Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic and terrestrial environments. The main objective of this review was to summarize the current knowledge of the impacts of EDCs on reproductive success in wildlife and humans. The examples selected often include a retrospective assessment of the knowledge of reproductive impacts over time to discern how the effects of EDCs have changed over the last several decades. Collectively, the evidence summarized here within reinforce the concept that reproduction in wildlife and humans is negatively impacted by anthropogenic chemicals, with several altering endocrine system function. These observations of chemicals interfering with different aspects of the reproductive endocrine axis are particularly pronounced for aquatic species and are often corroborated by laboratory-based experiments (i.e. fish, amphibians, birds). Noteworthy, many of these same indicators are also observed in epidemiological studies in mammalian wildlife and humans. Given the vast array of reproductive strategies used by animals, it is perhaps not surprising that no single disrupted target is predictive of reproductive effects. Nevertheless, there are some general features of the endocrine control of reproduction, and in particular, the critical role that steroid hormones play in these processes that confer a high degree of susceptibility to environmental chemicals. New research is needed on the implications of chemical exposures during development and the potential for long-term reproductive effects. Future emphasis on field-based observations that can form the basis of more deliberate, extensive, and long-term population level studies to monitor contaminant effects, including adverse effects on the endocrine system, are key to addressing these knowledge gaps.

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.

Impact of activated sludge configuration and operating conditions on in vitro and in vivo responses and trace organic compound removal

This study tested municipal sewage effluents generated at the pilot scale using conventional activated sludge (CAS), nitrifying activated sludge (CAS-N) and biological nutrient removal (BNR) in terms of the removal of trace organic compounds (TrOCs) and final effluent quality as indicated by yeast estrogenicity screening (YES), short term zebrafish reproduction and fathead minnow life-cycle tests. Under cold weather conditions (extended SRTs), the BNR configuration reduced the concentrations of the largest number of TrOCs while under warm weather conditions (reduced SRTs) the CAS-N was most effective. By comparison, YES test results indicated statistically lower responses in the BNR effluent in the warm weather tests and no difference between the effluents of CAS-N and BNR in the cold weather tests. Short term tests with adult zebrafish revealed no impact of the BNR and CAS-N effluents on egg production. By contrast egg production and gene expression in the CAS-exposed zebrafish were substantially less than that of control exposures and were similar to that of exposures to ammonia at similar concentrations as the CAS exposures. In fathead minnow life-cycle tests, exposures to CAS effluent (70-50% v/v) resulted in considerable mortality, reduced growth and reduced egg production that was likely due to the elevated ammonia concentrations. The CAS-N effluent (100% v/v) also resulted in some mortality and reduced growth and egg production in the fathead minnows. By contrast, the BNR effluent (100% v/v) had no effect on mortality, growth or egg production. The results suggest that enhancements to wastewater treatment plants that are associated with improved nitrogen removal can result in enhanced removal of TrOCs and can reduce the harmful effects of the effluents on aquatic biota.

Biology of lake sturgeon (Acipenser fulvescens) spawning below a dam on the Richelieu River, Quebec: behaviour, egg deposition, and endocrinology

Knowledge of the reproductive biology of wild sturgeon populations is critical to ensure the survival of this unique group of animals. We combined gill-netting surveys, nonlethal blood sampling, radiotelemetry, and egg collection to examine the reproductive biology of lake sturgeon (Acipenser fulvescens Rafinesque, 1817) at a suspected spawning ground below a dam on the Richelieu River, Quebec. Lake sturgeon were present at the beginning of sampling in early May, and spawning took place from 26 May to 5 June when water temperature averaged 13.4 ± 0.1 °C (range 11.5–15.5 °C). Daily spawning population estimates ranged from 285 to 1282 individuals and the sex ratio of spawners was estimated at 2.1 males per female. The presence of radio-tagged individuals on the spawning grounds peaked from 20 to 28 May, corresponding with known spawning bouts. Residence time of spawners on the spawning ground ranged from 1 to 27 days (median = 5 days) and there were no differences in residence time between sexes. Nonlethal blood sampling enabled the quantification of steroid levels to determine the spawning population sex ratio, and steroid levels were highest before spawning was known to occur and decreased concurrently with, and after, known spawning events.

Physiological condition differentially affects the behavior and survival of two populations of sockeye salmon during their freshwater spawning migration

Recently, a segment of the Adams-Shuswap sockeye salmon (Oncorhynchus nerka) population initiated freshwater migration several weeks earlier than historically recorded, resulting in high mortality rates. The comigrating Chilko population maintained their historic river entry timing and did not experience elevated mortality. To test the hypothesis that population-specific differences in physiological condition would differentially influence behavior and survival when exposed to fisheries capture stress, we physiologically sampled individuals from both populations at the onset of the freshwater phase of their reproductive migration and tracked the remainder of their migrations using radio telemetry. Adams-Shuswap individuals had slower migration rates and were less likely to reach natal subwatersheds relative to Chilko individuals. Metabolic and osmoregulatory impairment was related to mortality for Adams-Shuswap individuals but not for Chilko individuals. Similarly, physiological condition correlated with migration rate for Adams-Shuswap but not Chilko fish. Survival to natal subwatersheds was 1.9 times higher for Chilko relative to Adams-Shuswap, a result that did not emerge until individuals approached natal subwatersheds several days after the stressor was applied. We conclude that physiological condition differentially affects the behavior and survival of these two populations, which may be a consequence of the early-entry phenomenon by a segment of the Adams-Shuswap population.

