Androgen receptors in gonadotrophs in pituitary cultures from adult male monkeys and rats

Organizational Effects of Estrogens and Androgens on Estrogen and Androgen Receptor Expression in Pituitary and Adrenal Glands in Adult Male and Female Rats

Sex steroid hormones, such as androgens and estrogens, are known to exert organizational action at perinatal periods and activational effects during adulthood on the brain and peripheral tissues. These organizational effects are essential for the establishment of biological axes responsible for regulating behaviors, such as reproduction, stress, and emotional responses. Estradiol (E2), testosterone, and their metabolites exert their biological action through genomic and non-genomic mechanisms, bounding to canonical receptors, such as estrogen receptor (ER)α, ERβ, and androgen receptor (AR) or membrane receptors, such as the G protein-coupled estrogen receptor (GPER), respectively. Expression of ERs and AR was found to be different between males and females both in the brain and peripheral tissues, suggesting a sex-dependent regulation of their expression and function. Therefore, studying the ERs and AR distribution and expression levels is key to understand the central and peripheral role of sex steroids in the establishment of sex-specific behaviors in males and females. We investigated the organizational effects of estrogens and androgens in the pituitary and adrenal glands of adult male and female rats. For this, selective blockade of AR with flutamide or 5α-reductase with finasteride or aromatase with letrozole during the first 5 days of life has been performed in male and female pups and then quantification of ERs and AR expression in both glands has been carried out in adulthood. Data show that inhibition of dihydrotestosterone (DHT) and E2 production during the first five postnatal days mainly decreases the ER expression in male to female values and AR expression in female to male levels in the pituitary gland and increases AR expression in female to male levels in the adrenal gland. In contrast, blocking the action of androgens differentially modulates the ERs in males and females and decreases AR in both males and females in both glands. Altogether, the results suggest that neonatal modifications of the androgen and estrogen pathways can potentially lead to permanent modifications of the neuroendocrine functions of the pituitary and adrenal glands in the adulthood of both sexes.

Androgen Suppresses In Vivo and In Vitro LH Pulse Secretion and Neural Kiss1 and Tac2 Gene Expression in Female Mice

Androgens can affect the reproductive axis of both sexes. In healthy women, as in men, elevated exogenous androgens decrease gonad function and lower gonadotropin levels; such circumstances occur with anabolic steroid abuse or in transgender men (genetic XX individuals) taking androgen supplements. The neuroendocrine mechanisms by which endogenous or exogenous androgens regulate gonadotropin release, including aspects of pulsatile luteinizing hormone (LH) secretion, remain unknown. Because animal models are valuable for interrogating neural and pituitary mechanisms, we studied effects of androgens in the normal male physiological range on in vivo LH secretion parameters in female mice and in vitro LH secretion patterns from isolated female pituitaries. We also assessed androgen effects on hypothalamic and gonadotrope gene expression in female mice, which may contribute to altered LH secretion profiles. We used a nonaromatizable androgen, dihydrotestosterone (DHT), to isolate effects occurring specifically via androgen receptor (AR) signaling. Compared with control females, DHT-treated females exhibited markedly reduced in vivo LH pulsatility, with decreases in pulse frequency, amplitude, peak, and basal LH levels. Correlating with reduced LH pulsatility, DHT-treated females also exhibited suppressed arcuate nucleus Kiss1 and Tac2 expression. Separate from these neural effects, we determined in vitro that the female pituitary is directly inhibited by AR signaling, resulting in lower basal LH levels and reduced LH secretory responses to gonadotropin-releasing hormone pulses, along with lower gonadotropin gene expression. Thus, in normal adult females, male levels of androgen acting via AR can strongly inhibit the reproductive axis at both the neural and pituitary levels.

Immunohistomorphometric Changes of The Pituitary Gonadotropic Cells After Testosterone Application in a Rat Model of the Andropause

Andropause, the culminating phase of male ageing, is characterized by deregulation of the hypothalamic-pituitarygonadal axis and low circulating free testosterone. The aim of this study was to investigate the immunohistomorphometric characteristics of the pituitary gonadotropic i.e. follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) producing cells after testosterone application in a rat model of the andropause. Middle-aged Wistar rats were divided into orchidectomized (ORX; n=8) and testosterone treated orchidectomized (ORX+T; n=8) groups. Testosterone propionate (5 mg/kg b.m./day) was administered for three weeks, while the ORX group received the vehicle alone. Immunohistochemically stained FSH and LH cells underwent morphometric and optical density-related analysis, while circulating concentrations of the sex steroids were measured by immunoassays. Serum concentrations of testosterone and estradiol were significantly (p<0.05) increased by 24 and 2.7 fold respectively, compared to the ORX group. The volume of FSH and LH cells was significantly (p<0.05) decreased by 51.3% and 56.6% respectively, in comparison with ORX rats. Relative volume density of FSH and LH cells was also significantly (p<0.05) decreased by 54.0% and 72.8% respectively, compared to the ORX group. Results related to the optical density of gonadotropic cells (reflecting their hormonal content) were in line with the morphometric findings i.e. this parameter of FSH and LH cells was significantly (p<0.05) decreased by 25.7% and 16.2% respectively, in comparison with ORX rats. Conclusion: In conclusion, applied testosterone increased the serum concentrations of sex steroids, as well as it decreased morphometric parameters and optical density of gonadotropic cells in ORX rats.

