Growth Hormone Secretion: Its Regulation and the Influence of Nutritional Factors

Insulin-like growth factor 1 of wild vertebrates in a life-history context

Broad variation in intra- and interspecific life-history traits is largely shaped by resource limitation and the ensuing allocation trade-offs that animals are forced to make. Insulin-like growth factor 1 (IGF-1), a growth-hormone-dependent peptide, may be a key player in the regulation of allocation processes. In laboratory animals, the effects of IGF-1 on growth- and development (positive), reproduction (positive), and longevity (negative) are well established. We here review the evidence on these effects in wild vertebrates, where animals are more likely to face resource limitation and other challenges. We point out the similarities and dissimilarities in patterns of IGF-1 functions obtained in these two different study settings and discuss the knowledge we need to develop a comprehensive picture of the role of IGF-1 in mediating life-history variation of wild vertebrates.

Predicting the vulnerability of birds to trophic threat posed by phenological mismatch based on nutritional and physiological status of nestlings

Climate change induced phenological mismatches between nestlings and their optimal food resources have been found to negatively influence the survival of many bird species. Discriminating which species is vulnerable to such threat is difficult only based on the diet observation, and therefore it is necessary to establish a more reliable method to predict the vulnerability of bird species. In the case of Asian short-toed lark (Calandrella cheleensis), we predicted such vulnerability by evaluating whether nestlings can absorb equal level of nutrients from different diets and maintain equal physiological status. We compared the diet, plasma nutrients, plasma insulin-like growth factor-1 (IGF-1), body mass and survival rate of nestlings hatched under different optimal food (grasshopper nymph) abundance conditions in two breeding seasons. Plasma glucides, amino acids, tricarboxylic acid (TCA) cycle metabolites, some fatty acids, IGF-1, body mass and survival rate of the nestlings hatched under medium or low nymph abundance conditions were significantly lower than those of nestlings hatched under high nymph abundance condition. The relative abundance of plasma amino acids, glucides, TCA cycle metabolites and fatty acids were significantly, and positively, correlated with IGF-1 levels, which, in turn, was positively correlated with nestling body mass. These results indicate that the diet with low optimal food proportion was nutritionally inferior to the diet with high optimal food proportion and inhibited the growth of nestlings. Species like Asian short-toed lark is vulnerable to the trophic threat induced by phenological mismatch because the alternative food is insufficient to satisfy the nutritional requirement of nestlings.

Endocrine and metabolic disorders in patients with Gaucher disease type 1: a review

Background

Gaucher disease (GD) is one of the most prevalent lysosomal storage diseases and is associated with hormonal and metabolic abnormalities, including nutritional status disorders, hypermetabolic state with high resting energy expenditures, peripheral insulin resistance, hypoadiponectinaemia, leptin and ghrelin impairments, hypolipidaemia, linear growth deceleration and growth hormone deficiency, delayed puberty, hypocalcaemia and vitamin D deficiency. Specific treatments for GD such as enzyme replacement therapy and substrate reduction therapy display significant effects on the metabolic profile of GD patients.

Main body of the abstract

Hormonal and metabolic disturbances observed in both adult and paediatric patients with Gaucher disease type 1 (GD1) are discussed in this review. The PubMed database was used to identify articles on endocrine and metabolic disorders in GD1. GD1 appears to facilitate the development of disorders of nutrition, glucose metabolism and vitamin D insufficiency. Metabolic and hormonal diseases may have a significant impact on the course of the underlying disease and patient quality of life.

Conclusions

Conditions relating to hormones and metabolism can be wide-ranging in GD1. Obtained findings were intrinsic to GD either as a deleterious process or a compensatory response and some changes detected may represent co-morbidities. Actively seeking and diagnosing endocrine and metabolic disorders are strongly recommended in GD1 patients to optimize healthcare.

Pediatric Gaucher disease type I and mild growth hormone deficiency: a new feature?

A 5-year-old girl was referred to the Department of Pediatrics and Neonatology, Guglielmo da Saliceto Hospital, Italy, because of growth retardation. Clinical and laboratory investigations showed pallor, hepatosplenomegaly, anemia and low/normal platelet count. Further investigations led to the diagnosis of Gaucher disease (GD). We believe this is the first report of growth hormone deficiency in a growth-retarded child with GD. After 1 year of imiglucerase replacement enzyme therapy, her bone age had normalized, linear growth rate had accelerated, and insulin growth factor-1 (IGF-1) and, perhaps more interestingly, growth hormone deficiency, had normalized. While the pathophysiological mechanisms underlying compromised growth in GD are poorly understood, the response to imiglucerase reported in this patient suggests that growth hormone deficiency is related to the underlying metabolic disorder in GD, rather than a primary endocrine pathology. Growth hormone deficiency adds to an already extensive list of possible clinical manifestations of this heterogeneous and complex disorder.

