Effects of Aging And Dietary Restriction On The Structural Integrity of Rat Articular Cartilage

The objectives of this study were to investigate the effects of aging and diet restriction on the biomechanical properties of articular cartilage, using a well-controlled rat model (Fischer 344). This animal model is recommended by the National Institute of Aging specifically to study aging and diet issues. The intrinsic biomechanical properties of articular cartilage were obtained using a creep indentation approach. The ages chosen (6, 12, 18, 24 months of age) correspond to approximate human ages of 20 to 80 years old. The diet regimen employed in this study used either an ad libitum fed group or a group fed 60% of the mean food intake of the ad libitum group. The results demonstrate that, unlike bone, rat articular cartilage biomechanical properties are not affected in a discernible manner by diet restriction, despite the fact that diet-restricted animals were significantly lighter in terms of body weight. Age effects on biomechanical properties are found only at 6 and 12 months probably due to developmental reasons, but not at later ages. It appears that aging and diet restriction have profoundly different effects on articular cartilage and bone. Another significant result of this study was to establish the rat as a suitable animal model to study cartilage biomechanical properties. Thus, the rat can be added to the list of animals that can be used to study structure-function and pathophysiological relationships in articular cartilage. © 2000 Biomedical Engineering Society. PAC00: 8714Ee, 8715La, 8719Rr     

Influence of food restriction on lipid profile and spontaneous glucose levels in male rats subjected to paradoxical sleep deprivation

OBJECTIVES:

The purpose of this study was to determine the paired consequences of food restriction and paradoxical sleep deprivation on lipid profile and spontaneous glucose levels in male rats.

METHOD:

Food restriction began at weaning, with 6 g of food being provided per day, which was subsequently increased by 1 g per week until reaching 15 g per day by the eighth week. At adulthood, both rats subjected to food restriction and those fed ad libitum were exposed to paradoxical sleep deprivation for 96 h or were maintained in their home-cage groups.

RESULTS:

Animals subjected to food restriction exhibited a significant increase in high-density lipoprotein levels compared to animals that were given free access to food. After the paradoxical sleep deprivation period, the food-restricted animals demonstrated reduced concentrations of high-density lipoprotein relative to their respective controls, although the values for the food-restricted animals after sleep deprivation were still higher than those for the ad libitum group. The concentration of low-density lipoproteins was significantly increased in sleep-deprived animals fed the ad libitum diet. The levels of triglycerides, very low-density lipoproteins, and glucose in food-restricted animals were each decreased compared to both ad libitum groups.

CONCLUSION:

These results may help to illustrate the mechanisms underlying the relationship between sleep curtailment and metabolism and may suggest that, regardless of sleep deprivation, dietary restriction can minimize alterations in parameters related to cardiovascular risk.     

The effect of dorsomedial hypothalamic nuclei lesions on body weight regulation.

Prior to hypothalamic surgery 1 group of male rats was placed on a partial starvation regimen to lower their body weight. A second group was fed ad libitum. Just before surgery the 2 groups were divided into 2 sub groups. Bilateral electrolytic lesions were then placed in the dorsomedial hypothalamic nucleus in some of the partially starved and some of the ad libitum fed rats. The remaining animals were sham operated. After surgery all groups were fed ad libitum. Following hypothalamic operation the group that before surgery had been fed ad libitum showed the previously reported postoperative hypophagia and reduced body weight. On the other hand, the rats that were partially starved prior to placement of the lesion, ate significantly more than ad libitum fed lesioned animals during the first 9 days after surgery. The body weights of the partially starved, lesioned rats increased steadily from the day of the operation while lesioned rats fed ad libitum showed an initial delay of ponderal growth. The data suggest that the transient postoperative increase in food intake of the partially starved, lesioned rats is an active process to bring the body weight of these animals up to a new but lowered ‘body weight set point’ initiated by the hypothalamic destruction. Since previous studies had shown that rats with a lesion in the dorsomedial nucleus have a normal body composition, it is suggested that the lesions change the animals' ‘body weight set point’ and not the ‘body fat set point’, as has been suggested after ventromedial and lateral hypothalamic lesions.     

