GHRH and its analogues in central nervous system diseases.

Growth hormone-releasing hormone (GHRH) is primarily produced by the hypothalamus and stimulates the release of growth hormone (GH) in the anterior pituitary gland, which subsequently regulates the production of hepatic insulin-like growth factor-1 (IGF-1). GH and IGF-1 have potent effects on promoting cell proliferation, inhibiting cell apoptosis, as well as regulating cell metabolism. In central nerve system (CNS), GHRH/GH/IGF-1 promote brain development and growth, stimulate neuronal proliferation, and regulate neurotransmitter release, thereby participating in the regulation of various CNS physiological activities. In addition to hypothalamus-pituitary gland, GHRH and GHRH receptor (GHRH-R) are also expressed in other brain cells or tissues, such as endogenous neural stem cells (NSCs) and tumor cells. Alternations in GHRH/GH/IGF-1 axis are associated with various CNS diseases, for example, Alzheimer's disease, amyotrophic lateral sclerosis and emotional disorders manifest GHRH, GH or IGF-1 deficiency, and GH or IGF-1 supplementation exerts beneficial therapeutic effects on these diseases. CNS tumors, such as glioma, can express GHRH and GHRH-R, and activating this signaling pathway promotes tumor cell growth. The synthesized GHRH antagonists have shown to inhibit glioma cell growth and may hold promising as an adjuvant therapy for treating glioma. In addition, we have shown that GHRH agonist MR-409 can improve neurological sequelae after ischemic stroke by activating extrapituitary GHRH-R signaling and promoting endogenous NSCs-derived neuronal regeneration. This article reviews the involvement of GHRH/GH/IGF-1 in CNS diseases, and potential roles of GHRH agonists and antagonists in treating CNS diseases.

Brain morphometry and estimation of aging brain in subjects with congenital untreated isolated GH deficiency.

PURPOSE: Individuals with isolated GH deficiency (IGHD) due to a mutation in the GHRH receptor gene have a normal life expectancy and above 50 years of age, similar total cognitive performance, with better attention and executive function than controls. Our objectives were to evaluate their brain morphometry and brain aging using MRI. METHODS: Thirteen IGHD and 14 controls matched by age, sex, and education, were enrolled. Quantitative volumetric data and cortical thickness were obtained by automatic segmentation using Freesurfer software. The volume of each brain region was normalized by the intracranial volume. The difference between the predicted brain age estimated by MRI using a trained neuronal network, and the chronological age, was obtained. p < 0.005 was considered significant and 0.005 < p < 0.05 as a suggestive evidence of difference. RESULTS: In IGHD, most absolute values of cortical thickness and regional brain volumes were similar to controls, but normalized volumes were greater in the white matter in the frontal pole and in the insula bilaterally, and in the gray matter, in the right insula and in left Caudate (p < 0.005 for all comparisons) We also noticed suggestive evidence of a larger volume in IGHD in left thalamus (p = 0.006), right thalamus (p = 0.025), right caudate (p = 0.046) and right putamen (p = 0.013). Predicted brain ages were similar between groups. CONCLUSION: IGHD is primarily associated with similar absolute brain measurements, and a set of larger normalized volumes, and does not appear to alter the process of brain aging.

Expression of Growth Hormone-Releasing Hormone and Its Receptor Splice Variants in a Cohort of Hungarian Pediatric Patients with Hematological and Oncological Disorders: A Pilot Study.

