Characterization of an androgen receptor in salmonid lymphocytes: possible link to androgen-induced immunosuppression

Gene Duplication of Androgen Receptor As An Evolutionary Driving Force Underlying the Diversity of Sexual Characteristics in Teleost Fishes

Sexual dimorphism allows species to meet their fitness optima based on the physiological availability of each sex. Although intralocus sexual conflict appears to be a genetic constraint for the evolution of sex-specific traits, sex-linked genes and the regulation of sex steroid hormones contribute to resolving this conflict by allowing sex-specific developments. Androgens and their receptor, androgen receptor (Ar), regulate male-biased phenotypes. In teleost fish, ar ohnologs have emerged as a result of teleost-specific whole genome duplication (TSGD). Recent studies have highlighted the evolutionary differentiation of ar ohnologs responsible for the development of sexual characteristics, which sheds light on the need for comparative studies on androgen regulation among different species. In this review, we discuss the importance of ar signaling as a regulator of male-specific traits in teleost species because teleost species are suitable experimental models for comparative studies owing to their great diversity in male-biased morphological and physiological traits. To date, both in vivo and in vitro studies on teleost ar ohnologs have shown a substantial influence of ars as a regulator of male-specific reproductive traits such as fin elongation, courtship behavior, and nuptial coloration. In addition to these sexual characteristics, ar substantially influences immunity, inducing a sex-biased immune response. This review aims to provide a comprehensive understanding of the current state of teleost ar studies and emphasizes the potential of teleost fishes, given their availability, to find molecular evidence about what gives rise to the spectacular diversity among fish species.

Do different platforms of coronavirus vaccines have different impacts on psoriasis flares?

This study evaluated the impacts on psoriasis flares of 3 vaccine platforms: inactivated, viral vector and mRNA. Respectively, 198 and 96 psoriasis patients with and without COVID-19 vaccination during the study period. Group comparison revealed no increased risk of psoriasis flaring after COVID-19 vaccination. The vaccinated group received 425 doses of vaccine (140 inactivated, 230 viral vector and 55 mRNA). Patients' self-reported symptoms included all three platforms causing psoriasis flare, but the highest was among patients administered with mRNA vaccines. Most flares were mild to moderate, and most patients (89.8%) managed their flare-up lesions without rescue therapy. In conclusion, our study showed that the rate of psoriasis flare was not significantly different between vaccinated and unvaccinated groups. Factors that might explain psoriasis flare include vaccine-related psychological stress and side effects from vaccination. Different platforms of corona vaccines seemed to have different impact of psoriasis flares. Based on our results and the recommendations of several consensus guidelines, the benefits of COVID vaccinations outweigh the risks to patients with psoriasis. Patients with psoriasis should receive a COVID vaccine as soon as one is available.

Application in a biomonitoring context of three-spined stickleback immunomarker reference ranges

The relevance of a biomarker for biomonitoring programs was influenced both by the knowledge on biomarker natural inter-individual and site variabilities and by the sensitivity of the biomarker towards environmental perturbations. To minimize data misinterpretation, robustness reference values for biomarkers were important in biomonitoring programs. Specific three-spined stickleback, Gasterosteus aculeatus, immune reference ranges for field studies had been determined based on laboratory data and one reference station (Contentieuse river at Houdancourt). In this study, data obtained in one uncontaminated and three contaminated sites were compared to these reference ranges as a validation step before considering them for larger scale biomonitoring programs. When the field reference range were compared to data from the uncontaminated station (Béronelle), only few deviations were shown. In this way, data coming from uncontaminated station (Béronelle) was integrated in the field reference ranges to improve the evaluation of site variability. The new field reference ranges provided better discrimination of sites and spanned a larger range of fish lengths than the initial reference ranges. Furthermore, the results suggest lysosomal presence during several months and phagocytosis capacity in autumn may be the most relevant immunomarkers towards identifying contaminated sites. In the future, combining this reference value approach with active biomonitoring could facilitate the obtention of data in multiple stream conditions.

Sex steroids exert a suppressive effect on innate and cell mediated immune responses in fresh water teleost, Channa punctatus

The main objective of this study was to evaluate the potential role of two important sex steroids, crucial for reproductive success, on innate and cell mediated immune responses in a seasonally breeding, economically important fish, Channa punctatus. Intraperitoneal injections of testosterone and progesterone were given to different groups of fishes. Spleen and head kidney macrophages were isolated and studied for phagocytosis. Superoxide production and nitrite release by phagocytes were also investigated. Cell mediated immunity was measured by lymphocyte proliferation in presence of T and B cell mitogens. In vitro effect of steroids on mitogen induced lymphocyte proliferation was also analyzed. Results of the present investigation revealed the suppressive effects of testosterone and progesterone on immune responses of cells from spleen and head kidney. Concentration dependent effect of sex steroids were observed in vitro studies where phagocytosis and lymphocyte proliferation were suppressed. Immunosupression by these hormones may be the cost of reproduction and it is postulated that by suppressing immune responses, these steroids may, therefore, act as a physiological check regulating the relative amount of energy invested into either reproductive effort or immunocompetence.

The initiation of puberty in Atlantic salmon brings about large changes in testicular gene expression that are modulated by the energy status

Background

When puberty starts before males reach harvest size, animal welfare and sustainability issues occur in Atlantic salmon (Salmo salar) aquaculture. Hallmarks of male puberty are an increased proliferation activity in the testis and elevated androgen production. Examining transcriptional changes in salmon testis during the transition from immature to maturing testes may help understanding the regulation of puberty, potentially leading to procedures to modulate its start. Since differences in body weight influence, via unknown mechanisms, the chances for entering puberty, we used two feed rations to create body weight differences.

Results

Maturing testes were characterized by an elevated proliferation activity of Sertoli cells and of single undifferentiated spermatogonia. Pituitary gene expression data suggest increased Gnrh receptor and gonadotropin gene expression, potentially responsible for the elevated circulating androgen levels in maturing fish. Transcriptional changes in maturing testes included a broad variety of signaling systems (e.g. Tgfβ, Wnt, insulin/Igf, nuclear receptors), but also, activation of metabolic pathways such as anaerobic metabolism and protection against ROS. Feed restriction lowered the incidence of puberty. In males maturing despite feed restriction, plasma androgen levels were higher than in maturing fish receiving the full ration. A group of 449 genes that were up-regulated in maturing fully fed fish, was up-regulated more prominently in testis from fish maturing under caloric restriction. Moreover, 421 genes were specifically up-regulated in testes from fish maturing under caloric restriction, including carbon metabolism genes, a pathway relevant for nucleotide biosynthesis and for placing epigenetic marks.