Calorie restriction decreases platelet-derived growth factor (PDGF)-A and thrombin receptor mRNA expression in autoimmune murine lupus nephritis

Calorie restriction (CR) and supplementation with fish oil (FO) are known to increase the life span and diminish histological evidence of glomerulonephritis in lupus prone (NZB×NZW)F_l (B/W) mice. Cellular proliferation is an important pathological element in the development of lupus nephritis, and we have examined the expression of thrombin receptor (TR) and the mitogenic agents PDGF-A and -B. Weanling B/W mice were fed either ad libitum or a calorie restricted (CR; 40% less calories than ad libitum) diet supplemented with either 5% (w/w) corn oil (CO) or FO. CR animals consumed 2.7–3.0 g of wet food per day versus 4.5–5.0 g for the ad libitum animals. Renal RNA was extracted from young (3.5–4.0 months of age) and old (8–10 months of age) mice. Densitometric analysis (reference gene GAPDH) of blots from Northern (PDGF-A and -B) and ribonuclease protection assays (TR) produced the following data: (i) in young mice no signal was detected for PDGF-A, -B and TR in all four groups, while the signals were readily detectable in old mice; (ii) in old mice low and similar levels of PDGF-B were detected, and neither CR nor the source of lipid altered its expression; (iii) CR significantly inhibited PDGF-A and TR expression in both CO (ad libitumversus CR; PDGF-A, 3.25-fold, P<0.025; TR, 3.7-fold, P<0.01) and FO (ad libitumversus CR; PDGF-A, 4.56-fold, P<0.01; TR, 3.6-fold, P<0.025) groups; (iv) although FO (versus CO) produced a trend towards decreased expression, results were not statistically significant. We conclude that suppression of renal disease in lupus-prone mice by CR is accompanied by decreased expression of PDGF-A and the thrombin receptor.     

Effects of Cyclic Starvation-Feeding and of Splenectomy on the Development of Hemosiderosis in Rat Livers

The development of siderosis of liver and spleen was investigated in rats subjected alternately to periods of starvation and periods of feeding of diets rich in iron (0.71% or 1.23% Fe) or of control diets, during periods ranging up to 245 days. With 0.71% iron in the diet, cyclic starvation-feeding markedly enhanced the accumulation of iron in rat livers by comparison to feeding ad libitum even though rats fed ad libitum ingested far greater total amounts of iron than cyclically fed rats. With 1.23% iron in the diet, the concentration of iron in livers reached more or less the same plateau in cyclically starved-fed rats and in rats fed ad libitum (betwen 4 and 5 mg Fe/g wet weight); but the mean rate of accumulation of iron in the livers of cyclically starved and fed rats was more than twice that in rats fed ad libitum, whereas mean ingestion of iron per feeding day was only 16% higher in the former group. Surgical removal of the spleen enhanced the accumulation of iron in the liver in cyclically starved-fed rats and in rats fed ad libitum. Histologically, siderosis of the liver was moderate in rats fed the diet with 0.71% iron but was severe in rats fed the diet with 1.23% iron and most severe in those without spleens. Stainable iron was deposited in hepatocytes and in Kupffer cells. None of the rats developed cirrhosis of the liver. The data suggest that in rats a barrier to the absorption of iron from the gut, or to its later utilization, is surmounted if the concentration of iron in the food exceeds a certain limit value, somewhere between 0.71 and 1.23%. With iron in the food below this value, cyclic starvation-feeding markedly potentiates accumulation of iron in the liver in the course of several months, but siderosis is moderate. With iron in the food above the limit value, cyclic starvation-feeding and feeding ad libitum can equally lead to massive siderosis of the liver.     

