SEARCH · PubMed Health

Results for “testosterone”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources

PubMed1999

Lack of sexual activity from erectile dysfunction is associated with a reversible reduction in serum testosterone.

The role of androgenic hormones in human sexuality, in the mechanism of erection and in the pathogenesis of impotence is under debate. While the use of testosterone is common in the clinical therapy of male erectile dysfunction, hypogonadism is a rare cause of impotence. We evaluated serum testosterone levels in men with erectile dysfunction resulting either from organic or non-organic causes before and after non-hormonal impotence therapy. Eighty-three consecutive cases of impotence (70% organic, 30% non-organic, vascular aetiology being the most frequent) were subjected to hormonal screening before and after various psychological, medical (prostaglandin E1, yohimbine) or mechanical therapies (vascular surgery, penile prostheses, vacuum devices). Thirty age-matched healthy men served as a control group. Compared to controls, patients with impotence resulting from both organic and non-organic causes showed reduced serum levels of both total testosterone (11.1 +/- 2.4 vs. 17.7 +/- 5.5 nmol/L) and free testosterone (56.2 +/- 22.9 vs. 79.4 +/- 27.0 pmol/L) (both p < 0.001). Irrespective of the different aetiologies and of the various impotence therapies, a dramatic increase in serum total and free testosterone levels (15.6 +/- 4.2 nmol/L and 73.8 +/- 22.5 pmol/L, respectively) was observed in patients who achieved normal sexual activity 3 months after commencing therapy (p < 0.001). On the contrary, serum testosterone levels did not change in patients in whom therapies were ineffective. Since the pre-therapy low testosterone levels were independent of the aetiology of impotence, we hypothesize that this hormonal pattern is related to the loss of sexual activity, as demonstrated by its normalization with the resumption of coital activity after different therapies. The corollary is that sexual activity may feed itself throughout the increase in testosterone levels.

Adolescent↗

PubMed2001

Effects of testosterone on the electrical properties and nicotinic transmission of the major pelvic and coeliac ganglion neurones.

The effects of testosterone on the electrical properties and nicotinic activation of prevertebral ganglion neurones were investigated in vitro on the male rat major pelvic ganglion and rabbit coeliac ganglion. The electrical activity of the neurones was recorded using intracellular recording techniques. Nicotinic activation was triggered for neurones of the major pelvic ganglion by stimulating the hypogastric, pelvic and cavernous nerves and for coeliac neurones by stimulating the splanchnic nerves. Testosterone modified the resting membrane potential of neurones in the major pelvic ganglion by triggering a slow depolarization, and was without significant effect on the resting membrane potential of coeliac ganglion neurones. In neurones of the major pelvic and coeliac ganglia, testosterone had no significant effect on the firing pattern, on the characteristics of the action potential (firing threshold, duration, overshoot) and on the after-hyperpolarization (amplitude and duration). Testosterone affected, in opposite ways, the nicotinic activation of neurones of the two prevertebral ganglia. In the major pelvic ganglion, testosterone triggered an increase in the amplitude of excitatory postsynaptic potentials induced by stimulation of the hypogastric, pelvic and cavernous nerves with a single pulse, revealing a facilitation of nicotinic activation. On coeliac ganglion neurones, testosterone elicited a decrease in the amplitude of excitatory postsynaptic potentials induced by stimulation of the splanchnic nerves, indicating an inhibition of nicotinic activation. Our study shows that testosterone acts differently on neurones of prevertebral ganglia involved in the nervous control of different functions, its facilitatory action being exerted on neurones of the major pelvic ganglion which is particularly involved in the control of the urogenital tract. Our study reinforces the concept, derived from neuroanatomical and pharmacological studies, of the major pelvic ganglion as a major peripheral target for testosterone.

Animals↗

PubMed1999

Acute exposure to a low level of testosterone impairs relaxation in porcine coronary arteries.

