The development of a noncompetitive enzyme-linked immunosorbent assay for oncorhynchid growth hormone using monoclonal antibodies

Growth hormone and insulin-like growth factor gene expression prior to the development of the pituitary gland in rainbow trout (Oncorhynchus mykiss) embryos reared at two temperatures

Real time RT-PCR was used to measure the changes in the rates of synthesis of mRNA encoding for growth hormone-1 (GH1) and -2 (GH2) and insulin-like growth factor-1 (IGF-1) and -2 (IGF-2), and whole embryo GH content was measured in early stage rainbow trout (Oncorhynchus mykiss) embryos reared at two incubation temperatures (8.5 and 6.0 degrees C). Particular attention was paid to the phase of embryo development that preceded the appearance of the pituitary gland. GH was present in zygotes, and there were no significant changes in whole embryo GH content of the two temperature treatment groups from fertilization (t0) until the time at which GH was detectable in the pituitary gland by immunostaining. The expression of the two GH genes decreased during the first 24 h post-fertilization, and then increased significantly by 17 dpf in embryos reared at both temperatures. There was a subsequent steep increase in the number of copies of GH1 and GH2 mRNA associated with the formation of the pituitary gland evident at 23 and 34 dpf in the 8.5 and 6.0 degrees C groups, respectively. The number of copies of mRNA encoding for IGF-1 and IGF-2 did not change during the first 24 h post-fertilization; however, there was a significant increase in the numbers of transcripts for both genes evident by 13 dpf in embryos reared at the two incubation temperatures. The differences in the timing of the increases in GH and IGF mRNA may suggest that IGF gene expression is not GH-dependent at that stage. Moreover, the increased expression of the GH genes prior to the formation of the pituitary gland suggests that tissues other than the pituitary are expressing these genes in early embryos. The pattern of changes in GH content was similar to the pattern of GH gene expression in embryos reared at the two incubation temperatures when the age of embryos was plotted using degree-days. There were no apparent compensatory responses in GH1, GH2, IGF-1 or IGF-2 gene expression related to altered growth rates. The number of copies of IGF-2 mRNA was higher than that of IGF-1 mRNA during the early developmental period; this is consistent with the hypothesis that IGF-2 predominates during embryonic development. A differential expression of GH2 and GH1 was also observed with the overall copy numbers of GH2 mRNA being consistently higher than those of GH1.

Production, characterization and applications of mouse anti-grass carp (Ctenopharyngodon idellus) growth hormone monoclonal antibodies

Mouse anti-grass carp growth hormone (gcGH) monoclonal antibody (MAb) secretors were produced by PEG-mediated fusion of NS-1 myeloma cells and splenic B-lymphocytes of gcGH hyper-immunized mice. Positive secretors were screened by direct ELISA and cloned by limiting dilution. Three positive secretors, 21D3, 22G5 and 23B3, were obtained in a single fusion trial. Anti-gcGH MAbs were produced by growing hybridomas in the peritoneal cavity of pristane-primed mouse. The three MAbs were isotyped to be IgG2a, IgG2b and IgM, respectively. IgG MAbs were purified from ascitic fluid by Hitrap protein G column and IgM MAb was purified by gel filtration chromatography. The purified MAbs were highly specific and had moderate binding affinity. The MAbs were successfully used for the purification of native gcGH from mature grass carp pituitary extract by one-step immunoaffinity chromatography, for the quantification of gcGH by competitive sandwich ELISA, and for the probing of somatotropes in grass carp pituitary by immunohistochemistry.

Growth hormone secretion from the Arctic charr (Salvelinus alpinus) pituitary gland in vitro: effects of somatostatin-14, insulin-like growth factor-I, and nutritional status

This study investigated the influence of nutritional status on the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis in Arctic charr (Salvelinus alpinus). The objectives were to study the regulation of GH secretion in vitro by somatostatin-14 (SRIF) and hIGF-I, and to determine whether pituitary sensitivity to these factors is dependent upon nutritional status. Arctic charr were fed at three different ration levels (0, 0.35, and 0.70% BWd(-1)), and pituitary glands were harvested at 1, 2, and 5 weeks for in vitro study. Both SRIF and hIGF-I inhibited GH secretion from Arctic charr pituitary tissue in long-term (18 h) static hemipituitary culture, as well as after acute exposure in a pituitary fragment perifusion system. This response appeared to be dose-dependent for SRIF in static culture over the range of 0.01-1 nM, but not for hIGF-I. The acute inhibitory action of hIGF-I on GH release in the perifusion system suggests an action that is initially independent of any effects on GH gene expression or protein synthesis. Nutritional status did not affect the sensitivity of Arctic charr pituitary tissue to either SRIF or hIGF-I in vitro, indicating that changes in abundance of pituitary SRIF or IGF-I receptors may not explain the alterations in plasma GH levels found during dietary restriction.

