Estrogen effect on some enzymes in female rats after downhill running

The study investigates the effect of administered estrogen on plasma creatine kinase (CK) and lactate dehydrogenase (LD) levels in female ovariectomized rats after downhill running. Rats ovariectomized before sexual maturity were subcutaneously implanted with pellets containing 17 beta-estradiol or placebo. Three weeks later they were subjected to a 90-min intermittent downhill running protocol. Blood samples were obtained from the jugular vein immediately after and 72 h after exercise for determination of plasma CK, LD and 17 beta-estradiol levels. A two-way analysis of variance was used for data evaluation. Plasma CK and LD levels were significantly lower (p<0.05) in the estrogen-supplemented, ovariectomized animals which suggests that less muscle damage occurred compared to the controls immediately and 72 h after exercise. Estrogens may have a protective effect on muscle tissue possibly due to their antioxidant and membrane stabilizing properties.     

Treadmill running induces satellite cell activation in diabetic mice

Skeletal muscle-derived stem cells, termed as satellite cells, play essential roles in regeneration after muscle injury in adult skeletal muscle. Diabetes mellitus (DM), one of the most common metabolic diseases, causes impairments of satellite cell function. However, the studies of the countermeasures for the DM-induced dysfunction of satellite cells have been poor. Here, we investigated the effects of chronic running exercise on satellite cell activation in diabetic mice focused on the molecular mechanism including Notch and Wnt signaling, which are contribute to the fate determination of satellite cells. Male C57BL/6 mice 4 weeks of age were injected with streptozotocin and were randomly divided into runner group and control group. Runner group mice were performed treadmill running for 4 weeks. DM attenuated satellite cell activation and the expressions of the components of Notch and Wnt signaling. However, chronic running resulted in activation of satellite cells in diabetic mice and salvaged the inactivity of Wnt signaling but not Notch signaling. Our results suggest that chronic running induces satellite cell activation via upregulation of Wnt signaling in diabetic as well as normal mice.     

Delayed onset muscle soreness following repeated bouts of downhill running

Perceived muscle soreness ratings, serum creatine kinase (CK) activity, and myoglobin levels were assessed in three groups of subjects following two 30-min exercise bouts of downhill running (-10 degrees slope). The two bouts were separated by 3, 6, and 9 wk for groups 1, 2, and 3, respectively. Criterion measures were obtained pre- and 6, 18, and 42 h postexercise. On bout 1 the three groups reported maximal soreness at 42 h postexercise. Also, relative increases in CK for groups 1, 2, and 3 were 340, 272, and 286%, respectively. Corresponding values for myoglobin were 432, 749, and 407%. When the same exercise was repeated, significantly less soreness was reported and smaller increases in CK and myoglobin were found for groups 1 and 2. For example, the percent CK increases on bout 2 for groups 1 and 2 were 63 and 62, respectively. Group 3 demonstrated no significant difference in soreness ratings, CK activities, or myoglobin levels between bouts 1 and 2. It was concluded that performance of a single exercise bout had a prophylactic effect on the generation of muscle soreness and serum protein responses that lasts up to 6 wk.     

Electrical stimulation influences satellite cell proliferation and apoptosis in unloading-induced muscle atrophy in mice

Muscle atrophy caused by disuse is accompanied by adverse physiological and functional consequences. Satellite cells are the primary source of skeletal muscle regeneration. Satellite cell dysfunction, as a result of impaired proliferative potential and/or increased apoptosis, is thought to be one of the causes contributing to the decreased muscle regeneration capacity in atrophy. We have previously shown that electrical stimulation improved satellite cell dysfunction. Here we test whether electrical stimulation can also enhance satellite cell proliferative potential as well as suppress apoptotic cell death in disuse-induced muscle atrophy. Eight-week-old male BALB/c mice were subjected to a 14-day hindlimb unloading procedure. During that period, one limb (HU-ES) received electrical stimulation (frequency: 20 Hz; duration: 3 h, twice daily) while the contralateral limb served as control (HU). Immunohistochemistry and western blotting techniques were used to characterize specific proteins in cell proliferation and apoptosis. The HU-ES soleus muscles showed significant improvement in muscle mass, cross-sectional area, and peak tetanic force relative to the HU limb (p<0.05). The satellite cell proliferative activity as detected within the BrdU+/Pax7+ population was significantly higher (p<0.05). The apoptotic myonuclei (detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) and the apoptotic satellite cells (detected by cleaved Poly [ADP-ribose] polymerase co-labeled with Pax7) were reduced (p<0.05) in the HU-ES limb. Furthermore the apoptosis-inducing factor and cleaved caspase-3 were down-regulated while the anti-apoptotic Bcl-2 protein was up-regulated (p<0.05), in the HU-ES limb. These findings suggest that the electrical stimulation paradigm provides an effective stimulus to rescue the loss of myonuclei and satellite cells in disuse muscle atrophy, thus maintaining a viable satellite cell pool for subsequent muscle regeneration. Optimization of stimulation parameters may enhance the outcome of the intervention.     

