Muscle damaging eccentric exercise attenuates disuse-induced declines in daily myofibrillar protein synthesis and transiently prevents muscle atrophy in healthy men.

Short-term disuse leads to muscle loss driven by lowered daily myofibrillar protein synthesis (MyoPS). However, disuse commonly results from muscle damage, and its influence on muscle deconditioning during disuse is unknown. Twenty-one males [20 ± 1 yr, BMI = 24 ± 1 kg·m-2 (± SE)] underwent 7 days of unilateral leg immobilization immediately preceded by 300 bilateral, maximal, muscle-damaging eccentric quadriceps contractions (DAM; subjects n = 10) or no exercise (CON; subjects n = 11). Participants ingested deuterated water and underwent temporal bilateral thigh MRI scans and vastus lateralis muscle biopsies of immobilized (IMM) and nonimmobilized (N-IMM) legs. N-IMM quadriceps muscle volume remained unchanged throughout both groups. IMM quadriceps muscle volume declined after 2 days by 1.7 ± 0.5% in CON (P = 0.031; and by 1.3 ± 0.6% when corrected to N-IMM; P = 0.06) but did not change in DAM, and declined equivalently in CON [by 6.4 ± 1.1% (5.0 ± 1.6% when corrected to N-IMM)] and DAM [by 2.6 ± 1.8% (4.0 ± 1.9% when corrected to N-IMM)] after 7 days. Immobilization began to decrease MyoPS compared with N-IMM in both groups after 2 days (P = 0.109), albeit with higher MyoPS rates in DAM compared with CON (P = 0.035). Frank suppression of MyoPS was observed between days 2 and 7 in CON (IMM = 1.04 ± 0.12, N-IMM = 1.86 ± 0.10%·day-1; P = 0.002) but not DAM (IMM = 1.49 ± 0.29, N-IMM = 1.90 ± 0.30%·day-1; P > 0.05). Declines in MyoPS and quadriceps volume after 7 days correlated positively in CON (r2 = 0.403; P = 0.035) but negatively in DAM (r2 = 0.483; P = 0.037). Quadriceps strength declined following immobilization in both groups, but to a greater extent in DAM. Prior muscle-damaging eccentric exercise increases MyoPS and prevents loss of quadriceps muscle volume after 2 (but not 7) days of disuse.NEW & NOTEWORTHY We investigated the impact of prior muscle-damaging eccentric exercise on disuse-induced muscle deconditioning. Two and 7 days of muscle disuse per se lowered quadriceps muscle volume in association with lowered daily myofibrillar protein synthesis (MyoPS). Prior eccentric exercise prevented the decline in muscle volume after 2 days and attenuated the decline in MyoPS after 2 and 7 days. These data indicate eccentric exercise increases MyoPS and transiently prevents quadriceps muscle atrophy during muscle disuse.

Effect of gallium maltolate on a model of chronic, infected equine distal limb wounds.

Distal limb wounds are common injuries sustained by horses and their healing is fraught with complications due to equine anatomy, prevalence of infection, and challenges associated with wound management. Gallium is a semi-metallic element that has been shown to possess antimicrobial properties and aid in wound healing in various preclinical models. The effects of Gallium have not been studied in equine wound healing. Therefore, the objective of this study was to compare healing rates between gallium-treated and untreated wounds of equine distal limbs and to demonstrate the antimicrobial effects of gallium on wounds inoculated with S. aureus. Using an established model of equine wound healing we demonstrated beneficial effects of 0.5% topical gallium maltolate on equine wound healing. Specifically we documented reduced healing times, reduced bioburden, and reduced formation of exuberant granulation tissue in wounds treated with gallium maltolate as compared with untreated wounds. Gallium appeared to exert its beneficial effects via its well-described antimicrobial actions as well as by altering the expression of specific genes known to be involved in wound healing of horses and other animals. Specifically, gallium maltolate appeared to increase expression of transforming growth factor-ß in both infected and un-infected wounds. Further work is needed to document the effects of gallium on naturally occurring equine wounds and to compare the effects of gallium with other wound treatment options. These data, however, suggest that gallium may be an attractive and novel means of improving equine distal limb wound healing.

Adult Human Vein Grafts Retain Plasticity of Vessel Identity.

