Dietary components that regulate serum somatomedin-C concentrations in humans

Short-term gluten challenge in children with coeliac disease does not impair spontaneous growth hormone secretion

BACKGROUND

Growth retardation in children with coeliac disease has been attributed to impaired growth hormone (GH) secretion observed in stimulation tests.

OBJECTIVE

This study aimed at investigating the possible change in spontaneous GH secretion during a standardised gluten challenge.

PATIENTS

Twelve children with previous enteropathy suggesting coeliac disease and a normal pre-challenge biopsy on a gluten-free diet were included; eight of them completed all parts of the study, including repeated 24-h GH sampling.

METHODS

At the start and the end of a 5-6 weeks standardised gluten challenge, blood was drawn at a constant rate for 24 h and collected for GH analysis at 20-min intervals. The graph of plotted GH values was analysed by means of a computer program (PULSAR).

RESULTS

No significant changes were seen in the measures of maximum GH peak, baseline GH values, area under the curve over the baseline (AUCb), the number of GH peaks or mean GH concentration. GH secretion rate (GHt) increased slightly. None of the characteristics of the 24-h profile was significantly correlated to the change of IGF-I.

CONCLUSION

No impaired GH secretion was found. Thus, we speculate that decreased growth rate in celiac disease may not be primarily caused by changes in GH secretion. Instead it may be caused by changed peripheral sensitivity to GH.

Energy imbalance and prostate cancer

In this review, the emerging evidence that excessive energy intake relative to energy expenditure increases the risk of prostate cancer is discussed. The adverse effects of energy imbalance can be inferred from an experimental study demonstrating reduced prostate tumor growth, lower circulating concentrations of insulin-like growth factor-I and decreased expression of vascular endothelial growth factor with energy restriction in transplantable tumor models. The effects of energy restriction on factors mediating greater proliferation relative to apoptosis and angiogenesis suggest that energy imbalance may act late in the carcinogenic pathway. Energy intake also has been evaluated in relation to prostate cancer risk in 23 analytic epidemiologic studies. Among studies reporting effect estimates, 8 of 14 case-control studies support a direct association [top versus bottom quantile, OR(summary) = 1.3; 95% confidence interval (CI), 1.1-1.4], but none of four cohort studies do (RR(summary) = 1.0; 95% CI, 0.8-1.2). The four case-control studies that evaluated advanced disease suggest a higher risk with higher energy intake (OR(summary) = 1.6; 95% CI, 1.2-2.0). However, none of these studies considered the balance of energy intake with body size and physical activity, the major determinants of variability in energy demand. Numerous research questions remain to be addressed, including, Which biological pathways are adversely affected by energy imbalance? Does energy imbalance act early or late in prostate carcinogenesis? What is the optimal energy balance for minimizing risk of clinically important prostate cancer? Evidence is beginning to show that energy intake in excess of expenditure may affect prostate carcinogenesis and, in particular, risk of advanced disease.

High-protein induced renal enlargement is growth hormone independent

BACKGROUND

Growth hormone (GH) and insulin-like growth factors (IGFs) have been postulated as pathogenic factors in several forms of renal growth, including that induced by high-protein (HP) diets. Compensatory renal growth (CRG) following renal uninephrectomy is strictly GH dependent, while the exact role of GH as a regulating factor in HP induced renal growth has not been fully clarified.

METHODS

To elucidate a possible direct role for GH in HP-induced renal growth, we examined the effect of a newly developed specific GH-receptor (GHR) antagonist (B2036-PEG) on renal growth and renal GH/IGF-system expression in HP-fed mice.

RESULTS

Mice fed a HP diet (45% protein) for one week demonstrated renal hypertrophy and increased renal IGF-I. GH receptor antagonist (GHRA) treatment neither modified renal IGF-I nor abolished the renal hypertrophy. In contrast, however, GHRA administration did modify renal mRNA expression of many members of the GH and IGF systems.

CONCLUSIONS

The major new finding is that HP-induced renal growth in adult mice is GH independent.

Neurohormonal factors in the development of catabolic/anabolic imbalance and cachexia

Mechanisms that lead to cachexia are still poorly understood. The neurohormonal changes that occur in severe disease states may cause an imbalance between protein synthesis and degradation at the cellular level, followed by muscle wasting. Here, we review actions of angiotensin II, TNF-alpha, corticosteroids, insulin-like growth factor-I (IGF-I), and the IGF binding proteins, factors that may each contribute to the metabolic imbalance. The complex endocrine, autocrine and intracellular interactions between these factors will be described with examples from patient, rat and cell culture studies. Moreover, some of the data supporting that each of these hormones may directly affect cellular protein degradation mechanisms will be reviewed. Knowledge on these regulatory mechanisms will facilitate the development of new pharmaceutical strategies to treat cachexia.

IGF-I, IgA, and IgG responses to bovine colostrum supplementation during training

This study examined the effect of bovine colostrum (Dynamic colostrum) supplementation on blood and saliva variables (study 1) and the absorption of orally administered human recombinant insulin-like growth factor (IGF)-I (rhIGF-I) labeled with 123I (123I-rhIGF-I) (study 2). In study 1, adult male and female athletes were randomly assigned in a double-blind fashion to either an experimental (Dynamic; n = 19) or a control (Placebo; n = 11) group. The former consumed daily 20 g of Dynamic supplement, and the latter 20 g of maltodextrin during a 2-wk training period. After bovine colostrum supplementation, significant increases were noticed in serum IGF-I (P < 0.01) and saliva IgA (P < 0.01) in Dynamic compared with Placebo. In study 2, gel electrophoresis was carried out in 12 adult subjects with serum samples taken 60 min after ingestion of 123I-rhIGF-I and showed peaks at 0.6 and at 40-90 kDa, with the former inducing 96% and the latter 4% of the total radioactivity. It was concluded that a long-term supplementation of bovine colostrum (Dynamic) increases serum IGF-I and saliva IgA concentration in athletes during training. Absorption data show that ingested 123I-rhIGF-I is fragmented in circulation and that no radioactive IGF-I is eluted at the positions of free, or the IGF, binding proteins, giving no support to the absorption of IGF-I from bovine colostrum.

Dietary essential amino acid supplements increase bone strength by influencing bone mass and bone microarchitecture in ovariectomized adult rats fed an isocaloric low-protein diet

This study was designed to investigate whether the administration of dietary essential amino acid supplements in adult rats made osteoporotic by estrogen deficiency and reduced protein intake could reverse the deleterious effects caused by these maneuvers. This animal model was selected to mimic the situation observed in elderly women in whom estrogen deficiency and/or low-protein intake (but also calcium and vitamin D deficiency) are known to contribute to the pathogenesis of osteoporosis. Six-month-old rats were ovariectomized (OVX) and fed an isocaloric 2.5% casein diet for 10 weeks or sham-operated (SHAM) and fed an isocaloric 15% casein diet. The animals fed the 2.5% casein diet were given isocaloric supplements of essential amino acids in similar relative proportion to that of casein at doses of 2.5% or 5% of total diet for an additional 16 weeks. Vertebrae, femur, and tibia bone mineral density (BMD); ultimate strength; and microtomographic histomorphometry were evaluated before and after dietary essential amino acid supplements. Essential amino acid supplements increased vertebrae, femur, and tibia bone strength in OVX rats fed a low-protein diet. The mechanical changes induced by this dietary isocaloric supplement were associated with the prevention of a further BMD decrease or even with some increases and changes in microarchitecture such as from a rod to a plate trabecular spacial configuration and increased cortical thickness. Higher insulin-like growth factor (IGF) I levels, as well as greater bone formation and reduced bone resorption as assessed by biochemical markers of bone remodeling, were found in rats receiving essential amino acid supplements. In conclusion, dietary essential amino acid supplements increased bone strength through modifications of BMD, trabecular architecture, and cortical thickness possibly by an IGF-I-mediated process.

