| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Department of Anatomy (H.N, K.K) and Department of Neurosurgery (M.K), School of Medicine, Keio University, Tokyo 160, Japan; Department of Regulation Biology (K.I), Faculty of Science, Saitama University, Saitama 338, Japan; Second Department of Internal Medicine (H.M, A.I, S.K), National Defense Medical College, Saitama 359, Japan; and Department of Anatomy (S.H), Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki 305, Japan
Address all correspondence and requests for reprints to: Haruo Nogami, Ph.D., Department of Anatomy, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160, Japan.
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In MtT-S cells (a pituitary cell line established from an estrogen-induced tumor), DEX induced GHRH-R mRNA expression within 2 h in a dose-dependent manner. This induction was augmented by puromycin (100 µM) or cycloheximide (3.5 µM). However, the RNA synthesis inhibitor Actinomycin D (1 µM) completely inhibited GHRH-R mRNA accumulation in response to either DEX or DEX plus puromycin, suggesting that glucocorticoids induce GHRH-R mRNA mainly through stimulation of mRNA transcription.
These results suggest: that GHRH-R mRNA accumulation in the fetal pituitary gland of rats normally occurs at E19, probably because of the direct action of glucocorticoids on the pituitary gland, to stimulate GHRH-R mRNA transcription; and that the expression of glucocorticoid receptors is an important event in GH cell development in rats. Accordingly, immunocytochemical results suggest an increase in glucocorticoid receptors in immature GH cells between E17 and E18. The present results also imply that MtT-S cells may be a good model in which to further study the molecular mechanisms of the regulation of GHRH-R gene expression.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
On the other hand, GH cells are rare in the anterior pituitary gland before E18. They increase in number at E19 (6, 7). Expression of the GHRH receptor (GHRH-R) is a crucial step for the functional maturation of GH cells, because they are thus brought under hypothalamic regulation. The pituitary responds to GHRH by releasing GH, which indicates the presence of GHRH-R. GHRH-induced GH release has been detected by RIA at E18 (8) and by the reverse hemolytic plaque assay at E19 (7). The developmental pattern of GHRH-R mRNA has been studied in mice with in situ hybridization (1, 9). GHRH-R mRNA is first detected at E16.5, when GH mRNA is also first expressed and where GH mRNA and pit-1 mRNA are also detected. In the rat, GHRH-R mRNA expression was demonstrated at E19.5 (10) with an ribonuclease (RNase) protection assay. However, little is known about the mechanisms by which GHRH-R mRNA expression is induced in developing GH cells.
We previously reported that a transient increase in glucocorticoid levels in the fetal circulation, which is probably caused by the increased ACTH secretion at this stage (11), induces GH mRNA expression in pituitary GH cells (12, 13). Because glucocorticoids have been shown to up-regulate GHRH-R mRNA in adult rats (14), we examined in the present study whether the increased levels of glucocorticoids in the fetus induce the expression of GHRH-R mRNA in addition to the expression of GH mRNA. Our data indicate that glucocorticoids play a pivotal role in the induction of GHRH-R mRNA in fetal pituitary GH cells. The role of glucocorticoids in GHRH-R mRNA induction was also examined in MtT-S cells, a clonal cell line established from estrogen-induced pituitary tumor (15). MtT-S cells secrete only GH and display a normal GH cell-like ultrastructure, such as well-developed rough endoplasmic reticulum, Golgi apparatus, and abundant secretory granules that contain immunoreactive GH. Furthermore, they secrete an increased amount of GH in response to GHRH stimulation (15).
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-modification of MEM (MEM ; Gibco BRL, Grand Island,
NY) supplemented with glutamine and antibiotics. The experiments were
carried out in accordance with the animal experimentation guidelines of
Keio University.