Changes in power assessed by the Wingate Anaerobic Test following downhill running

Few studies have examined the effects of eccentric exercise-induced muscle damage on power despite power being a key performance variable in a number of sporting events. The aim of this study was to examine changes in anaerobic power (30-second Wingate Test), isometric strength of the knee extensors and flexors, muscle soreness, and plasma creatine kinase (CK) activity following downhill running. Eight men performed a 40-minute downhill (-7%) run on a treadmill, and measurements were taken on 6 occasions (2 baseline and 0.5, 24, 72, and 120 hours postrun). A second group of men (n = 5) had the measurements taken on 6 occasions without downhill running and served as a control group. A repeated measures analysis of variance revealed no significant changes in any measures across time for the control group. Following downhill running, significant (p < 0.05) decreases in strength (0.5-24 hours), and significant increases in muscle soreness (0.5-72 hours) and plasma CK activity (0.5-120 hours) were observed. A significant decrease in peak and average power (approximately 5%) was evident only 0.5 hours postrun, and the decrease was smaller in magnitude than that of strength (approximately 15%). These results suggest that power is less affected than strength after eccentric exercise, and the effect of reduced power on sport performance seems negligible.     

Effect of training on skeletal muscle injury from downhill running in rats

Experiments were conducted to test the hypothesis that injury to skeletal muscle in rats resulting from prolonged downhill running is prevented to a greater extent by prior downhill training than by either uphill or level training. Changes in plasma creatine phosphokinase (CPK) activity and glucose-6-phosphate dehydrogenase (G-6-PDase) activity in the soleus (S), vastus intermedius (VI), and medial head of triceps brachii (TM) muscles were evaluated as markers of muscle injury 48 h after 90 min of intermittent downhill running (16 m . min -1). Prior to this acute downhill run, groups of rats were trained by either downhill (-16 degrees), level (0 degrees), or uphill (+16 degrees) running (16 m . min -1) for 30 min/day. Training duration was either 5 days or 1 day. A training effect (i.e., reduced muscle injury) was indicated if muscle G-6-PDase or plasma CPK activity in a trained group following the 90-min downhill run was not different from that of nonexercised control animals and/or if it was lower than that of nontrained runners. A significant training effect was achieved in all three muscles with 5 days of either downhill or level training, but only in S after 5 days of uphill training. Elevation of plasma CPK activity was prevented by 5 days of training on all three inclines.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of downhill running on motoneuron pool excitability.

The purpose of this study was to compare alterations in motoneuron pool excitability after eccentric-biased (ECC-B) downhill running exercise with non-biased (NO-B) level running exercise. Six male subjects (25-34 yr) participated in the study, which included ECC-B exercise (-10% grade) and NO-B exercise (0% grade) at 50% of maximal O2 uptake for 20 min. The control trial consisted of 20 min of quiet rest with all subjects participating in all conditions (repeated measures). Motoneuron pool excitability was measured by the Hoffman reflex (H-wave), which was expressed as a ratio (H/M ratio) of the maximal electrically stimulated muscle action potential (M-wave). NO-B exercise resulted in a 9.3 +/- 2.7% (SE) reduction in the H/M ratio. ECC-B exercise resulted in a 24.6 +/- 5.7% reduction in the ratio (P less than 0.05 for both). The two exercise treatment conditions were also significantly different from one another (P less than 0.05). Twenty-four-hour postexercise H/M ratios were similar to baseline (P greater than 0.05). Postexercise subjective muscle soreness assessment (DOMS) produced significant increases in DOMS of 36 and 166% immediately and 24 h after exercise, respectively, for the ECC-B trial only (P less than 0.001). The data show that ECC-B exercise results in greater postexercise H/M ratio reductions than NO-B exercise and that H/M ratio changes post-ECC-B exercise are not solely associated with DOMS.     

