ORIGINAL RESEARCH—ENDOCRINOLOGY: Vaginal Application of Testosterone: A Study on Pharmacokinetics and the Sexual Response in Healthy Volunteers

INTRODUCTION

Androgen substitution is advocated to improve sexual functioning in women with androgen insufficiency. Nevertheless, the role of androgens in female sexual functioning is not yet unraveled. Even less is known about changes in androgens and the female sexual response.

AIM

The aim of the study is to describe the pharmacokinetics of a single dose of vaginally applied testosterone. In addition, the study aims to gain more insight into the relation between acute changes in testosterone levels and the sexual response in women.

METHODS

A randomized, double-blind, crossover study design was used to compare a single vaginal dose of testosterone propionate (2 mg) with placebo. Ten healthy premenopausal women participated. Serum levels of testosterone, free testosterone, and estradiol were measured. The sexual response was measured before application of medication and 4 and 8 hours after application. Erotic video fragments and erotic fantasies were used as stimuli. The genital sexual response was measured using vaginal plethysmography. The subjective sexual response was measured using a visual analog scale.

RESULTS

Vaginal administration of testosterone propionate induced a significant rise in serum testosterone levels and free testosterone levels, but not in serum estradiol levels. Peak levels were reached after 5.5 hours (range 2-12 hours). Mean peak levels of testosterone were 7.71 nmol/L after testosterone propionate and 2.99 nmol/L after placebo (P < 0.005). Mean peak levels of free testosterone were 0.12 nmol/L after testosterone propionate and 0.04 nmol/L after placebo (P < 0.005). Despite marked elevated levels of androgens this study was unable to detect a direct effect on the genital or subjective sexual response.

CONCLUSIONS

A single dose of vaginally applied testosterone propionate elevates serum levels of testosterone and free testosterone within 6 hours. Nevertheless, this acute rise in androgens has no effects on the female sexual response.

Comparison of the steady-state pharmacokinetics, metabolism, and variability of a transdermal testosterone patch versus a transdermal testosterone gel in hypogonadal men

AIM

To compare the pharmacokinetics (PK), metabolism, intra- and inter-subject variability of a permeation-enhanced testosterone patch versus a topical testosterone gel.

METHODS

28 hypogonadal men were treated with a testosterone patch (5 mg/day applied at 2200 h) and a 1% testosterone gel (5 g/day applied at 0800 h; nominal delivery 5 mg/day), each for 14 days, in an open-label crossover design. PK profiles of total testosterone (TT) and calculated free testosterone (cFT) were measured on day 7 and day 14 of each treatment, with patches or gel applied to the abdomen; dihydrotestosterone (DHT) and estradiol (E2) profiles were measured on day 14. The time-average (Cavg), maximum (Cmax), time of maximum (Tmax) and minimum concentrations (Cmin) were derived from each profile. The intra- and inter-subject coefficients of variation (CVintra and CVinter) of the TT and cFT parameters were computed by ANOVA.

RESULTS

Nightly applications of the patch produced a mean TT profile that mimicked the circadian pattern of healthy men. Morning applications of the gel produced a flatter mean profile; though individual subjects exhibited significant peaks at variable times. For TT, the mean and 90% confidence intervals of the patch/gel ratio of Cavg (1.030; 0.936-1.133; P > 0.05) and Cmax (1.086; 0.974-1.211; P > 0.05) met the criteria for bioequivalence. Cmin was lower for the patch. DHT levels and DHT/T ratios were 2 to 3-fold higher for the gel (P < 0.0001). E2 levels and E2/T ratios were comparable. CVintra and CVinter for Tmax approached 100% for the gel and were 23% and 42%, respectively, for the patch (P < 0.0001). Other variability parameters were generally comparable. Both products were well tolerated, and the patches adhered well.

CONCLUSIONS

These findings reflect the different mechanisms of transdermal absorption from the patch and gel and provide new considerations for selecting testosterone replacement therapies in hypogonadal men.

