Serum GHBP Research Articles

Exercise combined with lysine-inositol vitamin B12 promotes height growth in children with idiopathic short stature

ObjectiveThis study was aimed to systematically determine the effect of exercise combined with lysine-inositol vitamin B12 (VB12) therapy on the height of children with idiopathic short stature (ISS). MethodsSixty children with ISS were randomly divided into observation and control groups (N = 30). Each group was given lysine-inositol VB12 oral solution (10 mL bid). Simultaneously, the observation group exercised following the “ISS exercise instruction sheet”. The height (H), growth velocity (GV), height standard deviation score (HtSDS) and other indicators were compared after 6 and 12 months of intervention, respectively. After 12 months of intervention, the biochemical indicators of the two groups, together with the correlation between the average days of exercise per week and average minutes of exercise per day, GV and serum growth hormone were analyzed. ResultsAfter 6 and 12 months of treatment, the GV, serum GHRH, GHBP, GH, IGF-1, and IGFBP-3 levels in the observation group were significantly higher than those in the control group, and HtSDS was significantly lower than that in the control group (P<0.01). After 12 months of treatment, the height of the observation group was significantly higher than that of the control group (P<0.05). There was no significant difference in the biochemical indicators between two groups (P>0.05). Average days of exercise per week and average minutes of exercise per day were positively correlated with GV and GHBP levels. Serum GHRH, GH, IGF-1, and IGFBP-3 levels were negatively correlated. Average minutes of exercise per day were negatively correlated with GV and GHBP levels. Serum GHRH, GH, IGF-1, and IGFBP-3 levels were positively correlated. ConclusionRegular and moderate stretching exercises combined with lysine-inositol VB12 can effectively promote height growth of children with ISS, which is clinically safe. The mechanism promotes serum GHRH, GHBP, GH, IGF-1, and IGFBP-3 levels.

Growth hormone receptor gene expression in puberty.

The mechanisms regulating the synergic effect of growth hormone and other hormones during pubertal spurt are not completely clarified. We enrolled 64 females of Caucasian origin and normal height including 22 prepubertal girls, 26 pubertal girls, and 16 adults to evaluate the role of Growth Hormone/Insulin-like growth factor-I axis (GH/IGF-I) during the pubertal period. In these subjects both serum IGF-I and growth hormone binding protein levels, as well as quantitative growth hormone receptor (GHR) gene expression were evaluated in peripheral lymphocytes of all individuals by real-time PCR. Our results showed significantly lower IGF-I levels in women (148±10 ng/ml) and prepubertal girls (166.34±18.85 ng/ml) compared to pubertal girls (441.95±29.42 ng/ml; p<0.0001). Serum GHBP levels were significantly higher in prepubertal (127.02±20.76 ng/ml) compared to pubertal girls (16.63±2.97 ng/ml; p=0.0001) and adult women (19.95±6.65 ng/ml; p=0.0003). We also found higher GHR gene expression levels in pubertal girls [174.73±80.22 ag (growth hormone receptor)/5×10(5) ag (glyceraldehyde 3-phosphate dehydrogenase)] compared with other groups of subjects [women: 42.52±7.66 ag (growth hormone receptor)/5×10(5) ag (glyceraldehyde 3-phosphate dehydrogenase); prepubertal girls: 58.45±0.18.12 ag (growth hormone receptor)/5×10(5) ag (glyceraldehyde 3-phosphate dehydrogenase)], but the difference did not reach statistical significance. These results suggest that sexual hormones could positively influence GHR action, during the pubertal period, in a dual mode, that is, increasing GHR mRNA production and reducing GHR cleavage leading to GHBP variations.

