Biol Reprod
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.
Agricola
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.
Biology of Reproduction 66, 1267-1273 (2002)
© 2002 Society for the Study of Reproduction, Inc.

Regular Article

Estradiol Modulation of Growth Hormone Secretion in the Ewe: No Growth Hormone-Releasing Hormone Neurons and Few Somatotropes Express Estradiol Receptor {alpha}1

Niamh Scanlan2,,a, and Donal C. Skinnerb

a Department of Clinical Veterinary Science, University of Bristol, Langford, BS40 5DU, United Kingdom b Department Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Evidence suggests that estrogen modulates growth hormone (GH) release and that GH plays an important role in follicular and ovulatory processes. How estradiol affects GH secretion is unclear. Having verified that there is a coincident surge of GH at the time of the preovulatory LH surge, immunocytochemical studies incorporating high-temperature antigen retrieval were used to determine whether GH-releasing hormone (GHRH) neurons, somatotropes, or both, expressed estrogen receptor {alpha} (ER), in the ewe. Although GHRH neurons were surrounded by many ER cells, they did not express immunocytochemically detectable ERs. In contrast to gonadotropes, in which the majority expressed ERs, few somatotropes were estrogen receptive. These data suggest that estrogen does not act directly on GHRH neurons to influence GH secretion, and any direct effect on pituitary GH release, through the ER{alpha}, may be small.

anterior pituitary, estrogen receptor, growth hormone, growth hormone-releasing hormone, hypothalamic hormones, hypothalamus, luteinizing hormone


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Increasing evidence suggests growth hormone (GH) plays an important role in reproduction. GH is used successfully in the treatment of infertility in humans [1, 2] and data suggest that GH acts as a co-gonadotropin, whereby it enhances the effects of gonadotropins [3]. Furthermore, in hypophysectomized ewes, follicular growth and ovulation were not induced by exogenous gonadotropins unless GH was coadministered [4]. Other reports suggest that GH directly affects [5, 6] gametogenesis, gonadal differentiation, and gonadotropin responsiveness to GnRH [7–9].

Studies in humans have suggested that GH release is elevated around the time of the preovulatory LH surge [10] and that GH secretion is increased in postmenopausal women supplemented with estradiol [11, 12]. Estrogen administration to ovariectomized ewes is also associated with an increase in GH pulse amplitude [13]. Moreover, evidence obtained from sheep suggests that in addition to the estrogen-induced GnRH and thus, LH surges, there is also a concomitant GH surge [14]. Because this singular study did not describe the precise relationship between LH and GH release for the duration of the preovulatory surge, our first study sought to verify its occurrence and determine the temporal relationship.

How estrogen could modulate pituitary GH output remains poorly understood. GH secretion is regulated primarily by two hypothalamic factors, GH-releasing hormone (GHRH) and somatostatin, although the relative importance of these to tonic GH secretion appears to be species-dependant (see [13] for a review). An obvious hypothesis, therefore, is that estrogen acts directly on these neurons to modulate GH release. Studies on the rat [15] and a previous study on the ewe [16] have shown that somatostatin neurons in the periventricular region, which are the major, if not the only source of somatostatin in the hypophyseal portal system [17], do not express the estrogen receptor (ER). However, several studies on other species suggest that there is considerable overlap between regions displaying ER and GHRH immunoreactivity, including those in rats [18, 19], guinea pigs [20, 21], and monkeys [22, 23]. Moreover, a recent study in the male calf reported that estradiol increased GHRH released from perifused hypothalamic slices, but whether this was a direct effect on GHRH neurons was not determined [24]. Perhaps surprisingly, visualization of the location of GHRH neurons in sheep has proved difficult (I.J. Clarke, personal communication; [13, 25]), despite success in numerous other species, and is a fundamental first step toward understanding how steroids influence GHRH release in the sheep. Having determined the distribution of GHRH neurons, our third objective was to determine whether ovine GHRH neurons expressed ER.

There is evidence in sheep [26] and other species [27, 28] including humans [29] that estradiol can act directly on pituitary gonadotropes to augment the amount of gonadotropin secreted in response to a given GnRH stimulus. It is plausible to speculate, therefore, that estradiol may act similarly on somatotropes to augment their response to GHRH. Thus, the final objective of this study was to establish whether somatotropes were estrogen receptive.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Animals

Sexually mature ewes of mixed breed were ovariectomized under anesthesia and a 1-cm long (4.64 mm outside diameter; 3.35 mm inside diameter) Silastic 17ß-estradiol (Sigma, St. Louis, MO) implant was immediately inserted s.c. in the inner aspect of the left forelimb. Ewes were maintained under natural photoperiod, and studies were conducted during the breeding season. At the time of the experiment, two progesterone-releasing implants (CIDR; InterAg, Hamilton, New Zealand) were inserted intravaginally for 10 days. All procedures were carried out in accordance with Home Office License PPL 30/1670 and authorization A37801 of the French Ministry of Agriculture.

