The effect of physical training on insulin secretion of rat pancreatic islets

Rats were either physically trained by a 12-wk swimming program or were freely eating or weight matched, sedentary controls. Islets of Langerhans were isolated and incubated at various glucose concentrations. Within the range of physiological glucose concentrations the rate of insulin release from islets of trained rats was lower than that from islets of sedentary controls. The DNA content of the islets was similar in the different groups. The demonstrated decreased glucose sensitivity of the insulin secretory mechanism within the β-cells of trained rats may partly explain the finding of lower plasma insulin concentrations during intravenous glucose tolerance test in these rats compared with sedentary rats. Epididymal fat pads of trained rats were smaller than those of weight matched controls which in turn were smaller than those of freely eating controls, these differences being due to differences in fat cell size. The lower glucose sensitivity of the β-cells in trained rats was probably not a consequence of the low body weight and small fat depots in these rats.     

Differential effects of swimming and running on microsomal metabolism in middle-aged and aged Fischer 344 rats.

Cytochrome P-450 (P-450) content as well as p-nitroanisole (pNA) O-demethylase and UDP-glucuronyltransferase (UDPGT) activities were determined in livers of middle-aged (MA; 12 or 18 months) and aged (24-26 months) rats exercised by either treadmill running or swimming. In addition, aniline hydroxylase activity was measured in MA runners and aged swimmers and compared to respective sham and non-handled controls. Treadmill exercise consisted of running aged and MA rats on a motorized treadmill for 16 and 20 m/min respectively, 60 min/day and 4 times per week, for 8 weeks. Sham rats were placed on the treadmill twice per week for 5 min at 8 m/min. No differences were found in any parameter comparing sham rats to non-handled controls. Running did not affect body weight or hepatic microsomal protein during the 8-week study. A 33-35% decline in microsomal P-450 content in treadmill exercised MA and aged rats was found. PNA O-demethylase activity was decreased 30% in MA and 45% in aged runners and aniline metabolism was inhibited 21% in MA rats. UDPGT activity was not affected by running in MA or aged rats. Swimming exercise was accomplished by placing the rats in a tank of water (32-33 degrees C) filled to a depth of 2 ft. Swim time was 60 min twice daily, 5 times per week. The aged and MA rats were trained for 6 months and 1 year, respectively. Two control groups, non-swimming sedentary (dry control) and 1 min swim/day sham (wet control), were utilized. MA and aged wet controls and swimmers weighted 8% and 15% less respectively, than MA and aged sedentary rats. Microsomal protein was significantly increased in MA swimmers compared to sedentary (20%) and wet control (35%) but no change was found with swimming in the aged rats. The results of the enzymatic studies were variable in the MA rats. Increases in P-450 content were found in wet controls (16%) and swimmers (27%) of the MA group, but only the swimming change was significant. No significant change was determined for pNA metabolism between swimmers and wet (22%) or dry (17%) controls. Aged swimmers and wet controls were more consistent, with no change in any of the parameters except aniline metabolism which was significantly increased in wet controls (25%) and swimmers (28%) as compared to dry controls. No significant change in UDPGT activity was measured in either age group of swimmers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Increased hepatic glycogen synthetase and decreased phosphorylase in trained rats.

Rats were either physically trained by a 12 wk swimming program or were freely eating or weight matched, sedentary controls. Trained rats had a higher relative liver weight and total hepatic glycogen synthetase (EC 2.4.1.11) activity and a lower phosphorylase (EC 2.4.1.1) activity than the other groups of rats. These changes may partly explain the demonstrated training-induced increase in glucose tolerance. None of the findings could be ascribed to differences in foold intake or body weight.     

Increased hepatic glycogen synthetase and decreased phosphorylase in trained rats

Rats were either physically trained by a 12 wk swimming program or were freely eating or weight matched, sedentary controls. Trained rats had a higher relative liver weight and total hepatic glycogen synthetase (EC 2.4.1.11) activity and a lower phosphorylase (EC 2.4.1.1) activity than the other groups of rats. These changes may partly explain the demonstrated training-induced increase in glucose tolerance. None of the findings could be ascribed to differences in food intake or body weight.     

