Growth hormone and metabolism

Derivatization with fatty acids in peptide and protein drug discovery

Peptides and proteins are widely used to treat a range of medical conditions; however, they often have to be injected and their effects are short-lived. These shortcomings of the native structure can be addressed by molecular engineering, but this is a complex undertaking. A molecular engineering technology initially applied to insulin - and which has now been successfully applied to several biopharmaceuticals - entails the derivatization of peptides and proteins with fatty acids. Various protraction mechanisms are enabled by the specific characteristics and positions of the attached fatty acid. Furthermore, the technology can ensure a long half-life following oral administration of peptide drugs, can alter the distribution of peptides and may hold potential for tissue targeting. Due to the inherent safety and well-defined chemical nature of the fatty acids, this technology provides a versatile approach to peptide and protein drug discovery.

Non-alcoholic fatty liver disease across endocrinopathies: Interaction with sex hormones

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most frequent chronic liver disease globally. NAFLD is strongly associated with metabolic syndrome and it has been recently suggested that to rename NAFLD as metabolic dysfunction-associated fatty liver disease (MAFLD). NAFLD has been studied in different endocrine axes and accumulating body of clinical and experimental studies have suggested that NAFLD is associated with polycystic ovarian syndrome (PCOS), hypopituitarism, growth hormone deficiency (GHD), hypogonadism and other endocrine disorders. In fact, endocrine dysfunction may be considered as the major contributor for the development, progression, and severity of NAFLD. In the present comprehensive review, we discussed the epidemiological and clinical evidence on the epidemiology, pathophysiology, and management of NAFLD in endocrine disorders, with an emphasis on the effects of sex-specific hormones/conditions as well as molecular basis of NAFLD development in these endocrine diseases.

Appetite, Metabolism and Hormonal Regulation in Normal Ageing and Dementia

Feeding and nutrition follow the growth trajectory of the course of life. The profound physiological changes that human body experiences during ageing affect separate aspects of food intake, from tastant perception to satiety. Concurrent morbidities, such as neurodegeneration, as seen in dementia, and metabolic syndrome, may further shape nutritional behaviours, status and adequacy. In an effort to fill the gap between the exhausting basic research and the actual needs of professionals caring for the exponentially expanding ageing population, the current review addresses major factors relevant to appetite and eating disturbances. Does age alter the perception of food modalities? Is food generally still perceived as alluring and delicious with age? Is there an interplay between ageing, cognitive decline, and malnutrition? What tools can we adopt for proper and timely monitoring? Finally, what anatomical and pathophysiological evidence exists to support a hypothesis of central regulation of metabolic perturbations in normal and accelerated cognitive impairment, and how can we benefit from it in health practice?

Performance enhancement in chronic obstructive pulmonary disease

Background: Exercise limitation is a hallmark of chronic obstructive pulmonary disease (COPD) and is integral to the associated impaired health status of these patients. The poor exercise tolerance is multifactorial in origin, relating to airflow obstruction, disadvantageous lung mechanics, reduced oxygen delivery and skeletal muscle dysfunction. A number of interventions have been studied to determine whether they can impact on exercise performance. The most evidence-based of these is exercise training, which along with other approaches, both previously investigated and putative, are discussed in this review.

Depletion of suppressor of cytokine signaling-1a causes hepatic steatosis and insulin resistance in zebrafish

Suppressor of cytokine signaling-1a (SOCS1a) is a member of the suppressor of cytokine signaling family, a group of related molecules that mediate the negative regulation of the JAK-STAT pathway. Here, we depleted SOCS1a using the transcription activator-like (TAL) effector nuclease (TALEN) technique to understand its physiological roles in zebrafish. Although elevated levels of JAK-STAT5 activation and erythropoiesis have been observed in socs1a-deficient zebrafish, these animals exhibited normal growth during the early stages. Socs1a-deficient zebrafish began to grow slowly with certain mortalities after 20 days postfertilization (dpf), whereas the heterozygous socs1a-deficient zebrafish exhibited enhanced somatic growth. Decreased adiposity, hepatic steatosis, and insulin resistance were observed in our socs1a-deficient adult zebrafish, which is similar to the lipodystrophy phenotypes observed in mammals. Comparative transcriptomic analyses revealed elevated levels of gluconeogenesis, lipolysis, and hypoxia-inducible response and decreased activities of lipogenesis and glycolysis in the hepatocytes of socs1a-deflicient adult zebrafish. Evident mitochondrial dysfunction has also been observed in hepatocytes from socs1a-deficient zebrafish. Taken together, our results suggest that the negative regulatory roles of SOCS1a on JAK-STAT5 signaling may be involved in the suppression of the erythropoiesis and growth hormone activities, which was also reflected in the enhanced somatic growth performance observed in the heterozygous socs1a-deficient fish. The differences in the effects caused by SOCS1a depletion on insulin sensitivity, lipid metabolism, and inflammatory responses between zebrafish and mammalian models observed here may reflect differences between the functional mechanisms of SOCS members in terrestrial mammals and aquatic teleosts.

Growth hormone-regulated mRNAs and miRNAs in chicken hepatocytes

Growth hormone (GH) is a key regulatory factor in animal growth, development and metabolism. Based on the expression level of the GH receptor, the chicken liver is a major target organ of GH, but the biological effects of GH on the chicken liver are not fully understood. In this work we identified mRNAs and miRNAs that are regulated by GH in primary hepatocytes from female chickens through RNA-seq, and analyzed the functional relevance of these mRNAs and miRNAs through GO enrichment analysis and miRNA target prediction. A total of 164 mRNAs were found to be differentially expressed between GH-treated and control chicken hepatocytes, of which 112 were up-regulated and 52 were down-regulated by GH. A total of 225 chicken miRNAs were identified by the RNA-Seq analysis. Among these miRNAs 16 were up-regulated and 1 miRNA was down-regulated by GH. The GH-regulated mRNAs were mainly involved in growth and metabolism. Most of the GH-upregulated or GH-downregulated miRNAs were predicted to target the GH-downregulated or GH-upregulated mRNAs, respectively, involved in lipid metabolism. This study reveals that GH regulates the expression of many mRNAs involved in metabolism in female chicken hepatocytes, which suggests that GH plays an important role in regulating liver metabolism in female chickens. The results of this study also support the hypothesis that GH regulates lipid metabolism in chicken liver in part by regulating the expression of miRNAs that target the mRNAs involved in lipid metabolism.

