Dietary obesity and exercise in young rats

Food intake, body weight, body composition, resting metabolic rate (RMR) and the thermic effect of food (TEF) were measured in young rats, some of which were fed a high energy (HE) diet and some of which were forced to swim daily. In general, high energy feeding as compared to chow feeding, resulted in higher food intake, higher body weight, higher body fat, and a slightly lower TEF. In many cases, however, the specific effects varied with the age and sex of the animals. Animals forced to swim weighed less; were leaner; and had higher RMR and TEF than sedentary animals. The effects of exercise on energy balance were greatest in males, while the effects of the high energy diet on energy balance were greatest in females. All HE-fed rats were switched to lab chow at 104 days of age. Body weights of sedentary HE-fed rats returned to control levels but those of exercised HE-fed rats did not. Both HE-fed groups remained fatter than chow-fed controls, even two months after the diet switch.     

Effects of exercise-training on the thermic effect of food and body fatness of adult women

Resting metabolic rate (RMR), thermic effect of food (TEF), aerobic capacity (VO2max), body fat, and food intake were measured in 10 healthy women before and after a 10 week graded exercise program of jogging. Pretraining TEF was a linear function of VO2max. Following exercise training, the women showed a significant increase (20%) in VO2max and loss (10.4%) of body fat; body weight did not change. Fat loss was directly related to changes in VO2max and RMR. The women showed a wide variation of changes in RMR (-21 to +2%) and TEF (-32 to +66%) from their pretraining levels. The changes in RMR and TEF were significantly positively correlated with improvements in VO2max. Analyses using multiple regression techniques, indicated that the changes in RMR and TEF accounted for 96.2% of the total variation in the changes of VO2max. Analyses of food intake indicated that diet composition (but not caloric intake) was highly related to the changes in VO2max, RMR, TEF and body fatness. Present results support further our hypothesis, that VO2max is an important physiological index of dietary thermogenesis and fat loss of individuals of normal body weight and fatness. Possible nutritional and physiological factors that may explain the wide variation in RMR and TEF of the women are discussed.     

Cardiac remodeling and function following exercise and angiotensin II receptor antagonism

The purpose of this study was to test the impact of chronic exercise training combined with selective angiotensin II receptor (AT1) antagonism on systolic blood pressure (SBP) and the left-ventricular pressure–volume relationship in normotensive, non-infarcted rat hearts. Wistar rats (N = 19) were randomly assigned to either a sedentary control group (N = 8) or an exercise-trained group (N = 11). Losartan was administered to individually caged rats via the drinking water (10 mg/kg/d). Exercise training consisted of running on a motorized driven treadmill for 6 weeks at 30 m/min, 60 min/day, 5 days/week. Tail cuff SBP was measured weekly. Left ventricular performance was assessed in an ex vivo Langendorff isovolumic mode. One week of losartan treatment significantly reduced SBP in both groups by 13% relative to baseline (P < 0.05). SBP was lower in exercise-trained animals versus sedentary animals in the later weeks of the protocol (P < 0.05) Body weight was significantly lower in exercise-trained animals versus sedentary animals, but heart weight, heart to body weight ratio, atrial weight, and absolute left ventricular mass and length were similar between groups. The LV systolic pressure–volume relationship (PV) and systolic elastance were significantly greater in exercise-trained animals versus sedentary controls (P < 0.05). The left ventricular end-diastolic PV and diastolic stiffness were similar between exercise-trained and sedentary animals. These data suggest that chronic aerobic exercise training can improve the Starling response in the presence of AT1 receptor blockade without altering absolute cardiac size.     

Peripheral markers of thyroid status unaffected by endurance training in rats

In order to more clearly define the relationship between endurance exercise training and thyroid activity we have measured T₄ turnover in exercise-trained and sedentary rats under conditions of controlled food intake and body weight. Rats were run on rodent treadmills at gradually increasing speeds and durations until at the end of 12 weeks they were running 2 h per day at 31 m/min. Sedentary rats were either allowed to eatad libitum or were food restricted so that they gained weight at the same rate as controls. Relative heart weight and plantaris citrate synthase activity were both significantly increased in trained animals compared to controls. The thyroxine secretion and degradation rates were not affected by the training. In addition, liver mitochondrial -glycerophosphate dehydrogenase and citrate synthase were measured as indicators of the thyroid state at the tissue level. Neither of these enzymes were increased in the trained rats. We conclude that increased thyroid activity is not essential for inducing and maintaining the adaptations in muscle mitochondrial enzymes which occur in response to prolonged endurance exercise training.     

