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PubMed2006

Calculated free testosterone in men: comparison of four equations and with free androgen index.

BACKGROUND: Serum testosterone remains the most important investigation in the diagnosis of androgen deficiency in men. Most of the circulating testosterone is bound to albumin and sex hormone-binding globulin (SHBG), whereas free testosterone accounts for approximately 2% of total testosterone. Because direct measurement of free testosterone is impractical in routine practice, several equations are used to provide clinically useful estimates of free testosterone concentration. This study aimed to (1) obtain locally derived reference limits for total testosterone and calculated free testosterone (CFT) concentrations, and (2) critically evaluate the equations commonly used to estimate free testosterone. METHODS: Serum total testosterone, SHBG and albumin were assayed in morning blood samples obtained from 126 healthy men (aged 20-45 years) known to have normal semen analysis. CFT concentrations calculated using four published methods (i.e. the Sodergard, Nanjee-Wheeler, Vermeulen and Ly-Handelsman equations) were compared with one another and the free androgen index. RESULTS: Reference intervals for total testosterone and CFT by the Vermeulen equation were 9.4-31.0 nmol/L and 0.245-0.785 nmol/L (2.5-97.5 percentile), respectively. CFT values varied considerably with the four equations examined. Mean biases ranged from 5.8 to 56.0%; the Nanjee-Wheeler and Ly-Handelsman equations yielded positive and negative biases, respectively, against the other equations. Free androgen index was shown to correlate poorly with CFT (r2=0.21-0.46) and over-estimate the CFT at low SHBG concentrations. CONCLUSIONS: We have used various equations to derive reference ranges for CFT in healthy men aged 20-45 years. We suggest that CFT be incorporated into the investigation regimen for suspected hypogonadism when total testosterone results are equivocal.

Adult↗

PubMed2003

The associations of age, lifestyle factors and chronic disease with testosterone in men: the Tromsø Study.

OBJECTIVE: To study whether lifestyle factors and/or chronic disease are associated with the age-related decline of total and free testosterone in men, or if these factors might be associated with the variation of total and free testosterone but not with their age-related decline. DESIGN: A population-based, cross-sectional study was used. METHODS: Total testosterone and sex hormone binding globulin (SHBG) levels were analyzed and free testosterone levels were calculated in 1563 men participating in the Tromsø study in 1994/1995. Anthropometric characteristics were also measured and two standardized questionnaires completed, including lifestyle factors and medical history. The data were analyzed with multiple linear regression analysis of covariance, and logistic regression. RESULTS: Total and free testosterone were inversely associated (P=0.001 and P<0.001), while SHBG was positively associated (P<0.001) with age. Body mass index (BMI) was inversely associated with total (P<0.001) and free (P=0.016) testosterone and SHBG (P<0.001). Both total and free testosterone were positively associated with tobacco consumption (P<0.001 and P=0.004) and total testosterone was positively associated with coffee consumption (P<0.001). SHBG was positively associated with smoking (P=0.004) and coffee consumption (P<0.001). Men who reported having had a stroke or having a cancer diagnosis had lower levels of total testosterone (P<0.001 and P<0.01) and free testosterone (P<0.01). CONCLUSIONS: BMI and smoking are independent contributors to the variation of total and free testosterone and SHBG levels, and coffee consumption to the variation of total testosterone and SHBG. Thus, lifestyle factors can have a direct effect on circulating levels of free endogenous sex hormones and to total levels due to the effect on SHBG levels.

Adult↗

PubMed2003

Pharmacokinetic study in women of three different doses of a new formulation of oral testosterone undecanoate, Andriol Testocaps.