Testing the synergistic effects of GnRH and testosterone on the reproductive physiology of pre-adult pink salmon Oncorhynchus gorbuscha

To test the hypothesis that the hypothalmic gonadotropin-releasing hormone (GnRH) and testosterone (T) co-treatment stimulates both the hypothalmo-pituitary-gonadal (HPG) and hypothalmo-pituitary-interrenal axes, the reproductive and osmoregulatory responses of pre-adult pink salmon Oncorhynchus gorbuscha were compared after GnRH and T administration either alone or in combination. Relative to controls, neither GnRH nor T treatment resulted in significantly greater ovarian or testicular growth, but co-treatment significantly increased ovarian growth after 5 months. Interestingly, the stimulation was undetectable after 3 months. However, once daily photoperiod began shortening after the summer solstice, c. 2 months before the natural spawning date, GnRH+T-treated females were stimulated to produce larger ovaries. Final fish body length and the size of individual eggs did not differ among treatment groups. GnRH+T eggs, however, showed signs of advanced vitellogenesis relative to GnRH-treated and control eggs, whereas T-treated eggs became atretic. Testis size increased significantly from initial values and most males were spermiating, but this growth and development were independent of hormone treatments. Final plasma ion, metabolite and cortisol concentrations did not differ among treatment groups. It is concluded that GnRH+T co-treatment was effective in stimulating female but not male maturation. GnRH and T treatment, however, presumably had little effect on the hypothalmo-pituitary-interrenal axis as observed by ionoregulatory status.

An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation

This study explored the potential for ovarian-derived prostaglandins (PGs) to be involved in the regulation of oocyte maturation and ovulation in zebrafish. It was demonstrated that cultured vitellogenic follicles have the capacity to produce prostaglandin E(2) (PGE(2)) and PGF(2alpha) in response to arachidonic acid (AA) in a concentration-dependent manner, and that AA stimulates the in vitro production of 17beta-estradiol (E(2)). The production of AA-stimulated PGF(2alpha) was significantly reduced by treatment with the non-selective cyclooxygenase (COX) inhibitor, indomethacin (INDO). Treatment of full-grown follicles with AA did not induce oocyte maturation as assessed by germinal vesicle breakdown, but INDO significantly decreased the rate of spontaneous maturation. Using Real-Time PCR, it was shown that follicles of different developmental size classes (primary growth and pre-vitellogenic, early-vitellogenic, and mid- to full-grown vitellogenic) express enzymes that release (cytosolic phospholipase A(2) (cPLA(2)); phospholipase Cgamma1) or metabolize (COX-1, COX-2, and prostaglandin synthase-2) AA to PG metabolites. The expression of cPLA(2) was found to be significantly greater in full-grown follicles compared to follicles of the pre- and early-vitellogenic stages. In vivo studies demonstrated that breeding groups of zebrafish exposed to 100 microg/L INDO exhibited reduced spawning rates and clutch sizes compared with control and 1 microg/L INDO exposed fish. In other studies, it was shown that naturally spawning groups of females exhibit increased ovarian levels of PGF(2alpha), E(2), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (a maturation-inducing hormone in zebrafish) near the time of ovulation compared with non-breeding females. Collectively, these experiments indicate that the AA pathway in zebrafish ovaries is involved in the regulation of oocyte maturation and ovulation and a non-selective inhibitor of COX disrupts these processes.

Reproductive and stress hormone levels in goldfish (Carassius auratus) exposed to oil sands process-affected water

Athabasca oil sands mining in northern Alberta produces process-affected waters that are characterized by the presence of naphthenic acids, polycyclic aromatic hydrocarbons, and high salinity. The purpose of this study was to examine the impact of these process-affected waters on reproductive and stress related endpoints in mature goldfish, Carassius auratus. In two separate studies, testosterone and 17beta-estradiol levels in the plasma were significantly reduced in both male and female goldfish caged for 19 days in process-affected waters relative to controls. This effect was most pronounced in goldfish caged at a site containing mature fine tailing and tailings pond water (P5). Ovarian and testicular tissues from fish in the caging studies were incubated in vitro to evaluate potential differences in basal steroid production levels and responsiveness to human chorionic gonadotropin (hCG). Basal levels of testosterone were reduced significantly in males and females from P5 compared with the control pond (P1) demonstrating that the gonads from exposed fish had a diminished steroidogenic capacity. Gonadal tissues of fish from all ponds responded similarly to hCG suggesting that the steroid biosynthetic pathway remained functionally intact. Plasma cortisol levels were significantly higher in male goldfish caged in a pond containing mature fine tailings and capped with uncontaminated water (P3) and in P5 compared with P1. Collectively, these studies suggest that waste products of oil sands mining have the potential to disrupt the normal endocrine functioning in exposed fish through alterations to both reproductive and glucocorticoid hormone biosynthesis. In additional laboratory studies, exposure of goldfish to a naphthenic acid extract for 7 days failed to replicate the effects of processes-affected waters on plasma steroid levels and the causative agent(s) responsible for the effects on steroid biosynthesis remains to be identified.

Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration

Since 1996, some populations of Fraser River sockeye salmon ( Oncorhynchus nerka Walbaum in Artedi, 1792) have begun spawning migrations weeks earlier than normal, and most perish en route as a result. We suspect that a high midsummer river temperature is the principal cause of mortality. We intercepted 100 sockeye during normal migration near a spawning stream and measured somatic energy and aspects of plasma biochemistry. Fish were then held at either 10 or 18 °C for 24 days. Before release, fish were biopsied again and implanted with acoustic transmitters. A group of biopsied but untreated control salmon were released at the same time. Sixty-two percent (8 of 13) of control salmon and 68% (21 of 31) of 10 °C salmon reached spawning areas. The 18 °C-treated fish were half as successful (35%; 6 of 17). During the holding period, mortality was 2 times higher and levels of Parvicapsula minibicornis (Kent, Whitaker and Dawe, 1997) infection were higher in the 18 °C-treated group than in the 10 °C-treated group. The only physiological difference between treatments was a change in gill Na+,K+-ATPase activity. This drop correlated negatively with travel times for the 18 °C-treated males. Reproductive-hormone levels and stress measures did not differ between treatments but showed significant correlations with individual travel times.

Plasma steroid hormone concentrations, aromatase activities and GSI in ranid frogs collected from agricultural and non-agricultural sites in Michigan (USA)

The triazine herbicide atrazine has been hypothesized to disrupt sexual development in frogs by up-regulating aromatase activity, resulting in greater estradiol (E2) concentrations and causing feminization in males. The goal of this study was to collect native ranid frogs from atrazine-exposed ponds and determine whether relationships exist between measured atrazine concentrations and the gonadosomatic index (GSI), plasma concentrations of testosterone (T), E2 or 11-ketotestosterone (KT), or with aromatase activity. In the summer of 2002 and 2003, adult and juvenile green frogs (Rana clamitans), bullfrogs (R. catesbeiana) and Northern leopard frogs (R. pipiens) were collected from areas with extensive corn cultivation and areas where there was little agricultural activity in south-central Michigan. Atrazine concentrations were below the limit of quantification at non-agricultural sites. Atrazine concentrations did not exceed 2 microg/L at most agricultural sites, but a concentration of 250 microg atrazine/L was measured in one sample from one site in 2002. Plasma steroid concentrations varied among locations. Aromatase activity was measurable in less than 11% of testes in adult males, and in less than 4% of testes in juvenile males. Median aromatase activities in ovaries of adult females ranged from 3 to 245 pmol/h/mg protein, and maximum activities were 2.5-fold greater in juveniles than in adults. Atrazine concentrations were not significantly correlated with any of the parameters measured in this study. These results indicate that atrazine does not up-regulate aromatase in green frogs in the wild, and does not appear to affect plasma steroid hormone concentrations.

Atrazine concentrations, gonadal gross morphology and histology in ranid frogs collected in Michigan agricultural areas

The triazine herbicide atrazine has been suggested to be a potential disruptor of normal sexual development in male frogs. The goals of this study were to collect native ranid frogs from sites in agricultural and non-agricultural areas and determine whether hypothesised atrazine effects on the gonads could be observed at the gross morphological and histological levels. Juvenile and adult green frogs (Rana clamitans), bullfrogs (R. catesbeiana) and leopard frogs (R. pipiens) were collected in the summers of 2002 and 2003. Atrazine concentrations were below the limit of quantification at non-agricultural sites, and concentrations did not exceed 2 microg/L at most agricultural sites. One concentration greater than 200 microg atrazine/L was measured once at one site in 2002. Hermaphroditic individuals with both male and female gonad tissue in either one or both gonads, were found at a low incidence at both non-agricultural and agricultural sites, and in both adults and juveniles. Testicular oocytes (TO) were found in male frogs at most of the sites, with the greatest incidence occurring in juvenile leopard frogs. TO incidence was not significantly different between agricultural and non-agricultural sites with the exception of juveniles collected in 2003. Atrazine concentrations were not significantly correlated with the incidence of hermaphroditism, but maximum atrazine concentrations were correlated with TO incidence in juvenile frogs in 2003. However, given the lack of a consistent relationship between atrazine concentrations and TO incidence, it is more likely the TOs observed in this study result from natural processes in development rather than atrazine exposure.

Sex steroid regulation of brain glutamic acid decarboxylase (GAD) mRNA is season-dependent and sexually dimorphic in the goldfish Carassius auratus

GABA, the major inhibitory neurotransmitter of the vertebrate brain, has been shown to play an important role in vertebrate reproduction by regulating LH release and sexual behavior. We have studied the expression of the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD), in goldfish throughout the reproductive cycle in May (mature), November (early gonadal recrudescence) and February (late gonadal recrudescence) and in response to implanted sex steroids. Levels of GAD67 and GAD65 mRNA levels in the hypothalamus of both males and females were highest in the early stages of gonadal recrudescence. In the telencephalon, a different seasonal pattern of GAD expression was evident. The telencephalic expression GAD67, GAD65 and a novel isoform, GAD3, were highest in sexually mature fish in May. Five-day intraperitoneal implantation of gonad-intact fish with testosterone (T), estradiol (E2) or progesterone (P4) did not affect GAD expression in November and February. This is in contrast to results in May when sex differences in steroid responsiveness were evident. Progesterone decreased hypothalamic GAD67 and GAD65 in females and was without effect in males. All other treatments did not alter GAD67, GAD65 or GAD3 expression in the hypothalamus. Both T and P4 decreased GAD67 and GAD65 levels in the telencephalon of male goldfish but had no effect in females. Serum sex steroid levels in control and implanted mature males and females in May were similar so it is unlikely that sex differences in the GAD responses were a result of differences in serum sex steroid levels. These contrasting effects of sex steroids on males and females suggest important sex differences in the regulation of the GADs in sexually mature goldfish.