Protein intake and bone growth

Among osteotrophic nutrients, proteins play an important role in bone development, thereby influencing peak bone mass. Consequently, protein malnutrition during development can increase the risk of osteoporosis and of fragility fracture later in life. Both animal and human studies indicate that low protein intake can be detrimental for both the acquisition of bone mass during growth and its conservation during adulthood. Low protein intake impairs both the production and action of IGF-I (Insulin-like growth factor-I). IGF-I is an essential factor for bone longitudinal growth, as it stimulates proliferation and differentiation of chondrocytes in the epiphyseal plate, and also for bone formation. It can be considered as a key factor in the adjustments of calcium-phosphate metabolism required for normal skeletal development and bone mineralization during growth. In healthy children and adolescents, a positive association between the amount of ingested proteins and bone mass gain was observed in both sexes at the level of the lumbar spine, the proximal femur and the midfemoral shaft. This association appears to be particularly significant in prepubertal children. This suggests that, like for the bone response to either the intake of calcium or weight-bearing exercise, the skeleton would be particularly responsive to the protein intake during the years preceding the onset of pubertal maturation.

Treatment with growth hormone and insulin-like growth factor-I in critical illness

The wider availability of recombinant human growth hormone and insulin-like growth factor-I has resulted in an investigation into the potential benefits of the pharmacological administration of these anabolic peptides in a variety of clinical conditions, characterized by an increase in catabolic rate. The initial studies were small, often uncontrolled open investigations, but investigators have more recently concentrated on larger, controlled multi-centre trials. Studies to date have included patients with cardiac failure, sepsis, burns, cancer cachexia, end-stage renal failure, trauma and AIDS, and those prior to or following major surgery. The authors have in general cautiously interpreted positive effects of treatment with growth hormone and insulin-like growth factor-I, either alone or in combination, on net protein balance, body composition, well-being and performance. Two large, randomized, placebo-controlled European multi-centre studies have recently detailed the effects of growth hormone treatment in critically ill intensive care patients. Major increases in mortality and morbidity were associated with growth hormone treatment. The mechanism(s) accounting for the increased mortality remain poorly understood. These negative findings have led to a decrease in the clinical use of growth hormone and in research activity in the area of anabolic treatment in human illness.

Insulin, insulin-like growth factors and colon cancer: a review of the evidence

Insulin and insulin-like growth factor (IGF) axes are major determinants of proliferation and apoptosis and thus may influence carcinogenesis. In various animal models, modulation of insulin and IGF-1 levels through various means, including direct infusion, energy excess or restriction, genetically induced obesity, dietary quality including fatty acid and sucrose content, inhibition of normal insulin secretion and pharmacologic inhibition of IGF-1, influences colonic carcinogenesis. Human evidence also associates high levels of insulin and IGF-1 with increased risk of colon cancer. Clinical conditions associated with high levels of insulin (noninsulin-dependent diabetes mellitus and hypertriglyceridemia) and IGF-1 (acromegaly) are related to increased risk of colon cancer, and increased circulating concentrations of insulin and IGF-1 are related to a higher risk of colonic neoplasia. Determinants and markers of hyperinsulinemia (physical inactivity, high body mass index, central adiposity) and high IGF-1 levels (tall stature) are also related to higher risk. Many studies indicate that dietary patterns that stimulate insulin resistance or secretion, including high consumption of sucrose, various sources of starch, a high glycemic index and high saturated fatty acid intake, are associated with a higher risk of colon cancer. Although additional environmental and genetic factors affect colon cancer, the incidence of this malignancy was invariably low before the technological advances that rendered sedentary lifestyles and obesity common, and increased availability of highly processed carbohydrates and saturated fatty acids. Efforts to counter these patterns are likely to have the most potential to reduce colon cancer incidence, as well as cardiovascular disease and diabetes mellitus.

Protein intake and bone disorders in the elderly

Malnutrition, most notably protein deficiency, contributes to the occurrence of osteoporotic fractures not only by decreasing bone mass but also by altering muscle function. Furthermore, malnutrition is associated with increased morbidity in patients with osteoporotic fractures. The somatomedin system (IGF-1) may be directly involved in the pathogenesis of osteoporotic hip fractures and their complications in elderly patients. A low IGF-1 level is a risk factor for hip fracture. In subjects with appropriate intakes of vitamin D and calcium, giving protein supplements to correct an inadequate spontaneous protein intake increases circulating IGF-1 levels, improves clinical outcomes after hip fracture, and prevents bone mineral density loss at the proximal femur. Supplemental protein also significantly reduces the length of inpatient rehabilitation care. These data emphasize the importance of adequate nutrient intake in the prevention and treatment of osteoporotic fractures.

Effects of an endurance cycling competition on resting serum insulin-like growth factor I (IGF-I) and its binding proteins IGFBP-1 and IGFBP-3

OBJECTIVES

To determine whether consecutive bouts of intense endurance exercise over a three week period alters serum concentrations of insulin-like growth factor I (IGF-I) and/or its binding proteins.

METHODS

Seventeen professional cyclists (mean (SEM) VO(2)MAX, 74.7 (2.1) ml/kg/min; age, 27 (1) years) competing in a three week tour race were selected as subjects. Blood samples were collected at each of the following time points: t(0) (control, before the start of competition), t(1) (end of first week), and t(3) (end of third week). Serum levels of both total and free IGF-I and IGF binding proteins 1 and 3 (IGFBP-1 and IGFBP-3) were measured in each of the samples. Cortisol levels were measured in nine subjects.

RESULTS

A significant (p<0.01) increase was found in total IGF-I and IGFBP-1 at both t(1) and t(3) compared with t(o) (IGF-I: 110.9 (17.7), 186.8 (12.0), 196.9 (14.7) ng/ml at t(0), t(1), and t(3) respectively; IGFBP-1: 54.6 (6.6), 80.6 (8.0), and 89.2 (7.9) ng/ml at t(0), t(1), and t(3) respectively). A significant (p<0.01) decrease was noted in free IGF-I at t(3) compared with both t(o) and t(1) (t(0): 0.9 (0.1) ng/ml; t(1): 0.9 (0.1) ng/ml; t(3): 0.7 (0.1) ng/ml); in contrast, IGFBP-3 levels remained stable throughout the race.

CONCLUSIONS

It would appear that the increase in circulating levels of both IGF-I and its binding protein IGFBP-1 is a short term (one week) endocrine adaptation to endurance exercise. After three weeks of training, total IGF-I and IGFBP-1 remained stable, whereas free IGF-I fell below starting levels.

Utility of insulin-like growth factor-I and its binding protein assays

Insulin-like growth factor-I circulates in serum either in free form or bound to insulin-like growth factor-binding proteins that modulate its bioavailability. Insulin-like growth factor-binding proteins interfere with insulin-like growth factor-I assay, which remains technically difficult. Many assays have been developed, but their results are somewhat discordant. The choice of separation method, standard and tracer considerably influences the results. The circulating concentration of insulin-like growth factor-I, however, is clearly dependent on nutritional status, and total levels are a valuable marker of nutritional status. The clinical utility of free insulin-like growth factor-I assay and simultaneous assay, in the same sample, of total insulin-like growth factor-I and its binding proteins (reflecting the bioavailable insulin-like growth factor-I fraction), remains to be evaluated.

