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At least 217 records · Page 12Linked to original sources

PubMed1993

Simultaneous determination of free testosterone and testosterone bound to non-sex-hormone-binding globulin by equilibrium dialysis.

We describe a procedure based on equilibrium dialysis that allows the simultaneous determination of free testosterone and testosterone bound to non-sex-hormone-binding globulin (non-SHBG) in plasma. After saturating SHBG with 5 alpha-dihydrotestosterone (DHT) according to a technique recently described, the percentage of free testosterone in the treated and the untreated samples is measured by equilibrium dialysis with use of a semiautomated instrument that allows rigorous standardization of the experimental conditions. The present method is simpler and faster than the previously described technique in which, after the saturation of SHBG with DHT, the unbound fractions were measured by centrifugal ultrafiltration dialysis. The method is also reproducible and suited for the analysis of a large number of samples. The technique has been applied to the determination of the fractional distribution of testosterone in plasma pools from normally menstruating, pregnant, and postmenopausal women and from normal men.

Blood Proteins↗

PubMed1988

Expression of a rat liver microsomal cytochrome P-450 catalyzing testosterone 16 alpha-hydroxylation in Saccharomyces cerevisiae: vitamin D3 25-hydroxylase and testosterone 16 alpha-hydroxylase are distinct forms of cytochrome P-450.

Rat cytochrome P-450(M-1) cDNA was expressed in Saccharomyces cerevisiae TD1 cells by using a yeast-Escherichia coli shuttle vector consisting of P-450(M-1) cDNA, yeast alcohol dehydrogenase promoter and yeast cytochrome c terminator. The yeast cells synthesized up to 2 X 10(5) molecules of P-450(M-1) per cell. The microsomal fraction prepared from the transformed cells contained 0.1 nmol of cytochrome P-450 per mg of protein. The expressed cytochrome P-450 catalyzed 16 alpha- and 2 alpha-hydroxylations of testosterone in accordance with the catalytic activity of P-450(M-1), but did not hydroxylate vitamin D3 or 1 alpha-hydroxycholecalciferol at the 25 position. The expressed cytochrome P-450 also catalyzed the oxidation of several drugs and did not show 25-hydroxylation activity toward 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. However, it cross-reacted with the polyclonal and monoclonal antibodies elicited against purified P-450cc25 which catalyzed the 25-hydroxylation of vitamin D3. These results indicated that P-450(M-1) cDNA coded the 2 alpha- and 16 alpha-hydroxylase of testosterone, and that these two positions of testosterone are hydroxylated by a single form of cytochrome P-450. Vitamin D3 25-hydroxylase and testosterone 16 alpha- and 2 alpha-hydroxylase are different gene products, although these two hydroxylase activities are immunochemically indistinguishable.

Animals↗

PubMed1997

Effects of tamoxifen, an antiestrogen, on rat prostate carcinogenesis by 3,2'-dimethyl-4-aminobiphenyl and testosterone do not support an estrogen role in testosterone promotion.

BACKGROUND: Our previous data suggest that estrogen plays an important role in rat prostate carcinogenesis, particularly in promotion by testosterone. Therefore, in the present experiment, effects of an antiestrogen, tamoxifen (TAM), were investigated. METHODS: Male F344 rats initially received 3,2'-dimethyl-4-aminobiphenyl (DMAB) at 50 mg/kg bw every 2 weeks for 20 weeks and then TAM in Silastic tubes was subcutaneously given alone or together with testosterone propionate (TP) for 40 weeks. RESULTS: TAM significantly suppressed prostate weights, suggesting an estrogenic action, but the development of preneoplastic and/or neoplastic lesions of the prostate or seminal vesicles in rats given DMAB alone or DMAB and TP was not altered. TAM reversed the suppression of development of ventral atypical hyperplasias by TP. CONCLUSIONS: These findings suggest that estrogen, which is derived from testosterone by the action of aromatase, is not involved in the strong promotion by TP of DMAB prostate carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1984

Inhibition of testosterone biosynthesis by ethanol: relation to the pregnenolone-to-testosterone pathway.