Seasonal exposures to triazine and other pesticides in surface waters in the western Highveld corn-production region in South Africa

The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season. Pesticide residues were measured at regular intervals in surface water from eight ponds, three in a non-corn-growing area (NCGA) and five within the corn-growing area (CGA). Measured atrazine concentrations differed significantly among sites and between samples. In the five CGA sites, the maximum atrazine concentrations measured during the study ranged from 1.2 to 9.3 microg/L. Although no atrazine was recorded as being applied in the catchment of the three NCGA sites, maximum concentrations from 0.39 to 0.84 microg/L were measured during the study, possibly as a result of atmospheric transport. Maximum measured concentrations of terbuthylazine ranged from 1.22 to 2.1 microg/L in the NCGA sites and from 1.04 to 4.1 microg/L in the CGA sites. The source of terbuthylazine in the NCGA sites may have been in use other than in corn. The triazine degradation products, deisopropylatrazine (DIA) and deethylatrazine (DEA) and diaminochlorotriazine (DACT) were also found in water from both the CGA and NCGA sites. Concentrations of DIA were > or = 1 microg/L throughout the season, while DEA concentrations were mostly <0.5 microg/L before planting but increased after planting and application of herbicides to concentrations >2 microg/L in some locations. Concentrations of DACT were highly variable (LOD to 8 microg/L) both before and after planting and application, suggesting that they resulted from historical use of triazines in the area. Other herbicides such as simazine and acetochlor were only detected infrequently and pesticides such as S-metolachlor, cypermethrin, monocrotophos, and terbuphos, known to be used in the CGA, were not detected in any of the samples. Because of dilution by higher than normal rainfall in the study period, these concentrations may not be predictive of those in years of normal rainfall.

The effects of pulp mill effluent on the sex steroid binding protein in white sucker (Catostomus commersoni) and longnose sucker (C catostomus)

The objective of this study was to characterize the effects of pulp mill effluent on the properties of the sex steroid binding protein (SBP) in the plasma of white sucker (Catostomus commersoni) and longnose sucker (C. catostomus). SBPs which specifically bind estradiol and testosterone with high affinity (k(D) approximately 3 nM) and low capacity (B(max) approximately 73-81 nM) were identified in both species. Subsequent studies determined if the properties of the SBP in white sucker exposed to bleached kraft mill effluent (BKME) at Terrace Bay, ON, and in longnose sucker exposed to BKME at Grande Prairie, AB. differed from appropriate reference fish. There were no effects of BKME exposure on the binding affinity (k(D)) of the SBP in either species, but there was a significant increase in the binding capacity (B(max)) of longnose sucker SBP exposed to BKME. The livers of nai;ve white sucker exposed to effluent at Terrace Bay or a bleached sulfite/groundwood mill in Edmundston, NB, rapidly accumulated compounds of differing hydrophobicity that bound to both the white sucker and goldfish (Carassius auratus) SBP. Conversely, there was reduced accumulation of SBP ligands in the bile of effluent-exposed fish. We have demonstrated that constituents present within pulp mill effluent bind to both the white sucker and goldfish SBP, and that native species residing downstream of pulp mill effluents may experience modifications in the properties of their SBP.

Development of a retinoic acid receptor-binding assay with rainbow trout tissue: characterization of retinoic acid binding, receptor tissue distribution, and developmental changes

Retinoic acid (RA) regulates the transcription of various genes required for several essential functions in vertebrates through binding to two classes of nuclear receptors, the retinoic acid receptors (RAR) and retinoid X receptors (RXR). We investigated nuclear RA binding in tissues from rainbow trout using the radiolabeled all-trans and 9-cis isomers of RA. Specific binding (indicative of receptor binding) of both all-trans- and 9-cis-RA was found in all tissues tested, including the adult trout ovary, testis, gill, liver, kidney, blood, white muscle, and heart. The kinetics and absolute amount of RA binding were dependent on both the tissue and the isomer of RA used. All-trans-RA bound with high affinity (K(d) approximately 1.0-3.9 nM), and low capacity (B(max) approximately 75-484 fmol RA/mg protein), while 9-cis-RA bound with lower affinity (K(d) approximately 7-56 nM), but with a greater capacity (B(max) approximately 214-1076 fmol RA/mg protein). The B(max) results were used to estimate RAR and RXR levels and revealed that the gill possesses primarily RARs while the liver possesses primarily RXRs. The RAR-specific competitor TTNPB was able to effectively displace all-trans-[3H]RA in most tissues, and the RXR-specific competitor AGN 194204 was able to effectively displace 9-cis-[3H]RA. However, TTNPB and AGN 194204 could not displace all of the RA in the kidney and testis, suggesting the existence of another nuclear RA binding protein. Binding of all-trans- and 9-cis-RA was also found in developing trout embryos and fry. Kinetic analysis revealed that RAR levels predominated at the eyed-embryo stage, but decreased 87% by the swim-up fry stage, while RXR levels remained relatively constant over the same time period. These findings suggest that RA and its receptors may play a key role in early trout development. This study has provided a simple and rapid radioligand binding assay that can identify RAR and RXRs in trout tissues.