Insulin-like growth factors and leucine kinetics during exercise training in children with cystic fibrosis

BACKGROUND

Little is known about the metabolic effects of exercise training in children with cystic fibrosis. The hypothesis for the current study was that in patients with declining clinical status, exercise increases circulating insulin-like growth factors (IGFs) and improves protein kinetics.

METHODS

This was a prospective intervention study in 10 children with cystic fibrosis who participated in a structured isoenergetic exercise (cycling) training program for 3 months. Measurements of IGFs, protein kinetics (using intravenous [13C]-1-leucine tracer infusions) and nutritional balance studies were conducted at baseline and after 3 months.

RESULTS

Standard deviation scores of plasma IGF-I, IGF-II, and IGF binding protein (BP)-3 were all decreased at baseline (mean +/- SE: -2.0+/-0.2, -2.0+/-0.2. -0.6+/-0.2, respectively). IGF-I and IGF-II concentrations were significantly higher after exercise training (standard deviation scores -1.4+/-0.3 and -1.3 +/-0. 1, respectively; compared with baseline: one-tailed t-test P = 0.03 and 0.002). The standard deviation score of the IGF-I/IGF BP-3 ratio, an indicator of free IGF-I in the circulation, normalized during exercise training (0.0+/-0.6 vs. -1.3+/-0.2 SD units at baseline, one-tailed t-test P = 0.04). There was no significant difference in protein intake and fasting protein breakdown, oxidation, and protein synthesis or in energy balance and fat absorption.

CONCLUSIONS

These results show that isoenergetic exercise training can be safely recommended to patients with cystic fibrosis. It provides a positive anabolic stimulus to IGF status but is not sufficient to adequately augment protein accretion in patients with diminished nutritional status.

Does the GH-IGF axis play a role in cancer pathogenesis?

Recent case-controlled studies have found increases in the serum levels of insulin-like growth factor-I (IGF-I) in subjects who had, or who eventually developed, prostate or premenopausal breast cancers. Since growth hormone (GH) increases IGF-I levels, concern has been raised regarding its potential role as a cancer initiation factor. The epidemiological studies, which indicate an association between serum IGF-I levels and cancer risk, have not established causality. In fact, several alternative explanations for the elevated serum IGF-I levels in cancer patients may be proposed based on human and animal models. First, an effect of IGF-I causing symptomatic benign tissue hyperplasia may result in an ascertainment bias leading to an initiation of procedures resulting in the diagnosis of asymptomatic cancers. Second, elevated serum IGF-I in cancer patients may originate within the tumor (as suggested by some animal studies). Thirdly, serum IGF-I may actually be a surrogate marker of tissue IGF-I levels or of nutritional factors, which are not under GH control and may be involved in cancer initiation. The role of GH in cancer initiation is further negated by the fact that in acromegaly, the incidence of cancer, other than possibly colonic neoplasia does not appear to be significantly increased. Furthermore, GH transgenic mice, with high IGF-I levels, do not develop breast, prostate, or colonic malignancies. It is known that IGFBP-3 can inhibit IGF action on cancer cells in vitro and also can induce apoptosis via an IGF-independent mechanism. Importantly, in addition to increasing IGF-I levels, GH also increases the serum levels of IGFBP-3 and serum IGFBP-3 levels have been shown to be negatively correlated with the risk of cancer in the above mentioned epidemiological studies and in a similar study on colon cancer. These studies suggest that cancer risk is increased in individuals in whom both high IGF-I levels and low IGFBP-3 levels are present. In subjects treated with GH, IGF-I and IGFBP-3 levels both rise together and are not within the elevated cancer-risk range, based on published studies. Long-term studies are needed to assess the potential risks, including the long-term cancer risk associated with GH therapy. These should take into account several factors, including the duration of exposure, the risk magnitude associated with the degree of serum IGF-I elevation, and the adjusted risk based on a concomitant increase in IGFBP-3 levels. Since GH treated patients often have sub-normal IGF-I serum levels, which normalize on therapy, one might predict that their cancer risk on GH therapy should not increase above the normal population. Until further research in the area dictates otherwise, on-going cancer surveillance and routine monitoring of serum IGF-I and IGFBP-3 levels in GH-recipients should be the standard of care. At present, the data that are available do not warrant a change in our current management of approved indications for GH therapy.

Low dosages of exogenous growth hormone and its effect on growth in an animal model of suboptimal nutrition

In a previous study, weight gain, insulin growth factor-1 (IGF-1) and insulin growth factor binding protein-3 (IGFBP-3) were increased in rats fed suboptimal levels of energy and administered 0.1 mg/100 g of body weight of recombinant human growth hormone (rhGH). Our objective was to determine whether these anabolic effects were still obtained with lower dosages of rhGH in similarly fed rats. Three groups of male, prepubertal Sprague-Dawley rats were administered rhGH and three groups of similar rats were given normal saline solution daily (0.05 mg/100 g of body weight subcutaneously). All rats were fed a balanced 1:1 carbohydrate:fat ratio diet for 4 wk. Restricted rats within each treatment were pair fed 80% and 60% ad libitum. Daily body weight, food intake, and efficiency were recorded. After 4 wk, serum IGF-1 and IGFBP-3, body fat, fat-free mass, and total body water were determined. Total weight gain and serum IGFBP-3 were significantly higher, with a tendency for increased body fat, in rats treated with rhGH and fed at 60% ad libitum. However, within each treatment, energy restriction caused decreased body fat and total body water. These results suggest that lower dosages of rhGH provide anabolic effects during suboptimal energy intake.

Possible relevance of abnormal fatty acid metabolism in undernutrition: the relationship between oleic acid and growth

Energy, protein, essential fatty acids, vitamins and minerals are all necessary for normal growth and development of children. In undernutrition, there is evidence for abnormal fatty acid metabolism. High levels of oleic acid and low levels of docosahexaenoic acid in plasma phosphatidylcholine have been associated with weight-for-age Z-score shifts to the left (increased prevalence of underweight) and vice versa (reduced prevalence of underweight). An alternative hypothesis is proposed, which describes a possible physiological mechanism whereby omega3 fatty acids contribute to growth. High blood oleic acid levels under conditions of undernutrition are proposed to be an adaptation to conserve glucose in the form of glycogen. Replacement with docosahexaenoic acid under conditions of adequate nutrition enhances membrane functioning so that glucose and energy become available for muscle formation.

Nutritional factors in human cancers

A variety of external factors interacting with genetic susceptibility influence the carcinogenesis process. External factors including oxidative compounds, electrophilic agents, and chronic infections may enhance genetic damage. In addition, various hormonal factors which influence growth and differentiation are critically important in the carcinogenic process. Diet and nutrition can influence these processes directly in the gastrointestinal tract by providing bioactive compounds to specific tissues via the circulatory system, or by modulating hormone levels. Differences in certain dietary patterns among populations explain a substantial proportion of cancers of the colon, prostate and breast. These malignancies are largely influenced by a combination of factors related to diet and nutrition. Their causes are multifactorial and complex, but a major influence is the widespread availability of energy-dense, highly processed and refined foods that are also deplete in fiber. These dietary patterns in combination with physical inactivity contribute to obesity and metabolic consequences such as increased levels of IGF-1, insulin, estrogen, and possibly testosterone. These hormones tend to promote cellular growth. For prostate cancer, epidemiologic studies consistently show a positive association with high consumption of milk, dairy products, and meats. These dietary factors tend to decrease 1.25(OH)2 vitamin D, a cell differentiator, and low levels of this hormone may enhance prostate carcinogenesis. While the nutritional modulation of growth-enhancing and differentiating hormones is likely to contribute to the high prevalence of breast, colorectal, prostate, and several other cancers in the Western world, these cancers are relatively rare in less economically developed countries, where malignancies of the upper gastrointestinal tract are quite common. The major causes of upper gastrointestinal tract cancers are likely related to various food practices or preservation methods other than refrigeration, which increase mucosal exposure to irritants or carcinogens.