Effect of androgen on Kiss1 expression and luteinizing hormone release in female rats

Hyperandrogenic women have various grades of ovulatory dysfunction, which lead to infertility. The purpose of this study was to determine whether chronic exposure to androgen affects the expression of kisspeptin (ovulation and follicle development regulator) or release of luteinizing hormone (LH) in female rats. Weaned females were subcutaneously implanted with 90-day continuous-release pellets of 5α-dihydrotestosterone (DHT) and studied after 10 weeks of age. Number of Kiss1-expressing cells in both the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) was significantly decreased in ovary-intact DHT rats. Further, an estradiol-induced LH surge was not detected in DHT rats, even though significant differences were not observed between DHT and non-DHT rats with regard to number of AVPV Kiss1-expressing cells or gonadotrophin-releasing hormone (GnRH)-immunoreactive (ir) cells in the presence of high estradiol. Kiss1-expressing and neurokinin B-ir cells were significantly decreased in the ARC of ovariectomized (OVX) DHT rats compared with OVX non-DHT rats; pulsatile LH secretion was also suppressed in these animals. Central injection of kisspeptin-10 or intravenous injection of a GnRH agonist did not affect the LH release in DHT rats. Notably, ARC Kiss1-expressing cells expressed androgen receptors (ARs) in female rats, whereas only a few Kiss1-expressing cells expressed ARs in the AVPV. Collectively, our results suggest excessive androgen suppresses LH surge and pulsatile LH secretion by inhibiting kisspeptin expression in the ARC and disruption at the pituitary level, whereas AVPV kisspeptin neurons appear to be directly unaffected by androgen. Hence, hyperandrogenemia may adversely affect ARC kisspeptin neurons, resulting in anovulation and menstrual irregularities.

Localization of Fertility Factor SP22 to Specific Cell Types Within the Anterior Pituitary Gland

Sperm protein 22 (SP22) was recently identified in the anterior pituitary gland (AP) of male Golden Syrian hamsters using ion trap mass spectrometry. SP22 has been implicated in apoptosis, androgen receptor function, fertility, and ontogeny of early-onset Parkinson's disease. However, the role of SP22 in the pituitary has not been investigated. We cloned the cDNA for full-length SP22 from AP and posterior lobe (posterior pituitary and intermediate lobe) of the pituitary gland in adult male rats and Golden Syrian hamsters, confirming the presence of SP22 mRNA in the AP and posterior lobe. Because gonadal steroids are important regulators of AP function, and SP22 is associated with androgen receptor function, we used Western blots to compare SP22 in the AP of intact and orchidectomized male rats given placebo or a low or high dose of testosterone. SP22 did not differ with treatment, indicating that AP SP22 concentration was not regulated by testosterone. To localize SP22 to specific cells of the AP, mirror-image paraffin sections were labeled against SP22 and either luteinizing hormone (LH)β, thyroid-stimulating hormone (TSH)β, prolactin, adrenocorticotropic hormone (ACTH), or growth hormone (GH) using peroxidase-conjugated secondary antibody. Additional sections were colabeled with SP22 and one of the AP hormones using fluorescent secondary antibodies. SP22 colocalized in somatotropes and thyrotropes in rat and hamster. We identified SP22 in a small percentage of corticotropes, gonadotropes, and lactotropes. This is the first report that SP22 mRNA is present specifically in the AP, and SP22 is localized primarily in somatotropes and thyrotropes. SP22 may help regulate AP function and be particularly important for the control of GH and TSH secretion.

Pituitary androgen receptor signalling regulates prolactin but not gonadotrophins in the male mouse

Production of the androgen testosterone is controlled by a negative feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. Stimulation of testicular Leydig cells by pituitary luteinising hormone (LH) is under the control of hypothalamic gonadotrophin releasing hormone (GnRH), while suppression of LH secretion by the pituitary is controlled by circulating testosterone. Exactly how androgens exert their feedback control of gonadotrophin secretion (and whether this is at the level of the pituitary), as well as the role of AR in other pituitary cell types remains unclear. To investigate these questions, we exploited a transgenic mouse line (Foxg1^Cre/+; AR^fl/y) which lacks androgen receptor in the pituitary gland. Both circulating testosterone and gonadotrophins are unchanged in adulthood, demonstrating that AR signalling is dispensable in the male mouse pituitary for testosterone-dependent regulation of LH secretion. In contrast, Foxg1^Cre/+; AR^fl/y males have a significant increase in circulating prolactin, suggesting that, rather than controlling gonadotrophins, AR-signalling in the pituitary acts to suppress aberrant prolactin production in males.

