General and Comparative Endocrinology 141 (2005) 93–100 www.elsevier.com/locate/ygcen

Growth secretion from the Arctic charr (Salvelinus alpinus) in vitro: eVects of -14, -like growth factor-I, and nutritional status

C. Camerona,¤, R.D. Mocciab, J.F. Leatherlanda

a Department of Biomedical Sciences, University of Guelph, Guelph, Ont., Canada N1G 2W1 b Department of Animal and Poultry Science, University of Guelph, Guelph, Ont., Canada N1G 2W1

Received 27 February 2004; revised 3 November 2004; accepted 29 November 2004 Available online 8 January 2005

Abstract

This study investigated the inXuence of nutritional status on the (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 diVerent ration levels (0, 0.35, and 0.70% BW d¡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 cul- ture, 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 eVects on GH gene expression or protein synthesis. Nutri- tional status did not aVect 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.  2004 Elsevier Inc. All rights reserved.

Keywords: Growth hormone; Insulin-like growth factor-I; Ration level; Pituitary hormone secretion; Somatostatin; Arctic charr

1. Introduction peptide has been conWrmed in several teleost species (Holloway et al., 1997; Lin and Peter, 2001). Insulin-like The regulation of growth hormone (GH) secretion in growth factor-I (IGF-I), the mediator of many of the Wshes is multifactorial, with inputs from both neuroen- actions of GH, is another inhibitor of GH secretion, pro- docrine and circulating sources. Several members of the viding negative feedback on pituitary GH secretion in somatostatin family of peptides have been identiWed as many vertebrate species. This function has also been inhibitors of GH secretion, and this function, as well as conWrmed in several Wsh species (Blaise et al., 1995; peptide structure, has been highly conserved across the Fruchtman et al., 2000, 2002; Huang et al., 1997; Pérez- vertebrates (Lin et al., 1998). Somatostatin-14 (SRIF) Sánchez et al., 1992; Rousseau et al., 1997). has been conserved with identical primary structure in It is unclear from the studies in Wshes whether the all vertebrates, and the inhibition of GH release by this inhibition of GH secretion by IGF-I in vitro is a result of an instantaneous change in the rate of hormone secre- * Corresponding author. Fax: +1 613 562 5486. tion, changes in GH gene expression, or a combination E-mail address: [email protected] (C. Cameron). of these possibilities. Striped bass hybrid (Morone

