GHRH Analog Research Articles

Actions and Potential Therapeutic Applications of Growth Hormone-Releasing Hormone Agonists.

In this article, we briefly review the identification of GHRH, provide an abridged overview of GHRH antagonists, and focus on studies with GHRH agonists. Potent GHRH agonists of JI and MR class were synthesized and evaluated biologically. Besides the induction of the release of pituitary GH, GHRH analogs promote cell proliferation and exert stimulatory effects on various tissues, which express GHRH receptors (GHRH-Rs). A large body of work shows that GHRH agonists, such as MR-409, improve pancreatic β-cell proliferation and metabolic functions and facilitate engraftment of islets after transplantation in rodents. Accordingly, GHRH agonists offer a new therapeutic approach to treating diabetes. Various studies demonstrate that GHRH agonists promote repair of cardiac tissue, producing improvement of ejection fraction and reduction of infarct size in rats, reduction of infarct scar in swine, and attenuation of cardiac hypertrophy in mice, suggesting clinical applications. The presence of GHRH-Rs in ocular tissues and neuroprotective effects of GHRH analogs in experimental diabetic retinopathy indicates their possible therapeutic applications for eye diseases. Other effects of GHRH agonists, include acceleration of wound healing, activation of immune cells, and action on the central nervous system. As GHRH might function as a growth factor, we examined effects of GHRH agonists on tumors. In vitro, GHRH agonists stimulate growth of human cancer cells and upregulate GHRH-Rs. However, in vivo, GHRH agonists inhibit growth of human cancers xenografted into nude mice and downregulate pituitary and tumoral GHRH-Rs. Therapeutic applications of GHRH analogs are discussed. The development of GHRH analogs should lead to their clinical use.

The Effects of Tesamorelin on Phosphocreatine Recovery in Obese Subjects With Reduced GH

Few studies have assessed the relationship between GH and mitochondrial function. The objective of this study was to determine the effects of improving IGF-I using a GHRH analog, tesamorelin, on mitochondrial function assessed by phosphocreatine (PCr) recovery using (31)P magnetic resonance spectroscopy in obese adults with reduced GH. A total of 39 obese men and women with reduced GH secretion as determined by GHRH-arginine stimulation tests underwent magnetic resonance spectroscopy as part of a 12-month, double-blind, randomized, placebo-controlled trial comparing tesamorelin vs placebo. PCr recovery after submaximal exercise was assessed at baseline and at 12 months. At baseline, there were no differences in age, sex, race/ethnicity, and GH or PCr parameters between tesamorelin and placebo. After 12 months, tesamorelin treatment led to a significantly greater increase in IGF-I than did placebo treatment (change, 102.9±31.8 μg/L vs 22.8±8.9 μg/L, tesamorelin vs placebo; P=.02). We demonstrated a significant positive relationship between increases in IGF-I and improvements in PCr recovery represented as ViPCr (R=0.56; P=.01). The association between IGF-I and PCr recovery was even stronger among subjects treated with tesamorelin only (ViPCr: R=0.71; P=.03). This association remained significant after controlling for age, sex, race, ethnicity, and parameters of body composition and insulin sensitivity (all P<.05). Increases in IGF-I from 12 months of treatment with tesamorelin were significantly associated with improvements in PCr recovery parameters in obese men and women with reduced GH secretion, suggestive of improvements in mitochondrial function.

Sarcopenic obesity

The increasing prevalence of sarcopenic obesity in older adults has heightened interest in identifying the most effective treatment. This review highlights recent progress in the management, with an emphasis on lifestyle interventions and pharmacologic therapy aimed at reversing sarcopenic obesity. Whereas weight loss and exercise independently reverse sarcopenic obesity, they act synergistically in combination to improve body composition and physical function, beyond which is observed with either intervention alone. Optimizing protein intake appears to have beneficial effects on net muscle protein accretion in older adults. Myostatin inhibition is associated with favorable changes in body composition in animal studies, although experience in humans is relatively limited. Testosterone and growth hormone offer improvements in body composition, but the benefits must be weighed against potential risks of therapy. GHRH-analog therapy shows promise, but further studies are needed in older adults. At present, lifestyle interventions incorporating both diet-induced weight loss and regular exercise appear to be the optimal treatment for sarcopenic obesity. Maintenance of adequate protein intake is also advisable. Ongoing studies will determine whether pharmacologic therapy such as myostatin inhibitors or GHRH analogs have a role in the treatment of sarcopenic obesity.