Does long-term swimming participation have a deleterious effect on the adult female skeleton?

Swimming is a popular activity for Australian women with proven cardiovascular benefits yet lacks the features thought necessary to stimulate positive adaptive changes in bone. Given that peak bone mass is attained close to the end of the second decade, we asked whether swimming was negatively associated with bone mineral density in premenopausal women beyond this age. Bone mass and retrospective physical activity data were gathered from 43 female swimmers and 44 controls (mean ages 40.4 and 43.8 years, respectively). Swimmers were recruited from the Australian Union of Senior Swimmers International while controls were healthy community dwellers with similar lean mass, fat mass, height, weight and body mass index. None of the participants had a history of medical complaints nor use of medications known to affect bone. Dual energy X-ray absorptiometry was used to determine areal bone mineral density at total body, lumbar spine, proximal femur, distal radius and tibia while self-administered questionnaires were used to approximate historical and recent physical activity and calcium intake. Swimmers had averaged over 2 hours of swimming per week for the past 5 years and 1.45 h/week over lifetime with no systematic swimming exposure for controls. Lifetime exposure to weight bearing and impact exercise were similar. There were no intergroup differences for bone mass at any site though controls had higher incidence of low bone mass/osteoporosis. No differences in bone mass were detected between swimmers in the upper and lower quartiles for swim participation for any period. Long-term swim participation did not compromise areal bone mineral density.     

Lean body mass and bone mineral density in physically exercising postmenopausal women

OBJECTIVES: To investigate whether the relative contribution of body composition (lean and fat mass component) to postmenopausal bone mineral density (BMD) differs between women participating in physical exercise and sedentary women. METHODS: Subjects were 45 postmenopausal women participating in regular physical exercise and 89 sedentary controls aged 50-60 years. Baseline characteristics included age, height, weight, body mass index (BMI, Wt/Ht(2)), age at menopause, and years since menopause (YSM). Body fat mass, percentage of body fat, lean body mass, and lumbar spine BMD (L2-4) were measured by dual-energy X-ray absorptiometry. RESULTS: Although age, height, weight, BMI, and YSM did not differ between the two groups, lean body mass and lumbar spine BMD were significantly higher (P<0.05 and <0.001, respectively), while body fat mass and percentage of body fat mass were significantly lower in exercising women than in sedentary controls (P<0.05 and <0.05, respectively). In exercising women, BMD was positively correlated with lean body mass (r=0.415, P<0.01) but not with body fat mass (r=0.155, NS). Conversely, in sedentary controls, BMD was correlated with body fat mass (r=0.251, P<0.05) and lean body mass (r=0.228, P<0.05). CONCLUSIONS: Lean body mass is a more significant determinant of postmenopausal BMD in physically exercising women than in sedentary women.     

Adipocyte diameter distributions and body fat contents of sedentary and exercised female Zucker rats

The objective was to determine whether adipocyte diameter distributions were asymmetric in lean and obese female Zucker rats under conditions of ordinary activity (sedentary controls) as well as under conditions of enforced treadmill exercise. In sedentary animals, adipocyte diameter distributions were asymmetric in both lean and obese rats. Exercise abolished the asymmetry and markedly reduced body fat content of lean rats but had no such effects in obese ones. In contrast, exercise had no effect on average adipocyte diameter in either lean or obese rats. Results suggest that ability of exercise to reduce body fat content is more closely related to a decreased proportion of small adipocytes than to decreased average adipocyte diameter in female Zucker rats.     

No persistent effect of preweaning nutrition on postweaning food intake, feeding efficiency, or body energy stores in Long-Evans rats.