Association of serum components of the GH-IGFs-IGFBPs system with GHR-exon 3 polymorphism in normal and idiopathic short stature children

ObjectiveTo investigate the possible association of circulating components of GH-IGFs-IGFBPs system with the GHR-exon 3 genotype in normal and idiopathic short stature (ISS) children. DesignDescriptive, cross-sectional study in normal and ISS children. Subjects and methods192 normal and 81 ISS children (age: 5–17years) were included. Serum IGF-I, IGFBP3, ALS and GHBP levels were measured. GHR-exon 3 polymorphism (GHRd3) was analyzed by multiplex PCR assay. Normal and ISS children were divided according to GHR-exon 3 genotype: homozygous for the full-length GHR isoform (GHRfl) and carriers of one or two copies of the GHRd3 allele. ResultsGHRd3 genotype distribution (fl:fl/fl:d3/d3:d3,%) in normal (60:34:6) and ISS (64:32:4) was similar and reached Hardy–Weinberg equilibrium. ISS children had significantly reduced levels of GHBP and GH-dependent factors as compared to controls (p<0.0001). Within the normal group, homozygous carriers of the GHRfl allele had significantly higher GHBP serum levels than those with one or two copies of the GHRd3 allele (Mean±SEM; GHRfl: 3.2±0.2 vs GHRd3: 2.7±0.2nmol/L, p=0.04). No other significant association with GHR exon 3 polymorphism was found in either the normal or the ISS groups. ConclusionsGHR exon 3 polymorphism is distributed similarly in normal and ISS children, however only normal homozygous children for GHRfl allele showed higher GHBP levels. The lack of association between GHBP and GHR polymorphism in ISS children might be related to the heterogeneity of this group, where potential defects in GH receptor action may result in partial GH insensitivity.

Hormonal influences of early postnatal indomethacin and ibuprofen in neonatal rats

Objective Indomethacin and ibuprofen are administered to preterm neonates for symptomatic patent ductus arteriosus. The drugs suppress prostaglandins (PGs) which modulate growth and secretion of various hormones. We examined the hypothesis that early postnatal indomethacin and ibuprofen influence growth and GH-IGF-I-insulin and HPA axes in neonatal rats. Design Rat pups received IP injections of saline (Sal) on P1, P2, and P3; 10 mg/kg ibuprofen on P1 followed by 5 mg/kg on P2 and P3; or 0.2 mg/kg indomethacin on P1 followed by 0.1 mg/kg on P2 and P3. Serum and hepatic GH, GHBP and IGF-I; and serum corticosterone and insulin levels were determined. Results Ibuprofen suppressed somatic growth in the sucking rats, but the effect was transient, resolving by P14. Indomethacin had an opposite, latent effect on body weight and liver to body weight ratios in weanling rats. Both indomethacin and ibuprofen had profound hormonal effects that differed in magnitude and timing. Indomethacin resulted in a sustained elevation in corticosterone levels at P21, while ibuprofen increased serum and hepatic GH levels. Both drugs suppressed GHBP in serum at P7 and P14; and liver at P4 and P7, but a rebound increase in serum GHBP was noted at P21 with Ibuprofen only. Both drugs increased serum IGF-I at P7. The effect remained sustained with indomethacin. Conclusions These results provide evidence for an involvement of PGs in the regulation of growth as well as the GH-IGF and HPA axes. Therefore, early postnatal exposure to PG inhibitors may further exacerbate postnatal growth restriction and ability to cope with stress.