Macimorelin (AEZS-130)-Stimulated Growth Hormone (GH) Test: Validation of a Novel Oral Stimulation Test for the Diagnosis of Adult GH Deficiency

Context:In the absence of panhypopituitarism and low serum IGF-I levels, the diagnosis of adult GH deficiency (AGHD) requires confirmation with a GH stimulation test. Macimorelin is a novel, orally active ghrelin mimetic that stimulates GH secretion.Objective:The objective of the study was to determine the diagnostic efficacy and safety of macimorelin in AGHD.Design:This was a multicenter open-label study comparing the diagnostic accuracy of oral macimorelin with that of arginine+GHRH in AGHD patients and healthy, matched controls. After 43 AGHD patients and 10 controls were tested, the GHRH analog Geref Diagnostic [GHRH(1–29)NH2] became unavailable in the United States. The study was completed by testing 10 additional AGHD patients and 38 controls with macimorelin alone.Main Outcome Measure:Peak GH area under the receiver operating characteristic curve after macimorelin was measured.Results:Fifty AGHD subjects and 48 controls were evaluated. Peak GH levels in AGHD patients and controls after macimorelin were 2.36 ± 5.69 and 17.71 ± 19.11 ng/mL, respectively (P < .0001). With macimorelin, the receiver operating characteristic analysis yielded an optimal GH cut point of 2.7 ng/mL, with 82% sensitivity, 92% specificity, and 13% misclassification rate. For subjects receiving both tests, macimorelin showed discrimination comparable with arginine+GHRH (area under the receiver operating characteristic curve 0.99 vs 0.94, respectively, P = .29). Obesity (body mass index > 30 kg/m2) was present in 58% of subjects, and peak GH levels were inversely associated with body mass index in controls (r = −0.37, P = .01). Using the separate cut points of 6.8 ng/mL for nonobese and 2.7 for obese subjects reduced the misclassification rate to 11%. Only 1 drug-related serious adverse event, an asymptomatic QT interval prolongation on the electrocardiogram, was reported.Conclusion:Oral macimorelin is safe, convenient, and effective in diagnosing AGHD with accuracy comparable with the arginine+GHRH test.

OR03-4 Five months treatment with a long-acting GHRH analog improves cognition in healthy older men and women and in patients with mild cognitive impairment

specificity/90% accuracy. By modified intent-to-treat analysis, which included results from two patients in whom the diagnosis of GHD was not confirmed (MITT, n = 52 AGHD, 48 controls), these cutoffs provided 86% sensitivity/85% specificity/86% accuracy in lean/overweight subjects and 83% sensitivity/96% specificity/90% accuracy in the obese group. The areas under the curve for receiver operating characteristic (ROC) analysis also increased with BMI adjustment–from 0.923 unadjusted to 0.925 adjusted in the PP groups, and from 0.912 to 0.918 in the MITT groups.

Metabolic Effects of a Growth Hormone-Releasing Factor in Obese Subjects with Reduced Growth Hormone Secretion: A Randomized Controlled Trial

Obesity is associated with reduced GH secretion and increased cardiovascular disease risk. We performed this study to determine the effects of augmenting endogenous GH secretion on body composition and cardiovascular disease risk indices in obese subjects with reduced GH secretion. A randomized, double-blind, placebo-controlled study was performed involving 60 abdominally obese subjects with reduced GH secretion. Subjects received tesamorelin, a GHRH(1-44) analog, 2 mg once daily, or placebo for 12 months. Abdominal visceral adipose tissue (VAT) was assessed by abdominal computed tomography scan, and carotid intima-media thickness (cIMT) was assessed by ultrasound. Treatment effect was determined by longitudinal linear mixed-effects modeling. VAT [-16 ± 9 vs.19 ± 9 cm(2), tesamorelin vs. placebo; treatment effect (95% confidence interval): -35 (-58, -12) cm(2); P = 0.003], cIMT (-0.03 ± 0.01 vs. 0.01 ± 0.01 mm; -0.04 (-0.07, -0.01) mm; P = 0.02), log C-reactive protein (-0.17 ± 0.04 vs. -0.03 ± 0.05 mg/liter; -0.15 (-0.30, -0.01) mg/liter, P = 0.04), and triglycerides (-26 ± 16 vs. 12 ± 8 mg/dl; -37 (-67, -7) mg/dl; P = 0.02) improved significantly in the tesamorelin group vs. placebo. No significant effects on abdominal sc adipose tissue (-6 ± 6 vs. 3 ± 11 cm(2); -10 (-32, +13) cm(2); P = 0.40) were seen. IGF-I increased (86 ± 21 vs. -6 ± 8 μg/liter; 92 (+52, +132) μg/liter; P < 0.0001). No changes in fasting, 2-h glucose, or glycated hemoglobin were seen. There were no serious adverse events or differences in adverse events between the groups. Among obese subjects with relative reductions in GH, tesamorelin selectively reduces VAT without significant effects on sc adipose tissue and improves triglycerides, C-reactive protein, and cIMT, without aggravating glucose.

