17 beta-estradiol increases plasma calcitonin levels in salmonid fish

The protective role of curcumin against toxic effect of nonylphenol on bone development

INTRODUCTION

In the study, it was aimed to investigate the possible protective effects of curcumin, a potent antioxidant, against the toxic effect of nonylphenol on bone development.

METHODS

Thirty pregnant female Wistar albino rats were used. The rats were randomly divided into the following five groups; the control group, corn oil group (150 µl/kg/day), nonylphenol group (50 µl/kg/day), curcumin group (100 mg/kg/day) and curcumin + nonylphenol group (100 mg/kg/day + 50 µl/kg/day). The doses were given by gavage from the 5th day to the 20th day of gestation. The fetuses were removed out on the 20th day of pregnancy by cesarean at the end of the study. After the sacrifice of the animals, double skeletal staining in front extremity (clavicula, scapula, humerus, radius, ulna) and hind extremity (femur, tibia, fibula), additionally histological and immunohistochemical examinations in femur bone were performed.

RESULTS

The nonylphenol group offspring have the lowest weights of fetuses and placenta, head-to-hip lengths, biparietal and occipitofrontal length, and also, bone length percentage and percentage of the ossification area in all measurements of the front extremity and hind extremity Interestingly, the groups treated with curcumin showed close to the control group in terms of double skeletal staining, histological, and immunohistochemical examinations.

CONCLUSIONS

Our findings demonstrated an association between bone development and exposure to nonylphenol. The findings suggest that curcumin treatments may be effective in accelerating bone formation.

Possible role of C60 fullerene in the induction of reproductive toxicity in the freshwater fish, Anabas testudineus (Bloch, 1792)

In recent years, the impact of ultrafine nanomaterials on the aquatic organisms and their ecosystems contributed much concern due to their abundance in environment. Several toxicity studies have reported that nanoparticles induced reproductive stress and resulted in reproductive impairment of fishes. The present study was aimed to investigate the stress-induced toxicity of C₆₀ fullerene nanomaterial on various reproductive parameters of the freshwater fish, Anabas testudineus. Fish were exposed to two sublethal concentrations of fullerene C₆₀, one-tenth (5 mg/L) and one-fifth (10 mg/L) of LC₅₀-96 h, for 4, 7, 15, 30, and 60-day durations. At the end of exposure period, the activities of steroidogenic enzymes, 3β-, and 17β-hydroxysteroid dehydrogenase decreased in the testis and ovary thereby indicated that the nanomaterial affected gonadal steroidogenesis. The level of serum testosterone decreased significantly (p < 0.05) in male whereas the level of estradiol showed significant (p < 0.05) reduction in female fish with significant (p < 0.05) increase in the level of serum cortisol in both sexes in concentration- and time-dependent manner. The analysis of the levels of alkali-labile phosphates, plasma calcium, and total protein showed significant (p < 0.05) reduction in female fish without significant changes in male fish, and this could be due to the antiestrogenic action of fullerene C₆₀ nanomaterial. The activity of aromatase enzyme decreased significantly (p < 0.05) in the ovary and brain of female fish, and the decline in the enzyme activity was prominent only in the brain tissue of male fish. The present results suggested that the stress-induced by fullerene C₆₀ exposure provoked reproductive toxicity in the fish, Anabas testudineus.

Impact of prenatal exposure to bisphenol A on pregnant rats: Fetal bone development and immunohistochemistry implications

BACKGROUND:

Bisphenol A (BPA) is one of the most commonly produced chemicals in the world. BPA is used in products such as food packaging, personal care products, detergents, and plastic bottles. This study was conducted to determine the effect of BPA on fetal bone development.

MATERIAL AND METHODS:

In this study, 16 pregnant female Sprague-Dawley rats were used. The rats were divided into four groups: the control group and 0.5 mg/kg/day, 5 mg/kg/day, and 50 mg/kg/day dose BPA groups. The skeletal system development of fetuses was examined with double skeletal and immunohistochemistry (IHC) staining (tartrate resistant acid phosphatase (TRAP) and the alkaline phosphatase (AP) expressions) methods.

