Oxygen dependence of oestrogen production by human placental microsomes and cultured choriocarcinoma cells

The oxygen dependence of oestrogen (oestrone and 17 beta-oestradiol) formation from androstenedione and testosterone was studied in term human placental microsomes and in cultured human choriocarcinoma cells (BeWo line). Incubations were performed under various steady-state oxygen concentrations and the production of oestrone and 17 beta-oestradiol quantitated by specific radioimmunoassays. The aromatization of C19-steroids by both placental microsomes and choriocarcinoma cells was shown to be oxygen dependent over a wide range of O2 concentrations. The results indicate that placental oxygenation may be a critical factor in determining oestrogen production in vivo. Therefore, impaired oestrogen biosynthesis due to hypoxia could be an important factor in a variety of physiological and pathological conditions.     

In vitro metabolism of C19 steroids in human endometrium

In order to quantitate the extent of intracellular metabolic conversions of C19 steroids in human endometrium, specimens of proliferative and secretory tissue were superfused at a constant rate with several pairs of labeled compounds at low concentrations. About 16% of dehydroepiandrosterone sulfate interacting with endometrial cells was converted to dehydroepiandrosterone and about 3% of this compound was converted to androstenedione. Androstenedione was reversibly reduced to testosterone and the extent of this conversion was shown to be several-fold higher in secretory than in proliferative tissue. About 1% of testosterone entering the cells was reduced to 5 alpha-dihydrotestosterone. These results demonstrate that the conversion of the main circulating C19 steroids in women, i.e. dehydroepiandrosterone sulfate and androstenedione, to 5 alpha-dihydrotestosterone, the compound considered to be the true intracellular androgen, is very small. In contrast, formation of testosterone from androstenedione is extensive and increases during the luteal phase under the influence of progesterone, a hormone known to stimulate the activity of 17 beta-hydroxysteroid dehydrogenase in human endometrium.     

Steroid control of gonadotrophin secretion in the orchidectomized dog

The effects of s.c. administration of oil, testosterone, 5 alpha-dihydrotestosterone, 5 alpha-androstane-3 alpha, 17 beta-diol and oestradiol-17 beta on plasma concentrations of LH and FSH were determined in 5 orchidectomized dogs. The dosages for the androgens and oestradiol-17 beta were 500 and 50 micrograms/kg body weight, respectively. Testosterone and oestradiol-17 beta significantly reduced plasma gonadotrophin concentrations, although the onset and duration of their suppressive effects differed. Dihydrotestosterone and oil had no effect on either gonadotrophin. Administration of androstanediol had no effect on plasma concentrations of LH but did cause a temporary and significant reduction in FSH. It is concluded that testosterone and oestradiol-17 beta are major regulators of gonadotrophin secretion in the male dog, but the 5 alpha-reduction of testosterone seems to play only a minor role in this control.     

Androgen metabolism in rat L6 myoblast cells; high formation of 5 alpha-androstane-3 alpha,17 beta-diol from testosterone

We have studied androgen metabolism in L6 rat myoblasts. 4-androstene-3,17-dione (Adione), testosterone, 5 alpha-dihydrotestosterone (DHT), and 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) were used for substrates and the amounts of metabolites formed from the respective substrates in the medium were determined. Conversion of Adione to testosterone was dominant over the reverse conversion. DHT formation from testosterone was low and did not change with the duration of incubation, whereas 3 alpha-diol formation increased in a time-dependent manner. Major metabolite of testosterone was not DHT but 3 alpha-diol. A large amount of 3 alpha-diol was formed from DHT, however, DHT formation from 3 alpha-diol was very low. These data indicate that L6 cells have high 5 alpha-reductase activity and suggest that DHT formed from testosterone is rapidly metabolized to 3 alpha-diol in these cells.     

Androstenedione metabolism in human lung fibroblasts

Human lung fibroblasts in culture metabolized [3H]androstenedione to a number of different compounds, including testosterone, 5 alpha-androstanedione, androsterone, 5 alpha-dihydrotestosterone, isoandrosterone, and 5 alpha-androstane-3 alpha,-17 beta-diol. The major products were 5 alpha-androstanedione and testosterone. Estrone, estradiol-17 beta and 5 beta-reduced steroids were not formed. The production rates of testosterone and 5 alpha-androstanedione from [3H]androstenedione by lung fibroblasts were studied both as a function of incubation time and substrate concentration. The rates of formation of testosterone and 5 alpha-androstanedione remained linear with time up to 4 h. The apparent Km of human lung fibroblast 5 alpha-reductase was 1 microM, and that of 17 beta-hydroxysteroid oxidoreductase was 11 microM. The findings of this study suggest that mesenchyma may contribute to the metabolism of androstenedione in human lung tissue.     