Influence of glucocorticoids and growth hormone on insulin sensitivity in humans

The seminal concept proposed by Sir Harold Himsworth more than 75 years ago that a large number of patients with diabetes were 'insulin insensitive', now termed insulin resistance, has now expanded to include several endocrine syndromes, namely those of glucocorticoid excess, and growth hormone excess and deficiency. Synthetic glucocorticoids are increasingly used to treat a wide variety of chronic diseases, whereas the beneficial effects of recombinant growth hormone replacement therapy in children and adults with growth hormone deficiency have now been well-recognized for over 25 years. However, clinical and experimental studies have established that increased circulating levels of glucocorticoids and growth hormone can also lead to worsening of insulin resistance, glucose intolerance, overt diabetes mellitus and cardiovascular disease. Improved understanding of the physiological 24-h rhythmicity of glucocorticoid and growth hormone secretion and its influence on the dawn phenomenon and the Staub-Trauggot effect has therefore led to renewed interest in studies on the mechanisms of insulin resistance induced by exogenous administration of glucocorticoids and growth hormone in humans. In this review, we describe the physiological events that result from the presence of resistance to insulin action at the level of skeletal muscle, adipose tissue, and liver, describe the known mechanisms of glucocorticoid- and growth hormone-mediated insulin resistance, and provide an update of the contributions of glucocorticoids and growth hormone to understanding the pathophysiology of insulin resistance and its effects on several endocrine syndromes.

Dwarfism and increased adiposity in the gh1 mutant zebrafish vizzini

Somatic growth and adipogenesis are closely associated with the development of obesity in humans. In this study, we identify a zebrafish mutant, vizzini, that exhibits both a severe defect in somatic growth and increased accumulation of adipose tissue. Positional cloning of vizzini revealed a premature stop codon in gh1. Although the effects of GH are largely through igfs in mammals, we found no decrease in the expression of igf transcripts in gh1 mutants during larval development. As development progressed, however, we found overall growth to be progressively retarded and the attainment of specific developmental stages to occur at abnormally small body sizes relative to wild type. Moreover, both subcutaneous (sc) and visceral adipose tissues underwent precocious development in vizzini mutants, and at maturity, the sizes of different fat deposits were greatly expanded relative to wild type. In vivo confocal imaging of sc adipose tissue (SAT) expansion revealed that vizzini mutants exhibit extreme enlargement of adipocyte lipid droplets without a corresponding increase in lipid droplet number. These findings suggest that GH1 signaling restricts SAT hypertrophy in zebrafish. Finally, nutrient deprivation of vizzini mutants revealed that SAT mobilization was greatly diminished during caloric restriction, further implicating GH1 signaling in adipose tissue homeostasis. Overall, the zebrafish gh1 mutant, vizzini, exhibits decreased somatic growth, increased adipose tissue accumulation, and disrupted adipose plasticity after nutrient deprivation and represents a novel model to investigate the in vivo dynamics of vertebrate obesity.

Urine metabonomic profiling of a female adolescent with PIT-1 mutation before and during growth hormone therapy: insights into the metabolic effects of growth hormone

OBJECTIVE

Growth hormone (GH) is a protein hormone with important roles in growth and metabolism. The objective of this study was to investigate the metabolism of a human subject with severe GH deficiency (GHD) due to a PIT-1 gene mutation and the metabolic effects of GH therapy using Nuclear Magnetic Resonance (NMR)-based metabonomics. NMR-based metabonomics is a platform that allows the metabolic profile of biological fluids such as urine to be recorded, and any alterations in the profile modulated by GH can potentially be detected.

DESIGN

Urine samples were collected from a female subject with severe GHD before, during and after GH therapy, and from healthy age- and sex-matched controls and analysed with NMR-based metabonomics.

SETTING

The samples were collected at a hospital and the study was performed at a research facility.

PARTICIPANTS

We studied a 17 year old female adolescent with severe GHD secondary to PIT-1 gene mutation who had reached final adult height and who had ceased GH therapy for over 3 years. The subject was subsequently followed for 5 years with and without GH therapy. Twelve healthy age-matched female subjects acted as control subjects.

INTERVENTION

The GH-deficient subject re-commenced GH therapy at a dose of 1 mg/day to normalise serum IGF-1 levels.

MAIN OUTCOME MEASURES

Urine metabolic profiles were recorded using NMR spectroscopy and analysed with multivariate statistics to distinguish the profiles at different time points and identify significant metabolites affected by GH therapy.

RESULTS

NMR-based metabonomics revealed that the metabolic profile of the GH-deficient subject altered with GH therapy and that her profile was different from healthy controls before, and during withdrawal of GH therapy.

CONCLUSION

This study illustrates the potential use of NMR-based metabonomics for monitoring the effects of GH therapy on metabolism by profiling the urine of GH-deficient subjects. Further controlled studies in larger numbers of GH-deficient subjects are required to determine the clinical benefits of NMR-based metabonomics in subjects receiving GH therapy.

Glycemic control in non-diabetic critically ill patients

Hyperglycemia is a common and costly health care problem in hospitalized patients. In hospital hyperglycemia is defined as any glucose value >7.8 mmol/l (140 mg/dl). Hyperglycemia is present in 40% of critically ill patients and in up to 80% of patients after cardiac surgery, with ∼ 80% of ICU patients with hyperglycemia having no history of diabetes prior to admission. The risk of hospital complications relates to the severity of hyperglycemia, with a higher risk observed in patients without a history of diabetes compared to those with known diabetes. Improvement in glycemic control reduces hospital complications and mortality; however, the ideal glycemic target has not been determined. A target glucose level between 7.8 and 10.0 mmol/l (140 and 180 mg/dl) is recommended for the majority of ICU patients. This review aims to present updated recommendations for the inpatient management of hyperglycemia in critically ill patients with and without a history of diabetes.

Overexpression of SIRT1 in mouse forebrain impairs lipid/glucose metabolism and motor function

SIRT1 plays crucial roles in glucose and lipid metabolism, and has various functions in different tissues including brain. The brain-specific SIRT1 knockout mice display defects in somatotropic signaling, memory and synaptic plasticity. And the female mice without SIRT1 in POMC neuron are more sensitive to diet-induced obesity. Here we created transgenic mice overexpressing SIRT1 in striatum and hippocampus under the control of CaMKIIα promoter. These mice, especially females, exhibited increased fat accumulation accompanied by significant upregulation of adipogenic genes in white adipose tissue. Glucose tolerance of the mice was also impaired with decreased Glut4 mRNA levels in muscle. Moreover, the SIRT1 overexpressing mice showed decreased energy expenditure, and concomitantly mitochondria-related genes were decreased in muscle. In addition, these mice showed unusual spontaneous physical activity pattern, decreased activity in open field and rotarod performance. Further studies demonstrated that SIRT1 deacetylated IRS-2, and upregulated phosphorylation level of IRS-2 and ERK1/2 in striatum. Meanwhile, the neurotransmitter signaling in striatum and the expression of endocrine hormones in hypothalamus and serum T3, T4 levels were altered. Taken together, our findings demonstrate that SIRT1 in forebrain regulates lipid/glucose metabolism and motor function.

Improved insulin sensitivity, preserved beta cell function and improved whole-body glucose metabolism after low-dose growth hormone replacement therapy in adults with severe growth hormone deficiency: a pilot study

AIMS/HYPOTHESIS

Growth hormone-deficient patients show deterioration of insulin sensitivity and beta cell function. High-dose growth hormone treatment often induces further impairment of insulin sensitivity, leading to an increase in insulin and glucose levels or even, in cases of preexisting beta cell defect, to overt diabetes. However, low-dose treatment may improve insulin sensitivity, although data in humans with detailed metabolic phenotyping are as yet not available. We postulated that long-term low-dose growth hormone replacement, restoring IGF-1 to the low-normal range, might beneficially affect glucose metabolism.

