General and Comparative Endocrinology 141 (2005) 93–100
www.elsevier.com/locate/ygcen
Growth hormone secretion from the Arctic charr (Salvelinus alpinus)
pituitary gland in vitro: eVects of somatostatin-14, insulin-like growth
factor-I, and nutritional status
C. Camerona,¤, R.D. Mocciab, J.F. Leatherlanda
a
b
Department of Biomedical Sciences, University of Guelph, Guelph, Ont., Canada N1G 2W1
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 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 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 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 eVects on GH gene expression or protein synthesis. Nutritional 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
The regulation of growth hormone (GH) secretion in
Wshes is multifactorial, with inputs from both neuroendocrine and circulating sources. Several members of the
somatostatin family of peptides have been identiWed as
inhibitors of GH secretion, and this function, as well as
peptide structure, has been highly conserved across the
vertebrates (Lin et al., 1998). Somatostatin-14 (SRIF)
has been conserved with identical primary structure in
all vertebrates, and the inhibition of GH release by this
*
Corresponding author. Fax: +1 613 562 5486.
E-mail address: [email protected] (C. Cameron).
0016-6480/$ - see front matter  2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.ygcen.2004.11.019
peptide has been conWrmed in several teleost species
(Holloway et al., 1997; Lin and Peter, 2001). Insulin-like
growth factor-I (IGF-I), the mediator of many of the
actions of GH, is another inhibitor of GH secretion, providing negative feedback on pituitary GH secretion in
many vertebrate species. This function has also been
conWrmed in several Wsh species (Blaise et al., 1995;
Fruchtman et al., 2000, 2002; Huang et al., 1997; PérezSánchez et al., 1992; Rousseau et al., 1997).
It is unclear from the studies in Wshes whether the
inhibition of GH secretion by IGF-I in vitro is a result of
an instantaneous change in the rate of hormone secretion, changes in GH gene expression, or a combination
of these possibilities. Striped bass hybrid (Morone
94
C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100
saxatilis £ M. chrysops) somatotroph GH content and
protein synthesis are reduced after 18–20 h of exposure
of to IGF-I (Fruchtman et al., 2000), and tilapia (Oreochromis mossambicus) pituitary glands treated with
IGF-I for 24 h have reduced levels of GH mRNA,
although GH secretion does not diVer signiWcantly after
4 h (Kajimura et al., 2002). Conversely, injection of IGFI into catheterized rainbow trout (Oncorhynchus mykiss)
resulted in rapid (<60 min) reductions in plasma GH
concentrations (Blaise et al., 1995). In rat pituitary cells,
IGF-I inhibits GH secretion and reduces levels of GH
mRNA expression by somatotrophs in vitro (NiioriOnishi et al., 1999; Yamashita and Melmed, 1986). In
addition, IGF-I may also act at the hypothalamic level,
to stimulate the release of SRIF (Berelowitz et al., 1981),
increase SRIF mRNA synthesis, and decrease GH
releasing-hormone (GHRH) mRNA synthesis (Sato and
Frohman, 1993). There are many potential sites of action
of IGF-I on pituitary GH secretion, and it is unclear
from the previous studies in Wshes at which level(s) this
may be occurring.
The changes in the GH/IGF-I axis following dietary
restriction have been described in mammals (Straus,
1994), and there is evidence to suggest a similar control
in Wshes (Duan, 1998). In several Wsh species, the reduction in growth following dietary restriction is characterized by elevated plasma GH concentrations (Duan and
Plisetskaya, 1993; Farbridge and Leatherland, 1992;
Fukada et al., 2004; Sumpter et al., 1991), a decreased
level of hepatic IGF-I mRNA (Duan and Plisetskaya,
1993), and a reduced plasma IGF-I concentration
(Pérez-Sánchez et al., 1994a,b). It has been demonstrated that hepatic GH-binding and GH-receptor
mRNA expression is reduced during dietary restriction
in Wshes (Fukada et al., 2004; Gray et al., 1992; PérezSánchez et al., 1994a). It is generally accepted that the
reduction in negative feedback by circulating IGF-I
contributes to increases in GH secretion and plasma
GH.