Conclusions

Undifferentiated spermatogonia and Sertoli cell populations increased at the beginning of puberty, which was associated with the up-regulation of metabolic pathways (e.g. anaerobic and ROS pathways) known from other stem cell systems. The higher androgen levels in males maturing under caloric restriction may be responsible for the stronger up-regulation of a common set of (449) maturation-associated genes, and the specific up-regulation of another set of (421) genes. The latter opened regulatory and/or metabolic options for initiating puberty despite feed restriction. As a means to reduce the incidence of male puberty in salmon, however, caloric restriction seems unsuitable.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5869-9) contains supplementary material, which is available to authorized users.

Effects of Sex Steroids on Fish Leukocytes

In vertebrates, in addition to their classically reproductive functions, steroids regulate the immune system. This action is possible mainly due to the presence of steroid receptors in the different immune cell types. Much evidence suggests that the immune system of fish is vulnerable to xenosteroids, which are ubiquitous in the aquatic environment. In vivo and in vitro assays have amply demonstrated that oestrogens interfere with both the innate and the adaptive immune system of fish by regulating the main leukocyte activities and transcriptional genes. They activate nuclear oestrogen receptors and/or G-protein coupled oestrogen receptor. Less understood is the role of androgens in the immune system, mainly due to the complexity of the transcriptional regulation of androgen receptors in fish. The aim of this manuscript is to review our present knowledge concerning the effect of sex steroid hormones and the presence of their receptors on fish leukocytes, taking into consideration that the studies performed vary as regard the fish species, doses, exposure protocols and hormones used. Moreover, we also include evidence of the probable role of progestins in the regulation of the immune system of fish.

17α-Ethynylestradiol alters the peritoneal immune response of gilthead seabream

17α-Ethynylestradiol (EE₂), a synthetic estrogen used in most oral contraceptives pills and hormone replacement therapies, is found in many water bodies, where it can modulate the fish immune response. EE₂ acts as an endocrine disruptor in gilthead seabream, Sparus aurata L., a marine teleost fish of great economic value in Mediterranean aquaculture, as it induces hepatic vitellogenin gene (vtg) expression. Moreover, EE₂ also alters the capacity of gilthead seabream to appropriately respond to infection although it does not behave as an immunosuppressor. Nevertheless, these previous studies have mainly focused on the head kidney leukocytes and no information exists on peritoneal leukocytes, including mast cells. In the present work, juvenile gilthead seabream fish were fed a pellet diet supplemented with EE₂ for 76 days and intraperitoneally injected with hemocyanin plus imject alum adjuvant at the end of EE₂ treatment and 92 days later, and the peritoneal immune response was analyzed. EE₂ supplementation induced vtg expression but returned to basal levels by 3 months post-treatment. Interestingly, gilthead seabream peritoneal leukocytes express the genes encoding for the nuclear estrogen receptor α and the G protein-coupled estrogen receptor 1 and the dietary intake of EE₂ induced these expression. Moreover, EE₂ induced an inflammatory response in the peritoneal cavity in unvaccinated fish, which was largely maintained for several months after the cessation of the treatment. However, the impact of EE₂ in vaccinated fish was rather minor and transient. Taken together, the study provides fresh information about endocrine immune disruption, focusing on peritoneal leukocytes.

Expression of ayu antimicrobial peptide genes after LPS stimulation

Plecoglossus altivelis (ayu) is one of the most important fish species in the Japanese islands and in internal fish hatcheries. Living in open aquatic environments exposes fish to many pathogens. Therefore, they require rapid and strong immune defenses. We investigated in vivo the direct association between the ayu innate immune response, represented by the relative transcription of genes encoding the cathelicidin and hepcidin antimicrobial peptides, and lipopolysaccharide (LPS), a conventional pathogen-associated molecular patterns (PAMPs) of Gram-negative bacteria. Different concentrations of LPS (1, 10 and 100 µg/fish) were injected intraperitoneally into young (sexually immature) and adult (fully sexually mature) ayu. The relative expression of the antimicrobial peptide genes was measured 6 hr, 24 hr and 1 week after stimulation with LPS. We found a direct association between the expression of the antimicrobial peptide genes investigated and LPS stimulation. This relationship was time-, dose- and age-dependent. Further research is required to determine the cell-specific transcriptional regulation and posttranscriptional regulation of these antimicrobial peptides.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Effects of (Anti) Androgenic Endocrine Disruptors (DEHP and Butachlor) on Immunoglobulin M (IgM) and Leukocytes Counts of Male Rainbow Trout (Oncorhynchus mykiss)

The effect of two anti-androgenic endocrine disrupting compounds, i.e. the plasticizer di (2-ethylhexyl) phthalate (DEHP) and herbicide butachlor, were evaluated for their effects on immunoglobulin M (IgM) and leukocytes in male rainbow trout. Also, plasma testosterone (T) concentration was measured to confirm their anti-androgenic effects. In the first experiment, trout were treated with 50 mg/kg (body weight) DEHP intraperitoneally, and in the second one, fish were exposed to 0.39 mg/L butachlor for 10 days. The results showed that T concentrations and white blood cells were significantly lower in fish exposed to either DEHP or butachlor compared to control fish (p < 0.05). Fish showed significantly elevated neutrophil levels and decreased lymphocyte levels in the butachlor (p < 0.05); however, no significant difference was observed in lymphocyte and neutrophils values in the DEHP treatment (p > 0.05). In addition, no significant differences were found in IgM, eosinophil and monocyte parameters in either DEHP or butachlor treatments (p > 0.05). These results confirmed that leukocytes counts can be considered as a novel marker of immunotoxicity triggered by (anti) androgenic endocrine disruptors.