BACKGROUND: The spiral saphenous vein graft is an excellent choice for venous reconstruction after periphery vein injury, but only few cases have been reported. We implanted a segment of a single saphenous vein into both the popliteal vein as a venous vein graft and into the popliteal artery as an arterial vein graft at the same time in a trauma patient; we then had an extraordinary opportunity to harvest and examine both patent venous and arterial vein grafts at 2 weeks after implantation. METHODS: A spiral saphenous vein graft was made as previously described and implanted into the popliteal vein and artery as interposition grafts; because of the patient's serious injuries, an amputation was performed at day 18 after vascular reconstruction. The grafts were harvested, fixed, and examined using histology and immunohistochemistry. RESULTS: Both grafts were patent, and there was a larger neointimal area in the venous graft compared to the arterial graft. There were CD31- and vWF-positive cells on both neointimal endothelia, with subendothelial deposition of α-actin-, CD3-, CD45-, and CD68-positive cells. There were fewer cells in the venous graft neointima compared to the arterial graft neointima; however, there were more inflammatory cells in the neointima of the venous graft. Some of the neointimal cells were PCNA-positive, whereas very few cells were cleaved caspase-3 positive. The venous graft neointimal endothelial cells were Eph-B4 and COUP-TFII positive, while the arterial graft neointimal endothelial cells were dll-4 and Ephrin-B2 positive. CONCLUSIONS: The spiral saphenous vein graft remains a reasonable choice for vessel reconstruction, especially in the presence of diameter mismatch. Both the venous and arterial grafts showed similar re-endothelialization and cellular deposition; the venous graft had more neointimal hyperplasia and inflammation. At an early time, endothelial cells showed venous identity in the venous graft, whereas endothelial cells showed arterial identity in the arterial graft. CLINICAL RELEVANCE: Veins can be used as venous or arterial vein grafts but venous grafts have more neointimal hyperplasia and inflammation; vein grafts acquire different vessel identity depending on the environment into which they are implanted.

Role of PAX-7 as a tissue marker in mangled extremity: a pilot study.

The rising incidence of mangled extremity seen in modern trauma has lead to significant patient mortality. A lot of research is going on at microcellular level for a better understanding of tissue injury, repair and regeneration. PAX-7 is one such transcription factor, a marker of satellite stem cells in skeletal muscle. Though few studies have shown concrete evidence of increased expression of PAX-7 in the nearby injured zone in skeletal muscle post-injury, none has studied its expression in an event of mangled injury of limb in humans. We, hereby, attempted to identify whether PAX-7 expression of tissue near the zone of injury, after grievous trauma like mangled injury of extremities, actually increases, decreases or remains unaffected. A pilot study was conducted on 30 cases at a level 3 trauma centre; patients were segregated into two groups-group I with MESS score ≥ 7 and group II with score < 7. For group I patients, amputation was planned, and for group II, limb salvage surgery was planned. Skeletal muscle samples from three different zones (A, B and C) in group I, while pre- and post-debridement skeletal muscle samples in group II were sent for microscopic examination and IHC staining with PAX-7 antibody. A definite increase in PAX-7 expression, post-trauma near the zone of injury (Zone B and C in group I and post-debridement in group II), was noted. Increased expression of PAX-7 signifies increased recruitment of satellite stem cells near the injury zone, thereby reflecting the activation of skeletal muscle regeneration cascade. Hence, increased staining of PAX-7 in tissues could be a viable marker for identifying potential regeneration of skeletal muscle post-injury.

Mitochondrial dysfunction is an acute response of articular chondrocytes to mechanical injury.

Mitochondrial (MT) dysfunction is known to occur in chondrocytes isolated from end-stage osteoarthritis (OA) patients, but the role of MT dysfunction in the initiation and early pathogenesis of post-traumatic OA (PTOA) remains unclear. The objective of this study was to investigate chondrocyte MT function immediately following mechanical injury in cartilage, and to determine if the response to injury differed between a weight bearing region (medial femoral condyle; MFC) and a non-weight bearing region (distal patellofemoral groove; PFG) of the same joint. Cartilage was harvested from the MFC and PFG of 10 neonatal bovids, and subjected to injurious compression at varying magnitudes (5-17 MPa, 5-34 GPa/s) using a rapid single-impact model. Chondrocyte MT respiratory function, MT membrane polarity, chondrocyte viability, and cell membrane damage were assessed in situ. Cartilage impact resulted in MT depolarization and impaired MT respiratory function within 2 h of injury. Cartilage from a non-weight bearing region of the joint (PFG) was more sensitive to impact-induced MT dysfunction and chondrocyte death than cartilage from a weight-bearing surface (MFC). Our findings suggest that MT dysfunction is an acute response of chondrocytes to cartilage injury, and that MT may play a key mechanobiological role in the initiation and early pathogenesis of PTOA. CLINICAL SIGNIFICANCE: Direct therapeutic targeting of MT function in the early post-injury time frame may provide a strategy to block perpetuation of tissue damage and prevent the development of PTOA. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:739-750, 2018.

