Seasonal regulation of the growth hormone-insulin-like growth factor-I axis in the American black bear (Ursus americanus)

The American black bear maintains lean body mass for months without food during winter denning. We asked whether changes in the growth hormone/insulin-like growth factor-I (GH-IGF-I) axis may contribute to this remarkable adaptation to starvation. Serum IGF-I levels were measured by radioimmunoassay, and IGF-binding proteins (IGFBPs) were analyzed by ligand blotting. Initial studies in bears living in the wild showed that IGF-I levels are highest in summer and lowest in early winter denning. Detailed studies in captive bears showed that IGF-I levels decline in autumn when bears are hyperphagic, continue to decline in early denning, and later rise above predenning levels despite continued starvation in the den. IGFBP-2 increased and IGFBP-3 decreased in early denning, and these changes were also reversed in later denning. Treatment with GH (0.1 mg·kg(-1)·day(-1) × 6 days) during early denning increased serum levels of IGF-I and IGFBP-3 and lowered levels of IGFBP-2, indicating that denning bears remain responsive to GH. GH treatment lowered blood urea nitrogen levels, reflecting effects on protein metabolism. GH also accelerated weight loss and markedly increased serum levels of free fatty acids and β-hydroxybutyrate, resulting in a ketoacidosis (bicarbonate decreased to 15 meq/l), which was reversed when GH was withdrawn. These results demonstrate seasonal regulation of GH/IGF-I axis activity in black bears. Diminished GH activity may promote fat storage in autumn in preparation for denning and prevent excessive mobilization and premature exhaustion of fat stores in early denning, whereas restoration of GH/IGF activity in later denning may prepare the bear for normal activity outside the den.     

Alterations in the growth hormone-insulin-like growth factor axis in insulin dependent diabetes mellitus.

The growth hormone (GH)-insulin-like growth factor (IGF) axis and insulin are major anabolic effectors in promoting weight gain and linear growth. These two anabolic systems are interlinked at many levels, thus abnormalities in one of these systems effect the other causing disordered metabolic homeostasis. Insufficient portal insulinization in insulin dependent diabetes mellitus (IDDM) results in hepatic GH resistance and increased production of IGF-binding proteins-1 (IGFBP-1) and IGFBP-2. GH resistance is reflected by decreased hepatic IGF-I production. In addition, changes in other GH-dependent proteins are also observed in IDDM. Increased proteolysis of IGFBP-3 results in reduction of intact IGFBP-3. Serum ALS levels are also slightly diminished in untreated diabetic patients. Hepatic resistance to GH is, at least in part, caused by diminished GH receptors as reflected by diminished circulating GHBP levels. In addition, there is also evidence from experimental and human studies suggesting post-receptor defect(s) in GH action. As a result of these changes, circulating total and free IGF-I levels are decreased during insulinopenia. Lack of negative feed-back effect of IGF-I on GH secretion causes GH hypersecretion which increases hyperglycemia by decreasing sensitivity to insulin. GH hypersecretion in poorly controlled diabetic patients may play a role in the pathogenesis of diabetic vascular complications. Most of these abnormalities in the GH-IGF axis in diabetes are reversed by effective insulinization of the patient. Addition of IGF-I treatment to insulin in adolescents with IDDM allows correction of GH hypersecretion, improves insulin sensitivity and glycemic control, and decreases insulin requirements. The effect of IGF-I treatment on diabetic complications has yet to be seen.     

