Binding and functional studies with the growth hormone receptor antagonist, B2036-PEG (pegvisomant), reveal effects of pegylation and evidence that it binds to a receptor dimer

GH actions are dependent on receptor dimerization. The GH receptor antagonist, B2036-PEG, has been developed for treating acromegaly. B2036 has mutations in site 1 to enhance receptor binding and in site 2 to block receptor dimerization. Pegylation (B2036-PEG) increases half-life and lowers immunogenicity, but high concentrations are required to control insulin-like growth factor-I levels. We examined antagonist structure and function and the impact of pegylation on biological efficacy. Unpegylated B2036 had a 4.5-fold greater affinity for GH binding protein (GHBP) than GH but similar affinity for membrane receptor. Pegylation substantially reduced membrane binding affinity and receptor antagonism, as assessed by a transcription assay, by 39- and 20-fold, respectively. GHBP reduced antagonist activity of unpegylated B2036 but did not effect antagonism by B2036-PEG. B2036 down-regulated receptors, and membrane binding sites doubled in the presence of dimerization-blocking antibodies, suggesting that B2036 binds to a receptor dimer. It is concluded that the high concentration requirement of B2036-PEG for clinical efficacy relates to pegylation, which decreases binding to membrane receptor but has the advantages of reduced clearance, immunogenicity, and interactions with GHBP. Our studies suggest that B2036 binds to a receptor dimer and induces internalization but not signaling.

The amygdala: a critical modulator of sensory influence on sleep

The influence of external stimuli and the memories of both unpleasant and pleasant conditions clearly can have a considerable impact on the quality of sleep. The amygdala, a structure that plays an important role in coding the emotional significance of stimuli and is heavily interconnected with brainstem nuclei known to be involved in sleep control, has received little attention from sleep researchers. We report on a series of studies, focusing on its central nucleus (Ace). Presence of serotonin (5-HT) in Ace caused a rapid change of state when injected in rapid- eye-movement sleep (REM) compared with non-REM (NREM) injections. A 5-HT antagonist released ponto-geniculo-occipital waves (PGO) into NREM. Stimuli conditioned by pairing with aversive stimuli in a fear-conditioning paradigm significantly increased sound-elicited PGO and reduced REM.

In rats with sepsis, the acute fall in IGF-I is associated with an increase in circulating growth hormone-binding protein levels

OBJECTIVE

Growth hormone (GH) given to reverse muscle catabolism in critical illness increased mortality, illustrating the need for better understanding of the pathophysiology of the GH axis. We describe the relationship between changes in plasma insulin-like growth factor-I (IGF-I) and growth hormone-binding protein (GHBP) levels and hepatic growth hormone-binding in rats with sepsis.

DESIGN

Randomised, controlled study.

SETTING

University research laboratory.

SUBJECTS

One hundred and eleven male Wistar rats.

INTERVENTION

Three groups of rats underwent caecal ligation and puncture (CLP) and three groups laparotomy only (LAP). Survivors were killed at 24, 72, and 96 h. All animals were starved during the study. Twelve rats were killed at the start of the experiment (baseline) and twelve (allowed food) at 96 h.

MEASUREMENTS AND RESULTS

Plasma levels of IGF-I and GHBP and binding of 125I-labelled human GH in liver homogenates were measured. IGF-I fell significantly following both CLP and LAP; at 24 h, IGF-I levels were lower after CLP than LAP (950 +/- 74 vs 1,522 +/- 60 microg/l, P = < 0.001). GHBP increased at 24 h following both CLP and LAP (45.6 +/- 1.87 and 47.7 +/- 3.01 vs 38.7 +/- 1.98 ng/ml at baseline, P = < 0.05). In LAP animals GHBP fell to below baseline by 72 h, and significantly so by 96 h (33.5 +/- 1.43, P = < 0.05), whereas GHBP remained elevated 72 h following CLP, returning to baseline by 96 h. The density of GH-binding sites in liver tended to increase, following both CLP and LAP at both 24 and 96 h, but these changes failed to achieve statistical significance.

