Evidence that immature rat liver is capable of participating in steroidogenesis by expressing 17alpha-hydroxylase/17,20-lyase P450c17

Enhanced expression of Cyp17a1 and production of DHEA-S in the liver of late-pregnant rats

Cytochrome P450 17A1 (CYP17A1) catalyzes two enzymatic reactions in the biosynthesis of dehydroepiandrosterone (DHEA) from pregnenolone. In pregnant humans, the adrenal gland is responsible for DHEA biosynthesis, which is then sulfated by SULT2A1 and released into the bloodstream. This sulfated DHEA is subsequently taken up by the placenta and deconjugated to serve as a precursor for estrogen biosynthesis. The expression of Cyp17a1 is regulated by methylation, typically showing marked interspecies differences, including repression of Cyp17a1 expression in the adrenal gland of rodents. This study focused on the liver, an extragonadal steroidogenic organ showing active sulfate conjugation, as a site for DHEA-sulfate (DHEA-S) biosynthesis during pregnancy in rodents, rather than the adrenal glands. Cyp17a1 expression in rat liver was significantly lower than in the testis, with no differences between sexes. However, Cyp17a1 expression increased significantly before parturition (gestational days [GD] 19-21) compared to late pregnancy (GD 15-18). The Sult2a family were expressed in the livers of both pregnant and non-pregnant rats. We also observed increased DHEA and DHEA-S levels in the liver of pregnant rats before parturition compared to non-pregnant rats, with DHEA-S concentrations being significantly higher at GD 19-21 than at days 15-18. These findings suggest that increased expression of Cyp17a1 in the last trimester enhances DHEA synthesis in the liver, and that DHEA is quickly conjugated by Sult2a. In rodents, the liver may be involved in DHEA-S biosynthesis before parturition, compensating for the repression of Cyp17a1 in the adrenal glands.

Effects of PM2.5 and high-fat diet interaction on blood glucose metabolism in adolescent male Wistar rats: A serum metabolomics analysis based on ultra-high performance liquid chromatography/mass spectrometry

Fine particulate matter (PM_2.5) and high-fat diet (HFD) are known to contribute to blood glucose metabolic disorders. However, limited research has investigated the combined impact of PM_2.5 and HFD on blood glucose metabolism. This study aimed to explore the joint effects of PM_2.5 and HFD on blood glucose metabolism in rats using serum metabolomics and to identify involved metabolites and metabolic pathways. The 32 male Wistar rats were exposed to filtered air (FA) or PM_2.5 (real-world inhaled, concentrated PM_2.5, 8 times the ambient level, ranging from 131.42 to 773.44 μg/m³) and fed normal diet (ND) or HFD for 8 weeks. The rats were divided into four groups (n = 8/group): ND-FA, ND-PM_2.5, HFD-FA and HFD-PM_2.5 groups. Blood samples were collected to determine fasting glucose (FBG), plasma insulin and glucose tolerance test and HOMA Insulin Resistance (HOMA-IR) index was calculated. Finally, the serum metabolism of rats was analyzed by ultra-high performance liquid chromatography/mass spectrometry (UHPLC-MS). Then we constructed the partial least squares discriminant analysis (PLS-DA) model to screen the differential metabolites, and performed pathway analysis to screen the main metabolic pathways. Results showed that combined effect of PM_2.5 and HFD caused changes in glucose tolerance, increased FBG levels and HOMA-IR in rats and there were interactions between PM_2.5 and HFD in FBG and insulin. By metabonomic analysis, the serum differential metabolites pregnenolone and progesterone, which involved in steroid hormone biosynthesis, were two different metabolites in the ND groups. In the HFD groups, the serum differential metabolites were L-tyrosine and phosphorylcholine, which involved in glycerophospholipid metabolism, and phenylalanine, tyrosine, and tryptophan biosynthesis. When PM_2.5 and HFD coexist, they may lead to more severe and complex effects on glucose metabolism by affecting lipid metabolism and amino acid metabolism. Therefore, reducing PM_2.5 exposure and controlling dietary structure are important measures for preventing and reducing glucose metabolism disorders.

