Development and validation of a salmon growth hormone radioimmunoassay

Orexin and neuropeptide Y: tissue specific expression and immunoreactivity in the hypothalamus and preoptic area of the cichlid fish Cichlasoma dimerus

Neuropeptide Y (NPY) and orexin are neuropeptides involved in the regulation of feeding in vertebrates. In this study we determined the NPY and orexin mRNA tissue expression and their immunoreactivity distribution in both preoptic area and hypothalamus, regions involved in the regulation of feeding behavior. Both peptides presented a wide expression in all tissues examined. The NPY-immunoreactive (ir) cells were localized in the ventral nucleus posterioris periventricularis (NPPv) and numerous ir-NPY fibers were found in the nucleus lateralis tuberis (NLT), the nucleus recess lateralis (NRL) and the neurohypophysis. Ir-orexin cells were observed in the NPPv, dorsal NLT, ventral NLT, lateral NLT (NLTl) and the lateral NRL. Ir-orexin fibers were widespread distributed along all the hypothalamus, especially in the NLTl. Additionally, we observed the presence of ir-orexin immunostaining in adenohypophyseal cells, especially in somatotroph cells and the presence of a few ir-orexin-A fibers in the neurohypophysis. In conclusion, both peptides have an ubiquitous mRNA tissue expression and are similarly distributed in the hypothalamus and preoptic area of Cichlasoma dimerus. The presence of ir-orexin in adenohypohyseal cells and the presence of ir-orexin and NPY fibers in the neurohypophysis suggest that both peptides may play an important neuroendocrine role in anterior pituitary.

Effect of gonadotropin-releasing hormone on phagocytic leucocytes of rainbow trout

To clarify the role of gonadotropin-releasing hormone (GnRH) in the fish immune system, in vitro effect of GnRH was examined in phagocytic leucocytes of rainbow trout (Oncorhynchus mykiss). Gene expression of GnRH-receptor was detected by RT-PCR in leucocytes from head kidney. Administration of sGnRH increased proliferation and mRNA levels of a proinflammatory cytokine, tumor necrosis factor (TNF)-α, in trout leucocytes. Superoxide production in zymosan-stimulated phagocytic leucocytes was also increased by sGnRH in a dose-related manner from 0.01 to 100 nM. There was no significant effect of sGnRH on mRNA levels of growth hormone (GH) expressed in trout phagocytic leucocytes. Immunoneutralization of GH by addition of anti-salmon GH serum into the medium could not block the stimulatory effect of sGnRH on superoxide production. These results indicate that GnRH stimulates phagocytosis in fish leucocytes through a GnRH-receptor-dependent pathway, and that the effect of GnRH is not mediated through paracrine GH in leucocytes.

The role of growth hormone in growth, lipid homeostasis, energy utilization and partitioning in rainbow trout: interactions with leptin, ghrelin and insulin-like growth factor I

The growth-promoting effects of in vivo growth hormone (GH) treatment were studied in relation to size and lipid content of energy stores including liver, mesentery, white muscle and belly flap in rainbow trout. In order to elucidate endocrine interactions and links to regulation of growth, adiposity and energy metabolism, plasma levels of GH, insulin-like growth factor I (IGF-I), leptin (Lep) and ghrelin, were assessed and correlated to growth and energy status. In addition tissue-specific expression of lepa1 mRNA was examined. Juvenile rainbow trout were implanted with sustained-release bovine GH implants and terminally sub-sampled at 1, 3 and 6 weeks. GH increased specific growth rate, reduced condition factor (CF) and increased feed conversion efficiency resulting in a redistribution of energy stores. Thus, GH decreased mesenteric (MSI) and liver somatic index (LSI). Lipid content of the belly flap increased following GH-treatment while liver and muscle lipid content decreased. Independent of GH substantial growth was accompanied by an increase in muscle lipids and a decrease in belly flap lipids. The data suggest that the belly flap may function as an energy buffering tissue during episodes of feeding and lean growth. Liver and muscle lipids were positively correlated to body weight, indicating a size-dependent change in adiposity. Hepatic lepa1 mRNA positively correlated to MSI and CF and its expression decreased following GH treatment, coinciding with decreased hepatic lipid content. Plasma Lep was positively correlated to MSI and belly flap lipid content, suggesting that Lep may communicate energy status. In summary, the observed GH tissue-specific effects on lipid metabolism in rainbow trout highlight the complex physiology of the energy reserves and their endocrine control.

Pituitary and plasma growth hormone dynamics during sexual maturation of female Atlantic salmon

Growth hormone in fish regulates many important physiological processes including growth, metabolism and potentially reproduction. In salmonid fish, GH secretion is episodic with irregularly spaced GH peaks. Plasma GH reflects secretion episodes as well as the clearance rate of the hormone, and plasma levels may thus not always reflect the level of activation of the GH axis. This study measured the production dynamics of GH over a 17-month period in sexually maturing female Atlantic salmon which included final maturation and spawning. For the first time, the level of pituitary GH mRNA, pituitary GH protein and plasma GH protein were analyzed concurrently in the same individuals. mRNA and protein were extracted in parallel from the same samples with subsequent real time quantitative PCR to measure mRNA transcripts and radioimmunoassay to measure pituitary and plasma GH protein. Further, the effects of photoperiod manipulation on these parameters were studied. The results show no correlation between mRNA and protein levels except at some time points, and indicate that it is inappropriate to correlate pooled temporal data and averages in time series unless the relationship among the variables is stable over time. The results indicate complex and shifting relationships between pituitary GH mRNA expression, pituitary GH content and plasma GH levels, which could result from changes in clearance rather than secretion rate at different times and its episodic secretion. The study also suggests that there is a functionally important activation of the GH system during spring leading up to maturation and spawning.