Pharmacokinetics and metabolism of a selective androgen receptor modulator in rats: implication of molecular properties and intensive metabolic profile to investigate ideal pharmacokinetic characteristics of a propanamide in preclinical study

S-1 [3-(4-fluorophenoxy)-2-hydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide] is one member of a series of potent selective androgen receptor modulators (SARMs) that are being explored and developed for androgen-dependent diseases. Recent studies showed that S-1 holds great promise as a novel therapeutic agent for benign hyperplasia [W. Gao, J. D. Kearbey, V. A. Nair, K. Chung, A. F. Parlow, D. D. Miller, and J. T. Dalton (2004) Endocrinology 145:5420-5428]. We examined the pharmacokinetics and metabolism of S-1 in rats as a component of our preclinical development of this compound and continued interest in structure-activation relationships for SARM action. Forty male Sprague-Dawley rats were randomly assigned to treatment groups and received either an i.v. or a p.o. dose of S-1 at a dose level of 0.1, 1, 10, or 30 mg/kg. S-1 demonstrated a low clearance (range, 3.6-5.2 ml/min/kg), a moderate volume of distribution (range, 1460-1560 ml/kg), and a terminal half-life ranging from 3.6 to 5.2 h after i.v. doses. The oral bioavailability of S-1 ranged from 55% to 60%. Forty phase I and phase II metabolites of S-1 were identified in the urine and feces of male Sprague-Dawley rats dosed at 50 mg/kg via the i.v. route. The two major urinary metabolites of S-1 were a carboxylic acid and a sulfate-conjugate of 4-nitro-3-trifluoromethylphenylamine. Phase I metabolites arising from A-ring nitro reduction to an aromatic amine and B-ring hydroxylation were also identified in the urinary and fecal samples of rats. Furthermore, a variety of phase II metabolites through sulfation, glucuronidation, and methylation were also found. These studies demonstrate that S-1 is rapidly absorbed, slowly cleared, moderately distributed, and extensively metabolized in rats.

Interspecies differences in pharmacokinetics and metabolism of S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethylphenyl)-propionamide: the role of N-acetyltransferase

N-Acetyltransferase (NAT) is one of the major phase II enzymes involved in drug metabolism. Both species differences and polymorphism are observed in NAT expression. During the preclinical development of a novel selective androgen receptor modulator, S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide (S4), we also observed species differences in S4 metabolism due to the interaction between the deacetylation metabolite M1 and NAT, which converted M1 back to S4 both in vitro and in vivo. During incubation with human liver cytosol or rat liver S9 fraction in the presence of acetyl-CoA, more than 50% of M1 (2 microM) was converted back to S4, but this conversion was not observed in the incubation with dog liver S9 fraction or human liver microsome. In vivo pharmacokinetic experiments showed that M1 could be rapidly converted back to S4 in rats, but a similar conversion was not observed in dogs. When S4 was administered, the formation of M1 was only observed in dogs due to the absence of NAT expression. Simultaneous fitting of the concentration-time profiles of both S4 and M1 showed that more than 50% of S4 was deacetylated to M1 in dogs after i.v. administration of S4, whereas more than 80% of M1 was converted to S4 in rats after i.v. administration of M1. Considering the polymorphism in NAT expression, the interaction between M1 and NAT may raise concerns for drug-drug interactions during clinical applications of S4. The observed species differences suggested that interspecies scaling might not be applicable for predicting the metabolism and disposition of S4 in humans.

Androgen replacement therapy in women

Physiologically, androgens in women either derive from direct ovarian production or from the peripheral conversion of the adrenal sex steroid precursor dehydroepiandrosterone to the active androgens. Therefore, loss of adrenal or ovarian function, as in Addison's disease or after bilateral oophorectomy, usually results in severe androgen deficiency. Androgen replacement in these women may produce significant improvements, particularly in libido and mood. Physiological menopause is not necessarily associated with androgen deficiency and therefore does not routinely require androgen therapy. The number of randomized controlled trials of androgen use in women is still limited. Choosing both a convenient and efficient mode of androgen administration in women remains a challenge and currently none of the available preparations is officially approved for use in women.

In vitro and in vivo evaluation of a novel nonscrotal matrix-type transdermal delivery system of testosterone

A matrix-type testosterone (TS) transdermal delivery system for nonscrotal skin was developed with DuroTak 87-2510 as an adhesive polymer. When 3% dodecylamine was used in combination with 10% span 80, the in vitro rat permeation rate increased from 2.29 microg/cm2/hr to 6.51 microg/cm2/ hr as the TS loading dose increased from 2% to 6%. The maximum flux of experimental patch was about 14-fold higher than that of Testoderm. Release kinetics of TS from the patches was proportional to t1/2 following the Higuchi equation, and the release rate of TS increased as TS loading dose increased. Also, a good linear relationship between the skin permeation rate and the release rate was observed, which implies that the release rate is the rate-limiting process of the skin permeation. In vivo study showed that the plasma concentration of TS promptly increased and reached the peak level within 3-6 hours of application of the experimental patch. Area under the curve (AUC0 approximately 48) and Cmax also linearly increased in a dose-dependent manner up to 6% of TS. These results demonstrate the feasibility of developing a nonscrotal matrix-type transdermal delivery system of TS.