MtT-S cell culture
MtT-S cells were grown in DMEM/Ham’s F12 medium (DMEM/F12;
Gibco BRL) containing 10% horse serum, 2.5% FBS, and
antibiotics (control medium). When the cells were grown in
serum-containing medium, the basal level of GHRH-R mRNA expression was
measured. All experiments were carried out after deinduction of mRNA
expression as follows. Approximately 2 x 105 cells
were placed in a 10-cm poly-L-lysin-coated dish with 10 ml
of control medium and were cultured for 10–12 days, with medium
changes every 3 days, after which the medium was replaced with DMEM/F12
containing charcoal-stripped serum (hormone-deficient medium) and
cultured for 4 days. The medium was then replaced with serum-free
DMEM/F12 and cultured for 4 days. The cells were harvested after the
experiments with trypsin digestion and stored at -80 C.
Chemicals
The following chemicals were purchased from Sigma Chemical Co. (St. Louis, MO) and used at the stated concentrations:
dexamethasone (DEX, 0.01 nM–1 µM),
T3 (0.1 nM), estradiol (E2, 10
nM), dibutyryl-cAMP (cAMP, 1 mM), forskolin (1
µM), puromycin (100 µM), cycloheximide (3.5
µM), actinomycin D (1 µM), and all
trans-retinoic acid (RA, 1 µM). GHRH was
purchased from Peptide Institute (Osaka, Japan) and used
at 1 nM.
Complementary RNA (cRNA) probe and RNase protection assay
A 240-bp rat GHRH-R complementary DNA (cDNA) (2–241 from ATG)
(16) was obtained with RT-PCR from the pituitary RNA of adult rats and
cloned into a pBSIISK-plasmid (Stratagene, La Jolla, CA).
The plasmid was linearized with HindIII digestion and
transcribed with T3-polymerase to give a 32P-cRNA
probe (345 b) with -32P-uridine 5'-triphosphate
(ICN Biomedicals, Inc., Costa Mesa, CA). A 125-bp fragment
that encodes most of the sequences of the second exon of the rat GH
gene was isolated from a cloned rat GH gene prepared by Takeuchi
et al. (17) and subcloned into a pGEM4Z plasmid
(Promega Corp., Madison, WI). The plasmid was linearized
with HindIII digestion, and the 32P-labeled cRNA
probe (185 b) was synthesized with SP-6 polymerase. A 221-bp rat pit-1
cDNA (143–363 from ATG) (18) was obtained with RT-PCR from the
pituitary total RNA of adult rats and cloned into the SmaI
site of a pGEM4Z plasmid. The plasmid was linearized with
EcoRI digestion and transcribed with T7-polymerase to give a
cRNA probe (273 b). A 100-bp (483–582 from ATG) (19) fragment of rat
glyceraldehyde-3-phosphate dehydrogenase (GAPDH) cDNA was obtained with
RT-PCR and cloned in pBSIISK-plasmid. The plasmid was linearized
with Xba-I digestion and transcribed with T7 polymerase to give a 295 b
cRNA probe. Sequences of the probes were determined with the dideoxy
chain termination method (20) to confirm identity with the authentic
cDNA sequences. The 32P-labeled RNAs of known length (564,
370, and 185 b) were prepared and used as size markers.
Total RNA was isolated from fetal pituitary glands (3–5 pituitaries were pooled for one assay) or MtT-S cells, as described previously (21), and extracted with phenol/chloroform. The RNA concentration was determined spectrophotometrically, and 6–12 µg fetal pituitary RNA or 20 µg MtT-S RNA was subjected to mRNA determination with the RNase protection assay. Total RNA was dissolved in 20 µl hybridization buffer (400 mM NaCl, 1 mM EDTA, 40 mM piperazine diethanesulfonic acid (pH 6.4), 80% formamide) containing 2 x 104 cpm cRNA probe and incubated at 65 C for 5 min and then at 55 C for 4 h or overnight. After hybridization, 150 µl digestion buffer, composed of 300 mM sodium acetate, 5 mM EDTA, 10 mM Tris-HCl (pH 7.5), containing 10 µg/ml RNase A and 100 U/ml RNase T1 (both from Boehringer Mannheim, Mannheim, Germany), was added to the reaction mixture and incubated for 30 min at 37 C. Then, 2.5 µl proteinase K (Boehringer Mannheim, 20 mg/ml) and 10 µl of 10% sodiumdodecylsulfate was added and incubated at 37 C for an additional 15 min. The protected fragments were precipitated with ethanol and analyzed on an 8% polyacrylamide gel containing 8 M urea. The mRNA level was determined with a BAS2000 image analyzer (Fuji Photo Film Co., Ltd. Film, Tokyo, Japan).