Evidence that acute stress inhibits ovarian steroidogenesis in rainbow trout in vivo, through the action of cortisol

Sexually mature (preovulatory) rainbow trout exposed to confinement stress showed a transitory increase in plasma cortisol levels that was accompanied by a similarly brief depression in plasma testosterone (T) levels. Plasma levels of maturational gonadotropin (GtH) and 17beta-estradiol (E(2)) were unaffected by stress. A similar pattern was displayed by fish exposed to stress in midvitellogenesis. Treatment of vitellogenic fish with exogenous cortisol resulted in significant increases in plasma cortisol at 1 and 3 h postinjection (p.i.). This was associated with significant depression of plasma T levels at 1 and 3 h p.i. and plasma E(2) levels at 3 and 6 h p.i. Plasma levels of GtH were unaffected by treatment with cortisol. Treatment of fish at an earlier stage of vitellogenesis with two different doses of cortisol resulted in very high elevations of plasma cortisol, but no effect on plasma levels of E(2) or GtH. In contrast, plasma T levels showed a stepwise decline over time. These results suggest that the inhibitory effects of stress on reproduction are mediated by cortisol and that the effect does not involve inhibition of GtH secretion and possibly acts at the level of GtH signal-transduction.

Peptide growth factors modulate prostaglandin E and F production by goldfish ovarian follicles

This study examines the effect of epidermal growth factor (EGF) on prostaglandin synthesis by goldfish ovarian follicles at different developmental stages. Early vitellogenic follicles (EVIT), vitellogenic follicles (VIT), and prematurational full-grown follicles (PMFG) were examined. EGF alone had no effect on prostaglandin synthesis whereas production of PGE2 and PGF2alpha was enhanced in the presence of the eicosaniod precursor arachidonic acid (AA) in all three follicle classes. EGF enhanced AA stimulation of PGE2 production in both VIT and PMFG follicles. In the same follicles, AA-induced PGF2alpha production either was reduced or was unaffected by EGF. This suggests regulation of prostaglandin synthesis at a point downstream of the conversion of AA to PGH2: the precursor for both PGE2 and PGF2alpha. EGF had no effect on AA stimulation of either PGE2 or PGF2alpha in EVIT follicles. While only VIT and PMFG follicles were responsive to EGF, Western blotting with an antibody to the human EGF-receptor (EGF-R) suggests that all three classes of follicle may possess the receptor protein. Additional tests showed that insulin-like growth factor-I (IGF-I) had no effect on the production of either PGE2 or PGF2alpha by PMFG follicles. By comparison both TGFalpha (which binds to the EGF receptor) and TGFbeta (which acts through a different receptor) enhanced AA-stimulated PGE2 production while having no effect on AA-stimulated PGF2alpha production. In summary, this study demonstrates that several growth factors (EGF, TGFalpha, TGFbeta) may play a role in the regulation of ovarian prostaglandin synthesis and that the actions of EGF change during ovarian follicular development in the goldfish.

Suppression of apoptosis by gonadotropin, 17beta-estradiol, and epidermal growth factor in rainbow trout preovulatory ovarian follicles

In this study we present the first evidence for the occurrence of apoptotic cell death in ovarian follicles from teleost fish. Preovulatory ovarian follicles from mature hatchery-raised rainbow trout (Oncorhynchus mykiss) were collected and either immediately frozen in liquid nitrogen or incubated in serum-free medium at 18 degrees for 24 hr. The extent of ovarian apoptotic DNA fragmentation was determined using 3'-end labeling of DNA with [32P]dideoxy-ATP, size fractionation by agarose gel electrophoresis, and quantification of low-molecular-weight (<15 kb) DNA using autoradiography and liquid scintillation counting. The extent of apoptotic DNA fragmentation was eightfold greater in immediately frozen preovulatory follicles than in previtellogenic ovarian follicles collected from immature rainbow trout (P < 0.05), suggesting differences in the degree of apoptosis at different stages of follicular development. In preovulatory trout follicles, the extent of apoptotic DNA fragmentation was fivefold greater in follicles incubated for 24 hr. Treatment of incubated preovulatory follicles with either partially purified salmon gonadotropin SG-G100 (1 microg/ml) or epidermal growth factor (EGF; 100 ng/ml) suppressed apoptotic DNA fragmentation by 31 and 41%, respectively, in comparison to untreated incubated follicles (P < 0.01). Treatment of incubated follicles with 17beta-estradiol (1-100 ng/ml) caused a concentration-dependent suppression of apoptotic DNA fragmentation (P < 0.05). These results suggest that apoptosis is involved in teleost ovarian development and that several of the hormonal factors acting as follicle survival factors in mammalian and avian ovaries may play a similar role in teleost ovarian follicles.

Overripening as the cause of low survival to hatch in Lake Erie coho salmon (Oncorhynchus kisutch) embryos

We investigated the cause of the low survival to hatch of embryos of coho salmon (Oncorhynchus kisutch) from the Fairview, Pennsylvania, stock in Lake Erie. In 1988, survival to hatch of this stock was only 42%, whereas another Great Lakes coho salmon stock of similar genetic origin had an 84% survival to hatch. Laboratory cross-fertilization studies between the Fairview stock and a reference Lake Erie stock from Simcoe, Ontario, showed that eggs from the Fairview stock were the probable source of the low fertility. The presence of overripe eggs in Fairview females was associated with poor fertilization and low survival to hatch. Plasma gonadotropin II levels were similar in preovulatory females taken from the Fairview and Simcoe stocks, but testosterone and 17α, 20β-dihydroxy-4-pregnen-3-one levels were significantly lower in the Fairview females. Increasing the triiodo-L-thyronine (T3) content of the eggs by the administration of T3 to the preovulatory females did not enhance egg fertility. We propose that the low survival to hatch of the Fairview embryos is due to delayed oocyte maturation and ovulation and vent maturation, which may have been caused by exposure of the Fairview salmon to warmer water during the period of late ovarian maturation and migration.

