Depressant effect of androgens on the cat brain electrical activity and its antagonism by ruthenium red

Sex Differences in Major Depressive Disorder (MDD) and Preclinical Animal Models for the Study of Depression

Depression and related mood disorders constitute an enormous burden on health, quality of life, and the global economy, and women have roughly twice the lifetime risk of men for experiencing depression. Here, we review sex differences in human brain physiology that may be connected to the increased susceptibility of women to major depressive disorder (MDD). Moreover, we summarize decades of preclinical research using animal models for the study of mood dysfunction that uncover some of the potential molecular, cellular, and circuit-level mechanisms that may underlie sex differences and disease etiology. We place particular emphasis on a series of recent studies demonstrating the central contribution of the circuit projecting from ventral hippocampus to nucleus accumbens and how inherent sex differences in the excitability of this circuit may predict and drive depression-related behaviors. The findings covered in this review underscore the continued need for studies using preclinical models and circuit-specific strategies for uncovering molecular and physiological mechanisms that could lead to potential sex-specific diagnosis, prognosis, prevention, and/or treatments for MDD and other mood disorders.

Sex differences in anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

Rapid actions of androgens

The biological activity of androgens is thought to occur predominantly through binding to intracellular androgen-receptors, a member of the nuclear receptor family, that interact with specific nucleotide sequences to alter gene expression. This genomic-androgen effect typically takes at least more than half an hour. In contrast, the rapid or non-genomic actions of androgens are manifested within in seconds to few minutes. This rapid effect of androgens are manifold, ranging from activation of G-protein coupled membrane androgen-receptors or sex hormone-binding globulin receptors, stimulation of different protein kinases, to direct modulation of voltage- and ligand gated ion-channels and transporters. The physiological relevance of these non-genomic androgen actions has not yet been determined in detail. However, it may contribute to modulate several second messenger systems or transcription factors, which suggests a cross-talk between the fast non-genomic and the slow genomic pathway of androgens. This review will focus on the rapid effects of androgens on cell surface and cytoplasmic level.

Non-genomic actions of androgens

Previous work in the endocrine and neuroendocrine fields has viewed the androgen receptor (AR) as a transcription factor activated by testosterone or one of its many metabolites. The bound AR acts as transcription regulatory element by binding to specific DNA response elements in target gene promoters, causing activation or repression of transcription and subsequently protein synthesis. Over the past two decades evidence at the cellular and organismal level has accumulated to implicate rapid responses to androgens, dependent or independent of the AR. Androgen's rapid time course of action; its effects in the absence or inhibition of the cellular machinery necessary for transcription/translation; and in the absence of translocation to the nucleus suggest a method of androgen action not initially dependent on genomic mechanisms (i.e. non-genomic in nature). In the present paper, the non-genomic effects of androgens are reviewed, along with a discussion of the possible role non-genomic androgen actions have on animal physiology and behavior.

Abuso de esteróides anabolizantes e seu impacto sobre a função tireóidea

A utilização de esteróides anabolizantes por indivíduos que desejam aumentar sua performance física, ou simplesmente para fins estéticos, tem atingido índices alarmantes nas últimas três décadas. Além dos efeitos desejados, uma infinidade de efeitos colaterais já foi bem descrita na literatura, como vários tipos de câncer, ginecomastia, peliosis hepatis, insuficiência renal, virilização, dentre outros. Sobre a função tireóidea, o efeito mais pronunciado em seres humanos é a diminuição da TBG, com conseqüente diminuição sérica de T3 e T4 totais, dependendo, porém, da susceptibilidade da molécula à aromatização e conseqüente transformação em estrógeno. Em ratos, o tratamento com esteróides anabolizantes altera a metabolização periférica dos hormônios tireóideos e também parece causar importante efeito proliferativo sobre as células tireóideas. Assim, o presente artigo visa rever os dados publicados acerca dos efeitos de doses suprafisiológicas de esteróides anabolizantes sobre a função tireóidea, reforçando o perigo que a utilização indiscriminada dessas drogas pode causar à saúde.