METHODS

We studied prospectively the metabolic responses to 24 and 48 weeks of growth hormone treatment in a small group of six adults with severe growth hormone deficiency (four men, two women; age 40-59 years; BMI 30.2 +/- 1 kg/m(2); mean growth hormone dose 0.3 +/- 0.04 mg/day). All participants underwent an oral glucose tolerance test, euglycaemic-hyperinsulinaemic clamp and hyperglycaemic-hyperinsulinaemic clamp plus i.v. L: -arginine on three occasions. Insulin sensitivity was measured by calculating the M value during the steady state of the euglycaemic-hyperinsulinaemic clamp. Insulin secretion and clearance were estimated from AUC(C-peptide), AUC(insulin) and their ratio at each phase of the hyperglycaemic-hyperinsulinaemic clamp.

RESULTS

Growth hormone significantly improved insulin sensitivity (M value 13.8 +/- 2.6 [baseline] vs 19.6 +/- 2.6 [24 weeks] and 23.7 +/- 1.9 [48 weeks] micromol kg(-1) min(-1); p < 0.01). Although the insulin response to glucose and arginine decreased slightly, the disposition index, integrating insulin sensitivity and secretion, significantly increased (p < 0.01), indicating an improvement in whole-body glucose metabolism. Insulin clearance was not affected during treatment (p > 0.05).

CONCLUSIONS/INTERPRETATION

Our data indicate that long-term low-dose growth hormone treatment may improve insulin sensitivity and whole-body glucose metabolism in adults with severe growth hormone-deficiency.

Cardiovascular risk factors in hypopituitary GH-deficient adults

Design Data on lipids, body composition, and blood pressure (BP) from all published KIMS papers are summarized and compared with a literature review. Results KIMS data confirm and extend previous research showing that adults with GH deficiency (GHD) have an adverse cardiovascular risk profile. GHD patients have high levels of dyslipidemia, elevated body mass index, unfavorable waist-to-hip ratio and body composition, and a high risk of hypertension. These abnormalities are likely to explain the increased cardiovascular mortality observed in patients with hypopituitarism. When given GH replacement therapy, an improvement is seen in KIMS as well as earlier studies for lipid profile, body composition, and BP. The added value of the different KIMS papers over previous research is that KIMS involves a much larger number of patients, that lipid concentrations and IGF1 are measured in a single central laboratory, and that the effects of GH replacement therapy can be followed longer than the duration of earlier trials. By the large number of patients, KIMS gives insight into the effects of GH in different patients' subgroups such as elderly patients, patients with idiopathic GHD, patients with craniopharyngioma, patients after irradiation, and so on. In addition, KIMS has made it possible to calculate more exactly the influence of baseline parameters on these cardiovascular risk parameters and their response to GH. Conclusions Taken together, data from KIMS confirm earlier knowledge about the important benefits of GH replacement therapy, but also on the use of GH in specific subgroups such as isolated GHD, patients above 65 years, and patients after irradiation. No subgroup yet has been identified as not responding well to GH.

Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects

In evolutionary terms, GH and intracellular STAT 5 signaling is a very old regulatory system. Whereas insulin dominates periprandially, GH may be viewed as the primary anabolic hormone during stress and fasting. GH exerts anabolic effects directly and through stimulation of IGF-I, insulin, and free fatty acids (FFA). When subjects are well nourished, the GH-induced stimulation of IGF-I and insulin is important for anabolic storage and growth of lean body mass (LBM), adipose tissue, and glycogen reserves. During fasting and other catabolic states, GH predominantly stimulates the release and oxidation of FFA, which leads to decreased glucose and protein oxidation and preservation of LBM and glycogen stores. The most prominent metabolic effect of GH is a marked increase in lipolysis and FFA levels. In the basal state, the effects of GH on protein metabolism are modest and include increased protein synthesis and decreased breakdown at the whole body level and in muscle together with decreased amino acid degradation/oxidation and decreased hepatic urea formation. During fasting and stress, the effects of GH on protein metabolism become more pronounced; lack of GH during fasting increases protein loss and urea production rates by approximately 50%, with a similar increase in muscle protein breakdown. GH is a counterregulatory hormone that antagonizes the hepatic and peripheral effects of insulin on glucose metabolism via mechanisms involving the concomitant increase in FFA flux and uptake. This ability of GH to induce insulin resistance is significant for the defense against hypoglycemia, for the development of "stress" diabetes during fasting and inflammatory illness, and perhaps for the "Dawn" phenomenon (the increase in insulin requirements in the early morning hours). Adult patients with GH deficiency are insulin resistant-probably related to increased adiposity, reduced LBM, and impaired physical performance-which temporarily worsens when GH treatment is initiated. Conversely, despite increased LBM and decreased fat mass, patients with acromegaly are consistently insulin resistant and become more sensitive after appropriate treatment.

Glucose metabolism in lymphocytes is a regulated process with significant effects on immune cell function and survival

Lymphocytes require glucose uptake and metabolism for normal survival and function. The signals that regulate the expression and localization of glucose transporter 1 (Glut1) to allow glucose uptake in T cells are now beginning to be understood. Resting T cells require extracellular signals, such as cytokines, hormones, and growth factors, or low-level TCR stimulation to take up adequate glucose to maintain housekeeping functions. In the absence of extrinsic signals, resting T cells internalize and degrade Glut1 and cannot maintain viability. Activated T cells have dramatically increased metabolic requirements to support the energy and biosynthetic needs necessary for growth, proliferation, and effector function. In particular, glucose metabolism and aerobic glycolysis fuel this demand. Therefore, activation of T cells causes a large increase in Glut1 expression and surface localization. If glucose uptake is limited, glycolytic flux decreases to a level that no longer sustains viability, and proapoptotic Bcl-2 family members become activated, promoting cell death. However, excessive glucose uptake can promote hyperactive immune responses and possible immune pathology. Tight regulation of glucose uptake is required to maintain immune homeostasis, and understanding of these metabolic pathways may lead to therapeutic strategies to target some forms of cancer or autoimmunity.

Current perioperative treatment of patients with type 1 and type 2 diabetes

Diabetes mellitus is rapidly increasing, diabetic patients are likely to undergo surgical procedures more than non-diabetic patients, the hospital stay of diabetic patients is longer, and diabetic patients have increased mortality and morbidity. The correct treatment of diabetic patients in the perioperative period is crucial to improve clinical outcomes. Diabetic patients must be carefully evaluated for cardiovascular risk, keeping in mind micro- and macroangiopathic diabetic complications. Metabolic control deserves great attention because hyperglycemia is related to increased complications and worse outcomes. Insulin infusion regimens to achieve near normoglycemia must be implemented in surgical and critically ill patients.