RESULTS:

The highest ossification rates in the humerus, radius, and ulna were detected as 41.05%, 39.25%, and 37.26% in the control group, respectively. The highest ossification rates in the femur, tibia, and fibula were detected as 23.04%, 30.73%, and 32.78% in the control group, respectively. Statistically significant differences were found between control and experimental groups in the TRAP and AP expression of the femur by IHC staining ( p < 0.001).

CONCLUSION:

Exposure to BPA during pregnancy adversely affected ossification and bone growth. A dose-dependent decrease was observed in the rate of ossification.

Calcitonin receptor family evolution and fishing for function using in silico promoter analysis

In the present study the calcitonin receptor (CTR) sub-family of family B G-protein coupled receptors (GPCRs) in teleosts is evaluated and put in the context of the families overall evolution from echinodermates to vertebrates. Echinodermates, hemichordates, cephalochordates and tunicates have a single gene that encodes a receptor that bears similarity to the vertebrate calcitonin receptor (CTR) and calcitonin-like receptor (CTR/CLR). In tetrapods one gene encodes the calcitonin receptor (CALCR) and another gene the calcitonin receptor-like receptor (CALCRL). The evolution of CALCR has been under strong conservative pressure and a single copy is also found in fishes and high conservation of gene organisation and synteny exits from teleosts to human. A teleost specific CTR innovation that occurred after their divergence from holostei is the presence of several HBDs in the N-terminus. CALCRL had a different evolutionary trajectory from CALCR and although a single gene copy is present in tetrapods the sarcopterygii fish, the coelacanth, has 1 copy of CALCRL but also a fish specific form CALCRL3. The ray-finned fish, the spotted gar, has 1 copy of CALCRL and 1 of CALCRL3 but the teleost specific whole genome duplication has resulted in a CALCRL1 and CALCRL2 in addition to the fish specific CALCRL3. Strong conservation of CALCRL gene structure exists from human to fish. Promoter analysis in silico reveals that the duplicated CALCRL genes in the teleosts, zebrafish, takifugu, tetraodon and medaka, have divergent promoters and different putative co-regulated gene partners suggesting their function is different.

Enhancement of reproductive performances of Gangetic leaffish, Nandus nandus through up regulation of serum Ca²⁺ concentration, improved morphological alteration of liver and ovary with dietary polyunsaturated fatty acids

Incorporation of polyunsaturated fatty acids (PUFAs) as biofunctional compounds with feed is an effective way for gonadal maturation without any hazardous effects on animal health, and thus it is possible to save the vulnerable species from the danger of extinction. In the present study sperm quality, level of Ca(2+) concentration in serum, histological structure of the liver and developmental stages of ovary of an endangered fish species, Nandus nandus were investigated for the confirmation of the positive effects of PUFAs in reproduction and gonadal maturation. Fishes were collected from Brahmaputra River, Mymensingh, Bangladesh. Treated group was fed 1% squid extracted phospholipid supplemented diet that was mixed with silver carp fish muscle where as controlled group was fed the same except phospholipid. For histology of liver and gonads, samples were dehydrated, cleaned and infiltrated, embedded in paraffin wax and sectioned. After that, the samples were stained with hematoxylin and eosin. The photomicrographs of the stained samples were taken by using light microscope. In comparison with the control group, treated group exhibited higher gonadal maturation which resulted in spontaneous spawning. Treated female demonstrated advanced gonadal developmental stages in comparison with the controlled female during different months. During spawning season, lipid granules and normal morphological alteration were observed in case of treated fish liver, whereas less lipid granules with more histological alteration of liver were observed in control group. Serum Ca(2+) concentration in treated female was found significantly higher (P < 0.01) in contrast to the controlled female during the breeding season which was an indicator of the augment of estrogen secretion during ovarian maturation. Better sperm quality, early maturation of oocytes, less histological alteration of liver hepatocytes and spontaneous spawning performances of PUFA-treated fish were as a result of the efficiency of PUFAs in enhancing maturation. The experiment suggests that supplementation of dietary PUFAs improve the spawning performances of fish.