Hydroxylation and lyase reactions of steroids catalyzed by mouse cytochrome P450 17A1 (Cyp17a1)

Cytochrome P450 17A1 (CYP17A1) catalyzes 17α-hydroxylation and 17,20-lyase reactions with steroid hormones. Mice contain an orthologous Cyp17a1 enzyme in the genome, and its amino acid sequence has high similarity with human CYP17A1. We purified recombinant mouse Cyp17a1 and characterized its oxidation reactions with progesterone and pregnenolone. The open reading frame of the mouse Cyp17a1 gene was inserted and successfully expressed in Escherichia coli and then purified using Ni²⁺-nitrilotriacetic acid (NTA) affinity column chromatography. Purified mouse Cyp17a1 displayed typical Type I binding titration spectral changes upon the addition of progesterone, 17α-OH progesterone, pregnenolone, and 17α-OH pregnenolone, with similar binding affinities to those of human CYP17A1. Catalytic activities for 17α-hydroxylation and 17,20-lyase reactions were studied using ultra-performance liquid chromatography (UPLC)-mass spectrometry analysis. Mouse Cyp17a1 showed cytochrome b₅ stimulation in catalysis. In comparison to human enzyme, much higher specificity constants (k_cat/K_m) were observed with mouse Cyp17a1. In the reactions of Δ4-steroids (progesterone and 17α-OH progesterone), the specificity constants were 2100 times higher than the human enzyme. The addition of cytochrome b₅ produced significant stimulation of 17,20-lyase activities of mouse Cyp17a1. Two Arg mutants of mouse Cyp17a1 (R347H and R358Q) displayed a larger decrease in 17,20-lyase reaction (from 17α-OH pregnenolone to dehydroepiandrosterone, DHEA) than 17α-hydroxylation, indicating that -as in human CYP17A1-these basic residues in mouse Cyp17a1 are important in interacting with the cytochrome b₅ protein in the lyase reactions.

Seasonal expression of P450c17 and 5α-reductase-2 in the scented gland of male muskrats (Ondatra zibethicus)

Cytochrome P450 17A1 (P450c17) is the key enzyme required for the production of androgenic sex steroids by converting progestogens to androgens. 5α-reductases are enzymes that convert testosterone (T) to dihydrotestosterone (DHT), which has a greater affinity for androgen receptors (AR) and stronger action than T. Our previous studies revealed that the scented glands of male muskrats expressed AR during the breeding and nonbreeding seasons. To further seek evidence of the activities of androgens in scented glands, the expression patterns of P450c17 and 5α-reductase 2 were investigated in the scented glands of male muskrats during the breeding and nonbreeding seasons. The weight and size of scented glands in the breeding season were significantly higher than those of the nonbreeding season. Immunohistochemical data showed that P450c17 and 5α-reductase 2 were presented in the glandular cells and epithelial cells of scented glands in both the seasons. The protein and mRNA expression of P450c17 and 5α-reductase 2 were significantly higher in the scented gland during the breeding season than those during the nonbreeding season. In addition, the levels of DHT and T in the scented gland were remarkably higher during the breeding season. Taken together, these results suggested that the scented glands of male muskrats were capable of locally synthesizing T and DHT, and T and DHT might play an important role in the scented glandular function via an autocrine or paracrine manner.

The impact of nandrolone decanoate and growth hormone on biosynthesis of steroids in rats

