A 5-Week Guided Active Play Program Modulates Skin Microvascular Reactivity in Healthy Children

PURPOSE

Children's poor levels of physical activity (PA) participation and early-onset vascular aging are identified as global health challenges. Children's guided activity play (GAP)-based PA programs have emerged as effective strategies to improve cardiovascular risk factors and health-related fitness. This study proposes to investigate whether GAP improves children's cutaneous microvascular reactivity and health-related fitness.

METHODS

Children's (n = 18; 9.8 [1.5] y) PA during a 5-week (4 d/wk; 1 h/d) GAP program was assessed (accelerometry) with preassessments and postassessments for anthropometric, musculoskeletal fitness, blood pressure, estimated aerobic power, and cutaneous microvascular reactivity.

RESULTS

PA averaged 556 (132) kcal·week-1 at 34.7% (7.5%) time at moderate to vigorous intensity. Resting heart rate (-9.5%) and diastolic blood pressure (-7.8%) were reduced without changes in health-related fitness indices. Cutaneous microvascular reactivity to sodium nitroprusside iontophoresis increased the average perfusion (+36.8%), average cutaneous vascular conductance (+30%), the area under the curve (+28.8%), and a faster rise phase (+40%) of perfusion (quadratic modeling; P ≤ .05). Chi-square and crosstabulation analysis revealed significant association between children's PA levels and sodium nitroprusside average perfusion levels, where children with PA levels ≥205.1 kcal.55 minute-1 were overrepresented in the medium/high levels of sodium nitroprusside perfusion.

CONCLUSION

A 5-week GAP modified the microvascular reactivity in children without changes in body mass, musculoskeletal fitness, or estimated aerobic power.

Scientific meeting report: International Biochemistry of Exercise 2022

Exercise is one of the only nonpharmacological remedies known to counteract genetic and chronic diseases by enhancing health and improving life span. Although the many benefits of regular physical activity have been recognized for some time, the intricate and complex signaling systems triggered at the onset of exercise have only recently begun to be uncovered. Exercising muscles initiate a coordinated, multisystemic, metabolic rewiring, which is communicated to distant organs by various molecular mediators. The field of exercise research has been expanding beyond the musculoskeletal system, with interest from industry to provide realistic models and exercise mimetics that evoke a whole body rejuvenation response. The 18th International Biochemistry of Exercise conference took place in Toronto, Canada, from May 25 to May 28, 2022, with more than 400 attendees. Here, we provide an overview of the most cutting-edge exercise-related research presented by 66 speakers, focusing on new developments in topics ranging from molecular and cellular mechanisms of exercise adaptations to exercise therapy and management of disease and aging. We also describe how the manipulation of these signaling pathways can uncover therapeutic avenues for improving human health and quality of life.

Guided Active Play Promotes Physical Activity and Improves Fundamental Motor Skills for School-Aged Children

Reports show that children's physical activity (PA) levels are related to FMS proficiency; however, whether PA levels directly improve FMS is uncertain. This study investigated the responses of PA levels and FMS proficiency to active play (AP) and guided active play (GAP) interventions. Three community programs (seven-weeks; 4d·wk^-1) were randomly assigned to: i) active play (CON); ii) locomotor skills (LOC) guided active play (GAP); and iii) object control skills (OC) GAP groups. Children's (n = 52; 6.5 (0.9) yr) interventions included continuous and/or intermittent cooperative games focused on either locomotor skills (i.e. blob tag, red-light-green-light) or object control skills i.e., hot potato, racket balloons, 4-way soccer). PA levels (accelerometers) were assessed on 2 of 4 sessions per week throughout the program. The Test of Gross Motor Development-2 (TGMD-2) was used to assess FMS scores. The changes for CON and LOC interventions for locomotor standard scores were -0.83 (2.61) vs. 2.6 (2.64) (α = 0.022), for locomotor percentiles -9.08 (36.7) vs. 20.1 (30.4) (α = 0.033) and for gross motor quotient percentiles -4.3 (30.3) vs. 24.1 (29.6) (α = 0.022). Children's PA levels averaged 158.6 (6.6) kcal·55min^-1 for CON vs. 174.5 (28.3) kcal.55min^-1 for LOC (α = 0.089) and 170.0 (20.1) kcal·55min^-1 for OC (α = 0.144). Moderate-Vigorous PA was 18.4 (8.0) %, 47.9 (7.8) % (α = 0.000) and 51.9 (6.0) % (α = 0.000) for CON, LOC and OC, while time at sedentary/very light PA was 36.4 (9.8) %, 15.1 (4.9) % (α = 0.000) and 14.9 (15.9) %Sed/VL (α = 0.001) during the 7-week program. The OC intervention showed more upper body movement experiences compared to the LOC program (p = 0.020). A guided active play program using LOC cooperative games showed increases in energy expenditure and %MVPA and improved FMS proficiency, but active play did not. For school-aged children (5-7 yr) guided active play using cooperative games may be an effective strategy to improve FMS and promote health and fitness benefits.

Children and adolescent physical activity participation and enjoyment during active play

BACKGROUND

Girls' (9-19 years) participation in physical activity (PA) is known to decrease at a faster rate than boys. A reduction in PA attractiveness (enjoyment) and lower psychosocial profile of girls approaching biological maturity may underlie the decreasing rate of PA participation. Since engaging children in active play programs improves health related quality of life indictors and enjoyment levels; the purposes of this study were to: 1) assess psychosocial status and PA attractiveness/enjoyment of boys and girls to an eight-week active play program; and 2) investigate the relationships among PA participation, psychosocial status and PA attractiveness with both age and maturity status for boys and girls following an active play PA program.

METHODS

Thirty-three children (age 9.8±1.3 years; weight 43.1±13.4 kg; BMI 20.8±3.2 kg/m2) were recruited to participate in an active play program for 8 weeks (4x/week; 1hr/d). M-S estimates ranged from -6.7 to -2.5 years away from biological maturity Daily program PA was assessed and compared to pre-post measures of psychosocial functioning and PA attractiveness. Statistical procedures were performed using ANOVA and/or Pearson's correlation r (SPSS v. 22.0) with P=0.05.

RESULTS

PA participation in the active play program showed a group average of 39±11% time spent in moderate-vigorous PA (%MVPA) with boys averaging 45% MVPA and girls averaging 30% MVPA (P<0.05). PA attractiveness scores for boys did not change following the program; whereas girls improved from 67±13% to 76±9% (P<0.05). Minimal changes were noted for the health-related quality of life measures as a result of the PA program. Comparing PA attractiveness to %MVPA, 80% of girls reporting positive changes or no change; in contrast 56% of boys responded with negative/less PA attractiveness. PA attractiveness for all children was negatively associated with age (r=-0.19) and/or M-S (r=-0.29). The relationships, however, were gender specific with boys exhibiting a coefficient of -0.28 (age) and -0.61 (M-S) (P<0.05). For girls, increased PA attractiveness promoted less decline in %MVPA for M-S (r=0.18) compared to age (r=-0.17).

CONCLUSIONS

For girls, approaching biological maturity, PA enjoyment/attractiveness can be positively influenced with an active play program, which is a major consideration promoting PA participation in girls but not boys.

Characteristics of children's physical activity during active play

BACKGROUND

Emerging evidence suggests that oxygen consumption (VO2) for self-paced physical activity (PA) is underestimated when applying laboratory-based treadmill (TM)-derived regression equations. This study examines the accelerometer (ACC) characteristics for paced TM PA and self-paced children's PA to ascertain if the predictable regulated patterns of paced PA are implicated in the inferior estimates of VO2.

METHODS

Children's (9.3±1.2 years) (N.=21) VO2 (portable oxygen analyzer) and PA (accelerometry) were measured for paced treadmill PA (4-10 km/h). Active playing of children's games in a camp setting was used for self-paced PA. Treadmill and self-paced PA were compared by linear regression and Bland-Altman analysis. Relative contribution of each axes (% axis difference) for paced and self-paced PA were assessed (N.=21).

