Intramyocellular lipid content and insulin sensitivity are increased following a short-term low-glycemic index diet and exercise intervention

The relationship between intramyocellular (IMCL) and extramyocellular lipid (EMCL) accumulation and skeletal muscle insulin resistance is complex and dynamic. We examined the effect of a short-term (7-day) low-glycemic index (LGI) diet and aerobic exercise training intervention (EX) on IMCL and insulin sensitivity in older, insulin-resistant humans. Participants (66 ± 1 yr, BMI 33 ± 1 kg/m(2)) were randomly assigned to a parallel, controlled feeding trial [either an LGI (LGI/EX, n = 7) or high GI (HGI/EX, n = 8) eucaloric diet] combined with supervised exercise (60 min/day, 85% HR(max)). Insulin sensitivity was determined via 40 mU·m(-2)·min(-1) hyperinsulinemic euglycemic clamp and soleus IMCL and EMCL content was assessed by (1)H-MR spectroscopy with correction for fiber orientation. BMI decreased (kg/m(2) -0.6 ± 0.2, LGI/EX; -0.7 ± 0.2, HGI/EX P < 0.0004) after both interventions with no interaction effect of diet composition. Clamp-derived insulin sensitivity increased by 0.91 ± 0.21 (LGI/EX) and 0.17 ± 0.55 mg·kg(-1)·min(-1) (HGI/EX), P = 0.04 (effect of time). HOMA-IR was reduced by -1.1 ± 0.4 (LGI/EX) and -0.1 ± 0.2 (HGI/EX), P = 0.007 (effect of time), P = 0.02 (time × trial). Although both interventions increased IMCL content, (Δ: 2.3 ± 1.3, LGI/EX; 1.4 ± 0.9, HGI/EX, P = 0.03), diet composition did not significantly effect the increase. However, the LGI/EX group showed a robust increase in the [IMCL]/[EMCL] ratio compared with the HGI/EX group (Δ: 0.5 ± 0.2 LGI/EX vs. 0.07 ± 0.1, P = 0.03). The LGI/EX group also demonstrated greater reductions in [EMCL] than the HGI/EX group (Δ: -5.8 ± 3.4, LGI/EX; 2.3 ± 1.1, HGI/EX, P = 0.03). Changes in muscle lipids and insulin sensitivity were not correlated; however, the change in [IMCL]/[EMCL] was negatively associated with the change in FPI (r = -0.78, P = 0.002) and HOMA-IR (r = -0.61, P = 0.03). These data suggest that increases in the IMCL pool following a low glycemic diet and exercise intervention may represent lipid repartitioning from EMCL. The lower systemic glucose levels that prevail while eating a low glycemic diet may promote redistribution of lipid stores in the muscle.     

A short-term diet and exercise intervention ameliorates inflammation and markers of metabolic health in overweight/obese children

The present study was designed to examine the effects of short-term diet and exercise on markers of metabolic health, serum-stimulated production of inflammatory biomarkers from cultured monocytes and adipocytes, and serum lipomics. Twenty-one overweight/obese children (9 boys and 12 girls, age 13.0 ± 0.5 yr, BMI 33.0 ± 1.8 kg/m(2)) were placed on a 2-wk ad libitum, high-fiber, low-fat diet and daily exercise regimen. Fasting serum samples were taken pre- and postintervention for determination of cytokines, metabolic risk markers, and lipomics. Monocytes and adipocytes were incubated with pre- and postintervention serum to investigate changes in cytokine secretion. Correlative associations were calculated, followed by hierarchical clustering to determine relationships between fatty acid (FA) species and clinical biomarkers. Despite remaining overweight/obese, interleukin (IL)-6, IL-8, TNFα, PAI-1, resistin, amylin, leptin, insulin, and IL-1ra decreased and adiponectin increased. Culture studies indicated decreases in monocyte secretion of IL-6, TNFα, and IL-1β and adipocyte secretion of IL-6. Lipomic analysis revealed a decrease in total lipids and decreases in saturated FAs and an increase in 18:1/18:0. In general, Pearson's correlations revealed that inflammatory markers are negatively associated with a cluster of polyunsaturated FAs and positively correlated with several saturated FAs. These results indicate significant modification of multiple indices of metabolic health with short-term rigorous lifestyle modification in overweight/obese children prior to obesity reversal.     

