Effect of level of dietary protein and total or partial starvation on catalase and superoxide dismutase activity in cardiac and skeletal muscles in young rats

In cells the level of potentially toxic superoxide radical (O2-) is controlled by superoxide dismutase (SOD); the level of hydrogen peroxide (H2O2), also potentially toxic, is controlled by catalase and glutathione peroxidase. To study the effects of altered food intake or dietary protein content on SOD and catalase in cardiac and skeletal muscles, young rats were fed ad libitum diets containing 3, 6 or 25% casein or were subjected to total or partial food restriction (resulting in similar body weight losses). Rats fed a diet containing 3 or 6% casein had much lower growth rates than those fed 25% casein, but the muscle catalase activities were similar in all three groups. Catalase activities in muscles of rats whose food intake was restricted were twice those in rats fed ad libitum. Rats fed ad libitum had higher muscle SOD activities at 41 days of age than did 25-day-old rats, irrespective of the amount of dietary protein or the rate of growth. Twenty-five-day-old rats whose food intake was totally restricted for 2 days had skeletal muscle SOD activities similar to the higher activities seen at 41 days of age in ad libitum-fed rats, but SOD activity in the heart was unchanged after food restriction. The responses of catalase and SOD in muscles differ from the responses reported for these enzymes in liver and erythrocytes when food intake or dietary protein is altered.     

Food restriction attenuates blood lipid peroxidation in carbon tetrachloride-intoxicated rats

OBJECTIVE: We investigated whether food restriction offers protection against the toxicity of carbon tetrachloride (CCl(4)) and, if so, at what percentage of restriction. METHODS: The effects of food restriction (75% and 50% of food intake) and food restriction followed by CCl(4) treatment on lipid peroxidation and antioxidant enzymes were studied in female Wistar rats. A single dose of CCl(4) (3 mL/kg of body weight, subcutaneous) was administered at the end of the 30-d feeding period. RESULTS: The magnitude of increase in lipid peroxidation was less after CCl(4) treatment in food-restricted animals than in animals fed ad libitum (control), whereas alanine transaminase, aspartate transaminase, and alkaline phosphatase activities in plasma were enhanced due to CCl(4) treatment. The magnitude of increase in the marker enzymes was less in food-restricted animals than in control animals. Erythrocytes from food-restricted rats were more resistant to hydrogen peroxide-induced peroxidation than were those from control rats. The activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase were higher in food-restricted animals. CONCLUSIONS: The present results suggested that food restriction can minimize drug-related increases in peroxidation and protect the system against drug toxicity, presumably by induction of antioxidant potential.     

Energy restriction and the partitioning of energy among the costs of reproduction in rats in relation to growth of the progeny

Compared with well-nourished controls, progeny of energy-restricted females are smaller and grow less well. The mechanisms behind these effects are frequently studied in rats but interpretation of such studies requires knowledge about the partitioning of dietary energy among the costs of reproduction and maternal needs. Energy partitioning was studied in rats fed ad libitum or 70% of ad libitum intake from 24-34 d before conception until d 14 of lactation and in virginal controls. Body composition was estimated for adult rats on d 1 of gestation, for adult rats and litters on d 1, 9 and 14 of lactation and for virginal controls after 65 d of dietary treatment. Milk production and composition were also studied. Dams in the two groups retained similar amounts of energy during pregnancy. Mobilized body energy corresponded to only 6 and 12% of the energy in milk for ad libitum-fed and restricted rats, respectively. Adult energy-restricted rats were smaller than their ad libitum-fed counterparts and thus needed less energy for maintenance. During lactation, energy-restricted rats used less energy per unit body size than ad libitum-fed rats. Pups of restricted dams were not only smaller, they also utilized milk energy less efficiently than did pups of well-fed dams.     

