GH-releasing Hormone Injection Research Articles

Peripheral Injection of Chicken Growth Hormone-Releasing Hormone Inhibits Feeding Behavior in Chicks.

Growth hormone-releasing hormone (GHRH), a stimulator of growth hormone (GH) secretion, is known to have several physiological roles such as the regulation of feeding behavior in mammals. Recently, we have reported that central injection of chicken GHRH decreased food intake in chicks, however, its peripheral role on feeding behavior has not been clarified. The purpose of the present study was to investigate the effect of peripheral injection of GHRH on feeding behavior in chicks (Gallus gallus). Intraperitoneal (IP) injection of GHRH47 (1 nmol), full length form of chicken GHRH significantly decreased food intake in chicks although the injection of GHRH27 and GHRH27-NH2, short forms of chicken GHRH had no effect. The IP injection of GHRH47 did not induced any abnormal behavior, suggesting that GHRH47-induced anorexia might not be related to abnormal behavior such as sleeping, hyperactivity and convulsion. The anorexigenic effect of GHRH47 seemed not to be related to GH because IP injection of bovine GH did not affect feeding behavior in chicks. Collectively, these results suggest that peripheral GHRH is related to inhibit feeding behavior in chicks.

Effects of hypothalamic dopamine on growth hormone‐releasing hormone‐induced growth hormone secretion and thyrotropin‐releasing hormone‐induced prolactin secretion in goats

The aim of the present study was to clarify the effects of hypothalamic dopamine (DA) on the secretion of growth hormone (GH) in goats. The GH-releasing response to an intravenous (i.v.) injection of GH-releasing hormone (GHRH, 0.25 μg/kg body weight (BW)) was examined after treatments to augment central DA using carbidopa (carbi, 1 mg/kg BW) and L-dopa (1 mg/kg BW) in male and female goats under a 16-h photoperiod (16 h light, 8 h dark) condition. GHRH significantly and rapidly stimulated the release of GH after its i.v. administration to goats (P < 0.05). The carbi and L-dopa treatments completely suppressed GH-releasing responses to GHRH in both male and female goats (P < 0.05). The prolactin (PRL)-releasing response to an i.v. injection of thyrotropin-releasing hormone (TRH, 1 μg/kg BW) was additionally examined in male goats in this study to confirm modifications to central DA concentrations. The treatments with carbi and L-dopa significantly reduced TRH-induced PRL release in goats (P < 0.05). These results demonstrated that hypothalamic DA was involved in the regulatory mechanisms of GH, as well as PRL secretion in goats.

Effects of growth hormone-releasing hormone on sleep and brain interstitial fluid amyloid-β in an APP transgenic mouse model.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by impairment of cognitive function, extracellular amyloid plaques, intracellular neurofibrillary tangles, and synaptic and neuronal loss. There is substantial evidence that the aggregation of amyloid β (Aβ) in the brain plays a key role in the pathogenesis of AD and that Aβ aggregation is a concentration dependent process. Recently, it was found that Aβ levels in the brain interstitial fluid (ISF) are regulated by the sleep-wake cycle in both humans and mice; ISF Aβ is higher during wakefulness and lower during sleep. Intracerebroventricular infusion of orexin increased wakefulness and ISF Aβ levels, and chronic sleep deprivation significantly increased Aβ plaque formation in amyloid precursor protein transgenic (APP) mice. Growth hormone-releasing hormone (GHRH) is a well-documented sleep regulatory substance which promotes non-rapid eye movement sleep. GHRHR(lit/lit) mice that lack functional GHRH receptor have shorter sleep duration and longer wakefulness during light periods. The current study was undertaken to determine whether manipulating sleep by interfering with GHRH signaling affects brain ISF Aβ levels in APPswe/PS1ΔE9 (PS1APP) transgenic mice that overexpress mutant forms of APP and PSEN1 that cause autosomal dominant AD. We found that intraperitoneal injection of GHRH at dark onset increased sleep and decreased ISF Aβ and that delivery of a GHRH antagonist via reverse-microdialysis suppressed sleep and increased ISF Aβ. The diurnal fluctuation of ISF Aβ in PS1APP/GHRHR(lit/lit) mice was significantly smaller than that in PS1APP/GHRHR(lit/+) mice. However despite decreased sleep in GHRHR deficient mice, this was not associated with an increase in Aβ accumulation later in life. One of several possibilities for the finding is the fact that GHRHR deficient mice have GHRH-dependent but sleep-independent factors which protect against Aβ deposition.

