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In an attempt to shorten recovery time and improve performance, strength and endurance athletes occasionally turn to the illicit use of anabolic-androgenic steroids AAS. The effects of AAS mesterolone: M on specific phenotypic adaptations muscle wet weight, cross-sectional area, and fiber type composition in three hindlimb muscles soleus: Body weight gain occurred throughout the study for all groups.
However, the body weight gain was significantly minimized with exercise. This effect was blunted with mesterolone treatment. Both AAS treatment Sed-M and high-intensity, aerobic training ex-C increased the wet weights of all three muscles and induced differential hypertrophy of pure and hybrid fibers. Combination of AAS and training ex-M resulted in enhanced hypertrophy. Overall, the AAS-induced differential adaptive changes amounted to significant fiber type transformations in the fast-to-slow direction in SOL.
AAS treatment had a significant effect on muscle weights and fiber type composition in SOL, TA and GAS which was even maximized in animals subjected to metabolically high-intensity aerobic exercise.
July 22, ; Accepted: October 17, ; Published: This is an open-access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors have declared that no competing interests exist. Anabolic-androgenic steroids AAS are synthetic derivatives of testosterone which have been chemically modified to maximize anabolic effects and minimize undesirable androgenic effects [ 1 ].
Although banned from sports, the illicit use of AAS by professional and recreational athletes continues despite a long list of serious side effects [ 3 ]. In general, these athletes are interested in decreasing body fat while increasing muscle mass and strength in an effort to enhance physical performance [ 4 ]. Skeletal muscle has the ability to respond to new endogenous and exogenous physiological demands by changing its phenotypic characteristics [ 5 ]. The large diversity of myosin heavy chain MHC isoforms expressed in muscle helps to form the basis for this remarkable plasticity.
It is the expression and co-expression of these various MHC isoforms within a given fiber that ultimately delineates the entire range of fiber types [ 6 - 8 ]. The prevalence of certain types of these fibers accounts for the functional and structural characteristics of a given muscle, and hence its phenotype.
The present study was undertaken to examine the effects of mesterolone an anabolic-androgenic steroid on the fiber type composition and cross-sectional area of skeletal muscle fibers of sedentary and high-intensity, aerobically-exercised transgenic mice. Thus, the aim was to investigate the role of mesterolone in a supposed catabolic environment.
Does the interaction of anabolic hormone treatment and high-intensity aerobic exercise produce an increase in muscle mass and redistribution of skeletal muscle fiber types? Are muscles with distinct metabolic and contractile properties i. As such, three skeletal muscles were studied under these experimental conditions: The entire range of pure and hybrid fiber types were delineated using myofibrillar adenosine triphosphatase mATPase histochemical methods allowing the detection of subtle changes in type composition.
The mice used in the current study were genetically engineered to exhibit a lipid profile closer to humans allowing for a more relevant comparison. The transgenic mice used in this study have been described in detail elsewhere [ 9 , 10 ]. This transgenic mouse, as compared with the wild-type, exhibits a lipid profile closer to humans and hence, is more akin to a human model from a comparative physiological perspective. Monday, Wednesday, and Friday.
Mesterolone 1 alpha-methyl beta-hydroxy-5 alpha-androstanone was chosen for two reasons: Gum arabic compatible as a vehicle for the hydrophobic mesterolone is inert, non-toxic, and has been used to improve absorption in the small intestine [ 11 ]. Body weights were tracked weekly throughout the study Table 2. At the end of the experimental period, fasted mice were anesthetized with a 1: Soleus SOL , tibialis anterior TA , and gastrocnemius GAS muscles were carefully removed, weighed, and the animals were sacrificed with an overdose of the anesthetic.
Weekly body weight BW taken over the course of the study. The middle portion of each muscle was separated, oriented in a mixture of gum tragacanth Sigma, St. Fiber types were identified using myofibrillar adenosine triphosphatase mATPase histochemistry [ 14 ] following pre-incubation at pH 4. In some cases, the alkaline pH was slightly adjusted to optimize the reaction The muscle sections obtained following pre-incubation at pH 4.
The fields were randomly selected, and all muscle fibers encompassed in these fields were evaluated. Insufficient numbers of hybrid fiber types IC and IIAC were found to obtain statistically meaningful cross-sectional values. There was a tendency for BW to gradually increase throughout the trial period for all groups Table 2. However, the smallest overall weight gain was achieved by the training mice treated only with gum arabic Ex-C.
Mesterolone treatment appeared to counteract the attenuated weight gain effect of exercise. The wet weights of all three muscles soleus, tibialis anterior, and gastrocnemius were smallest in sedentary animals treated with gum arabic Sed-C and largest in exercised animals treated with mesterolone Ex-M Table 3. The effect of mesterolone in sedentary mice Sed-C vs. Sed-M was stronger than in exercised mice Ex-C vs. Ex-M suggesting exercise blunted the steroid effect. The effect of exercise per se in promoting a significant increase in MW was comparable among the muscles and was stronger than induced by mesterolone with the exception of TA: Sed-C and Sed-M vs.
Exercise plus mesterolone appeared to have an additive effect, such that the largest muscle wet weights were obtained by the Ex-M group for all three muscles. This effect was blunted by exercise. On the other hand, the various treatments exercise, mesterolone, and the combination of both had a minimal impact on fiber type distribution in the predominantly fast muscles TA and GAS Table 4. Compared to the other groups, SOL of Sed-C showed the least variability in fiber type cross-sectional areas among the different fiber types.