How to diagnose a lipodystrophy syndrome

The spectrum of adipose tissue diseases ranges from obesity to lipodystrophy, and is accompanied by insulin resistance syndrome, which promotes the occurrence of type 2 diabetes, dyslipidemia and cardiovascular complications. Lipodystrophy refers to a group of rare diseases characterized by the generalized or partial absence of adipose tissue, and occurs with or without hypertrophy of adipose tissue in other sites. They are classified as being familial or acquired, and generalized or partial. The genetically determined partial forms usually occur as Dunnigan syndrome, which is a type of laminopathy that can also manifest as muscle, cardiac, neuropathic or progeroid involvement. Gene mutations encoding for PPAR-gamma, Akt2, CIDEC, perilipin and the ZMPSTE 24 enzyme are much more rare. The genetically determined generalized forms are also very rare and are linked to mutations of seipin AGPAT2, FBN1, which is accompanied by Marfan syndrome, or of BANF1, which is characterized by a progeroid syndrome without insulin resistance and with early bone complications. Glycosylation disorders are sometimes involved. Some genetically determined forms have recently been found to be due to autoinflammatory syndromes linked to a proteasome anomaly (PSMB8). They result in a lipodystrophy syndrome that occurs secondarily with fever, dermatosis and panniculitis. Then there are forms that are considered to be acquired. They may be iatrogenic (protease inhibitors in HIV patients, glucocorticosteroids, insulin, graft-versus-host disease, etc.), related to an immune system disease (sequelae of dermatopolymyositis, autoimmune polyendocrine syndromes, particularly associated with type 1 diabetes, Barraquer-Simons and Lawrence syndromes), which are promoted by anomalies of the complement system. Finally, lipomatosis is currently classified as a painful form (adiposis dolorosa or Dercum's disease) or benign symmetric multiple form, also known as Launois-Bensaude syndrome or Madelung's disease, which are sometimes related to mitochondrial DNA mutations, but are usually promoted by alcohol. In addition to the medical management of metabolic syndrome and the sometimes surgical treatment of lipodystrophy, recombinant leptin provides hope for genetically determined lipodystrophy syndromes, whereas modifications in antiretroviral treatment and tesamorelin, a GHRH analog, is effective in the metabolic syndrome of HIV patients. Other therapeutic options will undoubtedly be developed, dependent on pathophysiological advances, which today tend to classify genetically determined lipodystrophy as being related to laminopathy or to lipid droplet disorders.

Effects of a Growth Hormone-Releasing Hormone Analog on Endogenous GH Pulsatility and Insulin Sensitivity in Healthy Men

Strategies to augment pulsatile GH may be beneficial in patients with excess visceral adiposity, in whom GH secretion is reduced. The objective of this study was to determine the effects of a novel GHRH (GHRH(1-44)) analog, tesamorelin, on endogenous GH pulsatility and insulin sensitivity in healthy men. Thirteen males (mean age 45 ± 3 yr and body mass index 27.3 ± 1.2 kg/m(2)) received tesamorelin 2 mg sc once daily for 2 wk, with assessment made at baseline, after 2 wk of treatment, and after 2 wk of withdrawal. The primary end point was change in mean overnight GH as determined by overnight frequent sampling. Secondary end points included insulin-stimulated glucose uptake as measured by euglycemic hyperinsulinemic clamp; IGF-I; and GH secretion parameters, including pulse area, pulse frequency, and basal secretion. Tesamorelin treatment increased mean overnight GH (change +0.5 ± 0.1 μg/liter, P = 0.004), average log(10) GH peak area (change +0.4 ± 0.1 log(10) μg/liter, P = 0.001), and basal GH secretion (change +0.008 ± 0.003 μg/liter · min, P = 0.008). IGF-I increased by 181 ± 22 μg/liter (P < 0.0001). Neither fasting glucose (P = 0.93) nor insulin-stimulated glucose uptake (P = 0.61) was significantly affected by tesamorelin. Once-daily short-term treatment with a GHRH(1-44) analog, tesamorelin, augments basal and pulsatile GH secretion. Moreover, although tesamorelin significantly increases IGF-I, peripheral insulin-stimulated glucose uptake appears to be preserved.