There is evidence in Wshes that pituitary sensitivity to
the factors that regulate the synthesis and secretion of
GH are inXuenced by reproductive and hormonal status
(Cardenas et al., 2003; Holloway and Leatherland, 1998;
Peng and Peter, 1997). However, there is currently little
information on the eVects of changes in nutritional status on pituitary sensitivity to various GH secretagogues.
The changes in plasma GH concentrations related to
nutritional status could be explained by altered pituitary
sensitivity to factors that inhibit GH secretion, such as
SRIF or IGF-I. Pituitary sensitivity to these factors
depends on the abundance of SRIF or IGF-I receptors,
and changes in the abundance of these receptors has
been observed in relation to nutritional and hormonal
status of Wsh (Pesek and Sheridan, 1996; Planas et al.,
2000). Sensitivity to hypothalamic factors that stimulate
GH secretion may also be important, however, GHRH
does not appear to be as potent in salmonid Wshes (Holloway and Leatherland, 1998).
The purpose of the present study was to investigate
the eVects of SRIF and IGF-I on GH secretion from
Arctic charr pituitary glands in vitro, and to determine if
nutritional status has an inXuence on pituitary sensitivity to these factors. Static hemipituitary gland culture
was used to study changes in GH secretion after longterm exposure to peptides, whereas pituitary gland perifusion was used for acute exposures.
2. Materials and methods
2.1. Animals
All experimental protocols used in this study were
approved by the University of Guelph Animal Care
Committee. Arctic charr (Salvelinus alpinus) of the Labrador strain were obtained from the Alma Aquaculture
Research Station (Alma, Ont.). Fish had been maintained outdoors in 10 m circular tanks, with a water
temperature of 8.5 °C, and were fed a standard commercial diet (Martin Mills, Elmira, Ont.) using demand
feeders.
2.2. Experimental design
Approximately 900 male and female Arctic charr
(average weight D 397.9 g) were randomly distributed
among nine 2 m tanks with a target initial stocking density of 40 kg m¡3. The tanks were located indoors under
a natural photoperiod. Water Xow rates were adjusted
to 30 L min¡1; water temperature was 8.5 °C; dissolved
oxygen was monitored regularly and remained within
normal limits for the duration of the study (8.5–
10 mg L¡1).
After three days, the Wsh in all tanks were fed the
same commercial diet at 0.70% BW d¡1 via automatic
belt feeders. This was maintained for a period of 12
weeks during which growth and feed conversion
eYciency were monitored. At the beginning of the study
(March 11 2002) the tanks were randomly assigned to
one of three ration groups (0, 0.35, or 0.70% BW d¡1; 3
tanks/ration level). The 0.70% BW d¡1 ration was
selected as a full ration as the apparent feed conversion
eYciencies observed during the 12 week acclimation
period indicated that a portion of this ration remained
uneaten in some tanks (data not shown). The experimental ration levels were maintained for a period of Wve
weeks.
A sample of 12 Wsh was taken from each tank after 1,
2, and 5 weeks. Fish were removed from the tanks in the
morning prior to feeding (8:30–10:30) and euthanized
with MS-222 (>125 mg L¡1). Pituitary glands were
removed from each Wsh and placed in ice-cold 80%
C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100
HBSS (Gibco-BRL, Canadian Life Technologies, Burlington, Ont.; with 4.17 mM NaHCO3, 0.1% BSA, pH
7.5, diluted to 80%).
