD大鼠各脏器均有绿色荧光出现,并随时间增长而增强;在肾脏组织中灰度值最高,脑组织最少。提示骨髓间充质干细胞干预重症急性胰腺炎大鼠后能在各脏器稳定分布。 关键词：重症急性胰腺炎;器官分布;骨髓间充质干细胞;干预;鼠 doi:10.3969/j.issn.1673-8225.2012.10.001     

热应激诱导大鼠延髓内脏带神经元Fos蛋白的表达

为了探讨不同温度下,大鼠的行为表现及大鼠延髓内脏带内神经元Fos蛋白的表达情况,本研究将成年SD大鼠置于不同温度(24℃、34℃、38.5℃、42℃),相对湿度60%的实验仓内60min,观察大鼠的行为表现。应用免疫组化法,观察大鼠延髓内脏带内Fos和酪氨酸羟化酶(TH)阳性神经元的形态、分布和数量的变化。行为学结果显示:(1)24℃时,大鼠无异常表现,直肠温度为36℃左右;(2)34℃时大鼠直肠温度升高至38℃左右,但动物行为亦无明显变化;(3)在38.5℃和42℃时,大鼠直肠温度升高至39℃以上,且大鼠的行为最初表现为精神萎靡,而随后转为兴奋状态。免疫组化染色结果显示:(1)24℃时,延髓内脏带的孤束核与延髓腹外侧区内Fos阳性胞核较少;(2)34℃时,上述部位内Fos阳性胞核的数量增加;(3)38.5℃时,Fos阳性胞核的数量达到峰值;Fos/TH双标神经元的比率分别占TH或Fos单标神经元的69%和43%;(4)42℃时,Fos阳性胞核又降低,并观察到三种Fos阳性细胞:胞核为Fos阳性,胞浆为Fos阳性,以及胞浆、胞核均为Fos阳性。以上结果提示:延髓内脏带参与了热应激过程,Fos蛋白的表达随温度的升高而发生明显的变化,且TH阳性神经元可能参与了这种作用的调节。     

Hepatic vagotomy disrupts somatotropin-induced protein selection

Rats treated with somatotropin (STH) and allowed to self-select between diets varying in protein content will consume more of the high-protein diet. The objective of this study was to determine the role of the hepatic vagus nerve in this ability to select protein. Female Sprague-Dawley rats (n=40) received a hepatic vagotomy (HVAGX) or a sham surgery. Postsurgery, the rats were maintained on pelleted diets for 2 weeks, after which the rats were adapted to selecting between powdered diets with 5% casein and 30% casein. After a 7-day adaptation to diet selection, rats in each surgical treatment group were treated with STH (4 mg/day) or physiological saline for 14 days. Body weight and intake were recorded daily. STH treatment increased growth rate to a similar degree in both sham and HVAGX groups. Despite causing an increase in total food intake, there was no effect of HVAGX alone on body weight. Relative to the sham-saline group, sham-STH in treated rats had greater total food intake that was accounted for entirely by increased consumption of the 30% protein diet and no change in intake of the 5% diet. In contrast, HVAGX+STH rats exhibited 20-30% increases in consumption of both the 5% and 30% protein diets. Thus, the HVAGX+STH rats recognized an increased need for protein, but were unable to distinguish between the high- and low-protein diets and selected more of both. The data suggest that the ability to alter diet selection in response to a stimulation of protein accretion is at least partially mediated through the liver and hepatic branch of the vagus nerve.     

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.     

Protein selection, food intake, and body composition in response to the amount of dietary protein

Though not universally observed, moderately low-protein diets have been found to increase caloric intake and body fat. It appears that animals overeat in calories in order to obtain more dietary protein. For animals to control protein intake, they must be able to distinguish between two isocaloric diets containing different percentages of protein and make the appropriate dietary selection on the basis of their previous history of protein intake. Experiment 1 examined the 24-h diet selection (5 vs. 35% casein) of Sprague-Dawley rats that had been previously fed diets containing various percentages of dietary protein (5, 10, 20, 35, or 60% casein). Animals fed 5, 10, or 20% dietary protein showed a preference for the higher protein selection diet. In contrast, no significant diet preference was found in animals pre-fed the two higher levels of dietary protein (35 or 60% casein). In this study, daily food intake and body fat of rats fed the low-protein diets (5 and 10% casein) were similar to rats fed the 20% casein diet. Experiment 2 examined the effects of the level of methionine supplementation on rats fed 10% casein. In this study, food intake and body fat were increased by approximately 20% in rats fed 10% casein diets, regardless of the level of methionine supplementation (0.3 vs. 0.15%). Together, the results suggest that the presence of low-protein-induced hyperphagia helps maintain body protein levels in the face of moderately low dietary protein and promotes an increase in the amount of body fat and energy.