Growth hormone (GH) and anabolic androgenic steroids (AAS) are commonly used in sports communities. Several studies have suggested an association between GH and AAS. We have investigated the impact of GH in rats treated with nandrolone decanoate (ND). Male Wistar rats received ND (15 mg/kg) every third day during three weeks and were subsequently treated with recombinant human GH (1.0I U/kg) for ten consecutive days. Plasma samples were collected and peripheral organs (i.e. heart, liver, testis and thymus) were dissected and weighed. Concentration of thirteen endogenous steroids was measured in the rat plasma samples using high specificity LC-MS/MS methods. Seven steroids were detected and quantified, and concentrations of estrone, testosterone, and androstenedione were significantly different among the groups, while concentrations of pregnenolone, DHEA, 17-hydroxyprogesterone and corticosterone were not altered. Administration of rhGH alone altered the plasma steroid distribution, and the results demonstrated significantly increased concentrations of plasma estrone as well as decreased concentrations of testosterone and androstenedione in the ND-treated rats. Administration of rhGH to ND-pretreated rats did not reverse the alteration of the steroid distribution induced by ND. Administration of ND decreased the weight of the thymus, and addition of rhGH did not reverse this reduction. However, rhGH administration induced an enlargement of thymus. Taken together, the plasma steroid profile differed in the four groups, i.e. control, AAS, rhGH and the combination of AAS and rhGH treatment.

Cyp17a1 and Cyp19a1 in the zebrafish testis are differentially affected by oestradiol

Oestrogens can affect expression of genes encoding steroidogenic enzymes in fish gonads. However, little information is available on their effects at the protein level. In this context, we first analysed the expression of key steroidogenic enzyme genes and proteins in zebrafish testis, paying attention also to other cell types than Leydig cells. Gene expression was analysed by quantitative PCR on fluorescence-activated cell-sorting fractions coupled or not to differential plating, while protein synthesis was studied by immunohistochemistry using specific antibodies against zebrafish Cyp17a1, Cyp19a1a and Cyp19a1b. Furthermore, we have evaluated the effect of oestrogen treatment (17β-oestradiol (E(2)), 10 nM) on the localization of these enzymes after 7 and 14 days of in vivo exposure in order to study how oestrogen-mediated modulation of their expression is linked to oestrogen effects on spermatogenesis. The major outcomes of this study are that Leydig cells express Cyp17a1 and Cyp19a1a, while testicular germ cells express Cyp17a1 and both, Cyp19a1a and Cyp19a1b. As regards Cyp17a1, both protein and mRNA seem to be quantitatively dominating in Leydig cells. Moreover, E(2) exposure specifically affects only Leydig cell Cyp17a1 synthesis, preceding the disruption of spermatogenesis. The oestrogen-induced suppression of the androgen production capacity in Leydig cells is a major event in altering spermatogenesis, while germ cell steroidogenesis may have to be fuelled by precursors from Leydig cells. Further studies are needed to elucidate the functionality of steroidogenic enzymes in germ cells and their potential role in testicular physiology.

DHEA and estradiol levels in brain, gonads, adrenal glands, and plasma of developing male and female European starlings

Traditionally, sexual differentiation of the brain was thought to be driven by gonadal hormones, particularly testosterone (T). However, recent studies in songbirds suggest that other steroids may also be important. For example, dehydroepiandrosterone (DHEA) can be synthesized by the gonads, adrenal glands, and/or brain and locally metabolized into T and 17β-estradiol (E(2)). Here, we examined DHEA and E(2) levels in the brain, peripheral tissues, and plasma of wild European starlings (Sturnus vulgaris). In Study 1, samples were collected from males and females at P0 (day of hatch), P6, and P8. In Study 2, samples were collected at P4. At P0, DHEA levels in the diencephalon were higher in males than females. DHEA levels were generally high in the gonads and adrenals, and they were higher in testes than ovaries at P8. Further, E(2) levels were non-detectable in most brain samples, suggesting that DHEA was not metabolized to E(2) or that locally produced E(2) was rapidly inactivated. At P4, DHEA levels in telencephalic regions were lower in males than females. Taken together, these data suggest that sex differences in peripheral DHEA secretion and neural DHEA metabolism at specific ages during development might play a role in sexual differentiation of the songbird brain.