No influence of prednisolone on IGFBP-3 proteolysis in healthy young men

AIMS: The impact of growth hormone (GH) and prednisolone on the GH/insulin-like growth factor (IGF) axis with special emphasis on IGF binding protein-3 (IGFBP-3) proteolysis was studied in 8 healthy adults in a double-blind cross-over study with four periods: (1) placebo; (2) s.c. GH 0.1 IU/kg/day; (3) oral prednisolone 50 mg/day, and (4) co-administration of GH and prednisolone. METHODS: Each treatment period lasted for 4 days followed by a washout period of 10 days. We measured IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 by immunoassays, IGFBP-3 by Western ligand blotting (WLB) and finally in vitro IGFBP-3 proteolysis by a (125)I-IGFBP-3 degradation assay. RESULTS: IGF-I levels increased by 99% during GH administration and 67% during co-administration of GH and prednisolone (p < 0.0005), whereas no significant change was seen during prednisolone alone. IGFBP-1 levels decreased 55% during the prednisolone period (p < 0.002), but the between period changes were not significant (p < 0.1). IGFBP-2 decreased 33% during co-administration of GH and prednisolone (p < 0.002). IGFBP-3 increased 12% during GH and 7% during co-administration of GH and prednisolone (p < 0.003 and p < 0.03 compared to placebo, respectively), whereas prednisolone alone induced no significant changes. IGFBP-3 measured by WLB did not change significantly, neither did IGFBP-3 proteolysis. CONCLUSIONS: Prednisolone administration induces only minimal changes in circulating components of the IGF axis and is not accompanied by alterations in IGFBP-3 proteolysis. This indicates that the metabolic effects of glucocorticoids do not depend on serum IGF-I.     

Insulin-like growth factor-binding protein-2 levels in pediatric patients with growth hormone deficiency, eating disorders and acute lymphoblastic leukemia

Insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) is altered in different diseases and might be used as an indication of its severity. The aims of our study were to investigate: (1) the developmental pattern of the serum IGFBP-2 concentration at birth and during childhood and adolescence; (2) whether the serum IGFBP-2 level could be a marker for the diagnosis and evolution of diseases where the growth hormone (GH)-IGF axis is altered, and (3) whether this binding protein shows a relationship with IGF-I, its free fraction, IGFBP-1 and -3. We report reference values for 55 normal full-term newborns and 221 normal children who were divided into 5 groups according to their Tanner stage. Serum levels were higher in newborns when compared with Tanner stages I-V (p < 0.001, ANOVA), with no further changes throughout development. Furthermore, we studied IGFBP-2 levels in 24 children with congenital GH deficiency (GHD), 26 with acute lymphoblastic leukemia (ALL), 75 obese children, and 60 girls with anorexia nervosa (AN) at diagnosis and during a follow-up period. IGFBP-2 at diagnosis was increased in GHD, ALL and AN, and decreased in obesity (p < 0.05, ANOVA). During the follow-up, IGFBP-2 concentrations tended to normalize. IGFBP-2 correlated positively with IGFBP-1 and negatively with IGF-I and IGFBP-3 in normal subjects and at diagnosis of the pathologies studied. Although IGFBP-2 functions are not well understood, these results suggest a possible role for this protein in diseases where the GH-IGF axis is altered.     

The matrix metalloproteinase-9 regulates the insulin-like growth factor-triggered autocrine response in DU-145 carcinoma cells

The androgen-independent human prostate adenocarcinoma cell line DU-145 proliferates in serum-free medium and produces insulin-like growth factors (IGF)-I, IGF-II, and the IGF type-1 receptor (IGF-1R). They also secrete three IGF-binding proteins (IGFBP), IGFBP-2, -3, and -4. Of these, immunoblot analysis revealed selective proteolysis of IGFBP-3, yielding fragments of 31 and 19 kDa. By using an anti-IGF-I-specific monoclonal antibody (mAb), we detect surface receptor-bound IGF-I on serum-starved DU-145 cells, which activates IGF-1R and triggers a mitogenic signal. Incubation of DU-145 cells with blocking anti-IGF-I, anti-IGF-II, or anti-IGF-I plus anti-IGF-II mAb does not, however, inhibit serum-free growth of DU-145. Conversely, anti-IGF-1R mAb and IGFBP-3 inhibit DNA synthesis. IGFBP-3 also modifies the DU-145 cell cycle, decreases p34(cdc2) levels, and IGF-1R autophosphorylation. The antiproliferative IGFBP-3 activity is not IGF-independent, since des-(1-3)IGF-I, which does not bind to IGFBP-3, reverses its inhibitory effect. DU-145 also secretes the matrix metalloproteinase (MMP)-9, which can be detected in both a soluble and a membrane-bound form. Matrix metalloproteinase inhibitors, but not serpins, abrogate DNA synthesis in DU-145 associated with the blocking of IGFBP-3 proteolysis. Overexpression of an antisense cDNA for MMP-9 inhibits 80% of DU-145 cell proliferation that can be reversed by IGF-I in a dose-dependent manner. Inhibition of MMP-9 expression is also associated with a decrease in IGFBP-3 proteolysis and with reduced signaling through the IGF-1R. Our data indicate an IGF autocrine loop operating in DU-145 cells, specifically modulated by IGFBP-3, whose activity may in turn be regulated by IGFBP-3 proteases such as MMP-9.     