1. While the gender bias associated with coronary artery disease has been suggested to be partially accounted for by the protective effects of oestrogens, the role of testosterone remains unclear. The aim of the present study was to determine whether vasorelaxation could be affected by acute administration of testosterone with and without 17 beta-oestradiol. 2. Precontracted porcine coronary artery rings were relaxed with sodium nitroprusside (SNP), levcromakalim, bradykinin (BK) or A23187. At 1 nmol/L, testosterone impaired relaxations to BK and A23187, while the same concentration of 17 beta-oestradiol potentiated levcromakalim- and SNP-induced relaxations. The impairment of relaxation responses by testosterone was reduced in the presence of 17 beta-oestradiol, while the enhancement by 17 beta-oestradiol was decreased by testosterone. 3. We demonstrate that a low level of testosterone can impair agonist-induced relaxation, an effect that is reduced by 17 beta-oestradiol. This further supports evidence indicating a detrimental role for testosterone in coronary artery disease and suggests that circulating levels of testosterone may undermine the beneficial effects of oestrogen in women.

Animals↗

PubMed1999

Testosterone and leptin in a group of Chinese with and without diabetes.

AIM: Leptin levels in the overweight and differences between men and women may be confounded by sex hormones in obesity-related type 2 diabetes. We carried out a study of leptin and testosterone and the effect of diabetes on this relationship in 71 Chinese subjects (51 with type 2 diabetes and 20 healthy non-diabetics) of whom 32 were overweight (body mass index (b.m.i.) > 25.0 kg/m2). METHODS AND RESULTS: Leptin levels were similar in the diabetic (median 7.4, interquartile range 4.2-10.6 ng ml-1) and non-diabetic (11.3 (6.0-16.3) ng ml-1) subjects. Testosterone and free testosterone in diabetics and non-diabetics were similar for both gender. Regardless of diabetes status, testosterone and its free form tend to increase in overweight women and decrease in men. Leptin correlated with testosterone in women with diabetes (Pearson correlation coefficient r = 0.495, p = 0.037) but not in diabetic men. Sixty-eight per cent of leptin variance was affected by b.m.i, insulin, sex (female) and diabetes status in a regression model that excluded testosterone (total and free). However, testosterone and insulin were predictors of leptin changes in the non-diabetic subjects. In diabetes, b.m.i., sex (female) and insulin remained as predictors of leptin changes. CONCLUSIONS: These results suggest that apart from body adiposity, testosterone also influences leptin levels and that diabetes has a significant effect on this association.

Adult↗

PubMed1996

Dihydrotestosterone and testosterone levels in men screened for prostate cancer: a study of a randomized population.

