Distribution of immunoreactive growth hormone-releasing hormone in the human brain and intestine and its production by tumors

Acromegaly Caused by Ectopic Growth Hormone Releasing Hormone Secretion: A Review

INTRODUCTION

Ectopic acromegaly is a rare condition caused most frequently by growth hormone releasing hormone (GHRH) secretion from neuroendocrine tumors. The diagnosis is often difficult to establish as its main symptoms do not differ from those of acromegaly of pituitary origin.

OBJECTIVES

To determine most common clinical features and diagnostic challenges in ectopic acromegaly.

PATIENTS AND METHODS

A search for ectopic acromegaly cases available in literature was performed using PubMed, Cochrane, and MEDline database. In this article, 127 cases of ectopic acromegaly described after GHRH isolation in 1982 are comprehensively reviewed, along with a summary of current state of knowledge on its clinical features, diagnostic methods, and treatment modalities. The most important data were compiled and compared in the tables.

RESULTS

Neuroendocrine tumors were confirmed in 119 out of 121 patients with histopathological evaluation, mostly of lung and pancreatic origin. Clinical manifestation comprise symptoms associated with pituitary hyperplasia, such as headache or visual field disturbances, as well as typical signs of acromegaly. Other endocrinopathies may also be present depending on the tumor type. Definitive diagnosis of ectopic acromegaly requires confirmation of GHRH secretion from a tumor using either histopathological methods or GHRH plasma concentration assessment. Hormonal evaluation was available for 84 patients (66%) and histopathological confirmation for 99 cases (78%). Complete tumor resection was the main treatment method for most patients as it is a treatment of choice due to its highest effectiveness. When not feasible, somatostatin receptor ligands (SRL) therapy is the preferred treatment option. Prognosis is relatively favorable for neuroendocrine GHRH-secreting tumors with high survival rate.

CONCLUSION

Although ectopic acromegaly remains a rare disease, one should be aware of it as a possible differential diagnosis in patients presenting with additional symptoms or those not responding to classic treatment of acromegaly.

Paraneoplastic endocrine syndromes

The majority of neoplasms are responsible for symptoms caused by mass effects to surrounding tissues and/or through the development of metastases. However, occasionally neoplasms, with or without endocrine differentiation, acquire the ability to secrete a variety of bioactive substances or induce immune cross-reactivity with the normal tissues that can lead to the development of characteristic clinical syndromes. These syndromes are named endocrine paraneoplastic syndromes when the specific secretory components (hormones, peptides or cytokines) are unrelated to the anticipated tissue or organ of origin. Endocrine paraneoplastic syndromes can complicate the patient's clinical course, response to treatment, impact prognosis and even be confused as metastatic spread. These syndromes can precede, occur concomitantly or present at a later stage of tumour development, and along with the secreted substances constitute the biological 'fingerprint' of the tumour. Their detection can facilitate early diagnosis of the underlying neoplasia, monitor response to treatment and/or detect early recurrences following successful initial management. Although when associated with tumours of low malignant potential they usually do not affect long-term outcome, in cases of highly malignant tumours, endocrine paraneoplastic syndromes are usually associated with poorer survival outcomes. Recent medical advances have not only improved our understanding of paraneoplastic syndrome pathogenesis in general but also enhanced their diagnosis and treatment. Yet, given the rarity of endocrine paraneoplastic syndromes, there is a paucity of prospective clinical trials to guide management. The development of well-designed prospective multicentre trials remains a priority in the field in order to fully characterise these syndromes and provide evidence-based diagnostic and therapeutic protocols.

Acromegaly induced by ectopic secretion of GHRH: a review 30 years after GHRH discovery

Ectopic acromegaly is very rare and since the discovery of growth hormone-releasing hormone (GHRH), 30 years ago, only 74 cases have been reported in the literature. Except for a recent French series of 21 cases, most of them were case reports. The present review summarizes the current knowledge on clinical presentation, diagnosis and prognosis. Tumors secreting GHRH are neuroendocrine tumors, usually well differentiated and mainly from pancreatic or bronchial origin. They are usually large and easy to localize using TDM and somatostatin receptor scintigraphy. Clinical presentation is an acromegaly of variable intensity, whose features are similar to that of a somatotropic adenoma. Pituitary may be normal or enlarged at MRI which may be difficult to interpret especially in MEN1 patients where the association of a microprolactinoma to a pancreatic tumor secreting GHRH may be misleading. GHRH plasmatic measurement has an excellent specificity for the diagnosis, using a threshold of 250 to 300ng/L and is a good tool for follow-up of patients after treatment. These tumors have a good overall prognosis, even in metastatic forms which represent 50% of cases. Surgical approach is recommended and, when a complete tumoral resection is feasible, results, in most patients, in long-lasting remission. In such cases, GHRH concentration is normalized and its increase is an accurate indicator of recurrence. In uncured patients, somatostatin analogs control GH secretion but inhibit, only partially, GHRH secretion. MEN1 mutation should be systematically investigated in patients with a pancreatic tumor.

Clinical characteristics and outcome of acromegaly induced by ectopic secretion of growth hormone-releasing hormone (GHRH): a French nationwide series of 21 cases

CONTEXT

Ectopic GHRH secretion is a rare cause of acromegaly, and case reports are mainly isolated.

SETTING

From the registry of the sole laboratory performing plasma GHRH assays in France, we identified cases of ectopic GHRH secretion presenting with acromegaly between 1983 and 2008.

PATIENTS

Twenty-one patients aged 14-77 yr were identified from 12 French hospitals. Median GHRH was 548 (270-9779) ng/liter.

MAIN OUTCOME MEASURES

Outcome measures included description of tumor features and outcome and the relation between plasma GHRH values and tumor site, size, and spread.

RESULTS

The primary neuroendocrine tumor was identified for 20 of 21 patients (12 pancreatic, seven bronchial, one appendicular). Tumors were large (10-80 mm), identified on computed tomography scan in 18 cases and by endoscopic ultrasound and somatostatin receptor scintigraphy in two. Somatostatin receptor scintigraphy had a similar sensitivity to computed tomography scan (81 vs. 86%). Tumors were all well differentiated; 47.6% had metastasized at the time of diagnosis of acromegaly. After a median follow-up of 5 yr, 85% of patients were alive. Ninety-one percent of patients whose tumor was completely removed were considered in remission, and most had normalized plasma GHRH. The remaining patients were treated with somatostatin analogs: IGF-I normalized except for one patient who required pegvisomant, but GHRH levels remained elevated. No correlations were found between GHRH levels and tumor site or size or the existence of metastases. Identification of increased plasma GHRH during follow-up was an accurate indicator of recurrence.