0016-6480/$ - see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2004.11.019 94 C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100 saxatilis £ M. chrysops) somatotroph GH content and does not appear to be as potent in salmonid Wshes (Hol- protein synthesis are reduced after 18–20 h of exposure loway and Leatherland, 1998). of to IGF-I (Fruchtman et al., 2000), and tilapia (Ore- The purpose of the present study was to investigate ochromis mossambicus) pituitary glands treated with the eVects of SRIF and IGF-I on GH secretion from IGF-I for 24 h have reduced levels of GH mRNA, Arctic charr pituitary glands in vitro, and to determine if although GH secretion does not diVer signiWcantly after nutritional status has an inXuence on pituitary sensitiv- 4h (Kajimura et al., 2002). Conversely, injection of IGF- ity to these factors. Static hemipituitary gland culture I into catheterized rainbow trout (Oncorhynchus mykiss) was used to study changes in GH secretion after long- resulted in rapid (<60 min) reductions in plasma GH term exposure to peptides, whereas pituitary gland peri- concentrations (Blaise et al., 1995). In rat pituitary cells, fusion was used for acute exposures. IGF-I inhibits GH secretion and reduces levels of GH mRNA expression by somatotrophs in vitro (Niiori- Onishi et al., 1999; Yamashita and Melmed, 1986). In 2. Materials and methods addition, IGF-I may also act at the hypothalamic level, to stimulate the release of SRIF (Berelowitz et al., 1981), 2.1. Animals increase SRIF mRNA synthesis, and decrease GH releasing-hormone (GHRH) mRNA synthesis (Sato and All experimental protocols used in this study were Frohman, 1993). There are many potential sites of action approved by the University of Guelph Animal Care of IGF-I on pituitary GH secretion, and it is unclear Committee. Arctic charr (Salvelinus alpinus) of the Lab- from the previous studies in Wshes at which level(s) this rador strain were obtained from the Alma Aquaculture may be occurring. Research Station (Alma, Ont.). Fish had been main- The changes in the GH/IGF-I axis following dietary tained outdoors in 10 m circular tanks, with a water restriction have been described in mammals (Straus, temperature of 8.5 °C, and were fed a standard commer- 1994), and there is evidence to suggest a similar control cial diet (Martin Mills, Elmira, Ont.) using demand in Wshes (Duan, 1998). In several Wsh species, the reduc- feeders. tion in growth following dietary restriction is character- ized by elevated plasma GH concentrations (Duan and 2.2. Experimental design Plisetskaya, 1993; Farbridge and Leatherland, 1992; Fukada et al., 2004; Sumpter et al., 1991), a decreased Approximately 900 male and female Arctic charr level of hepatic IGF-I mRNA (Duan and Plisetskaya, (average weight D 397.9 g) were randomly distributed 1993), and a reduced plasma IGF-I concentration among nine 2 m tanks with a target initial stocking den- (Pérez-Sánchez et al., 1994a,b). It has been demon- sity of 40 kg m¡3. The tanks were located indoors under strated that hepatic GH-binding and GH-receptor a natural photoperiod. Water Xow rates were adjusted mRNA expression is reduced during dietary restriction to 30 L min¡1; water temperature was 8.5 °C; dissolved in Wshes (Fukada et al., 2004; Gray et al., 1992; Pérez- oxygen was monitored regularly and remained within Sánchez et al., 1994a). It is generally accepted that the normal limits for the duration of the study (8.5– reduction in negative feedback by circulating IGF-I 10 mg L¡1). contributes to increases in GH secretion and plasma After three days, the Wsh in all tanks were fed the GH. same commercial diet at 0.70% BWd¡1 via automatic There is evidence in Wshes that pituitary sensitivity to belt feeders. This was maintained for a period of 12 the factors that regulate the synthesis and secretion of weeks during which growth and feed conversion GH are inXuenced by reproductive and hormonal status eYciency were monitored. At the beginning of the study (Cardenas et al., 2003; Holloway and Leatherland, 1998; (March 11 2002) the tanks were randomly assigned to Peng and Peter, 1997). However, there is currently little one of three ration groups (0, 0.35, or 0.70% BWd¡1; 3 information on the eVects of changes in nutritional sta- tanks/ration level). The 0.70% BW d¡1 ration was tus on pituitary sensitivity to various GH secretagogues. selected as a full ration as the apparent feed conversion The changes in plasma GH concentrations related to eYciencies observed during the 12 week acclimation nutritional status could be explained by altered pituitary period indicated that a portion of this ration remained sensitivity to factors that inhibit GH secretion, such as uneaten in some tanks (data not shown). The experimen- SRIF or IGF-I. Pituitary sensitivity to these factors tal ration levels were maintained for a period of Wve depends on the abundance of SRIF or IGF-I receptors, weeks. and changes in the abundance of these receptors has A sample of 12 Wsh was taken from each tank after 1, been observed in relation to nutritional and hormonal 2, and 5 weeks. Fish were removed from the tanks in the status of Wsh (Pesek and Sheridan, 1996; Planas et al., morning prior to feeding (8:30–10:30) and euthanized 2000). Sensitivity to hypothalamic factors that stimulate with MS-222 (>125 mgL¡1). Pituitary glands were GH secretion may also be important, however, GHRH removed from each Wsh and placed in ice-cold 80% C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100 95

