Identification and expression analysis of two growth hormone receptors in zanzibar tilapia (Oreochromis hornorum)

Growth hormone plays important roles in various physiological processes such as growth, metabolism, and reproduction. In this study, two cDNAs encoding growth hormone receptor (GHR) were isolated from the liver of zanzibar tilapia (Oreochromis hornornum). The two cDNAs were 2,831 and 2,044 bp in length and named GHR1 and GHR2, respectively. GHR1 and GHR2 shared 57.4% similarity in nucleotide sequences and 33.5% similarity in deduced amino acid sequences. Consequently, it was presumed that they were two different genes. Conserved regions of GHR1 and GHR2 in zanzibar tilapia were different from those of other vertebrates. For example, conserved box2 regions of GHR1 and GHR2 in zanzibar tilapia were, respectively, WVELM and WVEFT, while it was WVEFI for GHRs in other vertebrates. Similar to other fish species, GHR1 and GHR2 were expressed in brain, gill, liver, muscle, spleen, gonad, stomach, kidney, and pituitary in zanzibar tilapia. The expression levels were the highest in liver. Unlike fathead minnow (Pimephales promelas) and mossambique tilapia (O. mossambicus), the expression levels of GHR1 in most female fish tissues were higher than those in male fish. No significant difference in GHR2 expression was found in all the tissues in male and female of zanzibar tilapia. Under fasting condition, the expressions of GHRs and IGF-II were significantly up-regulated (P < 0.05) in liver, while the expression of IGF-I remained stable. This observation would contribute to understanding the evolution of the GHR family in further investigation of growth regulation of zanzibar tilapia.     

Insulin-like growth factor I of Japanese eel, Anguilla japonica: cDNA cloning, tissue distribution, and expression after treatment with growth hormone and seawater acclimation

In an attempt to understand growth regulation in the Japanese eel, Anguilla japonica, we cloned insulin-like growth factor-I (IGF-I) cDNAs and examined their mRNA expression in several tissues. Two eel IGF-I (eIGF-I) cDNAs encoding preprohormones, eIGF-I-Ea1and eIGF-I-Ea2, were cloned from the liver by polymerase chain reaction (PCR). The preproIGF-Is were identical in signal peptide and mature IGF-I, but different in the E domain—eIGF-I-Ea2 mRNA was 36 bp longer than eIGF-I-Ea1 mRNA. Eel IGF-I was 83–94% identical with that of teleosts, 71% identical with that of dogfish, 87% identical with that of bullfrog and chicken, and 83% identical with that of humans. In both males and females the highest eIGF-I-Ea1 mRNA levels were observed in the liver, with detectable levels also found in the gills, heart, stomach, spleen, kidney, intestine, swim-bladder, muscle, and gonads. eIGF-I-Ea1 mRNA levels in the liver were higher in females than in males whereas in the intestine they were lower than in males. eIGF-I-Ea2 mRNA was detected in all the tissues examined and at similar levels in males and females. In this experiment higher eIGF-I-Ea1 mRNA levels were observed in the liver of larger glass eels than in those of smaller fish. eIGF-I-Ea2 mRNA levels were also higher in larger eels, although they were lower than IGF-I-Ea1 mRNA levels. Both eIGF-I mRNA levels in liver were positively correlated with the body size of the␣glass eels. Intraperitoneal injection of recombinant eel GH (reGH), 0.25 μg g⁻¹ body weight, into glass eels resulted in a significant increase in both eIGF-I mRNAs in the liver 1 day after injection compared with control fish, but no elevation was observed 2 days after injection. Incubation of liver slices with reGH at concentrations of 10, 100, and 1,000 ng mL⁻¹ for 24 h resulted in a significant concentration-dependent increase in the levels of both eIGF-I mRNAs. Higher levels of eIGF-I-Ea1 and Ea2 mRNA were observed in the gills ofseawater-reared eels than in those of freshwater-reared fish, but no differenceswere observed in the whole kidney. These results suggest that IGF-I is involved in the regulation of somatic growth and also in adaptation of the Japanese eel to seawater.     

