Placental growth hormone (GH), GH-binding protein, and insulin-like growth factor axis in normal, growth-retarded, and diabetic pregnancies: correlations with fetal growth

We previously described significant changes in GH-binding protein (GHBP) in pathological human pregnancy. There was a substantial elevation of GHBP in cases ofnoninsulin-dependent diabetes mellitus and a reduction in insulin-dependent diabetes mellitus. GHBP has the potential to modulate the proportion of free placental GH (PGH) and hence the impact on the maternal GH/insulin-like growth factor I (IGF-I) axis, fetal growth, and maternal glycemic status. The present study was undertaken to investigate the relationship among glycemia, GHBP, and PGH during pregnancy and to assess the impact of GHBP on the concentration of free PGH. We have extended the analysis of specimens to include measurements of GHBP, PGH, IGF-I, IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 and have related these to maternal characteristics, fetal growth, and glycemia. The simultaneous measurement of GHBP and PGH has for the first time allowed calculation of the free component of PGH and correlation of the free component to indexes of fetal growth and other endocrine markers. PGH, free PGH, IGF-I, and IGF-II were substantially decreased in IUGR at 28-30 weeks gestation (K28) and 36-38 weeks gestation (K36). The mean concentration (+/-SEM) of total PGH increased significantly from K28 to K36 (30.0 +/- 2.2 to 50.7 +/- 6.2 ng/mL; n = 40), as did the concentration of free PGH (23.4 +/- 2.3 to 43.7 +/- 6.0 ng/mL; n = 38). The mean percentage of free PGH was significantly less in IUGR than in normal subjects (67% vs. 79%; P < 0.01). Macrosomia was associated with an increase in these parameters that did not reach statistical significance. Multiple regression analysis revealed that PGH/IGF-I and IGFBP-3 account for 40% of the variance in birth weight. IGFBP-3 showed a significant correlation with IGF-I, IGF-II, and free and total PGH at K28 and K36. Noninsulin-dependent diabetes mellitus patients had a lower mean percentage of free PGH (65%; P < 0.01), and insulin-dependent diabetics had a higher mean percentage of free PGH (87%; P < 0.01) than normal subjects. Mean postprandial glucose at K28 correlated positively with PGH and free PGH (consistent with the hyperglycemic action of GH). GHBP correlated negatively with both postprandial and fasting glucose. Although GHBP correlated negatively with PGH (r = -0.52; P < .001), free PGH and total PGH correlated very closely (r = 0.98). The results are consistent with an inhibitory function for GHBP in vivo and support a critical role for placental GH and IGF-I in driving normal fetal growth.     

The effect of anorexia nervosa and refeeding on growth hormone-binding protein, the insulin-like growth factors (IGFs), and the IGF-binding proteins.

We studied the relationship of serum insulin-like growth factor-I (IGF-I), IGF-II, the IGF-binding proteins IGFBP-1, IGFBP-2, and IGFBP-3, and GH-binding protein (GHBP; which is postulated to be derived from the extracellular portion of the GH receptor) in normal volunteers and patients with anorexia nervosa before and after a refeeding program. Serum GHBP, IGF-I, and IGFBP-3 were all significantly decreased in low weight patients with anorexia nervosa and returned to nearly normal levels with refeeding. Fasting serum GH and serum IGFBP-1 and IGFBP-2 were significantly increased in low weight patients with anorexia nervosa and also returned to nearly normal levels with refeeding. Serum IGF-II was 27% lower in the low weight group than in normal subjects, but this difference was not statistically significant. Both serum IGF-I and IGF-II were positively correlated with serum IGFBP-3 and negatively correlated with serum IGFBP-1 and IGFBP-2. These data are consistent with the hypothesis that nutritional deprivation alters the GH-IGF axis by down-regulation of the GH receptor or its postreceptor mechanisms, and that this effect is reversible with refeeding.     

The IGF-system is not affected by a twofold change in protein intake in patients with type 1 diabetes.

OBJECTIVE: In type 1 diabetes the circulating IGF-system is altered with low IGF-I and changes in levels of IGF-binding proteins (IGFBPs) which may be of importance for the development of diabetes complications. Our aim was to study if IGF-I, as supported by experimental data in animals, can be affected by dietary protein intake. DESIGN AND METHODS: Twelve patients with type 1 diabetes, age 37.5+/-10.0 years (mean+/-SD), diabetes duration 20.1+/-9.3 years and HbA1c 6.3+/-0.6% were allocated to isocaloric diets with either low normal protein content (LNP), (10 E%; 0.9 g protein/kg body weight) or high normal protein content (HNP) (20 E%; 1.8 g protein/kg body weight) in an open randomised cross-over study. Each diet was taken for 10 days with a wash-out period of 11 days in between. Circulating levels of total and free IGF-I and -II, IGFBP-1, -2 and -3 and GH-binding protein (GHBP) as well as ghrelin were measured with validated in-house immunoassays. RESULTS: At day 10, urinary urea excretion was 320+/-75 mmol/24h during LNP diet compared with 654+/-159 mmol/24h during HNP diet (p<0.001). There were no changes in body weight or glycaemic control between the diets. Fasting levels of total IGF-I were 121+/-33 microg/L after LNP and 117+/-28 microg/L after HNP diet (ns) and the corresponding concentrations of IGFBP-1 were 142(141) and 132(157)mug/L [median (IQR)] (ns). There were no differences in plasma concentrations of total IGF-II, free IGF-I and -II, IGFBP-3, GHBP and ghrelin, whereas a small difference was found for IGFBP-2 (302+/-97 vs. 263+/-66 microg/L; LNP vs. HNP; p<0.04). CONCLUSIONS: A twofold change of the dietary protein intake does not influence the altered circulating IGF-system in type 1 diabetes. In order to affect the IGF-system other interventions must be used.     