Early and late effects of steroid hormones on the central nervous system

Steroids have fast and probably partly GABA-mediated central anaesthetic effects for which a strict structure-function correlation is required. They also affect short- and long-term activity in the CNS in other ways. One of these is long-term potentiation (the persistent facilitation of synaptic transmission), which occurs particularly in the hippocampus after repetitive stimulation of a fibre pathway. Two clearly distinguished components of the evoked response can be studied in the hippocampus: the excitatory postsynaptic potential (EPSP) which denotes the graded depolarization of the somadendritic region of the neuron and the population spike (PS), a manifestation of the all-or-none discharge of the cell action potential. Corticosterone had a significant depressant effect on the EPSP component of the evoked response immediately and 15 min after injection. Thereafter EPSP amplitudes were within normal values. Corticosterone significantly decreased the PS immediately after the train, the component remaining low 30 min after the train. 5 alpha-Dihydrocorticosterone (a ring A-reduced metabolite of corticosterone) significantly reduced the PS component of the response at all times after injection. 18-Hydroxydeoxycorticosterone and deoxycorticosterone significantly decreased both EPSP and PS components of the evoked response from the time of infusion. Contrary to expectation, tetrahydrodeoxycorticosterone was ineffective in decreasing, and if anything, enhanced the development of long-term potentiation. 18-Hydroxydeoxycorticosterone 21-acetate behaved like vehicle, except for the first 30 min after injection, when the EPSP was decreased. Different steroids can selectively affect different parts of a neuron and appear to show a different structure-function correlation for long-term potentiation from that required for anaesthesia.

Anticonvulsant activity of androsterone and etiocholanolone

PURPOSE

Men with epilepsy often have sexual or reproductive abnormalities that are attributed to alterations in androgen levels, including subnormal free testosterone. Levels of the major metabolites of testosterone-androsterone (5alpha-androstan-3alpha-ol-17-one; 5alpha,3alpha-A), a neurosteroid that acts as a positive allosteric modulator of GABA(A) receptors, and its 5beta-epimer etiocholanolone (5beta-androstan-3alpha-ol-17-one; 5beta,3alpha-A)-also may be reduced in epilepsy. 5alpha,3alpha-A has been found in adult brain, and both metabolites, which also can be derived from androstenedione, are present in substantial quantities in serum along with their glucuronide and sulfate conjugates. This study sought to determine whether these endogenous steroid metabolites can protect against seizures.

METHODS

The anticonvulsant activity of 5alpha,3alpha-A and 5beta,3alpha-A was investigated in electrical and chemoconvulsant seizure models in mice. The steroids also were examined for activity against extracellularly recorded epileptiform discharges in the CA3 region of the rat hippocampal slice induced by perfusion with 55 microM 4-aminopyridine (4-AP).

RESULTS

Intraperitoneal injection of 5alpha,3alpha-A-protected mice in a dose-dependent fashion from seizures in the following models (ED50, dose in mg/kg protecting 50% of animals): 6-Hz electrical stimulation (29.1), pentylenetetrazol (43.5), pilocarpine (105), 4-AP (215), and maximal electroshock (224). 5beta,3alpha-A also was active in the 6-Hz and pentylenetetrazol models, but was less potent (ED50 values, 76.9 and 139 mg/kg, respectively), whereas epiandrosterone (5alpha,3beta-A) was inactive (ED50, <or=300 mg/kg). 5alpha,3alpha-A (10-100 microM) also inhibited epileptiform discharges in a concentration-dependent fashion in the in vitro slice model, whereas 5beta,3alpha-A was active but of lower potency, and 5alpha,3beta-A was inactive.

CONCLUSIONS

5alpha,3alpha-A and 5beta,3alpha-A have anticonvulsant properties. Although of low potency, the steroids are present in high abundance and could represent endogenous modulators of seizure susceptibility.

Nongenomic androgen activation of phosphatidylinositol 3-kinase/Akt signaling pathway in MC3T3-E1 osteoblasts

Androgens have important effects on the bone metabolism. However, the effect and mechanism of androgen action on the osteoblasts remains unknown. Here we showed that androgens increase phosphorylation and nuclear translocation of Akt. siRNA-AR prevented androgen-induced Akt activation in MC3T3-E1 cells. This suggests that nongenomic androgen activation of Akt is mediated by androgen receptor in osteoblasts.