Pulsatile Secretion of Growth Hormone (GH) Persists during Continuous Stimulation by CJC-1295, a Long-Acting GH-Releasing Hormone Analog

Pulsatile GH secretion is considered important for many of the hormone's physiological effects. Short-term GHRH infusions enhance GH pulsatility and increase IGF-I, but the short GHRH half-life limits its therapeutic use. A synthetic GHRH analog (CJC-1295) that binds permanently to endogenous albumin after injection (half-life = 8 d) stimulates GH and IGF-I secretion in several animal species and in normal human subjects and enhances growth in rats. Our objective was to assess GH pulsatility after a single injection of CJC-1295 and determine which GH secretion parameters correlated to the increase in IGF-I production. GH pulsatility was assessed by 20-min blood sampling during an overnight 12-h period in healthy 20- to 40-yr-old men before and 1 wk after injection of either 60 or 90 microg/kg CJC-1295. GH secretion was increased after CJC-1295 administration with preserved pulsatility. The frequency and magnitude of GH secretory pulses were unaltered. However, basal (trough) GH levels were markedly increased (7.5-fold; P < 0.0001) and contributed to an overall increase in GH secretion (mean GH levels, 46%; P < 0.01) and IGF-I levels (45%; P < 0.001). No significant differences were observed between the responses to the two drug doses. The IGF-I increases did not correlate with any parameters of GH secretion. CJC-1295 increased trough and mean GH secretion and IGF-I production with preserved GH pulsatility. The marked enhancement of trough GH levels by continuous GHRH stimulation implicates the importance of this effect on increasing IGF-I. Long-acting GHRH preparations may have clinical utility in patients with intact pituitary GH secretory capability.

Cortistatin Inhibits Growth Hormone Release from Human Fetal and Adenoma Pituitary Cells and Prolactin Secretion from Cultured Prolactinomas

Cortistatin (CST) is a neuropeptide that shares high homology with somatostatin and binds with high affinity to all somatostatin receptor (SSTR) subtypes. Many of its endocrine and biological activities overlap with those of somatostatin. The objective of the study was to assess the direct in vitro effects of CST on human pituitary hormone secretion. This study was performed in the endocrine laboratory of a tertiary academic medical center. Primary cell cultures of human fetal (21-25 wk gestation) pituitary tissues and cultured hormone-secreting adenoma cells were used in this study. Cell cultures were incubated with CST-14 or CST-17, somatostatin, GHRH, SSTR analogs, and ghrelin analogs, and hormone secretion was analyzed. GH and prolactin (PRL) medium concentrations were tested by hormone assay, and SSTR mRNA was tested by RT-PCR. CST-14 (10 nm) inhibited GH secretion by up to 65% in all fetal pituitary specimens after 4-h incubation (P < 0.05). CST-14 or CST-17 (10 nm) inhibited basal GH secretion in six of the 13 GH-cell adenomas and two of the three GH-PRL mixed adenomas. CST-17 (100 nm) suppressed the GH response to GHRH and ghrelin analog (10 nm each) by 30-50% in adenomas (P < 0.05). Three PRL-adenomas treated with CST-17 (10 nm) showed a 20-40% inhibition of PRL release (P < 0.05), whereas in three others no suppression or mild response was achieved at this concentration. A comparable inhibition of PRL secretion was obtained with SSTR5-selective analog but significantly less with SSTR2-preferential compounds. RT-PCR revealed the expression of both SSTR2 and SSTR5 in all GH-cell and mixed adenomas studied and all PRL-secreting adenomas studied, except for two of the CST-resistant prolactinomas, in which SSTR5 was absent. This is the first report of in vitro CST suppression of human GH and PRL in cultured pituitary tissues. The regulation of PRL release from cultured adenomas appears to be primarily mediated by SSTR5.