Ghrelin and its relationship to growth hormones during normal pregnancy

Ghrelin and GH secretagogue receptors have been found in reproductive organs, including the placenta. The physiology of ghrelin in pregnancy has not been explored. In human pregnancy, pituitary GH is gradually replaced by placental GH (PGH). The present study was undertaken to examine serum ghrelin levels during normal pregnancy and to determine to what extent changes in ghrelin levels coincide with changes in serum levels of free and total GH and PGH. Design Prospective study with blood sampling from pregnant women in gestational weeks 8, 18, 26 and 36 and postpartum. Eleven nondiabetic pregnant women with singleton pregnancies. Serum ghrelin was determined using an in-house radioimmunoassay. Serum PGH was determined in a solid-phase immunoradiometric assay, serum GH and insulin in a time-resolved immunofluorometric assay, and serum GHBP in an in-house immunofunctional assay. Serum ghrelin levels peaked in week 18 (1.20 +/- 0.09 microg/l) and the lowest levels were observed in late third trimester (0.87 +/- 0.06 microg/l), corresponding to a mean decrease of 27.7% (P < 0.001) from peak levels. An increase was observed again postpartum. Serum GH diminished throughout pregnancy to low third-trimester values (0.12 +/- 0.03 microg/l; P < 0.001), and PGH increased to 25.7 +/- 2.86 microg/l (P < 0.001) in week 36. Neither total nor calculated free levels of growth hormones correlated to ghrelin levels, and no significant correlations were observed between ghrelin and maternal body mass index (BMI) or fasting insulin levels. Serum ghrelin levels peak around mid-gestation in human pregnancy. Ghrelin levels during pregnancy are at their lowest in the third trimester at a time of increased body weight, development of insulin resistance and high serum levels of PGH. However, no associations were observed between ghrelin and the two growth hormones.

Growth hormone (GH) and estradiol regulation of membrane-associated GH binding protein and GH receptors in GH releasing hormone transgenic mice.

Growth hormone (GH) releasing hormone (GHRH) transgenic mice were used to examine the influence of GH on GH receptor (GHR) and membrane-associated GH binding protein (MA-GHBP) levels by means of specific radioimmunoassays and Western blot analysis, since MA-GHBP was described as the major constituent of somatogenic binding to liver membranes in mice. In transgenic animals, a 10-fold increment over normal values was found for hepatic somatogenic binding that could be accounted for by a 3--4-fold increase in GHR and a 9-fold augmentation of MA-GHBP levels. The apparent molecular weight of MA-GHBP was smaller than that of serum GHBP, a difference that was partially abolished by endoglycosidase F digestion. In vivo treatment of female mice with 17 beta-estradiol led to an unexpected down-regulation of MA-GHBP and GHR by 60--75% only in transgenic animals. MA-GHBP and GHR levels are strongly up-regulated by GH, although MA-GHBP up-regulation is much more important than that of GHR.

Mutations of the Growth Hormone Receptor Found in Japanese Short Children.

We present here two mutations of the growth hormone (GH) receptor (GHR) gene in Japanese patients with GH insensitivity syndrome (GHIS) or idiopathic short stature (ISS). One is a heterozygous point mutation of the donor splice site in intron 9 of the GHR gene in 2 siblings with GHIS, whose serum GHBP levels were high. The same mutation was also found in their mother as well. The analysis of RNA from the peripheral leukocytes revealed complete skipping of exon 9 from one allele, but not the other, in the GHR cDNA and appearance of a premature stop codon in exon 10. This mutation caused truncation of GHR with a dominant negative effect on GH signaling, which is probably responsible for their short stature and high serum GHBP levels. The other mutation is a heterozygous missense mutation, C422F, in the intracellular domain of GHR. Although this mutation was previously reported in a patient with GH insensitivity syndrome (GHIS), it has not been clear whether this mutation causes GH insensitivity. To clarify the effect of this mutation on GH signal transduction, mutant GHR was expressed in CHO cells and its functional properties were investigated. Neither GH-induced tyrosine phosphorylation of STAT5b nor STAT5-mediated transcriptional activation were found in GHR-C422F-expressing cells. In addition, the analysis of genotypes and phenotypes of this family revealed that a C422F mutation was found in family members showing normal height, indicating that the C422F missense mutation of GHR is not responsible for short stature.

Evidence for two distinct classes of high affinity growth hormone binding proteins in pregnant rat serum.

