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Results for “General and Comparative Endocrinology”

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USGS1998

Evidence for growth hormone/insulin-like growth factor I axis regulation of seawater acclimation in the euryhaline teleost Fundulus heteroclitus

The ability of ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I), recombinant human insulin-like growth factor II (rhIGF-II), and bovine insulin to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity, 320 mOsm/kg H 2 O) were injected with a single dose of hormone and transferred to seawater (SW, 35 ppt salinity, 1120 mOsm/kg H 2 O) 2 days later. Fish were sampled 24 h after transfer and plasma osmolality, plasma glucose, and gill Na + ,K + -ATPase activity were examined. Transfer from BW to SW increased plasma osmolality and gill Na + ,K + -ATPase activity. Transfer from BW to BW had no effect on these parameters. rbIGF-I (0.05, 0.1, and 0.2 μg/g) improved the ability to maintain plasma osmolality and to increase gill Na + , K + -ATPase activity in a dose-dependent manner. oGH (0.5, 1, and 2 μg/g) also increased hypoosmoregulatory ability but only the higher doses (2 μg/g) significantly increased gill Na + ,K + -ATPase activity. oGH (1 μg/g) and rbIGF-I (0.1 μg/g) had a significantly greater effect on plasma osmolality and gill Na + ,K + -ATPase activity than either hormone alone. rhIGF-II (0.05, 0.1, and 0.2 μg/g) and bovine insulin (0.01 and 0.05 μg/g) were without effect. The results suggest a role of GH and insulin-like growth factor I (IGF-I) in seawater acclimation of F. heteroclitus. Based on these findings and previous studies, it is concluded that the capacity of the GH/IGF-I axis to increase hypoosmoregulatory ability may be a common feature of euryhalinity in teleosts.

Connecticut↗

USGS2011

Environmental endocrinology of salmon smoltification

Smolting is a hormone-driven developmental process that is adaptive for downstream migration and ocean survival and growth in anadromous salmonids . Smolting includes increased salinity tolerance, increased metabolism, downstream migratory and schooling behavior, silvering and darkened fin margins, and olfactory imprinting. These changes are promoted by growth hormone, insulin-like growth factor I, cortisol , thyroid hormones, whereas prolactin is inhibitory. Photoperiod and temperature are critical environmental cues for smolt development, and their relative importance will be critical in determining responses to future climate change. Most of our knowledge of the environmental control and endocrine mediation of smolting is based on laboratory and hatchery studies, yet there is emerging information on fish in the wild that indicates substantial differences. Such differences may arise from differences in environmental stimuli in artificial rearing environments, and may be critical to ocean survival and population sustainability. Endocrine disruptors, acidification and other contaminants can perturb smolt development, resulting in poor survival after seawater entry.

General and Comparative Endocrinology↗

USGS1995

Identification of sex in hatchling loggerhead turtles (Caretta caretta) by analysis of steroid concentrations in chorioallantoic/amniotic fluid

A major difficulty in sea turtle conservation is the inability to nonlethally and noninvasively identify the sex of hatchling sea turtles. Traditional sexing techniques such as plasma sex steroid quantification cannot be applied to hatchlings without sacrificing the hatchlings or utilizing invasive procedures. This paper presents a technique for sexing hatchling sea turtles by analysis of sex steroid concentrations in egg chorioallantoic/amniotic fluid (CAF). Metabolites of estradiol-17β (E) and testosterone (T) in CAF are best expressed as an index or E:T ratio. Chorioallantoic/amniotic fluid E:T ratios for males (0.5 ± 0.1) were significantly lower than those for females (2.2 ± 0.3). When separated by utilizing an E:T ratio of 1.25 as the determinant index value, 27 of 28 hatchlings were designated correctly as males (E:T < 1.25) or females (E:T ⩾ 1.25). Sex was verified for all hatchlings by gonadal histology. This study shows significant concentrations of T and E metabolites in CAF and plasma of hatchling loggerhead turtles and illustrates the use of a nonlethal, noninvasive method for determining sex, which could be potentially utilized for other endangered reptile and avian species.