RESULTS

The VO2 responses during paced treadmill exercise was linear with ACC quantified PA (for vertical axis r=0.95±0.03 and for vector magnitude [VM] r=0.95±0.05, P>0.05). During self-paced PA, the VO2 responses for ACC quantified PA were not linear (for vertical axis r=0.20±0.11 and for VM r=0.25±0.09) over the same range of ACC PA (0-1500 counts/10 s). VO2 estimates for self-paced PA (using TM-derived equations) were underestimated (P<0.05) across the range of intensities, which increased as the intensity of PA increased (>6 METs). Comparing paced versus self-paced PA the % axis dominance (i.e., difference between the highest and lowest axis) contribution to PA was 41±14% for paced and 3±2% for self-paced PA (P<0.05).

CONCLUSIONS

This study reveals that the inferior estimates of VO2 for self-paced PA (using-derived linear equations) is attributable to the presence of a dominant axis with paced TM PA, which inflates the calculation of VM and the predicted VO2 for self-paced PA where no % axis difference exists.

Cardiorespiratory and metabolic responses associated with children’s physical activity during self-paced games

The aim of this study was to explore the possibility of identifying clusters of children’s games based on estimated energy expenditures and (or) intensity when performed in a guided active play format. The study also investigated whether the identified active play game clusters were repeatable when the games were performed on different days. Children (9.7 ± 1.1 years; n = 12) were assessed for oxygen consumption, heart rate, energy expenditure (EE), and metabolic equivalent (MET) on a treadmill (at 4, 6, and 8 km·h–1(0% grade)). HR and ActiGraph GT1M accelerometer (ACC) generated linear regression equations were used to estimate EE. The ACC (3 s epochs) were used for estimating METs in assigning percent time at medium–vigorous physical activity (%MVPA) of 10 self-paced games. The results showed a consistent range of EEs (ACC-equation) from 13.57 kcal·(5 min)–1to 25.00 kcal·(5 min)–1(p < 0.05); EEs (HR-equation) from 29.72 to 42.49 kcal·(5 min)–1(p < 0.05); and %MVPA from 10% to 34% (p < 0.05) (from ACC equations) across all games. These were reproducible from day to day (p > 0.05). This study confirms the existence of active play children’s game clusters that might be useful in formatting guided active play in a dose–response manner for children.

Calpain/calpastatin activities and substrate depletion patterns during hindlimb unweighting and reweighting in skeletal muscle

Unloading of skeletal muscle by hindlimb unweighting (HU) is characterized by atrophy, protein loss, and an elevation in intracellular Ca(2+) levels that may be sufficient to activate Ca(2+)-dependent proteases (calpains). In this study, we investigated the time course of calpain activation and the depletion pattern of a specific structural protein (desmin) with unloading and subsequent reweighting. Rats underwent 12 h, 24 h, 72 h or 9 days of HU, followed by reweighting for either 0, 12 or 24 h. Total calpain-like activity was elevated with HU in skeletal muscle (P < 0.05) and was further enhanced with reweighting (P < 0.05). The increases in calpain-like activity were associated with a proportional increase in activity of the particulate fraction (P < 0.05). Activity of the mu-calpain isoform was elevated with 12 and 24 h of HU (P < 0.05) and returned to control levels thereafter. With reweighting, activities of mu-calpain were elevated above control levels for all HU groups except 9 days (P < 0.05). In contrast, minimal changes in m-calpain and calpastatin activity were observed with HU and reweighting. Although desmin depletion levels did not reach statistical significance, a significant inverse relationship was found between the mu-calpain/calpastatin ratio and the amount of desmin in isolated myofibrils (R = -0.83, P < 0.001). The results suggest that calpain activation is an early event during unloading in skeletal muscle, and that the majority of the increase in calpain activity can be attributed to the micro-isoform.

Early activation and redistribution of calpain activity in skeletal muscle during hindlimb unweighting and reweighting

The aims of this study were the following: (i) to determine whether activation of the Ca2+-activated protease, calpain, is an early event during hindlimb unweighting (HU) in skeletal muscle; and (ii) to assess whether calpain activity is greater during reweighting compared with HU alone. Rats were exposed to 12, 24, and 72 h, or 9 d of HU, followed by reweighting for 0, 12, or 24 h. Calpain activities were assayed for total, soluble, and particulate fractions. Total calpain activity was increased in the soleus at all HU time points, whereas activities were elevated in the gastrocnemius only after 9 d of HU. With reweighting, calpain activity remained elevated at all time points for both muscles. In general, reweighting the gastrocnemius increased its calpain activity more than during HU only, whereas reweighting the soleus did not produce additional increases in its calpain activity. The increases in calpain activity were associated with a proportional increase in activity of the particulate (membrane- and protein-associated) fraction. The results suggest that calpain activation is an early event during HU in the soleus, and that the increases in calpain activity in both muscles are associated with a redistribution of activity from cytosolic to particulate fractions.

Differential effect of oestrogen on post-exercise cardiac muscle myeloperoxidase and calpain activities in female rats

The effects of oestrogen administration on 1 h post-exercise cardiac muscle myeloperoxidase (MPO) and calpain activities were determined in female rats. Rats were ovariectomized and implanted for 2 weeks with either oestrogen (25 mg 17-oestradiol) or placebo pellets or left with ovaries intact. Rats were then run for 1 h at 21 m min-1, 12% grade, killed 1 h post-exercise and cardiac muscle and blood samples were removed. Control animals from each group were killed without prior exercise. Serum oestrogen levels in the order of the highest to lowest were; ovariectomized oestrogen replaced rats > intact ovaries rats > ovariectomized placebo rats. Oestrogen induced significant (P < 0.05) elevations in cardiac MPO activity at rest and at 1 h post-exercise in ovariectomized rats. No significant elevations in cardiac MPO activity were evident in placebo ovariectomized or normal ovary rats at rest or post-exercise. Cardiac calpain activities were similar in all unexercised groups. Ovariectomized placebo and intact ovary rats had significantly (P < 0.05) elevated cardiac calpain activities 1 h post-exercise while calpain activity was not significantly elevated in hearts from ovariectomized oestrogen rats. These results demonstrate that oestrogen supplementation in ovariectomized rats induces elevations in cardiac muscle MPO activities at rest and at 1 h post-exercise. This is opposite to the effect of oestrogen in post-exercise skeletal muscle and implies a greater neutrophil infiltration into cardiac muscle caused by oestrogen. This effect cannot be explained by changes in 1 h post-exercise cardiac muscle calpain activity, the elevation of which was suppressed by oestrogen administration. Oestrogen influences cardiac calpain activity similarly to its effect in skeletal muscle. Thus, oestrogen administration to ovariectomized rats induces elevations in cardiac MPO activity while suppressing cardiac calpain activity.

Metabolic responses to prolonged work during treadmill and water immersion running

The primary aim of this study was to compare the physiological responses to prolonged treadmill (TM) and water immersion to the neck (WI) running at threshold intensity. Ten endurance runners performed TM and WI running VO2max tests. Subjects completed submaximal performance tests at ventilatory threshold (Tvent) intensities under TM and WI conditions and responses at 15 and 42 minutes examined. VO2 was lower in WI (p<0.05) at maximal effort and Tvent. The Tvent VO2 intensities interpolated from the TM and WI VO2max tests were performed in both TM (i.e., TM@TM(tvent),TM@WI(tvent), corresponding to 77.6 and 71.3% respectively of TM VO2max) and WI conditions (i.e., WI@TM(tvent), WI@WI(tvent), corresponding to 85.5% and 78.2% respectively of WI VO2max). Each of the dependent variables was analyzed using a 3-way repeated measures ANOVA (2 conditions X 2 exercise intensities X 7 time points during exercise). VO2max values were significantly lower in the WI (52.4(5.1) ml.kg(-1) min(-1)) versus TM (59.7(6.5) ml.kg(-1) min(-1)) condition. VO2 during submaximal tests were similar during the TM and WI conditions. HR and [BLa] responses to exercise at and above WI(tvent) were similar during short-term exercise, but values tended to be lower during prolonged exercise in the WI condition. There were no statistical differences in VE responses in the 2 conditions, however as with HR and [BLa] an upward trend was noted with TM exercise over the 42 minute duration of the tests. RPE at WI(tvent) was similar for TM and WI exercise sessions, however, RPE at TM(tvent) was higher during WI compared to TM running. Cardiovascular drift was observed during prolonged TM but not WI running. Results suggest differences in metabolic responses to prolonged submaximal exercise in WI, however it can be used effectively for cross training.

