Search

It is unknown whether activity-based physical therapy (ABPT) modalities that mobilize the paralyzed limbs improve bone integrity at the highly fracture-prone epiphyseal regions of the distal femur and proximal tibia following severe spinal cord injury (SCI). In this study, 4-mo-old skeletally mature littermate-matched male Sprague-Dawley rats received either SHAM surgery or severe contusion SCI. At 1 wk postsurgery, SCI rats were stratified to undergo no-ABPT, two 20-min bouts/day of quadrupedal bodyweight-supported treadmill training (qBWSTT), or hindlimb passive isokinetic bicycle (cycle) training, 5 days/wk for another 3 wk. We assessed locomotor recovery and plantar flexor muscle mass, tracked cancellous and cortical bone microstructure at the distal femoral and proximal tibial epiphyses using in vivo microcomputed tomography (microCT), and evaluated bone turnover at the tibial epiphysis with histomorphometry. All SCI animals displayed persistent hindlimb paralysis and pervasive muscle atrophy. Over the initial 2 wk, which included 1 wk of no exercise and 1 wk of ABPT acclimation, a similar magnitude of bone loss developed in all SCI groups. Thereafter, cancellous bone loss and cortical bone decrements increased in the SCI no-ABPT group. qBWSTT attenuated this trabecular bone loss but did not prevent the ongoing cortical bone deficits. In comparison, twice-daily cycle training increased the number and activity of osteoblasts versus other SCI groups and restored all bone microstructural parameters to SHAM levels at both epiphyseal sites. These data indicate that a novel passive isokinetic cycle training regimen reversed cancellous and cortical bone deterioration at key epiphyseal sites after experimental SCI via osteoblast-mediated bone anabolic mechanisms, independent of locomotor recovery or increased muscle mass. NEW & NOTEWORTHY: This study was the first to assess how quadrupedal bodyweight-supported treadmill training or passive isokinetic bicycle (cycle) training impacts bone recovery at the distal femoral and proximal tibial epiphyses in a rat model of severe contusion spinal cord injury. Our results demonstrate that passive isokinetic cycle training completely restored cancellous and cortical bone microstructural parameters at these sites via osteoblast-mediated bone anabolic actions, independent of locomotor recovery or increased plantar flexor muscle mass. [ABSTRACT FROM AUTHOR]

Bone may contain an intraskeletal reservoir of sex steroids that is capable of producing biological effects. The purposes of these experiments were to 1) establish and validate methods to extract and measure intraskeletal sex hormones, 2) compare serum and intraskeletal sex hormone abundance, and 3) determine the impact of testosterone-enanthate administration and orchiectomy on intraskeletal sex hormone concentrations. Tibiae from male F344 rats were crushed, suspended in an aqueous buffer, disrupted mechanically and sonically, extracted with organic solvents, dried, and reconstituted in assay buffer appropriate for measurement of testosterone, dihydrotestosterone, and estradiol by immunoassay. Prior to extraction, bone homogenate was spiked with [[sup.3]H]testosterone, [[sup.3]H]dihydrotestosterone, or [[sup.3]H]estradiol, and >80% of each [sup.3]H-labeled sex hormone was recovered. Extracted bone samples were also assayed with and without known amounts of unlabeled sex hormones, and >97% of the expected hormone concentrations were measured. Administration of testosterone-enanthate increased intraskeletal testosterone 11-fold and intraskeletal dihydrotestosterone by 82% without altering intraskeletal estradiol (P < 0.01). Conversely, orchiectomy did not alter intraskeletal testosterone or estradiol but increased intraskeletal dihydrotestosterone by 39% (P < 0.05). In intact rats, intraskeletal testosterone and dihydrotestosterone were directionally higher than in serum, whereas intraskeletal estradiol was directionally lower than serum. Serum androgens were positively correlated with intraskeletal androgens (r = 0.74-0.96, P < 0.001); however, neither serum nor intraskeletal androgens nor serum estradiol were correlated with intraskeletal estradiol. We report the validation of a novel method for measuring intraskeletal sex hormones. Our findings demonstrate that the intraskeletal sex steroid reservoirs are modifiable and only partially influenced by circulating sex hormones. testosterone; estrogen; intracrine; dihydrotestosterone; estradiol doi: 10.1152/ajpendo.00384.2010.

High-dose testosterone enanthate (TE) may prevent hypogonadism-induced osteopenia. For this study, 3-too-old male and female Fisher SAS rats underwent sham surgery, gonadectomy (GX), or GX plus 28 days TE administration (7.0 mg/wk). GX reduced serum sex hormones (i.e., testosterone, dihydrotestosterone, and estradiol) (P < 0.05) in both sexes and bone concentrations of testosterone (males only), and estradiol (females only). GX also elevated urine deoxypyridinoline/creatinine in both sexes and serum osteocalcin (females only), findings that are consistent with high-turnover osteopenia. GX reduced cancellous bone volume (CBV) and increased osteoid surfaces in tibia of both sexes. GX males also experienced reduced trabecular number and width and increased trabecular separation, whereas GX females experienced increased osteoblast and osteoid surfaces. Bone biomechanical characteristics remained unaffected by GX, except that femoral stiffness was reduced in females. In contrast, TE administration to GX rats elevated serum and bone androgens to supraphysiological concentrations in both sexes but altered neither serum nor bone estradiol in males. Additionally, TE did not prevent GX-induced reductions in serum or bone estradiol in females. TE also reduced markers of high-turnover osteopenia in both sexes. In males, TE prevented GX-induced changes in trabecular number and separation, CBV, and osteoid surfaces while diminishing osteoblast and osteoclast surfaces; however, these changes were not fully prevented in females. In both sexes, TE increased femoral length and femoral maximal strength to above that of Sham and GX animals while preventing the loss of femoral stiffness in females. In conclusion, TE administration appears protective of cancellous bone in male rats and augments cortical bone strength in both sexes. androgen; osteoblast; osteoclast; osteoporosis; osteopenia