STUDY OBJECTIVE: To assess the pharmacokinetic parameters of testosterone undecanoate after administration of a new oral formulation, Andriol Testocaps. DESIGN: Randomized, open-label, group-comparative, parallel-design, dose-proportionality study. SETTING: Clinical pharmacology unit. SUBJECTS: Forty-five healthy women without childbearing potential. INTERVENTION: Two oral doses each of testosterone undecanoate 20, 40, or 80 mg were administered with meals, separated by a 12-hour dosing interval. MEASUREMENTS AND MAIN RESULTS: Serum concentrations of testosterone undecanoate were assayed by liquid chromatography with mass spectrometric detection, and of testosterone and 5alpha-dihydrotestosterone (DHT) by gas chromatography with mass spectrometric detection. Pharmacokinetic parameters were calculated using standard methods. Statistical analysis of dose proportionality was performed on the log(e)-transforms of dose-normalized area under the serum concentration-time curve from 0-12 hours (AUC(0-12)) and from zero to the sampling time of the last measurable concentration after administration of the second dose (AUC(0-t(last)), and maximum serum concentration after the first dose (C(max)l). For testosterone undecanoate, testosterone, and DHT, dose-related increases in plasma concentrations were found with increasing doses of testosterone undecanoate; maximum concentrations were found 5-7 hours after administration. Using baseline-corrected testosterone values, dose proportionality for testosterone was found for AUC(0-12), AUC(0-t)(last), and C(max)(l). After higher doses, plasma levels of testosterone undecanoate were higher and plasma levels of DHT lower than could be expected assuming dose proportionality. CONCLUSION: Serum testosterone levels are dose proportional after oral administration of two doses of a new formulation of testosterone undecanoate 20, 40, and 80 mg, Andriol Testocaps.

Administration, Oral↗

PubMed1988

Re-evaluation of the intratesticular level of testosterone required for quantitative maintenance of spermatogenesis in the rat.

The amount of testosterone required for quantitative maintenance of spermatogenesis has been re-evaluated using techniques aimed at minimizing the synthesis of testosterone after removal of the testis. Adult male rats were treated with ethane dimethane-sulphonate (EDS) to destroy the Leydig cells, and were supplemented with 25, 5 or 1 mg testosterone esters by injection every 3 days for 21 days. Serum hormone levels, testicular morphology and spermatogenesis were assessed and the intratesticular levels of testosterone compared in testes either removed under ether anaesthesia and placed in liquid nitrogen (right testis) or removed after collection of blood and placed in ice (left testis). Data for testosterone-supplemented rats were compared with those for control rats and rats treated with EDS alone. All doses of testosterone suppressed LH and FSH levels in serum to within the hypophysectomized range, and Leydig cell regeneration in EDS-treated rats was prevented completely. Treatment of EDS-injected rats with 25 or 5 mg testosterone maintained testicular weight, the number of germ cells and the diameter of seminiferous tubules at stage VII within or above the control range, although there was a significant increase in the number of degenerating pachytene spermatocytes at stage VII with 5 but not 25 mg testosterone; none of these parameters was maintained at control levels by a dose of 1 mg testosterone. Levels of testosterone in testosterone-supplemented rats differed little between testes collected in ice and liquid nitrogen, but in controls and rats treated with EDS alone, testosterone levels were overestimated by 75 and 27% respectively when comparing testes collected in ice with those collected in liquid nitrogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1999

Risks versus benefits of testosterone therapy in elderly men.

'Andropause', like menopause, has received significant attention in recent years. It results in a variety of symptoms experienced by the elderly. Many of these symptoms are nonspecific and vague. For this reason, many authors have questioned the value of androgen replacement in this population. Also in dispute is the normal cutoff level for testosterone beyond which therapy should be initiated, and whether to measure free or total testosterone. Testosterone levels decline with age, with the lowest level seen in men older than 70 years. This age-related decline in testosterone levels is both central (pituitary) and peripheral (testes) in origin. With aging, there is also a loss of circadian rhythm of testosterone secretion and a rise in sex hormone binding globulin (SHBG) levels. Total testosterone level is the best screening test for patients with suspected hypogonadism. If the total testosterone concentration is low, free testosterone levels should be obtained. Prostate cancer remains an absolute contraindication to androgen therapy. Testosterone replacement results in an improvement in muscle strength and bone mineral density. Similar effects are observed on the haematopoietic system. Data on cognition and lipoprotein profiles are conflicting. Androgen therapy can result in polycythemia and sleep apnoea. These adverse effects can be deleterious in men with compromised cardiac reserve. We recommend that elderly men with symptoms of hypogonadism and a total testosterone level <300 ng/dl should be started on testosterone replacement. This review discusses the pros and cons of testosterone replacement in hypogonadal elderly men and attempts to answer some of the unanswered questions. Furthermore, emphasis is made on the regular follow-up of these patients to prevent the development of therapy-related complications.

Aged↗

PubMed2003

Testosterone causes simultaneous decrease of [Ca2+]I and tension in rabbit coronary arteries: by opening voltage dependent potassium channels.