Insulin-like growth factors, insulin-like growth factor-binding proteins, insulin-like growth factor-binding protein-3 protease, and growth hormone-binding protein in lipodystrophic human immunodeficiency virus-infected patients

Human immunodeficiency virus (HIV)-lipodystrophy is associated with impaired growth hormone (GH) secretion. It remains to be elucidated whether insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs), IGFBP-3 protease, and GH-binding protein (GHBP) are abnormal in HIV-lipodystrophy. These parameters were measured in overnight fasting serum samples from 16 Caucasian males with HIV-lipodystrophy (LIPO) and 15 Caucasian HIV-infected males without lipodystrophy (NONLIPO) matched for age, weight, duration of HIV infection, and antiretroviral therapy. In LIPO, abdominal fat mass and insulin concentration were increased (>90%, P < .01) and insulin sensitivity (Log10ISI(composite)) was decreased (-50%, P < .001). Total and free IGF-I, IGF-II, IGFBP-3, and IGFBP-3 protease were similar between groups (all P > .5), whereas, in LIPO, IGFBP-1 and IGFBP-2 were reduced (-36%, P < .05 and -50%, P < .01). In pooled groups, total IGF-I, free IGF-I, total IGF-II, and IGFBP-3, respectively, correlated inversely with age (all P < .01). In pooled groups, IGFBP-1 and IGFBP-2 correlated positively with insulin sensitivity (age-adjusted all P < .05). IGFBP-3 protease correlated with free IGF-I in pooled groups (r(p) = 0.47, P < .02), and in LIPO (r(p) = 0.71, P < .007) controlling for age, total IGF-I, and IGFBP-3. GHBP was increased, whereas GH was decreased in LIPO (all P < .05). GH correlated inversely with GHBP in pooled groups (P < .05). Taken together the similar IGFs and IGFBP-3 concentrations between study groups, including suppressed GH, and increased GHBP in LIPO, argue against GH resistance of GH-sensitive tissues in LIPO compared with NONLIPO; however, this notion awaits examination in dose-response studies. Furthermore, our data suggest that IGFBP-3 protease is a significant regulator of bioactive IGF-I in HIV-lipodystrophy.     

Low serum levels of free and total insulin-like growth factor I (IGF-I) in patients with anorexia nervosa are not associated with increased IGF-binding protein-3 proteolysis

Patients with anorexia nervosa (AN) are GH resistant, with elevated GH levels and low serum levels of total insulin-like growth factor I (IGF-I). IGF-I action is modulated by IGF-binding proteins (IGFBPs), and a variety of catabolic states has been characterized by the presence of increased IGFBP-3 proteolysis. The present study was performed to examine the levels of free IGFs in AN and to clarify whether AN is associated with increased IGFBP-3 proteolytic activity. In 24 patients and 10 age-matched controls, the fasting serum concentrations of free IGF-I and -II were measured using ultrafiltration by centrifugation. In addition, GH, GH-binding protein, total IGFs, IGFBP-1 to -4, and IGFBP-3 proteolytic activity were measured. The IGFBPs were measured by both immunoassays and Western ligand blotting. Twelve of the patients were restudied 3 months after a minor increase in body mass index. In AN, the levels of GH-binding protein, free and total IGF-I, free IGF-II, and IGFBP-3 were significantly reduced; total IGF-II, IGFBP-2, and IGFBP-4 levels were unchanged; and IGFBP-1 was increased. No increased IGFBP-3 proteolytic activity could be detected in AN. In conclusion, the mechanisms responsible for the adaption of the GH-IGF-IGFBP axis in AN may be different from other catabolic conditions, because the low levels of free and total IGF-I in AN are not associated with increased IGFBP-3 proteolysis.     

Residual beta-cell function more than glycemic control determines abnormalities of the insulin-like growth factor system in type 1 diabetes

The GH-IGF-I axis is disturbed in patients with type 1 diabetes. Our aim was to investigate whether abnormalities are found in patients in very good glycemic control and, if so, to estimate the role of residual beta-cell function. Patients with hemoglobin A1c (HbA1c) less than 6% (reference range, 3.6-5.4%) were selected for the study. Twenty-two men and 24 women, aged 41.3 +/- 13.8 yr (mean +/- SD), with a diabetes duration of 17.8 +/- 14.6 yr participated. Healthy controls (15 women and nine men), aged 41.3 +/- 13.0 yr, were also studied. Overnight fasting serum samples were analyzed for HbA1c, C peptide, free and total IGFs, IGF-binding proteins (IGFBPs), GH-binding protein, and IGFBP-3 proteolysis. HbA1c was 5.6 +/- 0.5% in patients and 4.4 +/- 0.3% in controls. Total IGF-I was 148 +/- 7 microg/liter in patients and 178 +/- 9 microg/liter in controls (P < 0.001). Free IGF-I, total IGF-II, IGFBP-3, and GH-binding protein were lower, whereas IGFBP-1, IGFBP-1-bound IGF-I, and IGFBP-2 were elevated compared with control values. Patients with detectable C peptide (> or =100 pmol/liter) had higher levels of total IGF-I, free IGF-I, and total IGF-II and lower levels of IGFBP-1 and IGFBP-2 than those with an undetectable C peptide level despite having identical average HbA1c. IGFBP-3 proteolysis did not differ between patients and controls. Despite very good glycemic control, patients with type 1 diabetes and no endogenous insulin production have low free and total IGF-I. Residual beta-cell function, therefore, seems more important for the disturbances in the IGF system than good metabolic control per se, suggesting that portal insulin delivery is needed to normalize the IGF system.     