HBSS (Gibco-BRL, Canadian Life Technologies, Bur- 2.5. Assays lington, Ont.; with 4.17 mM NaHCO3, 0.1% BSA, pH 7.5, diluted to 80%). For measurement of GH secreted in vitro, a non-com- petitive enzyme-linked immunosorbent assay (ELISA) 2.3. Static hemipituitary gland culture developed for oncorhynchid species (Farbridge and Lea- therland, 1991), modiWed by Holloway and Leatherland Pituitary glands were dissected along the sagittal axis (1997), and validated for use in Arctic charr (Cameron et into two equal parts. The hemipituitaries were then al., 2002), was used. rinsed in 80% HBSS, placed individually into single wells of 24-well tissue culture plates (Corning Costar, Corn- 2.6. Statistics ing, NY), and cultured for 1 h in 1 ml of 80% HBSS at 10 °C on a shaker platform. The medium was then The percent of control GH released into the culture replaced with 1 ml M199 (Sigma Chemical, St. Louis, medium following treatment for 18 h was compared to MO; with 4.17 mM NaHCO3, 25 mM Hepes, 0.1% BSA, the percent of control GH released into medium during ¡1 0.7 mM L-glutamine, 100 gml streptomycin, and basal (pre-treatment) release period using a paired t test. 100,000 UL¡1 penicillin-G, pH 7.5) and incubated for 4 h A 2-way ANOVA was used for comparison of percent at 10 °C to establish basal release. The medium was then GH release between diVerent doses and ration levels replaced with either fresh M199 (control halves) or with over the 18 h culture. fresh M199 containing the test substance (treatment For pituitary fragment perifusion data, the average con- halves). Treatments consisted of recombinant human centration of GH in the 10 fractions prior to a pulse of test IGF-I (GroPep, Adelaide, Australia) or SRIF-14 (Sigma substance was normalized to 100%. Each fraction follow- Chemical) at concentrations of 0.01 or 1 nM. After an ing the pulse was then calculated as a percentage of this 18 h incubation, the medium was removed and stored at prepulse value for comparison. This correction was neces- ¡20 °C prior to hormone assay. sary because of the variation in GH release from individual pituitary glands in culture. The percent of control GH 2.4. Pituitary gland fragment perifusion released in each Wve minute fraction during perifusion fol- lowing administration of test substance was compared to The pituitary fragment perifusion procedure is based prepulse values using a Student’s t test. The average maxi- upon techniques developed for use with goldWsh (Mar- mal inhibition observed within 60min, as well as the aver- chant et al., 1987; Marchant and Peter, 1989), which age of the Wrst 10 fractions following a pulse, were were subsequently modiWed and validated for use with compared to the prepulse (100%) using a Student’s t test. rainbow trout (Holloway and Leatherland, 1997). Pitu- In all cases in which perifusion data failed tests of normal- itary glands were cut into fragments, rinsed with 80% ity, a Mann–Whitney rank-sum test was used. For all sta- HBSS, and three fragmented glands were incubated in tistical tests, a p< 0.05 was considered signiWcant. each perifusion chamber. The pituitary fragments were perifused with M199 for 5–6 h at a rate of 5 ml h¡1, after which the rate of Xow was increased to 15 ml h¡1. 3. Results Sample collection began 2 h after this increase in Xow rate. 3.1. Static hemipituitary gland culture For the pituitary fragment perifusion validation experiment 10 min fractions were collected for 7 h, then The total GH secreted into the medium from treated 5 min fractions were collected for 1 h prior to, and fol- hemipituitaries is expressed as a percentage of GH lowing, treatment. Forskolin (10 M; Sigma Chemical) secreted from the control hemipituitaries from Wsh sam- was solubilized in DMSO so that the Wnal concentration pled at 1, 2, and 5 weeks (Figs. 1A–C, respectively). With of DMSO in the test pulse was 0.008%. For pituitary three exceptions (SRIF at 0.01 nM, and hIGF-I at 1 nM, glands collected from Wsh in the ration level experiment, after 1 week in Wsh fed the 0.70% BWd¡1 ration, and the collection of 5 min fractions began 2 h prior to the hIGF-I at 0.01 nM after 2 weeks in food-deprived Wsh), Wrst treatment pulse (hIGF-I or SRIF-14; 0.01 and GH secretion from Arctic charr hemipituitary glands was 1 nM). Four culture chambers were used for each ration signiWcantly inhibited by SRIF and hIGF-I at both treat- treatment group and pituitary glands from each group ment levels (0.01 or 1 nM). However, there was no appar- were exposed to all treatment and dose combinations, ent eVect of dietary treatment on GH suppression. There with an elapsed time between treatment pulses of 90 to appeared to be a dose-related suppression of GH by 120 min. To minimize any eVect of previous treatment on SRIF, but no such dose–response was evident for hIGF-I. the results, each incubation chamber within a treatment No signiWcant diVerences were observed between the per- group received doses in a diVerent order. Fractions were cent of control GH release, at any dose of SRIF or hIGF- stored at ¡20 °C prior to hormone assay. I, when compared across the three sampling periods. 96 C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100