Florida, North Carolina↗

USGS1996

Circulating levels of prolactin and progesterone in a wild population of red kangaroos (Macropus rufus) Marsupialia: Macropodidae

Circulating progesterone and prolactin levels were measured in shot and live-caught wild red kangaroos using radioimmunoassays validated for the red kangaroo. The objective of the study was to correlate hormone profiles with reproductive status and determine if red kangaroos follow the general pattern elucidated for other macropodids. During Phase 2a lactation (<70 days) plasma progesterone concentrations were <189 pg/ml ( n = 41). This value increased to >600 pg/ml ( n = 32) during the transition to Phase 3 lactation (181 to 235 days) when the quiescent corpus luteum and embryo were reactivated. Progesterone concentrations then decreased to <300 pg/ml ( n = 29) during dual lactation when females were suckling a neonate and a young at foot. Concentrations of prolactin during Phase 2a were <6 ng/ml ( n = 17). Coincident with the period of reactivation of the diapausing blastocyst (181 to 235 days), plasma prolactin concentrations increased to 15 ng/ml ( n = 32), then decreased and remained low through the subsequent stage of dual lactation. These results indicate that progesterone and prolactin profiles in wild red kangaroos follow patterns found previously in other macropodid species, the tammar and Bennett's wallabies.

General and Comparative Endocrinology↗

USGS1997

Physiological levels of testosterone kill salmonid leukocytes in vitro

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

General and Comparative Endocrinology↗

USGS1998

Regulation of gill cytosolic corticosteroid receptors in juvenile Atlantic salmon: Interaction effects of growth hormone with prolactand triiodothyronine

The potential effects of growth hormone (GH), prolactin (Prl), and triiodothyronine (T 3 ) on gill Na + ,K + -ATPase activity and corticosteroid receptor (CR) concentration ( B max ) and dissociation constant ( K d ) were examined in juvenile Atlantic salmon ( Salmo salar ). Compared to controls, fish injected with GH (ovine, 5.0 μg g −1 ) had significantly greater gill Na + ,K + -ATPase activity after 7 and 14 days. Gill CR B max and K d were significantly elevated on day 7, but not day 14. T 3 also significantly increased CR B max . The effect of GH on CR B max was also additive with T 3 (5.0 μg g −1 ) treatment. There was a synergistic effect on CR B max when purified coho salmon GH (csGH, 0.1 μg g −1 ) was injected in combination with T 3 (1.6 μg g −1 ). Prl (ovine, 5.0 μg g −1 ; purified coho salmon, 0.1 μg g −1 ) did not significantly alter gill CR B max . Although Prl limited the increase in CR B max by GH, the effect was not signicant. T 3 and Prl did not have an effect on K d . GH significantly increased gill Na + ,K + -ATPase activity, T 3 administration did not have a significant effect, and Prl-treated fish had significantly lower gill Na + ,K + -ATPase activity. The results indicate that T 3 acts additively with GH, while Prl has no effect in regulating CR B max . An increase in cytosolic CR by GH and T 3 , but not Prl, may regulate gill responsiveness to cortisol and be an important mechanism in the endocrine control of physiological changes during the parr–smolt transformation.

General and Comparative Endocrinology↗

USGS1999

Cloning, in Vitro expression, and novel phylogenetic classification of a channel catfish estrogen receptor

We obtained two channel catfish estrogen receptor (ccER) cDNA from liver of female fish using RT–PCR. The two fragments were identical in sequence except that the smaller one had an out-of-frame deletion in the E domain, suggesting the existence of ccER splice variants. The larger fragment was used to screen a cDNA library from liver of a prepubescent female. A cDNA was obtained that encoded a 581-amino-acid ER with a deduced molecular weight of 63.8 kDa. Extracts of COS-7 cells transfected with ccER cDNA bound estrogen with high affinity ( K d = 4.7 nM) and specificity. Maximum parsimony and Neighbor Joining analyses were used to generate a phylogenetic classification of ccER on the basis of 18 full-length ER sequences. The tree suggested the existence of two major ER branches. One branch contained two clearly divergent clades which included all piscine ER (except Japanese eel ER) and all tetrapod ERα, respectively. The second major branch contained the eel ER and the mammalian ERβ. The high degree of divergence between the eel ER and mammalian ERβ suggested that they also represent distinct piscine and tetrapod ER. These data suggest that ERα and ERβ are present throughout vertebrates and that these two major ER types evolved by duplication of an ancestral ER gene. Sequence alignments with other members of the nuclear hormone receptor superfamily indicated the presence of 8 amino acids in the E domain that align exclusively among ER. Four of these amino acids have not received prior research attention and their function is unknown. The novel finding of putative ER splice variants in a nonmammalian vertebrate and the novel phylogenetic classification of ER offer new perspectives in understanding the diversification and function of ER.

