Stimulatory effect of lactate on testosterone production by rat Leydig cells

Is digit ratio (2D:4D) a biomarker for lactate? Evidence from a cardiopulmonary test on professional male footballers

BACKGROUND

Lactate accumulation is associated with vigorous exercise, cardiovascular disease and a number of cancers. Digit ratio (2D:4D) has also been linked to oxygen metabolism, myocardial infarction and various cancers. Such similarities suggest the possibility that 2D:4D is a biomarker of lactate. Here, we consider the relationship between 2D:4D and lactate during an incremental cardiopulmonary exercise test.

METHOD

The participants were male professional football players. The treadmill test began at a speed of 8 km/h when the first lactate measurement was taken. The speed was increased by 2 km/h every 3.15 min, with measurements at 10, 12, 14 and 16 km/h.

RESULTS

There were 72 Caucasian and 7 Black participants, results are reported for the most numerous group. Lactate levels increased with running speed and were not correlated with age, body size or body composition. Median splits of digit ratios (right, left and right-left 2D:4D [Dr-l]) were calculated. In comparison to the Low ratio group, the High ratio group showed higher lactate levels across speeds. Effect sizes varied from very large to huge (right 2D:4D), large (left 2D:4D) and medium (Dr-l). At the individual level, positive correlations between digit ratios and lactate at the five different speeds varied from large (right 2D:4D), medium (left 2D:4D) and small (Dr-l).

CONCLUSION

There were large positive associations between right 2D:4D and lactate at all running speeds. We discuss our findings in relation to oxygen metabolism and suggest that 2D:4D may be a biomarker for lactate in the wider context of the latter's importance in health and disease.

Bioactive metabolites reveal the therapeutic consistency of epimedii folium from multi-plant sources for the treatment of kidney-yang deficiency

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedii Folium (Yin-yang-huo in Chinese), a traditional and commonly used herbal medicine (HM), is a representative of multi-plant sources. To date, little is known about the reasons for similar therapeutic effects of this HM from multi-plant sources.

AIM OF THE STUDY

To investigate the underlying reasons for the similar pharmacological effects of Epimedii Folium from two botanical sources (Epimedium koreanum Nakai and Epimedium wushanense T. S. Ying).

MATERIALS AND METHODS

Firstly, the phytochemicals of the extracts of E. koreanum and E. wushanense were systematically analyzed. Meanwhile, their pharmacological effects on kidney-yang deficiency (KYD) syndrome were evaluated in rats induced by hydrocortisone. Subsequently, we proposed a combined effect index (CEI) to assess the effects of two plants on the secretion of testosterone by combing the system exposure of twelve active components in vivo with their regulation activities of testosterone production in vitro. Moreover, the label-free proteomics and Western blot analysis were conducted to evaluate the possible mechanism of Epimedii Folium from two botanical sources.

RESULTS

E. koreanum and E. wushanense exhibited similar pharmacological effects on KYD syndrome with promoting the mating behaviors and testosterone levels of rats, although there is a certain difference in the main components between two plants. The CEI analysis showed that there was no difference (P > 0.05) in the sum of CEIs of two Epimedium, indicating that their similar therapeutic effects are attributed to bioactive metabolites in vivo. Furthermore, Epimedii Folium can regulate testosterone production in rat Leydig cell via reversing expressions of key steroidogenic enzymes, such as steroidogenic acute regulatory protein (StAR) and 3β-hydroxysteroid dehydrogenase (3β-HSD).

CONCLUSION

Our results supply critical evidence for the similar pharmacological effects of two Epimedium species, acting by consistent bioactive components directly exposing in vivo, not chemical compositions presenting in herbs. It provides a reasonable scientific basis for understanding of the HMs originated from multi-plant sources for the same clinical application.

Body composition and testosterone in men: a Mendelian randomization study

Background

Testosterone is an essential sex hormone that plays a vital role in the overall health and development of males. It is well known that obesity decreases testosterone levels, but it is difficult to determine the causal relationship between body composition and testosterone.

Methods

To investigate potential causal associations between body composition and testosterone levels by a first time application of Mendelian randomization methods. Exposure variables in men included body composition (fat mass, fat-free mass, and body mass index). In addition to whole body fat and fat-free mass, we examined fat and fat-free mass for each body part (e.g., trunk, left arm, right arm, left leg and right leg) as exposures. Instrumental variables were defined using genome-wide association study data from the UK Biobank. Outcome variables in men included testosterone levels (total testosterone [TT], bioavailable testosterone [BT], and sex hormone-binding globulin [SHBG]). A one-sample Mendelian randomization analysis of inverse-variance weighted and weighted median was performed.

Results

The number of genetic instruments for the 13 exposure traits related to body composition ranged from 156 to 540. Genetically predicted whole body fat mass was negatively associated with TT (β=-0.24, P=5.2×10-33), BT (β=-0.18, P=5.8×10-20) and SHBG (β=-0.06, P=8.0×10-9). Genetically predicted whole body fat-free mass was negatively associated with BT (β=-0.04, P=2.1×10-4), but not with TT and SHBG, after multiple testing corrections. When comparing the causal effect on testosterone levels, there was a consistent trend that the effect of fat mass was more potent than that of fat-free mass. There were no differences between body parts.

Conclusion

These results show that reducing fat mass may increase testosterone levels.

Biomarkers to Be Used for Decision of Treatment of Hypogonadal Men with or without Insulin Resistance

Male hypogonadism is a result of low testosterone levels, but patients could be insulin-sensitive (IS) or insulin-resistant (IR), showing different impaired metabolic pathways. Thus, testosterone coadministration, which is commonly used to reestablish testosterone levels in hypogonadism, must take into account whether or not insulin is still active. By comparing metabolic cycles recorded in IS and IR plasma before and after testosterone therapy (TRT), it is possible to know what metabolic pathways can be reactivated in the two different groups upon testosterone recovery, and it is possible to understand if antagonism or synergy exists between these two hormones. IS hypogonadism uses glycolysis, while IR hypogonadism activates gluconeogenesis through the degradation of branched-chain amino acids (BCAAs). Upon administration of testosterone, acceptable improvements are observed in IS patients, wherein many metabolic pathways are restored, while in IR patients, a reprogramming of metabolic cycles is observed. However, in both subgroups, lactate and acetyl-CoA increases significantly. In IS patients, lactate is used through the glucose-lactate cycle to produce energy, while in IR patients, both lactate and acetyl-CoA are metabolized into ketone bodies, which are used to produce energy. Thus, in IR patients, an ancestral molecular mechanism is activated to produce energy, mimicking insulin effects. Regarding lipids, in both groups, the utilization of fatty acids for energy (β-oxidation) is blocked, even after TRT; free fatty acids (FFAs) increase in the blood in IS patients, while they are incorporated into triglycerides in those with IR. In both subgroups of hypogonadism, supplementation of useful chemicals is recommended during and after TRT when metabolites are not restored; they are listed in this review.

Lactate as a myokine and exerkine: drivers and signals of physiology and metabolism

No longer viewed as a metabolic waste product and cause of muscle fatigue, a contemporary view incorporates the roles of lactate in metabolism, sensing and signaling in normal as well as pathophysiological conditions. Lactate exists in millimolar concentrations in muscle, blood, and other tissues and can rise more than an order of magnitude as the result of increased production and clearance limitations. Lactate exerts its powerful driver-like influence by mass action, redox change, allosteric binding, and other mechanisms described in this article. Depending on the condition, such as during rest and exercise, following carbohydrate nutrition, injury, or pathology, lactate can serve as a myokine or exerkine with autocrine-, paracrine-, and endocrine-like functions that have important basic and translational implications. For instance, lactate signaling is: involved in reproductive biology, fueling the heart, muscle adaptation, and brain executive function, growth and development, and a treatment for inflammatory conditions. Lactate also works with many other mechanisms and factors in controlling cardiac output and pulmonary ventilation during exercise. Ironically, lactate can be disruptive of normal processes such as insulin secretion when insertion of lactate transporters into pancreatic β-cell membranes is not suppressed, and in carcinogenesis when factors that suppress carcinogenesis are inhibited, whereas factors that promote carcinogenesis are upregulated. Lactate signaling is important in areas of intermediary metabolism, redox biology, mitochondrial biogenesis, neurobiology, gut physiology, appetite regulation, nutrition, and overall health and vigor. The various roles of lactate as a myokine and exerkine are reviewed.NEW & NOTEWORTHY Lactate sensing and signaling is a relatively new and rapidly changing field. As a physiological signal lactate works both independently and in concert with other signals. Lactate operates via covalent binding and canonical signaling, redox change, and lactylation of DNA. Lactate can also serve as an element of feedback loops in cardiopulmonary regulation. From conception through aging lactate is not the only a myokine or exerkine, but it certainly deserves consideration as a physiological signal.