Estradiol-Induced LH and GH Surges

Twenty-four hours after the removal of the progesterone implants, LH surges were induced in 3 ewes by s.c. insertion of four 3-cm-long (4.64 mm outside diameter, 3.35 mm inside diameter) Silastic 17ß-estradiol implants in the inner aspect of the left hind limb. This treatment raises circulating estradiol concentrations to peak follicular phase values (approximately 7.1 pg/ml; [30]). Blood samples were collected every 2 h for 30 h starting 9 h after insertion of the estrogen implants, and plasma was stored at -20°C until assayed.

Plasma LH concentrations were determined in duplicate 100-µl aliquots by a double antibody radioimmunoassay and were expressed in terms of National Hormone and Pituitary Program oLH-I-4 (Harbor-UCLA Medical Center, Torrance, CA) as previously described [31]. All samples were assayed in a single assay, and assay sensitivity, defined as 2SD from the zero standard, was 0.12 ng/ml, and the intraassay coefficient of variation was 6.3%. Plasma GH concentrations were estimated in 100-µl aliquots by a double antibody radioimmunoassay and were expressed in terms of National Hormone and Pituitary Program oGH-I-5 as previously described [32]. Assay sensitivity was 1.4 ng/ml, and the intraassay coefficient of variation was 9%.

Tissue Preparation for Immunocytochemistry

For the immunocytochemical studies, ewes (n = 8) were killed 12 h after progesterone removal and, thus, the steroid status was comparable to the early follicular phase of intact animals.

Animals were injected with 25 000 IU heparin, killed by exsanguination by a licensed butcher, and decapitated. Catheters were inserted into both carotid arteries, and the cranial circulation was flushed with 0.5 L of 0.9% NaCl before fixation with 3 L of 4% paraformaldehyde in 0.1 M PBS solution (pH 7.6). Less than 2 min elapsed between the time of death and the start of the perfusion, which was carried out at a rate of 175 ml/min.

The pituitary and a block containing the preoptic area and hypothalamus were dissected out and placed in 4% paraformaldehyde in PBS at 4°C for 24 h. The tissue blocks were subsequently immersed in 40% sucrose in PBS at 4°C until infiltrated. Six identical sets of 60-µm-thick coronal sections (i.e., each section within a set was 360 µm apart from the preceding section) were cut on a freezing microtome from the septum through to the caudal hypothalamus at the level of the mamillary bodies. Pituitary sections were cut at 40 µm. Sections were stored in cryoprotectant [33] at -20°C until immunocytochemistry was performed.

Distribution of GHRH Neurons

Free-floating sections were removed from cryoprotectant and washed in 0.05 M Tris-buffered saline (TBS, pH 7.8), for 5 min. All washes were repeated three times. Antigens were unmasked according to methods described in detail previously [34]. Briefly, sections were boiled for 15 min in high-temperature antigen retrieval solution (pH 6.8; 100°C; Vector Laboratories, Burlingame, CA) and left to cool in the unmasking solution for 20 min. Sections were washed, immersed in 40% methanol/1% H2O2/TBS solution for 10 min, washed, and transferred to 20% normal goat serum/0.1% Triton/TBS for 1 h. Sections were incubated for 48–72 h at 4°C in rabbit polyclonal antisera:anti-human GHRH (1:20 000; Peninsula Laboratories, San Carlos, CA) or anti-rat GHRH (1:2000; a gift from Dr. W. Vale, Salk Institute for Biological Studies). At room temperature, sections were washed, incubated in secondary antiserum (1:300; for 90 min; biotinylated goat anti-rabbit immunoglobulin [Ig] G; Vector), washed, and placed in streptavidin-horseradish peroxidase (1:100; Amersham Pharmacia Biotech, Little Chalfont, U.K.). Visualization of immunoreactivity was performed with diaminobenzidene tetrahydrochloride (DAB) as described [35]. Sections were mounted on gelatinized slides and coverslipped.

Do GHRH Neurons Express ERs?

Sections were treated as above but were first placed in monoclonal rat antiserum raised against the human {alpha}ER (H222, 2 µg/ml; a gift from Dr. A.E. Herbison) and biotinylated secondary anti-rat IgG (1:300; Vector), followed by incubation in Vectastain Elite kit (1:50 for 90 min; Vector). Nuclear immunoreactivity was visualized using nickel-intensified DAB [35]. Sections were washed in TBS, transferred to 40% methanol, 0.3% H2O2 TBS for 10 min to deactivate remaining peroxidases, and then placed in the GHRH antiserum for 48 to 72 h. Cytoplasmic immunoreactivity was visualized with DAB.