Cloning and expression of P450c17-I (17α-hydroxylase/17,20-lyase) in brain and ovary during gonad development in Cynoglossus semilaevis

Cytochrome P450c17 (CYP17, 17a-hydroxylase/17,20-lyase) is a critical enzyme in the production of androgens and estrogens in vertebrates. A 2,469 bp full length cDNA of P450c17-I (CYP17A1) has been isolated from the ovary of half-smooth tongue sole, Cynoglossus semilaevis which encodes 509 amino acids. Additionally, a relatively shorter cDNA (1,742 bp), a likely result of polyadenylation, was also found. The putative P450c17-I enzyme shares high sequence identity with that of the fathead minnow (73%), zebrafish (71%), the Japanese eel (70%), catfish (70%), tilapia (79%), three-spined stickleback (81%), medaka (79%), dogfish (60%), chicken (65%), rat (47%), and human (49%). Semi-quantitative RT-PCR analysis of spatial expression showed the enzyme was predominantly expressed in the ovaries and the brain. P450c17-I was also detected in the stomach, intestine, gill, spleen, kidney, and head kidney, albeit weakly. Further examination of temporal expression pattern of P450c17-I in ovary and brain revealed developmental stage-dependency. In addition to this our data on T and E2 levels further endorse the critical role of P450c17-I during shift in steroidogenesis. Based on the present study we indicate an important role for P450c17-I during ovarian development. However, further studies are needed at transcriptional regulation level for deeper insights into the physiological functions of P450c17-I.

Neurosteroid transport by the organic solute transporter OSTα-OSTβ

A variety of steroids, including pregnenolone sulfate (PREGS) and dehydroepiandrosterone sulfate (DHEAS) are synthesized by specific brain cells, and are then delivered to their target sites, where they exert potent effects on neuronal excitability. The present results demonstrate that [(3)H]DHEAS and [(3)H]PREGS are relatively high affinity substrates for the organic solute transporter, OSTα-OSTβ, and that the two proteins that constitute this transporter are selectively localized to steroidogenic cells in the cerebellum and hippocampus, namely the Purkinje cells and cells in the cornu ammonis region in both mouse and human brain. Analysis of Ostα and Ostβ mRNA levels in mouse Purkinje and hippocampal cells isolated via laser capture microdissection supported these findings. In addition, Ostα-deficient mice exhibited changes in serum DHEA and DHEAS levels, and in tissue distribution of administered [(3)H]DHEAS. OSTα and OSTβ proteins were also localized to the zona reticularis of human adrenal gland, the major region for DHEAS production in the periphery. These results demonstrate that OSTα-OSTβ is localized to steroidogenic cells of the brain and adrenal gland, and that it modulates DHEA/DHEAS homeostasis, suggesting that it may contribute to neurosteroid action.

Corticosterone and dehydroepiandrosterone in songbird plasma and brain: effects of season and acute stress

Prolonged increases in plasma glucocorticoids can exacerbate neurodegeneration. In rats, these neurodegenerative effects can be reduced by dehydroepiandrosterone (DHEA), an androgen precursor with anti-glucocorticoid actions. In song sparrows, season and acute restraint stress affect circulating levels of corticosterone and DHEA, and the effects of stress differ in plasma collected from the brachial and jugular veins. Jugular plasma is an indirect index of the neural steroidal milieu. Here, we directly measured corticosterone and DHEA in several brain regions and jugular plasma, and examined the effects of season and acute restraint stress (30 min) (n = 571 samples). Corticosterone levels were up to 10x lower in brain than in jugular plasma. In contrast, DHEA levels were up to 5x higher in brain than in jugular plasma and were highest in the hippocampus. Corticosterone and DHEA concentrations were strongly seasonally regulated in plasma but, surprisingly, not seasonally regulated in brain. Acute stress increased corticosterone levels in plasma and brain, except during the molt, when stress unexpectedly decreased corticosterone levels in the hippocampus. Acute stress increased DHEA levels in plasma during the molt but had no effects on DHEA levels in brain. This is the first study to measure (i) corticosterone or DHEA levels in the brain of adult songbirds and (ii) seasonal changes in corticosterone or DHEA levels in the brain of any species. These results highlight several critical differences between systemic and local steroid concentrations and the difficulty of using circulating steroid levels to infer local steroid levels within the brain.