New testosterone buccal system (Striant) delivers physiological testosterone levels: pharmacokinetics study in hypogonadal men

A new mucoadhesive testosterone buccal system (Striant), 30 mg testosterone (T), was applied twice daily in 82 hypogonadal men for 3 months. Serum T, free T, and 5alpha-dihydrotestosterone were measured during this period. T pharmacokinetics were determined from the data obtained during a 24-h sampling at wk 12. Physiological mean serum T concentrations were steady and consistently maintained. The mean percentage of time over a 24-h period that total serum T concentrations were above the lower limit of adult male range was 80.1%. During treatment, mean serum 5alpha-dihydrotestosterone, free T, and estradiol concentrations paralleled serum T. T pharmacokinetics were not significantly affected by body mass index, age, food or beverage, gum abnormalities, or medications known to cause dry mouth. Gum-related adverse events occurred in 16.3% of subjects. Except for three subjects, the gum adverse effects occurred early during treatment, did not cause interruption of treatment, and resolved rapidly and completely. The T buccal system is a novel T formulation that offers a safe, effective, and convenient alternative to existing formulations for physiological T replacement therapy in hypogonadal men.

Penile development is initiated in the tammar wallaby pouch young during the period when 5alpha-androstane-3alpha,17beta-diol is secreted by the testes

Virilization of the urogenital tract is under the control of testicular androgens in all mammals. In tammar young, prostate differentiation begins between d 20 and d 40 under the control of the testicular androgen 5alpha-androstane-3alpha,17beta-diol (5alpha-adiol), but uncertainties exist about the control of penile development. We performed longitudinal studies up to d 150 of pouch life to define normal penile development and the effects of androgen administration and castration. In control animals the male phallus was longer than the female phallus by d 48. Closure of the urethra in males begins around d 60 and continues to at least d 150. Administration of supraphysiological doses of testosterone to females caused penile development equivalent to that of the male and also induced partial closure of the urethral groove by d 150. Castration of male pouch young at d 25 prevented penile development, whereas the penis in males castrated at d 40, 80, or 120 had partial closure of the urethral groove. Administration of 5alpha-adiol to females from d 20-40 also caused partial closure of the urethral groove and some growth of the phallus at d 150, whereas 5alpha-adiol treatment from d 40-80 or 80-120 caused some penile growth but had little effect on urethral development. These findings, together with the fact that we found no sex differences in plasma levels of testosterone, dihydrotestosterone, 5alpha-adiol, dehydroepiandrosterone, or androstenedione from d 51-227, clearly indicate that the action of 5alpha-adiol between d 20 and 40 imprints later differentiation of the male penis.

Transdermal testosterone application: pharmacokinetics and effects on pubertal status, short-term growth, and bone turnover

The aim of the study was to assess the effect of transdermal testosterone on free testosterone concentrations in saliva and on short-term growth and bone turnover in boys with growth or pubertal delay. A prospective, randomized, crossover study was conducted over 26 wk with 4 wk of run-in, 8 wk of treatment I (8 or 12 h), 4 wk of washout, 8 wk of treatment II (8 or 12 h), and 4 wk of final washout. The main outcome measures were salivary testosterone profiles during the different study periods; weekly change in lower leg length (LLL) as measured by knemometry, i.e. LLL velocity; absolute and percentage change in bone alkaline phosphatase (bALP) levels; and deoxypyridinoline cross-links measured in urine. Eight boys who took part in the study had a median age of 13.5 yr (range, 12.4-14.9 yr), testicular volume of 3 ml (range, 2-6 ml), height SD score of -2.4 (range, -1.44 to -3.35), and bone age delay of 2 yr (range, 1-3.2 yr). Median salivary testosterone during 8- and 12-h treatments [179 pg/ml (range, 7-3579 pg/ml) and 150 pg/ml (range, 12-3472 pg/ml) (not significant)] was significantly higher than during the run-in and washout blocks (P < 0.0001) [9 pg/ml (range, <7 to 122 pg/ml) and 13 pg/ml (range, <7 to 285 pg/ml) (not significant)]. LLL velocity in the treatment blocks (median, 0.64 mm/wk; range, 0.1-1.08 mm/wk) was significantly higher than during the run-in and washout periods (median, 0.48 mm/wk; range, -0.06 to 0.92 mm/wk) (P < 0.001). The main rise in bALP occurred during the first treatment block with a median percentage change in bALP of 44.2% (range, -4 to 87%) and a smaller percentage change in bALP at the end of the second treatment block of 9.8% (range, -4 to 55%). The increases in bALP were not significantly different between the 8- and 12-h treatment periods, and there was no significant decline during the washout periods. Overnight transdermal testosterone application, as Virormone (5 mg), may be a potentially acceptable method of induction of puberty and stimulates short-term growth and bone turnover.