Hematological and oncological diseases are still among the leading causes of childhood mortality. Expression of growth hormone-releasing hormone (GHRH) and its receptors (GHRH-R) has been previously demonstrated in various human tumors, but very limited findings are available about the presence and potential function of GHRH-Rs in oncological and hematological disorders of children. In this study, we aimed to investigate the expression of mRNA for GHRH and splice variant 1 (SV) of GHRH-R in 15 pediatric hematological/oncological specimens by RT-PCR. The presence and binding characteristics of GHRH-R protein were also studied by Western blot and ligand competition assays. Of the fifteen specimens studied, eleven pediatric samples (73%) showed the expression of mRNA for GHRH. These eleven samples also expressed mRNA for GHRH receptor SV1. GHRH-R protein was found to be expressed in two benign tumor samples and five malignant tumors examined by Western blot. The presence of specific, high affinity binding sites on GHRH-R was demonstrated in all of the seven human pediatric solid tumor samples investigated. Our results show that the expression of GHRH and SV1 of GHRH-R in hemato-oncological diseases in children can pave the way for further investigation of GHRH-Rs as potential molecular targets for diagnosis and therapy.

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of human malignant pleural mesothelioma.

Malignant pleural mesothelioma (MPM) is an aggressive malignancy associated with exposure to asbestos, with poor prognosis and no effective therapies. The strong inhibitory activities of growth hormone-releasing hormone (GHRH) antagonists have been demonstrated in different experimental human cancers, including lung cancer; however, their role in MPM remains unknown. We assessed the effects of the GHRH antagonists MIA-602 and MIA-690 in vitro in MPM cell lines and in primary MPM cells, and in vivo in MPM xenografts. GHRH, GHRH receptor, and its main splice variant SV1 were found in all the MPM cell types examined. In vitro, MIA-602 and MIA-690 reduced survival and proliferation in both MPM cell lines and primary cells and showed synergistic inhibitory activity with the chemotherapy drug pemetrexed. In MPM cells, GHRH antagonists also regulated activity and expression of apoptotic molecules, inhibited cell migration, and reduced the expression of matrix metalloproteinases. These effects were accompanied by impairment of mitochondrial activity and increased production of reactive oxygen species. In vivo, s.c. administration of MIA-602 and MIA-690 at the dose of 5 µg/d for 4 wk strongly inhibited the growth of MPM xenografts in mice, along with reduction of tumor insulin-like growth factor-I and vascular endothelial growth factor. Overall, these results suggest that treatment with GHRH antagonists, alone or in association with chemotherapy, may offer an approach for the treatment of MPM.

Disruption of the GHRH receptor and its impact on children and adults: The Itabaianinha syndrome.

Since 1994, we have been studying an extended kindred with 105 subjects (over 8 generations) residing in Itabaianinha County, in the Brazilian state of Sergipe, who have severe isolated GH deficiency (IGHD) due to a homozygous inactivating mutation (c.57 + 1G > A) in the GH releasing hormone (GHRH) receptor (GHRHR) gene. Most of these individuals have never received GH replacement therapy. They have low GH, and very low and often undetectable levels of serum IGF-I. Their principal physical findings are proportionate short stature, doll facies, high-pitched-voice, central obesity, wrinkled skin, and youthful hair with delayed pigmentation, and virtual absence of graying. The newborns from this cohort are of normal size, indicating that GH is not needed for intra-uterine growth. However, these IGHD individuals exhibit a myriad of phenotypic changes throughout the body, with a greater number of beneficial than harmful consequences. This GHRH signal disruption syndrome has been a valuable model to study the GH roles in body size and function. This reviews summarized the findings we have reported on this cohort.

Growth hormone-releasing hormone receptor antagonists inhibit human gastric cancer through downregulation of PAK1-STAT3/NF-κB signaling.

Gastric cancer (GC) ranks as the fourth most frequent in incidence and second in mortality among all cancers worldwide. The development of effective treatment approaches is an urgent requirement. Growth hormone-releasing hormone (GHRH) and GHRH receptor (GHRH-R) have been found to be present in a variety of tumoral tissues and cell lines. Therefore the inhibition of GHRH-R was proposed as a promising approach for the treatment of these cancers. However, little is known about GHRH-R and the relevant therapy in human GC. By survival analyses of multiple cohorts of GC patients, we identified that increased GHRH-R in tumor specimens correlates with poor survival and is an independent predictor of patient prognosis. We next showed that MIA-602, a highly potent GHRH-R antagonist, effectively inhibited GC growth in cultured cells. Further, this inhibitory effect was verified in multiple models of human GC cell lines xenografted into nude mice. Mechanistically, GHRH-R antagonists target GHRH-R and down-regulate the p21-activated kinase 1 (PAK1)-mediated signal transducer and activator of transcription 3 (STAT3)/nuclear factor-κB (NF-κB) inflammatory pathway. Overall, our studies establish GHRH-R as a potential molecular target in human GC and suggest treatment with GHRH-R antagonist as a promising therapeutic intervention for this cancer.

