Effects of prior or concurrent food restriction on amylin-induced changes in body weight and body composition in high-fat-fed female rats

Amylin infusion reduces food intake and slows body weight gain in rodents. In obese male rats, amylin (but not pair feeding) caused a preferential reduction of fat mass with protein preservation despite equal body weight loss in amylin-treated (fed ad libitum) and pair-fed rats. In the present study, the effect of prior or concurrent food restriction on the ability of amylin to cause weight loss was evaluated. Retired female breeder rats were maintained on a high-fat diet (40% fat) for 9 wk. Prior to drug treatment, rats were either fed ad libitum or food restricted for 10 days to lose 5% of their starting body weight. They were then subdivided into treatment groups that received either vehicle or amylin (100 microgxkg(-1)xday(-1) via subcutaneous minipump) and placed under either a restricted or ad libitum feeding schedule (for a total of 8 treatment arms). Amylin 1) significantly reduced body weight compared with vehicle under all treatment conditions, except in always restricted animals, 2) significantly decreased percent body fat in all groups, and 3) preserved lean mass in all groups. These results indicate that amylin's anorexigenic and fat-specific weight loss properties can be extended to a variety of nutritive states in female rats.     

Both Maternal Over- and Undernutrition During Gestation Increase the Adiposity of Young Adult Progeny in Rats

FIOROTTO, MARTA L, TERESA A DAVIS, PATRICIA SCHOKNECHT, HARRY J MERSMANN AND WILSON G POND. Both maternal over- and undernutrition during gestation increase the adiposity of young adult progeny in rats. ObesRes. 1995;3:131–141. We examined the influence of maternal diet during gestation on the growth and body composition of the progeny. On day 1 of gestation, rat dams were assigned to one of four feeding regimens: free access to standard rodent chow throughout gestation (AL); 20 g feed/day (prebreeding intake) throughout gestation (PB); 10 g feed/day from day 1 to day 14, then ad libitum from day 15 to parturition (RAL); 10 g feed/day from day 1 to 14, then 20 g/day to parturition (RPB). Progeny were fed ad libitum on standard chow diet from 3 to 12 weeks of age; food intake and weight gain were measured over this time. Body composition was measured at 12 weeks. The PB regimen restricted maternal food intake during the third trimester only; the RAL regimen restricted intake by 50% for two trimesters and produced hyperphagia in the third; the RPB regimen restricted intake by 50% for two trimesters, then intake (per unit body weight) was similar to that of AL dams during the third trimester. Litter size and progeny birth, weaning, and 12-week body weights were similar among the four groups. At 12 weeks of age, PB progeny had the highest body fat (per kg fat-free mass), despite similar feed intake during the 9-week postweaning period. The increased fat was proportionally distributed among intra-abdominal and subcutaneous depots. Progeny of RAL, AL, and RPB dams had similar amounts of body fat, but in RAL progeny more fat was present in intra-abdominal depots. The weights of fat-free mass, gastrointestinal tract and hindlimb skeletal muscles were unaffected by maternal diet Restriction of maternal feed intake during the third week of gestation had subtle effects on the body composition of young adult progeny that could not be explained on the basis of differences in postweaning voluntary feed intake.     

Effects of rearing temperature and level of food intake on organ size and tissue composition in piglets

Piglets are particularly susceptible to cold and nutritional stress because of their poor insulation and low body fat. The purpose of this study was to examine how ambient temperature and level of food intake affect development in piglets. Thirty-two piglets were reared individually from 14 to 56 days of age in either a cold (10 degrees C) or a warm (35 degrees C) environment. Two feeding regimens, restricted and ad libitum, were used to assess the effect of food intake on organ mass. The ad libitum fed pigs in both environments gained weight at the same rate. Paired t-tests of organ weights of ad libitum fed pigs revealed that the mass of the heart, liver, kidneys, stomach, and small intestine, and total nitrogen and the length of the small intestine were greater in cold-reared than in warm-reared littermates of the same body weight. The skin mass and total fat mass, the lengths of the body, extremities, and individual long bones, and the total surface area were greater in warm-reared than in cold-reared individuals. A regression analysis showed body weight was the most important determinant of size for all tissues measured except fat mass, which was affected slightly more by rearing temperature. Of the organs and tissue components that differed in size in warm- and cold-reared pigs, heart, kidney, stomach, skin, nitrogen, and fat mass, and small intestine length and surface area were generally affected more by rearing temperature than by level of food intake. Liver and small intestine mass and femur length were affected more by level of food intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Patterns in food intake correlate with body mass index