CONCLUSION

Reduced IGF-I levels in sepsis in the rat are associated with elevations in GHBP and a trend to increased hepatic GH binding. This suggests that in sepsis 'GH resistance' is not associated with reduced GH receptor numbers.

High-dose growth hormone does not affect proinflammatory cytokine (tumor necrosis factor-alpha, interleukin-6, and interferon-gamma) release from activated peripheral blood mononuclear cells or after minimal to moderate surgical stress

High-dose GH therapy, with GH doses 10-20 times the normal replacement dose for GH-deficient adults, has been used as an anti-catabolic agent in a number of different patient groups. A recent study, however, has shown an increase in mortality in critically ill patients treated with high-dose GH. The increased mortality was associated with multiorgan failure, septic shock, and uncontrolled infection, suggesting that GH may have altered the immune response. The GH receptor and GH are both expressed in peripheral blood mononuclear cells (PBMCs); thus, GH could act as either an endocrine or an autocrine modulator of the immune response. We have examined the hypothesis that high-dose GH therapy may induce proinflammatory cytokines, which are implicated in septic shock. To do this we measured cytokine production by PBMCs incubated in conditions that simulated high-dose GH therapy, and we measured cytokine levels in patients undergoing laparoscopic cholecystectomy who were randomized to receive either high-dose GH therapy (13 IU/m2 x day) or placebo. To confirm the biological activity of GH in our cell culture system we used a Stat5 functional assay. In this assay GH induced a bell-shaped curve, with a maximal response at GH levels between 100-1,000 ng/mL. PBMCs from healthy volunteers were incubated with GH in doses from 1-1,000 ng/mL for 6-72 h under resting conditions and after activation with endotoxin and the mixed lymphocyte reaction. Studies were repeated with PBMCs from six individuals using a GH dose of 100 ng/mL (the level of GH found after high-dose GH therapy) and an endotoxin dose that gave a submaximal response (0.01 ng/mL). GH had no effect on cell proliferation or the production of tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6), or interferon-gamma (IFNgamma). In patients undergoing laparoscopic cholecystectomy there was a time-related effect of surgery on cytokine levels. There was a rise in IL-6 and a fall in TNFalpha at 24 h after surgery; however, high-dose GH therapy had no effect on the cytokine response. We considered the possibility that endogenous GH production by PBMCs could influence the cytokine response in activated PBMCs; however, incubation of PBMCs in the presence of the GH receptor antagonist, B2036, had no effect on TNFalpha, IL-6, or IFNgamma production by PBMCs in either the mixed lymphocyte reaction or when activated by endotoxin. These results suggest that high-dose GH therapy does not alter the proinflammatory cytokine response to surgery or endotoxin. The results do not exclude an effect of GH on the immune response, but they suggest that the mortality seen in critically ill patients may be due to factors other than immune modulation.

Distribution and abundance of messenger ribonucleic acid for growth hormone receptor isoforms in human tissues

Two alternatively spliced exon 9 variants of human GH receptor (GHR) messenger ribonucleic acid (mRNA), GHR-(1-279) and GHR(1-277), were recently identified in liver. They encode receptor proteins lacking most of the intracellular domain and inhibit GH action in a dominant negative manner. Little is known about tissue distribution and abundance of these GHR isoforms. We have developed quantitative RT-PCR assays specific for the full-length and truncated GHRs and investigated their expression in various human tissues and cell lines. The mRNA of full-length GHR and GHR-(1-279) were readily detectable in all tissues investigated, with liver, fat, muscle, and kidney showing high levels of expression. These two receptor isoforms were also detected in a range of human cell lines, with strongest expression in IM9, a lymphoblastoid cell line. In contrast, GHR-(1277) message was expressed at low levels in liver, fat, muscle, kidney, and prostate and in trace amount in IM9 cells. Full-length GHR was the most abundant isoform, accounting for over 90% of total receptor transcripts in liver, fat, and muscle for quantitative RT-PCR. However, liver had 2- to 4-fold more full-length receptor mRNA and 16- to 40-fold more GHR-(1-277) mRNA than fat and muscle, whereas the mRNA levels of GHR-(1-279) were similar in the three tissues. GHR-(1-279) constituted less than 4% in liver and 7-10% in fat and muscle. GHR-(1-277) accounted for 0.5% of total GHR transcripts in liver and less than 0.1% in the other two tissues. These data suggest that the absolute and relative abundance of mRNA of the three GHR isoforms may be tissue specific. The regulation of expression of exon 9 alternatively spliced GHR variants may provide a potential mechanism for modulation of GH sensitivity at the tissue level.