2.3. Static hemipituitary gland culture
Pituitary glands were dissected along the sagittal axis
into two equal parts. The hemipituitaries were then
rinsed in 80% HBSS, placed individually into single wells
of 24-well tissue culture plates (Corning Costar, Corning, NY), and cultured for 1 h in 1 ml of 80% HBSS at
10 °C on a shaker platform. The medium was then
replaced with 1 ml M199 (Sigma Chemical, St. Louis,
MO; with 4.17 mM NaHCO3, 25 mM Hepes, 0.1% BSA,
0.7 mM L-glutamine, 100 g ml¡1 streptomycin, and
100,000 U L¡1 penicillin-G, pH 7.5) and incubated for 4 h
at 10 °C to establish basal release. The medium was then
replaced with either fresh M199 (control halves) or with
fresh M199 containing the test substance (treatment
halves). Treatments consisted of recombinant human
IGF-I (GroPep, Adelaide, Australia) or SRIF-14 (Sigma
Chemical) at concentrations of 0.01 or 1 nM. After an
18 h incubation, the medium was removed and stored at
¡20 °C prior to hormone assay.
2.4. Pituitary gland fragment perifusion
The pituitary fragment perifusion procedure is based
upon techniques developed for use with goldWsh (Marchant et al., 1987; Marchant and Peter, 1989), which
were subsequently modiWed and validated for use with
rainbow trout (Holloway and Leatherland, 1997). Pituitary glands were cut into fragments, rinsed with 80%
HBSS, and three fragmented glands were incubated in
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.
Sample collection began 2 h after this increase in Xow
rate.
For the pituitary fragment perifusion validation
experiment 10 min fractions were collected for 7 h, then
5 min fractions were collected for 1 h prior to, and following, treatment. Forskolin (10 M; Sigma Chemical)
was solubilized in DMSO so that the Wnal concentration
of DMSO in the test pulse was 0.008%. For pituitary
glands collected from Wsh in the ration level experiment,
the collection of 5 min fractions began 2 h prior to the
Wrst treatment pulse (hIGF-I or SRIF-14; 0.01 and
1 nM). Four culture chambers were used for each ration
treatment group and pituitary glands from each group
were exposed to all treatment and dose combinations,
with an elapsed time between treatment pulses of 90 to
120 min. To minimize any eVect of previous treatment on
the results, each incubation chamber within a treatment
group received doses in a diVerent order. Fractions were
stored at ¡20 °C prior to hormone assay.
95
2.5. Assays
For measurement of GH secreted in vitro, a non-competitive enzyme-linked immunosorbent assay (ELISA)
developed for oncorhynchid species (Farbridge and Leatherland, 1991), modiWed by Holloway and Leatherland
(1997), and validated for use in Arctic charr (Cameron et
al., 2002), was used.
2.6. Statistics
The percent of control GH released into the culture
medium following treatment for 18 h was compared to
the percent of control GH released into medium during
basal (pre-treatment) release period using a paired t test.
A 2-way ANOVA was used for comparison of percent
GH release between diVerent doses and ration levels
over the 18 h culture.
For pituitary fragment perifusion data, the average concentration of GH in the 10 fractions prior to a pulse of test
substance was normalized to 100%. Each fraction following the pulse was then calculated as a percentage of this
prepulse value for comparison. This correction was necessary because of the variation in GH release from individual
pituitary glands in culture. The percent of control GH
released in each Wve minute fraction during perifusion following administration of test substance was compared to
prepulse values using a Student’s t test. The average maximal inhibition observed within 60 min, as well as the average of the Wrst 10 fractions following a pulse, were
compared to the prepulse (100%) using a Student’s t test.
In all cases in which perifusion data failed tests of normality, a Mann–Whitney rank-sum test was used. For all statistical tests, a p < 0.05 was considered signiWcant.
3. Results
3.1. Static hemipituitary gland culture
The total GH secreted into the medium from treated
hemipituitaries is expressed as a percentage of GH
secreted from the control hemipituitaries from Wsh sampled at 1, 2, and 5 weeks (Figs. 1A–C, respectively). With
three exceptions (SRIF at 0.01 nM, and hIGF-I at 1 nM,
after 1 week in Wsh fed the 0.70% BW d¡1 ration, and
hIGF-I at 0.01 nM after 2 weeks in food-deprived Wsh),
GH secretion from Arctic charr hemipituitary glands was
signiWcantly inhibited by SRIF and hIGF-I at both treatment levels (0.01 or 1 nM). However, there was no apparent eVect of dietary treatment on GH suppression. There
appeared to be a dose-related suppression of GH by
SRIF, but no such dose–response was evident for hIGF-I.