Insulin-like growth factor-I, but not growth hormone, is dependent on a high protein intake to increase nitrogen balance in the rat

The aim of the present study was to investigate the influence of dietary protein level on the protein anabolic effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I). Female growing rats were fed on either a high- or a low-protein diet with crude protein contents of 222 and 83 g/kg respectively. The diets contained the same amount of metabolizable energy (15·1 MJ/kg) and were given during a 14 d period. During the same time, three groups of rats (n 8) on each diet received subcutaneous infusions of either saline, recombinant human GH (rhGH) or recombinant human IGF-I (rhIGF-I). rhGH and rhIGF-I were given in doses of 360 and 500 μg/d respectively. The low-protein diet alone reduced significantly (P < 0·05) IGF-I concentrations in serum and in tissue taken from the gastrocnemius muscle as well as IGF-I mRNA from the same muscle. The responses to rhGH and rhIGF-I in terms of muscle IGF-I and its mRNA were variable. However, when rhIGF-I was infused into rats on the high-protein diet, significantly elevated levels of IGF-I in muscle tissues could be observed. This was associated with a significantly (P < 0·05) increased N balance, whereas rhGH significantly (P < 0·05) enhanced the N balance in rats on the low-protein diet. Thus, it can be concluded that the level of dietary protein ingested regulates not only the effect of IGF-I on whole-body N economy but also the regulation of IGF-I gene expression in muscles. The exact mechanism by which GH exerts its protein anabolic effect, however, remains to be elucidated.

Therapeutic aspects of growth hormone and insulin-like growth factor-I treatment on visceral fat and insulin sensitivity in adults

Growth hormone (GH) is generally considered to exert anti-insulin actions, whereas insulin-like growth factor I (IGF-I) has insulin-like properties. Paradoxically, GH deficient adults and those with acromegaly are both predisposed to insulin resistance, but one cannot extrapolate from these pathological conditions to determine the normal metabolic roles of GH and IGF-I on glucose homeostasis. High doses of GH treatment have major effects on lipolysis, which plays a crucial role in promoting its anti-insulin effects, whereas IGF-I acts as an insulin sensitizer that does not exert any direct effect on lipolysis or lipogenesis. Under physiological conditions, the insulin-sensitizing effect of IGF-I is only evident after feeding when the bioavailability of circulating IGF-I is increased. In contrast, many studies in GH deficient adults have consistently shown that GH replacement improves the body composition profile although these studies differ considerably in terms of age, the presence or absence of multiple pituitary hormone deficiency, and whether GH deficiency was childhood or adult-onset. However, the improvement in body composition does not necessarily translate into improvements in insulin sensitivity presumably due to the anti-insulin effects of high doses of GH therapy. More recently, we have found that a very low dose GH therapy (0.1 mg/day) improved insulin sensitivity without affecting body composition in GH-deficient adults and in subjects with metabolic syndrome, and we postulate that these effects are mediated by its ability to increase free 'bioavailable' IGF-I without the induction of lipolysis. These results raise the possibility that this low GH dose may play a role in preventing the decline of beta-cell function and the development of type 2 diabetes in these "high risk" subjects.

Perioperative glucose control in the diabetic or nondiabetic patient

Patients with diabetes are more likely to undergo surgery than nondiabetics, and maintaining glycemic control in subjects with diabetes can be challenging during the perioperative period. Surgery in diabetic patients is associated with longer hospital stay, higher health care resource utilization, and greater perioperative mortality. In addition, several observational and interventional studies have indicated that hyperglycemia is associated with adverse clinical outcomes in surgical and critically ill patients. This paper reviews the pathophysiology of hyperglycemia during trauma and surgical stress and will provide practical recommendations for the preoperative, intraoperative, and postoperative care of diabetic patients.

Impact of treatment with recombinant human GH and IGF-I on visceral adipose tissue and glucose homeostasis in adults

Supraphysiological doses of growth hormone (GH) therapy are generally thought to antagonize the effects of insulin, whereas the insulin-like growth factor I (IGF-I) potentiates insulin-like actions. Paradoxically, adults with GH deficiency and patients with acromegaly are both predisposed to glucose intolerance and insulin resistance; however, one cannot extrapolate from these pathological conditions to determine the true metabolic roles of GH and IGF-I in glucose homeostasis. Growth hormone also promotes lipolysis, which has been shown to be the principal determinant of its insulin-antagonistic properties; on the other hand, IGF-I, which acts as an insulin sensitizer, does not exert any direct effect on lipolysis or lipogenesis. Under physiological conditions, the insulin-sensitizing effect of IGF-I is evident only after feeding, when the bioavailability of circulating IGF-I is increased. In contrast to supraphysiological GH doses, low doses of GH treatment have been shown to increase circulating IGF-I levels and IGF-I bioavailability and, thus, may theoretically enhance insulin sensitivity without inducing lipolysis. We have recently reported that a fixed administration of a very low GH dose (1.7 microg/kg/day or 0.1mg/day) improved insulin sensitivity in adults with GH deficiency and increased peripheral glucose uptake in subjects with impaired glucose tolerance and the metabolic syndrome. Our data raise the possibility that this very low GH dose may play a role in maintaining beta-cell function and possibly delay the progression to type 2 diabetes in these high-risk patients.

A liver specific gene that is expressed in growth hormone transgenic mice and in normal female mice as a function of age

Growth hormone (GH) acts on various organs to exert its growth and metabolic effects. GH induces transcription of a number of genes in different organs including liver. By performing subtractive hybridization analysis on liver cDNAs of GH transgenic and non-transgenic mice, differentially expressed cDNAs were obtained. This paper describes the isolation and characterization of a liver cDNA, termed cDNA #5, that contains 1897 bp and is predicted to encode a protein (P5) of 512 aa residues. P5 has five immunoglobulin related domains thus allowing it to be classified as a member of the immunoglobulin super family (IGSF). Also, P5 shows significant similarity to both rat and human alpha-1-B glycoprotein which is an acidic serum protein of unknown function. mRNA #5 was detected in the liver hepatocytes of male and female GH transgenic mice and in the liver of female, but not of male, non-transgenic mice. mRNA #5 was not present in dwarf mice including the Ames dwarf, those that express a GH antagonist and those with the GH receptor and binding protein gene disrupted. These findings suggest that induction of mRNA #5 in the liver requires a continuous pattern of GH secretion and an intact GH-GH receptor-signaling complex. mRNA #5 levels in female non-transgenic mice were observed to vary with age implying that gender-specific age-dependent factor(s) may be involved in the induction of mRNA #5. The appearance of mRNA #5 in post-hepatectomized liver that coincides with the proliferative phase of liver regeneration suggests that it may be involved in hepatocyte proliferation. Together these data suggest that expression of cDNA #5 is liver-specific, sexually dimorphic, age-dependent, and may be involved in hepatocyte hyperplasia and liver enlargement.

Recombinant human growth hormone improves muscle amino acid uptake and whole-body protein metabolism in chronic hemodialysis patients

BACKGROUND

Intradialytic parenteral nutrition (IDPN), with or without exercise, has been shown to reverse the net negative whole-body and forearm muscle protein balances observed during hemodialysis. Pharmacologic doses of recombinant human growth hormone (rhGH) constitute another potential anabolic therapy in chronic hemodialysis patients.

OBJECTIVE

Our goal was to examine the potential additive anabolic effects of rhGH compared with IDPN and exercise on protein and energy homeostasis.