GH, IGF-I and binding proteins in altered nutritional states

Nutritional state has profound actions at all levels of the GH/IGF-I axis and growth hormone has potent effects on nutritional state. The growth promoting effects of GH on linear height in children has long been recognised and, more recently, the important action of GH in maintaining adult body composition have been appreciated. The strong anabolic actions of GH have made it a drug of abuse among athletes and, of interest, clinicians, as a potent anti-catabolic therapy. In this review we consider the effects of nutrition on the GH/IGF-I axis and then discuss its potential use as an anti-catabolic agent. We also note the recent study in critically ill patients which has been associated with a poor outcome using high dose GH therapy.

Stimulation of endogenous GH and interleukin-6 receptors selectively activates different Jaks and Stats, with a Stat5 specific synergistic effect of dexamethasone

The interaction of GH, interleukin (IL)-6 and glucocorticoids is likely to be important in regulating the GH-insulin-like growth factor (IGF)-I axis. The signalling cascades activated by GH and IL-6 appear to be very similar, as demonstrated by studies using overexpression of the receptor and other components of the Jak-Stat and mitogen-activated protein (MAP) kinase pathways. Here we show that the human embryonic kidney cell line 293 (HEK293) expresses GH and IL-6 receptors endogenously. To determine which specific pathways might be activated by the two cytokines, at physiological levels of all components, we studied GH and IL-6 mediated signal transduction both under basal conditions and in the presence of overexpressed receptors and Stat proteins. Our results suggest a receptor specificity of Jak2 for GH receptors, and Jak1 for IL-6 receptors. Stat activation in response to GH and IL-6 was determined by reporter gene induction. Both GH and IL-6 were able to induce the reporter gene containing the Stat5 responsive element (LHRE) but the IL-6 response appeared to be mediated mainly through Stat3 activation. In contrast, the reporter gene containing the Stat3 responsive element (SIE) was IL-6 specific. The levels of gene induction by GH and IL-6 were not altered by the co-stimulation with GH and IL-6, suggesting that there is little cross-talk at the Jak-Stat activation level between the two cytokines. Neither GH nor IL-6 activated the MAP-kinase responsive serum response element (SRE), unless GH receptors or gp130 were overexpressed. Transfection of Stat3 or Stat5 expression vectors enhanced the response to GH and IL-6. Stimulation with dexamethasone synergistically enhanced GH activation of the LHRE reporter gene but had no effect on the IL-6 activation of the same reporter or on the SIE reporter gene. Thus, our studies suggest that while each cytokine, GH and IL-6, may activate various members of the Jak-Stat pathway in overexpression studies, specific activation of Stat3 by IL-6 and of Jak2 and Stat5 by GH can be observed in HEK293 cells and that in this system the synergistic effect of dexamethasone appears specific for Stat5.

