Testosterone In Healthy Men Research Articles

Age-stratified reference ranges for directly measured serum free testosterone in healthy men

Age-stratified reference ranges for directly measured serum free testosterone in healthy men

Serum Testosterone and Cortisol Concentrations After Single-Dose Administration of 100-Mg Transdermal Testosterone in Healthy Men.

The growing interest in testosterone's effects on men's social behaviors, in particular aggressive, risk-taking, or status maintenance behaviors, is accompanied by a paucity of dose-dependent pharmacokinetic data. Examining the neurophysiological effects of transdermal testosterone typically includes a 4h delay before further brain-behavior measurements. Nevertheless, high heterogeneity regarding the timing of follow-up measurements and dosage remains. In a double-blind placebo-controlled design, we examined the short-term pharmacokinetic profile of 100-mg transdermal testosterone (Testotop®) to determine the optimal time for detecting testosterone-mediated effects. Across two studies, 35 healthy men received a single dose of testosterone and placebo in two separate sessions. In study one (n = 16), serum testosterone and cortisol were assessed serially every 30 min up to 2 h posttreatment. In study two (n = 19), we assessed serum testosterone and cortisol at baseline, 2 h, and 4.15 h (255 min) posttreatment. Relative to baseline and placebo, transdermal testosterone significantly increased total serum testosterone concentrations 90 min posttreatment, reaching maximum concentration between 2 h and 3 h posttreatment. Albeit elevated, serum testosterone levels gradually decreased between 2 h and 4 h following treatment. Transdermal testosterone did not suppress cortisol release. Instead, cortisol concentrations decreased according to cortisol's known circadian rhythm. Unlike previous findings showing significant testosterone concentration increases as soon as 60 min and as late as 3 h post 150-mg testosterone treatment, our 100-mg testosterone manipulation significantly increased testosterone concentrations 90 min following treatment. These pharmacokinetic data are important in facilitating the optimization of timing parameters for future testosterone challenge studies.

Association Between Serum Testosterone and Serum PSA Among Men With and Without Partial Androgen Deficiency.

Serum prostatic specific antigen (PSA) and serum testosterone levels share an undefined relationship with each other, with many conflicting studies showing both positive and negative correlation between them. Our aim was to assess association between serum PSA and serum testosterone in healthy men with normal testosterone levels and men with partial androgen deficiency (PADAM). A cross sectional study was conducted at a teaching hospital setting where serum testosterone and aging male symptom scale(AMS) scores along with PSA were studied in 255 men (> 50years) with and without PADAM. Mean total testosterone and serum PSA was 9.35 ± 1.33nmol/L, 1.96 ± 0.76ng/mL in males with PADAM and 15.30 ± 1.95nmol/L, 1.85 ± 0.73ng/mL respectively in males without PADAM. No significant relationship was observed between serum PSA and serum testosterone levels among healthy males irrespective of PADAM in the study population. We suggest, there is no need to adjust PSA values for biopsy decisions according to testosterone levels.

Vitamin D and Testosterone in Healthy Men: A Randomized Controlled Trial.

Available evidence shows an association of vitamin D with androgen levels in men. However, results from preliminary randomized controlled trials (RCTs) are conflicting. To evaluate whether vitamin D supplementation increases total testosterone (TT) levels in healthy men. The Graz Vitamin D&TT-RCT is a single-center, double-blind, randomized, placebo-controlled trial conducted between December 2012 and January 2017. Endocrine outpatient clinic at the Medical University of Graz, Austria. Ninety-eight healthy men with TT levels ≥10.4 nmol/L and 25-hydroxyvitamin D [25(OH)D] levels <75 nmol/L completed the study. Subjects were randomly assigned to receive 20,000 IU/wk of vitamin D3 (n = 50) or placebo (n = 50) for 12 weeks. Primary outcome was TT measured using mass spectrometry. Secondary outcomes were free testosterone, sex hormone-binding globulin, estradiol, follicle-stimulating hormone, and luteinizing hormone levels; free androgen index; metabolic characteristics; and body composition. In healthy men [mean values ± standard deviation: age, 39 years (±13 years); 25(OH)D level, 53.3 nmol/L (±18.3 nmol/L); TT, 19.1 nmol/L (±5.6 nmol/l)], no significant treatment effect on TT was found; however, there were significant effects on quantitative insulin sensitivity check index (QUICKI) and a trend toward decreased Matsuda index. In the treatment group, median (interquartile range) changes for TT, QUICKI, and Matsuda index were 0.5 nmol/L (-0.63 to 0.63 nmol/L; P = 0.497), -0.02 (-0.04 to 0.01; P = 0.034), and -0.9 (-3.2 to 0.8; P = 0.051), respectively. Vitamin D treatment had no effect on TT levels in middle-aged healthy men with normal baseline TT, but it significantly decreased QUICKI. Additional studies investigating vitamin D effects on TT and insulin sensitivity in healthy men are required.