The trenbolone acetate affects the immune system in rainbow trout, Oncorhynchus mykiss

In aquatic systems, the presence of endocrine-disrupting chemicals (EDC) can disrupt the reproductive function but also the immune system of wildlife. Some studies have investigated the effects of androgens on the fish immune parameters but the mechanisms by which the xenoandrogens alter the immunity are not well characterized. In order to test the effects of trenbolone acetate (TbA) on fish immune system, we exposed rainbow trout male juveniles during three weeks to TbA levels at 0.1 and 1μg/L. The present results suggest that TbA impacts, in a tissue-dependent manner, the rainbow trout immunity by affecting primarily the humoral immunity. Indeed, TbA inhibited lysozyme activity in plasma and liver and enhanced the alternative complement pathway activity (ACH50) in kidney. In plasma, the modulation of the complement system was time-dependent. The mRNA expression of genes encoding some cytokines such as renal TGF-β1, TNF-α in skin and hepatic IL-1β was also altered in fish exposed to TbA. Regarding the cellular immunity, no effect was observed on the leucocyte population. However, the expression of genes involved in the development and maturation of lymphoid cells (RAG-1 and RAG-2) was decreased in TbA-treated fish. Among those effects, we suggest that the modulation of RAG-1 and mucus apolipoprotein-A1 gene expression as well as plasma and hepatic lysozyme activities are mediated through the action of the androgen receptor. All combined, we conclude that trenbolone affects the rainbow trout immunity.

Detection of immunotoxic effects of estrogenic and androgenic endocrine disrupting compounds using splenic immune cells of the female three-spined stickleback, Gasterosteus aculeatus (L.)

Today, the list of endocrine disrupting compounds (EDCs) in freshwater and marine environments that mimic or block endogenous hormones is expanding at an alarming rate. As immune and reproductive systems may interact in a bidirectional way, some authors proposed the immune capacities as attractive markers to evaluate the hormonal potential of environmental samples. Thus, the present work proposed to gain more knowledge on direct biological effects of natural and EDCs on female fish splenic leucocyte non-specific immune activities by using ex vivo assays. After determining the optimal required conditions to analyze splenic immune responses, seven different EDCs were tested ex vivo at 0.01, 1 and 100nM over 12h on the leucocyte functions of female three-spined stickleback, Gasterosteus aculeatus. In summary, we found that natural hormones acted as immunostimulants, whilst EDCs were immunosuppressive.

Social regulation of cortisol receptor gene expression

In many social species, individuals influence the reproductive capacity of conspecifics. In a well-studied African cichlid fish species, Astatotilapia burtoni, males are either dominant (D) and reproductively competent or non-dominant (ND) and reproductively suppressed as evidenced by reduced gonadotropin releasing hormone (GnRH1) release, regressed gonads, lower levels of androgens and elevated levels of cortisol. Here, we asked whether androgen and cortisol levels might regulate this reproductive suppression. Astatotilapia burtoni has four glucocorticoid receptors (GR1a, GR1b, GR2 and MR), encoded by three genes, and two androgen receptors (ARα and ARβ), encoded by two genes. We previously showed that ARα and ARβ are expressed in GnRH1 neurons in the preoptic area (POA), which regulates reproduction, and that the mRNA levels of these receptors are regulated by social status. Here, we show that GR1, GR2 and MR mRNAs are also expressed in GnRH1 neurons in the POA, revealing potential mechanisms for both androgens and cortisol to influence reproductive capacity. We measured AR, MR and GR mRNA expression levels in a microdissected region of the POA containing GnRH1 neurons, comparing D and ND males. Using quantitative PCR (qPCR), we found D males had higher mRNA levels of ARα, MR, total GR1a and GR2 in the POA compared with ND males. In contrast, ND males had significantly higher levels of GR1b mRNA, a receptor subtype with a reduced transcriptional response to cortisol. Through this novel regulation of receptor type, neurons in the POA of an ND male will be less affected by the higher levels of cortisol typical of low status, suggesting GR receptor type change as a potential adaptive mechanism to mediate high cortisol levels during social suppression.

Toxicity of atrazine and nonylphenol in juvenile rainbow trout (Oncorhynchus mykiss): effects on general health, disease susceptibility and gene expression

Atrazine (ATZ) and nonylphenol (NP) are commonly identified contaminants in aquatic habitats; however, few studies have considered the impact of these endocrine disrupters on immune function and resistance to disease. This study examined the immunotoxicological effects of ATZ and NP at multiple levels of biological organization. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to a solvent control (0.00625%, v/v anhydrous ethanol), or sub-lethal concentrations of ATZ (59 μg/L and 555 μg/L) or NP (2.3 μg/L or 18 μg/L) for 4d. At the end of exposure, fish were assessed for a number of physiological endpoints, including a host resistance challenge, and liver gene expression was assessed using a salmonid microarray (cGRASP, 32K version 1). While the low ATZ and low NP treatments had no measurable effects on the physiological endpoints measured, fish exposed to the high ATZ concentration (555 μg/L) exhibited significantly elevated plasma cortisol, a decrease in SSI, and decreased lymphocytes and increased monocytes in peripheral blood, with suppression of early immune system processes apparent at the molecular level. In contrast, fish exposed to the high NP concentration (18 μg/L) showed physiological (e.g. significantly elevated LSI) and gene expression changes (e.g. induction of vitellogenin) consistent with estrogenic effects, as well as decreased lymphocytes in the peripheral blood and more limited alterations in immune system related pathways in the liver transcriptome. Fish exposed to high ATZ or NP concentrations incurred higher mortality than control fish following a disease challenge with Listonella anguillarum, while fish exposed to the lower concentrations were unaffected. Microarray analysis of the liver transcriptome revealed a total of 211 unique, annotated differentially regulated genes (DRGs) following high ATZ exposure and 299 DRGs following high NP exposure. Functional (enrichment) analysis revealed effects on immune system function, metabolism, oxygen homeostasis, cell cycle, DNA damage, and other processes affected by ATZ or NP exposure. Overall, this study provides evidence at multiple levels of biological organization that both ATZ and NP are immunotoxic at sub-lethal concentrations and highlights the potential risk posed by these chemicals to wild fish populations.