DESIGN

We studied 7 chronic hemodialysis patients in a crossover design study in which each subject participated in 2 protocols: GH (rhGH + IDPN + exercise) and no GH (IDPN + exercise). During the GH protocol, the subjects were studied after 3 daily doses of rhGH. Each subject was studied 2 h before, 4 h during, and 2 h after a hemodialysis session with the use of a primed, constant infusion of l-[1-(13)C]leucine.

RESULTS

Whole-body net protein balance was -0.50 +/- 0.07 mg x kg fat-free mass(-1) x min(-1) when the patients did not receive rhGH and -0.39 +/- 0.04 mg x kg fat-free mass(-1) x min(-1) when the patients received rhGH, a 22% improvement in prehemodialysis whole-body protein homeostasis (P < 0.05). Essential amino acid muscle loss was also significantly less during the prehemodialysis period when rhGH was administered (-18 +/- 23 compared with -71 +/- 20 mmol/L; P < 0.05). The whole-body anabolic effects of rhGH observed during the prehemodialysis period persisted throughout the entire study, as evidenced by a lack of significant interaction or main effect of treatment during hemodialysis and in the posthemodialysis period.

CONCLUSION

rhGH improves whole-body protein homeostasis in chronic hemodialysis patients.

SOCS2 negatively regulates growth hormone action in vitro and in vivo

Mice deficient in SOCS2 display an excessive growth phenotype characterized by a 30-50% increase in mature body size. Here we show that the SOCS2-/- phenotype is dependent upon the presence of endogenous growth hormone (GH) and that treatment with exogenous GH induced excessive growth in mice lacking both endogenous GH and SOCS2. This was reflected in terms of overall body weight, body and bone lengths, and the weight of internal organs and tissues. A heightened response to GH was also measured by examining GH-responsive genes expressed in the liver after exogenous GH administration. To further understand the link between SOCS2 and the GH-signaling cascade, we investigated the nature of these interactions using structure/function and biochemical interaction studies. Analysis of the 3 structural motifs of the SOCS2 molecule revealed that each plays a crucial role in SOCS2 function, with the conserved SOCS-box motif being essential for all inhibitory function. SOCS2 was found to bind 2 phosphorylated tyrosines on the GH receptor, and mutational analysis of these amino acids showed that both were essential for SOCS2 function. Together, the data provide clear evidence that SOCS2 is a negative regulator of GH signaling.

Long-term monitoring of insulin sensitivity in growth hormone-deficient adults on substitutive recombinant human growth hormone therapy

Since the effects of recombinant human growth hormone (rhGH) replacement therapy on glucose metabolism are still a matter of debate, the aim of the present study was to evaluate the impact of long-term rhGH treatment on insulin sensitivity. Simple indices of insulin resistance (IR) and insulin sensitivity (IS), based on fasting glucose and insulin, such as the homeostasis model assessment of insulin resistance (HOMA-IR) and the quantitative insulin check index (QUICKI), were used to estimate the degree of IR and IS in 20 normoglycemic patients (11 men and 9 women; mean age, 44 +/- 14 years) with severe adult-onset GH deficiency (GHD). Measurements were determined at baseline and after 1 and 5 years of continuous rhGH therapy. Basal values were compared to those obtained in 20 healthy sex- and age-matched controls. Starting rhGH dose ranged from 3 to 8 microg/kg/d in keeping with sex and age, then doses were titrated according to insulin-like growth factor-I (IGF-I) levels. At baseline all patients had low IGF-I levels (10 +/- 5.4 nmol/L), high body mas index (BMI; 27.5 +/- 4 kg/m(2)), and elevated body fat percentage (BF%; 31.8 +/- 9.6). Fasting glucose and insulin levels, as well as HOMA-IR and QUICKI, did not differ significantly from those recorded in the control group. After 1 year of rhGH replacement therapy, normalization in IGF-I levels and a significant reduction in BF% were observed (P <.001), and these effects were maintained after 5 years of treatment. Fasting glucose increased from 79 +/- 10 to 87 +/- 13, and 87 +/- 12 mg/dL (P <.05) after 1 and 5 years of therapy, respectively. Fasting insulin significantly increased after 1 year, without further modifications in the long-term follow-up. HOMA-IR significantly increased from 2.1 +/- 1.7 to 2.5 +/- 1.7 (P <.05) after 1 year, then decreased to 2.3 +/- 1.5 (P = not significant [NS] v basal) after 5 years. A specular decrease in QUICKI from 0.37 +/- 0.05 to 0.34 +/- 0.03 (P <.01) occurred after 1 year, with a trend to increase (0.35 +/- 0.04; P = NS v basal) after 5 years. No patient developed impaired fasting glucose. In conclusion, rhGH therapy determined an increase in fasting glucose and insulin levels, causing in the short-term period a worsening of IS. The sustained reduction in BF%, without further deterioration of IS, suggests that long-term beneficial effects on body composition may overcome the negative influence of GH on glucose metabolism.

Hormone use and abuse: what is the difference between hormones as fountain of youth and doping in sports?

GH can induce changes in body composition that are considered to be advantageous to aging subjects especially. However, there are no results indicating that the use of GH during aging should be advocated, because of the lack of any proven efficacy for whatever parameter. Also, data indicate that calorie restriction can extend life spans by altering the rate of decline in reserve capacity as well as by reducing the cumulative exposure to GH. Moreover, animal data suggest that lower GH actions are positively correlated with longevity. The abuse of GH by sportsmen is based on the belief that it has potent anabolic effects, while it is difficult to detect the abuse. Again, this supposed efficacy cannot be supported by any scientific data.

Effects of growth hormone on lipid metabolism in humans

The most immediate effect of growth hormone (GH) administration in humans is a significant increase in free fatty acids after 1-2 h, reflecting stimulation of lipolysis and ketogenesis. This stimulation represents an important physiological adaptation to stress and fasting. When the capacity of GH to increase lipolysis is blocked, the protein-retaining and insulin-antagonistic effects of GH on glucose metabolism are either abolished or weakened dramatically, compatible with a key role for lipolysis in orchestrating the metabolic actions of GH.

Regulation of growth-hormone-receptor gene expression by growth hormone and pegvisomant in human mesangial cells

BACKGROUND

Mice transgenic for growth hormone develop mesangial proliferation, glomerular hypertrophy, and progressive glomerular sclerosis suggesting that the growth hormone-insulin-like growth factor I (IGF-I) pathway plays an important role. Therefore, we studied the impact of variable concentrations of 22 kD, 20 kD growth hormone, as well as of the growth hormone receptor antagonist pegvisomant (B2036-PEG), on both the growth hormone receptor (GHR/GHBP) gene expression and growth hormone binding protein (GHBP) formation in a human glomerular mesangial cell line. Further, the impact on collagen, IGF-I and IGF binding protein-1 (IGFBP-1) formation was studied.

METHODS

In order to assess transcription, quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used.