Ground reaction forces during downhill and uphill running

We investigated the normal and parallel ground reaction forces during downhill and uphill running. Our rationale was that these force data would aid in the understanding of hill running injuries and energetics. Based on a simple spring-mass model, we hypothesized that the normal force peaks, both impact and active, would increase during downhill running and decrease during uphill running. We anticipated that the parallel braking force peaks would increase during downhill running and the parallel propulsive force peaks would increase during uphill running. But, we could not predict the magnitude of these changes. Five male and five female subjects ran at 3m/s on a force treadmill mounted on the level and on 3 degrees, 6 degrees, and 9 degrees wedges. During downhill running, normal impact force peaks and parallel braking force peaks were larger compared to the level. At -9 degrees, the normal impact force peaks increased by 54%, and the parallel braking force peaks increased by 73%. During uphill running, normal impact force peaks were smaller and parallel propulsive force peaks were larger compared to the level. At +9 degrees, normal impact force peaks were absent, and parallel propulsive peaks increased by 75%. Neither downhill nor uphill running affected normal active force peaks. Combined with previous biomechanics studies, our normal impact force data suggest that downhill running substantially increases the probability of overuse running injury. Our parallel force data provide insight into past energetic studies, which show that the metabolic cost increases during downhill running at steep angles.     

Exercise-induced satellite cell activation in senescent soleus muscle.

The purposes of this study were 1) to determine satellite cell mitotic activity and myofiber nuclear density in the soleus muscle of aged rats and 2) to examine the effect of exercise training on these same parameters. Twenty-four-month-old specific pathogen-free female Fischer 344 rats were assigned to either a training or a control group. The trained group performed 10 wk of progressive treadmill running that resulted in a significant increase (P less than or equal to 0.05) in vastus lateralis muscle malate dehydrogenase activity compared with control rats. Training produced a doubling of soleus muscle satellite cell mitotic activity (trained 1.28 +/- 0.33, control 0.52 +/- 0.13 thymidine-labeled satellite cells per 1,000 nuclei; P less than or equal to 0.05). Training also resulted in a doubling in the number of damaged fibers in the soleus muscle (P less than or equal to 0.05). Mean myofiber nuclear density was unaltered by exercise training but varied as a function of soleus muscle fiber size. Nuclear density of a subpopulation of small fibers (cross-sectional area less than one standard deviation below the mean cross-sectional area of all fibers examined) was significantly higher (P less than or equal to 0.05) than in other fibers in the soleus muscle. A high nuclear density and small size suggest that these fibers were immature. In addition, the soleus muscle from trained rats had significantly more (P less than or equal to 0.05) small fibers with high nuclear density than muscle from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of the oxygen drift in downhill vs. level running.

This investigation explored the recent theory that muscle damage causes the drift in oxygen consumption (VO2) during low-intensity downhill running. Seven subjects participated in a maximal VO2 (VO2max) test and three submaximal bouts [one level (Level) and two downhill runs (Down 1, Down 2) at 40% peak VO2]. Two downhill runs (30 min at -10% grade) were performed to vary the extent of muscle damage. Creatine kinase (CK) increased more after Down 1 (61%) than after Down 2 (11%), as did soreness ratings, indicating reduced muscle damage during Down 2. Significantly greater increases in VO2 over time were noted for Down 1 (15.6%) and Down 2 (14.7%) than for Level (1.2%). Heart rate increased 8 beats/min for Level but 29 and 25 beats/min for Down 1 and Down 2, respectively. Expired ventilation increased more for Down 1 (20.5%) and Down 2 (24%) than for Level (3.5%). Rectal temperature increased approximately 0.8 degree C for all bouts. Because the magnitude of the drift was similar in the two downhill bouts, the findings suggest that muscle damage does not cause the drift in VO2 during low-intensity downhill running.     