CONCLUSIONS

The prognosis of endocrine tumors responsible for GHRH secretion appears relatively good. Plasma GHRH assay is an accurate tool for diagnosis and follow-up.

A role for central nervous growth hormone-releasing hormone signaling in the consolidation of declarative memories

Contributions of somatotropic hormonal activity to memory functions in humans, which are suggested by clinical observations, have not been systematically examined. With previous experiments precluding a direct effect of systemic growth hormone (GH) on acute memory formation, we assessed the role of central nervous somatotropic signaling in declarative memory consolidation. We examined the effect of intranasally administered growth hormone releasing-hormone (GHRH; 600 µg) that has direct access to the brain and suppresses endogenous GHRH via an ultra-short negative feedback loop. Twelve healthy young men learned word-pair associates at 2030 h and were administered GHRH and placebo, respectively, at 2100 h. Retrieval was tested after 11 hours of wakefulness. Compared to placebo, intranasal GHRH blunted GH release within 3 hours after substance administration and reduced the number of correctly recalled word-pairs by ∼12% (both P<0.05). The impairment of declarative memory consolidation was directly correlated to diminished GH concentrations (P<0.05). Procedural memory consolidation as examined by the parallel assessment of finger sequence tapping performance was not affected by GHRH administration. Our findings indicate that intranasal GHRH, by counteracting endogenous GHRH release, impairs hippocampal memory processing. They provide first evidence for a critical contribution of central nervous somatotropic activity to hippocampus-dependent memory consolidation.

Neuroendocrine tumors secreting growth hormone-releasing hormone: Pathophysiological and clinical aspects

Hypothalamic GHRH is secreted into the portal system, binds to specific surface receptors of the somatotroph cell and elicits intracellular signals that modulate pituitary GH synthesis and/or secretion. Moreover, GHRH is synthesized and expressed in multiple extrapituitary tissues. Excessive peripheral production of GHRH by a tumor source would therefore be expected to cause somatotroph cell hyperstimulation, increased GH secretion and eventually pituitary acromegaly. Immunoreactive GHRH is present in several tumors, including carcinoid tumors, pancreatic cell tumors, small cell lung cancers, endometrial tumors, adrenal adenomas, and pheochromocytomas which have been reported to secrete GHRH. Acromegaly in these patients, however, is uncommon. The distinction of pituitary vs. extrapituitary acromegaly is extremely important in planning effective management. Regardless of the cause, GH and IGF-1 are invariably elevated and GH levels fail to suppress (<1 microg/l) after an oral glucose load in all forms of acromegaly. Dynamic pituitary tests are not helpful in distinguishing acromegalic patients with pituitary tumors from those harbouring extrapituitary tumors. Plasma GHRH levels are usually elevated in patients with peripheral GHRH-secreting tumors, and are normal or low in patients with pituitary acromegaly. Unique and unexpected clinical features in an acromegalic patient, including respiratory wheezing or dyspnea, facial flushing, peptic ulcers, or renal stones sometimes are helpful in alerting the physician to diagnosing non pituitary endocrine tumors. If no facility to measure plasma GHRH is available, and in the absence of MRI evidence of pituitary adenoma, a CT scan of the thorax and abdominal ultrasound could be performed to exclude with good approximation the possibility of an ectopic GHRH syndrome. Surgical resection of the tumor secreting ectopic GHRH should be the logical approach to a patient with ectopic GHRH syndrome. Standard chemotherapy directed at GHRH-producing carcinoid tumors is generally unsuccessful in controlling the activated GH axis. Somatostatin analogs provide an effective option for medical management of carcinoid patients, especially those with recurrent disease. In fact, long-acting somatostatin analogs may be able to control not only the ectopic hormonal secretion syndrome, but also, in some instances, tumor growth. Therefore, although cytotoxic chemotherapy, pituitary surgery, or irradiation still remain available therapeutic options, long-acting somatostatin analogs are now preferred as a second-line therapy in patients with carcinoid tumors and ectopic GHRH-syndrome.

A mouse with targeted ablation of the growth hormone-releasing hormone gene: a new model of isolated growth hormone deficiency

The proliferation of pituitary somatotroph cells and the synthesis and secretion of GH are under the stimulatory control of the hypothalamic peptide GHRH. GHRH is initially synthesized as pre-prohormone and then enzymatically cleaved to its mature form (44 amino acids in humans and 42 in mice). Although mutations in the GHRH receptor cause isolated GH deficiency (IGHD) both in humans and mice, mutations in the GHRH gene have never been described. To determine the consequences of generalized lack of GHRH, we have created a mouse with targeted disruption (knockout) of the GHRH gene (GHRHKO). We have substituted a portion of the gene that encodes for the initial 14 amino acids of the 1-42 GHRH with a neomycin resistance cassette. Heterozygous founder (+/-) mice were mated to obtain -/- animals. The expected Mendelian ratio was conserved (25.8% of offspring were +/+, 52.8% were +/-, and 21.4% were -/-), showing no lethality in the GHRHKO embryos. GHRHKO mice appeared normal at birth. Starting at 3 wk of age, -/- mice showed significant growth retardation. By 12 wk of age, their weight was about 60% of +/+ and +/- littermates. Growth retardation was due to IGHD, as shown by reduced pituitary GH mRNA and protein content, reduced serum IGF-I, and reduced liver IGF-I mRNA. The phenotype of the GHRHKO mice is similar to the one observed in the mouse with mutated GHRH receptor, including pituitary hypoplasia. Heterozygous mice had normal growth, although adult +/- males (but not females) had mild reduction in serum IGF-I. In conclusion, we demonstrate that ablation of the GHRH gene causes IGHD in mice. The GHRHKO mouse will be the new useful model of IGHD.

GH-RH antagonist (MZ-4-71) inhibits VEGF secretion and proliferation of murine endothelial cells

Angiogenesis plays a key role in solid tumor formation, invasiveness and metastasis. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen that is necessary in the process of neovascularisation. Antagonists of growth hormone-releasing hormone (GH-RH) have been shown to suppress both in vivo and in vitro growth and metastasis of many human cancer cell lines. The mechanisms that mediate the antitumorigenic actions of these antagonists involve direct and indirect pathways, but are not completely elucidated. We have examined the effect of GH-RH antagonist MZ-4-71 on proliferation activity and VEGF release from cultured murine endothelial cells HECa10 in vitro. MZ-4-71 at 10(-8) to 10(-6) M concentrations inhibited the proliferative activity of cultured cells and suppressed the release of VEGF into supernatants of 72 h endothelial cell cultures. To our knowledge this is the first study reporting antiangiogenic properties of GH-RH antagonists.