General and Comparative Endocrinology↗

USGS2000

Gonadotropin-Releasing hormones in the brain and pituitary of the white sucker

The present study investigated GnRH forms within the brain of a representative of the order Cypriniformes, the white sucker, Catostomus commersoni, using HPLC, RIA, and immunocytochemistry . Several immunoreactive (ir) GnRH forms were identified in the brain of the white sucker by chromatography and radioimmunoassay , including ir-salmon GnRH, ir-lamprey GnRH-I and -III, and ir-chicken GnRH-II. Results from immunocytochemical studies were consistent with multiple GnRH forms distributed in different patterns, particularly for fibers. Neuronal perikarya containing ir-salmon GnRH and ir-lamprey-like GnRH were found laterally within the preoptic area and rostral hypothalamus . Cells containing exclusively ir-salmon GnRH appeared slightly more rostrally, but in the same region. Fibers containing ir-salmon GnRH and ir-lamprey-like GnRH were seen throughout the caudal telencephalon and extended into the diencephalon , toward the pituitary . Fibers containing ir-chicken-II-like GnRH were also seen in the caudal telencephalon, but were concentrated more dorsally in the diencephalon. Within the pituitary, fibers containing ir-salmon GnRH and ir-lamprey-like GnRH entered the neurohypophysis , but differed in their destinations. Fibers containing ir-salmon GnRH remained within the neurohypophysis, while fibers containing ir-lamprey-like GnRH targeted adenohypophyseal tissue. These findings are consistent with the hypothesis that multiple GnRH forms with multiple functions exist within the brain and pituitary of teleosts and provide further evidence of a lamprey-like GnRH within an early evolved teleost species.

General and Comparative Endocrinology↗

USGS2000

Phylogenetic sequence analysis, recombinant expression, and tissue distribution of a channel catfish estrogen receptor beta

An estrogen receptor β (ERβ) cDNA fragment was amplified by RT-PCR of total RNA extracted from liver and ovary of immature channel catfish. This cDNA fragment was used to screen an ovarian cDNA library made from an immature female fish. A clone was obtained that contained an open reading frame encoding a 575-amino-acid protein with a deduced molecular weight of 63.9 kDa. Maximum parsimony and Neighbor Joining analyses were used to generate a phylogenetic classification of channel catfish ERβ on the basis of 25 full-length teleost and tetrapod ER sequences. The consensus tree obtained indicated the existence of two major vertebrate ER subtypes , α and β. Within each subtype, and in accordance with established phylogenetic relationships , teleost and tetrapod ER were monophyletic confirming the results of a previous analysis (Z. Xia et al ., 1999, Gen. Comp. Endocrinol . 113, 360–368). Extracts of COS-7 cells transfected with channel catfish ERβ cDNA bound estrogen with high affinity ( K d = 0.21 nM) and specificity. The affinity of channel catfish ERβ for estrogen was higher than previously reported for channel catfish ERα. As determined by qualitative RT-PCR, the tissue distributions of ERα and ERβ were similar but not identical. Both ER subtypes were present in ovary and testis. ERα was found in all other tissues examined from juvenile and mature fish of both sexes. ERβ was also found in most tissues except, in most cases, whole blood and head kidney. Interestingly, the pattern of expression of ER subtypes in head kidney always corresponded to the pattern in whole blood. In conclusion, we isolated a channel catfish ERβ with ligand-binding affinity and tissue expression patterns different from ERα. Also, we confirmed the validity of our previously proposed general classification scheme for vertebrate ER into α and β subtypes and within each subtype, into teleost and tetrapod clades.

