Steroid 5 alpha-reductase type 1 immunolocalized in the adrenal gland of normal, gonadectomized, and sex hormone-supplemented rats

Local effect of allopregnanolone in rat ovarian steroidogenesis, follicular and corpora lutea development

Allopregnanolone (ALLO) is a known neurosteroid and a progesterone metabolite synthesized in the ovary, CNS, PNS, adrenals and placenta. Its role in the neuroendocrine control of ovarian physiology has been studied, but its in situ ovarian effects are still largely unknown. The aims of this work were to characterize the effects of intrabursal ALLO administration on different ovarian parameters, and the probable mechanism of action. ALLO administration increased serum progesterone concentration and ovarian 3β-HSD2 while decreasing 20α-HSD mRNA expression. ALLO increased the number of atretic follicles and the number of positive TUNEL granulosa and theca cells, while decreasing positive PCNA immunostaining. On the other hand, there was an increase in corpora lutea diameter and PCNA immunostaining, whereas the count of TUNEL-positive luteal cells decreased. Ovarian angiogenesis and the immunohistochemical expression of GABAA receptor increased after ALLO treatment. To evaluate if the ovarian GABAA receptor was involved in these effects, we conducted a functional experiment with a specific antagonist, bicuculline. The administration of bicuculline restored the number of atretic follicles and the diameter of corpora lutea to normal values. These results show the actions of ALLO on the ovarian physiology of the female rat during the follicular phase, some of them through the GABAA receptor. Intrabursal ALLO administration alters several processes of the ovarian morpho-physiology of the female rat, related to fertility and oocyte quality.

Mechanisms for establishment of GABA signaling in adrenal medullary chromaffin cells

γ-Aminobutyric acid (GABA) is thought to play a paracrine role in adrenal medullary chromaffin (AMC) cells. Comparative physiological and immunocytochemical approaches were used to address the issue of how the paracrine function of GABA in AMC cells is established. GABA_A receptor Cl^- channel activities in AMC cells of rats and mice, where corticosterone is the major glucocorticoid, were much smaller than those in AMC cells of guinea-pigs and cattle, where cortisol is the major. The extent of enhancement of GABA_A receptor α3 subunit expression in rat pheochromocytoma (PC12) cells by cortisol was larger than that by corticosterone in parallel with their glucocorticoid activities. Thus, the species difference in GABA_A receptor expression may be ascribed to a difference in glucocorticoid activity between corticosterone and cortisol. GABA_A receptor Cl^- channel activity in mouse AMC cells was enhanced by allopregnanolone, as noted with that in guinea-pig AMC cells, and the enzymes involved in allopregnanolone production were immunohistochemically detected in the zona fasciculata in both mice and guinea pigs. The expression of glutamic acid decarboxylase 67 (GAD67), one of the GABA synthesizing enzymes, increased after birth, whereas GABA_A receptors already developed at birth. Stimulation of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors, but not nicotinic or muscarinic receptors, in PC12 cells, resulted in an increase in GAD67 expression in a protein-kinase A-dependent manner. The results indicate that glucocorticoid and PACAP are mainly responsible for the expressions of GABA_A receptors and GAD67 involved in GABA signaling in AMC cells, respectively.

Sexual dimorphism in cortisol metabolism throughout pubertal development: a longitudinal study

OBJECTIVE

Sex differences in disease susceptibility might be explained by sexual dimorphism in hypothalamic-pituitary-adrenal axis activity, which has been postulated to emerge during puberty. However, studies conducted thus far lacked an assessment of Tanner pubertal stage. This study aimed to assess the contribution of pubertal development to sexual dimorphism in cortisol production and metabolism.

METHODS

Participants (n = 218) were enrolled from a population-based Netherlands Twin Register. At the ages of 9, 12 and 17 years, Tanner pubertal stage was assessed and early morning urine samples were collected. Cortisol metabolites were measured with GC-MS/MS and ratios were calculated, representing cortisol metabolism enzyme activities, such as A-ring reductases, 11β-HSDs and CYP3A4. Cortisol production and metabolism parameters were compared between sexes for pre-pubertal (Tanner stage 1), early pubertal (Tanner stage 2-3) and late-pubertal (Tanner stage 4-5) stages.