Protein undernutrition-induced bone loss is associated with decreased IGF-I levels and estrogen deficiency

Protein undernutrition is a known factor in the pathogenesis of osteoporotic fracture in the elderly, but the mechanisms of bone loss resulting from this deficiency are still poorly understood. We investigated the effects of four isocaloric diets with varying levels of protein content (15, 7.5, 5, and 2.5% casein) on areal bone mineral density (BMD), bone ultimate strength, histomorphometry, biochemical markers of bone remodeling, plasma IGF-I, and sex hormone status in adult female rats. After 16 weeks on a 2.5% casein diet, BMD was significantly decreased at skeletal sites containing trabecular or cortical bone. Plasma IGF-I was decreased by 29-34% and no estrus sign in vaginal smear was observed. To investigate the roles of estrogen deficiency and protein undernutrition, the same protocol was used in ovariectomized (OVX) or sham-operated (SHAM) rats, pair-fed isocaloric diets containing either 15 or 2.5% casein. Trabecular BMD was decreased by either manipulation, with effects appearing to be additive. Cortical BMD was decreased only in rats on a low-protein diet. This was accompanied by an increased urinary deoxypyridinoline excretion without any change in osteocalcin levels, suggesting an uncoupling between resorption and formation. Isocaloric protein undernutrition decreased bone mineral mass and strength. This effect might be related to decreased plasma IGF-I and/or estrogen deficiency with a consequent imbalance in bone remodeling.

Insulin-like growth factor (IGF)-1 and IGF-binding protein-1 concentrations in serum of normal subjects after alcohol ingestion: evidence for decreased IGF-1 bioavailability

OBJECTIVE

Both insulin-like growth factor (IGF)-1 and insulin-like growth factor-binding protein (IGFBP)-1 are synthesized by the liver. It is well known that chronic alcohol abuse impairs liver function, but less is known about how an acute intake of moderate quantities of alcohol affects hepatic production of IGF-1 and IGFBP-1. The objective of the present investigation was to study this issue by measuring serum levels of IGF-1 and IGFBP-1 in normal subjects before, during and after ingestion of a moderate dose of ethanol.

SUBJECTS AND DESIGN

Eight healthy subjects were tested on two occasions. On one occasion (experiment A), three 150-ml doses of ordinary drinking-water were given at 08.00, 09.30, and 11.00 h. On another occasion (experiment B), three 150-ml drinks of diluted ethanol were given instead of water. Each drink contained 0.45 g ethanol/kg b.w. Experiments A and B were performed in random order, 1 week apart. Blood samples were collected before, during and after the drinks over a period of 7 h (08.00-15.00 h). One blood sample was also drawn at 08.00 h the following day.

MEASUREMENTS

Blood glucose and serum concentrations of ethanol, insulin, growth hormone (GH), IGF-1 and IGFBP-1 were determined.

RESULTS

When alcohol had been ingested, the serum ethanol concentration rose to a peak value of 28.6 +/- 0.9 mmol/l (mean +/- SEM). The serum IGF-1 level declined significantly toward the end of the 7-h period. The serum IGFBP-1 level increased promptly in response to ethanol, and reached a maximum 2.7 times above basal as the ethanol level peaked. Neither IGF-1, nor IGFBP-1 levels changed significantly after water intake. The IGF-1 : IGFBP-1 ratio declined markedly after ethanol (from 15.7 +/- 3.9 to 3.9 +/- 0.6; P < 0.01), but not after water intake. The blood glucose and serum levels of insulin and GH were unaffected by both ethanol and water.

CONCLUSIONS

Ingestion of moderate amounts of alcohol by healthy individuals results in an acute and profound increase in the serum IGFBP-1 level and a protracted and less powerful decline in the IGF-1 level. The mechanism behind the IGFBP-1 increase is probably a direct effect on the liver, since neither insulin, nor glucose or GH concentrations changed significantly in response to the ethanol challenge.

Vegan proteins may reduce risk of cancer, obesity, and cardiovascular disease by promoting increased glucagon activity

Amino acids modulate the secretion of both insulin and glucagon; the composition of dietary protein therefore has the potential to influence the balance of glucagon and insulin activity. Soy protein, as well as many other vegan proteins, are higher in non-essential amino acids than most animal-derived food proteins, and as a result should preferentially favor glucagon production. Acting on hepatocytes, glucagon promotes (and insulin inhibits) cAMP-dependent mechanisms that down-regulate lipogenic enzymes and cholesterol synthesis, while up-regulating hepatic LDL receptors and production of the IGF-I antagonist IGFBP-1. The insulin-sensitizing properties of many vegan diets--high in fiber, low in saturated fat--should amplify these effects by down-regulating insulin secretion. Additionally, the relatively low essential amino acid content of some vegan diets may decrease hepatic IGF-I synthesis. Thus, diets featuring vegan proteins can be expected to lower elevated serum lipid levels, promote weight loss, and decrease circulating IGF-I activity. The latter effect should impede cancer induction (as is seen in animal studies with soy protein), lessen neutrophil-mediated inflammatory damage, and slow growth and maturation in children. In fact, vegans tend to have low serum lipids, lean physiques, shorter stature, later puberty, and decreased risk for certain prominent 'Western' cancers; a vegan diet has documented clinical efficacy in rheumatoid arthritis. Low-fat vegan diets may be especially protective in regard to cancers linked to insulin resistance--namely, breast and colon cancer--as well as prostate cancer; conversely, the high IGF-I activity associated with heavy ingestion of animal products may be largely responsible for the epidemic of 'Western' cancers in wealthy societies. Increased phytochemical intake is also likely to contribute to the reduction of cancer risk in vegans. Regression of coronary stenoses has been documented during low-fat vegan diets coupled with exercise training; such regimens also tend to markedly improve diabetic control and lower elevated blood pressure. Risk of many other degenerative disorders may be decreased in vegans, although reduced growth factor activity may be responsible for an increased risk of hemorrhagic stroke. By altering the glucagon/insulin balance, it is conceivable that supplemental intakes of key non-essential amino acids could enable omnivores to enjoy some of the health advantages of a vegan diet. An unnecessarily high intake of essential amino acids--either in the absolute sense or relative to total dietary protein--may prove to be as grave a risk factor for 'Western' degenerative diseases as is excessive fat intake.