The expression of growth hormone-releasing hormone (GHRH) and splice variants of its receptor in human gastroenteropancreatic carcinomas

Splice variants (SVs) of receptors for growth hormone-releasing hormone (GHRH) have been found in primary human prostate cancers and diverse human cancer cell lines. GHRH antagonists inhibit growth of various experimental human cancers, including pancreatic and colorectal, xenografted into nude mice or cultured in vitro, and their antiproliferative action could be mediated in part through SVs of GHRH receptors. In this study we examined the expression of mRNA for GHRH and for SVs of its receptors in tumors of human pancreatic, colorectal, and gastric cancer cell lines grown in nude mice. mRNA for both GHRH and SV(1) isoform of GHRH receptors was expressed in tumors of pancreatic (SW1990, PANC-1, MIA PaCa-2, Capan-1, Capan-2, and CFPAC1), colonic (COLO 320DM and HT-29), and gastric (NCI-N87, HS746T, and AGS) cancer cell lines; mRNA for SV(2) was also present in Capan-1, Capan-2, CFPAC1, HT-29, and NCI-N87 tumors. In proliferation studies in vitro, the growth of pancreatic, colonic, and gastric cancer cells was stimulated by GHRH(1-29)NH(2) and inhibited by GHRH antagonist JV-1-38. The stimulation of some gastroenteropancreatic cancer cells by GHRH was followed by an increase in cAMP production, and GHRH antagonist JV-1-38 competitively inhibited this effect. Our study indicates the presence of an autocrine/paracrine stimulatory loop based on GHRH and SV(1) of GHRH receptors in human pancreatic, colorectal, and gastric cancers. The finding of SV(1) receptor in human cancers provides an approach to an antitumor therapy based on the blockade of this receptor by specific GHRH antagonists.

Ectopic secretion of growth hormone-releasing hormone (GHRH) in neuroendocrine tumors: relevant clinical aspects

The aim of this article is to briefly review the physiology of growth hormone-releasing hormone (GHRH) and the diagnosis and treatment of GHRH-mediated acromegaly. Moreover, the role of GHRH and its antagonists in the pathogenesis and treatment of cancer will be reviewed. Hypothalamic GHRH is secreted into the portal system, binds to specific surface receptors of the somatotroph cell and elicits intracellular signals that modulate pituitary GH synthesis and/or secretion. GHRH-producing neurons have been well characterized in the hypothalamus by immunostaining techniques. Hypothalamic tumors, including hamartomas. choristomas, gliomas. and gangliocitomas. may produce excessive GHRH with subsequent GH hypersecretion and resultant acromegaly. GHRH is synthesized and expressed in multiple extrapituitary tissues. Excessive peripheral production of GHRH by a tumor source would therefore be expected to cause somatotroph cell hyperstimulation and increased GH secretion. The structure of hypothalamic GHRH was infact elucidated from material extracted from pancreatic GHRH-secreting tumors in two patients with acromegaly. Immunoreactive GHRH is present in several tumors, including carcinoid tumors, pancreatic cell tumors, small-cell lung cancers, adrenal adenomas, and pheochromocitomas which have been reported to secrete GHRH. Acromegaly in these patients. however, is uncommon. In a retrospective survey of 177 acromegalic patients only a single patient was identified with elevated plasma GHRH levels. Measuring GHRH plasma levels therefore provides a precise and cost-effective test for the diagnosis of ectopic acromegaly. Peripheral GHRH levels are not elevated in patients with hypothalamic GHRH- secreting tumors, supporting the notion that excess eutopic hypothalamic GHRH secretion into the hypophyseal portal system does not appreciably enter the systemic circulation. Elevated circulating GHRH levels, a normal or small-size pituitary gland, or clinical and biochemical features of other tumors known to be associated with extrapituitary acromegaly, are all indications for extrapituitary imaging. An enlarged pituitary is, however, often found on MRI of patients with peripheral GHRH-secreting tumors, and the radiologic diagnosis of a pituitary adenoma may be difficult to exclude. Surgical resection of the tumor secreting ectopic GHRH should reverse the hypersecretion of GH, and pituitary surgery should not be necessary in these patients. Nonresectable, disseminated or reccurrent carcinoid syndrome with ectopic GHRH secretion can also be managed medically with long-acting somatostatin analogs (octreotide and lanreotide). The presence of GHRH and its receptors in several extrahypothalamic tissues, including ovary, testis and the digestive tract, suggests that GHRH may have a regulatory role in these tissues. As previously mentioned, biologically or immunologically active GHRH and mRNA encoding GHRH have been found in several human malignant tumors. including cancers of the breast, endometrium and ovary and their cell lines. The synthesis and evaluation of analogs with various modifications revealed that certain hydrophobic and helix-stabilizing amino acid substitutions can produce antagonists with increased GH releasing inhibitory potencies and GHRH receptor-binding affinities in vitro. The review of experimental results of these substances are promising altrough no clinical data are yet available. Finally, the advent of these antagonists has allowed significant progress in the understanding of the role of the central and tissue GHRH-GH-IGFs system in the pathogenesis of tumors.

Human uterine and ovarian expression of growth hormone-releasing hormone messenger RNA in benign and malignant gynecologic conditions

OBJECTIVE

To determine uterine and ovarian expression of growth hormone-releasing hormone (GHRH) messenger RNA (mRNA) in benign and pathologic gynecologic states.

DESIGN

Case-control study.

SETTING

Tertiary-care academic department.

PATIENT(S)

Women undergoing hysterectomy for benign or malignant gynecologic conditions.

INTERVENTION(S)

Ovarian and uterine tissue was obtained for measurement of GHRH mRNA levels by reverse transcription polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

Levels of GHRH mRNA in normal tissues were compared with those in tissues with pathologic abnormalities.

RESULT(S)

Growth hormone-releasing hormone mRNA was detectable in the ovary, endometrium, myometrium, fallopian tubes, and placenta. Levels of GHRH mRNA were significantly increased in secretory endometrium compared with proliferative endometrium. Hormone replacement therapy did not affect endometrial GHRH mRNA levels. Uterine myomas expressed similar levels of GHRH mRNA as normal myometrium. No changes in endometrial GHRH mRNA were detected in endometrial cancers compared with normal endometrium or myometrium obtained from the same patient; however, these levels were higher than those in noncancerous myometrial tissue obtained from other patients with benign gynecologic disease. In ovarian tissue, no differences in GHRH mRNA were found between premenopausal and postmenopausal women. Ovarian GHRH mRNA was significantly decreased in endometriotic cysts, whereas significantly greater GHRH expression occurred in ovarian cancer compared with normal ovarian tissue.