The effect of lighting conditions on the rhythmicity of growth hormone secretion in Holstein steers

Growth hormone (GH) secretion regularity and the effects of lighting condition and GH-releasing hormone (GHRH) on GH release were determined in steers. First, steers were kept under 12:12 L : D conditions (light: 06.00-18.00 hours). The animals were then subjected to a 1-h advancement in lighting on/off conditions (05.00 and 17.00 hours, respectively). Blood was sampled for 24 h at 1-h interval on the seventh day of each condition. Second, GHRH was injected intravenously (IV) at 12.00 and 00.00 hours under 12:12 L : D and blood was sampled at 15-min interval for 4-h (1 h before and 3 h after the injection). Plasma GH concentrations were measured by a radioimmunoassay. Periodicity of GH secretory profile was calculated by power spectrum analysis using the maximum entropy method. Plasma GH concentrations showed a characteristic pattern consisting of four distinct peaks. Mean periodicity of GH secretory profile was 5.7 h, and it was not altered by any change in lighting conditions. IV injection of GHRH increased GH secretion during the day and night. The increase in GH secretory volume after GHRH injection during the night was equal to that during the day. The present results suggest that GH secreted from the anterior pituitary have regularity in steers.

The Effects of Protein Ingestion on GH Concentrations in Visceral Obesity

Growth hormone (GH), a hormone originating from the anterior pituitary gland, is an important regulator of metabolism and body composition. Low GH secretion is associated with features of the metabolic syndrome, in particular increased visceral body fat and decreased lean body mass. It has been shown that GH release can be promoted by ingestion of protein, in particular gelatin protein. The question remains; is the GH-promoting effect of gelatin protein also present in a population with blunted GH response, such as visceral obesity? 8 lean women (age: 23+/-3 years, BMI: 21.6+/-2.0 kg/m (2)) and 8 visceral obese women (age: 28+/-7 years, BMI: 33.8+/-5.5 kg/m (2)) were compared with regard to their 5-h GH response after oral ingestion of gelatin protein (0.6 g protein per kg bodyweight), placebo (water), or injection of growth hormone releasing hormone (GHRH) (1 mu/kg body weight), in a randomized crossover design. GH response after placebo, gelatin protein, or GHRH was higher in lean subjects than in visceral obese subjects (p<0.05). Ingestion of gelatin protein increased GH response compared with placebo in both visceral obese (182.1+/-81.6 microg/l.5 h vs. 28.4+/-29.8 microg/l.5 h) and lean (631.7+/-144.2 microg/l.5 h vs. 241.0+/-196.8 microg/l.5 h) subjects (p<0.05). GH response after ingestion of gelatin protein in visceral obese did not differ from that in lean, placebo-treated subjects (p=0.45). GH concentrations after GHRH injection correlated significantly with GH concentrations after gelatin ingestion (AUC; r=0.71, p<0.01, Peak; r=0.81, p<0.01). Further research is needed to investigate if gelatin protein is able to improve metabolic abnormalities in hyposomatotropism in the long term or to investigate the relevance of protein as diagnostic tool in hyposomatotropism.

Central administration of growth hormone-releasing hormone and corticotropin-releasing hormone stimulate downstream movement and thyroxine secretion in fall-smolting coho salmon ( Oncorhynchus kisutch)

The ultimate signal triggering downstream migration in anadromous salmonids is unknown. A plasma surge of T 4 (T 4 surge) occurs during downstream migration in salmonids; however, the causal relationship between migratory behavior and the T 4 surge is not well known. We first examined the progression of smolt indicators (skin silvering, condition factor (CF), gill Na +, K +-ATPase (NKA) activity and plasma T 4 levels) in underyearling, fall-smolting coho salmon ( Oncorhynchus kisutch) from August to December. In November, the fish showed the characteristics of fully developed smolts, i.e. the skin completely covered with silvery scales, CF at a nadir, and peak NKA activity and plasma T 4 levels. Based on these results, we examined the effects of four neuropeptides, thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), and gonadotropin-releasing hormone (GnRH), on the downstream movement (negative rheotaxis) and T 4 surge in fully smoltified underyearling coho salmon. The experiment was run in circular-shaped channel tanks and the neuropeptide treatment was performed as intracerebroventricular (ICV) injections. ICV injection of GHRH and CRH stimulated both downstream movement and plasma T 4 level. TRH injection stimulated plasma T 4 level but suppressed downstream movement. GnRH injection had no effect. It is hypothesized that GHRH and CRH play key roles in triggering downstream migration of anadromous salmonids, and that the accompanying T 4 surge is a consequence of the neuroendocrine processes that trigger migration.