Inflammatory cytokines and acquired growth hormone resistance

Resistance to growth hormone (GH)-mediated induction of insulin-like growth factor I (IGF-I) is a common complication of catabolic diseases, including critical illness and post-surgical conditions. This resistance to GH is believed to be permissive to the development of protein catabolism, cachexia and wasting, which are associated with an increased mortality rate. Data from in vitro studies and animal models suggest that increased levels of inflammatory cytokines can induce cachexia and might inhibit the effects of GH on target tissues. The molecular mechanisms involved are unclear, although an effect of cytokines on GH receptor signalling has been suggested. The GH-activated pathways that mediate the increase in IGF-I levels are not well understood, thereby impeding the elucidation of the effect of inflammatory cytokines. Several signalling cascades, like the JAK-STAT and MAP kinase pathways, have been shown to be activated by GH and some inflammatory cytokines, hence raising the possibility of crosstalk on this level. Our data, however, indicate that inflammatory cytokines have little or no effect on GH-mediated JAK-STAT signalling. In this review, we discuss these results and the possibility that secondary changes in the structure of chromatin are likely to be involved in the induction of IGF-I gene transcription by GH.

Multidecadal changes in the vertical temperature structure of the tropical troposphere

Trends in global lower tropospheric temperature derived from satellite observations since 1979 show less warming than trends based on surface meteorological observations. Independent radiosonde observations of surface and tropospheric temperatures confirm that, since 1979, there has been greater warming at the surface than aloft in the tropics. Associated lapse-rate changes show a decrease in the static stability of the atmosphere, which exceeds unforced static stability variations in climate simulations with state-of-the-art coupled ocean-atmosphere models. The differential temperature trends and lapse-rate changes seen during the satellite era are not sustained back to 1960.

Association of elevated insulin-like growth factor binding protein-1 with insulin resistance in hyperthyroidism

OBJECTIVE

Insulin-like growth factor binding-protein-1 (IGFBP-1) has a role in glucose homeostasis and is present at high concentrations in hyperthyroidism. We have investigated the relationship between IGFBP-1 concentration and glucose homeostasis in hyperthyroidism.

DESIGN

Patients and controls had intravenous glucose tolerance tests (IVGTT) and/or oral glucose tolerance tests (OGTT). Patients were tested when hyperthyroid and when euthyroid whilst the controls were tested once. The IVGTT was used to assess insulin sensitivity and the OGTT to establish that the study group had abnormal glucose tolerance. The hyperthyroid patients were treated with methimazole to restore euthyroidism.

PATIENTS

Ten patients (9 females) and 13 healthy controls (9 females) consented to the study. Ten patients and nine controls (7 females) had IVGTT. Six patients (5 females) and six controls (4 females) had OGTT.

MEASUREMENTS

Glucose, insulin, glucagon, GH and IGFBP-1 were measured during GTT. IGF-I, free thyroid hormones, and TSH concentrations were measured basally.

RESULTS

Hyperthyroid subjects were insulin resistant and 67% had impaired glucose tolerance. Fasting IGFBP-1 levels were doubled in hyperthyroid subjects compared to healthy controls and correlated positively with free T4 (r = 0.84, P < 0.0001), with peak glucose during the OGTT (r = 0.68, P < 0.005) with peak insulin during the IVGTT (r = 0.51, P < 0.005) and negatively with glucose disappearance constant (r = - 0.52, P < 0.005). IGFBP-1 was highly phosphorylated in hyperthyroid and control subjects. Fasting insulin and IGFBP-1 levels were unrelated but IGFBP-1 suppressed acutely during GTT in all groups. GH levels fell less in patients with hyperthyroidism than in normals during GTTs.

CONCLUSIONS

We conclude that in hyperthyroidism thyroid hormones directly increase fasting IGFBP-1 concentration but acute regulation of IGFBP-1 by insulin is normal and that elevated fasting phosphorylated IGFBP-1 concentration is associated with insulin resistance.