Repeated exposure to high-frequency low-amplitude vibration induces degeneration of murine intervertebral discs and knee joints.

OBJECTIVE: High-frequency, low-amplitude whole-body vibration (WBV) is being used to treat a range of musculoskeletal disorders; however, there is surprisingly limited knowledge regarding its effect(s) on joint tissues. This study was undertaken to examine the effects of repeated exposure to WBV on bone and joint tissues in an in vivo mouse model. METHODS: Ten-week-old male mice were exposed to vertical sinusoidal vibration under conditions that mimic those used clinically in humans (30 minutes per day, 5 days per week, at 45 Hz with peak acceleration at 0.3g). Following WBV, skeletal tissues were examined by micro-computed tomography, histologic analysis, and immunohistochemistry, and gene expression was quantified using real-time polymerase chain reaction. RESULTS: Following 4 weeks of WBV, intervertebral discs showed histologic hallmarks of degeneration in the annulus fibrosus, disruption of collagen organization, and increased cell death. Greater Mmp3 expression in the intervertebral disc, accompanied by enhanced collagen and aggrecan degradation, was found in mice exposed to WBV as compared to controls. Examination of the knee joints after 4 weeks of WBV revealed meniscal tears and focal damage to the articular cartilage, changes resembling osteoarthritis. Moreover, mice exposed to WBV also demonstrated greater Mmp13 gene expression and enhanced matrix metalloproteinase-mediated collagen and aggrecan degradation in articular cartilage as compared to controls. No changes in trabecular bone microarchitecture or density were detected in the proximal tibia. CONCLUSION: Our experiments reveal significant negative effects of WBV on joint tissues in a mouse model. These findings suggest the need for future studies of the effects of WBV on joint health in humans.

Lineage tracing and genetic ablation of ADAM12(+) perivascular cells identify a major source of profibrotic cells during acute tissue injury.

Profibrotic cells that develop upon injury generate permanent scar tissue and impair organ recovery, though their origin and fate are unclear. Here we show that transient expression of ADAM12 (a disintegrin and metalloprotease 12) identifies a distinct proinflammatory subset of platelet-derived growth factor receptor-α-positive stromal cells that are activated upon acute injury in the muscle and dermis. By inducible genetic fate mapping, we demonstrate in vivo that injury-induced ADAM12(+) cells are specific progenitors of a major fraction of collagen-overproducing cells generated during scarring, which are progressively eliminated during healing. Genetic ablation of ADAM12(+) cells, or knockdown of ADAM12, is sufficient to limit generation of profibrotic cells and interstitial collagen accumulation. ADAM12(+) cells induced upon injury are developmentally distinct from muscle and skin lineage cells and are derived from fetal ADAM12(+) cells programmed during vascular wall development. Thus, our data identify injury-activated profibrotic progenitors residing in the perivascular space that can be targeted through ADAM12 to limit tissue scarring.

Single high-energy impact load causes posttraumatic OA in young rabbits via a decrease in cellular metabolism.

Articular cartilage deterioration commonly occurs following traumatic joint injury. Patients with posttraumatic osteoarthritis (PTA) experience pain and stiffness in the involved joint causing limited mobility and function. The mechanism by which PTA occurs has not been fully delineated. The goal of this study was to determine if a single high-energy impact load could cause the development of PTA in 3-month-old NZ White rabbits. Each rabbit underwent the application of a single, rapid, high-energy impact load to the posterior aspect of their right medial femoral condyle using a previously validated mechanism. At regular intervals (0, 1, 6 months) the injured cartilage was harvested and analyzed for the presence of PTA. Each specimen was assessed histologically for cell and tissue morphology and chondrocyte metabolism, including BMP-2 production and synthesis of extracellular matrix (type II procollagen mRNA). Cartilage from the contralateral sham limb, as well as uninjured cartilage from the experimental limb served as internal controls for each animal. Significant changes were found in the morphology of the cartilage including proteoglycan loss along with decreased BMP-2 and type II procollagen mRNA staining. These findings confirm that a single high-energy impact load can cause the development of PTA by disrupting the extracellular matrix and by causing a decrease in chondrocyte metabolism.