The relationship between the level of testosterone and the incidence of coronary heart disease is still controversial in the view of the results of clinical and epidemiologic studies. This uncertainty might be partly due to relatively small number of experimental studies undertaken to investigate the cellular mechanism underlying the vascular responses to testosterone. To further investigate the cellular mechanisms of testosterone with respect to vascular response, we investigated the effect of testosterone on contractility and intracellular Ca2+ regulation in a rabbit coronary artery and evaluated the underlying mechanism of testosterone-induced changes of coronary vascular tone by using various pharmacological blockers. Testosterone was found to relax rabbit coronary arteries in a dose-dependent manner, and no significant difference was found in the relaxation response to testosterone with or without endothelium. Similar results were obtained in male and non-pregnant female rabbit coronary arteries. The relaxation response of rabbit coronary arteries to testosterone was greater for PGF2alpha-contracted rings than for KCl contracted rings, which suggest the involvement of K+ channels. Furthermore, the relaxation response to testosterone was significantly reduced by 4-aminopyridine, a sensitive blocker of voltage dependent K+ channels, but not by low doses of tetraethylammonium or iberiotoxin, a Ca2+ activated K+ channel blocker. Testosterone simultaneously reduced the intracellular Ca2+ concentration ([Ca2+]i) and tension, and 4-AP effectively antagonized the testosterone-induced change of [Ca2+]i and tension. Therefore, it may be concluded that the stimulation of voltage dependent K channels is responsible, at least in part, for the testosterone-induced relaxation of rabbit coronary arteries.

Androgens↗

PubMedDate not supplied

Testosterone treatment in hypogonadal men: prostate-specific antigen level and risk of prostate cancer.

OBJECTIVE: To assess prostate-specific antigen (PSA) levels in hypogonadal men after testosterone replacement by three different methods and attempt to determine any possible relationship between hypogonadism and prostate cancer in this study population. METHODS: A total of 90 consecutive men who had erectile dysfunction and were found to have hypogonadism were monitored with digital rectal examination (DRE) and measurement of PSA levels before and after testosterone replacement therapy. The patients were treated with one of three options: (1) testosterone enanthate by intramuscular injections, 200 or 300 mg every 2 or 3 weeks (N = 25); (2) testosterone nonscrotal patches, 5 mg daily (N = 16); or (3) clomiphene citrate, 50 mg orally three times a week, in patients with functional secondary hypogonadism (N = 49). Treatment was continued for 2 to 3 months, after which PSA levels were reassessed. Patients with suspicious results on DRE and increased PSA levels before or after treatment with testosterone underwent prostate biopsy. For statistical analysis, patients were categorized into two age-groups--40 to 60 years old and 61 to 80 years old. RESULTS: With all methods of testosterone replacement, PSA levels increased in both age-groups. Endogenous testosterone elevation from clomiphene stimulation raised PSA levels the highest, and testosterone patches yielded the least PSA response. Ten men underwent biopsy of the prostate. In one patient, a nodule was found on DRE; the other nine men underwent biopsy because of suspicious PSA levels. Of these patients, two were found to have adenocarcinoma, and a third man who underwent rebiopsy was also found to have cancer. Therefore, 3 of the 90 patients (3.3%) had prostate cancer. CONCLUSIONS: PSA levels increased in response to all types of testosterone replacement, regardless of whether the testosterone level was raised endogenously or exogenously. PSA levels are inappropriately low in hypogonadal men and may mask an underlying cancer. Determining PSA levels before and after testosterone treatment is recommended. Elevated PSA levels before or after testosterone therapy should prompt performance of a urologic evaluation for possible prostate biopsy.

Administration, Cutaneous↗

PubMedDate not supplied

Compounded percutaneous testosterone gel: use and effects in hypogonadal men.