CONCLUSION(S)

Endometrial and ovarian GHRH gene transcription are altered in selective physiologic and pathologic states and are influenced by such factors as ovarian hormones. Because it is a growth factor, GHRH may promote endometrial proliferation and may be involved in the pathogenesis of ovarian and endometrial cancer and endometriosis.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Structure and function of the growth-hormone-releasing hormone receptor

Growth-hormone-releasing hormone (GHRH) stimulates growth hormone (GH) secretion and GH synthesis and is also thought to cause somatotroph proliferation. Specific high-affinity binding sites for GHRH have been demonstrated on pituitary membranes using iodinated GHRH analogs. The complementary DNA encoding for the human GHRH receptor (GHRH-R) was recently cloned. The open reading frame was shown to extend 1269 bp and thus to encode a protein of 423 amino acids with a predicted molecular weight of 47 kDa. Expression is restricted to specific tissues. Analysis of the genomic structure revealed that the human GHRH-R gene spans 15 kb and consists of 13 exons. The 5'-flanking region of the human GHRH-R gene was recently characterized. Transcriptional regulation of the GHRH-R is discussed in this review. Mechanisms of signal transduction for control of GH transcription and secretion are presented. Furthermore, the role of the GHRH-R in proliferation and differentiation of the somatotrophic pituitary cell as well as in disease is examined.

Antagonists of growth hormone-releasing hormone arrest the growth of MDA-MB-468 estrogen-independent human breast cancers in nude mice

Since antagonists of growth hormone-releasing hormone (GH-RH) inhibit proliferation of various tumors, in this study we investigated the effects of GH-RH antagonists MZ-5-156 or JV-1-36 on growth of estrogen-independent MDA-MB-468 human breast cancers xenografted into nude mice. Both GH-RH antagonists administered at a dose of 20 microg/day induced regression of some and growth-arrest of other tumors, while control tumors continued to grow. After 5 weeks of therapy with MZ-5-156 or JV-1-36, final volume and weight of MDA-MB-468 tumors were significantly decreased (all p values < 0.001) and serum IGF-I levels as well as tumor IGF-I mRNA expression were reduced as compared with controls. High affinity binding sites for IGF-I were detected by the ligand binding method. Gene expression of human IGF-I receptors, as measured by the RT-PCR, was not significantly different in control and treated MDA-MB-468 tumors. In cell culture, IGF-I did not stimulate, GH-RH slightly stimulated, while MZ-5-156 and JV-1-36 inhibited proliferation of MDA-MB-468 cells known to possess defective insulin and IGF-I receptor signaling. The expression of mRNA for human GH-RH was found in five of 8 tumors treated with GH-RH antagonists, and in one of the five control tumors. These results suggest that GH-RH antagonists inhibit MDA-MB-468 breast cancers possibly through mechanisms involving interference with locally produced GH-RH.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Tissue-specific molecular heterogeneity of human growth hormone-releasing hormone receptor protein

A site-directed anti-peptide antibody (anti-hGHRHRc18) was generated against the cytoplasmic tail of human GHRH receptor. The dissociation constant (Kd) and the antibody binding site (AbT) of anti-hGHRHRc18 were 2.5 nmol/l and 0.54 nmol/l, respectively. In an immunoblotting experiment, affinity-purified anti-hGHRHRc18 specifically recognized a single 50-kDa protein in human pituitary. In a screening of the expression of GHRH receptor protein in extra-pituitary tissues, only human kidney showed a single 52-kDa protein. Our results suggest that the GHRH receptor protein exhibits tissue-specific molecular heterogeneity.

Pituitary adenylate cyclase activating polypeptide (PACAP)-like immunoreactivity in pheochromocytomas

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel hypothalamic peptide consisting of 38 amino acids [PACAP(1-38)] with a potent stimulatory action on adenylate cyclase in rat pituitary. The presence of immunoreactive (IR-) PACAP in the tumor tissue of pheochromocytomas was studied by radioimmunoassay and immunocytochemistry. The antibody to PACAP was raised in a rabbit injected with a peptide containing amino acids 28-38 of PACAP. This antibody showed no significant cross-reactivity with either PACAP(1-27) or vasoactive intestinal polypeptide. The tumor tissue concentrations of IR-PACAP(1-38) were 0.5-57.5 pmol/g wet weight (n = 13) (24.5 +/- 22.4 pmol/g wet weight, mean +/- SD), while those in the normal adrenal glands were 3.58 +/- 2.02 pmol/g wet weight (n = 7) and those in the adrenal cortical tumors were 5.58 +/- 2.02 pmol/g wet weight (n = 6). The IR-PACAP(1-38) concentrations in 7 out of 13 pheochromocytomas exceeded 18 pmol/g wet weight. Sephadex G-50 column chromatography revealed that the IR-PACAP(1-38) in extracts of pheochromocytomas eluted in both the positions of PACAP(1-38) and a larger molecular weight. Reverse-phase high performance liquid chromatography of the tumor extracts revealed a peak in the position of PACAP(1-38) and at least four other peaks. Immunocytochemistry of pheochromocytomas showed numerous immunoreactive cells. The immunostaining was abolished by absorption of the antiserum with synthetic PACAP(1-38). These findings indicate that multiple forms of IR-PACAP(1-38) are present in pheochromocytomas.

The function of the hypothalamo-pituitary axis in brain dead patients

In order to find out the function of the hypothalamo-pituitary axis in brain dead patients, pituitary and hypothalamic hormone concentrations were measured and several anterior pituitary releasing tests were carried out in 39 brain dead patients. In addition, cerebral blood flow measurements were simultaneously performed. In almost all cases, the blood concentration of pituitary and hypothalamic hormones were above the sensitivity of the assay. Anterior pituitary releasing tests indicated that efficient functions of the hypothalamus were severely suppressed, while the normal secretory mechanism of the anterior pituitary was partially preserved in brain dead patients. Histological changes of hypothalamic neurons varied from barely detectable ghost cells to nearly normal cells even in the same case. Although, the remaining circulation seemed not to be sufficient enough to maintain integrated hypothalamo-pituitary function, as shown by the examinations of cerebral blood flow, the presence of hypothalamic hormones in the systemic circulation suggests that these hormones were released and carried from the hypothalamus by minimal flow which is preserved even after the diagnosis of brain death.