Quantifying eating behavior may give clues to both the physiological and behavioral mechanisms behind weight regulation. We analyzed year-long dietary records of 29 stable-weight subjects. The records showed wide daily variations of food intake. We computed the temporal autocorrelation and skewness of food intake mass, energy, carbohydrate, fat, and protein. We also computed the cross-correlation coefficient between intake mass and intake energy. The mass of the food intake exhibited long-term trends that were positively skewed, with wide variability among individuals. The average duration of the trends (P = 0.003) and the skewness (P = 0.006) of the food intake mass were significantly correlated with mean body mass index (BMI). We also found that the lower the correlation coefficient between the energy content and the mass of food intake, the higher the BMI. Our results imply that humans in neutral energy balance eating ad libitum exhibit a long-term positive bias in the food intake that operates partially through the mass of food eaten to defend against eating too little more vigorously than eating too much.     

Changes in growth,appetite, food conversion efficiency and body composition in mice selected for high post-weaning weight gain on restricted feeding

Summary This study aimed to test the hypothesis that if animals were fed the same amount over the same time period, selection of the fastest growers would result in a change in the partitioning of metabolisable energy toward more protein and less fat deposition. Two mouse lines (S1 and S2) were selected for high 5 to 9 week weight gain corrected to mean 5 week weight. Appetite variation between mice was eliminated by feeding a fixed amount to each mouse daily. After 6 generations of selection, the lines were compared with an unselected control (C) on restricted and ad libitum levels of feeding for growth rate, appetite, food conversion efficiency and chemical body composition.Realised heritabilities of 5 to 9 week gain were 0.36+ 0.05 and 0.19±0.04 for S1 and S2 respectively. Nine week weights were increased by an average of 13% on both feeding levels. Most of this increase, particularly in S2, occurred before 5 weeks and was therefore outside the period of measurement used in selection. On ad libitum feeding, selection increased food intake per unit time by 6% but there was no increase per unit body weight. Food conversion efficiency (gain/food) increased by 12%. Compared with controls at 9 weeks, 3% more of the body weights of selected mice was fat and 1% less was protein. These differences were reduced but were still in the same direction when comparisons were made at the same body weight. Thus the expected change in energy partitioning toward greater protein and less fat deposition in the S lines did not occur.It was concluded that the increased growth and energy retention in the S lines was brought about by a reduction in maintenance requirement. To achieve the desired change in energy partitioning using a similar selection scheme, higher levels of dietary protein should be fed, and some measure of protein deposition rather than growth rate used as the selection criterion.     

Effect of food restriction on cold adaptability of rats

To determine the role of the nutritional state in nonshivering thermogenesis during cold adaptation, cold adaptability was compared between cold-adapted (5 degrees C for 4-5 weeks) rats fed ad libitum and cold-adapted rats pair fed with warm controls having the same food intake. Cold-adapted pair-fed rats suffered a significant loss in body weight during cold exposure. However, brown adipose tissue (BAT) in both cold-adapted ad libitum fed and cold-adapted pair-fed rats was enlarged to the same extent as compared with that in control rats. Fat-free dry matter in BAT also increased in cold-adapted ad libitum fed and cold-adapted pair-fed rats to the same extent. Cold tolerance as assessed by the change in the colonic temperature at -5 degrees C was improved relative to control rats and was the same for cold-adapted ad libitum fed and cold-adapted pair-fed rats. Nonshivering thermogenesis as estimated by the noradrenaline-induced increase in oxygen consumption was significantly greater in the cold-exposed rats and there was no significant difference between cold-adapted ad libitum fed and cold-adapted pair-fed rats. These results suggest that an improved cold tolerance by means of nonshivering thermogenesis in brown adipose tissue is closely related to the low temperature itself but not the increased food intake which occurred in the cold.     