BACKGROUND: Current methods of testosterone replacement therapy are limited to fixed-dosage patches and depot injections. Neither of these methods provides ideal therapy because of the inflexibility of dosing and other nuisance problems associated with the patches and nonphysiologic hormone levels when depot injections are used. Testosterone gels offer the potential for convenience and ease of administration, as well as flexible dosing regimens, by means of a simple topical application. METHODS: Ten hypogonadal men were selected from the author's general practice, ranging in age from 44 to 77 years. Four of these men had newly diagnosed and 6 had preexisting hypogonadism. Patients were withdrawn from their previous hormone therapy (where applicable), and baseline laboratory studies were obtained for total testosterone, free testosterone, dihydrotestosterone, estradiol, luteinizing hormone, follicle-stimulating hormone, complete blood counts, lipid panels, and chemistry panels. The patients then started taking increasing dosages of the testosterone gel until physiologic levels of testosterone were realized or until the study period (6 weeks) was concluded. There was no blinding, and each patient served as his own control. Testosterone and free testosterone levels were monitored weekly, and estradiol and dihydrotestosterone less frequently. At the conclusion of the study, all the baseline laboratory tests were repeated. A questionnaire evaluating the psychosexual well-being of the patients was administered before and after the treatment period. RESULTS: The average total testosterone level rose from 136 ng/dL to 442.9 ng/dL (P < .001). Average free testosterone levels rose from 34.2 pg/mL to 120.3 pg/mL (P < .001). Average dihydrotestosterone levels rose from 20.5 to 199.2 ng/dL (P = .006). Average estradiol levels rose only slightly from 34.1 pg/mL to 40.0 pg/mL P = .191). Average total androgens (testosterone plus dihydrotestosterone) rose in all patients to therapeutic levels, from 149.3 ng/dL to 642.1 ng/dL (P = .001). The ratio of total androgen to estradiol rose from 5.1 to 17.1 (P < .002). Luteinizing hormone was suppressed in the 6 patients for whom meaningful data were available, and decreased on average from 5.66 to 1.10 mIU/mL (P = .005) Lipid effects were measured, and a 15% drop in all cholesterol fractions was noted (P < .005). Evaluation of the questionnaire showed considerable improvements in sexual function and overall well-being in all but 1 patient. No adverse effects or nuisance-problems were detected during the duration of the study. CONCLUSION: Topically applied testosterone gels are an effective and convenient means of hormone replacement in hypogonadal men.

Administration, Cutaneous↗

PubMed2002

Oral testosterone replacement in Korean patients with PADAM.

INTRODUCTION: After middle age, some men show androgen-deficiency symptoms leading to so-called PADAM (partial androgen deficiency in aging males). We tested the oral form of testosterone, testosterone undecanoate (Andriol, NV Organon, The Netherlands), in men with PADAM and evaluated its efficacy and safety in Korean male patients. METHODS: We included those patients with the clinical symptoms of PADAM who had decreased levels of serum total testosterone (< 2.8 ng/ml) or free testosterone (< 13 pg/ml). We excluded patients with biopsy-confirmed prostrate cancer, abnormal findings in digital rectal examination or prostate specific antigen testing (until prostrate cancer was ruled out), breast cancer, severe voiding symptoms and secondary hypogonadism. At the first visit, the International Prostate Symptom Score (IPSS), International Index of Erectile Function (IIEF) and Korean Andropause Questionnaires were administered; complete blood count, the lipid profile, and levels of total and free testosterone, prolactin, luteinizing hormone, follicle stimulating hormone and prostate specific antigen were measured and a digital rectal examination was given. Patients were administered oral testosterone undecanoate 160 mg daily for 3 weeks. The dosage was then decreased to 80 mg daily and changes in symptoms were assessed at every visit. After 3 months, serum tests, including testosterone, were repeated. RESULTS: We evaluated 28 patients who had received testosterone undecanoate for more than 3 months. The patients' mean age was 56.1 (48-68) years. The score of the Korean Andropause Questionnaire changed from 56.2 +/- 21.7 at baseline to 52.9 +/- 21.3 (p = 0.03) after 3 weeks, to 49.3 +/- 19.3 (p = 0.03) after 8 weeks, and to 46.5 +/- 25.6 (p = 0.028) after 12 weeks. With respect to sexual function, mean IIEF scores were 37.2 +/- 19.6 at baseline and 38.7 +/- 19.2 and 40.2 +/- 22.0 (p = 0.033) after 3 and 12 weeks, respectively. Serum total testosterone increased from 2.13 +/- 1.20 ng/ml at baseline to 6.04 +/- 3.08 ng/ml (p = 0.005) after 12 weeks, and free testosterone was marginally significantly changed from 8.60 +/- 2.25 pg/ml to 11.40 +/- 3.81 pg/ml (p = 0.13). However, there were no significant changes in liver function tests, red blood cell count or lipid profiles. There were no significant adverse reactions that led to the cessation of the administration of oral testosterone. CONCLUSION: Oral administration of testosterone undecanoate can improve symptoms of PADAM in Koreans. It may, therefore, be an appropriate treatment option with few adverse effects for PADAM patients.