Estrogenic compounds decrease growth hormone receptor abundance and alter osmoregulation in Atlantic salmon

Exposure of Atlantic salmon smolts to estrogenic compounds is shown to compromise several aspects of smolt development. We sought to determine the underlying endocrine mechanisms of estrogen impacts on the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis. Smolts in freshwater (FW) were either injected 3 times over 10 days with 2 μgg(-1) 17β-estradiol (E2) or 150μgg(-1) 4-nonylphenol (NP). Seawater (SW)-acclimated fish received intraperitoneal implants of 30 μgg(-1) E2 over two weeks. Treatment with these estrogenic compounds increased hepatosomatic index and total plasma calcium. E2 and NP reduced maximum growth hormone binding by 30-60% in hepatic and branchial membranes in FW and SW, but did not alter the dissociation constant. E2 and NP treatment decreased plasma levels of IGF-I levels in both FW and SW. In FW E2 and NP decreased plasma GH whereas in SW plasma GH increased after E2 treatment. Compared to controls, plasma chloride concentrations of E2-treated fish were decreased 5.5mM in FW and increased 10.5mM in SW. There was no effect of NP or E2 on gill sodium-potassium adenosine triphosphatase (Na(+)/K(+)-ATPase) activity in FW smolts, whereas E2 treatment in SW reduced gill Na(+)/K(+)-ATPase activity and altered the number and size of ionocytes. Our data indicate that E2 downregulates the GH/IGF-I-axis and SW tolerance which may be part of its normal function for reproduction and movement into FW. We conclude that the mechanism of endocrine disruption of smolt development by NP is in part through alteration of the GH/IGF-I axis via reduced GH receptor abundance.

Effects of hexazinone and atrazine on the physiology and endocrinology of smolt development in Atlantic salmon

Exposure to hexazinone (HEX) and atrazine (ATZ), highly mobile and widely used herbicides along rivers in the United States, is potentially harmful to Atlantic salmon, which have been listed as an endangered species. To determine the effects of these contaminants on smolt development, juvenile Atlantic salmon were exposed under flow-through conditions to 100 microgl(-1) HEX, 10 and 100 microgl(-1) ATZ in fresh water (FW) for 21 days at 10 degrees C beginning in mid-April. Twelve fish per treatment were sampled in FW, following a 24h seawater (SW) challenge and after growth for 3 months in SW. Exposure to 100 microgl(-1) HEX or 10microgl(-1) ATZ caused no mortalities of smolts in FW or after SW challenge, while 9% of the fish exposed to 100 microgl(-1) ATZ died during exposure. Fish exposed to 100 microgl(-1) ATZ reduced feeding after 10 days of exposure and had an impaired growth rate in FW and during the first month in SW; compensatory growth occurred in the second and third month in SW. HEX and ATZ at 10 microgl(-1) exposure had no effect on plasma levels of cortisol, growth hormone (GH), insulin growth factor I (IGF-I), thyroxine (T(4)) and plasma 3,5,3'-triiodo-l-thyronine (T(3)), Cl(-), Mg(2+), Na(+), Ca(2+) in FW or after SW challenge. FW smolts exposed to 100 microgl(-1) ATZ had decreased plasma Cl(-), Mg(2+), Na(+) and Ca(2+) ions and increased cortisol. No effect on plasma levels of GH, IGF-I, T(4) or T(3) was found in FW smolts exposed to 100 microgl(-1) ATZ. Following SW challenge, fish previously exposed to 100 microgl(-1) ATZ had significant increases in hematocrit, plasma cortisol, Cl(-), Mg(2+), Na(+), Ca(2+) and a decrease in T(4) and T(3). It is concluded that under the conditions imposed in this study, HEX does not affect salinity tolerance of Atlantic salmon smolts, while ATZ causes ionoregulatory, growth and endocrine disturbance.

Evolution of the CT/CGRP family: comparative study with new data from models of teleosts, the eel, and cephalopod molluscs, the cuttlefish and the nautilus