Modelling the lactate response to short-term all out exercise

Background

The maximum post exercise blood lactate concentration (BLC_max) has been positively correlated with maximal short-term exercise (MSE) performance. However, the moment when BLC_max occurs (TBLC_max) is rather unpredictable and interpretation of BLC response to MSE is therefore difficult.

Methods

We compared a 3- and a 4-parameter model for the analysis of the dynamics of BLC response to MSEs lasting 10 (MSE10) and 30 s (MSE30) in eleven males (24.6 ± 2.3 yrs; 182.4 ± 6.8 cm; 75.1 ± 9.4 kg). The 3-parameter model uses BLC at MSE-start, extra-vascular increase (A) and rate constants of BLC appearance (k₁) and disappearance (k₂). The 4-parameter model includes BLC at MSE termination and amplitudes and rate constants of increase (A₁, y₁) and decrease (A₂, y₂) of post MSE-BLC.

Results

Both models consistently explained 93.69 % or more of the variance of individual BLC responses. Reduction of the number of parameters decreased (p < 0.05) the goodness of the fit in every MSE10 and in 3 MSE30. A (9.1 ± 2.1 vs. 15.3 ± 2.1 mmol l^-1) and A₁ (7.1 ± 1.6 vs. 10.9 ± 2.0 mmol l^-1) were lower (p < 0.05) in MSE10 than in MSE30. k₁ (0.610 ± 0.119 vs. 0.505 ± 0.107 min^-1), k₂ (4.21 10^-2 ± 1.06 10^-2 vs. 2.45 10^-2 ± 1.04 10^-2 min^-1), and A₂ (-563.8 ± 370.8 vs. -1412.6 ± 868.8 mmol l^-1), and y₁ (0.579 ± 0.137 vs. 0.489 ± 0.076 min^-1) were higher (p < 0.05) in MSE10 than in MSE30. No corresponding difference in y₂ (0.41 10^-2 ± 0.82 10^-2 vs. 0.15 10^-2 ± 0.42 10^-2 min^-1) was found.

Conclusion

The 3-parameter model estimates of lactate appearance and disappearance were sensitive to differences in test duration and support an interrelation between BLC level and halftime of lactate elimination previously found. The 4-parameter model results support the 3-parameter model findings about lactate appearance; however, parameter estimates for lactate disappearance were unrealistic in the 4-parameter model. The 3-parameter model provides useful information about the dynamics of the lactate response to MSE.

     

Cytokine response to eccentric exercise in young and elderly humans

To examine the plasma interleukin(IL)-6 response in elderly (E) and young (Y) humans, 10 E and 10 Ysubjects completed 60 min of eccentric lower limb exercise at the samerelative oxygen uptake. Plasma IL-6 was measured before, immediatelyafter, and 5 days into recovery from exercise, as were the biochemicalmarkers of muscle damage, creatine kinase (CK), and myoglobin. In both groups, IL-6 increased (P < 0.05) immediately afterexercise and peaked 4 h after exercise at 4.35 ± 1.7 vs.5.05 ± 3.17 pg/ml for E and Y subjects, respectively. However,the increase in IL-6 in both groups was modest relative to theincreases in CK peaking at 539 ± 413 vs. 10,301 ± 5,863 U/lfor E and Y subjects, respectively. In addition, the increase in IL-6was less pronounced (P < 0.05) in E subjects comparedwith Y subjects. These results suggest that IL-6 increasesprogressively after eccentric exercise, suggesting that this increaseis related to muscle damage. However, the modest increase in IL-6,despite large increases in CK, suggests that the IL-6 response tomuscle damage does not make an important contribution to the largeincrease in IL-6 observed during concentric exercise of long duration.Our data also suggest that aging may be associated with impaired repairmechanisms for exercise-induced muscle damage.

