Yolk sac tumor and dysgerminoma in the left gonad following gonadoblastoma in the right gonad in a 46,XY DSD with a novel SRY missense mutation: a case report.

BACKGROUND: Approximately 10-15% of 46,XY disorders of sex development (DSDs) have an SRY mutation residing in the high mobility group (HMG) domain. Here, we present a case of 46,XY DSD caused by a novel missense mutation in the HMG region of SRY rapidly progressing to germ cell tumors (GCTs). CASE PRESENTATION: An adolescent female (15 years old) exhibiting primary amenorrhea was later diagnosed as a 46,XY female with bilateral gonadal dysplasia on the basis of peripheral lymphocyte karyotype 46,XY and a novel missense mutation in SRY (c.281 T > G, p.L94R). The novel missense mutation (c.281 T > G, p.L94R) and its adjacent region were conserved. Protein structure analysis showed that the mutant site was located in the middle of the HMG domain, and the mutant protein had a diminished ability to bind to DNA. Imaging examination revealed an adolescent female with a naive uterus. Laparoscopy and initial pathological examination revealed left gonadal dysplasia and right gonadal dysplasia with gonadoblastoma (GB). Right gonadectomy by laparoscopy was performed upon consent from the patient's parents. Less than 1 year postoperatively, the left gonadal gland deteriorated as observed by the findings of a mass in the left adnexal region by pelvic MRI and serum AFP > 1000 ng/ml by serological tests, and then total hysterectomy and adnexal and left gonadectomy by laparoscopy were performed. The GCT stage was classified as stage Ic according to FIGO. At this time, pathologic examination showed that the left gonad had progressed to yolk sac tumor and dysgerminoma. The patient underwent chemotherapy post-operatively but developed type III myelosuppression and tumor recurrence several months later. CONCLUSIONS: The patient initially presented with right gonadoblastoma but chose only right gonadectomy by laparoscopy to preserve the female sex characteristics, which resulted in rapid deterioration of the left gonad and poor treatment outcomes. This case demonstrates the importance of early genetic diagnosis and treatment of 46,XY female DSD.

Luteinizing Hormone and GATA4 Action in the Adrenocortical Tumorigenesis of Gonadectomized Female Mice.

BACKGROUND/AIMS: Physiological role of luteinizing hormone (LH) and its receptor (LHCGR) in adrenal remains unknown. In inhibin-α/Simian Virus 40 T antigen (SV40Tag) (inhα/Tag) mice, gonadectomy-induced (OVX) elevated LH triggers the growth of transcription factor GATA4 (GATA4)-positive adrenocortical tumors in a hyperplasia-adenoma-adenocarcinoma sequence. METHODS: We investigated the role of LHCGR in tumor induction, by crossbreeding inhα/Tag with Lhcgr knockout (LuRKO) mice. By knocking out Lhcgr and Gata4 in Cα1 adrenocortical cells (Lhcgr-ko, Gata4-ko) we tested their role in tumor progression. RESULTS: Adrenal tumors of OVX inhα/Tag mice develop from the hyperplastic cells localized in the topmost layer of zona fasciculata. OVX inhα/Tag/LuRKO only developed SV40Tag positive hyperplastic cells that were GATA4 negative, cleaved caspase-3 positive and did not progress into adenoma. In contrast to Lhcgr-ko, Gata4-ko Cα1 cells presented decreased proliferation, increased apoptosis, decreased expression of Inha, SV40Tag and Lhcgr tumor markers, as well as up-regulated adrenal- and down-regulated sex steroid gene expression. Both Gata4-ko and Lhcgr-ko Cα1 cells had decreased expression of steroidogenic genes resulting in decreased basal progesterone production. CONCLUSION: Our data indicate that LH/LHCGR signaling is critical for the adrenal cell reprogramming by GATA4 induction prompting adenoma formation and gonadal-like phenotype of the adrenocortical tumors in inhα/Tag mice.

What do we do about women athletes with testes?

Elite sport and the measures imposed to prevent 'men' from 'cheating' by posing as women in women's events cast interesting light on notions of sex and gender. Some women have testes, organs that produce testosterone, because they are trans women or they have an intersex state. Testosterone is recognised as a performance-enhancing substance in at least some circumstances, and therefore, women with testes may possess an advantage when competing in some sport against women without testes, though this has never been subjected to rigorous scientific testing. The International Olympic Committee and the International Association of Athletics Federation have decreed that such individuals can compete only if they undergo medical and surgical treatment, which is likely to mean gonadectomy. This might be considered to impose an unethical demand on the individual concerned and constitute an infringement of bodily autonomy for that individual. It also suggests a binary view of sex/gender that is simplistic and not scientifically accurate. I discuss this approach and consider alternative methods of approaching the problem of women with testes in athletics.