Effects of ageing on the energy balance of food‐restricted rats

Aims: Age can alter energy balance by decreasing the resting metabolic rate. Food restriction can also change energy balance by decreasing energy expenditure as a mechanism of energy conservation. We investigated the influence of food restriction on the energy balance of rats at different ages. Methods: Wistar EPM‐1 female rats were used at ages of 3, 9, 15 and 21 months. At each age, two food intake schedules were provided: control (ad libitum) and food restriction (50%). Animals remained under these schedules for 30 days, and throughout this period body weight, food intake, and stool collection were controlled daily. On the 30th day, animals were killed, blood was collected and the carcasses and faeces were processed for analysis by pump calorimetry. Blood glucose, T₃, T₄ and rT₃ levels were determined. Results: Food restriction reduced energy gain and gross food efficiency of animals at different ages, but more so in older animals. Food‐restricted rats also had lower energy expenditure than controls. This reduction was about 40% of the energy expenditure of control animals irrespective of age. Water content increased and fat content decreased in the carcass of food‐restricted animals. Serum T₃ and T₄ levels were lower in food‐restricted animals pointing out to a major role of thyroid hormones in the mechanism of energy conservation exhibited by food‐restricted animals. Conclusions: The mechanism of energy conservation takes place in all restricted animals and is very important for survival and for species preservation, mainly in aged animals in which food restriction is frequently aggravated by senescence‐related organic disorders.     

Effects of oxytocin on the IGF-axis and some gastrointestinal hormones in ad libitum fed and food-restricted female rats

The aims of this study were to investigate if administration of oxytocin to ad libitum fed and food-restricted female rats affects weight gain, body fatness, the IGF-axis, and some vagally mediated gastrointestinal hormones, such as gastrin, cholecystokinin (CCK) and somatostatin. Ad libitum fed and food-restricted (receiving 70% of the food intake of the ad libitum fed group) female rats were injected subcutaneously, once a day, for 10 days, with saline (control) or oxytocin (1 mg kg^–1 bodyweight). The animals were killed 5 days after the last injection. Oxytocin-treated food-restricted females had more body fat and lower plasma levels of IGF-I, IGFBP-1 and IGFBP-3 compared with saline-treated counterparts. Oxytocin-treated ad libitum fed rats also had lower plasma levels of IGFBP-1 but contained less body fat, compared with saline-treated counterparts. There was no effect of oxytocin treatment on body weight or weight gain in either of the feeding groups. Except for gastrin, which was lower, there was no effect of oxytocin on the gastrointestinal hormones studied. The results indicate that oxytocin treatment influences fat deposition and the IGF-axis in female rats, but that the results are dependent on the nutritional status of the animal.     

Change with age of UV absorbance and fluorescence of collagen and accumulation of epsilon-hexosyllysine in collagen from Wistar rats living on different food restriction regimes

Accumulation of glycation products (as revealed by the thiobarbituric test and hexosyllysine assay) and the pigmented products (350 nm UV absorbance and 370ex/440em nm fluorescence) in aortal and skin collagen was investigated under the conditions of different nutritional regimes. Four groups of animals were tested: (1) ad libitum fed controls, (2) animals which were food restricted throughout their whole life (50% food intake), (3) animals fed ad libitum during their first year of life and then food restricted and (4) animals food restricted when young and fed ad libitum from the age of 1 year onwards. It was shown that all food-restricted animals showed lower levels of glycation and pigmentation products in collagen preparations from skin and aorta. The lowest accumulation was observed in group 4 which exhibited the longest 50% survival (29.4 months, as compared with 18.3 months in normally-fed controls). Of particular interest is the fact that in this group the decreased rate of accumulation of the glycated and pigmented products was preserved even after 1 year of life, i.e., when the animals had a free access to food. Though not directly supporting the glycation theory of aging (Cerami, 1985), our data are indicative of the involvement of glucose metabolism in the ageing process. Correlation between the levels of glycated and pigmented products in aortal and skin collagen as well as the correlation between the rate of accumulation of these products and 50% survival was impossible to establish. Nevertheless, each time that food restriction was imposed on the animals it always resulted in decreased accumulation of glycated and pigmented products and increased 50% survival. Possible mechanisms for this process are discussed.     

