Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

Testosterone and estradiol potentiate the serum gonadotropin response to gonadotropin-releasing hormone in goldfish

The effects of gonadal steroids on gonadosomatic index (GSI; gonad wt/total body wt x 100), pituitary gonadotropin (GTH) content, and serum GTH response to [D-Ala6,Pro9-Net]-luteinizing hormone-releasing hormone (LHRH-A) were investigated throughout the seasonal reproductive cycle of the goldfish. Gonad-intact female fish were implanted i.p. for 5 days with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g). The serum GTH response at 6 h following i.p. injection of saline or 0.1 microgram/g LHRH-A was assessed. In blank-implanted, saline-injected animals, seasonal variations in GSI, pituitary GTH content, and serum GTH levels were evident; maximal and minimal levels were noted in the spring and summer months, respectively. In blank-implanted fish, LHRH-A effectively stimulated GTH release in females undergoing gonadal recrudescence (late autumn and winter) and in sexually mature (spring) females, but not in sexually regressed (summer and early autumn) females. Implantation of T or E2 raised serum steroid levels to those found during ovulation in goldfish. Steroid treatments did not affect unstimulated serum GTH levels at any time of the year. Testosterone effectively potentiated the serum GTH response to LHRH-A during the entire reproductive cycle, whereas the positive effects of E2 were evident in sexually regressed and post-spawning females only. Both T and E2 potentiated the GTH response to LHRH-A in male fish. To examine the involvement of T aromatization in mediating its actions on induced GTH secretion, male and female fish were implanted with T or the nonaromatizable androgens 5 alpha-dihydroxytestosterone (DHT; 100 micrograms/g) and 11-keto-testosterone (11-KT; 250 micrograms/animal). Testosterone potentiated the GTH response to LHRH-A in both males and females whereas DHT and 11-KT were without effect. Furthermore, the positive action of T on induced GTH secretion was blocked by 2-day pretreatment with the aromatase inhibitor 1,4,6-androstatrien-3,17-dione (100 or 300 micrograms/g). Multiple i.p. injections of hCG (0.2 microgram/g every 3 days for 39 days), probably through stimulation of endogenous T secretion, resulted in potentiation of the GTH response to LHRH-A in mature male goldfish. These results clearly demonstrate that T, through aromatization to E2, can increase pituitary responsiveness to exogenous LHRH-A in gonad-intact male and female goldfish.     

Pituitary-gonadal Relationship in the Catfish Clarias batrachus (L): A Study Correlating Gonadotrophin-II and Sex Steroid Dynamics

A heterologous radioimmunoassay was developed for measuring gonadotrophin-II (GTH-II) in the catfish Clarias batrachus. Serum and/or pituitary levels of GTH-II showed significant annual/seasonal variations in male and female catfish, which could be correlated with both gonadosomatic index and/or serum testosterone level. GTH-II was not detected in resting phase, increased during gonadal recrudescence to peak values in late prespawning /spawning phases, and declined to low values in postspawning phase. During gonadal recrudescence, the pituitary and serum levels of GTH-II maintained positive or inverse relationships implying differential rates of hormone release and synthesis/storage. Gonadectomy resulted in increased release of GTH-II; the release pattern varied in females and hemi-castrated or completely castrated males. In females, the GTH-II increase followed a distinct biphasic pattern with the peak rise at week 4 of ovariectomy. In males, castration resulted in significant rise of serum GTH-II levels at all duration except week 5, but the magnitude of the rise was higher in completely castrated fish (weeks 1, 2 and 3). Testosterone replacement in 3-week hemi-castrated fish restored the GTH-II level to that of the sham control vehicle group. In intact fish, administration of testosterone elicited an increase in serum GTH-II levels in the low dose (0.25 and 0.5 mug / g BW) groups and no change in the high dose (1.0 mug / g BW) group. Methallibure treatment inhibited GTH-II levels in a dose-dependent manner. The reduction was greater in males. Withdrawal of the drug treatment restored the GTH-II and testosterone levels after 15 days in the low dose group (2 mug / g BW). The results indicate that there exists a dynamic positive or negative feedback relationship between gonadal steroids and GTH-II, which is essential to control the release and availability of circulating GTH-II.     