Androgen dynamics in vitro in the human prostate gland. Effect of cyproterone and cyproterone acetate

Hyperplastic and adenocarcinomatous human prostatic tissue was superfused in vitro with radioactively labelled androst-4-ene-3,17-dione, testosterone and 5alpha-dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one), with and without addition of the anti-androgens cyproterone and cyproterone acetate. Cyproterone competitively inhibited the entry of the androgens into the majority of the tissues, whereas cyproterone acetate increased this entry. These findings indicated that transport of androstenedione, testosterone and 5alpha-dihydrotestosterone into prostatic tissue is performed by a specific mechanism, possibly involving a carrier situated in the cell membrane. The extent of metabolism of the three androgens was also modified: formation of 5alpha-dihydrotestosterone from testosterone, and of the latter from androstenedione, was decreased by cyproterone and increased by the acetate. Acetate was more effective than cyproterone in decreasing the ;uptake' of the perfused androgens by the tissue; at the same time, it increased the androgen clearance from the tissue. As cyproterone acetate is the more potent of the two anti-androgens, the possibility that these findings in vitro are related to the different anti-androgenic potency exhibited by the two compounds in vivo is discussed. ;Uptake' of the two anti-androgens and the response to their action on androgen dynamics were similar in adenocarcinomatous and hyperplastic glands.     

The proliferative effects of 5-androstene-3 beta,17 beta-diol and 5 alpha-dihydrotestosterone on cell cycle analysis and cell proliferation in MCF7, T47D and MDAMB231 breast cancer cell lines

Epidemiological studies suggest that precursor steroids are implicated in the aetiology of breast cancer. However, our understanding of the role of precursor steroids in breast cancer is complicated by fact that there are many precursor steroids, which are metabolically inter-related and have divergent proliferative activities on the growth of breast cancer cell lines. In this study the proliferative affects of 5 alpha-dihydrotestosterone and 5-androstene-3 beta,17 beta-diol, which may be considered true metabolites acting at a tissue level, on MCF7, T47D and MDAMB231 breast cancer cell lines have been examined by a flow cytometric technique. DNA cell cycle analysis demonstrates that 5-androstene-3 beta,17 beta-diol stimulates the proliferation of hormone-dependent cell lines at physiological levels by an oestrogen receptor mediated mechanism whereas 5 alpha-dihydrotestosterone does not affect the proliferation of MCF7 and T47D cell lines at physiological levels over short (48 h) incubations. Both 5 alpha-dihydrotestosterone and 5-androstene-3 beta,17 beta-diol stimulate proliferation of hormone-dependent cell lines at pharmacological levels via and interaction with the oestrogen receptor. In long (6-9 days) incubations both 5 alpha-dihydrotestosterone and 5-androstene-3 beta,17 beta-diol inhibit the 17 beta-oestradiol induced proliferation of MCF7 and T47D cell lines, however, 5 alpha-dihydrotestosterone inhibits while 5-androstene-3 beta,17 beta-diol stimulates basal proliferation. These cell line studies suggest a model for the role of precursor steroids in pre- and postmenopausal breast cancer.     

Simultaneous increase in the aromatization of testosterone into estrogens and secretion of inhibin by Sertoli cells in culture

17 beta oestradiol and inhibin production by Sertoli cells has been investigated in vitro. In basal conditions, 17 beta-oestradiol secretion is weak whereas inhibin production is undetectable on days 7 and 9 of culture. Addition of PMSG (FSH-like gonadotrophin) and testosterone to the culture medium induces a simultaneous increase in 17 beta-oestradiol and inhibin production. PMSG alone has no effect neither on inhibin nor on 17 beta-oestradiol secretion. Testosterone alone significantly increases 17 beta-oestradiol and inhibin production. Human chorionic gonadotrophin (LH-like gonadotrophin) does not modify inhibin secretion. Dihydrotestosterone stimulates inhibin production without affecting oestrogens secretion. Thus, stimulation of aromatization of testosterone into 17 beta-oestradiol is associated with an increase of inhibin production, but this effect seems to be due to a direct action of androgens.     