Activities of cerebral dihydropteridine reductase and tyrosine hydroxylase in chronic uremia in rats

The effect of chronic uremia on activities of cerebral dihydropteridine reductase (DHPR) and tyrosine hydroxylase (TH) and content of norepinephrine and dopamine was investigated in the male Sprague-Dawley rats. The uremic animals were fed diets containing either 8% or 18% casein ad libitum, and sham-operated pair-fed and ad libitum fed animals were used as controls. There were no significant differences in TH activity between the groups fed the two levels of protein. Uremic rats had lower activity of TH than pair-fed controls, and pair-fed controls had lower activity than ad libitum-fed animals. DHPR activity and norepinephrine and dopamine content did not differ among the groups. Our study suggests that the chronic uremic condition or restricted feeding causes a decrease in brain TH activity which is not mediated by decreased DHPR activity. Further, this decreased enzyme activity does not result in depressed catecholamine content, indicating the presence of a highly regulated mechanism controlling catecholamine levels.     

The effect of age and dietary restriction on bone strength, calcium and phosphorus contents of male F344 rats

At 6 weeks of age, male Fischer F344 rats were fed a purified, casein based diet either ad libitum or in the amount of 60% of the diet consumed by the rats, fed ad libitum (restricted diet). Femur bone tissues were obtained from the rats at 4 and 13 months of age. The femurs of the animals fed ad libitum were significantly stronger than the femurs of the animals fed a restricted diet both at the age of 4 and 13 months [p0.01]. The body weight and bone weight of the animals fed ad libitum were also higher than that of the animals on the restricted diet. The bone ash weight was significantly lower for food restricted animals [p0.013] when compared to the animals fed ad libitum. The bone phosphorus content was significantly higher in the diet restricted older animals [p0.02] when compared to the diet restricted younger animals. Results indicate that food restriction will delay bone maturation.     

Response of adult lean and obese female Zucker rats to intermittent food restriction/refeeding

Previously, it was found that lean and obese Zucker rats (9-15 wk of age) responded differently to the first of four cycles of food restriction/refeeding. In later cycles, they responded similarly. The present study was undertaken to determine if this finding was due to age, adaptation to the intervention or the obesity. Adult (35-wk-old) lean and obese rats were classified into four groups, ad libitum-fed lean and obese and food-restricted lean and obese. Food-restricted rats underwent four 3-wk periods when they were fed 50% of their ad libitum intake, each followed by a 3-wk period of ad libitum refeeding. Food-restricted rats lost and regained sufficient weight in each cycle to weigh a similar amount as their ad libitum-fed groups by the end of each refeeding period. In lean rats, there were no permanent effects of this intervention except for a 25% reduction in carbohydrate intake. Similar results were found in obese rats, although they did have significantly lower retroperitoneal fat pad weight and serum triacylglycerol levels than ad libitum-fed obese rats at the end of the experiment. These results indicate that lean and obese adult rats respond to each food restriction/refeeding cycle in a similar manner. Results in the earlier experiment would appear to be due both to age and genotype.     

Effect of dietary restriction on the age-dependent changes in the expression of antioxidant enzymes in rat liver

The effects of aging and dietary restriction on the expression of several enzymes (superoxide dismutase, catalase and glutathione peroxidase) that are involved in free radical detoxification were studied in liver tissue from male Fischer F344 rats. The expression (i.e., activities and mRNA levels) of superoxide dismutase (Cu-Zn) and catalase decreased with age in liver. Dietary restriction (40% restriction of energy intake) increased the activities of superoxide dismutase (24 to 38%) and catalase (64 to 75%) in liver at 21 and 28 mo of age. Glutathione peroxidase activity in liver of diet-restricted rats was significantly higher (37%) at 28 mo of age than that of rats fed ad libitum. The age-related changes in the relative levels of mRNA for superoxide dismutase, catalase and glutathione peroxidase paralleled the changes in the activities of these enzymes in rats fed ad libitum or rats fed the restricted diet. Thus, the changes in the activities of superoxide dismutase, catalase and glutathione peroxidase with age and dietary restriction appear to arise from changes in the levels of mRNAs coding for these enzymes. Free radical damage, as measured by thiobarbituric acid-reactive material and lipofuscin accumulation, was lower in diet-restricted rats than in rats fed ad libitum.     