Serum leptin levels during the menstrual cycle of healthy fertile women

Leptin is a protein, produced by adipose tissue, which has cytokine and hormonal properties. Serum leptin levels can be considered as a measure of body fat mass, and are involved in regulation of body weight. Previous studies suggest that leptin may have an additional role in reproduction, and there is also evidence for involvement in the hypothalamic-pituitary-gonadal axis. In this study, we investigate the possible changes in serum leptin concentration throughout the menstrual cycle. Samples were collected from apparently healthy, fertile women at different stages in their menstrual cycle, timed precisely according to the luteinising hormone (LH) surge. Mean serum leptin levels were significantly higher in the luteal phase (median 11.4 ng/mL) than in the follicular phase (median 10.0 ng/mL) (P < 0.001). In addition, mean serum leptin levels correlated with body mass index (r = 0.54, P < 0.05), but showed no correlation with luteal-phase progesterone levels. Results showed that levels of serum leptin vary during the menstrual cycle, and add to the mounting evidence that leptin has a role in reproduction. These fluctuations should be taken into account whenever studies are performed using female subjects.

Leptin binding activity changes with age: the link between leptin and puberty

The timing of the physical transition from child to adult is determined by a biological clock that switches off the pituitary gonadal axis during infancy until puberty. Body composition (and in particular, fat mass), through leptin, are critical signals to this clock. However, no direct relationship between leptin and puberty has been demonstrated. Leptin is bound in the circulation by a high-affinity binding protein, which has been identified as a soluble leptin receptor. We found circulating levels of leptin binding activity (LBA) to be low at birth, to be high in the prepubertal years, to fall through puberty, and then to remain stable during adult life. LBA correlated with pubertal status in both boys and girls. We postulate that the fall in LBA, associated with increasing age and puberty, reflects a reduction in expression of truncated leptin receptors, and leptin is then available to the full-length receptor, which transmits the biological signal for leptin. The high levels of LBA occur during the years when the pituitary gonadal axis is quiescent. Thus, the change in LBA could explain how leptin regulates puberty.

Effects of growth hormone replacement on physical performance and body composition in GH deficient adults

OBJECTIVES

Adults with GH deficiency complain frequently of low energy levels resulting in a low perceived quality of life. Body composition is altered, with increased fat mass and decreased lean body mass, and muscle strength is reduced. The aims of this study were to determine the effects of GH replacement on physical performance and body composition in GH deficient (GHD) adults.

STUDY DESIGN

The study consisted of a 6-month randomised, double-blind, placebo controlled study of the administration of GH (0.25 IU/Kg/week (0.125 IU/kg/week for the first four weeks)) followed by a 6-month open phase of GH therapy.

PATIENTS

Thirty-five GHD adults (17F), mean age 39.8 years (range 21.1-59.9), on conventional replacement therapy as required.

METHODS

Maximum aerobic capacity was measured using an incremental walking test to volitional exhaustion on a motorized treadmill. Quadriceps muscle strength was assessed by measuring maximum voluntary contractions and body composition by dual energy X-ray absorptiometry (DEXA).

RESULTS

There were no statistically significant changes in quadriceps muscle strength between the GH and placebo groups. In both groups, there was a significant increase in quadriceps muscle strength compared to baseline during the double-blind period (GH group: P = 0.016; placebo group: P = 0.048). Compared to baseline, muscle strength was further improved in the GH treatment group after 12 months of treatment (P = 0.007). No further improvement was noted in the placebo group after 6 months on open GH treatment. In the placebo group, maximum aerobic capacity decreased during the placebo period (P = 0.017). No significant change was observed in the GH group. During open GH treatment the previously placebo treated group had a significant increase of maximum aerobic capacity (P < 0.049) whereas no significant improvement could be seen in the GH group. In the GH group there was a significant increase in lean body mass (P = 0.001) and a significant decrease in fat mass (P < 0.001). No statistically significant changes were noted in the placebo group: the differences in these changes between treatment groups were statistically significant (lean body mass: P = 0.009; fat mass: P < 0.001). The changes in body composition in the GH group during the 6 month placebo-controlled period were maintained during continued open treatment. Similar changes in body composition to those observed in the GH group during the 6 month placebo-controlled period were also seen in the placebo group once the patients received GH treatment.