Administration, Oral↗

PubMed2003

A pilot study on the effects of testosterone in hypogonadal aging male patients with Alzheimer's disease.

The male aging process brings about declines in hormonal function including a gradual decline in bioavailable testosterone levels. Animal studies suggest that testosterone modulates cognitive function through enhancing acetylcholine release and up-modulation of nicotinic receptors. Tau protein deposition is also affected by androgen supplementation in animals. We hypothesize that testosterone replacement in elderly hypogonadal males may improve cognition, in particular the visual-spatial domain. Thirty-six male patients with a new diagnosis of Alzheimer's disease had their total and bioavailable testosterone levels measured. None of the patients had been on acetylcholinesterase inhibitors. Ten of the 36 patients (28%) were deemed biochemically hypogonadal (total testosterone < 240 ng/dl or 7 nmol/l). Five of the hypogonadal patients were randomized to testosterone and five to placebo. Initial Alzheimer's Disease Assessment Scale cognitive subscale (ADAScog) and Mini Mental Status Examination (MMSE) ranged from 31 to 19 and from 17 to 22, respectively. The clock drawing test (CDT) and the pentagon-tracing portion of the MMSE were used as measures of visual-spatial abilities. Normal prostate-specific antigen (PSA) levels were essential before treatment with intramuscular testosterone, 200 mg every 2 weeks. Measurement of testosterone, complete blood count, lipids, PSA and neuropsychological cognitive tests were repeated at 3, 6, 9 and 12 months of treatment. In the testosterone-treated group, levels of total testosterone increased from a mean of 126.4 ng/dl to 341 ng/dl or 3.6 nmol/l to 9.7 nmol/l (p = 0.11). Bioavailable testosterone also increased from a mean of 48.7 ng/dl to 142 ng/dl or 1.39 nmol/l to 4.05 nmol/l (p = 0.10). PSA levels were also elevated from a mean of 0.98 to 1.37 ng/ml (p = 0.07). ADAScog improved from a mean of 25 to 16.3 (p = 0.02); MMSE improved from a mean of 19.4 to 23.2 (p = 0.02), CDT also improved from 2.2 to 3.2 (p = 0.07). One patient stopped treatment because of hypersexual behavior. The placebo-treated group deteriorated gradually. This small pilot study performed in aging male patients suggests that testosterone could indeed improve cognition, including visual-spatial skills in mild to moderate Alzheimer's disease.

Aged↗

PubMed1992

Effect of testosterone on the growth properties and on epidermal growth factor receptor expression in the teratoma-derived tumorigenic cell line 1246-3A.

1246-3A is an insulin-independent tumorigenic cell line isolated from the C3H mouse teratoma-derived adipogenic cell line 1246. In the present paper, we have demonstrated that testosterone inhibits the in vivo tumorigenic properties of the 1246-3A cells. Castrated male mice receiving injections of 1246-3A cells developed larger tumors at a higher frequency than sham-operated animals. Administration of testosterone to castrated male mice resulted in a dramatic decrease in tumor development. In vitro studies indicated that testosterone inhibited by 50% the proliferation of the 1246-3A cells in culture. However, growth inhibition was observed only if the cells had been cultivated in the presence of testosterone for at least 4 days. In contrast, testosterone had little effect on the proliferation of the parent cell line 1246. Binding of several polypeptide growth factors was examined in cells cultivated in the absence and in the presence of testosterone. Testosterone increased 125I-EGF specific binding to 1246-3A cells. Scatchard analysis of EGF binding indicated that testosterone treatment induced a 2.4-fold increase in the number of cell surface EGF binding sites. This was accompanied by an increase in the intensity of cross-linked EGF receptors on the cells treated with testosterone. In addition, 1246-3A cells cultivated for 9 days in the presence of testosterone displayed a 10-fold increase in the level of EGF receptor mRNA when compared to 1246-3A cells maintained in its absence. Similar to its action on cell proliferation, the increase in EGF receptor number and mRNA expression was observed mainly if 1246-3A cells had been exposed to testosterone for 9 days. The data presented in this paper demonstrate that both in vivo and in vitro, testosterone induces in the teratoma-derived 1246-3A cell line phenotypic changes such as growth inhibition and modulation of EGF receptor expression.

Animals↗

PubMedDate not supplied

Testosterone decreases 3beta-hydroxysteroid dehydrogenase-isomerase messenger ribonucleic acid in cultured mouse Leydig cells by a strain-specific mechanism.