RESULTS

Cortisol metabolite excretion rate decreased with pubertal maturation in both sexes, but did not significantly differ between sexes at any pubertal stage, although in girls a considerable decrease was observed between early and late-pubertal stage (P < 0.001). A-ring reductase activity was similar between sexes at pre- and early pubertal stages and was lower in girls than in boys at late-pubertal stage. Activities of 11β-HSDs were similar between sexes at pre-pubertal stage and favored cortisone in girls at early and late-pubertal stages. Cytochrome P450 3A4 activity did not differ between sexes.

CONCLUSIONS

Prepubertally, sexes were similar in cortisol parameters. During puberty, as compared to boys, in girls the activities of A-ring reductases declined and the balance between 11β-HSDs progressively favored cortisone. In addition, girls showed a considerable decrease in cortisol metabolite excretion rate between early and late-pubertal stages. Our findings suggest that the sexual dimorphism in cortisol may either be explained by rising concentrations of sex steroids or by puberty-induced changes in body composition.

Seasonal changes in plasma testosterone and cortisol suggest an androgen mediated regulation of the pituitary adrenal axis in the Tarabul's gerbil Gerbillus tarabuli (Thomas, 1902)

In the desert gerbil Gerbillus tarabuli (Thomas, 1902), cortisol is the main glucocorticosteroid produced by the adrenal glands. Plasma cortisol concentrations show highest values when testosterone is reduced and lowest values during the breeding season which occurs from early winter to late spring. In order to specify the implication of testicular androgens in these corticosteroid seasonal variations we investigated the effects induced by gonadectomy performed during the breeding season on the pituitary adrenal axis. The animals collected in winter were assessed into three groups: sham-operated (Controls; n=13), gonadectomised (GDX; n=13) and testosterone replaced gonadectomised (GDX+T; n=13). Physiological replacement of testosterone enanthate (75µg/100gb.w./twice daily) was applied during one week, while GDX group received the vehicle (40µL sesame oil) alone. The right adrenal glands removed from euthanized animals were fixed for histomorphometry and androgen receptors (ARs) immunohistochemistry and the left ones were frozen with plasma samples until hormonal assays. Gonadectomy induces the enlargement of the adrenal cortex essentially due to that of zonae fasciculata (ZF) and reticularis (ZR) and perimedullary connective tissue which is abundant in the gerbil adrenals. The ARs immunostaining present at both cytoplasmic and nucleus level, is enhanced intensely in the ZR and moderately in the ZF and zona glomerulosa (ZG) cells. GDX group shows reduced plasma ACTH concentration (p=0.0126) by 61% despite the increase in cortisol concentration occurring both in plasma (+216%; p=0.0436) and adrenal tissue (+117%; p=0.0348). Plasma aldosterone is also enhanced significantly (p=0.0147) by 189% but androstenedione synthesis increased in adrenal tissue (p=0.0459) by 65% instead a decrease at circulatory level (p=0.0355) by 58% due to lack of testicular origin. So, testosterone deprivation activates corticosteroidogenesis also evidenced by the adrenal structure changes and the gonadectomy-induced increase in the plasma cholesterol. All of the gonadectomy-induced responses are reversible after physiological testosterone replacement. We conclude that the assessment of circulating adrenocorticotropic hormone (ACTH) concentrations together with cortisol levels essentially, reflecting the hypothalamic-pituitary adrenal (HPA) axis feedback loop control during the annual endogenous changes of testosterone secretion, represents a well-adapted response of this desert species living in an extreme environment.