4-Nitro-3-phenylphenol has both androgenic and anti-androgenic-like effects in rats

To investigate the effect of endocrine disruption of 4-nitro-3-phenylphenol (PNMPP) on immature male Wistar-Imamichi rats, the rat pituitary was exposed to PNMPP (10^–5–10^–9 M) for 24 h with or without gonadotropin-releasing hormone (GnRH) in experiment I. In addition, the Leydig cells (10^–5–10^–9 M) were exposed to PNMPP for 24 h with or without human chronic gonadotropin (hCG) in experiment II. Our results showed that the PNMPP at 10^–5–10^–7 M suppressed follicle-stimulating hormone (FSH) and luteinizing hormone (LH) productions from GnRH-stimulated pituitary cells. At the same time, PNMPP 10^–5–10^–7 M induced an increase in testosterone production from the Leydig cells treated with or without hCG. Based on our results, it can be concluded that that PNMPP might have both androgen agonist action by decreasing FSH and LH production in the pituitary and anti-androgenic action by increasing testosterone production in the Leydig cell.

Dopamine-2 receptor activation suppresses PACAP expression in gonadotrophs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed at a high level in the fetal pituitary and decreases profoundly between embryonic day 19 and postnatal day 1 (PN1), with a further decrease from PN1 to PN4. In this series of experiments, we investigated the hypothesis that dopamine 2 receptor (Drd2) activation interrupts a cAMP-dependent feed-forward loop that maintains PACAP expression at a high level in the fetal pituitary. Using single-cell RT-PCR of pituitary cell cultures from newborn rats, Drd2 mRNA was identified in gonadotrophs that were also positive for PACAP mRNA. PACAP expression in pituitary cultures from embryonic day 19 rats was suppressed by the PACAP6-38 antagonist and by the Drd2 agonist bromocriptine. Increasing concentrations of bromocriptine inhibited cAMP production as well as cAMP signaling based on cAMP response element-luciferase activity, decreased PACAP promoter activity, and decreased PACAP mRNA levels in αT3-1 gonadotroph cells. Furthermore, blockade of dopamine receptors by injecting haloperidol into newborn rat pups partially reversed the developmental decline in pituitary PACAP mRNA that occurs between PN1 and PN4. These results provide evidence that dopamine receptor signaling regulates PACAP expression under physiological conditions and lend support to the hypothesis that a rise in hypothalamic dopamine at birth abrogates cAMP signaling in fetal gonadotrophs to interrupt a feed-forward mechanism that maintains PACAP expression at a high level in the fetal pituitary. We propose that this perinatal decline in pituitary PACAP reduces pituitary follistatin which permits GnRH receptors and FSH-β to increase to facilitate activation of the neonatal gonad.

Role of estrogen receptors and g protein-coupled estrogen receptor in regulation of hypothalamus-pituitary-testis axis and spermatogenesis

Male reproductive function is under the control of both gonadotropins and androgens through a negative feedback loop that involves the hypothalamus, pituitary, and testis known as hypothalamus-pituitary-gonadal axis (HPG). Indeed, estrogens also play an important role in regulating HPG axis but the study on relative contribution to the inhibition of gonadotropins secretion exerted by the amount of estrogens produced within the hypothalamus and/or the pituitary or by the amount of circulating estrogens is still ongoing. Moreover, it is known that the maintenance of spermatogenesis is controlled by gonadotropins and testosterone, the effects of which are modulated by a complex network of locally produced factors, including estrogens. Physiological effects of estrogens are mediated by the classical nuclear estrogen receptor alpha and estrogen receptor beta, which mediate both genomic and rapid signaling events. In addition, estrogens induce rapid non-genomic responses through a membrane-associated G protein-coupled estrogen receptor (GPER). Ours and other studies reported that, in the testis, GPER is expressed in both normal germ cells and somatic cells and it is involved in mediating the estrogen action in spermatogenesis controlling proliferative and/or apoptotic events. Interestingly, GPER expression has been revealed also in the hypothalamus and pituitary. However, its role in mediating estrogen rapid actions in this context is under investigation. Recent studies indicate that GPER is involved in modulating gonadotropin-releasing hormone (GnRH) release as well as gonadotropins secretion. In this review, we will summarize the current knowledge concerning the role of estrogen/estrogen receptors molecular pathways in regulating GnRH, follicle-stimulating hormone, and luteinizing hormone release at the hypothalamic and pituitary levels in males as well as in controlling specific testicular functions such as spermatogenesis, focusing our attention mainly on estrogen signaling mediated by GPER.

Sertoli cell androgen receptor expression regulates temporal fetal and adult Leydig cell differentiation, function, and population size