Reduction of enhanced mammary carcinogenesis in LA/N-cp (corpulent) rats by energy restriction

Restriction of energy intake significantly reduces mammary tumorigenesis in normal rats exposed to carcinogens. Genetically obese LA/N-cp (corpulent) female rats were given 7,12-dimethylbenz[a]anthracene and fed purified diets ad libitum or restricted to 60% of the ad libitum caloric intake. Phenotypically lean littermates were also fed ad libitum. Obese animals developed large mammary tumors more rapidly than genetically normal rats so that 100% of the animals had tumors in less than 16 weeks. Only 21% of the lean animals developed tumors; the energy restricted obese animals had a tumor incidence of 27%. Although obese rats fed the restricted diet weighed significantly less than those fed ad libitum, percent body fat was not reduced, indicating that lean tissue was affected more. Obese animals were markedly hyperinsulinemic (1003 +/- 193 microunits/ml) and energy restriction reduced this to 328 +/- 41; the lean animals had insulin levels of 12 +/- 2. Tumor-bearing rats had higher insulin levels than rats without tumors. These data suggest that body fatness is not directly associated with risk of carcinogenesis. Lean body mass, adipose tissue mass, and their interaction with insulin in its capacity as a growth factor rather than body fatness per se may be determinants of tumor promotion.     

Effects of dietary fat content on adiposity during energy restriction in genetically obese rats.

The effects of the amount of fat provided in a restricted diet on weight loss and body composition were studied in this work. Lean male (Fa/?) Zucker rats were fed a control diet ad libitum. Obese (fa/fa) Zucker rats were divided into three groups: one group was fed a control diet ad libitum and the other two groups were fed 75% energy-restricted diets, which provided 10 or 50% of calories as fat. After 4 weeks, energy restriction normalized body weight but not body composition in the genetically obese rats. Reductions in adipose tissue weights and adipocyte size, without changes in the cellularity, were observed. Differences only reached statistical significance in subcutaneous adipose tissue. A standard fat content in the diet induced the same fat-free mass reduction as a higher amount of this macronutrient, but a greater body fat reduction. This suggests that the restriction of dietary fat, as well as energy, is necessary to achieve dietary management in obesity.     

Significance of reduced food and water consumption in rats intoxicated with vanadium.

1. Male Wistar rats were given, for four weeks, a limited amount of food, or the amount of food and water equal to that consumed by rats drinking solely an aqueous solution of ammonium metavanadate instead of water (AMV) of 0.3 mg V/cm3 concentration. 2. In rats with limited access to food but free access to water, a significant decrease of body weight increment was observed, together with an increase of the haemoglobin level and a decrease in the percentage of reticulocytes and polychromatophilic erythrocytes in the peripheral blood. 3. In the rats which did not receive food and water ad libitum a significant decrease of the body weight increment and an increase of the haemoglobin level were noted. 4. In animals drinking the aqueous AMV solution instead of water the body weight increment diminished significantly, and so did the erythrocyte count and haemoglobin level, whereas the percentage of reticulocytes and polychromatophilic erythrocytes increased in the peripheral blood.     

Effects of food restriction and restoration on gonadotropin and growth hormone secretion in immature male rats

This experiment concerned the changing patterns in secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and growth hormone (GH) under conditions of food restriction and subsequent catch-up growth. Weanling male rats were given either restricted (4 g food/day) or unrestricted access to food until 60 days of age. At this age, food-restricted rats weighed only 25% as much as rats fed ad libitum. Food restriction resulted in a dramatic decrease in the frequency of LH and GH pulses, and in the amplitude of GH pulses. It also slightly but significantly decreased mean blood levels of FSH (which was not secreted in a pulsatile manner in 60-day-old controls fed ad libitum). When restricted rats were given unrestricted access to food, frequency of LH and GH pulses and mean levels of FSH increased significantly and simultaneously within 2 days in half of the animals. Only an additional 8-10% of their body weight decrement was recovered at this time. After 10 days of food restoration, when restricted rats still weighed 50% less than controls, their secretory patterns of all three hormones were not significantly different from those of controls. Thus, recovery of gonadotropin and GH secretion was relatively rapid. Except for the quantitatively lesser impact of food restriction on FSH secretion, there was no evidence of any priorities in the secretion of the three hormones. Under conditions of rapid catch-up growth, the secretory patterns of LH, FSH, and GH appeared to develop simultaneously.     