Influence of energy deficiency on the insulin-like growth factor I axis in a military training program.

The aim of this study was to determine wether continuous heavy physical activities as well as lack of food and sleep during military training (three weeks of conditioning followed by a five-day combat course) alter serum concentrations of IGF-I and/or its binding proteins, evaluating the relationship to metabolic changes. Before and after training, we measured serum levels of both total and free IGF-I, IGFBP-1 and IGFBP-3 as well as plasma levels of branched-chain amino acids (valine, leucine and isoleucine) and glucose from 26 cadets (21 +/- 2 yr). Total and free IGF-I levels were decreased after training from 228 +/- 12 to 160 +/- 7 ng/ml and from 0.80 +/- 0.08 to 0.52 +/- 0.06 ng/ml, p < 0.001 respectively) as well as IGFBP-3 (p < 0.001), while IGFBP-1 levels were increased (p < 0.001). BCAA levels were decreased from 245.4 +/- 7.5 to 215.9 +/- 5.1 micromol/l, p < 0.001, while those of glucose remained unchanged. There were correlations between changes in total IGF-I and IGFBP-3 (p < 0.05) and between free IGF-I and IGFBP-1 (p < 0.01). Several correlations appeared between changes in all the components of the IGF-I axis and branched-chain amino acids. We concluded that responses of the IGF-I system during an intense training could represent an adaptative response to the encountered energy deficiency, resulting a diversion of substrate from growth to acute metabolic needs.     

Production of Insulin-like Growth Factors and Their Binding Proteins in Primary Cultures of Rat Liver Parenchymal and Nonparenchymal Cells

Regulation of the production of insulin-like growth factor (IGF)-I, IGF-II, IGF binding proteins (IGFBPs), and their related proteins by various hormones was investigated in primary cultures of rat liver parenchymal and nonparenchymal cells.

Freshly isolated parenchymal cells contained mRNAs of IGF-I, IGF-II, IGFBP-1, IGFBP-4, growth hormone (GH) receptor, and the acid-labile subunit (ALS), which forms a ternary complex with IGF-I and IGFBP-3; however, parenchymal cells did not express the IGFBP-3 gene. In contrast, nonparenchymal cells contained IGFBP-3 mRNA exclusively, as we reported previously [Takenaka et al. Agric. Biol. Chem., 55, 1191–1193 (1991)]. Cultured rat parenchymal cells produced IGF-I, IGFBP-1, and IGFBP-4 prominently. In these cells, secretion of IGF-I and the content of IGF-I mRNA was greatly increased in the presence of GH in the medium. Insulin also increased the production of IGF-I. Secretion of IGFBP-l into the medium was enhanced by treatment with glucagon, dibutyrylcyclic AMP (Bu₂cAMP), and dexamethasone (Dex) and these enhancements with glucagon and Dex reflected the increase in its mRNA content. Insulin depressed the secretion of IGFBP-l. The content of IGFBP-4 in the parenchymal cells was increased by insulin, Bu₂cAMP, and triiodothyronine (T₃), thereby enhancing the production of IGFBP-4 and secretion into the medium. Cultured liver nonparenchymal cells of rats produced IGFBP-1, IGFBP-3, and IGFBP-4. Secretion of IGFBP-l was increased by Bu₂cAMP in the medium, that of IGFBP-3 by IGF-I, and that of IGFBP-4 by both IGF-I and Bu2cAMP. Regulation of the production of IGFBP-3 by IGF-I was demonstrated in these investigations.