Ghrelin decreases food intake in juvenile rainbow trout (Oncorhynchus mykiss) through the central anorexigenic corticotropin-releasing factor system

Ghrelin stimulates pituitary growth hormone (GH) release, and has a key role in the regulation of food intake and adiposity in vertebrates. To investigate the central effect of native rainbow trout ghrelin (rtghrelin) on food intake in rainbow trout, as well as its possible mode of action, four groups of fish received a single injection into the third brain ventricle (i.c.v. injection): (1) control group (physiological saline) (2) ghrelin-treated group (2.0 ng rtghrelin g bwt(-1)), (3) group given the corticotropin-releasing hormone receptor antagonist alpha-helical CRF 9-41 (ahCRF) (4.0 ng g bwt(-1)) and (4) group receiving the same dose of both ghrelin and ahCRF. Food intake was assessed 1h after treatment. In addition, the presence of the GHS-R (the ghrelin receptor) in the rainbow trout CNS was examined with Western blot. To investigate peripheral effects of ghrelin, rainbow trout received an intraperitoneal cholesterol-based implant with or without rtghrelin, and daily food intake was measured during 14 days. Weight and length were measured at the start and termination of the experiment and specific growth rates were calculated. Mesenteric fat stores, muscle and liver lipid content were analysed after the treatment period. Central ghrelin injections decreased food intake compared with controls, and treatment with ahCRF abolished the ghrelin-effect. Western blot analysis of the GHS-R revealed a single band at around 60 kDa in pituitary, hypothalamus, brain and stomach. Long-term peripheral ghrelin treatment decreased daily food intake compared with controls. This was reflected in a ghrelin-induced decrease in weight growth rate (p<0.06). There was no effect of ghrelin on plasma GH levels or tissue fat stores. The conclusion from this study is that the GHS-R is indicated in the CNS in rainbow trout and that ghrelin may act there as an anorexigenic hormone, through a CRF-mediated pathway. Elevated peripheral ghrelin levels also seem to lead to decreased feed intake in the longer term.

A homologous salmonid leptin radioimmunoassay indicates elevated plasma leptin levels during fasting of rainbow trout

The present study was conducted to establish a homologous radioimmunoassay (RIA) for quantifying plasma leptin (Lep) levels in salmonid species, and to study Lep levels in relation to nutritional status. A part of the Lep peptide, a 14 amino acid long sequence, identical between a Salmo and an Oncorhynchus species was synthesised. Polyclonal antibodies were raised in rabbit against this antigen and both were subsequently used in the development of a RIA protocol for assessing plasma Lep levels. The limit of detection of the assay was 0.3 nM, and intra- and interassay coefficient of variation (CV) were 8.4% and 13%, respectively. Apart from Atlantic salmon and rainbow trout, the assay exhibits measuring parallelism for a range of fish species, including arctic char, Atlantic cod and turbot, suggesting that the established RIA is useful for quantifying Lep levels in several fish species. The RIA indicates that Lep is found in salmonid plasma at levels of 0.5-5 nM, which is comparable with other peptide hormones, and well within the measuring range of the RIA. A study of fed and fasted rainbow trout showed elevated plasma Lep levels during fasting. In addition there was no correlation between Lep levels and condition factor. These data suggest that the relation between circulating Lep levels and energy status differs from that in mammals. While Lep is linked to energy balance, it may not act as an adiposity signal in salmonids, possibly pointing to functional divergence among ectothermic and endothermic vertebrates.

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.

Plasma ghrelin levels in rainbow trout in response to fasting, feeding and food composition, and effects of ghrelin on voluntary food intake

Ghrelin, a peptide hormone which stimulates growth hormone (GH) release, appetite and adiposity in mammals, was recently identified in fish. In this study, the roles of ghrelin in regulating food intake and the growth hormone (GH)-insulin-like growth factor I (IGF-I) system of rainbow trout (Oncorhynchus mykiss) were investigated in three experiments: 1) Pre- and postprandial plasma levels of ghrelin were measured in relation to dietary composition and food intake through dietary inclusion of radio-dense lead-glass beads, 2) the effect of a single intraperitoneal (i.p.) injection with rainbow trout ghrelin on short-term voluntary food intake was examined and 3) the effect of one to three weeks fasting on circulating ghrelin levels and the correlation with plasma GH and IGF-I levels, growth and lipid content in the liver and muscle was studied. There was no postprandial change in plasma ghrelin levels. Fish fed a normal-protein/high-lipid (31.4%) diet tended to have higher plasma ghrelin levels than those fed a high-protein/low-lipid (14.1%) diet. Plasma ghrelin levels decreased during fasting and correlated positively with specific growth rates, condition factor, liver and muscle lipid content, and negatively with plasma GH and IGF-I levels. An i.p. ghrelin injection did not affect food intake during 12-hours post-injection. It is concluded that ghrelin release in rainbow trout may be influenced by long-term energy status, and possibly by diet composition. Further, in rainbow trout, ghrelin seems to be linked to growth and metabolism, but does not seem to stimulate short-term appetite through a peripheral action.