Effects of Bushen Yiyuan recipe on testosterone synthesis in Leydig cells of rats with exercise-induced low serum testosterone levels

CONTEXT

Bushen Yiyuan recipe (BYR) is an effective Chinese prescription with antifatigue and antioxidation effects.

OBJECTIVE

The effects of BYR on testosterone synthesis in rat Leydig cells with exercise-induced low serum testosterone levels (EILST) are assessed.

MATERIALS AND METHODS

Thirty-two Sprague-Dawley rats were chronically trained for 6 weeks to establish an EILST model. EILST rats were divided into model (physiological saline), EFE (700 mg/kg ethanol extract of Epimedii folium, the dried leaves of Epimedium brevicornu Maxim [Berberidaceae]), and BYR groups (350 and 700 mg/kg) for 6 weeks. Expression of HMG-CoA, LDL-R, SR-BI, STAR and CYP11A1 were quantified by RT qPCR and Western blots.

RESULTS

Compared with the model group (115.52 ± 13.05 μg/dL; 67.83 ± 14.29; 0.32 ± 0.04; 0.33 ± 0.02; 0.38 ± 0.01), serum testosterone, testosterone/cortisol ratio, HMG-CoA, STAR and CYP11A1 relative protein expression significantly increased in low-dose BYR (210.60 ± 5.08 μg/dL; 119.38 ± 13.02; 0.47 ± 0.01; 0.46 ± 0.03; 0.46 ± 0.02), high-dose BYR (220.57 ± 14.71 μg/dL; 124.26 ± 14.79; 0.49 ± 0.02; 0.42 ± 0.03; 0.51 ± 0.02), and EFE groups (206.83 ± 5.54 μg/dL; 119.53 ± 25.04; 0.45 ± 0.02; 0.42 ± 0.02; 0.41 ± 0.02) (all p < 0.01, except for CYP11A1 in EFE group). HMG-CoA, STAR and CYP11A1 mRNA relative expression significantly increased in low-dose and high-dose BYR group compared to model group (all p < 0.01).

CONCLUSIONS

BYR affects endogenous cholesterol synthesis and testosterone synthesis to prevent and treat EILST levels in rats. It can improve the body's sports ability.

On the Need to Distinguish between Insulin-Normal and Insulin-Resistant Patients in Testosterone Therapy

Male hypogonadism is a disorder characterized by low levels of the hormone testosterone and patients may also have insulin sensitivity (IS) or insulin resistance (IR), such that they show different clinical complications and different metabolic pathways. In this review, we compare metabonomic differences observed between these two groups before and after testosterone therapy (TRT) in order to obtain information on whether the two hormones testosterone and insulin are synergistic or antagonistic. IS hypogonadism uses glucose as the main biofuel, while IR activates gluconeogenesis by the degradation of branched-chain amino acids. The Krebs (TCA) cycle is active in IS but connected with glutaminolysis, while in IR the TCA cycle stops at citrate, which is used for lipogenesis. In both cases, the utilization of fatty acids for energy (β-oxidation) is hampered by lower amounts of acetylcarnitine, although it is favored by the absence of insulin in IR. Increased free fatty acids (FFAs) are free in the blood in IS, while they are partially incorporated in triglycerides in IR. Thus, upon TRT, the utilization of glucose is increased more in IS than in IR, revealing that in IR there is a switch from preferential glucose oxidation to lipid oxidation. However, in both cases, a high production of lactate and acetyl-CoA is the final result, with these levels being much higher in IR. Lactate is used in IS in the glucose–lactate cycle between the liver and muscle to produce energy, while in IR lactate and acetyl-CoA are biotransformed into ketone bodies, resulting in ketonuria. In conclusion, the restoration of testosterone values in hypogonadism gives better results in IS than in IR patients: in IS, TRT restores most of the metabolic pathways, while in IR TRT impairs insulin, and when insulin is inactive TRT activates an ancestral molecular mechanism to produce energy. This evidence supports the hypothesis that, over time, hypogonadism switches from IS to IR, and in the latter case most of the insulin-related metabolisms are not reactivated, at least within 60 days of TRT. However, testosterone therapy in both IS and IR might be of benefit given supplementation with metabolites that are not completely restored upon TRT, in order to help restore physiological metabolisms. This review underlines the importance of using a systems biology approach to shed light on the molecular mechanisms of related biochemical pathways involving insulin and testosterone.

Beyond Mechanical Tension: A Review of Resistance Exercise-Induced Lactate Responses & Muscle Hypertrophy

The present review aims to explore and discuss recent research relating to the lactate response to resistance training and the potential mechanisms by which lactate may contribute to skeletal muscle hypertrophy or help to prevent muscle atrophy. First, we will discuss foundational information pertaining to lactate including metabolism, measurement, shuttling, and potential (although seemingly elusive) mechanisms for hypertrophy. We will then provide a brief analysis of resistance training protocols and the associated lactate response. Lastly, we will discuss potential shortcomings, resistance training considerations, and future research directions regarding lactate's role as a potential anabolic agent for skeletal muscle hypertrophy.

The effects of metformin and forskolin on sperm quality parameters and sexual hormones in type II diabetic male rats

This study aimed to investigate the effects of metformin and forskolin independently and in combinations on the sperm quality parameters and sexual hormones of diabetic male rats. Fifty adult male rats were divided randomly into five identical groups, and diabetes mellitus was induced to the rats, except for the rats in the control group, using a high-fat diet and injection of Streptozotocin. Daily administration of metformin and forskolin independently and in combinations were performed for 8 weeks in different groups. Sperm quality parameters (including sperm count, morphology, sperm motility and Johnson score), testosterone, blood sugar level, Bax to Bcl-2 ratio mRNA expression level and oxidative stress levels were measured and compared between the investigated groups. Treating diabetic rats with metformin and forskolin resulted in significant improvement in sperm quality parameters, increased testosterone levels, reduced oxidative stress in blood and testicular tissue, and decreased blood sugar, and Bax to Bcl-2 ratio level. Although the combination of metformin with forskolin had a higher effect in some parameters such as testosterone levels compared to treatment with metformin or forskolin alone, this combination had not shown a synergistic effect in all the sperm quality parameters. Metformin and forskolin are effective anti-diabetic agents, which significantly improve the sperm quality and sexual hormone levels in diabetic rats. Combining metformin and gorskolin resulted in significantly better testosterone level and antioxidant activity in blood serum without significant effect on sperm quality of diabetic rats.