     

Haemodynamic response to exercise in healthy young and elderly subjects

Whereas with advancing age, peak heart rate (HR) and cardiac index (CI) are clearly reduced, peak stroke index (SI) may decrease, remain constant or even increase. The aim of this study was to describe the patterns of HR, SI, CI, arteriovenous difference in oxygen concentration (C _a-vO₂), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), stroke work index (SWI) and mean systolic ejection rate index (MSERI) in two age groups (A: 20–30 years, n = 20; B: 50–60 years n = 20. After determination of pulmonary function, an incremental bicycle exercise test was performed, with standard gas-exchange measurements and SI assessment using electrical impedance cardiography. The following age-related changes were found: similar submaximal HR response to exercise in both groups and a higher peak HR in A than in B[185 (SD 9) vs 167 (SD 14) beats · min⁻¹, P < 0.0005]; increase in SI with exercise up to 60–90 W and subsequent stabilization in both groups. As SI decreased towards the end of exercise in B, a higher peak SI was found in A [57.5 (SD 14.0) vs 43.6 (SD 7.7) ml · m⁻², P < 0.0005]; similar submaximal CI response to exercise, higher peak CI in A [10.6 (SD 2.5) vs 7.2 (SD 1.3) l · min⁻¹ · m⁻², P < 0.0005]; no differences in C _a-vO₂ during exercise; higher MAP at all levels of exercise in B; higher SVRI at all levels of exercise in B; lower SWI in B after recovery; higher MSERI at all levels of exercise in A. The decrease in SI with advancing age would seem to be related to a decrease in myocardial contractility, which can no longer be compensated for by an increase in preload (as during submaximal exercise). Increases in systemic blood pressure may also compromise ventricular function but would seem to be of minor importance. Accepted: 24 September 1996     

Phenotypic and evolutionary plasticity of organ masses in response to voluntary exercise in house mice

We used a novel mouse model to study the effects of selectivebreeding for high locomotor activity (14 generations) on relativeorgan sizes, hematocrit (Hct), and blood hemoglobin (Hb) concentration.We also examined effects of exercise training and genotype-by-environmentinteractions by housing animals for 8 weeks with wheels thatwere either free to rotate or locked. Mice from the four replicateHigh-Runner (HR) lines were smaller in total body mass but hadlarger body mass-adjusted kidneys relative to the four Controllines (P < 0.05). Control and HR lines did not differ significantlyfor mass-adjusted tail length or masses of the "triceps surae"hindlimb muscle group, heart (ventricle), spleen, liver, adrenalglands or gonads. Wheel access caused a reduction in body massand an increase in relative heart mass. In females only, wheelaccess caused a reduction in relative spleen mass. Wheel accessdid not affect relative tail length or relative mass of thetriceps surae, liver, adrenal gland or gonads. Significant interactionsbetween selection history and wheel access were observed infemales for spleen, liver, and gonad mass as well as Hct andHb. Wheel access caused increases in both Hct and Hb, mainlyin the HR lines. The mini-muscle phenotype, caused by a Mendelianrecessive allele that halves hindlimb muscle mass, was significantlyassociated with several other body composition traits, includingreduced body mass, increased tail length, increased heart mass,increased liver mass (females only), increased mean adrenalgland mass (females only), increased mean kidney mass (malesonly), and reduced Hct (wheel-access females only). Resultsare discussed in context of the beneficial acclimation hypothesis,genotype-by-environment interactions, and the potential for"nurture" to be self-reinforcing of "nature" in some complexbehavioral-physiological phenotypes.     