We recently created a mouse model displaying precocious Sertoli cell (SC) and spermatogenic development induced by SC-specific transgenic androgen receptor expression (TgSCAR). Here we reveal that TgSCAR regulates the development, function, and absolute number of Leydig cells (LCs). Total fetal and adult type LC numbers were reduced in postnatal and adult TgSCAR vs control testes, despite normal circulating LH levels. Normal LC to SC ratios found in TgSCAR testes indicate that SC androgen receptor (SCAR)-mediated activity confers a quorum-dependent relationship between total SC and LC numbers. TgSCAR enhanced LC differentiation, shown by elevated ratios of advanced to immature LC types, and reduced LC proliferation in postnatal TgSCAR vs control testes. Postnatal TgSCAR testes displayed up-regulated expression of coupled ligand-receptor transcripts (Amh-Amhr2, Dhh-Ptch1, Pdgfa-Pdgfra) for potential SCAR-stimulated paracrine pathways, which may coordinate LC differentiation. Neonatal TgSCAR testes displayed normal T and dihydrotestosterone levels despite differential changes to steroidogenic gene expression, with down-regulated Star, Cyp11a1, and Cyp17a1 expression contrasting with up-regulated Hsd3b1, Hsd17b3, and Srd5a1 expression. TgSCAR males also displayed elevated postnatal and normal adult serum testosterone levels, despite reduced LC numbers. Enhanced adult-type LC steroidogenic output was revealed by increased pubertal testicular T, dihydrotestosterone, 3α-diol and 3β-diol levels per LC and up-regulated steroidogenic gene (Nr5a1, Lhr, Cyp11a1, Cyp17a1, Hsd3b6, Srd5a1) expression in pubertal or adult TgSCAR vs control males, suggesting regulatory mechanisms maintain androgen levels independently of absolute LC numbers. Our unique gain-of-function TgSCAR model has revealed that SCAR activity controls temporal LC differentiation, steroidogenic function, and population size.

Effects of castration on androgen receptors and gonadotropins in the pituitary of adult male viscachas

The aims of the present study were to determine whether castration results in quantitative immunohistochemical changes in androgen receptors (AR), LH-immunoreactive (IR) cells and FSH-IR cells, and to analyse the colocalisation of AR and gonadotropins in the pituitary pars distalis (PD) of viscachas. Pituitaries were processed for light and electron microscopy. AR-IR, LH-IR and FSH-IR cells were detected by immunohistochemistry. In morphometric studies, the percentage of AR-IR, LH-IR, FSH-IR, LH-IR/AR-IR and FSH-IR/AR-IR cells was determined. In intact viscachas, AR were distributed throughout the PD; they were numerous at the caudal end, with intense immunostaining. LH-IR cells and FSH-IR cells were found mainly in the ventral region and at the rostral end of the PD. Approximately 45%-66% of LH-IR cells and 49%-57% of FSH-IR cells expressed AR in the different zones of the PD. In castrated viscachas, there was a significant decrease in the percentage of AR-IR, LH-IR, FSH-IR, and FSH-IR/AR-IR cells. Some pituitary cells from castrated viscachas also exhibited ultrastructural changes. These results provide morphological evidence that gonadal androgens are directly related to the immunolabelling of AR, LH and FSH. Moreover, the colocalisation of AR and FSH is most affected by castration, suggesting the existence of a subpopulation of gonadotrophs with different regulatory mechanisms for hormonal synthesis, storage and secretion.

Androgen receptor drives transcription of rat PACAP in gonadotrope cells

Gonadotropin expression is precisely regulated within the hypothalamic-pituitary-gonadal axis through the complex interaction of neuropeptides, gonadal steroids. and both gonadal- and pituitary-derived peptides. In the anterior pituitary gland, the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) modulates gonadotropin biosynthesis and secretion, acting both alone and in conjunction with GnRH. Steroid hormone feedback also influences gonadotropin expression via both direct and indirect mechanisms. Evidence from nonpituitary tissues suggests that PACAP may be a target for gonadal steroid regulation. In the present study, we show that androgen markedly stimulates rat (r) PACAP promoter-reporter activity in the LβT2 mature mouse gonadotrope cell line. 5'-Serial deletion analysis of reporter constructs identifies 2 regions of androgen responsiveness located at (-915 to -818) and (-308 to -242) of the rPACAP promoter. Androgen receptor (AR) binds directly to DNA cis-elements in each of these regions in vitro. Site-directed mutagenesis of 3 conserved hormone response element half-sites straddling the (-308 to -242) region dramatically blunts androgen-dependent PACAP promoter activity and prevents AR binding at the mutated promoter element. Chromatin immunoprecipitation demonstrates that endogenous AR binds the homologous region on mouse chromatin in LβT2 cells in both the presence and absence of androgen. These data demonstrate that androgen stimulates PACAP gene expression in the pituitary gonadotrope via direct binding of AR to a specific cluster of evolutionarily conserved hormone response elements in the proximal rPACAP gene promoter. Thus, androgen regulation of pituitary PACAP expression may provide an additional layer of control over gonadotropin expression within the hypothalamic-pituitary-gonadal axis.

Expression of androgen receptor and estrogen receptor-alpha in the developing pituitary gland of male sheep lamb

To explore the expression of androgen receptor (AR) and estrogen receptor alpha (ERα) in the developing pituitary of male lamb, we detected AR and ERα expression in the anterior pituitary of lambs aged 2-7 months old by immunohistochemistry. The results showed that both AR immunoreactivity (AR-ir) and ERα immunoreactivity (ERα-ir) were localized in the nuclei of anterior pituitary cell. The percentage of the anterior pituitary cells expressing ERα fluctuated from 8.79±0.02% to 11.80±0.04% during the examined stages, but fell significantly to the lowest level at 6 months. While the proportion of AR-ir showed significant changes, it was in 11.52±1.26% at 2 months, it firstly increased to 19.86±1.03% at 3 months, and then significantly decreased to 8.18±1.17% at 6 months (P<0.05). The expression of both AR-ir and ERα-ir were the lowest level at 6 months old. By staining for PCNA, we observed that the changes in expression of AR and ERα at different lamb ages did not result from cell proliferation of anterior pituitary cells. These results indicate that both AR and ERα are important in regulation of secretary function of anterior pituitary in sheep lamb, although the related mechanism needs to be elucidated further.