Bioactive insulin-like growth factor-I in obesity

CONTEXT

In obesity, total IGF-I is not reduced to the degree predicted by low GH levels, and free IGF-I levels are normal to high. Total and free IGF-I may not reflect IGF-I biological activity because immunoassays cannot account for the modifying effects of IGF binding proteins on interactions between IGF-I and its receptor.

OBJECTIVE

The aim of the study was to investigate the biological activity of IGF-I in obesity.

DESIGN AND SETTING

We conducted a cross-sectional study at a General Clinical Research Center.

STUDY PARTICIPANTS

Thirty-four healthy women (11 lean, 12 overweight, and 11 obese) of comparable age (overall mean, 30.7 +/- 1.3 yr) participated in the study.

INTERVENTION

There were no interventions.

MAIN OUTCOME MEASURES

We measured bioactive IGF-I (as measured by a kinase receptor activation assay), IGFBP-1, and GH using 6-h pools of serum collected every 10 min for 24 h, and fasting IGF-I and IGFBP-3.

RESULTS

Mean 24-h GH (R = -0.76; P < 0.0001), total IGF-I (R = -0.36; P = 0.040), and IGFBP-1 (R = -0.41; P = 0.017) levels were inversely associated with BMI, whereas bioactive IGF-I and IGFBP-3 levels were not. Mean bioactive IGF-I was similar in the groups [2.72 +/- 0.22 (lean), 3.10 +/- 0.32 (overweight), and 2.43 +/- 0.23 [corrected] (obese) microg/liter; overall P = 0.22]. Percentage bioactive IGF-I [(bioactive/total IGF-I) x 100] was higher in obese subjects than both lean and overweight subjects (P = 0.039).

CONCLUSIONS

Despite low GH secretion in obesity and decreasing IGFBP-1 with increasing BMI, 24-h mean bioactive IGF-I levels are not reduced in obese women and do not correlate with BMI or IGFBP-1 levels. This argues against elevated bioactive IGF-I as the etiology of reduced GH secretion through a feedback mechanism in obesity.

Change of the growth hormone–insulin-like growth factor-I axis in patients with gastrointestinal cancer: related to tumour type and nutritional status

Changes in the growth hormone (GH)–insulin-like growth factor-I (IGF-I) axis, especially acquired GH resistance, develop in many severe illnesses, including cachexia. To study changes in the GH–IGF-I axis in patients with cancer cachexia, biochemical markers and body composition parameters were measured in eighty-eight gastric cancer patients, thirty colorectal cancer patients (subclassified according to the presence or absence of cachexia) and twenty-four healthy control subjects. Fifty-nine patients were defined as cachectic, based on the percentage of weight loss compared with their previous normal weight. The remaining fifty-nine patients were defined as non-cachectic. Measurements were repeated in twenty-seven patients (sixteen with gastric cancer and eleven with colorectal cancer) 3 months after radical operation. Compared with the controls, the cachectic gastric cancer patients had high GH levels (1·36 v. 0·32 ng/ml; P=0·001), a trend towards high IGF-I levels (223·74 v. 195·15 ng/ml; P=0·128 compared with non-cachectic patients) and a low log IGF-I/GH ratio (2·55 and 2·66 v. 3·00; P=0·002), along with a decreased BMI; the cachectic colorectal cancer patients showed the biochemical characteristics of acquired GH resistance: high GH (0·71 v. 0·32 ng/ml; P=0·016), a trend towards decreased IGF-I levels (164·18 v. 183·24 ng/ml; P=0·127) and a low log IGF-I/GH ratio (2·54 v. 2·99; P=0·005), with increased IGF-I levels following radical surgery (200·49 v. 141·91 ng/ml; P=0·046). These findings suggest that normal GH reaction and sensitivity occur in gastric cancer patients, controlled by nutritional status, whereas acquired GH resistance develops in cachectic colorectal cancer patients, which may be caused by tumour itself.

Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women

BACKGROUND

There is currently no consensus on the effect of dietary protein intake on the skeleton, but there is some indication that low calcium intakes adversely influence the effect of dietary protein on fracture risk.