Exaggerated ANF response to exercise in middle-aged vs. young runners

Hormonal, electrolyte, and renal responses were measured before, during, and after a marathon (42.2 km) in 14 runners: 8 young (Y) (mean age 27.8 yr) and 6 middle aged (MA) (mean aged 46.7 yr). No differences between groups in prerun values for heart rate (HR), plasma osmolality (OSM), antidiuretic hormone (ADH), aldosterone (ALDO), atrial natriuretic factor (ANF), or plasma renin activity (PRA) were found. Renal and urinary measurements were also similar between groups before the marathon. After 10 km of running, both groups had significant increases in HR, ALDO, ANF, and PRA, while OSM, Na+, and ADH remained unchanged from prerun values. The increase in plasma ANF concentrations at this point was significantly greater in the MA subjects compared with the Y (mean increase 104.1 vs. 42.8 pg/ml, respectively; P less than 0.01). Immediate postmarathon values for OSM, ADH, and Na+ were significantly higher than initial values in both groups, while HR, PRA, and ALDO continued to increase above the elevated levels found at 10 km. ANF values immediately postmarathon remained higher than prerun concentrations but were significantly reduced from those obtained at 10 km. In contrast, HR continued to rise until the completion of the run. These data are consistent with recent reports of an exaggerated ANF response in older subjects in response to central blood volume expansion.     

Use of perceived effort ratings to control exercise intensity in young healthy adults

The purpose of this study was to evaluate the use of the rating of perceived exertion (RPE) as a means of regulating the intensity of exercise during running. The subjects were healthy, relatively fit young adults (16 men and 12 women). Estimates of effort were recorded using the Borg 6-20 Scale whilst the maximal oxygen uptake of the subjects was measured as they ran on an electrically driven treadmill. In a further session, the same subjects were requested to run on the treadmill at constant exercise intensity based on their interpretation of levels 9, 13 and 17 of the Borg Scale. They regulated their running speed and the treadmill gradient but had no knowledge of performance from the equipment display panel. A linear regression analysis was carried out to examine the relationship between heart rate, perceived exertion and relative metabolic demand. This revealed that the rating of perceived exertion was at least as good a predictor of exercise intensity as heart rate in both the graded exercise test and effort production test. The results support the view that RPE may be used to predict relative metabolic demand, especially at higher workloads and could be a useful medium for controlling intensity of effort during vigorous exercise in such subjects.     

Effect of exercise on response of liver lipogenic enzymes to a high fructose diet.

Meal-fed Long-Evans rats fed a high fructose diet and exercised for 2-hr daily on a treadmill for three days had lower levels of several hepatic lipogenic enzymes (acetyl CoA carboxylase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, malic enzyme and citrate cleavage enzyme) than did sedentary rats pair-fed the diet. Accumulation of triglycerides in plasma following ingestion of a fat-free, high fructose meal and injection of Triton WR-1339, an inhibitor of plasma triglyceride clearance, was not significantly different in the two groups of animals. All of the hepatic lipogenic enzymes measured, with the exception of citrate cleavage enzyme, attained similar levels in the runners as in the controls after 5 days on the high fructose diet. Thus the exercise appeared to affect the time course of the increase in the levels of activity of most of the lipogenic enzymes but not the final steady state levels attained.     

Prior heavy-intensity exercise speeds VO2 kinetics during moderate-intensity exercise in young adults.