Cognitive performance during senescence in untreated congenital isolated GH deficiency.

Individuals with untreated isolated GH deficiency (IGHD) due to a mutation in the GHRH receptor gene from Itabaianinha Brazil have increased insulin sensitivity, normal life expectancy, and an extended health span, i.e. the period of life free from disabilities. We hypothesize that their prolonged health span is accompanied by a delayed cognitive decline in senescence. To test this hypothesis, we have administered the Literacy-Independent Cognitive Assessment (LICA) to 15 IGHD individuals aged over 50 years and 15 controls matched by age, sex, years of education, and percentage of illiteracy. All individuals were negative for HIV and syphilis serology, and there were no differences in serum levels of folate, vitamin B12 and TSH between the two groups, while free T4 was higher in the IGHD group. IGHD subjects had a higher total LICA score than controls, 215 (22.7) vs 204.2 (18.1), without reaching statistical significance. Scores of memory, visuoconstruction, language and calculation were similar between the two groups, with better attention (9.5 (1.4) vs 8.3 (1.1), P = 0.01) and executive function (38.3 (4.8) vs 35.1 (2.5), P = 0.03) scores in IGHD. MANCOVA revealed that group (but no age) had a significant effect on the LICA variables (partial eta squared of 0.455, power of 0.812, P = 0.02). This effect is verified on attention (partial eta squared 0.216, power of 0.749, P = 0.01) and executive function (partial eta squared 0.154, power of 0.570, P = 0.03. In conclusion, IGHD in senescence is associated with similar total cognitive performance but better attention and executive function than controls.

Skin assessment in congenital untreated isolated GH deficiency.

PURPOSE: The separation between the inside and outside through the skin was fundamental for the evolution of prevertebrates, which grow through extrapituitary circuits, to vertebrates, which grow through the somatotrophic axis, namely pituitary growth hormone (GH). and circulating IGF1.Individuals with untreated isolated growth hormone (GH) deficiency (IGHD) due to a mutation in the GH-releasing hormone receptor (GHRH) gene, residing in Itabaianinha, Brazil, are vulnerable to skin cancer and have reduced sweating. However other aspects of their skin physiology are still unknown. Our objectives were to evaluate the number of skin cancers, skin aging, and functional aspects of the skin in this IGHD cohort. METHODS: Twenty-six IGHD individuals and 26 controls matched by age, sex, ethnicity, and occupation were submitted to a biochemical, dermatological and a functional skin assessment by the Multi Probe Adapter Cutometer® MPA 580. RESULTS: There was no difference in the number of skin cancers and in the degrees of photodamage between the groups. The melanin content in the forearm was similar between the groups but was lower in the buttocks (p = 0.005), as well as skin resistance (p < 0.0001) and elasticity (p = 0.003), lower in the IGHD. There was no difference in hydration and sebum content between the two groups. CONCLUSION: IGHD is apparently associated with a neutral profile in terms of skin cancer and photodamage, with similar melanin on the forearm and lower buttocks, lower skin resistance and elasticity, with hydration and sebum similar to controls.

Signaling mechanism of growth hormone-releasing hormone receptor.