These results suggest that GH increases production of IGF-I in the parenchymal cells and this IGF-I, in turn, increases the production of IGFBP-3 in nonparenchymal cells. As we found GH also increases ALS production in parenchymal cells, by these mechanisms, GH increases the formation of the ternary complex of IGF-I, IGFBP-3, and ALS. This study clearly demonstrates the interrelationship between parenchymal and nonparenchymal cells in the production of IGF-I and IGFBPs in the liver.     

Combined ingestion of protein and carbohydrate improves protein balance during ultra-endurance exercise

The aims of this study were to compare different tracer methods to assess whole body protein turnover during 6 h of prolonged endurance exercise when carbohydrate was ingested throughout the exercise period and to investigate whether addition of protein can improve protein balance. Eight endurance-trained athletes were studied on two different occasions at rest (4 h), during 6 h of exercise at 50% of maximal O2 uptake (in sequential order: 2.5 h of cycling, 1 h of running, and 2.5 h of cycling), and during subsequent recovery (4 h). Subjects ingested carbohydrate (CHO trial; 0.7 g CHO.kg(-1.)h(-1)) or carbohydrate/protein beverages (CHO + PRO trial; 0.7 g CHO.kg(-1).h(-1) and 0.25 g PRO.kg(-1).h(-1)) at 30-min intervals during the entire study. Whole body protein metabolism was determined by infusion of L-[1-13C]leucine, L-[2H5]phenylalanine, and [15N2]urea tracers with sampling of blood and expired breath. Leucine oxidation increased from rest to exercise [27 +/- 2.5 vs. 74 +/- 8.8 (CHO) and 85 +/- 9.5 vs. 200 +/- 16.3 mg protein.kg(-1).h(-1) (CHO + PRO), P < 0.05], whereas phenylalanine oxidation and urea production did not increase with exercise. Whole body protein balance during exercise with carbohydrate ingestion was negative (-74 +/- 8.8, -17 +/- 1.1, and -72 +/- 5.7 mg protein.kg(-1).h(-1)) when L-[1-13C]leucine, L-[2H5]phenylalanine, and [15N2]urea, respectively, were used as tracers. Addition of protein to the carbohydrate drinks resulted in a positive or less-negative protein balance (-32 +/- 16.3, 165 +/- 4.6, and 151 +/- 13.4 mg protein.kg(-1).h(-1)) when L-[1-13C]leucine, L-[2H5]phenylalanine, and [15N2]urea, respectively, were used as tracers. We conclude that, even during 6 h of exhaustive exercise in trained athletes using carbohydrate supplements, net protein oxidation does not increase compared with the resting state and/or postexercise recovery. Combined ingestion of protein and carbohydrate improves net protein balance at rest as well as during exercise and postexercise recovery.     

Effects of GH and/or sex steroids on circulating IGF-I and IGFBPs in healthy, aged women and men

Circulating GH, IGF-I, IGFBP-3, and sex steroid concentrations decrease with age. GH or sex steroid treatment increases IGFBP-3, but little is known regarding the effects of these hormones on other IGFBPs. We assessed the effects of 26 wk of administration of GH, sex steroids, or GH + sex steroids on AM levels of IGF-I, IGFBPs 1-5, insulin, glucose, and osteocalcin and 2-h urinary excretion of deoxypyridinolline (DPD) cross-links in 53 women and 71 men aged 65-88 yr. Before treatment, in women and men, IGF-I was directly related to IGFBP-3 (P < 0.001 and P < 0.0001) and IGFBP-1 to IGFBP-2 (P = 0.0001). In women, IGFBP-1 was inversely related to insulin (P < 0.0005) and glucose (P < 0.005) and IGFBP-4 to osteocalcin (P < 0.01). IGFBP-4 and IGFBP-5 were not significantly related to DPD cross-links. GH and/or sex steroid increased IGF-I levels in both sexes, with higher concentrations in men (P < 0.001). In women, the IGF-I increment after GH was attenuated by hormone replacement therapy (HRT) coadministration (P < 0.05). Hormone administration also increased IGFBP-3. IGFBP-1 was unaffected by GH + sex steroids, whereas GH decreased IGFBP-2 by 15% in men (P < 0.05). Hormone administration did not change IGFBP-4, whereas in men IGFBP-5 increased by 20% after GH (P < 0.05) and 56% after GH + testosterone (P = 0.0003). These data demonstrate sexually dimorphic IGFBP responses to GH. Additionally, HRT attenuated or prevented GH-mediated increases in IGF-I and IGFBP-3. Whether GH and/or sex steroid administration alters local tissue production of IGFBPs and whether the latter influence autocrine or paracrine actions of IGF-I remain to be determined.     