Analysis of the effects of growth hormone, exercise and food restriction on cancellous bone in different bone sites in middle-aged female rats

The aim of this study is to determine the effects of growth hormone (GH), exercise (EX), GH+EX and food restriction on cancellous bone in middle-aged female rats. Female F344 rats aged 13 months were divided into (1) age-matched controls; (2) GH treated (2.5 mg/kg. 5 day/week); (3) EX (voluntary wheel running); (4) GH+EX; and (5) food restricted (FR) (fed 60% of the ad libitum food intake). The animals were treated for 18 weeks, at the end of which they were sacrificed. Cancellous bone and cortical bone in the fourth lumbar vertebra, proximal tibial metaphysis (PTM), distal femoral metaphysis (DFM) and femoral neck (NF) were analyzed using peripheral quantitative computerized tomography (pQCT) densitometry. Growth hormone increased cancellous bone area, cancellous bone mineral content, cortical bone area and cortical bone mineral content in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly after GH treatment. Exercise increased the cancellous bone area in the vertebra, PTM and DFM. Cortical bone area and cortical bone mineral content increased after EX in the vertebra, PTM, DFM and NF. No significant change was seen in the tibial muscle wet weight after EX. Growth hormone+EX increased cancellous bone area in the vertebra PTM and DFM but had no effect in neck of the femur. Cancellous bone mineral content, cortical bone area and cortical bone mineral content increased with GH+EX in the vertebra, PTM, DFM and NF. The tibial muscle wet weight was increased significantly with GH+EX. Food restriction decreased cancellous bone area and cancellous bone mineral content in all the bones studied. The decrease was statistically significant only at the distal femoral metaphysis. The tibial muscle wet weight decreased when compared with the age-matched control, but this decrease was not statistically significant. We conclude that the effect of the dose of GH used and the levels of voluntary wheel running EX used increased cancellous bone in intact rats; the effect of GH is much greater and different bones respond with varying intensities. The effects of combined treatment of GH and EX on cancellous bone are not always significantly higher than those of GH alone. FR at the level studied has a mostly negative effect on cancellous bone.     

Effect of intermittent fasting on circadian rhythms in mice depends on feeding time

Calorie restriction (CR) resets circadian rhythms and extends life span. Intermittent fasting (IF) also extends life span, but its affect on circadian rhythms has not been studied. To study the effect of IF alongside CR, we imposed IF in FVB/N mice or IF combined with CR using the transgenic FVB/N alphaMUPA mice that, when fed ad libitum, exhibit spontaneously reduced eating and extended life span. Our results show that when food was introduced during the light period, body temperature peak was not disrupted. In contrast, IF caused almost arrhythmicity in clock gene expression in the liver and advanced mPer2 and mClock expression. However, IF restored the amplitudes of clock gene expression under disruptive light condition regardless whether the animals were calorically restricted or not. Unlike daytime feeding, nighttime feeding yielded rhythms similar to those generated during ad libitum feeding. Taken together, our results show that IF can affect circadian rhythms differently depending on the timing of food availability, and suggest that this regimen induces a metabolic state that affects the suprachiasmatic nuclei (SCN) clock.     

An electron microscopic examination of age-related changes in the rat liver. The influence of diet

The influence of age and diet on the ultrastructure of hepatocytes is reported. The following dietary manipulations were investigated: Group 1, fed ad libitum a diet containing 21% protein; Group 2, fed a similar diet but restricted to 60% of the intake of Group 1 from 6 weeks of age onwards; Group 3, restricted from 6 weeks to 6 months of age and thereafter fed ad libitum; Group 4, restriction started at 6 months of age; Group 5, fed ad libitum a diet containing 12.6% protein. In all groups the size of hepatocytes was found not to increase during adult life. The size of hepatocytes in Groups 2 and 4 was the same as or larger than that of the other groups; thus food restriction resulted in a decreased number of hepatocytes. Changes in the structure of some organelles and the accumulation of lipofuscin granules occurred with advancing age and the extent of these age-related changes was less in Groups 2 and 4 than in the other groups. These morphologic findings in conjunction with our previously reported metabolic findings provide a new view of the action of food restriction on the aging process.     