OBJECTIVE: To investigate the possible relationship between serum levels of prostate specific antigen (PSA), dihydrotestosterone (DHT), testosterone, sexual-hormone binding globulin (SHBG) and tumour stage, grade and ploidy in 65 cases of prostate cancer diagnosed in a screening study compared to 130 controls from the same population. PATIENTS, SUBJECTS AND METHODS: From a population of 26,602 men between the ages of 55 and 70 years, 2400 were selected randomly and invited to undergo screening for prostate cancer using a digital rectal examination, transrectal ultrasonography and PSA analysis. Among the 1782 attendees, 65 cases of prostate cancer were diagnosed. Each case was matched with two control subjects of similar age and prostate volume from the screening population. Frozen serum samples were analysed for PSA, DHT, testosterone and SHBG, and compared to the diagnosis and tumour stage, grade and ploidy. Comparisons between these variables, and multivariate and regression analyses were performed. RESULTS: There were significant differences in PSA level with all variables except tumour ploidy. DHT levels were slightly lower in patients with prostate cancer but the difference was not statistically significant. There was a trend towards lower DHT values in more advanced tumours and the difference for T-stages was close to statistical significance (P = 0.059). Testosterone levels were lower in patients with cancer than in the control group, but the differences were not significant. There was no correlation between testosterone levels, tumour stage and ploidy, but the differences in testosterone level in tumours of a low grade of differentiation compared to those with intermediate and high grade was nearly significant (P = 0.058). The testosterone/DHT ratio tended to be higher in patients with more advanced tumours. SHBG levels were lower in patients with cancer than in controls but the differences were not statistically significant. There were no systematic variations of tumour stage, grade and ploidy. Multivariate analysis showed that if the PSA level was known, then DHT, testosterone or SHBG added no further information concerning diagnosis, stage, grade or ploidy. Regression analysis on T-stage, PSA level and DHT showed an inverse linear relationship between PSA and DHT for stage T-3 (P = 0.035), but there was no relationship between PSA and testosterone. CONCLUSION: PSA was of value in discriminating between cases and controls and between various tumour stages and grades, but no statistically significant correlation was found for ploidy. If PSA level was known, no other variable added information in individual cases. Within a group, DHT levels tended to be lower among cases and in those with more advanced tumours. There was an inverse relationship between tumour volume, as defined by PSA level, and 5 alpha-reductase activity, as defined by DHT level, and the testosterone/DHT ratio. This trend was most obvious with T-stage. No systematic variation were found in the levels of testosterone or SHBG.

Aged↗

PubMed2004

Testosterone modulates K(+)ATP channels in Sertoli cell membrane via the PLC-PIP2 pathway.

Testosterone at physiological intratesticular concentrations induces a dose-dependent depolarisation and an increase in input resistance together with an increment of 45Ca2+ uptake in the Sertoli cells from seminiferous tubules of immature rat. Previous studies have implicated K(+)ATP channels in these testosterone actions. This study demonstrates that testosterone and sulphonylureas (glibenclamide and tolbutamide) depolarise the membrane potential, augment resistance and 45Ca2+ uptake in the Sertoli cells of seminiferous tubules from 10-15 day-old rats. These actions were nullified by the presence of the K(+)ATP channel opener diazoxide. The depolarisation was also observed with the impermeant bovine serum albumin-bound testosterone. Testosterone actions were blocked by both pertussis toxin and the phospholipase C (PLC) inhibitor U73122 implying the involvement of PLC - phosphatidylinositol 4-5 bisphosphate (PIP2) hydrolysis via G protein in testosterone actions. Polycations, including spermine and LaCl3, depolarised the membrane potential and increased the resistance. Hyperpolarisation caused by EGTA was reversed by LaCl3 and by the presence of testosterone. This last effect was nullified by the presence of U73122. All of the above results indicate that the action of testosterone on the Sertoli cell membrane is exercised on the K(+)ATP channels through PLC-PIP2 hydrolysis that closes the channel, depolarises the membrane, and stimulates 45Ca2+ uptake.

Adenosine Triphosphate↗

PubMed2006

Testosterone therapy for postmenopausal women: efficacy and safety.

The treatment of postmenopausal women with a variety of androgen formulations is increasing, despite the lack of clear guidelines regarding the diagnosis of androgen insufficiency. This review summarizes evidence on the efficacy and safety of adding testosterone to hormone therapy in postmenopausal women. Fair to good evidence exists that the use of testosterone in combination with hormone therapy has both benefits and risks. The benefits are an improvement in sexual function with various regimens of testosterone use (good evidence), an improved sense of well-being with transdermal testosterone (fair evidence), and a reduction in triglyceride levels with methyl testosterone (fair evidence). The most consistent risk is a reduction in high-density lipoprotein (HDL) cholesterol, particularly with methyl testosterone (good evidence). There has been insufficient reporting of other side effects; hence, testosterone therapy should be used with caution. The use of testosterone may be justified in specific clinical circumstances and should be limited to short-term use; long-term studies are not available. Close surveillance for HDL cholesterol and other side effects is necessary.