MP84-14 THE RELATIONSHIPS BETWEEN LIFESTYLE AND TESTOSTERONE; NIGHT WAKING, SMOKING HISTORY, DRINK HABIT AND THE LENGTH OF TIME USING INTERNET AND PLAYING GAMES ARE ASSOCIATED WITH TESTOSTERONE LEVEL

You have accessJournal of UrologySexual Function/Dysfunction: Evaluation II1 Apr 2017MP84-14 THE RELATIONSHIPS BETWEEN LIFESTYLE AND TESTOSTERONE; NIGHT WAKING, SMOKING HISTORY, DRINK HABIT AND THE LENGTH OF TIME USING INTERNET AND PLAYING GAMES ARE ASSOCIATED WITH TESTOSTERONE LEVEL Shinichiro Fukuhara, Norichika Ueda, Tetsuji Soda, Hiroshi Kiuchi, Yasushi Miyagawa, Akira Tsujimura, and Norio Nonomura Shinichiro FukuharaShinichiro Fukuhara More articles by this author , Norichika UedaNorichika Ueda More articles by this author , Tetsuji SodaTetsuji Soda More articles by this author , Hiroshi KiuchiHiroshi Kiuchi More articles by this author , Yasushi MiyagawaYasushi Miyagawa More articles by this author , Akira TsujimuraAkira Tsujimura More articles by this author , and Norio NonomuraNorio Nonomura More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.2655AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Evaluation and treatment of men with low testosterone have become an important part of urological practice. However prevalence of symptoms associated with low testosterone in healthy men especially aged <50 years were still unclear. We have reported the association between testosterone levels and symptoms related to low testosterone using aging male symptom score (AMS score) in healthy young men. Also the association between lifestyle and testosterone level in healthy young men was still unclear. The objective of this study was to examine the association between lifestyle and total testosterone levels in healthy young and elderly adult. METHODS This study included 1557 healthy men who were working for our university and taking annual medical check-up between the ages of 22-73; 145 in 20′s, 582 in 30′s, 446 in 40′s, 291 in 50′s and 93 over 60. Serum testosterone was measured by electro-chemiluminescence immunoassay. The number of waking time during night, smoking history, drink habit, the length of time using the internet and playing game, the times of night shift per month and the number of taking breakfast per week were obtained from questionnaire. Each items were dichotomized into more than one time night waking and none, having smoking history and none, drinking every day and not every day, more than thirty minutes and less, more than five times night shift and less, taking breakfast every day and not every day, respectively. The relationships between testosterone and lifestyles were analyzed by locally weighted linear regression. RESULTS More than one time waking up during night, the habit drinking every day, having smoking history were related to lower testosterone level. About the length of time using internet and playing game, there was the relationship that lower testosterone was related to low probability of using internet more than thirty minutes (Figure). There was no relationship between testosterone level and the times of night shift per month and the number of taking breakfast per week. CONCLUSIONS Lifestyles such as internet use, night waking, drinking habit and smoking in healthy young and elderly adults are associated with testosterone levels. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e1144-e1145 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Shinichiro Fukuhara More articles by this author Norichika Ueda More articles by this author Tetsuji Soda More articles by this author Hiroshi Kiuchi More articles by this author Yasushi Miyagawa More articles by this author Akira Tsujimura More articles by this author Norio Nonomura More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

P.3.010 Endogenous plasma testosterone in healthy men is negatively associated with hippocampal serotonin receptor 4 binding