The purpose of this study was to determine the relative importance of pre- and postweaning nutrition on body mass, body fat, and feeding efficiency in Long-Evans rats up to a period of 18 weeks following weaning. Female rats were bred and pups were redistributed to form large (14-19 pups), normal (11-13 pups) and small (4 pups) litter groups. Weaned rats were housed as pairs (40 pairs) or singletons (n = 16) and fed either a mixed-fat diet (36.6% fat) or a standard chow diet (13.5% fat). Food intake, body mass, and feeding efficiency were measured at 4, 8, 12, and 18 weeks postweaning. Total body fat and depot fat pad mass were also measured at 18 weeks postweaning. At weaning, pups from small litters were fatter (p less than 0.001), and had a greater mass (p less than 0.03) than pups from large litters. There were no persistent effects of preweaning litter size after covarying for preweaning mass on body mass, and postweaning growth, food intake, feeding efficiency, or body fat accretion. Male rats ingesting the mixed-fat diet had a greater body mass (p less than 0.05), greater body fat accretion (p less than 0.008) and a higher feeding efficiency (p less than 0.001) than their chow-fed counterparts, despite an overall lower energy intake (p less than 0.05). Female rats ingesting the mixed-fat diet had a lower food energy intake (p less than 0.005) and a greater feeding efficiency (p less than 0.001) than chow-fed rats during the early postweaning period, only. Thus, postweaning nutrition may play a more important role in postweaning adult mass and depot fat in freely eating rats than early nutritional experiences.     

Functional capacity and body composition in top weight-lifters,swimmers, runners and skiers

Summary Groups of top weight lifters, swimmers, runners and skiers were examined as regards functional capacity (maximal oxygen consumption measured during graded work load on a horizontal tread-mill), body build and composition (densitometry). Significant differences in mean ages (highest in skiers, lowest in swimmers) and body dimensions, attributable to natural selection, were found (highest length dimensions in swimmers, lowest in weight lifters). According to the specificity of training in individual disciplines studied, runners had lowest body weight and highest lean body mass proportion, and weight-lifters (who had highest relative weight) had lowest lean body mass proportion. Highest values of ventilation, breathing frequency, maximal oxygen consumption and oxygen pulse in skiers simultaneously with lowest pulse frequency were found; the reverse applies for weight lifters. Mutual relationships between somatic and functional characteristics in individual groups were evaluated.     

Editorial

Aims: Ageing impairs endothelial function such as the regulation of vascular tone. The release of nitric oxide (NO), which has a potent vasodilator effect and antiatherosclerotic property, is decreased in the aorta of aged rats. Exercise training, however, has been reported to increase the expression of endothelial NO synthase (eNOS) in the aorta of young rats. In aged rats, it is not known whether the expression of eNOS is altered by exercise training. We hypothesized that exercise training would improve the ageing‐induced decrease in eNOS expression in vessels, and examined the messenger RNA (mRNA) and protein expression of eNOS in the aorta of sedentary‐young rats (sedentary‐young group; 4 months old), sedentary‐aged rats (sedentary‐aged group; 23 months old), and swim‐trained aged rats (training‐aged group; 23 months old, swimming training for 8 weeks, 5 days week^?1, 90 min day^?1). Results: Body weight was significantly lower, and citrate synthase activity in the epitrochlearis muscle was significantly higher in the training‐aged group compared with the sedentary‐aged group. The mRNA expression of eNOS in the aorta was significantly higher in the training‐aged group than in the sedentary‐aged group, while it was significantly lower in both the sedentary‐aged and training‐aged groups than in the sedentary‐young group. The expression of eNOS protein in the aorta was also significantly higher in the training‐aged group than in the sedentary‐aged group, while it was also significantly lower in the sedentary‐aged group, but not in the training‐aged group, than in the sedentary‐young group. Conclusion: The present results revealed that the production of eNOS in the aorta decreases with ageing, and that the decreased production is increased by exercise training in aged rats, which may produce beneficial effects on the impaired cardiovascular system caused by ageing.     