No signiWcant diVerences were observed between the percent of control GH release, at any dose of SRIF or hIGFI, 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 somatostatin-14 (SRIF-14) for 18 h in static culture after 1, 2, and 5 weeks of dietary treatment. Data are presented as the percent GH released from
treated hemipituitary relative to the control hemipituitary (means § SEM;
n D 3–6; *signiWcantly diVerent [p < 0.05] from control value).
3.2. Pituitary gland fragment perifusion
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). However, no signiWcant changes in GH secretion, relative to
prepulse values, were observed when comparisons were
made over a shorter period of time (1–2 h) during the
pre-experimental period (1 h prior to application of the
forskolin carrier, DMSO, Fig. 2A). Following the application of 0.008% DMSO in M199, small, but signiWcant
reductions in GH release were observed. However, treatment of pituitary fragments with 10 M forskolin elicited a signiWcant increase in GH secretion within 25 min,
overriding the suppressive eVects of DMSO, with a subsequent return to prepulse levels (Fig. 2B). These Wndings conWrm the viability of the pituitary preparations
and their ability to respond to secretagogues in vitro.
Figs. 3 and 4 show examples of the plots generated following exposure of Arctic charr pituitary gland fragments
to SRIF and hIGF-I pulses in the perifusion experiments.
The data from the full set of these plots are summarized
Fig. 2. Growth hormone (GH) release from Arctic charr pituitary fragments (A) following no application of test substance (control), and (B)
after exposure to 0.008% DMSO and 10 M forskolin, in the perifusion system. Data are presented as the percent of prepulse GH release
(means § SEM; n D 3; *signiWcantly diVerent [p < 0.05] from prepulse
value).
to show the maximal inhibition of GH release from pituitary fragments (Fig. 5). With the exception of 1 nM SRIF
in the 0.35 BW d¡1 group and 1 nM hIGF-I in the 0.70
BW d¡1 group after 2 weeks, both SRIF and hIGF-I signiWcantly inhibited the release of GH in the perifusion
experiment as measured by the maximal inhibition of GH
release whatever the concentration, sampling date or
ration level. Both secretagogues signiWcantly suppressed
GH secretion, regardless of time of sample, or of dietary
treatments, although it was not always evident for both
of the applied doses of the secretagogues.
4. Discussion
This study reveals that SRIF and hIGF-I inhibit GH
secretion from Arctic charr pituitary tissue in vitro with
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 fragments treated with 1 nM somatostatin-14 (SRIF-14) in the perifusion
system. Pituitary glands were taken after 5 weeks of dietary treatment.
Data are presented as the percent of prepulse GH release
(means § SEM; n D 3 (A) or 4 (B,C); *signiWcantly [p < 0.05] diVerent
from prepulse value).
Fig. 4. Growth hormone (GH) release from Arctic charr pituitary fragments treated with 1 nM human insulin-like growth factor-I (hIGF-I)
in the perifusion system. Pituitary glands were taken after 5 weeks of
dietary treatment. Data are presented as the percent of prepulse GH
release (means § SEM; n D 4; *signiWcantly [p < 0.05] diVerent from
prepulse value).
systems. Changes in nutritional status over a Wve-week
period did not result in any concomitant change in the
pituitary sensitivity to either SRIF or hIGF-I, suggesting
that pituitary sensitivity to these factors may not explain
changes in plasma GH concentrations during fasting.
The pituitary fragment perifusion validation demonstrates that the rate of GH secretion from Arctic charr
pituitary glands was stable, at least in the timescale over
which prepulse values were compared to response values
in these experiments. SigniWcant diVerences in GH
release were not observed in the absence of a secretagogue pulse, validating the argument that GH secretion
was inhibited by hIGF-I and SRIF rather than any
decline in somatotroph function. This experiment also
demonstrated that forskolin, an activator of adenylate
cyclase, was capable of stimulating GH secretion from
Arctic charr pituitary glands, as has also been found previously in other Wsh species (Chang et al., 1996; Falcón
et al., 2003; Kwong and Chang, 1997). The degree of
stimulation in Arctic charr, however, was considerably
lower than that observed from goldWsh pituitary cells
(Chang et al., 1996). This stimulation of GH release from
pituitary fragments in the perifusion system conWrms the
viability of Arctic charr somatotrophs in vitro and their
ability to respond to increases in intracellular cAMP.