General and Comparative Endocrinology↗

USGS2000

The presence of high-affinity, low-capacity estradiol-17β binding in rainbow trout scale indicates a possible endocrine route for the regulation of scale resorption

High-affinity, low-capacity estradiol-17β (E 2 ) binding is present in rainbow trout scale. The K d and B max of the scale E 2 binding are similar to those of the liver E 2 receptor ( K d is 1.6 ± 0.1 and 1.4 ± 0.1 nM, and B max is 9.1 ± 1.2 and 23.1 ± 2.2 fmol × mg protein -1 , for scale and liver, respectively), but different from those of the high-affinity, low-capacity E 2 binding in plasma ( K d is 4.0 ± 0.4 nM and B max is 625.4 ± 63.1 fmol × mg protein −1 ). The E 2 binding in scale was displaced by testosterone, but not by diethylstilbestrol. Hence, the ligand binding specificity is different from that of the previously characterized liver E 2 receptor, where E 2 is displaced by diethylstilbestrol, but not by testosterone. The putative scale E 2 receptor thus appears to bind both E 2 and testosterone, and it is proposed that the increased scale resorption observed during sexual maturation in both sexes of several salmonid species may be mediated by this receptor. No high-affinity, low-capacity E 2 binding could be detected in rainbow trout gill or skin.

General and Comparative Endocrinology↗

USGS2000

Novel transcripts of the estrogen receptor α gene in channel catfish

Complementary DNA libraries from liver and ovary of an immature female channel catfish were screened with a homologous ERα cDNA probe. The hepatic library yielded two new channel catfish ER cDNAs that encode N-terminal ERα variants of different sizes. Relative to the catfish ERα (medium size; 581 residues) previously reported, these new cDNAs encode Long-ERα (36 residues longer) and Short-ERα (389 residues shorter). The 5′-end of Long-ERα cDNA is identical to that of Medium-ERα but has an additional 503-bp segment with an upstream, in-frame translation-start codon. Recombinant Long-ERα binds estrogen with high affinity ( K d = 3.4 nM), similar to that previously reported for Medium-ERα but lower than reported for catfish ERβ. Short-ERα cDNA encodes a protein that lacks most of the receptor protein and does not bind estrogen. Northern hybridization confirmed the existence of multiple hepatic ERα RNAs that include the size range of the ERα cDNAs obtained from the libraries as well as additional sizes. Using primers for RT-PCR that target locations internal to the protein-coding sequence, we also established the presence of several ERα cDNA variants with in-frame insertions in the ligand-binding and DNA-binding domains and in-frame or out-of-frame deletions in the ligand-binding domain. These internal variants showed patterns of expression that differed between the ovary and liver. Further, the ovarian library yielded a full-length, ERα antisense cDNA containing a poly(A) signal and tail. A limited survey of histological preparations from juvenile catfish by in situ hybridization using directionally synthesized cRNA probes also suggested the expression of ERα antisense RNA in a tissue-specific manner. In conclusion, channel catfish seemingly have three broad classes of ERα mRNA variants: those encoding N-terminal truncated variants, those encoding internal variants (including C-terminal truncated variants), and antisense mRNA. The sense variants may encode functional ERα or related proteins that modulate ERα or ERβ activity. The existence of ER antisense mRNA is reported in this study for the first time. Its role may be to participate in the regulation of ER gene expression.

General and Comparative Endocrinology↗

USGS1976

Plasma luteinizing hormone and the development of ovarian follicles after loss of clutch in female mallards (Anas platyrhynchos)

The plasma level of LH and the extent of development of ovarian follicles were analyzed in incubating female Mallards. In both wild and game-farm stock, incubation was associated with a significant decline in plasma levels of LH from those of laying females. Within 1 day after removal of eggs, LH levels had increased to levels indistinguishable from those of laying females. The mean diameter of the largest follicle in wild females on the tenth day of incubation was 5.3 mm; it was 5.2 mm in game-farm stock at the same stage. Three days following removal of eggs, the mean of the largest follicles of wild-stock hens had increased to 14.0 mm and those of game-farm stock to 12.7 mm.

General and Comparative Endocrinology↗

USGS1985

The effects of cortisoland actinomycin D injections on choloride cells and branchial N+---K+-ATPase in rainbow trout (Salmo gairdneri)

Injections of cortisol, actinomycin D, or combined administration of the hormone and the antiobiotic did not effect rainbow trout ( Salmo gairdneri ) branchial Na + K + -ATPase activity. Numbers of chloride cells also did not change following cortisol and actinomycin D treatment. These results are discussed in light of a similar report concerning Atlantic salmon ( Salmo salar ).