The concentrations of metabolites in the pregnenolone in equilibrium testosterone pathway were determined in freeze-stopped testes in control rats and during ethanol intoxication (2 h after injection of 1.5 g ethanol/kg body wt). Ethanol lowered the mean testicular concentrations of testosterone (by 63-74%), androstenedione (49-81%), 17-hydroxyprogesterone (60-76%), progesterone (29-67%) and pregnenolone (12-25%). 4-Methylpyrazole had no effect on the ethanol-induced changes. The present results reveal no inhibition at the 17-hydroxyprogesterone----androstenedione----testosterone steps, but do not exclude inhibition before the step yielding pregnenolone and at the pregnenolone----progesterone----17-hydroxyprogesterone steps.

17-alpha-Hydroxyprogesterone↗

PubMed1988

Neonatal testosterone administration, but not in utero contiguity to males, augments the display of male sexual behavior by testosterone-treated adult female mice.

Male copulatory behavior of adult female mice given slow-release capsules of testosterone was examined in animals that developed in utero contiguous to two males (mFm) or to two females (fFf). Other females of unspecified uterine position which were injected with testosterone propionate on the day of birth as well as intact males also were examined. mFm and fFf females did not differ on any measure; latency to the first mount, number of mount bouts, number of mount bouts with genital thrusting. The perinatally androgenized females exhibited more mount bouts and more bouts accompanied by genital thrusting than did mFm and fFf subjects. The former also displayed more mount bouts with thrusting on the second pair of tests than males. Lastly, a greater proportion of perinatally androgenized females than mFm or fFf animals displayed male sexual behavior two weeks following removal of the testosterone-containing capsule.

Animals↗

PubMed1996

Biotransformation XXXIX. Metabolism of testosterone, androstenedione, progesterone and testosterone derivatives in Absidia coerulea culture.

The strain of Absidia coerulea was used to investigate the transformations of testosterone, androstenedione, progesterone and testosterone derivatives with additional Cl-C2 double bond and/or 17alpha-methyl group. All the examined substrates were transformed, mainly hydroxylated. It was found that the position and stereochemistry of the introduced hydroxyl group, as well as the yield of products, depended on the structure of the substrate. The first three substrates (hormones) underwent hydroxylation at C-14, and additional hydroxylation at 7alpha was observed in progesterone. The presence of the double bond (C1-C2) in 1-dehydrotestosterone did not influence the position of hydroxylation, but the product with additional C14-C15 double bond (at the same site as hydroxylation) was formed. 17alpha-Methyltestosterone was hydroxylated at the 7alpha position, and also the dehydrogenated product (at the same site, with C6-C7 double bond) was obtained. The testosterone derivative with both C1-C2 double bond and 17alpha-methyl group underwent hydroxylation at the 7alpha or 11beta position, and a little amount of 14alpha, 15alpha epoxide was formed.

Androstenedione↗

PubMed1975

Synthesis and biological activity of some ethers of testosterone. Implications concerning the biological activity of esters of testosterone.

The benzyl (2), allyl (4), propyl (10), 3-hydroxypropyl (12), 2,3-dihydroxypropyl (11), 4 pentenyl (7), and pentyl (8) ethers of testosterone were synthesized. Compounds 2, 4, 7, 8, 10, and 12 were found to be almost devoid of anabolic or androgenic activity in a modified Hershberger Assay, but 2,4,10, and 12 were found to be effective inhibitors of testosterone 5alpha-reductase from human skin. These findings suggest that esters of testosterone and of 19-nortestosterone must hydrolyze before interacting with the hormonal receptors, but that the esters may competitively compete with the parent alchohols for interaction with enzymes. The latter effect may shift the distribution of metabolites of the esters relative to the alchohols and thus influence the pharmacological effect of these compounds.

Animals↗

PubMed1984

Serum levels of testosterone precursors, testosterone and estradiol in 10 animal species.