Immunocytochemistry
The pituitary glands obtained from E17–E19 fetuses were fixed
in 10% formalin in 0.1 M phosphate buffer, pH 7.4, and
embedded in paraffin. Five-micrometer thick sections were cut and
placed on glass slides. The sections were heated at 45 C overnight.
Before staining, sections were deparaffinized and irradiated in a
microwave oven for 10 min in 10 mM citrate buffer, pH 6.0.
The sections were then incubated at 4 C overnight with a mixture of
mouse monoclonal antibody to rat glucocorticoid receptor (GCR) (BuGR2,
Affinity Bioreagents, Inc., NJ), and the antisera to rat
pituitary hormones were diluted in PBS (0.85% NaCl in 10
mM phosphate buffer, pH 7.4), containing 0.5% skim milk to
reduce nonspecific reactions. The rabbit antiserum to rat TSH
ß-subunit (TSH-ß) and the guinea-pig antiserum to rat LH
ß-subunit (LH-ß) were gifts from the National Hormone and Pituitary
Program, NIH, MD). The rabbit antirat GH (22) and antiporcine ACTH (23)
were prepared in our laboratory with rat GH B-7 (supplied by the
National Hormone and Pituitary Program) and porcine ACTH (grade II,
Sigma Chemical Co.) as immunogens. The working dilutions
of the antisera were 1:800 (BuGR2), 1:10000 (anti-ACTH, anti-TSH ß,
anti-LH ß, and anti-GH). The sections were rinsed with PBS and
incubated with peroxidase-labeled goat IgG antimouse IgG at 37 C for
1 h. After being washed with PBS, the sections were soaked in
3,3'-diaminobenzidine (DAB) solution (50 mM Tris-HCl, pH
7.5, containing 10 mg/dl DAB, 0.003% hydrogen peroxide) supplemented
by 50 mg/dl ammonium nickel sulfate to stain GCRs blue. After the
coloration, the sections were incubated with peroxidase-labeled goat
IgG antirabbit or guinea-pig IgG at 37 C for 1 h and then soaked
in a DAB solution, without ammonium nickel sulfate, to stain pituitary
hormones brown.
Statistical analyses
The significance of differences of the data was determined with
the Student’s t test or ANOVA followed by the
Student-Newman-Keuls test.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
). GHRH-R mRNA was not detected in
pituitary RNA extracts from E17 or E18 fetuses. GHRH-R mRNA was
detected first at E19 and increased linearly until E21.
|
for 24 h with or without 50 nM DEX
(Fig. 2). Treatment with DEX induced a
small amount of GHRH-R mRNA in the E17 pituitaries but markedly induced
GHRH-R mRNA in E18 pituitaries. In the control experiment, in which
pituitary glands were incubated for the same duration in a medium
without DEX, no GHRH-R mRNA accumulation was noted. The increase in the
GHRH-R mRNA was seen only after incubation with DEX and not after
incubation with either T3 (0.1 nM) or
cAMP (1 mM) (data not shown).
|
). The GHRH-R mRNA level gradually
increased, until 24 h, in the presence of 50 nM DEX.