In mammals, alternative splicing of the calcitonin gene generates two distinct peptides: calcitonin (CT), synthesised in the thyroid C cells and involved in the regulation of calcium metabolism, and calcitonin gene-related peptide (CGRP), brain neuromediator synthesised in the peripheral and central nerves. CGRP is well represented and molecularly conserved during evolution whereas CT has not been detected in any of the invertebrates analysed so far. In order to better understand the evolution of this CT/CGRP peptide family we reviewed the major data concerning its evolution from the literature and our recent data obtained in models of teleosts and cephalopod molluscs. The presence of both CGRP-like molecules and its specific bindings sites in the central nervous system of eel, cuttlefish and nautilus, suggests that the brain neurotransmitter role of CGRP could represent an ancient role in metazoa, already present in cephalopods and conserved among vertebrates, as still observed in mammals. In contrast, the presence of CGRP specific binding sites, and not the peptide itself, in the gills suggests an endocrine role for CGRP, in cephalopods and teleosts, that may have been lost during the evolution of the tetrapod lineage. These data, and the absence of CT-like molecules that we observed in cephalopods, support the hypothesis that CGRP represents the ancestral molecule of the CT/CGRP family, appeared in metazoa before the vertebrate emergence. The distinction between CT and CGRP receptors appears to be an event posterior to the emergence of ecdysozoan and lophotrochozoan protostomes, probably in relation to the CT appearance. The evolution of the CT/CGRP peptide family is probably similar to the evolution of the CT/CGRP receptor family. In fact, the genic duplication that induced the appearance of the two separate molecules, CT and CGRP, may constitute an event close to that, which induced the appearance of the two specific receptors. These events remain to be further studied in order to better understand the peptide and receptor evolution of the CT/CGRP family.

Endocrine disruption of parr-smolt transformation and seawater tolerance of Atlantic salmon by 4-nonylphenol and 17beta-estradiol

Sex steroids are known to interfere with the parr-smolt transformation of anadromous salmonids, and environmental estrogens such as nonylphenol have recently been implicated in reduced returns of Atlantic salmon in the wild. To determine the endocrine pathways by which estrogenic compounds affect smolt development and seawater tolerance, groups of juvenile Atlantic salmon were injected with one of five doses (0.5, 2, 10, 40 or 150 microg g(-1)) of branched 4-nonylphenol (NP), 2 microg g(-1) of 17beta-estradiol (E(2)), or vehicle, during the parr-smolt transformation in April, and the treatment was repeated 4, 8, and 11 days after the first injection. Plasma was obtained for biochemical analysis 7 and 14 days after initiation of treatment. After 14 days of treatment, additional fish from each treatment group were exposed to seawater for 24h to assess salinity tolerance. The E(2) treatment and the highest NP dose resulted in lower salinity tolerance and decreased plasma insulin-like growth factor I (IGF-I) levels, along with elevated levels of plasma vitellogenin and total calcium. Plasma growth hormone levels were elevated at intermediate NP doses only, and not affected by E(2). After 7 days, plasma thyroxine (T(4)) levels decreased in a strong, dose-dependent manner in response to nonylphenol, but after 14 days, this suppressive effect of T(4) occurred at the highest NP dose only. Similarly, E(2) decreased plasma T(4) levels at 7, but not 14 days. Plasma 3,3',5-triodo-l-thyronine was reduced by E(2) and the highest NP dose after 7 and 14 days of treatment. Plasma cortisol levels were not affected by any of the treatments. The results indicate that the parr-smolt transformation and salinity tolerance can be compromised by exposure to estrogenic compounds. Suppression of plasma IGF-I levels is a likely endocrine pathway for the effects of estrogenic compounds on hypo-osmoregulatory capacity, and the detrimental effects of E(2) and NP on thyroid hormone levels are also likely to compromise the normal parr-smolt transformation of Atlantic salmon.

Possible direct induction by estrogen of calcitonin secretion from ultimobranchial cells in the goldfish

The plasma level of calcitonin (CT), a calcium (Ca)-regulating hormone, is known to increase in female teleosts during the reproductive period. In the present study, a correlation between plasma CT and Ca and one between plasma CT and the gonad somatic index were demonstrated in the female goldfish but not in the male. To clarify the relationship between CT and Ca, we examined the plasma CT and Ca levels after injecting immature goldfish with estrogen. At day 1, the plasma CT level significantly increased, whereas the plasma Ca level was not changed from its initial level. This result suggests that the trigger of CT secretion is estrogen and that estrogen directly acts on the ultimobranchial gland (UBG), a CT-secreting organ. To determine whether the UBG is equipped with estrogen receptor (ER), an ER binding assay and immunohistochemical staining of UBG cells with an antibody against ER were conducted. As a result, estrogen-specific binding (Kd, 18.52 nM; Bmax, 1.35 pmol/mg protein) and ER-immunoreactivity in the UBG were demonstrated. Furthermore, the expression of alpha, beta, and gamma types of ER in the UBG was also detected by use of the reverse-transcription polymerase chain reaction. Thus, we concluded that estrogen acts on the UBG to induce the release of CT, which in turn plays an important role in reproduction directly and/or indirectly through Ca. This is the first report on the existence of ERs in a teleost UBG and the occurrence of CT secretion caused by estrogen.