The hypothalamic peptide growth hormone-releasing hormone (GHRH) stimulates the secretion of growth hormone (GH) from the pituitary through binding and activation of the pituitary type of GHRH receptor (GHRH-R), which belongs to the family of G protein-coupled receptors with seven potential membrane-spanning domains. Splice variants of GHRH-Rs (SV) in human tumors and other extra pituitary tissues were identified and their cDNA was sequenced. Among the SVs, splice variant 1 (SV1) possesses the greatest similarity to the full-length GHRH-R and remains functional by eliciting cAMP signaling and mitogenic activity upon GHRH stimulation. A large body of work have evaluated potential clinical applications of agonists and antagonists of GHRH in diverse fields, including endocrinology, oncology, cardiology, diabetes, obesity, metabolic dysfunctions, Alzheimer's disease, ophthalmology, wound healing and other applications. In this chapter, we briefly review the expression and potential function of GHRH-Rs and their SVs in various tissues and also elucidate and summarize the activation, molecular mechanism and signalization pathways of these receptors. Therapeutic applications of GHRH analogs are also discussed.

Function and form of the shoulder in congenital and untreated growth hormone deficiency.

OBJECTIVES: The shoulder is the most mobile joint in the entire human body. During arm elevation, it requires the integrity of a set of muscles, bones, and tendons. Individuals with short stature often need to raise their arms above the shoulder girdle and may have functional restriction or shoulder injuries. The impact of isolated GH deficiency (IGHD) on joints remains not well defined. The purpose of this work is to evaluate the function and structure of the shoulder in short-statured adult individuals with untreated IGHD due to the same homozygous mutation in the GHRH receptor gene. METHODS: A cross-sectional study (evidence 3) was carried out in 20 GH-naive IGHD subjects and 20 age-matched controls. They completed the disabilities of the arm, shoulder, and hand (DASH) questionnaire and shoulder ultrasound (US). Thickness of the anterior, medial, and posterior portions of the supraspinatus tendon and of subacromial space was measured, and the number of individuals with tendinosis or tearing of the supraspinatus tendon was registered. RESULTS: DASH score was similar between IGHD and controls, but IGHD subjects complained less of symptoms (p = 0.002). The number of individual with tears was higher in the controls (p = 0.02). As expected, the absolute US measurements were lower in IGHD, but the magnitude of the reduction was most pronounced in the thickness of the anterior portion of the supraspinatus tendon. CONCLUSION: Adults with lifetime IGHD do not have functional shoulder restrictions, complain less of problems in performing upper extremity activities, and have fewer tendinous injuries than controls.

Quantitative measures of the vascular and neural components of the retina in adult individuals with congenital and untreated growth hormone deficiency.

BACKGROUND: The somatotrophic axis, including hypothalamic growth hormone (GH)-releasing hormone (GHRH), pituitary GH and circulating IGF-I, is critical for body size. However, the local production of GH/IGF-I (and IGF-II) and other peptides is relevant for other body functions, such as vascular, brain, and retinal function. The consequences of GH deficiency (GHD) on the retinal structure are still unclear, possibly reflecting the heterogeneity of patients and the different types of assessment in previous publications. Our purpose was to assess quantitative measures of the vascular and neural components of the retina in subjects with severe congenital isolated GHD (IGHD). METHODS: A cross-sectional study was carried out in 25 adult IGHD subjects and 25 age- and gender-matched controls. Interview, physical examination, laboratory data, optical coherence tomography (OCT) and OCT angiography (OCTA) were performed. RESULTS: OCT revealed no difference in the areas of the nerve fiber layer average, nor in the areas of superior, inferior, or nasal quadrants, between the two groups. However, areas of the temporal quadrant (p = 0.041), the optical disc (p = 0.042), the cup (p < 0.0001), as well as the cup/disc ratio (p < 0.0001), were higher in IGHD subjects than controls. The rim area was smaller (p = 0.002), although still normal. In OCTA, there was no difference in the minimum foveal thickness, central fovea, foveal avascular zone, and retinal density in any assessed area. CONCLUSIONS: In conclusion, congenital IGHD does not affect quantitative measures of the vascular and neural retina, and it is associated with increased optical disc in this genetically homogeneous cohort.