Blood levels of testosterone precursors, i.e. pregnenolone, progesterone, 17 alpha-hydroxyprogesterone, androstendione, DHEA, and delta 5-androstendiol as well as testosterone and estradiol are measured in 10 animals each of 10 different species. The determination is done by radioimmunoassay with steroidspecific antibodies. Precursors of the delta 5-pathway (DHEA, androstendiol) are low in the red deer, dog, cat, rat and guinea pig. Precursors of the delta 4-pathway (progesterone, 17-hydroxprogesterone, androstendione) are lower in the bull, boar, ram, stallion and rabbit thus indicating a predominance of different pathways in the animal species studied herein. Pregnenolone concentrations are of equal height in all animals, testosterone is lowest in the cat and stallion. In the latter species the estradiol/testosterone ratio is spectacular high.

Androstenediols↗

PubMed1988

Testosterone metabolism and its testosterone-dependent activation in the uropygial gland of quail.

The in vitro metabolism in the uropygial gland of the male quail results into large yields of 5 beta-reduced and/or 17 alpha-hydroxylated metabolites. This metabolism was studied in glands of sexually quiescent quails five days after a single intra-muscular injection of testosterone to the birds. This treatment led to an increased production of inactive metabolites (epitestosterone and its 5 beta-reduced metabolites) and to a decrease of unmetabolized testosterone. Thus testosterone controls its own metabolism and by this way means to modulate its action in the uropygial gland of quail.

Animals↗

PubMed1997

Frequent serum sampling in healthy men discloses testosterone peaks exacerbated by testosterone propionate administration.

Interval samplings uncover blood diurnal oscillations for several hormones, highlighting the importance of short time intervals in the disclosure of subtle pulsatile patterns of some peptide hormones, namely LH. In a study designed to develop new probes against steroid misuse, venous blood was sampled at 5-min intervals for 4 hours from 12 eugonadal adult male athletes, 6 receiving transcutaneous administrations of testosterone propionate and 6 placebo subjects. Brief supraphysiologic serum testosterone peaks were disclosed, the amplitude and frequency of these peaks being larger for the treated group. No solid explanation could be given to explain these bursts. Neither the binding/dissociation kinetics of SHBG molecules with and without increased circulating level of dihydrotestosterone, nor brief testosterone-inducing LH bursts, nor increased Leydig cell release could be invoked to explain these peaks. Their occurrence, although relatively rare, could represent a threat and lead to improper treatment.

Administration, Cutaneous↗

PubMed1989

Relative diagnostic value of serum non-SHBG-bound testosterone, free androgen index and free testosterone in the assessment of mild to moderate hirsutism.

Recent evidence suggests that steroid hormone loosely bound to albumin is available for target-cell entry. Preliminary studies have suggested that a measure of this fraction, non-sex-hormone-binding globulin-bound testosterone (NSB-T), provides the best in vitro diagnostic test for idiopathic hirsutism. We compared the diagnostic value of NSB-T, total testosterone (T), free testosterone (fT), and the free androgen index (FAI) in supporting the clinical diagnosis in 22 pre-menopausal women with hirsutism. NSB-T supported the diagnosis in 50% of cases, compared with 23% for T, 55% for fT by analogue RIA, and 68% for FAI. We conclude that in mild to moderate hirsutism the measurement of NSB-T does not yield diagnostic information addition to that provided by the FAI.

Adolescent↗

PubMed1995

Pharmacokinetics, bioefficacy, and safety of sublingual testosterone cyclodextrin in hypogonadal men: comparison to testosterone enanthate--a clinical research center study.

