Maximal force is unaffected by emphysema-induced atrophy in extensor digitorium longus.

Patients with chronic obstructive pulmonary disease (COPD) demonstrate a limited exercise capacity. It is unknown whether muscle fiber atrophy and subsequent decrease in force production contributes to this functional limitation. Therefore, the purpose of this investigation was to determine whether emphysema-induced muscle fiber atrophy leads to a reduction in locomotory muscle force production. Maximal muscle force production and fiber cross-sectional area were measured in the almost exclusively fast-twitch extensor digitorium longus muscles at 4 and 8 months following saline (control, n=8/time period) or elastase (emphysema, n=15/time period) instillation in the lungs of hamsters. Excised lung volume increased 145 and 161% with emphysema at 4 and 8 months, respectively (both P<0.01). Muscle mass, maximal force, and fiber cross-section were unaltered at 4 months. However, absolute mass (-15%) and fiber cross-sectional area (-18%) were reduced at 8 months (both P<0.01). Surprisingly, maximal force was preserved in emphysema animals. These data demonstrate that maximal muscle force may be preserved in the face of emphysema-induced fiber atrophy.

Corticotropin releasing factor 2 receptor agonists reduce the denervation-induced loss of rat skeletal muscle mass and force and increase non-atrophying skeletal muscle mass and force.

Of the two corticotropin releasing factor receptors known, corticotrophin releasing factor 2 receptor (CRF2R) is expressed in skeletal muscle. The function of this receptor in skeletal muscle is at present unknown. In order to better understand the role of the CRF2R in skeletal muscle, we treated rats with CRF2R agonists and evaluated the effect of these agents on normal and denervated muscle mass. Rats treated with the non-selective CRFR agonist, sauvagine, did not demonstrate any significant and consistent change in non-denervated and denervated fast twitch [tibialis anterior (TA) or extensor digitorum longus (EDL)] or slow/mixed twitch [medial gastrocnemius (MG) or soleus] fiber muscle mass. In adrenalectomized rats, sauvagine treatment resulted in no significant and consistent change in non-denervated fast or slow/mixed twitch fiber muscles but did cause a significant and consistent increase in denervated fast twitch (TA and EDL) but not slow/mixed twitch muscle mass. Interestingly adrenalectomy had no effect on the degree of muscle atrophy. Rats treated with the CRF2R selective agonist urocortin 2 demonstrated an increase in non-denervated and denervated fast and slow/mix twitch fiber muscle mass. The urocortin 2 induced increase in muscle mass was accompanied by an increase in muscle fiber cross-sectional area and muscle absolute force. These studies demonstrated that activation of the CRF2R decreased the level of skeletal muscle mass, force, and myocyte cross-sectional area loss resulting from sciatic nerve damage and increased the mass, force and myocyte cross-sectional area of normal (non-atrophying) skeletal muscle. In addition, we also observed that removal of the adrenals increased the effectiveness of the non-selective CRFR agonists sauvagine, presumably via the removal of the pro-atrophy influence of adrenal produced corticosteroids. These results demonstrate that pharmacological modulation of the CRF2R may be a viable method to treat skeletal muscle atrophy.

Force and power output of fast and slow skeletal muscles from mdx mice 6-28 months old.

1. Differences in the effect of age on structure-function relationships of limb muscles of mdx (dystrophin null) and control mice have not been resolved. We tested the hypotheses that, compared with limb muscles from age-matched control mice, limb muscles of 6- to 17-month-old mdx mice are larger but weaker, with lower normalised force and power, whereas those from 24- to 28-month-old mdx mice are smaller and weaker. 2. The maximum isometric tetanic force (P(o)) and power output of limb muscles from 6-, 17-, 24- and 28-month-old mdx and control mice were measured in vitro at 25 degrees C and normalised with respect to cross-sectional area and muscle mass, respectively. 3. Body mass at 6 and 28 months was not significantly different in mdx and control mice, but that of control mice increased 16 % by 17 months and then declined 32 % by 28 months. The body masses of mdx mice declined linearly with age with a decrease of 25 % by 28 months. From 6 to 28 months of age, the range in the decline in the masses of EDL and soleus muscles of mdx and control mice was from 16 to 28 %. The muscle masses of mdx mice ranged from 9 % to 42 % greater than those of control mice at each of the four ages and, even at 28 months, the masses of EDL and soleus muscles of mdx mice were 17 % and 22 % greater than control values. 4. For mdx mice of all ages, muscle hypertrophy was highly effective in the maintenance of control values for absolute force for both EDL and soleus muscles and for absolute power of soleus muscles. Throughout their lifespan, muscles of mdx mice displayed significant weakness with values for specific P(o) and normalised power approximately 20 % lower than values for control mice at each age. For muscles of both strains, normalised force and power decreased approximately 28 % with age, and consequently weakness was more severe in muscles of old mdx than in those of old control mice.