The effects of physical exercise on body fat distribution and bone mineral density in postmenopausal women

OBJECTIVE: The present cross-sectional study investigated the effects of physical exercise on body fat distribution and bone mineral density (BMD). METHODS: Subjects were 57 postmenopausal women (mean age, 60.5+/-6.4 years) who had exercised regularly for at least 2 years. Controls were 130 age-matched sedentary women. Age, years since menopause (YSM), height, weight, and body mass index (BMI, wt./ht.(2)) were recorded. Total fat mass, percentage of body fat, trunk fat mass, leg fat mass, the ratio of trunk fat mass to leg fat mass (trunk-leg fat ratio), total body lean mass, percentage of body lean, and lumbar spine BMD (L2-L4) were measured by dual-energy X-ray absorptiometry. RESULTS: Baseline characteristics and leg fat mass did not differ between the two groups. Total fat mass, percentage of body fat, trunk fat mass, and trunk-leg fat ratio were lower (P<0.05, P<0.01, P<0.01 and P<0.001, respectively), while total body lean mass, percentage of body lean mass, and lumbar spine BMD were higher in exercising women (P<0.05, P<0.05 and P<0.01, respectively). Performing physical exercise was inversely correlated with trunk-leg fat ratio (standardized regression coefficient=-0.178, P<0.01), but positively correlated with BMD (0. 203, P<0.01) irrespective of age, height, YSM, and total fat mass. CONCLUSION: Physical exercise has beneficial effects on body fat distribution and BMD in postmenopausal women. Reduction of upper body fat distribution with physical exercise may be more attributable to the decrease in trunk fat mass.     

Effects of ageing and exercise on soleus and extensor digitorum longus muscles of female rats.

The effects of ageing and of exercise on muscle mass, fiber cross-sectional area, and fiber type composition of a weight-bearing muscle, the soleus and a non-weight-bearing muscle, the extensor digitorum longus (EDL) were investigated in female Long-Evans rats. The animals were exercised by means of voluntary wheel running beginning at 4 months. Runners and sedentary controls were studied at 9 months and 27 months of age. In sedentary rats, the soleus muscle weighed 26% less, and the EDL weighed 19% less at age 27 months, than at 9 months. This decline in muscle mass was accounted for by a similar decrease in muscle fiber cross-sectional area. The wheel running resulted in significant hypertrophy of the soleus in both 9- and 27-month-old rats; as a consequence the 27-month-old runners had larger soleus muscles than the 9-month-old sedentary rats. The running did not prevent atrophy of the EDL in the old rats, but did increase the proportion of type IIa fibers. The exercise also increased the number of capillaries per fiber in the soleus muscles of both young and old rats. In conclusion, the finding that wheel running prevented atrophy with ageing of the weight-bearing soleus but not of the non-weight-bearing EDL emphasizes the specificity of exercise, and shows that exercise-induced muscle hypertrophy can be maintained in old age by appropriate exercise.     

Molecular and morphometric description of adipose tissue during weight changes: a quantitative tool for assessment of tissue texture

The aim of this study was to evaluate the morphometric changes of adipose tissue of lean and obese rats as assessed by computerized image analysis (IA) system in experimental conditions, with different degrees of adiposity. Moreover, to validate measures obtained by image analysis by correlation with direct measures of adiposity (body weight, epididimal fat, mean fat cell size and serum leptin). Finally to correlate these changes to expression of genes involved in lipid deposition and mobilization in adipose tissue. Lean (Fa/?) and genetically obese (fa/fa) Zucker rats were studied. Obese rats were food-restricted or treated with retinoic acid (ATRA) in order to reduce body weight and fat content. Moreover, gene expression of two key enzymes involved in fat metabolism (HSL and DGAT) were assessed in adipose tissue by RT-PCR. Our results show that HSL expression in adipose tissue was lower in obese compared to lean rats (1.47+/-0.02 vs 0.35+/-0.03, p<0.005) and was upregulated during food restriction in obese rats. DGAT expression was similar in lean and obese rats and was reduced by treatment with ATRA in obese rats. Tissue texture assessed by IA was significantly higher in lean compared to obese rats (23.2+/-0.6 vs 11.6+/-2.4%; p=0.01). Tissue structure highly correlated with adiposity in obese rats with different amount of body fat (area fraction vs epididimal fat depot: p=0.001). Distribution of measures for each sample, an index of spread of adipose tissue texture, as expressed by the standard deviation, correlated with adiposity (standard deviation vs epididimal fat depot: p=0.002) thus suggesting that adipose tissue texture increases its heterogeneity when adiposity is lower. This observation is in agreement with the hypothesis that the process of lipid mobilization from adipose tissue is not uniform, but a subpopulation of slimming adipocytes undergoes a complete release of their fat content while the rest of the tissue is much less affected. Moreover, image analysis system seems a reliable quantitative tool for assessment of adipose tissue texture.     