Androgens↗

PubMed1996

Relationships between testosterone, cortisol and performance in professional cyclists.

In the literature the use of plasma levels of cortisol and the testosterone and testosterone: cortisol ratio for training management is encouraged. Decreased levels of testosterone and increased levels of cortisol are suggested to be indicative for a disturbance in the anabolic-catabolic balance, which may express itself in decreased performance. The purpose of the study was to examine if the acute hormonal response to a bout of exercise and the resting levels of testosterone, luteinizing hormone (LH) and cortisol are correlated to performance in cyclists. In addition, the effect of training on this correlation was studied. Ten professional cyclists participated and measurements took place before and after a defined period of training. Maximum workload (Pmax), determined on a cycle-ergometer with a slowly increasing protocol, increased by 30 watt (p < 0.001). Workload at a lactate level of 4 mmol/l (P4) increased by 18 watt (p < 0.05). Post training, resting testosterone levels decreased from 28.8 +/- 74 nmol/l to 24.6 +/- 90 nmol/l (p < 0.05). Resting cortisol levels increased from 272 +/- 110 nmol/l pre training to 379 +/- 242 nmol/l post training (p < 0.05). These results indicate an increased catabolic state. The acute hormonal response and the resting levels of LH were not changed post training. The resting levels of testosterone and cortisol and the acute response to exercise showed no correlation with performance pre and post training. In spite of an increased catabolic state post training there was an increase in performance. These results suggest that in endurance trained cyclists, decreased testosterone levels, increased cortisol levels and a decreased testosterone: cortisol ratio does not automatically lead to a decrease in performance or a state of overtraining.

Adult↗

PubMed1996

[Serum dihydrotestosterone versus total testosterone values of patients with laryngeal carcinomas and chronic laryngitis].

BACKGROUND: Paradoxically, the highest incidence of laryngeal carcinomas occurs in the presence of reduced gonadal androgen levels associated with ageing, while the stimulating effects of androgens on the laryngeal mucosa and their tumors have been reported in the literature. The decrease of testosterone values and nearly unchanged values of dihydrotestosterone in serum and tissues of elderly men have been documented in recent endocrinological literature. This trial was performed in an effort to resolve this apparent contradiction. METHODS: Twenty-two male laryngeal cancer patients and ten patients with chronic laryngitis were examined, and their dihydrotestosterone and total testosterone values in serum recorded. Blood sampling was performed for each patient between 7 and 10 a.m. before commencement of tumor therapy. An enzyme immunoassay (Serono automat SR 1) was used to determine the values of total testosterone, whereas a 5 alpha dihydrotestosterone (H 3)- radio-immuno-assay was carried out after serum extraction. RESULTS: The total testosterone values of the laryngeal cancer patients were found to be significantly lower than the values in the laryngitis group, but the mean levels of dihydrotestosterone were found to be comparable within both groups. However, the scattering of dihydrotestosterone values was much higher in the group of laryngeal cancer patients than in the laryngitis group. CONCLUSIONS: The average age of the cancer patients examined was 10 years higher than in the laryngitis group. The present results partially correspond to the reports in the endocrinological literature. Together with experimental results regarding the effects of pure substances of testosterone and dihydrotestosterone on permanent laryngeal cancer cell lines, the current results confirm the importance of the imbalance between testosterone and dihydrotestosterone as a cofactor in the development of squamous cell carcinomas of the larynx. Testosterone substitution as well as blocking of 5 alpha-reductase, the enzyme which facilitates formation of dihydrotestosterone from testosterone, are regarded as promising therapeutic opportunities for the future, especially for patients with laryngeal preneoplasias or as recurrence prophylaxis after primary tumor therapy.

Aged↗

PubMed2000

Transdermal testosterone treatment in women with impaired sexual function after oophorectomy.