Mechanisms of action of free arachidonic acid on ovarian steroid production in the goldfish

This study explores the mechanisms by which free arachidonic acid (AA) affects ovarian steroidogenesis by full-grown prematurational follicles of the goldfish in vitro. AA (6-400 microM) stimulated testosterone production and this action was mediated by prostaglandin E2 (PGE2). The steroidogenic actions of AA and the corresponding increase in the production of PGE2 were blocked by inhibitors of the cyclooxygenase pathway (indomethacin, ETYA). Exogenous PGE2 (20-2000 ng/ml) also stimulated steroid production. In the presence of human chorionic gonadotropin (hCG), AA had differential effects. AA potentiated the steroidogenic actions of low dosages of hCG (0.1 IU/ml), while with maximal gonadotropin (1-10 IU/ml) stimulation a high concentration of AA (400 microM) attenuated steroid production in spite of elevated PGE2 synthesis, nor did it affect the PGE2 production obtained with AA-treated follicles. The steroidogenic induction by AA via PGE2 was mediated in part by Ca2+ since the calcium channel blocker nifedipine (25 microM) inhibited stimulated steroid production by both AA and PGE2. The conversion of AA to PGE2 does not require Ca2+ since PGE2 production by AA-treated follicles was not affected by nifedipine. However, treatment with the calcium ionophore A23187 (1 microM) potentiated the stimulatory actions of AA on steroid and prostaglandin production. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (1 mM) potentiated the stimulatory actions of AA on testosterone production but had no effect on the conversion of AA to PGE2. The steroidogenic actions of AA and PGE2 involve both transcription and translation since stimulated steroidogenesis was inhibited by actinomycin D and and cycloheximide (1-10 micrograms/ml). The conversion of AA to PGE2 was also blocked by these inhibitors. These results underscore the importance of AA and PGE2 in the regulation of ovarian steroidogenesis in the goldfish.

Multifactorial regulation of DNA synthesis in goldfish ovarian follicles

The present study examines the interactive effects of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) with insulin, insulin-like growth factors I and II (IGF-I and IGF-II), and human chorionic gonadotropin (hCG) on DNA synthesis by goldfish ovarian follicles in vitro. DNA synthesis was assessed from the incorporation of [3H]thymidine. When tested individually, EGF, TGF alpha, insulin, IGFs, and hCG enhanced DNA synthesis by vitellogenic ovarian follicles. The interactive effects of EGF and TGF alpha on DNA synthesis by vitellogenic follicles were not additive, suggesting that these growth factors work through the same receptors. The most profound mitogenic effects of EGF and TGF alpha were seen when they were combined with insulin, IGF-I, or IGF-II. Unlike IGF-1, which had an additive effect when tested with hCG, EGF and hCG effects on DNA synthesis were not additive. Treatment with an antibody to EGF but neither gamma-globulin nor IGF-I antibody blocked the stimulatory actions of hCG on DNA synthesis by vitellogenic follicles. This suggests that EGF mediates the actions of hCG on DNA synthesis. In summary, these data support the concept that several growth factors and gonadotropins participate in the regulation of DNA synthesis in goldfish vitellogenic follicles.

Sulfation and uptake of the maturation-inducing steroid, 17α,20β-dihydroxy-4-pregnen-3-one by rainbow trout ovarian follicles

Rainbow trout ovarian follicles were incubated in vitro with tritiated 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P; maturation-inducing steroid). Within 18-24 h, 56-66% had been converted to tritiated 17α,20β-dihydroxy-4-pregnen-3-one 20-sulfate (identification confirmed by HPLC) and 27% had been taken up (absorbed) by the follicles. Addition of 125 ng of cold (non-tritiated) 17,20β-P to the incubations caused a decrease in the percentage of [(3)H]-17,20β-P which was sulfated (56% → 10%) and an increase in the percentage that was taken up (27% → 57%). Seven steroids were tested for their effectiveness in decreasing the sulfation and increasing the uptake of tritiated [(3)H]-17,20β-P. The order of effectiveness was in both cases the same: 17,20β-P > cortisol > 11-deoxycortisol > 17α,20β,21-trihydroxy-4-pregnen-3-one > 17α-hydroxy-4-pregnene-3,20-dione > 17β-estradiol > testosterone. This indicated that the processes of sulfation and uptake of [(3)H]-17,20β-P were related to each other and led to the hypothesis that, when cold 17,20β-P is added to the medium, it reduces the proportion of [(3)H]-17,20β-P which is sulfated and thus allows more free [(3)H]-17,20β-P to enter the ovarian follicles. This hypothesis was supported by the finding that each ovarian follicle had the capacity in vitro to sulfate only ca. 2 ng of [(3)H]-17,20β-P per 18h but a capacity to take up > 500 ng per 18h.Gonadotropin I, Gonadotropin II, forskolin and phorbol-12-myristate-13-acetate (which all have an affect on steroid biosynthesis) did not affect the amount of 17,20β-P which was sulfated. Sulfating activity was localized in the thecal cell layer of the follicle. The yolk fraction was shown to be responsible for absorbing the [(3)H]-17,20β-P.