Effects of gonadotrophin-releasing hormone outside the hypothalamic-pituitary-reproductive axis

Gonadotrophin-releasing hormone (GnRH) is a hypothalamic decapeptide with an undisputed role as a primary regulator of gonadal function. It exerts this regulation by controlling the release of gonadotrophins. However, it is becoming apparent that GnRH may have a variety of other vital roles in normal physiology. A reconsideration of the potential widespread action that this traditional reproductive hormone exerts may lead to the generation of novel therapies and provide insight into seemingly incongruent outcomes from current treatments using GnRH analogues to combat diseases such as prostate cancer.

Immunoexpression of androgen receptor in the nontumorous pituitary and in adenomas

Little information is available regarding androgen receptor immunoexpression (AR) in the normal and neoplastic human pituitary. Available experimental data links it to primarily gonadotroph cells. We undertook an immunohistochemical study of 41 autopsy-derived normal glands from patients of both sexes and all ages as well as 79 fully characterized pituitary adenomas of all types, the focus being upon AR expression in normal and neoplastic gonadotrophs. Nuclear AR immunoreactivity was noted in gonadotrophs and other normal adeno- and neurohypophysial cells. In addition to its presence in 74% of gonadotroph and 55% of null cell adenomas, lesser proportions of other adenoma types (adrenocorticotropic hormone 50%, prolactin 38%, growth hormone 33%) also exhibited AR immunoreactivity. No staining of thyroid-stimulating hormone adenomas was noted. The physiologic significance of our findings remains to be explored. The literature regarding AR expression in animal and human pituitaries is reviewed.

Effects of testosterone on hormonal content and calcium-dependent basal secretion in female rat pituitary cells

In vivo and in vitro effects of elevated androgens on agonist-induced gonadotropin secretion have been addressed previously. Here we investigated the effects of testosterone on hormonal content and basal (in the absence of agonists) hormone release in pituitary lactotrophs, somatotrophs and gonadotrophs from female rats. Furthermore we tested the hypothesis that testosterone action is dependent on the pattern of spontaneous and Bay K 8644 (a L-type calcium channel agonist) -induced calcium signalling. Mixed anterior pituitary cells were cultured in steroid containing or depleted media, and testosterone (1pM to 10nM) was added for 48h. Cells were studied for their spontaneous and Bay K 8644-induced calcium signalling pattern and total hormone levels (release and hormonal content). In lactotrophs, somatotrophs and gonadotrophs testosterone did not affect the pattern of spontaneous calcium signalling. Bay K 8644-induced calcium signalling and hormone release were not affected by testosterone. In both steroid-depleted and -containing medium, testosterone inhibited prolactin (PRL), luteinizing hormone (LH) and growth hormone (GH) cellular content and release in a dose-dependent manner, with IC(50)s in a sub-nanomolar concentration range. These results indicate that testosterone inhibits basal hormone release from lactotrophs, somatotrophs and gonadotrophs without affecting intracellular calcium signalling. This action of testosterone is not dependent on the presence of other steroid hormones.

Expression of androgen receptor and its co-localization with estrogen receptor-alpha in the developing pituitary gland of sheep fetus

No information is known concerning the expression of androgen receptor (AR) and its co-localization with estrogen receptor alpha (ERalpha) in the developing pituitary of sheep fetus. In the present study, we detected AR expression and its co-localization with ERalpha in the anterior pituitary of sheep fetus from day 60 of gestation to the postnatal by dual immunochemistry. The results showed that both AR immunoreactivity (AR-ir) and ERalpha immunoreactivity (ERalpha-ir) were predominantly localized in the nuclei of LH positive gonadotropes. The cell counting results showed that the percentage of the anterior pituitary cells expressing AR fluctuated from 13.51 +/- 0.92 to 17.05 +/- 1.83% during the examined stages, but there were no significant differences between sexes and among ages examined (P > 0.05). However, the proportion of AR-ir cells containing LH markedly increased from day 60 of gestation to the neonatal (P < 0.05). The percentage of AR-ir cells expressing ERalpha-ir significantly increased from day 60 of gestation to the neonatal, respectively (P < 0.05), but no significant differences were seen between genders at each stage examined. These results indicate that both AR and ERalpha are mainly expressed in the gonadotropes of anterior pituitary gland of sheep fetuses, whereas the functions and interaction of AR and ERalpha expressions in the developing pituitary gland are required to be elucidated further.