Bioenergetics and permeability transition pore opening in heart subsarcolemmal and interfibrillar mitochondria: Effects of aging and lifelong calorie restriction

Loss of cardiac mitochondrial function with age may cause increased cardiomyocyte death through mitochondria-mediated release of apoptogenic factors. We investigated ventricular subsarcolemmal (SSM) and interfibrillar (IFM) mitochondrial bioenergetics and susceptibility towards Ca²⁺-induced permeability transition pore (mPTP) opening with aging and lifelong calorie restriction (CR). Cardiac mitochondria were isolated from 8-, 18-, 29- and 37-month-old male Fischer 344 × Brown Norway rats fed either ad libitum (AL) or 40% calorie restricted diets. With age, H₂O₂ generation did not increase and oxygen consumption did not significantly decrease in either SSM or IFM. Strikingly, IFM displayed an increased susceptibility towards mPTP opening during senescence. In contrast, Ca²⁺ retention capacity of SSM was not affected by age, but SSM tolerated much less Ca²⁺ than IFM. Only modest age-dependent increases in cytosolic caspase activities and cytochrome c levels were observed and were not affected by CR. Levels of putative mPTP-modulating components: cyclophilin-D, the adenine nucleotide translocase (ANT), and the voltage-dependent ion channel (VDAC) were not affected by aging or CR. In summary, the age-related reduction of Ca²⁺ retention capacity in IFM may explain the increased susceptibility to stress-induced cell death in the aged myocardium.     

Food restriction and membrane fluidity.

The fluidity of the erythrocyte membrane derived from growing rats raised under restricted food intake was found to be higher than the fluidity of the respective membranes from ad libitum fed animals. Considering the apparent relationship between the decrease in membrane fluidity and aging, the results point to the possible beneficial effects of food restriction at a young age.     

AN ELECTRON MICROSCOPIC EXAMINATION OF AGE-RELATED CHANGES IN THE RAT LIVER. The Influence of Diet

The influence of age and diet on the ultrastructure of hepatocytes is reported. The following dietary manipulations were investigated: Group 1, fed ad libitum a diet containing 21% protein; Group 2, fed a similar diet but restricted to 60% of the intake of Group 1 from 6 weeks of age onwards; Group 3, restricted from 6 weeks to 6 months of age and thereafter fed ad libitum; Group 4, restriction started at 6 months of age; Group 5, fed ad libitum a diet containing 12.6% protein. In all groups the size of hepatocytes was found not to increase during adult life. The size of hepatocytes in Groups 2 and 4 was the same as or larger than that of the other groups; thus food restriction resulted in a decreased number of hepatocytes. Changes in the structure of some organelles and the accumulation of lipofuscin granules occurred with advancing age and the extent of these age-related changes was less in Groups 2 and 4 than in the other groups. These morphologic findings in conjunction with our previously reported metabolic findings provide a new view of the action of food restriction on the aging process. ACTA PATHOL JPN 38: 1119∼1130, 1988.     