Determination of ideal PtcO2 measurement time in evaluation of hypoxic wound patients.

OBJECTIVE: Evaluation of ideal time for baseline PtcO2 readings in air, elevation test, and oxygen challenge during evaluation of hypoxic wound patients. DESIGN: Retrospective analysis. IRB APPROVAL: Western IRB deemed this study exempt from requiring IRB approval. PATIENTS: 202 patients with lower extremity wounds. METHOD: Patients had PtcO2 measurements using 6 electrodes positioned in 3 paired locations along the limb (above the knee: AK; below the knee: BK; and foot). Measurements were made from each electrode at 7 different time-event occasions: position of limb (supine or elevated), type of breathing gas (sea level air or oxygen), and time of measurement. A total of 8,484 measurements were analyzed by first examining each electrode's data, and then pooling the data for each location pair. MAIN RESULTS: PtcO2 readings for air (10 minutes) were less than air at 20 minutes. Maximal readings were close to the 20-minute mark for AK and BK measurements, and closer to 30 minutes for the foot. Elevation test at 3 versus 5 minutes showed a continuing decline in PtcO2 values. Oxygen challenge readings at 5 and 10 minutes were significantly different: the latter always larger than the former. CONCLUSION: Ideal times for baseline readings, leg elevation test, and oxygen challenge test are at least 20, 5, and 10 minutes, respectively.

Radiocalcium absorption is reduced in postmenopausal women with vertebral and most types of peripheral fractures.

Intestinal calcium absorption accounts for 60% of the variance in calcium balance and is therefore a potentially very important determinant of bone status. Whether measured by the balance technique or with radiocalcium, it is known to be significantly reduced in postmenopausal women with vertebral and hip fractures. By contrast, there is very little information about calcium absorption in other types of postmenopausal fracture. We now report a series of 549 untreated, Caucasian postmenopausal women in whom we recorded prevalent fractures, measured radiocalcium absorption, and obtained radiographs of the lateral thoracic and lumbar spine. Of these women, 172 had no prevalent fractures, showed normal spine radiographs, and served as controls; 72 had one or more peripheral fractures but normal spine radiographs; 147 had one or more wedged or crushed vertebrae but no peripheral fractures; and 158 had a history of peripheral fracture and one or more fractured vertebrae. Age-adjusted radiocalcium absorption was significantly lower in the two groups with spinal fractures than in the controls ( P<0.001) but not in the group with peripheral fractures only. It was also lower in the cases with more than two spinal fractures than in those with two or less (P<0.001). In respect of peripheral fractures, the greatest age-adjusted absorption deficit was found in fractures of the humerus (35%) followed by hip (32%), spine (21%), wrist (19%), and rib 17% (all significant but not significantly different from each other). Lesser deficits in tibia, ankle and foot fractures were not significant but type 2 errors could not be excluded. We conclude that impaired calcium absorption is particularly associated with those fractures for which osteoporosis is a significant risk factor.

Optical measurements of tissue oxygen saturation in lower limb wound healing.

This review has highlighted the role of oxygen in wound healing and in the mechanism of preventing infection. Optical measurements of tissue SO2 in wounds can provide valuable information, not only about the inflammatory state of the wound, but also about healing potential in ulcers and critical limb ischaemia. The technique is fast, non-invasive and can be used without the necessity for contact with the skin.

[Monitoring of the early stages of bone healing process based on serum osteocalcin level changes]. / Monitorowanie wczesnych faz zrostu kostnego na podstawie zmian poziomu osteokalcyny w surowicy krwi.

The aim of this paper was assessment of utility of serum osteocalcin levels in monitoring early stages of bone healing and early detection of bone healing disorders. Serum osteocalcin level and alkaline phosphatase activity was assessed with acute long bone fractures and with delayed bone union and pseudoarthroses. 25 patients underwent the trial. The analysis of the results confirmed the utility of serum osteocalcin level as a prognostic factor in early detecting of union disorders and its correlation to radiological examination.

C-reactive protein to transthyretin ratio for the early diagnosis and follow-up of postoperative infection.