Pituitary Immunocytochemistry

ER{alpha} was visualized in pituitary sections from four ewes using the protocol described above for the rat H222 antiserum. Sections were then double-labeled with rabbit polyclonal antisera obtained from the National Hormone and Pituitary Program recognizing either GH (1:20 000) or ßLH (1:5000).

Antibody Specificity and Data Analysis

The specificity of the H222 antibody has been described previously [36]. The specificity of the GHRH antiserum was established by Peninsula Laboratories and displays no cross-reactivity with vasoactive intestinal peptide, secretin, or gastric inhibitory polypeptide. Controls in the current study included omission of primary antibody or preabsorption with synthetic ovine GHRH (500 µg/ml; American Peptide Company, Sunnyvale, CA). No specific immunoreactivity was evident following these treatments.

The location of GHRH-immunoreactive (IR) cells throughout the hypothalamus was determined for each ewe, and the number of GHRH-IR neurons was recorded in each area. The number of GH-IR cells and LH-IR cells and the number expressing ER-IR were counted in three 0.01 mm2 random sites within each pituitary section. The mean was calculated for each ewe and results are expressed as a percentage (mean ± SEM).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
GH Surge

A surge in GH secretion was observed at the time of the estradiol-induced LH surge in all three ewes (Fig. 1). In two ewes, this surge was coincident with the LH surge and in one ewe the GH surge peaked before the LH surge.



View larger version (18K):
[in this window]
[in a new window]
  		FIG. 1. Results from three ewes confirming that at the time of the estradiol-induced LH surge, there is a concomitant GH surge. Note that in the ewe in the top graph, the peak in GH preceded the LH peak

Estrogen Receptor Immunoreactivity

ER-immunoreactive cells were widely distributed in the ovine hypothalamus as described previously [35–38]. Intensively stained ER cells were observed throughout the central and medial aspects of the preoptic area, bordering the third ventricle and the organum vasculosum of the lamina terminalis. ER-IR cells were also found adjoining the anterior hypothalamic area, where there was a distinct cluster of cells evident in the dorsal anterior hypothalamic area. Many ER-IR cells were also found in the arcuate nucleus and lateral region of the ventromedial nucleus. ER-immunoreactivity within the cytoplasm was also found throughout the hypothalamus.

GHRH Immunoreactivity

No specific immunoreactive neurons were evident using the anti-rat GHRH antiserum. In contrast, the anti-human GHRH antibody revealed intensely stained GHRH neurons only in the hypothalamus. These neurons were restricted to the arcuate nucleus and a few were located in the ventromedial aspect of the ventromedial nucleus, extending rostro-caudally but with fewer neurons caudally (Fig. 2). Beaded GHRH-IR fibers were found throughout the hypothalamus but predominantly in the arcuate nucleus/ventromedial nucleus and a dense bed in the external zone of the median eminence.



View larger version (17K):
[in this window]
[in a new window]
  		FIG. 2. Brain drawings of coronal sections rostral to caudal (A–F) through the hypothalamus of a representative ewe showing the location of GHRH-immunoreactive cells. Each dot represents a neuron. Fx, Fornix; mt, mamillary tract; 3V, third ventricle

Although numerous ER-IR cells surrounded GHRH neurons, they did not express ER immunoreactivity (Fig. 3, A–E).



View larger version (110K):
[in this window]
[in a new window]
  		FIG. 3. Photomicrographs of sections double-labeled for ER{alpha} and GHRH. A and B) Medium-powered photomicrographs of numerous ER-immunoreactive cells surrounding GHRH neurons in the arcuate nucleus. C–F) High-powered photomicrographs in the arcuate nucleus showing ER-free GHRH neurons. Bar = 10 µm

Somatotropes and Gonadotropes

ER-IR, GH-IR, and LH-IR cells were distributed throughout the pars distalis of the ovine pituitary. Colocalization studies revealed the majority of LH cells (71.2% ± 2.1%; Fig. 4), whereas few GH cells (4.1% ± 0.8%; Fig. 5) expressed ER.



View larger version (90K):
[in this window]
[in a new window]
  		FIG. 4. A–C) Photomicrographs of pituitary sections double-labeled for ER{alpha} and LH. Arrow notes an LH-immunoreactive cell with no ER{alpha} staining; all other gonadotropes are colocalized with ER{alpha}. Bar = 10 µm



View larger version (122K):
[in this window]
[in a new window]
  		FIG. 5. A–C) Photomicrographs of pituitary sections double-labeled for ER{alpha} and GH, in which the majority of GH-immunoreactive cells do not exhibit ER{alpha} immunoreactivity. Arrow points to a GH-immunoreactive cell with ER{alpha} immunoreactivity; all other GH cells do not express ER{alpha}. *, A somatotrope with an ER{alpha}-immunoreactive nucleus immediately above it. Bar = 10 µm


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study supports an earlier investigation [14], that at the time of the estradiol-induced LH surge, there is a clear concomitant GH surge. It is important that this is the first immunocytochemical study to describe the distribution of GHRH neurons in the sheep and to provide evidence that the effect of estradiol on GH output is not through a direct action on GHRH neurons. Moreover, any direct effect on the somatotrope through the ER{alpha} is likely to be small.