The state of Sergipe contribution to GH research: from Souza Leite to Itabaianinha syndrome.

In the late 19th century, José Dantas de Souza Leite, a physician born in Sergipe, published the first detailed clinical description of acromegaly under the guidance of the French neurologist Pierre Marie. In 2014, the Brazilian Society of Endocrinology and Metabolism created the "José Dantas de Souza Leite Award", which is granted every two years to a Brazilian researcher who has contributed to the development of endocrinology. In 2022, the award was given to another physician from Sergipe, Manuel Hermínio de Aguiar Oliveira, from the Federal University of Sergipe for the description of "Itabaianinha syndrome" in a cohort of individuals with isolated GH deficiency due to a homozygous inactivating mutation in the GH-releasing hormone receptor gene. This research, which was carried out over almost 30 years, was performed in partnership with Roberto Salvatori from Johns Hopkins University and in collaboration with other researchers around the world. This review article tells the story of Souza Leite, some milestones in the history of GH, and summarizes the description of Itabaianinha syndrome.

Individuals with isolated congenital GH deficiency due to a GHRH receptor gene mutation appear to cope better with SARS-CoV-2 infection than controls.

PURPOSE: Several interactions exist between the GH/IGF axis and the immune system, including effects on innate immunity and humoral and cellular response. Acquired GH deficiency (GHD) has been recently proposed as a risk factor for severity of COVID-19 infections. However, acquired GHD is often associated to other factors, including pituitary tumors, surgery, radiotherapy, and additional pituitary hormones deficits and their replacements, which, together, may hinder an accurate analysis of the relationship between GHD and COVID-19. Therefore, we decided to assess the seroprevalence of SARS-CoV-2 antibodies and the frequency of symptomatic cases of COVID-19 in adults subjects with untreated isolated GHD (IGHD) due to a homozygous null mutation in the GHRH receptor gene. METHODS: A cross-sectional study was carried out in 27 adult IGHD subjects and 27 age- and gender-matched local controls. Interview, physical examination, bio-impedance, hematological and SARS-CoV-2 IgM and IgG antibodies were analyzed. RESULTS: There was no difference in the prevalence of positivity of anti-SARS-CoV-2 IgM and IgG antibodies between the two groups. Conversely, no IGHD individual had a previous clinical diagnosis of COVID-19 infection, while 6 control subjects did (p = 0.023). CONCLUSION: The production of anti-SARS-CoV-2 antibodies was similar between IGHD subjects due to a GHRH receptor gene mutation and controls, but the evolution to symptomatic stages of the infection and the frequency of confirmed cases was lower in IGHD subjects than in GH sufficient individuals.

Cerebral vasoreactivity, a surrogate marker of cerebrovascular disease, is not impaired in subjects with lifetime, untreated, congenital isolated GH deficiency.

OBJECTIVES: Cerebrovascular disease (CeVD) is a major cause of death and disability. The role of the GH/IGF-I axis on CeVD risk is controversial. Patients with GH deficiency (GHD) in the setting of hypopituitarism often exhibit CeVD predisposing factors, like low nitric oxide generation, endothelial dysfunction, increased visceral fat mass, increased levels of LDL cholesterol, and increased intima-media thickness, a surrogate marker of atherosclerosis. However, several confounders such as the primary hypothalamic-pituitary lesion, hormonal replacement therapies, consequences of surgery and radiotherapy, may influence this relationship. Therefore, we decided to assess cerebral vasoreactivity, a surrogate marker of CeVD, in adult subjects with untreated isolated GHD (IGHD) due to the same homozygous null mutation in the GHRH receptor gene. METHODS: A cross-sectional study was carried out in 25 adult IGHD subjects and 25 age- and gender-matched controls. Interview, physical examination, laboratory data, intima-media thickness measurement, and transcranial Doppler were performed. The intracranial hemodynamics (mean flow velocity, pulsatility and resistance indexes) were measured, and the response to the vasodilatory stimulus by breath-holding maneuver (breath-holding index) was calculated. RESULTS: IGHD and control groups were similar in Framingham risk score and intima-media thickness. Similarly, there was no difference in mean flow velocity, pulsatility, resistance, and breath-holding index. CONCLUSIONS: Lifetime, untreated IGHD does not cause impaired cerebral vasoreactivity.