General and Comparative Endocrinology↗

USGS1989

Plasma catecholamine concentrations in rainbow trout ( Salmo gairdneri ) at rest and after anesthesia and surgery

The effects of surgery and anesthesia on concentrations of plasma epinephrine (E), norepinephrine (NE), and dopamine (DA) were investigated in rainbow trout fitted with dorsal aorta cannulae. Baseline catecholamines (CA) concentrations, established in resting rainbow trout, were 1.55 ± 0.90 ϱmol/ml ( X ± SD) for E, 2.07 ± 1.26 for NE, and 1.33 ± 0.87 for DA. These values were based on the pooled analyses of five individual fish taken over seven different sampling periods. The E:NE ratio in resting fish was always less than 1.0. In a second experiment, fish were subjected to dorsal aorta cannulation and sequential blood samples were taken immediately after surgery, and 6, 24, and 48 hr later. Plasma E concentrations were 36 times greater than baseline values in the first sample; NE was 15 times greater and DA was 41 times greater. After surgery, plasma concentrations of all CAs fell rapidly but values were still higher than baseline 6 hr after surgery, then were near baseline at 24 and 48 hr after surgery. The E:NE ratio was about 3.0 immediately after surgery, dropped to 1.8 at 6 hr, and was about 1.0 at 24 and 48 hr. In a third experiment, plasma CAs were determined in a group of five animals anesthetized with tricaine methanesulfonate (100 mg/ml) to advanced anesthesia, and then allowed to recover in flowing well water over a 12-hr observation period. Plasma E and NE concentrations in the fish during early anes-thesia (1.14 ± 0.14 min) were not significantly different from preanesthesia values. During advanced anesthesia (2.31 ± 0.21 min), values for E and NE were significantly greater and continued to be elevated during the 12-hr recovery period. The E:NE ratio exceeded 1.0 during advanced anesthesia and for the rest of the experiment.

General and Comparative Endocrinology↗

USGS1991

Effects of prolacton chloride cells opercular membrane of seawater-adapted tilapia

Effects of prolactin on morphology and numbers of chloride cells in the opercular membrane of seawater-adapted tilapia ( Oreochromis mossambicus ) have been examined. Following five daily injections of ovine prolactin at a dose of 10 μg · g body wt −1 , blood samples were taken and opercular membranes were removed and stained with a fluorescent mitochondrial dye (dimethylaminostyrylethylpyridiniumiodine), a fluorescent derivative of ouabain (anthroylouabain), and a histological stain specific for the extensive tubular system of chloride cells (zinc-osmium-iodine). Mean plasma osmolarity and sodium increased 23–24% following prolactin injection. An increase in the relative frequency of chloride cells between 20 and 180 μm 2 in cross-sectional area and a decrease in the relative frequency of chloride cells greater than 180 μm 2 were observed following prolactin injections. Average cell size decreased 46–70% and cell height decreased 26–38% following prolactin injections. There was no significant change in cell density. Anthroylouabain staining was observed in both prolactin- and saline-injected fish, and no significant effect on Na + ,K + -adenosinetri-phosphatase activity was seen in either opercular membrane or gill tissue. The results demonstrate an effect of prolactin on chloride cell size and provide a morphological correlate for decreased secretory activity of chloride cells following prolactin injections.

General and Comparative Endocrinology↗

USGS1991

Developmental differences in the responsiveness of gill Na+, K+ and -ATPase to cortisol salmonids

The ability of cortisol to increase gill Na + , K + -ATPase activity was examined in several salmonid species during development. Coho salmon ( Oncorhynchus kisutch ) parr were unresponsive to cortisol in vitro (10 μg/ml for 2 days) in November. Responsiveness was significant from January to March, peaking in January just prior to seasonal increases in gill Na + , K + -ATPase activity. Gill tissue became unresponsive to in vitro cortisol in April when in vivo gill Na + , K + -ATPase activity peaked. The ability of cortisol to stimulate gill, Na + , K + -ATPase activity in postemergent fry (2–3 months after hatching) was examined in chum ( O. keta ), chinook ( O. tschawytscha ), coho, and Atlantic salmon ( Salmo salar ). Initial levels of gill Na + , K + -ATPase activity were elevated in chum salmon, which normally migrate as fry. Cortisol (10 μg/ml for 4 days in vitro ) increased gill Na + , K + -ATPase activity in chum salmon fry (48% above initial levels), had a limited but significant effect in chinook salmon fry, and had no effect in coho and Atlantic salmon fry. In an in vivo experiment, Atlantic salmon previously exposed to simulated natural photoperiod (SNP) and continuous light (L24) received four cortisol injections of 2 μg · g −1 every third day. SNP fish responded with increased gill Na + , K + -ATPase activity (+66%), whereas L24 fish were not affected. Atlantic salmon presmolts with initially low levels of gill Na + , K + -ATPase activity responded to cortisol in vitro , whereas smolts with initially high levels of gill Na + , K + -ATPase activity were unresponsive. Triiodothyronine (0.01–10 μg/ml), prolactin (0.1–10 μg/ml), growth hormone (0.1–10 μg/ml), insulin (0.01–10 μg/ml), and bovine insulin-like growth factor I (0.01–1 μg/ml) did not affect gill Na + , K + -ATPase activity in vitro , individually or with cortisol (1–10 μg/ml). Thus, changes in responsiveness to cortisol occur during salmonid development, vary among species, and may be important in the heterochrony that characterizes the parr-smolt transformation.