Plasma levels of total and active ghrelin in acromegaly and growth hormone deficiency

Ghrelin is an endogenous growth hormone (GH) secretagogue recently isolated from the stomach. Although it possesses a strong GH releasing activity in vitro and in vivo, its physiological significance in endogenous GH secretion remains unclear. The aim of this study was to characterize plasma ghrelin levels in acromegaly and growth hormone deficiency (GHD). We investigated plasma total and active ghrelin in 21 patients with acromegaly, 9 patients with GHD and 24 age-, sex- and BMI-matched controls. In all subjects, we further assessed the concentrations of leptin, soluble leptin receptor, insulin, IGF-I, free IGF-I and IGFBP-1, 2, 3 and 6. Patients with acromegaly and GHD as well as control subjects showed similar levels of total ghrelin (controls 2.004+/-0.18 ng/ml, acromegalics 1.755+/-0.16 ng/ml, p=0.31, GHD patients 1.704+/-0.17 ng/ml, p=0.35) and active ghrelin (controls 0.057+/-0.01 ng/ml, acromegalics 0.047+/-0.01 ng/ml, p=0.29, GHD patients 0.062+/-0.01 ng/ml, p=0.73). In acromegalic patients plasma total ghrelin values correlated negatively with IGF-I (p<0.05), in GHD patients active ghrelin correlated with IGF-I positively (p<0.05). In the control group, total ghrelin correlated positively with IGFBP-2 (p<0.05) and negatively with active ghrelin (p=0.05), BMI (p<0.05), WHR (p<0.05), insulin (p=0.01) and IGF-I (p=0.05). Plasma active ghrelin correlated positively with IGFBP-3 (p=0.005) but negatively with total ghrelin and free IGF-I (p=0.01). In conclusion, all groups of the tested subjects showed similar plasma levels of total and active ghrelin. In acromegaly and growth hormone deficiency plasma ghrelin does not seem to be significantly affected by changes in GH secretion.     

Food intake of children with short stature born small for gestational age before and during a randomized GH trial

Parents of short children born SGA often report that their children have a serious lack of appetite and a low food intake. In this study we investigated food intake, by using a standardized 7-day food questionnaire, in 88 short SGA children before start of GH treatment. The intake was compared with the recommended daily intake (RDI) of age-matched children. We also compared the food intake of GH-treated children (n=62) with randomized controls (n=26) after 1 year of GH treatment. In addition, we evaluated the effect of food intake and GH treatment on body composition and serum levels of IGF-I, IGFBP-3 and leptin. Our study shows that caloric intake, fat and carbohydrate intake of short SGA children aged 5.9 (1.6) years was significantly lower compared to the RDI for age-matched children. One year of GH treatment resulted in a significant increase of caloric, fat, carbohydrate and protein intake compared to baseline. Compared to randomized controls, caloric, carbohydrate and protein intake increased significantly after 1 year of GH treatment. Short SGA children had significantly lower SDS scores for LBM, fat mass, skinfold (SF) and BMI compared to age-matched references. They also had significantly lower serum IGF-I, IGFBP-3 and leptin levels. GH treatment resulted in a significant increase of height, LBM, BMI, IGF-I and IGFBP-3 SDS and a significant decrease of SF SDS and leptin SDS. In conclusion, our study shows that short SGA children have indeed a lower food intake than age-matched controls. During GH treatment the food intake increased significantly compared to baseline in contrast to the randomized control group.     