Adult individuals with congenital, untreated, severe isolated growth hormone deficiency have satisfactory muscular function.

PURPOSE: While growth hormone (GH) and the insulin-like growth factor type I (IGF-I) are known to exert synergistic actions on muscle anabolism, the consequences of prolonged GH deficiency (GHD) on muscle function have not been well defined. We have previously described a large cohort of subjects with isolated GHD (IGHD) caused by a mutation in the GH-releasing hormone receptor gene, with low serum levels of GH and IGF-I. The aim of this study was to assess muscular function in these IGHD subjects. METHODS: A total of 31 GH-naïve IGHD (16 males) and 40 control (20 males) subjects, matched by age and degree of daily physical activity, were enrolled. Fat free mass was measured by bioelectrical impedance; muscle strength by dynamometry of handgrip, trunk extension, and knee extension; myoelectric activity and muscle fatigue by fractal dimension; conduction velocity in vastus medialis, rectus femoris, and vastus lateralis muscles by surface electromyography. RESULTS: The IGHD group showed higher knee extension strength both when corrected for weight and fat free mass, and higher handgrip and trunk extension strength corrected by fat free mass. They also exhibit higher conduction velocity of the muscles vastus medialis, rectus femoris, and vastus lateralis, but lower free fat mass and myoelectric activity of the vastus medialis, rectus femoris and vastus lateralis. There were no differences between the two groups in fractal dimension in all studied muscles. CONCLUSION: Individuals with untreated IGHD have better muscle strength parameters adjusted for weight and fat free mass than controls. They also exhibit greater peripheral resistance to fatigue, demonstrating satisfactory muscle function.

The state of Sergipe contribution to GH research: from Souza Leite to Itabaianinha syndrome

ABSTRACT In the late 19th century, José Dantas de Souza Leite, a physician born in Sergipe, published the first detailed clinical description of acromegaly under the guidance of the French neurologist Pierre Marie. In 2014, the Brazilian Society of Endocrinology and Metabolism created the "José Dantas de Souza Leite Award", which is granted every two years to a Brazilian researcher who has contributed to the development of endocrinology. In 2022, the award was given to another physician from Sergipe, Manuel Hermínio de Aguiar Oliveira, from the Federal University of Sergipe for the description of "Itabaianinha syndrome" in a cohort of individuals with isolated GH deficiency due to a homozygous inactivating mutation in the GH-releasing hormone receptor gene. This research, which was carried out over almost 30 years, was performed in partnership with Roberto Salvatori from Johns Hopkins University and in collaboration with other researchers around the world. This review article tells the story of Souza Leite, some milestones in the history of GH, and summarizes the description of Itabaianinha syndrome.

Novel GHRH antagonists suppress the growth of human malignant melanoma by restoring nuclear p27 function.

Malignant melanoma is the deadliest form of skin cancer; the treatment of advanced and recurrent forms remains a challenge. It has recently been reported that growth hormone-releasing hormone (GHRH) receptor is involved in the pathogenesis of melanoma. Therefore, we investigated the effects of our new GHRH antagonists on a human melanoma cancer cell line. Antiproliferative effects of GHRH antagonists, MIA-602, MIA-606 and MIA-690, on the human melanoma cell line, A-375, were studied in vitro using the MTS assay. The effect of MIA-690 (5 µg/day 28 d) was further evaluated in vivo in nude mice bearing xenografts of A-375. Subcellular localization of p27 was detected with Western blot and immunofluorescent staining. MIA-690 inhibited the proliferation of A-375 cells in a dose-dependent manner (33% at 10 µM, and 19.2% at 5 µM, P < 0 .05 vs. control), and suppressed the growth of xenografted tumors by 70.45% (P < 0.05). Flow cytometric analysis of cell cycle effects following the administration of MIA-690 revealed a decrease in the number of cells in G2/M phase (from 19.7% to 12.9%, P < 0.001). Additionally, Western blot and immunofluorescent studies showed that exposure of A-375 cells to MIA-690 triggered the nuclear accumulation of p27. MIA-690 inhibited tumor growth in vitro and in vivo, and increased the translocation of p27 into the nucleus thus inhibiting progression of the cell cycle. Our findings indicate that patients with malignant melanoma could benefit from treatment regimens, which combine existing chemotherapy agents and novel GHRH-antagonists.