Plasma Metabonomics in Insulin-Resistant Hypogonadic Patients Induced by Testosterone Treatment

Hypogonadic subjects with insulin resistance (IR) showed different metabonomic profiles compared to normo-insulinemic subjects (IS). Testosterone replacement therapy (TRT) may have a different impact on the metabolisms of those with the presence or absence of insulin resistance. We evaluated the changes in the metabolism of IR hypogonadic patients before and after 60 days of TRT. The metabonomic plasma profiles from 20 IR hypogonadal patients were recorded using ultra-high-performance liquid chromatography (UHPLC) and high-resolution mass spectrometry (HRMS). Plasma metabolites, before and after 60 days of TRT, were compared. In hypogonadic patients, carnosine, which is important for improving performance during exercise, increased. Conversely, proline and lysine—amino acids involved in the synthesis of collagen—reduced. Triglycerides decreased and fatty acids (FFAs) increased in the blood as a consequence of reduced FFA β-oxidation. Glycolysis slightly improved, while the Krebs cycle was not activated. Gluconeogenesis (which is the main energy source for hypogonadal IR before TRT) stopped after treatment. As a consequence, lactate and acetyl CoA increased significantly. Both lactate and acetyl CoA were metabolized into ketone bodies which increased greatly, also due to leucine/isoleucine degradation. Ketone bodies were derived predominantly from acetyl CoA because the reaction of acetyl CoA into ketone bodies is catalyzed by mtHMGCoA synthase. This enzyme is inhibited by insulin, which is absent in IR patients but overexpressed following testosterone administration. Ketosis is an alternative route for energy supply and provides the same metabolic effects as insulin but at the metabolic or primitive control level, which bypasses the complex signaling pathway of insulin. After treatment, the hypogonadic patients showed clinical symptoms related to ketonuria. They presented similarly to those following a ketogenic diet, the so-called ‘keto flu’. This must be taken into account before the administration of TRT to hypogonadic patients.

Effect of different recovery modes during resistance training with blood flow restriction on hormonal levels and performance in young men: a randomized controlled trial

BACKGROUND

Resistance training with blood flow restriction (BFR) results in hypertrophy, and its magnitude depends on various training variables. This study aimed to compare the long-term effect of passive recovery (PR) and active recovery (AR) during low-intensity resistance training with BFR on hormonal levels and performance in young men.

METHODS

In the randomized clinical trial, 20 men were randomly divided into PR and AR groups during resistance training with BFR. The intervention consisted of six upper and lower body movements with 30% of one maximum repetition (1RM), three sessions per week for six weeks. Both groups wore pneumatic cuffs on the proximal part of thighs and arms. The cuff pressure was 60% of the calculated arterial blood occlusion and increased 10% every two weeks. The AR group performed seven repetitions in 30 s break between sets by one second for concentric and eccentric phases and two seconds rest, and the other group had passive rest. The blood samples and a series of performance tests were gathered before and after the intervention. A repeated measure ANOVA was used to analyze data.

RESULTS

AR and PR interventions significantly improved the C-reactive protein (CRP) (- 38% vs. - 40%), Lactate dehydrogenase (LDH) (- 11% vs. - 3%), Sargent jump (9% vs. 10%), peak power (20% vs.18%), and average power (14% vs. 14%), upper 1RM (8% vs. 8%) and no significant differences were observed between groups. The AR intervention significantly increased growth hormone (GH) (423% vs. 151%, p = 0.03), lower body 1RM (18% vs. 11%) and muscle endurance (34% vs. 22% for the upper body, p = 0.02 and 32% vs. 24% for the lower body, p = 0.04) than the PR group. The PR intervention further increased the minimum power than the AR group (19% vs. 10%). There were no significant changes in testosterone (p = 0.79) and cortisol (p = 0.34) following interventions.

CONCLUSION

The findings indicated that by increasing muscle activation and higher metabolic load, AR during resistance training with BFR might cause more remarkable improvements in serum GH, muscle strength, and endurance. Thus, to gain further benefits, AR during training with BFR is recommended.

TRIAL REGISTRATION

IRCT20191207045644N1. Registration date: 14/03/2020. URL: https://www.irct.ir/search/result?query=IRCT20191207045644N1.

Effects of a blood flow restriction exercise under different pressures on testosterone, growth hormone, and insulin-like growth factor levels

OBJECTIVE

To investigate the changes in serum growth hormone (GH), testosterone, and insulin-like growth factor 1 (IGF-1) during low-intensity resistance exercise under different cuff pressures.

METHODS

We performed a single-blind, cross-over design study. Twenty-five healthy young men performed three exercise protocols as follows: 1) no blood flow restriction exercise (control group), 2) resistance exercise at 40% of arterial occlusion pressure (AOP) (low group), and 3) resistance exercise at 70% of AOP (high group). Blood lactate, GH, testosterone, and IGF-1 levels were measured at four time points.

RESULTS

There were no differences in the indices before exercise. The blood flow restriction exercise under different pressures had different effects on each index and there was an interactive effect. GH levels were significantly higher in the high group than in the other groups after exercise. Immediately after exercise, IGF-1 and testosterone levels were significantly higher in the high group than in the other groups. At 15 minutes after exercise, testosterone levels were significantly higher in the high group than in the other groups.

CONCLUSIONS

Low-intensity resistance exercise combined with blood flow restriction effectively increases GH, IGF-1, and testosterone levels in young men. Increasing the cuff pressure results in greater levels of hormone secretion.

Influence of a Maximal Incremental Test Until Exhaustion on the Urinary Excretion of Steroid Hormones in Trained Cyclists

This study aimed to assess the effect of a maximum incremental stress test through urinary concentrations of steroid hormones in trained cyclists. Twenty male cyclists participated in the study (23.83 ± 2.3 years; 1.76 ± 0.03 m; 66.94 ± 3.59 kg; training volume: 20.50 ± 2.35 h/week). Athletes performed a maximum incremental test until exhaustion on a cycle ergometer and urine samples were collected at three different time points: before, immediately after, and 48 h after the test. Lactate, creatinine and urinary concentrations of testicular and adrenal androgens were obtained as well as urinary concentrations of glucocorticoid hormones. An increase in lactate was observed after the test (p < 0.01). There were decreases in the urinary excretion of androgenic hormones after the test, which were significant in testosterone, androsterone, androstenedione, total adrenal androgen and total testicular androgen (p < 0.05). The values were restored after 48 h (p < 0.05). Urinary cortisol concentrations decreased after the test (p < 0.05). A decrease was also observed in the ratio of anabolic/catabolic hormones (p < 0.05) increasing 48 h after the test (p < 0.05). Increased acute physical exercise until exhaustion causes variations in the urinary excretions of steroid hormones which were restored 48 h after exercise. Urinary excretion of steroid hormones could be a valid method of monitoring training loads.

Histomorphological testicular changes and decrease in the sperm count in pubertal rats induced by a high-sugar diet

BACKGROUND

During childhood and adolescence, excessive food consumption stimulates adipose tissue expansion promoting overweight in humans, and mice. A high-sucrose diet is related to obesity and metabolic syndrome. Infertility is commonly related to these pathologies. We aim to evaluate possible histomorphological testicular changes induced by a high-sucrose diet on sperm count during the post-weaning period.

METHODS

Wistar male rats aged 21 days, weaned, were randomly assigned into two groups: control (fed and hydrated normally) and sugar group (fed normally but hydrated with a solution containing 30% of diluted sucrose during 30 days). At the pubertal age of 51 days, animals were killed and blood samples were taken to measure testosterone and leptin. Testicles were collected and gonadal adipose tissue and semen samples from the epididymis were excised. Testicle samples were used for morphological description using H&E staining, as well as to quantify the triacylglycerol content and the lactate dehydrogenase (LDH) expression. Semen samples were used to assess motility, viability, and sperm count.

RESULTS

The sugar group presented an increase in the testicular weight, but a reduction in the cross-sectional area of seminiferous tubules. Moreover, disorganization of Sertoli cells and spermatogonia, an increase in the LDH expression within the entire seminiferous tubule, and a reduced sperm count and spermatozoid motility were found. These alterations were accompanied by high serum levels of testosterone and leptin.

CONCLUSIONS

Our results indicate strong damage of testis by sugar consumption during early life that may lead to the onset of infertility in adulthood.