These studies have established the presence of two major classes of high affinity growth hormone binding proteins in pregnant rat serum, designated GHBPa and GHBPb, with apparent native Mr of 257 K and 98 K respectively. GHBPa, which has not been identified previously, exhibits a binding affinity (2-5 nM(-1)) that is up to 20-fold higher than GHBPb (0.2-0.8 nM(-1)) and is the least abundant form, being approximately 15-20% of total serum GH-binding capacity. Western immunoblot analysis revealed that each GHBP is composed of several immunoreactive proteins which were reactive with carboxy-terminal (RB1615) and/or N-terminal (MAb263) domain antibodies, suggesting the presence of GHBPs with and without the hydrophilic tail. Of importance is that GHBPa exhibited significantly higher Mr (78-182 K, +DTT) than that predicted by GHBP cloning, suggesting that they may be covalently bound to other non-GH-binding proteins or may be distinct entities. GHBPb, on the other hand, was composed of smaller Mr (43/48 K, +DTT) "hydrophilic" tail-containing proteins, some of which were disulphide linked to a larger complex of approximately 110 K. These novel findings challenge the current view of the mechanism for generation of the rat serum GHBP and raise the intriguing possibility that the two classes of GHBP may play distinct and important roles in GH physiology.

DECREASED INSULIN-LIKE GROWTH FACTOR-I RECEPTOR SITES ON CIRCULATING MONONUCLEAR CELLS FROM CHILDREN WITH ACUTE LEUKEMIA

Insulin-like growth factor-I (IGF-I) is a known mitogen for various cell types, including those of the hematopoietic cell system. To study the role of IGF-I in the neoplastic process of leukemia in children, the authors have determined the number of IGF-I binding sites on circulating mononuclear cells of children with acute leukemia as compared to normal children, using binding assays. The IGF-I binding sites per cell on peripheral mononuclear cells of children with leukemia decreased compared to those of the control group (411 +/- 73 and 1334 +/- 227, respectively, p < .001), while their affinity increased (Kd = 0.14 +/- 0.04 and 0.43 +/- 0.16, respectively, p = .05). Furthermore, in the patients, the number of the IGF-I binding sites was significantly lower in the subgroup of the peripheral mononuclear cells, which included lymphocytes and monocytes, as compared to their number in the peripheral blast cells (254 +/- 43.6 and 536 +/- 98.6, respectively, p = .02). A significant reduction was found in serum GHBP levels in the patients as compared to the controls (28.21 +/- 1.93 and 35.83 +/- 2.90, respectively, p = .02), while serum IGF-I and growth hormone levels were similar in patient and control groups. These results suggest a possible involvement of IGF-I in childhood acute leukemia, but further studies are needed to establish whether IGF-I plays a role in this disease.

Nutrition related hormonal changes in obese children.

Children with simple obesity (SO) show increased linear growth with normal or high serum insulin-like growth factor-I (IGF-I) levels during prepubertal period, despite low GH secretion. We measured IGF-I, IGFBP-1, GHBP and other factors to clarify the hormonal relation between the nutrition and the linear growth in SO and compared these factors with children with normal short stature (NS). Subjects were 23 SO and 19 NS children, and their height standard deviation (SD) scores were 0.7 +/- 0.2 SD and -3.4 +/- 0.3 SD (mean +/- SEM) (P < 0.01), respectively. Oral glucose tolerance test (OGTT) was performed in all the subjects and GH-releasing factor (GRF) test was also performed in 13 of SO and 17 of NS. The peak levels of GH in the GRF test were significantly lower in SO than in NS (12.8 +/- 1.7 vs. 39.8 +/- 6.9 ng/ml) and showed a significantly positive correlation with sigma IGFBP-1 (r = 0.63, P < 0.01). Serum GHBP level and IGF-I level were significantly higher in SO than in NS on pubertal stage matching. There was a positive correlation between GHBP and sigma insulin during OGTT (r = 0.75, P < 0.01). When the sum of the values during OGTT was expressed as sigma, sigma insulin, sigma C-peptide and sigma glucose were significantly higher in SO than in NS on pubertal stage matching. Basal and sigma IGFBP-1 were significantly lower in SO than in NS, but IGFBP-3 levels showed no significant difference between the two groups either in prepuberty or midpuberty. In conclusion, it can be hypothesized that the overnutrition causes hyperinsulinemia which increases GH receptor and IGF-I secretion despite low GH secretion. Hyperinsulinemia also may increase free IGF-I by lowering IGFBP-1. These two mechanism are supposed to be the nutrition related hormonal changes in SO and can explain the growth of SO. In addition, the increased free IGF-I may contribute the decreased GH secretion due to negative feedback in SO.

Expression of growth hormone receptor by peripheral blood lymphocytes in children: evaluation in clinical conditions of impaired growth.

It is widely accepted that the haematopoietic system is a target of growth hormone action and that GH may act as a lymphokine. The expression of GH receptors (GHR) on human peripheral blood lymphocytes (PBL) has been reported previously in adult donors by dual fluorochrome flow cytometry. The aim of this study was to apply the cytofluorimetric method to the analysis of GHR expression on PBL in various human conditions characterized by different patterns of growth due to age or physiopathological conditions. PBL from 38 normal (control) subjects (7 newborns, 18 prepubertal children, 13 adults) were studied in order to provide age-related physiological data. Twenty-two short children (18 with idiopathic short stature, 4 with Ullrich-Turner syndrome) were studied to determine the expression of GHR in conditions of impaired longitudinal growth which may or may not require GH treatment. Analysis was performed using a fluorescein isothiocyanate (FITC)-conjugated antibody specific for the GHR (mAb263) and phycoerythrin (PE)-anti CD2 (T and natural killer cells) or PE-anti CD2 (B cells) in dual fluorochrome flow cytometric assays. Results were expressed as mean fluorescent intensity (MFI). Adult CD2+ coils exhibited a significantly higher GHR expression (MFI 347 +/- 40) than that expressed in children and newborns (MFI 285 +/- 36 and 299 +/- 41, respectively, P < 0.001). A significantly increased expression of GHR on CD2+ cells was also found in short children (MFI 330 +/- 42 vs 285 42- 36, respectively; P < 0.002), whereas Ullrich-Turner syndrome patients did not show any difference from their age and gender matched controls (254 +/- 52 and 288 +/- 40, respectively). A negative relationship was found between GHR expression on CD2+ cells and height-SDS (r - 0.54, P < 0.0001) or BMI (r - 0.4, P < 0.015) in controls and short children, independent of their GH secretory status. Expression of GHR and CD20+ cells was higher than that expressed on CD2+ cells in all subjects. No appreciable differences were found in the MFI levels of GHR expression on CD20+ cells either among the different age group controls or between short children or Ullrich-Turner syndrome patients. A significant downregulation of expression was shown in CD20+ (P < 0.008) but not CD2+ cells after 6 months of GH treatment in 6 short children who had a poor response to GH provocative tests. GH receptor expression on immune cells in non-syndromic short children appears to be inversely related to the linear growth expression and BMI of the subjects, contrary to findings with hepatic derived serum GHBP. This finding may reflect alternate exon usage in lymphoid cells, and indicates that GH has a distinctive role in the immune system.

Characterization of prolactin- and growth hormone-binding proteins in milk and their diversity among species