Effects of three-hour restricted food access during the light period on circadian rhythms of temperature, locomotor activity, and heart rate in rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten-wk-old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21-d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p < 0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.     

The effect of chronic food and water restriction on open-field behaviour and serum corticosterone levels in rats

In operant conditioning experiments, two methods are commonly used to motivate laboratory rats to perform designated tasks. The first is restricting food so that rats are forced to lose 20% of body weight within one week, followed by maintenance at 80% of the baseline weight for the remainder of the experiment. The second is restricting access to water to 15 min in each 24 h period. These methods are effective in motivating the animals. There is, however, little information available on the effects on performance in tests of behaviour that are not related to operant conditioning. In addition, it is not clear if these commonly used methods of food and water restriction will lead to physiological stress as indicated by an elevation of serum corticosterone. Male rats were either food-restricted to reduce and maintain their weight at 80% of baseline weight, or were restricted to 15 min access to water every 24 h. Activity in the open field was significantly greater in food-restricted rats than in water-restricted or control rats, but freezing behaviour was similar in all experimental groups. Food-restricted rats had a higher mean serum corticosterone level than water-restricted and control rats 37 days after the start of the experimental period. These data suggested that chronically restricting food and maintenance of body weight at 80% of baseline body weight led to significant behavioural changes and physiological stress. In contrast, water restriction did not lead to changes in behaviour or corticosterone levels. A second experiment was conducted to compare the effects of food restriction to 80% of baseline body weight, as described above, with a less stringent protocol in which test rats were initially reduced to 80% of baseline weight, but were then maintained at 80% of an ad libitum fed control rat's weight. Serum corticosterone levels and adrenal gland weights were measured after the initial week of forced weight loss and after maintenance for 21 days. Forced loss of 20% of body weight in the first week led to significantly increased serum corticosterone levels and adrenal gland weights compared to ad libitum fed controls. Serum corticosterone levels and adrenal gland weights in rats maintained at 80% of their initial body weight for 21 days remained higher than ad libitum fed control rats. However, rats maintained at 80% of an ad libitum fed control rat's weight did not differ from control rats in serum corticosterone levels or adrenal gland weights at the end of the 21-day study period. Adjustment of the feeding regimen in this manner eliminated physiological evidence of chronic stress.     

The responses of rats to various combinations of energy and protein. I. Diets made from purified ingredients

Male and female weanling rats were fed ad libitum for 28 days on purified diets with metabolizable energy levels of 8.0, 9.5, 11.0 or 12.5 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg at each energy level. Major nutrients were balanced in proportion to energy and protein. The following parameters were measured: food intake, bodyweight, body length, abdominal fat, liver and kidney weights. Increasing dietary energy level reduced food intake but the reduction was not sufficient to prevent an increase in energy intake. This was reflected by increases in bodyweight, body length, abdominal fat, and relative liver and kidney weights, especially in male rats. Higher energy intake increased weight gain and food conversion efficiency to a greater extent than higher protein intake. The response to protein intake at different energy levels was not consistent. There was no common protein:energy ratio for overall good performance. It is concluded that rat growth and other features can be controlled by the alteration of dietary energy and protein levels.     

The efficiency of growth during body weight recovery in young adult female rats

1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restriction followed by recovery of body weight in 36.2 +/- 4.28 days by ad libitum food intake. The regimen was then repeated, with 40% body weight loss in 105 days followed by recovery of body weight in 22.8 +/- 2.00 days. 2. Food intakes were measured continuously. 3. These rats used digestible energy more efficiently during the second recovery (49.1 +/- 3.11 v. 77.3 +/- 7.91 kJ digestible energy intake per g body wt gain). 4. Seven rats were subjected to one body weight loss and recovery. Five of them had an efficiency of 44.1 +/- 3.34 kJ/g live wt gain which was not significantly different from that of the first group during their second recovery; they may not have been capable of improvement after a second deprivation. 5. It is concluded that some rats can adapt after a period of severe body weight loss and recovery to utilize food more efficiently during body weight recovery after a second episode.     