Production and characterization of recombinantly derived peptides and antibodies for accurate determinations of somatolactin, growth hormone and insulin-like growth factor-I in European sea bass (Dicentrarchus labrax)

A specific radioimmunoassay (RIA) for European sea bass (Dicentrarchus labrax) growth hormone (GH) was developed and validated. For this purpose, a stable source of GH was produced by means of recombinant DNA technology in a bacteria system. The identity of the purified protein (ion exchange chromatography) was demonstrated by Western blot and a specific GH antiserum was raised in rabbit. In Western blot and RIA system, this antiserum recognized specifically native and recombinant GH, and it did not cross-react with fish prolactin (PRL) and somatolactin (SL). In a similar way, a specific polyclonal antiserum against the now available recombinant European sea bass SL was raised and used in the RIA system to a sensitivity of 0.3 ng/ml (90% of binding of tracer). Further, European sea bass insulin-like growth factor-I (IGF-I) was cloned and sequenced, and its high degree of identity with IGF-I peptides of barramundi, tuna, and sparid fish allowed the use of a commercial IGF-I RIA based on barramundi IGF-I antiserum. These assay tools assisted for the first time accurate determinations of SL and GH-IGF-I axis activity in a fish species of the Moronidae family. Data values were compared to those found with gilthead sea bream (Sparus aurata), which is currently used as a Mediterranean fish model for growth endocrinology studies. As a characteristic feature, the average concentration year round of circulating GH in growing mature males of European sea bass was higher than in gilthead sea bream. By contrast, the average concentration of circulating SL was lower. Concerning to circulating concentration of IGF-I, the measured plasma values for a given growth rate were also lower in European sea bass. These findings are discussed on the basis of a different energy status that might allowed a reduced but more continuous growth in European sea bass.

Development of an enzyme-linked immunosorbent assay for the measurement of plasma growth hormone (GH) levels in channel catfish (Ictalurus punctatus): assessment of environmental salinity and GH secretogogues on plasma GH levels

We report the development of a sensitive, and specific, competitive, antigen-capture enzyme-linked immunosorbent assay for the measurement of channel catfish (Ictalurus punctatus) growth hormone (cfGH). The detection limit of the assay (90% binding) was 2.0ng/ml and the ED(50) value (standard curve range 150-0.59 ng/ml) was 67.3 ng/ml. Recovery of cfGH-spiked plasma samples was determined to be 102%. Dose-response inhibition curves using serially diluted pituitary homogenates and plasma samples consistently showed parallelism with the standard curves using purified cfGH. The GH antibody (rabbit anti-catfish GH) specificity was demonstrated in competitive binding curves employing heterologous hormones and purified channel catfish prolactin (cfPRL). These studies show that there was no significant (0.006%) binding of cfPRL (competitive inhibition of cfGH binding), or heterologous hormones, within the working range of the assay. To physiologically validate the assay, catfish were injected (100 microg/g body weight, 3 injections every 5 days) with either bovine GHRH(1-29)-amide or the synthetic hexapeptide GHRP-2 (KP-102: D-Ala-D-beta-Nal-Ala-Trp-D-Phe-Lys-NH(2)) suspended in corn oil. Following the last injection, half of the animals were sampled for plasma and the remaining transferred from fresh water (FW) to 12 ppt seawater (BW: brackish water). Twenty-four hours after transfer to BW, animals were again sampled for plasma. Plasma GH levels were significantly (p<0.001) elevated in all the BW groups (control, KP-102, and bGHRH), compared with the FW (fresh water) groups. In addition, plasma GH levels were significantly (p<0.001) elevated by treatment with either of the GH secretogogues, KP-102 or bGHRH. Our findings demonstrate that two regulatory mechanisms of GH elevation, one which is seen in euryhaline teleosts (salinity-induced GH levels) and another, which has been recently described in teleosts (GHRP-induced GH levels), are present in the stenohaline channel catfish.