This is the first study reporting the distribution of immunoreactive GHRH neurons in the ewe and, in agreement with several other species; namely, rats [18, 19], guinea pigs [20], mice [39], cats [40], pigs and cows [41], monkeys [22] and humans [42], immunoreactive GHRH perikaryia are restricted to the arcuate and ventromedial nucleus of the hypothalamus. This distribution corresponds to that shown for the GHRH mRNA in the ewe [43].

To our knowledge, this is also the first study in any species to use immunocytochemical methods to determine whether GHRH neurons express ERs. This absence of steroid receptors in GHRH perikaryia agrees with a recent study in the male rat showing no colocalization with androgen receptors [44]. However, our discovery that GHRH neurons do not express ER{alpha} does not concur with an autoradiographic study in the female rat in which up to a third of GHRH neurons in the central portion of the arcuate nucleus were reported to concentrate [3H]estradiol within the nucleus [45]. Although it is possible in the ewe that GHRH neurons express ERß, this is extremely unlikely because ERß mRNA is undetectable in the regions displaying GHRH immunoreactivity [46]. Rather, the absence of ER in GHRH neurons in the ewe, as opposed to the rat, may indicate a possible species difference in how estradiol regulates GH release. In this respect, a recent report showing that up to 70% of GHRH neurons in the adult male rat contained ER{alpha} mRNA [47] supports this conjecture and, as pointed out in a recent review [13], it is important to note that the neuroendocrine regulation of GH release in the rat differs significantly from the sheep and other species, including humans. Alternatively, the different techniques applied to detect the ER in the female rat investigation [45] and our study, may be a contributing factor to the difference between the species. Specifically, in our study, a GHRH neuron that seemed to possess an ER was observed occasionally but, at higher magnification, it was clearly apparent that one side or portion of the stained nucleus lay outside the GHRH neuron and, thus, was not colocalized. It is probable that if autoradiographic analysis had been carried out, it would have yielded a false-positive identification.

It is well documented that estradiol sensitizes gonadotropes to GnRH stimulation [26–29]. This effect appears to be directly on gonadotropes and, in agreement with the present study, several studies have previously reported that ovine gonadotropes express ERs [48, 49]. It is plausible to speculate, therefore, that estradiol may similarly sensitize somatotropes. In the female rat, some studies found that preincubation of pituitary cells with estradiol had no effect on the response of GH to GHRH [50], whereas others have noted a stimulatory effect of estradiol on spontaneous and GHRH-induced GH secretion, as well as an increase in cellular GH content in pituitary cell cultures [51]. Similarly, in male rats, estradiol administration increased baseline plasma GH levels, possibly by exerting its effects directly at the level of the pituitary [52]. In the bovine, pituitary cells were unresponsive to estradiol [24] and in monkeys, estradiol had no effect on somatotrope cultures from adult males and females and juvenile females, but cultures from juvenile males showed increased responsiveness to GHRH [53]. Thus, the extent of the direct influence of estradiol on somatotropes remains controversial and may depend on the sex and prevailing steroidal milieu of an animal. In ewes, the present study revealed that few GH cells contained ER{alpha}, suggesting that any direct modulatory effect of estradiol on the somatotrope at the time of the estradiol-induced LH surge through the ER{alpha}, is likely to be minimal.

An earlier study in the ewe reported that only somatostatin neurons in the ventrolateral region of the ventromedial nucleus contain ER{alpha}, whereas no periventricular region somatostatin neurons colocalize with ER{alpha} [16]. These data concur with research in the rat [15]. Because periventricular somatostatin neurons are the major, if not the only source of somatostatin in the hypophyseal portal system [17], it is unlikely that estradiol directly modulates somatostatin levels in hypophyseal portal blood. However, it is possible that either the periventricular somatostatin neurons are affected indirectly by estradiol through an interneuronal system or that the estradiol-receptive somatostatin neurons in the ventromedial nucleus affect the nearby GHRH perikaryia. These two hypotheses are not mutually exclusive and further research is essential. It is also possible that other GH-releasing peptides, such as the recently identified ghrelin [54], may play a critical role in the regulation of GH secretion by estradiol.

A final point of note is the use of a high-temperature antigen retrieval technique in the current study. If sections were not subjected to this antigen retrieval method, or if sections were simply heated in TBS, then we were unable to visualize GHRH neurons (unpublished observations). McQuaid and colleagues [55] noted that the revelation and intensity of several antigens in the human central nervous system were markedly improved by microwave treatment. At least one recent study [34] has also shown that the immunoreactivity of steroid receptors is significantly increased or entirely dependent upon antigen retrieval. It should be noted, however, that antigen retrieval may have no effect on the ability of an antibody to detect its target antigen (e.g., GnRH [34]) or, possibly, damage or destroy certain antigens. It will be essential therefore to conduct comparative studies between antigen-retrieved and antigen-unretrieved tissue for every antibody if this procedure is used.