Specific and non-overlapping functions of testosterone and 11-ketotestosterone in the regulation of professional phagocyte responses in the teleost fish gilthead seabream

Sex hormones, both estrogens and androgens, have a strong impact on immunity in mammals. In fish, the role of androgens in immunity has received little attention and contradictory conclusions have been obtained. However, it is well known that sex steroids are involved in fish growth, osmoregulation and gonad remodelation. In this study, we examine the in vitro effects of testosterone and 11-ketotestosterone, the two main fish androgens, on the professional phagocytes of the teleost fish gilthead seabream (Sparus aurata L.). Although both testosterone and 11-ketotestosterone failed to modulate the respiratory burst of seabream phagocytes, testosterone but not 11-ketotestosterone was able to increase the phagocytic ability of non-activated phagocytes. Curiously, 11-ketotestosterone was more powerful than testosterone at inducing the expression of its own receptor, namely androgen receptor b (ARb), in acidophilic granulocytes (AGs), but none of them affected the basal ARb expression levels in macrophages (MØ). Furthermore, although physiological concentrations of testosterone exerted a pro-inflammatory effect on both AGs and MØs, 11-ketotestosterone showed an anti-inflammatory effect in AGs and a strong pro-inflammatory effect in MØs. Interestingly, both androgens modulated the expression of toll-like receptors in these two immune cell types, suggesting that androgens might regulate the sensitivity of phagocytes to pathogens and damage signals. Testosterone and 11-ketotestosterone have a competitive effect, at least, on the modulation of the expression of some genes. Therefore, our results show for the first time a non-overlapping role for testosterone and 11-ketotestosterone in the regulation of professional phagocyte functions in fish.

Pubertal effects of 17α-methyltestosterone on GH-IGF-related genes of the hypothalamic-pituitary-liver-gonadal axis and other biological parameters in male, female and sex-reversed Nile tilapia

The influence of 17α-methyltestosterone (MT) on growth responses, biological parameters and the expression of genes involved in the GH-IGF pathway of the hypothalamic-pituitary-liver-gonadal axis were investigated in female, male, and sex-reversed Nile tilapia to evaluate the relationship between sex and MT-induced changes in these parameters. Female fish had a lower growth rate than male and sex-reversed fish, and MT increased growth performance and duodenal villi in females. Most but not all biological parameters of sex-reversed fish were similar to those of male fish. Male fish had higher red blood cell counts and hemoglobin levels than female and sex-reversed fish, suggesting that these hematological indices reflect a higher metabolic rate in male fish. Greater blood triglyceride levels indicated the vitellogenin process in female fish. MT increased the alternative complement activity in female fish (P<0.05). Sex and MT had no significant effects on the hypothalamic mRNAs of GHRH and PACAP. Although not statistically significant, females tended to have higher GH mRNA levels than male and sex-reversed fish. Additionally, MT tended to decrease and increase GH mRNA levels in female and male fish, respectively. There were significant differences among sexes in the expression of GHR, and IGF mRNAs at the peripheral level in the liver and gonads. Females had lower hepatic GHRs and higher ovarian GHRs than male and sex-reversed fish. While the mRNA levels of IGF-1 were lower in the ovary, the levels of IGF-2 were higher compared with those in testes. A significant correlation between GHRs and IGFs was demonstrated in the liver and gonad (except for IGF-1). Multiple regression analysis showed a significant relationship between GH mRNA and both GHRs and IGFs in the liver and gonad. MT exerted androgenic and, to some extent, estrogenic effects on several physiological parameters and GH-IGF action.

The effects of an in vitro exposure to 17β-estradiol and nonylphenol on rainbow trout (Oncorhynchus mykiss) peripheral blood leukocytes

While xenoestrogens are routinely detected in the aquatic environment, there is little understanding of the immunotoxicological consequences of exposure to these chemicals in fish, or of the mechanisms through which these effects are mediated. This study was conducted to determine if estrogen receptors (ERs) are present in fish leukocytes and to characterize the effects of 17β-estradiol (E2) and the xenoestrogen nonylphenol (NP) on immune system endpoints in rainbow trout (Oncorhynchus mykiss). Q-PCR was used to confirm that freshly isolated peripheral blood leukocytes (PBLs) express ERs. Following 96-h incubations with E2 or NP (1 nM to 10 μM), PBL ER transcription was again examined using Q-PCR and lipopolysaccharide (LPS)-stimulated proliferation was assessed using flow cytometry. While the transcription of all four forms of rainbow trout ER was unaffected by treatment with E2 or NP, transcription of ERα1 and ERα2 was down-regulated following LPS stimulation. Both E2 and NP, at concentrations of ≥100 nM and 10nM respectively, suppressed leukocyte proliferation. This first report of ERs in rainbow trout PBLs suggests a mechanism through with E2 and other xenoestrogens can modulate immune function. These results highlight the potential for xenoestrogens to impact host resistance to pathogens in wild fish populations.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Role of maternally derived immunity in fish

Maternal immunity is of paramount importance for protection of young ones at early stage of life since the immune factors of an immunocompetent female are transferred transplacentally or through colostrum, milk or yolk to an immunologically naive neonate. Both innate and adaptive type of immunity are transferred of from mother to offspring in fishes. These factors include immunoglobulin (Ig)/antibody, complement factors, lysozymes, protease inhibitors like alpha macroglobulin, different types of lectins and serine proteases like molecules. Among different types of Ig viz. IgM, IgD, IgT/IgZ and IgM-IgZ chimera types, IgM is present in most of the teleostean fishes. In teleosts, IgM either as a reduced/breakdown product or monomeric form is usually transferred to the offsprings. The maternally derived IgM usually persists for a limited duration, exhausts within the completion of yolk absorption process, and completely disappears thereafter during larval stages. Maternal transfer of immunity which provides defense to embryo and larvae depends upon the health as well as the immune status of brood fish. The overall health status of brood fish can affect breeding performances, quality seed production and protection of offsprings. However, factors such as age, maturation, reproductive behaviour and nutrition (micro and macro-nutrients) may affect the immunity in brood fishes. Besides these, seasonal changes such as photoperiods, temperature, adverse environmental conditions, and stress conditions like handling, crowding, and water pollution/contamination can also affect the immunity of brood fishes. The maintenance of the brood stock immunity at high level during vitellogenesis and oogenesis, is utmost important for reducing mortalities at larval/post larval stages through maximum/optimum transfer of maternal immunity. Brood stock immunization prior to breeding as well as selective breeding among the disease resistant families might be the ideal criteria for producing quality seed.