Sex hormone profiles of premenarcheal athletes

Summary Female gymnasts have a delayed onset and probably retarded progression of puberty. The aim of this study was to test the hypothesis that the delay in onset of puberty in gymnasts as compared to girl swimmers is modulated by a lower estrone level due to a smaller amount of body fat. The sex-hormone and gonadotropin levels of 46 gymnasts and 37 girl swimmers of the same biological maturation (breast development: M=1 or M=2) were studied. In each subject the following hormones were measured in plasma: estrone, 17--estradiol, DHEAS, testosterone, androstenedione, LH, and FSH. In prepubertal children (M=1) the levels of estrone, testosterone, and androstenedione were lower in the gymnastic group as compared to the swimming group. In the early pubertal (M=2) gymnastic and swimming groups these hormone levels were no longer different. The other hormone levels were not significantly different in either the prepubertal groups or the early pubertal ones. Within the total prepubertal group there is a clear relationship between the estrone levels and the levels of testosterone and androstenedione, but not between estrone and 17--estradiol, nor between the calculated fat mass and any of the hormone levels. It appears that the androstenedione and testosterone levels are responsible for the difference in estrone level, rather than the amount of body fat.     

Responses to intensive training and methandrostenelone administration: II. Hormonal,organ weights,muscle weights and body composition

The hormonal levels of the gonadotropins, the weight of selected organs and of the triceps surae as well as body composition were determined in Sprague Dawley rats at 3 and 6 weeks after intensive training with or without a methandrostenelone (Dianabol) supplement (0.35 mg/kg/day). The controls were sedentary rats of similar age and weight at the start of the experiment. The dianabol treated rats in the sedentary and exercise groups had a depression of plasma LH levels. There were no differences in body weight, specific gravity, lean body weight, fat or % fat between the two trained groups. Dianabol had no apparent effect on the measured parameters other than a depression of LH.     

Relationship between soft tissue body composition and bone mass in perimenopausal women

OBJECTIVES: Perimenopause, the transition into menopause, marks the beginning of accelerated bone loss, contributing to the development of osteoporosis, a major public health problem. This perimenopausal transition has also been associated with a decrease in body lean mass, an increase in fat mass, and an increase in body weight. How these changes in fat mass and lean mass may influence bone mineral density (BMD) is currently unknown. The purpose of this study is to determine the independent effect and relative contribution of lean mass and fat mass to BMD in perimenopausal women. MATERIAL AND METHODS: The sample consisted of 43 sedentary perimenopausal women (age: mean = 49.6; S.D. = 3.2) with an intact uterus and ovaries, participating in a study of exercise and perimenopausal symptoms. Total body BMD, regional BMD, and soft tissue body composition were measured by dual-energy X-ray absorptiometry. Other measures including age, height, weight, and serum FSH and E2 were also obtained. RESULTS: Findings revealed that 14% of these perimenopausal women had low bone mass (osteopenia) in the lumbar spine and/or the femoral neck. Overall body fat mass and lean mass had positive relationships with BMD of lumber spine and the femur. However, using multiple regression analyses, only lean mass and ethnicity remained significant predictors for BMD of the femoral neck (r2 = 45%) with lean mass explaining more variance than ethnicity. Lean mass was the sole predictor of total proximal femur BMD explaining 38% of the variance. Fat mass was not a significant predictor of BMD at any skeleton site. CONCLUSIONS: These findings suggest that body lean mass, not fat mass, is a significant contributor to femoral BMD in perimenopausal women.     