Effect of rhIL-6 infusion on GH-->IGF-I axis mediators in humans

Exercise leads to simultaneous increases in mediators signaling apparently antagonistic functional responses such as growth factors and inflammatory mediators. The aim of the present study was to demonstrate the physiological effect of IL-6 on circulating components of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis. Twelve men (ages 26 +/- 2 yr) were divided into two groups (n = 6 in each group), receiving either albumin or recombinant human (rh) IL-6 infusion. IL-6 was infused via an antecubital vein, and a contralateral antecubital vein was used for blood sampling. The IL-6 dose was chosen to reach plasma levels of IL-6 characteristic of intense exercise (5 microg/h, for 3 h, resulting in plasma levels of 100 pg/ml). Blood samples for GH, GH binding protein, IGF-I, and IGF binding protein (IGFBP)-1 and -3 were collected at baseline, 30 min, and 1, 2, 3, 4, 5, and 8 h after the beginning of the rhIL-6 infusion. IL-6 levels increased only in the rhIL-6-infused group (P < 0.0005) and returned to baseline after the infusion was stopped. IL-6 infusion led to a significant increase in GH, peaking 1 h after the beginning of infusion (P < 0.001). A decrease in total IGF-I levels was noted only in the rhIL-6-infused group (P < 0.027). An initial decrease in IGFBP-1 levels was noted in both groups during infusion (P < 0.03). Following the initial decrease, there was a significant increase in IGFBP-1 levels only in the IL-6-infused participants, peaking at 2 after the infusion cessation (P < 0.001). IL-6 infusion had no effect on GH binding protein, IGFBP-3, and acid-labile subunit levels. rhIL-6 levels similar to the levels found after strenuous exercise induced a typical exercise-associated GH-->IGF-I axis response (increase GH, decreased IGF-I, and elevated IGFBP-1). The results suggest that IL-6 plays a role in the GH-->IGF-I response to intense exercise.     

Diurnal secretion of growth hormone, cortisol, and dehydroepiandrosterone in pre- and perimenopausal women with active rheumatoid arthritis: a pilot case-control study

Rheumatoid arthritis (RA) is associated with neuroendocrine and immunologic dysfunction leading to rheumatoid cachexia. Although excess proinflammatory cytokines can decrease somatotropic axis activity, little is known about the effects of RA on growth hormone/insulin-like growth factor-1 (GH/IGF-I) axis function. We tested the hypothesis that patients with active RA exhibit decreased GH/IGF-I axis activity. To do so, we conducted a pilot case-control study at a clinical research center in 7 pre- and perimenopausal women with active RA and 10 age- and body mass index-matched healthy women. Participants underwent blood sampling every 20 minutes for 24 hours (8 a.m. to 8 a.m.), and sera were assayed for GH, cortisol, and dehydroepiandrosterone (DHEA). Sera obtained after overnight fasting were assayed for IGF-I, IGF-binding protein (IGFBP)-1, IGFBP-3, C-reactive protein (CRP), interleukin-6 (IL-6), glucose, insulin, and lipids. Body composition and bone mineral density were evaluated by DEXA (dual emission x-ray absorptiometry) scans. In patients with RA, mean disease duration was 7.6 +/- 6.8 years, and erythrocyte sedimentation rate, CRP, and IL-6 were elevated. GH half-life was shorter than in control subjects (p = 0.0037), with no other significant group differences in GH deconvolution parameters or approximate entropy scores. IGF-I (p = 0.05) and IGFBP-3 (p = 0.058) were lower, whereas IGFBP-1 tended to be higher (p = 0.066), in patients with RA, with nonsignificantly increased 24-hour total GH production rates. There were no significant group differences in cortisol or DHEA secretion. Lean body mass was lower in patients with RA (p = 0.019), particularly in the legs (p = 0.01). Women with active RA exhibit a trend toward GH insensitivity and relatively diminished diurnal cortisol and DHEA secretion for their state of inflammation. Whether these changes contribute to rheumatoid cachexia remains to be determined. Trial registration number: NCT00034060.     