Androgen receptors in a cichlid fish, Astatotilapia burtoni: structure, localization, and expression levels

Androgens are an important output of the hypothalamic-pituitary-gonadal (HPG) axis that controls reproduction in all vertebrates. In male teleosts two androgens, testosterone and 11-ketotestosterone, control sexual differentiation and development in juveniles and reproductive behavior in adults. Androgenic signals provide feedback at many levels of the HPG axis, including the hypothalamic neurons that synthesize and release gonadotropin-releasing hormone 1 (GnRH1), but the precise cellular site of androgen action in the brain is not known. Here we describe two androgen receptor subtypes, ARalpha and ARbeta, in the cichlid Astatotilapia burtoni and show that these subtypes are differentially located throughout the adult brain in nuclei known to function in the control of reproduction. ARalpha was expressed in the ventral part of the ventral telencephalon, the preoptic area (POA) of the hypothalamus and the ventral hypothalamus, whereas ARbeta was more widely expressed in the dorsal and ventral telencephalon, the POA, and the ventral and dorsal hypothalamus. We provide the first evidence in any vertebrate that the GnRH1-releasing neurons, which serve as the central control point of the HPG axis, express both subtypes of AR. Using quantitative real-time PCR, we show that A. burtoni AR subtypes have different expression levels in adult tissue, with ARalpha showing significantly higher expression than ARbeta in the pituitary, and ARbeta expressed at a higher level than ARalpha in the anterior and middle brain. These data provide important insight into the role of androgens in regulating the vertebrate reproductive axis.

Effect of sex-steroid hormones, testosterone and estradiol, on humoral immune parameters of gilthead seabream

The role of sex-steroid hormones, testosterone (T) and 17beta-estradiol (E2), on the humoral immune parameters of the teleost gilthead seabream Sparus aurata was studied attempting to deepen on the knowledge of the immune-reproductive system interactions. Fish were injected intraperitoneally with coconut oil containing different dosages of T (0, 2, or 5 microg g(-1) body weight [bw]) or E2 (0, 1, or 2 microg g(-1) bw) and sampled 1, 3, and 7 days later. Hormonal levels and immune parameters (complement, peroxidase and antiprotease activities and IgM levels) were determined in plasma. Plasma hormone levels peaked at 1 day post-injection decreasing thereafter. Treatment with T significantly increased both complement and peroxidase activities after 3 days of injection but antiprotease activity and IgM levels remained unchanged. Treatment with E2 enhanced complement activity 1 day post-injection while decreased it after 3 and 7 days. However, peroxidase activity increased at 3 and 7 days post-injection while total IgM levels decreased. Implications of T and E2 in the immune-reproductive system interactions were discussed.

Alternative male reproductive tactics and the immunocompetence handicap in the Azorean rock-pool blenny, Parablennius parvicornis

In the Azorean rock-pool blenny (Parablennius parvicornis) reproductively active males display alternative morphotypes, which differ in the expression of secondary sexual characters (SSC). Males expressing SSC, the M+ morphotype, have high androgen levels and compete for crevices that will be visited by females to spawn. M+ males holding nests court females and care for the eggs. Males with low expression of SSC, the M- morphotype, have low levels of androgens and reproduce by stealing fertilizations from the M+ males. Based on the hypothesis that androgens are immunosuppressive, we expected these morphotypes to differ in immunocompetence. To test this hypothesis, we conducted a field study in which we collected repeated blood samples to monitor leukocyte populations (blood smears), and to measure the primary antibody response of males that were experimentally challenged with a foreign non-pathogenic antigen (sheep red blood cells). Circulating levels of 11-ketotestosterone and testosterone were higher in M+ males than in M- males. Neither granulocyte nor thrombocyte counts did covariate with androgens or male tactic. In contrast, lymphocyte counts and humoral antibody response were negatively correlated with body size, and as expected, both were lower in M+ than in M- males. Interestingly, in M+ males androgen levels decreased after immunization, and this was less in nest-holder males than in M+ males that were floating around in the pools. Within each morphotype we found no relationship between androgens and immunocompetence. The latter result is not supportive for androgen regulated immunosuppression in M+ males. A possible alternative is enhancement of immunity in M- males. These males had relatively high levels of injuries in comparison with M+ males. High immunity might be a consequence of high infection rate because of such injuries.

Plasma levels of androgens and cortisol in relation to breeding behavior in parental male bluegill sunfish, Lepomis macrochirus

Like many teleosts, male bluegill sunfish (Lepomis macrochirus) provide sole parental care. To understand some of the proximate costs of parental care, we measured body condition and plasma levels of testosterone (T), 11-ketotestosterone (11KT) and cortisol in nesting bluegill males during pre-spawning, spawning and parental care stages. T and 11KT were at their highest mean levels during the pre-spawning period and decreased to lower levels early during the parental care period before rising again when the eggs hatched. Cortisol levels fluctuated across the breeding stages, but there was a noticeable increase from low levels on the day of spawning during the first 2 days of parental care when egg fanning is most intense. Levels of all hormones varied considerably among males, with androgen levels often correlating positively with a male's body condition. We also demonstrate, using a brood reduction experiment and repeated sampling of known individuals, that the presence of eggs affects hormone levels shortly after eggs hatch. Parental males in better body condition had higher levels of androgens during parental care. Males that were known to renest later in the season also had higher androgen levels and were in better body condition during the first nesting bout than males only known to have nested once. However, circulating levels of cortisol did not differ significantly between these groups. We discuss our findings in the context of proximate and ultimate costs of parental care and propose several reasons why elevated androgen levels may not be as incompatible with the expression of paternal care in male teleosts, as compared with avian and mammalian fathers.