BACKGROUND: The ovaries provide approximately half the circulating testosterone in premenopausal women. After bilateral oophorectomy, many women report impaired sexual functioning despite estrogen replacement. We evaluated the effects of transdermal testosterone in women who had impaired sexual function after surgically induced menopause. METHODS: Seventy-five women, 31 to 56 years old, who had undergone oophorectomy and hysterectomy received conjugated equine estrogens (at least 0.625 mg per day orally) and, in random order, placebo, 150 microg of testosterone, and 300 microg of testosterone per day transdermally for 12 weeks each. Outcome measures included scores on the Brief Index of Sexual Functioning for Women, the Psychological General Well-Being Index, and a sexual-function diary completed over the telephone. RESULTS: The mean (+/-SD) serum free testosterone concentration increased from 1.2+/-0.8 pg per milliliter (4.2+/-2.8 pmol per liter) during placebo treatment to 3.9+/-2.4 pg per milliliter (13.5+/-8.3 pmol per liter) and 5.9+/-4.8 pg per milliliter (20.5+/-16.6 pmol per liter) during treatment with 150 and 300 microg of testosterone per day, respectively (normal range, 1.3 to 6.8 pg per milliliter [4.5 to 23.6 pmol per liter]). Despite an appreciable placebo response, the higher testosterone dose resulted in further increases in scores for frequency of sexual activity and pleasure-orgasm in the Brief index of Sexual Functioning for Women (P=0.03 for both comparisons with placebo). At the higher dose the percentages of women who had sexual fantasies, masturbated, or engaged in sexual intercourse at least once a week increased two to three times from base line. The positive-well-being, depressed-mood, and composite scores of the Psychological General Well-Being Index also improved at the higher dose (P=0.04, P=0.03, and P=0.04, respectively, for the comparison with placebo), but the scores on the telephone-based diary did not increase significantly. CONCLUSIONS: In women who have undergone oophorectomy and hysterectomy, transdermal testosterone improves sexual function and psychological well-being.

Administration, Cutaneous↗

PubMed2002

Effect of intravenous testosterone on myocardial ischemia in men with coronary artery disease.

BACKGROUND: Studies on the effect of estrogen on atherosclerotic coronary artery disease (CAD) risk in women have produced conflicting results. Similar confusion, but fewer data, exists on the effect of testosterone on CAD risk in men. METHODS: We used 99mTc sestamibi single-photon emission computed tomography (SPECT) myocardial perfusion imaging to examine the acute effect of intravenous testosterone in 32 men (mean age, 69.1 +/- 6.4 years) with provocable myocardial ischemia on standard medical therapy. Patients performed 3 exercise (n = 18) or adenosine (n = 16) stress tests during the infusion of placebo or 2 doses of testosterone designed to increase testosterone 2 or 6 times baseline. RESULTS: Serum testosterone increased 137 +/- 58% and 488 +/- 113%, and estradiol levels increased 27 +/- 46% and 76 +/- 57%, (P <.001 for all) during the 2 testosterone infusions. There were no differences among the placebo or testosterone groups in peak heart rate, systolic blood pressure, maximal rate pressure product, perfusion imaging scores, or the onset of ST-segment depression. CONCLUSIONS: Acute testosterone infusion has neither a beneficial nor a deleterious effect on the onset and magnitude of stress-induced myocardial ischemia in men with stable CAD.

Aged↗

PubMed1978

Effects of testosterone on the testes of sexually quiescent pheasants: evidence for a negative feedback mechanism.

1. The testicular response of sexually quiescent pheasants to testosterone was studied by injection of testosterone alone and in combination with chicken pituitary extract (CPE) for 20 d. 2. Testosterone alone caused a significant decrease in testicular weight, whereas CPE alone caused a significant increase. In combination testosterone and CPE caused no significant change in testicular weight, suggesting a suppression of the stimulatory effect of CPE by testosterone. The depressive effect of testosterone on testicular weight may be explained on the basis of negative feedback mechanism. 3. CPE alone stimulated the production of spermatogonia and primary spermatocytes whereas testosterone, alone or with CPE, did not elicit such a response. The lack of response of the germinal epithelium to testosterone may indicate the ineffectiveness of the hormone in initiating spermatogenesis in pheasants.