Androgens, progestins, and glucocorticoids induce follicle-stimulating hormone beta-subunit gene expression at the level of the gonadotrope

FSH is produced by the pituitary gonadotrope to regulate gametogenesis. Steroid hormones, including androgens, progestins, and glucocorticoids, have all been shown to stimulate expression of the FSHbeta subunit in primary pituitary cells and rodent models. Understanding the molecular mechanisms of steroid induction of FSHbeta has been difficult due to the heterogeneity of the anterior pituitary. Immortalized LbetaT2 cells are a model of a mature gonadotrope cell and express the endogenous steroid receptor for each of the three hormones. Transient transfection of each receptor, along with ligand treatment, stimulates the mouse FSHbeta promoter, but induction is severely diminished using receptors that lack the ability to bind DNA, indicating that induction is likely through direct DNA binding. All three steroid hormones act within the first 500 bp of the FSHbeta promoter where six putative hormone response elements exist. The -381 site is critical for FSHbeta induction by all three steroid hormones, whereas the -197 and -139 sites contribute to maximal induction. Interestingly, the -273 and -230 sites are also necessary for androgen and progestin induction of FSHbeta, but not for glucocorticoid induction. Additionally, we find that all three receptors bind the endogenous FSHbeta promoter, in vivo, and specifically bind the -381 site in vitro, suggesting that the binding of the receptors to this element is critical for the induction of FSHbeta by these 3-keto steroid hormones. Our data indicate that androgens, glucocorticoids, and progestins act via their receptors to directly activate FSHbeta gene expression in the pituitary gonadotrope.

Stimulation of the novel estrogen receptor-alpha intronic TERP-1 promoter by estrogens, androgen, pituitary adenylate cyclase-activating peptide, and forskolin, and autoregulation by TERP-1 protein

The estrogen receptor-alpha (ERalpha) pituitary-specific variant, TERP-1, is regulated dramatically by physiological status. We examined hormonal regulation of the TERP-1 promoter in transient transfection assays in GH3 somatolactotrope cells. We found that 17beta-estradiol (E2), genistein, androgen, pituitary adenylate cyclase-activating peptide, and forskolin (FSK) all stimulated TERP-1 promoter activity, whereas progesterone had no effect. ERalpha bound to a palindromic estrogen response element (ERE) and two half-site EREs; mutation of any of these sites decreased basal expression and completely obliterated E2 stimulation. In contrast, mutation of an activator protein-1 site decreased basal and FSK-stimulated promoter activity, but not E2 or androgen stimulation. The pure antiestrogen ICI 182,780 suppressed E2 and genistein, but not FSK or androgen, stimulation. Similarly, mutation of the ERE palindrome or half-site EREs suppressed promoter stimulation by E2 and genistein, but not by androgen or FSK. Because TERP-1 levels regulate ERalpha function on model promoters, we tested TERP-1 modulation of its own and other physiological promoters. TERP-1 suppressed basal and E2-stimulated expression of its own promoter. TERP-1 suppression required the ERE regions of the promoter, and the dimerization domain of TERP-1. TERP-1 overexpression also suppressed E2 stimulation of the progesterone receptor and prolactin promoters. Thus, estrogens, androgen, and FSK can stimulate TERP-1 promoter activity, and increased TERP-1 expression modulates E2 stimulation of physiological promoters. These data suggest that TERP-1 regulation may play a significant role in modifying pituitary ERalpha responses.

Phenotypic characterization of multi-functional somatotropes, mammotropes and gonadotropes of the mouse anterior pituitary

The existence of bihormonal anterior pituitary (AP) cells co-storing growth hormone and either prolactin (mammosomatotrope) or gonadotropins (somatogonadotrope) has been described. These cells have been proposed to be involved in "paradoxical" secretion [secretion of an AP hormone induced by a non-related hypothalamic releasing factor (HRH) and transdifferentiation (a phenotypic switch between different cell types without cell division]. Here we combine calcium imaging (to assess HRH responsiveness) and multiple sequential immunoassay of the six AP hormones to perform a single-cell phenotypic study of multifunctional somatotropes, mammotropes and gonadotropes in the normal male and female mouse pituitaries. AP cell phenotypes differed from the classic view, showing multiple HRH-receptor expression and/or hormone storage. Mammosomatotropes represented only 5-6% of somatotropes and were poorly responsive to HRHs, suggesting that their contribution to paradoxical secretion should be very limited. Somatogonadotropes were present only in females and contained adrenocorticotropic hormone. They responded to growth hormone-releasing hormone but failed to respond to gonadotropin-releasing hormone (LHRH). Other polyhormonal cells identified include (1) gonadocorticotropes, restricted to females, where they make up more than 50% of all the gonadotropes and contain other AP hormones; (2) gonadomammotropes, which are present preferentially in female cells and respond to LHRH; and (3) gonadothyrotropes, which are present similarly in male and female pituitaries.