Growth hormone-releasing hormone activates sleep regulatory neurons of the rat preoptic hypothalamus

We examined whether growth hormone-releasing hormone (GHRH) may promote non-rapid eye movement (NREM) sleep via activation of GABAergic neurons in the preoptic area. Male Sprague-Dawley rats were implanted with EEG, EMG electrodes and a unilateral intracerebroventricular cannula. Groups of rats received injections (3 microl icv) with gonadotropin-releasing hormone (GHRH) (0.1 nmol/100 g body wt) or equal volume of physiological saline at the onset of the dark period and were permitted spontaneous sleep for 90 min. Separate groups of rats were sleep deprived by gentle handling for 90 min, beginning at the time of GHRH or saline injection, at the onset of the dark period. Other groups of rats received intracerebroventricular octreotide (somatostatin analog OCT) injections, intracerebroventricular injection of one of two doses of competitive GHRH antagonist, or intracerebroventricular saline injection at light onset and were then permitted 90 min spontaneous sleep-waking. Rats were killed immediately after the 90-min sleep/wake monitoring period. Brain tissue was processed for immunohistochemistry for c-Fos protein and glutamic acid decarboxylase (GAD). Single c-Fos and dual Fos-GAD cell counts were determined in the median preoptic nucleus (MnPN), and in the core and the extended parts of the ventrolateral preoptic nucleus (cVLPO and exVLPO). Intracerebroventricular GHRH elicited a significant increase in NREM sleep amount. Double-labeled Fos+GAD cell counts were significantly elevated after GHRH injection in the MnPN and VLPO in both undisturbed and sleep-deprived groups. OCT and GHRH antagonist significantly decreased NREM sleep amount compared with control rats. OCT injection increased single c-Fos-labeled cell counts in the MnPN, but not in the VLPO. Double-labeled cell counts were significantly reduced after OCT and the high dose of GHRH antagonist injection in all areas examined. These findings identify GABAergic neurons in the MnPN and VLPO as potential targets of the sleep-regulatory actions of GHRH.

Plasma hormone and metabolite concentrations involved in the somatotropic axis of Japanese Black heifers in association with growth hormone gene polymorphism

Bovine growth hormone (bGH) gene polymorphism of leucine (Leu)-threonine (Thr) (allele A), valine (Val)-Thr (allele B), and Val-methionine (Met) (allele C) at codons 127 and 172 was shown to relate with carcass trait variations in Japanese Black cattle. In this study, 10-mo-old Japanese Black heifers with growth hormone (GH) genotypes AA, AB, BB, AC, BC, and CC (N = 141) were compared for basal GH, insulin-like growth factor-1 (IGF-1), insulin, ghrelin, glucose, and nonesterified fatty acid (NEFA) concentrations. Growth hormone release was also measured as response to growth hormone–releasing hormone (GHRH) (0.4 μg/kg body weight [BW]) using 18 heifers with GH genotypes AA, BB, and CC (n = 6 for each group). The genotype AA heifers showed the greatest BW among genotypes ( P < 0.05). Genotype AC, BC, and CC heifers showed greater GH concentrations than genotype AA, AB, or BB heifers, in which genotype CC heifers had the highest concentrations ( P < 0.05). However, IGF-1 concentrations did not significantly differ. The genotype AA and BB heifers had a greater GH release at 60 min following GHRH injection than did the genotype CC heifers. The area under the curve (AUC; P < 0.07) and incremental area (IA; P < 0.08) of GH responses to the GHRH challenge tended to be the highest in the genotype AA heifers and the lowest in the genotype CC heifers. In conclusion, GH gene polymorphism altered GH, which may have contributed to differences in BW and carcass traits among genotypes.