Effect of β-hydroxy-β-methylbutyrate in masticatory muscles of rats

The aim of this research was to examine the influence of β-hydroxy-β-methylbutyrate (HMB) on changes in the profile of muscle fibers, whether these alterations were similar between the elevator and depressor muscles of the jaw, and whether the effects would be similar in male and female animals. Fifty-eight rats aged 60 days (29 animals of each gender) were divided into four groups: the initial control group (ICG) was sacrificed at the beginning of the experiment; the placebo control group (PCG) received saline and was fed ad libitum; the experimental group (EG) received 0.3 g kg⁻¹ of HMB daily for 4 weeks by gavage as well as the same amount of food consumed by the PCG in the previous day; and the experimental ad libitum group (EAG) received the same dose of the supplement along with food ad libitum. Samples included the digastric and masseter muscles for the histoenzymological analysis. Data were subjected to statistical analysis with a significance level of P < 0.05. Use of HMB caused a decrease in the percentage of fast twitch glycolytic (FG) fibers and an increase in fast twitch oxidative glycolytic (FOG) fibers in males in both experimental groups (EG and EAG). However, it produced no increase in the muscle fiber area, in either gender, in the masseter muscle. In the digastric muscle, the HMB did not change the frequency or the area of any muscle fiber types in either gender. Our data suggest that the use of HMB caused small changes in the enzymological profile of fibers of the mastication muscles; the changes were different in the elevator and depressor muscles of the jaw and the results were different depending on gender.     

Changes of behavioral parameters during long-term food restriction in middle-aged Wistar rats

Food restriction (FR) has a beneficial effect on aging process and exerts a significant effect on the responses of rodents to standard behavioral tasks. The aim of this study was to assess the cumulative influence of FR on the behavioral and biochemical parameters in Wistar rats. Six-month-old rats were subjected to restrictive feeding (50% of the daily food intake, every-other-day feeding regimen) for one month or for six months until ages of 7 and 12 months, respectively. We examined the habituation of exploratory movement, amphetamine (AMPH)-induced motor activity, as well as changes in serum corticosterone (CORT) and glucose levels. The results obtained from FR animals were compared with ad libitum (AL)-fed age-matched control rats. Habituation of motor activity was only affected by six months of restrictive feeding. The sensitization of the motor response to AMPH that was observed in animals exposed to FR for one month was not observed in animals that were exposed to the same feeding regimen for six months. Serum CORT was increased and serum glucose was decreased in both FR groups. These results clearly show that despite the similarity of the biochemical changes that were induced by one and six months of FR, the nature of the changes in motor activities in these two groups of animals during habituation and after AMPH treatment was different. Our findings indicate that long-term FR has complex behavioral consequences that need to be carefully evaluated with respect to animal age, duration of FR and severity of the diet.     

Reproductive consequences of food restricition at low temperature in lines of mice divergently selected for thermoregulatory nesting

Female mice of lines divergently selected for thermoregulatory nesting were mated at 5°C and were fed eitherad libitum or restricted diets. Gestation period and litter size at birth were not affected by food restriction, but both fertility and litter size at weaning were significantly reduced by restriction. The reduction in litter size by restricted females was positively associated with the weight of both females and pups at weaning. The pattern of response to food restriction was generally more conservative than that expected on the basis of r-selection predictions. There was also a significant reduction in the proportion of males weaned by restricted females. Differences among the selected lines in both feeding regimes were generally consistent with the hypothesis that thermoregulatory nesting has a positive genetic correlation with Darwinian fitness at low temperatures.     

Changes in the serum levels of osteoprotegerin and soluble receptor activator for nuclear factor kappaB ligand after estrogen-progestogen therapy and their relationships with changes in bone mass in postmenopausal women