The effect of prior heavy-intensity warm-up exercise on subsequent moderate-intensity phase 2 pulmonary O2 uptake kinetics (tauVO2) was examined in young adults exhibiting relatively fast (FK; tauVO2 < 30 s; n = 6) and slow (SK; tauVO2 > 30 s; n = 6) VO2 kinetics in moderate-intensity exercise without prior warm up. Subjects performed four repetitions of a moderate (Mod1)-heavy-moderate (Mod2) protocol on a cycle ergometer with work rates corresponding to 80% estimated lactate threshold (moderate intensity) and 50% difference between lactate threshold and peak VO2 (heavy intensity); each transition lasted 6 min, and each was preceded by 6 min of cycling at 20 W. VO2 and heart rate (HR) were measured breath-by-breath and beat-by-beat, respectively; concentration changes of muscle deoxyhemoglobin (HHb), oxyhemoglobin, and total hemoglobin were measured by near-infrared spectroscopy (Hamamatsu NIRO 300). tauVO2 was lower (P < 0.05) in Mod2 than in Mod1 in both FK (20 +/- 5 s vs. 26 +/- 5 s, respectively) and SK (30 +/- 8 s vs. 45 +/- 11 s, respectively); linear regression analysis showed a greater "speeding" of VO2 kinetics in subjects exhibiting a greater Mod1 tauVO2. HR, oxyhemoglobin, and total hemoglobin were elevated (P < 0.05) in Mod2 compared with Mod1. The delay before the increase in HHb was reduced (P <0.05) in Mod2, whereas the HHb mean response time was reduced (P <0.05) in FK (Mod2, 22 +/- 3 s; Mod1, 32 +/- 11 s) but not different in SK (Mod2, 36 +/- 13 s; Mod1, 34 +/- 15 s). We conclude that improved muscle perfusion in Mod2 may have contributed to the faster adaptation of VO2, especially in SK; however, a possible role for metabolic inertia in some subjects cannot be overlooked.     

Effect of a short-term diet and exercise intervention on oxidative stress, inflammation, MMP-9, and monocyte chemotactic activity in men with metabolic syndrome factors.

The present study was designed to examine the effects of lifestyle modification on key contributing factors to atherogenesis, including oxidative stress, inflammation, chemotaxis, and cell adhesion. Obese men (n = 31), 15 of whom had metabolic syndrome, were placed on a high-fiber, low-fat diet in a 3-wk residential program where food was provided ad libitum and daily aerobic exercise was performed. In each subject, pre- and postintervention fasting blood was drawn for circulating levels of serum lipids, glucose and insulin (for estimation of insulin sensitivity), oxidative stress-generating enzyme myeloperoxidase and marker 8-isoprostaglandin F2alpha, the inflammatory protein C-reactive protein, soluble ICAM-1 as an indicator of endothelial activation, sP-selectin as a marker of platelet activation, the chemokine macrophage inflammatory protein-1alpha, and total matrix metalloproteinase-9. Using subject sera and human aortic endothelial cell culture systems, we measured VCAM-1 cell surface abundance and monocyte chemotactic protein-1, nitric oxide, superoxide, and hydrogen peroxide production in vitro by fluorometric detection. Also determined in vitro was serum-induced, monocyte adhesion and monocyte chemotactic activity. After 3 wk, significant reductions (P < 0.05) in body mass index, all serum lipids and lipid ratios, fasting glucose, insulin, homeostasis model assessment for insulin resistance, myeloperoxidase, 8-isoprostaglandin F2alpha, C-reactive protein, soluble ICAM-1, soluble P-selectin, macrophage inflammatory protein-1alpha, and matrix metalloproteinase-9 were noted. In vitro, serum-stimulated cellular VCAM-1 expression, monocyte chemotactic protein-1 production, and fluorometric detection of superoxide and hydrogen peroxide production decreased, whereas a concomitant increase in NO production was noted (all P < 0.01). Additionally, both monocyte adhesion (P < 0.05) and MCA (P < 0.01) decreased. Nine of 15 were no longer positive for metabolic syndrome postintervention. Intensive lifestyle modification may ameliorate novel coronary artery disease risk factors in men with metabolic syndrome factors before reversal of obesity.     

Lipid metabolism response to a single, prolonged bout of endurance exercise in healthy young men