Effects of carbohydrate feedings on plasma free tryptophan and branched-chain amino acids during prolonged cycling

Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [VO2max = 57.8 (SE 4.1) ml kg-1 min-1] cycled for up to 255 min at a power output corresponding to VO2 at lactate threshold (approximately 68% VO2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg-1 body wt-1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P < 0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P < 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Normal growth spurt and final height despite low levels of all forms of circulating insulin-like growth factor-I in a patient with acid-labile subunit deficiency

BACKGROUND: In a recently described patient with acid-labile subunit (ALS) deficiency, the inability to form ternary complexes resulted in a marked reduction in circulating total insulin-like growth factor (IGF)-I, whereas skeletal growth was only marginally affected. To further study the role of circulating versus locally produced IGF-I in skeletal growth in this patient, we now describe in detail growth changes and their relationship with several components of the circulating IGF system. DESIGN AND METHODS: We followed growth and development up to the final height in a patient with complete ALS deficiency and determined both spontaneous and growth hormone (GH)-stimulated changes in the IGF system, including measurements of total, free and bioactive IGF-I, total IGF-II and insulin-like growth factor binding protein (IGFBP)-1, IGFBP-2 and IGFBP-3. RESULTS: The patient had a delayed growth and pubertal onset. Six months of GH treatment had no effect on growth. At the age of 19.3 years, he spontaneously completed puberty and had a normal growth spurt for a late adolescent (peak height velocity of 8.4 cm/year). A normal final height was attained at 21.3 years (167.5 cm; -0.78 SDS). During as well as after puberty, basal levels of total, free and bioactive IGF-I were low, as were total IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3. GH treatment for 6 months normalized free IGF-I and increased bioactive IGF-I, but had no effect on growth velocity. CONCLUSIONS: This case story shows that in the presence of complete ALS deficiency, a height within normal limits can be obtained despite low levels of all forms of circulating IGF-I. Furthermore, the patient presented a delayed but normal growth spurt without any marked increment of circulating IGF-I.     

Age-related changes of the somatotropic axis in cloned Holstein calves

To determine if the development of the somatotropic axis in somatic clones (clones) is similar to that in heifers produced by artificial insemination (controls), serum samples were collected every 30 min for 6 h, once per month, for 7 mo from 4 clones generated from a 13-yr-old cow and from 4 age-matched controls. Average concentrations of growth hormone (GH) were not different between clones and controls, and GH concentrations declined over time in controls. Average concentrations of insulin-like growth factor I (IGF-I) were less in clones than controls, and IGF-I concentrations increased over time in both groups. Concentrations of IGF-binding protein 3 (IGFBP-3) were greater in controls than in clones and did not change over time. Average IGFBP-2 concentrations did not change over time and were not different between clones and controls. Clones and controls were challenged with GH-releasing hormone (GHRH) (3 microg/100 kg body weight) and somatostatin (somatotropin release-inhibiting factor [SRIF]) (1.87 and 5 microg/100 kg body weight) at 14 mo of age. GHRH-induced GH secretion was greater and SRIF inhibition of GHRH-induced GH was less in clones than in controls. We speculate that some of the differences between clones and controls in concentrations of GH, IGF-I, and IGFBP-3 may be related to the genetic merit of the animals. Although there were differences in concentrations of components of the somatotropic axis between these clones and their age-matched controls, the values recorded were all within the range reported for calves of similar ages.     

Thyroid hormone modulates insulin-like growth factor-I(IGF-I) and IGF-binding protein-3, without mediation by growth hormone, in patients with autoimmune thyroid diseases.

The expression and synthesis of insulin-like growth factor-1 (IGF-I) and IGF-binding protein-3 (IGFBP-3) are regulated by various hormones and nutritional conditions. We evaluated the effects of thyroid hormones on serum levels of IGF-I and IGFBP-3 levels in patients with autoimmune thyroid diseases including 54 patients with Graves' disease and 17 patients with Hashimoto's thyroiditis, and in 32 healthy age-matched control subjects. Patients were subdivided into hyperthyroid, euthyroid and hypothyroid groups that were untreated, or were treated with methylmercaptoimidazole (MMI) or L-thyroxine (L-T4). Serum levels of growth hormone (GH), IGF-I and IGFBP-3 were determined by radioimmunoassay. Serum GH levels did not differ significantly between the hyperthyroid and the age-matched euthyroid patients with Graves' disease. The serum levels of IGF-I and IGFBP-3 showed a significant positive correlation in the patients (R=0.616, P<0.001). The levels of both IGF-I and IFGBP-3 were significantly higher in the hyperthyroid patients with Graves' disease or in those with Hashimoto's thyroiditis induced by excess L-T4 administration than in control subjects. Patients with hypothyroid Graves' disease induced by the excess administration of MMI showed significantly lower IGFBP-3 levels as compared to those in healthy controls (P<0.05). Levels of IGFBP-3, but not IGF-I levels, showed a significant positive correlation with the levels of free T4 and free T3. In Graves' disease, levels of TPOAb, but not of TRAb, showed a significant positive correlation with IGFBP-3. We conclude that in patients with autoimmune thyroid diseases, thyroid hormone modulates the synthesis and/or the secretion of IGF-I and IGFBP-3, and this function is not mediated by GH.     