Acute and chronic effects of strenuous exercise on glucose metabolism in isolated, incubated soleus muscle of exercise-trained rats

Male and female Wistar rats were exercise-trained for 6 or 11 weeks respectively, to examine the effects of acute exercise or exercise training per se on insulin-stimulated glucose utilization in soleus muscles isolated and incubated in vitro. The maximal activities of hexokinase and 2-oxoglutarate dehydrogenase were significantly elevated (by greater than 50%) in gastrocnemius muscle of exercise-trained male and female rats, indicating an adaptation to the training regime. No significant differences in any of the variables studied were observed between appropriately matched male and female rats. There were no significant differences in the sensitivity or responsiveness of the rates of lactate formation or glycogen synthesis in soleus muscles isolated from exercise-trained and sedentary animals at rest (exercise-trained animals were studied 40 h after the last exercise bout). On the other hand, acute exercise caused significant changes in soleus muscle glucose metabolism. Basal and insulin-stimulated rates of glycogen synthesis were significantly elevated in soleus muscles incubated from both sedentary and exercise-trained rats immediately after an exercise bout. In addition, the responsiveness of glucose utilization to insulin in soleus muscles from exercise-trained rats was significantly increased after acute exercise. The results indicate that significant changes in the control of glucose metabolism by insulin in soleus muscle occur as a result of an acute exercise bout, while no adaptive changes in insulin sensitivity occur in soleus muscle after exercise training.     

Lack of diet-induced thermogenesis following lesions of paraventricular nucleus in rats

The effects of electrolytic lesions in the hypothalamus paraventricular nucleus were studied in adult male and female Sprague-Dawley rats, fed different diets, consisting of either palatable human food plus chow (cafeteria diet) or chow alone. The results showed that both cafeteria diet and lesions induced an increase in energy intake and weight gain in rats of both sexes. Oxygen consumption rate and colonic temperature were significantly decreased by lesions, while cafeteria diet increased the same parameters only in intact animals. The lesion decreased weight, protein and DNA, and temperature of brown adipose tissue, while cafeteria diet increased the values considered in brown adipose tissue of sham-injured rats, but not in lesioned animals. The response to norepinephrine administration was significantly greater in intact rats and those fed cafeteria diet. The results suggest that the larger body weight gain observed in lesioned rats, particularly evident in rats fed cafeteria diet, is partly due to the disappearance of diet-induced thermogenesis that depends on the reduced mass and functional activity of brown adipose tissue.     

Hyperactivity and obesity: The interaction of social isolation and cafeteria feeding

Rats were reared in social isolation or in social groups of 4 or 5 rats per cage from weaning and were fed either a lab chow diet or a diet of 4 palatable foods (cafeteria diet), in addition to the lab chow. The hyperactivity of isolation-reared rats appears to be a reactivity to novel environmental stimuli, since it was seen only in the 0.5 hr tests and not in the near 24 hr test. It was found that hyperactivity and increased body weight can develop within as few as 7 to 10 days in rats reared in isolation from weaning. Cafeteria feeding enhanced activity in isolation-reared rats, but suppressed it in group-reared rats. Isolation-reared rats fed a cafeteria diet had strong, stable preferences for their most preferred food over the 25 days of measurement. Rats reared in isolation had significantly different food preferences, as compared with rats reared in groups. Cafeteria fed rats had a significantly greater calorie intake and body weight than rats fed lab chow. On analysis, cafeteria fed rats had significantly greater carcass energy and an increased amount of parametrial white adipose tissue as compared with rats fed only lab chow. The interscapular brown adipose tissue (IBAT) weights of cafeteria fed rats were also greater. However, as there was no difference between the cafeteria and chow fed rats in the total amount of protein in the IBAT, it was concluded that the increased weight of the IBAT did not reflect a genuine hypertrophy of the tissue.     