OBJECTIVE

The objective of the present study was to determine whether supplemental calcium citrate malate and vitamin D influence any associations between protein intake and change in bone mineral density (BMD).

DESIGN

Associations between protein intake and change in BMD were examined in 342 healthy men and women (aged > or = 65 y) who had completed a 3-y, randomized, placebo-controlled trial of calcium and vitamin D supplementation. Protein intake was assessed at the midpoint of the study with the use of a food-frequency questionnaire and BMD was assessed every 6 mo by dual-energy X-ray absorptiometry.

RESULTS

The mean (+/-SD) protein intake of all subjects was 79.1 +/- 25.6 g/d and the mean total calcium intakes of the supplemented and placebo groups were 1346 +/- 358 and 871 +/- 413 mg/d, respectively. Higher protein intake was significantly associated with a favorable 3-y change in total-body BMD in the supplemented group (in a model containing terms for age, sex, weight, total energy intake, and dietary calcium intake) but not in the placebo group. The pattern of change in femoral neck BMD with increasing protein intake in the supplemented group was similar to that for the total body.

CONCLUSION

Increasing protein intake may have a favorable effect on change in BMD in elderly subjects supplemented with calcium citrate malate and vitamin D.

Growth hormone receptor gene expression in porcine skeletal and cardiac muscles is selectively regulated by postnatal undernutrition

During mild postnatal undernutrition, growth hormone receptor (GHR) mRNA abundance decreases in liver but increases in longissimus dorsi muscle. We tested the following hypotheses: 1) GHR gene expression is related to the metabolic and contractile characteristics of different muscles, and 2) the GHR response to nutrition depends on muscle type. Eight pairs of littermate pigs were weaned at 3 wk and given an optimal [60 g/(kg.d)] or low [(20 g/(kg.d)] food intake for the next 3 wk. All pigs grew, but at a slower rate in the low food intake group (P: < 0.001). Functionally distinct muscles were assessed for GHR mRNA (RNase protection analysis), oxidative myofibers (succinate dehydrogenase histochemistry) and type I slow myofibers (myosin immunocytochemistry). There were striking muscle-specific differences in GHR gene expression (P: < 0.001) and in its regulation by nutritional status. Relative expression of GHR mRNA in the optimal food intake group occurred in ascending order as follows: longissimus < diaphragm approximately rhomboideus < cardiac < soleus. There was a positive correlation with the proportion of oxidative myofibers (P: < 0.001) but not with type I myofibers (P: > 0.10). Compared with the high intake pigs, hepatic GHR mRNA was downregulated in the low intake pigs by 59% (P: < 0.01), whereas in the four muscles examined it was upregulated as follows: longissimus, 124% (P: < 0.05); rhomboideus, 19% (P: > 0.4); soleus, 65% (P: < 0. 05); cardiac, 51% (P: < 0.05). Moreover, the proportion of skeletal muscle fibers with high oxidative capacity was also greater in the low intake group (P: < 0.05). We conclude that postnatal GHR gene expression and its regulation by mild undernutrition are related to the metabolic, contractile and specific functional properties of different muscles.

Regulation of plasma insulin-like growth factor-I levels in brown trout (Salmo trutta)

In this study we report that the use of a heterologous radioimmunoassay (RIA) is valid for the detection of insulin-like growth factor-I (IGF-I) levels in plasma of a variety of fish species. Parallelism between standard curves and plasma dilutions were observed and the standard curve obtained with mammalian IGF-I presented the same characteristics as that obtained with coho salmon recombinant IGF-I. The RIA was biologically validated since total plasma IGF-I values were significantly modified by different experimental conditions. Hyperinsulinemia induced either by arginine or insulin injection was accompanied by increases in IGF-I plasma levels in brown trout (Salmo trutta). In contrast, parallel decreases in insulin and IGF-I circulating levels were observed after 45 days of fasting and 20 days after a single streptozotocin injection. Administration of arginine in fasted fish led to a relative increase in insulin and IGF-I plasma concentrations, while arginine injection in fish previously treated with streptozotocin increased IGF-I levels only. The above data suggest that insulin, together with other factors, may act to increase the levels of IGF-I in plasma.

The circulating insulin-like growth factor system in children with coeliac disease: an additional marker for disease activity

BACKGROUND

Chronic undernutrition resulting from coeliac disease (CD) could be associated with changes in the circulating insulin-like growth factor (IGF) system, which may participate in the pathogenesis of growth retardation occurring in these patients.