We previously reported a strain-related difference in basal 3beta-hydroxysteroid dehydrogenase-isomerase (3betaHSD) activity in response to testosterone in cultured Leydig cells. The data suggested that the response to testosterone was androgen receptor mediated and that testosterone was acting via a trans-acting factor distal to the androgen receptor to regulate Leydig cell basal 3betaHSD activity. This study was designed to determine whether the previous reported strain-related difference in basal 3betaHSD activity in response to testosterone was due to a difference at the 3betaHSD protein and/or at the mRNA level. In C57BL/6J Leydig cells, 2.0 microM testosterone significantly decreased basal 3betaHSD immunoreactive mass by day 6 in culture. Treatment with 2.0 microM testosterone and 2.0 microM hydroxyflutamide, an androgen receptor antagonist, negated the inhibitory effect of testosterone on C57BL/6J 3betaHSD immunoreactive mass. Treatment with 2.0 microM testosterone also significantly decreased 3betaHSD mRNA content in C57BL/6J Leydig cells, which was detectable on day 3 in culture. In contrast to Leydig cells from C57BL/6J mice, Leydig cells from C3H/HeJ mice were not susceptible to the inhibitory effect of testosterone on 3betaHSD. Treatment with 2.0 microM testosterone had no detectable effect on C3H/HeJ 3betaHSD immunoreactive mass or mRNA content at any time point in culture. These data indicate that the testosterone-induced loss of basal 3betaHSD activity in C57BL/6J Leydig cells can be accounted for by the loss of 3betaHSD immunoreactive mass, which is preceded by the loss of 3betaHSD mRNA, and that the strain-related difference in the regulation of 3betaHSD is present at all three levels. Thus, the putative trans-acting factor involved in the mechanism whereby testosterone decreases basal 3betaHSD is likely to regulate the amount of 3betaHSD mRNA.

Animals↗

PubMed1998

Development of a non-high pressure liquid chromatography assay to determine testosterone hydroxylase (CYP3A) activity in human liver microsomes.

The major pathway of testosterone oxidation by human liver microsomes is the formation of 6beta-hydroxytestosterone, which is catalyzed by CYP3A4/5 and which accounts for 75-80% of all metabolites formed. In the present study, we describe a non-high pressure liquid chromatography assay (HPLC) of CYP3A4/5 activity based on the release of tritium (with formation of tritiated water) upon incubation of [1,2,6,7-3H]testosterone with human liver microsomes and NADPH. Unreacted testosterone and its metabolites were quantitatively extracted from the incubation mixture with activated charcoal under conditions that resulted in no extraction of tritiated water. The amount of tritiated water formed was quantified by liquid scintillation spectrometry and compared with the amount of hydroxylated testosterone metabolites formed, as determined by HPLC. Rates of tritium release from [1,2,6, 7-3H]testosterone paralleled rates of testosterone 6beta-hydroxylation as a function of incubation time, the amount of microsomal protein, and the concentration of substrate (which yielded identical apparent Km and Vmax values). The sample-to-sample variation in tritium release from [1,2,6,7-3H]testosterone with a panel of human liver microsomes was highly correlated with rates of testosterone 6beta-hydroxylation and terfenadine metabolism, two commonly used markers of CYP3A activity. Several recombinant human P450 enzymes were incubated with [1,2,6,7-3H]testosterone, and only cDNA-expressed CYP3A4 catalyzed a high rate of tritium release. The close agreement between the tritium-release assay and HPLC procedure for measuring testosterone oxidation indicates that tritium release from [1,2,6,7-3H]testosterone provides a simple and rapid alternative to the HPLC procedure for measuring CYP3A4/5 activity in human liver microsomes. However, the tritium-release assay may have limited value in measuring CYP3A activity in liver microsomes from other species due to the presence of other P450 enzymes that can catalyze tritium release from [1,2,6,7-3H]testosterone.

Aryl Hydrocarbon Hydroxylases↗

PubMed2005

Sexual dimorphism of growth plate prehypertrophic and hypertrophic chondrocytes in response to testosterone requires metabolism to dihydrotestosterone (DHT) by steroid 5-alpha reductase type 1.