RESULTS

Physiologic doses of 22 kD or 20 kD growth hormone caused a dose-dependent and significant (P < 0.01) up-regulation of GHR/GHBP gene transcription, whereas supraphysiologic doses (50 and 500 ng/mL) resulted in down-regulation (P < 0.001). Whenever pegvisomant was used, there was no increase in GHR/GHBP expression. These data were confirmed using run-on experiments. Further, the assessment of GHBP presented a constant, dose-dependent increase, which was completely abolished in the experiments where pegvisomant was used.

CONCLUSION

We present data showing that growth hormone has a direct impact on GHR/GHPB gene transcription and that pegvisomant is a potent growth hormone receptor antagonist in human mesangial cells. In addition, although the GHR/GHBP gene transcription is down-regulated by supraphysiologic growth hormone concentrations, this effect was not found when GHBP levels were measured. This finding may reflect a self-inhibitory effect of growth hormone on the level of GHR/GHBP gene transcription, which does not involve the regulation of the shedding of GHBP and may, therefore, be of physiologic interest.

Growth hormone therapy and its relationship to insulin resistance, glucose intolerance and diabetes mellitus: a review of recent evidence

It is widely recommended that consideration should be given to the therapeutic use of growth hormone (GH) in adults with GH deficiency, whether the condition is of childhood or adult onset. One reason for this recommendation is the possibility that such treatment may reduce the excess cardiovascular risk which is associated with hypopituitarism. This excess risk has been well documented, with mortality ratios of 1.7 to 2.2 being quoted in different studies, and may be a result of the insulin resistance which occurs in hypopituitarism. However, it has also been suggested that this insulin resistance may itself be the result of GH deficiency, especially as GH deficiency is accompanied by suggestive morphological features such as central adiposity. There is, however, no direct evidence that the increase in cardiovascular risk in hypopituitarism is the result of GH deficiency, and the only prospective study designed to examine the relationship failed to find a statistically significant correlation between the two. Since GH administration may also have an independent adverse effect on insulin sensitivity and could thus cause a theoretical worsening of cardiovascular risk, it is important to review the observed effects of GH administration on carbohydrate metabolism in practice. Interpretation of the literature is made difficult by many confounding factors, including differences in study duration, biochemical tools adopted, the use of selected populations and the dose-dependent effect of GH on synthesis of insulin- like growth factor-1. One of the most sensitive markers of a deterioration in insulin sensitivity is the serum insulin level. A rise in serum insulin (fasting, or post-glucose load) was reported in all studies in which it was measured. The majority of studies have also reported a rise in fasting blood glucose. A smaller proportion of reports noted an associated increase in postprandial glucose and in glycosylated haemoglobin (HbA(1c)) while a few reported new cases of either impaired glucose tolerance or frank diabetes mellitus. In general, however, the observed deterioration in insulin sensitivity was small and increases which occurred in blood glucose were small. Nevertheless, these data indicate that rather than lead to an improvement in insulin resistance in hypopituitarism, GH treatment may actually make it worse. As it is also known that even minor reductions in insulin sensitivity may be associated with a clinically significant increase in cardiovascular risk, further large-scale controlled trials are required before the efficacy and safety of GH treatment of adults can be established.

Age dimorphism in the association between growth-hormone status and the respiratory quotient

OBJECTIVE

To investigate the impact of age on the association between the respiratory quotient (RQ) and growth-hormone (GH) secretion and to investigate the acute lipolytic response to an exogenous GH bolus.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study of 36 non-obese healthy subjects (18 women and 18 men) from two age groups was used: "younger" (mean age, 29.5 years; range, 27 to 34 years) and "older" (mean age, 50.8 years; range, 47 to 59 years). Endogenous GH secretion by means of deconvolution analysis of 24-hour serum GH concentrations was measured every 20 minutes. Resting RQ was measured after a 12-hour overnight fast. The lipolytic response to an intravenous exogenous GH bolus (200 microg) was assessed by measuring serum levels of free fatty acids as well as changes in RQ. Additional measurements included body composition (regional computed tomography scan and DXA) and physical fitness (VO(2)max).

RESULTS

Resting RQ did not differ between the two age groups: 0.81 +/- 0.01 (young) vs. 0.82 +/- 0.01 (older; not significant). Several estimates of GH release correlated positively with RQ in the younger group, whereas a negative correlation was detected in the older subjects [GH production rate (microg/liter x kg) vs. RQ: r = 0.62, p < 0.01 (younger); r = -0.53; p = 0.02 (older)]. By regression analysis, 52% to 58% of the variation in RQ could be explained by GH status. After an exogenous GH bolus, the incremental response in nonesterified fatty acid was slightly higher in younger individuals (p = 0.09).

DISCUSSION

Resting RQ is significantly correlated with GH status. This association is positive in younger individuals and negative in older individuals. The lipolytic response to exogenous GH is moderately higher in younger compared with older individuals. GH status should be taken into account when investigating the residual variation in RQ.

Growth hormone receptor antagonists: discovery and potential uses

Serum levels of growth hormone (GH) in the human body vary and can influence the levels of insulin-like growth factor I (IGF-1). Low levels of GH can result in a dwarf phenotype and have been positively correlated with an increased life expectancy. High levels of GH can lead to gigantism or a clinical syndrome termed acromegaly, and also have been implicated in diabetic eye and kidney damage. Additionally, it has been postulated that the GH-IGF-I system can be involved in several types of cancers. Overall, both elevated and suppressed circulating levels of GH can have pronounced physiological effects. More than a decade ago a new class of drug, a GH antagonist, was discovered. It is now being tested for its ability to combat the effects of high circulating levels of GH. In this review, we will discuss some of the detrimental actions of GH and how a GH antagonist may be used to combat these effects.

Biological effects of growth hormone and its antagonist

Serum levels of growth hormone (GH) can vary. Low levels of GH can result in a dwarf phenotype and have been positively correlated with an increased life expectancy. High levels of GH can lead to gigantism or a clinical syndrome termed acromegaly and has been implicated in diabetic eye and kidney damage. Additionally the GH/IGF-1 system has been postulated as a risk factor for several types of cancers. Thus both elevated and suppressed circulating levels of GH can have pronounced physiological effects. More than a decade ago the first drug of a new class, a GH antagonist, was discovered. This molecule is now being tested for its ability to combat the effects of high circulating levels of GH. Here, we discuss some of the detrimental actions of GH, and how a GH antagonist can be used to combat these effects.

Should we start and continue growth hormone (GH) replacement therapy in adults with GH deficiency?

During the last decade, growth hormone deficiency (GHD) in adults has been described as a clinical syndrome. Central features of this entity include increased fat mass, reduced muscle and bone mass, as well as impaired exercise capacity and quality of life. GH replacement therapy has been initiated on a wide scale, but patients do not profit equally from this expensive therapy. The decision to start and continue GH replacement should be made individually for each patient. An eligible patient should have a clear diagnosis of GHD. In addition, GH replacement therapy should be efficacious. Especially, the unique and valuable effects of GH replacement on exercise performance and quality of life are strong arguments in favour of continuation of therapy. In osteopenic patients, GH replacement increases bone mass. Also, GH induces improvements in the cardiovascular risk profile. However, it has not yet been proved whether GH replacement reduces the incidence of bone fractures and cardiovascular mortality and improves life expectancy. Thus far, long-term physiological GH replacement does not appear to be complicated by adverse effects. Therefore, available evidence warrants continuation of long-term GH replacement therapy in patients with a clear-cut diagnosis of GHD who demonstrate beneficial effects of this therapy, especially with regard to exercise performance and quality of life.