CONCLUSIONS

Our data show that GH replacement in GH deficient adults is associated with favourable changes in body composition, which could be important in the long term health outcome and physical activity of GH deficient patients. Our data support the concept that GH therapy alone, in the absence of some form of exercise programme, may increase the amount of lean tissue but not the quality or functional capacity of this tissue and it may be that training, in addition to GH therapy, may be necessary to significantly increase physical performance in these patients. We suggest that future trials with GH therapy and general approaches to the treatment of GH deficiency should include a planned activity programme as an approach to health improvement in these patients.

Leptin binding activity changes with age: the link between leptin and puberty

The timing of the physical transition from child to adult is determined by a biological clock that switches off the pituitary gonadal axis during infancy until puberty. Body composition (and in particular, fat mass), through leptin, are critical signals to this clock. However, no direct relationship between leptin and puberty has been demonstrated. Leptin is bound in the circulation by a high-affinity binding protein, which has been identified as a soluble leptin receptor. We found circulating levels of leptin binding activity (LBA) to be low at birth, to be high in the prepubertal years, to fall through puberty, and then to remain stable during adult life. LBA correlated with pubertal status in both boys and girls. We postulate that the fall in LBA, associated with increasing age and puberty, reflects a reduction in expression of truncated leptin receptors, and leptin is then available to the full-length receptor, which transmits the biological signal for leptin. The high levels of LBA occur during the years when the pituitary gonadal axis is quiescent. Thus, the change in LBA could explain how leptin regulates puberty.

The GH receptor and GH insensitivity

Growth hormone (GH) resistance/insensitivity (GHIS) is the finding of elevated GH levels associated with a reduction in the biologic actions of GH. It may be congenital or acquired. In congenital GHIS, over 30 mutations in the GH receptor (GHR) have been described. Dimerization of the GHR activates phosphorylation cascades involving MAP kinases and the Janus kinase, JAK2. This in turn activates the STAT (Signal transducers and activators of transcription) proteins, which translocate to the nucleus. A soluble form of the GHR circulates as a GH binding protein (GHBP), and is derived from the proteolytic cleavage of the extracellular domain of the GHR. The majority of GHR mutations resulting in GHIS are though to affect GH binding, hence the finding of low levels of GHBP in many patients. However, a small group of patients with GHIS have been identified in whom there are normal or high levels of GHBP. Mutations in these patients include, among others, a splice-site mutation that results in the skipping of exon 9. The resultant protein is a truncated GHR that lacks 97% of the intracellular domain of the normal receptor. Patients heterozygous for this mutation have GHIS. In vitro studies have shown the truncated receptor acts as a dominant-negative inhibitor of receptor signalling. The truncated receptor lacks the domains essential for internalization, and is therefore highly expressed on the cell surface. It heterodimerizes with the full-length receptor and blocks signaling. Analysis of GHIS has increased our understanding of the molecular basis for GHIS and helped elucidate the factors that regulate GHR trafficking and signalling.

Lack of association between thyroid and adrenal nodules: a histological study

The prevalence of thyroid nodules is increased in patients with Cushing's disease, but the possibility of an association between thyroid and adrenal nodules in other patient groups has not been formally tested. We have evaluated the co-existence of thyroid and adrenal nodules in retrospective and prospective autopsy studies. Retrospective (83 autopsies) and prospective (29 autopsies) blinded studies of thyroid and adrenal gland histopathology were performed by two experienced histopathologists in unselected autopsies. The presence of nodules, defined as areas of tissue having discrete edges within the gland parenchyma seen as a step difference between the cells or architecture adjacent to the nodule, was determined for each gland. No association was found between the presence of adrenal and thyroid nodules in either the retrospective or prospective studies (p>0.2 for both). In the retrospective study, 23% of specimens had thyroid nodules and 28% adrenal nodules. In the prospective study, 24% of specimens had thyroid nodules and 7% adrenal nodules. The proportion of patients with adrenal nodules in the prospective study was significantly less than that in the retrospective study. In conclusion, thyroid and adrenal nodules are frequent autopsy findings in the general population but we have found no evidence of a relationship between the occurrence of nodules in these glands.