Larval exposure to 4-nonylphenol and 17beta-estradiol affects physiological and behavioral development of seawater adaptation in Atlantic salmon smolts

Population declines of anadromous salmonids are attributed to anthropogenic disturbances including dams, commercial and recreational fisheries, and pollutants, such as estrogenic compounds. Nonylphenol (NP), a xenoestrogen, is widespread in the aquatic environment due to its use in agricultural, industrial, and household products. We exposed Atlantic salmon yolk-sac larvae to waterborne 10 or 100 microg L(-1) NP (NP-L or NP-H, respectively), 2 microg L(-1) 17beta-estradiol (E2), or vehicle, for 21 days to investigate their effects on smolt physiology and behavior 1 year later. NP-H caused approximately 50% mortality during exposure, 30 days after exposure, and 60 days after exposure. Mortality rates of NP-L and E2 fish were not affected until 60 days after treatment, when they were 4-fold greater than those of controls. Treatment with NP-L or E2 as yolk-sac larvae decreased gill sodium-potassium-activated adenosine triphosphatase (Na+,K(+)-ATPase) activity and seawater (SW) tolerance during smolt development, 1 year after exposure. Exposure to NP-L and E2 resulted in a latency to enter SW and reduced preference for SW approximately 2- and 5-fold, respectively. NP-L-exposed fish had 20% lower plasma insulin-like growth factor I (IGF-I) levels and 35% lower plasma triiodothyronine (T3). Plasma growth hormone and thyroxine (T4) were unaffected. Exposure to E2 did not affect plasma levels of IGF-I, GH, T3, or T4. Both treatment groups exhibited increased plasma cortisol and decreased osmoregulatory capacity in response to a handling stressor. These results suggest that early exposure to environmentally relevant concentrations of NP, and other estrogenic compounds, can cause direct and delayed mortalities and that this exposure can have long-term, "organizational" effects on life-history events in salmonids.

Involvement of somatolactin in background adaptation of the cichlid fish Cichlasoma dimerus

Somatolactin (SL) is a pituitary hormone present exclusively in fish that is involved in different physiological processes. The role of SL was evaluated in Cichlasoma dimerus (Teleostei, Perciformes) exposed for 10 days to a black and white background (BB and WB). Changes in alpha-melanophore stimulating hormone (alphaMSH) and melanin concentrating hormone (MCH) cells were also analyzed for comparison with SL. A melanin dispersing effect was observed in fish exposed to a BB, while a concentrating one was observed in those exposed to a WB. By Western blot, three SL-immunoreactive (ir) bands (32, 28 and 23.5 kD) were evidenced. Pituitary SL-ir levels were 2.66- and 2.67-fold greater in the 32 Kd and 28 kD bands, respectively, in BB fish compared with those of WB fish. The SL-ir 23.5 Kd band was not included in the analysis because of its unknown identity. In addition, SL-ir cell number and area were significantly higher in the BB condition (BB 22.73+/-1.46, WB 7.37+/-0.54 and BB 27.39+/-1.00 microm2; WB: 16.61+/-0.65 microm2). No significant differences were observed in the number of the hypothalamic MCH-ir neurons. However, a significant difference was observed in their nuclear area (BB 11.61+/-0.42 microm2, WB 17.80+/-0.84 microm2). alphaMSH-ir cells showed a marked increased in number (BB 35.96+/-1.22, WB 24.36+/-1.04), but no significant differences were observed in the cell area. In conclusion, this study presented clear evidence towards a possible involvement of SL in the adaptation to background colors in teleost together with alphaMSH and MCH.

Cloning, expression, and biological activity of growth hormone in bullfrog (Rana catesbeiana)

The cDNA (GenBank, AY251538) encoding bullfrog growth hormone (fGH) was cloned by RT-PCR from the total RNA of pituitary glands. Its sequence encoded a putative polypeptide of 215 amino acids, including a signal peptide of 25 amino acids with no change to those of other previous reported bullfrog GHs. The fGH precursor shares 98.1, 96.3, and 95.3% homologies to those of other bullfrog GHs (AAB24792, AAB19428, CAA31038) in amino-acid sequence and its nucleotide sequences of the coding region shares 99.1 and 98.5% homologies to those of previous bullfrog GH genes (S52027 and X12520). The fGH cDNA was also efficiently expressed in Escherichia coli carrying a plasmid pGfGH in which the cDNA was under the control of GST promoter of pGEX1-lambdaT. The expressed fusion protein GST-fGH is comprised about 29.3% of the total cellular protein in such bacteria. The purified GST-fGH cannot only showed a obvious dose-response curve when it reacted with the hepatic membrane receptor proteins from bullfrog, but also significantly increased the body weight and length of bullfrog after twice injection and such effects lasted two or three weeks after the last injection with purified GST-fGH.

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.

Effects of prolactin and growth hormone on proliferation and survival of cultured trout leucocytes

The in vitro effects of prolactin (PRL) and growth hormone (GH) on the proliferation and survival of leucocytes isolated from the blood of the rainbow trout (Oncorhynchus mykiss) were examined, with special reference to the immunosuppression by cortisol. Both PRL and GH induced a mitogenic effect in trout leucocytes. Contrary, the frequencies of annexin V-positive apoptotic cells and propidium iodide-positive dead cells were decreased by the administration of PRL, but were uninfluenced by GH. Administration of cortisol suppressed the mitotic activity and induced cell death of leucocytes. PRL inhibited the decrease in mitosis and the increase in cell death due to cortisol. GH significantly assisted recovery of cortisol-suppressed mitosis but did not influence the survival of leucocytes. These results suggest that PRL and GH are involved in the maintenance of specific immune functions in fish through a prevention of immunosuppression by cortisol.