Wilms' tumour 1 gene mutations in south Indian children with steroid-resistant nephrotic syndrome.

BACKGROUND & OBJECTIVES: Clinically, nephrotic syndrome (NS) is a diverse group of symptoms; about 20 per cent of NS cases are resistant to steroid treatment, and within ten years they progress to end-stage renal disease. The present study was undertaken to identify the mutations of Wilms' tumour 1 (WT1) gene in steroid-resistant NS (SRNS) children. METHODS: A total of 173 children with SRNS and 100 children in the control group were enrolled in the study. DNA extraction was done, screened for WT1 (exons 8 and 9) gene amplified by polymerase chain reaction and direct sequencing. Karyotype analyses were done for WT1 mutation cases. RESULTS: WT1 mutations were found in three of 173 SRNS cases (2 girls, 1 boy). All of them had intron 9 (IVS 9 + 4 C>T, 2; IVS + 5 G>A, 1) mutation. Of these three cases, one had familial and another two had sporadic history. Renal histology analysis showed two cases with focal segmental glomerulosclerosis (FSGS) and they had external female genitalia but 46,XY karyotype. Both of them had streak gonads. Of the three cases, one expired. INTERPRETATION & CONCLUSIONS: The findings of the present study indicate that all females with SRNS-FSGS should be screened for WT1 gene mutation to diagnose whether they have FS for possible gonadectomy.

Laparoscopic Removal of Streak Gonads in Turner Syndrome.

STUDY OBJECTIVE: To demonstrate the skills necessary for complete resection of bilateral streak gonads in Turner syndrome. DESIGN: Video case presentation with narration highlighting the key techniques used. The video was deemed exempt from formal review by our institutional review board. SETTING: Turner syndrome is a form of gonadal dysgenesis that affects 1 in 2500 live births. Patients often have streak gonads and may present with primary amenorrhea or premature ovarian failure. Patients with a mosaic karyotype that includes a Y chromosome are at increased risk for gonadoblastoma and subsequent transformation into malignancy. Gonadectomy is recommended for these patients, typically at adolescence. Streak gonads can be difficult to identify, and tissue margins are often in close proximity to critical retroperitoneal structures. Resection can be technically challenging and requires a thorough understanding of retroperitoneal anatomy and precise dissection techniques to ensure complete removal. INTERVENTIONS: Laparoscopic approach to bilateral salpingo-oophorectomy of streak gonads. Retroperitoneal dissection and ureterolysis are performed, with the aid of the Ethicon Harmonic Ace, to ensure complete gonadectomy. CONCLUSION: Careful and complete resection of gonadal tissue in the hands of a skilled laparoscopic surgeon is key for effective cancer risk reduction surgery in Turner syndrome mosaics.

Androgen Insensitivity Syndrome: Management Considerations from Infancy to Adulthood.

Androgen insensitivity syndrome (AIS) is an undervirilization syndrome in individuals with 46, XY karyotype. The undervirilization can be complete feminization or incomplete virilization with grades of ambiguity. AIS is caused by mutations in the androgen receptor, resulting in resistance to the physiologic activities of androgens. Differing degrees of resistance lead to three phenotypes: a complete form with female-appearing external genitalia, a partial form with a wide range of virilization, and a mild form with only minor undervirilization. AIS presents different challenges depending on whether resistance is complete or partial. Challenges include sex assignment, which impacts other medical decisions such as gonadectomy, hormonal replacement, and other surgical interventions. This review describes medical, psychosocial, and ethical concerns for each stage of development in complete and partial AIS, from the neonatal period to adulthood. These aspects of care should be addressed within an ethical framework by a multidisciplinary team, with the patients and families being the stakeholders in the decision-making process. We use the GRADE system when appropriate to appraise the existing evidence and provide recommendations and guidelines for management of AIS and appropriate transition of patients from pediatric to adult care.

Neither male gonadal androgens nor female reproductive costs drive development of sexual size dimorphism in lizards.