Immunochemiluminometric assays (ICMA) specific for growth hormone releasing hormone 1-44 NH2 and 1-40 OH

We describe specific two-site immunochemiluminometric assays able to directly measure human growth hormone-releasing hormone 1-44 NH2 and 1-40 OH concentrations in unextracted plasma. A common N-terminal antibody was purified from polyclonal rabbit antisera to growth hormone-releasing hormone 1-44 NH2 on a growth hormone-releasing hormone 1-29 NH2 linked affinity column and labelled with chemiluminescent acridinium ester. C-terminal specific monoclonal antibodies to growth hormone-releasing hormone 1-44 NH2 and 1-40 OH were raised in Balb/C mice and used as solid phase antibodies. Assay of fasting specimens from normal individuals gave medians (and ranges) of 23 pg/ml (2-200) and 30 pg/ml (3-134) for growth hormone-releasing hormone 1-44 NH2 and 1-40 OH, respectively. Samples from a series of acromegalics showed that most have values in the normal range though median values were higher, 56 pg/ml for growth hormone-releasing hormone 1-44 NH2 (P < 0.001) and 52 pg/ml for 1-40 OH (P < 0.001). Using these assays it will be possible for the first time to directly study the physiology and pathophysiology of these two peptides.

Interleukin-6 and corticotrophin-releasing hormone mRNA are modulated during differentiation of human neuroblastoma cells

Two cell clones [BE(2)-C and BE(2)-M17] derived from the human neuroblastoma cell line SK-N-BE(2) express corticotrophin-releasing hormone as well as interleukin-6 mRNA. Both genes are overexpressed, although with a different time course, following exposure to 5 microM retinoic acid, in parallel to the induction of neuroblastic differentiation. On the contrary, we are unable to detect interleukin-1 beta mRNA in these cell lines. Both cytokines are known to increase hypothalamic CRH mRNA. The production of cytokines and neuropeptides by neuroblastoma cells indicate a complex dialogue between tumour cells and anti-tumour immunity.

Effects of hypothalamic peptides on the aging brain

The hypothalamic peptide hormones, TRH, LHRH (GnRH), CRH, GHRH, and GHIRH (somatostatin), influence the release of the anterior pituitary hormones, which in turn promote the release of target endocrine gland hormones and other metabolites. These latter compounds feed back to the brain to help control the secretion of the hypothalamic hormones. This is a dynamic interaction that is influenced by the aging process: Most of these hormones systems become less responsive with advancing age, due to decreased function of peptide-containing secretory neurons, a loss of hormone receptor sensitivity, and/or a reduction in the output of the target endocrine glands. That the hypothalamic peptides themselves can influence brain function is supported by the fact that most are found in areas of the brain other than the hypothalamus and that receptors for them exist in these other areas. For example, CRH is contained in a number of central neural systems that can influence behavior, including limbic areas, the hypothalamus, locus coeruleus, median raphé nuclei, and cortical interneurons. CRH has been shown to be anxiogenic in animal models, and its effect can be blocked by CRH receptor antagonists. CRH content in the locus coeruleus is particularly increased by stress and may influence norepinephrine neurotransmitter function in this structure. In aging there is a gradual reduction of the sensitivity of the brain to the negative feedback of corticosteroids, such that CRH secretion becomes somewhat increased under basal conditions. The behavioral effects of this change are unclear, however, as is the influence of stress-related activation of CRH, ACTH, and glucocorticoid secretion on behavior in the elderly. Other hypothalamic peptides have different patterns of change with aging, and some are markedly altered in pathological conditions; for example, in Alzheimer's disease the content of CRH and somatostatin in certain brain areas is decreased. However, whether the changes in hypothalamic peptides precede or follow the pathological behavioral changes, and how they participate in the changes, is still unclear.

Secretion of growth hormone releasing hormone in obese children

We have evaluated baseline and l-dopa-stimulated peripheral growth hormone releasing hormone (pGHRH) secretion in 6 obese pre-pubertal children and in 7 age-matched controls. Baseline pGHRH levels were no different between obese (36.6 +/- 9.8 pg/ml, mean +/- SE) and control children (40.6 +/- 10.1 pg/ml). Administration of l-dopa (500 mg po) caused a significant increase of pGHRH levels in both the obese (65.3 +/- 19.8 pg/ml, p less than 0.05) and the control children (84.1 +/- 10.0 pg/ml, p less than 0.003). Mean peak pGHRH levels after l-dopa were not significantly different between the two groups, whereas mean peak GH levels were significantly lower (p less than 0.05) in the obese (7.9 +/- 1.9 ng/ml) than in the control children (20.5 +/- 4.9 ng/ml). We conclude that despite reduced GH secretion, obese children have normal baseline and l-dopa stimulated pGHRH levels.

Morphological and functional alterations of the hypothalamic-pituitary system in brain death with long-term bodily living

Hypothalamic hormones as well as anterior pituitary hormones were detected in the peripheral plasma after the diagnosis of brain death. It is possible that residual hypothalamic tissue was functioning after satisfying the usual criteria of total brain death. To examine this possibility, endocrinological and morphological alterations of the hypothalamic-pituitary system was evaluated in 28 brain dead patients. Intrinsic ADH was depleted in the plasma shortly after the diagnosis of brain death. Anterior pituitary hormones were initially detected in all patients, but gradually disappeared. The direct TRH (thyrotropin releasing hormone) stimulation to the anterior lobe was responded to well. Morphological studies showed a partial necrosis of the anterior lobe and the preservation of the posterior lobe for as long as a week. These data prove that the pituitary is partially preserved after brain death. LH-RH (luteinizing hormone releasing hormone) was detected in the peripheral plasma of all patients and GRF (growth hormone releasing factor) was detected in half of the patients for as long as 15 days, but autopsy revealed the fact that the brain tissue including the hypothalamus became extensively necrotic after the sixth day of brain death. In order to solve this controversy it is proposed that these hormones originate from extracranial tissues such as pancreas. The detection of hypothalamic hormones after the diagnosis of brain death therefore is not contradictory to the concept of total brain death.