Rapid eye movement sleep changes during the adaptation night in combat veterans with posttraumatic stress disorder

BACKGROUND

Hyperarousal in posttraumatic stress disorder (PTSD) is manifested during sleep as well as waking. Elevated rapid eye movement sleep (REMS) phasic activity, likely signifying central nervous system alerting, has been identified in PTSD. The authors reasoned that PTSD compared to control subjects would show particularly increased REMS phasic activity on the first night of polysomnography, with adaptation to a novel environment.

METHODS

First-night polysomnograms of 17 veterans with PTSD were compared with those of 11 control subjects. Sleep was also studied in subsets of both groups over two nights.

RESULTS

On the first night, the PTSD subjects had a higher density of rapid eye movements in the first REMS period. This measure was increased on the first compared to the second night, but there was no interaction effect between night and group.

CONCLUSIONS

REMS changes are again demonstrated in veterans with PTSD. Introduction to a novel environment activated a REMS phasic process, but not differentially in PTSD compared to control subjects.

The effects of dose, nutrition, and age on hexarelin-induced anterior pituitary hormone secretion in adult patients on maintenance hemodialysis

Malnutrition is common in chronic renal failure (CRF) and adversely affects prognosis. In view of the anabolic action of GH in CRF, we have studied the effects of hexarelin, a GH secretagogue, on CRF. An iv dose-response study in six 20- to 40-yr-old well nourished hemodialysis (HD) patients was followed by administration of the maximally effective dose to six 20- to 40-yr-old healthy controls, six 20- to 40-yr-old poorly nourished HD patients, and six 50- to 70-yr-old poorly nourished HD patients. GH secretion (area under the curve over 180 min, mean +/- SE) after 2 and 1 microg/kg doses (10.7 +/- 4.2 and 8.2 +/- 5.2 min/U x L, respectively) was greater than after placebo (0.60 +/- 0.11 min/U x L; P < 0.001 and P < 0.05, respectively). The most effective dose (2 microg/kg) produced similar GH secretion (11.4 +/- 3.3 min/U x L) in controls. GH secretion in the younger poorly nourished HD group (19.0 +/- 4.4 min/U x L) was not significantly different from that in the well nourished 20- to 40-yr-old HD patients (P = 0.06). GH secretion in the older, poorly nourished HD patients (9.4 +/- 2.2 min/U x L) was similar to that in the young, poorly nourished group (P = 0.18). ACTH and cortisol concentrations increased in all groups, whereas PRL concentrations were not affected in CRF. The profound action of hexarelin on GH secretion has been shown to extend to CRF. Trends were evident toward increasing efficacy in malnourished subjects and decreasing efficacy with age. Further studies are required to determine whether the acute actions of hexarelin can be translated into long term anabolic changes.

Electrical stimulation of the amygdala increases the amplitude of elicited ponto-geniculo-occipital waves

The amygdala projects massively via its central nucleus (CNA) into brain stem regions involved in alerting and ponto-geniculo-occipital (PGO) wave generation. Electrical stimulation of CNA is known to enhance the acoustic startle response (ASR) and influence spontaneous PGO waves. The role of the amygdala in the modulation of ASR and elicited PGO waves (PGOE) was investigated in albino rats. Electrically stimulating CNA within 25 ms prior to an auditory stimulus enhanced ASR and PGOE amplitude in a similar way, with the largest response occurring when the electrical and auditory stimuli were given simultaneously. The data suggest that CNA modulates alerting mechanisms.

New growth hormone receptor exon 9 mutation causes genetic short stature

A novel form of congenital growth hormone insensitivity syndrome (GHIS), which lacks the classic phenotype associated with this condition, is described. Dominant inheritance is shown to result from a heterozygous 876-1 G to C transversion of the 3' splice acceptor site preceding exon 9 in the growth hormone receptor (GHR) gene. The result of this mutation is a severely truncated cytoplasmic domain of the GHR, which is incapable of transmitting a signal. The mutant receptor is shown to form a heterodimer with the wild-type GHR, the activity of which is inhibited in a dominant-negative manner.