Inhibition of gonadotropin-stimulated ovarian steroid production by polyunsaturated fatty acids in teleost fish

The effects of the polyunsaturated fatty acids (PUFAs)--eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA)--on in vitro steroid production by full-grown prematurational ovarian follicles from goldfish and rainbow trout were investigated. EPA and DHA inhibited gonadotropin-stimulated testosterone production in a dose-related manner, but AA was inhibitory only at the highest dose tested (400 microM). AA alone stimulated testosterone production by increasing cAMP production, but the effects of other PUFAs alone were marginal. The inhibitory actions by PUFAs were not restricted to long-chain PUFAs, as linoleic and linolenic acids had similar actions in the goldfish. The inhibitory action of EPA on testosterone production was reversible upon removal of the PUFA from medium. Testosterone production stimulated by the addition of the cAMP analogues, dibutyryl cAMP, and 8-bromo cAMP, was attenuated by PUFAs, suggesting that they act at a site distal to cAMP formation. A post-cAMP site regulating cholesterol availability may be involved as testosterone production induced by addition of 25OH-cholesterol was not affected by the PUFAs in either fish species. Together, these findings underscore the importance of lipids in ovarian physiology and suggest that PUFAs may participate in the regulation of ovarian steroidogenesis in teleost fish.

Polyunsaturated fatty acids do not activate protein kinase C in the testis of the goldfish (Carassius auratus)

Earlier studies have established that polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid and docosahexaenoic acid inhibit steroid production in the goldfish testis. As PUFA inhibit testicular steroidogenesis in the rat through activation of protein kinase C (PKC), the present studies were undertaken to characterize the properties of PKC in the goldfish testis and to test the effects of selected PUFA on PKC activity. PKC activity was quantified in goldfish testis homogenate following partial purification by DEAE-cellulose chromatography by determining the transfer of radiolabelled phosphate from [γ - (32)P]ATP to histone III-S. Testicular PKC activity was defined by the amount of protein phosphorylation in the presence of phosphatidylserine, phasphatidylcholine, Ca(2+) ions and diolein (a 1,2-diacylglycerol analog) above that obtained in response to Ca(2+) ions alone. Western blot analysis of a crude testis homogenate using an antibody specific to the α and β isoforms of mammalian PKC led to the identification a single band of protein (80 kD) that co-migrated with PKC from rabbit brain cytosol. Addition of arachidonic, eicosapentaenoic or docosahexaenoic acids failed to activate PKC. However, PKC activity stimulated by phospholipid, Ca(2+) ions and diolein was inhibited in a dose related fashion by all of these fatty acids. These studies suggest that the inhibitory effects of EPA and DHA on testicular steroidogenesis are not mediated by activation of PKC. The lack of effect of PUFA on PKC activity in the goldfish testis suggests that either the distribution of PKC isoforms differs between the testis of mammals and fish or that PKC is not activated by PUFA in the goldfish.

Effects of 17β-estradiol on pituitary and testicular function in male goldfish

The potential involvement of 17β-estradiol in the regulation of pituitary and testicular function was investigated in male goldfish at various times during the seasonal reproductive cycle. Serum levels of testosterone, 11-ketotestosterone, and 17β-estradiol were 10, 16, and 4 times higher in mature males (tubercles on the pectoral fins and milt production; March) than in sexually regressed males (no tubercles or milt production; July). Intraperitoneal injection of [D-Arg6,Trp7,Leu8,Pro9-NEt]gonadotropin releasing hormone (sGnRH-A, 0.01 μg/g) elevated serum gonadotropin II levels within 6 h, and there was a concomitant increase in testosterone but not 17β-estradiol levels in sexually regressing male goldfish (October). Males in the early stage of testicular recrudescence (November) had increased serum levels of gonadotropin II and testosterone in response to [D-Ala6,Pro9-NEt]GnRH (LHRH-A, 0.1 μg/g) or the dopamine antagonist domperidone (5 μg/g). Males implanted intraperitoneally for 10 days with solid Silastic pellet implants containing 17β-estradiol (100 μg/g) had lower basal testosterone levels and a reduced testosterone response to both LHRH-A and domperidone. The serum gonadotropin II response to LHRH-A but not domperidone was enhanced by 17β-estradiol. Male goldfish in mid-recrudescence receiving 17β-estradiol implants for 4 days had lower basal testosterone and 11-ketotestosterone levels than controls. Combined treatment with sGnRH-A (0.1 μg/g) and domperidone (10 μg/g) elevated serum testosterone and 11-ketotestosterone levels at 24 h; the serum androgen response was reduced in 17β-estradiol-implanted fish. These studies support the concept that 17β-estradiol plays a role in the regulation of reproduction in male goldfish by enhancing pituitary gonadotropin II release and by reducing testicular androgen production.

Effect of a teleost GnRH analog on steroidogenesis by the follicle-enclosed goldfish oocytes, in vitro

The influence of an agonist analog of teleost GnRH [(D-Arg6, Trp7, Leu8, Pro9-NEt)-GnRH; tGnRH-A] on steroidogenesis was studied in prophase-I arrested, follicle-enclosed, goldfish oocytes in vitro. Incubation of the follicles with carp gonadotropin (GtH) significantly increased production of 17 alpha-hydroxyprogesterone (HP) and testosterone following 24 hr of incubation in vitro. Concomitant incubation with tGnRH-A (10(-7) M) significantly attenuated the dose-related increase in GtH-induced testosterone production, but was without effect on the GtH-induced HP level. Time course studies indicated that tGnRH-A exerted its maximum inhibitory action on the GtH-induced testosterone production during the initial 8 hr of incubation in vitro. The inhibition of GtH-induced testosterone production by tGnRH-A was dose dependent with an ED50 of 1.39 +/- 2.88 nM. A significantly higher testosterone level was obtained in the incubation media containing HP as substrate; concomitant treatment with tGnRH-A reduced the conversion of HP to testosterone. The incubation media also contained low, but measurable levels of 17 alpha-hydroxy-20 beta-dihydroprogesterone (DHP), which increased in the presence of 3-isobutyl-methyl-xanthine; lower levels of DHP were obtained in the groups incubated with tGnRH-A. In view of our present findings and previous observations concerning inhibitory effects of tGnRH-A on the progestogen and GtH-induced reinitiation of meiosis in the follicle-enclosed goldfish oocytes (H. R. Habibi, G. Van Der Kraak, E. Bulanski, and R. E. Peter, Amer. J. Physiol. 255, R268-R273 (1988] the influence of testosterone on the GtH- and DHP-induced meiosis in vitro was also studied. Testosterone (1 micrograms/ml) enhanced both GtH- and DHP-induced oocyte meiosis in the goldfish oocytes. Testosterone alone was also found to significantly increase oocyte meiosis in the goldfish oocytes in a dose-related fashion. The present findings demonstrate an inhibitory effect of a GnRH agonist on GtH-induced testosterone production in goldfish oocytes and suggest that tGnRH-A might influence oocyte meiosis in part by influencing steroidogenesis.