Growth Hormone Response to Growth Hormone-Releasing Hormone Is Reduced in Adult Asthmatic Patients Receiving Long-term Inhaled Corticosteroid Treatment

Some studies have demonstrated that the function of the growth hormone (GH)-insulin-like growth factor (IGF)-1 axis is significantly impaired in patients with oral corticosteroid (CS)-induced osteoporosis. The aim of study was to investigate the effects of long-term therapy with inhaled CSs (ICSs) on the hypothalamic-pituitary-GH axis by the GH response to GH-releasing hormone (GHRH), as well as bone turnover, in adult asthmatic patients. Cross-sectional study. Twenty-seven adult subjects with mild-to-moderate persistent asthma (long-term ICS therapy [ie, > 1 year], 20 patients; naive to ICS treatment, 7 patients) and 10 control subjects. Each subject underwent testing with an IV bolus (1 mug/kg) injection of human GHRH, and samples of GH were taken 15 min before the GHRH injection, at 0 min (ie, at the time of GHRH injection), and at 15, 30, 45, 60, and 90 min after injection to obtain values for peak GH and DeltaGH. At baseline, samples of serum IGF-1 and blood-urine were collected for bone turnover markers. The GH response to GHRH was significantly reduced in asthmatic patients receiving ICSs (peak GH, p < 0.05; and DeltaGH, p < 0.01) in comparison with control subjects and asthmatic patients who were naive to ICS therapy (peak GH and DeltaGH, p < 0.01). Baseline IGF-1 levels were similar in the three groups. Serum osteocalcin, a marker of bone formation, was significantly reduced (p < 0.01) and correlated with GH peak (r(2) = 0.34; p = 0.007) in asthmatic patients who were treated with ICSs. We conclude that GH secretion in response to GHRH is significantly reduced in adult asthmatic patients receiving therapy with ICS and that such inhibition could play a negative role in bone metabolism.

Effect in sheep of dietary concentrate content on secretion of growth hormone, insulin and insulin‐like growth factor‐I after feeding

ABSTRACTThis study was designed to examine the effects of the proportion of concentrate in the diet on the secretion of growth hormone (GH), insulin and insulin‐like growth factor‐I (IGF‐I) secretion and the GH‐releasing hormone (GHRH)‐induced GH response in adult sheep fed once daily. Dietary treatments were roughage and concentrate at ratios of 100:0 (0% concentrate diet), 60:40 (40% concentrate diet), and 20:80 (80% concentrate diet) on a dry matter basis. Mean plasma concentrations of GH before daily feeding (10.00–14.00 hours) were 11.4 ± 0.4, 10.1 ± 0.5 and 7.5 ± 0.3 ng/mL on the 0, 40 and 80% concentrate diet treatments, respectively. A significant decrease in plasma GH concentration was observed after daily feeding of any of the dietary treatments and these decreased levels were maintained for 8 h (0%), 12 h (40%) and 12 h (80%), respectively (P &lt; 0.05). Plasma IGF‐I concentrations were significantly decreased 8–12 h and 4–16 h after the end of feeding compared with the prefeeding level in the 40 and 80% concentrate diet treatments, respectively (P &lt; 0.05). GHRH injection brought an abrupt increase in the plasma GH concentrations, reaching a peak 10 min after each injection, but, after the meal, the peak plasma GH values for animals fed 40% (P &lt; 0.05) and 80% (P &lt; 0.01) concentrate diet were lower than that for roughage fed animals. The concentrate content of a diet affects the anterior pituitary function of sheep resulting in reduced baseline concentrations of GH and prolonged GH reduction after feeding once daily.

Hypothalamic Growth Hormone-Releasing Hormone (GHRH) Deficiency: Targeted Ablation of GHRH Neurons in Mice Using a Viral Ion Channel Transgene