Plasma calcium as a surrogate measure for vitellogenin in fathead minnows (Pimephales promelas)

Numerous reports have demonstrated the vitellogenic response of fish exposed to estrogenic compounds in the aquatic environment. A strong correlation has been shown to exist between plasma vitellogenin and plasma calcium concentrations in salmonid fish. This study examines the relationship between plasma vitellogenin and calcium in a cyprinid fish, the fathead minnow (Pimephales promelas), which is a species commonly used to monitor water quality. Plasma vitellogenin was determined after exposure of male and female fish to proprietary pharmaceutical estrogens using an enzyme-linked immunosorbent assay (ELISA) developed specifically for fathead minnows. Plasma calcium was determined by flame atomic absorption spectroscopy (AA). This study demonstrated significant (P < 0.05) linear correlations between plasma vitellogenin and plasma calcium for males (r2 = 0.70), females (r2 = 0.83), and males and females combined (r2 = 0.06), showing that plasma calcium could be an indirect measure of vitellogenin present in fathead minnows. Some of the limitations and advantages identified through these studies are discussed.

Bisphenol A suppresses osteoclastic and osteoblastic activities in the cultured scales of goldfish

The direct effect of bisphenol A on osteoclasts and osteoblasts was examined using a culture system of goldfish scales. Tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) were used as markers of osteoclasts and osteoblasts, respectively. Bisphenol A (10(5) M) significantly suppressed both TRAP and ALP activities. These data were reproduced in an in vivo experiment. From an analysis of a reverse transcription-polymerase chain reaction in the in vitro-cultured scales, it was demonstrated that the insulin-like growth factor (IGF)-1 mRNA expression decreased by a bisphenol A treatment. On the other hand, 17beta-estradiol (E(2)) stimulated both TRAP and ALP activities and did not change IGF-1 mRNA expression, suggesting that bisphenol A has a different effect from E(2) on bone metabolism. This study is the first to demonstrate that bisphenol A functions to suppress directly osteoblasts and osteoclasts among vertebrates, which strongly suggests that this scale in an in vitro assay system can be utilized for the evaluation of the effects of endocrine disrupters on bone cells.

Calcitonin-like immunoreactivity in serum and tissues of the bonnethead shark, Sphyrna tiburo

Calcitonin is a 32-amino acid peptide hormone that is best known for its actions in maintaining skeletal integrity and calcium homeostasis in mammals. Calcitonin also appears to function in regulating certain aspects of animal reproduction, but the nature of this role remains unclear, particularly in nonmammalian vertebrates. The present study investigated the relationship between calcitonin and reproduction in the bonnethead shark (Sphyrna tiburo), a well-studied member of the oldest living vertebrate group (i.e. elasmobranchs) known to possess a calcitonin-producing organ. Serum calcitonin concentrations were measured in 28 reproductively mature female S. tiburo using a heterologous enzyme-linked immunosorbent assay (ELISA) system. Sites of calcitonin immunoreactivity were detected in tissues of mature female and embryonic S. tiburo using immunocytochemistry. Significant increases in serum calcitonin concentrations of mature female S. tiburo occurred during early stages of gestation, a period characterized by yolk-dependency of developing embryos. Immunoreactive calcitonin was detected in the duodenum and pancreas of embryonic S. tiburo sampled during the same period. The results from this study suggest that calcitonin obtained from endogenous and/or maternal sources may function in regulating yolk digestion in embryonic S. tiburo. Therefore, the association between calcitonin and reproduction in elasmobranchs may reflect an important role for this hormone in embryonic development.