Down-regulation of the serum stimulatory components of the insulin-like growth factor (IGF) system (IGF-I, IGF-II, IGF binding protein [BP]-3, and IGFBP-5) in age-related (type II) femoral neck osteoporosis

Both a decrease in bone formation and an increase in bone resorption have been implicated in the pathogenesis of age-related (type II) femoral neck osteoporosis. While the increase in the bone resorption rate has been shown to be partially related to secondary hyperparathyroidism, the mechanisms underlying the decline in bone formation have not yet been identified. The aim of the present study was to test the hypothesis that the bone formation deficit associated with type II osteoporosis might be due to secondary hyperparathyroidism and/or to a deficiency of the insulin-like growth factor (IGF) system. Circulating concentrations of IGF-I, IGF-II, IGF binding protein (IGFBP)-3, IGFBP-4, IGFBP-5, 25-hydroxycholecalciferol (25(OH)D3), and intact parathyroid hormone (PTH) were measured in 50 elderly women after sustaining a hip fracture and in 50 healthy age-matched controls. In addition, serum levels of osteocalcin (OC), skeletal alkaline phosphatase, and N-terminal procollagen peptide and urinary pyridinium cross-links were determined as markers of bone remodeling, and bone mineral density (BMD) was assessed at the proximal femur. In the patient group, serum was drawn within 18 h of the fracture and prior to surgery. Circulating protein concentrations did not change over this time frame. No difference was found between mean IGFBP-4 serum levels in the two groups studied, while mean levels of IGF-I, IGF-II, IGFBP-3, IGFBP-5, 25(OH)D3, and markers of bone formation were significantly lower (p < 0.006) in patients as compared with healthy subjects. Serum PTH and urinary pyridinium cross-links, however, were markedly increased (p < 0.001) in the osteoporotic group. In pooled data from the normal and osteoporotic populations, age-adjusted multiple regression models based on IGF-I, IGF-II, IGFBP-3, and IGFBP-5 were found to be highly predictive of serum OC (R2 = 19%, p < 0.001) and BMD of femoral neck (R2 = 49%, p < 0.0001), consistent with an effect of the anabolic IGF components on overall bone formation rate. Similar models based on 25(OH)D3 and PTH, however, were statistically unrelated to OC. To address further the potential impact of trauma on circulating IGF system components, we measured IGF system component levels in 10 male patients within 18 h following tibial fracture and in 10 age-matched normal male subjects. There was no significant difference in serum level of any of the IGF system components between the two groups. Although limited by its cross-sectional design, the present study suggests that, in addition to bone resorption resulting from secondary hyperparathyroidism, impaired bone formation associated with deficiency of the IGF system might predispose elderly women to fragility fracture of the proximal femur.

Low insulin-like growth factor (IGF-1) in the cerebrospinal fluid of children with progressive encephalopathy, hypsarrhythmia, and optic atrophy (PEHO) syndrome and cerebellar degeneration

PURPOSE

In patients with progressive encephalopathy, hypsarrhythmia, and optic atrophy (PEHO) syndrome, the pathophysiology underlying early progressive cerebellar and brainstem degeneration and severe epilepsy is unknown. Because insulin-like growth factor (IGF)-1 has been shown significantly to promote survival of cerebellar neurons, we wanted to see if the IGF system played a role in the pathogenesis of cerebellar atrophy.

METHODS

We used a sensitive enzyme immunoassay kit for measuring cerebrospinal fluid (CSF) IGF-1 and insulin-like growth-binding protein (IGFBP)-3 in four groups of patients: PEHO syndrome patients (eight), PEHO-like patients (seven), age-matched controls (31), and patients with other types of cerebellar atrophy (11).

RESULTS

Patients with PEHO syndrome and those with other progressive, degenerative cerebellar diseases had lower levels of CSF IGF-1 than the controls with other neurologic diseases. The CSF IGF-1 also allowed us to differentiate the "true" PEHO patients from the "PEHO-like" patients (those with similar clinical symptoms but without the typical neuroophthalmologic or neuroradiologic findings). The concentrations of IGFBP-3 did not significantly differ in any of the patient or control groups studied.

CONCLUSIONS

CSF IGF-1 levels might be used as a marker of the degeneration of neurons in specific areas.

Bone physiology during pregnancy and lactation in young macaques

We used a nonhuman primate model (Macaca nemestrina) of adolescent human pregnancy to characterize bone remodeling at midpregnancy and at weaning and the associated changes in bone mass. In this longitudinal study, 125 nulliparous females were followed through pregnancy, 6 months of lactation, and 3 months postweaning; 13 nonpregnant females served as controls. Between early pregnancy and midpregnancy, the whole body bone mineral increased. There was no significant change between midpregnancy and parturition. Between parturition and 3 months lactation, the animals lost 3.0% of their bone mineral (p < 0.01), which was regained by 3 months after weaning. The vertebral bone mineral apparent density decreased during pregnancy and 6 months of lactation, followed by an increase during the 3 months after weaning. Calcium, phosphate, 25-hydroxyvitamin D, and osteocalcin increased significantly from midpregnancy to weaning whereas 1,25-dihydroxyvitamin D values showed significant decreases. Histomorphometric measurements from bone biopsies showed significant increases in most parameters of bone formation between pregnancy and weaning. These results are consistent with the hypothesis that at midpregnancy bone formation is decreased and cancellous bone resorption may have increased. During lactation, losses occur in both cortical and cancellous bone, partially depleting the maternal reservoir of calcium, but a subsequent increase in bone formation enables restoration of bone mineral after weaning to values similar to those in the control group.

[Children with chronic renal failure: evaluation of the nutritional status and management]

Since malnutrition is a well recognized problem in children with chronic renal failure, nutritional management of these children is essential. This review describes methods for nutritional assessment and suggests guidelines for providing maximal dietary support in children with chronic renal insufficiency. Optimal nutritional management includes an adequate caloric and protein intake, a restriction of phosphorus intake and an appropriate intake of electrolytes and vitamins.

[Malnutrition and osteoporosis]

Undernutrition, particularly protein undernutrition, contributes to the occurrence of osteoporotic fracture, by lowering bone mass and altering muscle strength. Furthermore, the rate of medical complications after fracture can also be increased by nutritional deficiency. The IGF-I system appears to be directly involved in the pathogenetic mechanisms leading to osteoporotic hip fracture in elderly and to its complications. In the presence of adequate calcium and vitamin D supplies, protein supplements increasing the intakes from low to normal, raises IGF-I levels, improves the clinical outcome after hip fracture, and attenuates the decrease in proximal femur bone mineral density in the year following the fracture. This nutritional approach is associated with a significant reduction of the stay in rehabilitation hospital. This underlines the importance of nutritional supports in preventing and healing osteoporotic fractures.

Insulin-like growth factor-I and insulin-like growth factor binding protein-3 during maintenance chemotherapy of acute lymphoblastic leukemia in children

PURPOSE

To assess the effect of maintenance chemotherapy (MT) on growth factors and growth in children with acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Twenty-one children (10 girls, 11 boys) with standard risk pre-B ALL treated with chemotherapy had serum insulin-like growth factor-I (IGF-I), serum IGF binding protein-3 (IGFBP-3) levels, and linear growth and weight data measured every 3 months during MT. The levels of the cytotoxic metabolites of methotrexate (MTX) and 6-mercaptopurine (6MP) (i.e., erythrocyte MTX polyglutamates [E-MTX], and erythrocyte 6-thioguanine nucleotides [E-6TGN]), s-aminotransferases, and white blood counts (WBC) were measured at least monthly.

RESULTS

At the beginning of MT, the median IGF-I standard deviation scores (SDS) and IGFBP-3 SDS were -0.52 and -0.09, respectively, which declined during MT to -1.67 (P < 0.001) and -1.82 (P < 0.001), respectively. At the time of diagnosis, the median height SDS was -0.4, which declined during MT to a median height SDS of -0.9 at cessation of therapy. No significant correlations were found between growth factor levels, growth and body mass index (BMI) versus the doses of MTX, and 6MP, E-MTX, E-6TGN, s-aminotransferases, or WBC.

CONCLUSIONS

A significant decline in IGF-I, IGFBP-3, and growth retardation may not be directly related to the treatment intensity during MT.