Stimulatory effect of free fatty acids on growth hormone releasing hormone secretion by fetal rat neurons in monolayer culture

The effects of free fatty acids (FFAs) on growth hormone releasing hormone (GHRH) secretion by fetal rat cortical and hypothalamic neurons in monolayer culture have been investigated. Treatment with caprylic or oleic acids for 90 min, induced a dose-dependent increase in GHRH secretion. The stimulatory effect of caprylic acid was time-dependent, being present after 90 min and 5 h but not after 24 h. Finally, GHRH release induced by 56 mM KCl or by the calcium ionophore A23187 was not modified by 5 x 10(-3) M caprylic acid. These data support a role for FFAs on GHRH secretion.

Expression of the rat growth hormone-releasing hormone gene in placenta is directed by an alternative promoter

Growth hormone-releasing hormone (GHRH) is a hypothalamic peptide that plays a critical role in controlling the synthesis and secretion of growth hormone by the anterior pituitary. GHRH has also been detected in other nonneural extrahypothalamic tissues, including rat placenta, although its role in the hormonal control of pregnancy and/or fetal development has not yet been defined. Here we present the isolation and characterization of cDNA clones corresponding to rat placental GHRH. The placental GHRH mRNA codes for a pre-pro-GHRH identical to that found in the hypothalamus, suggesting that the mature placental GHRH is identical to its hypothalamic counterpart. Nevertheless, the placental and the hypothalamic GHRH mRNAs differ in the region corresponding to the untranslated exon 1 because of the use of an alternative promoter in the placenta located 10 kilobases upstream from the hypothalamic promoter. A combined mechanism involving the use of tissue-specific alternative promoters and the differential splicing of exon 1 generates the mature GHRH transcript in placenta and hypothalamus. Multiple transcription initiation sites have been found in the placental GHRH mRNA, which correlates to the lack of a consensus TATA box in the promoter region.

Plasma growth hormone (GH)-releasing hormone levels in patients with lung carcinoma

OBJECTIVE

The aim was to investigate the serum levels of growth hormone releasing hormone and GH in patients with lung carcinoma. DESIGN After an overnight fast a plasma sample was collected for determination of growth hormone releasing hormone and GH.

PATIENTS

The investigation was performed in 28 patients with non small cell lung carcinoma, in 44 patients with small cell lung carcinoma, and 10 patients with non malignant lung disease. A group of 37 normal subjects served as control.

MEASUREMENTS

Growth hormone releasing hormone and GH were determined by radioimmunoassay.

RESULTS

Patients with small cell lung carcinoma showed higher plasma growth hormone releasing hormone levels (49 +/- 9.4 ng/l) than control subjects (16.3 +/- 2.1 ng/l; P less than 0.05), patients with non small cell lung carcinoma (23.9 +/- 8.8 ng/l; P less than 0.05), and patients with non malignant lung disease (12.7 +/- 5.5; P less than 0.05). Basal GH level was lower than 5 micrograms/l in all patients except five patients with small cell lung carcinoma and one patient with non small cell lung carcinoma.

CONCLUSIONS

The higher plasma growth hormone releasing hormone levels in patients with small cell lung carcinoma compared to normal controls and patients with non small cell lung carcinoma and patients with non malignant lung disease, confirm the frequent neuroendocrine activity of this particular tumour.

Elevated adrenocorticotropic hormone and cortisol levels in a patient with medullary carcinoma of the thyroid containing ectopic immunoreactive corticotropin-releasing hormone and bombesin

Pituitary adrenocorticotropic hormone-dependent Cushing's syndrome due to ectopic production of corticotropin-refeasing hormone (CRH) or bombesin (gastrin-releasing peptide) is an extremely rare cause of pituitary adrenocorticotropic hormone (ACTH) hypersecretion. We report a patient with elevated ACTH and cortisol levels due to ectopic secretion of both bombesin and CRH by metastatic medullary carcinoma of the thyroid (MCT). A 45-year-old man was investigated because of diabetes insipidus and visual field disturbances due to suprasellar metastasis of the MCT. On physical examination, he was a chronically ill man with a body mass index of 18.5 and was darkly pigmented but without other features typical of Cushing's syndrome. Hypogonadotropic hypogonadism, thyroid-stimulating hormone (TSH) deficiency, and hyperprolactinemia were due to pituitary stalk disorder, in light of these deficiencies, we were surprised to find elevated plasma ACTH, cortisol, and growth hormone (GH) levels throughout the day. Plasma ACTH at 9AM was 118 pg/ml and plasma cortisol was 859 nmol/L. At 12PM, ACTH was 89 pg/ml whereas plasma cortisol was 540 nmol/L. Urinary 17 OH CS were elevated (38 nmol/24 hr). The mean of the four-point day curve for GH was elevated. Plasma electrolytes were normal. The presence of both CRH and bombesin was documented by immunocytologic studies in the metastases (lymph node and suprasellar biopsy). ACTH was not found in any of the metastases. Because of the close proximity of the suprasellar metastasis to the portal pituitary circulation, CRH and bombesin could have been readily provided to the pituitary corticotrophs.

Corticotropin-releasing hormone, luteinizing hormone-releasing hormone, growth hormone-releasing hormone, and somatostatin-like immunoreactivities in biopsies from breast cancer patients

The presence of immunoreactive adrenocorticotropin-releasing hormone (CRH), luteinizing hormone-releasing hormone (LHRH), growth hormone-releasing hormone (GHRH), and somatostatin has been investigated by immunohistochemistry in forty biopsies from breast cancer patients. All of these hypothalamic hormones were found in about 30% of the samples, seen in the cytoplasm or in the nuclei of the tumor cells. Positive immunostaining for the hypothalamic hormones was present in colloid, lobular, and infiltrating ductal carcinomas. There was not a clear relationship between occurrence of staining for the hypothalamic hormones and the histologic grade of tumors or the clinical stage of the disease. Immunoreactive LHRH was more frequently found in breast tumors with estrogen and progesterone receptors. On the other hand, preneoplastic breast lesions expressed mainly somatostatin, while immunoreactivity was absent in normal mammary tissue.

The growth hormone releasing hormone (GHRH) response to a mixed meal is blunted in young adults with insulin-dependent diabetes mellitus whereas the somatostatin response is normal

Following a standard mixed meal, plasma concentrations of growth hormone releasing hormone (GHRH), somatostatin (SMS) and growth hormone (GH) were measured every 30 min for 300 min in six young adults with type I insulin-dependent diabetes mellitus (IDDM) and five normal controls. Mean blood glucose concentrations were higher and mean free insulin levels lower in the diabetics compared with controls both in fasting specimens and at all times following the mixed meal. Basal concentrations (mean +/- SEM) of GHRH were similar in diabetic (12.7 +/- 1.8 pg/ml) and control subjects (11.8 +/- 1.1 pg/ml). Following ingestion of the mixed meal, a rise in GHRH was observed in the control subjects maximal between 30 and 240 min (P less than 0.025) but the response was blunted in the diabetics. Mean GHRH concentrations were greater in the controls than in the diabetic subjects at all stages during the test, the maximum difference being noted at 120 mins (P less than 0.04). Basal SMS concentrations and those observed after the mixed meal were similar in diabetic and control subjects. These results indicate that glucose and insulin may play a role in the regulation of GHRH release following a mixed meal but circulating levels of GHRH and SMS are unlikely to be relevant to the abnormal regulation of GH in IDDM.