The inhibition of GH secretion by SRIF and hIGF-I
from Arctic charr pituitary glands in static culture was
similar to that seen in static rainbow trout pituitary cell
cultures (Blaise et al., 1995; Pérez-Sánchez et al., 1992;
Weil et al., 1999). The perifusion experiments in the present study revealed that there is a sustained inhibition of
GH release following a treatment of Arctic charr pituitary fragments with SRIF. This response diVered from
that observed in goldWsh at similar doses of SRIF, in
which the rates of GH secretion return rather rapidly to
prepulse levels (Marchant et al., 1987; Marchant and
Peter, 1989). In addition, the degree of inhibition of GH
release does not appear to be as great in the Arctic charr
as compared to these previous studies with goldWsh,
suggesting a diVerence in species sensitivity, as was also
suggested by Holloway and Leatherland (1998).
The relatively rapid decline in GH output by Arctic
charr pituitary fragments exposed to hIGF-I (and SRIF)
in perifusion are consistent with responses seen in rainbow trout given injections of hIGF-I in vivo (Blaise et al.,
1995). The rapidity of these responses suggests that this
early inhibition of GH secretion is at least initially independent of changes in pituitary GH mRNA level or protein synthesis. However, changes in rates of GH gene
expression, or other genes involved in GH secretion, may
also contribute to these responses after continued exposure. The apparent lack of dose dependency in some
groups, which may indicate that maximal inhibition of
GH secretion was achieved, may also be due to a
98
C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100
Fig. 5. Maximal inhibition of growth hormone (GH) release from Arctic charr pituitary fragments in the perifusion system during 60 min
following a pulse of human insulin-like growth factor-I (hIGF-I) or
somatostatin-14 (SRIF-14). Pituitary glands were taken after 1, 2, and
5 weeks of dietary treatment. Data are presented as the percent of
prepulse GH release (means § SEM; n D 4; *signiWcantly [p < 0.05]
diVerent from prepulse value).
variation in GH output by pituitary preparations combined with a limited secretagogue dose range. The inhibition of GH release from rainbow trout pituitary cells by
hIGF-I and SRIF has been demonstrated to be dosedependent over a much wider range of doses (0.01–
100 nM) (Pérez-Sánchez et al., 1992). The doses of hIGFI used (0.01 and 1 nM; 0.076 and 7.649 ng ml¡1, respectively) are within the physiological range reported for
several salmonid species, and free IGF-I in the circulation
of coho salmon has been estimated to be around 0.3% of
total IGF-I (Shimizu et al., 1999). If this relationship can
be extended to Arctic charr, then estimates of free IGF-I
in Arctic charr plasma (unpublished results) would
exceed the doses of hIGF-I employed in the in vitro portion of this study.
It is not possible to determine at which level these factors, particularly hIGF-I, inhibit GH secretion, because
the pituitary gland fragments used in both the static and
perifusion studies contained both hypothalamic and adenohypophysial tissue. In mammals, IGF-I can regulate
GH secretion through modulation of hypothalamic fac-
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 elevations 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 controlling GH secretion that are lacking in the in vitro systems.
This may include the changes in plasma IGF-I concentrations, but also other hormones 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 stimulatory eVect on GH secretion in this, and other, Wsh species
(Kaiya et al., 2003; Riley et al., 2002; Unniappan and
Peter, 2004).
In summary, the release of GH from Arctic charr pituitary tissue in vitro was inhibited by both SRIF and hIGFI in both long-term static and short-term perifusion culture. Of particular interest was the ability of hIGF-I to
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 history of the animal, suggesting that if these peptides are
involved in the changes in circulating levels of GH that
are observed as a result of altered nutritional status, it is
not due to changes in pituitary sensitivity to these factors.