We studied and compared the pharmacokinetics and bioefficacy of two doses of sublingual testosterone cyclodextrin (SLT; 2.5 and 5.0 mg, administered three times per day) with testosterone enanthate (TE; 200 mg) given once every 20 days by im injections over a 60-day study period in 63 hypogonadal men. After SLT administration, serum testosterone (T) levels peaked at 20 min and then fell, reaching baseline levels by 360 min. The calculated half-lives were 60.3 +/- 7.5 and 68.8 +/- 5.0 min after a single dose of 2.5 and 5.0 mg SLT, respectively. The mean area under curve (AUC) of serum T was computed over 20-day periods for the 3 treatment groups. The mean net AUC of serum T after TE administration was about 4- and 2-fold higher than that in the 2.5 and 5 mg groups over the last 20 days. Serum estradiol and dihydrotestosterone followed the same pattern as serum T. Serum estradiol to T ratios decreased after T replacement in all 3 groups, whereas serum dihydrotestosterone to T ratios were not significantly changed by T treatment. Suppression of serum LH and FSH levels was more marked in the patients treated with TE than in those given SLT. Similarly, serum sex hormone-binding globulin levels showed significant decreases with androgen replacement only in the TE and SLT 5.0 mg range groups. There were no significant adverse effects based on comprehensive physical examinations, urea, electrolytes, and renal or liver function tests. Hematocrit levels increased in the TE-treated group, but remained slightly lower than baseline levels in the SLT groups. Serum high density lipoprotein cholesterol showed a small, but significant, decrease with time of treatment in all groups. Despite the differences in the AUC of serum T levels achieved by different androgen replacement therapies, all patients showed significant improvements in sexual motivation and performance, with no significant difference between the treatment groups. We conclude that SLT may be a useful addition to the currently available injectable and transdermal delivery systems for treatment of hypogonadal men. Because of the ease of administration, rapid reversibility of effects, and lower AUC of serum T levels achieved compared to those of TE injections, SLT may be especially suitable for treatment of boys with delayed puberty and older men with androgen deficiency.

Administration, Sublingual↗

PubMed1998

Testosterone versus testosterone and testolactone in treating reproductive and sexual dysfunction in men with epilepsy and hypogonadism.

Antiepileptic drug-induced reductions in serum levels of biologically active testosterone and elevations in serum estradiol (E2) may contribute to sexual dysfunction among men with epilepsy. Treatment using a combination of testosterone and the aromatase inhibitor testolactone may have significantly better effects on sexual function and also seizure frequency than testosterone alone.

Adult↗

PubMed2005

Empirical estimation of free testosterone from testosterone and sex hormone-binding globulin immunoassays.

BACKGROUND: The growing interest in measuring blood free testosterone (FT) is constrained by the unsuitability of the laborious reference methods for wider adoption in routine diagnostic laboratories. Various alternative derived testosterone measures have been proposed to estimate FT from either additional assay steps or calculations using total testosterone (TT) and sex hormone-binding globulin (SHBG) measured in the same sample. However, none have been critically validated in large numbers of blood samples. METHODS: We analyzed a large dataset comprising over 4000 consecutive blood samples in which FT as well as TT and SHBG were measured. Dividing the dataset into samples with blood TT above and below 5 nM, using a bootstrap regression modeling approach guided by Akaike Information Criterion for model selection to balance parsimony against reduction of residual error, empirical equations were developed for FT in terms of TT and SHBG. RESULTS: Comparison between the empirical FT equations with the laboratory FT measurements as well as three widely used calculated FT methods showed the empirical FT formulae had superior fidelity with laboratory measurements while previous FT formulae overestimated and deviated systematically from the laboratory FT values. CONCLUSION: We conclude that these simple, assumption-free empirical FT equations can estimate accurately blood FT from TT and SHBG measured in the same samples with the present assay methods and have suitable properties for wider application to evaluate the clinical utility of blood FT measurements.

Adult↗

PubMed1984

Seasonal changes in testicular contents of testosterone and androstenedione and in the metabolic clearance rate of testosterone in the sand rat (Psammomys obesus).