Enzymic synthesis of steroid sulphates. XI. Study of the oestrogen binding site of oestrogen sulphotransferase by affinity labelling with 4-mercuri-17beta-oestradiol.

Oistrogen sulphotransferase (3"-phosphoadenylylsulphate: oestrone sulphotransferase, EC 2.8.2.4) contains asingle sulphydryl group thought to be at, or near, the oestrogen-binding site. 4-mercuri-17beta-oestradiol, the activity of the enzyme decreased with increasing concentration of the oestrogen derivative. However, some 40% of the activity remained when all the sulphydryl had reacted to form mercaptide. Formation of mercaptide was only marginally decreased in the presence of the substrate 17beta-oestradiol. Other steroids, such as 11-deoxycorticosterone and testosterone, which are non-substrates for the enzyme, were more effective than 17beta-oestradiol in inhibiting mercaptide formation. Bovine serum albumin also reacted with 4-mercure-17beta-oestradiol and the effects of various steroids on mercaptide formation by the affinity label closely paralleled those found for the enzyme. 2t is concluded that the single sulphydryl group in the enzyme is not directly involved in the binding of oestrogen at the active site but is perhaps in closer proximity to a second site capable of binding certain non-substrate steroids.     

Synthesis and characterization by 1H and 13C nuclear magnetic resonance spectroscopy of 17 alpha-hexanoic derivatives of 5 alpha-dihydrotestosterone and testosterone.

The synthesis and characterization of 17 alpha-(6'-hexanoic acid) derivatives of 5 alpha-dihydrotestosterone and testosterone, useful as ligands for affinity chromatography purification or as precursors for affinity-labeling of androgen-binding proteins, is described. Alkynylation of 3-ethylenedioxy-, 3 beta-hydroxy-, and 3 beta,5-dihydroxy-5 alpha-androstan-17-one precursors with the potassium derivative of 5-hexyn-1-ol led to the corresponding 17 alpha-(6'-hydroxyhex-1'-ynyl) derivatives, which were hydrogenated over 10% Pt-C catalyst to give 17 alpha-(6'-hydroxyhexyl) derivatives. Chromic acid oxidation of the primary hydroxy group of the 3-ethylenedioxy-17-hexyl intermediate into carboxylic acid followed by acid cleavage of the 3-ketal group gave 17 alpha-(5'-carboxypentyl)-5 alpha-dihydrotestosterone, which was also obtained directly by chromic acid oxidation of the 3 beta-hydroxy intermediate. Chromic acid oxidation of the primary hydroxy group of the 3 beta,5 alpha-dihydroxy precursor resulted in a 5 alpha-hydroxy-3-oxo intermediate, which was dehydrated to give 17 alpha-(5'-carboxypentyl)testosterone. The 17 alpha configuration of these derivatives and of synthetic precursors was established by comparing their molecular rotations and their 1H and 13C nuclear magnetic resonance (NMR) spectra including solvent effects, with data reported for 17 alpha- or 17 beta-substituted steroid analogs as well as with 1H and 13C NMR reference data recorded in this work for 17 alpha-ethynyltestosterone, 17 alpha-ethynyl-19-nortestosterone, 17 alpha-ethyl-19-nortestosterone, 17 alpha-methyltestosterone, and 17 alpha-methyl-5 alpha-dihydrotestosterone.     

Testosterone metabolism in the uropygial gland of the quail

The metabolism of testosterone in the uropygial gland of the quail principally results in the production of 17 alpha, 5 beta derivatives. Moreover, an unusually small amount of testosterone is converted to 5 alpha-dihydrotestosterone. These results question the role played by intracellular 5 alpha-reduction in the response of the gland to testosterone stimulation.     

Conversion of androstenedione to testosterone and other androgens in guinea-pig alveolar macrophages

Alveolar macrophages obtained by bronchoalveolar lavage of lungs of male and female guinea pigs were incubated with tritium-labelled androstenedione to evaluate the steroid metabolizing enzymes in these cells. The radiolabeled metabolites were isolated and thereafter characterized as testosterone, 5 alpha-androstanedione, 5 alpha-dihydrotestosterone, androsterone, isoandrosterone, 5 alpha-androstane-3 alpha, 17 beta-diol and 5 alpha-androstane-3 beta, 17 beta-diol. Thus, the following androstenedione metabolizing enzymes are present in guinea-pig alveolar macrophages: 17 beta-hydroxysteroid dehydrogenase, 5 alpha-reductase, 3 beta-hydroxysteroid dehydrogenase and 3 alpha-hydroxysteroid dehydrogenase. The predominant androstenedione metabolizing enzyme activity present in alveolar macrophages was 17 beta-hydroxysteroid dehydrogenase. The rate of testosterone formation increased with incubation time up to 4 h, and with macrophage number up to 1.6 X 10(7) cells per ml. Androstenedione metabolism was similar in alveolar macrophages obtained both from male and female guinea pigs. These results suggest that alveolar macrophages may be a site of peripheral transformation of blood-borne androstenedione to biologically potent androgens in vivo and, therefore, these cells may contribute to the plasma levels of testosterone in the guinea pig.     