To discover the alterations in lipid metabolism linked to postexercise hypotriglyceridemia, we measured lipid kinetics, lipoprotein subclass distribution and lipid transfer enzymes in seven healthy, lean, young men the day after 2 h of cycling and rest. Compared with rest, exercise increased fatty acid rate of appearance and whole body fatty acid oxidation by approximately 65 and 40%, respectively (P < 0.05); exercise had no effect on VLDL-triglyceride (TG) secretion rate, increased VLDL-TG plasma clearance rate by 40 +/- 8%, and reduced VLDL-TG mean residence time by approximately 40 min and VLDL-apolipoprotein B-100 (apoB-100) secretion rate by 24 +/- 8% (all P < 0.05). Exercise also reduced the number of VLDL but almost doubled the number of IDL particles in plasma (P < 0.05). Muscle lipoprotein lipase content was not different after exercise and rest, but plasma lipoprotein lipase concentration increased by approximately 20% after exercise (P < 0.05). Plasma hepatic lipase and lecithin:cholesterol acyltransferase concentrations were not affected by exercise, whereas cholesterol ester transfer protein concentration was approximately 10% lower after exercise than after rest (P = 0.052). We conclude that 1) greater fatty acid availability after exercise does not stimulate VLDL-TG secretion, probably because of the increase in fatty acid oxidation and possibly also fatty acid use for restoration of tissue TG stores; 2) reduced secretion of VLDL-apoB-100 lowers plasma VLDL particle concentration; and 3) increased VLDL-TG plasma clearance maintains low plasma TG concentration but is not accompanied by similar increases in subsequent steps of the delipidation cascade. Acutely, therefore, the cardioprotective lowering of plasma TG and VLDL concentrations by exercise is counteracted by a proatherogenic increase in IDL concentration.     

Characterization of the cortisol response to incremental exercise in physically active young men

This study examined the cortisol response to incremental exercise; specifically to see if there was an increase in blood cortisol levels at low intensity exercise (i.e., < 60% VO2 intensity threshold) and determine whether a linear relationship existed between the blood cortisol responses and exercise of increasing workloads (i.e., intensity). Healthy, physically active young men (n = 11) completed exercise tests involving progressive workload stages (3 min) to determine peak oxygen uptake responses (VO2). Blood specimens were collected at rest and at the end of each stage and analyzed for cortisol. Results showed cortisol was significantly increased from resting levels at the end of the first exercise stage (80 W; 41.9 +/- 5.4% peak VO2) and remained significantly elevated from rest until the exercise ended. Interestingly, however, the cortisol concentrations observed at 80 W through 200 W did not significantly differ from one another. Thereafter, during the final two stages of exercise the cortisol concentrations increased further (p < 0.01). The subjects exceeded their individual lactate thresholds over these last two stages of exercise. Regression modeling to characterize the cortisol response resulted in significant regression coefficients (r = 0.415 [linear] and r = 0.655 [3rd order polynominal], respectively; p < 0.05). Comparative testing (Hotelling test) between the two regression coefficents revealed the polynominal model (sigmoidal curve) was the significantly stronger of the two (p = 0.05). In conclusion, the present findings refute the concept that low intensity exercise will not provoke a significant change in blood cortisol levels and suggest the response to incremental exercise involving increasing exercise workloads (i.e., intensities) are not entirely linear in nature. Specifically, a sigmoid curve more highly accurately characterizes the cortisol response to such exercise.     

Comparison of short-term diet and exercise on insulin action in individuals with abnormal glucose tolerance.

The effects of a 10-day low-calorie diet (LCD; n = 8) or exercise training (ET; n = 8) on insulin secretion and action were compared in obese men (n = 9) and women (n = 7), aged 53 +/- 1 yr, with abnormal glucose tolerance by using a hyperglycemic clamp with superimposed arginine infusion and a high-fat drink. Body mass (LCD, 115 +/- 5 vs. 110 +/- 5 kg; ET, 111 +/- 7 vs. 109 +/- 7 kg; P < 0. 01) and fasting plasma glucose (LCD, 115 +/- 10 vs. 99 +/- 4 mg/dl; ET, 112 +/- 4 vs. 101 +/- 5 mg/dl, P < 0.01) and insulin (LCD, 23.9 +/- 5.6 vs. 15.2 +/- 3.9 microU/ml; ET, 17.6 +/- 1.9 vs. 13.9 +/- 2. 4 microU/ml; P < 0.05) decreased in both groups. There was a 40% reduction in plasma insulin during hyperglycemia (0-45 min) after LCD (peak: 118 +/- 18 vs. 71 +/- 14 microU/ml; P < 0.05) and ET (69 +/- 14 vs. 41 +/- 7 microU/ml; P < 0.05) and trends for reductions during arginine infusion and a high-fat drink. The 56% increase in glucose uptake after ET (4.95 +/- 0.90 vs. 7.74 +/- 0.82 mg. min-1. kg fat-free mass-1; P < 0.01) was significantly (P < 0.01) greater than the 19% increase (5.72 +/- 1.12 vs. 6.80 +/- 0.94 mg. min-1. kg fat-free mass-1; P = not significant) that occurred after LCD. The marked increase in glucose disposal after ET, despite lower insulin levels, suggests that short-term exercise is more effective than diet in enhancing insulin action in individuals with abnormal glucose tolerance.     