Effect of dietary protein and food restriction on milk production and composition, maternal tissues and enzymes in lactating rats

Lactating rats have been fed either a protein-restricted diet (10 vs. 20% casein in the control diet) or the control diet at 80, 60 and 40% of the voluntary intake for 7 d from d 7 of lactation. Food consumption, changes in maternal live weight, litter live weight gain and the mass of several maternal tissues were determined together with the activity of several mammary and liver enzymes, including 10 that are essential for fatty acid and complex lipid synthesis. Milk production was estimated from the litter weight gain and litter weight. Lactating rats fed the 20% protein diet ad libitum consumed three times that of nonlactating rats; their liver and kidney masses were significantly higher and their adipose mass was lower. The livers of the lactating rats were fatty, containing 118 mg lipid/g compared with 42 mg/g for the nonlactating rats. Lactating rats fed either the protein-restricted diet or the control diet at 40 and 60% of the ad libitum intake of the control diet had lower mammary, liver and kidney masses than rats consuming the control diet ad libitum. Both protein and food restriction led to lower rates of milk production than those of ad libitum-fed control rats as evidenced by the decrease in litter live weight gains. The concentrations of total lipid, total protein and lactose in milk were not affected by these dietary treatments. The concentration of alpha-lactalbumin in milk of rats fed the low protein diet was, however, lower than that in the milk of all rats receiving the control diet, irrespective of intake. Consumption of the restricted diets resulted in only small changes in specific activities (mu/mg protein) of 15 mammary enzymes. In the livers, lactation led to higher specific activities of all four soluble lipogenic enzymes examined but did not affect the particulate enzymes involved in complex lipid synthesis. The dietary restrictions resulted in lower specific activities of the soluble enzymes compared with those of the lactating rats consuming the control diet ad libitum without affecting the particulate enzymes. Total activities of these enzymes were, however, lower than those for the control rats as a result of the smaller liver mass in the rats receiving the restricted diets.     

Genetic differences in effects of food restriction on aging in mice

Lifelong food restriction to two-thirds of normal ad libitum consumption extended mean and maximum life spans more than 200 d in male B6CBAF1 hybrid mice, already a long-lived genotype. The following biological systems were improved by food restriction, with values for older mice being similar to those previously found for younger individuals: tight wire clinging, a measure of neuromuscular performance; open field movement, a measure of voluntary activity; tail tendon denaturation rate, a measure of collagen solubility; urine concentrating ability, a measure of renal function, and hair regrowth rate, a measure of the frequency of hair follicle cycling. However, wound healing was slower in food-restricted mice than in ad libitum-fed controls. The same food restriction treatment had entirely different effects on longevities of a different genotype, male B6 (C57BL/6J) mice, reducing mean and maximum life spans 265 and 27 d, respectively. This surprising deleterious effect was not predicted by tests of tight wire clinging, open field movement and tail tendon denaturation, but was predicted by hair regrowth rates, as these were lower in restricted B6 mice than in fed controls. In genetically obese (ob/ob) B6 mice, food restriction extended mean and maximum longevities 327 and 440 d, yet no biological systems tested performed better than those of food-restricted normal (+/+) mice whose life spans were reduced. Thus the food restriction regimen that increased longevities for individuals of two genotypes decreased them for individuals of a third genotype tested in the same set of experiments.     

Effect of moderate caloric restriction and/or weight cycling on mammary tumor incidence and latency in MMTV-Neu female mice

Recently, we reported that intermittent caloric restriction-refeeding reduces mammary tumor (MT) incidence and extends latency in murine mammary tumor virus (MMTV)-transforming growth factor (TGF)-a mice to a greater extent than does chronic caloric restriction. Here, this same weight-cycling protocol was applied to MMTV-Neu female mice, which develop MTs at a much younger age than do TGF-a mice. This study consisted of three experimental groups: mice fed an AIN-93M diet ad libitum, mice intermittently fed an AIN-93 modified diet (2-fold increase in protein, fat, vitamins, and minerals) at 50% of the amount fed to the ad libitum-fed mice for 3-wk intervals and then fed an AIN-93M diet ad libitum for 3-wk intervals, and mice chronically restricted, pair fed to the intermittently restricted mice by feeding 2:1 mixtures of AIN-93M-AIN-93 modified diets for each 6-wk feeding interval. Mice were euthanized when MTs reached a length of 20 mm or at 80 wk of age. Cumulative caloric intake was 10% lower (not significant) for intermittently restricted mice and 16% lower (P < 0.05) for chronically restricted mice than for ad libitum-fed mice. Final body weights were significantly different as follows: ad libitum-fed > intermittently restricted > chronically restricted. Fat pad weights were greater in ad libitum-fed than in intermittently restricted and chronically restricted mice. MT incidence of ad libitum-fed mice was 37% compared with 22% for intermittently restricted mice and 33% for chronically restricted mice (not significant). There were no differences in MT weight or number among the groups. These results indicate that intermittent caloric restriction-refeeding provides a moderate protective effect, whereas chronic caloric restriction provides no significant protection against MT development in transgenic Neu mice.     