Free IGF-I, IGFBP-1, and the binary complex of IGFBP-1 and IGF-I are increased during human pregnancy

BACKGROUND/AIMS: To investigate changes in free insulin-like growth factor I (IGF-I) and IGF-binding protein 1 (IGFBP-1) complexed IGF-I during human pregnancy. METHODS: Overnight fasting serum was obtained in a longitudinal design from 11 women with non-complicated pregnancy at gestation weeks 6-10, 16-20, 24-28 and 35-38 and, for comparison, 5 weeks post-partum. All samples were analyzed for total and free IGF-I and IGF-II, IGFBP-3 and IGFBP-3 proteolysis, total and non-phosphorylated (np-) IGFBP-1, and IGFBP-1 complexed IGF-I. RESULTS: Total IGF-I was increased in late pregnancy (week 35-38) (p < 0.001), whereas free IGF-I was significantly increased by 77% already at week 6-10 (p = 0.004) and by 140% (p = 0.002) at week 34-38, when compared to post-partum levels. At weeks 16-20 and 24-28, levels of free IGF-I were not significantly different from post-partum levels. Significant IGFBP-3 proteolysis was detectable from week 6-10 and throughout pregnancy (p < 0.05). Total and np-IGFBP-1 were significantly increased from 16-20 weeks of pregnancy (both p < 0.05) and IGFBP-1 complexed IGF-I was increased 2-fold from week 16-20 and throughout pregnancy (p < 0.05). However, the saturation of IGFBP-1 remained constant at 27-29% during the study. CONCLUSION: We found evidence of increased free IGF-I and increased IGF-I in binary complexes during pregnancy, possibly caused by IGFBP-3 proteolysis and decreased ternary complex formation.     

Influence of exercise duration on serum insulin-like growth factor and its binding proteins in athletes

The changes in circulating concentrations of insulin-like growth factors during exercise have to date remained incomplete in their documentation. Therefore, we examined in 25 healthy athletes the effects of three different durations of three types of exercise – incremental ergometer cycling exercise (ICE), long-distance Nordic ski race (NSR) and a treadmill-simulated soccer game (TSG) lasting 20 min, 3 h, and 2 × 45 min separated by a 15-min half-time rest respectively, on plasma concentrations of growth hormone ([GH]), insulin-like growth factor-1 ([IGF-I]) and its binding proteins 1 and 3 ([IGFBP-1], [IGFBP-3]). Compared to baseline, serum [GH] increased by 15.2-fold after ICE (P < 0.001), 2.9-fold after NSR (P < 0.01) and 4.6-fold after TSG. Serum [IGF-I] rose by 11.9% after ICE (P < 0.001), while it decreased by −14.6% after NSR (P < 0.001) and was unchanged after TSG. Serum [IGFBP-1] was slightly increased (1.7-fold) after ICE (P < 0.01), but increased markedly (11.8-fold) after NSR (P < 0.001) and by 6.3-fold after the second session of TSG (P < 0.01) (it remained unchanged at the end of the first period of TSG, i.e. after 45-min exercise). The [IGFBP-3] increased by 14.7% after ICE (P < 0.001) and by 6% after TSG (P < 0.05) while it did not change after NSR. From our results it would appear that [IGFBP-1] increase to bind free IGF and hinder their insulin-like action during long-term exercise (lasting beyond 45 min). It is suggested that IGFBP-1 might thus contribute both to preventing hypoglycaemic action of IGF and to facilitating glucose uptake by muscle cells when muscle glycogen stores become deplete. Accepted: 27 May 1998