Lack of diet-induced thermogenesis in brown adipose tissue of obese medial hypothalamic-lesioned rats

Radiofrequency heat lesions were made in the medial hypothalamus of 12-week old male and female Holtzman rats. Two to three days later rats were offered a palatable cafeteria diet in addition to chow or were fed chow alone for the next 3-4 weeks. Male lesioned rats were only slightly hyperphagic on the chow diet and gained little extra weight. When fed the cafeteria diet, energy intake of male lesioned rats almost doubled in comparison with chow-fed lesioned rats and a very rapid extra weight gain occurred. Despite the marked hyperphagia, thermogenesis in brown adipose tissue was suppressed in the cafeteria-fed lesioned rats, as indicated by low mitochondrial guanosine diphosphate (GDP) binding. In female rats, lesions induced much greater hyperphagia and body weight gain than in male rats, particularly when they ate the cafeteria diet. Again, thermogenesis in brown adipose tissue was suppressed in the cafeteria-fed female lesioned rats. The proportion of energy derived from carbohydrate was not altered by the cafeteria diet in either male or female rats, whether lesioned or not, but there was an increase in the proportion of energy derived from fat at the expense of protein. No sex differences in food selection were observed. The accumulation of body fat was always greater in female lesioned rats than in male lesioned rats for similar food intakes. It is concluded that medial hypothalamic lesions prevent the normal occurrence of diet-induced thermogenesis in brown adipose tissue despite extreme overeating by the rats of a palatable cafeteria diet.     

Effects of exercise training on pathological cardiac hypertrophy related gene expression and apoptosis

This study determined whether exercise training prevents pathological hypertrophy in the left ventricle by modulation of myocardial and apoptosis-associated genes. We used spontaneously hypertensive rats (n=15, non-exercise SHR), exercise-trained SHR (n=15, treadmill exercise for 12 weeks), and sedentary Wistar-Kyoto (WKY) rats (n=15). Exercise-trained SHR expressed adaptive changes such as reduced body weight, heart rate, blood pressures, left ventricle wall thickness, lipid profiles, and homocysteine level. The mRNA expression of angiotensin converting enzyme, endothelin-1, and brain natriuretic peptides in the heart was lower in the exercise-trained SHR and in the WKY than in the non-exercise SHR, whereas mRNA expression of caveolin-3 and eNOS in the heart was higher. Bcl-2 protein was higher in the exercise-trained SHR than in the WKY and the non-exercise SHR. In contrast, Bax protein levels were lower in the exercise-trained SHR and in the WKY than in the non-exercise SHR. Furthermore, the levels of the active forms of caspase-3 (20 kDa) were lower in the exercise-trained SHR and in the WKY than in the non-exercise SHR. These findings suggest that exercise training prevents pathological hypertrophy in the left ventricle by modulation of myocardial genes and that it interferes with a signal transduction pathway of apoptosis secondary to the pathological cardiac hypertrophy.     

Exercise and the development and persistence of dietary obesity in male and female rats

Adult male and female hooded rats were housed in sedentary conditions or were given free access to a running wheel. Exercising and sedentary rats received either a palatable, mixed, high energy diet with chow (experimental group) or only chow (control group). Exercise reduced the weight gain of the males but not of the females. All experimental groups preferentially selected the palatable foods. Both exercising and sedentary females and the sedentary males became obese compared to their controls, but the exercising males did not. The mixed diet was withdrawn after 10 weeks: thereafter the male and female sedentary experimental groups maintained the elevated body weight. The exercising experimental females showed significant weight loss. Analysis of x-ray photographs indicated that elevated body weight in the experimental rats probably reflected increased deposition of fat and not skeletal growth. The results show that the effect of exercise on the development of dietary obesity is different in males and females, and that sedentary male and female rats can both show persistent dietary obesity after withdrawal of the palatable foods.     