Colocalization of GH, TSH and prolactin, but not ACTH, with betaLH-immunoreactivity: evidence for pluripotential cells in the ovine pituitary

Increasing evidence suggests that multihormonal cells in the pituitary gland may be more commonplace than previously thought. This has forced us to reconsider our classical view of cell populations in the pituitary gland. Studies so far have focused almost exclusively on the rat, and there is a dearth of information on other species. Our first objective was to determine whether a subpopulation of gonadotropes also express somatotropin in the ewe, as reported in the rat. In addition, we sought to determine whether gonadotropes express any of the other known pituitary hormones. Finally, we investigated whether the stage of the estrous cycle influenced the occurrence of these pluripotential gonadotropes. We found that a small population of betaLH-immunoreactive cells also expresses immunoreactive GH, prolactin and TSH. No gonadotropes colocalized with ACTH. Significantly (P<0.001) more gonadotropes expressed GH during the luteal (10.7+/-0.4%) than the late follicular (5.4+/-0.3%) phase but there was no difference between the luteal and follicular phases in the proportion of gonadotropes expressing prolactin (follicular: 5.7+/-0.7%; luteal: 5.5+/-0.6%) or TSH (follicular: 3.1+/-0.7%; luteal: 4.2+/-0.5%). Similarly, there was a significant (P<0.05) difference in the proportion of GH-immunoreactive cells expressing betaLH immunoreactivity in the luteal (5.9+/-0.3%) and follicular (3.4+/-0.5%) phases but no difference in the proportion of prolactin- (follicular: 2.2+/-0.7%; luteal: 2.0+/-0.8%) or TSH-immunoreactive cells (follicular: 9.6+/-3.7%; luteal: 10.8+/-2.9%) expressing betaLH. The specific function of these multihormonal gonadotropes in sheep remains to be determined.

Anterior pituitary thyrotropes are multifunctional cells

Anterior pituitary (AP) contains some unorthodox multifunctional cells that store and secrete two different AP hormones (polyhormonal cells) and/or respond to several hypothalamic-releasing hormones (HRHs; multiresponsive cells). Multifunctional cells may be involved in paradoxical secretion (secretion of a given AP hormone evoked by a noncorresponding HRH) and transdifferentiation (phenotypic switch between different mature cell types without cell division). Here we combine calcium imaging (to assess responses to the four HRHs) and multiple sequential immunoassay of the six AP hormones to perform a single-cell phenotypic study of thyrotropes in normal male and female mice. Surprisingly, most of the thyrotropes were polyhormonal, containing, in addition to thyrotropin (TSH), luteinizing hormone (40-42%) and prolactin (19-21%). Thyrotropes costoring growth hormone and/or ACTH were found only in females (24% of each type). These results suggest that costorage of the different hormones does not happen at random and that gender favors certain hormone combinations. Our results indicate that thyrotropes are a mosaic of cell phenotypes rather than a single cell type. The striking promiscuity of TSH storage should originate considerable mix-up of AP hormone secretions on stimulation of thyrotropes. However, response to thyrotropin-releasing hormone was much weaker in the polyhormonal thyrotropes than in the monohormonal ones. This would limit the appearance of paradoxical secretion under physiological conditions and suggests that timing of hormone and HRH receptor expression during the transdifferentiation process is finely and differentially regulated.

Testosterone stimulates follicle-stimulating hormone beta transcription via activation of extracellular signal-regulated kinase: evidence in rat pituitary cells

This study investigated whether estradiol (E2) or testosterone (T) activate extracellular signal-regulated kinase (ERK) and calcium/calmodulin-dependent kinase II (Ca/CaMK II), as indicated by enzyme phosphorylation in rat pituitaries. In vivo studies used adult female rats given E2, T, or empty silastic capsules (vehicle controls). Twenty-four hours later, the rats were given a single pulse of GnRH (300 ng) or BSA-saline (to controls) and killed 5 min later. GnRH stimulated a two- to three-fold rise in activated Ca/CaMK II, and E2 and T had no effect on Ca/CaMK II activation. In contrast, both GnRH and T stimulated threefold increases in ERK activity, with additive effects seen following the combination of GnRH+T. E2 had no effect on ERK activity. In alpha T3 clonal gonadotrope cells, dihydrotestosterone did not activate ERK alone but enhanced and prolonged the ERK responses to GnRH, demonstrating direct effects on the gonadotrope. Thus, the ERK response to GnRH plus androgen was enhanced in both rat pituitary and alpha T3 cells. In vitro studies with cultured rat pituitary cells examined the effect of GnRH+/-T in the presence of the mitogen-activated protein (MAP) kinase kinase inhibitor, PD-098059 (PD). Results showed that PD suppressed ERK activational and FSH beta transcriptional responses to T. These findings suggest that one site of T regulation of FSH beta transcription is through the selective stimulation of the ERK pathway.

Intra-pituitary regulation of gonadotrophs in male rodents and primates

Paracrine and autocrine regulation is well established in many organs including the gonads, but the notion of communication among pituitary cells is a relatively new concept. The FSH-beta and GnRH-receptor genes are up-regulated by pituitary activin and down-regulated by pituitary follistatin, and circulating inhibin disrupts this local regulation by functioning as an endogenous competitor of the activin receptor. Activin and follistatin production by folliculostellate cells may play a central role in these responses. alpha-Subunit expression is maintained at high levels in the absence of GnRH through unknown mechanisms. There is evidence that the intra-pituitary regulation of FSH-beta and GnRH-receptor gene expression may activate pubertal maturation in male rats. Finally, there are marked differences in follistatin expression and its regulation by GnRH and androgens in male primates and rats that appear to explain species differences in the differential secretion of FSH and LH, although the physiological significance of these differences is not yet known.