Regulation of immunocompetence by different androgen metabolites in a blenny with alternative reproductive tactics

In Parablennius parvicornis, small reproductive males with relatively low expression of secondary sexual characters (M- morphotype) parasite on the parental investment of the larger nest-holder males which have fully developed secondary sexual characters (M+ morphotype). In comparison with M+ males, M- males have relatively low levels of androgens while having high blood cell percentages of lymphocytes and antigen responsiveness. Here we test the hypothesis that androgens are a causal factor for these differences in immunocompetence between morphotypes. After drawing an initial blood sample, males received a silastic implant containing either oil only (C), or oil with testosterone (T) or 11-ketotestosterone (KT). Males were re-caught 2 weeks later for drawing of the final blood sample. KT but not T induced the development of secondary sexual characters in M- males. M- males treated with KT showed lower swimming activity than the males treated with T or C implants, suggesting that KT also mediates behavioral changes in M- males. As expected, blood cell percentages of lymphocytes, but not of granulocytes, were higher in M- males than in M+ males. Overall, lymphocyte percentages increased in the C group which might have been a response to the surgery/treatment. In concordance with the hypothesis, lymphocyte percentages were suppressed in males treated with T in comparison with controls. However, no significant change was found in KT-treated males. This suggests that androgens modulate central, morphological and immunological traits by partly independent androgen mechanisms in P. parvicornis.

p,p'-DDE depresses the immune competence of chinook salmon (Oncorhynchus tshawytscha) leukocytes

p,p'-DDE, the main metabolite of DDT, is still detected in aquatic environments throughout the world. Here, the effects and mechanisms by which p,p'-DDE exposure might affect the immune system of chinook salmon (Oncorhynchus tshawytscha) was studied. Isolated salmon splenic and pronephric leukocytes were incubated with different concentrations of p,p'-DDE, and cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry and Alamar Blue assay. p,p'-DDE significantly reduced cell viability and proliferation and increased apoptosis. The effect of p,p'-DDE on pronephric leukocytes was more severe than on splenic leukocytes, likely because pronephric leukocytes had a higher proportion of granulocytes, cells that appear more sensitive to p,p'-DDE. The effect of p,p'-DDE on leukocytes appeared to vary between developmental stages or seasonal differences. The mitogenic response of leukocytes of chinook salmon exposed to p,p'-DDE in vivo exhibited a biphasic dose-response relationship. Only leukocytes isolated from salmon treated with 59 ppm p,p'-DDE had a significantly lower percentage of Ig+ blasting cells than controls, although the response was biphasic. These results support the theory that exposure to chemical contaminants could lead to an increase in disease susceptibility and mortality of fish due to immune suppression.

Androgen control of immunocompetence in the male house finch, Carpodacus mexicanus Müller

The immunocompetence handicap (ICH) hypothesis predicts that elevated levels of the gonadal androgen testosterone (T) entail obligatory costs, such as immunosuppression, but evidence supporting this immunosuppressive influence is equivocal. To investigate this question, adult males house finches, Carpodacus mexicanus, were exposed to short days and chronically treated with T-filled (T males; N=10) or empty (C males; N=10) Silastic capsules. Testosterone administration increased plasma T levels and the size of the cloacal protuberance, an androgen-dependent secondary sexual characteristic. To study humoral immunity, finches received injections of sheep red blood cells (SRBC) and we measured circulating concentrations of antibodies to these cells with a hemagglutination test. All males produced antibodies following four SRBC injections at weekly intervals. Antibody titers in T and C males did not differ 5 days after the fourth injection, but were 59% lower in T than C males 2 weeks later. To study cell-mediated immunity, we measured the local inflammatory response to an injection of phytohemaglutinin (PHA). This response in T and C males was similar 1 day after PHA injection, but was 58% less in T than C males 2 days following the injection. Thus, T and C males mounted similar humoral and cell-mediated immune responses, but T treatment compromised maintenance of these responses. The results, demonstrating immunosuppressive effects of elevated T, are consistent with the ICH hypothesis.

Sex-dependent effects of gonadal steroids and cortisol on cardiac contractility in rainbow trout

The purpose of this study was to determine whether steroid hormones modulate cardiac function in rainbow trout (Oncorhynchus mykissWalbaum). We assessed the effects of exogenously administered steroids on isolated ventricle strips and report that physiological concentrations of androgens, 17β-estradiol and cortisol rapidly (&lt;10 min) enhance inotropism (30–40%) in a sex-specific manner. These effects were specific to the hormones studied, absent if animals were anesthetized chemically and dependent upon steroid concentration and contraction frequency. Based on the use of specific steroid receptor antagonists and key enzyme inhibitors, it appears that testosterone, 11-ketotestosterone and cortisol each act through specific intracellular receptors in males and that the positive inotropism requires the synthesis of polyamines and nitric oxide. Cortisol and 17β-estradiol, but not androgens, had similar effects in females and also involved similar signaling pathways. Androgen and cortisol effects were additive in males but cortisol and 17β-estradiol were not additive in females, suggesting sex differences in the pathways through which these hormones stimulate inotropism. In summary, gonadal steroids and cortisol promote ventricular contractility in a sex-dependent manner through mechanisms that appear multifaceted. Ultimately, steroid-mediated improvements in cardiac performance might involve non-genomic pathways and be physiologically important during migration, spawning or stressful periods.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Suppression in function of phagocytic cells in common carp Cyprinus carpio L. injected with estradiol, progesterone or 11-ketotestosterone

The modulation of phagocytic cells by beta-estradiol, 11-ketotestosterone, progesterone and cortisol was analysed in common carp (Cyprinus carpio L.). Carp were injected intraperitoneally (1 and 5 microg/kg fish) with each steroid and the activity of kidney macrophages was recorded 1 and 3 days post-injection. Bovine serum albumin-injected fish served as controls. Phagocytosis, superoxide anion and nitric oxide production were suppressed in all sex steroid treatments, and the suppression was in a dose-dependent manner. Cortisol treatment also inhibited the immune parameters to an extent similar to each of the steroid hormone. These results show that sex steroids can modulate the function of the phagocytic cells.

Effects of estradiol, progesterone and testosterone on the function of carp, Cyprinus carpio, phagocytes in vitro

The modulation of phagocytic cells by beta-estradiol, 11-ketotestosterone and progesterone was analyzed in common carp Cyprinus carpio. Carp kidney leukocytes were cultured in RPMI 1640 medium containing 0.1, 1, 10, 100 or 1000 nM concentration of each hormone. The production of superoxide anion, nitric oxide (NO) and phagocytosis were measured in vitro. Similar concentrations of cortisol were used as control. Phagocytic activities of carp macrophages was suppressed by treatment with beta-estradiol, progesterone and 11-ketotestosterone. The production of NO in carp macrophages was suppressed by progesterone and 11-ketotestosterone. However, carp macrophages incubated with beta-estradiol, progesterone and 11-ketotestosterone did not show any difference in the production of superoxide anion in comparison with control macrophages in the absence of hormones. Carp macrophages treated with cortisol suppressed phagocytosis and the production of nitric oxide and superoxide anion.