Effects of a 7-day continuous infusion of octreotide on circulating levels of growth factors and binding proteins in growth hormone (GH)-treated GH-deficient patients

In patients with acromegaly, clinical improvement has been reported after octreotide (OCT) treatment, even in cases of only a moderate suppression of growth hormone (GH) levels. In rats, OCT suppresses IGF-I mRNA expression and generation of serum and tissue IGF-I levels. A direct effect of OCT on the IGF system could have therapeutical implications in diabetes mellitus, cardiovascular disease, and certain malignancies in which IGF-I might be involved. The aim of this study was to examine possible GH-independent effects of OCT on IGF components in humans. Six GH-deficient (GHD) patients were studied for 24 h after each of the following treatment regimens (each of 1 weeks duration): (a) daily s.c. GH injection (2 IU/m(2)); (b) as (a) + continuous s.c. infusion of OCT (200 microg/24 h) by means of a portable pump (Nordic Infuser); (c) no treatment. Serum GH binding protein (GHBP) levels tended to be lower after GH and OCT than after GH alone (P =0.10). OCT reduced the GH induced increase in serum IGF-I levels (P<0.05, ANOVA). Mean integrated levels (microg/l) were 359.1+/-49.6 (GH), and 301.6+/-58.9 (GH+OCT). OCT did not significantly reduce serum IGFBP-3 levels (microg/l) [3460+/-270 (GH), and 3112+/-435 (GH+/-OCT);P =0.14]. Serum levels of free IGF-I (P =0.39), IGF-II (P =0.54), and of the acid-labile subunit (ALS) of the ternary complex (P =0.50) were similar during GH+/-OCT as compared with GH alone. After 1 week off GH treatment, significantly lower levels of IGF-I, IGF-II, IGFBP-3, and ALS were recorded (P<0.001). Serum IGFBP-1 levels were significantly higher after GH+OCT than after GH alone (P<0.0001), and levels were even higher without GH. Serum insulin levels (pmol/l) were significantly higher after GH alone as compared with no GH (P<0.05, ANOVA), whereas OCT partly suppressed the insulinotropic effect of GH (P<0. 05) [mean: 114.5+/-33.0 (GH), 91.3+/-29.6 (GH+OCT), 65.9+/-22.5 (no GH)]. This was also reflected in higher blood glucose levels during GH+OCT. Finally, GH+OCT reduced glucagon levels significantly as compared with GH alone (P =0.02). In conclusion, 7 days' administration of OCT to GH-treated GHD patients slightly attenuated serum IGF-I generation, and tended to decrease levels of the other components of the 150 kDa ternary complex. Whether these effects are mediated directly by OCT or indirectly via the accompanying changes in insulin levels remains to be investigated.     

Normal growth despite GH, IGF-I and IGF-II deficiency.

A 6.5-year-old male with normal linear growth, despite septo-optic dysplasia, panhypopituitarism and a deficient GH/IGF axis, is presented. In addition to measuring IGF-I, IGF-II and IGFBP-3, serum IGFBP-1, -2, -4 and -5 were measured. A human osteosarcoma cell line was used to assess growth-promoting activity in the patient's serum. The role of leptin in linear growth in this case was investigated. There was no evidence for hyperinsulinism or hyperandrogenism. GH was undetectable upon multiple stimulation. GHBP was elevated. Serum IGF-I (25 microg/l), IGF-II (194 microg/l), IGFBP-3 (0.4 mg/l), and IGFBP-5 (87 microg/l) levels were low compared to age-matched prepubertal children. Serum IGFBP-4 level was normal. Molecular size of IGF-II in the patient's serum was normal, suggesting normal IGF-II bioavailability. Human osteosarcoma cell proliferation in response to the patient's serum was similar to sera from age-matched normal controls. Leptin levels were markedly elevated. Osteoblast cell proliferation was not stimulated by leptin. The data demonstrate that normal growth and osteoblast cell proliferation in this patient is not mediated by GH, total IGFs, insulin, or leptin, and suggest the presence of a yet unidentified growth factor or mechanism. The case offers a detailed picture of binding proteins in a case of growth without GH. It introduces osteoblast cell proliferation as a method of assessing serum growth-promoting activity in such cases. It adds IGF-II and leptin to the list of excluded growth-promoting candidates in GH-independent growth, and further demonstrates our incomplete understanding of the phenomenon of growth.     

Effects of short-term administration of low-dose rhGH on IGF-I levels in obesity and Cushing's syndrome: indirect evaluation of sensitivity to GH