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, T(3), T(4) and rT(3) 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 T(3) and T(4) 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.     

Prediction of body fat content in an inuit community

The age- and sex-specific generic predictions of body density, and thus body fat content, as obtained by the skinfold equations of Durnin and Womersley (1974, Br J Nutr 32:77–97) have been compared with direct hydrostatic estimates of body density in a sample of 51 moderately acculturated Canadian Inuit men, ages 18–36 years. In general, the Durnin and Womersley equations indicate somewhat too high a body density and thus too low a percentage of body fat relative to the hydrostatic data; the error amounts to 1–3% body fat, depending on the age and the skinfold thicknesses of the subject. Possible explanations of the discrepancy include (1) a low bone density, (2) a high muscle/bone mass ratio, or (3) a high ratio of internal to superficial body fat. Specific rather than generic equations would seem necessary for the accurate prediction of body fat content from skinfold readings in the Inuit, although continuing acculturation to a sedentary lifestyle currently hampers the development of generalizable equations for this population. © 1994 Wiley-Liss, Inc.     

Salivary testosterone and body composition among Ariaal males

To determine if testosterone is negatively related to acute and/or chronic nutritional status among men in a subsistence society, saliva samples and anthropometric measures were compared among nomadic and settled Ariaal pastoralists of northern Kenya. Fifty‐six nomadic men and 62 settled men facing drought conditions, estimated ages 22–96 years, were sampled. Measures included height, weight, four skinfolds, and %body fat by bioelectric impedance (BIA). Saliva samples were assayed for testosterone using radioimmunoassay. Overall, both body mass index (BMI) (avg. = 17.8 ± 6.0 kg/m²) and salivary testosterone (T) levels (avg. am value = 176.8 ± 74.8 pmol/l) were low compared to values from Western populations. Comparison of the two subpopulations revealed no significant difference in height, weight, BMI, or lean body mass. However, nomadic males exhibited significantly smaller skinfolds. Evening, but not morning, salivary T values differed between the subpopulations. Age‐related changes in body composition included a significant decline in BMI with age, related to loss of body fat, but with little change in lean body mass. Age‐related declines in BMI and %body fat were more pronounced among the nomadic males. am salivary T values declined with age; again, the decline was significantly greater among nomadic males. pm salivary T levels showed no significant decline with age. When controlled for residence and age, salivary T was positively related to %body fat and WHR ratio, but not lean body mass. These results provide evidence that salivary T is related to acute nutritional status among males in an energetically stressed subsistence population, in accordance with life history theories of somatic allocation. Am. J. Hum. Biol. 15:697–708, 2003. © 2003 Wiley‐Liss, Inc.     

The endocrine system and ageing

Complex changes occur within the endocrine system of ageing individuals. This article explores the changes that occur in the metabolism and production of various hormones and discusses the resulting clinical consequences. As individuals age there is a decline in the peripheral levels of oestrogen and testosterone, with an increase in luteinizing hormone, follicle-stimulating hormone and sex hormone-binding globulin. Additionally there is a decline in serum concentrations of growth hormone, insulin-like growth factor-I and dehydroepiandrosterone and its sulphate-bound form. Even though there are complex changes within the hypothalmo-pituitary-adrenal/thyroid axis, there is minimal change in adrenal and thyroid function with ageing. The clinical significance of these deficiencies with age are variable and include reduced protein synthesis, decrease in lean body mass and bone mass, increased fat mass, insulin resistance, higher cardiovascular disease risk, increase in vasomotor symptoms, fatigue, depression, anaemia, poor libido, erectile deficiency and a decline in immune function. For each endocrine system, studies have been carried out in an attempt to reverse the effects of ageing by altering the serum hormonal levels of older individuals. However, the real benefits of hormonal treatment in older individuals are still being evaluated.