Acknowledgments
The thank Mrs. Lucy Lin for her technical assistance
and the staV at the Alma Aquaculture Research Station
for maintenance of research animals. The work was supported by NSERC and OMAF grants to JFL and an
OMAFRA grant to RDM.
References
Berelowitz, M., Szabo, M., Frohman, L.A., Firestone, S., Chu, L., 1981.
Somatomedin-C mediates growth hormone negative feedback by
eVects on both the hypothalamus and the pituitary. Science 212,
1279–1281.
C. Cameron et al. / General and Comparative Endocrinology 141 (2005) 93–100
Blaise, O., Weil, C., Le Bail, P.-Y., 1995. Role of IGF-I in the control of
GH secretion in rainbow trout (Oncorhynchus mykiss). Growth
Regul. 5, 142–150.
Cameron, C., 2003. Nutritional regulation of the somatotropic axis in
Arctic charr, Salvelinus alpinus. Guelph, Canada; University of
Guelph, MSc Thesis, 210 pp.
Cameron, C., Gurure, R., Reddy, K., Moccia, R., Leatherland, J., 2002.
Correlation between dietary lipid: protein ratios and plasma
growth and thyroid hormone levels in juvenile Arctic charr, Salvelinus alpinus (Linnaeus). Aquacult. Res. 33, 383–394.
Cardenas, R., Lin, X., Canosa, L.F., Luna, M., Arámburo, C., Peter,
R.E., 2003. Estradiol reduces pituitary responsiveness to somatostatin (SRIF-14) and down-regulates the expression of somatostatin sst2 receptors in female goldWsh pituitary. Gen. Comp.
Endocrinol. 132, 119–124.
Chang, J.P., Abele, J.T., Van Goor, F., Wong, A.O.L., Neumann, C.M.,
1996. Role of arachidonic acid and calmodulin in mediating dopamine D1- and GnRH-stimulated growth hormone release in goldWsh pituitary cells. Gen. Comp. Endocrinol. 102, 88–101.
Duan, C., 1998. Nutritional and developmental regulation of insulinlike growth factors in Wsh. J. Nutr. 128, 306S–314S.
Duan, C., Plisetskaya, E.M., 1993. Nutritional regulation of insulin-like
growth factor-I mRNA expression in salmon tissues. J. Endocrinol.
139, 243–252.
Falcón, J., Besseau, L., Fazzari, D., Attia, J., Gaildrat, P., Beauchaud,
M., Boeuf, G., 2003. Melatonin modulates secretion of growth hormone and prolactin by trout pituitary glands and cells in culture.
Endocrinology 144, 4648–4658.
Farbridge, K.J., Leatherland, J.F., 1991. The development of a noncompetitive enzyme-linked immunosorbent assay for oncorhynchid
growth hormone using monoclonal antibodies. Gen. Comp. Endocrinol. 83, 7–17.
Farbridge, K.J., Leatherland, J.F., 1992. Temporal changes in plasma
thyroid hormone, growth hormone and free fatty acid concentrations, and hepatic 5⬘-monodeiodinase activity, lipid and protein
content during chronic fasting and re-feeding in rainbow trout
(Oncorhynchus mykiss). Fish Physiol. Biochem. 10, 245–257.
Fruchtman, S., Jackson, L., Borski, R., 2000. Insulin-like growth factor
I disparately regulates prolactin and growth hormone synthesis and
secretion: studies using the teleost pituitary model. Endocrinology
141, 2886–2894.
Fruchtman, S., McVey, D.C., Borski, R.J., 2002. Characterization of
pituitary IGF-I receptors: modulation of prolactin and growth hormone. Am. J. Physiol. Regul. Integr. Comp. Physiol. 283, R468–
R476.
Fukada, H., Ozaki, Y., Pierce, A.L., Adachi, S., Yamauchi, K., Hara, A.,
Swanson, P., DickhoV, W.W., 2004. Salmon growth hormone receptor: molecular cloning, ligand speciWcity, and response to fasting.