The clinical usefulness of C-reactive protein (CRP) and of transthyretin (TTR) for the early diagnosis and follow-up of infection after an open fracture was prospectively investigated (cohort A). It was complemented by a retrospective study of trauma patients admitted to an intensive care unit (cohort B). Serial determinations of serum CRP and TTR concentrations were first performed in uninfected patients from cohort A to define a reference profile during the early postoperative period. It showed a concomitant increase in CRP and decrease in TTR concentrations, followed by progressive return to initial values in patients free from bacterial infection. Variations of the CRP/TTR ratio were analyzed. Recovery phase was defined by an exponential evolution of the two plasma proteins and of their ratio value. The CRP and TTR concentrations were independent of sex and severity of the trauma. In the case of postoperative infection, patients of cohort A revealed amplified CRP and TTR responses usually preceding the occurrence of clinical signs. During successful antibiotic therapy, their recovery response became superimposable to that of the reference group. The same profiles were recorded in cohort B patients admitted with lower limb fractures or various types of trauma. This suggests that observations made on cohort A can be extrapolated to othertrauma patients. We recommend that serial measurements of CRP and TTR and of their ratio should be performed every 2 days to appropriately follow-up these patients.

Oxidant production and immune response after stretch injury in skeletal muscle.

PURPOSE: This study investigated oxidant production and associated immune response after acute muscle stretch injury. METHODS: A standardized single stretch injury was performed on the tibialis anterior (TA) muscle of 36 male New Zealand white rabbits while contralateral control limbs underwent a sham surgery. Animals were sacrificed 0, 4, 12, 24, 48, and 72 h after injury. Potential sites of oxidant production, measured with a dichlorofluorescein (DCF) probe, were evaluated using two separate buffers. RESULTS: Nonmitochondrial oxidant production measured under basal buffer conditions (0.1 M potassium phosphate) was increased in both injured and control limbs at 24 h (P < 0.01) and was greater in the injured limb at 12 and 48 h (P < 0.01). There was also an interaction of time and injury (P < 0.05). Maximum oxidant production by neutrophils and macrophages, stimulated by the induced buffer (including 1.7 mM ADP, 0.1 mM NADPH, 0.1 mM FeCl3), was increased in both injured and control limbs at 4 h (P < 0.01) and was greater in the injured limb at 48 h (P < 0.01). Myeloperoxidase (MPO) activity, indicating the presence of activated neutrophils, was higher in the injured limb at 4 and 48 h (P < 0.01). The activities of superoxide radical producing and quenching enzymes, xanthine oxidase (XO) and superoxide dismutase (SOD), were elevated at 24 (P < 0.01) and 4 h (P < 0.05), respectively, but showed no difference between injured and control limbs. CONCLUSION: We conclude that acute muscle stretch injury and the required surgeries to generate the injury result in a biphasic increase in oxidant production in both injured and control limbs, suggesting a systemic immune response. The increase in oxidant production at 4 h may be caused by an increase in activated neutrophils, whereas XO activity may contribute to oxidant generation at 24 h.

Comparison of measures of physiologic stress during treadmill exercise in a patient with 20% lower extremity burn injuries and healthy matched and nonmatched individuals.

Patients with burn injuries are referred for rehabilitation within days after the injuries to encourage early ambulation and functional training. Many of these patients are hypermetabolic at rest. Metabolic demands of activity are added to the already hypermetabolic state and elevate total energy requirements and some physiologic measures. Reports on the physiologic stress imposed by therapeutic activities for patients with burn injuries are limited to low levels of metabolic demand (< or =2 metabolic equivalents [METS]). The degree of stress imposed by functional activities such as ambulation (3 METS) and stair climbing (5 METS) is not known for adults with burn injuries. The purpose of this study was to report the clinical measures of myocardial and physiologic stress in a patient with 20% lower extremity total body surface area burns during an exercise challenge equivalent to stair climbing. Physiologic measures were assessed before and during a treadmill activity (5 METS) for a 40-year-old obese man 3 weeks after he had lower extremity burn injuries. These measures were compared with mean values for 62 healthy counterparts and 6 healthy subjects matched for age, gender, and fitness level. Heart rate, systolic blood pressure, rate pressure product, and the rating of perceived exertion for the patient with burn injuries were higher at baseline and during exercise than the mean values for the 62 healthy individuals and the 6 matched subjects. The steady state exercise values for heart rate, systolic blood pressure, rate pressure product, and rating of perceived exertion at 6 minutes were 189 beats per minute, 190 mm Hg, 3591, and 17, respectively, for the patient with burn injuries and were 111.3 beats per minute, 149 mm Hg, 1680, and 11.7, respectively, for the 6 matched subjects. Ventilation during exercise also increased for the patient with burn injuries more than for the matched subjects (3/4 vs 1/4). Pain experienced by the patient with burn injuries decreased with activity (9.8 vs 7.3 on a 15-cm scale). Treadmill walking produced near maximal responses for most physiologic measures for this patient who was hypermetabolic at rest. We provided normative data to assist therapists who work with patients with similar burn injuries.