Fig. 1. Growth hormone (GH) release from Arctic charr hemipituitaries exposed to human insulin-like growth factor-I (hIGF-I) and somato- statin-14 (SRIF-14) for 18 h in static culture after 1, 2, and 5 weeks of die- tary treatment. Data are presented as the percent GH released from treated hemipituitary relative to the control hemipituitary (means §SEM; Fig. 2. Growth hormone (GH) release from Arctic charr pituitary frag- nD3–6; *signiWcantly diVerent [p< 0.05] from control value). ments (A) following no application of test substance (control), and (B) after exposure to 0.008% DMSO and 10 M forskolin, in the perifu- 3.2. Pituitary gland fragment perifusion sion system. Data are presented as the percent of prepulse GH release (means § SEM; n D 3; *signiWcantly diVerent [p < 0.05] from prepulse value). Perifused Arctic charr pituitary fragments displayed a 13.8 § 1.9% fall in GH release into the medium during the 7 h pre-experimental period (data not shown). How- to show the maximal inhibition of GH release from pitui- ever, no signiWcant changes in GH secretion, relative to tary fragments (Fig. 5). With the exception of 1 nM SRIF prepulse values, were observed when comparisons were in the 0.35 BWd¡1 group and 1 nM hIGF-I in the 0.70 made over a shorter period of time (1–2 h) during the BWd¡1 group after 2 weeks, both SRIF and hIGF-I sig- pre-experimental period (1 h prior to application of the niWcantly inhibited the release of GH in the perifusion forskolin carrier, DMSO, Fig. 2A). Following the appli- experiment as measured by the maximal inhibition of GH cation of 0.008% DMSO in M199, small, but signiWcant release whatever the concentration, sampling date or reductions in GH release were observed. However, treat- ration level. Both secretagogues signiWcantly suppressed ment of pituitary fragments with 10 M forskolin elic- GH secretion, regardless of time of sample, or of dietary ited a signiWcant increase in GH secretion within 25 min, treatments, although it was not always evident for both overriding the suppressive eVects of DMSO, with a sub- of the applied doses of the secretagogues. sequent return to prepulse levels (Fig. 2B). These Wnd- ings conWrm the viability of the pituitary preparations and their ability to respond to secretagogues in vitro. 4. Discussion Figs. 3 and 4 show examples of the plots generated fol- lowing exposure of Arctic charr pituitary gland fragments This study reveals that SRIF and hIGF-I inhibit GH to SRIF and hIGF-I pulses in the perifusion experiments. secretion from Arctic charr pituitary tissue in vitro with The data from the full set of these plots are summarized similar potency in both static and perifusion culture C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100 97