Glucose tolerance in response to a high-fat diet is improved by a high-protein diet

Consumption of a high-fat (HF) diet results in insulin resistance and glucose intolerance. Weight loss is often recommended to reverse these metabolic alterations and the use of a high-protein (HP), low-carbohydrate diet is encouraged. In lean rats, consumption of a HP diet improves glycemic control. However, it is unknown whether this diet has a similar effectiveness in rodents with impaired glucose tolerance. Rats were fed a HF or a chow (CH) diet for 6 weeks and then switched to a HP diet or a CH or pair-fed (PF) to the amount of kcals consumed per day by the HP group. Following the diet switch, body weight gain was attenuated as compared to HF rats, and similar between HP, CH, and PF rats. Despite similar weight progression, HP and PF rats had a significant decrease in body fat after 2 weeks, as compared to HF rats. In contrast, CH rats did not show this effect. Glucose tolerance was attenuated more quickly in HP rats than in CH or PF rats. These results indicate that a HP diet may be more effective than a balanced diet for improving glycemic control in overweight individuals.     

Morphological plasticity of white clover (Trifolium repens L.) in response to spatial and temporal resource heterogeneity

Heterogeneity in resource distribution has been an important selective force shaping morphological plasticity in plants. When resources are patchily distributed, changes in morphology are assumed to affect placement of the resource-acquiring structures (roots and leaves) such that they enhance the plant's capacity for resource uptake. Morphological development of four white clover (Trifolium repens) genets was studied in two glasshouse experiments. In the spatial experiment, two substrates (potting soil and sand) were used to create the following discrete patch combinations, sand-sand, soil-sand, sand-soil, and soil-soil. Stolons grew across each combination and consecutive ramets from a given stolon permitted rooting in each substrate pair. In the temporal experiment, the two ramets were first rooted in sand only. After a predetermined period, the sand was replaced and the same substrate combinations created as in the spatial experiment. In each experiment, total developmental time within a given substrate combination was held constant. All measurements were conducted on the second (i.e., younger) of the ramet pairs. In the spatial experiment, ramets rooted in soil had significantly greater branching frequencies than ramets rooted in the sand substrate, regardless of genotype or the preceding substrate type. Ramets occupying the sand-sand combination had the lowest branching frequencies but branch production for the ramet rooted in sand was higher if the preceding ramet was rooted in soil. The substrate occupied by a preceding ramet had no influence upon branching propensity if a ramet was rooted in soil. There were no significant differences in branching frequencies between the sand and soil substrates in the temporal experiment. The relationship between branching and substrate thus depended upon whether a ramet was exposed to a given substrate type during its early development. In both experiments, branched ramets in the soil-soil combinations had significantly greater shoot mass than corresponding ramets in the sand-sand combinations. Internode length was significantly shorter in the soil versus sand combinations of the spatial experiment but was unaffected by substrate in the temporal experiment. Leaf area and stolon width showed significant genotype2treatment interactions in both experiments but no consistent trends were evident; petiole length was unaffected by substrate.     

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

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.(ABSTRACT TRUNCATED AT 250 WORDS)