In vivo and in vitro effect of recombinant salmon growth hormone treatment on IGF-I and IGFBPs in yellowtail <Emphasis Type="Italic">Seriola quinqueradiata</Emphasis>

The role of growth hormone (GH) in regulating hepatic mRNA expression of insulin-like growth factor-I (IGF-I) and IGF binding proteins (IGFBPs) in yellowtail Seriola quinqueradiata was examined using in vivo and in vitro assays. Yellowtail hepatic IGF-I, IGFBP-1, IGFBP-2, IGFBP-3, and IGFBP-5 mRNAs were measured by real-time quantitative RT-PCR. Intraperitoneal injection of recombinant GH of chum salmon Oncorhynchus keta (rsGH) at a dose of 1 μg/g body weight resulted in a significant increases in hepatic IGF-I, IGFBP-3, and IGFBP-5 mRNA levels, whereas significant reductions in hepatic IGFBP-1 and IGFBP-2 mRNA levels were observed. For in vitro assays, liver slices were incubated with rsGH at different concentrations (doses: 0, 1, 10, 100, 500, and 1,000 ng/ml). Liver slices incubated with 100 ng/ml rsGH elicited a significant increase in IGF-I mRNA level. Similarly, a slight increase in IGFBP-3 and IGFBP-5 mRNA levels were also observed in liver explants incubated with rsGH. In contrast, a significant decline in IGFBP-1 mRNA levels was observed in liver slices incubated with 1,000 ng/ml rsGH. A slight decline in the level of IGFBP-2 mRNA was noted in liver explants with rsGH treatment. This study demonstrates the modulating effect of GH on the IGF system.     

Cichlasoma dimerus responds to refeeding with a partial compensatory growth associated with an increment of the feed conversion efficiency and a rapid recovery of GH/IGFs axis

Many fish species display compensatory growth (CG), a phenomenon by which fasted fish grow faster during refeeding. However, most studies use a group‐housed fish approach that could be problematic in social fish when interaction between individuals is not considered or eliminated. Additionally, the growth hormone (GH)/insulin‐like growth factors’ (IGF‐1 and IGF‐2) axis is implicated in postnatal growth in vertebrates, but its relevance in CG is not fully understood. Thus, the aim of this work was to determine whether CG occurs in a social fish, Cichlasoma dimerus, using an individually held fish approach and secondly, to evaluate the GH/IGFs expression profile during refeeding by 3 days and 3 weeks. C. dimerus showed partial CG. The feed conversion efficiency (FCE) was higher in three‐day‐refed fish, which presented higher GH plasma and mRNA levels than controls but shown no differences in liver and muscle GH receptors (GHR1 and GHR2) and IGFs mRNA levels. Surprisingly, three‐week‐refed fish exhibited GHR1 and IGF‐2 increments, but a reduction in GHR2 expression in muscle. These results show a strong association between GH levels, growth rate and FCE during refeeding, and a long‐lasting effect of refeeding on muscular expression of GHRs and IGF‐2.     

Effects of largely different feeding intensities on serum insulin‐like growth factor‐1 concentrations,quantified by enzyme immunoassay,leptin and growth hormone receptor 1 mRNA in rainbow trout (Oncorhynchus mykiss)