Links Between Testosterone, Oestrogen, and the Growth Hormone/Insulin-Like Growth Factor Axis and Resistance Exercise Muscle Adaptations

Maintenance of skeletal muscle mass throughout the life course is key for the regulation of health, with physical activity a critical component of this, in part, due to its influence upon key hormones such as testosterone, estrogen, growth hormone (GH), and insulin-like growth factor (IGF). Despite the importance of these hormones for the regulation of skeletal muscle mass in response to different types of exercise, their interaction with the processes controlling muscle mass remain unclear. This review presents evidence on the importance of these hormones in the regulation of skeletal muscle mass and their responses, and involvement in muscle adaptation to resistance exercise. Highlighting the key role testosterone plays as a primary anabolic hormone in muscle adaptation following exercise training, through its interaction with anabolic signaling pathways and other hormones via the androgen receptor (AR), this review also describes the potential importance of fluctuations in other hormones such as GH and IGF-1 in concert with dietary amino acid availability; and the role of estrogen, under the influence of the menstrual cycle and menopause, being especially important in adaptive exercise responses in women. Finally, the downstream mechanisms by which these hormones impact regulation of muscle protein turnover (synthesis and breakdown), and thus muscle mass are discussed. Advances in our understanding of hormones that impact protein turnover throughout life offers great relevance, not just for athletes, but also for the general and clinical populations alike.

Lifestyle modifications and pharmacological approaches to improve sexual function and satisfaction in men with spinal cord injury: a narrative review

STUDY DESIGN

A narrative review describing various components of sexual dysfunction in men with spinal cord injury (SCI), as well as addressing potential therapeutic approaches.

OBJECTIVES

Restoration of sexual function is considered one of the most important health priorities for individuals with SCI. The purpose of this review is to provide information regarding the factors that are less appreciated when considering changes to sexual function in men with SCI. We also propose therapeutic approaches, with a focus on lifestyle modifications, which have been shown to improve sexual function.

METHODS

A literature search was performed and limited evidence for therapeutic approaches in individuals with SCI was supplemented by consistent findings from the able-bodied population.

RESULTS

We evaluated the less addressed factors known to contribute to sexual dysfunction in men with SCI, including hormonal influences (i.e., testosterone deficiency, thyroid hormone, and cortisol), psychological factors (i.e., pain, fatigue, depression, and body image), and secondary SCI complications (i.e., urinary tract infection, pressure sores, and autonomic dysreflexia). To address these factors beyond standard medical treatments for sexual dysfunction, options include physical activity/exercise, diet, and specific medications for symptom relief (i.e., testosterone replacement therapy and selective serotonin reuptake inhibitors for depression).

CONCLUSIONS

Physical activity's potential application, efficacy across multiple aspects of sexuality, and the lack of side effects, suggests that long-term exercise is a viable solution to directly or indirectly improve sexual function in males with SCI. Diet and supplemental medications may further promote body composition changes, which more broadly affect sexuality.

Acute effects of whole body vibration combined with blood restriction on electromyography amplitude and hormonal responses

The purpose of this study was to investigate the effects of whole body vibration (WBV) exercise with and without blood flow restriction (BFR) on electromyography (EMG) amplitude and hormonal responses. Eight healthy male adults who lacked physical activity participated in this study and completed 10 sets of WBV and WBV + BFR sessions in a repeated measures crossover design. In the WBV + BFR session, the participants wore a BFR device inflated to 140 mmHg around the proximal region of the thigh muscles. The results indicated that the EMG values from the rectus femoris and vastus lateralis during the WBV + BFR session were significantly higher than those during the WBV session (p < 0.05). Two-way analysis of variance with repeated measures showed that the WBV + BFR and WBV exercise sessions induced a significant (simple main effect for time) increase in lactate (LA) (0.61–4.68 vs. 0.46–3.44 mmol/L) and growth hormone (GH) (0.48–3.85 vs. 0.47–0.82 ng/mL) responses after some of the post-exercise time points (p < 0.05). WBV + BFR elicited significantly higher LA and GH (simple main effect for trial) responses than did WBV after exercise (p < 0.05). Although no significant time × trial interactions were observed for testosterone (T) (604.5–677.75 vs. 545.75–593.88 ng/dL), main effects for trial (p < 0.05) and for time (p < 0.05) were observed. In conclusion, WBV + BFR produced an additive effect of exercise on EMG amplitude and LA and GH responses, but it did not further induce T responses compared to those with WBV alone.

Is there a difference in testosterone levels and its regulators in men carrying BRCA mutations?

Background

Male BRCA mutation carriers are at risk for an early onset aggressive prostate cancer. No data exist on the association of testosterone levels among these patients. We aimed to analyze testosterone and associated hormonal levels among male BRCA carriers and non-carriers.

Patients and methods

Overall 87 male carriers and 43 non-carriers aged 40-70 were prospectively enrolled. Clinical data were collected and all patients were tested for total testosterone (TT), prostate specific antigen (PSA), follicle stimulating hormone (FSH), luteinizing hormone (LH), free androgen index (FAI), sex hormone binding globulin (SHBG) and prolactin. Multivariate linear regression analysis was performed to predict TT levels.

Results

The median age, mean BMI, comorbidities, PSA, FSH, LH and SHBG levels in both groups were similar. However, mean TT and FAI were higher in the carriers (16.7 nmol/l vs 13.5 nmol/l, p=0.03 and 39.5 vs 34.8, p=0.05, respectively), while prolactin was significantly lower. Multivariate analysis demonstrated that while BMI was inversely correlated to TT levels in both groups, LH was a predictor only in non-carriers.

Conclusions

Carriers have higher TT and FAI levels and lower prolactin levels; but LH does not predict their TT levels. Further research in a larger cohort of BRCA carriers with and without prostate cancer should be performed.

Do metabolites that are produced during resistance exercise enhance muscle hypertrophy?

Many reviews conclude that metabolites play an important role with respect to muscle hypertrophy during resistance exercise, but their actual physiologic contribution remains unknown. Some have suggested that metabolites may work independently of muscle contraction, while others have suggested that metabolites may play a secondary role in their ability to augment muscle activation via inducing fatigue. Interestingly, the studies used as support for an anabolic role of metabolites use protocols that are not actually designed to test the importance of metabolites independent of muscle contraction. While there is some evidence in vitro that metabolites may induce muscle hypertrophy, the only study attempting to answer this question in humans found no added benefit of pooling metabolites within the muscle post-exercise. As load-induced muscle hypertrophy is thought to work via mechanotransduction (as opposed to being metabolically driven), it seems likely that metabolites simply augment muscle activation and cause the mechanotransduction cascade in a larger proportion of muscle fibers, thereby producing greater muscle growth. A sufficient time under tension also appears necessary, as measurable muscle growth is not observed after repeated maximal testing. Based on current evidence, it is our opinion that metabolites produced during resistance exercise do not have anabolic properties per se, but may be anabolic in their ability to augment muscle activation. Future studies are needed to compare protocols which produce similar levels of muscle activation, but differ in the magnitude of metabolites produced, or duration in which the exercised muscles are exposed to metabolites.

Interactive Effect of Corticosterone and Lactate on Regulation of Testosterone Production in Rat Leydig Cells

The increasing intensity of exercise enhanced corticosterone and lactate production in both humans and rodents. Our previous studies also demonstrated that lactate could stimulate testosterone production in vivo and in vitro. However, the production of testosterone in response to combined corticosterone and lactate on Leydig cells, and underlying molecular mechanisms are remained unclear. This study investigated the changes in testosterone levels of Leydig cells upon exposure to lactate, corticosterone or combination of both, and revealed the detailed mechanisms. Leydig cells were isolated from rat testes, and treated with different concentrations of lactate (2.5-20 mM), cortiosterone (10^-9 -10^-4  M) and lactate plus corticosterone. The production of testosterone were assayed by radioimmunoassay, and the key molecular proteins, including luteinizing hormone receptor (LHR), protein kinase A (PKA), steroidogenic acute regulatory protein (StAR), and cholesterol P450 side-chain cleavage enzyme (P450scc) involved in testosterone production were performed by Western blot. Results showed that testosterone levels were significantly increased with lactate, while decresed with corticosterone and lactate plus corticosterone treatment. Protein expressions of LHR and P450scc were upregulated with lactate treatment. However, PKA and P450scc were downregulated by lactate plus corticosterone treatment. This downregulation was followed by decreased testoterone levels in Leydig cells. Furthermore, acetylated cAMP, which activates testosterone production was increased with lactate, but not altered by conrtiosterone. Our findings conclude that corticosterone may interfere with lactate, and restrict lactate-stimulated testosterone production in Leydig cells. J. Cell. Physiol. 232: 2135-2144, 2017. © 2016 Wiley Periodicals, Inc.

