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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

Increases in gill cytosolic corticosteroid receptor abundance and saltwater tolerance in juvenile coho salmon (Oncorhynchus kisutch) treated with growth hormone and placental lactogen

Juvenile coho salmon ( Oncorhynchus kisutch ) were injected with one of two recombinant bovine hormones, growth hormone (bGH; 5.0 and 0.5 μg · g -1 body wt) or placental lactogen (bPL; 5.0, 0.5, μg · g -1 body wt) to determine the effect on growth, plasma cortisol concentration, cytosolic corticosteroid receptors (CR) in the gills, and the development of hypoosmoregulatory ability. One week following a single injection or six weekly injections of bGH or bPL, the first were measured and samplest for CR concentration and Na + , K + . ATPase activity in the gills. Fish were also challenged with salt water (salinity 25%) for 24 hr to determine saltwater tolerance at the end of the 6-week treatment. Treatment with bPL and bGH significantly increased weight and length of the fish. The 0.05-μg bPL dose significantly elevated plasma cortisol concentration, whereas all other hormone treatments did not affect cortisol levels. bPL and bGH also significantly increased CR concentration and Na + , K + -ATPase activity in the gills. The perturbation in plasma sodium concentration was least in animals receiving the highest dose bPL and the bGH-treated animals following transfer to seawater. An increase in cytosolic CR by bGH and bPL may increase responsiveness of the gills to cortisol and partially accout for the increase in Na + , K + -ATPase activity and greater ability to regulate plasma sodium in seawater as exhibited by the experimental groups.

General and Comparative Endocrinology↗

USGS1995

Size-dependent, sex-dependent and seasonal changes in insulin-lige growth-factor-I in the loggerhead sea turtle

This study examines size-dependent, sex-dependent, and seasonal fluctuations in plasma insulin-like growth factor-I (IGF-I) concentrations in loggerhead sea turtles ( Caretta caretta ). Loggerhead turtles ( n = 158) were captured in shrimp trawler nets during a 12-month survey in Cape Canaveral Channel, Florida. Plasma samples were analyzed using a validated heterologous radioimmunoassay. Large turtles (>75 cm straight-line carapace length) had significantly higher plasma IGF-I concentrations than small turtles (⩽75 cm; P < 0.0001). Plasma IGF-I concentrations did not vary seasonally in small turtles, but large turtles had significantly higher plasma IGF-I concentrations during the spring and summer months (P < 0.005). Within the large turtles, adult males had significantly lower IGF-I concentrations than females and subadult males ( P < 0.05). These results and a review of loggerhead turtle natural history suggest that the seasonal fluctuations in plasma IGF-I of adult turtles are due to elevated IGF-I levels in reproductively active female turtles. Further research is needed to examine correlations between reproductive activities and plasma IGF-I concentrations in reptiles.

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

Effects of growth hormone and insulin-like growth factor I on salinity tolerance and gill Na+, K+ and -ATPase in Atlantic salmon (Salmo salar): Interaction with cortisol

The potential roles of growth hormone (GH) and insulin-like growth factor I (IGF-I) in seawater (SW) acclimation of juvenile Atlantic salmon ( Salmo salar ) were examined. Compared to controls, fish in 12 ppt seawater given one or three injections (2–6 days) of GH (ovine, 0.2 μ g · g −1 ) or IGF-I (recombinant bovine, 0.05–0.2 μ g · g −1 ) had significantly greater salinity tolerance as judged by lower plasma sodium, osmolality, and muscle moisture content following transfer to 34 ppt. Single injections of GH and IGF-I in fish in fresh water failed to improve salinity tolerance following transfer to 25 ppt SW. Treatment of fish in 12 ppt with GH or IGF-I for 2–6 days did not increase gill Na + , K + -ATPase activity, but treatment with GH prevented decreases in gill Na + , K + -ATPase activity that occurred in controls following transfer to 34 ppt seawater. Fish in fresh water administered GH by implants (5.0 μ g · g −1 ) or osmotic minipumps (0.5 μ g · g −1 day −1 ) for 7–14 days had greater gill Na + , K + -ATPase activity and salinity tolerance than controls. IGF-I administered by implants (0.5–1.0 μ g · g −1 ) or osmotic minipumps (0.1 μ g · g −1 day −1 ) for 4–14 days did not increase salinity tolerance or gill Na + , K + -ATPase activity. Cortisol implants (50 μ g · g −1 ) also increased gill Na + , K + -ATPase activity and salinity tolerance after 14 days, and in combination with GH had a synergistic effect. Although IGF-I and cortisol implants had no significant effect after 7 days, in combination they significantly increased gill Na + , K + -ATPase activity. The results indicate that GH and cortisol can increase salinity tolerance and gill Na + , K + -ATPase activity of Atlantic salmon and together act in synergy. Although IGF-I can increase salinity tolerance in short-term treatments (2–6 days) in 12 ppt, it is less effective than GH in increasing salinity tolerance and gill Na + , K + -ATPase activity in long-term treatments (7–14 days) and in interacting with cortisol.