Amylin blunts hyperphagia and reduces weight and fat gain during recovery in socially stressed rats

During recovery from social stress in a visible burrow system (VBS), during which a dominance hierarchy is formed among the males, rats display hyperphagia and gain weight preferentially as visceral adipose tissue. By proportionally increasing visceral adiposity, social stress may contribute to the establishment of metabolic disorder. Amylin was administered to rats fed ad libitum during recovery from VBS stress in an attempt to prevent hyperphagia and the resultant gain in body weight and fat mass. Amylin treatment reduced food intake, weight gain, and accumulation of fat mass in male burrow rats, but not in male controls that spent time housed with a single female rather than in the VBS. Amylin did not alter neuropeptide Y (NPY), agouti-related peptide (AgRP), or proopiomelanocortin (POMC) mRNA expression in the arcuate nucleus of the hypothalamus as measured at the end of the recovery period, nor did it affect plasma corticosterone or leptin. Amylin exerted most of its effect on food intake during the first few days of recovery, possibly through antagonism of NPY and/or increasing leptin sensitivity. The potential for chronic social stress to contribute to metabolic disorder is diminished by amylin treatment, though the neuroendocrine mechanisms behind this effect remain elusive.     

Differential effect of long-term food restriction on fatty acid synthase and leptin gene expression in rat white adipose tissue.

Long-term food restriction (85%, 70% and 50% of ad libitum energy intake for one month) induced a substantial fall in serum leptin concentration and leptin mRNA levels in epididymal white adipose tissue in rats. Surprisingly, this suppression was not reversed by refeeding ad libitum for 48 h. The reduction in serum leptin concentration and leptin mRNA level did not strictly correlate with reduction in fat or body mass. Unlike serum leptin concentration and epididymal adipose tissue leptin mRNA levels, fatty acid synthase activity, fatty acid synthase protein abundance and fatty acid synthase mRNA levels increased significantly in white adipose tissue after refeeding rats subjected to food restriction. The increase in serum insulin concentration was observed in all groups on different degrees of food restriction and refed ad libitum for 48 h compared to controls. A decrease in serum insulin concentration was found in the rats not refed before sacrifice. Long-term food restriction did not significantly affect serum glucose concentrations in either refed or non-refed rats. The data reported in this paper indicate that there is no rapid rebound in serum leptin concentration or leptin gene expression in contrast to the increase in serum insulin concentration and fatty acid gene expression in white adipose tissue of rats refed ad libitum after one month's food restriction.     

Effects of photoperiod and food availability on growth, leptin, sexual maturation and maintenance in the Mongolian gerbils (Meriones unguiculatus)

Reproductive activity of Mongolian gerbils is regulated by photoperiod nevertheless body weight regulation is controlled without ambient photoperiod. Food intake is a major factor affecting rodent reproductive efficiency. Leptin is a hormone secreted by adipose tissue and modulates food intake, energy expenditure and body fat stores. In this study we studied the interaction of photoperiod and food availability on growth, sexual maturation and leptin concentration in the male and female gerbils. Gerbils were gestated and reared in either 14L:10D or 2L:22D. At weaning, gerbils were housed individually and divided into three groups: fed ad libitum, fed 80% of ad libitum or fed 60% of ad libitum. Body weights were recorded at weaning and every week thereafter. After twelve weeks of treatment, animals were sacrificed and testes and uterine weights were determined and blood was collected for leptin measurement. Food restriction reduced body weight and inhibited reproductive development. Absolute paired testis weights were similar in ad lib and 80% of ad lib groups but significantly different compared with the 60% of ad lib group in both photoperiods. Body weights were also directly dependent upon the level of food restriction. Uterine mass was only affected in the 60% of ad lib group in 14L but both food restriction levels significantly affected the uterine weights in 2L. Significant variations were found in leptin profiles. Leptin concentration was highest in ad lib and 80% of ad lib groups and lowest in 60% of ad lib groups. These results suggest that the reproductive activity of Mongolian gerbils is sensitive to food intake and multiple potential environmental cues (e.g., food availability, temperature) can be utilized.     

