Glucose ingestion acutely lowers pulsatile LH and basal testosterone secretion in men

Chronic hyperglycemia inhibits the male gonadal axis. The present analyses test the hypothesis that acute glucose ingestion also suppresses LH and testosterone (T) secretion and blunts the LH-T dose-response function. The design comprised a prospectively randomized crossover comparison of LH and T secretion after glucose vs. water ingestion in a Clinical Translational Research Center. The participants were healthy men (n = 57) aged 19-78 yr with body mass index (BMI) of 20-39 kg/m(2). The main outcome measurements were deconvolution and LH-T dose-response analyses of 10-min data. LH-T responses were regressed on glucose, insulin, leptin, adiponectin, age, BMI, and CT-estimated abdominal visceral fat. During the first 120 min after glucose ingestion, for each unit decrease in LH concentrations, T concentrations decreased by 86 (27-144) ng/dl (r = 0.853, P < 0.001). Based upon deconvolution analysis, glucose compared with water ingestion reduced 1) basal (nonpulsatile; P < 0.001) and total (P < 0.001) T secretion without affecting pulsatile T output and 2) pulsatile (P = 0.043) but not basal LH secretion. By multivariate analysis, pulsatile LH secretion positively predicted basal T secretion after glucose ingestion (r = 0.374, P = 0.0042). In addition, the glucose-induced fall in pulsatile LH secretion was exacerbated by higher fasting insulin concentrations (P = 0.054) and attenuated by higher adiponectin levels (P = 0.0037). There were no detectable changes in the analytically estimated LH-T dose-response curves (P > 0.30). In conclusion, glucose ingestion suppresses pulsatile LH and basal T secretion acutely in healthy men. Suppression is influenced by age, glucose, adiponectin, and insulin concentrations.     

Comparison of changes in testosterone concentrations after strength and endurance exercise in well trained men

Changes in the testosterone concentrations after single sessions of endurance and strength training were measured in seven well trained men, experienced in both forms of training. Both training sessions were rated as hard to very hard on the Borg scale. Blood samples for testosterone measurements were taken before, immediately after, and 2, 4 and 6 h after the training sessions as well as the next morning. The mean testosterone concentration increased 27% (P less than 0.02) and 37% (P less than 0.02) during the strength and endurance training session, respectively. Two hours after the training sessions the mean testosterone concentration had returned to the pre-training level and remained at that level for the length of the observation period. There were no significant differences in the changes in testosterone concentration after strength and endurance training but there were large differences in the testosterone response at the level of the individual. A high correlation (r = 0.98; P less than 0.001) for individuals was found between increases in testosterone concentration after strength and after endurance training. It was concluded that the changes in mean testosterone values followed the same timecourse after single sessions of strength and endurance training of the same duration and perceived exertion. The interindividual differences in testosterone response may be of importance for individual adaptation to training.     

The secretion of LH and testosterone in the rabbit.

In the male rabbit, LH and testosterone are secreted as 4–6 discrete pulses per day. The testosterone response to LH is rapid. The testosterone data did not show a normal distribution, but the same data expressed logarithmically were more nearly so. There was no evidence of a 24 h cycle in plasma testosterone levels.     

Comparable testosterone responses are produced by constant infusion of LH or GnRH in normal men

Luteinizing hormone (LH) was infused continuously at a rate of 1.3 IU/min to 4 normal adult men. A 4 to 5-fold increase in serum LH was noted by 8 hours. Serum FSH declined steadily throughout the infusion period in the face of rising concentrations of gonadal steroids. Basal plasma testosterone of 4.7 +/- 0.4 ng/ml rose progressively to a peak of 11.1 +/- 0.9 ng/ml at hour 56 (p less than 0.005). A similar pattern was demonstrated by plasma androstenedione. Plasma 17 alpha-hydroxyprogesterone rose from a basal concentration of 0.81 +/- 0.14 ng/ml to a peak concentration of 2.6 +/- 0.3 ng/ml at hour 36 of the infusion and subsequently declined. A similar course was followed by serum estradiol-17 beta, which achieved a maximal concentration of 70.0 +/- 10.4 pg/ml at hour 36. Results are compared to those obtained with continuous infusion of GnRH in normal adult men. Testosterone responses were similar, whereas elevations in 17 alpha-hydroxyprogesterone and estradiol were higher following GnRH infusion. This difference may be consequent upon a direct gonadal effect of GnRH, or may be secondary to local regulation of testicular steroidogenesis by estradiol-17 beta.     