In summary, there is increasing evidence that GH plays a critical role in the regulation of reproduction. In sheep and humans, evidence suggests that estradiol augments GH secretion, but the mechanisms are unknown. Taken together with studies on the distribution of ERß in several species [56–58], including sheep [46], indicating that there is little or no overlap with the distribution of GHRH neurons reported in all species described to date [18, 20, 39–42], our study provides compelling evidence that estradiol does not act directly on GHRH neurons to modulate ovine GH release. The present study also suggests that any direct effect of estradiol through the pituitary {alpha}ER on the secretion of GH is likely to be small. Whether GnRH is able to stimulate GH release in the ewe, as it can in the rat [59] and fish [60], or whether the neurons responsible for generating the estradiol-induced GnRH surge are also driving a GHRH surge warrants further investigation.


   ACKNOWLEDGMENTS
 
We are grateful to Dr. A.E. Herbison (Babraham Institute, Cambridge, U.K.) for the ER{alpha} antibody, Dr. A.F. Parlow (National Hormone and Pituitary Program) for the GH and LH antisera, and Dr. W. Vale, Salk Institute for Biological Studies) for the anti-rat GHRH antiserum.


   FOOTNOTES
 
First decision: 28 September 2001.

1 N.S. was funded by a University of Bristol postgraduate studentship. Back

2 Correspondence. FAX: 0117 928 9582; n.scanlan{at}bristol.ac.uk Back

Accepted: November 27, 2001.