When E19 pituitaries were incubated in a serum-free medium without DEX,
GHRH-R mRNA levels rapidly decreased to about 13% of the 0 h
value after 24 h. A difference in GHRH-R mRNA levels between
DEX-treated and -untreated pituitaries was observed within 4 h of
the start of incubation.
|
). In this experiment, E19 pituitary
glands were incubated in a serum-free MEM for 8 h. After
incubation, GHRH-R mRNA levels in DEX-treated pituitaries were about
2.5 times higher than those in control cultures. Puromycin (100
µM), a protein synthesis inhibitor, did not affect GHRH-R
mRNA levels when used alone. In our previous experiment, 100
µM puromycin inhibited incorporation of
35S-methionine to an acid insoluble fraction by 87%. When
the pituitaries were incubated with both DEX and puromycin, induction
of GHRH-R mRNA was 40% higher than that of DEX alone. These results
suggest that DEX does not require ongoing protein synthesis to induce
GHRH-R mRNA.
|
). The following experiments were
carried out after deinduction of GHRH-R mRNA. GHRH-R mRNA was induced
24 h after treatment of deinduced MtT-S cells with DEX (50
nM) but was not induced after treatment with either
T3 (0.1 nM), E2 (10
nM), cAMP (1 mM), forskolin (1
µM), or GHRH (1 nM) (Fig. 5A). The mRNA
induction by DEX was dose-dependent (Fig. 5B); the increase in GHRH-R
was observed within 2 h and was followed by a sharp increase in
the mRNA level until 24 h later (Fig. 5C). The characteristics of
GHRH-R mRNA expression in MtT-S cells were similar to those observed in
the fetal pituitary gland.
|
). Treatment of deinduced MtT-S cells
with 50 nM DEX for 6 h induced detectable levels of
GHRH-R mRNA. This induction by DEX was significantly enhanced by
puromycin (100 µM) or cycloheximide (3.5
µM), which inhibit an incorporation of
35S-methionine to an acid insoluble fraction by 87% or
90%, respectively. These inhibitors of protein synthesis alone did not
affect the levels of GHRH-R mRNA. In contrast, actinomycin D (1
µM), an RNA synthesis inhibitor, suppressed the GHRH-R
mRNA responses both to DEX and to DEX-plus-protein synthesis inhibitors
(Fig. 6).
|
). Treatment with RA
increased pit-1 mRNA by 74% in the absence of DEX. DEX increased GH
mRNA by 76% but did not affect the pit-1 mRNA level. cAMP did not
affect pit-1 mRNA or GH mRNA levels under these experimental
conditions. These results indicate that the effect of DEX is specific
for GH mRNA and GHRH-R mRNA expression.
|
), whereas GCR-positive LH or TSH cells
were rarely found in any of the stages examined. On the other hand,
cells in the pituitary gland that were positive for GCR, but not for
ACTH, were increased in number at E18 (Fig. 8B). At E19, many GH cells
appeared, most of which were positive for GCR (data not shown).
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
). Previous reports in mice
have demonstrated that GHRH-R mRNA is first expressed at E16.5,
corresponding to the timing of GH mRNA expression (1, 9). In agreement
with this finding, our present and previous studies (12, 13) in rats
demonstrate that both GH mRNA and GHRH-R mRNA are expressed at
substantial levels on the same gestational day, E19. The simultaneous
expression of both GH mRNA and GHRH-R mRNA lead us to speculate that a
common factor may trigger expression of the two mRNAs in the fetal
pituitary gland.
Our present finding that treatment of E18 pituitaries with DEX for
24 h induced GHRH-R mRNA expression suggests that glucocorticoids
are primary factors required for the initiation of GHRH-R mRNA
expression in the fetal rat pituitary gland (Fig. 2). Because
immunoneutralization of GHRH decreased GHRH-R mRNA levels in the
pituitary gland of neonatal rats, it is conceivable that hypothalamic
GHRH is required to maintain GHRH-R mRNA levels during the neonatal
period (25). However, the present results of in vitro
experiments demonstrate that glucocorticoids initiate GHRH-R mRNA
expression in E18 GH cells in the absence of hypothalamic factors. On
the other hand, it is possible that factors derived from the
hypothalamus or other (as yet, unidentified) factors may be involved in
the rapid elevation of pituitary GHRH-R mRNA levels at E20 and E21.