Fig. 3. Growth hormone (GH) release from Arctic charr pituitary frag- Fig. 4. Growth hormone (GH) release from Arctic charr pituitary frag- ments treated with 1 nM somatostatin-14 (SRIF-14) in the perifusion ments treated with 1 nM human insulin-like growth factor-I (hIGF-I) system. Pituitary glands were taken after 5 weeks of dietary treatment. in the perifusion system. Pituitary glands were taken after 5 weeks of Data are presented as the percent of prepulse GH release dietary treatment. Data are presented as the percent of prepulse GH § D W V (means SEM; n 3 (A) or 4 (B,C); *signi cantly [p <0.05] di erent release (means § SEM; n D 4; *signiWcantly [p <0.05] diVerent from from prepulse value). prepulse value). systems. Changes in nutritional status over a Wve-week similar to that seen in static rainbow trout pituitary cell period did not result in any concomitant change in the cultures (Blaise et al., 1995; Pérez-Sánchez et al., 1992; pituitary sensitivity to either SRIF or hIGF-I, suggesting Weil et al., 1999). The perifusion experiments in the pres- that pituitary sensitivity to these factors may not explain ent study revealed that there is a sustained inhibition of changes in plasma GH concentrations during fasting. GH release following a treatment of Arctic charr pitui- The pituitary fragment perifusion validation demon- tary fragments with SRIF. This response diVered from strates that the rate of GH secretion from Arctic charr that observed in goldWsh at similar doses of SRIF, in pituitary glands was stable, at least in the timescale over which the rates of GH secretion return rather rapidly to which prepulse values were compared to response values prepulse levels (Marchant et al., 1987; Marchant and in these experiments. SigniWcant diVerences in GH Peter, 1989). In addition, the degree of inhibition of GH release were not observed in the absence of a secreta- release does not appear to be as great in the Arctic charr gogue pulse, validating the argument that GH secretion as compared to these previous studies with goldWsh, was inhibited by hIGF-I and SRIF rather than any suggesting a diVerence in species sensitivity, as was also decline in somatotroph function. This experiment also suggested by Holloway and Leatherland (1998). demonstrated that forskolin, an activator of adenylate The relatively rapid decline in GH output by Arctic cyclase, was capable of stimulating GH secretion from charr pituitary fragments exposed to hIGF-I (and SRIF) Arctic charr pituitary glands, as has also been found pre- in perifusion are consistent with responses seen in rain- viously in other Wsh species (Chang et al., 1996; Falcón bow trout given injections of hIGF-I in vivo (Blaise et al., et al., 2003; Kwong and Chang, 1997). The degree of 1995). The rapidity of these responses suggests that this stimulation in Arctic charr, however, was considerably early inhibition of GH secretion is at least initially inde- lower than that observed from goldWsh pituitary cells pendent of changes in pituitary GH mRNA level or pro- (Chang et al., 1996). This stimulation of GH release from tein synthesis. However, changes in rates of GH gene pituitary fragments in the perifusion system conWrms the expression, or other genes involved in GH secretion, may viability of Arctic charr somatotrophs in vitro and their also contribute to these responses after continued expo- ability to respond to increases in intracellular cAMP. sure. The apparent lack of dose dependency in some The inhibition of GH secretion by SRIF and hIGF-I groups, which may indicate that maximal inhibition of from Arctic charr pituitary glands in static culture was GH secretion was achieved, may also be due to a 98 C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100

tors such as SRIF and GHRH (Berelowitz et al., 1981; Sato and Frohman, 1993), and similar mechanisms may exist in Wsh. Thus, the responses observed in this study may include actions at the hypothalamic and pituitary (somatotroph) levels. The quantity and the integrity of the hypothalamic tissue within the pituitary fragments may account for the high individual variation in basal and secretagogue-stimulated GH release in vitro. The total GH output by control pituitary fragments was similar for all dietary treatment groups (Cameron, 2003). This indicates that nutritional status may not aVect the GH secretion potential of the somatotroph, and perhaps other mechanisms are responsible for eleva- tions in plasma GH levels during fasting, such as changes in plasma clearance rates. Alternatively, there may be in vivo diVerences in the levels of factors control- ling GH secretion that are lacking in the in vitro systems. This may include the changes in plasma IGF-I concen- trations, but also other linked to nutritional status and GH synthesis and secretion, including several neuropeptides that are involved both in food intake and GH secretion (Lin et al., 2004; Peng and Peter, 1997). Other possibilities include the gut peptide ghrelin, which in goldWsh is increased during fasting and stimulates food intake (Unniappan et al., 2004), and has a stimula- tory eVect on GH secretion in this, and other, Wsh species (Kaiya et al., 2003; Riley et al., 2002; Unniappan and Fig. 5. Maximal inhibition of growth hormone (GH) release from Arc- Peter, 2004). tic charr pituitary fragments in the perifusion system during 60 min In summary, the release of GH from Arctic charr pitui- following a pulse of human insulin-like growth factor-I (hIGF-I) or tary tissue in vitro was inhibited by both SRIF and hIGF- somatostatin-14 (SRIF-14). Pituitary glands were taken after 1, 2, and I in both long-term static and short-term perifusion cul- 5 weeks of dietary treatment. Data are presented as the percent of ture. Of particular interest was the ability of hIGF-I to prepulse GH release (means § SEM; n D 4; *signiWcantly [p <0.05] diVerent from prepulse value). inhibit GH secretion after acute exposure in a manner similar to that of SRIF. Pituitary sensitivity to the two secretagogues was not inXuenced by the nutritional his- variation in GH output by pituitary preparations com- tory of the animal, suggesting that if these peptides are bined with a limited secretagogue dose range. The inhibi- involved in the changes in circulating levels of GH that tion of GH release from rainbow trout pituitary cells by are observed as a result of altered nutritional status, it is hIGF-I and SRIF has been demonstrated to be dose- not due to changes in pituitary sensitivity to these factors. dependent over a much wider range of doses (0.01– 100nM) (Pérez-Sánchez et al., 1992). The doses of hIGF- ¡1 I used (0.01 and 1 nM; 0.076 and 7.649 ng ml , respec- Acknowledgments tively) are within the physiological range reported for several salmonid species, and free IGF-I in the circulation The thank Mrs. Lucy Lin for her technical assistance of coho salmon has been estimated to be around 0.3% of and the staV at the Alma Aquaculture Research Station total IGF-I (Shimizu et al., 1999). If this relationship can for maintenance of research animals. The work was sup- be extended to Arctic charr, then estimates of free IGF-I ported by NSERC and OMAF grants to JFL and an in Arctic charr plasma (unpublished results) would OMAFRA grant to RDM. exceed the doses of hIGF-I employed in the in vitro por- tion of this study. It is not possible to determine at which level these fac- tors, particularly hIGF-I, inhibit GH secretion, because References the pituitary gland fragments used in both the static and perifusion studies contained both hypothalamic and ade- Berelowitz, M., Szabo, M., Frohman, L.A., Firestone, S., Chu, L., 1981. Somatomedin-C mediates growth hormone negative feedback by nohypophysial tissue. In mammals, IGF-I can regulate eVects on both the hypothalamus and the pituitary. Science 212, GH secretion through modulation of hypothalamic fac- 1279–1281. C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100 99