Pharmacokinetics and tolerability of a bioadhesive buccal testosterone tablet in hypogonadal men

OBJECTIVE

A phase I single centre, open label study of the pharmacokinetics and tolerability of a buccal testosterone tablet (COL 1621) was carried out.

DESIGN

Twelve testosterone-deficient males were treated with the buccal tablet twice daily for 7 consecutive days. Multiple blood samples were drawn for testosterone, dihydrotestosterone (DHT), bioavailable testosterone and sex hormone-binding globulin (SHBG).

RESULTS

After COL 1621, means+/-S.D. serum testosterone level increased to a peak concentration of 26.6+/-5.8 nmol/l (7.7+/-1.7 ng/ml) at 4.8+/-5.8 h and stayed in the eugonadal range. Steady state was achieved within the first 24 h and was maintained in the normal range. The bioavailable testosterone, DHT and free testosterone index followed a pattern very similar to that of testosterone. The mean serum testosterone to DHT ratio was within the normal male range throughout treatment. There was only one treatment-related adverse event (headache). Two-thirds of patients indicated that treatment with COL 1621 was acceptable and that the tablet was convenient to use. Six patients (50.0%) preferred COL 1621 to their previous testosterone replacement therapy, two patients gave preference to their previous treatment and three patients found both treatments to be equally acceptable. Data for one patient was not available.

CONCLUSION

We conclude that COL 1621 can efficiently elevate serum testosterone and DHT levels in hypogonadal men within the first day of application, achieve a steady state within 24 h and maintain serum testosterone in the normal range with a twice-daily treatment regimen. COL 1621 provides an effective alternative oral testosterone replacement therapy that gives physiological levels of testosterone and is well tolerated by the patients.

Oral testosterone-triglyceride conjugate in rabbits: single-dose pharmacokinetics and comparison with oral testosterone undecanoate

Development of a safe and effective oral form of testosterone has been inhibited by the rapid hepatic metabolism of nonalkylated androgens. Since triglycerides are absorbed via lymphatics and bypass the liver, we hypothesized that a testosterone-triglyceride conjugate (TTC) might allow for safe and effective oral testosterone therapy. Therefore, we studied the single-dose pharmacokinetics of oral administration of TTC in rabbits. Female New Zealand rabbits were administered 2, 4, or 8 mg/kg of TTC in sesame oil by gastric lavage. Testosterone undecanoate (TU) by gastric lavage was used as a positive control. Blood was sampled from a catheter in the auricular artery at 0, 15, 30, 60, 90, 120, 180, 240, 360, 480, and 600 minutes after drug administration. Samples were assayed for testosterone by a fluoroimmunoassay. Mean serum testosterone, area under the curve (AUC), and terminal half-life were calculated. Oral TTC administration resulted in rapid and marked increases in serum testosterone. Oral TTC resulted in higher maximum serum testosterone concentrations than oral TU at 8 mg/kg (TTC: 28.6 +/- 7.9 nmol/L vs TU: 11.9 +/- 2.1 nmol/L; P <.001) and 4 mg/kg (TTC: 11.5 +/- 4.2 nmol/L vs TU: 3.6 +/- 1.0 nmol/L; P <.001). In addition, the AUC was 1.8 to 2.6 times greater for TTC than TU at both doses (P <.05). The terminal half-life for both TU and TTC was between 3 and 5 hours and was not significantly different. We conclude that oral TTC is rapidly absorbed from the rabbit intestine and results in elevated concentrations of serum testosterone. The absorption of TTC appears to be superior to that of TU; however, the in vivo persistence of the 2 compounds is similar. TTC may offer an alternative to the use of TU for oral testosterone therapy. Further testing of this compound is warranted.

Three-peptide control of pulsatile and entropic feedback-sensitive modes of growth hormone secretion: modulation by estrogen and aromatizable androgen

The present review highlights a simplified perspective of growth hormone (GH) secretory control, which incorporates the individual and joint effects of final-common signals that converge on somatotrope cells. Critical peptidyl effectors are GH-releasing hormone (GHRH), GH-releasing peptide (GHRP, ghrelin), and somatostatin. The latter three-peptide ensemble mediates stimulation, inhibition, and feedback suppression of GH secretion via homologous and heterologous interactions. Pubertal sex steroids putatively act via post-aromatized estrogen (e.g., testosterone converted to estradiol by aromatase) to augment sensitivity to GHRH, potentiate GHRP action, and mute somatostatin restraint. The dynamic interactions in this three-peptide network, rather than the activity of any single effector, subserve core adaptations in GH secretion across development.