Peptide purification, complementary deoxyribonucleic acid (DNA) and genomic DNA cloning, and functional characterization of ghrelin in rainbow trout

We have identified ghrelin from the stomach of rainbow trout. Four isoforms of ghrelin peptide were isolated: the C-terminal amidated type of rainbow trout ghrelin (rt ghrelin) composed of 24 amino acids (GSSFLSPSQKPQVRQGKGKPPRV-amide) is a basic form; des-VRQ-rt ghrelin, which deleted three amino acids (V13R14Q15) from rt ghrelin; and further two types of rt ghrelin that retained the glycine residue at the C terminus, rt ghrelin-Gly, and des-VRQ-rt ghrelin-Gly. The third serine residue was modified by octanoic acid, decanoic acid, or the unsaturated form of those fatty acids. In agreement with the isolated peptides, two cDNAs of different lengths were isolated. The rt ghrelin gene has five exons and four introns, and two different mRNA molecules are predicted to be produced by alternative splicing of the gene. A high level of ghrelin mRNA expression was detected in the stomach, and moderate levels were detected in the brain, hypothalamus, and intestinal tracts. Des-VRQ-rt ghrelin stimulated the release of GH in the rat in vivo. Furthermore, des-VRQ-rt ghrelin stimulated the release of GH, but not the release of prolactin and somatolactin in rainbow trout in vivo and in vitro. These results indicate that ghrelin is a novel GH secretagogue in rainbow trout that may affect somatic growth or osmoregulation through GH. Because ghrelin is expressed in various tissues other than stomach, it may play important role(s) in cellular function as a local regulator.

Dopaminergic innervation of the rainbow trout pituitary and stimulatory effect of dopamine on growth hormone secretion in vitro

To elucidate which factors regulate growth hormone (GH) secretion in rainbow trout, dopaminergic innervation of the rainbow trout pituitary along with the action of dopamine in vitro, were studied. Brains with attached pituitaries were double-labeled for putative dopaminergic neuronal fibers and somatotropes, using fluorescence immunohistochemistry. A direct dopaminergic innervation to the proximal pars distalis (PPD) with dopaminergic fibers terminating adjacent to somatotropes was demonstrated. Growth hormone secretion from whole pituitaries was measured in perifusate using a homologous GH-RIA. Dopamine (DA; 10(-7)-2x10(-6) g ml(-1)) increased basal GH secretion, with the GH secretion normalizing again after the DA exposure was halted. When pituitaries were pre-treated with somatostatin-14 (SRIF-14; 10(-12)-10(-9) g ml(-1)), before being exposed to different doses of DA, there was an inhibition of GH secretion which was not reversed after treatment of SRIF-14 was halted, unless DA was added. It is concluded that dopamine can function as a GH secretagogue in the rainbow trout pituitary gland.

Effects of prolactin and growth hormone on plasma immunoglobulin M levels of hypophysectomized rainbow trout, Oncorhynchus mykiss

Immunoglobulin M (IgM) is a major component of the humoral immune system of teleosts. This study examines the effects of hypophysectomy and subsequent replacement with prolactin (PRL) or growth hormone (GH) upon the plasma IgM levels of the rainbow trout (Oncorhynchus mykiss). Plasma IgM levels of the hypophysectomized fish were decreased to 30% of those in sham-operated fish 1 or 4 weeks after operation. Implantation of a cholesterol pellet containing salmon PRL or GH restored plasma IgM levels of the hypophysectomized fish, suggesting important roles for PRL and GH in the regulation of circulating IgM level in trout.

Development of an ELISA for chum salmon (Oncorhynchus keta) growth hormone

A specific and sensitive enzyme-linked immunosorbent assay (ELISA) was developed for the measurement of low levels of serum growth hormone (GH) in chum salmon (Oncorhynchus keta). The antiserum to GH (a-rsGH) was obtained from a rabbit immunized with recombinant chum salmon GH. The noncompetitive ELISA was performed by a sandwich method using a-rsGH rabbit IgG as the first antibody, its biotinylated Fab' fragment as the second antibody, and the avidin-biotin reaction for signal amplification. This assay could be run in 3 days and routinely detected GH at concentrations as low as 0.5 ng/ml. The development of an ELISA for GH made possible quantification of serum GH levels. In this assay system, parallel dilution curves were obtained using purified chum salmon GH and GH's from several species of the genus Oncorhynchus.

The use of recombinant gilthead sea bream (Sparus aurata) growth hormone for radioiodination and standard preparation in radioimmunoassay

A gilthead sea bream growth hormone (sbGH) obtained by cloning and expression of sbGH cDNA was used to develop a sensitive and specific radioimmunoassay (RIA). Iodination of recombinant sbGH (rsbGH) was performed by the classical Chloramine-T method. Specific antiserum, raised in rabbits, was added in a final dilution of 1/36,000. The minimum detectable dose was 30 pg, and the midrange of the assay (ED50) was 275 pg. Intra- and inter-assay coefficients of variation (CV) were 3.3 and 5.8% at ED50 levels. Human GH (hGH), ovine GH (oGH), carp gonadotropin (cGtH), chinook salmon gonadotropin (sGtH), ovine prolactin (oPRL) and recombinant tilapia prolactin (rtiPRL) did not show cross-reactivity. Serial dilutions of chinook salmon GH (sGH) and recombinant rainbow trout GH (rtGH) showed a low but significant cross-reactivity. A good parallelism between rsbGH standard and serial dilutions of native sbGH, plasma and pituitary extracts was observed. In addition, when plasma and pituitary samples were analyzed for GH quantification, non-significant differences were observed within this and previous RIA for native sbGH. Therefore, it appears conclusive that our rsbGH can be used successfully as a standard and radioiodinated hormone in GH assays for gilthead sea bream, which is extensively cultured in the Mediterranean area.