Gender differences in the vasomotor effects of different steroid hormones in rat pulmonary and coronary arteries.

It is well recognised that oestrogens possess vasodilatory properties, and similar responses to testosterone have been demonstrated. However, vasomotor effects of other steroid hormones have not been well described. Direct comparisons of the relative vasoactivity of different steroid hormones in different vascular beds in male and female genders have not been made. Coronary and pulmonary arteries from adult Wistar rats were mounted in a wire myograph, loaded to 100 and 17 mmHg respectively, maximally pre-contracted with 1 x 10(-4) M prostaglandin-F-2-alpha, and dose response curves to 1 x 10(-6) to 1 x 10(-3) or 3 x 10(-3) M of 17 beta-oestradiol, testosterone, progesterone, and cortisol dissolved in water were constructed. Addition of each steroid hormone caused acute, dose dependent dilatation in coronary and pulmonary vessels. In coronary arteries the order of activity was testosterone > progesterone > 17 beta-oestradiol > cortisol, p < 0.001. In pulmonary arteries, the order of activity was progesterone > testosterone > cortisol > 17 beta-oestradiol, p < 0.001. Pulmonary arteries from male animals were more sensitive to the effects of testosterone than those from female animals, p = 0.003, whereas coronary arteries from female animals were more sensitive to the effects of 17 beta-oestradiol than those from male animals, p < 0.001. We have demonstrated significant differences in the in vitro vasomotor effects of different steroid hormones in two distinct vascular beds. Gender differences in vasomotor responses to steroid hormones may play a role in the aetiology of vasospastic diseases.     

4-Azasteroidal 5 alpha-reductase inhibitors without affinity for the androgen receptor

In efforts to develop potent 5 alpha-reductase inhibitors without affinity for the androgen receptor, synthetic 3-oxo-5 alpha-steroids were tested for their ability to inhibit 5 alpha-reductase, using [14C]testosterone as the substrate, and for their ability to inhibit the binding of [3H]5 alpha-dihydrotestosterone to the androgen receptor of rat prostate cytosol. 2',3' alpha-Tetrahydrofuran-2'-spiro-17-(5 alpha-androstan-3-one) is not an inhibitor of 5 alpha-reductase and has a high affinity for the androgen receptor; substitution of the -CH2- at the 4-position with N-H resulted in a good inhibitor of 5 alpha-reductase. The 4-N-CH3 derivative is even more active, whereas the N-CH2-CH3 derivative is inactive. These 4-aza derivatives have much lower affinity for the androgen receptor than the parent compound. The 4-N-H derivatives of several 3-oxo-5 alpha-steroids were found to be 20-100% as potent as their corresponding 4-N-CH3 analogs as inhibitors of 5 alpha-reductase, whereas their androgen receptor affinities were at least 40-fold lower than their 4-N-CH3 analogs. Their 5 beta-isomers did not inhibit either 5 alpha-reductase or the androgen receptor binding of [3H]5 alpha-dihydrotestosterone. Two of these 4-N-H steroids, 17 beta-N,N-diethylcarbamoyl-4-aza-5 alpha-androstan-3-one and 17 beta-N, N-diisopropylcarbamoyl-4-aza-5 alpha-androstan-3-one, are potent 5 alpha-reductase inhibitors with Ki values equal to 29.2 +/- 1.7 and 12.6 +/- 0.8 nM, respectively, but have little affinity for the androgen receptor. The inhibition of 5 alpha-reductase by both compounds is competitive with testosterone. When [3H]testosterone was incubated with minced rat prostate in the presence of either of these two 4-azasteroids, the nuclear concentration of 5 alpha-dihydrotestosterone decreased and that of testosterone increased. The total nuclear uptake of testosterone plus 5 alpha-dihydrotestosterone was not significantly affected. These 4-azasteroids should be useful for investigating the importance of 5 alpha-reductase in androgen action in vivo.     