OBJECTIVE: To verify the hypothesis of an increased sensitivity to GH in obesity (OB) and Cushing's syndrome (CS). DESIGN: We studied the effects of short-term administration of low-dose rhGH on circulating IGF-I levels in patients with simple OB or CS and in normal subjects (NS). METHODS: Nineteen women with abdominal OB aged (mean +/- s.e.m.) 38.2+/-3.1 years, body mass index 40.7+/-2.5 kg/m(2), waist to hip ratio 0.86+/-0.02, ten with CS (50.4+/-4.2 years, 29.7 +/- 3.3 kg/m(2)) and 11 NS (35.0+/-3.6 years, 20.5+/-0.5 kg/m(2)) underwent s.c. administration of 5 microg/kg per day rhGH at 2200 h for four days. Serum IGF-I, IGF-binding protein-3 (IGFBP-3), GH-binding protein (GHBP), insulin and glucose levels were determined at baseline and 12 h after the first and the last rhGH administration. RESULTS: Basal IGF-I levels in NS (239.3+/-22.9 microg/l) were similar to those in OB (181.5+/-13.7 microg/l) and CS (229.0+/-29.1 microg/l). Basal IGFBP-3, GHBP and glucose levels in NS, OB and CS were similar while insulin levels in NS were lower (P<0.01) than those in OB and CS. In NS, the low rhGH dose induced a sustained rise of IGF-I levels (279.0+/-19.5 microg/l, P<0.001), a non-significant IGFBP-3 increase and no change in GHBP, insulin and glucose levels. In OB and CS, the IGF-I response to rhGH showed progressive increase (246.2+/-17.2 and 311.0+/-30.4 microg/l respectively, P<0.01 vs baseline). Adjusting by ANCOVA for basal values, rhGH-induced IGF-I levels in CS (299.4 microg/l) were higher than in OB (279.1 microg/l, P<0.01), which, in turn, were higher (P<0.05) than in NS (257.7 microg/l). In OB, but not in CS, IGFBP-3 and insulin levels showed slight but significant (P<0.05) increases during rhGH treatment, which did not modify glucose levels in any group; thus, in the OB patient group a significant fall in glucose/insulin ratio was observed. CONCLUSIONS: Short-term treatment with low-dose rhGH has enhanced stimulatory effect on IGF-I levels in OB and, particularly, in hypercortisolemic patients. These findings support the hypothesis that hyperinsulinism and hypercortisolism enhance the sensitivity to GH in humans.     

Impact of gender and androgen status on IGF-I levels in normal and GH-deficient adults

OBJECTIVE: The regulation of IGF-I levels is complex and not only dependent on GH status, as the diagnostic sensitivity of serum IGF-I levels for GH deficiency (GHD) in adults is low. Other GH-related parameters have so far not proven to be of additional diagnostic value in GHD adults. In the present study we evaluated the impact of gender and androgen status on IGF-I levels and the diagnostic value of IGF-I and GH-related parameters in a population of adult hypopituitary patients and age- and gender-matched healthy subjects. DESIGN: A cross-sectional study. SUBJECTS: Fifty-nine GHD patients (40 males, mean age 39.3+/-1.7 (s.e.m.) years, and 19 females, mean age 41.9+/-2.6 years) and 69 healthy subjects (42 males, mean age 36. 7+/-1.5 years, and 27 females, mean age 38.9+/-2.1 years). RESULTS: IGF-I levels were low in the GHD patients (91+/-7 vs 173+/-7 microgram/l, P<0.001), and lower in female patients than in male (68+/-10 vs 100+/-8 microgram/l, P=0.03). In the control group there was no gender-related difference in IGF-I levels (males: 178+/-8, females: 164+/-12 microgram/l, P=0.23). IGF-II and IGF-binding protein-3 (IGFBP-3) were also decreased in GHD without any gender-related differences. GH-binding protein (GHBP) levels were increased in the patient group. The diagnostic sensitivity (%) of IGF-I, IGF-I/GHBP, IGF-I/IGFBP-3, and of the combination of IGF-I plus IGF-II (both low or one normal and one low), was higher in female patients than in male (IGF-I: 57.8 vs 22.0, P<0.0001; IGF-I/GHBP: 84.2 vs 48.8, P=0. 002; IGF-I/IGFBP-3: 36.8 vs 7.3 P=0.001; IGF-I+IGF-II: 77.8 vs 52.6, P=0.01). Testosterone levels were reduced in the female patients compared with female controls (0.5+/-0.3 vs 2.1+/-0.2nmol/l, P<0.001). Forward regression analyses revealed that IGFBP-3 was a significant predictor of IGF-I levels in both patients and healthy subjects. In a combined analysis of both patients and controls, sex hormone-binding globulin (SHBG) level was the main contributor as an explanatory variable. Gender and prolactin also predicted IGF-I in patients, whereas SHBG and estradiol were significant predictors only in the control group. CONCLUSION: (i) Levels of IGF-I, and of IGF-I/IGFBP-3 and IGF-I/GHBP ratios are lower in females compared with male adult GHD patients. (ii) IGF-I/GHBP has a high diagnostic sensitivity of adult GHD, in particular in women. (iii) We hypothesize that the gender difference in IGF-I levels among adult GHD patients are causally related to the very low androgen levels observed among females.     

A paradoxical gender dissociation within the growth hormone/insulin-like growth factor I axis during protracted critical illness