Diabetes mellitus associated with recombinant human growth hormone for HIV wasting syndrome

Recombinant human growth hormone (rhGH) is an important treatment option for patients with human immunodeficiency virus (HIV) wasting syndrome. Side effects of rhGH are minimal when administered at physiologic and moderately high dosages, as seen in growth hormone deficiency and Turner's syndrome, respectively. The dosage of rhGH is significantly higher to treat wasting syndrome and still is being studied to determine its long-term efficacy and safety. Individuals with HIV infection are at increased risk for adverse effects due to polypharmacy, immune system alterations, and treatment with newer agents that lack long-term safety data. In addition, rhGH's potential for side effects becomes greater when given at high dosages for wasting syndrome. Clinically significant hyperglycemia developed in an HIV-positive man who started rhGH for wasting syndrome 38 days before the diagnosis of diabetes mellitus.

Short-term effects of growth hormone on myocardial glucose uptake in healthy humans

Cardiac muscle is characterized by insulin resistance in specific heart diseases such as coronary artery disease and congestive heart failure, but not in generalized disorders like diabetes mellitus and essential hypertension when cardiac manifestations are absent. To examine whether the insulin antagonistic effect of growth hormone (GH) acts upon the heart, we compared insulin-stimulated whole body and myocardial glucose uptake with and without GH administration during a 3.5-h euglycemic-hyperinsulinemic clamp in eight healthy males. Myocardial 2-deoxy-2-[(18)F]fluoro-D-glucose uptake was measured with positron emission tomography. The data were converted to myocardial glucose uptake by tracer kinetic analysis. GH did not change the rate-pressure product. GH decreased whole body insulin-stimulated glucose disposal by 26% (48.0 +/- 12.1 vs. control 62.8 +/- 6.1 micromol. kg(-1). min(-1), P < 0.02). Free fatty acids were suppressed to a similar extent with and without GH during the insulin clamp. Insulin-stimulated myocardial glucose uptake was similar in the presence and in the absence of GH (0.34 +/- 0.05 and 0.31 +/- 0.03 micromol. g(-1). min(-1), P = 0.18). In conclusion, GH does not impair insulin-stimulated myocardial glucose uptake despite a considerable whole body insulin antagonistic effect. Myocardial insulin resistance is not an inherent consequence of whole body insulin resistance.

Protection against diabetes-induced nephropathy in growth hormone receptor/binding protein gene-disrupted mice

To further investigate the role of GH in diabetic nephropathy, experimental diabetes was induced with streptozotocin (STZ) in mice in which the GH receptor/binding protein gene was disrupted. Body weight, blood glucose, and renal histology and morphometry were studied 10 weeks after diabetes induction in wild-type (+/+) mice and in mice heterozygous (+/-) and homozygous (-/-) for the disruption. Equivalent levels of hyperglycemia developed in all diabetic groups. Normal weight gain was absent in +/+ and +/- diabetic groups, and -/- diabetics lost weight during the study. Diabetic +/+ and +/- groups both showed evidence of glomerulosclerosis, increases in glomerular volume, and increases in the ratio of mesangial area to total glomerular area, whereas diabetic -/- mice showed none of these pathological changes. These results extend our previous findings of protection against diabetes-associated kidney damage in transgenic mice expressing a GH antagonist. Taken together, the results argue for an important role of GH in the development of diabetes induced end-organ damage.

The growth hormone axis, feeding, and central allocative regulation: lessons from giant transgenic growth hormone mice

Lifetime consumption rates of male transgenic growth hormone (GH) mice and normal controls were measured on either a 38% protein diet (HP), the standard rodent diet (STD) (23.5% protein), or the standard diet supplemented with a free choice of sucrose (CARB). On STD, daily intake of normal mice increased little at sizes greater than 20 g, but larger transgenic mice ate progressively more. Both kinds of mice showed declining daily mass-specific consumption with increasing age. Transgenic mice consistently ate 13.3% less food than normal mice on a mass-specific basis across all ages. On the self-selective CARB diet, normal mice exhibited increasing age-specific daily consumption, whereas transgenic mice exhibited a trend towards age-related decline in mass-specific feeding that proved significant on the basis of body mass. Transgenic mice ingested more sucrose than standard chow and this did not vary with age. In contrast, normal mice ate less sucrose than chow and chose a declining proportion of sucrose with age. Transgenic and normal mice showed a unitary relationship of daily intake of HP in relation to body mass, resulting in constant mass-specific feeding across all ages. Transgenic GH animals, including livestock, show numerous defects that we have attributed to relative energetic stress associated with excessive allocation to lean growth. This is exacerbated by failure to offset increased demands of growth by increasing mass-specific feeding. Results presented here document altered feeding regulation in transgenic GH mice and suggest underlying mechanisms.

The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the effect on the human prolactin receptor

Previously we have demonstrated that 20-kDa human GH (20K-hGH) is a full agonist for hGH receptor (hGHR) even though its complex formation with hGHR and hGH-binding protein differs from that of 22-kDa human GH (22K-hGH). In this study, we focused on the effect of 20K-hGH on human PRL receptor (hPRLR). To elucidate the effects of 20K-hGH on hPRLR and compare them with those of 22K-hGH, we prepared two cells stably expressing full-length hPRLR, Ba/F3-hPRLR and CHO-hPRLR. In the proliferation of Ba/F3-hPRLR cells, which can grow in a dose-response to lactogenic hormones, both 20K- and 22K-hGH exhibited bell-shaped curves in the absence of exogenous zinc ion (Zn2+); however, the curve of 20K-hGH was shifted to a 10-fold higher concentration than that of 22K-hGH in view of EC50 value (the EC50 of 20K- and 22K-hGH were 15 nM and 1.5 nM, respectively). Addition of Zn2+ up to 25 microM increased the activities of both 20K- and 22K-hGH; however, the enhancement by Zn2+ was greater in 20K-hGH than in 22K-hGH, thereby the activities of both hGH isoforms reached the same level at 25 microM Zn2+. Nevertheless, in the presence of 0.25-1 microM free Zn2+, which is equal in human serum, the activity of 20K-hGH was still lower than that of 22K-hGH. The modest effect of 20K-hGH on activating hPRLR in the absence of Zn2+ was confirmed in the rat serine protease inhibitor 2.1 (Spi2.1) gene promoter activation and JAK2/Stat5 tyrosine phosphorylation in CHO-hPRLR. In addition, in human breast cancer cell T-47D, 20K-hGH was proved to stimulate Stat5 tyrosine phosphorylation to much lower degree than 22K-hGH via not hGHR but hPRLR. Taken together, our data suggest that 20K-hGH may be a weaker agonist for hPRLR than 22K-hGH in the human body; therefore 20K-hGH may alleviate the hPRLR-mediated side-effects such as breast cancer when administered to human body.