Truncated growth hormone receptor isoforms

Truncated forms of the growth hormone receptor (GHR) that lack the majority of the cytoplasmic domain have been identified in a number of human tissues. In vitro, these truncated receptors act as dominant-negative inhibitors of the growth hormone (GH) signal and also generate large amounts of growth hormone binding protein (GHBP). Mutations that lead to high levels of expression of the truncated GHR are associated with short stature and GH insensitivity. Thus, truncated GHRs may be important as a physiological regulator of GH signalling in addition to providing a mechanism for the production of GHBP.

Comparison of the diagnostic utility of the simplified and standard i.m. glucagon stimulation test (IMGST)

OBJECTIVE

To compare the peak GH and cortisol responses to the simplified and standard i.m. glucagon stimulation test (IMGST) in order to determine whether the use of a simplified form of this test results in a loss of diagnostic utility. PATIENT AND DESIGN: A retrospective study of 35 consecutive patients with pituitary disease who underwent a standard IMGST to measure GH (n = 34) or cortisol (n = 21) reserve at the programmed investigation unit of the Northern General Hospital, Sheffield.

MEASUREMENTS

Cortisol, glucose and GH levels were measured at baseline and 30, 60, 90, 120, 150, 180, 210 and 240 min during the standard IMGST. We used the hormone levels at baseline, 150 and 180 min for the simplified IMGST and compared the cortisol and GH responses achieved.

RESULTS

The median (range) peak GH and cortisol responses to simplified and standard IMGST were comparable 4.2 (0.5-47.5) vs 5.4 (0.5-47.5) mU/l (P = 0.75) and 635 (306-1669) vs 647 (306-1669) nmol/l (P = 0.801), respectively. Using the standard 'cut-off' points to assess GH (9 mU/l) or cortisol deficiency (580 nmol/l) there was no significant loss of diagnostic utility (P = 0.98 and P = 1.00, respectively).

CONCLUSIONS

The simplified and standard IMGST have a similar diagnostic utility. The simplified IMGST could replace the standard IMGST as a screening test for GH and cortisol reserve in pituitary disease. The insulin-induced hypoglycaemia stress test can be reserved for cases in which a second assessment of pituitary reserve is clinically indicated or because of an indeterminate biochemical result.

Cirrhotic liver expresses low levels of the full-length and truncated growth hormone receptors

In cirrhosis, as in other conditions of protein catabolism, there is a state of acquired GH resistance, as defined by high circulating GH levels with low insulin-like growth factor I levels. However, patients with end-stage liver failure respond to supraphysiological doses of GH with an increase in circulating insulin-like growth factor I levels. The present study represents a detailed analysis of GH receptor (GHR) expression in cirrhotic liver from 17 patients with end-stage liver disease. Specific binding of labeled GH was identified in all cirrhotic livers studied. The binding affinity for the GHR was similar in cirrhotic and normal livers, but the number of binding sites per mg protein of liver membrane was variable in both normal and cirrhotic liver, although it were generally lower in cirrhotic liver. GHR expression was identified in cirrhotic liver by Northern blotting, RT-PCR, and ribonuclease protection assay. On Northern blotting, a single transcript of 4.8 kb was identified in normal and cirrhotic tissues. RT-PCR identified expression of both full-length GHR and a truncated form of the GHR; this was confirmed by ribonuclease protection assay. In situ hybridization and immunohistochemistry confirmed the expression of GHR in regenerating hepatocytes and isolated cells in fibrous tissue. In conclusion, 1) the low level of GHR in cirrhotic liver may contribute to the acquired GH resistance found in cirrhotic patients; 2) the reduced expression of both full-length and truncated GHR is compatible with the low level of GH-binding protein found in cirrhosis, as this truncated receptor has previously been reported to generate large amounts of GH-binding protein; and 3) the demonstration of GH binding to cirrhotic liver explains why these patients with GH resistance may still respond to supraphysiological doses of GH.