Female gender appears to protect against adverse outcome from prolonged critical illness, a condition characterized by blunted and disorderly GH secretion and impaired anabolism. As a sexual dimorphism in the GH secretory pattern of healthy humans and rodents determines gender differences in metabolism, we here compared GH secretion and responsiveness to GH secretagogues in male and female protracted critically ill patients. GH secretion was quantified by deconvolution analysis and approximate entropy estimates of 9-h nocturnal time series in 9 male and 9 female patients matched for age (mean +/- SD, 67+/-11 and 67+/-15 yr), body mass index, severity and duration of illness, feeding, and medication. Serum concentrations of PRL, TSH, cortisol, and sex steroids were measured concomitantly. Serum levels of GH-binding protein, insulin-like growth factor I (IGF-I), IGF-binding proteins (IGFBPs), and PRL were compared with those of 50 male and 50 female community-living control subjects matched for age and body mass index. In a second study, GH responses to GHRH (1 microg/kg), GH-releasing peptide-2 (GHRP-2; 1 microg/ kg) and GHRH plus GHRP-2 (1 and 1 microg/kg) were examined in comparable, carefully matched male (n = 15) and female (n = 15) patients. Despite identical mean serum GH concentrations, total GH output, GH half-life, and number of GH pulses, critically ill men paradoxically presented with less pulsatile (mean +/- SD pulsatile GH fraction, 39+/-14% vs. 67+/-20%; P = 0.002) and more disorderly (approximate entropy, 0.946+/-0.113 vs. 0.805+/-0.147; P = 0.02) GH secretion than women. Serum IGF-I, IGFBP-3, and acid-labile subunit (ALS) levels were low in patients compared with controls, with male patients revealing lower IGF-I (P = 0.01) and ALS (P = 0.005) concentrations than female patients. Correspondingly, circulating IGF-I and ALS levels correlated positively with pulsatile (but not with nonpulsatile) GH secretion. Circulating levels of GH-binding protein and IGFBP-1, -2, and -6 were higher in patients than controls, without a detectable gender difference. In female patients, PRL levels were 3-fold higher, and TSH and cortisol tended to be higher than levels in males. In both genders, estrogen levels were more than 3-fold higher than normal, and testosterone (2.25+/-1.94 vs. 0.97+/-0.39 nmol/L; P = 0.03) and dehydroepiandrosterone sulfate concentrations were low. In male patients, low testosterone levels were related to reduced GH pulse amplitude (r = 0.91; P = 0.0008). GH responses to GHRH were relatively low and equal in critically ill men and women (7.3+/-9.4 vs. 7.8+/-4.1 microg/L; P = 0.99). GH responses to GHRP-2 in women (93+/-38 microg/L) were supranormal and higher (P<0.0001) than those in men (28+/-16 microg/L). Combining GHRH with GHRP-2 nullified this gender difference (77+/-58 in men vs. 120+/-69 microg/L in women; P = 0.4). In conclusion, a paradoxical gender dissociation within the GH/ IGF-I axis is evident in protracted critical illness, with men showing greater loss of pulsatility and regularity within the GH secretory pattern than women (despite indistinguishable total GH output) and concomitantly lower IGF-I and ALS levels. Less endogenous GHRH action in severely ill men compared with women, possibly due to profound hypoandrogenism, accompanying loss of the putative endogenous GHRP-like ligand action with prolonged stress in both genders may explain these novel findings.     

Responses of the growth hormone (GH) and insulin-like growth factor axis to exercise, GH administration, and GH withdrawal in trained adult males: a potential test for GH abuse in sport.

GH abuse by elite athletes is currently undetectable. To define suitable markers of GH doping, we assessed the effects of acute exercise, GH administration, and GH withdrawal on the GH/insulin-like growth factor (IGF) axis in athletic adult males. Acute endurance-type exercise increased serum GH, GH-binding protein (GHBP), total IGF-I, IGF-binding protein (IGFBP)-3, and acid-labile subunit (ALS), each peaking at the end of exercise. IGFBP-1 increased after exercise was completed. Free IGF-I did not change with exercise. Recombinant human GH treatment (0.15 IU/kg x day) for 1 week increased serum total IGF-I, IGFBP-3, and ALS, exaggerating the responses to exercise. IGFBP-2 and IGFBP-1 were trivially suppressed. After GH withdrawal, the GH response to identical exercise was suppressed. Total IGF-I, IGFBP-3, and ALS returned to baseline over 3-4 days. In summary, 1) acute exercise transiently increased all components of the IGF-I ternary complex, possibly due to mobilization of preformed intact complexes; 2) GH pretreatment augmented the exercise-induced changes in ternary complexes; 3) postexercise IGFBP-1 increments may protect against delayed onset hypoglycemia; 4) serum total IGF-I, IGFBP-3, and ALS may be suitable markers of GH abuse; and 5) differences in disappearance times altered the sensitivity of each marker for detecting GH abuse.     

Monitoring serum insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), IGF-I/IGFBP-3 molar ratio and leptin during growth hormone treatment for disordered growth

OBJECTIVE: Serum IGF-I levels are monitored during GH replacement treatment in adults with GH deficiency (GHD) to guide GH dose adjustment and to minimize occurrence of GH-related side-effects. This is not routine practice in children treated with GH. The aim of this study was to evaluate changes in (1) serum IGF-I, IGFBP-3 and IGF-I/IGFBP-3 molar ratio, and (2) serum leptin, an indirect marker of GH response, during the first year of GH treatment in children with disordered growth. DESIGN: An observational prospective longitudinal study with serial measurements at five time points during the first year of GH treatment was carried out. Each patient served as his/her own control. PATIENTS: The study included 31 patients, grouped as (1) GHD (n = 20) and (2) non-GHD (Turner syndrome n = 7; Noonan syndrome n = 4), who had not previously received GH treatment. MEASUREMENTS: Serum IGF-I, IGFBP-3 and leptin levels were measured before treatment and after 6 weeks, 3 months, 6 months and 12 months of GH treatment, with a mean dose of 0.5 IU/kg/wk in GHD and 0.7 IU/kg/wk in non-GHD groups. IGF-I, IGFBP-3 and the calculated IGF-I/IGFBP-3 molar ratio were expressed as SD scores using reference values from the local population. RESULTS: In the GHD group, IGF-I SDS before treatment was lower compared with the non-GHD (-5.4+/-2.5 vs. -1.8+/-1.0; P<0.001). IGF-I (-1.8 SDS +/- 2.2) and IGFBP-3 (-1.1 SDS +/- 0.6) levels and their molar ratios were highest at 6 weeks and remained relatively constant thereafter. In the non-GHD group, IGF-I levels increased throughout the year and were maximum at 12 months (0.3 SDS +/- 1.4) while IGFBP-3 (1.1 SDS +/- 0.9) and IGF-I/IGFBP-3 molar ratio peaked at 6 months. In both groups, IGF-I SDS and IGF-I/IGFBP-3 during treatment correlated with the dose of GH expressed as IU/m2/week (r-values 0. 77 to 0.89; P = 0.005) but not as IU/kg/week. Serum leptin levels decreased significantly during GH treatment in the GHD (median before treatment 4.0 microg/l; median after 12 months treatment 2.4 microg/l; P = 0.02) but not the non-GHD (median before treatment 3.0 microg/l; median after 12 months treatment 2.6 microg/l). In the GHD group, serum leptin before treatment correlated with 12 month change in height SDS (r = 0.70, P = 0.02). CONCLUSIONS: The pattern of IGF-I, IGFBP-3 and their molar ratio during the first year of GH treatment differed between the GHD and non-GHD groups. Calculation of GH dose by surface area may be preferable to calculating by body weight. As a GH dose-dependent increase in serum IGF-I and IGF-I/IGFBP-3 may be associated with adverse effects, serum IGF-I and IGFBP-3 should be monitored routinely during long-term GH treatment. Serum leptin was the only variable that correlated with first year growth response in GHD.     