Editorial [Hot Topic: GHRH Analogs and Cancer (Guest Editor: Hippokratis Kiaris )

Editorial [Hot Topic: GHRH Analogs and Cancer (Guest Editor: Hippokratis Kiaris )

Prolonged Stimulation of Growth Hormone (GH) and Insulin-Like Growth Factor I Secretion by CJC-1295, a Long-Acting Analog of GH-Releasing Hormone, in Healthy Adults

Therapeutic use of GHRH to enhance GH secretion is limited by its short duration of action. The objective of this study was to examine the pharmacokinetic profile, pharmacodynamic effects, and safety of CJC-1295, a long-acting GHRH analog. The study design was two randomized, placebo-controlled, double-blind, ascending dose trials with durations of 28 and 49 d. The study was performed at two investigational sites. Healthy subjects, ages 21-61 yr, were studied. CJC-1295 or placebo was administered sc in one of four ascending single doses in the first study and in two or three weekly or biweekly doses in the second study. The main outcome measures were peak concentrations and area under the curve of GH and IGF-I; standard pharmacokinetic parameters were used for CJC-1295. After a single injection of CJC-1295, there were dose-dependent increases in mean plasma GH concentrations by 2- to 10-fold for 6 d or more and in mean plasma IGF-I concentrations by 1.5- to 3-fold for 9-11 d. The estimated half-life of CJC-1295 was 5.8-8.1 d. After multiple CJC-1295 doses, mean IGF-I levels remained above baseline for up to 28 d. No serious adverse reactions were reported. Subcutaneous administration of CJC-1295 resulted in sustained, dose-dependent increases in GH and IGF-I levels in healthy adults and was safe and relatively well tolerated, particularly at doses of 30 or 60 microg/kg. There was evidence of a cumulative effect after multiple doses. These data support the potential utility of CJC-1295 as a therapeutic agent.

Study on the constructions and activities of three novel hGHRH analogs with N-terminal prolyl modulation +

Growth hormone releasing hormone is one of the hormones secreted by the hypothalamus. Because of its potential applications in agriculture and medicine, its short half-life and its expensive chemical synthesis, an analog with high GHRH activity and prolonged half-life has been looked for. The fusion partner gene with 127 amino acid residues of the C-terminus from l-asparaginase was recombined respectively with asp-pro-pro-hGHRH(1–44), asp-pro-hGHRH(1–44) or asp- 1 pro-GHRH(2–44) genes synthesized by PCR method to form three kinds of fusion proteins with unique acid labile linker Asp-Pro. The Pro-Pro-hGHRH(1–44), Pro-hGHRH(1–44), and 1Pro-GHRH(2–44) peptides were purified to homogeneity by means of cell disruption, washing of inclusion body, ethanol fraction precipitation, acid hydrolysis, SP-Sephadex C-25 and Sephadex G-10 column chromatography. The peptide molecular mass of 5235, 5139 or 4975 Da was determined by ESI mass spectroscopy and purity was determined by SDS-PAGE. In the study of in vitro activity, the antiserum kit against human GH and peptide doses of 0.1, 1.0 and 10 μg/ml were used. These peptides obviously increased GH releases both from human pituitary and from rat pituitary. The activity comparisons showed that there was significant difference between Pro-Pro-hGHRH(1–44)-Gly-Gly-Cys and Pro-Pro-hGHRH(1–44) at 1.0 μg/ml, or between 1Pro-hGHRH(2–44) and Pro-Pro-hGHRH(1–44) or Pro-hGHRH(1–44) at 10 μg/ml. The structure-activity relationships showed that at the original C-terminus, for rat pituitary the activity of the GHRH analog with 1Tyr→Pro was more than that of Pro-Pro-hGHRH(1–44) or Pro-hGHRH(1–44). The results showed that the analogs had good GH-releasing activity and species specificity.

Immunohistochemical detection of GHRH and its receptor splice variant 1 in primary human breast cancers.