Gen. Comp. Endocrinol. 139, 61–71.
Gray, E.S., Kelley, K.M., Law, S., Tsai, R., Young, G., Bern, H.A., 1992.
Regulation of hepatic growth hormone receptors in coho salmon
(Oncorhynchus kisutch). Gen. Comp. Endocrinol. 88, 243–252.
Holloway, A.C., Leatherland, J.F., 1997. The eVects of N-methyl-D,Laspartate and gonadotropin-releasing hormone on in vitro growth
hormone release in steroid-primed immature rainbow trout,
Oncorhynchus mykiss. Gen. Comp. Endocrinol. 107, 32–43.
Holloway, A.C., Leatherland, J.F., 1998. Neuroendocrine regulation of
growth hormone secretion in teleost Wshes with emphasis on the
involvement of gonadal sex steroids. Rev. Fish Biol. Fish. 8, 409–
429.
Holloway, A.C., Sheridan, M.A., Leatherland, J.F., 1997. 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. Gen. Comp. Endocrinol. 106,
407–414.
Huang, Y.-S., Rousseau, K., Le Belle, N., Vidal, B., Burzawa-Gérard,
E., Marchelidon, J., Dufour, S., 1997. Opposite eVects of insulin-like
99
growth factors (IGFs) on gonadotropin (GtH-II) and growth hormone (GH) production by primary culture of European eel
(Anguilla anguilla) pituitary cells. Aquaculture 177, 73–83.
Kaiya, H., Kojima, M., Hosoda, H., Riley, L.G., Hirano, T., Grau, E.G.,
Kangawa, K., 2003. Amidated Wsh ghrelin: puriWcation, cDNA
cloning in the Japanese eel and its biological activity. J. Endocrinol.
176, 415–423.
Kajimura, S., Uchida, K., Yada, T., Hirano, T., Aida, K., Grau, E.G.,
2002. EVects of insulin-like growth factors (IGF-I and -II) on
growth hormone and prolactin release and gene expression in euryhaline tilapia, Oreochromis mossambicus. Gen. Comp. Endocrinol.
127, 223–231.
Kwong, P., Chang, J.P., 1997. Somatostatin inhibition of growth hormone release in goldWsh: possible targets of intracellular mechanisms of action. Gen. Comp. Endocrinol. 108, 446–456.
Lin, X., Peter, R.E., 2001. Somatostatins and their receptors in Wsh.
Comp. Biochem. Physiol. 129B, 543–550.
Lin, X., VolkoV, H., Narnaware, Y., Bernier, N.J., Peyon, P., Peter, R.E.,
2004. Brain regulation of feeding behavior and food intake in Wsh.
Comp. Biochem. Physiol. 126A, 415–434.
Lin, X.-W., Otto, C.J., Peter, R.E., 1998. Evolution of neuroendocrine
peptide systems: Gonadotropin-releasing hormone and somatostatin. Comp. Biochem. Physiol. 119C, 375–388.
Marchant, T.A., Fraser, R.A., Andrews, P.C., Peter, R.E., 1987. The
inXuence of mammalian and teleost somatostatins on the secretion
of growth hormone from goldWsh (Carassius auratus L.) pituitary
fragments in vitro. Regul. Pept. 17, 41–52.
Marchant, T.A., Peter, R.E., 1989. Hypothalamic peptides inXuencing
growth hormone secretion in the goldWsh, Carassius auratus. Fish
Physiol. Biochem. 7, 133–139.
Niiori-Onishi, A., Iwasaki, Y., Mutsuga, N., Oiso, Y., Inque, K., Saito,
H., 1999. Molecular mechanisms of the negative eVect of insulinlike growth factor-I on growth hormone gene expression in MtT/S
somatotroph cells. Endocrinology 140, 344–349.
Pérez-Sánchez, J., Marti-Palanca, H., Le Bail, P.-Y., 1994a. Homologous
growth hormone (GH) binding in gilthead sea bream (Sparus aurata).