Effect of 17beta-estradiol on the expression of somatostatin genes in rainbow trout (Oncorhynchus mykiss)

In the present study, the effects of 17beta-estradiol (E(2)) treatment on the expression of preprosomatostatin (PPSS) I, PPSS II', and PPSS II" mRNA in the hypothalamus and endocrine pancreas (Brockmann body), as well as the effects of E(2) treatment on plasma somatostatin (SS)-14 and -25 concentrations in sexually immature rainbow trout (Oncorhynchus mykiss), were investigated. E(2) treatment significantly (P < 0.001) depressed both plasma SS-14 and SS-25. In the hypothalamus, E(2) treatment significantly (P < 0.001) decreased the levels of PPSS I and PPSS II" mRNA. However, there was no effect of E(2) treatment on PPSS II' mRNA levels. In the pancreas, E(2) treatment had no significant effect on the levels of either PPSS II' mRNA or PPSS II" mRNA. However, E(2) treatment significantly (P < 0.005) decreased levels of PPSS I mRNA. These data suggest that E(2) acts, in part, to increase plasma growth hormone levels in rainbow trout by decreasing the endogenous inhibitory somatostatinergic tone by inhibiting plasma levels of both SS-14 and SS-25 and hypothalamic levels of mRNA encoding these proteins.

Correlations of plasma growth hormone with somatostatin, gonadal steroid hormones and thyroid hormones in rainbow trout during sexual recrudescence

The study explores the interrelationships among growth hormone (GH), somatostatin-14 (SRIF), non-esterified fatty acids (NEFA), gonadal steroid hormones and thyroid hormones (THs) in sexually recrudescent rainbow trout (Oncorhynchus mykiss) to examine aspects of the complex set of physiological changes associated with gonadal growth and maturation. Females exhibited significant decreases in plasma SRIF, NEFA and triiodo-L-thyronine (T3) concentrations, and a significant increase in plasma GH concentration associated with gonadal maturation, whereas in males, only SRIF and NEFA concentrations showed significant changes during testicular maturation. The declining SRIF levels during gonadal recrudescence may indicate a role for the hormone in the energy repartitioning processes that occur in both sexes at this time. Correlation analysis of plasma variables revealed a direct correlations between plasma NEFA and 17 beta-estradiol (E2) in females, an inverse correlation between NEFA and testosterone (T) in males, inverse correlations between GH and SRIF in both males and females, and inverse correlations between THs and SRIF concentrations in females. These marked gender differences in correlations likely reflect the different physiological challenges faced by the two sexes and emphasizes the need to consider gender, as well as maturity when studying the interactions of hormones.

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 effects of N-methyl-D,L-aspartate and gonadotropin-releasing hormone on in vitro growth hormone release in steroid-primed immature rainbow trout, Oncorhynchus mykiss

In the present study we investigated the effects of 17 beta-estradiol (E2) and 5 alpha-dihydrotestosterone (5 alpha DHT) on the ability of the glutamate agonist, N-methyl-D,L-aspartate (NMA), to stimulate growth hormone (GH) release from perifused pituitary glands of sexually immature rainbow trout (Oncorhynchus mykiss). Two weeks after steroid hormone implantation, pituitary glands were removed from the fish and challenged with NMA (10(-8) M) in a perifusion unit. NMA rapidly and significantly elevated GH release from perifused pituitary fragments taken from all treatment groups, and there was a main effect of in vivo steroid hormone treatment on the in vitro GH response to NMA. To examine the relationship between NMA and gonadotropin-releasing hormone on GH release, pituitaries from E2- and 5 alpha DHT-primed and control fish were exposed to a single pulse of salmon gonadotropin-releasing hormone (sGnRH) which also elicited a significant elevation in GH release from perifused pituitary fragments, although the response in the E2- and 5 alpha DHT-primed fish was significantly smaller (P < 0.05) than that for the NMA challenge. Administration of a specific GnRH antagonist, D-pGlu1,D-Phe2,D-Trp3,6-LHRH, did not affect the GH response to NMA, whereas administration of the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid blocked the GH response to NMA. These data suggest that NMA acts to stimulate GH release directly at the level of the somatotroph, likely through the NMDA receptor and not through increased release of GnRH.