GABA Signaling and Neuroactive Steroids in Adrenal Medullary Chromaffin Cells

Gamma-aminobutyric acid (GABA) is produced not only in the brain, but also in endocrine cells by the two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67. In rat adrenal medullary chromaffin cells only GAD67 is expressed, and GABA is stored in large dense core vesicles (LDCVs), but not synaptic-like microvesicles (SLMVs). The α3β2/3γ2 complex represents the majority of GABAA receptors expressed in rat and guinea pig chromaffin cells, whereas PC12 cells, an immortalized rat chromaffin cell line, express the α1 subunit as well as the α3. The expression of α3, but not α1, in PC12 cells is enhanced by glucocorticoid activity, which may be mediated by both the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). GABA has two actions mediated by GABAA receptors in chromaffin cells: it induces catecholamine secretion by itself and produces an inhibition of synaptically evoked secretion by a shunt effect. Allopregnanolone, a neuroactive steroid which is secreted from the adrenal cortex, produces a marked facilitation of GABAA receptor channel activity. Since there are no GABAergic nerve fibers in the adrenal medulla, GABA may function as a para/autocrine factor in the chromaffin cells. This function of GABA may be facilitated by expression of the immature isoforms of GAD and GABAA receptors and the lack of expression of plasma membrane GABA transporters (GATs). In this review, we will consider how the para/autocrine function of GABA is achieved, focusing on the structural and molecular mechanisms for GABA signaling.

Role of sex steroids in progesterone and corticosterone response to acute restraint stress in rats: sex differences

Adrenal progesterone secretion increases along with corticosterone in response to stress in male and female rats to modulate some stress responses. Here we investigated the role of sex steroids in sex differences in the progesterone response to 60 min of restraint stress in adult male and female rats. Comparisons between males and females in the progesterone response were evaluated in parallel with corticosterone responses. From day 5 to 7 after gonadectomy, female and male rats were treated with estradiol or testosterone, respectively (OVX-E and ORCH-T groups), or oil (OVX and ORCH groups). Female rats in proestrus, intact and 7 d adrenalectomized (ADX) male rats were also studied. At 10:00 h, blood samples were withdrawn via an implanted jugular cannula before (-5 min), during (15, 30, 45, 60 min) and after (90 and 120 min) restraint stress to measure plasma progesterone and corticosterone concentrations by radioimmunoassay. Intact male and proestrus female rats exhibited similar progesterone responses to stress. Gonadectomy did not alter the amount of progesterone secreted during stress in female rats but decreased secretion in male rats. Unlike corticosterone, the progesterone response to stress in females was not influenced by estradiol. In males, testosterone replacement attenuated the progesterone and corticosterone responses to stress. Basal secretion of progesterone among intact, ORCH and ADX males was similar, but ADX-stressed rats secreted little progesterone. Hence, the gonads differently modulate adrenal progesterone and corticosterone responses to stress in female and male rats. The ovaries enhance corticosterone but not progesterone secretion, while the testes stimulate progesterone but not corticosterone secretion.

5α-Reduced glucocorticoids: a story of natural selection

5α-Reduced glucocorticoids (GCs) are formed when one of the two isozymes of 5α-reductase reduces the Δ(4-5) double bond in the A-ring of GCs. These steroids are largely viewed inert, despite the acceptance that other 5α-dihydro steroids, e.g. 5α-dihydrotestosterone, retain or have increased activity at their cognate receptors. However, recent findings suggest that 5α-reduced metabolites of corticosterone have dissociated actions on GC receptors (GRs) in vivo and in vitro and are thus potential candidates for safer anti-inflammatory steroids. 5α-Dihydro- and 5α-tetrahydro-corticosterone can bind with GRs, but interest in these compounds had been limited, since they only weakly activated metabolic gene transcription. However, a greater understanding of the signalling mechanisms has revealed that transactivation represents only one mode of signalling via the GR and recently the abilities of 5α-reduced GCs to suppress inflammation have been demonstrated in vitro and in vivo. Thus, the balance of parent GC and its 5α-reduced metabolite may critically affect the profile of GR signalling. 5α-Reduction of GCs is up-regulated in liver in metabolic disease and may represent a pathway that protects from both GC-induced fuel dyshomeostasis and concomitant inflammatory insult. Therefore, 5α-reduced steroids provide hope for drug development, but may also act as biomarkers of the inflammatory status of the liver in metabolic disease. With these proposals in mind, careful attention must be paid to the possible adverse metabolic effects of 5α-reductase inhibitors, drugs that are commonly administered long term for the treatment of benign prostatic hyperplasia.