Insulin‐like growth factor‐1 (IGF‐1), somatolactin and leptin are involved in growth regulation and energy metabolism in fish. We herein focused on serum IGF‐1 concentration analysed by enzyme‐linked immunosorbent assay in restrictively fed rainbow trout (Oncorhynchus mykiss). The animals were fed a high‐fat/low‐protein diet at daily feed increases (DFI) ranging from 0.5% to 2% of initial body weight (IBW), starting either at 62 or 176 g IBW. In selected groups, growth hormone receptor 1 (GHR1) and leptin mRNA were quantified in liver, and GHR1 mRNA also in visceral adipose tissue. Serum IGF‐1 concentrations in both IBW groups were highest at 2% and 1% DFI and were nonlinearly decreasing with reduced DFI. The low‐IBW groups had mostly lower IGF‐1 concentrations than the high‐IBW groups. Leptin and GHR1 mRNA decreased with feeding intensity in liver, but GHR1 mRNA increased in adipose tissue. IGF‐1 is related to growth and may help to mitigate oxidative stress in consequence of lipid mobilization during restrictive feeding. IGF‐1 secretion associated with stress response in addition to its function in growth and energy metabolism seemed to reach a point of inflection at DFI 1%. Leptin and GHR1 might be linked to lipid metabolism and free fatty acid partitioning towards liver.     

Gene expression levels of growth hormone receptor and insulin-like growth factor-I in gonads of maturing coho salmon (Oncorhynchus kisutch)

The expression levels of growth hormone receptor (GHR) and insulin-like growth factor (IGF-I) in gonads of maturing coho salmon were measured by real-time PCR. The GHR and IGF-I mRNAs showed different gene expression pattern between male and female. These results suggest that a sexual dimorphism may exist in the GHR and IGF-I mRNA expressions of coho salmon during gonadal maturation     

Disrupting actions of bisphenol A and malachite green on growth hormone receptor gene expression and signal transduction in seabream

Environmental estrogen could mimic natural estrogens thereby disrupting the endocrine systems of human and animals. The actions of such endocrine disruptors have been studied mainly on reproduction and development. However, estrogen could also affect the somatotropic axis via multiple targets such as growth hormone (GH). In the present study, two endocrine disruptors were chosen to investigate their effects on the expression level and signal transduction of growth hormone receptor (GHR) in fish. Using real-time PCR, it was found that exposure to both the estrogenic (bisphenol A) and anti-estrogenic (malachite green) compounds could attenuate the expression levels of GHR1 and GHR2 in black seabream (Acanthopagrus schlegeli) hepatocytes. The expression level of IGF-I, the downstream effector of GHR activation in the liver, was decreased by bisphenol A but not by malachite green. Luciferase reporter assay of the β-casein promoter was used to monitor GHR signaling in transfected cells. In the fish liver cell line Hepa-T1, both GHR1 and GHR2 signaling were attenuated by bisphenol A and malachite green. This attenuation could only occur in the presence of estrogen receptor, indicating that these agents probably produce their actions via the estrogen receptor. Results of the present study demonstrated that estrogenic or anti-estrogenic compounds could down-regulate the somatotropic axis in fish by affecting both the gene expression and signaling of GHR. In view of the increasing prevalence of these compounds in the environment, the impact on fish growth and development both in the wild and in aquaculture would be considerable.     

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.

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Résumé Cet article est une revue des effets osmorégulateurs de l'hormone de croissance et de son mode d'action. Nous présentons des résultats qui suggèrent que le facteur de croissance de type insuline (IGF-I) est un médiateur de certaines des actions de la GH sur l'adaptation à l'eau de mer. Les concentrations plasmatiques et le renouvellement de la GH augmentent après transfert en eau de mer. La GH exogène stimule (in vivo) l'activité Na⁺,K⁺-ATPase et le nombre de cellules à chlorure branchialeset inhibe les augmentations de l'osmolarité et des concentrations ioniques du plasma observées après transfert en eau de mer. Une seule classe de récepteurs à haute affinité pour la GH est présent dans le foie, les branchies, l'intestin et le rein. Les niveaux d'ARNm d'IGF dans le foie, les branchies et le rein augmentent après injection de la GH. Après transfert en eau de mer, les ARNm de l'IGF augmentent dans les branchies et dans le rein en suivant l'augmentation de GH plasmatique, bien qu'aucune modification ne soit observée au niveau du foie. L'injection d'IGF augmente la capacité du poisson à maintenir ses niveaux de sodium plasmatique après transfert en eau de mer. Le traitement à la GH augmente la sensibilité à l'adrenocorticotropine (ACTH) et stimule donc les niveaux de cortisol. A la fois le cortisol et l'IGF-I semblent impliqués comme médiateurs des effets de la GH dans l'adaptation à l'eau de mer, bien que les études sur les effets de la GH sur la physiologie de l'osmorégulation chez les espèces non-salmonidés restent encore limitées. Un modèle intégré des actions de la GH sur l'osmorégulation est présenté et les domaines de recherche à développer sont soulignés.