Steroid metabolism by rat nasal mucosa: studies on progesterone and testosterone

The metabolism of [4-14C]progesterone and [4-14C]testosterone by slices of the nasal mucosa from rats was studied. As shown by gas chromatography-mass spectrometry there was a preferential formation of reduced progesterone-metabolites (5 alpha-pregnane-3,20-dione, 3 alpha- and 3 beta-hydroxy-5 alpha-pregnane-20-one, 20 alpha- and 20 beta-hydroxypregn-4-en-3-one, 2 alpha,3 alpha-dihydroxy-5 alpha-pregnane-20-one, 3 alpha,16 alpha-dihydroxy-5 alpha-pregnane-20-one) and reduced testosterone-metabolites (4-androstene-3,17-dione, 5 alpha-dihydrotestosterone, 3 alpha-hydroxy-5 alpha-androstane-17-one, and 5 alpha-androstane-3 alpha, 17 beta-diol, 2 alpha-hydroxy-5 alpha-dihydrotestosterone, 5 alpha-androstane-2 alpha,3 alpha, 17 beta-triol) indicating the presence of 5 alpha-reductase, 3 alpha-, 3 beta-, 17 beta-, 20 alpha- and 20 beta-hydroxysteroid oxidoreductase activities in this tissue. Progesterone-metabolites hydroxylated at positions 2 alpha, 6 alpha, 6 beta, 15 alpha and 16 alpha and testosterone-metabolites hydroxylated at positions 1 beta, 2 alpha, 6 beta, 15 beta and 16 alpha were also identified, indicating the presence of several steroid hydroxylases in the nasal mucosa. Autoradiography of the nasal region of rats injected with [4-14C]progesterone or [4-14C]testosterone showed a selective localization of radioactivity in the mucosa covering the olfactory region of the nasal cavity.     

Sexual difference in properties of 5 alpha-reductase in microsome of rat submandibular glands

The properties of 5 alpha-reductase activity in the submandibular glands of rats were investigated using microsomal fraction in the presence of NADPH, and we found a sexual difference in these properties. The formation of 5 alpha-dihydrotestosterone and 5 alpha-androstane-3 alpha, 17 beta-diol from testosterone demonstrated 5 alpha-reductase in the rat microsomal fraction of this tissue sample. Apparent michaelis constants (Km) of the 5 alpha-reductase activity for testosterone was 1.02 x 10(-6) M for the female tissue. Microsomal fraction of submandibular glands of male rats had two Kms and were determined as 1.12 x 10(-6) M and 1.01 x 10(-5) M. The lower Km of 5 alpha-reductase for male rats was similar to for the females.     

Mass spectrometric assay and physiological-pharmacological activity of androgenic neurosteroids

Steroid hormones play a key role in the pathophysiology of several brain disorders. Testosterone modulates neuronal excitability, but the underlying mechanisms are obscure. There is emerging evidence that testosterone-derived "androgenic neurosteroids", 3alpha-androstanediol and 17beta-estradiol, mediate the testosterone effects on neural excitability and seizure susceptibility. Testosterone undergoes metabolism to neurosteroids via two distinct pathways. Aromatization of the A-ring converts testosterone into 17beta-estradiol. Reduction of testosterone by 5alpha-reductase generates 5alpha-dihydrotestosterone, which is then converted to 3alpha-androstanediol, a powerful GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Although the 3alpha-androstanediol is an emerging neurosteroid in the brain, there is no specific and sensitive assay for determination of 3alpha-androstanediol in biological samples. This article describes the development and validation of mass spectrometric assay of 3alpha-androstanediol, and the molecular mechanisms underlying the testosterone modulation of seizure susceptibility. A liquid chromatography-tandem mass spectrometry assay to measure 3alpha-androstanediol is validated with excellent linearity, specificity, sensitivity, and reproducibility. Testosterone modulation of seizure susceptibility is demonstrated to occur through its conversion to neurosteroids with "anticonvulsant" and "proconvulsant" actions and hence the net effect of testosterone on neural excitability and seizure activity depends on the levels of distinct testosterone metabolites. The proconvulsant effect of testosterone is associated with increases in plasma 17beta-estradiol concentrations. The 5alpha-reduced metabolites of testosterone, 5alpha-dihydrotestosterone and 3alpha-androstanediol, had powerful anticonvulsant activity. Overall, the testosterone-derived neurosteroids 3alpha-androstanediol and 17beta-estradiol could contribute to the net cellular actions of testosterone in the brain. Because 3alpha-androstanediol is a potent positive allosteric modulator of GABA(A) receptors, it could serve as an endogenous neuromodulator of neuronal excitability in men. The 3alpha-androstanediol assay is an important tool in this area because of the growing interest in the potential to use adjuvant aromatase inhibitor therapy to improve treatment of epilepsy.     