Lactate as a Signaling Molecule That Regulates Exercise-Induced Adaptations

Lactate (or its protonated form: lactic acid) has been studied by many exercise scientists. The lactate paradigm has been in constant change since lactate was first discovered in 1780. For many years, it was unfairly seen as primarily responsible for muscular fatigue during exercise and a waste product of glycolysis. The status of lactate has slowly changed to an energy source, and in the last two decades new evidence suggests that lactate may play a much bigger role than was previously believed: many adaptations to exercise may be mediated in some way by lactate. The mechanisms behind these adaptations are yet to be understood. The aim of this review is to present the state of lactate science, focusing on how this molecule may mediate exercise-induced adaptations.

Airflow-Restricting Mask Reduces Acute Performance in Resistance Exercise

BACKGROUND

The aim of this study was to compare the number of repetitions to volitional failure, the blood lactate concentration, and the perceived exertion to resistance training with and without an airflow-restricting mask.

METHODS

Eight participants participated in a randomized, counterbalanced, crossover study. Participants were assigned to an airflow-restricting mask group (MASK) or a control group (CONT) and completed five sets of chest presses and parallel squats until failure at 75% one-repetition-maximum test (1RM) with 60 s of rest between sets. Ratings of perceived exertion (RPEs), blood lactate concentrations (Lac^-), and total repetitions were taken after the training session.

RESULTS

MASK total repetitions were lower than those of the CONT, and (Lac^-) and MASK RPEs were higher than those of the CONT in both exercises.

CONCLUSIONS

We conclude that an airflow-restricting mask in combination with resistance training increase perceptions of exertion and decrease muscular performance and lactate concentrations when compared to resistance training without this accessory. This evidence shows that the airflow-restricting mask may change the central nervous system and stop the exercise beforehand to prevent some biological damage.

Effect of swimming on the production of aldosterone in rats

It has been demonstrated that exercise is one of the stresses known to increase the aldosterone secretion. Both potassium and angiotensin II (Ang II) levels are shown to be correlated with aldosterone production during exercise, but the mechanism is still unclear. In an in vivo study, male rats were catheterized via right jugular vein (RJV), and divided into four groups namely water immersion, swimming, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitro study, rat zona glomerulosa (ZG) cells were challenged by lactate (1–10 mM) in the presence or absence of Ang II (10⁻⁸ M) for 60 min. The levels of aldosterone in plasma and medium were measured by radioimmunoassay. Cell lysates were analyzed by immunoblotting assay. After exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. Swimming for 10 min significantly increased the plasma Ang II levels in male rats. Administration of lactate plus Ang II significantly increased aldosterone production and enhanced protein expression of steroidogenic acute regulatory protein (StAR) in ZG cells. These results demonstrated that acute exercise led to the increase of both aldosterone and Ang II secretion, which is associated with lactate action on ZG cells and might be dependent on the activity of renin-angiotensin system.

Salivary and plasma cortisol and testosterone responses to interval and tempo runs and a bodyweight-only circuit session in endurance-trained men

The aim of this study was to examine the acute response to plasma and salivary cortisol and testosterone to three training protocols. Ten trained endurance athletes participated in three experimental trials, such as interval training (INT), tempo run (TEMP) and bodyweight-only circuit training (CIR), on separate days. Blood and saliva samples were collected pre- and 0, 15, 30 and 60 min post-exercise. Peak post-exercise salivary cortisol was higher than pre-exercise in all trials (P < 0.01). After INT, salivary cortisol remained elevated above pre-exercise than 60 min post-exercise. Salivary testosterone also increased post-exercise in all trials (P < 0.05). Plasma and salivary cortisol were correlated between individuals (r = 0.81, 0.73-0.88) and within individuals (r = 0.81, 0.73-0.87) (P < 0.01). Plasma and salivary testosterone was also correlated between (r = 0.57, 0.43-0.69) and within individuals (r = 0.60, 0.45-0.72), (P < 0.01). Peak cortisol and testosterone levels occurred simultaneously in plasma and saliva, but timing of post-exercise hormone peaks differed between trials and individuals. Further investigation is required to identify the mechanisms eliciting an increase in hormones in response to CIR. Furthermore, saliva is a valid alternative sampling technique for measurement of cortisol, although the complex, individual and situation dependent nature of the hormone response to acute exercise should be considered.

Effects of strongman training on salivary testosterone levels in a sample of trained men

Strongman exercises consist of multi-joint movements that incorporate large muscle mass groups and impose a substantial amount of neuromuscular stress. The purpose of this study was to examine salivary testosterone responses from 2 novel strongman training (ST) protocols in comparison with an established hypertrophic (H) protocol reported to acutely elevate testosterone levels. Sixteen men (24 ± 4.4 years, 181.2 ± 6.8 cm, and 95.3 ± 20.3 kg) volunteered to participate in this study. Subjects completed 3 protocols designed to ensure equal total volume (sets and repetitions), rest period, and intensity between the groups. Exercise sets were performed to failure. Exercise selection and intensity (3 sets × 10 repetitions at 75% 1 repetition maximum) were chosen as they reflected commonly prescribed resistance exercise protocols recognized to elicit a large acute hormonal response. In each of the protocols, subjects were required to perform 3 sets to muscle failure of 5 different exercises (tire flip, chain drag, farmers walk, keg carry, and atlas stone lift) with a 2-minute rest interval between sets and a 3-minute rest interval between exercises. Saliva samples were collected pre-exercise (PRE), immediate postexercise (PST), and 30 minutes postexercise (30PST). Delta scores indicated a significant difference between PRE and PST testosterone level within each group (p ≤ 0.05), with no significant difference between the groups. Testosterone levels spiked 136% (225.23 ± 148.01 pg·ml(-1)) for the H group, 74% (132.04 ± 98.09 pg·ml(-1)) for the ST group, and 54% (122.10 ± 140.67 pg·ml) for the mixed strongman/hypertrophy (XST) group. A significant difference for testosterone level occurred over time (PST to 30PST) for the H group p ≤ 0.05. In conclusion, ST elicits an acute endocrine response similar to a recognized H protocol when equated for duration and exercise intensity.

Endurance exercise and conjugated linoleic acid (CLA) supplementation up-regulate CYP17A1 and stimulate testosterone biosynthesis

A new role for fat supplements, in particular conjugated linoleic acid (CLA), has been delineated in steroidogenesis, although the underlying molecular mechanisms have not yet been elucidated. The aims of the present study were to identify the pathway stimulated by CLA supplementation using a cell culture model and to determine whether this same pathway is also stimulated in vivo by CLA supplementation associated with exercise. In vitro, Leydig tumour rat cells (R2C) supplemented with different concentrations of CLA exhibited increasing testosterone biosynthesis accompanied by increasing levels of CYP17A1 mRNA and protein. In vivo, trained mice showed an increase in free plasma testosterone and an up-regulation of CYP17A1 mRNA and protein. The effect of training on CYP17A1 expression and testosterone biosynthesis was significantly higher in the trained mice supplemented with CLA compared to the placebo. The results of the present study demonstrated that CLA stimulates testosterone biosynthesis via CYP17A1, and endurance training led to the synthesis of testosterone in vivo by inducing the overexpression of CYP17A1 mRNA and protein in the Leydig cells of the testis. This effect was enhanced by CLA supplementation. Therefore, CLA-associated physical activity may be used for its steroidogenic property in different fields, such as alimentary industry, human reproductive medicine, sport science, and anti-muscle wasting.