Calcitonin gene-related peptide-like immunoreactivities in pheochromocytomas

Calcitonin gene-related peptide (CGRP) is reported to exist in high concentrations in plasma and tumor tissues of medullary thyroid carcinomas. CGRP-like immunoreactivity (LI) in tumor tissues of pheochromocytomas was investigated by radioimmunoassay. CGRP-LI in 9 pheochromocytomas ranged from 0.50 to 1240 ng/g wet tissue. Sephadex G-50 column chromatography revealed that most of CGRP-LI in tumor extracts was eluted in an identical position to synthetic human CGRP. Reverse-phase high pressure liquid chromatography revealed that CGRP-LI in tumor extracts was eluted in an identical position to synthetic human CGRP and in a more hydrophobic position. These results indicate that high concentrations of CGRP-LI also exist in tumor tissues of pheochromocytomas.

Plasma growth hormone-releasing hormone levels in type 1 (insulin-dependent) diabetic children following a mixed meal

Following a mixed meal, plasma hormone responses were measured in four type 1 diabetic children and in eight short normal children. Between 60 and 150 min after ingestion of the mixed meal there was a significant increase in circulating growth hormone-releasing hormone values both in diabetic and in normal children. Mean plasma GHRH peak values were not different between diabetic patients (27.0 +/- 3.9 ng/l) and controls (24.6 +/- 4.9 ng/l). No time relationship to spontaneous growth hormone peaks was observed. Whereas normal children showed a characteristic biphasic plasma somatostatin response, somatostatin plasma levels in diabetic children did not change. In normal children plasma insulin values increased between 30 and 150 min, but remained unchanged in type 1 diabetic patients. Blood glucose response was more pronounced in diabetic children than in short normal children. These results indicate that circulating growth hormone-releasing hormone does not play a dominant role in the regulation of insulin and somatostatin.

Resolution of acromegaly after removal of a bronchial carcinoid shown to secrete growth hormone releasing factor

A 29 year old woman with an enlarged pituitary fossa and classical acromegaly, possibly present for ten years, had biochemical and partial somatic resolution of the disorder after removal of a bronchial carcinoid tumour. In addition, galactorrhea stopped, menstruation returned after two years, and amenorrhea and elevated prolactin levels fell towards normal. Immunocytochemistry showed numerous growth hormone releasing factor (GRF) staining cells in the tumour. The tumour cells, when cultured, produced a supernatant selectivity stimulating human pituitary somatotrophic cell cultures to produce growth hormone (GH). The bronchial carcinoid did not secrete detectable GH, but extracts of it, and preoperative serum contained GRF immunoreactivity which coeluted with synthetic human pancreatic GRF.

Growth hormone releasing hormone

Human growth hormone releasing hormone (GHRH) was originally extracted from two pancreatic tumours in patients with acromegaly, and is now known to consist of a 44 residue amidated peptide or its C-terminal-shortened derivatives. The sequence of rat GHRH has also been determined; this 43 residue peptide shows approximately 70% homology with human GHRH, and is located mainly in the arcuate nucleus of the hypothalamus. Pulsatile GH release in the rat is principally a consequence of the pulsatile release of hypothalamic GHRH, although this appears to be associated with a transient suppression of somatostatin release. Exogenous GHRH specifically increases circulating GH in many species, and in the long term may increase growth. In normal man, several analogues of GHRH have been shown to be safe, sensitive and specific stimuli to GH release; although there may be a variable prolactin response, this is usually of small magnitude. Continuous infusion of GHRH leads to a decrement in responsiveness, due at least in part to changes in hypothalamic somatostatin. The GH response to GHRH is also modulated by obesity, blood sugar, free fatty acids, and GH itself. Many children with 'GH deficiency' (idiopathic, radiation-induced, or secondary to hypothalamopituitary tumours) respond to intravenous GHRH with an acute rise in serum GH. Early studies also indicate that long-term therapy with subcutaneous GHRH may increase growth velocity in some of these children. It is concluded that analogues of GHRH are useful in the investigation of the hypothalamopituitary axis, and may be important in the therapy of short stature.

Production and secretion of immunoreactive growth hormone-releasing factor by pheochromocytomas

The production and secretion of immunoreactive growth hormone-releasing factor (IR-GRF) by pheochromocytomas were examined immunohistochemically and immunochemically. GRF-immunoreactive (GRF-IR) cells were found, although sparsely, in 2 of 13 tumors (Cases 1 and 2), while somatostatin (SRIF)-IR cells and vasoactive intestinal peptide (VIP)-IR cells were found in nine and five tumors, respectively. Concentrations of tissue IR-GRF of 29.8 and 17.2 ng/g wet weight tissue, respectively, were found in two (Cases 1 and 2) of three tumors examined. These three tumors also contained IR-SRIF at 19.5-105.5 ng/g wet weight tissue and IR-VIP at 13.6-24.8 ng/g wet weight tissue. An increased plasma IR-GRF concentration (30.0 pg/ml) was found in a blood sample taken from the inferior vena cava near the adrenal tumor in Case 1. This is the first report that some pheochromocytomas produce GRF and secrete it into the blood circulation.

Normal circulating immunoreactive growth hormone releasing factor (hGRF) concentrations in patients with functional hypothalamic hGRF deficiency

Using a highly specific radioimmunoassay we have measured the concentrations of human growth hormone releasing factor (ir-hGRF) in the peripheral circulation of six individuals with acquired hypothalamic hGRF deficiency. Despite their hypothalamic dysfunction venous plasma ir-hGRF increased normally in every patient after the stimulus of a mixed breakfast, from an average concentration basally of 13.6 +/- 6.0 pg/ml to a maximum of 29.0 +/- 8.4 pg/ml (mean +/- SEM) at 120 min. The findings indicate that circulating hGRF is at least in large part extrahypothalamic in origin, which in turn implies a physiological role for hGRF in the periphery.