Potential prostate cancer drug target: bioactivation of androstanediol by conversion to dihydrotestosterone

High-affinity binding of dihydrotestosterone (DHT) to the androgen receptor (AR) initiates androgen-dependent gene activation, required for normal male sex development in utero, and contributes to prostate cancer development and progression in men. Under normal physiologic conditions, DHT is synthesized predominantly by 5α-reduction of testosterone, the major circulating androgen produced by the testis. During androgen deprivation therapy, intratumoral androgen production is sufficient for AR activation and prostate cancer growth, even though circulating testicular androgen levels are low. Recent studies indicate that the metabolism of 5α-androstane-3α, 17β-diol by 17β-hydroxysteroid dehydrogenase 6 in benign prostate and prostate cancer cells is a major biosynthetic pathway for intratumoral synthesis of DHT, which binds AR and initiates transactivation to promote prostate cancer growth during androgen deprivation therapy. Drugs that target the so-called backdoor pathway of DHT synthesis provide an opportunity to enhance clinical response to luteinizing-hormone-releasing hormone (LHRH) agonists or antagonists, AR antagonists, and inhibitors of 5α-reductase enzymes (finasteride or dutasteride), and other steroid metabolism enzyme inhibitors (ketoconazole or the recently available abiraterone acetate).

Activation of the androgen receptor by intratumoral bioconversion of androstanediol to dihydrotestosterone in prostate cancer

The androgen receptor (AR) mediates the growth of benign and malignant prostate in response to dihydrotestosterone (DHT). In patients undergoing androgen deprivation therapy for prostate cancer, AR drives prostate cancer growth despite low circulating levels of testicular androgen and normal levels of adrenal androgen. In this report, we demonstrate the extent of AR transactivation in the presence of 5α-androstane-3α,17β-diol (androstanediol) in prostate-derived cell lines parallels the bioconversion of androstanediol to DHT. AR transactivation in the presence of androstanediol in prostate cancer cell lines correlated mainly with mRNA and protein levels of 17β-hydroxysteroid dehydrogenase 6 (17β-HSD6), one of several enzymes required for the interconversion of androstanediol to DHT and the inactive metabolite androsterone. Levels of retinol dehydrogenase 5, and dehydrogenase/reductase short-chain dehydrogenase/reductase family member 9, which also convert androstanediol to DHT, were lower than 17β-HSD6 in prostate-derived cell lines and higher in the castration-recurrent human prostate cancer xenograft. Measurements of tissue androstanediol using mass spectrometry demonstrated androstanediol metabolism to DHT and androsterone. Administration of androstanediol dipropionate to castration-recurrent CWR22R tumor-bearing athymic castrated male mice produced a 28-fold increase in intratumoral DHT levels. AR transactivation in prostate cancer cells in the presence of androstanediol resulted from the cell-specific conversion of androstanediol to DHT, and androstanediol increased LAPC-4 cell growth. The ability to convert androstanediol to DHT provides a mechanism for optimal utilization of androgen precursors and catabolites for DHT synthesis.

The neurosteroid allopregnanolone modulates specific functions in central and peripheral glial cells

Since the first observations on the existence of "neurosteroids" in the 1980s, our understanding of the importance of these endogenous steroids in the control of the central and peripheral nervous system (PNS) has increased progressively. Although most of the observations were made in neuronal cells, equally important are the effects that neurosteroids exert on glial cells. Among the different classes of neurosteroids acting on glial cells, the progesterone 5α-3α metabolite, allopregnanolone, displays a particular mechanism of action involving primarily the modulation of classic GABA receptors. In this review, we focus our attention on allopregnanolone because its effects on the physiology of glial cells of the central and PNS are intriguing and could potentially lead to the development of new strategies for neuroprotection and/or regeneration of injured nervous tissues.

Non-traditional metabolic pathways of adrenal steroids

Metabolic pathways are reconstructed from biochemical evidence to conceptualize the predominant route to important biomolecules. Pathways have heuristic value in their capacity to explain the metabolic derangements in genetic diseases of enzyme deficiencies and during pharmacologic inhibition of these enzymes. Implicit in the description of these pathways is the potential existence of alternate routes, variable order of reactions, and the inevitable by-products generated by incomplete efficiencies and competing enzymes. This chapter will consider alternate fates encountered by steroid hormone precursors in the adrenal gland, the variables influencing flux through these secondary pathways, and the significance of these diversions in health and disease.