Animal and clinical models of GHRH excess suggest that GHRH provides an important trophic drive to pituitary somatotrophs. We have adopted a novel approach to silence or ablate GHRH neurons, using a modified H37A variant of the influenza virus M2 protein ((H37A)M2). In mammalian cells, (H37A)M2 forms a high conductance monovalent cation channel that can be blocked by the antiviral drug rimantadine. Transgenic mice with (H37A)M2 expression targeted to GHRH neurons developed postweaning dwarfism with hypothalamic GHRH transcripts detectable by RT-PCR but not by in situ hybridization and immunocytochemistry, suggesting that expression of (H37A)M2 had silenced or ablated virtually all the GHRH cells. GHRH-M2 mice showed marked anterior pituitary hypoplasia with GH deficiency, although GH cells were still present. GHRH-M2 mice were also deficient in prolactin but not TSH. Acute iv injections of GHRH in GHRH-M2 mice elicited a significant GH response, whereas injections of GHRP-6 did not. Twice daily injections of GHRH (100 microg/d) for 7 d in GHRH-M2 mice doubled their pituitary GH but not PRL contents. Rimantadine treatment failed to restore growth or pituitary GH contents. Our results show the importance of GHRH neurons for GH and prolactin production and normal growth.

Postprandial changes in plasma GH and insulin concentrations, and responses to stimulation with GH-releasing hormone (GHRH) and GHRP-6 in calves around weaning

Changes in plasma concentrations of GH and insulin in response to feeding and stimulation with GH-releasing hormone (GHRH) or GH-releasing peptide (GHRP-6, a ligand for endogenous GH secretagogue receptors) were compared between 3-week-old (milk-fed) and 12-week-old (concentrate and hay-fed) calves. Feeding of a milk-replacer diet in 3-week-old animals significantly increased the basal (prefeeding) concentrations of GH, insulin and glucose in plasma, whereas feeding of concentrate and hay in 12-week-old animals did not cause a significant change in these traits. However, in the animals maintained on a milk-replacer diet until 12 weeks of age, postprandial plasma GH concentrations and AUC (area under the curve) were not different from those in the age-matched weaned group. The venous injection of either GHRH (0.25 microg/kg) or GHRP-6 (2.5 microg/kg) significantly increased plasma GH concentrations in both 3- and 12-week-old animals, but GH AUC was significantly greater in 3-week-old than in 12-week-old animals. Insulin concentration was transiently but significantly increased by the injection of GHRP-6 only in 12-week-old animals, the AUC being greater in 12-week-old than 3-week-old animals. From these results, we conclude that postprandial levels of plasma GH and insulin concentrations are altered after weaning and by aging, and that the quality of diets or development of the neuroendocrine functions in the digestive-pituitary system may be involved in this alteration.

Growth hormone releasing hormone reverses endotoxin-induced localized inflammatory hyperalgesia without reducing the upregulated cytokines, nerve growth factor and gelatinase activity

During inflammatory processes, the hypothalamic-pituitary axis is activated which can subsequently result in analgesia. For example, hypothalamic corticotrophin-releasing hormone (CRH) that is released during such activation has been attributed with analgesic actions. It is believed that the somatotrophic axis is also activated during inflammation. The aim of this study was to determine the analgesic actions of growth hormone-releasing hormone (GHRH), in a rat model of localized inflammatory hyperalgesia, induced by intraplantar (i.pl.) endotoxin (ET) injections. Pretreatment with intraperitoneal (i.p.) injections of GHRH (2, 5, 10 μg kg −1) 30 min before i.pl. ET injection (1.25 μg in 50 μl saline) prevented, in a dose-dependent manner, both mechanical hyperalgesia determined by the paw pressure (PP) test and thermal hyperalgesia determined by the hot plate (HP) and paw immersion (PI) tests. Pretreatment with GHRH had no significant effect on the elevated levels of the inflammatory mediators, interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6 and nerve growth factor (NGF) due to i.pl. ET injection. No significant effect was obtained by pretreatment with GHRH, on the increased expression of gelatinase B due to ET injection. In conclusion, GHRH reverses inflammatory hyperalgesia in the rat without affecting the upregulated inflammatory mediators and these actions may be clinically important.