Estradiol inhibits plasma somatostatin 14 (SRIF-14) levels and inhibits the response of somatotrophic cells to SRIF-14 challenge in vitro in rainbow trout, Oncorhynchus mykiss

In the present study, the effects of 17 beta-estradiol (E2) treatment on plasma growth hormone (GH) and somatostatin 14 (SRIF-14) concentrations were investigated, as well as the effect of in vivo E2 treatment on the in vitro GH response to SRIF-14 challenge in sexually immature rainbow trout (Oncorhynchus mykiss). Two weeks after receiving a steroid hormone implant, plasma E2 and GH levels were significantly (P < 0.05) elevated, and plasma SRIF levels were significantly (P < 0.05) lowered relative to the control. Pituitary glands were taken from E2-primed and control fish and challenged with a single pulse of SRIF-14 (10(-8) M) in a perifusion unit to evaluate the effect of E2 on the response of somatotrophs to the effect of SRIF-14. Whereas SRIF-14 challenge significantly (P < 0.01) inhibited GH release from pituitary fragments taken from control fish, there was no such response in E2-primed fish. Furthermore, GH release following SRIF-14 administration (at the point of maximal inhibition) was significantly depressed in control fish with respect to the E2 treatment group. These data suggest that E2 treatment may increase plasma GH concentrations by altered somatotroph responsiveness to SRIF-14 inhibition. Furthermore, E2 may increase plasma GH by suppressing plasma SRIF-14 levels, although the role of circulating SRIF-14 on the regulation of GH release has not been fully determined in teleosts.

Effect of feeding time on hepatic nucleic acid, plasma T3, T4, and GH concentrations in rainbow trout

The effect of feeding time (dawn, midnight) on the growth performance and daily pattern of liver nucleic acid concentrations, plasma thyroid hormone, and growth hormone concentrations was studied in immature rainbow trout (Oncorhynchus mykiss, mean individual weight: 55 g). Fish were held in groups of 20 individuals (12 groups per treatment) and maintained in flow-through tanks supplied with river water under natural photoperiod. Food pellets (Aqualim, 49% crude protein) were delivered daily over a 30-min period by means of belt feeders. Growth performance and protein retention efficiency were higher for trout fed at dawn than for those fed at midnight, whereas both groups of fish ingested the same total amount of feed. All parameters studied showed significant daily variations. The daily patterns of liver RNA concentrations, RNA/DNA, and protein/DNA ratios were significantly different between fish fed at dawn and at midnight, indicative of a higher liver protein synthesis in the trout fed at dawn. On average, plasma thyroid hormone levels were higher and plasma GH concentrations were lower in trout fed at dawn compared with those fed at midnight. The hormonal patterns were only affected by feeding time when the fish were fed at dawn. These results suggested that the observed differences in growth and protein retention efficiency were linked to the observed differences in plasma hormone levels.

Influence of the combination of time of feeding and ration level on the diurnal hormone rhythms in rainbow trout

The study examined the combined effects of time of feeding (post-dawn, midday-pre-dusk) and ration level (1.5%, 2.0%, 2.5%) on the diurnal rhythms of plasma growth hormone (GH), L-thyroxine (T4), triiodo-L-thyronine (T3), cortisol and glucose concentrations in rainbow trout (Oncorhynchus mykiss) maintained under constant ambient water temperature and natural photoperiod.Plasma GH and glucose concentrations exhibited marked diurnal rhythms, with significant postprandial peaks that were phase-shifted with time of feeding. The ration level did not appear to alter these feeding time-entrained rhythms, but the amplitude of the changes (peaks) were more pronounced in trout fed the higher ration levels. Plasma cortisol concentrations showed distinct diurnal rhythms, with peaks during the photophase and the scotophase in all the treatment groups. The time of feeding did not appear to influence these rhythms, and there was no evidence of a postprandial increase in any group.Plasma GH, cortisol and glucose concentrations were significantly higher in groups fed the 2.5% ration compared with animals fed either 1.5 or 2.0% rations.The diurnal rhythms of plasma T4 concentrations were not affected by the time of feeding or ration level; the peak values generally occurred during the photophase in all the treatment groups. Plasma T3 concentrations did not show any significant diurnal patterns, nor were they influenced by ration levels or time of feeding.

Does the time of feeding affect the diurnal rhythms of plasma hormone and glucose concentration and hepatic glycogen content of rainbow trout?

The diurnal rhythms of plasma glucose, cortisol, growth hormone (GH) and thyroid hormone (T4, T3) concentrations and hepatic glycogen content were measured in rainbow trout that had been entrained to a specific time of daily feeding (post-dawn, midday, pre-dusk); the purpose of the study was to investigate the significance of feeding time on hormones and metabolite patterns. Plasma GH, cortisol and T4 concentrations all showed evidence of a diurnal rhythm in some treatment groups. There was a significant interaction between the time of feeding and plasma GH and cortisol concentration rhythms; for GH, this appeared to be related to the phase-shifting of the post-prandial increases in plasma GH concentrations, and for cortisol, the rhythms were only evident in fish fed in the post-dawn period [diurnal rhythms were not evident in treatment groups fed in at midday or pre-dusk]. Peak plasma T4 concentrations were evident during the photophase in all three treatment groups; however, the time of feeding had a negligible effect on the timing of those peaks. There were no apparent diurnal rhythms of plasma T3 and glucose concentrations, hepatic glycogen content or hepatosomatic index in any of the three treatment groups.