Effect of treadmill exercise on food intake and body weight in lean and obese rats

Body weight and food intake of lean and obese, male and female Osborne-Mendel rats following treadmill exercise were compared. Rats were assigned, separately by sex, to one of three diet groups; Group 1 was fed a low fat (10%) diet throughout the study, Group 2 was fed a high fat (55%) diet for 16 weeks and then switched to the low fat diet 1 week prior to exercise, and Group 3 was fed the high fat diet throughout the study. To control for differences in work output between the leanest and heaviest animals, exercise intensity was adjusted across groups such that all exercised rats had equivalent energy expenditure. After a 3 day training period, the exercise was successively increased over 8 days until a work output of 374.9J was reached. Relative to their respective controls, obese exercised males showed a reduction in body weight but no change in food intake. In contrast, exercised females showed no change in body weight or food intake, regardless of dietary condition.     

Influence of regular exercise on age-related changes in arterial elasticity: mechanistic insights from wall compositions in rat aorta.

Arterial stiffness increases with age in healthy sedentary adults. We previously reported that the age-related increases in arterial stiffness are absent or attenuated in regularly exercising adults. However, the mechanism underlying this training effect is unknown. One possibility is that regular exercise minimizes age-related changes in the arterial wall composition of elastin and collagen. To gain insight into this issue, we studied four groups of rats (N = 23): young (42-46 wks) and old (80-84 wks), sedentary and exercise-trained. The exercise group swam 1 hr.d-1, 6 d.wk-1 for 17-21 weeks. There was no significant difference in the incremental elastic modulus between young sedentary and exercise-trained rats. The elastic moduli of the old exercise-trained rats were 31% lower than in the old sedentary controls. As such, the magnitude of age-related increase in the elastic modulus was smaller in the exercise-trained (110%) vs. the sedentary group (151%) (p < 0.05). In both activity groups, elastin content was lower and collagen content was higher in old vs. young rats (p < 0.05). However, there were no significant differences between the two activity groups. These results are not consistent with the hypothesis that regular physical exercise minimizes age-related compositional changes in the arterial wall and attenuates the age-related increase in arterial stiffness.     

Sexually dimorphic effects of forced exercise on food intake and body weight in the rat

The food intake (FI), body weight (BWt) and water intake (WI) of adult male and female rats were compared during a seven day period of forced exercise in a treadmill. Work loads for the exercised groups were gradually increased across the seven-day test period, whereas work loads for the sedentary controls were maintained at the same level used during a previous three-day training period. Relative to their respective control groups, male rats showed a decrease in FI and BWt in response to the exercise challenge, but female rats showed an increase in FI sufficient to maintain their BWt at control levels. Both male and female rats showed a reliable increase in WI during the period of forced exercise. These sexually dimorphic changes in FI and BWt in response to forced exercise indicate that female rats are capable of demonstrating a more vigorous defense of BWt than are male rats and suggest that there is a sex difference in the long-term control of feeding behavior in the rat.     

Ageing, exercise and food restriction: effects on body composition

This study was undertaken to reevaluate the effect of ageing on body composition and to compare the effects of exercise and food restriction on body fat content in rats. Body fat content increased progressively between ages 12 and 28 months in sedentary freely eating male Long-Evans rats. A program of 3 h of swimming/day caused body weight to plateau at a level approximately 20% below that of the freely eating sedentary rats, primarily due to a more than 100 g lower body fat content in the swimmers. Lean body mass and protein content decreased progressively with ageing; in the sedentary animals, this decrease was significant by 18 months. The swimming protected against the decline in lean body mass and protein content up to age 18 months, but did not prevent a large decrease in lean body mass between ages 18 and 24 months. Food restriction that kept the sedentary rats at the same weight as the swimmers had its major effect on body fat content, which was approximately 40% lower than in the sedentary freely eating rats at all ages. The differences in body composition between the swimmers and food restricted sedentary animals were relatively small and consisted primarily of a lower body fat content in the swimmers. In conclusion, our results show that lean body mass declines with ageing in rats and that this loss of lean tissue is counterbalanced by an increase in fat. Exercise is highly effective in minimizing the increase in body fat, and may delay the decline in lean body mass, with ageing.     