Regulation of P450c17 expression in the early embryo depends on GATA factors

The enzyme P450c17 is required for glucocorticoid, sex steroid, and some neurosteroid biosynthesis. Defective human P450c17 causes sexual infantilism and 46,XY sex reversal but is compatible with life, whereas ablation of the corresponding mouse gene causes embryonic lethality at around E7. Normal mouse embryos express P450c17 protein and activity in the embryonic endoderm at E7. Adult adrenal and gonadal steroidogenesis requires steroidogenic factor-1 (SF-1), but SF-1 is not expressed in the early mouse embryo. We show that P450c17 is expressed in differentiated mouse parietal and visceral endoderm lineages, in cultured mouse F9 embryonic carcinoma stem cells, in mouse embryonic stem cells, and in cultured mouse P19 stem cells. Bases -110 to -55 (which contain an SF-1 site and two potential GATA sites) of the rat cyp17 gene confer promoter activity in F9 cells. Overexpression of SF-1 has no effect, whereas overexpression of GATA4 in F9 cells increases transcription from -110/-55 fused to a reporter and increases endogenous P450c17 mRNA. Chromatin immunoprecipitation assays show that GATA4 binds to -215/+55 of mouse cyp17. Stimulating F9 cells with retinoic acid and cAMP differentiates them into visceral and parietal endoderm. Commensurate with cell differentiation, quantitative PCR showed increased GATA4 and GATA6 mRNAs, temporally followed by increased P450c17 mRNA. Small interfering RNA inhibition of GATA4 or GATA6 in undifferentiated or differentiated F9 cells diminished endogenous cyp17 expression. Thus, P450c17 is expressed in mouse embryonic stem cells, its expression increases upon differentiation to an early embryonic endoderm lineage, and GATA4/6 are responsible for activation of P450c17 gene expression at this early stage of embryonic development.

Species-specific regulation of PXR/CAR/ER-target genes in the mouse and rat liver elicited by o, p'-DDT

BACKGROUND

Dichlorodiphenyltrichloroethane (DDT) is a persistent estrogenic organochlorine pesticide that is a rodent hepatic tumor promoter, with inconclusive carcinogenicity in humans. We have previously reported that o, p'-DDT elicits primarily PXR/CAR-mediated activity, rather than ER-mediated hepatic responses, and suggested that CAR-mediated effects, as opposed to ER-mediated effects, may be more important in tumor promotion in the rat liver. To further characterize species-specific hepatic responses, gene expression analysis, with complementary histopathology and tissue level analyses were investigated in immature, ovariectomized C57BL/6 mice treated with 300 mg/kg o, p'-DDT, and compared to Sprague-Dawley rat data.

RESULTS

Rats and mice exhibited negligible histopathology with rapid o, p'-DDT metabolism. Gene expression profiles were also similar, exhibiting PXR/CAR regulation with the characteristic induction of Cyp2b10 and Cyp3a11. However, PXR-specific target genes such as Apoa4 or Insig2 exhibited more pronounced induction compared to CAR-specific genes in the mouse. In addition, mouse Car mRNA levels decreased, possibly contributing to the preferential activation of mouse PXR. ER-regulated genes Cyp17a1 and Cyp7b1 were also induced, suggesting o, p'-DDT also elicits ER-mediated gene expression in the mouse, while ER-mediated effects were negligible in the rat, possibly due to the inhibitory effects of CAR on ER activities. In addition, o, p'-DDT induced Gadd45a, Gadd45b and Cdkn1, suggesting DNA damage may be an additional risk factor. Furthermore, elevated blood DHEA-S levels at 12 h after treatment in the mouse may also contribute to the endocrine-related effects of o, p'-DDT.

CONCLUSION

Although DDT is known to cause rodent hepatic tumors, the marked species differences in PXR/CAR structure, expression patterns and ligand preference as well as significant species-specific differences in steroidogenesis, especially CYP17A1 expression and activity, confound the extrapolation of these results to humans. Nevertheless, the identification of potential modes of action as well as species-specific responses may assist in the selection and further development of more appropriate models for assessing the toxicity of DDT to humans and wildlife.