Establishment of type II 5alpha-reductase over-expressing cell line as an inhibitor screening model

Dihydrotestosterone (DHT) is the most potent male hormone that causes androgenetic alopecia. The type II 5alpha-reductase is an enzyme that catalyzes the conversion of testosterone (T) to DHT, therefore it can be expected that specific inhibitors for type II 5alpha-reductase may improve the pathophysiologic status of androgenetic alopecia. In this study, we attempted to establish the reliable and convenient screening model for type II 5alpha-reductase inhibitors. After transfection of human cDNA for type II 5alpha-reductase into HEK293 cells, the type II 5alpha-reductase over-expressing stable cells were selected by G418 treatment. RT-PCR and Western blot analyses confirmed that type II 5alpha-reductase gene was expressed in the stable cells. In in vitro enzymatic assay, 10 microg of stable cell extract completely converted 1 microCi (approximately 0.015 nmol) of T into DHT. The type II 5alpha-reductase activity was inhibited by finasteride in a dose-dependent manner, confirming the reliability of screening system. In cell culture condition, 2 x 10(5) of stable cells completely converted all the input T (approximately 0.03 nmol) into DHT by 4h incubation, demonstrating that the stable cell line can be used as a cell-based assay system. Using this system, we selected the extracts of Curcumae longae rhizoma and Mori ramulus as the potential inhibitors for type II 5alpha-reductase. These results demonstrate that the type II 5alpha-reductase over-expressing stable cell line is a convenient and reliable model for screening and evaluation of inhibitors.

Adrenocortical insufficiency in Otsuka Long-Evans Tokushima Fatty rats, a type 2 diabetes mellitus model

In diabetes, dysregulation of the hypothalamic-pituitary-adrenocortical (HPA) axis causes effects such as elevation of corticotropin (ACTH) and glucocorticoids. Cholecystokinin and its receptors are involved in the HPA axis and influence the regulation of the HPA axis. We examined adrenocortical function in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus, that lack the cholecystokinin A receptor. We measured adrenal weight, plasma ACTH, serum and urinary corticosterone, and serum leptin in OLETF rats at 5 to 36 weeks of age. Messenger RNA (mRNA) expression of 11beta-hydroxysteroid dehydrogenase and 5alpha-reductase type 1 in adrenal glands of the rats were examined. Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In OLETF rats at 32 to 36 weeks of age, plasma ACTH was significantly higher (P < .001); serum corticosterone and 24-hour urinary corticosterone were significantly lower (P < .005); and adrenal weight was significantly lower (P < .005) than those in LETO rats. At the same ages, serum leptin in OLETF rats was significantly higher (P < .001) than that in LETO rats. In the younger OLETF rats, these changes were not observed. Overall, there was an inverse correlation between serum corticosterone and serum leptin (r = -0.374, P < .0005), whereas there was a positive correlation between plasma ACTH and serum leptin (r = 0.654, P < .0001). At 5 and 36 weeks of age, mRNA expression of 5alpha-reductase type 1 in the adrenal gland of OLETF rats was significantly higher (P < .05) than that of LETO rats, whereas there was no significant difference in mRNA expressions of 11beta-hydroxysteroid dehydrogenase types 1 and 2. We showed that adrenocortical insufficiency and adrenal atrophy were acquired in OLETF rats, and the possibility of elevated serum leptin relates to this phenomenon.

Tibolone, transdermal estradiol or oral estrogen-progestin therapies: effects on circulating allopregnanolone, cortisol and dehydroepiandrosterone levels