Sexual size dimorphism (SSD) is an extensively studied phenomenon in animals, including reptiles, but the proximate mechanism of its development is poorly understood. The most pervasive candidates are: (1) androgen-mediated control of growth, i.e. a positive effect of gonadal androgens (testosterone) on male growth in male-larger species, and a negative effect in female-larger species; and (2) sex-specific differences in energy allocation to growth, e.g. sex with larger reproductive costs should result in smaller body size. We tested these hypotheses in adults of the male-larger lizard Paroedura picta by conducting castrations with and without testosterone implants in males and manipulating reproductive status in females. Castration or testosterone replacement had no significant effect on final body length in males. High investment to reproduction had no significant effect on final body length in intact females. Interestingly, ovariectomized females and females with testosterone implants grew to larger body size than intact females. We did not find support for either of the above hypotheses and suggest that previously reported effects of gonadal androgens on growth in male lizards could be a consequence of altered behaviour or social status in manipulated individuals. Exogenous testosterone in females led to decreased size of ovaries; its effect on body size may be caused by interference with normal ovarian function. We suggest that ovarian factors, perhaps estrogens, not reproductive costs, can modify growth in female lizards and may thus contribute to the development of SSD. This hypothesis is largely supported by published results on the effect of testosterone treatment or ovariectomy on body size in female squamates.

Hormonal regulation of Cyp4a isoforms in mouse liver and kidney.

Mouse Cyp4a subfamily, including Cyp4a10, Cyp4a12a, Cyp4a12b and Cyp4a14, demonstrate a gender- and strain-specific expression in liver and kidney. In C57BL/6 mouse liver and kidney, Cyp4a12a and 4a12b are male-predominant, whereas Cyp4a14 is female-predominant. Cyp4a10 is female-predominant in liver, but shows no gender difference in kidney. The present study was aimed to determine whether sex hormones and/or growth hormone (GH) secretion patterns are responsible for the gender-specific Cyp4a expression in C57BL/6 mice. Gonadectomized mice, GH-releasing hormone receptor-deficient little (lit/lit) mice and hypophysectomized mice were used with replacement of sex hormones or GH in male or female secretion patterns. Both androgens and male-pattern GH regulated the gender-divergent Cyp4a10, 4a12a and 4a12b in liver, whereas androgens played an exclusive role in regulating Cyp4a10 and 4a12a in kidney. In contrast, Cyp4a12b was increased by male-pattern GH but not androgens in kidney. The female-predominant Cyp4a14 in liver and kidney was due to a combined effect of male-pattern GH and androgens. In addition, estrogens played a minor role in regulation of Cyp4a isoforms through an indirect pathway. In conclusion, gender-divergent Cyp4a mRNA expression in liver is caused by male-pattern GH secretion pattern and androgens, whereas in kidney, Cyp4a mRNA expression is primarily regulated by androgens.

Discontinuous splenogonadal fusion: new sonographic findings.

Splenogonadal fusion is an uncommon cause of scrotal mass in children that is rarely diagnosed before surgery. Occasionally it leads to unnecessary orchiectomy. We report a case highlighting US findings that could help with correct diagnosis.

Timing of gonadectomy in adult women with complete androgen insensitivity syndrome (CAIS): patient preferences and clinical evidence.

OBJECTIVE: Adult women with complete androgen insensitivity syndrome (CAIS) are increasingly likely to defer or decline gonadectomy despite counselling about malignancy risk. The objectives of this study were to review the evidence on the risk of gonadal malignancy in adult women with CAIS and to explore women's reasons for deferring gonadectomy. STUDY DESIGN: A case series and literature review. PATIENTS: Sixteen women with CAIS over the age of 18 years who have elected to defer gonadectomy. RESULTS: Sixty-two relevant papers were identified. Of these, 14 confirmed that tumours had been reported in 98 adults. Taking into account the limitations of combining historic case series, this review estimates a risk of gonadal malignancy of 14% (range 0% and 22%) in adults with CAIS. The most common reasons women offered for deferring gonadectomy included inconvenience of surgery, concern about surgical risk and reluctance to take hormone replacement therapy. CONCLUSIONS: Perceived benefits for retaining gonads in women with CAIS are prompting more women to keep their gonads in situ. An accurate estimate for adult malignancy risk is unavailable, and the risks currently quoted may be falsely reassuring.