EVect of fasting and refeeding on hepatic GH-binding and plasma
somatomedin-like immunoreactivity. J. Fish Biol. 44, 287–301.
Pérez-Sánchez, J., Marti-Palanca, H., Le Bail, P.-Y., 1994b. Seasonal
changes in circulating growth hormone (GH), hepatic GH-binding
and plasma insulin-like growth factor-I immunoreactivity in a
marine Wsh, gilthead sea bream, Sparus aurata. Fish Physiol. Biochem. 13, 199–208.
Pérez-Sánchez, J., Weil, C., Le Bail, P.-Y., 1992. EVects of human insulin-like growth factor-I on release of growth hormone by rainbow
trout (Oncorhynchus mykiss) pituitary cells. J. Exp. Zool. 262,
287–290.
Peng, C., Peter, R.E., 1997. Neuroendocrine regulation of growth hormone secretion and growth in Wsh. Zool. Stud. 36, 79–89.
Pesek, M.J., Sheridan, M.A., 1996. Fasting alters somatostatin binding
to liver membranes of rainbow trout (Oncorhynchus mykiss). J.
Endocrinol. 150, 179–186.
Planas, J.V., Méndez, E., Baños, N., Capilla, E., Navarro, I., Gutiérrez,
J., 2000. Insulin and IGF-I receptors in trout adipose tissue are
physiologically regulated by circulating hormone levels. J. Exp.
Biol. 203, 1153–1159.
Riley, L.G., Hirano, T., Grau, E.G., 2002. Rat ghrelin stimulates
growth hormone and prolactin release in the tilapia, Oreochromis
mossambicus. Zool. Sci. 19, 797–800.
Rousseau, K., Huang, Y.-S., Le Belle, N., Vidal, B., Marchelidon, J.,
Epelbaum, J., Dufour, S., 1997. Long-term inhibitory eVects of
somatostatin and insulin-like growth factor 1 on growth hormone
release by serum-free primary culture of pituitary cells from European eel (Anguilla anguilla). Neuroendocrinology 67, 301–309.
Sato, M., Frohman, L.A., 1993. DiVerential eVects of central and
peripheral administration of growth hormone (GH) and insulinlike 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
133, 793–799.
Shimizu, M., Swanson, P., DickhoV, W.W., 1999. Free and proteinbound insulin-like growth factor-I (IGF-I) and IGF-binding proteins in plasma of coho salmon, Oncorhynchus kisutch. Gen. Comp.
Endocrinol. 115, 398–405.
Straus, D.S., 1994. Nutritional regulation of hormones and growth factors that control mammalian growth. FASEB J. 8, 6–12.
Sumpter, J.P., LeBail, P.-Y., Pickering, A.D., Pottinger, T.G., Carragher, J.F., 1991. The eVect of starvation on growth and plasma
growth hormone concentrations of rainbow trout, Oncorhynchus
mykiss. Gen. Comp. Endocrinol. 83, 94–102.
Unniappan, S., Canosa, L.F., Peter, R.E., 2004. Orexigenic actions of
ghrelin in goldWsh: feeding-induced changes in brain and gut
mRNA expression and serum levels, and responses to central and
peripheral injections. Neuroendocrinology 79, 100–108.
Unniappan, S., Peter, R.E., 2004. In vitro and in vivo eVects of ghrelin
on luteinizing hormone and growth hormone release in goldWsh.
Am. J. Physiol. Integr. Comp. Physiol. 286, R1093–1101.
Weil, C., Carré, F., Blaise, O., Breton, B., Le Bail, P.-Y., 1999. DiVerential eVect of insulin-like growth factor I on in vitro gonadotropin (I
and II) and growth hormone secretions in rainbow trout
(Oncorhynchus mykiss) at diVerent stages of the reproductive cycle.
Endocrinology 140, 2054–2062.
Yamashita, S., Melmed, S., 1986. Insulin-like growth factor I action on
rat anterior pituitary cells: suppression of growth hormone secretion and messenger ribonucleic acid levels. Endocrinology 118,
176–182.