Changes in plasma somatolactin levels during spawning migration of chum salmon (Oncorhynchus keta)

Plasma somatolactin (SL) concentrations were examined in chum salmon in relation to gonadal maturation; immature salmon in the Bering Sea at various stages of maturation, and mature salmon during upstream migration caught at the ocean, bay and river. Plasma SL concentrations as well as plasma prolactin (PRL) and growth hormone (GH) levels in the immature fish caught in the Bering Sea were maintained essentially at similar levels. Plasma SL in mature salmon increased significantly from the fish in the ocean to the fish in the river in both sexes. Although all the fish had fully developed gonads, females completed ovulation while still in the bay, whereas final spermeation in males was achieved after entry into the river. Thus, no clear correlation was seen between plasma SL levels and final gonadal maturation. On the other hand, plasma PRL concentrations in both male and female fish were higher in the fish in the river than those in the ocean and bay, and plasma GH levels were higher in both sexes in the fish in the bay and river than those in the ocean. Plasma levels of triglycerides, glucose, free fatty acids and ionized sodium and calcium were also examined. Significant-negative correlations were seen between plasma SL and plasma ionized calcium in mature male salmon, and between plasma SL and plasma triglycerides in mature female salmon. Although our findings do not rule out the possibility of the involvement of SL in final maturation, the results indicate that SL seems to be involved at least in energy and/or calcium metabolism during the spawning migration.

Osmoregulatory actions of growth hormone and its mode of action in salmonids: A review

Osmoregulatory actions of growth hormone (GH) and its mode of action in salmonids are reviewed. We present evidence suggesting that insulin-like growth factor I (IGF-I) mediates some of the actions of GH on seawater acclimation. Plasma concentration and turnover of GH rise following exposure to seawater. Exogenous GH (in vivo) increases gill Na(+),K(+)-ATPase activity and the number of gill chloride cells, and inhibits an increase in plasma osmolarity and ions following transfer of fish to seawater. A single class of high affinity GH receptors is present in the liver, gill, intestine, and kidney. The levels of IGF-I mRNA in the liver, gill and kidney increased after GH-injection. After transfer to seawater, IGF-I mRNA increased in the gill and kidney following the rise in plasma GH, although no significant change was seen in the liver. Injection of IGF-I improved the ability of the fish to maintain plasma sodium levels after transfer to seawater. GH treatment also sensitizes the interrenal to adrenocorticotropin (ACTH), increasing cortisol secretion. Both cortisol and IGF-I may be involved in mediating the action of GH in seawater adaptation, although studies on the effect of GH on osmoregulatory physiology of non-salmonid species are limited. An integrated model of the osmoregulatory actions of GH is presented, and areas in need of research are outlined.

Insulin-like growth factor I (IGF-I) mRNA expression in coho salmon, Oncorhynchus kisutch: Tissue distribution and effects of growth hormone/prolactin family proteins

To examine the hormonal and nutritional regulation of insulin-like growth factor I (IGF-I) mRNA expression, a sequence-specific solution hybridization/RNase protection assay for coho salmon IGF-I mRNA was developed. This assay is both rapid and sensitive and has low inter- (less than 15%) and intra-assay variations (less than 5%). Using this assay, the tissue distribution of IGF-I mRNA and effects of growth hormone (GH), prolactin (PRL) and somatolactin (SL) on hepatic IGF-I mRNA expression in coho salmon were examined in vivo. Liver had the highest IGF-I mRNA level of 16 pg/μg DNA. Significant amounts of IGF-I mRNA were also found in all other tissues examined (intestine 4.1, kidney 3.8, gill arch 2.4, brain 2.4, ovary 2.3, muscle 2.1, spleen 1.7 and fat 1.1 pg/μg DNA). Injection of coho salmon GH at doses of 0.1 and 1 μg/g body weight significantly increased the hepatic IGF-I mRNA levels in a dose-dependent manner. Injection of coho salmon SL, a recently discovered member of the GH/PRL family, stimulated the IGF-I mRNA expression at the higher dose (1 μg/g), whereas coho salmon PRL had no effect at either dose. Concentration-dependent stimulation by coho salmon GH was also obtained in vitro in primary culture of salmon hepatocytes in concentrations ranging from 0.01 to 1 μg/ml. These results indicate that IGF-I mRNA expression occurs in a variety of tissues in coho salmon, and that at least the hepatic expression is under the regulation of GH and possibly other hormones. The sequence-specific assay established in the present study can be used for accurate quantitation of IGF-I mRNA in salmonid species, and can contribute to a better understanding of the physiology of IGF-I in salmonids.

Expression of insulin-like growth factor I gene in osmoregulatory organs during seawater adaptation of the salmonid fish: possible mode of osmoregulatory action of growth hormone

Growth hormone has been shown to contribute to seawater adaptation of salmonid fishes. The growth influence of growth hormone is mediated largely by hepatic production of insulin-like growth factor I (IGF-I). To study the growth hormone-IGF-I axis in osmoregulation, we measured IGF-I mRNA in the liver, gill, and body kidney from rainbow trout by Northern analysis. The levels of IGF-I mRNA in all tissues increased significantly after injection of growth hormone. Transfer of trout from fresh water to 80% seawater evoked an increase in plasma growth hormone after 1 day. IGF-I mRNA was not altered significantly in the liver, but it was increased in the gill and body kidney after 1 and 8 days, respectively. These observations indicate that the IGF-I gene is expressed differently among these organs during seawater adaptation. Growth hormone may stimulate hypoosmoregulatory ability by inducing local expression of IGF-I in osmoregulatory organs, although the possibility that IGF-I expression might occur in part independently of growth hormone during seawater adaptation cannot be excluded.