INTRODUCTION

Androgens have important effects on the human skeleton in both males and females. However, the mechanism of androgen action on bone metabolism remains unknown. The aims of this study were to determine the effect and mechanism of androgen action on the osteoblast cells.

MATERIALS AND METHODS

Here we showed that 5alpha-dihydrotestosterone (DHT) accelerates cell growth of the MC3T3-E1 cell line in a time- and dose-dependent manner. The specific phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294002 and kinase-deficient Akt mutant can repress the androgen effect on MC3T3-E1 cells. Western blot analysis showed that DHT, 17beta-estradiol, and testosterone (T) induce a rapid and transient phosphorylation of Akt in MC3T3-E1 cells. This activation reached to a plateau after 15 minutes and gradually diminished after 60 minutes of DHT treatment.

RESULTS

Fluorescence microscopy showed a distinct increase in immunostaining intensity in the nuclear interior after androgen treatment but no change in the subcellular distribution of Akt when the cells were pretreated with hydroxyflutamide (HF) or LY294002. In addition, small interfering RNA against androgen receptor (siRNA-AR) prevented DHT-induced Akt phosphorylation and cell growth.

CONCLUSION

These findings represents the first physiological finding to indicate how steroid hormones such as androgens can mediate the nuclear localization of Akt/PKB in osteoblasts that has previously mainly been linked to growth factor-induced events occurring at the plasma membrane level.

Biochemical characterization of a membrane androgen receptor in the ovary of the atlantic croaker (Micropogonias undulatus)

Membrane androgen receptors have been biochemically characterized in only a few vertebrate species to date. Therefore, the purpose of the current study was to comprehensively investigate the binding characteristics of a putative membrane androgen receptor in the ovary of the teleost, Atlantic croaker (Micropogonias undulatus). Specific androgen binding to an ovarian plasma membrane fraction was demonstrated using a radioreceptor assay protocol consisting of a short-term incubation with [(3)H]testosterone (T) and subsequent filtration of bound steroid from free steroid. Saturation and Scatchard analyses of T binding to an ovarian plasma membrane fraction indicated the presence of a single, high-affinity (K(d) = 15.32 +/- 2.68 nM [mean +/- SEM]), low-capacity (B(max) = 2.81 +/- 0.31 pmol/mg protein), androgen-binding site. Specific androgen binding to the receptor was readily displaceable, and the association and dissociation kinetics were rapid (half-time = 3.7 +/- 1.7 and 4.7 +/- 0.2 min, respectively). Competitive binding assays showed that 5alpha-dihydrotestosterone, T, and 11-ketotestosterone had relative binding affinities (RBAs) of 193%, 100%, and 13%, respectively, whereas none of the C(18) or C(21) steroids tested bound with high affinity except for progesterone (RBA = 191%). This androgen-binding moiety with high affinity for progesterone is unlikely to mediate the physiological actions of progestins in croaker, because it has low binding affinity for fish progestin hormones. Androgen-binding sites were also detected in membrane fractions of the brain, liver, kidney, and drumming muscle, whereas little or no binding was detected in the trunk muscle, heart, gills, or intestine. Receptor levels increased 10-fold during ovarian recrudescence, reaching maximum levels in fully mature ovaries, which suggests a likely physiological role for this receptor during the reproductive cycle of female croaker. It is concluded that the androgen-binding moiety identified in the plasma membrane fraction of Atlantic croaker ovarian tissue fulfils all the criteria for its designation as a steroid receptor.