Pituitary Androgen Receptor Signalling Regulates Prolactin but Not Gonadotrophins in the Male Mouse

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

Regulation of gonadotropin beta subunit gene expression by testosterone and gonadotropin-releasing hormones in the goldfish, Carassius auratus

Sex steroids differentially regulate gonadotropin (GTH) beta subunits (FSHbeta and LHbeta) gene expression in the pituitary of goldfish: a strong in vivo inhibitory effect on FSHbeta mRNA production, but a weak stimulatory effect on LHbeta in sexually immature and recrudescent fish. In the present study, to examine a direct effect of testosterone (T) and gonadotropin-releasing hormone (GnRH) on the mRNA levels of FSHbeta and LHbeta subunits in the pituitary, in vitro experiments were performed using dispersed pituitary cells of sexually immature, recrudescent, mature and regressed goldfish. T treatment in vitro did not significantly decrease FSHbeta mRNA levels, but increased that of LHbeta only in the cells of immature fish. Salmon-type GnRH increased FSHbeta mRNA levels in cells of mature fish, but decreased the levels in cells of sexually regressed fish. From these results, it was suggested that: (1) in vivo effect of sex steroids on gene expression of GTH beta subunits is not always exerted on the pituitary; and (2) the different responses of GTH beta subunits by sex steroids between in vivo and in vitro are partly due to a complex pathway through hypothalamic factors, such as GnRH, in the case of in vivo.     

Reproductive toxicity in male mice caused by organic extracts in tap water from the Jialing River in Chongqing, China

BACKGROUND : Recently, male reproductive disturbances caused by organic pollutants have aroused particular public concern about the safety of drinking water. The aim of this study was to investigate the toxicity of organic extracts (OE) in tap water from the source of the Jialing River in China on the reproductive system of male mice. METHODS : Kunming male mice were randomly divided into four groups, which included a solvent control (dimethylsulfoxide), a low‐, mid‐, and high‐dose of OE (12.5, 25, and 50 l/kg bw/day, respectively) treated groups. Mice were administered intraperitoneal injections of OE at different doses for five consecutive days. On the 15th day, after treatments, the mice were sacrificed. RESULTS : The results showed that the number of epididymal sperm in the high OE group was decreased significantly (p<0.05); however, the frequency of sperm abnormalities in all treated groups were increased significantly (p<0.05). In addition, serum testosterone and follicle‐stimulating hormone levels in the treated groups were also decreased significantly (p<0.05), and mid‐ and high‐doses of OE resulted in a significant decrease in the activity of acid phosphatase and increased activity of γ‐glutamyl transpeptidase (p<0.05). Histological changes were observed in the mid‐ and high‐dose OE‐treated groups. CONCLUSIONS : The findings of this study suggest that mid and high doses of OE could disturb the male reproductive system in mice. The potential adverse effects of these compounds on the male reproductive system are worthy of further study. Birth Defects Res (Part B) 92:1–9, 2010. © 2011 Wiley‐Liss, Inc.     

Year round plasma leptin and androgen concentrations in a tropical bat

The detailed reproductive patterns and their associated endocrine characteristics have been documented only for a few species of bats. The objective of this study was to examine seasonal changes in plasma concentrations of leptin and compare it with the changes in body mass, circulating concentrations of testosterone, androstenedione and its correlation with prolonged survival of sperm during winter dormancy in the male sheath-tailed batTaphozous longimanus Hardwicke, 1825. Six bats were captured every month for three consecutive years during 2002 to 2005 from Varanasi, a subtropical part of India. The changes in the body mass were positively correlated with circulating concentration of leptin. Leptin concentration reached a peak (14 ng/ml) in November coinciding with peak body mass. Leptin levels declined during other months of the year except for a rise in March and August. Plasma leptin was positively correlated with androstenedione concentration, but did not show significant correlation with testosterone level. We noticed a significant increase in testosterone secretionin vitro in response to leutinizing hormone (LH) stimulation. However, we did not notice any increase in testosterone or androstenedione secretionin vitro in response to leptin stimulation. Plasma leptin concentration did not show any correlation with testis mass in this study. The higher concentration of testosterone and androstenedione may be responsible for the prolonged survival of sperm in the epididymidies and higher levels of leptin in November may be responsible for maintaining reproductive function during winter dormancy. We suggest that inT. longimanus, higher leptin concentrations in November may be responsible for the gonadal recrudescence and reproductive response during winter dormancy is modified by energy availability and by changing leptin concentrations during this period.     