Dopamine D2/D3 receptor availability at rest and its association with individual pain perception was investigated using the [11C] raclopride PET-method in 24 female Fibromyalgia (FMS) participants with (FMS+, N=11) and without (FMS−, N=13) comorbid depression and in 17 healthy women. Thermal pain thresholds (TPT) and pain responses were assessed outside the scanner. We compared the discriminative capacity, i.e. the individual׳s capacity to discriminate between lower and higher pain intensities and the response criterion, i.e. the subject׳s tendency to report pain during noxious stimulation due to psychological factors. [11C] raclopride binding potential (BP), defined as the ratio of specifically bound non-displaceable radioligand at equilibrium (BPND) was used as measure of D2/D3 receptor availability. We found significant group effects of BPND in striatal regions (left ventral striatum, left caudate nucleus and left nucleus accumbens) between FMS+ and FMS− compared to healthy subjects. Correlational analysis showed negative associations between TPT and D2/D3 receptor availability in the left caudate nucleus in FMS-, between TPT and D2/D3 receptor availability in the right caudate nucleus in FMS + and positive associations between TPT and D2/D3 receptor availability in the left putamen and right caudate nucleus in healthy controls. The response criterion was positively associated with D2/D3 receptor availability in the right nucleus accumbens in FMS − and negatively with D2/D3 receptor availability in the left caudate nucleus in healthy controls. Finally, no significant associations between D2/D3 receptor availability and discriminative capacity in any of the groups or regions were determined. These findings provide further support for a disruption of dopaminergic neurotransmission in FMS and implicate DA as important neurochemical moderator of differences in pain perception in FMS patients with and without co-morbid depression.

The influence of a passion flower extract on free testosterone in healthy men: a two part investigation involving younger and older men

Plant-based nutrients have been studied for their potential impact on testosterone production in men. We investigated the influence of a novel passion flower extract on free testosterone in healthy men. In part one of this study, 18 younger men (35.9 ± 1.6 years) were assigned to consume placebo tablets or tablets containing a passion flower extract, in a random order, double-blind, cross-over design. The treatment period for each condition was 15 days, with a two-week washout period between conditions. Blood and saliva were collected both in the morning and the evening on days 1, 8, and 15—both before and one hour following ingestion of the assigned condition. In part two of this study, seven older men (55.9 ± 2.7 years) were assigned to consume the passion flower extract or placebo tablets in a random order, double-blind, cross-over design. The treatment period was the same as for part one and but only saliva was collected in the morning on days 1, 3, 8, and 15. All subjects completed a questionnaire on the morning of each test day to determine their subjective feelings associated with the condition treatment. Passion flower extract did not appear to influence free testosterone or subjective feelings in younger men. However, free salivary testosterone was increased an average of 13% in older men. In addition, an increase of 17% was noted from day 1 to day 15 for perceived energy level, while an increase of 9% was noted for libido when older men used the extract. A novel passion flower extract does not influence testosterone concentrations or subjective feelings in younger men but may have an influence on these outcomes in selected older men. It is possible that the treatment may be more effective when delivered to those with low baseline testosterone values.

Medical Castration Using the Investigational Oral GnRH Antagonist TAK-385 (Relugolix): Phase 1 Study in Healthy Males

TAK-385 is a highly selective, oral, nonpeptide GnRH antagonist being investigated as a possible prostate cancer treatment. The objectives were to evaluate safety, tolerability, pharmacokinetics, and pharmacodynamics of TAK-385 on LH and testosterone. This was a three-part, randomized, double-blind, placebo-controlled, phase 1 dose-escalation study in 176 healthy male UK volunteers. Part 1, single doses of TAK-385 (0 [placebo], 80, 120, 180, or 360 mg). Part 2, 14-day TAK-385 (0, 20, 40, 80, or 180 mg) daily. Part 3, 28-day TAK-385 (40 [with loading dose], 60, 80, or 160 mg) or placebo daily. Parts 2 and 3 included men aged 40-75 years. Main outcome measures included plasma concentrations of TAK-385, LH, and testosterone. Oral TAK-385 was readily absorbed, and steady state was reached in ≤ 14 days. Food reduced TAK-385 systemic exposure by 47-52%. Mean serum testosterone levels declined ≤ 6 hours after TAK-385 administration. Loading doses up to 360 mg on day 1 or 360 mg on day 1 followed by 240 mg on day 2 reduced the time to achieve castrate testosterone levels from ≥ 7 to <3 days. TAK-385 doses ≥ 80 mg/d achieved sustained medical castration and trough TAK-385 concentrations >4 ng/mL. After discontinuation of TAK-385 on day 28, testosterone levels normalized in most subjects in ≤ 28 days. Common adverse events included bradycardia, headache, and hot flush (all grade ≤ 2). Oral TAK-385 (40-180 mg/d) was well tolerated and effectively lowered testosterone in healthy men. Planned phase 2 doses in men with hormone-sensitive prostate cancer are 80 and 120 mg/d.

Population pharmacokinetic/pharmacodynamic assessment of pharmacological effect of a selective estrogen receptor β agonist on total testosterone in healthy men.