Because corticosterone circulates from mother to fetus through the
placenta (26, 27), serum glucocorticoid levels are believed to be in an
equilibrium between the maternal and fetal compartments during
gestation. Hence, glucocorticoids are supplied to the developing
pituitary gland long before GHRH-Rs are expressed. However, GHRH-R mRNA
is not expressed until E19. Two explanations for this can be proposed.
One is a unique temporal pattern of development of GCRs in fetal GH
cells. Although GCRs have been shown in the fetal pituitary gland as
early as E15, cellular localization of GCRs has been demonstrated only
in ACTH cells at this stage (28). Little is known about the temporal
pattern of expression of GCRs in GH progenitor cells. The present
immunocytochemical results suggest that extremely few GH cells express
GCRs or that GCRs are expressed at low levels in GH cells at E17. This
may be a reason why pituitary GHRH-R mRNA expression was not detected
at this stage. However, the distinct response of E18 pituitaries to DEX
through the expression of GHRH-R mRNA (Fig. 2) may indicate an increase
in the number of GH cells that express GCRs at this stage, as suggested
by results of immunocytochemical studies. Therefore, another reason
should be proposed for the lack of GHRH-R mRNA expression in the E18
pituitaries in vivo, namely, a change in plasma
corticosterone levels in fetuses during late gestation. Previous
reports indicate that the plasma levels of corticosterone in rats
increase from E17–E19 and decline thereafter (11, 29). This transient
elevation of plasma corticosterone levels in the fetal rat is believed
to be caused by adrenal hyperactivity induced by increased secretion of
ACTH at this stage (11). Our inability to detect GHRH-R mRNA at E18
(Fig. 1) may be caused by circulating corticosterone levels at
this stage being below the threshold necessary to stimulate
GHRH-R mRNA expression.
Accumulating data indicate that GHRH-R gene expression is regulated by
multiple factors in rats. In adult animals and in adult pituitary cells
in primary culture, glucocorticoids and thyroid hormones up-regulate
GHRH-R (30) and its mRNA (31, 32, 33, 34), whereas estrogen down-regulates
GHRH-R mRNA (33). Aleppo et al. (35) found that a reduction
or removal of serum from the culture medium markedly down-regulates
GHRH-R mRNA expression in the pituitary primary culture of rats and
that the addition of DEX to the medium restores mRNA levels. These
results indicate the dependence of basal GHRH-R mRNA expression on
glucocorticoids, which was also observed in this study, in the fetal
pituitary gland and in MtT-S cells (Figs. 3 and 5A). In neonatal rats,
GHRH is required for GHRH-R mRNA expression (25); whereas, in adult
rats, GHRH either down-regulates GHRH-R mRNA expression as an acute
effect (35) or up-regulates GHRH-R mRNA expression by chronic
stimulation (36). The cAMP that mediates GHRH activity in GH cells has
also been shown to stimulate GHRH-R mRNA expression in primary culture
of the adult pituitary gland (36).
However, little is known about factors regulating GHRH-R mRNA
expression during the functional development of fetal GH cells. In the
present study, we examined the effect of T3,
E2, cAMP, forskolin, GHRH, and DEX on GHRH-R mRNA levels.
Only DEX affected GHRH-R mRNA levels in fetal pituitaries and MtT-S
cells (Fig. 5). Although glucocorticoids might be required for general
GH cell functions, the results shown in Fig. 7 do not support this
possibility. RA was found to increase pit-1 mRNA levels in the E19
pituitary gland in the absence of glucocorticoids, in agreement with a
previous study in pituitary cell lines (37). On the other hand, DEX
enhanced expression of both GH mRNA and GHRH-R mRNA but did not affect
expression of pit-1 mRNA. Thus, the effect of glucocorticoids seems to
be specific for the expression of GH mRNA and GHRH-R mRNA. It is
unknown why several factors that have been shown to stimulate GHRH-R
mRNA expression in the adult rat are ineffective in the fetal pituitary
gland or in MtT-S cells. Only the direct effects of these factors on
GHRH-R mRNA expression were observed in the present in vitro
study. Glucocorticoids might act directly at the pituitary level,
whereas in vivo, other factors might act indirectly. Another
explanation for this inconsistency is that the regulatory mechanisms of
GHRH-R mRNA may differ among the various developmental stages.