Mechanism of accumulation of 99mTc-MDP to bone: correlation of in vivo data with in vitro data.

The uptake of 99mTc-methylene diphosphonate (99mTc-MDP) to bone was studied in two types of bone diseases using the tibial bone of rats. One was a planned, specific bone injury, and the other was an osteomyelitis model. Both models were evaluated with scintigraphy (for scintigram and uptake ratio) and 31P-magnetic resonance spectroscopy [for pH, mineral (inorganic) phosphate to creatine phosphate (Pi/PCr) ratio and ATP/PCr ratio] over a period of three weeks. Results in the scintigram of the injured bone model demonstrated a distinct uptake spot, while that in the scintigram of the osteomyelitis model showed a diffuse uptake. The scintigraphy demonstrated an increase in the 99mTc-MDP uptake ratio in the both models with a peak approximately one week after treatment, after which the uptake ratio gradually decreased. The uptake ratio of the injured bone model was greater than that of the osteomyelitis model. There was no significant change in pH, Pi/PCr or ATP/PCr in the injured bone model during that period. There was a significant change in pH and ATP/PCr, but not in Pi/PCr, in the osteomyelitis model during that period. Further, in the osteomyelitis model, an increased 99mTc-MDP uptake ratio reach a peak at about one week, while the pH and the ATP/PCr were at their lowest values at about two weeks. These results suggest that the accumulation of 99mTc-MDP to the bone will be affected by the type of disease or environmental factors such as pH and concentration of phosphates.

[The mechanism of the effect of insulin on the interhormonal relations of androgens and glucocorticoids in the body]. / Mekhanizm vplyvu insulinu na mizhhormonal'ni vidnoshennia androheniv ta hliukokortykoïdov v orhanizmi.

Forty-six essentially healthy persons, 96 patients with carcinoma of the stomach (stage II, III and IV), 26 patients with idiopathic aseptic necrosis of the head of the femur and 42 patients in the time course of their medical condition related to traumata were studied for changes in the excretion of metabolites of androsteroidogenesis and glucocorticoids under the influence of insulin. It has been established that insulin actions on steroidogenesis depend upon interhormonal relations of androgens and glucocorticoids under their values being low, insulin stimulates androsteroidogenesis and reduces the production of glucocorticoids, while their high values are associated with activation of hypothalamic-pituitary-adrenal axis due to insulin hypoglycemia, with the production of glucocorticoids rather that androgens tending to be on the increase. There has been revealed for the first time the ability of insulin to stimulate, under dyscorticism, androsteroidogenesis and lower the production of glucocorticoids, which facts permit recommending the use of insulin to lessen catabolic, contrainsular, and immunodepressive effects of glucocorticoids in the organism.

Ultrastructural events following acute muscle trauma.

The purpose of this study was to determine the ultrastructural events occurring in skeletal muscle following acute blunt trauma. Male rats weighing 250 g were subjected to a single impact trauma to the medial gastrocnemius muscle while under general anesthesia. Hemorrhage, inflammation, non-necrotic degeneration, and later regeneration were observed. In the short term following impact (6-24 h), the damaged segments showed gross tearing and degeneration. A large number of mononuclear cells were seen in the intercellular connective tissue and within the damaged muscle cells. By 24-48 h, there was an increase in the number of sarcolemmal nuclei, some of which were likely of satellite cell origin. By day 3, regenerating muscle cells displayed central nuclei and reorganizing sarcomeres. By day 6, further progression of regeneration was seen. Moreover, focal interstitial collagen formation suggested minimal to mild scar formation. On days 14, 21, and 30 after trauma, the muscle appeared to have healed and no abnormalities could be found at the site of injury. In parallel with the ultrastructural events noted, the injured muscles underwent a marked catabolic response and showed a reproducible fall (-27%, P less than 0.001) in total protein content within 48 h. Muscle protein accumulation commenced after day 3; however, complete repletion of the loss did not occur until day 21 post-injury.