Time course of diaphragm injury and calpain activity during resistive loading

The purpose of this study was to determine the time course of arterial blood gas (ABG) deterioration, increased calpain activity, and diaphragm injury during 4 d of resistive loading. Adult Sprague- Dawley rats were divided into control (C) animals and groups that were tracheally banded (TB) for 1 d (TB1), 2 d (TB2), 3 d (TB3), and 4 d (TB4). In TB rats, the carotid artery was cannulated and the trachea was banded during anesthesia. TB groups (TB1, TB2, TB3, and TB4) had a 67% smaller internal cross-sectional area of the trachea than did C animals. ABG samples from awake rats showed a decreased arterial oxygen tension (Pa(O(2))) and a respiratory acidosis in the TB1, TB2, and TB3 groups. Calpain activity was higher in the diaphragm of TB than of C rats; calpainlike activities in soluble fractions of diaphragm tissue were greater in all TB groups than in C rats, whereas those in bound fractions were greater in the TB2 and TB3 groups. Point counting of hematoxylin and eosin-stained cross-sections showed that the area fraction (A(A)) of normal diaphragm was lower and the A(A) of abnormal muscle and connective tissue was higher in TB3 than in C rats. Increased resistive loading induced by tracheal banding was associated with hypercapnic ventilatory failure, increased calpain activity, and diaphragm injury. Ventilatory failure in response to resistive loading may be due to diaphragm injury and/or to decreased minute ventilation.

Chronic resistive loading induces diaphragm injury and ventilatory failure in the hamster

The purpose of this study was to examine the effects of tracheal banding for 30 days on arterial blood gases, and diaphragm structure and function. Hamsters were tracheal banded (TB) or underwent a sham procedure (C) (n = 16 and 18, respectively). After 30 days, arterial blood gases from awake TB hamsters showed hypoxemia and a respiratory acidosis. Histochemical analysis of diaphragm cross-sections showed a five-fold greater area fraction of abnormal muscle; a greater variation in fiber size; and a 3% higher proportion of type 1 fibers in TB than C hamsters. In vitro physiologic studies of costal strips from TB hamsters showed lower stress (45-70% over 10-100 Hz) than C values. Maximal esophageal pressure during occlusion was 45% higher and normalized diaphragm mass was 10% higher in TB hamsters than C hamsters. We conclude that the lower stress in vitro was attributable, at least in part, to diaphragm injury. Hypercapnea was present in spite of the higher diaphragm mass and maximal esophageal pressures in banded hamsters.

Exercise promotes a subcellular redistribution of calcium-stimulated protease activity in striated muscle

The aims of this study were (i) to investigate whether the contractile activity associated with running increases calcium-stimulated, calpastatin-inhibited protease activity (calpain-like) in a time-dependent manner and (ii) to determine whether the changes, if any, are proportionately distributed between soluble (cytosolic) and particulate (bound) fractions of striated muscle in vivo. Calcium-dependent, calpastatin-inhibited caseinolysis (i.e., calpain-like activity) was measured in control and exercised rats (25 m/min, 0% grade) at 2, 5, 15, 30, and 60 min. Total calpain-like activity in skeletal muscle increased by 26% (13.2 +/- 1.3 vs. 17.9 +/- 2.2 U/g wet wt.) (p < 0.05) after running (60 min), accompanied by an increased activity in the particulate fraction. In cardiac muscle, exercise (60 min) increased total calpain-like activity by 33% (p < 0.05), which was attributable to increases in both the cytosolic and particulate fractions. Both tissues responded with an early (2-5 min) activation of total calpain-like activity (p < 0.05), supported by early increases for particulate fractions from skeletal muscle; whereas for cardiac muscle, a noticeable early drop (p < 0.05) occurred in the particulate fraction. Minimal changes were observed for total, cytosolic, and particulate fractions of noncontracting tissue (i.e., liver). The results of this study support the hypothesis that the total calpain-like activity increases associated with level running occur early on with exercise and that the increases are accompanied by changes in the redistribution of soluble to particulate fractions. The changes would set the stage for enhanced rates of protein degradation known to occur in striated muscle with exercise.

Exercise promotes a subcellular redistribution of calcium-stimulated protease activity in striated muscle

The aims of this study were (i) to investigate whether the contractile activity associated with running increases calcium-stimulated, calpastatin-inhibited protease activity (calpain-like) in a time-dependent manner and (ii) to determine whether the changes, if any, are proportionately distributed between soluble (cytosolic) and particulate (bound) fractions of striated muscle in vivo. Calcium-dependent, calpastatin-inhibited caseinolysis (i.e., calpain-like activity) was measured in control and exercised rats (25 m/min, 0% grade) at 2, 5, 15, 30, and 60 min. Total calpain-like activity in skeletal muscle increased by 26% (13.2 ± 1.3 vs. 17.9 ± 2.2 U/g wet wt.) (p < 0.05) after running (60 min), accompanied by an increased activity in the particulate fraction. In cardiac muscle, exercise (60 min) increased total calpain-like activity by 33% (p < 0.05), which was attributable to increases in both the cytosolic and particulate fractions. Both tissues responded with an early (2-5 min) activation of total calpain-like activity (p < 0.05), supported by early increases for particulate fractions from skeletal muscle; whereas for cardiac muscle, a noticeable early drop (p < 0.05) occurred in the particulate fraction. Minimal changes were observed for total, cytosolic, and particulate fractions of noncontracting tissue (i.e., liver). The results of this study support the hypothesis that the total calpain-like activity increases associated with level running occur early on with exercise and that the increases are accompanied by changes in the redistribution of soluble to particulate fractions. The changes would set the stage for enhanced rates of protein degradation known to occur in striated muscle with exercise.Key words: nonlysosomal proteases, calcium-dependent proteolysis, muscle damage.

Effect of energy restriction on muscle function and calcium stimulated protease activity in recreationally active women

The purpose of this study was to investigate whether changes in substrate oxidation that are caused by energy restriction influenced muscle function and skeletal muscle calcium stimulated protease activity in female athletes. Endurance athletes were randomly assigned to maintenance energy (100% kcal) or energy restricted (75% kcal) diet treatment groups for 14 days while maintaining regular activity. Body weight significantly decreased in the 75% diet group (-1.7 +/- 0.3 kg; p < .05), while fat oxidation increased (p < .05). Minimal changes in quadriceps function (assessed using the Kin/Com isokinetic dynamometer) were observed following diet treatment, except selected loss of muscle function in the 75% diet group at a movement velocity of 120 deg/s. These results suggest that increased fat oxidation that is induced by an acute energy restriction does not promote loss of general muscle function and activation of calcium-sensitive muscle proteases.

Striated muscle calcium-stimulated cysteine protease (calpain-like) activity promotes myeloperoxidase activity with exercise

An inflammatory response triggered by neutrophil accumulation into muscle tissue is thought to occur with exercise-induced muscle damage. To investigate the relationship between Ca2+-stimulated proteolysis (calpain-like activity) and neutrophil accumulation [myeloperoxidase (MPO) activity], cardiac and plantaris muscles from rats (n = 10) completing 1 h exercise (25 m/min) were investigated. Exercise promoted increases (P<0.05) in both calpain-like and MPO activities; ranging from 2.79 to 58.9 U/g wet weight (ww) and 0.03 to 4.88 U/g ww respectively. Pearson's correlational analysis (r) on calpain-like and MPO activities for cardiac and plantaris muscle data were 0.97 (P<0.001) and 0.68 (P<0.05) respectively, with a combined r of 0.83 (P<0.001) for both muscles across all conditions. To investigate further the extent to which calpain-like activity may promote neutrophil accumulation, another exercise group (n = 5) was pre-injected with the cysteine protease inhibitor, E64c, 1 h before exercise. Administration of E64c lowered calpain-like and MPO activities by 66% and 56% respectively (average from both muscles). From these results it is concluded that a relationship exists between Ca2+-stimulated proteolysis and neutrophil accumulation into striated muscle with exercise, and that the calpain system is involved in localizing the neutrophilic response with exercise.