Motivation to obtain preferred foods is enhanced by ghrelin in the ventral tegmental area

Ghrelin is an orexigenic peptide that acts within the central nervous system to stimulate appetite and food intake via the growth hormone secretagogue receptor (GHS-R). It has been hypothesized that ghrelin modulates food intake in part by stimulating reward pathways in the brain and potentially stimulating the intake of palatable foods. Here we examined the effects of chronic ghrelin administration in the ventral tegmental area (VTA) via osmotic minipumps on 1) ad libitum food intake and bodyweight; 2) macronutrient preference; and 3) motivation to obtain chocolate pellets. In the first study rats receiving ghrelin into the VTA showed a dose-dependent increase in the intake of regular chow, also resulting in increased body weight gain. A second study revealed that intra-VTA delivery of the ghrelin receptor antagonist [Lys-3]-GHRP-6 selectively reduced caloric intake of high-fat chow and reduced body weight gain relative to control and ghrelin treated rats. The third study demonstrated that food restricted rats worked harder for food pellets when infused with ghrelin than when infused with vehicle or ghrelin receptor antagonist treated rats. Finally, rats trained on an FR1 schedule but returned to ad libitum during ghrelin infusion, responded at 86% of baseline levels when they were not hungry, whereas saline infused rats responded at 36% of baseline. Together, these results suggest that ghrelin acts directly on the VTA to increase preference for and motivation to obtain highly-palatable food.     

Motivation to obtain preferred foods is enhanced by ghrelin in the ventral tegmental area

Ghrelin is an orexigenic peptide that acts within the central nervous system to stimulate appetite and food intake via the growth hormone secretagogue receptor (GHS-R). It has been hypothesized that ghrelin modulates food intake in part by stimulating reward pathways in the brain and potentially stimulating the intake of palatable foods. Here we examined the effects of chronic ghrelin administration in the ventral tegmental area (VTA) via osmotic minipumps on 1) ad libitum food intake and bodyweight; 2) macronutrient preference; and 3) motivation to obtain chocolate pellets. In the first study rats receiving ghrelin into the VTA showed a dose-dependent increase in the intake of regular chow, also resulting in increased body weight gain. A second study revealed that intra-VTA delivery of the ghrelin receptor antagonist [Lys-3]-GHRP-6 selectively reduced caloric intake of high-fat chow and reduced body weight gain relative to control and ghrelin treated rats. The third study demonstrated that food restricted rats worked harder for food pellets when infused with ghrelin than when infused with vehicle or ghrelin receptor antagonist treated rats. Finally, rats trained on an FR1 schedule but returned to ad libitum during ghrelin infusion, responded at 86% of baseline levels when they were not hungry, whereas saline infused rats responded at 36% of baseline. Together, these results suggest that ghrelin acts directly on the VTA to increase preference for and motivation to obtain highly-palatable food.     

Ultrastructural morphometry of matrical changes induced by exercise and food restriction in the rat calcaneal tendon.

The ultrastructural morphometry of collagen fibril populations in 24 calcaneal tendons obtained from 12 Fischer 344 rats were studied to elucidate matrical changes induced by food restriction and/or endurance exercise. Rats were randomly assigned to four equal groups: ad libitum control (AC), ad libitum exercise (AE), restricted diet control (RC) and restricted diet exercise (RE) groups. Beginning from 6 weeks of age, animals in the two food restriction groups were fed 60% of the mean food consumption of ad libitum fed rats. Then, starting from 6-7 months of age, the rats in the two exercise groups performed 40-50 min of treadmill running at 1.2-1.6 miles h-1 every day for a total of 10 weeks. Endurance training did not significantly alter body weight, but food restriction with or without exercise resulted in a significant loss of body weight. In ad libitum fed controls, food restriction alone did not significantly alter the mean collagen fibril CSA, but predisposed a preponderance of small-sized collagen fibrils. Endurance training per se induced a significant (32%) increase in mean fibril CSA (P less than 0.05), but this adaptive response to exercise was prevented by food restriction, as indicated by a 33% decline in fibril CSA (P less than 0.05). These findings demonstrate that dietary restriction modifies the adaptation of tendon collagen morphometry in response to endurance training, and that weight loss is better achieved with food restriction than endurance exercise.