Body composition and circulating levels of insulin, insulin-like growth factor-binding protein-1 and growth hormone (GH)-binding protein affect the pharmacokinetics of GH in adults independently of age

The aim of our study was to scrutinize the association among age, body composition, and GH status in healthy adults. Using two-step, primed constant infusions of GH during suppression of endogenous GH secretion with octreotide in a group of 26 healthy nonobese men [mean age, 37.3 yr (range, 22-55 yr); body mass index, 24.6 +/- 0.4 kg/m(-2)] we investigated the contributions of age, body composition, insulin, and binding proteins to the variability in the pharmacokinetics and acute actions of GH. All subjects were investigated twice, with the infusion rates of GH calculated according to either total body weight or intraabdominal fat mass. Body composition was determined using computed tomography and bioimpedance measurements. There was no correlation between age and body weight, yet strong positive correlations were observed between age and intraabdominal fat area (r = 0.78; P < 0.0001) and waist to hip ratio (r = 0.71; P < 0.0001) and to a lesser degree to sc fat area (r = 0.42; P < 0.03). The between-subject variability in steady state GH levels was significantly larger when GH was administered per cm(2) intraabdominal fat area than per kg BW (P < 0.001). During primed constant infusions of GH at rates of 1.5 and 3.0 microg/kg x h, the corresponding MCRs of GH were 148.8 +/- 5.4 and 89.8 +/- 2.4 ml/min x m(-2), respectively, and the MCRs were inversely related to the achieved steady state GH levels (P < 0.0001). The MCR was unrelated to age, but was negatively correlated to baseline concentrations of IGF-binding protein-1 (IGFBP-1; r = -0.53, P < 0.01) and positively correlated to basal levels of insulin (r = 0.46; P < 0.05), GH-binding protein (GHBP; r = 0.52; P < 0.01), IGFBP-3 (r = 0.47; P < 0.05), and total body fat (r = 0.44; P < 0.05). GH infusion caused significant changes in the concentrations of IGF-I, free fatty acids, GHBP, IGFBP-1, and insulin, but none of these effects was correlated to age. Based on our results we conclude that 1) the clearance of GH is concentration dependent; 2) the pharmacokinetics and acute effects of GH are not affected by age per se; and 3) basal levels of insulin, IGFBP-1, and GHBP as well as age-related changes in body composition are important predictors of GH pharmacokinetics.     

Growth hormone-binding protein is directly and IGFBP-3 is inversely associated with risk of female breast cancer

OBJECTIVE: Several components of the GH and IGF systems have been implicated in the development of malignancies. All components of these hormonal systems have never been jointly evaluated in female breast cancer, and previous studies have not examined the role of IGF-binding proteins (IGFBP-4, IGFBP-6) or GH-binding protein (GHBP). DESIGN: Hospital-based case-control study. METHODS: In this sample of primarily postmenopausal women, we obtained serum measures of IGF-I, IGF-II, and binding proteins IGFBP-1, IGFBP-3, IGFBP-4, IGFBP-6, as well as GHBP, insulin, and leptin from 74 breast cancer cases and 76 control subjects. RESULTS: In crude analyses, we found lower age-standardized mean IGF-I, IGFBP-3, IGFBP-4, IGFBP-6, and higher IGFBP-1 and GHBP in breast cancer cases when compared with controls. Multivariate models mutually adjusted for other GH-IGF system components and classical breast cancer risk factors demonstrated an inverse association between IGFBP-3 and risk of breast cancer (odds ratio (OR) = 0.2, P < 0.01) and a direct association between GHBP and disease risk (OR = 3.3, P < 0.01). No significant associations were detected in multivariate analyses among IGF-I, IGF-II or IGFBP-1, IGFBP-4, IGFBP-6 with risk of breast cancer, indicating that these factors may not have effects independent of and/or comparable with IGFBP-3 and GHBP. CONCLUSIONS: These results support a protective role of IGFBP-3 and demonstrate for the first time an increased risk of breast cancer with higher GHBP, after accounting for variation in IGFs, IGFBPs, and classical breast cancer risk factors.     

Expression of serum insulin-like growth factors, insulin-like growth factor-binding proteins, and the growth hormone-binding protein in heterozygote relatives of Ecuadorian growth hormone receptor deficient patients.