Returning 'cafeteria-fed' rats to a chow diet: negative contrast and effects of obesity on feeding behaviour

Two experiments examined the feeding behaviour and body weight changes of rats returned to a standard chow diet after prolonged periods of cafeteria feeding. In the first, both overweight (ad lib fed) and 'normal' weight (fed a restricted ration of cafeteria foods) cafeteria rats became hypophagic compared to chow-fed rats following their return to chow feeding. However, the overweight rats' hypophagia was initially more severe and was longer lasting. In the second experiment, analysis of meal patterns recorded throughout the first 4 weeks on chow after 26-32 weeks of ad lib cafeteria feeding showed that the hypophagia was due to a reduction in mean meal size (MMS) and meal frequency (MF). Food intake and MMS subsequently recovered to within control levels (by 2-3 weeks), but MF remained persistently low. There was a decrease and then a recovery in eating rate (ER) which paralleled the changes in MMS. The previously cafeteria-fed rats lost only 60% of their excess body weight. These findings are interpreted in terms of a negative contrast effect (changes in MMS and ER) and an inhibitory action of increased adiposity on feeding (affecting mainly MF).     

Exercise training in rats impairs the replenishment of white adipose tissue after partial lipectomy

The aim of this study was to evaluate the effect of exercise training on the metabolism of rats following the partial removal of fat pads. Three-month-old male Wistar rats were subjected to the partial removal (L) of retroperitoneal white adipose tissue (RET) and epididymal white adipose tissue (EPI), or a sham operation (Sh). Seven days after surgery, both sets of rats were subdivided into exercised (LE or ShE) (swimming 90 min/day, 5 days/week, 6 weeks) and sedentary (LS or ShS) groups. Partial removal of the fat pads increased the lipogenesis rates in both the RET and EPI and decreased the weight and lypolysis rate of the EPI, while the RET weight was not significantly affected by lipectomy. In both lipectomized and sham-operated groups, exercise training caused a reduction in carcass lipid content, food intake, RET and EPI weights, and RET lipogenesis rate. On the other hand, the exercise training increased the percentage of diet-derived lipid accumulation in both tissues, either in sham and lipectomized rats. These results confirmed that regrowth is not uniform and depends on the particular fat pad that is excised. They also demonstrated that exercise training following the partial removal of fat pads modified adipose tissue metabolism, impaired the replenishment of adipose tissue, and decrease body adiposity.     

Effect of short-term exercise training on muscle glycogen in resting conditions in rats fed a high fat diet

Summary It has been reported that exercise training increases muscle glycogen storage in rats fed a high carbohydrate (CHO) diet in resting conditions. The purpose of this study was to examine whether a 3-week swimming training programme would increase muscle glycogen stores in rats fed a high-fat (FAT) diet in resting conditions. Rats were fed either the FAT or CHO diet for 7 days ad libitum, and then were fed regularly twice a day (between 0800 and 0830 hours and 1800 and 1830 hours) for 32 days. During this period of regular feeding, half of the rats in both dietary groups had swimming training for 3 weeks and the other half were sedentary. The rats were not exercised for 48 h before sacrifice. All rats were killed 2 h after their final meal (2030 hours). The glycogen contents in red gastrocnemius muscle, heart and liver were significantly higher in sedentary rats fed the CHO diet than in those fed the FAT diet. Exercise training clearly increased glycogen content in soleus, red gastrocnemius and heart muscle in rats fed the CHO diet. In rats fed the FAT diet, however, training did not increase glycogen content in these muscles or the heart. Exercise training resulted in an 87% increase of total glycogen synthase activity in the gastrocnemius muscle of rats fed the CHO diet. However, this was not observed in rats fed the FAT diet. The total glycogen phosphorylase activity in the gastrocnemius muscle of the rats of both dietary groups was increased approximately twofold by training. These results suggested that muscle glycogen was enhanced in rats fed the CHO diet and that the glycogen content of the muscle of rats fed the FAT diet was not increased by exercise training.     