General and Comparative Endocrinology↗

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↗

USGS1999

Plasma steroid concentrations and male phallus size in juvenile alligators from seven Florida lakes

Neonatal and juvenile alligators from contaminated Lake Apopka in central Florida exhibit abnormal plasma sex steroid concentrations as well as morphological abnormalities of the gonad and phallus. This study addresses whether similar abnormalities occur in juvenile alligators inhabiting six other lakes in Florida. For analysis, animals were partitioned into two subsets, animals 40-79 cm total length (1-3 years old) and juveniles 80-130 cm total length (3-7 years old). Plasma testosterone (T) concentrations were lower in small males from lakes Apopka, Griffin, and Jessup than from Lake Woodruff National Wildlife Refuge (NWR). Similar differences were observed in the larger juveniles, with males from lakes Jessup, Apopka, and Okeechobee having lower plasma T concentrations than Lake Woodruff males. Plasma estradiol-17?? (E2) concentrations were significantly elevated in larger juvenile males from Lake Apopka compared to Lake Woodruff NWR. When compared to small juvenile females from Lake Woodruff NWR, females from lakes Griffin, Apopka, Orange, and Okeechobee had elevated plasma E2 concentrations. Phallus size was significantly smaller in males from lakes Griffin and Apopka when compared to males from Lake Woodruff NWR. An association existed between body size and phallus size on all lakes except Lake Apopka and between phallus size and plasma T concentration on all lakes except lakes Apopka and Orange. Multiple regression analysis, with body size and plasma T concentration as independent covariables, explained the majority of the variation in phallus size on all lakes. These data suggest that the differences in sex steroids and phallus size observed in alligators from Lake Apopka are not limited to that lake, nor to one with a history of a major pesticide spill. Further work examining the relationship of sex steroids and phallus size with specific biotic and abiotic factors, such as antiandrogenic or estrogenic contaminants, is needed.

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↗

USGS2001

Effects of growth hormone and cortisol on Na+-K+-2C1-cotransporter localization and abundance the gills of Atlantic salmon

The hormones responsible for the regulation of the teleostean gill Na + –K + –2Cl − cotransporter have not been elucidated. With Western blotting and immunocytochemistry, Na + –K + –2Cl − cotransporter abundance and localization were examined in the gills of Atlantic salmon ( Salmo salar ) following 2-week treatment with growth hormone (GH; 5.0 μg · g −1 ), cortisol (50 μg · g −1 ), and both hormones in combination (GH+cortisol). GH and cortisol treatments increased gill Na + –K + –2Cl − cotransporter abundance over levels seen in controls, and both hormones together (GH+cortisol) produced a greater effect than either hormone alone. Gill Na + ,K + –ATPase activity was also elevated by all three hormone treatments. Compared to controls, Na + –K + –2Cl − cotransporter immunoreactive chloride cells on the primary filament were greater in number and size following all three treatments. Although the number of immunoreactive chloride cells on the secondary lamellae did not differ among the treatment groups, GH+cortisol increased their size. These data indicate that GH and cortisol increase gill Na + –K + –2Cl − cotransporter abundance through chloride cell proliferation and differentiation in the gills of Atlantic salmon and are likely the hormones responsible for Na + –K + –2Cl − cotransporter regulation during smolting and seawater acclimation.

Massachusetts↗

USGS2001

Effects of maturation-inducing hormone on heterologous gap junctional coupling in ovarian follicles of Atlantic croaker

A previous ultrastructural study of heterologous (granulosa cell-oocyte) gap junction (GJ) contacts in ovarian follicles of Atlantic croaker suggested that these contacts disappear late during the process of resumption of oocyte meiosis. This observation suggested that, unlike scenarios proposed for a number of other species, uncoupling of GJ is not necessary for the onset of meiotic resumption in croaker follicles. However, the functionality of heterologous GJ contacts and the temporal association between maturation-inducing hormone (MIH)-induced changes in heterologous coupling and resumption of oocyte meiosis have not been examined in Atlantic croaker. These questions were addressed with a cell-cell coupling assay that is based on the transfer of a GJ marker, Lucifer Yellow, from oocytes to granulosa cells. Follicle-enclosed oocytes injected with Lucifer Yellow allowed transfer of the dye into the follicle cell layer, thus confirming that there is functional heterologous coupling between the oocyte and the granulosa cells. Dye transfer was observed in vitellogenic, full-grown/maturation-incompetent, and full-grown /maturation-competent follicles. Treatment of maturation-competent follicles with MIH caused a time-dependent decline in the number of follicles transferring dye. However, although GJ uncoupling in some of the follicles was observed before germinal vesicle breakdown (GVBD, index of meiotic resumption), about 50% of the follicles maintained the ability to transfer dye even after GVBD had occurred. Further, a known GJ inhibitor (phorbol 12-myristate 13-acetate) blocked heterologous GJ within a time frame similar to that seen with MIH but without inducing any of the morphological changes (including GVBD) associated with follicular maturation. In conclusion, uncoupling of heterologous GJ seems insufficient and unnecessary for the onset of meiotic resumption in ovarian follicles of Atlantic croaker. ?? 2001 Elsevier Science.

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↗