The effect of diazepan and exercise training on selected biochemical and histochemical properties of rat skeletal muscle

The effects of chronic diazepam (D) treatment and exercise training on total body mass (TBM), microsomal protein yield (MPY), calcium uptake by fragmented sarcoplasmic reticulum (SR), muscle fibre cross-sectional area, and both PFK and SDH activities were investigated in the tibialis anterior (TA), soleus (Sol), and plantaris (Plt) muscles of 50 male albino Sprague-Dawley rats. Rats were assigned randomly to control (C), sprint-trained (S), or endurance-trained (E) groups. Training was of 12 weeks duration. One-half of each group received daily intraperitoneally D doses of 5 mg kg-1 of TBM. Exercise reduced TBM (p < 0.05); increased the relative BM of the TA (E = 2.02 +/- 0.02, p < 0.01) and Plt (E = 1.15 +/- 0.02, p < 0.01; S = 1.13 +/- 0.03, p < 0.01), as well as the Ca++ uptake of the Sol SR (C = 0.08 +/- 0.02, E = 0.16 +/- 01, p < 0.05). MPY was elevated in S-Sol (C = 1.12 +/- 0.6, S = 1.52 +/- 0.1, p < 0.01). D elevated Sol MPY as well as TA PFK. S-trained animals had lower mean fibre areas than the E-trained (D-treated and untreated) animals. The elevated relative masses of TA and Plt are explained by a decreased TBM with exercise. The increased Ca++ uptake of the Sol indicates that E enhances this function, and the increased MPY probably implies an increased SR. The D could be responsible for the D-elevated Sol MPY as well as the TA PFK. El D did not reduce neuromuscular activity to a level adversely affecting oxidative enzyme activity, but in the case of PFK activity in the TA muscle, such a reduction was evident.

Exercise-induced muscle injury: a calpain hypothesis

It is well established that periods of increased contractile activity result in significant changes in muscle structure and function. Such morphological changes as sarcomeric Z-line disruption and sarcoplasmic reticulum vacuolization are characteristic of exercise-induced muscle injury. While the precise mechanism(s) underlying the perturbations to muscle following exercise remains to be elucidated, it is clear that disturbances in Ca2+ homeostasis and changes in the rate of protein degradation occur. The resulting elevation in intracellular [Ca2+] activates the non-lysosomal cysteine protease, calpain. Because calpain cleaves a variety of protein substrates including cytoskeletal and myofibrillar proteins, calpain-mediated degradation is thought to contribute to the changes in muscle structure and function that occur immediately following exercise. In addition, calpain activation may trigger the adaptation response to muscle injury. The purpose of this paper is to: (i) review the chemistry of the calpain-calpastatin system; (ii) provide evidence for the involvement of the non-lysosomal, calcium-activated neutral protease (calpain) in the response of skeletal muscle protein breakdown to exercise (calpain hypothesis); and (iii) describe the possible involvement of calpain in the inflammatory and regeneration response to exercise.

A calcium stimulated cysteine protease involved in isoproterenol induced cardiac hypertrophy

The purpose of this study was to test the relationship between biochemical and functional changes accompanying beta-agonist induced cardiac hypertrophy and the activation of a calcium stimulated cysteine protease. Because the ultrastructural and ionic changes accompanying beta-agonist induced cardiac hypertrophy are reminiscent of the actions of the calcium activated neutral protease, calpain, it was hypothesized that lowering calpain activity (by the use of an exogenous inhibitor(s)) would reduce the extent of hypertrophy. Rats (275-300 g) were randomly assigned to either a control, beta-agonist (iso) or cysteine protease inhibitor (E64c) group. Isoproterenol administration (1 mg/kg) resulted in changes for ventricular weight to body weight ratio (increases 19%), ventricular [RNA] (increases 105.6%), rate of pressure development (increases 22% for +dP/dt) and maximum developed left ventricular pressure (increases 19%) (p < 0.05) after 3 days. Calpain-like activity (assessed by microplate method) increased by 45% (p < 0.05), while [cAMP] returned to control levels (following a transient rise at 1 day; 606.03 +/- 124.1 pmol/g/wet/wt to 937.9 +/- 225 (p < 0.05)). E64c (administered 1 h prior to iso) reduced the extent of hypertrophy, from 19 to 12%, and prevented the increases in; total [RNA], left ventricular function, the initial [cAMP] increase and calpain-like activity. It is concluded that a calcium stimulated cysteine protease(s), such as calpain, may be involved in the biochemical and functional changes associated with isoproterenol induced cardiac hypertrophy.

Role of calcium-activated neutral protease (calpain) with diet and exercise

Although the proteolytic events accompanying acute and chronic perturbations in striated muscle protein turnover remain to be fully elucidated, the purpose of this paper is to (a) review the chemistry of the nonlysosomal calpain-calpastatin system, and (b) provide evidence for the involvement of a nonlysosomal, calcium-activated neutral protease (calpain) in the response of skeletal muscle protein breakdown to altered nutritional status (diet composition; energy restriction) and increased periods of contractile activity (exercise). In reviewing the literature, it is apparent that calpain is involved in the protein catabolism which accompanies alterations in diet composition and/or energy restriction. The precise mechanism of calpain action remains to be elucidated; however, the role of altered metabolic status contributing to calcium imbalances is discussed relative to increasing protein degradation. Hypotheses for further investigation are provided in regard to identifying the targeting of selected proteins (and organelles) for degradation by calpain.

Heart, liver, and skeletal muscle myeloperoxidase activity during exercise

The purpose of this study was to determine whether contractile activity associated with running exercise was a prerequisite for neutrophil infiltration into rat tissues. H2O2-dependent myeloperoxidase (MPO) activity for rat (n = 8) liver, heart, and gastrocnemius muscles was assayed after 58 +/- 11 min of running to voluntary exhaustion (25 m/min; 0% grade). MPO activity values measured with 0.6 mM H2O2 were 0.988 +/- 0.331 (SD) U/g (skeletal muscle), 1.563 +/- 0.303 U/g (heart), and 1.652 +/- 0.510 U/g (liver) for control samples, compared with 1.690 +/- 0.321, 3.128 +/- 1.221, and 2.752 +/- 0.437 U/g, respectively, for the exercise group (P < or = 0.05). Kinetic analysis revealed that maximum velocity for all tissues increased as a result of the exercise (P < 0.05). The Michaelis constant (Km) values at rest for all tissues were similar (range 0.53-0.57 mM H2O2; P > or = 0.05). Exercise did not alter the Km values for cardiac and liver samples; however, for skeletal muscle, the Km was 28% lower than control (P < or = 0.05). The results of this study show that, with prolonged running, MPO activity is elevated in most rat tissues and not exclusively in skeletal muscle. Moreover, the metabolic status of the tissues may be an important factor for neutrophil infiltration with exercise and not exclusively the type of muscle contraction, as previously hypothesized.

Creatine Phosphokinase:in VitroActivity Modification And Proteolysis with Calpain

Abstract:

Disturbances in the CPK system are usually observed during conditions when the intracellular calcium activated neutral protease (CANP) is active. To determine if CPK could be a substrate for calpain in vitro; purified CPK, (MM isoform) activity was measured after incubation with increasing amounts of calpain. CPK activity was initially increased then progressively lost. These activity changes paralleled increasing degrees of limited proteolysis of MM-CPK which produced two large fragments of approximately 38 and 35 kilodaltons

Calcium-supported calpain degradation rates for cardiac myofibrils in diabetes. Sulfhydryl and hydrophobic interactions

OBJECTIVE

The purpose was to investigate the calcium required for calpain-mediated degradation of selected cardiac myofibril proteins modified by diabetes, sulfhydryl (SH) and hydrophobic reagents.

METHODS

After 20 weeks of streptozotocin-induced (55 mg.kg-1) diabetes, calcium sensitive calpain (1.5 U.ml-1) degradation rates of purified cardiac myofibrillar proteins (1 mg.ml-1) were measured, in vitro, and compared to degradation rates for N-ethylmaleimide (NEM) and 2-p-toluidinylnapthalene-6-sulfonate (TNS) treated samples.

RESULTS

Diabetes (blood glucose of 550 +/- 32 mg.dl-1) reduced the yield of purified myofibrillar protein with minimal change in fibril protein composition. Total SH group reactivities (nmol.mg-1.30min) were 220 +/- 21, 163 +/- 17 and 156 +/- 24 for control, diabetic and NEM-treated (0.5 mM) myofibrils (p < or = 0.05). Calpain degradation rates were faster for all diabetic and SH modified myofibrillar proteins (p < or = 0.05), with a 45 and 35% reduction in the pCa50 for a 37 kDa protein of diabetic and NEM-treated fibril complexes. For control myofibrils, both 100 and 200 uM TNS, reduced calpain degradation rates to a similar extent for all substrate proteins. In contrast, diabetic and NEM-treated samples showed a further reduction in calpain degradation rates with increasing TNS from 100 to 200 uM.