Rat costochondral growth plate chondrocytes exhibit sex-specific and cell maturation dependent responses to testosterone. Only male cells respond to testosterone, although testosterone receptors are present in both male and female cells, suggesting other mechanisms are involved. We examined the hypothesis that the sex-specific response of rat costochondral cartilage cells to testosterone requires further metabolism of the hormone to dihydrotestosterone (DHT). Resting zone (RC) and growth zone (GC, prehypertrophic and upper hypertrophic zones) chondrocytes from male and female Sabra strain rats exhibited sex-specific responses to testosterone and DHT: only male cells were responsive. Testosterone and DHT treatment for 24 h caused a comparable dose-dependent increase in [3H]-thymidine incorporation in quiescent preconfluent cultures of male GC cells, and a comparable increase in alkaline phosphatase specific activity in confluent cultures. RC cells responded in a differential manner to testosterone and DHT. Testosterone decreased DNA synthesis in male RC cells but DHT had no effect and alkaline phosphatase specific activity of male RC cells was unaffected by either hormone. Inhibition of steroid 5alpha-reductase activity with finasteride (1, 5, or 10 microg/ml), reduced the response of male GC cells to testosterone in a dose-dependent manner, indicating that metabolism to DHT was required. RT-PCR showed that both male and female cells expressed mRNAs for steroid 5alpha-reductase type 1 but lacked mRNAs for the type 2 form of the enzyme. Male cells also exhibited 5alpha-reductase activity but activity of this enzyme was undetectable in female cells. These observations show that sex-specific responses of rat growth zone chondrocytes to testosterone requires the further metabolism of the hormone to DHT and that the effect of DHT in the male growth plate is maturation-state dependent. Failure of female chondrocytes to respond to testosterone may reflect differences in testosterone metabolism, since these cells possess greater ability to aromatize the hormone to estradiol.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed2002

Addition of testosterone to estrogen replacement therapy in oophorectomized women: effects on sexuality and well-being.

OBJECTIVE: To evaluate the effect of adding testosterone undecanoate 40 mg daily to estrogen replacement on sexual function, psychological well-being and self-esteem in surgically postmenopausal women. METHODS: A letter of invitation to participate in the study was mailed to women who had undergone hysterectomy and bilateral oophorectomy for benign disorders during 1990-98. Fifty women, 45-60 years old, were consecutively recruited and randomly assigned to oral treatment with testosterone undecanoate 40 mg plus estradiol valerate 2 mg daily or placebo plus estradiol valerate 2 mg daily for 24 weeks. A double-blind design was chosen, with cross-over to the other regimen for another 24 weeks of treatment. Forty-four women completed the study. Outcome included scores on McCoy's sex scale questionnaire, the Psychological General Well-Being index and a self-esteem questionnaire, at baseline and after 24 weeks of either treatment. Serum concentrations of total testosterone, sex hormone binding globulin, free testosterone, dihydrotestosterone, androstenedione, estradiol, follicle stimulating hormone and luteinizing hormone were analyzed at baseline and after 24 weeks of both treatment regimens. RESULTS: After 24 weeks, both treatment regimens had significantly improved some of the sexual variables. The addition of testosterone had a significantly better effect on the sex variables 'enjoyment of sex', 'satisfaction with frequency of sexual activity' and 'interest in sex'. The total McCoy score was significantly increased by both treatments, but there was a stronger effect when testosterone was also given. Although both regimens improved psychological well-being and self-esteem, we found no significant differences between testosterone-estrogen or estrogen alone at 24 weeks. Serum levels of all androgens, with considerable individual variation, increased significantly from baseline after 24 weeks of testosterone-estrogen treatment. Supraphysiological levels were achieved in a significant proportion of the women. Increases in estradiol and sex hormone binding globulin were less marked when testosterone was also given. Both treatments reduced gonadotropin levels. CONCLUSIONS: The addition of testosterone undecanoate improved specific aspects of sexual function more than treatment with estrogen alone. Improvements in well-being and self-esteem were similar for both treatments. If testosterone undecanoate 40 mg daily should be used for clinical treatment, regular monitoring of androgen serum levels is needed.

Cross-Over Studies↗

PubMed1996

Environment modifies the testosterone levels of a female bird and its eggs.