Blaise, O., Weil, C., Le Bail, P.-Y., 1995. Role of IGF-I in the control of growth factors (IGFs) on gonadotropin (GtH-II) and growth hor- GH secretion in rainbow trout (Oncorhynchus mykiss). Growth mone (GH) production by primary culture of European eel Regul. 5, 142–150. (Anguilla anguilla) pituitary cells. Aquaculture 177, 73–83. Cameron, C., 2003. Nutritional regulation of the somatotropic axis in Kaiya, H., Kojima, M., Hosoda, H., Riley, L.G., Hirano, T., Grau, E.G., Arctic charr, Salvelinus alpinus. Guelph, Canada; University of Kangawa, K., 2003. Amidated Wsh ghrelin: puriWcation, cDNA Guelph, MSc Thesis, 210 pp. cloning in the Japanese eel and its biological activity. J. Endocrinol. Cameron, C., Gurure, R., Reddy, K., Moccia, R., Leatherland, J., 2002. 176, 415–423. Correlation between dietary lipid: protein ratios and plasma Kajimura, S., Uchida, K., Yada, T., Hirano, T., Aida, K., Grau, E.G., growth and thyroid hormone levels in juvenile Arctic charr, Salveli- 2002. EVects of insulin-like growth factors (IGF-I and -II) on nus alpinus (Linnaeus). Aquacult. Res. 33, 383–394. growth hormone and prolactin release and gene expression in eury- Cardenas, R., Lin, X., Canosa, L.F., Luna, M., Arámburo, C., Peter, haline tilapia, Oreochromis mossambicus. Gen. Comp. Endocrinol. R.E., 2003. Estradiol reduces pituitary responsiveness to somato- 127, 223–231. statin (SRIF-14) and down-regulates the expression of somato- Kwong, P., Chang, J.P., 1997. Somatostatin inhibition of growth hor- W W statin sst2 receptors in female gold sh pituitary. Gen. Comp. mone release in gold sh: possible targets of intracellular mecha- Endocrinol. 132, 119–124. nisms of action. Gen. Comp. Endocrinol. 108, 446–456. Chang, J.P., Abele, J.T., Van Goor, F., Wong, A.O.L., Neumann, C.M., Lin, X., Peter, R.E., 2001. and their receptors in Wsh. 1996. Role of arachidonic acid and calmodulin in mediating dopa- Comp. Biochem. Physiol. 129B, 543–550. mine D1- and GnRH-stimulated growth hormone release in gold- Lin, X., VolkoV, H., Narnaware, Y., Bernier, N.J., Peyon, P., Peter, R.E., Wsh pituitary cells. Gen. Comp. Endocrinol. 102, 88–101. 2004. Brain regulation of feeding behavior and food intake in Wsh. Duan, C., 1998. Nutritional and developmental regulation of insulin- Comp. Biochem. Physiol. 126A, 415–434. like growth factors in Wsh. J. Nutr. 128, 306S–314S. Lin, X.-W., Otto, C.J., Peter, R.E., 1998. Evolution of neuroendocrine Duan, C., Plisetskaya, E.M., 1993. Nutritional regulation of insulin-like peptide systems: Gonadotropin-releasing hormone and somato- growth factor-I mRNA expression in salmon tissues. J. Endocrinol. statin. Comp. Biochem. Physiol. 119C, 375–388. 139, 243–252. Marchant, T.A., Fraser, R.A., Andrews, P.C., Peter, R.E., 1987. The Falcón, J., Besseau, L., Fazzari, D., Attia, J., Gaildrat, P., Beauchaud, inXuence of mammalian and teleost somatostatins on the secretion M., Boeuf, G., 2003. Melatonin modulates secretion of growth hor- of growth hormone from goldWsh (Carassius auratus L.) pituitary mone and prolactin by trout pituitary glands and cells in culture. fragments in vitro. Regul. Pept. 17, 41–52. Endocrinology 144, 4648–4658. Marchant, T.A., Peter, R.E., 1989. Hypothalamic peptides inXuencing Farbridge, K.J., Leatherland, J.F., 1991. The development of a non- growth hormone secretion in the goldWsh, Carassius auratus. Fish competitive enzyme-linked immunosorbent assay for oncorhynchid Physiol. Biochem. 7, 133–139. growth hormone using monoclonal antibodies. Gen. Comp. Endo- Niiori-Onishi, A., Iwasaki, Y., Mutsuga, N., Oiso, Y., Inque, K., Saito, crinol. 83, 7–17. H., 1999. Molecular mechanisms of the negative eVect of insulin- Farbridge, K.J., Leatherland, J.F., 1992. Temporal changes in plasma like growth factor-I on growth hormone gene expression in MtT/S thyroid hormone, growth hormone and free fatty acid concentra- somatotroph cells. Endocrinology 140, 344–349. tions, and hepatic 5Ј-monodeiodinase activity, lipid and protein Pérez-Sánchez, J., Marti-Palanca, H., Le Bail, P.