Sex-specific effects of spironolactone on blood pressure in gonadectomized male and female Wistar rats.

A low-salt diet is known to decrease and salt excess to increase blood pressure in humans and rodents. Sex steroids seem to play a role in salt dependent hypertension. However, little is known about sex differences in mineralocorticoid receptor blockade between male and female rats. The objective of the work was at first to investigate the effects of a low-salt vs. a high-salt diet on blood pressure without the influence of gonadal steroids in male and female rats. Second, to determine the sex-specific effects of mineralocorticoid receptor blockade by spironolactone in high-salt and low-salt fed gonadectomized male and female animals. Normotensive male and female Wistar rats were gonadectomized and put on a low (NaCl<0.03%) or high (NaCl=4%) salt diet. On each diet animals received spironolactone or placebo. Blood pressure was measured by tail-cuff-method; 24-h urine samples were collected in metabolic cages and blood was collected for hormonal measurements. High-salt diet significantly increased systolic blood pressure in both sexes. This effect could be blocked effectively by spironolactone only in male rats. Spironolactone treatment significantly increased aldosterone levels in males and females independent of the sodium content of the diet. High sodium diet significantly increased relative kidney weight, which was not altered by spironolactone treatment. Independently of gonadal steroids a high-salt diet increased blood pressure in gonadectomized male and female rats. Spironolactone lowered blood pressure only in male not in female rats on a high-salt diet clearly indicating sex-specific effects of the mineralo-corticoid antagonist spironolactone.

GPR109A gene deletion ameliorates gonadectomy-induced bone loss in mice.

Sex steroid deficiency plays critical roles in the pathophysiology of bone as the result of uncertain bone remodeling, i.e., increased bone resorption with equivocal bone formation. We have previously shown that GPR109A, a G protein coupled receptor, controls osteoclastogenesis and bone resorption, where global GPR109A deletion decreased osteoclast bone resorption and increased bone mass. Here, we used global GPR109A gene deletion, ovariectomized (OVX) and orchidectomized (ORX) mouse models to probe the role of GPR109A in gonadectomy-induced bone loss in female and male mice. Six months old GPR109A-/- mice and their wild type littermates were allocated to Sham or gonadectomized groups for six weeks. Using densitometric micro-CT confirmed by peripheral quantitative CT (pQCT) scans on tibia and spine, and three-point bending test on femur ex vivo, we found the bone volume, trabecular number, as well as bone mineral density and content in both trabecular and cortical sites were significantly decreased in wild type OVX and ORX compared with respective Sham groups. While bone mass in both male and female GPR109A-/- Sham groups were significantly higher compared with their respective wild type Sham groups, global GPR109A gene deletion ameliorated gonadectomy-induced bone loss. In GPR109A-/- females, most of bone mass and strength parameters measured by micro-CT, pQCT and three-point bending test were not different between Sham and OVX groups. In wild type but not in GPR109-/- mice, bone remodeling marker measurements indicated that both bone resorption (Cathepsin K) and bone formation (osteocalcin) markers were increased in gonadectomized mice compared to sham, with the exception of bone specific ALP, which was decreased in gonadectomized mice. Expression of bone resorption markers (Cathepsin K) were significantly lower, but ß-catenin expression was higher in GPR109A-/- mice compared with their wild type littermates. Collectively, these data indicate that global GPR109A deletion ameliorates gonadectomy-induced bone loss through suppression of bone resorption.

Blood pressure and mesenteric vascular reactivity in spontaneously hypertensive rats 7 months after gonadectomy.

OBJECTIVE: Sexual dimorphism in the degree of high blood pressure (BP) has been observed in both animal and human hypertension. However, the mechanisms are still poorly understood. We tested the hypothesis that long-term loss of sex steroids promotes changes in mesenteric vascular reactivity that impact the maintenance of hypertension in the spontaneously hypertensive rats (SHR). METHODS: Male SHR were sham operated (M-SHAM) or castrated (M-CX), and female SHR were sham-operated (F-SHAM) or ovariectomized (F-OVX) at 3 weeks of age. Seven months later, BP was measured in anesthetized rats, and vascular responsiveness was evaluated in the isolated perfused mesentery. RESULTS: Mean arterial BP (mm Hg) was significantly greater in M-SHAM (186 ± 6) compared with F-SHAM (159 ± 5). Gonadectomy reduced BP in male SHR (M-CX: 160 ± 4) but had no significant effect in female SHR (F-OVX: 153 ± 7). Norepinephrine-induced constriction was similar in all groups. Gonadectomy attenuated serotonin-induced vasoconstriction in the mesentery. Acetylcholine (ACh)- and isoproterenol (ISO)-induced vasodilation was greater in female than male SHR. Ovariectomy of female SHR blunted ACh and ISO dilatory responses. ISO dose-response curves were shifted to the left in castrated male SHR. CONCLUSIONS: Gonadectomy exerts long-term effects on mesenteric vascular reactivity and hypertension in the SHR.