Differential involvement of signaling pathways in the regulation of growth hormone release by somatostatin and growth hormone-releasing hormone in orange-spotted grouper (Epinephelus coioides).

Somatostatin is the most effective inhibitor of GH release, and GHRH was recently identified as one of the primary GH-releasing factors in teleosts. In this study, we analyzed the possible intracellular transduction pathways that are involved in the mechanisms induced by SRIF and GHRH to regulate GH release. Using a pharmacological approach, the blockade of the PLC/IP/PKC pathway reversed the SRIF-induced inhibition of GH release but did not affect the GHRH-induced stimulation of GH release. Furthermore, SRIF reduced the GH release induced by two PKC activators. Inhibitors of the AC/cAMP/PKA pathway reversed both the SRIF- and GHRH-induced effects on GH release. Moreover, the GH release evoked by forskolin and 8-Br-cAMP were completely abolished by SRIF. The blockade of the NOS/NO pathway attenuated the GHRH-induced GH release but had minimal effects on the inhibitory actions of SRIF. In addition, inhibitors of the sGC/cGMP pathway did not modify the SRIF- or GHRH-induced regulation of GH release. Taken together, these findings indicate that the SRIF-induced inhibition of GH release is mediated by both the PLC/IP/PKC and the AC/cAMP/PKA pathways and not by the NOS/NO/sGC/cGMP pathway. In contrast, the GHRH-induced stimulation of GH secretion is mediated by both the AC/cAMP/PKA and the NOS/NO pathways and is independent of the sGC/cGMP pathway and the PLC/IP/PKC system.

Role of Glucocorticoids in Fasting-induced Changes in Hypothalamic and Pituitary Components of the Growth Hormone (GH)-axis.

To directly test if elevated glucocorticoids are required for fasting-induced regulation of growth hormone (GH)-releasing hormone (GHRH), GHRH receptors (GHRH-R) and ghrelin receptors (GHS-R) expression, male rats were bilaterally adrenalectomized or sham operated. After 7 days, animals were fed ad libitum or fasted for 48 h. Bilateral adrenalectomy increased hypothalamic GHRH to 146% and decreased neuropeptide Y (NPY) mRNA to 54% of SHAM controls. Pituitary GHRH-R and GHS-R mRNA levels were decreased by adrenalectomy to 30% and 80% of sham-operated controls. In shamoperated rats, fasting suppressed hypothalamic GHRH (49%) and stimulated NPY (166%) mRNA levels, while fasting increased pituitary GHRH-R (391%) and GHS-R (218%) mRNA levels. However, in adrenalectomized rats, fasting failed to alter pituitary GHRH-R mRNA levels, while the fasting-induced suppression of GHRH and elevation of NPY and GHS-R mRNA levels remained intact. In fasted adrenalectomized rats, corticosterone replacement increased GHRH-R mRNA levels and intensified the fasting-induced decrease in GHRH, but did not alter NPY or GHS-R response. These data suggest that elevated glucocorticoids mediate the effects of fasting on hypothalamic GHRH and pituitary GHRH-R expression, while glucocorticoids are likely not the major determinant in fasting-induced increases in hypothalamic NPY and pituitary GHS-R expression.