The effect of infusions of 5 alpha-dihydrotestosterone or estradiol-17 beta on the concentration of some steroids in the human testicular vein and artery

The concentrations of testosterone, 5 alpha-dihydrotestosterone, 5 alpha-androstan-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol, estradiol-17 beta and testosterone-glucosiduronate were measured in the plasma of the testicular vein and artery simultaneously with the estimation in peripheral venous and arterial plasma 60 min after an infusion of 3000 micrograms dihydrotestosterone (DHT) or estradiol (E2), respectively, in patients undergoing orchiectomy for prostatic cancer. The results were as follows; following infusion of DHT or E2, both steroids were completely metabolized by the testes. After DHT the testicular secretion of E2 was significantly reduced. In peripheral plasma 3 alpha-diol concentration was increased. Following E2 a transient elevation of testosterone in the spermatic vein was observed, whereas a slight decrease of DHT and an increase especially of 3 beta-diol levels occurred. It is assumed that DHT as well as E2 plays a role as intratesticular regulator of steroid synthesis and metabolism.     

Testicular responsiveness to human chorionic gonadotrophin during transient hypogonadotrophic hypogonadism induced by androgenic/anabolic steroids in power athletes

Serum concentrations of testosterone, 17-hydroxyprogesterone, estradiol and several other unconjugated and sulphated steroids were analyzed before and after a single dose of hCG in 6 power athletes, who had used high doses of testosterone and anabolic steroids for 3 months. The study was carried out 3 weeks after cessation of drug use, but the study subjects were still characterized by hypogonadotrophic hypogonadism. The mean concentrations of serum LH and FSH were 2.6 +/- 0.3 and 1.1 +/- 0.03 mIU/ml (mean +/- SEM), respectively, and the concentrations of several precursors and metabolites of testosterone were lower than those before drug use. In contrast, circulating concentrations of steroid sulphates were not decreased, with the exception of dehydroepiandrosterone sulphate. After hCG injection serum testosterone and 5 alpha-dihydrotestosterone concentrations increased significantly, whereas no increases in estradiol and 17-hydroxyprogesterone concentrations were observed. These results demonstrate that during transient hypogonadotrophism in adult men, the testicular responsiveness to a single injection of hCG is similar to that in prepubertal boys without any sign of steroidogenic lesion at the 17,20-desmolase step. Therefore, the appearance of the possibly estradiol-mediated inhibition at the level of C21-steroid side-chain splitting in testosterone biosynthesis seems to be dependent on priming by gonadotrophins.     

Progesterone, androstenedione, testosterone, 5 alpha-dihydrotestosterone and androsterone concentrations in specific regions of the human brain

The concentrations of progesterone, androstenedione, testosterone, 5 alpha-dihydrotestosterone and androsterone were determined in tissue samples from the human hypothalamus, anterior pituitary, pineal, amygdala and parietal cortex, taken at autopsy from male (n = 4) and female cadavers (n = 4) of various ages. The measurements were performed using radioimmunoassays for the individual steroids after the chromatographic purification of solvent extracts of tissue samples on Lipidex-5000TM. Preliminary qualitative analyses of the chromatographic profiles of various steroids by radioimmunoassay demonstrated the presence of these steroids in various regions of the brain, but an immunoreactive peak corresponding to 17-hydroxyprogesterone was not found. The concentrations (ng/g tissue wet wt.) of all steroids measured were either very low or below the limit of detection in brain tissues taken from male and female infants. In the adult brain, there was no difference in the distribution of steroids between the various regions studied. There was no sex difference in the brain tissue steroid concentrations, with the exception of testosterone which was clearly much higher in brain tissues from men as compared to women. Although testosterone was undetectable in most samples taken from adult women. 5 alpha-dihydrotestosterone could be measured in almost all samples, which suggests that this is the most important androgen in the human brain. When brain tissue steroid levels are compared with serum concentrations, it can be postulated that a state of equilibrium exists between the fraction of serum steroids which are not bound to high-affinity binding proteins and the amount of steroids in brain tissues.