Force and power output of diaphragm muscle strips from mdx and control mice after clenbuterol treatment.

Based on its anabolic properties, treatment with the beta(2)-adrenoceptor agonist, clenbuterol, has been proposed as a strategy for ameliorating the symptoms of muscular dystrophy. In the dystrophic mdx mouse, only the diaphragm muscle exhibits progressive and severe degeneration in muscle structure and function similar to that observed in Duchenne muscular dystrophy. We tested the hypothesis that 20 weeks of clenbuterol treatment ( approximately 1.5-2 mg kg(-1)day(-1)) would increase the force and power output of diaphragm muscle strips of 6-month-old mdx and control mice. At this age, the diaphragm muscles of mdx mice show extensive degeneration and impaired contractility compared with control mice. Clenbuterol treatment did not increase the normalized force or power output of diaphragm strips from either mdx or control mice. The degeneration and necrosis within the diaphragm muscle of mdx mice was also not ameliorated by clenbuterol treatment. The results indicate that clenbuterol treatment does not improve the structure or function of diaphragm muscles from mdx mice.

Continuous low-level topical heat in the treatment of dysmenorrhea.

OBJECTIVE: To compare the efficacy of topically applied heat for menstrual pain with oral ibuprofen and placebo treatment. METHODS: We conducted a randomized placebo and active controlled (double dummy), parallel study using an abdominal patch (heated or unheated) for approximately 12 consecutive hours per day and oral medication (placebo or ibuprofen 400 mg) three times daily, approximately 6 hours apart for 2 consecutive days. Pain relief and pain intensity were recorded at 17 time points. There was at least 85% power to detect a true one-unit difference in the 2-day pain relief treatment means for comparisons with the unheated patch plus oral placebo group using a one-tailed test at the.05 level of significance, based on an observed within-group standard deviation of 1.147. RESULTS: Eighty-four patients were enrolled and 81 completed the study protocol. Over the 2 days of treatment, the heated patch plus placebo tablet group (mean 3.27, P <.001), the unheated patch plus ibuprofen group (mean 3.07, P =.001), and the combination heated patch plus ibuprofen group (mean 3.55, P <.001) had significantly greater pain relief than the unheated patch plus placebo group (mean 1.95). Greater pain relief was not observed for the combination heated patch plus ibuprofen group compared with the unheated patch plus ibuprofen group (P =.096); however, the time to noticeable pain relief was statistically significantly shorter for the heated patch plus ibuprofen group (median 1.5 hours) compared with the unheated patch plus ibuprofen group (median 2.79 hours, P =.01). CONCLUSION: Continuous low-level topical heat therapy was as effective as ibuprofen for the treatment of dysmenorrhea.

Proteomic analysis of the atrophying rat soleus muscle following denervation.

A proteomic analysis was performed comparing normal rat soleus muscle to denervated soleus muscle at 0.5, 1, 2, 4, 6, 8 and 10 days post denervation. Muscle mass measurements demonstrated that the times of major mass changes occurred between 2 and 4 days post denervation. Proteomic analysis of the denervated soleus muscle during the atrophy process demonstrated statistically significant (at the p < 0.01 level) changes in 73 soleus proteins, including coordinated changes in select groups of proteins. Sequence analysis of ten differentially regulated proteins identified metabolic proteins, chaperone and contractile apparatus proteins. Together these data indicate that coordinated temporally regulated changes in the proteome occur during denervation-induced soleus muscle atrophy, including changes in muscle metabolism and contractile apparatus proteins.

Power output of fast and slow skeletal muscles of mdx (dystrophic) and control mice after clenbuterol treatment.

The mdx mouse is the most commonly used animal model for Duchenne muscular dystrophy. We tested the null hypothesis that 20 weeks of clenbuterol treatment ( approximately 2 mg kg-1 day-1) of mdx and control mice would have no effect on the absolute and specific force (Po, kN m-2) and absolute and normalised power output (W kg-1) of extensor digitorum longus (EDL) and soleus muscles. For mdx and control mice, clenbuterol treatment produced modest increases in the mass of the two muscles but did not increase absolute or specific force or normalised power output. For absolute power output, only the EDL muscles of mdx mice showed a difference following treatment, with the power output of treated mice being 118 % that of the untreated mice. The modest effects of clenbuterol treatment on the dynamic properties of skeletal muscle provide little support for any improvement in muscle function for the dystrophic condition.