Received: September 6, 2001.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Homburg R, Eshel A, Abdalla HI, Jacobs HS. Growth hormone facilitates ovulation induction by gonadotrophins. Clin Endocrinol (Oxf) 1988; 29:113-117[Medline]
  2. Blumenfeld Z, Amit T. The role of growth hormone in ovulation induction. Ann Med 1994; 26:249-254[Medline]
  3. Childs GV. Growth hormone cells as co-gonadotropes: partners in the regulation of the reproductive system. Trends Endocrinol Metab 2000; 11:168-175[CrossRef][Medline]
  4. Eckery DC, Moeller CL, Nett TM, Sawyer HR. Localization and quantification of binding sites for follicle-stimulating hormone, luteinizing hormone, growth hormone, and insulin-like growth factor I in sheep ovarian follicles. Biol Reprod 1997; 57:507-513[Abstract]
  5. Andreani C, Lazzarin N, Pierro E, Lanzone A, Mancuso S. Somatostatin action on rat ovarian steroidogenesis. Hum Reprod 1995; 10:1968-1973[Abstract/Free Full Text]
  6. Kanzahi M, Morris P. Growth hormone regulates steroidogenic acute regulatory protein expression and steroidogenesis in Leydig cell progenitors. Endocrinology 1999; 140:1681-1686[Abstract/Free Full Text]
  7. Hugues J, Torresani T, Herve F, Martin-Pont B, Tamboise A, Santarelli J. Interest of growth hormone-releasing hormone administration for improvement of ovarian responsiveness to gonadotropins in poor responder women. Fertil Steril 1991; 55:945-951[Medline]
  8. Zachmann M. Interrelationships between growth hormone and sex hormones—physiology and therapeutic consequences. Horm Res 1992; 38:1-8
  9. Franks S. Growth hormone and ovarian function. Baillier's Clin Endocrinol Metab 1998; 12:331-340[Medline]
  10. Faria ACS, Bekenstein LW, Booth RA, Vaccaro VA, Asplin CM, Veldhuis JD, Thorner MO, Evans WS. Pulsatile growth hormone release in normal women during the menstrual cycle. Clin Endocrinol 1992; 36:591-596[Medline]
  11. Genazzani A, Gamba O, Nappi L, Volpe A, Petraglia F. Modulatory effects of a synthetic steroid (tibolone) and estradiol on spontaneous and GH-RH-induced GH secretion in postmenopausal women. Maturitas 1997; 28:27-33[CrossRef][Medline]
  12. Friend K, Hartman M, Pezzoli S, Clasey J, Thoner M. Both oral and transdermal estrogen increase growth hormone release in postmenopausal women—a clinical research center study. J Clin Endocrinol Metab 1996; 81:2250-2256[Abstract]
  13. Dutour A, Briard N, Guillaume V, Magnan E, Cataldi M, Sauze N, Oliver C. Another view of GH neuroregulation: lessons from the sheep. Eur J Endocrinol 1997; 136:553-565[Medline]
  14. Landefeld TD, Suttie JM. Changes in messenger ribonucleic acid concentrations and plasma levels of growth hormone during the ovine estrous cycle and in response to exogenous estradiol. Endocrinology 1989; 125:1474-1478[Abstract]
  15. Herbison AE, Theodosis DT. Absence of estrogen receptor immunoreactivity in somatostatin (SRIF) neurons of the periventricular nucleus but sexually dimorphic colocalization of estrogen receptor and SRIF immunoreactivities in neurons of the bed nucleus of the stria terminalis. Endocrinology 1993; 132:1707-1714[Abstract]
  16. Herbison AE. Neurochemical identity of neurones expressing oestrogen and androgen receptors in the sheep hypothalamus. J Reprod Fertil Suppl 1995; 49:371-383
  17. Epelbaum J. Somatostatin in the central nervous system: physiology and pathological modification. Prog Neurobiol 1986; 27:63-100[CrossRef][Medline]
  18. Sawchenko P, Swanson L, Rivier J, Vale W. The distribution of growth hormone-releasing factor (GRF) immunoreactivity in the central nervous system of the rat: an immunohistochemical study using antisera directed against rat hypothalamic GRF. J Comp Neurol 1985; 237:100-115[CrossRef][Medline]
  19. Menchenthaler I, Vigh S, Schally A, Petrusz P. Immunocytochemical localization of growth hormone-releasing hormone in the rat hypothalamus. Endocrinology 1984; 114:1082-1085[Abstract]
  20. Beauvillain J, Tramu G, Mazzuca M. Fine structural studies of growth hormone-releasing factor (GRF)-immunoreactive neurons and their synaptic connections in the guinea pig arcuate nucleus. J Comp Neurol 1987; 255:110-123[CrossRef][Medline]
  21. Brown TJ, Yu J, Gagnon M, Sharma M, MacLusky NJ. Sex differences in estrogen and progestin receptor induction in the guinea pig hypothalamus and preoptic area. Brain Res 1996; 725:37-48[Medline]
  22. Bloch B, Brazeau P, Bloom F, Ling N. Topographical study of the neurons containing hpGRF immunoreactivity in monkey hypothalamus. Neurosci Lett 1983; 37:23-28[CrossRef][Medline]
  23. Herbison AE, Horvath TL, Naftolin F, Leranth C. Distribution of estrogen receptor-immunoreactive cells in monkey hypothalamus: relationship to neurones containing luteinizing hormone-releasing hormone and tyrosine hydroxylase. Neuroendocrinology 1995; 61:1-10[CrossRef][Medline]
  24. Hassan HA, Enright WJ, Tucker HA, Merkel RA. Estrogen and androgen elicit growth hormone release via dissimilar patterns of hypothalmic neuropeptide secretion. Steroids 2001; 66:71-80[CrossRef][Medline]
  25. Polkowska J, Krejci P, Snochowski M. The long-term effect of low protein diet on the somatostatin hypothalamic neuronal system and the pituitary growth hormone cells in growing ewe. Exp Clin Endocrinol Diabetes 1996; 104:59-66
  26. Kaynard AH, Malpaux B, Robinson JE, Wayne NL, Karsch FJ. Importance of pituitary and neural actions of estradiol in induction of the luteinizing hormone surge in the ewe. Neuroendocrinology 1988; 48:296-303[Medline]
  27. Hsueh AJW, Erickson GF, Yen SSC. The sensitizing effect of estrogens and catechol estrogen on cultured primary cells to luteinizing hormone-releasing hormone: its antagonism by progestins. Endocrinology 1979; 104:807-813[Medline]
  28. Colin IM, Jameson JL. Estradiol sensitization of rat pituitary cells to gonadotropin-releasing hormone: involvement of protein kinase C- and calcium-dependent signaling pathways. Endocrinology 1998; 139:3796-3802[Abstract/Free Full Text]
  29. Dumesic DA, Goldsmith PC, Jaffe RB. Estradiol sensitization of cultured human fetal pituitary cells to gonadotropin-releasing hormone. J Clin Endocrinol Metab 1987; 65:1147-1153[Abstract]
  30. Evans NP, Dahl GE, Glover BH, Karsch FJ. Central regulation of pulsatile GnRH secretion by estradiol during the period leading up to the preovulatory GnRH surge in the ewe. Endocrinology 1994; 134:1806-1811[Abstract]
  31. Niswender GD, Reichert LE, Midgley AR, Nalbandov AV. Radioimmunoassay for bovine and ovine luteinizing hormone. Endocrinology 1969; 84:1166-1173[Medline]