The aim of the present study was to evaluate, in healthy postmenopausal women, the impact of tibolone (2.5 mg), transdermal estradiol (50 microg) (TE) and different oral estrogen-progestin regimens, conjugated equine estrogens (0.625 mg) plus medroxyprogesterone acetate (5 mg) (CEE + MPA) and estradiol (2 mg) plus norethisterone acetate (1 mg) (E2 + NETA) on circulating estradiol, progesterone, allopregnanolone, cortisol and dehydroepiandrosterone (DHEA) levels. Blood samples were collected before and after 1, 3, 6 and 9 months of treatment in 85 postmenopausal women. Estradiol levels increased (p < 0.001) in the TE, CEE + MPA and E2 + NETA groups after 1 month of therapy, but did not change in the tibolone group during the entire follow-up period. Both E2 + NETA and tibolone treatments induced an increase in progesterone levels (p < 0.05) after 1 year of therapy. Allopregnanolone levels showed an increase in all estrogen-based groups, being significant after 3 months of treatment (p < 0.01). Patients receiving tibolone showed a significant increase in allopregnanolone levels at 3 months (p < 0.05), but lower than in the other groups. Cortisol levels decreased significantly in the TE and CEE + MPA groups after 6 months and 12 months of treatment, respectively. Neither tibolone nor E2 + NETA treatments modified circulating cortisol levels. DHEA levels significantly (p < 0.05) decreased after 6 months of TE or estrogen-progestin therapies independently of the presence or the type of progestin used. In contrast, DHEA remained stable throughout the 12 months of treatment with tibolone. The increase of allopregnanolone, a steroid with sedative and anxiolytic properties, in response to these different treatments could underlie, at least in part, the central effects that hormone replacement therapy and tibolone have on anxiety, mood and behavior. Unlike estrogen-based therapy, tibolone treatment did not reduce the DHEA milieu in the menopause, and thus did not enhance the androgen deficiency syndrome in postmenopausal women.

Stress-induced deoxycorticosterone-derived neurosteroids modulate GABA(A) receptor function and seizure susceptibility

Stress affects seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, we provide evidence that GABA(A) receptor-modulating neurosteroids derived from deoxycorticosterone (DOC) play a role in stress-related changes in seizure control. DOC, an adrenal steroid whose synthesis is enhanced during stress, undergoes sequential metabolic reduction by 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase to form 5alpha-dihydrodeoxycorticosterone (DHDOC) and allotetrahydrodeoxycorticosterone (THDOC), a GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Acute swim stress in rats significantly elevated plasma THDOC concentrations and raised the pentylenetetrazol (PTZ) seizure threshold. Small systemic doses of DOC produced comparable increases in THDOC and PTZ seizure threshold. Pretreatment with finasteride, a 5alpha-reductase inhibitor that blocks the conversion of DOC to DHDOC, reversed the antiseizure effects of stress. DOC also elevated plasma THDOC levels and protected mice against PTZ, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, picrotoxin, and amygdala-kindled seizures in mice (ED50 values, 84-97 mg/kg). Finasteride reversed the antiseizure activity of DOC (ED50, 7.2 mg/kg); partial antagonism was also obtained with indomethacin (100 mg/kg), an inhibitor of 3alpha-hydroxysteroid oxidoreductase. Finasteride had no effect on seizure protection by DHDOC and THDOC, whereas indomethacin partially reversed DHDOC but not THDOC. DHDOC, like THDOC, potentiated GABA-activated Cl- currents in cultured hippocampal neurons (< or =1 microm) and directly activated GABA(A) receptor currents (> or =1 microm), compatible with a role for DHDOC in the antiseizure activity of DOC. DOC is a mediator of the physiological effects of acute stress that could contribute to stress-induced changes in seizure susceptibility through its conversion to neurosteroids with modulatory actions on GABA(A) receptors including THDOC and possibly also DHDOC.

Steroid 5alpha-reductase type 1 immunolocalized in the rat peripheral nervous system and paraganglia

Steroid 5alpha-reductase is an enzyme that converts a number of steroids with a C-4, 5 double bond and C-3 ketone to 5alpha-reduced metabolites. This enzyme has been suggested to play a role in brain development and myelination in the rat nervous system. In the present study, we examined the cellular and subcellular localization of the enzyme immunocytochemically in the rat peripheral nervous system and paraganglia using a polyclonal antibody against rat 5alpha-reductase type 1. Light and electron microscopical studies localized 5alpha-reductase in the Schwann cells of myelinated and unmyelinated nerve fibres, the satellite cells of the ganglia, the enteric glial cells and the supporting/sustentacular cells of the paraganglia. In the myelinated nerve fibres, immunoreactivity was observed in the outer loops, the nodes of Ranvier and the Schmidt-Lanterman incisures. Subcellularly, the immunoreactivity was localized in the cytoplasm of various glial cells. No immunoreactivity was observed in the myelin membrane, the axon or the neuronal perikaryon. These findings suggest that 5alpha-reductase is widely distributed in glial cells, and that, in addition to myelination, 5alpha-reduced steroids play a role in some glial functions in the peripheral nervous system.