METHODS

We performed a cross-sectional study in CD subjects attempting to (1) document the pattern of serum IGF-I and IGF binding protein (IGFBP) 1 and 3 at diagnosis and (2) assess the response of circulating IGF system to dietary treatments, in comparison with the response of clinical and laboratory findings utilized for the diagnosis of CD. Thirty-two prepubertal CD children were divided into three groups based on the dietetic treatment: at diagnosis (D, n=18); on gluten-free diet for at least 6 months (GFD, n=7); and on gluten challenge for at least 3 months (CH, n=7). Six postpubertal CD patients were also studied at diagnosis.

RESULTS

In prepubertal children IGF-I levels were significantly reduced (by 29%) in D vs sex- and age-matched normal control (NC) subjects, with reductions being more pronounced before 3 years of age. Likewise, serum IGFBP-3 concentrations were decreased by 22%, whereas circulating IGFBP-1 levels were increased by 60%, compared with NC, with more marked IGFBP changes in older children. Similar alterations were observed in postpubertal patients. Changes in the circulating IGF system disappeared in GFD subjects and reappeared in CH children, as positivity of disease-specific antibodies. Body mass index (BMI) also improved in GFD subjects, but did not decrease in CH children. Changes in IGF-I and IGFBPs did not correlate with each other. Levels of IGF-I, but not of IGFBPs, maintained the relation with age and correlated significantly with BMI and positivity of antibodies.

CONCLUSIONS

These results demonstrate that CD patients show significant changes in serum IGF-I, in younger children, and IGFBPs (particularly IGFBP-1), in older children and adolescents, correlating with clinical course and response to dietary treatments. The alteration in the circulating IGF system could be implicated in the pathogenesis of growth retardation occurring in CD and may provide an additional tool in monitoring of the disease.

Roles of insulin and amino acids in the regulation of protein synthesis in the neonate

Neonates deposit protein at a very high rate and efficiently utilize dietary amino acids for protein deposition. This high efficiency is associated with an elevated stimulation of tissue protein synthesis by feeding. Our recent studies have focused on identification of the factors that mediate this response in the neonate. A positive curvilinear relationship between skeletal muscle protein synthesis and plasma insulin concentration was identified in fasted and fed suckling pigs; the relationship changes with development. To test the specific effects of insulin on protein metabolism in the neonate, a procedure to clamp amino acids, under hyperinsulinemic conditions, was developed. By using this technique, we showed that insulin-stimulated whole-body amino acid disposal is elevated in the neonate, and this response may account for the efficient use of dietary amino acids for protein accretion. More recent studies suggest that the enhanced stimulation of skeletal muscle protein synthesis by feeding in the neonate is primarily insulin mediated; however, the stimulation of liver protein synthesis by feeding seems to be largely a function of amino acid concentration.

The role of IGFs in catabolism

The hypercatabolic response to trauma, extensive surgery and sepsis is characterized by an increased metabolic rate, severe muscle wasting and a negative nitrogen balance. This process of 'autocannibalism' may be in part a consequence of a disordered growth hormone (GH)/insulin-like growth factor (IGF) axis. In this chapter the normal physiology of the GH/IGF axis is first briefly reviewed. This is followed by a discussion of the changes that accompany fasting and catabolic illness, the effects of IGF-1 administration in health and disease and a comparison of the effects of IGF-1, GH and insulin on catabolism. Although initial investigations of IGF-1 administration in animals and human volunteers have often been encouraging, studies in catabolic patients have so far proved disappointing. Combined treatment with GH, IGF-1 (and insulin) or with IGF-1 and its major binding protein, may prove more effective, especially when used in conjunction with nutritional supplements such as glutamine.

Growth hormone release induced by an amino acid mixture from primary cultured anterior pituitary cells of goats

The effects of amino acids on growth hormone (GH) release and cytosolic calcium concentration ([Ca2+]i) were investigated in caprine anterior pituitary cells cultured for 3 d in Dulbecco modified Eagle medium. The addition of an amino acid mixture consisting of seven nonessential amino acids (NEAA: L-Asp, Gly, L-Ala, L-Ser, L-Pro, L-Asn, and L-Glu; concentration of each 12.5-200 mumol/l) in the medium significantly raised GH release from the cultured cells in a concentration-dependent manner with the maximum release at 200 mumol/l NEAA. Although an addition of L-Asp (0.1-100 mumol/l) caused a significant rise in GH release in a concentration-dependent manner, neither the individual amino acids contained in NEAA except L-Asp nor others (L-Leu, L-Phe, L-Gln, L-Met, and L-Arg) caused a rise in GH release when added alone to the medium. The rise in GH release induced by NEAA (200 mumol/l) and GH-releasing hormone (GHRH, 10 nmol/l) was significantly reduced by the addition of EGTA (1.8 mmol/l) and nifedipine (1 mumol/l) to the medium, respectively. The addition of NEAA (200 mumol/l) caused a rapid and transient [Ca2+]i increase, followed thereafter by a steady increase. The prior addition of nifedipine (1 mumol/l), which itself significantly reduced the basal [Ca2+]i, completely abolished the response induced by NEAA or GHRH. From these findings, we conclude that: 1) NEAA raises GH release and [Ca2+]i in cultured caprine anterior pituitary cells, and 2) Ca2+ influx from the medium may be responsible for the cellular action of NEAA.