Expression of 3beta-hydroxysteroid dehydrogenase, cytochrome P450-c17, and sulfotransferase 2B1 proteins in liver and testis of pigs of two breeds: relationship with adipose tissue androstenone concentration

An excessive accumulation of androstenone in pig adipose tissue is a major contributor to the phenomenon of boar taint. Androstenone deposition is dependent on the rate of androstenone biosynthesis in testis and androstenone degradation in liver. The aim of the current study was to examine the possibility of the existence of breed-specific mechanisms controlling androstenone accumulation in pig adipose tissue. The specific objective was to investigate the expression of some of the key enzymes involved in testicular and hepatic androstenone metabolism in pigs of 2 breeds by using animals with high and low androstenone concentrations within each breed. The study was conducted with Norwegian Landrace (N. Landrace) and Duroc boars. The mean androstenone values for the low- and high-androstenone groups were 0.1 +/- 0.01 microg/g and 7.58 +/- 0.68 microg/g for N. Landrace boars, and 0.22 +/- 0.04 microg/g and 13.55 +/- 1.14 microg/g for Duroc boars. The enzymes investigated were 3beta-hydroxysteroid dehydrogenase (3beta-HSD), cytochrome P450-c17, and sulfotransferase 2B1 (SULT2B1). Expression of cytochrome P450-c17 in liver and testis did not differ between animals with high and low androstenone concentrations in either the N. Landrace or Duroc breed. Expression of hepatic 3beta-HSD, which catalyzes the first stage of androstenone degradation, was decreased in high-androstenone N. Landrace boars (P < 0.01), but not in high-androstenone Duroc boars. In contrast, the expression of hepatic SULT2B1, which catalyzes the second stage of steroid catabolism, was decreased in high-androstenone Duroc animals (P < 0.05), but not in high-androstenone N. Landrace animals. Sulfotransferase 2B1 was also inhibited in testis of high-androstenone pigs of both breeds compared with low-androstenone animals. We report breed differences in expression of the androstenone-metabolizing enzymes 3beta-HSD and SULT2B1 in the liver of high- and low-androstenone pigs. It is suggested that accumulation of androstenone in adipose tissue of N. Landrace boars might be related to a low rate of hepatic androstenone degradation in metabolic stage I, whereas the high androstenone concentration in Duroc boars might be related to a low rate of androstenone metabolism in metabolic stage II.

Developmental changes of serum steroids produced by cytochrome P450c17 in rat

Serum levels of 17-hydroxypregnenolone, dehydroepiandrosterone, 17-hydroxyprogesterone, and androstenedione were measured during the postnatal development of rats 1-14 weeks of age. A significant decrease in the serum levels of these steroids with increasing age was observed, using multiple regression analysis: 17-hydroxypregnenolone (beta= -1.56, S.E.= 0.25, P < 0.00001), dehydroepiandrosterone (beta= -0.43, S.E.= 0.07, P < 0.00001), 17-hydroxyprogesterone (beta= -2.51, S.E.= 0.45, P < 0.00001), and androstenedione (beta= -1.63, S.E.= 0.33, P < 0.00001). A sex-related difference was not found. The observed decline in the serum levels of the steroids was directly proportional to the previously reported decrease in mRNA expression and enzyme activity of cytochrome P450c17 in the rat liver. Yet, despite this decrease to undetectable levels in liver after 7-8 weeks, significant amounts of 17-hydroxypregnenolone, 17-hydroxyprogesterone, dehydroepiandrosterone, and androstenedione were still observed in the rat serum. This may partly be due to the mRNA expression of cytochrome P450c17 in tissues other than the liver, such as the testis and/or duodenum, after 4 weeks of age. Serum levels of pregnenolone, progesterone, and corticosterone in the developing rats were also examined.