  32. Jaffe CA, Huffman BW, Demott-Friberg R. Insulin hypoglycemia and growth hormone secretion in sheep: a paradox revisited. Am J Physiol 1999; 277:E253-E258[Abstract/Free Full Text]
  33. Watson RE, Weigand SJ, Clough RW, Hoffman G. Use of a cryoprotectant to maintain long-term peptide immunoreactivity and tissue morphology. Peptides 1986; 7:155-159[Medline]
  34. Skinner D, Caraty A, Allingham R. Unmasking the progesterone receptor in the preoptic area and the hypothalamus of the ewe; no co-localisation with gonadotropin-releasing neurons. Endocrinology 2001; 142:573-579[Abstract/Free Full Text]
  35. Herbison AE, Robinson JE, Skinner DC. Distribution of estrogen receptor-immunoreactive cells in the preoptic area of the ewe: co-localization with glutamic acid decarboxylase but not luteinizing hormone-releasing hormone. Neuroendocrinology 1993; 57:751-759[Medline]
  36. Lehman MN, Ebling FJP, Moenter SM, Karsch FJ. Distribution of estrogen receptor-immunoreactive cells in the sheep brain. Endocrinology 1993; 133:876-886[Abstract]
  37. Blache D, Batailler M, Fabre-Nys C. Oestrogen receptors in the preoptico-hypothalamic continuum: immunohistochemical study of the distribution and cell density during induced oestrous cycle in ovariectomized ewe. J Neuroendocrinol 1994; 6:329-339[CrossRef][Medline]
  38. Skinner DC, Herbison AE. Effects of photoperiod on estrogen receptor, tyrosine hydroxylase, neuropeptide Y, and ß-endorphin immunoreactivity in the ewe hypothalamus. Endocrinology 1997; 138:2585-2595[Abstract/Free Full Text]
  39. Nurhidayat , Tsukamoto Y, Sigit K, Sasaki F. Sex differentiation of growth hormone-releasing hormone and somatostatin neurons in the mouse hypothalamus: an immunohistochemical and morphological study. Brain Res 1999; 821:309-321[CrossRef][Medline]
  40. Bugnon C, Gouget A, Fellmann D, Clavequin MC. Immunocytochemical demonstration of a novel peptidergic neurone system in the cat brain with an anti-growth hormone-releasing factor serum. Neurosci Lett 1983; 38:131-137[CrossRef][Medline]
  41. Leshin LS, Barb CR, Kiser TE, Rampacek GB, Kraeling RR. Growth hormone-releasing hormone and somatostatin neurons within the porcine and bovine hypothalamus. Neuroendocrinology 1994; 59:251-264[Medline]
  42. Bloch B, Brazeau P, Ling N, Bohlen P, Esch F, Wehrenberg WB, Benoit R, Bloom F, Guillemin R. Immunohistochemical detection of growth hormone-releasing factor in brain. Nature 1983; 301:607-608[CrossRef][Medline]
  43. Henry BA, Rao A, Tilbrook AJ, Clarke IJ. Chronic food-restriction alters the expression of somatostatin and growth hormone-releasing hormone in the ovariectomised ewe. J Endocrinol 2001; 170:R1-R5[Abstract]
  44. Fodor M, Oudejans CB, Delemarre-Van De Waal HA. Absence of androgen receptor in the growth hormone releasing hormone-containing neurones in the rat mediobasal hypothalamus. J Neuroendocrinol 2001; 13:724-727[CrossRef][Medline]
  45. Shirasu K, Stumpf WE, Sar M. Evidence for direct action of estradiol on growth hormone-releasing factor (GRF) in rat hypothalamus: localization of [3H]estradiol in GRF neurons. Endocrinology 1990; 127:344-349[Abstract]
  46. Scott C, Tilbrook A, Simmons D, Rawson J, Chu S, Fuller P, Ing N, Clarke I. The distribution of cells containing estrogen receptor-{alpha} (ER{alpha}) and ERß messenger ribonucleic acid in the preoptic area and hypothalamus of the sheep: comparison of males and females. Endocrinology 2000; 141:2951-2962[Abstract/Free Full Text]
  47. Kamegai J, Tamura H, Shimizu T, Ishii S, Sugihara H, Wakabayashi I. Estrogen receptor (ER){alpha}, not ERß, gene is expressed in the growth hormone-releasing hormone neurons of the male rat hypothalamus. Endocrinology 2001; 142:538-543[Abstract/Free Full Text]
  48. Skinner DC, Herbison AE, Robinson JE. Immunocytochemical identification of oestrogen receptors in the ovine pars tuberalis: localization within gonadotrophs. J Neuroendocrinol 1992; 4:659-662[CrossRef]
  49. Sheng C, McNeilly AS, Brooks AN. Immunohistochemical distribution of oestrogen receptor and luteinizing hormone B subunit in the ovine pituitary gland during foetal development. J Neuroendocrinol 1998; 10:713-718[CrossRef][Medline]
  50. Wehrenberg WB, Baird A, Ying SY, Ling N. The effects of testosterone and estrogen on the pituitary growth hormone response to growth hormone-releasing hormone. Biol Reprod 1985; 32:369-375[Abstract]
  51. Simard J, Hubert J, Hosseinzadeh T, Labrie F. Stimulation of growth hormone release and synthesis by estrogens in rat anterior pituitary cell culture. Endocrinology 1986; 119:2004-2011[Abstract]
  52. Carlsson L, Eriksson E, Seeman H, Jansson J. Oestradiol increases baseline growth hormone levels in the male rat: possible direct action on the pituitary. Acta Physiol Scand 1987; 129:393-399[Medline]
  53. Bethea CL. Estrogen action on growth hormone in pituitary cell cultures from adult and juvenile macaques. Endocrinology 1991; 129:2110-2118[Abstract]
  54. Tannenbaum GS, Bowers CY. Interactions of growth hormone secretagogues and growth hormone-releasing hormone/somatostatin. Endocrine 2001; 14:21-27[CrossRef][Medline]
  55. McQuaid S, McConnell R, McMahon J, Herron B. Microwave antigen retrieval for immunocytochemistry on formalin-fixed, paraffin-embedded post-mortem CNS tissue. J Pathol 1995; 176:207-216[CrossRef][Medline]
  56. Laflamme N, Nappi RE, Drolet G, Labrie C, Rivest S. Expression and neuropeptidergic characterization of estrogen receptors (ERalpha and ERbeta) throughout the rat brain: anatomical evidence of distinct roles of each subtype. J Neurobiol 1998; 36:357-378[CrossRef][Medline]
  57. Shughrue P, Scrimo P, Lane M, Askew R, Merchenthaler I. The distribution of estrogen receptor-beta mRNA in forebrain regions of the estrogen receptor-alpha knockout mouse. Endocrinology 1997; 138:5649-5652[Abstract/Free Full Text]
  58. Pau CY, Pau K-YF, Spies HG. Putative estrogen receptor ß and {alpha} mRNA expression in male and female rhesus macaques. Mol Cell Endocrinol 1998; 146:59-68[CrossRef][Medline]
  59. Penzias AS, Goodman SR, Rossi G, Shamma FN, Aten RF, Behrman HR, Jones EE. Preliminary evidence that GnRH has the properties of a growth hormone-releasing factor in vivo in the rat. J Soc Gynecol Investig 1995; 2:623-629[CrossRef][Medline]
  60. Marchant TA, Chang JP, Nahorniak CS, Peter RE. Evidence that gonadotropin-releasing hormone also functions as a growth hormone-releasing factor in the goldfish. Endocrinology 1989; 124:2509-2518[Abstract]