(Q) SAR study on the metabolic stability of steroidal androgens

Metabolic stability is a key issue in the development of orally active androgens for Partial Androgen Deficiency in Aging Males (PADAM) and male contraception. Rates of metabolism in human hepatocyte suspensions provide useful information on the stability of compounds that undergo a first pass metabolism. We have derived a structure-pharmacokinetic relationship for a data set of 32 in-house steroidal androgens by means of the decision-trees technique. Volume, shape, number of rotatable bonds, and surface turned out to be the most important descriptors for classification. Only 2 of the 32 compounds were misclassified. The most stable compounds were classified in three leaf nodes on different branches of the tree, suggesting that higher metabolic stability can be achieved for the same substrate by different steric modifications. Further, it is generally assumed that the first step in cytochrome P450s oxidation reactions takes place by hydrogen abstraction to form a radical intermediate. An electronic model for hydrogen abstraction in steroidal androgens was, therefore, developed by means of ab initio calculations. Activation energies of steroid radical systems calculated as energy differences between the reactants equilibrium geometry energies and their corresponding transition states energies could be used to predict relative rates of metabolism to guide the design and redesign process of metabolically more stable steroidal androgens.

Human prostatic cell line PNT1A, a useful tool for studying androgen receptor transcriptional activity and its differential subnuclear localization in the presence of androgens and antiandrogens

The human immortalized prostatic cell line PNT1A has been proved to be a good model for analysis of cellular processes such as the prostatic epithelium proliferation in response to androgens and growth factors. Here we used this cell line for studying the transcriptional activity and trafficking of the androgen receptor (AR) by analyzing several actions of antiandrogens. Transient transfection experiments with PNT1A cells were performed with wild type human AR and an androgen-responsive gene reporter. We demonstrated that the transcription of reporter gene could be triggered by natural androgens (testosterone and dihydrotestosterone) in PNT1A cells as well as in the prostatic carcinoma cell line DU-145. With competitive experiments in the two cell lines, we observed no difference between the antagonistic capacity of cyproterone acetate (CPA) and hydroxyflutamide at 10(-7) M. At this concentration, bicalutamide antagonist activity was lower. In parallel, we compared the subcellular localization of the modified green fluorescent protein (EGFP)-AR in COS-7, PNT1A and DU-145 cell lines under fluorescence microscopy: we found different distributions between nucleus and cytoplasm, depending on the cell line and the culture medium. Androgen induced cluster formation within the nucleus of the PNT1A and DU-145 cells. However, the cytonuclear trafficking of androgen bound EGFP-AR in the same living cell and nuclear foci were easier to examine in the PNT1A cells. The antiandrogen capacity of bicalutamide was manifested by a slower androgen-dependent nuclear transfer of EGFP-AR and a homogeneous nuclear localization. A delayed advent of nuclear clusters was observed in presence of CPA. We conclude that the PNT1A cell line is a better model than the DU-145 cell line to analyze the trafficking of AR and the association of AR on the nuclear matrix, as well as to observe the action of antiandrogens on these critical steps in prostate cells.

Comparison of animal models for the evaluation of radiolabeled androgens

Biodistribution of two 18F-labeled androgens and an 124I/125I-labeled androgen were studied in five androgen receptor (prostate) animal models with or lacking sex hormone binding globulin (SHBG). As models for androgen-receptor positive ovarian cancer, xenografts of three human ovarian cancer cell lines were tested in SCID mice. SHBG in the prostate model systems significantly affects the metabolism, clearance, and distribution of the radiolabeled androgens in several tissues, but ovarian cancer animal models were disappointing.

A novel isoform of human fibroblast growth factor 8 is induced by androgens and associated with progression of esophageal carcinoma

Human esophageal carcinomas occur more frequently in males, suggesting that androgens may play a role in the regulation of gene expression associated with malignant transformation. We previously established an androgen-sensitive squamous cell carcinoma line, KSE-1, from a male patient with esophageal cancer; recently a novel isoform of human fibroblast growth factor 8 (FGF8f, isoform FGF8b) was identified and expressed following androgen stimulation of KSE-1 cells. The predicted amino acid sequence of FGF8f contained an additional 29 amino acids when compared to FGF8b. Flutamide, an androgen antagonist, inhibited both FGF8b and FGF8f transcription in a dose-dependent manner. Tissue analysis from tumors revealed FGF8b expression in 24 of 41 male, but in 0 of 9 female esophageal carcinomas (58.5%), and none in adjacent normal esophageal mucosa. In addition, FGF8f was detected in 9 of 24 FGF8b-positive tumors (37.5%), and this observation was significantly associated with a poor prognosis (P < 0.001). Our observations suggest that androgenic exposure will induce FGF isoforms in tumor cells, and expression of these growth factors is associated with the prevalence and prognosis of esophageal carcinoma in males.