Regulation of luteinizing hormone-beta and follicle-stimulating hormone (FSH)-beta gene transcription by androgens: testosterone directly stimulates FSH-beta transcription independent from its role on follistatin gene expression

The gonadotropin beta-subunit mRNAs are differentially regulated by androgens. Testosterone (T) suppresses LH-beta and increases FSH-beta. We aimed to determine whether androgens regulate LH-beta and FSH-beta transcription [as measured by changes in primary transcript (PT)] and to determine whether androgens act directly on FSH-beta or via the intrapituitary activin/follistatin (FS) system. In castrate + GnRH antagonist-treated rats, T increased FSH-beta PT between 3 and 48 h. In contrast, T suppressed LH-beta PT. The increases in FSH-beta mRNA and PT were associated with reduced FS mRNA. Activin betaB mRNA was modestly suppressed. The increase in FSH-beta PT after T was androgen specific. Both T and dihydrotestosterone (DHT) increased FSH-beta PT 2-fold and decreased both FS and betaB mRNA. Estradiol suppressed FSH-beta PT 3-fold and had no effect on FS or betaB mRNAs. LH-beta PT was suppressed by DHT. To determine whether T stimulation of FSH-beta PT reflected a decrease in pituitary FS, we gave androgen in the presence of exogenous FS in vitro. T and DHT increased FSH-beta PT 2- to 3-fold. FS alone decreased FSH-beta PT 40% but did not diminish the increase FSH-beta PT in response to T. T, DHT, and FS did not affect FS mRNA, betaB mRNA, or LH-beta PT. In conclusion, androgens acting directly on the pituitary increase FSH-beta and decrease LH-beta transcription. The increase in FSH-beta PT in response to T was androgen specific and occurs in the presence of excess FS, suggesting that T stimulates FSH-beta transcription independently of modulation of FS.

Evidence that gonadotropin-releasing hormone (GnRH) II stimulates luteinizing hormone and follicle-stimulating hormone secretion from monkey pituitary cultures by activating the GnRH I receptor

Mammalian gonadotropin-releasing hormone (GnRH) I is the neuropeptide that regulates reproduction. In recent years, a second isoform of GnRH, GnRH II, and its highly selective type II GnRH receptor were cloned and identified in monkey brain, but its physiological function remains unknown. We sought to determine whether GnRH II stimulates LH and FSH secretion by activating specific receptors in primary pituitary cultures from male monkeys. Dispersed pituitary cells were maintained in steroid-depleted media and stimulated with GnRH I and/or GnRH II for 6 h. Cells were also treated with Antide (Bachem, King of Prussia, PA), a GnRH I antagonist, to block gonadotropin secretion. In monkey as well as rat pituitary cultures, GnRH II was a less effective stimulator of LH and FSH secretion than was GnRH I. In both cell preparations, Antide completely blocked LH and FSH release provoked by GnRH II as well as GnRH I. Furthermore, the combination of GnRH I and GnRH II was no more effective than either agonist alone. These results indicate that GnRH II stimulates FSH and LH secretion, but they also imply that this action occurs through the GnRH I receptor. The GnRH II receptors may have a unique function in the monkey brain and pituitary other than regulation of gonadotropin secretion.

Multifunctional cells of mouse anterior pituitary reveal a striking sexual dimorphism

The existence of cells storing and secreting two different anterior pituitary (AP) hormones (polyhormonal cells) or responding to several hypothalamic releasing hormones (HRHs) (multiresponsive cells) has been reported previously. These multifunctional cells could be involved in paradoxical secretion (AP hormone secretion evoked by a non-corresponding HRH) and transdifferentiation (phenotypic switch between mature cell types without cell division). Despite their putative physiological relevance, a comprehensive characterization of multifunctional AP cells is lacking. Here we combine calcium imaging (to assess responses to the four HRHs) and multiple sequential immunoassay of the six AP hormones in the same individual cells to perform a complete phenotypic characterization of mouse AP cells. Polyhormonal and multiresponsive cells were identified within all five AP cell types. They were scarce in the more abundant cell types, somatotropes and lactotropes, but quite frequent in corticotropes and gonadotropes. Cells with mixed phenotypes were the rule rather than the exception in thyrotropes, where 56-83 % of the cells stored two to five different hormones. Multifunctional AP cells were much more abundant in females than in males, indicating that the hormonal changes associated with the sexual cycle may promote transdifferentiation. As the phenotypic analysis was performed here after stimulation with HRHs, the fraction of polyhormonal cells might have been underestimated. With this limitation, the polyhormonal cells detected here responded to the HRHs less than the monohormonal ones, suggesting that they might contribute less than expected a priori to paradoxical secretion. Overall, our results reveal a striking sexual dimorphism, the female pituitary being much more plastic than the male pituitary.