Growth hormone releasing factor-like immunoreactivity in human milk

The presence of immunoreactive growth hormone-releasing factor (GRF) in human milk has been demonstrated. By using sequential high performance liquid chromatography, it has been shown that most of the immunoreactivity co-elutes with the synthetic, hypothalamic-like, GRF (1-40). The concentrations of GRF detected (between 152 and 432 pg GRF/ml milk) exceed several fold its values in plasma.

Growth hormone-releasing factor (somatocrinin) stimulates epithelial cell proliferation in the rat digestive tract

The possible influence of growth hormone-releasing factor (GHRF) on epithelial cell proliferation in the digestive tract was investigated. Fasted young rats received five hourly subcutaneous injections of either GHRF or saline. They were killed 6, 12, or 18 h after the initial injection and 45 min after [3H]thymidine pulse labeling. At the time of death, blood was taken to determine circulating growth hormone and gastrin levels. After radioautography, DNA synthetic and mitotic activities were estimated in the fundic, antral, duodenal, jejunal, and colonic mucosae. Growth hormone-releasing factor significantly increased labeling indices 6, 12, and 18 h after the initial injection in fundic mucosa, and 6 and 18 h after injection in antral and duodenal mucosae. Furthermore, GHRF significantly increased mitotic indices at 12 h in fundic mucosa and at 12 and 18 h in jejunal mucosa. No effect was seen in the colon. At the three checkpoint times, circulating growth hormone showed no change, but plasma gastrin was increased in the rats treated with GHRF as compared with controls. However, whether the reported stimulatory effect of the GHRF on target cells is direct or indirect remains to be determined.

Effect of vasoactive intestinal peptide, peptide histidine isoleucine and growth hormone-releasing factor-40 on bombesin-like immunoreactivity, somatostatin and gastrin release from the perfused rat stomach

Bombesin-like immunoreactivity (BLI) has been demonstrated in neurons of the gastrointestinal tract and gastric BLI secretion can be demonstrated in response to the classical neurotransmitter acetylcholine. Since structurally related peptides VIP, PHI and GRF have to be considered as peptidergic neurotransmitters it was of interest to determine their effect on gastric BLI secretion. Additionally, somatostatin (SLI) and gastrin secretion was examined. The isolated stomach of overnight fasted rats was perfused with Krebs-Ringer buffer via the celiac artery and the effluent was collected via the portal vein. The gastric lumen was perfused with isotonic saline at pH7 or pH2. All four peptides were tested at a dose of 10(-11) M and 10(-8) M at both pH levels and in addition the effect of VIP and PHI was examined at 10(-14) M and 10(-12) M during luminal pH2. At luminal pH7 VIP and PHI stimulated SLI release at 10(-8) M but had no effect on BLI or gastrin secretion. rGRF and hpGRF were both ineffective on SLI and gastrin release while rGRF inhibited and hpGRF stimulated BLI secretion. This effect was not dose related. At luminal pH2 all four peptides stimulated BLI secretion. Stimulation by PHI was already observed at a dose of 10(-14) M while VIP elicited a stimulatory effect at 10(-12) M. PHI at the two lowest concentrations of 10(-14) and 10(-12) M elicited a stimulation of SLI and gastrin release while the same doses of VIP and the higher doses of all four peptides had no effect on SLI and gastrin secretion at an acidic intraluminal pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretin receptor activity in rat gastric glands. Binding studies, cAMP generation and pharmacology

We measured 125I-secretin binding to membranes prepared from rat fundic glands and compared the abilities of natural and synthetic secretin (SN) analogs to inhibit 125I-secretin binding and to activate the cAMP generating system in glandular and subcellular preparations from the fundus and antrum. The natural peptides structurally related to porcine secretin (pSN) included: chicken secretin (cSN), vasoactive intestinal peptide (VIP), porcine peptide with N-terminal histidine and C-terminal isoleucine amide (PHI), helodermin, growth hormone releasing factors isolated from the rat hypothalamus (rhGRF-43, rhGRF-29) or from a human pancreatic tumour (hpGRF-40). These peptides inhibited the binding of 125I-secretin to rat fundic membranes: pSN greater than cSN greater than PHI, VIP and activated the cAMP generating system in fundic glands, according to the following order of potency; pSN greater than cSN greater than PHI, VIP greater than rhGRF-29 greater than rhGRF-43. Porcine peptide with N-terminal tyrosine and C-terminal tyrosine (PYY), GIP, SOM and hpGRF-40 were inactive. Structural requirements for secretin receptor activity were evaluated with four synthetic secretin analogs corresponding to porcine secretin substituted at the N-terminal end by sequence portion of VIP, GIP, GLU and SOM: Ala4-Val5-SN(VIP-SN); Tyr1-Ala2-Glu3-SN (GIP-SN); Gln3-SN (GLU-SN) and Phe1-Phe1-Trp3-Lys4-SN (SOM-SN). The relative potencies of the analogs in fundic and antral preparations were: pSN greater than VIP-SN greater than VIP, GIP-SN greater than GLU-SN greater than SOM-SN for 125I-secretin displacement and cAMP production (glandular cAMP generation and adenylate cyclase activation).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone secretion dynamics in a patient with ectopic growth hormone-releasing factor production

A female patient with acromegaly, hypercalcemia, and Zollinger-Ellison syndrome was found to have a very high plasma concentration (average 2,300 pmol/liter; normal less than 50 pmol/liter) of growth hormone-releasing factor as measured by a radioimmunoassay to human pituitary growth hormone-releasing factor-1-44. The plasma concentration of growth hormone averaged 25 mIU/liter (normal less than 5 mIU/liter) and there was no rise following an intravenous 100 micrograms bolus of human pituitary growth hormone-releasing factor-1-44. Plasma growth hormone and growth hormone-releasing factor levels were unaffected by bromocriptine, insulin-induced hypoglycemia, and sleep. A long-acting somatostatin analogue lowered both the growth hormone-releasing factor and the growth hormone levels. Thyrotropin-releasing hormone stimulation and oral glucose tolerance tests produced significant increases in plasma growth hormone levels whereas the growth hormone-releasing factor level remained unchanged, suggesting that when normal somatotrophs are exposed to maximal growth hormone-releasing factor stimulation, thyrotropin-releasing hormone becomes a secretagogue of growth hormone from the pituitary. It is proposed that in the absence of a radioimmunoassay for growth hormone-releasing factor, a lack of growth hormone response to growth hormone-releasing factor in a patient with acromegaly is compatible with a source of ectopic growth hormone-releasing factor production.