Influence of oral dehydroepiandrosterone (DHEA) on urinary steroid metabolites in males and females

Oral dehydroepiandrosterone (DHEA) replacement therapy may have a multitude of potential beneficial effects and exerts its action mainly via peripheral bioconversion to androgens (and estrogens). A daily dose of 50-mg DHEA has been shown by us and others to restore low endogenous serum DHEA concentrations to normal youthful levels followed by an increase in circulating androgens and estrogens. As the hepatic first-pass effect may lead to a non physiological metabolism of DHEA after oral ingestion we studied the influence of two single DHEA doses (50 and 100 mg) on the excretion of steroid metabolites in 14 elderly males [age 58.8+/-5.1 years (mean +/- SEM)] with endogenous DHEAS levels <1500 ng/ml and in 9 healthy females (age 23.3+/-4.1 years) with transient suppression of endogenous DHEA secretion induced by dexamethasone (dex) pretreatment (4x0.5 mg/day/4 days). Urinary steroid profiles in the elderly males were compared to the steroid patterns found in 15 healthy young men (age 28.9+/-5.1 years). In the females the results were compared to their individual baseline excretion without dex pretreatment. Urinary steroid determinations were carried out by semiautomatic capillary gas-liquid chromatography. In both genders DHEA administration induced significant increases in urinary DHEA (females: baseline vs. 50 mg vs. 100 mg: 361+/-131 vs. 510+/-264 vs. 1541+/-587 microg/day; males: placebo vs. 50 mg vs. 100 mg: 434+/-154 vs. 1174+/-309 vs. 4751+/-1059 microg/day) as well as in the major DHEA metabolites androsterone (A) and etiocholanolone (Et). Fifty mg DHEA led to an excretion of DHEA and its metabolites only slightly above baseline levels found in young females and in young men, respectively, whereas 100 mg induced clearly supraphysiological values. After 50 mg DHEA the ratios of urinary DHEA metabolites (A/DHEA, Et/DHEA) were not significantly different between elderly males vs. young male volunteers and young healthy females versus their individual baseline levels. In conclusion, an oral dose of 30 to 50 mg DHEA restores a physiological urinary steroid profile in subjects with DHEA deficiency without evidence for a relevant hepatic first-pass effect on urinary metabolites.

[Finasteride: a new drug for the treatment of male hirsutism and androgenetic alopecia?]

Finasteride is a drug which inhibits the transformation of testosterone into its active metabolite, dihydrotestosterone, in the target organs, i.e. the skin, the scalp, the liver and the prostate. In the pathogenic mechanism of hirsutism and androgenetic alopecia, and important role is presumably played by alterations of the mechanisms which transform testosterone into dihydrotestosterone. In some conditions an increase in dihydrotestosterone has been demonstrated, due to increased activity of the enzyme 5 alpha-reductase. The effect of finasteride develops above all at the level of type II 5 alpha-reductase. Recent studies have evaluated the effect of finasteride in patients of both sexes with hirsutism and androgenetic alopecia. In women with various forms of hyperandrogenism, the use of the drug at the doses commonly used for the treatment of benign prostatic hyperplasia seems to have induced a significant reduction in the degree of hirsutism. Furthermore, both in animals and men with alopecia, the drug seems to have led to an increase in the number and an improvement in the shape of the follicles in the anagen phase, and a simultaneous decrease of dehydrotestosterone at the level of the scalp. This study represents a review of the main results obtained over the last two years and reports the prospects which the use of finasteride may have in this context.

Pharmacokinetic and pharmacologic variation between different estrogen products

Due to the complex nature of endogenous and exogenous hormone concentration, formation, and metabolism and assay complexity, the pharmacokinetics of estrogen are difficult to study. Oral estrogens have minimal systemic bioavailability (2% to 10%) due to gut and liver (first-pass) metabolism. High concentrations of estrone are achieved with oral administration, whereas higher concentrations of estradiol are generally achieved after percutaneous absorption. Although vaginal products (such as gel, rings, etc.) are administered locally, they achieve high serum concentrations. Estradiol and estrone concentrations and estradiol-to-estrone ratios vary with different estrogen therapies. Approximately 95% to 98% of estradiol is bound loosely to albumin or tightly to sex hormone binding globulin, the major binding protein. The terminal half lives for the different estrogen compounds (after oral or intravenous administration) vary from 1-12 hours. Some conversion rates have been calculated between estrogen and its metabolites. Smoking decreases achievable estrogen concentrations, and has a greater effect on oral products. Oral contraceptives have been found to decrease antipyrine clearance. In the one study evaluating conjugated estrogens, antipyrine clearance was not altered. Oral contraceptives have a variable effect on the elimination of medications. Acetaminophen clearance is increased, whereas clearance of some benzodiazepines, caffeine,and prednisolone is decreased. Phenytoin increases the metabolism of conjugated estrogens. The various estrogen products may produce different clinical effects based on composition. The metabolites (minor components) of conjugated estrogens have been found to have significant effects on lipid concentrations, uterine weight, liver generated compounds, and bone resorption. Because transdermal products bypass the first-pass effect, delayed or decreased effects on lipid profiles and liver generated compounds have been observed.