General and Comparative Endocrinology↗

USGS1992

Stimulation of coho salmon growth by insulin-like growth factor I

The effect of insulin-like growth factor I on growth rate of coho salmon ( Oncorhynchus kisutch ) was examined. Juvenile coho salmon received implants of osmotic minipumps containing recombinant bovine insulin-like growth factor I (rbIGF-I) or saline for a period of 3 to 4 weeks. High doses of rbIGF-I (>0.13 μg · g −1 · d −1 ) resulted in hypoglycemia and death. In 2-year-old coho salmon, 0.09 μg · g −1 · d −1 rbIGF-I administered for 25 days doubled linear growth rate and increased growth rate in weight by 40%. In rapidly growing, 1-year-old coho salmon, growth rate was not altered by rbIGF-I at 0.01 or 0.05 μg · g −1 · d −1 for 31 days. In ration-limited fish exhibiting slow growth in the control group, rbIGF-I (0.02 to 0.12 μg · g −1 · d −1 ) increased linear growth rate by up to threefold and growth rate in weight by up to fourfold. The results indicate that exogenous treatment with mammalian IGF-I can stimulate coho salmon growth under some conditions, and that endogenous IGF-I may be an important factor in regulating growth of teleosts.

General and Comparative Endocrinology↗

USGS2004

Interaction of xenobiotics with estrogen receptors α and β and a putative plasma sex hormone-binding globulin from channel catfish ( Ictalurus punctatus )

Estrogens are important regulators of physiological functions. Although environmental contaminants (xenoestrogens) which interfere with estrogen signaling are of increasing concern, there is only limited information about their ability to interact with estrogen-binding proteins (SHBG) or receptors (ER). Recombinant ER?? and ?? were obtained after transient transfection of COS-7 cells with channel catfish ER cDNA. Plasma from adult female channel catfish was the source of SHBG. Tritiated estradiol ( 3H-E2) was used in standard radioligand-binding assays to characterize the binding properties of channel catfish SHBG (ccfSHBG) and to estimate the inhibition constants for various estrogenic compounds. Binding of 3H-E2 to ccfSHBG was saturable and of high affinity with a Kd (??SE) of 1.9??0.14nM and a Bmax of 14.3??2.4pmol/mg protein (n=3 assays). Additionally, ccfSHBG displayed binding specificity for androgens and estrogens. Endosulfan, 4-nonylphenol, and 4-octylphenol displaced 3H-E2 binding to ccfSHBG albeit only at very high concentrations, whereas dieldrin and atrazine showed little displacement activity even at the highest concentrations used. The synthetic estrogen ethynylestradiol had higher affinity than E2 for ccfSHBG. This finding differs from results with human and rainbow trout SHBG. The alkylphenolic compounds (4-octylphenol and 4-nonylphenol) displayed some ability to displace 3H-E2 binding from ER?? and ?? at high concentrations, but dieldrin and atrazine had little binding activity for both ER subtypes and endosulfan for ER??. The xenobiotics tested generally showed equivalent or greater affinity for ER?? than ER??, whereas natural estrogens had much greater affinity for ER?? than ER??. These observations suggest that results of studies using fish tissue ER extracts must be interpreted with caution, since both ER subtypes may be present, and that the binding of xenoestrogens to SHBG must be taken into account for proper assessment of endocrine disruption caused by environmental contaminants.

General and Comparative Endocrinology↗