Glycogen depletion and resynthesis in the rat after downhill running

To study the effect of downhill running on glycogen metabolism, 94 rats were exercised by running for 3 h on the level or down an 18 degrees incline. Muscle and liver glycogen concentrations were measured before exercise and 0, 48 and 52 h postexercise. Rats were not fed during the first 48 h of recovery but ingested a glucose solution 48 h postexercise. Downhill running depleted glycogen in the soleus muscle and liver significantly more than level running (P less than 0.01). The amount of glycogen resynthesized in the soleus muscle and liver in fasting or nonfasting rats was not altered significantly by downhill running (P greater than 0.05). On every day of recovery the rats were injected with dexamethasone, which induced similar increases in glycogen concentration in the soleus muscle and liver after the 52nd h of the postexercise period in the case of downhill and level running. The glycogen depletion and repletion results indicated that, under our experimental conditions, downhill running in the rat, a known model of eccentric exercise, affected muscle glycogen metabolism differently from eccentric cycling in humans.     

Relationship between fat-to-fat-free mass ratio and decrements in leg strength after downhill running.

The purpose of this study was to determine whether greater body fat mass (FM) relative to lean mass would result in more severe muscle damage and greater decrements in leg strength after downhill running. The relationship between the FM-to-fat-free mass ratio (FM/FFM) and the strength decline resulting from downhill running (-11% grade) was investigated in 24 male runners [age 23.4 +/- 0.7 (SE) yr]. The runners were divided into two groups on the basis of FM/FFM: low fat (FM/FFM = 0.100 +/- 0.008, body mass = 68.4 +/- 1.3 kg) and normal fat (FM/FFM = 0.233 +/- 0.020, body mass = 76.5 +/- 3.3 kg, P < 0.05). Leg strength was reduced less in the low-fat (-0.7 +/- 1.3%) than in the normal-fat individuals (-10.3 +/- 1.5%) 48 h after, compared with before, downhill running (P < 0.01). Multiple linear regression analysis revealed that the decline in strength could be predicted best by FM/FFM (r2 = 0.44, P < 0.05) and FM-to-thigh lean tissue cross-sectional area ratio (r2 = 0.53, P < 0.05), with no additional variables enhancing the prediction equation. There were no differences in muscle glycogen, creatine phosphate, ATP, or total creatine 48 h after, compared with before, downhill running; however, the change in muscle glycogen after downhill running was associated with a higher FM/FFM (r = -0.56, P < 0.05). These data suggest that FM/FFM is a major determinant of losses in muscle strength after downhill running.     

Energy cost of walking and running at extreme uphill and downhill slopes.

The costs of walking (Cw) and running (Cr) were measured on 10 runners on a treadmill inclined between -0.45 to +0.45 at different speeds. The minimum Cw was 1.64 +/- 0.50 J. kg(-1). m(-1) at a 1.0 +/- 0.3 m/s speed on the level. It increased on positive slopes, attained 17.33 +/- 1.11 J. kg(-1). m(-1) at +0.45, and was reduced to 0.81 +/- 0.37 J. kg(-1). m(-1) at -0.10. At steeper slopes, it increased to reach 3.46 +/- 0.95 J. kg(-1). m(-1) at -0.45. Cr was 3.40 +/- 0.24 J. kg(-1). m(-1) on the level, independent of speed. It increased on positive slopes, attained 18.93 +/- 1.74 J. kg(-1). m(-1) at +0.45, and was reduced to 1.73 +/- 0.36 J. kg(-1). m(-1) at -0.20. At steeper slopes, it increased to reach 3.92 +/- 0.81 J. kg(-1). m(-1) at -0.45. The mechanical efficiencies of walking and running above +0.15 and below -0.15 attained those of concentric and eccentric muscular contraction, respectively. The optimum gradients for mountain paths approximated 0.20-0.30 for both gaits. Downhill, Cr was some 40% lower than reported in the literature for sedentary subjects. The estimated maximum running speeds on positive gradients corresponded to those adopted in uphill races; on negative gradients they were well above those attained in downhill competitions.     

Elevated small GTPase activation influences the cell proliferation signaling control in Niemann-Pick type C fibroblasts

Niemann-Pick type C (NPC) disease is characterized at the cellular level by the intracellular accumulation of free cholesterol. We have previously identified a similar phenotype in cystic fibrosis (CF) cell models that results in the activation of the small GTPase RhoA. The hypothesis of this study was that NPC cells would also exhibit an increase in small GTPase activation. An examination of the active, GTP-bound form of GTPases revealed a basal increase in the content of the active-form Ras and RhoA small GTPases in NPC fibroblasts compared to wt controls. To assess whether this increase in GTP-bound Ras and RhoA manifests a functional outcome, the expression of the proliferation control proteins p21/waf1 and cyclin D were examined. Consistent with increased GTPase signaling, p21/waf1 expression is reduced and cyclin D expression is elevated in NPC fibroblasts. Interestingly, cell growth rate is not altered in NPC fibroblasts compared to wt cells. However, NPC sensitivity to statin treatment is reversed by addition of the isoprenoid geranylgeranyl pyrophosphate (GGPP), a modifier of RhoA. It is concluded that Ras and RhoA basal activation is elevated in NPC fibroblasts and has an impact on cell survival pathways.     