The effect of ACTH administration on plasma testosterone, dihydrotestosterone and serum LH concentrations in normal men

Plasma cortisol (F), testosterone (T), dihydrotestosterone (DHT) and serum luteinizing hormone (LH) concentrations were measured in 8 normal young men at 8 AM on two control days. Exogenous adrenocorticotrophin (ACTH) 20 U.S.P. units per m² of body surface area every 12 or 6 hours was administered intramuscularly for 4 days. Twenty-four hours after starting ACTH administration, the plasma T and DHT concentrations were significantly lower than those of the control days on a paired t test. No significant change in serum LH concentration could be demonstrated. Similar results were observed after 48, 72 and 96 hours of ACTH stimulation.     

Plasma concentrations of testosterone and LH in the male dog

Blood samples were withdrawn every 20 min from 3 conscious intact and 2 castrated mature males during non-consecutive periods of 12 h during the light and dark phases of the lighting schedule (intact dogs) and of 11 h during the light period (castrated dogs). In the intact dogs testosterone concentrations ranged from 0.4 to 6.0 ng/ml over the 24-h period. LH concentrations varied from 0.2 to 12.0 ng/ml. In all animals, LH peaks were clearly followed, after about 50 min, by corresponding testosterone peaks, but no diurnal rhythm could be established. LH concentrations in the castrated dogs were high (9.8 +/- 2.7 (s.e.m.) ng/ml), and still showed an episodic pattern in spite of the undetectable plasma testosterone levels.     

Effects of age on testosterone responses to resistance exercise and musculoskeletal variables in men

This study compared serum total testosterone (TT) and free testosterone (FT) responses of young (20-26 years, n = 8), middle-aged (38-53 years, n = 7), and older (59-72 years, n = 9) men to resistance exercise. We also examined the relationships between testosterone (T) levels and strength, bone mineral density (BMD), and body composition variables for each age group. Subjects were tested for isotonic muscular strength (1 repetition maximum [1RM]), BMD (dual-energy x-ray absorptiometry [DXA]) and body composition (DXA). Each group performed an acute exercise protocol (3 sets, 10 repetitions, 80% of 1RM, 6 exercises). Blood samples were obtained at baseline, immediately postexercise, and 15 minutes postexercise for the TT and FT assays. The older age group had significantly (p < 0.05) lower T levels than the young group, but each group exhibited an increase (p < 0.05) in TT and FT immediately postexercise. Total T and FT were significantly correlated (p < 0.05) with strength in middle-aged and older men and with bone-free lean tissue mass in older men. In conclusion, middle-aged and older men showed similar relative T responses to those of younger men to a single bout of high-intensity resistance exercise. However, T levels were related to strength and muscle mass only in middle-aged or older men. On a practical application level, older men can complete a high-intensity resistance exercise program resulting in spikes in T that may attenuate age-related muscle and BMD loss.     

Elevated endogenous testosterone concentrations potentiate muscle androgen receptor responses to resistance exercise

The purpose of this study was to determine the influence of endogenous circulating testosterone (T) on muscle androgen receptor (AR) responses to acute resistance exercise (RE). Six healthy men (26 ± 4 years; 176 ± 5 cm; 75.8 ± 11.4 kg) performed a knee extension exercise protocol on two occasions separated by 1–3 weeks. Rest preceded one trial (i.e., control [CON] trial) and a high-volume upper-body RE protocol designed to increase circulating T preceded the other trial (i.e., high T [HT] trial). Serial blood samples were obtained throughout each trial to determine circulating T concentrations. Biopsies of the vastus lateralis were obtained pre-RE (REST), 10-min post-RE (+10), and 180-min post-RE (+180) to determine muscle AR content. Circulating T concentrations remained stable during CON. Alternately, HT significantly (p ≤ 0.05) increased T concentrations above resting values (+16%). Testosterone area-under-the-time curve during HT exceeded CON by 14%. AR content remained stable from REST to +10 in both trials. Compared to the corresponding +10 value, muscle AR content at +180 tended to decrease during CON (−33%; p = 0.10) but remained stable during HT (+40%; p = 0.17). Muscle AR content at +180 during the HT trial exceeded the corresponding CON value. In conclusion, acute elevations in circulating T potentiated muscle AR content following RE.     