-Y., 1994a. Homologous content during chronic fasting and re-feeding in rainbow trout growth hormone (GH) binding in gilthead sea bream (Sparus aurata). (Oncorhynchus mykiss). Fish Physiol. Biochem. 10, 245–257. EVect of fasting and refeeding on hepatic GH-binding and plasma Fruchtman, S., Jackson, L., Borski, R., 2000. Insulin-like growth factor somatomedin-like immunoreactivity. J. Fish Biol. 44, 287–301. I disparately regulates prolactin and growth hormone synthesis and Pérez-Sánchez, J., Marti-Palanca, H., Le Bail, P.-Y., 1994b. Seasonal secretion: studies using the teleost pituitary model. Endocrinology changes in circulating growth hormone (GH), hepatic GH-binding 141, 2886–2894. and plasma insulin-like growth factor-I immunoreactivity in a Fruchtman, S., McVey, D.C., Borski, R.J., 2002. Characterization of marine Wsh, gilthead sea bream, Sparus aurata. Fish Physiol. Bio- pituitary IGF-I receptors: modulation of prolactin and growth hor- chem. 13, 199–208. mone. Am. J. Physiol. Regul. Integr. Comp. Physiol. 283, R468– Pérez-Sánchez, J., Weil, C., Le Bail, P.-Y., 1992. EVects of human insu- R476. lin-like growth factor-I on release of growth hormone by rainbow Fukada, H., Ozaki, Y., Pierce, A.L., Adachi, S., Yamauchi, K., Hara, A., trout (Oncorhynchus mykiss) pituitary cells. J. Exp. Zool. 262, Swanson, P., DickhoV, W.W., 2004. Salmon growth hormone recep- 287–290. tor: molecular cloning, ligand speciWcity, and response to fasting. Peng, C., Peter, R.E., 1997. Neuroendocrine regulation of growth hor- Gen. Comp. Endocrinol. 139, 61–71. mone secretion and growth in Wsh. Zool. Stud. 36, 79–89. Gray, E.S., Kelley, K.M., Law, S., Tsai, R., Young, G., Bern, H.A., 1992. Pesek, M.J., Sheridan, M.A., 1996. Fasting alters somatostatin binding Regulation of hepatic growth hormone receptors in coho salmon to liver membranes of rainbow trout (Oncorhynchus mykiss). J. (Oncorhynchus kisutch). Gen. Comp. Endocrinol. 88, 243–252. Endocrinol. 150, 179–186. Holloway, A.C., Leatherland, J.F., 1997. The eVects of N-methyl-D,L- Planas, J.V., Méndez, E., Baños, N., Capilla, E., Navarro, I., Gutiérrez, aspartate and gonadotropin-releasing hormone on in vitro growth J., 2000. Insulin and IGF-I receptors in trout adipose tissue are hormone release in steroid-primed immature rainbow trout, physiologically regulated by circulating hormone levels. J. Exp. Oncorhynchus mykiss. Gen. Comp. Endocrinol. 107, 32–43. Biol. 203, 1153–1159. Holloway, A.C., Leatherland, J.F., 1998. Neuroendocrine regulation of Riley, L.G., Hirano, T., Grau, E.G., 2002. Rat ghrelin stimulates growth hormone secretion in teleost Wshes with emphasis on the growth hormone and prolactin release in the tilapia, Oreochromis involvement of gonadal sex steroids. Rev. Fish Biol. Fish. 8, 409– mossambicus. Zool. Sci. 19, 797–800. 429. Rousseau, K., Huang, Y.-S., Le Belle, N., Vidal, B., Marchelidon, J., Holloway, A.C., Sheridan, M.A., Leatherland, J.F., 1997. Estradiol Epelbaum, J., Dufour, S., 1997. Long-term inhibitory eVects of inhibits plasma somatostatin 14 (SRIF-14) levels and inhibits the somatostatin and insulin-like growth factor 1 on growth hormone response of somatotrophic cells to SRIF-14 challenge in vitro in release by serum-free primary culture of pituitary cells from Euro- rainbow trout, Oncorhynchus mykiss. Gen. Comp. Endocrinol. 106, pean eel (Anguilla anguilla). Neuroendocrinology 67, 301–309. 407–414. Sato, M., Frohman, L.A., 1993. DiVerential eVects of central and Huang, Y.-S., Rousseau, K., Le Belle, N., Vidal, B., Burzawa-Gérard, peripheral administration of growth hormone (GH) and insulin- E., Marchelidon, J., Dufour, S., 1997. Opposite eVects of insulin-like like growth factor on hypothalamic GH-releasing hormone and 100 C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100