Recently, an isolated population of apparent GH-receptor deficient (GHRD) patients has been identified in the Loja province of southern Ecuador. These individuals presented many of the physical and biochemical phenotypes characteristic of Laron-Syndrome and are believed to have a defect in the GH-receptor gene. In this study, we have compared the biochemical phenotypes between the affected individuals and their parents, considered to be obligate heterozygotes for the disorder. Serum GH, insulin-like growth factor I and II (IGF-I and IGF-II) levels were measured by RIA Insulin-like growth factor binding proteins. (IGFBPs) were measured by Western ligand blotting (WLB) of serum samples, following separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and relative quantitation of serum IGFBPs was performed with a scanning laser densitometer. Serum GH-binding protein (GHBP) levels were measured with a ligand-mediated immunofunctional assay using a monoclonal antibody raised against the GHBP. These values were then compared to values obtained from normal, sex-matched adult Ecuadorian controls, to determine if the above parameters were abnormal in the heterozygotes. The serum IGF-I levels of the GHRD patients were less than 13% of control values for adults and 2% for children. However, the IGF-I levels of both the mothers and fathers were not significantly different from that of the control population. The serum IGF-II levels of the GHRD patients were approximately 20% of control values for adults and 12% for the children. The IGF-II levels of the mothers were reduced, but were not significantly different from that of the control population. However, IGF-II levels of the fathers were significantly lower than those of controls (64% of control male levels). WLB analysis of serum IGFBP levels of the affected subjects demonstrated increased IGFBP-2 and decreased IGFBP-3, suggesting an inverse relationship between these IGFBPs. The GHRD patients who had the lowest serum IGFBP-3 levels (as measured by WLB) demonstrated a serum protease activity that could proteolyze 125I-IGFBP-3. GHRD patients who had higher serum IGFBP-3 levels lacked this serum protease activity. There were no differences in the serum IGFBP profiles of the mothers or the fathers for either IGFBP-2 or IGFBP-3, and serum from both groups lacked the ability to significantly proteolyze 125I-IGFBP-3. While GHRD patients had very low levels of serum GHBP, some patients did have measurable GHBP levels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Leptin does not mediate short-term fasting-induced changes in growth hormone pulsatility but increases IGF-I in leptin deficiency states

CONTEXT: States of acute and chronic energy deficit are characterized by increased GH secretion and decreased IGF-I levels. Objective: The objective of the study was to determine whether changes in levels of leptin, a key mediator of the adaptation to starvation, regulate the GH-IGF system during energy deficit. DESIGN, SETTING, PATIENTS, AND INTERVENTION: We studied 14 healthy normal-weight men and women during three conditions: baseline fed and 72-h fasting (to induce hypoleptinemia) with administration of placebo or recombinant methionyl human leptin (r-metHuLeptin) (to reverse the fasting associated hypoleptinemia). We also studied eight normal-weight women with exercise-induced chronic energy deficit and hypothalamic amenorrhea at baseline and during 2-3 months of r-metHuLeptin treatment. MAIN OUTCOME MEASURES: GH pulsatility, IGF levels, IGF and GH binding protein (GHBP) levels were measured. RESULTS: During short-term energy deficit, measures of GH pulsatility and disorderliness and levels of IGF binding protein (IGFBP)-1 increased, whereas leptin, insulin, IGF-I (total and free), IGFBP-4, IGFBP-6, and GHBP decreased; r-metHuLeptin administration blunted the starvation-associated decrease of IGF-I. In chronic energy deficit, total and free IGF-I, IGFBP-6, and GHBP levels were lower, compared with euleptinemic controls; r-metHuLeptin administration had no major effect on GH pulsatility after 2 wk but increased total IGF-I levels and tended to increase free IGF-I and IGFBP-3 after 1 month. CONCLUSIONS: The GH/IGF system changes associated with energy deficit are largely independent of leptin deficiency. During acute energy deficit, r-metHuLeptin administration in replacement doses blunts the starvation-induced decrease of IGF-I, but during chronic energy deficit, r-metHuLeptin administration increases IGF-I and tends to increase free IGF-I and IGFBP-3.     

Effect of growth hormone administration frequency on 24-hour growth hormone profiles and levels of other growth related parameters in girls with Turner's syndrome*

OBJECTIVE The optimal dose and frequency of GH administration in Turner's syndrome is unknown. There is some evidence that a schedule which mimics normal pulsatile GH secretion may be more effective than a single dally dose. We therefore wished to study the influence of the frequency of GH administration on 24-hour GH profiles and levels of other growth-related factors in Turner's syndrome. DESIGN Four weeks after initiation of 005 μg/kg/day ethinyl oestradiol, we compared twice daily (b.I.d.-fractionated dose) with once daily (o.d.) s.c. injections of 6 IU GH/m2/day in a 2-week cross-over design with a 2-week washout Interval. Each treatment period was concluded with 24-hour GH profile tests. Pretreatment plasma/serum levels of GH, IGF-I, binding proteins for GH (GHBP) and IGF-I (IGFBP-3) were used as a basis for comparison of the levels found after each regimen. A one-compartment open model was used for estimation of pharmacokinetic parameters. SUBJECTS Ten previously untreated girls with Turner's syndrome aged 11 years. MEASUREMENTS Plasma levels of GHBP by standardized binding assay; GH, IGF-I, and IGFBP-3 serum/plasma levels by radioimmunoassay. RESULTS There were significantly higher maximum GH levels and a greater area under the curve with o.d. than with b.I.d. GH, while GH clearance was greater with b.I.d. The pharmacokinetic values with o.d. injections were in conformity with values for healthy and GH-deficient children. Pretreatment GHBP levels tended to be high compared with values in healthy prepubertal children. These levels decreased with GH therapy, significantly so with b.I.d. GH only. There was a significant increase in levels of IGF-I and IGFBP-3, irrespective of regimen. The IGF-I to IGFBP-3 ratio, a possible indicator of the growth response, rose significantly and comparably with both regimens. There was no consistent diurnal variation with either regimen in GHBP, IGF-I or IGFBP-3 levels. Four-hourly levels of GH, GHBP, IGF-I and IGFBP-3 were not correlated. CONCLUSIONS Although the 24-hour profiles differed during once or twice daily administration of the same total growth hormone dose, the diurnal pattern and mean levels of factors involved in the biological effects of GH are comparable for both regimens.     