The vasodepressor effect of androgens in pithed rats: potential role of calcium channels

Estrogens induce vasodilatation and/or hypotension in several experimental models, probably by a blockade of calcium currents. However, very little is known about the potential cardiovascular effects of androgens. We have previously shown that 5 beta-reduced androgens are more potent vasorelaxants than their precursors (delta 4-3 keto), 5-reduced progestins and 17beta-estradiol. The present study set out to investigate if this vasorelaxant effect of 5-reduced androgens is operative in vivo in the analysis of the potential vasodepressor effect of these compounds in vagosympathectomized, pithed rats. After increasing diastolic blood pressure (DBP) by a continuous infusion of norepinephrine (0.059 micromol x kg(-1)min(-1)), i.v. bolus injections of 3 alpha-hydroxy-5 beta-androstan-17-one (etiocholanolone), 5 beta-dihydrotestosterone (5 beta-DHT), and its isomer 5 alpha-dihydrotestosterone (5 alpha-DHT) (5-25 micromol x kg(-1) each) produced, separately, dose-dependent vasodepressor responses. These responses were biphasic: an immediate fall in DBP (reaching the nadir within 1.7 min) was followed by a further slow decrease that reached a maximum between 80 and 100 min after steroid administration. The order of potency of androgens in decreasing DBP was: 5 beta-DHT>5 alpha-DHT=etiocholanolone for the short-lasting response and 5 alpha-DHT>5 beta-DHT>or=etiocholanolone for the longer lasting response. Importantly, the same doses of these compounds produced no significant changes in heart rate. Moreover, 5 beta-DHT significantly antagonized the vasopressor responses to methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluromethylphenyl)-pyridine-5-carboxylate (Bay K 8644) with a blocking profile similar to that of nifedipine (NIF). This finding suggests that a blockade of voltage-operated calcium channels may be involved in androgen-induced hypotension.

The roles of androgen receptors and androgen-binding proteins in nongenomic androgen actions

The biological activity of testosterone and dihydrotestosterone is thought to occur predominantly through binding to the androgen receptor (AR), a member of the nuclear receptor superfamily that functions as a ligand-activated transcription factor. However, androgens have also been reported to induce the rapid activation of kinase-signaling cascades and modulate intracellular calcium levels. These effects are considered to be nongenomic because they occur in cell types that lack a functional AR, in the presence of inhibitors of transcription and translation, or are observed to occur too rapidly to involve changes in gene transcription. Such nongenomic effects of androgens may occur through AR functioning in the cytoplasm to induce the MAPK signal cascade. In addition, androgens may function through the sex hormone binding globulin receptor and possibly a distinct G protein-coupled receptor to activate second messenger signaling mechanisms. The physiological effect of nongenomic androgen action has yet to be determined. However, it may ultimately contribute to regulation of transcription factor activity, including mediation of the transcriptional activity of AR.

The role of neurosteroids and non-genomic effects of progestins and androgens in mediating sexual receptivity of rodents

Progestins and androgens modulate sexual receptivity in rodents, in part through mechanisms independent of traditional intracellular steroid receptors. Progesterone (PROG) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) facilitates lordosis but has different actions in these brain areas. Primarily using lordosis in rodents as an in vivo experimental model, we have examined the effects that progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that PROG's actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alters lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with PROG's metabolism to, or the biosynthesis of, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG or allopregnanolone), the most effective endogenous GBR agonist, in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhances neurosteroid production, by infusions of an MBR agonist to the VTA enhances lordosis. 3alpha,5alpha-TH PROG is increased in the midbrain of mated>proestrous>diestrous rodents. These data suggest that in the VTA, PROG may facilitate lordosis following metabolism to and/or biosynthesis of 3alpha,5alpha-TH PROG, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents. The 3alpha-hydroxysteroid oxidoreduced metabolite of dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol), is important for termination of sexual receptivity in rodents and has these effects in the absence of functional intracellular androgens receptors. As well, altering GBR function in the hypothalamus can influence 3alpha-androstanediol's inhibition of sexual receptivity. Through actions in the hypothalamus that are independent of intracellular androgen receptors but involving GBRs, 3alpha-androstanediol inhibits lordosis. These findings suggest that the PROG metabolite and pregnane neurosteroid, 3alpha,5alpha-TH PROG, and the testosterone metabolite and androstane neurosteroid, 3alpha-androstanediol, can have proximate influences on lordosis that is via nonclassical actions at intracellular steroid receptors.