Exercise and dietary cholesterol alter rat myocardial capillary ultrastructure

The effects of a cholesterol-rich diet and exercise training on the myocardial capillary network and capillary ultrastructure were examined using Sprague-Dawley rats subjected to a 7-week exhaustive swimming scheme. A total of 16 animals were randomly divided into four groups consisting of normal dietinactive, normal dietexercise, cholesterol dietinactive, and cholesterol dietexercise. Following the experimental regimen the largest heart-mass-to-body-mass ratios were measured for the exercised rats fed a normal diet and the smallest ratios were found for the cholesterol-fed inactive rats. The capillary-to-fiber ratios and the capillary densities of the exercise-trained animals fed normal and cholesterol-containing diets were higher than those of either of the inactive groups. Diet and exercise had significant and opposing effects on the number of capillary pinocytotic vesicles and no significant effect on vesicle size. The capillary endothelium of the exercise-trained animal groups occupied a smaller proportion of the capillary area when compared to diet-matched inactive groups. The results of this study imply that exercise training and a cholesterol-containing diet have opposite effects on the heart-mass-to-body-mass ratio and capillary pinocytotic vesicle number. Furthermore, exercise increases the capillary network of the myocardium and may facilitate receptor-mediated transport in heart capillaries.     

Aerobic exercise training induces metabolic benefits in rats with metabolic syndrome independent of dietary changes

OBJECTIVES:

We evaluated the effects of aerobic exercise training without dietary changes on cardiovascular and metabolic variables and on the expression of glucose transporter Type 4 in rats with metabolic syndrome.

METHODS:

Twenty male spontaneously hypertensive rats received monosodium glutamate during the neonatal period. The animals were allocated to the following groups: MS (sedentary metabolic syndrome), MS-T (trained on a treadmill for 1 hour/day, 5 days/week for 10 weeks), H (sedentary spontaneously hypertensive rats) and H-T (trained spontaneously hypertensive rats). The Lee index, blood pressure (tail-cuff system), insulin sensitivity (insulin tolerance test) and functional capacity were evaluated before and after 10 weeks of training. Glucose transporter Type 4 expression was analyzed using Western blotting. The data were compared using analysis of variance (ANOVA) (p<0.05).

RESULTS:

At baseline, the MS rats exhibited lower insulin sensitivity and increased Lee index compared with the H rats. Training decreased the body weight and Lee index of the MS rats (MS-T vs. MS), but not of the H rats (H-T vs. H). There were no differences in food intake between the groups. At the end of the experiments, the systolic blood pressure was lower in the two trained groups than in their sedentary controls. Whole-body insulin sensitivity increased in the trained groups. Glucose transporter Type 4 content increased in the heart, white adipose tissue and gastrocnemius muscle of the trained groups relative to their respective untrained groups.

CONCLUSION:

In conclusion, the present study shows that an isolated aerobic exercise training intervention is an efficient means of improving several components of metabolic syndrome, that is, training reduces obesity and hypertension and increases insulin sensitivity.     

Thermoregulatory responses to acute heat loads in rats following spontaneous running

Earlier studies showed that spontaneous exercise training in rodents shifted their core temperature and thermoeffector thresholds to high levels. The present study investigated heat loss and heat production responses to acute heat loads of exercise-trained rats. The exercise-trained rats were allowed to run in a running wheel freely for 6 months, while the sedentary controls were denied access to the wheel during the same period. Then, they were loosely restrained and put in a direct calorimeter. After thermal equilibrium had been attained, they were warmed for 30 min with an intraperitoneal electric heater (internal heating). At least 2 h later, the rats were externally warmed for 90 min by raising the ambient temperature from 24 to 38C (external warming). Hypothalamic temperature (Thy), evaporative and nonevaporative heat loss (R+C+K) and heat production were measured. Internal and external heating significantly increased Thy. During internal heating, the magnitude of the increase in Thy was significantly smaller and the amount of increase in (R+C+K) was significantly greater in the exercise-trained rats than in the controls. The slope showing the relationship between Thy and (R+C+K) in the trained rats was significantly steeper than that in the controls. During external warming, the magnitude of increase in Thy of the exercise-trained rats was significantly greater than that of the controls. The slope showing the relationship between Thy and (R+C+K) in the trained rats was not different from that in the controls. Changes in evaporative heat loss and heat production during the two types of heat load did not differ between the two groups. The results suggest that, in rats, exercise training with voluntary running improves heat tolerance through enhancing nonevaporative heat loss response. However, this may be the case only when the rats are subjected to a direct internal heat load.