The Reduced Release of GH by GHRH in 8 Subjects Aged 65–69 Years Is Augmented Considerably by Rivastigmine, a Drug for Alzheimer’s Disease

Background: The growth hormone (GH) secretion declines by 14% with each decade of adult life. Several attempts have been made to reverse the manifestations of the senile GH deficiency, termed somatopause, but GH substitution treatment in old age has not yet developed an established regimen. Cholinesterase inhibitors like pyridostigmine are able to elicit GH secretion when administered alone and to enhance the GH response to growth hormone releasing hormone (GHRH), but its clinical use is limited due to the strong peripheral cholinergic side effects. Objective: The aims of our experiments were to find out whether the GH response to GHRH can be augmented by rivastigmine, a new orally applicable and well-tolerated selective inhibitor of cerebral acetylchoinesterase. Methods: Eight healthy volunteers (age range 65–69 years) were studied. After an overnight fast, GHRH tests were done: 1 µg/kg GHRH was injected as an intravenous bolus. Blood samples for an immunoradiometric GH assay were taken at the time of GHRH injection (time 0) and after 15, 30, 45, 60, and 120 min. First, the baseline experiment was done: it consisted of two subsequent GHRH tests which were carried out within an interval of 120 min. Four weeks later the rivastigmine experiment was done identically, but 60 min before performing the second GHRH test, rivastigmine (4.5 mg) was administered orally. The GH secretory responses were expressed as areas under the curve (AUC; median, interquartile range), Wilcoxon’s signed-rank test was used for statistical comparisons. Results: Baseline experiment: The GH AUC of the first GHRH test was 1,040 (range 420–1,250) ng/ml/h. The repeated GHRH stimulation after 120 min (second GHRH test) showed a 13-fold decrease to 80 (range 60–130) ng/ml/h. Rivastigmine experiment: The GH AUC of the first GHRH test was 950 (range 540–1,430) ng/ml/h and, therefore, similar to that of the baseline experiment. 60 min after ingestion of the single oral dose of rivastigmine (4.5 mg), the following GHRH stimulation (second GHRH test) nearly doubled the GH AUC to 1,580 (range 860–3,330) ng/ml/h. Comparing the ΔGH AUC values (ΔGH AUC = GH AUC of the first GHRH test minus GH AUC of the second GHRH test), baseline experiment versus rivastigmine experiment, there was a 20-fold (p = 0.018) increase in GH AUC after rivastigmine pretreatment. Conclusions: Rivastigmine is a powerful drug to enhance GH release to repeated GHRH stimulation in healthy elderly human subjects. Future investigations are necessary to find out whether rivastigmine can restore the senile decline of the circadian GH secretion in the long term and, therefore, has new implications for patient treatment.

The hypothalamus–pituitary function after pituitary stereotactic radiosurgery: evaluation of growth hormone deficiency

Radiation therapy to the pituitary gland means a considerable risk of developing hypopituitarism. The aim of the study was to investigate the growth hormone releasing hormone (GHRH)-growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis after treatment with stereotactic radiosurgery to the pituitary because of Cushing's disease. Inpatient ward in university clinic. Eleven adult patients (eight women, three men), 20-65 years of age were studied 2.5-11.3 years after stereotactic radiosurgery (isocentre dose 50-100 Gy lesion-1) and compared with healthy controls. Spontaneous GH secretion was evaluated as 12-h night GH profiles. Stimulated GH responses were evaluated in seven of 11 patients using arginine-insulin and GHRH tests. Serum IGF-I levels were measured in fasting serum morning samples. All patients except one displayed blunted nocturnal GH profiles. After arginine-insulin challenge, six of seven patients displayed low GH release. GH response was higher after GHRH injection compared with both the response to arginine-insulin and to the maximum GH levels in the nocturnal profiles. Seven patients had an IGF-I standard deviation score (SDS) within the normal range for age. Serum IGF-I values were correlated to mean GH values in the 12-h night profile (r = 0.67, P < 0.05) and both these variables were negatively correlated to time elapse since last radiation treatment (r = -0.64, P < 0.05 and r = -0.78, P < 0.05, respectively). Our patients with Cushing's disease evaluated several years after stereotactic radiosurgery as the primary and only treatment, demonstrated severely blunted spontaneous GH secretion and GH response to arginine-insulin. A disturbed regulation at the hypothalamic level was suggested as mechanism for this. Noteworthy is that serum IGF-I values correlated to the mean values of the 12-h GH profile.

Sleep in mice with nonfunctional growth hormone-releasing hormone receptors.