LY500307 is a highly selective estrogen receptor β (ERβ) agonist, which loses its selectivity at high dose and leads to undesirable suppression of total testosterone (TT) concentration. The objective of the present analysis was to define the LY500307 dose with minimal effect on TT METHODS: LY500307 and TT concentrations were obtained from a single ascending-dose study in a total of 30 healthy male subjects. LY500307 (in the range of 0.5 to 500 mg) or placebo was administered orally as a single dose on 2 occasions with a 3-week washout period. A population pharmacokinetics/pharmacodynamics (PK/PD) model that integrated Fourier series in an indirect response model was developed to describe the circadian rhythm of TT and the exposure-response relationship of LY500307 on TT. The maximum TT suppression (Emax ) was approximately 28.6%. The potency (EC50 ) of LY500307 on TT suppression was approximately 1.69 ng/mL with a 95%CI of 0.871 to 4.44 ng/mL. This model could provide inferences on LY500307 dose levels that would result in various magnitudes of TT suppression. Population PK/PD modeling is a highly sensitive tool to detect exposure-response relationships on top of the complicated and highly variable circadian rhythm of TT.

Oxytocin plasma concentrations after single intranasal oxytocin administration – A study in healthy men

The neuropeptide oxytocin has become a subject of great interest in studies investigating human social cognition. Single intranasal administration of the hormone has been reported to have positive behavioral effects, such as increasing trust or facilitating social approach, 45-80 min after administration. However, little is still known about the long-term pharmacokinetics of oxytocin nasal spray application in humans. This study addressed the question how long oxytocin plasma levels remain elevated following nasal spray administration. Another goal was to examine the influence of oxytocin administration on endogenous steroid hormones since such alterations might modulate social behavior via an indirect way. Eight healthy Caucasian men were challenged with a single intranasal application of 26 international units of oxytocin. Changes in oxytocin blood plasma levels, as well as steroid hormone levels of progesterone, testosterone and estradiol were assessed at 5 consecutive time points over a period of 3.5 h (-5, +30, +90, +150, +210 min relative to oxytocin administration). Results gave evidence for a substantial rise of oxytocin plasma levels 30 min after intranasal administration, observed in 7 of 8 participants. Group mean oxytocin plasma level was found to have returned to baseline already 90 min post administration, though in some individuals the plasma levels was still elevated relative to sampling at post 150 min. Steroid hormone analyses yielded a slight augmentation of endogenous testosterone levels 210 min after oxytocin administration. Our data confirms previous findings that oxytocin administered as a nasal spray enters the blood circulation, elevating oxytocin plasma levels for a limited time. Our findings suggest that this time window differs between individuals, but that, for the used dose, it does not extend beyond 150 min post administration. The data further provides preliminary evidence that intranasal oxytocin has an enhancing effect on testosterone in healthy men.

Aggression—Interactions of serotonin and testosterone in healthy men and women

Serotonin (5-HT) and testosterone (T) have both been implicated in the regulation of aggression. Findings in humans however are very inconclusive, with respect to main effects of either system. Animal models implicate T to modulate 5-HT system activity, and furthermore have shown behaviorally relevant interactions of T and 5-HT with respect to aggression. We tested for associations between habitual T-level and 5-HT system activity, as well as behaviorally relevant interactions of T and 5-HT with respect to trait aggression in 48 healthy male and female subjects. 5-HT activity was measured by means of neuroendocrine challenge paradigm with S-citalopram. T-levels were measured in saliva samples. Trait aggression was assessed by self-report measures. T-levels were not associated with indices of central 5-HT activity. Results showed significant interaction effects between 5-HT and T for trait aggression in men only ( p < 0.05). Trait aggression was significantly higher in the combinations “high T + high cortisol responses” (indicating decreased 5-HT availability), and “low T + low cortisol responses” (indicating increased 5-HT availability), after S-citalopram. Results support the notion of behaviorally relevant interactions between T and 5-HT, with respect to aggression in humans, but also indicate the need for further studies.