Modulation of the fish immune system by hormones

Immune-neuroendocrine interactions in fish, as in mammals, have become a focus of considerable interest, with the modulation of immune responses by hormones receiving particular attention. Cortisol, growth hormone (GH), prolactin (PRL), reproductive hormones, melanin-concentrating hormone (MCH) and proopiomelanocortin (POMC)-derived peptides have all been shown to influence immune functions in a number of fish species. This review summarises the known effects of these hormones on the fish immune system, as well as the often complex interactions between different hormones. The possible implications for fish health, with respect to aquaculture and the changes in immunocompetence that take place during different stages in the fish life cycle are also discussed.

Effects of primary- and secondary-treated bleached kraft mill effluents on the immune system and physiological parameters of roach

The present study was designed to examine, whether, effluents from a modern pulp and paper mill using elemental chlorine-free/total chlorine-free (ECF/TCF) bleaching, exert effects on the immune system of fish and, in addition, to relate these findings to physiological parameters known to be affected by bleached kraft-mill effluents (BKME). Roach (Rutilus rutilus) were exposed in laboratory conditions to primary- or secondary-treated effluent from a pulp and paper mill. In order to study their capability to respond to foreign antigens they were immunised with bovine gamma-globulin (BGG) prior to exposure. The number of anti-BGG antibody-secreting cells (ASC) and the number of immunoglobulin-secreting cells (ISC) in the spleen and blood as well as the level of anti-BGG specific antibodies and concentration of plasma immunoglobulin (IgM) were studied. Phagocytosis and migration of granulocytes of the head kidney were also determined. In addition to the immunological parameters, the activity of hepatic biotransformation enzymes, the carbohydrate metabolism and osmoregulation were examined. Exposure of roach for 21 days to BKME affected several immunological parameters. Both effluents, primary- and secondary-treated, impaired the immunoreactivity of the fish. Sex-related differences in the immune responses were evident in many parameters e.g. in the number of blood ISC and splenic ASC. Sex also had effects on cortisol levels and in the induction of 7-ethoxyresorufin O-deethylase (EROD). These results demonstrate that both primary- and secondary-treated effluent from a pulp and paper mill using ECF/TCF bleaching have effects on fish immune functions. Further, these findings suggest that steroids may contribute to immunomodulation in fish.

Androgen binding profiles of two distinct nuclear androgen receptors in Atlantic croaker (Micropogonias undulatus)

In the present study, the binding affinities of 28 androgens for two nuclear androgen receptors (AR), termed AR1 and AR2, in Atlantic croaker (Micropogonias undulatus) brain and ovarian tissues, respectively, were determined using competitive binding assays. The 5alpha-reduction of steroids, in general, increased the metabolite's binding affinity for AR2 while decreasing it for AR1. In addition, few androgens bound to AR1 with high affinity and modifications to the basic 3-ketone,4-ene,17beta-hydroxy structure of testosterone usually reduced its binding affinity for AR1. However, androgens with ketone groups at the 3- and 17-position bound with high affinity to AR1 provided that the androgen had either a 5alpha-reduced A-ring or a third ketone group at the 11-position. This suggests that there may be several high affinity conformations that AR1 can occupy depending upon whether an androgen possesses a ketone or a hydroxyl group at the 17-position. The binding of androgens to AR2 showed a more predictable pattern, 5alpha-reduced steroids bound better than 4-ene steroids and any changes to the basic 3-keto,17-hydroxy motif of 5alpha-dihydrotestosterone lowered the binding affinity of a steroid. However, these structural changes often caused only minor decreases in binding affinity, such that AR2 has a broader affinity for androgens and a greater affinity than AR1 for structurally diverse androgens. Widely different androgen binding affinities of AR1 and AR2 suggest that these two nuclear androgen receptors may mediate the physiological actions of different androgens in teleosts.

Rainbow trout androgen receptor-alpha fails to distinguish between any of the natural androgens tested in transactivation assay, not just 11-ketotestosterone and testosterone

We have recently isolated two androgen receptor cDNA clones from the rainbow trout testis. To investigate the functions of the rainbow trout androgen receptor-alpha (rtAR-alpha), we investigated the ligand binding ability and transcriptional activity of rtAR-alpha. Interestingly, in ligand-competition experiments, testosterone (T) (IC(50) 3 x 10(-9) M) competed with [(3)H]mibolerone binding for rtAR-alpha slightly more potently than the teleost fish-specific natural androgen 11-ketotestosterone (11KT) (IC(50) 8 x 10(-9) M), which is thought to be the functional spermatogenesis inducer. In contrast, T (EC(50) 5 x 10(-9) M) and 11KT (EC(50) 6 x 10(-9) M) showed similar efficiency upon cotransfection into EPC cells with a rtAR-alpha expression vector and an androgen-responsive element-based reporter gene. These results indicated that activation of rtAR-alpha does not distinguish between 11KT and T and suggested that a specific system, which is mediated only by 11KT, may exist in the rainbow trout.

Identification of two nuclear androgen receptors in kelp bass (Paralabrax clathratus) and their binding affinities for xenobiotics: comparison with Atlantic croaker (Micropogonias undulatus) androgen receptors