Mast cell activation and tissue cell proliferation

Summary The effect of mast cell activation and degranulation on the proliferation in the intact mesentery was studied in Sprague-Dawley rats. Mast cell activation was achieved by a single intraperitoneal injection of Compound 48/80.The proliferation was studied using three independent methods for estimation of cell production and DNA synthesis: 1. the mitotic index, 2. the relative number of cells having a DNA content in the S and G2 regions, by Feulgen photometric measurement in individual cells, and 3. the specific DNA activity, employing a method which combines a liquid scintillation technique after an intravenous injection of ³H-thymidine and Feulgen photometric determination of the DNA content per membrane preparation.It was found that the proliferation of the normal mesenchymal cells adjacent to the activated and degranulated mast cells in the mesentery was significantly increased within 24 and 32 h, the maximum increase being more than 20-fold compared to untreated controls. The results suggest that the common type of mast cell may have a pathophysiological function related to stimulation of local cell proliferation.Supported by grants from the Swedish Medical Research Council (Project 12X-2235) and from the Medical Faculty, University of LinköpingWe thank Brita Söderlund, Margareta Odenö and Iréne Svensson for skilful technical assistance, and Erik Leander, Ph. D., for help with statistical methodsPart of this work was presented at the 7th Meeting of the European Study Group for Cell Proliferation, 5–9 May 1975, in Amsterdam, The Netherlands     

Exercise-enhanced satellite cell proliferation and new myonuclear accretion in rat skeletal muscle.

The effects of increased functional loading on early cellular regenerative events after exercise-induced injury in adult skeletal muscle were examined with the use of in vivo labeling of replicating myofiber nuclei and immunocyto- and histochemical techniques. Satellite cell proliferation in the soleus (Sol) of nonexercised rats (0.4 +/- 0.2% of fibers) was unchanged after an initial bout of declined treadmill exercise but was elevated after two (1.0 +/- 0.2%, P < or = 0.01), but not four or seven, daily bouts of the same task. Myonuclei produced over the 7-day period comprised 0.9-1.9% of myonuclei in isolated fibers of Sol, tibialis anterior, and vastus intermedius of nonexercised rats. The accretion of new myonuclei was enhanced (P < or = 0.05) in Sol and vastus intermedius by the initial exercise followed by normal activity (to 3.1-3.4% of myonuclei) and more so by continued daily exercise (4.2-5.3%). Observed coincident with a lower incidence of histological fiber injury and unchanged fiber diameter and myonuclei per millimeter, the greater new myonuclear accretion induced by continued muscle loading may contribute to an enhanced fiber repair and regeneration after exercise-induced injury.     

Estrogen stimulation of ovarian surface epithelial cell proliferation

Summary Ovarian cancer is the leading cause of gynecological cancer mortality, and 85–90% of this malignancy originates from the ovarian surface epithelium (OSE). The etiology of ovarian epithelial cancer is unknown but a role for estrogens has been suspected. However, the effect of estrogens on OSE cell proliferation remains to be determined. Using the rabbit model, our studies have demonstrated that 17β-estradiol stimulates OSE cell proliferation and the formation of a papillary ovarian surface morphology similar to that seen in human ovarian serous neoplasms of low malignant potential. Immunohistochemical staining of ovarian tissue sections with an antibody to the estrogen receptor α demonstrates its expression in both OSE cells and stromal interstitial cells. In primary ovarian cell cultures, the proliferative response of the epithelial cells to 17β-estradiol depends on the expression of the estrogen receptor α in the epithelial cells. However, when the epithelial cells are grown together with ovarian stromal cells, their proliferative response to this hormone is greatly enhanced, suggesting the involvement of stromal-epithelial interactions. These studies suggest a role for estrogens and the estrogen receptor α in OSE growth.