GHRH is secreted by the hypothalamus and, upon binding to specific GHRH receptors in the pituitary, stimulates growth hormone (GH) production and release from the pituitary. In addition to this neuroendocrine action, accumulated evidence implies additional roles for GHRH in carcinogenesis in non-pituitary tissues. In vitro and in vivo studies have shown that splice variant 1 (SV1) of the GHRH receptor, which is widely expressed in non-pituitary tissues and cancers, can mediate the proliferative effects of GHRH. The aim of the present study was to investigate the operation of an autocrine stimulatory loop between GHRH and SV1 in primary breast tumors. Fifty-three primary breast tumors were evaluated for GHRH and SV1 expression. Expression of GHRH and SV1 was assessed by immunohistochemistry using anti-GHRH SV95 and anti-SV1 2317/5 polyclonal antibodies. About 40% of the specimens tested express GHRH and/or SV1 (approx. 25% each), while in 35% of these positive specimens co-expression of these antigens was detected (P<0.01). Furthermore, a correlation of GHRH, but not SV1, expression was detected in lobular compared with ductal carcinomas. These results constitute the first demonstration for the expression of GHRH and SV1 in primary breast cancers, and provide evidence for the operation of an autocrine stimulatory loop between GHRH and SV1 in primary cancers. Our findings indicate that GHRH analogs could have diagnostic and therapeutic applications for the management of breast cancer.

Preparation and a simple one-step purification of [His1-mono-125I-Tyr10,Nle27]-hGHRH(1-32)-NH2

A one-step purification of [His1-mono-125I-Tyr10,Nle27]-hGHRH(1-32)-NH2, prepared using chloramine-T, by HPLC with isocratic elution is described. The labeled GHRH analog was suitable for GHRH receptor binding assays. Copyright © 2002 John Wiley & Sons, Ltd.

Preparation and a simple one‐step purification of [His1‐mono‐125I‐Tyr10,Nle27]‐hGHRH(1‐32)‐NH2

AbstractA one‐step purification of [His1‐mono‐125I‐Tyr10,Nle27]‐hGHRH(1‐32)‐NH2, prepared using chloramine‐T, by HPLC with isocratic elution is described. The labeled GHRH analog was suitable for GHRH receptor binding assays. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Endométriose colorectale. Diagnostic et prise en charge

Endometriosis occurs in 5 to 10% of the female population. Bowel involvement present in 6 to 30% of cases is predominantly localized in the pelvic parts of the colon and rectum, close to the uterus. The goal of this work was to describe the present diagnostic and therapeutic management of deep colorectal endometriosis defined as infiltrating the digestive wall and usually requiring surgery. Colorectal endometriosis is a disabling disease. Anatomic lesions mimic those of a cancer. Modern investigations include endorectal endosonography, recognized as the best mean to assess the depth of invasion into the intestinal wall, and magnetic resonance imaging. Associated to exploratory laparoscopy, these investigations allow to select the optimal operative strategy for multifocal and complexe lesions. Surgical objective is a total resection of endometriomas, to guarantee symptom relief and avoid recurrence. Difficulties in these procedures are usually due to fibrotic and vascularised lesions and associated gynaecological disorders. In elective cases, preoperative GH-RH analog hormonal treatment makes easier the surgical procedure. Colonic and/or rectal restorative resections, performed through laparoscopic approach or more frequently through laparotomy, have to be done acccording to the usual standards of colorectal surgery. Conservative surgery of the ovaries is mandatory in premenopausal patients.

Antiproliferative actions of growth hormone-releasing hormone antagonists on MiaPaCa-2 human pancreatic cancer cells involve cAMP independent pathways

We evaluated the effects of GHRH antagonists on the proliferation of MiaPaCa-2 human pancreatic cancer cells and cAMP signaling in vitro. GHRH antagonists inhibited the proliferation of MiaPaCa-2 cells in vitro in a dose-dependent way and caused a significant elevation in cAMP production. In a superfusion system, short-term exposure of the cells to GHRH antagonists evoked an acute, dose-dependent release of cAMP into the medium. Native GHRH, which stimulates cAMP efflux from pituitary at nanomolar doses, did not influence cAMP release from cultured or superfused MiaPaCa-2 cells even at 10–30 μM. VIP, PACAP, secretin and glucagon also did not influence cell proliferation or cAMP production. Adenylate cyclase activator forskolin (FSK) caused a greater cAMP response, but a smaller antiproliferative effect than GHRH antagonists. Combined treatment with FSK and GHRH antagonist JV-1-38 potentiated the cAMP-inducing effect of FSK, but did not produce a greater inhibition of cell proliferation than JV-1-38 alone. A selective accumulation of radiolabeled GHRH antagonist [ 125I]JV-1-42 in vivo in MiaPaCa-2 carcinoma xenografted into nude mice was also observed. In conclusion, second messengers other than cAMP participate in the signal transduction pathways of GHRH analogs mediated by tumoral GHRH receptors.