Transgenic models of growth hormone action

A growth-promoting principle of the pituitary gland was discovered in 1921, and bovine growth hormone (GH) was isolated in 1944. Since then, the structure of GH as it relates to its biological activities has been an exciting research topic. Equally fascinating is the relationship between GH structure and its metabolic activities. In attempts to define some of these activities, several investigators have used GH transgenic mice as models. In this review we summarize what is known about the molecular mechanisms of GH action. We then describe some of the GH transgenic models and point out potential targets for nutrition research.

Growth hormone stimulates the tyrosine kinase activity of JAK2 and induces tyrosine phosphorylation of insulin receptor substrates and Shc in rat tissues

GH stimulates the tyrosine phosphorylation of various cellular polypeptides, including the GH receptor itself, in an early part of the intracellular response. Some of these phosphorylations are catalyzed by a GH receptor-associated kinase identified as JAK2, a member of the Janus family of tyrosine kinases. In cultured cells, GH stimulates the tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), IRS-2, and Shc. This study investigated whether GH could cause the tyrosine phosphorylation of IRSs and Shc proteins in fasted rat tissues in vivo. GH was administered to fasted Wistar rats via a portal vein, and extracts of different tissues were immunoprecipitated with specific antibodies. GH increased the tyrosine phosphorylation of IRS-1, IRS-2, JAK2, and Shc proteins in the liver, heart, kidney, muscle, and adipose tissue of rats. The roles of these substrates as signaling molecules for GH were further demonstrated by the finding that GH stimulated the association of IRS-1/2 with phosphatidylinositol 3-kinase, Grb2, and phosphotyrosine phosphatase and of Shc with Grb2. The correlation between JAK2 tyrosyl phosphorylation and IRS-1 tyrosyl phosphorylation in response to GH together with the results of the in vitro tyrosine kinase assay are consistent with the hypothesis that JAK2 may mediate GH-induced phosphorylation of IRS-1.

Transgenic rabbits overexpressing growth hormone develop acromegaly and diabetes mellitus

Transgenic rabbits expressing the bovine growth hormone (bGH) gene in liver and kidney were obtained to study the long-term effects of chronic exposure to GH in nonrodent animals. These rabbits presented high levels of bGH and insulin-like growth factor I in serum. In spite of chronic exposure to bGH, transgenic rabbits had similar body weight to controls. However, enlargement of the head and limbs and reduction of visceral fat were observed in these animals. They also showed marked hyperinsulinemia, hyperglycemia, and hypertriglyceridemia, indicating that they developed insulin resistance. Furthermore, serious histopathological alterations, including marked fibrosis, were observed in liver, kidney, and skeletal muscle. These anatomical, metabolic, and histological alterations closely resemble those found in patients with acromegaly. Thus, transgenic rabbits overexpressing GH may be a good model of the human disease.

Exercise capacity and hormonal response in adults with childhood onset growth hormone deficiency during long-term somatropin treatment

Growth hormone (GH) deficiency in adults in associated with reduced muscular strength and peak oxygen uptake (peak Vo2). How these variables are influenced by long-term somatropin therapy in adults with childhood onset GH-deficiency has not been precisely defined. The effect of somatropin treatment in 20 childhood onset GH-deficient adults on muscular strength, maximal exercise capacity, and hormonal response to exercise were therefore examined in a double-blind placebo-controlled study with recombinant human GH (rhGH, 12 microg/kg/day) for 6 months, followed by 36 months of open-labeled uninterrupted therapy, after which treatment was stopped for 9 months. After 6 months of treatment, exercise capacity increased significantly, as assessed by time to exhaustion [mean change (95% CI) 0.8 (0.2, 1.4) min, P<0.05], total (accumulated) work [11.6 (0.8, 22.4) kJ, P<0.05] and peak Vo2 [2.6 (0.3, 4.9) ml/kg/min, P<0.01], whereas no significant changes were observed during placebo. This effect on exercise capacity remained unchanged during long-term somatropin treatment, mainly due to increased capacity among patients with isolated GH deficiency. Nine months after stopping treatment, peak Vo2 decreased by 11% from 32.8+/-2.5 to 29.1+/-2.1 ml/kg/min (P<0.05). Maximal muscular handgrip strength was not affected by treatment. Long-term GH therapy resulted in decreased respiratory exchange value (R value) at rest and during exercise (P<0.001), suggesting a metabolic role with increased fat combustion. Resting and submaximal noradrenaline levels decreased during somatropin treatment (P<0.05), while no effect was observed for other exercise-induced hormonal responses, including adrenaline, insulin, prolactin, renin, and ACTH. We conclude that somatropin therapy to childhood onset GH deficient adults has a favourable effect on exercise capacity and may have a potentially beneficial effect on plasma catecholamines.

Plasma growth hormone secretion is impaired in obesity-prone rats before onset of diet-induced obesity

Sprague-Dawley rats, which become obese (obesity prone) when fed a moderately high-fat (MHF; 32.5% of kcal as fat) diet, have decreased growth hormone (GH) concentrations compared with obesity-resistant rats fed the same diet. To determine whether plasma GH concentrations are different in obesity-prone rats compared with obesity-resistant rats before diet-induced obesity occurs, total integrated GH concentrations were determined in male Sprague-Dawley rats before exposure to the MHF diet. After initial blood sampling, rats were fed an MHF diet for 15 wk, over which time the animals were separated into two discrete populations based on body weight gain. Analysis of GH in episodic blood samples showed that the obesity-prone group had a GH secretion deficit before the onset of obesity (115.2 +/- 12.9 ng . ml-1 . 200 min-1) compared with obesity-resistant rats (237.2 +/- 47.1 ng . ml-1 . 200 min-1). The GH concentration difference was due to a decrease in mean GH peak height in rats that later became obese (34.8 ng/ml) compared with rats that remained lean (74.2 ng/ml). The results suggest that GH secretion impairment exists before dietary challenge or onset of obesity and may contribute to the susceptibility to obesity observed in these animals.

Growth hormone deficiency and cardiovascular risk

It is now recognized that growth hormone (GH) deficiency in adults represents a distinct clinical syndrome that encompasses reduced psychological well-being as well as specific metabolic abnormalities. The latter features, which include hypertension, central obesity, insulin resistance, dyslipidaemia and coagulopathy, closely resemble those of metabolic insulin resistance syndrome. The increased cardiovascular morbidity and mortality demonstrated in these GH-deficient (GHD) adults reinforce the close association between the two syndromes. Replacement of GH in GHD adults has resulted in a marked reduction of central obesity and significant reduction in total cholesterol but little change in other risk factors, in particular insulin resistance and dyslipidaemia. The persistent insulin resistance and dyslipidaemia, together with the elevation of plasma insulin levels and lipoprotein (a) with GH replacement in these subjects are of concern. Long-term follow-up data are required to assess the impact of GH replacement on the cardiovascular morbidity and mortality of GHD adults. Further exploration of the appropriateness of the GH dosage regimens currently being employed is also indicated.