Petersenn et al. (38) examined regulatory regions of the
human GHRH-R gene and demonstrated, through transient expression
studies, that transcription of the human GHRH-R gene is significantly
enhanced by glucocorticoids. Although they were unable to find the
consensus glucocorticoid response element in a 2-kb upstream region of
the human GHRH-R gene, their results suggest the presence of
unidentified positive glucocorticoid response elements within this
region. Lin et al. (9) demonstrated that pit-1 is required
for the stimulation of rat GHRH-R gene transcription in
vitro. The present results showed, however, that the effect of DEX
on GHRH-R mRNA expression was not mediated by the increased expression
of pit-1 (Fig. 7). The molecular basis of glucocorticoid effects on
GHRH-R mRNA expression is still unclear.
To examine the mechanisms of glucocorticoid regulation of GHRH-R mRNA
expression, we studied the effects of protein synthesis inhibitors and
an RNA synthesis inhibitor. Puromycin unexpectedly enhanced the effect
of DEX, both in fetal pituitary glands and in MtT-S cells. In contrast,
actinomycin D clearly inhibited the effect of DEX, suggesting that the
primary effect of DEX is the stimulation of GHRH-R gene transcription
(Fig. 6). These results are similar to those of Miller and Mayo (14) in
cultured pituitary cells of adult rats. Unfortunately, we were unable
to demonstrate any effect of actinomycin D on the fetal pituitary
because this metabolic inhibitor induced progressive cell death in our
tissue fragments.
Another possible cause of the increase in the pituitary GHRH-R mRNA level is an increase by glucocorticoids in the population of preexisting GHRH-R mRNA-expressing cells between E18 and E19. However, recent studies by Porter and colleagues (39, 40) do not support this supposition. They showed, by reverse hemolytic plaque assay in chicken embryo, that glucocorticoids markedly increase the number of GH cells in the pituitary gland at E12, when only a few GH cells are normally present (39, 40). The effect of glucocorticoids was not blocked by a mitosis inhibitor; and less than 10% of GH cells, newly differentiated in response to glucocorticoids, were labeled with 3H-thymidine (39). These results suggest that glucocorticoids do not stimulate proliferation of GH cells.
Finally, it seems worthwhile to note the effects of puromycin on
glucocorticoid-induced GHRH-R mRNA accumulation. Puromycin and
cycloheximide, which inhibit protein synthesis, enhanced the effects of
DEX on GHRH-R mRNA accumulation in MtT-S cells but had little effect on
the level of GHRH-R mRNA when used without DEX (Fig. 6). These findings
suggest the possibility that an unknown protein facilitates degradation
of GHRH-R mRNA. Because GHRH-R mRNA undergoes rapid degradation in the
absence of glucocorticoids, as seen in E19 pituitaries (Fig. 3),
suppression of degradation would significantly increase GHRH-R mRNA
levels. Another possibility is that a protein suppresses transcription
of the GHRH-R gene. The down-regulation of this type of suppressor
would result in the activation of transcription.