Changes in growth hormone and prolactin messenger ribonucleic acid levels during seawater adaptation of amago salmon (Oncorhynchus rhodurus)

To examine the changes in secretion of growth hormone (GH) and prolactin (PRL) with reference to their osmoregulatory roles, changes in pituitary mRNA levels and plasma concentrations of these hormones were examined during seawater adaptation in silvery juveniles (smolts) and precociously mature males (dark parr) of amago salmon (Oncorhynchus rhodurus). Transfer to seawater increased plasma sodium levels in both smolts and dark parr. Smolts adjusted their plasma sodium to the level associated with seawater-adaptation (165 mEq/liter) within 3 days, whereas no adjustment was seen in dark parr; the latter failed to survive in seawater for more than 3 days. In smolts, plasma GH levels increased significantly 1 day after transfer, whereas there was no significant change in dark parr. An increase in GH mRNA levels was observed in smolts in association with increased plasma GH, whereas there was no change in dark parr. In contrast, a reduction in plasma PRL levels was consistently observed in both smolts and dark parr after transfer to seawater. However, there was no significant change in PRL mRNA levels in either smolts or dark parr. These results suggest that both gene expression and release of GH are activated by seawater transfer only in smolts with adequate seawater adaptability, whereas PRL gene expression is decreased after seawater transfer regardless of seawater adaptability.

Immunoaffinity purification and partial characterization of sea bass (Dicentrarchus labrax) growth hormone

Growth hormone (GH) was isolated from sea bass (Dicentrarchus labrax) pituitary extract by a simple one-step procedure involving immunoaffinity chromatography. A monoclonal antibody raised against chicken GH and found to immunostain very specifically the GH cells in the pituitary of the sea bass was coupled to CNBr-activated Sepharose 4B. Sea bass pituitary extracts were run on the affinity column, and the eluted material was analyzed on reversed-phase HPLC and found to consist of one single peak. The yield of purified hormone was 2.4 mg/g pituitary. Two monomeric forms (MW = 20,000 and 22,000 Da) of sea bass GH were identified by gel electrophoresis. Gel electrofocusing revealed apparent isoelectric points of 6.15, 6.50, and 6.95. Amino acid composition is consistent with other vertebrate GHs. The immunological relatedness was tested by immunoblotting using antisera raised against GH of different species. Polyclonal antisera raised against the isolated hormone exhibited a specific labeling of the GH cells in sea bass pituitary sections as well as of the immunoblotted purified GH.

Effects of acute and chronic stress on the levels of circulating growth hormone in the rainbow trout, Oncorhynchus mykiss

The acute stress of handling followed by confinement for a period of 1 or 24 hr caused a typical stress response in rainbow trout (elevation of plasma ACTH and cortisol) and a significant reduction in the concentration of circulating growth hormone. The chronic stress of low oxygen levels in both crowded and uncrowded tanks of fish caused a significant elevation of circulating GH levels, an effect which was abolished by the provision of additional aeration to the rearing tanks. This chronic elevation of GH levels was closely correlated with an elevation of plasma cortisol in the same fish. These findings are discussed in relation to stress-induced growth suppression and to the links between the hypothalamic-pituitary-interrenal axis and somatotrope activity.

Development and validation of a highly sensitive radioimmunoassay for chinook salmon (Oncorhynchus tshawytscha) growth hormone

This study describes the development of a highly specific and very sensitive radioimmunoassay for salmonid growth hormone. Antiserum raised against chinook (Oncorhynchus tshawytscha) GH2, which did not recognize 125I-sPRL and 125I-sGTH (at 1:1000 initial dilution), was able to inhibit growth when injected into rainbow trout (Oncorhynchus mykiss). 125I-sGH2, used as tracer, was not recognized by anti-sGTH or by anti-sPRL. Mammalian GH and ACTH and salmonid GTH, TSH, and PRL did not cross-react in the sGH assay. The inhibition curves for pituitary extracts and plasma from salmonids were parallel to the salmon GH standard, whereas those from carp, tilapia, and catfish showed no significant cross reactivity. The RIA ED90 and ED50 values were 0.2 and 1.5 ng/ml, respectively. Using this RIA for measuring GH release by cultured pituitary cell we observed a strong inhibiting effect of SRIF (10(-6) M) and a stimulatory effect of hGRF (10(-6) M). This RIA allowed us also to detect daily fluctuations in the plasma GH concentration in cannulated rainbow trout.

The effect of starvation on growth and plasma growth hormone concentrations of rainbow trout, Oncorhynchus mykiss

Two experiments, one using 0+ the other 1+ rainbow trout, were conducted to investigate the effect of prolonged starvation on plasma growth hormone levels. The results from both experiments were essentially the same. As expected, starvation resulted in cessation of growth and in a lower coefficient of condition, whereas fed fish continued to grow and remained in good condition. Starvation had relatively little effect on the plasma cortisol level; in one experiment levels were elevated temporarily in starved fish, although by the end of the experiment there was no longer any difference between starved and fed fish, and in the other experiment plasma cortisol levels remained very low throughout the course of the experiment in both starved and fed fish. In contrast, in both experiments starvation had a pronounced effect on the plasma growth hormone level, which rose steadily during both experiments, such that it was six times higher after 1 month of starvation in 0+ fish, and five times higher after 6 weeks of starvation in 1+ fish. Thus, paradoxically, fed fish had very low plasma growth hormone levels and grew rapidly, whereas starved fish had elevated plasma growth hormone levels but did not grow. In both experiments a strong negative correlation was observed between the plasma growth hormone level and the coefficient of condition of the fish. The results are discussed with regard to the well-established metabolic changes that occur during starvation, and it is suggested that a major role of growth hormone during starvation is to aid in the mobilisation of fatty acids and glycerol from adipose stores.