Genetic determinants of serum testosterone concentrations in men

Testosterone concentrations in men are associated with cardiovascular morbidity, osteoporosis, and mortality and are affected by age, smoking, and obesity. Because of serum testosterone''s high heritability, we performed a meta-analysis of genome-wide association data in 8,938 men from seven cohorts and followed up the genome-wide significant findings in one in silico (n = 871) and two de novo replication cohorts (n = 4,620) to identify genetic loci significantly associated with serum testosterone concentration in men. All these loci were also associated with low serum testosterone concentration defined as <300 ng/dl. Two single-nucleotide polymorphisms at the sex hormone-binding globulin (SHBG) locus (17p13-p12) were identified as independently associated with serum testosterone concentration (rs12150660, p = 1.2×10⁻⁴¹ and rs6258, p = 2.3×10⁻²²). Subjects with ≥3 risk alleles of these variants had 6.5-fold higher risk of having low serum testosterone than subjects with no risk allele. The rs5934505 polymorphism near FAM9B on the X chromosome was also associated with testosterone concentrations (p = 5.6×10⁻¹⁶). The rs6258 polymorphism in exon 4 of SHBG affected SHBG''s affinity for binding testosterone and the measured free testosterone fraction (p<0.01). Genetic variants in the SHBG locus and on the X chromosome are associated with a substantial variation in testosterone concentrations and increased risk of low testosterone. rs6258 is the first reported SHBG polymorphism, which affects testosterone binding to SHBG and the free testosterone fraction and could therefore influence the calculation of free testosterone using law-of-mass-action equation.     

Fat metabolism and acute resistance exercise in trained men.

The purpose of this study was to investigate the effect of acute resistance exercise (RE) on lipolysis within adipose tissue and subsequent substrate oxidation to better understand how RE may contribute to improvements in body composition. Lipolysis and blood flow were measured in abdominal subcutaneous adipose tissue via microdialysis before, during, and for 5 h following whole body RE as well as on a nonexercise control day (C) in eight young (24 +/- 0.7 yr), active (>3 RE session/wk for at least 2 yr) male participants. Fat oxidation was measured immediately before and after RE via indirect calorimetry for 45 min. Dialysate glycerol concentration (an index of lipolysis) was higher during (RE: 200.4 +/- 38.6 vs. C: 112.4 +/- 13.1 micromol/l, 78% difference; P = 0.02) and immediately following RE (RE: 184 +/- 41 vs. C: 105 + 14.6 micromol/l, 75% difference; P = 0.03) compared with the same time period on the C day. Energy expenditure was elevated in the 45 min after RE compared with the same time period on the C day (RE: 104.4 +/- 6.0 vs. C: 94.5 +/- 4.0 kcal/h, 10.5% difference; P = 0.03). Respiratory exchange ratio was lower (RE: 0.71 +/- 0.004 vs. C: 0.85 +/- .03, 16.5% difference; P = 0.004) and fat oxidation was higher (RE: 10.2 +/- 0.8 vs. C: 5.0 +/- 1.0 g/h, 105% difference; P = 0.004) following RE compared with the same time period on the C day. Therefore, the mechanism behind RE contributing to improved body composition is in part due to enhanced abdominal subcutaneous adipose tissue lipolysis and improved whole body fat oxidation and energy expenditure in response to RE.     

The relationship between testosterone and dehydroepiandrosterone sulfate concentrations, insulin resistance and visceral obesity in elderly men

INTRODUCTION: Sex hormones deficiency--hypotestosteronemia (20-30% of men) and dehydroepian-drosterone sulfate deficiency (60-70% of men) are often observed in elderly men. In these men also changes of body composition (visceral obesity, increasing of fat mass), and metabolic disturbances (hypercholesterolemia, hyperinsulinism and insulin resistance) are common disorders. Visceral obesity and insulin resistance may be either reasons or effects of testosterone deficiency. Probably also DHEA-S deficiency is the risk factor of visceral obesity and insulin resistance, but it is not clear, whether this possible influence is independent from testosterone deficiency. OBJECTIVES: The aim of this study was to analyze the association between testosterone and DHEA deficiency and waist/hip ratio (WHR), levels of glucose and insulin resistance (HOMA and FG/FI) in elderly men as well as analysis, whether these sex hormones influent on measured parameters separately. MATERIAL AND METHODS: Together 85 men with age from 60 to 70 years men (mean 66.3+/-1.5 years; mean+/-SEM) was analyzed. Testosterone levels<4 ng/ml or DHEA levels<2000 ng/ml and BMI<30 kg/m2 were including criteria. Patients were divided into three groups: 52 with testosterone deficiency (L-T), 32 with DHEA deficiency (L-DHEA-S) and 67 with deficiency of both sex hormones (L-T/DHEA-S). Statistical analysis was made using Student-t, Kruskal-Wallis, and Mann-Whitney tests. RESULTS: Testosterone levels in L-T, L-DHEA and L-T/DHEA groups were respectively 3.19+/-0.23 ng/ml, 4.89+/-0.45 ng/ml and 3.25+/-0.34 g/ml (p<0.002). While DHEA-S levels were respectively 2498+/-98 ng/ml, 1435+/-1010 ng/ml and 1501+/-89 ng/ml). BMI values do not differ between groups. WHR ratio values were the highest in L-T/DHEA-S group (p<0.05 vs. L-T) group, significant lower in L-T group (p<0.005 vs. L-DHEA-S) and the lowest in L-DHEA-S group. Insulin fasting levels were lowest in L-DHEA-S group, higher in L-T group (p<0.01) and the highest in L-T/DHEA-S group (p<0.001 vs, L-T group). FG/FI values were the highest in L-DHEA-S group, lower in L-T group (NS) and lowest in L-T/DHEA group (p<0.002 vs. L-T group). HOMA ratio values similarly did not change significantly between L-T (6.6+/-3.21) and L-DHEA-S group (5.5+/-2.92), although tendency to higher values in L-T group was noticed, while WHR ratio values were significantly higher in L-T/DHEA group (7.3+/-2.45; p<0.002 vs. L-T group). CONCLUSIONS: DHEA-S and testosterone deficiency were independently associated with higher insulin resistance and obesity. WHR ratio seems to be more sensitive then BMI ratio to reflect the androgen deficiency on obesity and body composition in elderly men.     