Year-long clenbuterol treatment of mice increases mass, but not specific force or normalized power, of skeletal muscles.

1. Clenbuterol has been proposed for the treatment of muscle wasting disorders, but its long-term effects on skeletal muscle function have not been tested rigorously. We tested the hypothesis that year-long treatment of young (6 months) mice with clenbuterol would increase skeletal muscle mass and in vitro measurements of specific force (Po) and power output. 2. Male mice (C57BL/10ScSn) were divided into treated (n = 6) or untreated (n = 8) groups. Treated mice received clenbuterol (1.5-2 mg/kg per day) in their drinking water for 52 weeks, following a staggered 3 day on/3 day off schedule to attenuate the response to clenbuterol. 3. Clenbuterol treatment increased the absolute mass of each muscle tested: the heart by 28%, extensor digitorum longus (EDL) by 16%, soleus by 22% and tibialis anterior by 17%. For treated compared with untreated mice, absolute Po (mN) was greater in soleus muscles but not different in EDL muscles. Absolute power output (mW) of the EDL and soleus muscles was not different and no differences were observed for the specific Po (kN/m2) or normalized power output (W/kg) of EDL muscles, soleus muscles or diaphragm muscle strips. 4. We conclude that, following year-long treatment of mice with clenbuterol, the mass of the heart and both fast and slow skeletal muscles is increased, but the lack of any change in normalized Po or power output indicates that clenbuterol has little therapeutic effect on the functional properties of skeletal muscle.

Functional deficits in medial gastrocnemius grafts in rats: relation to muscle metabolism and beta-AR regulation.

This study tested the hypothesis that alterations in the metabolic integrity of grafted muscle contribute to its diminished ability to sustain power. Compared with control muscles, muscles studied 120 days after the grafting procedure had lower specific force and sustained power. The sustained power protocol resulted in a depletion of muscle glycogen in control (83%) and grafted (85%) animals. Grafts had lower pre- and poststimulation glycogen, diminished citrate synthase activity, and greater hexokinase activity. No differences were observed in phosphofructokinase activity, glucose transporter GLUT-4 content, fiber type, beta-adrenergic-receptor (beta-AR) density, or binding affinity. Isoproterenol-stimulated adenylyl cyclase activity was lower in grafted vs. control muscle, suggesting an uncoupling of the beta-AR-effector complex. Thus the diminished ability of the grafted muscle to sustain power may be explained, in part, by a decrease in energy available from glycogen stores and/or a decrease in oxidative capacity.

Contractile properties of diaphragm muscle segments from old mdx and old transgenic mdx mice.

Diaphragm muscles of young (4- to 6-mo-old) mdx mice show severe fiber necrosis and have normalized forces and powers 60 and 46% of the values for control C57BL/10 mice. In contrast, microinjection of mdx mouse embryos with a truncated dystrophin minigene has produced young transgenic mdx (tg-mdx) mice with a level of dystrophin expression and structural and functional properties of diaphragm muscle strips measured in vitro not different from those of control mice. Whether dystrophin expression and functional corrections persist for the life span of these animals is not know. We tested the null hypothesis that, in old (24 mo) tg-mdx mice, dystrophin expression is adequate and diaphragm muscle strips have forces and powers not different from values for diaphragm muscle strips from young tg-mdx mice or control mice. Compared with control values, diaphragm muscle strips from old mdx mice had normalized forces and powers of 48 and 31%, respectively. Expression of dystrophin persisted in diaphragm muscles of old tg-mdx mice, and functional properties were not different from diaphragm muscles of young tg-mdx or young or old control mice. These results suggest that, with a transgenic animal approach, dystrophin expression and functional corrections persist for the life span of the animals.

Expression of full-length and truncated dystrophin mini-genes in transgenic mdx mice.

Duchenne and Becker muscular dystrophy are caused by defects in the dystrophin gene, and are candidates for treatment by gene therapy. We have shown previously that overexpression of a full-length dystrophin cDNA prevents the development of dystrophic symptoms in mdx mice. We show here that this functional correction can be achieved by expressing the full-length muscle isoform at a lower level than is present in control animals. Gene therapy for DMD may necessitate the use of truncated dystrophin mini-genes to accommodate the limited cloning capacity of current-generation viral delivery vectors. We have constructed both murine and human mini-genes deleted for exons 17-48, and have demonstrated that expression of either mini-gene can almost completely prevent the development of dystrophic symptoms in transgenic mdx mice. These results suggest that viral-mediated expression of moderate levels of a truncated dystrophin could be an effective treatment for DMD.