Adult male sand rats (Psammomys obesus) were caught in the Béni-Abbès area. The highest testicular contents of androgens (ng/testis) were observed in autumn and in winter (testosterone: 7.6 +/- 1.1; androstenedione: 0.76 +/- 0.11) and the lowest in early summer (June) (testosterone: 1.5 +/- 0.3; androstenedione: 0.20 +/- 0.05). Values had increased by late July. Annual variations of the testosterone metabolic clearance rate (litres/24 h/100 g body wt) were similar to those of testicular androgens; values were high in winter (6.7 +/- 0.7) and lowest in June (3.2 +/- 0.3). The onset of testicular endocrine activity in sand rats was concomitant both with the highest temperatures and the start of reduction in photoperiod; its regression occurred when temperature and photoperiod were increasing.

Androstenedione↗

PubMed1986

Effect of testosterone oenanthate on spermatogenesis and serum testosterone concentrations in adult mice.

Administration of 80 or 160 micrograms testosterone oenanthate s.c. three times per week for 8 or 12 weeks reduced testis weight and increased seminal vesicle weight in mice. Radioimmunoassay indicated that treatment increased serum testosterone concentrations. Treatment with testosterone oenanthate decreased the number of step 16 and step 7 spermatids, pachytene spermatocytes and type A spermatogonia, and particularly reduced the proportion of step 7 spermatids which matured to form step 16 spermatids.

Animals↗

PubMed1977

In-vitro metabolism of [3H]testosterone by scalp and back skin: conversion of testosterone into 5alpha-androstane-3beta, 17beta-diol.

The in-vitro metabolism of [3H]testosterone by human scalp and back skin was examined for possible differences in enzyme activity in skin from these two areas, both of which contain large sebaceous glands but only one of which, the back, is prone to develop acne. Punch biopsy specimens of skin, obtained from the scalp and back of adult men, were minced and incubated with [3H]testosterone. The metabolic products were diluted with carrier steroids, then separated and measured by thin-layer chromatography and by gas chromatography on an instrument equipped with a splitter. The results showed that of the 5alpha-reduced metabolites identified, a major one in both the scalp and back skin incubations was 5alpha-androstane-3beta,17beta-diol. Formation of the androstanediol was especially pronounced in scalp skin where it accounted for up to 50% of the 5alpha-reduced metabolites produced. This finding that 5alpha-androstane-3beta,17beta-diol is a major product of testosterone metabolism in vitro by human skin containing sebaceous glands, supports the possibility, previously suggested by studies in the rat, that this steroid can stimulate sebum secretion.

Androstane-3,17-diol↗

PubMed1994

On the origin of physiologically high ratios of urinary testosterone to epitestosterone: consequences for reliable detection of testosterone administration by male athletes.

Testosterone administration to male athletes can be safely detected in the vast majority of cases by the urinary excretion ratio of testosterone to epitestosterone glucuronides (TG/EG), which may not exceed 6. Some rare cases of physiologically high TG/EG ratios (between 6 and 12) are encountered; these may be attributed to a dysregulation of the testicular secretions of epitestosterone which is decreased, and of epitestosterone sulphate (ES) which is normal or increased. Impaired hydrolysis of circulating epitestosterone sulphate by deficiency of a specific sulphatase acting on 17 alpha-sulphates must also be considered as a possible reason for the decreased availability of epitestosterone for hepatic glucuronidation. Urinary excretions of conjugates and metabolites of testosterone and epitestosterone (expressed in nmol/mmol creatinine) have been determined by gas chromatography-mass spectrometry associated with stable isotope dilution, in a reference population of 90 healthy male subjects and in 12 subjects with chronic TG/EG > 4. Urinary excretion ratios such as TG/(EG+ES), EG/ES and TG/5-androstene-3 beta,17 alpha-diol glucuronide are shown to be efficient criteria which allow discrimination between physiologically high and pharmacologically high TG/EG ratios. A simple oral loading test with deuterium-labelled epitestosterone demonstrates the difference between hepatic and total epitestosterone metabolism clearly, particularly in subjects with physiologically high TG/EG in comparison with subjects with normal TG/EG.

Adolescent↗