Kinetic studies of growth hormone and prolactin during adaptation of coho salmon, Oncorhynchus kisutch, to different salinities

The kinetics of growth hormone (GH) and prolactin (PRL) in coho salmon (Oncorhynchus kisutch) transferred from fresh water (FW) to seawater (SW) and vice versa were examined to help clarify the osmoregulatory roles of the two hormones during periods of migration to different salinities. Chum salmon GH or PRL was administered by a single injection intraarterially, and metabolic clearance rate (MCR) and secretion rate (SR) of injected hormones were calculated from the disappearance of the hormones from the plasma. When coho salmon smolts were acclimated to SW, MCR, SR, and plasma level of GH in SW-adapted (2-3 weeks) fish were twice as great as those in fish in FW. On the other hand, there was no difference in the kinetics of GH between the adult coho salmon in SW and those adapted to FW (2-3 weeks). The transfer of the adult coho salmon from SW to FW was followed after 2 days by a rise in plasma level and SR of PRL, which tended to stay at high levels after 2-3 weeks. The MCR of PRL increased significantly after 2-3 weeks in FW. These results support the likelihood of an important role of GH in SW adaptation and of PRL in FW adaptation in coho salmon.

Seasonal changes in seawater adaptability and plasma levels of prolactin and growth hormone in landlocked sockeye salmon (Oncorhynchus nerka) and amago salmon (O. rhodurus)

In order to clarify the roles of prolactin (PRL) and growth hormone (GH) in the development of seawater adaptability in salmonids, seasonal changes in salinity tolerance, plasma PRL, and plasma GH were examined in juvenile landlocked sockeye salmon (Oncorhynchus nerka) and amago salmon (O. rhodurus). Assessed by the 24-hr seawater-challenge test, the landlocked sockeye salmon possessed seawater adaptability as underyearlings in spring, which was maintained throughout the year, and a further increase was observed as yearlings the next spring. An increase in seawater adaptability was observed in silvery juvenile amago salmon as underyearlings from autumn to winter, when some of the wild population migrate to the sea. Precociously mature amago salmon, which did not develop a silvery body color but maintained distinct parr marks, also showed an improvement in seawater adaptability during autumn to winter, although plasma sodium levels after transfer to seawater were still higher than those of the silvery juveniles. In both sockeye and amago salmon, seasonal changes in plasma levels of PRL and GH were not correlated with development of seawater adaptability. In both species, acclimation to seawater resulted in decreased plasma levels of PRL irrespective of their adaptability to seawater, in agreement with the inhibitory effects of PRL in seawater adaptation. On the other hand, plasma GH levels increased only when seawater adaptability was high, in agreement with previous observations indicating an important role of GH in seawater adaptation of salmonids.

Homologous radioimmunoassay for bullfrog growth hormone

Antiserum against bullfrog growth hormone (fGH) was produced by immunizing rabbits with the highly purified fGH obtained from adenohypophyses of adult bullfrogs. Histological studies on bullfrog adenohypophyses revealed that the cells that immunologically reacted with the antiserum against fGH corresponded to the ones positively stained with the antiserum against rat GH. The antiserum together with fGH and 125I-fGH was employed to develop a radioimmunoassay (RIA) for fGH. Several dilutions of plasma and of pituitary homogenate of both adult and larval bullfrogs yielded dose-response curves which were parallel to the standard curve. Ovine prolactin (PRL), and growth hormone (GH); eel and salmon GHs; and bullfrog LH, FSH, TSH, PRL, and neurointermediate lobe homogenate did not react in this assay. Plasma from hypophysectomized bullfrogs had no detectable immunoreactive GH. Pituitary homogenates of Bufo japonicus, Xenopus laevis, and Cynops pyrrhogaster gave inhibition curves which did not parallel the standard. The homologous RIA for bullfrog GH thus developed was applied for the determination of plasma and pituitary GH levels in the larvae and adults. Plasma GH levels were relatively low during preclimax period and rose as metamorphosis progressed. Plasma GH concentrations were maximum in the juvenile frogs and decreased as the animals grew up. Pituitary GH concentrations also increased as metamorphosis progressed. After metamorphosis, pituitary GH concentrations declined as the frogs gained weight. There was no sex difference in plasma and pituitary GH levels in the adult.

Development of a homologous radioimmunoassay for eel prolactin

A highly specific and homologous radioimmunoassay (RIA) for the measurement of prolactin (PRL) in the plasma and the pituitary of the eel was developed using a rabbit antiserum to eel PRL. PRL was purified from the pituitary of Japanese eel (Anguilla japonica). Pituitary extracts and plasma from the Japanese and European eels exhibited displacement curves parallel to the eel PRL standard. Plasma and pituitary extracts from chum salmon, rainbow trout, Japanese charr, tilapia, goldfish, and carp, as well as plasma from hypophysectomized eel, showed negligible cross-reactivity. PRL and growth hormone (GH) preparations from chum salmon, tilapia, and sheep, carp PRL, and eel GH did not cross-react with the antibody. The RIA sensitivity was less than 0.1 ng eel PRL per milliliter. Intra- and interassay coefficients of variations were 2.4 and 11.8%, respectively. The immunoreactive PRL levels in plasma and pituitary of the eel adapted to 50% seawater were significantly lower than those of the eel in fresh water. Plasma PRL levels increased maximally 2 days after transfer from seawater to fresh water, as would be expected from the well-established role of PRL in freshwater adaptation in several euryhaline teleosts.