The metabolic, hormonal, biochemical, and neuromuscular function responses to a backward sled drag training session

We examined the metabolic, hormonal, biochemical, and neuromuscular function (NMF) responses to a backward sled drag training session (STS) in strength-trained men (n = 11). After baseline collection of saliva (testosterone and cortisol), whole blood (lactate and creatine kinase [CK]), and countermovement jumps (peak power output), participants completed 5 sets of 2 × 20-m (30 second-recovery between drags and 120 second-recovery between sets) maximal backward sled drags (loaded with 75% body mass). Participants were retested immediately, 15 minutes, 1, 3, and 24 hours after STS. Peak power output decreased after STS (baseline, 4,445 ± 705 vs. 0 minute, 3,464 ± 819 W; p = 0.001) and remained below baseline until recovering at both the 3- and 24-hour time points. No changes in CK levels were seen at any time point after STS. Blood lactate increased immediately after STS (baseline, 1.7 ± 0.5 vs. 0 minute, 12.4 ± 2.6 mmol·L-1; p = 0.001) and remained elevated at 60 minutes (3.8 ± 1.9 mmol·L-1; p = 0.004) before returning to baseline at 3 and 24 hours. Testosterone peaked at 15 minutes post (baseline, 158 ± 45 vs. 15 minutes, 217 ± 49 pg·ml-1; p < 0.001) before decreasing below baseline at the 3-hour time point (119 ± 34 pg·ml-1; p = 0.008), but then increased again above baseline at 24 hours (187 ± 56 pg·ml-1; p = 0.04). Cortisol tended to increase at 15 minutes (baseline, 3.4 ± 1.8 vs. 15 minutes, 5.2 ± 2.7 ng·ml-1; p = 0.07) before declining below baseline at 3 hours (1.64 ± 0.93 ng·ml-1; p = 0.012) and returning to baseline concentrations at 24 hours. In conclusion, sled dragging provides an effective metabolic stimulus, with NMF restored after ≤3 hours of recovery. Characterizing the recovery time course after sled training may aid in athlete training program design.

Effect of acute DHEA administration on free testosterone in middle-aged and young men following high-intensity interval training

With advancing age, plasma testosterone levels decline, with free testosterone levels declining more significantly than total testosterone. This fall is thought to underlie the development of physical and mental weakness that occurs with advancing age. In addition, vigorous exercise can also lower total and free testosterone levels with the decline greatest in physically untrained men. The purpose of the study was to evaluate the effect of oral DHEA supplementation, a testosterone precursor, on free testosterone in sedentary middle-aged men during recovery from a high-intensity interval training (HIIT) bout of exercise. A randomized, double-blind, placebo-controlled crossover study was conducted for 8 middle-aged participants (aged 49.3 ± 2.4 years) and an additional 8 young control participants (aged 21.4 ± 0.3 years). Each participant received DHEA (50 mg) and placebo on separate occasions one night (12 h) before a 5-session, 2-min cycling exercise (100% VO₂max). While no significant age difference in total testosterone was found, middle-aged participants exhibited significantly lower free testosterone and greater luteinizing hormone (LH) levels than the young control group. Oral DHEA supplementation increased circulating DHEA-S and free testosterone levels well above baseline in the middle-aged group, with no significant effect on total testosterone levels. Total testosterone and DHEA-S dropped significantly until 24 h after HIIT for both age groups, while free testosterone of DHEA-supplemented middle-aged men remained unaffected. These results demonstrate acute oral DHEA supplementation can elevate free testosterone levels in middle-aged men and prevent it from declining during HIIT. Therefore, DHEA supplementation may have significant benefits related to HIIT adaptation.

Effect of zinc and selenium supplementation on serum testosterone and plasma lactate in cyclist after an exhaustive exercise bout

Zinc and selenium are essential minerals and have roles for more than 300 metabolic reactions in the body. The purpose of this study was to investigate how exhaustive exercise affects testosterone levels and plasma lactate in cyclists who were supplemented with oral zinc and selenium for 4 weeks. For this reason, 32 male road cyclists were selected equally to four groups: PL group, placebo; Zn group, zinc supplement (30 mg/day); Se group, selenium supplement (200 μg/day); and Zn-Se group, zinc-selenium supplement. After treatment, free, total testosterone, and lactate levels of subjects were determined before and after exhaustive exercise. Resting total, free testosterone, and lactate levels did not differ significantly between groups, and were increased by exercise (P > 0.05). Serum total testosterone levels in Zn group were higher than in Se group after exercise (P < 0.05). Serum-free testosterone levels in the Zn group were higher than the other groups (P < 0.05).There was an insignificant difference between levels of lactate in the four groups after exercise (P > 0.05). The results showed that 4-week simultaneous and separately zinc and selenium supplementation had no significant effect on resting testosterone and lactate levels of subjects who consume a zinc and selenium sufficient diet. It might be possible that the effect of zinc supplementation on free testosterone depends on exercise.

The differences of sarcopenia-related phenotypes: effects of gender and population

Sarcopenia is a serious condition especially in the elderly population mainly characterized by the loss of skeletal muscle mass and strength with aging. Extremity skeletal muscle mass index (EMMI) (sum of skeletal muscle mass in arms and legs/height2) is gaining popularity in sarcopenia definition (less than two standard deviations below the mean of a young adult reference group), but little is known about the gender- and population-specific differences of EMMI. This study aimed at investigating the differences of EMMI, arm muscle mass index (AMMI), and leg muscle mass index (LMMI) between gender groups and populations (Chinese vs. Caucasians). The participants included 1,809 Chinese and 362 Caucasians with normal weight aged from 19 to 45 years old. Extremity muscle mass, arm muscle mass, and leg muscle mass were measured by using dual energy x-ray absorptiometry. Independent sample t tests were used to analyze the differences in muscle mass indexes between the studied groups. All the study parameters including EMMIs, AMMIs, and LMMIs were significantly higher (P ≤ 0.0003) in the Caucasian group than in the Chinese group and also higher in the male group than in the female group, and these significant differences (P ≤ 0.0005) remained after adjusting for age by simple regressions. The detected differences of muscle mass indexes between different gender and ethnic groups may provide important implications in their different risk of future sarcopenia.

Inhibitory actions of mibefradil on steroidogenesis in mouse Leydig cells: involvement of Ca(2+) entry via the T-type Ca(2+) channel

Intracellular cAMP and Ca(2+) are involved in the regulation of steroidogenic activity in Leydig cells, which coordinate responses to luteinizing hormone (LH) and human chorionic gonadotropin (hCG). However, the identification of Ca(2+) entry implicated in Leydig cell steroidogenesis is not well defined. The objective of this study was to identify the type of Ca(2+) channel that affects Leydig cell steroidogenesis. In vitro steroidogenesis in the freshly dissociated Leydig cells of mice was induced by hCG incubation. The effects of mibefradil (a putative T-type Ca(2+) channel blocker) on steroidogenesis were assessed using reverse transcription (RT)-polymerase chain reaction analysis for the steroidogenic acute regulatory protein (StAR) mRNA expression and testosterone production using radioimmunoassay. In the presence of 1.0 mmol L(-1) extracellular Ca(2+), hCG at 1 to 100 IU noticeably elevated both StAR mRNA level and testosterone secretion (P < 0.05), and the stimulatory effects of hCG were markedly diminished by mibefradil in a dose-dependent manner (P < 0.05). Moreover, the hCG-induced increase in testosterone production was completely removed when external Ca(2+) was omitted, implying that Ca(2+) entry is needed for hCG-induced steroidogenesis. Furthermore, a patch-clamp study revealed the presence of mibefradil-sensitive Ca(2+) currents seen at a concentration range that nearly paralleled those inhibiting steroidogenesis. Collectively, our data provide evidence that hCG-stimulated steroidogenesis is mediated at least in part by Ca(2+) entry carried out by the T-type Ca(2+) channel in the Leydig cells of mice.