Free insulin-like growth factors in human obesity

It is well established that spontaneous and stimulated growth hormone (GH) secretion is diminished in human obesity. In contrast to classic GH deficiency, obesity is not associated with hypopituitary levels of circulating total (extractable) insulin-like growth factor-I (IGF-I) and reduced somatic growth. Thus, the riddle of "normal growth without GH" in obese children and the mechanisms behind the GH suppression have remained unsolved. Insulin reduces hepatic production of IGF-binding protein-1 (IGFBP-1), an in vitro inhibitor of IGF bioactivity, and it has been suggested that the obesity-related hyperinsulinemia may increase free (bioactive) IGF in vivo by reducing the concentration of IGFBP-1. We have recently developed a method that during near in vivo conditions isolates the free, unbound fractions of IGF-I and IGF-II in human serum. Using this method, we have determined overnight fasting serum levels of free IGFs in obese subjects and compared the results with levels of total (extractable) IGFs, IGFBPs, GH, and insulin. The study included 92 healthy subjects (56 males and 36 females) allocated to three age-matched groups depending on body mass index (BMI): 31 controls (BMI < or = 25), 33 subjects with moderate obesity (25 < BMI < 30), and 28 subjects with severe obesity (BMI > or = 30). Fasting serum insulin correlated positively (r = .61, P < .0001) with BMI and was significantly elevated in moderate and severe obesity (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

[Role of anabolic hormonal factors in surgery in adults]

Hormonal agents with anabolic effect are virtually able to limit or even to counteract the adverse effects of stress and to act in synergy with nutritional support. Hormones with a high theoretic anabolic power include recombinant human growth hormone (rGH), insulin, insulin-like growth factor and testosterone. Other molecules favour anabolism in modifying the catabolic effect of diseases (anti-cytokines, beta-adrenoceptor agonists), in promoting intestinal absorption of substrates or in stimulating epithelial growth (EGF). The results of preliminary studies cannot be transferred into routine clinical practice. The rGH favours the preservation of body mass integrity and various functions. Therefore it could improve postoperative outcome and decrease the duration of hospital stay. A study in severely burnt children showed the metabolic benefits of rGH as well as a shortening of hospital stay because of a decrease of cicatrisation delay after skin grafting. Finally it demonstrated that rGH allows major financial savings in severe burns. The IGF-1 stimulates host defences and decreases the rate of wound infections. The rGH potentiates nitrogen sparing effect of IGF-1 and decreases hypoglycaemia induced by IGF-1. However a study on patients in stress is yet lacking. A combination of growth factors could be virtually efficient, however the cost seems exorbitant. An unquestionable evidence of their clinical efficiency is required before a clinical use in routine can be considered. The postoperative protein catabolism could be decreased by nandrolone decanoate or its derivatives. On the other hand, it has not been proven that protein synthesis, the muscle function or clinical prognosis can be improved by such a treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal profile of growing male and female diploids and triploids of the blue tilapia,Oreochromis aureus, reared in intensive culture

Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower growth rate of females. When females and males are considered separately, the growth rate is not significantly different in diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and 17β-estradiol (E2)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but the difference is not always significant.Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months compared to the triploid females and diploid males. 3,5,3'-triiodo-L-thyronine (T3) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in 4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth rate of males may be related to the high circulating levels of T3 and 11kT.

Influence of thyroid hormones on the GH-IGF-I axis

There is a complex relationship between thyroid hormones, GH, and the insulin-like growth factors (IGFs). Thyroid hormones act at many sites from the hypothalamic control of GH release to the tissue expression of IGF-I and its binding proteins (IGFBPs). In this review, we present current knowledge of the effects of altered thyroid status on the GH-IGF-I axis, concentrating on the changes seen in IGF-I gene expression and circulating levels of GH and IGFBPs.