Regulation of insulin-like growth factor-I in starvation and injury

Both starvation and sepsis are characterized by growth hormone (GH) insensitivity, which leads to a reduction in circulating insulin-like growth factor (IGF)-I. Because of the anabolic properties of this growth factor, its decline may contribute to the growth arrest and the catabolic reaction observed in starvation and sepsis. This review focuses on the mechanisms responsible for the reduction in circulating IGF-I and impairment of GH responsiveness that occur during starvation and sepsis. A clearer understanding of the complex nature of GH resistance should lead to the development of new therapeutic strategies aimed at restoring the beneficial effects of anabolic agents such as GH and IGF-I.

Failure of IGF-I and IGFBP-3 to diagnose growth hormone insufficiency

BACKGROUND

Growth hormone insufficiency (GHI) is diagnosed conventionally by short stature and slow growth, and is confirmed by diminished peak GH response to a provocation test. Insulin-like growth factor I (IGF-I) and IGF binding protein 3 (IGFBP-3) have previously been considered individually

OBJECTIVE

To test the hypothesis that the combined analysis of IGF-I and IGFBP-3 could act as a surrogate marker for the diagnosis of GHI.

DESIGN

Reference ranges for IGF-I and IGFBP-3 were calculated using 521 normal individuals. A retrospective analysis was performed on 318 children referred for investigation of short stature.

RESULTS

No significant difference was found between either the IGF-I or IGFBP-3 standard deviation scores (SDSs) in children with and without GHI. If the requirement were for both tests to be positive (< -2 SDS) for a diagnosis of GHI, then 99% of children without GHI would be correctly identified; however, the sensitivity of the test was only 15%.

CONCLUSIONS

Neither IGF-I nor IGFBP-3 alone is a marker for GHI. In addition, they cannot be used as an effective screening test in combination.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Monthly measurements of insulin-like growth factor I (IGF-I) and IGF-binding protein-3 in healthy prepubertal children: characterization and relationship with growth: the 1-year growth study

The usefulness of measurements of IGF-I or IGF-binding protein-3 (IGFBP-3) in the clinical management of growth disorders is dependent on the extent of physiologic variation in their concentrations. Our purpose was therefore to investigate the longitudinal intraindividual variation in serum concentration of IGF-I and IGFBP-3 in healthy prepubertal children. Monthly serum samples and auxologic measurements were taken over a period of 1 y from 65 prepubertal children (38 boys, 27 girls; mean age 9.1 y, range 7.8-10.8). Concentrations of IGF-I and IGFBP-3 were measured by RIA. The mean (+/-SD) serum concentration of IGF-I in the children was 165 +/- 42.0 microg/L, with a mean coefficient of variation (CV) of 13.9% around the annual mean serum concentration for each child. The corresponding mean concentration of IGFBP-3 was 3273 +/- 604.5 microg/L, and the mean CV for each child was 9.7%. These monthly longitudinal variations in IGF-I and IGFBP-3 were parallel to changes in longitudinal growth. Short-term changes (1 mo) in IGF-I were positively correlated with changes in weight (r(s) = 0.42, p < 0.0005) and body mass index (r(s) = 0.45, p < 0.0005), and negatively correlated with minor intercurrent illnesses (-0.32; p < 0.05). Seasonal fluctuations also occurred, with short term changes in IGF-I (1 mo) and IGFBP-3 (3 mo), increasing with increasing outdoor temperatures (r(s) = 0.30, p < 0.05 and r(s) = 0.39, p < 0.005, respectively). We conclude, that there are significant changes in both IGF-I and IGFBP-3 that occur in association with growth, and that IGF-I is more sensitive than IGFBP-3 to short-term changes in weight, body mass index, and intercurrent illnesses. Physiologic short-term changes must therefore be taken into consideration when using serum levels of IGF-I or IGFBP-3 in the evaluation of the short or slowly growing child.

Endotoxin-induced changes in IGF-I differ in rats provided enteral vs. parenteral nutrition

The purpose of the present study was to determine whether acute changes in the insulin-like growth factor (IGF) system induced by mild surgical trauma/fasting or endotoxin [lipopolysaccharide (LPS)] are differentially modulated by total enteral nutrition (TEN) or total parenteral nutrition (TPN). Rats had vascular catheters and a gastrostomy tube surgically placed and were fasted overnight. The next morning animals randomly received an isocaloric, isonitrogenous (250 kcal. kg-1. day-1, 1.6 g N. kg-1. day-1) infusion of either TEN or TPN for 48 h. Then rats were injected intravenously with Escherichia coli LPS (1 mg/kg) while nutritional support was continued. Time-matched control animals were injected with saline. After mild surgical trauma and an 18-h fast, TEN was more effective at increasing plasma IGF-I levels than TPN. Subsequent injection of LPS decreased IGF-I in blood, liver, and muscle in both TEN- and TPN-fed rats compared with saline-injected control animals. However, this decrease was approximately 30% greater in rats fed TPN compared with those fed TEN. LPS-induced downregulation of IGF-I mRNA expression in liver and muscle was also more prominent in TPN-fed rats. The LPS-induced increase in plasma corticosterone and tumor necrosis factor-alpha was greater (2- and 1.6-fold, respectively) in TPN-fed rats, and these changes were consistent with the greater reduction in IGF-I seen in these animals. In similarly treated rats allowed to survive for 24 h after LPS injection, the LPS-induced increase in the urinary 3-methylhistidine-to-creatinine ratio was smaller in TEN-fed rats. In summary, LPS reduced systemic levels of IGF-I as well as IGF-I protein and mRNA in critical target organs. Enteral feeding greatly attenuated this response. Maintenance of higher IGF-I levels in TEN-fed rats was associated with a reduction in inflammatory cytokine levels and lower rates of myofibrillar degradation.

Nutritional alterations and the effect of fish oil supplementation in dogs with heart failure

Alterations in body composition and nutritional status are common in humans with heart failure and are related, in part, to increases in cytokine concentrations. Cytokines have not been studied previously in dogs with naturally occurring cardiac disease nor has fish oil administration been used in this population to decrease cytokine production. The purposes of this study were to characterize nutritional and cytokine alterations in dogs with heart failure and to test the ability of fish oil to reduce cytokines and improve clinical outcome. Body composition, insulinlike growth factor-1, fatty acids, and cytokines were measured in 28 dogs with heart failure and in 5 healthy controls. Dogs with heart failure then were randomized to receive either fish oil or placebo for 8 weeks. All parameters were measured again at the end of the study period. At baseline, 54% of dogs with heart failure were cachectic and the severity of cachexia correlated with circulating tumor necrosis factor-alpha concentrations (P = .05). Cytokine concentrations at baseline, however, were not significantly increased in dogs with heart failure compared to controls. Baseline plasma arachidonic acid (P = .02), eicosapentaenoic acid (P = .03), and docosahexaenoic acid (P = .004) concentrations were lower in dogs with heart failure than in controls. Fish oil supplementation decreased interleukin-1 beta (IL-1) concentrations (P = .02) and improved cachexia (P = .01) compared to the placebo group. The mean caloric intake of the heart failure dogs as a group was below the maintenance energy requirement (P < .001), but no difference was found in food intake between the fish oil and placebo groups. Insulinlike growth factor-1 concentrations (P = .01) and reductions in circulating IL-1 concentrations over the study period (P = .02) correlated with survival. These data demonstrate that canine heart failure is associated with cachexia, alterations in fatty acids, and reduced caloric intake. Fish oil supplementation decreased IL-1 concentrations and improved cachexia. In addition, reductions in IL-1 predicted survival, suggesting that anticytokine strategies may benefit patients with heart failure.