The high-intensity exercise per se or in steroid-treated mice Sed-C vs. Ex-C or Sed-M vs. Ex-M also caused large, significant increases in the sizes of all major fiber types in SOL.
For the most part, exercise per se Sed-C vs. Ex-C or in mesterolone-treated mice Sed-M vs. Ex-M or Sed-M vs. Professional and recreational athletes continue to use AAS with the hope of enhancing performance by increasing muscle mass and strength [ 4 ]. Continued research in this area could yield important information regarding the impact of AAS on skeletal muscle fiber type distribution and size, giving insight into potential AAS-induced alterations in phenotypic profile.
For this purpose, the present study meticulously delineated the entire range of mATPase-based fiber types utilizing a transgenic mice specifically engineered to express a lipid profile similar to humans. The present study used a 6-week, high-intensity treadmill running program typically catabolic in nature to evaluate the interaction of a 3-week anabolic-androgenic oral program known to promote body and muscle mass gains.
In this study, all animals gained body weight BW over the course of the 6-week program. However, the BW gain of the exercising mice both with and without AAS supplementation was minimized compared to the control groups. These data are consistent with studies demonstrating aerobic exercise plays a key role in body weight control [ 4 ].
In addition, the anabolic effect of mesterolone in exercised mice appeared to play a role in counteracting this catabolic effect. The high-intensity, aerobic exercise caused a significant increase in muscle wet weights with an additional increase following mesterolone treatment.
In all three muscles, the effect of mesterolone in sedentary mice was stronger than in exercised mice suggesting that the effect of exercise partially blunted the anabolic effect of mesterolone. Skeletal muscles express a variety of different types of proteins associated with metabolism, inflammation, and contractile activity in response to exercise.
A large number of different systemic and muscular proteins could also result from anabolic-androgenic steroid treatment. Although the elucidation of the complex molecular mechanisms underlying the ergogenic effects of AAS treatment was not the aim of the present study, muscle function may be improved by increasing protein synthesis or membrane stabilization [ 18 ].
This may be accomplished via a competitive occupancy of glucocorticoid receptors by AAS which would act antagonistically to the catabolic action of glucocorticoid hormones. In the present study, adaptive differences observed among the three muscles examined implies alternative binding of the steroid to a number of androgen receptors resulting in agonistic promotion of skeletal muscle protein synthesis [ 19 , 20 ].
Androgens receptors AR are expressed in satellite cells, differentiated myofibers, intramuscular fibroblasts, and different types of motoneurons. In addition, the regulation of plasmatic levels of insulin-like growth factor-1 IGF-1 , growth hormone, and thyroid hormone as well as, the antagonism of glucocorticoids are roles linked to anabolic-androgenic signaling [see 21].
The effects of the combination of mesterolone treatment and exercise on skeletal muscle of CETP transgenic mice are unknown. Previous studies utilizing CETP mice have shown that the plasmatic level of thyroid hormones influences lipoprotein metabolism. A previous study from our laboratory using this same transgenic mouse model has shown that mesterolone treatment in sedentary mice caused an increase in total cholesterol, triglycerides, LDL-c and VLDL-c, whereas the combination of AAS treatment and exercise resulted in the reverse i.
Taken together, these data suggest the effect of AAS treatment on muscle growth and the additive hypertrophic effect following exercise may be the result of a transcriptional program involving thyroid regulation, IGF-1 and its splice variant mechano growth factor MGF [ 21 ].
Such a transcription program would likely differ on the basis of the metabolic and twitch characteristics of the muscle. To date, studies investigating the effects of AAS on muscle fiber type composition have reported equivocal results. Although comparisons between the various studies are difficult, most research in this area has shown no effect of AAS administration on fiber type distribution or relative myosin heavy chain isoform content in various muscles from both human [ 25 - 28 ] and rat [ 12 , 23 - 32 ].
A few studies have, however, documented AAS-induced alterations in fiber type composition. Egginton and Dimauro et al. Indeed, this increase in the number of oxidative fibers may explain the significant improvement in EDL fatigue resistance after weeks of AAS treatment [ 35 ]. These data have more recently been supported by Fontana et al. The present study supports and extends these findings with conversions in the fast-to-slow direction found in the soleus muscle after AAS administration and high-intensity exercise.
Variable results have also been documented regarding the impact of AAS administration on muscle and fiber size. Although some studies have reported no change [ 29 , 36 , 38 , 39 ] or even a decrease [ 14 ] in fiber size following steroid treatment, most have demonstrated a significant increase in muscle mass and fiber size [ 12 , 25 , 28 , 34 , 37 , 40 , 41 ].
AAS administration has been shown to increase muscle protein synthesis [ 42 , 43 ] and ultimately muscle mass. This increase in muscle mass is predominantly the result of muscle fiber hypertrophy [ 28 ] and involves satellite cell activation and incorporation into the muscle fiber [ 44 ]. In the present study, mesterolone treatment alone resulted in hypertrophy of most fiber types and significant increases in the wet weights of all three muscles.
Compared to AAS-treatment alone, the high-intensity exercise protocol caused comparable increases in fiber sizes and wet weight of all three muscles. However, the combination of high-intensity, endurance exercise and mesterolone treatment resulted in an additive hypertrophic effect in fiber sizes and muscle wet weights.