17alpha-hydroxylase/C17-20 lyase cytochrome P450 mRNA expressions and enzyme activities during the development of arthritis in collagen-induced arthritis mice

In our previous study, we have investigated the serum levels of dehydroepiandrosterone (DHEA) in type II collagen (CII)-induced arthritis (CIA) mice. During the study, we found that in normal control mice, serum levels of DHEA in the latter half of the experimental period (13-16 weeks old) were significantly lower than those at the beginning of the experiment (10 weeks old). However, in CIA mice, such decreases were not observed by CII treatment. To examine the cause of the retention of DHEA during the development of arthritis in CIA mice in this study, 17alpha-hydroxylase/C17-20 lyase P450 (CYP17) mRNA expressions were measured by real time RT-PCR and the CYP17 enzyme activities were investigated in the liver and testis on days 6, 13, 28 and 48 after CII treatment in DBA/1J mice. There were no significant differences of CYP17 expressions in the liver between control and CIA mice at each experimental day, while a significant increase of expression in the testis of CIA mice was observed on day 48. On the other hand, CYP17 enzyme activities on days 28 and 48 in testis microsome (Mc) from the CIA mice were significantly higher than those of the control on the same day, while no significant differences of activities in liver Mc were observed between the CIA and control mice. These findings suggested that the cause of the retention of DHEA on days 28 and 48 after CII treatment may be the increase of CYP17 expression and the enzyme activities in the testis.

Cloning of zebrafish ovarian P450c17 (CYP17, 17alpha-hydroxylase/17, 20-lyase) and characterization of its expression in gonadal and extra-gonadal tissues

Cytochrome P450c17 (CYP17, 17alpha-hydroxylase/17, 20-lyase) has been viewed as a critical enzyme for the biosynthesis of gonadal and adrenal steroids in vertebrates. A full-length cDNA coding for P450c17 has been cloned from the zebrafish ovary. It encodes 519 amino acids and shares high sequence identity with that of fathead minnow (92%), rainbow trout (74%), chicken (64%), rat (47%), and human (48%). Northern blot analysis demonstrated that it is predominantly expressed in the ovary and testis; however, a weak hybridization signal was also detected in the whole kidney of the zebrafish, suggesting a role for P450c17 in the steroidogenesis of both gonads and renal/interrenal tissues. We further examined the expression of P450c17 in the developing ovarian follicles. Northern analysis and RT-PCR revealed abundant expression of the enzyme in the follicles of all major stages including pre-vitellogenic, vitellogenic and post-vitellogenic full-grown follicles; however, unlike P450c17 in the rainbow trout and eel, the expression of zebrafish P450c17 did not show significant temporal difference among different developmental stages, similar to the finding in the fathead minnow. The constitutive nature of P450c17 expression during zebrafish follicle development may partly explain the poor transcriptional response of the enzyme to the treatments with gonadotropin or activin, both of which enhance oocyte maturation in this species. It is also of interest to note that when assayed by RT-PCR, the enzyme P450c17 also seemed to be expressed in several other non-gonadal tissues including the brain, gill, liver and intestine, and its expression did not show significant sexual dimorphism in the brain of adult zebrafish. The physiological relevance of these findings remains to be further elucidated.

Aromatase activity in the European sea bass (Dicentrarchus labrax L.) brain. Distribution and changes in relation to age, sex, and the annual reproductive cycle