Prostate Specific Antigen Working Group Guidelines on Prostate Specific Antigen Doubling Time

Prostate specific antigen is a glycoprotein found almost exclusively in normal and neoplastic prostate cells. Prostate specific antigen doubling time, or the change in prostate specific antigen over time, has emerged as a useful predictive marker for assessing disease outcome in patients with prostate cancer. It is important to agree on definitions and values for the calculation of prostate specific antigen doubling time, and to develop a common approach to outcome analysis and reporting. In September 2006 a conference was held at the National Cancer Institute in Bethesda, Maryland to define these parameters and develop guidelines for their use. The Prostate Specific Antigen Working Group defined criteria regarding prostate specific antigen doubling time including the calculation of prostate specific antigen doubling time, evidence to support prostate specific antigen doubling time as a predictive factor in the setting of biochemical recurrence and the use of prostate specific antigen doubling time as a stratification factor in clinical trials. We propose that investigators calculate prostate specific antigen doubling time before enrolling patients in clinical studies and calculate it as an additional measurement of therapeutic activity. We believe we have developed practical guidelines for the calculation of prostate specific antigen doubling time and its use as a measurement of prognosis and outcome. Furthermore, the use of common standards for prostate specific antigen doubling time in clinical trials is important as we determine which treatments should progress to randomized trials in which "hard" end points such as survival will be used.

Mood changes, body mass index and bioavailable testosterone in healthy men: results of the Androx Vienna Municipality Study

To determine whether sex hormones alone or in combination with body mass index (BMI) influence mood in men. Blood samples were taken from 669 manual workers (aged 43-67 years) to measure sex hormone levels, in particular bioavailable testosterone (BAT). At the same time BMI was calculated. All participants completed the Beck's Depression Inventory (BDI) for the evaluation of depression. Then BMI and BAT were correlated to the BDI scores, to determine a possible interaction. There was a quadratic main effect for BAT on the BDI scores, i.e. an increased risk of depression with an odds ratio of 1.871 (P = 0.029) for hypo- and hypergonadal men. Also, there was an interaction between BAT and BMI, which was mainly detected in underweight and obese men. This U-shaped effect for underweight and obese men was not detected in men with a 'normal' weight, who had a significantly linear decrease in the risk of depression by changing from the hypogonadal to the eugonadal subgroup, as well as for changing from the eugonadal to the hypergonadal subgroup, with a mean odds ratio of 0.513 (P = 0.032). Depression depends on BAT and BMI; in men of normal weight, an increase in BAT reduces the risk of depression, which is not the case in underweight and obese men. Consequently eugonadal men with normal testosterone levels have the lowest risk of depression.

Licorice consumption and serum testosterone in healthy man.

We have previously found that licorice can reduce serum testosterone in healthy men. These results were not confirmed in another study, where the same amounts of licorice did not decrease salivary testosterone values. In the actual study we treated more cases with the same amount of licorice and reproduced our previous data. The mean testosterone values decreased by 26 % after one week of treatment (p < 0.01). There was also a significant increase in 17-OHP and LH concentrations and a slight, but not significant decrease in free testosterone. Licorice treatment, in addition, did not affect the response of testosterone and 17-OHP to stimulation with beta-HCG.

Age-related change in serum concentrations of testosterone in middle-aged Korean men

The objective of this study was to determine whether testosterone and sex hormone binding globulin (SHBG) levels are different between healthy men and men with chronic illness, and to evaluate the age-related changes of testosterone and SHBG in healthy men in Korea. Enrolment took place between January 2000 and December 2001 at Pundang CHA General Hospital in Korea. All men who came for male climacteric and geriatric health screening examinations were eligible. Of the 762 men recruited, 136 men had at least one present or previous medical illness and 626 men were healthy. Higher serum concentrations of total testosterone (5.31 ± 1.88 ng/ml vs. 4.96 ± 1.43 ng/ml; p < 0.05), free androgen index (16.60 ± 7.36 vs. 14.57 ± 5.55; p < 0.01) and calculated bioavailable testosterone (8.88 ± 3.52 nmol/l vs. 7.91 ± 2.52 nmol/l; p < 0.01) were demonstrated in the healthy compared with the disease group. Total testosterone declined at a rate of 0.2% per year, SHBG increased by 1.74% per year, calculated bioavailable testosterone declined by 0.8% per year, and free androgen index declined by 1.15% per year in healthy subjects aged between 40 and 70. The above results seem to be consistent with previous Western studies, showing higher concentrations of testosterone in healthy men, that decline with increasing age.