This article has been cited by other articles:


Home page
 EndocrinologyHome page
M. Iruthayanathan, Y.-H. Zhou, and G. V. Childs
Dehydroepiandrosterone Restoration of Growth Hormone Gene Expression in Aging Female Rats, in Vivo and in Vitro: Evidence for Actions via Estrogen Receptors
Endocrinology, December 1, 2005; 146(12): 5176 - 5187.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
T. Yonezawa, K. Mogi, J. Y. Li, R. Sako, K. Yamanouchi, and M. Nishihara
Modulation of Growth Hormone Pulsatility by Sex Steroids in Female Goats
Endocrinology, June 1, 2005; 146(6): 2736 - 2743.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
G. V. Childs, M. Iruthayanathan, N. Akhter, G. Unabia, and B. Whitehead-Johnson
Bipotential Effects of Estrogen on Growth Hormone Synthesis and Storage in Vitro
Endocrinology, April 1, 2005; 146(4): 1780 - 1788.
[Abstract] [Full Text] [PDF]

Home page
 Biol. Reprod.Home page
D. Pillon, A. Caraty, C. Fabre-Nys, D. Lomet, M. Cateau, and G. Bruneau
Regulation by Estradiol of Hypothalamic Somatostatin Gene Expression: Possible Involvement of Somatostatin in the Control of Luteinizing Hormone Secretion in the Ewe
Biol Reprod, July 1, 2004; 71(1): 38 - 44.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
M. Yan, M. E. E. Jones, M. Hernandez, D. Liu, E. R. Simpson, and C. Chen
Functional Modification of Pituitary Somatotropes in the Aromatase Knockout Mouse and the Effect of Estrogen Replacement
Endocrinology, February 1, 2004; 145(2): 604 - 612.
[Abstract] [Full Text] [PDF]

Home page
 Biol. Reprod.Home page
N. Scanlan, L. Dufourny, and D. C. Skinner
Somatostatin-14 Neurons in the Ovine Hypothalamus: Colocalization with Estrogen Receptor {alpha} and Somatostatin-28(1-12) Immunoreactivity, and Activation in Response to Estradiol
Biol Reprod, October 1, 2003; 69(4): 1318 - 1324.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.
Agricola
Right arrow Articles by Scanlan, N.
Right arrow Articles by Skinner, D. C.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS