Serum GH-binding Protein Levels Research Articles

Measurement of growth hormone-binding protein in the rat by a ligand immunofunctional assay.

We have developed a ligand immunofunctional assay (LIFA) for quantifying the circulating functional GH-binding protein (GHBP) in the rat. This two-site solid-phase assay uses a capture monoclonal antibody (4.3) specific to the hydrophilic C-terminal segment of rat GHBP (rGHBP), saturation of binding with human GH, and a detection system of rabbit antihuman GH polyclonal antibody and peroxidase-conjugated antirabbit immunoglobulin G antibody. Results were compared with Scatchard estimates derived by immuno-precipitation with monoclonal antibody 4.3. This assay was used to determine the GHBP levels in male and female rats and to investigate the diurnal properties and dynamics of GH and GHBP interaction in 15-min blood sampling over a 6-h period. The dynamic range of the rLIFA was 0.15-20.0 nM recombinant rGHBP, with intraassay and interassay coefficients of variation of 10.5% (n = 20) and 12.9% (n = 12), respectively. Serum GHBP levels determined by the rLIFA and those derived from Scatchard estimates were strongly correlated (n = 8; beta = 0.55; r2 = 0.89; P = 0.0005). Male rats had lower GHBP levels (6.5 +/- 0.7 nM; mean +/- SE; n = 14) than female rats (35.4 +/- 2.7 nM; n = 15; P = 0.0001). In the diurnal study, male rats had higher GH peaks (312.5 +/- 121.6 ng/ml; n = 7) than female rats (96.5 +/- 15.4 ng/ml; n = 9; P < 0.0001). In contrast to the pulsatile secretion of GH, GHBP levels in both sexes remained stable and showed no relationship to secretory pulses of GH. However, the GH bursts significantly altered the distribution of the GH-GHBP complex in male rats. By saturation and mass analysis, the greater GH pulsatile secretion in male rats resulted in occupancy of GHBP from less than 5% at nadir to about 80% at secretory peaks, in contrast to the less than 5-15% range of GHBP occupancy in female rats. In male rats, greater than 80% of GH at secretory peaks existed in the free form, whereas in female rats, 16-23% of GH existed in the free form during pulsatile secretion. In summary, the rLIFA shows good correlation to Scatchard analysis using an identical antibody. We conclude that this assay provides a rapid, sensitive, and accurate measurement of the circulating functional GHBP in the rat, and that it facilitates the study of GH and GHBP dynamics under a range of physiological conditions.

Disturbances in growth hormone secretion and action in adolescents with anorexia nervosa

Women in whom anorexia nervosa develops during adolescence have failure of linear growth associated with low levels of insulin-like growth factor I (IGF-I). To investigate the pathophysiology of growth retardation in adolescents with anorexia nervosa, we measured basal growth hormone (GH), growth hormone-binding protein (GHBP), IGF-I, and insulin-like growth factor binding protein-3 (IGFBP-3) in three groups of patients: (1) 28 recently hospitalized female adolescents with anorexia nervosa, (2) 23 of the same patients after partial weight restoration, and (3) 28 healthy control subjects matched for age, sex, and pubertal stage. Fasting GH levels in group 1 did not differ significantly from those in group 3. In contrast, serum GHBP ( p <0.001), IGF-I ( p<0.001), and IGFBP-3 ( p <0.01) were significantly lower in group 1 than in group 3. Serum GHBP and IGFBP-3 levels were positively correlated with body mass index. Serum GHBP levels were low in patients in all five pubertal stages and even in those shown to have adequate GH secretion. In group 2 (after refeeding) the serum IGF-I concentration increased significantly and GHBP and IGFBP-3 returned to normal. We conclude that patients with anorexia nervosa have diminished GH action resulting in decreased secretion of IGF-I. The positive correlation with body mass index and the reversibility with refeeding suggest that these changes are secondary to malnutrition. Altered GH function that occurs during the years of active growth can explain the growth retardation seen in anorexia nervosa. (J P EDIATR 1994;125:655-60)

Dexamethasone increases growth hormone receptor messenger ribonucleic acid levels in liver and growth plate

Glucocorticoid inhibits linear growth and renders target tissues, particularly liver and growth plate, insensitive to GH. We hypothesized that glucocorticoid-induced GH insensitivity is due to decreased gene expression of the GH receptor at the messenger RNA (mRNA) level. To test this hypothesis, we treated 4.5-wk-old male rabbits (n = 6-9 per group) with ip dexamethasone or vehicle and measured GH receptor mRNA levels (by RNase protection assay) and serum GH-binding protein levels (by radioimmunoprecipitation assay). Contrary to our hypothesis, dexamethasone administered in growth-suppressing doses did not decrease GH receptor mRNA levels in liver or growth plate. Instead a tissue-specific stimulation of GH receptor mRNA levels was observed. The dose-response relationship of this effect was biphasic, since the lower growth-suppressing dose of dexamethasone (0.1 mg/kg.day) caused the greater increase in GH receptor mRNA levels, whereas the higher growth-suppressing dose (4 mg/kg.day) had less effect. The dexamethasone-induced increase in GH receptor mRNA was observed in growth plate and liver, target tissues important for linear growth, but not in kidney. Serum GH-binding protein levels also showed a stimulatory response to dexamethasone treatment, with a biphasic dose-response relationship. These data suggest that glucocorticoid-induced GH insensitivity cannot be explained by decreased GH receptor mRNA levels. To the contrary, dexamethasone causes a tissue-specific stimulation in GH receptor mRNA levels with a biphasic dose-response relationship.

Dexamethasone increases growth hormone receptor messenger ribonucleic acid levels in liver and growth plate.

Glucocorticoid inhibits linear growth and renders target tissues, particularly liver and growth plate, insensitive to GH. We hypothesized that glucocorticoid-induced GH insensitivity is due to decreased gene expression of the GH receptor at the messenger RNA (mRNA) level. To test this hypothesis, we treated 4.5-wk-old male rabbits (n = 6-9 per group) with ip dexamethasone or vehicle and measured GH receptor mRNA levels (by RNase protection assay) and serum GH-binding protein levels (by radioimmunoprecipitation assay). Contrary to our hypothesis, dexamethasone administered in growth-suppressing doses did not decrease GH receptor mRNA levels in liver or growth plate. Instead a tissue-specific stimulation of GH receptor mRNA levels was observed. The dose-response relationship of this effect was biphasic, since the lower growth-suppressing dose of dexamethasone (0.1 mg/kg.day) caused the greater increase in GH receptor mRNA levels, whereas the higher growth-suppressing dose (4 mg/kg.day) had less effect. The dexamethasone-induced increase in GH receptor mRNA was observed in growth plate and liver, target tissues important for linear growth, but not in kidney. Serum GH-binding protein levels also showed a stimulatory response to dexamethasone treatment, with a biphasic dose-response relationship. These data suggest that glucocorticoid-induced GH insensitivity cannot be explained by decreased GH receptor mRNA levels. To the contrary, dexamethasone causes a tissue-specific stimulation in GH receptor mRNA levels with a biphasic dose-response relationship.

Clinical Significance of Growth Hormone-Binding Protein Measurements in Children

To investigate the role of growth hormone (GH) and its downstream axis in normal growth and growth disorders, we measured serum GH-binding protein (GHBP) levels in children by ligand-mediated immunofunctional assay (LIFA). Samples were taken from 512 healthy children of normal stature, 146 healthy neonates, 153 short but otherwise normal children, and 27 patients with GH deficiency. Serum GHBP showed no significant diurnal variation. Serum GHBP levels were low in neonates, acutely rose within 6 months, and gradually increased toward midpuberty in normal children (r = 0.2, P < 0.01, assessed among subjects over 1 year old). Neither significant sexual dimorphism nor rapid pubertal changes were observed. In normal short children and patients with GH deficiency, GHBP was lower than normal, but not significant. These data suggest that one of the etiologies for growth disorder in children could be resistance to, or low efficacy for, utilization of GH.

Growth hormone-binding proteins during human pregnancy: maternal, fetal and neonatal data.

Serum levels of growth hormone-binding protein (GHBP) were measured by high-performance liquid chromatography (HPLC) gel filtration in serum of 30 pregnant women and in cord serum of 69 preterm and term infants. In pregnant women, the mean +/- SD serum level of GHBP was 32.4% +/- 5.6%. Polynomial regression analysis showed a significant (P = 0.01) second-order relationship between the duration of pregnancy and serum GHBP levels, with increasing levels during the first half of pregnancy and decreasing levels thereafter. In cord serum, the mean +/- SD serum level of GHBP was 3.1% +/- 1.4% (n = 51) in preterm and 4.2% +/- 1.3% (n = 18) in term neonates. Serum GHBP concentrations were related to gestational age (r = 0.35; P < 0.005) and to intrauterine nutritional state as evaluated by the ponderal index (r = 0.30; P < 0.02). In four term neonates, serum levels of GHBP were measured before and after an exchange transfusion (ET). Before the ET the serum GHBP level was 6.7% +/- 2.4% and at the end it was 25.3% +/- 2.6%. Thereafter, serum GHBP levels decreased slowly. Analysis of the elimination curve by exponential stripping showed a biexponential elimination pattern: GHBP (%) = 40.e(-5.1E-03 x time) + 64.e(-2.5E-04 x time). The serum half-life of the GHBP complex was estimated to be about 2 days.

Growth Hormone-Binding Protein Measurements in Normal Children and Children with Short Statute Using Ligand-Mediated Immunofunctional Assay

To investigate the role of growth hormone (GH) and its downstream axis in normal growth and growth disorders, we measured serum GH-binding protein (GHBP) levels in normal children and children with short stature by ligand-mediated immunofunctional assay (LIFA). Samples were obtained from 512 healthy children with normal stature, 146 5-day-old healthy neonates, and 153 short children with normal GH secretion (normal short children). Serum GHBP showed significant correlation with percent overweight (r=0.71, P<0.01) in normal children. Diurnal variations in serum GHBP were scarcely observed. Serum GHBP levels were low in neonates, rose acutely within 6 months, and gradually increased toward pubertal age in normal children (r=0.2, P<0.01, assessed among subjects over 1 year old). Neither significant sex differences nor rapid peaked changes during puberty were observed. In normal short children, GHBP levels were lower than in normal controls.These data suggest resistance to GH or low efficacy of GH utilization could be one of the etiologies of growth disorder in normal short children.

Normative data for insulin-like growth factors (IGFs), IGF-binding proteins, and growth hormone-binding protein in a healthy Spanish pediatric population: age- and sex-related changes.

The normal values of insulin-like growth factors (IGFs) after extraction, their binding proteins, and the high affinity GH-binding protein are not well established in infancy or childhood. We report the relationship between serum IGF-I, IGF-II, their binding proteins IGFBP-1 and IGFBP-3, and GH-binding protein in 600 normal Spanish children who were divided into 5 groups according to Tanner stage: I, 150 males and 102 females; II, 40 males and 42 females; III, 45 males and 45 females; IV, 42 males and 55 females; and V, 23 males and 56 females. Serum IGF-I levels increase slowly during childhood in both sexes, exhibiting a dramatic increase during puberty and a significant decline [P < 0.001, by analysis of variance (ANOVA)] during adulthood. The pubertal peak occurs approximately 2 yr earlier in girls than in boys. In contrast, serum IGF-II levels remain stable throughout childhood, showing no pubertal peak. In boys, there is a significant decline in IGF-II levels during adulthood (P < 0.001). Serum IGFBP-3 levels show a pattern similar to that of IGF-I, with a significant increase during childhood and a significant decline during adulthood (P < 0.001, ANOVA) in both males and females. In contrast, serum IGFBP-1 levels decrease dramatically during childhood in both boys and girls (P < 0.001 and P < 0.005, respectively, by ANOVA). A significant decline in serum GH-binding protein levels is observed between prepubertal and pubertal children of both sexes (P < 0.001). There is a close linear correlation between the sum of serum IGF-I plus IGF-II levels vs. serum IGFBP-3 (r = 0.724; P < 0.0001). In contrast, there is a nonlinear correlation between serum IGF-I vs. serum IGFBP-3 (concave curve) as well as between serum IGF-II and serum IGFBP-3 (convex curve). A negative correlation was found between serum IGF-I vs. IGFBP-1 (r = -0.51; P < 0.0001) as well as between the sum of serum IGF-I plus IGF-II vs. IGFBP-1 (r = -0.47; P < 0.0001), but not between serum IGF-II and IGFBP-1. These data emphasize that when these tests are performed in the clinic, their interpretation should be based upon age- and sex-specific criteria.

A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. I. Serum growth hormone-binding protein.

Previous studies have provided compelling evidence that GH secretion increases transiently during midpuberty in normally growing children. Although it is likely that the increase in GH production serves a primary role in generating the pubertal growth spurt, such a conclusion necessarily assumes that other essential "down-stream" components of the GH axis responsible for mediating the effects of GH remain unchanged. To investigate this concept, we assessed longitudinally another important component of the endogenous GH axis, the serum GH-binding protein (GHBP)/receptor system, in a cohort of 11 normal boys as they matured through normal puberty. At 4-month intervals over 4.0-5.1 yr, 24-h serum GH concentration profiles and serum GHBP activity were evaluated. Serum GHBP levels varied over a more than 12-fold range (40-504 pmol/L) among all subjects. However, the values for individual subjects consistently varied within more narrow limits. The coefficient of variation for values from all subjects was 51% compared to the mean intrasubject coefficient of variation of only 30% (P < 0.05). Although the highest GHBP level (all subjects) was 12.6-fold greater than the lowest, the mean intrasubject range was only 3.1 +/- 0.5-fold (P < 0.05). The overall mean serum GHBP level correlated directly with the overall mean body mass index (r = 0.69; P = 0.018), but correlated inversely with the mean 24-h GH concentration (r = -0.61; P < 0.05). There was no significant increase in the GHBP level during puberty. However, because mean 24-h GH concentrations did increase during midpuberty, the data suggest that an increase in the relative amounts of free vs. bound GH develops during the period of the pubertal growth spurt. These data indicate that serum GHBP levels are regulated in individual children within much more narrow limits than those present in the larger population and do not undergo the dramatic changes during puberty typical of GH secretion and linear growth velocity. As a consequence, alterations may develop in the relative amounts of free vs. bound GH present in serum during the midpubertal years compared to those present during either the prepubertal or postpubertal periods. The majority of the known age-related increase in serum GHBP levels probably occurs before the period of active pubertal development. These findings strengthen further the concept that the midpubertal changes in GH secretion serve a primary role in generating the growth spurt.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormone-binding protein (GH-BP) levels in follicular fluid from human preovulatory follicles: correlation with serum GH-BP levels.

Serum GH-binding protein (GH-BP), which is identical with the extracellular domain of the GH-receptor, has important implications for the distribution and physiological activity of GH and may enable evaluation of GH-receptor function. Recent studies suggest that GH plays an important role in the modulation of ovarian function and GH-receptors/BPs are found in the female reproductive system. The purpose of the present study was to investigate the presence of GH-BP in human follicular fluid (FF) and compare the levels of FF GH-BP with those detectable in serum, in 46 women undergoing in vitro fertilization. Levels of GH-BP were determined by incubation of [125I]hGH with 50 microL FF or serum, in the absence or presence of excess hGH and specific binding was expressed as a percentage of the total counts per min incubated. The mean GH-BP level in patient FF was 12.39 +/- 0.63% (mean +/- SE) and this correlated significantly with serum GH-BP levels (r = 0.82; P < 0.001). The binding of hGH to FF was dose dependent, highly specific, and of high affinity and low capacity. The affinity constants (Ka) obtained by Scatchard analysis for hGH binding to patient's FFs and sera were not significantly different. Furthermore, we have analyzed the sodium dodecyl sulfate gel electrophoretic pattern of GH-BP in FF and serum by both the ligand-blot technique and after cross-linking with [125I]hGH. Our results show that there is close similarity between serum and FF GH-BPs. Significantly lower FF GH-BP levels were measured in patients older than 36 yr compared to younger women (P < 0.05), whereas increased values were obtained both in patients with elevated E2 concentrations in serum (> 7000 pmol/L) and in FF (> 2200 nmol/L), (P < 0.02 and P < 0.05, respectively). This first demonstration of GH-BP in FF is expected to increase our understanding of the possible direct effect of GH on ovarian steroidogenesis, and suggests a possible regulatory role for GH-BP in folliculogenesis.

Growth hormone-binding protein (GH-BP) levels in follicular fluid from human preovulatory follicles: correlation with serum GH-BP levels

Growth hormone-binding protein (GH-BP) levels in follicular fluid from human preovulatory follicles: correlation with serum GH-BP levels

Growth hormone insensitivity associated with elevated circulating growth hormone-binding protein in children with Alagille syndrome and short stature.

The purpose of this study was to assess GH sensitivity in children with Alagille syndrome (syndromic intrahepatic bile duct paucity) by examining their response to short term administration of recombinant human GH (rhGH). Serum levels of insulin-like growth factor-I (IGF-I) were low despite elevated overnight integrated serum GH concentrations. Administration of rhGH (0.05 mg/kg.day for 3 days) to four growth-retarded children with Alagille syndrome did not significantly alter the serum concentrations of IGF-I and insulin, blood urea nitrogen, or urinary calcium excretion. In contrast, circulating IGF-I increased 2-fold in two children with Alagille syndrome and normal stature. In the control group, consisting of seven prepubertal children with GH deficiency, the predicted changes in response to rhGH in serum concentrations of IGF-I and insulin, urea nitrogen, and urinary calcium excretion were observed. Serum GH-binding protein levels, measured by a ligand-mediated immunofunctional assay, were significantly higher in children with Alagille syndrome than in children with cirrhosis or GH deficiency. We conclude that growth-retarded children with Alagille syndrome are insensitive to GH. The growth disturbances and metabolic defects may be due in part to failure to increase IGF-I concentrations in response to GH, implying that growth-retarded children with Alagille syndrome may benefit from IGF-I treatment.

SERUM GH-BINDING PROTEIN BEFORE AND AFTER LIVER TRANSPLANTATION IN CHILDREN WITH CONGENITAL BILIARY ATRESIA

Changes of serum GH-binding protein (GHBP) levels in children with congenital biliary atresia were studied before and after living related liver transplantation (LT). Of 6 children, 3 showed growth retardation (less than −2 SDS of height) before LT. All of them were free from post-operative complication. Steroids were discontinued within the first 3 months. Blood samples were drawn before LT, 1, and 6 months after LT for determination of GHBP levels (ligand mediated immunofunctional assay) and plasma IGF-I levels (RIA, direct method). Preoperative GHBP levels were reduced for their age in 3 of the 6 patients, and IGF-I levels were less than 0.22 U/ml in all 6 children. No correlation was found neither between preoperative height SDS and preoperative GHBP level, nor between the former and preoperative IGF-I level. In the three children with decreased GHBP levels preoperatively, GHBP levels increased markedly a month after LT and stayed normal at 6 months. In the remaining 3 children with normal preoperative GHBP levels, two showed normal values throughout the observation period but one showed reduced serum GHBP level at 6 months after LT. Post-transplantation IGF-I levels were more than 10 times at one month and more than 4 times at 6 months compared with those of pre-transplantation in all but one patient. Height SDS evaluated at 6 months improved in 5 of 6 children. The patient who showed reduced GHBP level could not undergo postoperative catch-up growth in spite of the increased IGF-I level at 6 months. These findings suggest that the increase of GHBP and IGF-I after liver transplantation might reflect the regeneration of transplanted liver as well as the metabolic improvement. Long term observation would be necessary for evaluation of GHBP as an indicator of catch-up growth after liver transplantation.

Growth hormone-binding protein in partially hepatectomized rats.

The role of the liver in regulating serum growth hormone-binding protein (GH-BP) was studied. We measured rat serum GH-BP and insulin-like growth factor 1 (IGF-1) 30 min to 96 h after 70% partial hepatectomy (PHP) or sham operation in adult male rats. Serum GH-BP declined sharply from 5.8 +/- 0.1% at baseline to 3.9 +/- 0.5% by 48 h following PHP. By 72 h serum GH-BP at baseline to 3.9 +/- 0.5% by 48 h following PHP. By 72 h serum GH-BP returned to baseline level and remained at that level 96 h postoperatively. In sham-operated female rats, serum GH-BP was about 2-fold higher than in males (10.5 +/- 1.46 versus 5.8 +/- 0.2%), whereas 24 h after hepatectomy a significant drop of about 50% was observed (p < 0.001). Serum IGF-1 decreased within 2-4 h postoperatively in both sham-operated and PHP groups, but thereafter was lower in the PHP rats, up to 48 h after operation, compared to sham-operated rats (p < 0.03). The study shows that the liver has an important role in the determination of serum GH-BP levels. The return to normal GH-BP level, even before the liver regained its full size following hepatectomy, suggests an increase in GH-BP production by the regenerating liver.

Serum growth hormone (GH)-binding protein and insulin-like growth factor-I levels in Turner's syndrome before and during treatment with recombinant human GH and ethinyl estradiol.

Serum levels of GH-binding protein (GH-BP) and insulin-like growth factor-I (IGF-I) were measured in 14 adolescent girls with Turner's syndrome (TS) before and during treatment with recombinant human GH (rhGH) and oral ethinyl estradiol (EE2). Before treatment, the mean +/- SE GH-BP level in TS patients was 33.2 +/- 2.0%; this was higher (P < 0.05) than that in bone age-matched (27.9 +/- 1.1%; n = 13) or chronological age-matched (28.1 +/- 0.8%; n = 17) control girls. The mean +/- SE IGF-I level in TS girls (283 +/- 26 micrograms/L) was comparable to that in bone age-matched controls (255 +/- 17 micrograms/L), but lower (P < 0.005) than that in chronological age-matched pubertal controls (568 +/- 35 micrograms/L). In 7 TS girls treated with daily sc injections of rhGH in a dose of 0.8 U/kg.week for 18 months, serum levels of IGF-I increased from 330 +/- 39 to 707 +/- 48 micrograms/L after 3 months of treatment and remained elevated for the entire observation period (P < 0.002). In contrast, GH-BP levels did not change significantly. In 7 other TS girls, puberty was induced after 2 yr of daily sc injections with rhGH (1 U/kg.week) by adding 100 ng/kg.day EE2, orally, during ongoing rhGH therapy. During 18 months of pubertal induction, serum GH-BP levels increased gradually from 31.4 +/- 2.7% at the start of EE2 treatment to a maximum of 49.2 +/- 0.8% after 1 yr (P < 0.001). Serum IGF-I levels, in contrast, did not change significantly. These results show that in adolescent TS patients 1) pretreatment serum GH-BP levels are higher than in bone age-matched or chronological age-matched control girls, and IGF-I levels are similar to those in bone age-matched but lower than those in chronological age-matched controls; 2) during rhGH treatment GH-BP levels do not change, whereas IGF-I levels increase significantly; and 3) oral EE2 treatment during ongoing rhGH treatment increases GH-BP levels markedly, but does not modify IGF-I levels.

Serum levels of growth hormone-binding protein and insulin-like growth factor-I during puberty.

The aim was to investigate the effect of pubertal development on serum levels of growth hormone binding protein (GHBP) and IGF-I, and to study the relationship between GHBP levels and height standard deviation score (SDS), nutritional state and IGF-I levels. The investigation was performed on serum samples from 72 healthy adolescents of different pubertal stage. Results were compared to those obtained in 46 prepubertal children. Serum levels of GHBP were measured by HPLC gel filtration and IGF-I levels were measured by RIA after acid-ethanol extraction. No effect of pubertal stage on serum levels of GHBP was found. A positive relationship was found between serum levels of GHBP and height SDS (r = 0.38; P < 0.005) and weight expressed as percentage of median weight for height age (r = 0.46; P < 0.0005). Serum levels of IGF-I increased during puberty and were not correlated with height SDS or weight for height age. In pubertal subjects, no relationship existed between serum levels of GHBP and IGF-I. In prepubertal subjects, however, a significantly positive relationship between GHBP and IGF-I levels (r = 0.66; P < 0.0005) was found. Pubertal development does not seem to influence serum levels of GHBP. Height SDS and nutritional state are related to the concentration of GHBP. Before puberty, the level of GHBP is positively related to IGF-I levels; during puberty, however, the increase in serum IGF-I levels is not accompanied by changes in the amount of circulating GHBP.

Effect of human growth hormone (GH)-binding protein in human serum on GH binding to rabbit liver membranes

The sequence identity of growth hormone-binding protein (GH-BP) with the extracellular domain of GH receptors raised the possibility that circulating GH-BP might affect the binding of human GH (hGH) to its receptors, and thus, its biological effects. To test this hypothesis, we tested the effects of sera with low GH-BP levels (obtained from prepubertal children, girls with anorexia nervosa [AN], and patients with hepatic cirrhosis), normal control sera, and sera with high GH-BP levels (obtained from obese patients) on hGH binding to its receptors. GH-BP activity in patients' sera was measured by incubation with [ 125I]hGH and the separation of bound hGH from free hGH with dextran-coated charcoal. The effect of GH-BP was studied by preincubation of patients' sera with increasing concentrations of hGH, followed by incubation with [ 125I]hGH and a rabbit liver membrane preparation known to be rich in GH receptors, and finally by measuring hGH bound to the receptors. In this study, we report on the ability of GH-BP to reduce the inhibitory capacity (IC 50) of hGH on [ 125I]hGH binding to GH receptors. The concentration of GH-BP in serum is positively correlated with the IC 50 of hGH incubated with different sera on [ 125I]hGH binding to its receptors (n = 21; r = .886, P < .001). In the presence of high serum GH-BP levels, such as those observed in obesity ( 20.13% ± 0.71% 0.05mL serum), the IC 50 values were significantly higher than those obtained with sera containing GH-BP levels lower than those measured in human control subjects, such as from prepubertal children, AN patients, and cirrhotic patients. Based on these findings, it is proposed that increasing levels of GH-BP may modulate GH binding to its receptor, and thus may exert a negative feedback on receptor recycling and synthesis and on GH-BP cleavage from the membrane receptor or its independent expression.

Serum growth hormone-binding protein, insulin-like growth factor-I, and growth hormone in patients with liver cirrhosis

We determined serum growth hormone-binding protein (GHBP), insulin-like growth factor-I (IGF-I), and growth hormone (GH) levels in patients with cirrhosis and in age-matched control subjects, and investigated their relationships. Serum GHBP levels in cirrhotic patients (14.6% ± 3.9%) (means ± SD) were significantly lower than those in normal subjects (20.4% ± 4.7%). GHBP levels had positive correlations with cholinesterase ( r = .58, P < .001) and Normotest ( r = .66, P < .001), both of which represent liver function in cirrhotic patients. Basal GH levels in cirrhotic patients (range, 0.35 to 13.0 μg/L; median, 3.9 μg/L) were significantly higher than those in normal subjects (0.015 to 6.0 μg/L; 0.19 μg/L). GHBP levels in cirrhotic patients correlated positively with IGF-I levels ( r = .39, P < .01), and negatively with GH levels ( r = −.33, P < .01). These results may indicate that the serum GHBP level reflects the number of hepatic GH receptors, and that the high basal GH level observed in cirrhotic patients is, at least in part, attributable to decreased clearance of GH by these receptors.

Growth-hormone-binding protein in patients with acromegaly.

The present study was undertaken to investigate the possible regulatory effect of chronic exposure to human growth hormone (hGH), in patients with acromegaly, on growth-hormone-binding protein (GH-BP). Nineteen patients with active acromegaly, before, during or after treatment, comprised the subjects of this study. Serum GH was measured by radioimmunoassay and GH-BP by a binding assay with dextran-coated charcoal separation. The specific binding of [125I]hGH (1 ng) obtained with 50 microliters serum was expressed as a percentage of total cpm. To evaluate the impact of the lower GH-BP on GH activity, we studied the effect of acromegalic serum on hGH displacement of [125I]hGH binding to GH receptors in rabbit liver membranes. Compared to normal controls (11.43 +/- 0.37%), the acromegalic patients had low serum levels of GH-BP (5.45 +/- 0.40%; p < 0.001), which correlated negatively with serum GH levels (p < 0.01). In 7 patients, GH-BP normalized within 2-3 months of successful therapy. The lower GH-BP was due to a reduction in binding capacity, whereas binding affinity remained unchanged. Acromegalic serum, with its low GH-BP, resulted in a shift to the left of the GH displacement curve when compared with normal human sera: IC50 values were 7.47 +/- 0.29 and 11.19 +/- 0.84 ng (p < 0.02) for acromegalic and normal human sera, respectively. We conclude that acromegaly is characterized by low levels of GH-BP due to a decrease in serum-binding capacity. The decrease in GH-BP may render the acromegalic serum GH relatively more active in the GH receptor assay.

Effects of sex and age on serum GH binding protein levels in normal adults

The effects of sex and age on serum growth hormone binding protein (GHBP) levels during adulthood were investigated. The levels of GHBP, insulin-like growth factor-I (IGF-I), and growth hormone (GH) were determined and analysed as a function of sex and age. We studied 101 normal adults (45 men, aged 20-77 years; 56 women, aged 20-80 years). GHBP levels were determined using an Ultrogel AcA 44 minicolumn. During the second and third decade, GHBP levels were not different between men (22.8 +/- 1.1%) (mean +/- SE) and women (23.2 +/- 0.8%). After the age of 40 years, however, GHBP levels in men were significantly decreased (19.1 +/- 0.7%), and were lower than those in women (22.7 +/- 0.9%). IGF-I levels correlated positively with GHBP levels in men (r = 0.51, P less than 0.01) but not in women (r = 0.16, NS). These results indicate that both sex and age may have some effects on the GH-GH receptor-IGF-I axis.