Two distinct nuclear androgen receptors (ARs) were identified in brain and ovarian tissues of kelp bass, Paralabrax clathratus, termed kbAR1 and kbAR2, which correspond to the two nuclear ARs we have previously characterized in Atlantic croaker, Micropogonias undulatus, termed acAR1 and acAR2. Scatchard analysis of nuclear fractions of whole brain tissue demonstrated that kbAR1 had a single class of high-affinity binding sites for testosterone (T; K(d) of 1. 8 nM and B(max) of 1.0 pmol/g tissue), whereas cytosolic fractions of kbAR2 ovarian tissue had a single class of high-affinity binding sites for dihydrotestosterone (DHT; K(d) of 0.1 nM and B(max) of 0.5 pmol/g tissue). Competition studies showed that both kbAR1 and kbAR2 were specific for androgens. However, kbAR1 bound only T with high affinity, whereas kbAR2 bound DHT, mibolerone, 17alpha-methyl-testosterone, T, and 11-ketotestosterone with high affinity. In addition, we examined the binding affinities of dichlorodiphenyltrichloroethane and its derivatives, several hydroxylated polychlorinated biphenyl (PCB) congeners, PCB mixtures, and the fungicide vinclozolin and its two metabolites M1 and M2 for the two ARs in Atlantic croaker ovarian, testicular, and brain tissues and in kelp bass ovarian and brain tissues. Only 4, 4'-PCB-3-OH and 2',5'-PCB-3-OH demonstrated greater than 50% displacement of [(3)H]testosterone from either acAR1 or kbAR1. In contrast, with the exception of vinclozolin, all of the xenobiotics examined demonstrated binding to acAR2 in testicular and ovarian tissues. The binding affinities were highest in the testicular tissue with M2, 2,2'5'-PCB-4-OH, and o,p'-DDD all binding with EC(50)s less than 10 microM. The binding affinities of xenobiotics to kbAR2 in ovarian tissue were similar to their binding affinities for ovarian acAR2. The finding that AR1 and AR2 possess different binding affinities for natural androgens and synthetic steroids, as well as for xenobiotics, suggests that the activities of androgens and of certain xenobiotics will depend upon the type of AR present within the target tissue.

Characterization of two nuclear androgen receptors in Atlantic croaker: comparison of their biochemical properties and binding specificities

Two distinct androgen receptors (ARs) with different characteristics were identified in the brain and ovary of Atlantic croaker, Micropogonias undulatus. A nuclear AR, AR1, was identified in the brain that had high affinity binding sites for testosterone (T; Kd, 1.1 +/- 0.15 nM; binding capacity, 1.4 +/- 0.14 pmol/g tissue; n = 16). A second nuclear AR, AR2, was found in the ovary that had high affinity binding sites for 5alpha-dihydrotestosterone (DHT; Kd, 0.62 +/- 0.1 nM; binding capacity, 0.38 +/- 0.06 pmol/g tissue; n = 14). AR2 has physiochemical properties similar to those of other vertebrate ARs. AR2 has high affinity binding for a broad spectrum of natural and synthetic androgens, including 17alpha-methyl-5alpha-dihydrotestosterone, which has a relative binding affinity of DHT = 100% > T > mibolerone > 11-ketotestosterone = 16%, a rapid association (t1/2, 44 min) and a slow dissociation (t1/2, 45 h) rate, as well as specific binding to purified DNA. The cytosolic AR2 interacts with heat shock proteins in a manner similar to other steroid receptors, as sodium molybdate stabilizes the receptor, and it has a 7.4-7.8S sedimentation coefficient in a 5-20% sucrose gradient. In contrast, AR1 is highly specific for only a few androgens, with T = 100% relative binding affinity >> DHT >> 11-ketotestosterone > mibolerone > 17alpha-methyl-5alpha-dihydrotestosterone = 0, has rapid association (t1/2, 15 min) and dissociation (t1/2, 2.6 +/- 0.7 h) rates, and has specific binding to purified DNA upon heat activation. The cytosolic binding component sediments at 5.6-5.7S in a 5-20% sucrose gradient and is not affected by sodium molybdate, which suggests that AR1 does not interact with heat shock proteins in the usual manner. This is the first report of the presence of two different nuclear ARs displaying markedly different steroid binding specificities within a single vertebrate species.

Sex steroids and the initiation of puberty in male African catfish (Clarias gariepinus)

The effects of sex steroids on spermatogenesis and testicular androgen secretion were studied in juvenile (spermatogonia present in testes) African catfish. Fish were implanted with Silastic pellets containing 11-ketotestosterone (KT), 11beta-hydroxyandrostenedione (OHA), androstenetrione (OA), androstenedione (A), testosterone (T), 5alpha-dihydrotestosterone (DHT), or estradiol-17beta (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were incubated with African catfish luteinizing hormone (LH) and the amount of OHA secreted in vitro (the main androgen produced by African catfish testes) was quantified. Tissue fragments were then fixed for histological analysis of spermatogenesis. Treatment with KT, OHA, and OA stimulated testicular growth and spermatogenesis (spermatocytes and spermatids were found), whereas T, DHT, A, or E2 had no such effects. All steroids, except for DHT and E2, reduced OHA secretion in the absence and presence of LH to approximately 10% of the control values. Previous studies have shown that KT, OHA, and OA have little effect on circulating LH levels in juvenile male African catfish, so that these androgens probably had direct effects on the testis. Inasmuch as OHA, OA, and KT have largely similar effects and because OHA and OA are converted to KT in vivo, we suggest that KT is physiologically the most relevant androgen for the initiation of spermatogenesis in African catfish.

The role of androgens in female vertebrates

The role of androgens in vertebrate females has been overlooked until recently. We examine the functional significance of androgens in females by reviewing studies that document relatively high levels of circulating plasma androgens, androgen receptors, or androgen-metabolizing enzymes in females. Among the mechanisms of androgenic action identified are enhanced neuron survival, stimulation of muscle satellite cell proliferation, alteration of ion current kinetics, and release of somatostatin. These mechanisms are not sex specific and thus we hypothesize that androgens play a significant role in normal female development. We encourage study in this nontraditional research area.

Physiological levels of testosterone kill salmonid leukocytes in vitro

Adult spring chinook salmon (Oncorhynchus tshawytscha) elaborate high plasma concentrations of testosterone during sexual maturation, and these levels of testosterone have been shown to reduce the salmonid immune response in vitro. Our search for the mechanism of testosterone's immunosuppressive action has led to the characterization of an androgen receptor in salmonid leukocytes. In the present study we examined the specific effects that testosterone had on salmonid leukocytes. Direct counts of viable leukocytes after incubation with and without physiological levels of testosterone demonstrate a significant loss of leukocytes in cultures exposed to testosterone. At least 5 days of contact with testosterone was required to produce significant immunosuppression and addition of a "conditioned media" (supernatant from proliferating lymphocytes not exposed to testosterone) did not reverse the immunosuppressive effects of testosterone. These data lead us to conclude that testosterone may exert its immunosuppressive effects by direct action on salmonid leukocytes, through the androgen receptor described, and that this action leads to the death of a significant number of these leukocytes.