The present study was undertaken to identify and characterize the diversity and species distribution of soluble prolactin binding-protein (PRL-BP) and growth hormone-binding protein (PRL-BP) in mammalian milk. We previously divided mammalian serum GH-BP into four main groups and identified a GH-BP with shared lactogenic/somatogenic properties in rabbit, horse, dog, pig and cat (Type III species). Here we describe PRL-BP in milk of Type III species and show it is relatively conserved within the group, having similar characteristics in terms of binding affinity for hGH (0.74−5.5×10 10 M −1), specificity towards the lactogenic hormones and molecular weight (∼35 kDa), except for the more heterogeneous pig milk (∼43 to ∼88 kDa) Furthermore, high affinity PRL-BP was also demonstrated in sheep milk, having pure lactogenic specificity and an M r of ∼35 kDa. Human milk contained a high affinity PRL-BP/GH-BP, which was recognized by both hPRL and hGH and also having an M r of ∼35 kDa. In rabbit milk a separate GH-BP was also detected; it was clearly distinguished from the corresponding milk PRL-BP on the basis of its M r of ∼44 kDa (vs. ∼32 kDa for PRL-BP), its shared lactogenic/somatogenic hormonal specificity (vs. purely lactogenic for PRL-BP) and also on the basis of its relative resistance to heating at 56°C for up to 3 h, while PRL-BP activity was completely destroyed within 30 min. This diversity of milk PRL-BP and GH-BP among mammalian species fits in with our earlier classification of serum GH-BP and also with the reported evolutionary rates of PRL and GH; this suggests these BPs may play important species-specific roles in the suckling newborn and/or maternal mammary gland, in keeping with the functions described for GH-BP.

The obese growth hormone (GH)-deficient dwarf rat: body fat responses to patterned delivery of GH and insulin-like growth factor-I.

We describe a new animal model of obesity and GH deficiency and report the effects on body fat of administering (GH) and insulin-like growth factor (IGF-I) in the model. Female GH-deficient dwarf rats fed a high-fat diet became obese and insulin-resistant compared with chow-fed controls. They were treated with recombinant human GH (rhGH 100-500 micrograms/day, s.c. for 14 days) by daily injection or minipump infusion with or without rhIGF-I (200 micrograms/day, sc infusion). Injections of rhGH increased body weight; infusions of rhGH caused weight loss. RhIGF-I by itself, or rhIGF-I plus GH injections had little effect, whereas rhGH infusions plus rhIGF-I caused a weight loss equivalent to the weight gained during the high-fat feeding and a decrease in fat pad weight. For some responses (serum IGF-1 and GHBP), the obese rats were GH resistant. Fat was lost from the internal fat pads when obese rats were returned to a chow diet, and injections of rhGH surprisingly attenuated this loss of fat. In obese dwarf rats, the lipolytic effects of rhGH are dose-regime dependent. By itself IGF-I is not insulin-like, but in the presence of GH it has antiinsulin actions causing a powerful net lipolysis. If GH plus IGF-I have similar effects in humans they may be useful for reducing body fat.

The individual responsiveness to growth hormone (GH) treatment in GH-deficient adults is dependent on the level of GH-binding protein, body mass index, age, and gender.

The aim of the present trial was to study the individual responsiveness to GH treatment in terms of body composition and to search for possible predictors of the response in GH-deficient adults. Sixty-eight patients (44 men and 24 women) with a mean age of 44.3 (1.2) yr and verified GH deficiency participated in a 2-phase treatment trial with an initial randomized, double blind, placebo-controlled, 6-month period, followed by an open treatment period, thereby ensuring all patients 12 months of GH treatment. Recombinant human GH was administered sc daily at bedtime, with a target dose of 12 micrograms/kg x day. GHBP was measured by ligand-mediated immunofunctional assay, and serum insulin-like growth factor I (IGF-I) was determined by RIA after acid-ethanol extraction, using a truncated IGF-I analog as the radioligand. Lean body mass (LBM) and body fat (BF) were determined by dual energy x-ray absorptiometry, and total body water (TBW) was determined by bioelectrical impedance. During the placebo control period, serum IGF-I,LBM, and TBW increased (P < 0.001), whereas BF decreased (P < 0.001) and serum GHBP was unchanged in the group treated with GH compared with the patients treated with placebo. After 12 months of GH treatment, the individual changes in BF ranged from -12.5 to 4.3 kg and from -4.5 to 10.1 kg in LBM. Age (P < 0.05) and baseline GHBP level (P < 0.01) were inversely correlated with the increase in LBM. The GH-induced increment in IGF-I and TBW was greater in men than in women (P < 0.01), whereas the decreases in BF were similar in men and women. This trial demonstrates the variability in responsiveness to GH administration in GH-deficient adults. The best response to GH was obtained in younger patients with low GHBP levels. Furthermore, men responded better than women.