CONCLUSION

Our results support the hypothesis that in diabetes the calcium requirements for calpain degradation rates are reduced and dependent upon sulfhydryl group status and Ca(2+)-induced hydrophobic interactions, implicating a 37 kDa myofbillar-complexed protein.

Diaphragm injury and myofibrillar structure induced by resistive loading

The purpose of this study was to determine whether ventilatory failure is associated with muscle fiber damage and myofibrillar protein alterations. Ventilatory failure was induced by tightening a polyvinyl band around the trachea of hamsters (TB; n = 14) for 6 days, which resulted in severe respiratory acidosis (PCO2: 97.9 +/- 29.6 vs. 51.6 +/- 19.6 Torr; pH: 7.16 vs. 7.35), hypoxemia (PO2: 42.8 +/- 16.8 vs. 65.9 +/- 25.8 Torr), and increased pulmonary resistance (1.89 +/- 1.61 vs. 0.29 +/- 0.27 cmH2O.ml-1 x min; P < 0.05). The point-counting technique of hematoxylin- and eosin-stained cross sections showed a higher area fraction of abnormal muscle and inflammatory cells in the costal [0.133 +/- (SE) 0.33 vs. 0.040 +/- 0.010] and crural regions (0.069 +/- 0.020 vs. 0.012 +/- 0.003) of the diaphragm in TB hamsters than in control hamsters. Electron micrographs revealed sarcomeric disruption and Z band streaming in the diaphragm of TB hamsters. Myofibrillar changes of the diaphragm associated with ventilatory failure were quantitative (i.e., a lower yield of purified myofibrils) but not qualitative (similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles); however, sulfhydryl group reactivities were reduced (P < 0.05). Proteolysis of purified myofibrils from the diaphragm digested with calpain showed faster degradation rates for tropomyosin and alpha-actinin but not for all proteins for the TB animals. Ventilatory failure induced by resistive loading was associated with diaphragm injury; some of this injury was linked to changes in myofibrillar complexes, specifically their susceptibility to calpain-mediated degradation.

Circadian rhythm of glycogen in the hamster diaphragm

The purpose of this study was to determine the diurnal fluctuation of glycogen stores for the whole hemidiaphragm and within a specific myofibrillar ATPase (M-ATPase) fibre type and diaphragmatic region. Fifty-six golden Syrian hamsters were randomly divided into six groups according to the time of sampling biopsies from the diaphragm: 03:00, 07:00, 11:00, 15:00, 19:00, and 23:00. The right hemidiaphragm was quick frozen and biochemically assayed for glycogen levels. Biopsies from the left hemidiaphragm of the same animal were cut from the anterior costal and crural regions, and stained with periodic acid--Schiff (PAS) and for M-ATPase. Optical density measures of PAS-stained fibres were determined to quantitate glycogen in different M-ATPase fibre types and diaphragmatic regions. Biochemical assay of the entire hemidiaphragm showed slightly greater glycogen content of biopsies taken at 11:00 and 15:00 than at 03:00, 19:00, and 23:00 (range of differences: 6.4-10.0%). However, glycogen levels within a specific M-ATPase fibre type and diaphragm region were not different in biopsies sampled at different times. Because the hamster has a small diurnal variation of glycogen in the diaphragm, which is similar to the small diurnal variation of glycogen in human skeletal muscle, this species may be a good animal model for metabolic studies of the diaphragm that could be affected by diurnal glycogen variability.

Function of skeletal muscle sarcoplasmic reticulum vesicles with exercise

In this study the response of sarcoplasmic reticulum (SR) to prolonged moderate-intensity exercise was examined in highly purified native vesicles isolated from rat gastrocnemius muscle. Maximal Ca(2+)-dependent ATP hydrolysis was reduced by 12.6% within 2 min after the onset of exercise. The reduction in Ca(2+)-dependent adenosinetriphosphatase activity progressed to 18% at 30 min of exercise and was maintained throughout the subsequent 90-100 min of exercise. Oxalate stimulation of unidirectional Ca2+ transport (Ca2+ loading) was unaffected by exercise. However, in the absence of anion stimulation, steady-state Ca2+ uptake (bidirectional flux) was 51.2 +/- 7.3 nmol Ca2+/mg SR after exercise compared with 36.2 +/- 2.5 nmol Ca2+/mg SR for the control period (P < 0.05). Anion-induced Ca2+ release increased from a control value of 33.9 +/- 4.3 to 55.9 +/- 9.8 nmol Ca2+/mg SR after exercise (P < 0.05). The mechanistic basis for the increase in apparent Ca(2+)-ATP coupling is unclear, although the early onset of the changes suggests the potential for functional adaptation for the SR in response to increased contractile activity.

Skeletal muscle calcium-activated neutral protease (calpain) with exercise

The purpose of this study was to investigate whether exercise could induce calpain activation by altering the Ca2+ required for half-maximal activity (pCa50) and/or susceptibility of digestible muscle protein substrates. Rats (225 g) were assigned to control, exercise (25 m/min, 0% grade), and 24-h recovery groups. Exercise resulted in a generalized 48 +/- 18% loss of muscle glycogen and a twofold increase in plasma creatine kinase levels (P < or = 0.05). Exercise increased total caseinolysis of diethylaminoethyl Sepharose-prepared low (u) and high (m) Ca2+ calpain isoforms by 22 and 30%, respectively (P < or = 0.05). The pCa50 of u- and m-calpain with exercise increased from 5.98 +/- 0.12 to 6.20 +/- 0.15 (P > or = 0.05) and from 3.63 +/- 0.10 to 3.90 +/- 0.16 (P > or = 0.05), respectively. In vitro, calpain-mediated degradation/disappearance rates (i.e., percentage of protein degraded in 10 min) for control tropomyosin and alpha-actinin were 69 and 30% compared with 92 and 61% after exercise (P < or = 0.05). The results of this study confirm that level running increases total nonlysosomal Ca2+ specific protease activity, which may promote exercise-induced muscle damage or fatigue.

Calcium-activated neutral protease effects upon skeletal muscle sarcoplasmic reticulum protein structure and calcium release

In this study, the effects of Ca(2+)-activated neutral protease (CANP) upon skeletal muscle heavy sarcoplasmic reticulum (HSR) structure and function were investigated. CANP was immunolocalized to the 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid detergent-insoluble fraction of purified HSR membranes. Ca2+ activation of the endogenous membrane-bound CANP produced a characteristic partial fragmentation of the HSR 565-kDa Ca2+ release channel. Similarly, the major substrate for both micromolar and millimolar Ca(2+)-sensitive isoforms of exogenous CANP was the Ca2+ release channel with proteolysis of a 88-kDa HSR protein also observed. Ca2+ release channel proteolysis was initiated at a single cleavage site with coincidental production of 410- and 150-kDa peptide fragments. Appearance of 160- and 137-kDa limiting peptides accompanied secondary proteolysis of the primary 410- and 150-kDa fragments, respectively. Despite extensive proteolysis of the Ca2+ release channel, CANP did not dramatically alter the Ca2+ handling and ryanodine binding properties of HSR membranes. The association of CANP with isolated HSR membranes suggests that, in vivo, this protease may modify an additional property of the Ca2+ release channel. This may be related to the CANP-susceptible structural association of the Ca2+ release channel with dihydropyridine receptors at T-tubule/sarcoplasmic reticulum junctions.