Influence of gender and brain region on neurosteroid modulation of GABA responses in rats

Neuroactive steroid derivatives of progesterone, testosterone and glucocorticoids can alter physiological responses to gamma-aminobutyric acid (GABA), apparently through direct, non-steroid receptor mechanisms. The present study examined gender-related differences and regional variations in the ability of tetrahydrodeoxycorticosterone (THDOC), 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha-5alpha-THP, tetrahydroprogesterone), androsterone, and dihydroandrosterone (DHA) to alter physiological GABA responses. Steroid modulation of GABA-activated 36chloride influx into microsac preparations from cortex, hippocampus, amygdala, cerebellum and hypothalamus-preoptic area in adrenalectomized-gonadectomized rats of both sexes were tested. The effects of THDOC and 3alpha-5alpha-THP were also examined in groups of intact male and female rats. All four steroids increased GABA-activated chloride influx, although the maximal enhancement in GABA responses differed significantly among brain regions. The rank order of maximal THDOC and 3alpha-5alpha-THP effects was hippocampus > cortex approximately amygdala > hypothalamus-preoptic area approximately cerebellum. Regional differences in potentiation of GABA responses were seen with androsterone, but not dihydroandrosterone. The rank order of androgenic potentiation of GABA responses was amygdala approximately hippocampus > cortex approximately HPA > cerebellum. Slight gender-related differences in responses to steroids were seen with THDOC, with males showing greater maximal enhancement of GABA responses with THDOC than females in the amygdala and hypothalamus-preoptic area. Since sex differences were observed with the glucocorticoid derivative THDOC, but not the progesterone derivative 3alpha-5alpha-THP or androgenic steroids, it appears neuroactive steroid modulation of GABA responses can be differentially affected by the hormonal milieu in a regionally-specific manner.

Behavioral effects of 3 alpha-androstanediol. II: Hypothalamic and preoptic area actions via a GABAergic mechanism

We investigated whether 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-androstanediol; 3 alpha-Diol), a neurosteroid whose effects are primarily inhibitory to sexual behavior, may act through interactions with gamma-aminobutyric acid (GABA) receptor complexes (GBRs) in the medial basal hypothalamus (MBH) and the preoptic area (POA). In Experiment (Exp.) 1, ovariectomized (ovx) rats were implanted with bilateral guide cannulae aimed above the MBH and were later treated with 17 beta-estradiol (E2, 2 injections of 1 microgram/0.2 ml in 10% ethanol) and either 3 alpha-Diol (3.0 mg/kg, s.c.) or vehicle. Progesterone (0.5 mg, s.c.) was given 24 h after the first E2 injection and a pre-test for lordosis responsiveness was carried out 4 h later. The GABAA agonist, muscimol (50 ng), then was infused into the MBH and rats were tested 10, 30 and 60 min later. Muscimol infusion facilitated lordosis behavior in vehicle-treated controls, but 3 alpha-Diol-treated animals failed to show this facilitation. To ascertain whether 3 alpha-Diol would also prevent muscimol's action in the POA, a site in which muscimol inhibits, rather than facilitates, sexual receptivity, ovx animals in Exp.2 were implanted with bilateral guide cannulae aimed above the POA and were treated with E2, 3 alpha-Diol, and P and infused and tested as in Exp. 1. Muscimol and 3 alpha-Diol each significantly inhibited receptivity; when they were combined, the inhibition was more pronounced. In Exp. 3, POA infusions of the GABAA antagonist, bicuculline, counteracted muscimol's and 3 alpha-Diol's inhibition of sexual behavior. In Exp. 4, in vitro treatment of POA and MBH membrane fractions with 3 alpha-Diol (30 microM) enhanced maximal [3H]muscimol binding without altering the affinity of the binding sites for the agonist. These data suggest that 3 alpha-Diol inhibits E2 and progestin-induced lordosis behavior via actions at the GBR in both the MBH and POA.