Diet, nutrition, and prostate cancer

Cancer of the prostate gland is one of the most common malignancies in affluent nations, in part due to the application of new screening and diagnostic tools. The development of life-threatening prostate cancer is the culmination of a complex series of initiation and promotional events over a period of decades and under the influence of many interacting genetic and environmental factors. A rapidly accumulating scientific literature provides compelling evidence for the hypothesis that diet and nutrition are important factors modifying risk of prostate cancer. Additional resources devoted to interactive research efforts by laboratory scientists and epidemiologists will provide further enlightenment and continued refinement of our assessment of risks and benefits for specific nutrients and dietary patterns. These studies provide hope that evidence-based dietary interventions will significantly impact the risk of prostate cancer and enhance the efficacy of therapeutic interventions.

Growth hormone and IGF-I plasma concentrations and macronutrient intake measured in a free-living elderly population during a one-year period

OBJECTIVE

To determine seasonal variations in circulating concentrations of growth hormone and IGF-I in healthy, free-living elderly and to identify correlates between dietary intake, growth hormone and IGF-I concentrations in this population.

METHODS

Seven-day diet records and plasma samples were collected throughout a 1-year period. Plasma growth hormone and IGF-I were determined by RIA. Dietary macronutrient intake was determined using Nutritionist IV.

RESULTS

The dietary intake of the population corresponded to the established recommendations for percentage of fat, carbohydrate and protein. Carbohydrate intake differed significantly during the year, but protein and fat did not. Hormone concentrations were constant throughout the year, with no significant differences observed. No correlation between plasma growth hormone and IGF-I was observed. Growth hormone and IGF-I concentrations did not correlate with macronutrient intake, however subjects with the lowest energy intakes tended to have higher growth hormone and lower IGF-I than those with higher energy intakes.

CONCLUSIONS

This study provides important information on the dietary intake and hormone concentrations in normal, healthy elderly which will be useful in comparison with persons of similar age with complicating illnesses or nutrient deficiencies.

Acquired growth hormone resistance in adults

Acquired growth hormone resistance (AGHR) may be defined as the combination of a raised serum growth hormone (GH) concentration, low serum insulin-like growth factor-1 (IGF-1) concentration and a reduced anabolic response to exogenous GH. A wide range of conditions exhibit the syndrome to a variable degree, including sepsis, trauma, burns, AIDS, cancer, and renal or liver failure. The primary defect seems to be a reduction in IGF-1 concentration which then leads to increased GH concentration by a loss of negative feedback. It is not clear whether IGF-1 concentration falls because of decreased production or increased clearance from the circulation, or both. Treatment to reverse the biochemical defect by restoring IGF-1 levels, either by the administration of GH or IGF-1, has resulted in improvements in a wide range of metabolic parameters and, more recently, to definite clinical benefit in well-defined groups, such as patients with AIDS. These results cannot be extrapolated to other groups with AGHR as a recent unpublished report suggested increased mortality in critically ill patients treated with GH. Research needs to focus on the molecular basis of AGHR if we are to develop therapies for catabolism.

Effects of exogenous recombinant human growth hormone on an animal model of suboptimal nutrition

BACKGROUND

Nutritional dwarfing, a form of suboptimal nutrition, has been identified as a frequent cause of short stature and delayed sexual development in children. Retarded growth is an adaptive response to suboptimal nutrition.

OBJECTIVE

To assess whether recombinant human growth hormone (rhGH) may promote growth during various levels of suboptimal nutrition.

METHODS

Using a previously developed rat model of suboptimal nutrition, six groups of rats (six rats/group) were fed a balanced 1:1 carbohydrate:fat ratio diet for 4 weeks. Three of the groups were administered daily injections of rhGH (0.1 mg/100 g BW) subcutaneously in the back while the other three groups were kept as controls and were given similar dosages of normal saline solution (NSS). Restricted rats within each treatment group were pair fed 80 and 60% of the ad-libitum rats intake. Daily intake of the 80 and 60% fed groups were determined based on the intake of the ad-libitum fed groups. Serum IGF-I and insulin were determined after 4 weeks of dietary treatment by radioimmunoassay while IGFBP-3 was determined by an immunoradiometric assay. Body composition was assessed in all rats by carcass analysis.

RESULTS

After 4 weeks, total weight gain and tail growth were higher (p < 0.05) in the rhGH treated group at 80 and 60% of-libitum energy intake. Serum levels of IGF-I and IGFBP-3 were higher (p < 0.05) in rhGH treated rats fed at 60% of ad-libitum. In comparison to the NSS groups, administration of rhGH in rats fed ad-libitum increased total body water. Energy restriction caused decreased fat percentage (p < 0.05) in both rhGH and NSS groups without differences among treated groups.

CONCLUSION

These results suggest that the anabolic effects of rhGH may overcome mild to moderate energy restriction.

Is growth hormone hypersecretion in diabetic adolescent girls also a daytime problem?

OBJECTIVES

Glycaemic control often deteriorates during puberty in girls with insulin dependent diabetes mellitus (IDDM). This may be due in part to the normal psychosocial changes associated with adolescence. Puberty is, however, also characterized by rapid somatic development, orchestrated by hormonal changes. Some of these hormones play a major role in glucose homeostasis. We have examined the insulin-GH-IGF-I axis in 11 adolescent girls with poorly controlled insulin dependent diabetes and compared the data with those of 10 non-diabetic girls matched for age, pubertal stage and body mass index (BMI).

METHODS

Serum profiles of glucose, insulin, GH and IGF binding protein 1 (IGFBP1) were analysed in addition to IGF-I in serum and nocturnal urinary excretion of GH.

MEASUREMENTS

Serum glucose, insulin and IGFBP1 were measured every hour for 24 h, whereas GH in serum was measured every 30 minutes during the same period. Nocturnal urinary GH was analysed as a mean of three consecutive nights.

RESULTS

The insulin profiles of the IDDM patients were flat with low post-prandial peaks, corresponding to only one-third of the peaks of the non-diabetic girls. The integrated insulin levels, both during 24-h sampling and during daytime, were significantly lower in the diabetic group. There were no differences during night-time. The diabetic patients had elevated mean baseline levels of serum GH (IDDM 2.8 +/- 0.5 mU/l, controls 0.7 +/- 0.2; P < 0.001), a higher 24-h mean serum GH level (9.8 +/- 1.7 mU/l vs. 4.4 +/- 0.7; P < 0.001), significantly more peaks and a urinary GH excretion twice as high as in the non-diabetic group. An interesting observation was the finding of marked differences in daytime GH concentrations between the groups, both regarding overall integrated levels (GH AUC 103 +/- 15.8 and 35.9 +/- 7.1 mU/l x 12 h, respectively; P < 0.005) as well as baseline levels (3.8 +/- 0.6 mU/l vs. 0.7 +/- 0.2; P < 0.001). In contrast, during night-time only the mean basal levels of GH differed. The level of IGF-I was reduced in the diabetic group compared with the healthy controls (IDDM 233 +/- 19 micrograms/l vs. controls 327 +/- 21; P < 0.005). In addition, the IDDM patients had significantly increased concentrations of IGFBP 1, but kept a normal diurnal rhythm with a pronounced night peak.

CONCLUSION

Hypoinsulinaemia in adolescent IDDM patients, particularly in the portal hepatic circulation, results in decreased IGF-I and increased IGFBP 1 production in the liver. High levels of IGFBP 1 may, in turn, reduce the bioactivity of IGF-I even further. Low levels of IGF-I will lead to increased GH secretion. Earlier studies on the relationship between GH and diabetic control have focused on elevated GH levels during the night. In this study we have observed markedly elevated levels of GH also during daytime in adolescent IDDM patients. This indicates increased insulin resistance and insulin demand also during the day in diabetic subjects. The increased insulin resistance may result in hyperglycaemia leading to additional insulin resistance. A vicious circle may thus be induced, accelerating metabolic impairment in poorly controlled adolescent IDDM girls.