Effect of liver denervation on compensatory changes in food intake, body composition and hepatic enzyme induction after food restriction in rats

The mechanisms involved in the recovery of body fat and liver metabolism after food restriction and refeeding are not understood. This study's aim was to determine the need for hepatic neural input for the compensatory changes in food intake, body composition and hepatic lipogenic enzymes seen upon realimentation after energy restriction. Rats underwent total surgical hepatic denervation or had sham operations. One group of sham-operated and denervated rats was fed a semipurified diet ad libitum; a second group was restricted to 40% ad libitum levels for 7 d, then given free access to food during a 2-d refeeding period. Body fat content and body fat recovery rate from below "set point" were not altered by hepatic denervation. These observations do not rule out liver involvement because blood-borne factors communicating energy status information to the central nervous system could be released from the liver. The activities of hepatic enzymes--glucose-6-phosphate dehydrogenase, malic enzyme and citrate cleavage enzyme--were stimulated at least twofold by restriction and refeeding when compared to ad libitum feeding. Hepatic denervation had no effect on basal enzyme levels in ad libitum-fed animals or on elevated enzyme activity induced by refeeding after food restriction. This study clearly demonstrates that hepatic innervation is not essential for energy balance and body composition regulation. The induction of lipogenic enzymes by food restriction and refeeding does not depend on central nervous system input to the liver.     

Regional fat pad growth and cellularity in obese zucker rats: modulation by caloric restriction

OBJECTIVE: To investigate, in young obese male Zucker rats, the effects of chronic food restriction and subsequent refeeding on: 1). parameters of nonadipose and adipose growth, 2). regional adipose depot cellularity [fat cell volume (FCV) and number], and 3). circulating leptin levels. RESEARCH METHODS AND PROCEDURES: Obese (fa/fa) and lean (Fa/?) male Zucker rats were studied from age 5 to 19 weeks. After baseline food intake monitoring, 10 obese rats were subjected to 58 days of marked caloric restriction from ad libitum levels [obese-restricted (OR)], followed by a return to ad libitum feeding for 22 days. Ten lean control rats and 10 obese control rats were fed ad libitum for the entire experiment. All rats were fed using a computer-driven automated feeding system designed to mimic natural eating patterns. RESULTS: After food restriction, OR rats weighed significantly less than did lean and obese rats and showed a significant diminution in body and adipose growth as compared with obese rats. Relative adiposity was not different between obese and OR rats and was significantly higher than that of lean rats. The limitation in growth of the adipose tissue mass in OR rats was due mostly to suppression of fat cell proliferation because the mean FCV in each of the four depots was not affected. Serum leptin levels of OR and obese rats were not different from each other but were significantly higher than those of lean rats. DISCUSSION: Marked caloric restriction affects obese male Zucker rats in a manner different from that of nongenetic rodent models (i.e., Wistar rats). In comparison with the response to caloric deprivation of Wistar rats, these calorically restricted obese male Zucker rats appeared to defend their relative adiposity and mean FCV at the expense of fat cell number. These findings indicate that genetic and/or tissue-specific controls override the general consequences of food restriction in this genetic model of obesity.     