OBJECTIVE: To investigate changes in the serum levels of osteoprotegerin (OPG) and soluble receptor activator for nuclear factor kappaB ligand (sRANKL) after estrogen plus progestogen therapy (EPT) and to determine their relationships with changes in bone mineral density (BMD) and bone turnover markers in postmenopausal women. DESIGN: Serum levels of OPG, sRANKL, and bone turnover markers, such as osteocalcin and type I C-telopeptide breakdown products, parathyroid hormone, calcitonin, calcium, and phosphorus, and BMD at the lumbar spine and proximal femur were measured in 297 postmenopausal Korean women. In all, 143 women were treated with sequential EPT for 1 year. RESULTS: Before EPT, serum OPG and sRANKL levels and RANKL/OPG ratios were not related to BMD at the lumbar spine and proximal femur, except for a negative correlation (r = -0.13, P < 0.05) between serum OPG and BMD at the trochanter. Of the bone markers, serum parathyroid hormone alone correlated negatively with serum OPG (r = -0.19, P < 0.005) and positively with serum sRANKL (r = 0.23, P < 0.001) and sRANKL/OPG ratios (r = 0.28, P < 0.001). After 6 months of EPT, serum OPG and sRANKL levels were unchanged, but sRANKL/OPG ratios and serum levels of bone turnover markers, such as osteocalcin, type I C-telopeptide breakdown products, and phosphorus decreased significantly. The 1-year change in BMD at the lumbar spine and proximal femur after EPT was not found to be correlated with basal levels of serum OPG, sRANKL, and sRANKL/OPG ratios and their changes at 6 months after EPT. After 6 months of EPT, changes in all bone markers were not associated with changes in circulating OPG, sRANKL levels, and sRANKL/OPG ratios. CONCLUSIONS: After EPT, sRANKL/OPG ratios in the circulation decreased, but changes in this OPG-sRANKL system have no association with changes in any bone marker or BMD. The OPG-sRANKL system in the circulation might be involved in reduced bone resorption after EPT, but does not seem to be clinically useful for predicting BMD or bone turnover status and bone response after hormone therapy.     

The effect of low protein-high dextrin diet and subsequent food restriction upon life prolongation in Fischer 344 male rats

Fischer 344 rats fed low protein-high dextrin diet exhibit a higher median (but not 10th percentile) survival as compared to controls. The effect of this diet appears already if the diet is administered between 6 weeks and 6 months of age; after this treatment median survival of experimental animals is increased by 96 days while the 10th percentile is not different from standard diet-fed controls. Further treatment of animals with the same diet has minimum effect as animals that lived on this regimen throughout the whole life exhibited a median lifespan increase by 120 days and increase in the 10th percentile by 41 days. However, if such animals at the age of 6 months are transferred to a restricted (60%) food intake regimen (control diet, not carbohydrate enriched) a further increase in median and 10th percentile lifespan prolongation can be observed reaching +328 and +396 days respectively as compared to controls. The effects of this early feeding (6 weeks to 6 months) with a low protein-high carbohydrate diet available ad libitum and the food restricted regimen (standard diet 60% controls) fed from the age 6 months onwards are additive, the final results being identical to those obtained if the animals were kept on the 60% food restricted intake throughout the whole life. The fact that animals fed the low protein-high carbohydrate diet and those kept on 60% standard diet food restriction had different survival though they were equal in daily (identical) protein intake is emphasized.     

Differential responses of white adipose tissue and brown adipose tissue to caloric restriction in rats

Caloric restriction (CR) slows the aging process and extends longevity, but the exact underlying mechanisms remain debatable. It has recently been suggested that the beneficial action of CR may be mediated in part by adipose tissue remodeling. Mammals have two types of adipose tissue: white adipose tissue (WAT) and brown adipose tissue (BAT). In this study, proteome analysis using two-dimensional gel electrophoresis combined with MALDI-TOF MS, and subsequent analyses were performed on both WAT and BAT from 9-month-old male rats fed ad libitum or subjected to CR for 6 months. Our findings suggest that CR activates mitochondrial energy metabolism and fatty acid biosynthesis in WAT. It is likely that in CR animals WAT functions as an energy transducer from glucose to energy-dense lipid. In contrast, in BAT CR either had no effect on, or down-regulated, the mitochondrial electron transport chain, but enhanced fatty acid biosynthesis. This suggests that in CR animals BAT may change its function from an energy consuming system to an energy reservoir system. Based on our findings, we conclude that WAT and BAT cooperate to use energy effectively via a differential response of mitochondrial function to CR.