Seasonal changes in serum thyroid hormone levels of the feral brown bullhead, Ictalurus nebulosus Lesueur

Seasonal changes in serum L-thyroxine (T4) and triiodo-L-thyronine (T3) concentrations were measured in a feral population of brown bullheads, Ictalurus nebulosus . Serum T4 was elevated in mid April concomitant with the onset of gonadal recrudescence and the increase in ambient temperatures from the winter level. Thereafter, serum T4 levels were constant throughout the late spring and summer (except for a significant lowering in levels associated with the spawning and early postspawning period), declining to a low overwintering level by mid December. Serum T3 levels increased in April, and apart from a significant decrease in July associated with the postspawning period, rose progressively until August, after which levels declined progressively to reach overwintering levels again by mid December. Between mid April and mid May serum T4/T3 ratios fell from the high values found in fish during the winter months. Apart from variations associated with the fluctuations of T4 and T3 concentrations in the spawning and early postspawning periods, serum T4/T3 ratios remained at a low level throughout the summer and early autumn months, and rose again in October to the overwintering levels. The circannual cycles are discussed in relation to the possible role of the thyroid hormone in gonadal maturation and metabolism in this species.     

Milt characteristics and plasma levels of gonadal steroids in greenback flounder Rhombosolea tapirina following treatment with exogenous hormones

Fish were treated with exogenous hormones, and milt and blood samples were collected for up to 96 h post‐treatment. Blood plasma samples were assayed for the gonadal steroids testosterone (T), 11‐ketotestosterone (11KT) and 17,20ß‐dihydroxy‐4‐pregnen‐3‐one (17.20ßP). Milt volume, spermatocrit and sperm motility were measured from milt samples. Non‐spermiated fish showed increased plasma T and 11KT in response to human chorionic gonadotropin (hCG) but not luteinising hormone releasing hormone analogue (LHRHa). Fish did not become spermiated in response to treatment with hCG, LHRHa, 11KT, 17‐hydroxyprogesterone (17P) or 17,20ßP. Spermiated fish showed an increase in milt volume in response to hCG and LHRHa but not exogenous steroids. Sperm motility declined to zero over 120 s and was not affected by hormone treatment or sampling time. Increased milt volume was accompanied by increased plasma T and 11KT, but not 17.20ßP levels. In a separate experiment, LHRHa delivered by injection or pellet was equally effective at increasing milt volume but had no effect on plasma steroid levels. Spermatocrit declined with stripping but was not affected by hormone treatment, nor was sperm motility. Co‐treatment of fish with 17P plus LHRHa had no additive effect on plasma steroid concentrations or milt volume. The results suggest that as in other teleosts, gonadotropin mediates milt production in greenback flounder.     

Effects of intracerebroventricular administration of irisin on the hypothalamus–pituitary–gonadal axis in male rats

Irisin is a product of fibronectin type III domain-containing protein 5 (FNDC5) and plays an important role in energy homeostasis. In this study, we aimed to determine effects of intracerebroventricular administration of irisin on the hypothalamus–pituitary–gonadal axis by molecular, biochemical, and morphological findings. Fourty male Wistar-Albino rats were used and divided into four groups including control, sham (vehicle), 10, and 100 nM irisin infused groups (n = 10). Hypothalamic gonadotropin releasing hormone (GnRH) level and serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone levels were determined. Testicular tissue histology and spermiogram analysis were also performed. Both irisin concentrations significantly reduced hypothalamic GnRH messenger RNA (mRNA) and protein levels (p < 0.05). It was found that serum LH, FSH, and testosterone levels and Sertoli and Leydig cell numbers were decreased by irisin administration (p < 0.05). In addition, irisin administration reduced sperm density and mobility (p < 0.05). However, it did not cause any change in testicular and epididymis weights and tubular diameter. Our results reveal that irisin can play a role in the central regulation of reproductive behavior and also reduces testosterone levels by suppressing LH and FSH secretion. These results suggest that the discovery of irisin receptor antagonists may be beneficial in the treatment of infertility.     

The effect of hormonal stimulation on steroid levels in tissue incubates of the sterlet (<Emphasis Type="Italic">Acipenser ruthenus</Emphasis> L.)