Effect of energy restriction on riboflavin retention in normal and deficient tissues of the rat

We investigated the effects of energy restriction on tissue riboflavin depletion and subsequent repletion of deficient tissues. Groups of male Sprague Dawley rats with average body weights between 268 and 275g were placed on energy-restricted diets consisting of 8g (31kcal or 130kJ) per day of a basal diet adequate in all other nutrients and either 12mg of riboflavin/kg or no added riboflavin. The ad libitum controls received additional energy as a mixture of sucrose, starch, and corn oil (10:3:1 by wt). No significant difference in the degree of riboflavin deficiency was detected between energy-restricted and ad libitum-fed rats as assessed by riboflavin concentrations in the liver and gastrocnemius and soleus muscles and by the erythrocyte glutathione reductase activity coefficient (EGRAC). Additional energy-restricted riboflavin-deficient rats were subsequently repleted by feeding either the supplemented basal diet with no additional energy or with ad libitum energy. Repletion of liver riboflavin concentration and reduction of the EGRAC values to control levels occurred regardless of energy intake. Muscle riboflavin concentrations were normal in the ad libitum-fed group but decreased in the energy-restricted rats despite 4 weeks of supplementation. The latter group had muscle riboflavin levels similar to those in the rats fed the riboflavin-deficient diet for 8 weeks. The results suggest that energy restriction impairs flavo-protein synthesis in muscle but not in the liver.     

Effect of dietary restriction on liver protein synthesis in rats

At 6 wk of age, male Fischer F344 rats were fed a purified, casein-based diet either ad libitum or in the amount of 60% of the diet consumed by the rats fed ad libitum (restricted diet). Hepatocytes were isolated from the rats between 2.5 and 19 mo of age. The protein content of the hepatocytes isolated from the rats fed the restricted amount of diet was significantly lower than that of hepatocytes isolated from rats fed ad libitum. The DNA and RNA content of the hepatocytes were similar for the rats fed the two dietary regimens. The absolute rate of protein synthesis for hepatocytes isolated from rats fed ad libitum decreased 55% between 2.5 and 19 mo of age. However, the rate of protein synthesis by hepatocytes from rats fed the restricted amount of diet decreased only slightly with increasing age. At 19 mo of age, the rate of protein synthesis by hepatocytes from the rats fed the restricted amount of diet was significantly higher than the rate of protein synthesis for hepatocytes from rats fed ad libitum. Therefore, dietary restriction retards the age-related decline in liver protein synthesis.     

Effect of meal-feeding on the daily variations of insulin, glucose, and NADP-linked dehydrogenases in rats.

Normal and adrenalectomized rats were either ad libitum fed or meal-fed a 66.5% glucose diet for 1 to 3 weeks. Ad libitum-fed rats exhibited synchronized daily rhythms in the levels of immunoreactive insulin, glucose, hepatic glucose-6-phosphate dehydrogenase, and malic enzyme activities. These rhythms were shifted late-morning 2-hour feeding period. The rhythms of adrenalectomized ad libitum-fed rats were different from those for nonadrenalectomized rats. These results indicate that differences between ad libitum- and meal-fed animals may be attributable to the timing of food intake with respect to the timing of observation rather than to meal-feeding alone. It is further concluded that the adrenals play a role in the maintenance of these rhythms.     

One cycle of reproduction consisting of pregnancy, lactation or no lactation, and recovery: effects on carcass composition in ad libitum-fed and food-restricted rats

Groups of nine ad libitum-fed and food-restricted Osborne-Mendel rats weighing between 200 and 220 g at mating were killed on day 21 of pregnancy, day 21 of lactation and day 21 of the postweaning recovery period. Restricted rats were fed 70% of the mean daily ad libitum intake. Groups of nine ad libitum-fed animals, not permitted to suckle their young, were killed on day 21 postpartum and day 21 of the recovery period. Groups of nine nonpregnant rats of comparable initial body weight were killed at appropriate times to serve as advancing age and growth controls. Changes in carcass composition were determined in each group at the end of the pregnancy, lactation and recovery periods. Carcass fat was elevated in the nonlactating group on day 21 postpartum compared to lactating animals and nonpregnant controls. At the end of the study, carcass weight was highest in the ad libitum-fed lactating group. This was due to increased carcass water and not to increased carcass fat. In fact, carcass fat was significantly reduced in the ad libitum-fed lactating group compared to nonpregnant controls. During the recovery period, the absolute increase in carcass fat was greater in the restricted group than in the ad libitum-fed group. The data indicate that 1) pregnancy followed by no lactation results in an increase in carcass fat content and 2) the postweaning recovery period is marked by a tendency to increase carcass fat even in food-restricted rats.     