Estradiol-17β-induced calcium uptake and resorption in juvenile rainbow trout, Oncorhynchus mykiss

Juvenile rainbow trout, Oncorhynchus mykiss, were injected with estradiol-17β (E2) in order to study the source of extra calcium needed during vitellogenesis. E2-treatment increased the calcium uptake from the external medium as well as calcium mobilization from muscle and scale. Judged by the increase in plasma protein-bound calcium levels, the E2-induced increase in calcium uptake is an apparent over-mobilization of calcium, i.e., the calcium uptake of the fish is in excess of what is found bound to plasma proteins. As the calcium excretion and calcium space (calculated from free plasma calcium levels) were unaffected, the excess calcium is suggested to be incorporated into internal calcium stores. This implies that the systems regulating vitellogenesis and calcium balance are integrated on the mechanistic or endocrine level, and that E2 causes calcium mobilization of a magnitude geared to the needs of the sexually maturing female.

Immunoreactive somatolactin cells in the pituitary of young, migrating, spawning and spent chinook salmon, Oncorhynchus tshawytscha

Immunocytochemical techniques using an antiserum to cod somatolactin (SL) demonstrated the presence of SL cells in the intermediate lobe of the pituitary in Oncorhynchus tshawytscha. The cells were small in yearling fish. Two groups of maturing fish were studied. In the spring run salmon collected in April and May during the upstream migration, the SL cells appeared stimulated. In September, during spawning, SL cell stimulation was maximal with indices of hypertrophy and degranulation often more marked in females than in males. In the other group, salmon of the fall run collected in the Pacific Ocean in August had well developed gonads, large gonadotropes and abundant SL cells. In spawning salmon (September) the SL cells were stimulated, mainly in females. However, the final stimulation was less intense than in spring run spawning fish. The SL cells were smaller, without evident granule release, but still abundant in spent salmon of the fall run caught at the end of November. Various factors (time spent in rivers before spawning, starvation, decalcification, stress, hypothalamic influences) were considered which might explain differences between spring and fall run salmon. These observations suggest that SL may play a role in the control of gonadal maturation in chinook salmon as it may also do in sockeye and chum salmon previously studied, and that SL cells may be sensitive to the ambient salinity.

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss)

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 17 beta-estradiol on calcitonin secretion and content in a human medullary thyroid carcinoma cell line

The presence of a direct estrogen effect on calcitonin secretion is controversial. Because most of the data available were obtained from complex in vivo systems, we chose an in vitro approach to assess the problem. Using a human C cell carcinoma cell line (TT cells) with well-documented estrogen receptors, we investigated the effect of 17 beta-estradiol (E2) on basal and stimulated calcitonin secretion, on calcitonin content, and on total cellular protein. After short (30 and 180 minutes) and long-term (24 h to 6 days) incubation of the cells with different concentrations of E2 (from 0.01 to 100 nM) we observed no stimulatory but a transient dose-dependent inhibitory effect on CT secretion and content. The nadir of the effect on CT secretion appeared at 24 h, demonstrating a reduction to 80.5 +/- 7.8% of control at 1 nM and to 59.1 +/- 15% of control at 100 nM E2. After 72 h, the CT levels of the E2-exposed groups returned to control levels. The acute stimulation of the cells with TPA plus forskolin after preincubation with E2 up to 6 days showed no difference in the increment of CT release compared to the control groups. Additionally, E2 had a dose-dependent stimulatory effect on cell protein content. The data demonstrate the absence of a direct stimulatory effect of E2 on CT secretion, revealing a dose-dependent inhibitory effect on CT secretion and content.

Expression of the calcitonin gene during migration of the Pacific salmon, Oncorhynchus gorbuscha

Plasma calcitonin levels increase during reproduction in female salmon. Whether these changes in circulating levels of the hormone are due to increased secretion and or increased biosynthesis is not established. We measured total and poly A+ RNAs and calcitonin content of ultimobranchial bodies of male and female pink salmon during the different stages of the reproductive cycle. Calcitonin mRNAs were analysed by hybridization of northern and dot blots with a specific probe for salmon calcitonin. Dot blot autoradiography indicated that female animals had higher levels of CT mRNA than males and these values were correlated with plasma calcitonin levels. In conclusion, sexual hormones still to be identified, are probably implicated in the expression of the calcitonin gene in females during the reproductive cycle.