At replacement doses, testosterone produces only modest increases in muscle strength and bone mineral density in older hypogonadal men. Although higher doses of testosterone are more anabolic, there is concern over increased adverse effects, notably prostate enlargement. We tested a novel strategy for obtaining robust anabolic effects without prostate enlargement. Orchiectomized (ORX) male rats were treated for 56 days with 1.0 mg testosterone/day, with and without 0.75 mg/day of the 5 [alpha]-reductase inhibitor MK-434. Testosterone administration elevated the prostate dihydrotestosterone concentration and caused prostate enlargement. Both effects were inhibited by MK-434. ORX produced a catabolic state manifested in reduced food intake, blunted weight gain, reduced hemoglobin concentration, decreased kidney mass, and increased bone resorption, and in the proximal tibia there was both decreased cancellous bone volume and a decreased number of trabeculae. In soleus and extensor digitorum longus muscles, ORX reduced both the percentage of type I muscle fibers and the cross-sectional area of type 1 and 2 fibers. Testosterone administration caused a number of anabolic effects, including increases in food intake, hemoglobin concentration, and grip strength, and reversed the catabolic effects of ORX on bone. Testosterone administration also partially reversed ORX-induced changes in muscle fibers. In contrast to the prostate effects of testosterone, the effects on muscle, bone, and hemoglobin concentration were not blocked by MK-434. Our study demonstrates that the effects of testosterone on muscle and bone can be separated from the prostate effects and provides a testable strategy for combating sarcopenia and osteopenia in older hypogonadal men. dihydrotestosterone; prostate; body composition; bone resorption

We studied the effect of the 5[alpha]-reductase inhibitor MK-434 on responses to testosterone (T) in orchiectomized (ORX) male Brown Norway (BN) rats aged 13 too. At 4 wk after ORX or sham surgery, a second surgery was performed to implant pellets delivering 1 mg T/day or placebo pellets. During the second 4 wk of the study, rats received injections of MK-434 (0.75 mg/day) or vehicle injections. Treatment with T elevated serum T to 75% above that for sham animals (P = 0.002) and did not affect serum dihydrotestosterone (DHT) or serum estradiol. T treatment also caused an elevation of prostate T and a marked elevation of prostate DHT. During the second half of the study, ORX rats lost an average of 18.86 [+ or -] 4.62 g body wt. T completely prevented weight loss, and the effect was not inhibited by MK-434 (P < 0.001). ORX produced a nonsignificant trend toward a small (5%) decrease in the mass of the gastrocnemius muscle (P = 0.0819). This trend was also reversed by T, and the effect of T was not blocked by MK-434. T caused a significant 16% decrease in subcutaneous fat that was not blocked by MK-434 (P < 0.05). Finally, T caused a 65% decrease in urine excretion of deoxypyridinoline, a marker of bone resorption, and again the effect was not blocked by MK-434 (P < 0.0001). In contrast, T caused a greater than fivefold increase in prostate mass, and the effect was almost completely blocked by MK-434 (P < 0.0001). This study demonstrates that 5[alpha]-reductase inhibitors may block the undesirable effects oft on the prostate, without blocking the desirable anabolic effects of T on muscle, bone, and fat. Dihydrotestosterone; body composition; bone resorption

Neutralization of tumor necrosis factor-[alpha] reverses insulin resistance in skeletal muscle but not adipose tissue. Am J Physiol Endocrinol Metab 287: E934-E938, 2004. First published June 22, 2004; doi:10.1152/ajpendo.00054.2004.--We examined the possible role of tumor necrosis factor-[alpha] (TNF-[alpha]) as a mediator of insulin resistance in maturing male Sprague-Dawley rats. Rats were treated either with goat anti-murine TNF-[alpha] IgG (anti-TNF-[alpha]) or goat nonimmune IgG (NI) for 7 days. Vascular catheters were implanted, and rats were fasted overnight before hyperinsulinemic euglycemic clamp (HUC) studies were performed. TNF-[alpha] neutralization increased the rate of glucose infusion required to maintain euglycemia by 68%. Insulin-stimulated glucose transport into individual tissues was measured after bolus administration of 2-deoxy-[[sup.14.C]]glucose during HUC. Anti-TNF-[alpha] administration increased glucose transport in muscles composed predominantly of fast-twitch fibers: white gastrocnemius muscle (68% increase) and tibialis anterior muscle (64% increase). There were nonsignificant trends for increased glucose transport in the slow-twitch soleus muscle and in the mixed-fiber red gastrocnemius muscle. Glucose transport was unchanged in visceral and subcutaneous fat. Anti-TNF treatment did not alter body weight, muscle mass, or fat mass. Anti-TNF-[alpha] did not alter the distribution of the 17-kDa and 26-kDa forms of TNF-[alpha] in either muscle or fat. However, anti-TNF-[alpha] treatment caused an ~50% reduction in the secretion of TNF-[alpha] bioactivity in vitro by explants of visceral and subcutaneous fat. We conclude that TNF-[alpha] neutralization reversed insulin resistance substantially in fast-twitch muscle and may have done so in other muscles, while having little effect in fat. TNF-[alpha] eneutralization was accompanied by reduced TNF-[alpha] bioactivity without tissue depletion of TNF-[alpha] protein. glucose transport; muscle fiber type; soluble tumor necrosis factor-[alpha]; membrane tumor necrosis factor-[alpha]