[Study on transepithelial movement of 3H-androgen in the rat seminiferous and epididymal tubules]

The mechanisms involved in the maintenance of the endocrinological microenvironment of the seminiferous and epididymal tubules were examined in a series of experiments utilizing in vivo microperifusion, microperfusion, and micropuncture technique. The intraluminal 3H-androgen concentration in the seminiferous tubules increased linearly as the interstitial 3H-androgen concentrations increased from 10 nM to 2,000 nM, but in the caput epididymidal tubules, the intraluminal 3H-androgen concentration increased hyperbolically across the same range of peritubular 3H-androgen concentration. Intraluminal 3H-androgen concentrations in the caput epididymidis did not rise above approximately 340 nM even when the peritubular 3H-androgen concentration exceeded 2,000 nM. Perifusion of caput tubules with 0.1 mM dinitrophenol or potassium cyanide or 100 micrograms/ml cyclohexamide significantly reduced the proluminal 3H-androgen movement, but tubules perifused with control medium did not support antigrade 3H-androgen movement in the absence of native lumen fluids which contain androgen-binding protein. Energy-requiring protein synthesis is necessary for antigrade 3H-androgen movement in the caput epididymidis, but the mechanism for the interaction of intracellular protein(s) and 3H-androgen movement remains undetermined.

Prejunctional regulatory actions of androgens on a hormone sensitive muscle

The influence of androgens and time course of effects induced by hormone deprivation were examined on the spontaneous transmitter release in the levator ani (LA) muscle of 30-180-day-old male rats. The resting membrane potential (RMP) and miniature endplate potentials (mepps) were recorded intracellularly from LA muscle fibers of intact animals or gonadectomized at different ages. In intact animals, the frequency of mepps increased proportionately to the muscle fiber growth up to 60 days, stabilizing thereafter. Gonadectomy at any age did not affect the RMP, but increased the frequency of mepps by 65% to 140%. The effect was detected after 15 days and was unrelated to the degree of muscle atrophy. Independently of the age of gonadectomy control values of mepp frequency were restored after 90 days, while the accompanying postjunctional changes persisted. These results indicate that androgens exert a prejunctional inhibitory influence on the spontaneous transmitter release in the rat LA muscle. The transient nature of the prejunctional effect induced by hormone deprivation indicates an adjustment of nerve terminals to persistent postjunctional alterations.

Androgen and estrogen dynamics: relationships with age, weight, and menopausal status

Previous studies have shown a relationship between age and weight and the MCR and conversions ([rho]) of androgens and estrogens. To assess the relative importance of these relationships in the metabolism and conversion of the androgens and estrogens, we used a series of statistical analyses, including t test, Pearson's correlation, and a step-wise regression analysis of the data obtained from the constant infusion of radiolabeled androgens and estrogens to normal women, 18-90 yr old. The MCRs of testosterone (T), androstenedione (A), and estrone (E1) were strongly correlated with weight, but not age or menopausal status. The MCR of estradiol (E2) was strongly correlated with weight and less strongly correlated with age, but was not correlated with menopausal status. The interconversions of the androgens ([rho]T,ABB and [rho]A,TBB, i.e. percentage of precursor infused measured as product in blood) and estrogens ([rho]E1,E2BB and [rho]E2,E1BB) were not correlated with age or weight, but there was a weak correlation between [rho]T,ABB and menopausal status. The aromatization of androgens to estrogens ([rho] A,E1BM and [rho]T,E2BM, i.e. percentage of androgens infused measured as estrogen glucuronide in the urine) was highly correlated with age, less strongly correlated with weight, and not correlated with menopausal status. The correlation with weight and MCR is a reflection of the extrasplanchnic metabolism of steroids. The lack of correlation with weight for the interconversions of androgens and estrogens indicates that the enzyme(s) responsible is affected differently in extrasplanchnic tissue than is the aromatase complex. The relationship between age and aromatization, while strong, remains unexplained.