Emerging diversities in the mechanism of action of steroid hormones

The classical genomic action of steroid hormones acting through intracellular receptors is well recognized. Within this concept of action, questions regarding the ultimate fate of the hormone and lack of a tight correlation between tissue uptake and biological activity with receptor binding remain unanswered. Evidence has accumulated that steroid hormones can exert non-classical action that is characterized by rapid effect of short duration. In most of these cases, the hormone effects occurs at the membrane level and is not associated with entry into the cell. The possible mechanisms for these non-classical actions are: (a) changes in membrane fluidity; (b) steroid hormone acting on receptors on plasma membranes; (c) steroid hormones regulating GABAA receptors on plasma membranes; and (d) activation of steroid receptors by factors such as EGF, IGF-1 and dopamine. Data have also been obtained indicating that receptor-mediated insertion of steroid hormones into DNA may take place with the steroid acting as a transcription factor. These new proposed mechanism of action of steroid hormones should not be viewed as a challenge to the classical mechanism. These diverse modes of action provide for an integrated action of hormones which may be rapid and of short duration or prolonged to address the physiological needs of the individual.

Effect of 5 alpha-dihydrotestosterone and flutamide on the facilitation of lordosis by LHRH and naloxone in estrogen-primed female rats

Although 5 alpha-dihydrotestosterone (DHT) is a potent inhibitor of lordosis behavior in ovariectomized estrogen-primed female rats, the mechanism(s) by which this steroid has this action is unknown. The present experiments sought to determine whether DHT inhibits lordosis by preventing the known facilitatory actions of luteinizing hormone-releasing hormone (LHRH), naloxone, and Substance P on lordosis. Lordosis behavior was examined in ovariectomized, estrogen-primed rats prior to or 30, 60, 90, and 180 min following intracerebroventricular (ICV) infusion of LHRH (500 ng), naloxone (1 microgram). Substance P (1 microgram), or saline and 0.01 N acetic saline vehicles, and the effects of DHT (2.5 mg/rat) following similar treatment were examined. In Experiment 1, LHRH and naloxone increased lordosis within 30 min after infusion, while Substance P and the saline or acetic saline vehicles had no effect. Treatment with DHT in combination with estrogen prevented the facilitation of lordosis by LHRH and naloxone. In Experiment 2, ovariectomized, estrogen-primed females shown to be responsive to LHRH during a first screening test were tested for lordosis after receiving either DHT or DHT in combination with the androgen receptor antagonist, Flutamide (7.5 mg/injection x 3). Again, DHT prevented the facilitatory action of LHRH; however, Flutamide did not counteract that effect. In Experiment 3, Flutamide did not counteract the inhibitory effect of DHT on estrogen and progesterone-induced lordosis. These results demonstrate that the inhibitory effect of DHT cannot be overridden by neuroactive peptides which themselves stimulate receptivity. It seems unlikely that DHT inhibits lordosis either by interfering with the behavioral action of these peptides or by activation of the androgen receptor.

Dehydroepiandrosterone sulfate improves memory in aging mice

Middle-aged (18 month old) and old (24 month old) mice showed poorer retention of footshock active avoidance training (FAAT) than young mice (2 month old). Immediate post-training subcutaneous injection of dehydroepiandrosterone sulfate (DHEAS) improved retention of FAAT in middle-aged and old mice to the high levels observed in young mice. DHEAS, a major naturally occurring adrenal steroid that decreases in blood serum with age, could be rate-limiting in achievement of retention of learning.

Modulatory action of 5-reduced androgens and progestins on the excitability of CNS and smooth muscle

A hypothesis is proposed for the physiological role of the many 5 alpha and 5 beta-reduced metabolites of both testosterone and progesterone. The effects of 5-reduced steroids are observed mostly in excitable tissues. The outstanding effects are depression of neuronal activity, inhibition of neurotransmitters and smooth muscle relaxation. A clear chemical-structure-biological-activity relationship is observed. Thus, 5 beta-progestins are the most prominent, whereas 5 alpha-3-keto compounds are practically ineffective. An intermediate effect is observed with the delta 4 precursors and compounds with the configuration 3 alpha-hydroxy-5 alpha. Membranal stabilization and a Ca2+ antagonism are proposed as mechanisms of action. The main conclusion is that testosterone and progesterone are pre-hormones in the membranal effects of 5-reduced steroids. Likewise, these compounds participate in the cellular control of calcium influx, thereby modulating excitability in general.