A two-sample method for assessing growth hormone response to growth hormone-releasing hormone challenge: use as a predictor of gain in beef bulls.

In two experiments, Black Angus bulls were challenged at weaning with GHRH analog and evaluated for their GH response to determine whether GH response can predict subsequent growth characteristics. The GH response was determined by measuring GH in blood serum collected 0 and 10 min after GHRH injection (Exp. 1: 1.5 microg/100 kg BW human GHRH, n = 34; Exp. 2: 1.5 and 4.5 microg/100 kg BW bovine GHRH [treatments LGHRH and HGHRH, respectively] administered 3 h after a 4.5 microg/100 kg BW "clearance dose" of GHRH, n = 38]. In Exp. 1, GH response did not predict growth or carcass measurements. In Exp. 2, GH response to LGHRH was positively related to ADG (R2 = .18; P = .007) during a 112-d controlled feeding trial. In addition, there was a tendency for bulls with a greater GH response to HGHRH to exhibit greater ADG than animals with a low response. However, GH response to GHRH was not related to changes in hip height (HH) or carcass ultrasound measurements at d 112 of the growth performance trial. Response of GH to repeated GHRH challenges was consistent within animal over time (r = .47; P = .003). The use of a clearance dose 3 h prior to GHRH challenge improved the relationship between GH response and ADG. Results of this study suggest that GH response to GHRH challenge is a useful tool for identifying beef bulls with superior growth potential.

Synthesis and biological evaluation of antagonists of growth hormone-releasing hormone with high and protracted in vivo activities.

Some antagonists of human growth hormone-releasing hormone (hGH-RH) synthesized previously were shown to inhibit in vivo proliferation of various human cancers in nude mice. However, the activity of these analogs requires an increase to assure clinical efficacy. In an attempt to prepare hGH-RH antagonists with a high and protracted activity, we synthesized and biologically tested 22 antagonistic analogs of hGH-RH(1-29)NH2. The ability of the antagonists to inhibit hGH-RH-induced GH release was evaluated in vitro in a superfused rat pituitary system, as well as in vivo after i.v. injection into rats. The binding affinity of the peptides to GH-RH receptors also was determined. All antagonistic analogs had the common core sequence [PhAc-Tyr1,D-Arg2, Phe(4-Cl)6 (para-chlorophenylalanine), Abu15 (alpha-aminobutyric acid), Nle27]hGH-RH(1-29)NH2 and contained Arg, D-Arg, homoarginine (Har), norleucine (Nle), and other substitutions. The following analogs were determined to have a high and/or protracted antagonistic activity: [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6,Arg9,Abu15,Nle27, D-Arg29]hGH-RH(1-29)NH2 (JV-1-10), [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6, Abu15,Nle27,D-Arg28,Har29]hGH-RH(1-29)NH2 (MZ-6-55), [PhAc-Tyr1, D-Arg2,Phe(4-Cl)6,Arg9,Abu15,Nle27,D-Arg28,Har29 ]hGH-RH(1-29)NH2 (JV-1-36), and [PhAc-Tyr1,D-Arg2,Phe(4-Cl)6,Har9,Tyr(Me)10,Abu15, Nle27,D-Arg28,Har29]hGH-RH(1-29)NH2 (JV-1-38). Among the peptides tested, analog JV-1-36 showed the highest GH-RH antagonistic activity in vitro and also induced a strong and prolonged inhibition of GH release in vivo for at least 30 min. The antagonist JV-1-38 was slightly less potent than JV-1-36 both in vitro and in vivo but proved to be very long-acting in vivo, suppressing the GH-RH-induced GH release even after 60 min. High and protracted in vivo activities of these antagonists indicate an improvement over earlier GH-RH analogs. Some of these hGH-RH antagonists could find clinical applications in the treatment of cancers dependent on insulin-like growth factors I and II.