In summary, the present results suggest that: 1) glucocorticoids induce GHRH-R mRNA expression in the fetal pituitary gland, as previously demonstrated in adult tissues (33, 34, 35, 36), and that this may be the normal mechanism responsible for the onset of GHRH-R mRNA expression in immature GH cells in the fetus; and 2) GHRH-R mRNA induction by glucocorticoids is caused by stimulation of mRNA transcription.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
Received October 16, 1998.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
 |
|
 |
|
  A. T. McElvaine, A. I. Korytko, S. M. Kilen, L. Cuttler, and K. E. Mayo Pituitary-Specific Expression and Pit-1 Regulation of the Rat Growth Hormone-Releasing Hormone Receptor Gene Mol. Endocrinol., August 1, 2007; 21(8): 1969 - 1983. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. H. Y. Kwok, Y. Wang, C. Y. Wang, and F. C. Leung Cloning of Chicken Glucocorticoid Receptor (GR) and Characterization of its Expression in Pituitary and Extrapituitary Tissues Poult. Sci., February 1, 2007; 86(2): 423 - 430. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. M Luque, M. D Gahete, R. J Valentine, and R. D Kineman Examination of the direct effects of metabolic factors on somatotrope function in a non-human primate model, Papio anubis. J. Mol. Endocrinol., August 1, 2006; 37(1): 25 - 38. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. E. Porter, L. E. Ellestad, A. Fay, J. L. Stewart, and I. Bossis Identification of the Chicken Growth Hormone-Releasing Hormone Receptor (GHRH-R) mRNA and Gene: Regulation of Anterior Pituitary GHRH-R mRNA Levels by Homologous and Heterologous Hormones Endocrinology, May 1, 2006; 147(5): 2535 - 2543. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Nogami, Y. Hiraoka, K. Ogasawara, S. Aiso, and S. Hisano The role of pit-1 in the regulation of the rat growth hormone-releasing hormone receptor gene transcription by glucocorticoids J. Mol. Endocrinol., December 1, 2005; 35(3): 477 - 488. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C Mogi, H Goda, K Mogi, A Takaki, K Yokoyama, M Tomida, and K Inoue Multistep differentiation of GH-producing cells from their immature cells J. Endocrinol., January 1, 2005; 184(1): 41 - 50. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Ozawa, F. Han, and M. Kawata Exocytosis sensitivity to growth hormone-releasing hormone in subsets of GH cells in rats under different corticosterone conditions. Ultrastructural study using microwave irradiation for fixation and immunocytochemistry J. Endocrinol., December 1, 2004; 183(3): 507 - 515. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. P. Mohammad, R. A. Abbud, A. F. Parlow, J. S. Lewin, and J. H. Nilson Targeted Overexpression of Luteinizing Hormone Causes Ovary-Dependent Functional Adenomas Restricted to Cells of the Pit-1 Lineage Endocrinology, October 1, 2003; 144(10): 4626 - 4636. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Nogami, Y. Hiraoka, M. Matsubara, E. Nonobe, T. Harigaya, M. Katayama, N. Hemmi, S. Kobayashi, K. Mogi, S. Aiso, et al. A Composite Hormone Response Element Regulates Transcription of the Rat GHRH Receptor Gene Endocrinology, April 1, 2002; 143(4): 1318 - 1326. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. M. Lasko, A. I. Korytko, W. B. Wehrenberg, and L. Cuttler Differential GH-releasing hormone regulation of GHRH receptor mRNA expression in the rat pituitary Am J Physiol Endocrinol Metab, April 1, 2001; 280(4): E626 - E631. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Nogami, M. Matsubara, T. Harigaya, M. Katayama, and K. Kawamura Retinoic Acids and Thyroid Hormone Act Synergistically with Dexamethasone to Increase Growth Hormone-Releasing Hormone Receptor Messenger Ribonucleic Acid Expression Endocrinology, December 1, 2000; 141(12): 4396 - 4401. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Bossis and T. E. Porter Ontogeny of Corticosterone-Inducible Growth Hormone-Secreting Cells during Chick Embryonic Development Endocrinology, July 1, 2000; 141(7): 2683 - 2690. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
) 50
nM DEX, for the duration indicated. Sizes of the marker
RNAs were indicated to the left. The representative
autoradiogram (exposed for 10 days) was shown, in which 8 µg of the
total RNA was used. The amount of GHRH-R mRNA was normalized for GAPDH
mRNA, and the results were expressed as percent of 0 h value
(mean ± SEM, n = 3). *, P <
0.05; NS, not significant vs. without DEX, by the
Student’s t test.