somatostatin gene expression in GH-deWcient rats. Endocrinology mRNA expression and serum levels, and responses to central and 133, 793–799. peripheral injections. Neuroendocrinology 79, 100–108. Shimizu, M., Swanson, P., DickhoV, W.W., 1999. Free and protein- Unniappan, S., Peter, R.E., 2004. In vitro and in vivo eVects of ghrelin bound insulin-like growth factor-I (IGF-I) and IGF-binding pro- on luteinizing hormone and growth hormone release in goldWsh. teins in plasma of coho salmon, Oncorhynchus kisutch. Gen. Comp. Am. J. Physiol. Integr. Comp. Physiol. 286, R1093–1101. Endocrinol. 115, 398–405. Weil, C., Carré, F., Blaise, O., Breton, B., Le Bail, P.-Y., 1999. DiVeren- Straus, D.S., 1994. Nutritional regulation of hormones and growth fac- tial eVect of insulin-like growth factor I on in vitro gonadotropin (I tors that control mammalian growth. FASEB J. 8, 6–12. and II) and growth hormone secretions in rainbow trout Sumpter, J.P., LeBail, P.-Y., Pickering, A.D., Pottinger, T.G., Carra- (Oncorhynchus mykiss) at diVerent stages of the reproductive cycle. gher, J.F., 1991. The eVect of starvation on growth and plasma Endocrinology 140, 2054–2062. growth hormone concentrations of rainbow trout, Oncorhynchus Yamashita, S., Melmed, S., 1986. Insulin-like growth factor I action on mykiss. Gen. Comp. Endocrinol. 83, 94–102. rat anterior pituitary cells: suppression of growth hormone secre- Unniappan, S., Canosa, L.F., Peter, R.E., 2004. Orexigenic actions of tion and messenger ribonucleic acid levels. Endocrinology 118, ghrelin in goldWsh: feeding-induced changes in brain and gut 176–182.