Age-related change in serum concentrations of testosterone in middle-aged Korean men

The objective of this study was to determine whether testosterone and sex hormone binding globulin (SHBG) levels are different between healthy men and men with chronic illness, and to evaluate the age-relatedchanges of testosterone and SHBG in healthy men in Korea. Enrolment took place between January 2000 and December 2001 at Pundang CHA General Hospital in Korea. All men who came for male climacteric andgeriatric health screening examinations were eligible. Of the 762 men recruited, 136 men had at least one present or previous medical illness and 626 men were healthy. Higher serum concentrations of totaltestosterone (5.31 ± 1.88 ng/ml vs. 4.96 ± 1.43 ng/ml; p < 0.05), free androgen index (16.60 ± 7.36 vs. 14.57 ± 5.55; p < 0.01) and calculated bioavailabletestosterone (8.88 ± 3.52 nmol/l vs. 7.91 ± 2.52 nmol/l; p < 0.01) were demonstrated in the healthy compared with the disease group. Total testosterone declined at a rate of 0.2%per year, SHBG increased by 1.74% per year, calculated bioavailable testosterone declined by 0.8% per year, and free androgen index declined by 1.15% per year in healthy subjects aged between 40 and 70.The above results seem to be consistent with previous Western studies, showing higher concentrations of testosterone in healthy men, that decline with increasing age.

Effect of cigarette smoking on levels of bioavailable testosterone in healthy men

Effect of cigarette smoking on levels of bioavailable testosterone in healthy men

Effect of cigarette smoking on levels of bioavailable testosterone in healthy men

The effect of smoking on androgen levels is important given the recent interest in the link between low levels of androgens and the development of cardiovascular disease. Numerous studies examining the effects of cigarette smoking on the levels of total and free testosterone have reported conflicting findings, but there has been no accurate assessment of the effects of cigarette smoking on the levels of bioavailable testosterone [not bound to sex hormone-binding globulin (SHBG)]. We attempted to determine whether smoking affects the level of bioavailable testosterone. We undertook a case-control study of 25 healthy male smokers and 25 healthy never-smokers, matched by age and body mass index. Early morning levels of total, free and bioavailable testosterone, 17beta-oestradiol, SHBG and cotinine were determined and compared between the two groups. Levels of total (18.5+/-4.6 nM versus 15.1+/-4.9 nM, P=0.01) and free testosterone (462+/-91 pM versus 402+/-93 pM, P=0.03) were found to be higher in smokers compared with non-smokers respectively, as was SHBG (34.1+/-12.8 versus 28.1+/-9.0 nM, P=0.06). There were no significant differences in the levels of bioavailable testosterone (3.78+/-1.59 versus 3.51+/-1.26 nM, P=0.49) or 17beta-oestradiol (44.5+/-11.4 versus 42.3+/-11.5 pM, P=0.50) between smokers and non-smokers respectively. These data suggest that cigarette smoking has no significant effect on the biologically active fraction of testosterone, but may influence the levels of total and free testosterone through changes in the levels of SHBG.

Failure of short-term hyperinsulinemia to affect testosterone production rates in healthy men

Production rates for testosterone were determined in seven healthy men before and during a euglycemic clamp using a stable labeled tracer (1α-2α- d-testosterone 0.13 ± 0.4 mg/h) and analysis by gas chromatograph—mass spectrometry (GC-MS). Following an equilibration period of 12 hours (8 pm to 8 am), blood sample obtained at 20-minute intervals from 8 am until 2 pm were subsequently pooled and evaluated for three 2-hour periods. Following determination of basal endogenous production (8 am to 10 am), the investigation was continued during two 2-hour periods of induced euglycemic hyperinsulinemia (10 am to 2 pm). Production rates for testosterone (basal, 245 ± 91 μg/h) remained unchanged during the first (234 ± 87 μ/h) and second (207 ± 94 μg/h) period of this euglycemic clamp. These results suggest that short-term hyperinsulinemia has no effect on endogenous production rates of testosterone in healthy men.

Disturbing the light-darkness pattern reduces circulating testosterone in healthy men.

This is an analytic-sagital-observational-endocrinological study of the environmental stress induced by disturbing the light-darkness pattern. A population of 15 males, ages 28-59 years old, participated at random. All had had a pattern sleep of 22:00-6:00 h. A blood peripheral sample was obtained in each between 8:00 and 9:30 h several days before 6 April 1997 (summer daylight change) (phase I). A second blood sample was obtained in the following 72 h right after 6 April 1997. No significant changes in estradiol levels were observed; however, on an individual basis 12/15 males showed a testosterone reduction ranging from 5.0 to 48.6%, and, on a group basis testosterone reduction was 4.5 +/- 1.3 vs. 3.5 +/- 1.0 (ng/mL) +/- SD, p = .05, comparing phase I vs. phase II. This finding shows the need to balance economical gain vs. changes in the health status of the population exposed to light-dark stress and may help slow the human biology deteriorating process.