The role of the somatotropic axis in sleep regulation was studied by using the lit/lit mouse with nonfunctional growth hormone (GH)-releasing hormone (GHRH) receptors (GHRH-Rs) and control heterozygous C57BL/6J mice, which have a normal phenotype. During the light period, the lit/lit mice displayed significantly less spontaneous rapid eye movement sleep (REMS) and non-REMS (NREMS) than the controls. Intraperitoneal injection of GHRH (50 microg/kg) failed to promote sleep in the lit/lit mice, whereas it enhanced NREMS in the heterozygous mice. Subcutaneous infusion of GH replacement stimulated weight gain, increased the concentration of plasma insulin-like growth factor-1 (IGF-1), and normalized REMS, but failed to restore normal NREMS in the lit/lit mice. The NREMS response to a 4-h sleep deprivation was attenuated in the lit/lit mice. In control mice, intraperitoneal injection of ghrelin (400 microg/kg) elicited GH secretion and promoted NREMS, and intraperitoneal administration of the somatostatin analog octretotide (Oct, 200 microg/kg) inhibited sleep. In contrast, these responses were missing in the lit/lit mice. The results suggest that GH promotes REMS whereas GHRH stimulates NREMS via central GHRH-Rs and that GHRH is involved in the mediation of the sleep effects of ghrelin and somatostatin.

Growth Hormone-Releasing Peptide-2 (GHRP-2) Acts Synergistically with Growth Hormone-Releasing Hormone (GHRH) to Release Growth Hormone (GH) in Swine

The aim of the present study was to examine the growth hormone (GH) response to the combined and repeated administrations of growth hormone-releasing peptide-2 (GHRP-2) plus growth hormone releasing hormone (GHRH) in swine. Six cross-bred castrated male swine, 130-135 days of age were used in this study. Animals were given a single intravenous (i.v.) injection of either GHRP-2 (30μg/kg BW), GHRH (1μg/kg BW) and GHRP-2 (30μg/kg BW) plus GHRH (1μg/kg BW) or 5ml saline (served as control) in random order with two days apart. GHRP-2 or GHRH alone and in combination with together stimulated the release of GH in swine. The peak concentrations of GH and areas under the GH response curve (GH AUC) for 120min after these treatments were significantly higher (P<0.01) than those in controls. The combined administration of these two peptides [GHRP-2 (30μg/kg BW) and GHRH (1μg/kg BW)] resulted in a GH AUC significantly greater than the arithmetic sum of those following their separate administrations (P<0.05), demonstrating the synergistic effect for GH release. GH responses to two successive i.v. injections of GHRP-2 (30μg/kg BW) plus GHRH (1μg/kg BW) at 2h interval in swine were increased after each injection; however, peak concentration of GH and GH AUC for 120min after the second injection were significantly lower (P<0.01) than those after the first injection. These results of the present study indicated that the combined administration of GHRP-2 and GHRH synergistically stimulates the release of GH in swine, and the GH responses to the co-administration of these two peptides decrease after the repeated injection. These findings suggest that GHRP-2 and GHRH act through different receptors and intracellular signal transduction and can be used together for stimulating further release of GH in swine.

Feeding-induced increases in insulin do not suppress secretion of growth hormone☆

Secretion of growth hormone (GH) is reduced for several hours after feeding when access to feed is restricted to a 2-hr period each day. We hypothesized that increased secretion of insulin after feeding inhibits release of GH from the anterior pituitary gland. Our objectives were to determine whether: 1) alloxan prevents concentrations of insulin from increasing after feeding steers; 2) concentrations of GH remain high after feeding alloxan-treated steers; and 3) GH-releasing hormone (GHRH) stimulates greater release of GH in alloxan-treated, than in control, steers after feeding. Steers were injected iv with either saline (control) or with alloxan (110 mg/kg) ( n = 4 per group). Concentrations of insulin were not different (P = 0.61) between control and alloxan-treated steers before feeding (87.5 ± 33.6 pmol/l). However, alloxan prevented insulin from increasing (P < 0.001) after feeding (131.8 pmol/l) compared with control steers (442.0 pmol/l) (pooled SEM = 47.5). Overall, GH was higher (P < 0.05) in alloxan-treated (6.4 ng/ml) than in control steers (3.7 ng/ml) (pooled SEM = 0.7), but GH decreased (P < 0.001) after feeding in both groups. Iv injection of GHRH stimulated release of GH 1 hr before, but not when injected 1 hr after feeding (P < 0.001). In addition, net areas under the GH curve were not significantly different between control and alloxan-treated groups. We conclude that increased concentrations of insulin after feeding do not mediate feeding-induced suppression of GH secretion in steers.