Radioreceptor assay for growth hormone in coho salmon (Oncorhynchus kisutch) and its application to the study of stunting

Binding sites for native chum salmon growth hormone (sGH) in coho salmon (Oncorhynchus kisutch) hepatic membranes were analyzed by radioreceptor assay. Displaceable (specific) binding represented up to 25% of total radiolabeled sGH added. Binding was dependent on buffer pH and membrane protein concentration, and was complete by 24 hours at 15 degrees C. Specific binding was greatest in liver membranes, and was also detected in muscle, ovary, gill, kidney, and brain. Scatchard analyses indicated a single class of hepatic binding sites that were specific for sGH. In stunts, abnormal seawater salmon with elevated plasma GH levels and inhibited growth, specific binding of sGH to liver membranes was three times lower than in normal seawater smolts. The concentration of salmon GH binding sites was decreased in stunt livers by 60%, while their affinity for sGH was unchanged. Down-regulation of hepatic GH receptors by high plasma GH levels may explain in part the low sGH binding in stunts.

Separation of rainbow trout (Salmo gairdneri) growth hormone by gel electrophoresis

Pituitaries from immature (n = 12) and mature female (n = 15) rainbow trout were cultured separately in vitro and subjected to polyacrylamide gel electrophoresis. Four protein bands were identified from the immature rainbow trout and three from the adults. The material from the immature trout was used to raise antisera. Three of the bands, including those with the highest (0.74) and lowest (0.27) Rf values, produced antibodies. Immunocytochemical studies revealed that all of the antisera bound strongly to the growth hormone cells and weakly, if at all, to prolactin cells in pituitary sections from rainbow trout.

Plasma growth hormone levels increase during seawater exposure of sexually mature Atlantic salmon parr (Salmo salar L.)

At the time of smoltification in May, smolts and sexually mature male parr were transferred to seawater (25% salinity) and sampled after 6 and 24 hr. Plasma levels of growth hormone (GH) were measured by radioimmunoassay. There was no difference in GH levels between smolts and mature parr in fresh water. GH levels did not change during exposure of smolts to seawater. In the mature male parr, plasma GH levels increased after 24 hr, when the levels were almost five times those of the freshwater controls. In the mature male parr, there was an increase in plasma osmolality, sodium, and magnesium after 24 hr in seawater; magnesium also increased after 6 hr. The levels of potassium and calcium did not change in either immature parr or mature male parr. The increase in plasma GH levels in the mature parr in seawater may be part of a mechanism to increase hypoosmoregulatory ability in fish not ready for seawater entry.

Changes in plasma hormone levels during loss of hypoosmoregulatory capacity in mature chum salmon (Oncorhynchus keta) kept in seawater

Returning chum salmon (Oncorhynchus keta) in northern Honshu Island, Japan, complete gonadal maturation while in the bay. Mature fish caught in the bay failed to survive in seawater for more than a week, whereas they adapted to fresh water efficiently. Mortality in seawater seems to be due primarily to an increased plasma osmolality. Maladaptation to seawater was more pronounced in the fish caught deep in the bay than those caught outside the bay, and also greater in females than in males. In close correlation with the increased plasma osmolality and electrolyte concentrations, plasma levels of cortisol and growth hormone increased in the fish kept in seawater. Cortisol and growth hormone may be secreted in response to the increased plasma osmolality and would not be the direct cause of the maladaptation to seawater. Plasma prolactin remained low in the seawater fish, indicating that the increased secretion of prolactin, a freshwater-adapting hormone, is not the cause of maladaptation to seawater either. On the other hand, when the fish caught in the river were kept in fresh water, an increase in plasma prolactin concentrations was seen, particularly in females, whereas no significant change was seen in plasma cortisol and growth hormone. Concentrations of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one in the female and of testosterone in both the male and female were extremely high in the bay fish and decreased slightly but significantly after 7 days in fresh water. The gonadal steroids may have inhibitory effects on osmoregulation in the mature salmon in seawater.

Salmonid pituitary gonadotrophs. I. Distinct cellular distributions of two gonadotropins, GTH I and GTH II

Using antisera specific for the beta subunits of two distinct coho salmon gonadotropins, GTH I and GTH II, an immunocytochemical study of rainbow trout and Atlantic salmon pituitaries was done. Cells which immunostained with anti-GTH I beta were distributed in the periphery of the glandular cords of the proximal pars distalis (PPD), in close association with somatotrophs. On the other hand, cells immunostained with anti-GTH II beta were located in the central parts of the glandular cords of the PPD. Neither the GTH I-producing nor the GTH II-producing cells stained with antisera against chum salmon growth hormone or the beta subunit of human thyroid-stimulating hormone. Moreover, GTH I and GTH II were localized in distinctly different cells. In no case was colocalization of these GTHs in the same cell observed. Finally, it was concluded that classification of GTH cells as globular and vesicular forms does not reflect the type of hormone produced by the cell, but may reflect differences in the physiological conditions of the cells.