Past studies have shown that the yolk of the canary (Serinus canaria) egg contains maternal testosterone, that its concentrations increase in the subsequently formed eggs of a clutch, and that testosterone influences development. The present study investigated 1) if the testosterone levels vary in the female during yolk formation; 2) how such putative variations may be related to the concentrations of maternal testosterone in the yolk; and 3) if environmental factors, such as day length, can modify the testosterone levels in the mother and her eggs. Maternal testosterone levels, measured in the females' feces, increased during yolk formation and egg laying, and decreased during incubation. This pattern was modified by day length. In a photoperiod of 12 h of light and 12 h of darkness (12L 12D), female testosterone levels decreased after the last egg of the clutch was laid while in a photoperiod of 16L 8D, they decreased after the first egg was laid. These different patterns were reflected in the testosterone concentrations in the egg yolk. Further, the eggs of subsequent clutches that were produced under a naturally changing photoperiod differed significantly in their testosterone concentrations. Finally, the doses of testosterone in the yolk of individual eggs were positively correlated with the concentrations of testosterone in the female during the yolk phase of each egg. I conclude that here we have a mechanism which communicates environmental conditions from the mother to the offspring, and that this mechanism serves to optimize reproduction and/or modify offspring traits.

Animals↗

PubMed2000

Interaction of BDNF and testosterone in the regulation of adult perineal motoneurons.

In androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB), we investigated the interaction of BDNF (brain-derived neurotrophic factor) and testosterone to understand whether each factor gates the ability of the other to regulate androgen receptor expression and soma size, and whether each factor requires the presence of the other for its action. We axotomized SNB motoneurons and applied BDNF or PBS (phosphate-buffered saline) to the cut ends of the axons in rats that were castrated and treated with either testosterone or placebo. Control groups were either not castrated or not axotomized, or had intact SNB axons and were castrated and treated with testosterone or placebo. We found that testosterone determined the expression of nuclear androgen receptor, and this effect was enhanced by both BDNF and contact with the target muscles. The effect of BDNF on androgen receptor expression was seen only when testosterone was present. In the regulation of soma size, BDNF dominated. The application of BDNF completely compensated for the loss of testosterone in castrated males so that the testosterone effect on soma size was seen only in intact SNB motoneurons and in axotomized motoneurons treated with PBS. Moreover, testosterone increased androgen receptor and soma size in axotomized SNB motoneurons, indicating that testosterone can act on sites other than the target muscles of the SNB to regulate each of these. These results indicate that the regulation of androgen receptor by testosterone does not require BDNF, but the regulation of androgen receptor by BDNF does require testosterone. The regulation of soma size by BDNF does not require high expression of nuclear androgen receptor.

Animals↗

PubMed1987

Regulation of testosterone hydroxylation by rat liver microsomal cytochrome P-450.

The pathways of testosterone oxidation catalyzed by purified and membrane-bound forms of rat liver microsomal cytochrome P-450 were examined with an HPLC system capable of resolving 14 potential hydroxylated metabolites of testosterone and androstenedione. Seven pathways of testosterone oxidation, namely the 2 alpha-, 2 beta-, 6 beta-, 15 beta-, 16 alpha-, and 18-hydroxylation of testosterone and 17-oxidation to androstenedione, were sexually differentiated in mature rats (male/female = 7-200 fold) but not in immature rats. Developmental changes in two cytochrome P-450 isozymes largely accounted for this sexual differentiation. The selective expression of cytochrome P-450h in mature male rats largely accounted for the male-specific, postpubertal increase in the rate of testosterone 2 alpha-, 16 alpha, and 17-oxidation, whereas the selective repression of cytochrome P-450p in female rats accounted for the female-specific, postpubertal decline in testosterone 2 beta-, 6 beta-, 15 beta-, and 18-hydroxylase activity. A variety of cytochrome P-450p inducers, when administered to mature female rats, markedly increased (up to 130-fold) the rate of testosterone 2 beta-, 6 beta-, 15 beta-, and 18-hydroxylation. These four pathways of testosterone hydroxylation were catalyzed by partially purified cytochrome P-450p, and were selectively stimulated when liver microsomes from troleandomycin- or erythromycin estolate-induced rats were treated with potassium ferricyanide, which dissociates the complex between cytochrome P-450p and these macrolide antibiotics. Just as the testosterone 2 beta-, 6 beta-, 15 beta-, and 18-hydroxylase activity reflected the levels of cytochrome P-450p in rat liver microsomes, so testosterone 7 alpha-hydroxylase activity reflected the levels of cytochrome P-450a; 16 beta-hydroxylase activity the levels of cytochrome P-450b; and 2 alpha-hydroxylase activity the levels of cytochrome P-450h. It is concluded that the regio- and stereoselective hydroxylation of testosterone provides a functional basis to study simultaneously the regulation of several distinct isozymes of rat liver microsomal cytochrome P-450.

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