In vivo effects of the steroid analogue RU486 on some aspects of intermediary and thyroid metabolism of brook charr, Salvelinus fontinalis

The glucocorticoid analogue RU486 was administered by intraperitoneal injection to brook charr (Salvelinus fontinalis) to further explore the role of cortisol on aspects of intermediary and thyroid hormone metabolism of the species. RU486 significantly elevated the hepatosomatic index, hepatic G3PDH activity, and hepatic glycogen content, but was without effect on hepatic protein content, hepatic FPBase activity, or plasma glucose concentration. However, the stressor-related increase in plasma glucose concentration that was evident in brook charr 24 h following handling and injection was suppressed in RU486-treated groups. The distribution volume, turnover rates, and metabolic clearance rates of [3H]cortisol were similar in RU486- and vehicle-treated groups. Plasma T3 and T4 concentrations were similar in RU486- and vehicle-treated groups, but hepatic T3 production and hepatic T3 content were lower in RU486-treated fish; TSH had no effect on hepatic T3 content of vehicle-treated brook charr but significantly increased T3 content in the RU486-treated group. These observations support the concept of a role of cortisol in the control of peripheral monodeiodination of T4 in salmonid fish and suggest that RU486 may be a useful drug for evaluating the role of cortisol in fish in vivo.

Chronic fasting reduces the response of the thyroid to growth hormone and TSH, and alters the growth hormone-related changes in hepatic 5'-monodeiodinase activity in rainbow trout, Oncorhynchus mykiss

Chronically fasted rainbow trout (Oncorhynchus mykiss) had significantly lower plasma L-thyroxine (T4) and triiodo-L-thyronine (T3), and higher plasma growth hormone (GH) concentrations than fed animals. Fasted and fed trout were administered bovine thyrotropic hormone (bTSH), native ovine GH (oGH), or recombinant human GH (rhGH) alone, or GH in combination with bTSH to further study the effects of food deprivation on the activity of the pituitary-thyroid axis and on the control of hepatic T3 production. Although the fasted rainbow trout retained the ability to respond to bTSH challenge, the resultant elevation in plasma T4 concentration was significantly lower than that of fed animals; there was no plasma T3 response to bTSH challenge in either fed or fasted trout, except for a significant elevation in fed bTSH-injected fish and a significant depression in fed saline-injected fish sampled 2.5 hr after the injection. GH when administered alone had no significant effect on plasma T4 concentrations of either fed or fasted animals, and stimulated an increase in plasma T3 concentration and an increased hepatic T3 content only in the fed fish, despite a significant stimulation by both oGH and rhGH of in vitro hepatic 5'-monodeiodinase activity (MDA) in both fed and fasted groups. bTSH appeared to suppress rhGH- and oGH-stimulated MDA in fasted groups, and rhGH-stimulated MDA in fed trout. The data suggest that chronic fasting induced a down-regulation of the response of thyroid tissue to bTSH challenge, and of the GH-stimulation of T3 production, in vivo, although in vitro hepatic MDA was elevated following GH administration to both fed and fasted rainbow trout.

Circadian pattern of hepatosomatic index, liver glycogen and lipid content, plasma non-esterified fatty acid, glucose, T3, T 4, growth hormone and cortisol concentrations in Oncorhynchus mykiss held under different photoperiod regimes and fed using demand-feeders

The circadian patterns of several tissue and plasma metabolites, and several plasma hormone concentrations are described in rainbow trout (Oncorhynchus mykiss) that were held in groups under three different photoperiod regimes, and given free access to a demand-feeder. Regardless of photoperiod regime, all the measured parameters showed significant diel rhythms that appeared to be synchronized by dawn; dawn was represented by the concomitant onset of both light and feeding. The diel increases in hepatic glycogen content, and plasma T4 and cortisol concentrations were in phase with the main period of feeding activity, whereas the peaks in plasma T3 and glucose concentrations that may also be triggered by feeding activity, were delayed by several hours. The peaks in hepatosomatic index, plasma non-esterified fatty acids and plasma growth hormone concentrations were 180° out of phase with the main period of feeding activity, and associated with periods of hypophagia and low activity.