Sex differences in social interaction of methamphetamine-treated rats.

Our previous study showed that single injection of methamphetamine decreases social interaction (SI) in a dose-dependent manner that was further affected by stressful environment conditions. The aim of this study was to examine the effect of methamphetamine and its interaction with gonadal hormones on SI. Adult male and female rats were gonadectomized and assigned to testosterone-treated and oil-treated groups in male rats and estradiol-treated and oil-treated groups in female rats, respectively. Hormones were administered 30 min before each habituation in the open field. All four hormonal groups were further divided to control (without injection), saline (1 ml/kg saline injection), and methamphetamine (1 mg/kg) groups. Injections were applied 30 min before the SI test. The total duration and the total number of SI and nonsocial behavioral patterns were assessed. This study showed that an acute methamphetamine administration in a dose of 1 mg/kg decreased different types of SI in both sexes. In contrast, the same dose of methamphetamine increased locomotion and rearing behavior in male and female rats. The frequency and/or duration of SI (especially mutual sniffing and allogrooming) was lower in adult female rats relative to gonadectomized male rats, but locomotion was increased in female relative to male rats regardless of the presence or absence of gonadal hormones. In conclusion, this study is novel especially because it examines SI in both sexes in relation to the presence or absence of gonadal hormones.

Tumor risk and clinical follow-up in patients with disorders of sex development.

A subset of patients with disorders of sex development (DSD) is at risk for malignant germ cell tumors (GCTs). The degree of gonadal differentiation (or "testicularization" in the presence of a specific part of the Y chromosome), in combination with expression of embryonic germ cell markers, and (a) Y specific gene(s) related to cell-cycle control and proliferation, determines this risk. Incompletely matured Sertoli/granulosa cells are insufficiently capable of directing the normal mitotic block/meiotic induction germ cell program, and as a result, embryonic germ cells are delayed or blocked in their normal maturation process. Thereby, they remain pluripotent and gain increased mitotic and survival characteristics, being the first step in the pathogenesis of GCTs. The patient's underlying genetic defect and phenotype might be informative in assessing the degree of gonadal "testicularization" on a clinical basis. Current knowledge allows development of an informative cancer risk assessment of DSD patients.

Frasier syndrome in 17-year-old girl--case report.

The authors present a case of Frasier syndrome in a 17-year-old girl with nephrotic syndrome and male pseudohermaphroditism. Due to the existing risk of developing tumors in dysgenetic gonads, the patient was admitted to the clinic for prophylactic gonadectomy The operation was then postponed as a result of rapid progression to end-stage renal failure, and the patient was placed on hemodialysis. During subsequent laparoscopy both ovaries and dysgenetic gonads were resected. Histopathological examination revealed the presence of both seminal ducts and epididymis. Early prophylactic resection of dysgenetic gonads, such as was undertaken in this patient, is indicated in children with Frasier syndrome to prevent the development of germ cell tumors.

Prophylactic gonadectomy in 46 XY females; why, where and when?

OBJECTIVES: We compared cases of phenotypic female patients who presented with male karyotype and underwent prophylactic gonadectomy. CASE PRESENTATION: Five patients with female phenotypes presented in early adulthood with primary amenorrhoea with varying degrees of puberty. One was tall with breast development. Another was very short with clitoromegaly and multiple co-morbidities. The other three had no secondary sexual characteristics. They were examined, after which hormonal profile, karyotyping, ultrasound examination and magnetic resonance imaging were done to assess the site of gonads. Gonadectomy was performed once their 46 XY karyotype was confirmed. Results of histopathological examination of their gonads ranged from dysgenetic gonads to having testicular tissues and malignancy. CONCLUSION: Female patients with 46 XY karyotypes require prophylactic gonadectomy performed at different timings depending on diagnosis due to the malignancy risk. Pre-operative assessment is essential to locate the gonads prior to surgery.