     

Stimulation of insulin-like growth factor-I production by recombinant bovine growth hormone in Mozambique tilapia, Oreochromis mossambicus

We have previously reported growth-promoting effects of recombinant bovine growth hormone (rbGH) in Mozambique tilapia, Oreochromis mossambicus, after 4 weekly injections or a single injection of slow-releasing formulation (Posilac^®) (Leedom et al. 2002). In order to obtain further understanding of the role of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis in growth in the tilapia, the effects of rbGH on plasma and mRNA levels of IGF-I were examined. Plasma IGF-I levels were significantly increased after rbGH and Posilac^® injections, and a significant correlation was observed between plasma IGF-I levels, body length and mass in both treatments. IGF-I mRNA levels in the liver and in the skeletal muscle were also significantly increased after rbGH and Posilac^® injections, indicating that IGF-I gene expression in these tissues is under control of circulating GH. IGF-I mRNA levels in the gill were not affected by treatment. Liver IGF-I mRNA levels were significantly correlated with body length and with body mass after rbGH and Posilac^® injections. These results indicate that the growth-promoting effect of rbGH in this species is mediated to a significant extent via its stimulation of hepatic production of IGF-I and the resulting increase in plasma IGF-I, and also possibly through locally produced IGF-I in the skeletal muscle, acting in a paracrine or autocrine fashion.     

Effects of cysteamine on mRNA levels of growth hormone and its receptors and growth in orange-spotted grouper (Epinephelus coioides)

Effects of cysteamine (CS) on growth hormone (GH) mRNA, two types of growth hormone receptor (GHR) mRNAs and growth rate in orange-spotted grouper (Epinephelus coioides) were investigated. CS could cause a modification in the structure of somatostatin, which is the most important neuroendocrine inhibitor of basal and stimulated growth hormone synthesis and release, and renders it nonimmunoreactive probably through interaction with the disulfide bonds. In the present study, cysteamine hydrochloride (CSH) enhanced the level of pituitary GH mRNA in a dose-dependent manner through attenuating or deleting the inhibiting action of somatostatin on GH mRNA expression. CSH at relatively low doses (from 1 to 3 mg/g diet) enhanced the levels of two types of GHR mRNAs in dose-dependent manner, whereas the stimulation induced by CSH declined from the peak at higher dose of CSH (4 mg/g diet). It might be attributed to the variation in GH-induced up-regulation of GHRs at different doses of GH. Feeding of CSH could induce remarkable enhancement of growth rate in orange-spotted grouper. In addition, the stimulatory effect of CSH could be potentiated by the additive effect of luteinizing hormone-releasing hormone analog (LHRH-A). Compared with individual treatments, combined feeding of CSH and LHRH-A caused more efficient elevation of growth rate after 8 weeks of feeding. CSH and LHRH-A individually and in combination remarkably increased the levels of GH and GHR mRNAs compared with the control. The combined administration of CSH and LHRH-A in diet was most effective to enhance the level of GH and GHR1 mRNA. The morphological characteristics of the experimental fish were evaluated. Compared with control, the ratios of muscle RNA/DNA, condition factors (CF) and feed conversion efficiency (FCE) were significantly enhanced in the treated groups, while the highest values were observed in the combined treatment. All the results suggested that CSH (1–3 mg/g diet) is an effective, economical and feasible feed additive in orange-spotted grouper culture.     