A comparative study of the selectivity and efficiency of target tissue uptake of five tritium-labeled androgens in the rat

A comparative study of the tissue distribution of five tritium-labeled androgens was done in rats to determine the efficiency and selectivity of their uptake by target tissue. Testosterone (T), 5 alpha-dihydrotestosterone (DHT), 19-nortestosterone (nor-T), mibolerone (Mib) and methyltrienolone (R1881) all showed selective uptake by the ventral prostate in one-day castrated rats (250 g) that was 61-90% displaceable by co-injection of an excess of unlabeled steroid. The greatest uptake was with R1881 (0.69% injected dose per gram prostate tissue (%ID/g) at 1 h), and Mib (0.56% ID/g); the other three showed lower uptake (approx. 0.4% ID/g). The target tissue activity remained high for all compounds up to 4 h after injection, and at 2-4 h the prostate to blood ratio for Mib and R1881 exceeded 10 and 20, respectively. The uptake efficiency and selectivity of these five androgens appear to be related to their affinity for the androgen receptor and their resistance to metabolism. Mib and R1881 have substantial affinity for other steroid receptors, which might account for some of their prostate uptake. However, co-administration of triamcinolone acetonide, which has high affinity for progesterone and corticosteroid receptors but not for the androgen receptor, failed to block their uptake significantly, whereas co-administration of DHT, the most selective ligand for the androgen receptor, blocked their uptake as completely as the unlabeled tracer itself. The prostate uptake of Mib and R1881 in intact animals was significantly lower than in castrated animals, but treatment of the intact animals with diethylstilbestrol restored their uptake nearly to the level seen in castrated animals. These uptake patterns are consistent with earlier studies of in vivo androgen uptake and with known changes in androgen receptor content and occupancy as a result of castration or diethylstilbestrol treatment. They further suggest that high affinity androgens labeled with suitable radionuclides--particularly derivatives of mibolerone (Mib) or methyltrienolone (R1881)--may be effective receptor-based imaging agents for androgen target tissues and tumors, even when patients are already receiving hormonal therapy.

Stable isotope methodology in the pharmacokinetic studies of androgenic steroids in humans

The use of stable isotopically labeled steroids combined with gas chromatography/mass spectrometry (GC/MS) has found a broad application in pharmacologic studies. Initially, stable isotopically labeled steroids served as the ideal analytic internal standard for GC/MS analysis; however, their in vivo use has expanded and has proven to be a powerful pharmacokinetic tool. We have successfully used stable isotope methodology to study the pharmacokinetic/bioavailability of androgens. The primary advantage of the technique is that endogenous and exogenous steroids with the same basic structure can be differentiated by using stable isotopically labeled analogs. The method was used to examine the pharmacokinetics of testosterone and testosterone propionate, and to clarify the influence of endogenous testosterone. Another advantage of the isotope methods is that steroidal drugs can be administered concomitantly in two formulations (e.g., solution and solid dosage). A single set of blood samples serves to describe the time course of the formulations being compared. This stable isotope coadministration technique was used to estimate the relative bioavailability of 17 alpha-methyltestosterone.

On the proluminal movement of 3H-androgens across the rat epididymal epithelium

3H-Androgens in rat epididymal interstitium have previously been shown to move into the epididymal lumen against a concentration gradient. This is true especially in the caput epididymidis. The present investigation used the technique of in vivo epididymal perifusion and tubule micropuncture to demonstrate that the proluminal movement of 3H-androgens is subject to competitive inhibition (unlabeled testosterone in the perifusion fluid at 10 times and 100 times the concentration of 3H-testosterone significantly reduced proluminal movement of isotope) and is not energy-dependent (1 mM 2,4-dinitrophenol in perifusion fluid did not reduce the proluminal movement of isotope). Additionally, dry-mount autoradiography demonstrated high intraluminal concentrations of isotope relative to interstitial concentrations after caput tubule incubation in 3H-dihydrotestosterone (3H-DHT), and showed that the high intraluminal concentrations of isotope were not dependent on the presence of spermatozoa, i.e. proluminal movement of 3H-androgens was not due to binding to intraluminal spermatozoa. Isolation of caput epididymidal sperm on filters followed by 3H-DHT binding experiments also failed to demonstrate the presence of specific binding of this androgen to spermatozoa. Finally, it was confirmed that electrophoresed epididymal lumen fluid contains a single 3H-DHT binding peak that is at its highest concentration in the caput epididymal fluid. These data are consistent with the conclusion that intraluminal androgen-binding protein is an important factor in transepithelial androgen movement.