Intraluminal Ca2+ dependence of Ca2+ and ryanodine-mediated regulation of skeletal muscle sarcoplasmic reticulum Ca2+ release

The action of ryanodine upon sarcoplasmic reticulum (SR) Ca2+ handling is controversial with evidence for both activation and inhibition of SR Ca2+ release. In this study, the role of the intraluminal SR Ca2+ load was probed as a potential regulator of ryanodine-mediated effects upon SR Ca2+ release. Through dual-wavelength spectroscopy of Ca2+:antipyrylazo III difference absorbance, the intraluminal Ca2+ dependence of ryanodine and Ca(2+)-induced Ca2+ release (CICR) from skeletal SR vesicles was examined. Ryanodine addition after initiation of Ca2+ uptake (a) increased the intraluminal Ca2+ sensitivity of CICR and (b) stimulated spontaneous Ca2+ release with a delayed onset. These ryanodine effects were inversely proportional to the intraluminal Ca2+ load. Ryanodine also inhibited subsequent CICR after reaccumulation of Ca2+ released from the initial CICR. These results provide evidence that ryanodine inhibits transitions between low and high affinity Ca2+ binding states of an intraluminal Ca2+ compartment, possibly calsequestrin. Conformational transitions of calsequestrin may be reciprocally coupled to transitions between open and closed states of the Ca2+ release channel.

Effect of manipulation of plasma lactate on integrated EMG during cycling

This investigation was undertaken to record electromyographic activity of the vastus lateralis muscle during incremental cycling exercise and to determine whether it would be sensitive to altered dynamics of plasma lactate increases seen with intense exercise. Trained cyclists (N = 6) performed two progressive, stepwise exercise tests (23.5 W.min-1) to fatigue on a cycle ergometer at 90 rpm. One of the exercise tests was preceded by arm ergometer exercise in an attempt to elevate the circulating plasma lactate levels prior to starting the criterion exercise test. The starting mean plasma lactate values were 4.59 and 26.69 mmol lactate.-1 for the two exercise sessions. Cardiorespiratory values did not differ significantly between exercise sessions completed in the absence and presence of increased circulating plasma lactate. The no-arm trial (i.e., nonelevated plasma lactate condition) was associated with a plasma lactate inflection point (Tlac) at 72.6% VO2max. Previous arm exercise elevated the lactate such that during the criterion exercise plasma lactate values were decreasing with increasing power output at lower exercise intensities. As exercise intensity increased lactate values also increased beginning at a power output of about 76% VO2 max. Mean per cycle integrated EMG (CIEMG) increased linearly with increased power output in both exercise sessions. The slopes of the EMG-power output curve were not significantly different (P less than 0.05). There were no inflection points in these curves. The absence of an inflection point show that surface EMG does not provide an indication of Tlac.

Regulation of ATP-stimulated releasable myofilaments from cardiac and skeletal muscle myofibrils

The mechanism underlying the formation of easily releasable myofilaments, from myofibrils treated with an ATP-containing relaxing solution, was examined in this investigation. The proportion of releasable myofilaments purified from myofibrils of cardiac, fast- and slow-twitch muscles increased as the [ATP] was raised from 0 to 8.5 mM. The protein composition of the easily releasable myofilaments did not differ with increasing ATP concentrations as observed by 5-15% linear gradient SDS-PAGE. There is a nucleotide specificity to the release of myofilaments in the order of ATP greater than GTP much greater than UTP greater than CTP. Experiments with AMP-PNP and inorganic phosphate (Pi) showed that ATP hydrolysis and the build up of Pi are not requirements in the formation of the easily releasable myofilaments. The release of myofilaments was found to be insensitive to variations in pH from 6.5 to 7.5. The ATP stimulation of myofilaments release is ubiquitin-independent, since incubation of purified myofibrils with ubiquitin (1-100 micrograms/ml) at both 20 and 37 degrees C did not change the amount released. Modifying the free sulfhydryl group content by treatment of myofibrils with NEM (0.01-1 mM) or silver nitrate (0.1-10 mM) decreased the proportion of myofilaments that were releasable. Exclusion of 1 mM DTT from the preparation of myofibrils had similar results. These results indicate that the formation of easily releasable myofilaments can be mediated by metabolically related parameters such as the adenosine nucleotides and the reduction-oxidation status of the myofibrillar proteins of striated muscle.

Biochemical adaptation of cardiac and skeletal muscle to physical activity

1. Female Wistar rats were randomly assigned to control (C) or exercising (T) groups and subsequently portioned into 1, 3, 5 and 10 day T and C groups. The T groups completed a progressive endurance running program. Biochemical indices of adaptation were measured in cardiac muscle and in plantaris and soleus muscles of C and T animals after their last exercise bout. 2. In cardiac muscle, myofibrillar ATPase activity was significantly elevated in the 3T (0.241 +/- 0.031) and 5T (0.242 +/- 0.013) groups (P less than or equal to 0.05) compared to their respective controls (3C = 0.187 +/- 0.015 and 5C = 0.190 +/- 0.007). 3. After 10 days of training cardiac myofibrillar ATPase activity was elevated by 17% but this was not significant (P greater than or equal to 0.05). 4. No changes in myofibrillar ATPase activity were seen in skeletal muscle (P greater than or equal to 0.05), however, hexokinase activity progressively increased and was significantly elevated in the 3T, 5T and 10T soleus and plantaris muscles of rats over controls (P less than or equal to 0.05). 5. Minimal nonsignificant changes were noted in the hexokinase activity of the hearts of all T groups (P greater than or equal to 0.05). 6. These results indicate that metabolic adaptation of the heart and skeletal muscles takes place after as little as three training sessions. 7. Although the adaptation of the skeletal muscles continually progresses, the adaptation of the heart appears to be transitory.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucoregulatory response to moderate exercise in long-term islet cell autografted dogs

The glucoregulatory response to moderate treadmill exercise (approximately 60% maximum heart rate; 60 min at 100 m/min, 12% grade) was examined in six controls and six pancreatectomized dogs that had been normoglycemic and insulin independent for more than 1 year since autograft of isolated islets of Langerhans (Tx). There were no significant intergroup differences in plasma glucose levels during exercise, but return to baseline after exercise was delayed in Tx (p less than 0.05). In Tx, the initially suppressed insulin levels rose above baseline from 30 to 60 min. Within Tx, exercise-induced levels of plasma glucagon and epinephrine were more variable than control and strongly correlated (r = 0.81, p less than 0.001), perhaps indicating that the A cells within the grafted islets were regulated by circulating beta-adrenergic agonists. We conclude that the isolated islets were removed from direct central control. In Tx dogs, the variable counterregulatory responses and the diminished recovery of plasma glucose after exercise indicate reliance on alternative glucoregulatory mechanisms.

Improved resolution of the initial fast phase of heavy sarcoplasmic reticulum Ca2+ uptake by Ca2+:antipyrylazo III dual-wavelength spectroscopy

The effect of ATP upon difference absorbance due to Ca2+ and Mg2+ complexation with the metallochromic dye, Antipyrylazo III (AP III), was investigated. At divalent cation concentrations appropriate for Sarcoplasmic Reticulum Ca2+ transport, wavelengths (greater than 670 nm) were found whereupon the addition of up to 1mM nucleotide did not alter divalent cation:AP III difference absorbance. At these sample wavelengths an initial rapid uptake of Ca2+ by Heavy SR (HSR) was clearly resolved by dual wavelength spectroscopy of Ca2+:dye difference absorbance. Elimination of ATP interference of Ca2+:AP III absorbance by Mg2+ elevation (3-10mM) was shown to be an inappropriate general strategy for AP III spectroscopic studies of HSR Ca2+ transport due to Mg2+ inhibition of ryanodine receptor mediated Ca2+ release.

The influence of high-velocity circuit resistance training on VO2max and cardiac output

In order to investigate the influence of high-velocity circuit resistance training on maximal aerobic power, maximal stroke volume and cardiac output, and blood lactate removal during recovery, 16 habitually active males were blocked on initial VO2max into either training or control groups. The training group completed two (weeks 1 and 2) or three (weeks 3-6) circuits of 10 variable-resistance hydraulic exercise stations at an exercise: relief ratio of 1:2 on alternate days over six weeks. Angular velocities of movement were maintained at approximately 3.1 rad.s-1. Following training, the VO2max was increased (p less than .01) from 4.32 to 4.68 1.min-1. Maximal stroke volume was increased (p less than .05) from 120 to 129 mL and heart rate response to an absolute submaximal exercise load was decreased (p less than .05) from 153 to 146 beats.min-1. As well, enhanced (p less than .01) removal of lactate from the blood was observed during recovery from exhausting exercise. No changes were observed for control subjects. These results indicate that positive alterations in aerobic and cardiovascular function may be achieved consequent to high-velocity circuit resistance training.