Hypothalamic mediated action of free fatty acid on growth hormone secretion in sheep.

Experimental data suggest that elevated FFA levels play a leading role in the impaired GH secretion in obesity and may therefore contribute to the maintenance of overweight. GH has a direct lipolytic effect on adipose tissue; in turn, FFA elevation markedly reduces GH secretion. This suggests the existence of a classical endocrine feedback loop between FFA and GH secretion. However, the FFA mechanism of action is not yet understood. The involvement of somatostatin (SRIH) is controversial, and in vitro experiments suggest a direct effect of FFA on the pituitary. In sheep it is possible to collect hypophysial portal blood and quantify SRIH secretion in hypophysial portal blood under physiological conscious and unstressed conditions. In this study we determined the effects of FFA (Intralipid and heparin) infusion on peripheral GH and portal SRIH levels in intact rams chronically implanted with perihypophysial cannula and in rams actively immunized against SRIH to further determine SRIH-mediated FFA effects on GH axis. Immediately after initiation of Intralipid infusion, we observed a marked increase in the FFA concentration (2160 +/- 200 vs. 295 +/- 28 nmol/ml; P < 0.01) as well as a significant decrease in basal GH secretion (1.8 +/- 0.1 vs. 2.5 +/- 0.3 ng/ml; P < 0.05) and a drastic reduction of the GH response to i.v. GH-releasing hormone injection (4.8 +/- 0.7 ng/ml in FFA group vs. 35.8 +/- 9.7 ng/ml in saline group; P < 0.01). No change in plasma insulin-like growth factor I levels was observed. During the first 2 h of infusion, the GH decrease observed was concomitant with a significant increase in portal SRIH levels (22.1 +/- .2 vs. 13 +/- 1.6 pg/ml; P < 0.01). In rams actively immunized against SRIH, the effect of FFA on basal GH secretion was biphasic. During the first 90 min of infusion, the decrease in GH induced by FFA was significantly blunted in rams actively immunized against SRIH (57 +/- 9% for immunized rams vs. 23.5 +/- 2.5% for control rams). This corresponds to the period of increased SRIH portal levels. After this first 90-min period, no difference was seen between control and immunized rams. Our results show that FFA exert their inhibitory action on the GH axis at both pituitary and hypothalamic levels, the latter mainly during the first 90 min, through increased SRIH secretion.

Endotoxin Injection Increases Growth Hormone and Somatostatin Secretion in Sheep

Endotoxin has been shown to stimulate GH secretion in human and sheep. However, changes in hypothalamic neurohormones involved in the GH regulation by endotoxin have never been studied in vivo. In sheep it is possible to collect hypophysial portal blood (HPB) and quantify GH-releasing hormone (GHRH) and somatostatin (SRIH) secretion under physiological conditions. The purpose of this study was to determine the effect of an acute iv endotoxin administration on the secretion of these peptides in sheep. Endotoxin induced a sustained increase of GH (×6.2 ± 1.3) in intact rams. This stimulation was delayed and less marked when compared with the hypothalamic-pituitary-adrenal axis. Surprisingly, the GH increase was associated with an important rise of jugular (×10.6± 2.4) and portal (×7.9 ± 3) SRIH levels, without a significant GHRH increase. To determine if the portal SRIH increase was a consequence of an increased short feedback of GH, we studied GH response to endotoxin after a previous GHRH injection to deplete the pituitary pools of GH. In that case, despite the absence of increase of GH after endotoxin treatment, SRIH levels was markedly increased. For the first time we have observed an experimental situation in sheep with a simultaneous and closed amplitude increase in jugular and portal SRIH. The source of jugular SRIH is likely the gastrointestinal tract and the increased jugular SRIH release in systemic circulation might be in part responsible for the increase of hypophysial portal SRIH. Ultimately our results show that endotoxin induced a complex reaction at multiple levels with a specific increase in both portal and peripheral SRIH levels. The surprising association of a lack of change in GHRH release and an increased secretion of SRIH with the increase of GH suggests that the effect of endotoxin on GH axis is mainly a pituitary one. The selective blockade of somatostatin should be useful for a better knowledge of the role of SRIH stimulation in the physiopathology of septic shock.