Dopamine inhibits gonadotropin secretion in the Chinese loach (Paramisgurnus dabryanus)

The effects of dopamine on gonadotropin (GtH) secretion in sexually mature Chinese loach were investigated. Spontaneous secretion of GtH was inhibited within 1 h following an intramuscular injection of dopamine (100 μg/g body wt). Similarly, dopamine (50 and 100 μg/g body wt) caused a significant reduction in serum GtH in fish with elevated GtH levels as a result of pretreatment with gonadotropin-releasing hormone (GnRH) analogs either alone or in combination with the dopamine receptor antagonist domperidone. In summary, the present study provides direct evidence that dopamine functions as a gonadotropin-release inhibitory factor in the Chinese loach by blocking spontaneous and GnRH-stimulated GtH release.

Effects of temperature on triiodothyronine plasma levels, kinetics, and hepatocyte nuclear binding in rainbow trout, Salmo gairdneri

Plasma levels of 3,5,3′-triiodo-L-thyronine (T3), plasma T3 kinetics, and properties of in vivo T3 binding to saturable hepatocyte nuclear sites were studied in fed immature rainbow trout maintained at 12 °C and then held for up to 14 d at 5, 11–12, or 19 °C. Elevation (19 °C) or depression (5 °C) of plasma T3 occurred during the first 3 h following abrupt transfer from 11 °C, but from 12 h to 7 d, plasma T3 did not differ significantly among the three temperatures. In contrast, the plasma T3 degradation rate increased fourfold from 5 to 19 °C largely because of an increased fractional rate of turnover of the plasma T3 pool. Outer-ring deiodination of T3 was negligible at 5 and 12 °C and slight at 19 °C. Temperature did not influence the proportion of [125I]T3 lost via the enterohepatic route. Uptake of [125I]T3 into the liver and liver nuclear fraction was most rapid at 19 °C, intermediate at 12 °C, and least rapid at 5 °C. Saturable nuclear binding of [125I]T3 occurred at all temperatures. The apparent affinity of T3 for hepatic nuclear sites was similar at 12 and 19 °C but lower at 5 °C; the apparent site capacity underwent no significant change with temperature. In conclusion, over the range of 5 to 19 °C there are marked increases in plasma T3 clearance, rate of T3 uptake from plasma to liver, and rate of T3 uptake by the liver nuclear fraction, but relatively small changes in plasma T3 level, proportion of T3 excreted via the enterohepatic route, and properties of the saturable T3-binding nuclear sites.

Reproductive development and plasma levels of reproductive hormones of goldeye, Hiodon alosoides (Rafinesque), taken from the North Saskatchewan River during the open-water season

Changes in gonadal condition and plasma levels of gonadotropin and sex steroids were measured in goldeye (Hiodon alosoides) captured from the North Saskatchewan River, Edmonton, Alberta, from May to October in both 1983 and 1984. Mature females and spermiated males were captured in May and June and spent fish were captured in June. Gonadal recrudescence occurred over the summer and by October, relative gonad weights had reached 70% (females) and 90% (males) of the prespawning maxima. In females, plasma calcium was significantly elevated in spent fish in June, and in August there was a decrease in liver weight. Plasma levels of gonadotropin were highest in females during June, and in males during May. 17α,20β-Dihydroxy-4-pregnen-3-one was elevated in preovulatory or spent females and prespawning males, then decreased throughout the summer, whereas testosterone was only detectable in the plasma of prespawning fish. Estradiol-17β and estrone were not detectable in the plasma of females at any stage, including the period of vitellogenesis.

Steroidogenic capacity of coho salmon ovarian follicles throughout the periovulatory period

Coho salmon follicles obtained at various times throughout the periovulatory period were incubatedin vitro with graded amounts of partially purified salmon gonadotropin (SG-G100) for 24 h and the amounts of 17β-estradiol, testosterone and 17α20β dihydroxy-4-pregnen-3-one (17α20βP) released into the media determined by radioimmunoassay. By this approach, the pattern of steroid secretion by ovarian follicles was shown to change in relation to the developmental status of the oocyte. Full-grown immature follicles produced large amounts of 17β-estradiol but negligible amounts of testosterone and 17α20βP. Both basal and gonadotropin-stimulated 17β-estradiol production was subsequently reduced with advancing oocyte development. In contrast, the production of testosterone and 17α20βP increased during the course of ovarian development with testosterone production highest in follicles with a peripheral germinal vesicle and 17α20βP production highest in matured and postovulatory follicles. These data are discussed in relation to information on the preovulatory changes in circulating levels of steriod hormones in salmonids.