Dietary carbohydrate-to-fat ratio: influence on whole-body nitrogen retention, substrate utilization, and hormone response in healthy male subjects

The effect of a high-carbohydrate and a high-fat diet on nitrogen retention, substrate utilization, and serum hormone concentrations was assessed in six healthy male subjects. Both diets were fed at a level estimated to provide maintenance and 75% maintenance energy requirements. Urine and feces were collected and analyzed for N and energy content. Anthropometric measurements; fasting and postprandial oxygen consumption; and serum levels of glucose, triglycerides, and metabolic hormones were measured. The high-fat diet increased N retention at both energy levels with significance reached at maintenance energy intakes (p less than 0.05). The high-fat diet resulted in less weight loss (p less than 0.05) at low energy and a consistently lower respiratory quotient (p less than 0.05), indicative of increased fat oxidation. The N sparing effect of the high-fat diet did not appear to be explained by hormone levels observed but may be substrate mediated.

Effects of strenuous maternal exercise on fetal organ weights and skeletal muscle development in rats

The purpose of the present study was to observe the effects of strenuous maternal aerobic exercise throughout gestation on fetal outcome in the rat. The strenuous exercise intensity consisted of a treadmill speed of 30 m.min-1 on a 10 degrees incline, for 120 min.day-1, 5 days.week-1. The rats were conditioned to run on a motor-driven treadmill by following a progressive two-week exercise program, so that by the end of the two weeks the rats were capable of running comfortably at this strenuous intensity in the non-pregnant state. Following the two-week running programme, the rats were paired by weight and randomly assigned to either a pregnant group that continued the running program throughout gestation (pregnant runner), or a pregnant group that did not continue the running program throughout pregnancy (pregnant control). At birth the neonates born to the pregnant running group did not differ in average neonatal body weight values, number per litter or total litter weight values when compared to controls, nor were superficial gross abnormalities observed in neonates born to the pregnant control or pregnant running groups. The strenuous maternal exercise intensity did not alter neonatal organ weight values (brain, heart, liver, lung, kidney), nor neonatal skeletal muscle (gastrocnemius, sternomastoid, diaphragm) when compared to control values. It is suggested that maternal exercise of this intensity throughout gestation does not affect fetal outcome in the rat, and may be due to the animals accustomization to the strenuous exercise protocol prior to pregnancy.

Time dependent response of cardiac myofibrillar ATPase activity to exercise

1. The purpose of the present study was to investigate the time course of run training effects on the Ca2+ kinetics of the cardiac myofibrillar ATPase activity in female Sprague-Dawley rats. 2. The cardiac myofibrillar ATPase activity was measured at varying Ca2+ levels, and the Hill-n and pCa50 were measured in the hearts of rats after 3, 6 and 9 weeks of running training with a training program that began with an initially high intensity (HINT) and a training program with a more progressive increase in intensity (PROG). 3. After 3 and 6 weeks of training cardiac myofibrillar ATPase activity in the hearts of the trained rats in both training programs was elevated by 28-40% over the control group (P less than 0.05) at a pCa5 but was not different from the control groups after 9 weeks of training (P greater than or equal to 0.05). 4. Also the Ca2+ co-operativity as measured by the Hill-n was elevated in the hearts of the trained rats after 6 and 9 weeks of training when compared to control groups suggesting changes in the regulatory proteins of the myofibrils of hearts from trained rats. 5. The elevations in cardiac myofibrillar ATPase activity suggest that the myocardium responded to the training stimulus in a phasic manner. 6. The regression of cardiac myofibrillar ATPase in the late weeks of training might be related to a reduction or a loss of a specific training stimulus for the myocardium.

An improved method for the isolation of rat cardiac sarcoplasmic reticulum

Preparations of cardiac sarcoplasmic reticulum (CSR) isolated from the rat by differential centrifugation have been widely used for measuring alterations in intracellular calcium flux in response to metabolic and pharmacologic disruptions. However, the purity of these SR fractions has not been firmly established. Using a combination of differential and linear sucrose gradient centrifugation, we have isolated rat CSR with high specific activity and purity. By SDS-PAGE analysis, the preparation is enriched in a protein (110 kD) of similar size to the Ca2+-ATPase of SR from other sources. Gels stained with the dye 'Stains-All' reveal a blue colored 55 kD band, confirming the presence of calsequestrin, the intraluminal low-affinity calcium binding protein of SR. The presence of the transmembrane 53 kD glycoprotein of SR was confirmed by endoglycosidase-H treatment followed by SDS-PAGE and also by a modified Western blotting technique. The rate of calcium uptake in this preparation averages 130 nmol/mg over the first minute of accumulation, approximately 4 times that previously reported for rat CSR. Calcium uptake in our preparation was essentially complete within 5 minutes. Preparations isolated by this method should be of value in future studies measuring alterations in rat CSR function.

Influence of exercise on cardiac and skeletal muscle myofibrillar proteins

The purpose of this study was to examine the Ca2+-Mg2+ myofibrillar ATPase and protein composition of cardiac and skeletal muscle following strenuous activity to voluntary exhaustion. Sprague-Dawley rats (200 g) were assigned to a control and exercised group, with the run group completing 25 m.min-1 and 8% grade for 1 hour. Following activity, the myocardial Ca2+-Mg2+ myofibrillar ATPase activity -pCa relationship had undergone a rightward shift in the curve. Electrophoretic analysis revealed a change in the pattern of cardiac myofibrillar protein bands, particularly in the 38-42 Kdalton region. Enzymatic analysis of myofibrillar proteins from plantaris muscle, revealed no change in Ca2+ regulation following exercise. Electronmicrographic and electrophoretic analysis revealed extensively disrupted sarcomeric structure and a change in the ratio of several plantaris myofibrillar proteins. No difference was observed for myosin: Actin: tropomyosin ratios; however a dramatic reduction in 58 and 95 Kdalton proteins were evident. The results indicate that prolonged running is associated with similar responses in cardiac and skeletal muscle myofibrillar protein compositions. The abnormalities in myofibrillar ultrastructure may implicate force transmission failure as a factor in exercised-induced muscle damage and/or fatigue.

The role of intermediary metabolism in the maintenance of proton and charge balance during exercise

The purpose of this investigation was to examine the role of intermediary metabolism in the maintenance of proton and charge balance in rainbow trout white muscle during exercise. With increasing power outputs, there was a greater reliance on white fibers and anaerobic processes for energy production. Glycogen content declined from a pre-exercise (pre-ex) level of 23 to less than 1 mumol/g following the exhaustive swim, with its greatest rate of decline occurring during the burst swim. Lactate accumulation reached a maximum of 43 mumol/g during the exhaustive swim. PCr declined from about 20 to less than 2 mumol/g at exhaustion with a concomitant accumulation of Cr. ATP decreased from about 7.3 to 2.7 mumol/g while inorganic phosphate and IMP increased to about 56 and 4.3 mumol/g, respectively. The intramuscular pH fell from 6.97 to 6.93 during the sustained swim, declining further to 6.65 during the burst swim and reaching a minimum of 6.56 at exhaustion. Exercise induced depletions of high energy compounds and accumulations of metabolic end products nearly stabilized the accompanying intracellular perturbations in charge and proton levels. Compensatory shifts in Na+, K+ and Cl- served to negate the residual imbalances such that electrical neutrality, membrane potential and pH were preserved.

Metabolic and hormonal responses in theophylline-increased cold resistance in males

The effects of theophylline (a phosphodiesterase inhibitor-adenosine receptor antagonist) and substrate feeding (Ensure, 250 kcal/235 ml) on cold resistance were studied in seminude males undertaking submaximal (50% maximum O2 consumption), intermittent (34% of total time) exercise in the cold (-5 to 15 degrees C, individually adjusted) for 3 h. Each subject (n = 7) served as his own control and was tested on a weekly schedule. Under control treatment, rectal temperature (Tre) decreased by 0.9 degrees C to approximately 36.2 degrees C after cold exposure, whereas under theophylline and Ensure, the decrease of Tre was only 0.4 degrees C, indicating a significant increase (P less than 0.05) in cold resistance (50% better than control). The plasma concentration of theophylline was 4.8-5.9 micrograms/ml and was positively correlated with plasma concentration of free fatty acids. Plasma norepinephrine (NE) increased significantly during cold exposure; the absolute concentration was significantly higher after theophylline pretreatment. The plasma concentrations of glucose, epinephrine, cortisol, and adenosine 3',5'-cyclic monophosphate did not change and the changes of free thyroxine and triiodothyronine were minor. Together, the effectiveness of theophylline + Ensure in acutely increasing cold resistance may be due to increased substrate availability for thermogenesis, part of which, through theophylline's potentiation of both sympathetic release of NE and NE-stimulated lipolysis and part of which, through supplementary feeding of Ensure.