Salivary testosterone and cortisol responses in professional rugby players after four resistance exercise protocols

The acute response of free salivary testosterone (T) and cortisol (C) concentrations to four resistance exercise (RE) protocols in 23 elite men rugby players was investigated. We hypothesized that hormonal responses would differ among individuals after four distinct RE protocols: four sets of 10 repetitions (reps) at 70% of 1 repetition maximum (1RM) with 2 minutes' rest between sets (4 x 10-70%); three sets of five reps at 85% 1RM with 3 minutes' rest (3 x 5-85%); five sets of 15 reps at 55% 1RM with 1 minute's rest (5 x 15-55%); and three sets of five reps at 40% 1RM with 3 minutes' rest (3 x 5-40%). Each athlete completed each of the four RE protocols in a random order on separate days. T and C concentrations were measured before exercise (PRE), immediately after exercise (POST), and 30 minutes post exercise (30 POST). Each protocol consisted of four exercises: bench press, leg press, seated row, and squats. Pooled T data did not change as a result of RE, whereas C declined significantly. Individual athletes differed in their T response to each of the protocols, a difference that was masked when examining the pooled group data. When individual data were retrospectively tabulated according to the protocol in which each athlete showed the highest T response, a significant protocol-dependent T increase for all individuals was revealed. Therefore, RE induced significant individual, protocol-dependent hormonal changes lasting up to 30 minutes after exercise. These individual responses may have important ramifications for modulating adaptation to RE and could explain the variability often observed in studies of hormonal response to RE.     

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia II. LH and testosterone concentrations before and after GnRH

Plasma LH and testosterone (T) concentrations were measured before (basal) and two hours after (peak) GnRH stimulation in 52 Bos indicus strain bulls between one and two years of age. The animals comprised 13 1 2 Brahman, 20 3 4 Brahman, 8 1 2 Sahiwal and 11 3 4 Sahiwal cross bulls and samples were collected at approximately seven week intervals. Basal- and peak-T concentrations increased between one and two years of age, and basal LH concentrations decreased; no changes in peak LH were noted over time. Peak-T concentrations were significantly correlated with scrotal circumference (SC), sperm per ejaculate and seminal fructose. Significant genotype differences were noted, Sahiwal cross bulls had higher peak-T concentrations at puberty than Brahman cross bulls.     

No effect of short-term testosterone manipulation on exercise substrate metabolism in men.

Compared with women, men use proportionately more carbohydrate and less fat during exercise at the same relative intensity. Estrogen and progesterone have potent effects on substrate use during exercise in women, but the role of testosterone (T) in mediating substrate use is unknown. The purpose of this investigation was to assess how large variations in the concentration of blood T would impact substrate use during exercise in men. Nine healthy, active men were studied in three distinct hormonal conditions: physiological T (no intervention), low T (pharmacological suppression of endogenous T with a gonadotrophin-releasing hormone antagonist), and high T (supplementation with transdermal T). Total carbohydrate oxidation, blood glucose rate of disappearance, and estimated muscle glycogen use were assessed by using stable isotope dilution and indirect calorimetry at rest and while bicycling at approximately 60% of peak O2 consumption for 90 min. Relative to the physiological condition (T = 5.5 +/- 0.5 ng/ml), total plasma T was considerably suppressed in low T (0.8 +/- 0.1) and elevated in high T (10.9 +/- 1.1). Despite the large changes in plasma T, carbohydrate oxidation, glucose rate of disappearance, and estimated muscle glycogen use were very similar across the three conditions. There were also no differences in plasma concentrations of glucose, insulin, lactate, or free fatty acids. Plasma estradiol (E) concentrations were elevated in high T, but correlations between substrate use and plasma concentrations of T, E, or the T-to-E ratio were very weak (r2 < 0.20). In conclusion, unlike the effect of acute elevation in E to constrain carbohydrate use in women, acute changes in circulating T concentrations do not appear to alter substrate use during exercise in men.