Animals↗

PubMed2005

Physiologic testosterone therapy has no effect on serum levels of tumour necrosis factor-alpha in men with chronic heart failure.

Physiological testosterone therapy increases exercise capacity and reduces symptom scores in men with chronic heart failure (CHF). Tumour necrosis factor-alpha (TNF-alpha) exerts a significant pathologic activity in CHF, and physiologic testosterone replacement therapy is associated with reduced serum levels of TNF-alpha in hypogonadal men with concomitant coronary artery disease. It is unknown whether testosterone exerts a similar immunomodulatory action in men with CHF. Testosterone therapy administered in three placebo-controlled studies, for either 6 hours (two 30-mg buccal tablets, n=12) or 3 months (fortnightly 100 mg intra muscular injection, n=20; or daily 5 mg transdermally, n=62). The effects of testosterone were also assessed on lipopolysaccharide (LPS)-induced TNF- production in whole blood obtained from 27 men with CHF. Incubation with testosterone (10 nM, 1 M, and 100 M) resulted in a reduction in LPS-induced TNF- production from 12.6 +/- 1.3 to 11.2 +/- 1.1 (P = 0.053), 10.3 +/- 1.1 (P = 0.0046), and 9.2 +/- 1.1 (P = 0.000066) ng/ml, respectively. However in men with CHF, serum levels of TNF- were similar before and after treatment with testosterone or placebo, irrespective of the length of study or route of administration. The clinically beneficial actions of testosterone in men with CHF are unlikely to be mediated by reducing TNF-alpha.

Administration, Oral↗

PubMed2005

Percutaneous administration of testosterone gel in postmenopausal women--a pharmacological study.

We wished to investigate if a testosterone gel administered percutaneously to postmenopausal women could result in stable serum levels of the hormone and which dose was required to produce levels within the normal premenopausal range. Fifteen postmenopausal women, mean age 55.3 years (range 45-70 years), volunteered to participate in the study and were divided into three groups. They received 10, 20 or 30 mg of testosterone as a 1% testosterone hydroalcoholic gel at 09.00 hours daily for 14 days. The gel was applied in a thin layer on the outside of the thigh each morning, over an area of approximately 15 cm(2). Blood samples were collected hourly between 09.00 and 17.00 hours on days 1 and 14, and also at 08.00 hours on days 3, 5, 11, 12, 13 and finally day 16, i.e. 2 days after termination of treatment. The mean basal serum level of testosterone was 1.1 +/- 0.9 nmol/l and for 5a-dihydrotestosterone 208 +/- 143 pmol/l. There was a clear increase from the 10 mg to the 20 mg treatment (mean testosterone level during treatment 3.2 and 7.2 nmol/l, respectively) while serum testosterone values after 30 mg showed very little further increase (mean 7.5 nmol/l). Values for days 3-5 were quite similar to those for days 13-14. The present study suggests that adequate and acceptable serum levels of testosterone can be achieved with 10 mg testosterone applied transdermally.

Administration, Cutaneous↗

PubMed2003

One step enzyme linked immunosorbent assay for direct estimation of serum testosterone.