Reproductive hormone responses to resistance exercise

To investigate if changes in circulating testosterone levels during isokinetic resistance exercise in women were similar to those during intense aerobic exercise and to examine concomitant changes in hemoconcentration, specific binding protein (sex hormone binding globulin-binding capacity), non-sex hormone binding globulin bound testosterone, luteinizing hormone, follicle-stimulating hormone, cortisol, and lactate, blood samples were obtained through an indwelling cannula at 30 and 15 min before exercise, after each of six exercises on upper and lower body muscle groups, and at 15 and 30 min after exercise in seven normal menstruating women. Investigations lasting approximately 60 min were performed in the early follicular phase beginning at 3.30 p.m. after two months of training with isokinetic ("Nautilus") equipment. Baseline testosterone and non-sex hormone binding globulin bound testosterone levels were significantly higher in subjects than in a control group. Increased total and non-sex hormone binding globulin bound testosterone was observed immediately prior to exercise with further increases late in exercise, then with proportional increases in cortisol and lactic acid. Sex hormone binding globulin-binding capacity increased before exercise. The testosterone increments exceeded hemoconcentration. Luteinizing hormone and follicle-stimulating hormone levels increased during exercise. The data suggest that origins of the exercise-associated testosterone increment are complex, resulting from hemoconcentration and specific gonadal and adrenal responses.

Insulin and islet cell transplants: effects on diabetic rat cardiac myofibril ATPase

Streptozotocin-induced diabetes results in depression of growth rate, cardiac myofibril ATPase activity, and elevated plasma glucose levels. Reversibility of these changes with daily insulin injections and pancreatic islet cell transplants was investigated and compared. Cardiac myofibril ATPase activities (mumol Pi X mg-1 X min-1) were depressed in the uncontrolled diabetic (D) group over the complete range of Ca2+ concentrations tested (e.g., 0.057 +/- 0.017 at 10 microM free Ca2+) with respect to the control (C) group (0.113 +/- 0.009). Neither the transplanted (T) group (0.128 +/- 0.017) nor the insulin injected (I) group (0.111 +/- 0.014) was significantly different from the C animals. Normal growth rates were restored in both I and T groups, whereas in the D group weight gains were negligible in comparison. Cardiac myofibril protein yields (in mg/g wet wt) were not significantly different among groups. These findings indicate that both islet cell transplants and daily insulin injections are capable of normalizing plasma glucose levels, cardiac myofibril ATPase activity, and growth rates in STZ-diabetic rats.

Are indices of free radical damage related to exercise intensity

The possibility that plasma levels of malonaldehyde (MDA) are altered by exercise has been examined. The presence of MDA has been recognized to reflect peroxidation of lipids resulting from reactions with free radicals. Maximal exercise, eliciting 100% of maximal oxygen consumption (VO2max) resulted in a 26% increase in plasma MDA (P less than 0.005). Short periods of intermittent exercise, the intensity of which was varied, indicated a correlation between lactate and MDA (r2 = 0.51) (p less than 0.001). Blood lactate concentrations increased throughout this exercise regimen. A significant decrease (10.3%) in plasma MDA occurred at 40% VO2max. At 70% VO2max plasma MDA was still below resting values, however the trend to an increase in MDA with exercise intensity was evident. At exhaustion, plasma MDA and lactate were significantly greater than at rest. These results suggest, that exhaustive maximal exercise induces free radical generation while short periods of submaximal exercise (i.e. less than 70% VO2max) may inhibit it and lipid peroxidation.

Myofibril and sarcoplasmic reticulum changes during muscle development: activity vs inactivity

1. The purpose of this study was to determine whether biochemical changes of skeletal muscle that occur as a result of exercise in young rats persist into adulthood. 2. Littermates (10 days old) were assigned to a 3, 6 and 12 week control or training group. In addition, a rest-exercise group (R-E) and exercise-rest (E-R) group were included. 3. The rest-exercise and exercise-rest rats were maintained for the 12 weeks with the first 6 weeks being either rest or exercise and the condition reversed during the last 6 weeks of the experiment. 4. Myofibril ATPase activity of rat plantaris increased from the 10d to 12 week animals (P less than 0.05). As anticipated, training resulted in a lowered activity at 6 and 12 weeks compared to controls. 5. The Ca2+ uptake and Ca2+-ATPase activity of the sarcoplasmic reticulum followed a similar pattern. 6. With regard to the exercise-rest rats, the myofibril and SR ATPase activities at 12 weeks were comparable to the 12 weeks control rats. 7. The rest-exercise group approximated the 12 week training group with regard to myofibril and SR ATPase activities (P less than 0.05). 8. The results suggest that the training adaptations that occur during development of skeletal muscle return to normal, when training ceases in the adult rat. 9. Furthermore, animals that started to train prior to puberty do not have a greater capacity to adapt than animals which initiated training during adulthood.

Decrease in serum testosterone levels with maximal intensity swimming exercise in trained male and female swimmers

Circulating testosterone levels have generally been reported to increase during short term, intense running or bicycle ergometer exercise. Swimming differs from such activity because of the strenuous arm activity and because it is conducted in a liquid medium in the horizontal position with the weight totally supported. To investigate whether such differences modify the serum testosterone response to exercise, we measured serum testosterone levels before and after a maximal intensity swimming test in ten elite male and ten elite female swimmers. Levels of circulating testosterone fell in 19 of 20 swimmers in contrast to previous reports of exercise in the vertical position. In women mean testosterone levels declined by 39.4% from baseline values and in males, mean testosterone levels declined by 19.0%. Since the incremental protocol was similar to in design to maximal intensity tests conducted on a treadmill or bicycle ergometer, these data suggest that the differing physical circumstances of swimming lead to a qualitatively different testosterone response to exercise.

The effects of strenuous maternal exercise during gestation on maternal body components in rats

The effects of strenuous maternal exercise throughout gestation on the maternal rat were examined. The results indicated that maternal exercise of this nature (30 metres/minute, 10 degree incline, 120 minutes/day, 5 days/week) caused a significant decrease in the amount of weight gained by the running maternal rats when compared to controls. By analysing the maternal rat and various bodily components after parturition, it was suggested that subcutaneous tissue growth (fat deposits and mammary gland tissue) was significantly less in the running group. The carcass remainder component was also found to weigh less in the running group, even though the maternal running rats had just given birth to an equivalent (not significantly different) number of neonates of similar (not significantly different) weight to the control group.

Are anorexic tendencies prevalent in the habitual runner?

To investigate whether runners displayed any of the abnormalities characteristic of patients with anorexia nervosa, we conducted a cross sectional study of 31 high mileage, 18 low mileage runners and 18 non-running controls. Subjects completed a personal data questionnaire, the Jackson Personality Inventory (JPI) and the Eating Attitudes Questionnaire (EAT), underwent a body image test and a blood sample was obtained for measurement of reproductive, thyroid and adrenal hormones. High mileage runners scored significantly higher infrequency scores on the JPI than sedentary controls but there was no evidence of psychopathology. The high mileage runners also significantly overestimated waist width and there were small but statistically significant differences in EAT scores between controls and the runner groups. Ten of 49 runners had EAT scores beyond two standard deviations above the mean of non-running controls. Serum total, free and non-specifically bound testosterone and prolactin levels were significantly lower in high mileage runners than controls. LH, FSH, cortisol and thyroid hormones were not significantly different. There were no significant differences in any hormone between low mileage runners and controls. displayed no clear abnormalities characteristic of patients with anorexia The results suggested that running may have a chronic effect on serum testosterone and prolactin levels in high mileage but not low mileage runners. Although there was no significant evidence of anorexia nervosa on testing the runners with EAT, the overestimation of waist size provided some evidence of a distortion of body image in the high mileage runners. Runners displayed no clear abnormalities characteristic of patients with anorexia nervosa.