Free rather than total circulating insulin-like growth factor-I determines the feedback on growth hormone release in normal subjects

Pituitary GH secretion is feedback regulated by circulating IGF-I. However, it remains to be determined whether the feedback control is mediated through circulating free or total IGF-I. To study this, we compared the temporal changes in circulating levels of GH vs. free and total IGF-I during fasting. Seventeen healthy normal-weight subjects (body mass index 23.4 +/- 0.6 kg/m(2)) were studied during 80 h of fasting. Serum was assayed for GH every 3 h; total, free, and bioactive IGF-I, IGF binding protein (IGFBP)-1, -2, and -3 as well as IGFBP-1 bound IGF-I were assayed every morning. During fasting, mean 24-h GH levels increased from 1.41 +/- 0.20 to 3.01 +/- 0.46 and 2.09 +/- 0.30 microg/liter (d 1 vs. d 2 and 3; P < 0.03). After 24 h of fasting, free and bioactive IGF-I had decreased by 40 +/- 5 and 17 +/- 5%, respectively (P < 0.02), and both concentrations remained suppressed for the rest of the study. In contrast, total IGF-I remained unchanged until the end of d 3, at which levels were slightly reduced (P < 0.007). IGFBP-1 increased from 38 +/- 2 to 137 +/- 24, 212 +/- 32, and 214 +/- 22 microg/liter (d 1 vs. d 2, d 3, and end of d 3; P < 0.0001), and these changes closely paralleled those of IGFBP-1-bound IGF-I (P < 0.0001). IGFBP-2 increased only transiently at d 2 (P < 0.05), and IGFBP-3 remained unchanged. The increase in mean 24-h GH levels from d 1 to d 2 correlated inversely with the relative reduction in free IGF-I from d 1 to d 2 (r = -0.51; P = 0.04), i.e. the larger the reduction in free IGF-I, the larger the increase in GH. None of the other IGF-related parameters correlated with GH. In conclusion, the temporal relationship between the increase in GH and the reduction in free IGF-I supports the hypothesis that circulating free IGF-I mediates the feedback regulation of GH secretion.     

Recombinant human insulin-like growth factor-I (rhIGF-I) therapy in adults with type 1 diabetes mellitus: effects on IGFs, IGF-binding proteins, glucose levels and insulin treatment

OBJECTIVE: Insulin-like growth factor-I (IGF-I) has both insulin-like and anabolic actions but unlike insulin, IGF-I circulates bound to a number of specific binding proteins that regulate its availability and activity. Patients with type 1 diabetes mellitus have low levels of circulating IGF-I despite increased growth hormone (GH) secretion, and are a group that may benefit from rhIGF-I therapy. Understanding the relationship between IGF-I and its binding proteins is necessary to appreciate the actions of exogenously administered rhIGF-I. Therefore, we examined the effects of 19 days' subcutaneous administration of rhIGF-I (50 micrograms/kg BID) on the levels of IGF-I, IGF-II and the IGF-binding proteins (IGFBPs), as well as the daily dose of insulin necessary to maintain glycaemic control in patients with type 1 diabetes mellitus. DESIGN AND PATIENTS: This was an open study, and the patients were studied initially while resident (days 1-5) in the hospital and thereafter (days 6-24) as outpatients. Serum was collected at baseline and at intervals throughout the study for the measurement of total IGF-I, IGF-II, IGFBP-1, -2, -3, free insulin and growth hormone (GH). Daily insulin doses and glucometer readings were recorded throughout the study. The changes in each of these variables were examined. The subjects were six adults (35.3 +/- 4.0 years, mean +/- SE), with type 1 diabetes, and all had reasonable glycaemic control (HbA1c 7.2 +/- 0.5%). RESULTS: rhIGF-I administration increased circulating total IGF-I over two-fold (15.3 +/- 1.9 vs. 33.7 +/- 5.4 nmol/l, mean +/- SEM, P < 0.01, day 1 vs. day 20) and decreased plasma IGF-II concentration (85.0 +/- 4.7 vs. 50.6 +/- 4.7 nmol/l, P < 0.01, day 1 vs. day 20). The dose of insulin required for adequate glycaemic control decreased significantly during rhIGF-I therapy (46 +/- 7 vs. 31 +/- 8 U/day, P < 0.05, day -1 vs. day 19), as did the fasting free insulin concentration (8.4 +/- 1.5 vs. 5.0 +/- 0.8 mU/l, P < 0.05, baseline vs. day 5). IGFBP-2 concentration increased (388 +/- 115 vs. 758 +/- 219 micrograms/l, P < 0.05, day 1 vs. day 20), but IGFBP-1 and IGFBP-3 were unchanged during rhIGF-I treatment. Mean nocturnal GH concentration decreased (12.7 +/- 3.3 vs. 3.8 +/- 0.9 mU/l, P = 0.05) after 4 days' rhIGF-I therapy. CONCLUSION: Twice daily rhIGF-I therapy in adults with type 1 diabetes resulted in an increase in circulating IGF-I with a reciprocal decrease in IGF-II, and a marked elevation of IGFBP-2 concentration. The levels of IGFBP-1 and -3 were not dramatically changed despite a reduction in the concentration of serum free insulin, and a large decrease in the requirement for insulin. The mechanisms behind these changes remains unclear but alterations in circulating levels of of IGFBPs may alter IGF-I bioactivity. If rhIGF-I is to have an application in the management of adults with type 1 diabetes, further work is necessary to determine the metabolic consequences of the alterations seen in the IGFs and their binding proteins following rhIGF-I administration.