Seasonal changes in circulating growth hormone (GH), hepatic GH-binding and plasma insulin-like growth factor-I immunoreactivity in a marine fish,gilthead sea bream,Sparus aurata

We have studied the seasonal relationship between growth and circulating growth hormone (GH), hepatic GH-binding and plasma insulin-like growth factor-I immunoreactivity in gilthead sea bream,Sparus aurata. The seasonal increase in plasma GH levels preceded by several weeks the summer increase in growth rates. In contrast, a marked increase in hepatic GH-binding with a high degree of endogenous GH occupancy was found during the period of maximum growth which suggests an enhanced sensitivity of liver to GH action. Thus, circulating levels of immunoreactive IGF-I, probably derived from the liver in response to GH action, were positively correlated with growth throughout the experimental period although a consistent relationship between growth and circulating GH was not found. In spite of this, we consider that, in gilthead sea bream, as in several other teleosts, the availability of endogenous GH can limit growth. Thus, under environmental conditions of suboptimal growth, a single intraperitoneal injection of recombinant rainbow trout GH (rtGH) induced over the dose range tested (0.75, 1.5, 3 μg g BW⁻¹) an increase in plasma IGF-I-like immunoreactivity comparable to that seen during the period of maximum growth.     

Identification of growth hormone receptor in the ovary of tilapia, Oreochromis mossambicus

Growth hormone receptor (GH-R) cDNA was isolated and characterized in the tilapia, Oreochromis mossambicus. GH-R mRNA was expressed in the nucleus and cytoplasm of the young oocytes and in the follicles surrounding vitellogenic oocytes showing a correlation with ovarian IGF-I mRNA levels. However, no change was seen in liver GH-R/IGF-I mRNA levels or plasma GH/IGF-I levels during ovarian development, suggesting that GH/IGF-I axis may be involved in the ovarian development in paracrine or autocrine manner, independent of liver derived IGF-I.     

Genetic and structural characterization of the growth hormone gene and protein from tench, Tinca tinca

The analysis of the tench growth hormone gene structure revealed a comparable organization of coding and non-coding regions than other from cyprinid species. Based on the performed mRNA and amino acid sequence alignments, gh tench is related to Asian than to European representatives of Cyprinidae family. Second aim of the work was to characterize and predict protein structure of the tench growth hormone. Tinca tinca GH share many common features with human GH molecule. The Tench GH protein binds to the growth hormone receptor (GHR) using two regions I and II that are situated at opposite sites of molecule. Binding site I is placed in the central part of T. tinca GH and H 189 amino acid in the middle region of the IV helix is crucial for GH–GHR interactions.     

Survival of salmonids in seawater and the time-frame of growth hormone action

In salmonids, growth hormone (GH) effectively promotes adaptation of freshwater (FW) fish to seawater (SW), but it has been unclear whether GH has osmoregulatory actions apart from those consequent to an increase in body size. Our objectives were first, to examine the minimum time and dose required for GH to enhance SW adaptation; and second, to optimize the conditions for the acute GH response in developing a convenient GH bioassay based on its plasma ion lowering effect. Trout showed markedly improved SW survival when transferred from fresh water 6, 24, or 48h after a single chum salmon GH injection (0.25 μg/g). Preadapting trout to 1/3 SW enhanced the plasma ion lowering effect of ovine GH (oGH) injected 48h before transfer of the fish to 80% SW. Endogenous plasma GH levels were elevated in control trout switched from low salinities to 80% SW but were depressed in oGH-injected fish after transfer. Under optimal test conditions (1/3 SW preadaptation, 48h pre-transfer injection, and 100% SW final challenge), the reduction in plasma Na⁺, Ca⁺⁺, and Mg⁺⁺ levels of oGH-injected fish was dose-dependent. The oGH doses giving minimum and maximum responses were 50 and 200 ng/g, respectively. In short, GH exerts acute osmoregulatory actions that promote SW adaptation in the absence of changes in body size. Compared with growth GH bioassays, the osmoregulatory assay is superior in economy of time, animal costs, and hormone quantity required and potentially in specificity.     