Cytochrome P450 aromatase activity (AA) was measured in different tissues of the sea bass (Dicentrarchus labrax L.) using a tritiated water release assay that was previously optimized and validated for this species. In adult fish entering the reproductive season, AA was highest on a per mg protein basis, in the brain (2.04+/-0.4 pmol/mg prot/h; mean+/-SEM), followed by the ovary (0.59+/-0.1) and was detectable in visceral fat (0.21+/-0.05), liver (0.08+/-0.009), and head kidney (0.03+/-0.004). However, AA was negligible in the rest of the tissues tested: heart, testis, muscle, and spleen. Consistent with results obtained in other species, dissection of the brain into its major constitutive parts revealed that AA was concentrated in areas implicated in the control of reproduction, including the olfactory bulb, telencephalon, and hypothalamus (range: 2.6-16.2 pmol/mg prot/h), as well as the pituitary gland (6.2-9.3 pmol/mg prot/h). Lower AA was noted in the optic bulb, cerebellum, and medulla. However, in contrast to some previously published reports concerning the content and distribution of neural aromatase in fish, males consistently exhibited higher AA than females. In one-year-old juvenile fish completing the process of gonadal sex differentiation, brain AA (0.63 pmol/mg prot/h) was similar in both sexes and ten times lower than that measured in the brain of first time spawners (6.52 pmol/mg prot/h), in this case with males showing an overall higher (24%) activity than females. When surveyed throughout the year, brain AA dramatically changed during the reproductive cycle. Maximum average values of approximately 7 pmol/mg prot/h were obtained that coincided with the spawning season. The peak in brain AA was preceded by two and one months by the peak of plasma testosterone and the peak of the gonadosomatic index, respectively. This is the first measurement of the distribution of the activity of a steroidogenic enzyme in the sea bass, an established model in comparative endocrinology. Together, these results demonstrate sex- and seasonally-related variations in AA and establish the basis for further comparative studies of certain androgen-mediated actions through locally formed estrogen in both central and peripheral targets.

Participation of Endogenous Dehydroepiandrosterone and Its Sulfate in the Pathology of Collagen-Induced Arthritis in Mice

We have investigated the serum levels of dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) in type II collagen (CII)-induced arthritis (CIA) DBA/1J mice, an experimental model of human rheumatoid arthritis (RA). Serum levels of DHEA and DHEAS were measured by EIA and GC/MS, respectively. Sera were obtained from the mice on day 6, 13, 28 and 48 after the CII treatment. The disease onset of CIA was observed from day 28 (7%) to day 48 (80%) after CII immunization. The serum concentration of DHEA on day 13 did not differ from that on day 6 in CIA mice and untreated controls. Serum levels of DHEA on day 28 and 48 were significantly low compared with those on day 6 in controls. However, in CIA mice, DHEA levels on day 28 and 48 were not decreased from those on day 6. No difference in the serum DHEAS level on day 13 compared with day 6 was observed in either control or CIA mice. A significant decrease of DHEAS levels on day 28 and 48 compared with day 6 was found in both groups. The time point for the retention of DHEA in CIA mice, day 28 and day 48, coincided with the disease onset of CIA. In conclusion, endogenous DHEA may be produced as a result of physiological response for the protection against CIA.

Role of adrenal medulla in development of sexual dimorphism in inflammation

Many inflammatory diseases show a female predilection in adults, but not prepubertally. Because sex differences in the inflammatory response in the adult rat are mediated, in part, by sexual dimorphism in adrenal medullary function, we investigated the contribution of the adrenal medulla to the ontogeny of sexual dimorphism in inflammation. Whilst there was no sex difference in the magnitude of the plasma extravasation (PE) induced by the potent inflammatory mediator bradykinin (BK) in prepubertal rats, in adult rats BK-induced PE was markedly greater in males. Also, adult male rats, gonadectomized prior to puberty, had a lower magnitude of BK-induced PE than did adult male controls, whilst adult females gonadectomized prepubertally had higher BK-induced PE than did controls. In rats gonadectomized after puberty, the magnitude of BK-induced PE in adult males was not affected, whilst in females it resulted in significantly higher BK-induced PE, similar to the effect of prepubertal gonadectomy. When tested prepubertally, adrenal denervation increased the magnitude of BK-induced PE in females, but not in males. In contrast, in both males and females tested as adults, but castrated prepubertally, and in gonad-intact adult females, adrenal denervation significantly increased the magnitude of BK-induced PE. Adrenal denervation in prepubertal females given adult levels of 17beta-oestradiol produced a marked enhancement in the denervation-induced increase in magnitude of BK-induced PE compared to females not exposed prematurely to sex hormones. These studies suggest that an adrenal medulla-dependent inhibition of BK-induced PE is present in female but not male rats, and is enhanced by oestrogen but suppressed by testosterone.