Endocrine responses to upper- and lower-limb resistance exercises with blood flow restriction

To compare endocrine responses to low-intensity resistance exercise with blood flow restriction (BFR) for upperlimb (UL) and lower-limb (LL) muscles, we measured blood lactate, plasma noradrenaline, and serum growth hormone (GH), testosterone, cortisol and insulin-like growth factor-I (IGF-I) before and after the UL (biceps curl and triceps press down) and LL (leg extension and leg curl) exercises with BFR in nine men (26.3 +/- 3.1 yr). The load of 30% of one-repetition maximum (1RM) was used in all the exercises, in which the first set of 30 repetitions was followed by the second and third sets to failure. In each exercise program, the proximal portions of their upper arms (UL) or thighs (LL) were compressed bilaterally by elastic belts. Both the UL and LL caused significant increases in lactate, noradrenaline, GH, testosterone, cortisol, and IGF-I concentrations when compared to the pre-exercise values. A significant difference between the UL and LL was observed only in the area under the curve (AUC) of serum GH concentration, indicating that the LL induced greater GH response than did the UL. The greater GH secretion following the LL may be more advantageous for muscle hypertrophy induced by a long-term training period.

Effects of hypoxia on testosterone release in rat Leydig cells

The aim of this study was to explore the effect and action mechanisms of intermittent hypoxia on the production of testosterone both in vivo and in vitro. Male rats were housed in a hypoxic chamber (12% O(2) + 88% N(2), 1.5 l/ml) 8 h/day for 4 days. Normoxic rats were used as control. In an in vivo experiment, hypoxic and normoxic rats were euthanized and the blood samples collected. In the in vitro experiment, the enzymatically dispersed rat Leydig cells were prepared and challenged with forskolin (an adenylyl cyclase activator, 10(-4) M), 8-Br-cAMP (a membrane-permeable analog of cAMP, 10(-4) M), hCG (0.05 IU), the precursors of the biosynthesis testosterone, including 25-OH-C (10(-5) M), pregnenolone (10(-7) M), progesterone (10(-7) M), 17-OH-progesterone (10(-7) M), and androstendione (10(-7)-10(-5) M), nifedipine (L-type Ca(2+) channel blocker, 10(-6)-10(-4) M), nimodipine (L-type Ca(2+) channel blocker, 10(-5) M), tetrandrine (L-type Ca(2+) channel blocker, 10(-5) M), and NAADP (calcium-signaling messenger causing release of calcium from intracellular stores, 10(-6)-10(-4) M). The concentrations of testosterone in plasma and medium were measured by radioimmunoassay. The level of plasma testosterone in hypoxic rats was higher than that in normoxic rats. Enhanced testosterone production was observed in rat Leydig cells treated with hCG, 8-Br-cAMP, or forskolin in both normoxic and hypoxic conditions. Intermittent hypoxia resulted in a further increase of testosterone production in response to the testosterone precursors. The activity of 17β-hydroxysteroid dehydrogenase was stimulated by the treatment of intermittent hypoxia in vitro. The intermittent hypoxia-induced higher production of testosterone was accompanied with the influx of calcium via L-type calcium channel and the increase of intracellular calcium via the mechanism of calcium mobilization. These results suggested that the intermittent hypoxia stimulated the secretion of testosterone at least in part via stimulatory actions on the activities of adenylyl cyclase, cAMP, L-type calcium channel, and steroidogenic enzymes.

Leydig cell transplantation restores androgen production in surgically castrated prepubertal rats

Prepubertal testicular dysfunction and the subsequent development of hypogonadism affects an estimated one in 200 children worldwide. As the testosterone levels are dynamic during development and puberty, traditional hormone treatment regimens are often inadequate, thereby leaving associated physiological conditions unresolved. Therefore, we have investigated the potential therapeutic effect of mature Leydig cell transplantation for the treatment of prepubertal primary hypogonadism through the use of a surgically induced hypogonadistic rat model system. In the experiment, Leydig cells were surgically isolated from mature Sprague-Dawley rats and transplanted into prepubertal recipients. Serum testosterone levels and microscopic analysis of the stained testicular interstitium were compared with sham-treated controls, as well as with castrated and intact rats during sexual development. At 4 weeks post-implantation, serum testosterone was detectable in Leydig cell recipients, but not in surgical controls, and progressively increased as a function of time until reaching levels comparable with sexually mature males at 12 weeks post-implantation. Histological analysis revealed a high rate of Leydig cell survival as well as steroidogenic secretory activity. Therefore, we conclude that mature Leydig cell transplantation in prepubertal hypogonadism recipients has therapeutic potential in rats and merits further investigation for clinical application.

Cyclin-dependent kinase 5 regulates steroidogenic acute regulatory protein and androgen production in mouse Leydig cells

The roles of cyclin-dependent kinase 5 (Cdk5) in central nervous system and neurodegenerative diseases have been intensely investigated in recent decades. Because protein expressions of Cdk5 and its regulator, p35, have been identified in Leydig cells, it is informative to further explore the novel function of Cdk5/p35 in male reproduction. Here we show that Cdk5/p35 protein expression and kinase activity in mouse Leydig cells are regulated by human chorionic gonadotrophin (hCG) in both dose- and time-dependent manners. Blocking of Cdk5 by molecular inhibitors or small interfering RNA resulted in reduction of testosterone production by Leydig cells. cAMP, a second messenger in LH signaling, was identified as a factor in hCG-dependent regulation of Cdk5/p35. Importantly, Cdk5 protein and kinase activity could support accumulation of steroidogenic acute regulatory (StAR) protein, a crucial component of steroidogenesis. We additionally addressed the protein interaction between Cdk5/p35 and StAR. The Cdk5-dependent serine phosphorylation of StAR indicated a possible mechanism by which Cdk5 induced accumulation of StAR protein. In conclusion, Cdk5 modulates hCG-induced androgen production in mouse Leydig cells, possibly through regulation of StAR protein levels. These results indicate that Cdk5 may play an important role in male reproductive endocrinology and is a potential therapeutic target in androgen-related diseases.

Effects of arecoline on testosterone release in rats

Arecoline is one of the major components of betel nuts, which have been consumed as chewing gum in Southeast Asia. In this study, the effects of arecoline on testosterone (T) secretion were explored. Male rats were injected with human chorionic gonadotropin (hCG, 5 IU/kg) or arecoline (1 microg/kg) plus hCG via a jugular catheter. Blood samples were collected at several time intervals subsequent to the challenge. Rat anterior pituitary was treated with gonadotropin-releasing hormone in vitro with or without arecoline, and then the concentrations of luteinizing hormone (LH) in the medium were measured. Rat Leydig cells were purified by Percoll density gradient centrifugation and incubated with arecoline, hCG, forskolin, 8-bromo-cAMP (8-Br-cAMP), nifedipine, nimodipine, or tetrandrine at 34 degrees C for 1 h. A single intravenous injection of arecoline resulted in an increase of the hCG-induced level of plasma T. Administration of arecoline (10(-8) to 10(-6) M) in vitro increased T production in Leydig cells. The stimulatory effect of arecoline on T release in vitro was enhanced by hCG (0.001 IU/ml), forskolin (10(-6) M), or 8-Br-cAMP (10(-5) M). By contrast, nifedipine, nimodipine, or tetrandrine inhibited the increased T concentrations induced by arecoline. Western blot showed that arecoline increases steroidogenic acute regulatory (StAR) protein expression compared with vehicle. These results suggested that arecoline stimulates testosterone production by acting directly on Leydig cells via mechanisms involving an activation of L-type calcium channels, increasing the activity of 17beta-hydroxysteroid dehydrogenase and enhancing the expression of StAR.