Molecular regulation of insulin-like growth factor-I and its principal binding protein, IGFBP-3

The insulin-like growth factors (IGFs) have diverse anabolic cellular functions, and structure similar to that of proinsulin. The distribution of IGFs and their receptors in a wide variety of organs and tissues enables the IGFs to exert endocrine, paracrine, and autocrine effects on cell proliferation and differentiation, caloric storage, and skeletal elongation. IGF-I exhibits particular metabolic responsiveness, and circulating IGF-I originates predominantly in the liver. Hepatic IGF-I production is controlled at the level of gene transcription, and transcripts are initiated largely in exon 1. Hepatic IGF-I gene transcription is reduced in conditions of protein malnutrition and diabetes mellitus, and our laboratory has used in vitro transcription to study mechanisms related to diabetes. We find that the presence of sequences downstream from the major transcription initiation sites in exon 1 is necessary for the diabetes-induced decrease in IGF-I transcription. Six nuclear factor binding sites have been identified within the exon 1 downstream region, and footprint sites III and V appear to be necessary for metabolic regulation; region V probes exhibit a decrease in nuclear factor binding with hepatic nuclear extracts from diabetic animals. IGFs in biological fluids are associated with IGF binding proteins, and IGFs circulate as a 150-kDa complex that consists of an IGF, an IGFBP-3, and an acid-labile subunit. Circulating IGFBP-3 originates mainly in hepatic nonparenchymal cells, where IGF-I increases IGFBP-3 mRNA stability, but insulin increases IGFBP-3 gene transcription. Regulation of IGFBP-3 gene transcription by insulin appears to be mediated by an insulin-responsive element, which recognizes insulin-responsive nuclear factors in both gel mobility shift assays and southwestern blots. Studies of mechanisms underlying the modulation of IGF-I and IGFBP-3 gene transcription, and identification of critical nuclear proteins involved, should lead to new understanding of the role and regulation of these important growth factors in diabetes mellitus and other metabolic disorders.

Effect of protein restriction on messenger RNA of insulin-like growth factor-I and insulin-like growth factor-binding proteins in liver of ovariectomized rats

Effects of dietary protein restriction and ovariectomy on plasma concentrations and hepatic messenger RNA (mRNA) of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBP) were investigated in young female rats. Ovariectomy increased plasma IGF-I concentration in rats fed on either a 50 g casein/kg diet (protein-restricted diet) or a 200 g casein/kg diet (control diet), but it increased IGF-I mRNA in liver only in the rats fed on the control diet. On the other hand, by Western ligand blot analysis, we observed that ovariectomy increased plasma IGFBP-3 concentration, and decreased plasma IGFBP-4 concentration. Ovariectomy did not affect IGFBP-1 and IGFBP-2 mRNA in liver, but dietary protein restriction significantly increased them, which may correspond to their plasma concentrations. The present results show that ovarian hormones and dietary protein content affect the plasma concentrations of IGF-I, IGFBP-3 and IGFBP-4 and hepatic mRNA of IGF-I, IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4 in different manners.

MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism

The reversal of diet-induced negative nitrogen balance by GH suggests a possible therapeutic role for GH treatment in catabolic patients. A double-blind, randomized, placebo-controlled, two-period cross-over study was designed to investigate whether MK-677, an orally active nonpeptide mimic of GH-releasing peptide, can reverse diet-induced protein catabolism. Eight healthy volunteers (ages 24-39 yr) were calorically restricted (18 kcal/kg.day) for two 14-day periods. During the last 7 days of each diet period, subjects received either oral MK-677 25 mg or placebo once daily. There was a 14- to 21-day washout interval between periods. During the first week of caloric restriction (i.e. diet alone), daily nitrogen losses were similar for both treatment groups (mean +/- SE; MK-677 group -2.67 +/- 0.40 g/day vs. placebo group -2.83 +/- 0.26 g/day). During the second week (diet and study drug), mean daily nitrogen balance was 0.31 +/- 0.21 g/day in the MK-677 treatment group compared with -1.48 +/- 0.21 g/day in the placebo group (P < 0.01). MK-677 improved nitrogen balance integrated over the 7 days of treatment; area under the curve day 8-14 nitrogen balance response was +2.69 +/- 5.0 (SE) for MK-677 and -8.97 +/- 5.26 g.day for placebo (P < 0.001). MK-677 produced a peak GH response of 55.9 +/- 31.7 micrograms/L after single dose (day 1 of treatment) and 22.6 +/- 9.3 micrograms/L after a week of dosing compared with placebo treatment peak GH values of approximately 9 (treatment day 1) and approximately 7 micrograms/L (treatment day 7). Following the initial 7-day caloric restriction, insulin-like growth factor-I (IGF-I) declined from 232 +/- 25 to 186 +/- 19 ng/mL in the MK-677 group and from 236 +/- 19 to 174 +/- 23 ng/mL in the placebo group. Mean IGF-I concentration increased significantly during MK-677 to 264 +/- 31 ng/mL (mean for the last 5 days of treatment) compared with 188 +/- 19 ng/mL with placebo (P < 0.01). No significant difference in IGF binding protein-2 was found between the MK-677 and placebo treatments. However, the mean in IGF binding protein-3 for the last 5 days of MK-677 treatment was also significantly increased to 3273 +/- 330 ng/mL (mean +/- SE) compared with placebo 2604 +/- 253 ng/mL (P < 0.01). Neither the serum cortisol nor the PRL response was significantly greater after 7 days of MK-677 dosing compared with 7 days of placebo. MK-677 (25 mg) was generally well tolerated and without clinically significant adverse experiences. In conclusion, MK-677 reverses diet-induced nitrogen wasting, suggesting that if these short-term anabolic effects are maintained in patients who are catabolic because of certain acute or chronic disease states, it may be useful in treating catabolic conditions.

Effects of hormone replacement on growth hormone and prolactin exercise responses in postmenopausal women

Exercise elevates growth hormone (GH) and prolactin (PRL) blood concentrations in premenopausal women. Postmenopausal women taking hormone replacement therapy (HRT) maintain higher estrogen levels that could affect GH and PRL. The purpose of the study was to determine the effects of HRT on GH and PRL responses to treadmill exercise. Seventeen healthy women who were postmenopausal (naturally or surgically) [8 on HRT; 9 not on HRT (NHRT)], completed 30 min of treadmill exercise at 79.16 +/- 1.2% maximal O2 consumption (HRT group) and 80.19 +/- 0.91% maximal O2 consumption (NHRT) group). Blood samples were collected from an intravenous catheter during an exercise session and during a control session without exercise. GH and PRL concentrations were significantly higher in the exercise trial than in the nonexercise trial, whereas resting concentrations were similar for both trials. GH and PRL peaked at 10.8 +/- 1.60 and 12.67 +/- 2.58 ng/ml, respectively, for HRT subjects and at 4.90 +/- 1.18 and 9.04 +/- 2.17 ng/ml, respectively, for NHRT subjects. GH concentrations in the exercise trial were significantly higher for HRT than for NHRT subjects. This is the first study to demonstrate that HRT enhances treadmill-exercise-induced GH release and that similar PRL responses to treadmill exercise occur in postmenopausal women regardless of HRT status.