Sex steroid and cortisol levels were compared in Leibovitz’s L-15 cultural medium after incubation of tissue samples from the intact female and male sterlet (Acipenser rhutenus L.) and from the fishes exposed to hormonal stimulation of sexual maturation by a superactive analog of mammalian gonadotropin-releasing hormone (LH-RH-A). A higher level of 17,20β,21-trihydroxy-4-pregnen-3-one (20βS) was revealed in the cultural medium following incubation of ovarian follicles isolated from females 5 h after LH-RH-A stimulation, as compared to the data obtained for intact females. The addition of 1 μM progesterone (P₄) to the cultural medium before incubation of ovarian follicles also led to an increase in the 20βS level in the incubates by the end of the experiment. Cortisol and testosterone levels in the incubates exhibited the same tendency. The blood cortisol level significantly increased in females 5 h after their hormonal stimulation. In males, showing high levels of androgens (testosterone and 11-ketotestosterone) in the blood serum before hormonal stimulation, high levels of these hormones were also detected in the cultural medium after incubation of testicular and liver tissue samples. The addition of P₄ to the medium before incubation stimulated the production of sex steroids and cortisol by the gonadal fragments. Upon addition of P₄ to the incubation mixture, containing liver tissue samples, the 20βS level increased.     

The effect of gonadotropin-releasing hormone on growth hormone and gonadotropin subunit gene expression in the pituitary of goldfish, Carassius auratus

The goldfish brain contains at least two forms of gonadotropin-releasing hormone (GnRH): sGnRH and cGnRH-II. In goldfish sGnRH and cGnRH-II are present both in the brain and pituitary, and exert direct effects via specific GnRH receptors stimulating growth hormone (GH) and gonadotropin hormone (GtH) synthesis and secretion. In this study, we investigated the effects of sGnRH and cGnRH-II on GtH subunit (alpha, FSH-beta and LH-beta) and GH mRNA levels in the goldfish pituitary in vivo and in vitro. Injection of goldfish with sGnRH or cGnRH-II (4 microg/fish) stimulated GtH-alpha, FSH-beta and LH-beta mRNA levels after 24 h. For in vitro studies, goldfish pituitary fragments were treated continuously for 12 h with 10(-7) M sGnRH or cGnRH-II. Both sGnRH and cGnRH-II stimulated GtH-alpha, FSH-beta, LH-beta and GH mRNA levels, however, cGnRH-II appeared to have a more pronounced effect. Similar experiments were carried out using cultured dispersed goldfish pituitary cells. In this study, treatments for 12 h with 10(-7) M sGnRH or cGnRH-II also stimulated GtH and GH gene expression. The present results provide a basis for the investigation of the signal transduction pathways that mediate GnRH-induced changes in GtH subunit and GH mRNA levels in the goldfish pituitary.     

Older triploid fish retain impaired reproductive endocrinology in the European sea bass Dicentrarchus labrax

This paper reports on an evaluation of growth, gonadal development and reproductive endocrinology of older triploid (3n) European sea bass Dicentrarchus labrax in comparison with their diploid (2n) counterparts throughout their fifth and seventh annual cycle of life. While older triploids retained impaired reproductive endocrinology, a sexually related dimorphic growth was observed with 3n females attaining the largest sizes. Comparisons of some body indexes showed that 3n females had a significantly lower hepato‐somatic index (I_H) than 2n females but a significantly higher viscero‐somatic index (I_F). In contrast, both male and female triploids showed significantly lower gonado‐somatic index (I_G) than diploids. Accordingly, diploids produced mature gametes but triploids did not, demonstrating that despite the longer time given to triploids for gonadal development, they could not reproduce. Furthermore, older triploids had lower levels of plasma sex steroids (testosterone, T; 11‐ketotestosterone, 11‐KT and oestradiol‐17β, E₂) and luteinizing hormone (LH) than their 2n counterparts with 3n females showing drastic effects of triploidization on their reproductive endocrinology. Vitellogenin (VTG) was undetectable in 3n females. Gonadal content of steroid hormones and Sparus aurata‐type gonadotropin‐releasing hormone (sbGnRH) in the brain and pituitary were also lower in triploids compared with diploids. These results suggest that older 3n D. labrax retain functional sterility in both sexes, and 3n females might reach larger sizes than 3n males and their 2n counterparts in this species.