Disruption of LH-induced testosterone biosynthesis in testicular Leydig cells by triclosan: probable mechanism of action

Triclosan (TCS) is an antimicrobial chemical widely used in different commercial preparations. The present study demonstrated the mechanism of action of TCS-induced anti-androgenicity in rat Leydig cells. Treatment of purified cells with increasing concentrations of TCS (0.001, 0.01, 0.1, 1 and 10 microM) resulted in a significantly decreased activity of adenylyl cyclase enzyme which was followed by a decreased synthesis of cAMP. This decreased cAMP level resulted in the disruption of entire steroidogenic cascade causing a depressed synthesis of testosterone. However, TCS-induced decrease in the production of testosterone returned to normalcy when cells were treated with forskolin (an adenylyl cyclase activator). Transcription followed by translational of four prominent steroidogenic enzyme/proteins, cytochrome P450 side chain cleavage (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and steroidogenic acute regulatory (StAR) protein, also decreased in a dose-dependent manner in TCS-treated Leydig cells as determined by RT-PCR, enzyme assay and Western blot. These results suggested that the disruption of the activity of adenylyl cyclase enzyme by TCS in turn leads to the disruption of intermediate steroidogenic cascade causing a depressed testosterone production. The study further confirmed the anti-androgenic activity of TCS in Leydig cells with highest effective concentration at 1 microM.

Validity of the 3 min step test in moderate altitude: environmental temperature as a confounder

The 3 min step test is a widely used method to evaluate physical fitness, but whether this method is valid when performed at altitude is unknown. The purpose of this study was to examine the effect of altitude on the fitness score of the 3 min step test, and the role of ambient temperature in this effect. In study I, 11 healthy volunteers (aged 18.1 ± 1.1 years) performed a 3 min step test at sea level and at altitude (1950 m). Plasma lactate and stress hormones, as indicators of metabolic stress, were measured before and after the test. To determine the role of ambient temperature, we performed study II at sea level with the same step test simulating the altitude temperature condition (24 °C at high altitude versus 32 °C at sea level) with 23 subjects (aged 20.4 ± 0.4 y). In study I, plasma lactate of the subjects was elevated during the step test at sea level and to a greater extent at high altitude. Plasma cortisol and testosterone levels were elevated only at high altitude. However, the heart rate (HR) recovery after the step test was faster at high altitude than at sea level, producing a better physical fitness index. Furthermore, in study II, we demonstrated that the subjects who performed the 3 min step test at 24 °C exhibited faster HR recovery than at 32 °C. The current study therefore suggests that environmental conditions leading to temperature variation have strong confounding effects on the fitness score of the 3 min step test.

Comparison of hormone responses following light resistance exercise with partial vascular occlusion and moderately difficult resistance exercise without occlusion

Previous studies of contracting muscle with low loading and partial vascular occlusion demonstrated hypertrophy and strength adaptations similar to and exceeding those observed with traditional moderate to high resistance (Shinohara M, Kouzaki M, Yoshihisa T, and Fukunaga T. Eur J Physiol 77: 189-191, 1998; Takarada Y, Takazawa H, Sato Y, Takebayashi S, Tanaka Y, and Ishii N. J Appl Physiol 88: 2097-2106, 2000; Takarada Y, Sato Y, and Ishii N. Eur J Physiol 86: 308-314, 2002). The purpose of the study was to determine the anabolic and catabolic hormone responses to light resistance exercise combined with partial vascular occlusion. Three experimental conditions of light resistance with partial occlusion (LRO), moderate resistance with no occlusion (MR), and partial occlusion without exercise (OO) were performed by eight healthy subjects [mean 21 yr (SD 1.8)]. Three sets of single-arm biceps curls and single-leg calf presses were completed to failure with 1-min interset rest periods. Workloads of 30 and 70% one repetition maximum for each exercise were lifted for the LRO and MR trials, respectively. Blood samples were taken preexercise, postexercise, and 15 min postexercise for each experimental condition. Lactate increased significantly in the LRO and MR trials and was not significantly different from each other at any time point. Growth hormone (GH) increased significantly by fourfold from pre- to postexercise in the LRO session but did not change significantly during this time period in the MR and OO trials (8.3 +/- 2.3 vs. 2.1 +/- 1.2 and 2.6 +/- 0.94 microg/l; respectively, P < 0.05). There were no changes in resting total testosterone [T; mean 15.7 +/- 1.6 (SE) nmol/l], free testosterone (FT; 54.1 +/- 4.5 pmol/l), or cortisol (267.6 +/- 22 nmol/l) across all trials and times. In conclusion, with similar lactate responses, light exercise combined with partial vascular occlusion elicits a greater GH response than moderate exercise without occlusion but does not affect T, FT, or cortisol.

Hormonal responses and adaptations to resistance exercise and training

Resistance exercise has been shown to elicit a significant acute hormonal response. It appears that this acute response is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations, as many studies have not shown a significant change during resistance training despite increases in muscle strength and hypertrophy. Anabolic hormones such as testosterone and the superfamily of growth hormones (GH) have been shown to be elevated during 15-30 minutes of post-resistance exercise providing an adequate stimulus is present. Protocols high in volume, moderate to high in intensity, using short rest intervals and stressing a large muscle mass, tend to produce the greatest acute hormonal elevations (e.g. testosterone, GH and the catabolic hormone cortisol) compared with low-volume, high-intensity protocols using long rest intervals. Other anabolic hormones such as insulin and insulin-like growth factor-1 (IGF-1) are critical to skeletal muscle growth. Insulin is regulated by blood glucose and amino acid levels. However, circulating IGF-1 elevations have been reported following resistance exercise presumably in response to GH-stimulated hepatic secretion. Recent evidence indicates that muscle isoforms of IGF-1 may play a substantial role in tissue remodelling via up-regulation by mechanical signalling (i.e. increased gene expression resulting from stretch and tension to the muscle cytoskeleton leading to greater protein synthesis rates). Acute elevations in catecholamines are critical to optimal force production and energy liberation during resistance exercise. More recent research has shown the importance of acute hormonal elevations and mechanical stimuli for subsequent up- and down-regulation of cytoplasmic steroid receptors needed to mediate the hormonal effects. Other factors such as nutrition, overtraining, detraining and circadian patterns of hormone secretion are critical to examining the hormonal responses and adaptations to resistance training.

Chemosensory stimulation of luteinizing hormone secretion in male Siberian hamsters (Phodopus sungorus)

Male Siberian hamsters (Phodopus sungorus) housed in long days (LD), but not short days (SD) release luteinizing hormone (LH) when exposed to females. This study examined whether this response is specific to a female and identifies the source of a stimulus that induces LH release. Serum concentrations of LH, testosterone (T), follicle stimulating hormone (FSH), and cortisol were examined in all experiments. T concentrations mirrored the LH response; FSH and cortisol were unchanged in response to all stimuli. Exposure to an LD female, irrespective of her reproductive status, but not an SD female, elicited LH release. Exposure to another male did not trigger LH release. Males released LH when allowed physical contact with an anesthetized female, but not when separated from a normally active female, suggesting that tactile or nonvolatile chemosensory stimuli elicit LH release. Urine and secretions collected from the vagina as well as oral, midventral, perineal, and rectal glands, elicited marked behavioral responses in male P. sungorus. Despite these behavioral responses, only feces from females elicited LH release in males. Males released LH in response to feces extracted from the rectum and to cotton swabs that had been rubbed against the rectal mucosa, suggesting that a component of rectal secretions may trigger LH release in male Siberian hamsters. Taken together, these data and previous data from our laboratory indicate that both the production of and the response to a pheromone that triggers the selective release of LH is regulated by day length.