| dc.description.abstract | INTRODUCTION: Optimizing the concentration of hormones through variation of load, repetitions, and rest periods is suggested for building muscle mass in current resistance exercise prescription guidelines. Physiological actions of testosterone and cortisol occur when bound to their respective intracellular receptor. Muscle growth is initiated when testosterone binds to its androgen receptor (AR); conversely, muscle breakdown is initiated when cortisol binds to its glucocorticoid receptor (GR) in muscle cells. The secretion of both testosterone and cortisol increase following a single bout of resistance exercise (RE). While both in vitro and in vivo models indicate the significant contribution to muscle growth, the importance of the acute hormonal response in humans has been justified and refuted. However, there is recent evidence showing phosphorylation and regulation of ARs and GRs can occur in the absence of testosterone and cortisol. The equivocal results of prior studies on hormonal responses and muscle adaptation could be clarified by understanding how AR and GR are regulated. PURPOSE: The purpose of this study is to examine the differences in the androgen and glucocorticoid receptor phosphorylation between resistance trained and untrained men following an acute bout of moderate intensity resistance training. It will also look at the biopsy time point post resistance exercise for AR and GR phosphorylation following resistance training. METHODS: Ten resistance trained (RT) and ten untrained (UT) healthy, college aged (18-30) men volunteered for this study. One UT subject was unable to complete the protocol resulting in an N of 9. Subjects performed 1RM tests for back squat and leg extension 4-7 days prior to the RE protocol. There were no differences in the protocol between RT and UT groups. Subjects arrived at the lab at least 6 hours fasted and euhydrated between 10:00am-2:00pm to control for diurnal variations of hormones. Prior to training, baseline blood and muscle biopsy were collected for baseline levels. After a warm-up, subjects performed 6 sets of 10 repetitions at 75% of their 1RM with 1.5 minutes rest following each set followed by 4 set of 10 repetitions at 75% of their 1RM for leg extension with 1.5 minutes rest after each set. After completing the leg extension exercise, blood samples were collected at 5 min, 15 min, and 45 min post exercise, and biopsies were taken at 10 min, 30 min, 60 min, and 180 min post exercise. Hormonal data were analyzed using parametric methods. 2 x 4 (group x time) RMANOVAs were used to determine potential differences in testosterone and cortisol between groups (group) at PRE, 5P, 15P and 45P (time). Total receptor data were not normally distributed, thus total receptor data were analyzed using Mann-Whitney U test, Friedman test, and Wilcoxon signed-rank test. Performance data were analyzed using RMANOVAs and independent t tests. RESULTS: 1RM was significantly different between groups (p 0.05), although there were RPE significant differences across sets. There were significant differences for mean force (N) between RT and UT groups for all sets, and the RT group began to significantly decrease by set 6. There was a significant difference in work (J) between groups for sets 1 and 2, with the RT group significantly decreasing by sets 5 and 6. In both the RT and UT groups testosterone significantly increased from PRE values at 5min and 15min post exercise (p .05); however, there were differences between time points within the UT group (p = .016). In the UT group, total AR expression significantly decreased at 30P (-19.33%∆, z = -2.192, p = .027) and 60P (-10.89%∆, z = -2.192, p = .027) post exercise, but returned to baseline values by 180P (3%∆, z = -.178, p .05). There were significant decreases at 10P in p-AR Ser213 in both the RT (-28.73%∆, z = -2.293, p = .020) and UT (-32.25%∆, z = -2.073, p = .039) groups. There were no differences between or within groups (p .05) for p-AR Ser81, p-AR Ser515, or p-AR Ser650. For Total GR content, there were no differences between time points within the RT or UT groups (p .05). Total GR content was significantly greater in the RT group compared to the UT group at 10P (Mann-Whitney U = 19, z = -2.123, p = .035). For p-GR Ser134 the RT group was significantly higher than the UT group at PRE (Mann-Whitney U = 15, z = 2.449, p = .014), but the UT group was significantly higher than the RT group at 30P (Mann-Whitney U = 9, z = -2.939, p = .003). Within the RT group for p-GR Ser134 there were decreases compared to PRE at 10P (-33.13%∆, z = -2.395, p = .017), 30P (-32.89%∆, z = -2.803, p = .005), and 60P (-22.71%∆, z = -2.803, p = .005), but returned to baseline by 180P (-6.63%∆, z = -1.274, p = .203); conversely, in the UT group, increases were shown compared to PRE values at 30P (85.84%∆, z = -2.666, p = .008), 60P (111.24%∆, z = -2.666, p = .008), and 180P (68.30%∆, z = -2.666, p = .008). There were significant decreases in p-GR Ser211 from PRE to 60P (-30.76%∆, z = -2.701, p = .007) and 180P (-30.33%∆, z = -2.599, p = .009) in the RT group and from PRE to 180P (-42.98%∆, z = -2.666, p = .008) in the UT group. In p-GR Ser226, the UT group had a higher expression at 10P (Mann-Whitney U = 21, z = -1.960, p = .050) and 180P (Mann-Whitney U = 20, z = -2.041, p = .041) compared to the RT group. There were significant increases from PRE in both the RT group at 10P (311.5%∆, z = -2.803, p = .005), 30P (33.97%∆, z = -2.803, p = .005), 60P (387.42%∆, z = -2.803, p = .005), and 180P (240.16%∆, z = -2.803, p = .005) as well as the UT group at 10P (615.52%∆, z = -2.666, p = .008), 30P (568.66%∆, z = -2.666, p = .008), 60P (441.12%∆, z = -2.666, p = .008), and 180P (395.26%∆, z = -2.666, p = .008). CONCLUSION: When analyzing androgen and glucocorticoid receptors, training status needs to be accounted for as there are training status dependent differences. Although the importance of the acute hormonal response on muscle hypertrophy is still controversial, it appears to have some effect at the receptor level in preserving content and in phosphorylation of various receptor sites that cannot be ignored. The RT group was able to maintain their total AR content up to 180 min post RE; whereas, the UT group saw decreases at 30 min and 60 min post exercise. In addition, the ligand dependent GR Ser211 site did not show a phosphorylation decrease in the UT group, who had a prolonged elevation in cortisol compared to the RT group, until 180 min post RE, whereas the RT group decreased at 60 min post RE. Also, at the ligand dependent and independent GR Ser134 site we saw almost opposite effects in training group where the RT group decreased phosphorylation at 10P, 30P, and 60P, but the UT group saw and increase in phosphorylation at 30P, 60P, and 180P. Phosphorylation of GR Ser226 increased at all post time points in both groups, but was higher in the UT group at 10P and 180P. AR Ser213 decreased in both groups at 10P, and no differences were seen at AR Ser81, Ser515, or Ser650 sites in our moderate intensity protocol. Further research could elucidate the hormone-receptor and receptor phosphorylation responses to RE by looking at a variety of training protocols, later muscle collection time points, MAPK responses, chronic training, and responses in a fed state. | |