One step competitive enzyme linked immunosorbent assay (ELISA) for direct estimation of testosterone in human serum is described. Testosterone-3-O-carboxymethyl-oxime-bovine serum albumin (testosterone-3-O-CMO-BSA), was used as immunogen and testosterone-3-O-carboxymethyl-oxime-adipic-acid dihydrazide-horseradish peroxidase (testosterone-3-O-CMO-ADH-HRP) was used as tracer. To the testosterone antibody coated microtiter wells, standard or serum samples (100 microL), along with testosterone-3-O-CMO-ADH-HRP conjugate (100 microL) were incubated for 1 h at 37 degrees C. Bound enzyme activity was measured by using tetra methyl benzidine/hydrogen peroxide (TMB/H2O2) as a substrate. In this new strategy, charcoal stripped pooled human serum spiked with non-cross reactive C18, C19, C21, and C27 steroids, used for preparing the standards and blocking the sex hormone binding globulin (SHBG)/and other steroid binding globulins (SBG). The sensitivity of the assay was 0.015 ng/mL. The intra-assay and inter-assay coefficients of variation (CVs) were ranged from 7.8 to 11.8 and 4.8 to 10.4, respectively. The serum testosterone values, obtained by this method, were correlated well with those obtained by radioimmunoassay r = .98 (n = 100).

Adipates↗

PubMed2003

Effects of testosterone administration on fat distribution, insulin sensitivity, and atherosclerosis progression.

In spite of the widespread belief that testosterone supplementation increases the risk of atherosclerotic heart disease, evidence to support this premise is lacking. Although supraphysiological doses of testosterone, such as those used by athletes and recreational body builders, decrease plasma high-density lipoprotein (HDL) cholesterol concentrations, replacement doses of testosterone have had only a modest or no effect on plasma HDL in placebo-controlled trials. In epidemiological studies, serum total and free testosterone concentrations have been inversely correlated with intra-abdominal fat mass, risk of coronary artery disease, and type 2 diabetes mellitus. Testosterone administration to middle-aged men is associated with decreased visceral fat and glucose concentrations and increased insulin sensitivity. Testosterone infusion increases coronary blood flow. Similarly, testosterone replacement retards atherogenesis in experimental models of atherosclerosis. However, the long-term risks and benefits of testosterone administration in human immunodeficiency virus-infected men with fat redistribution syndrome have not been studied in randomized clinical trials.

Adipose Tissue↗

PubMed2006

Physiological effects on demography: a long-term experimental study of testosterone's effects on fitness.

Understanding physiological and behavioral mechanisms underlying the diversity of observed life-history strategies is challenging because of difficulties in obtaining long-term measures of fitness and in relating fitness to these mechanisms. We evaluated effects of experimentally elevated testosterone on male fitness in a population of dark-eyed juncos studied over nine breeding seasons using a demographic modeling approach. Elevated levels of testosterone decreased survival rates but increased success of producing extra-pair offspring. Higher overall fitness for testosterone-treated males was unexpected and led us to consider indirect effects of testosterone on offspring and females. Nest success was similar for testosterone-treated and control males, but testosterone-treated males produced smaller offspring, and smaller offspring had lower postfledging survival. Older, more experienced females preferred to mate with older males and realized higher reproductive success when they did so. Treatment of young males increased their ability to attract older females yet resulted in poor reproductive performance. The higher fitness of testosterone-treated males in the absence of a comparable natural phenotype suggests that the natural phenotype may be constrained. If this phenotype were to arise, the negative social effects on offspring and mates suggest that these effects might prevent high-testosterone phenotypes from spreading in the population.

Age Factors↗

PubMed1984

Serum testosterone measurements.

Serum testosterone and especially free testosterone is one of the parameters commonly used to evaluate androgen excess or deficiency. The authors equilibrated serum samples with 14C-labeled testosterone followed by an ammonium sulfate precipitation to compare the "apparent free testosterone concentration" with "total" serum testosterone concentration in the following populations: normal males and females; females presenting with gynecologic problems, particularly hirsutism and/or virilization; and males and females on maintenance hemodialysis. Total serum testosterone for each specimen was assayed with five different commercially available RIA kits encompassing a variety of technics: direct assay technics, assays utilizing extraction procedures prior to RIA; tritium-labeled tracer as well as iodine-labeled tracers. Clinical correlations improve strikingly when apparent free testosterone concentrations rather than total serum testosterone concentrations are used.

Female↗