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.

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Résumé Afin d'étudier les régulations homronales et nutritionnelles de l'expression des ARNm de l'IGF-I (insulin-like growth factor I), un dosage spécifique par hybridation en solution des ARNm d'IGF-I de saumon coho et protégé des RNases, a été développé. Ce dosage, à la fois rapide et sensible, présente un faible coefficient de variation inter- (< 15%) et intra- (< 5%) dosage. L'étude de la distribution tissulaire des ARNm de l'IGF-I et des effets de l'hormone de croissance (GH), de la prolactine (Prl) et de la somatolactine (SI) sur l'expression hépatique des ARNm de l'IGF-I, a été entreprise in vivo chez le saumon coho en utilisant ce dosage. Le foie présente les plus grandes quantités d'ARNm d'IGF-I (16 pg/μg d'ADN). Des quantités significatives d'ARNm d'IGF-I ont été également détectées dans tous les autres tissus étudiés (intestin 4,1; rein 3,8; branchie 2,4; ovaire 2,3; muscle 2,1; rate 1,7 et graisse 1,1 pg/μg d'ADN). L'injection à des saumons coho, de GH à des doses de 0,1 et 1 μg/g de poids vif, augmente significativement et de manière dose dépendante les niveaux hépatiques d'ARNm d'IGF-I. L'injection de SI de saumon coho, un membre récemment découvert de la famille GH/Prl, stimule avec la plus haute dose utilisée, l'expression des ARNm d'IGF-I alors que la Prl n'a aucun effet. La GH augmente de manière dose dépendante (0,01–1 μg/ml) l'expression in vitro des ARNm d'IGF-I par des ARNm d'IGF-I par des hépatocytes de saumon coho en culture. Ces résultats indiquent que, chez le saumon coho, l'expression des ARNm d'IGF-I est présente dans le nombreaux tissus et que, l'expression hépatique est, au moins en partie, régulée par la GH et peut-être par d'autres hormones. Le dosage par séquence spécifique mise au point dans le présent travail, peut-être utilisé pour la quantification précise des ARNm, d'IGF-I de salmonidés et devrait permettre une meilleure connaissance de la physiologie de L'IGF-I chez les salmonidés.

     

Disparate effects of gonadal steroid hormones on plasma and liver mRNA levels of insulin-like growth factor-I and vitellogenin in the tilapia, Oreochromis mossambicus

The tilapia, Oreochromis mossambicus, exhibits a sexually dimorphic pattern of growth, males growing larger than females. We examined the effects of E₂ and DHT on the GH/IGF-I axis and on VTG production in the tilapia. Sexually mature tilapia were injected with 5 μg g body weight of E₂ (males) or DHT (females) every 5 days for a total of 3 injections. Female tilapia had significantly higher plasma GH levels than males. However, plasma and liver mRNA levels of IGF-I were significantly lower in females than in males, whereas VTG levels in both the plasma and liver mRNA were significantly higher in females than in males. Although significant amounts of VTG were detected in control males (8 ± 0.3 μg ml), the levels in control females (3000 ± 500 μg ml) were about 400 times higher than in males. Males treated with E₂ exhibited a female-like GH/IGF-I profile. That is, they had significantly elevated levels of plasma GH with lower plasma IGF-I and liver IGF-I mRNA levels. Estradiol treatment significantly elevated both plasma and liver mRNA VTG levels. Dihydrotestosterone treatment in females induced a male-like GH/IGF-I profile: plasma GH levels were significantly reduced, whereas plasma and liver IGF-I mRNA levels were significantly elevated. Both plasma and liver mRNA levels of VTG were not altered by DHT treatment. Pituitary GH mRNA levels were similar in all treatment groups. These results clearly indicate that estrogens and androgens feminize and masculinize the GH/IGF-I axis, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.