Effect of dietary zinc deficiency and the associated drop in voluntary food intake on rat erythrocyte membrane polyamines

The effect of dietary zinc deficiency in the rat on the free (noncovalently bound) polyamine concentrations in erythrocyte membranes, in erythrocyte cytosol and in the blood plasma were determined. Weanling male Wistar rats were fed an egg white-based diet containing less than 1.0 mg Zn/kg diet for 3 wk ad libitum. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg Zn/kg diet. Tissue fractions were extracted with 0.2 M perchloric acid and polyamines were measured in the soluble fraction by dansylation, thin-layer chromatography and fluorescence spectrophotometry of the isolated dansylated polyamines. The depressed food intake associated with dietary zinc deficiency caused significantly (P less than 0.05) lower plasma spermidine, erythrocyte cytosol putrescine, spermidine and spermine and erythrocyte membrane spermidine concentrations. In addition, the depressed food intake caused significantly lower spermidine-spermine ratios in the erythrocyte membrane and cytosol and in blood plasma. Dietary zinc deficiency per se caused significantly (P less than 0.05) higher plasma spermidine and spermine and erythrocyte membrane spermine concentrations and significantly lower spermidine-spermine ratios in erythrocyte membrane and cytosol than in pair-fed, zinc-adequate controls.     

Effects of some nutritional deficiencies on parturition in rats.

Relation of food consumption to stress at parturition in rats was investigated in three experiments. (1) Females receiving a low thiamin intake during gestation were compared with those receiving a low zinc intake and those receiving either a restricted or ad libitum food intake with adequate zinc. Litter size was reduced in the low thiamin group. Malformed offspring were noted in the other three groups. Little stress at parturition was evident in any of the groups. Serum progesterone concentrations on day 18 were elevated in all three experimental groups relative to ad libitum controls. Urinary hydroxyproline in females with low zinc intakes did not differ from that in ad libitum controls. (2) A 5% protein diet increased food intake only slightly in females with low zinc intake and resulted in death at the end of gestation. (3) Force feeding of pregnant females was unsuccessful, but results with females given the low zinc diet or restricted amounts of the diet plus zinc supported results obtained in the other two experiments. The possibility that stress at parturition was related to the ability of the females to make normal hemodynamic adjustments to pregnancy is discussed.     

Loss of tissues in female rats subjected to food restriction during lactation or during both gestation and lactation

The effects of food restriction (50% of ad libitum-fed controls) on maternal tissues during lactation (LR) or during both gestation and lactation (GLR) were examined in rats. Skeletal muscle protein, RNA and fiber diameter were reduced in response to the LR and GLR treatments, but muscle DNA and fiber number were unchanged. Mean body weights of the pregnant (GLR) and nonpregnant female rats were not significantly different after the first 3 wk of food restriction (after delivery in pregnant GLR rats). Compared to the controls, pups of the GLR females had a significantly smaller mean birth weight. The LR females lost weight and catabolized fat pads, organs, and skeletal muscles while nonlactating females gained weight when given a similar amount of food. These results indicated that the demands of gestation did not significantly add to the loss of maternal body weight due to the restriction of food intake. However, the demands of lactation caused the food-restricted females to catabolize significant amounts of maternal tissues.     

Does food restriction increase life span in lean rats?

The effect of food restriction on survival of lean animals was investigated using WAG/Rij rats. In this strain, body weight of males and females fed ad libitum reached a plateau of 350 g and 220 g, respectively, at the age of 10 months. Their spontaneous food intake was 15 g per 24 h in males and 10 g in females, values which were 50 to 40 % lower than that reported for most strain of laboratory rats. A 30 % food restriction was initiated at the age of 10 months in both gender, and also at 20 months in males. In females, reduction in caloric intake had no effect on mean survival until 30 months, but change the slope of the survival curve in the last part of life. As a result, mean and maximal life span were increased by 10 %. In males, when reduction in food intake was initiated at 10 months, the survival curve of the restricted animals was shift to the right, also corresponding to a 10 % increase in mean and maximal survival, without change in the slope of mortality curve. When started at 20 months, diet restriction has no significant effect on survival of male rats. It was concluded that food restriction initiated in adults is mostly efficient to increase survival in rodents with large spontaneous food intake, but have a minor effect on lean strain, although it has beneficial effect on several aging processes.