[Laparoscopic gonadectomy for androgen insensitivity syndrome--case report]. / Laparoskopowa gonadektomia u pacjentki z kompletnym zespolem niewrazliwosci na androgeny--opis przypadku.

UNLABELLED: Androgen insensitivity syndrome (AIS, Morris syndrome) is an X-linked recessive disorder of sexual development caused by the mutation of the androgen receptor coding gene (locus Xq11-q12). We present a case of a 17-year-old girl diagnosed because of primary amenorrhea. Her cytogenetic analysis revealed the kariotype of 46, XY. Clinical examinations, based on the Quigley's scale, showed features of complete AIS. Hormonal tests brought the following results: FSH - 2.81 mIU/ml, LH - 13.88 mIU/ml. Testosterone value met the norm for a male individual in reproductive age (7.97 ng/ml). Family anamnesis revealed no episodes of genetic diseases. Due to the risk of neoplasia, the diagnosis was an indication for surgical gonads removal, which was performed laparoscopically. Histopathologic examination showed tubular adenoma with immature seminiferous tubules without spermatogenesis, and serous cysts. Patient was discharged on the next day after the operation in good general condition, and estrogen therapy was prescribed. CONCLUSION: Laparoscopy is an effective method in AIS treatment.

Clinical and Economic Value of Routine Pathological Examination of Hernia Sacs and Scheduled Clinic Follow-Ups After Inguinal Hernia and Hydrocele Repair in a Canadian Tertiary Care Children's Hospital.

BACKGROUND: The clinical and economical value of routine submission of hernia sacs for pathological examination and scheduled clinic follow-ups after inguinal hernia and hydrocele repair has been questioned. Herein, we assessed the institutional variability in these routine practices. METHODS: We retrospectively reviewed patients who underwent unilateral or bilateral inguinal hernia and/or hydrocele repair, open or laparoscopically, at our institution from 2015 to 2018. RESULTS: 1181 patients were included (1074 inguinal hernias and 157 hydroceles). Of 531 specimens obtained from 446 (38%) patients, 515 (97%) were normal. 16 (3%) abnormal pathological findings included 7 with mesothelial hyperplasia, 5 with nonfunctional genital ductal remnants, 3 with ectopic adrenal cortical tissues, and 1 epidydimal structure which was not recognized at the time of surgery. 418 (35%) patients had scheduled clinic follow-ups 65 (IQR 46-94) days postoperatively. 44 (4%) patients with unexpected postoperative Emergency Department visits within 30 days of surgery were identified. Only one patient required inpatient treatment, and the rest did not require intervention or admission. The total direct cost of analyzing specimens during the study period was $30,798 CAD ($10,266/year). The average cost to detect a potentially significant finding was $1924.88/specimen and $2053.20/patient. CONCLUSIONS: Routine pathological examination of hernia sacs and scheduled clinic follow-ups were associated with significant costs and predominantly nonsignificant findings. They should therefore be reserved for patients with a high clinical suspicion of injuries/abnormalities or risk factors for potential complications. LEVEL OF EVIDENCE: This is a level III evidence study.

Gonadectomy and Blood Sampling Procedures in the Small Size Teleost Model Japanese Medaka (Oryzias latipes).

Sex steroids, produced by the gonads, play an essential role in brain and pituitary tissue plasticity and in the neuroendocrine control of reproduction in all vertebrates by providing feedback to the brain and pituitary. Teleost fishes possess a higher degree of tissue plasticity and variation in reproductive strategies compared to mammals and appear to be useful models to investigate the role of sex steroids and the mechanisms by which they act. The removal of the main source of sex steroid production using gonadectomy together with blood sampling to measure steroid levels has been well-established and fairly feasible in bigger fish and is a powerful technique to investigate the role and effects of sex steroids. However, these techniques raise challenges when implemented in small size teleost models. Here, we describe the step-by-step procedures of gonadectomy in both males and female Japanese medaka followed by blood sampling. These protocols are shown to be highly feasible in medaka indicated by a high survival rate, safety for the life span and phenotype of the fish, and reproducibility in terms of sex steroid clearance. The use of these procedures combined with the other advantages of using this small teleost model will greatly improve the understanding of feedback mechanisms in the neuroendocrine control of reproduction and tissue plasticity provided by sex steroids in vertebrates.