Purification and Characterization of Recombinant Mouse Growth Hormone Binding Protein Produced in the Baculovirus Expression System

Sf21 insect cells were infected with recombinant baculovirus containing cDNA for the entire coding region of the mouse growth hormone binding protein (mGHBP). Recombinant (r) mGHBP was expressed at a yield of 17.3 mg/liter/3 days. The molecular size (Mr) of the rmGHBP was approximately 33,000 as estimated by SDS–PAGE. Amino-terminal sequence analysis of the recombinant protein yielded two sequences: one identical to amino acids 1–15 and another corresponding to amino acids 14–21 of the GHR/GHBP. Western blot analysis revealed that this is the sameMras that of one of the two majorMrforms of serum mGHBP. Deglycosylation of serum mGHBP and recombinant mGHBP caused a shift in the molecular size of both proteins to that expected after removal of all N-linked carbohydrates. Binding characteristics of the recombinant mGHBP to mouse growth hormone were similar to those for serum GHBP. Scatchard analysis showed an equilibrium association constant (Ka) for rmGHBP of 3.8 × 108± 0.6 × 108M−1(mean ± SEM,n= 3) andKaof 9.2 × 108± 2.0 × 108M−1(mean ± SEM,n= 3) for the serum mGHBP. In conclusion, this expression system should allow a production of relatively large quantities of mGHBP suitable for physiological studies on the role of this protein.

Growth hormone (GH) receptor and GH-binding protein deficiency in the growth failure of potassium-depleted rats.

Potassium (K+) deficiency is associated with growth retardation in both man and experimental animals. Growth hormone (GH) administration to such animals prevents, to some extent, weight loss and selective muscle atrophy, but does not affect tail and tibia length even with supraphysiological doses. The present study was undertaken to investigate the possible effect of K+ deficiency on the hepatic GH receptor and GH-binding protein (BP). Young female Wistar rats were maintained on K(+)-deficient fodder and distilled water, and compared with pair-fed and ad-libitum-fed control groups. After 15 days GH-BP and electrolytes were measured in sera, GH receptors were studied in liver membranes by 125I-labeled human GH binding and muscles were weighed and saved for electrolyte measurements. K(+)-deficient rats showed complete growth arrest compared with an intermediate weight gain of the pair-fed group. Serum K+ was very low, at 1.5 +/- 0.1 mmol/l, compared with the mean value of 5.3 mmol/l of control animals. Somatogenic and lactogenic receptors in liver membranes and serum GH-BP levels were significantly (P < 0.05) lower in K+ deficiency, as compared with their pair-fed controls. Liver GH receptors correlated significantly (P < 0.05) with serum GH-BP levels. The growth variables correlated positively with both hepatic somatogenic and lactogenic receptors and serum GH-BP levels, with correlation coefficients that were highest against serum GH-BP and lowest against liver lactogenic receptors. Serum and muscle K+ correlated significantly (P < 0.05) with both liver GH receptors and serum GH-BP, with correlation coefficients that were higher against serum GH-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation of the growth hormone and insulin-like growth factor-I axis to chronic and severe calorie or protein malnutrition.

The hierarchy of diet components (e.g., protein, carbohydrate, vitamins, and minerals) influencing growth hormone (GH), insulin-like growth factor-I (IGF-I), and their binding proteins (BP) is not well defined. Young adult rats were fed diets for 1 mo that included low protein or 60% and 40% of carbohydrate calories. We hypothesized that levels of both hormones, their dominant BPs and liver IGF-I mRNA would fall, and that part of the mechanism for decreasing serum IGF-I would be enhanced IGFBP-3 protease activity. By day 30, caloric deprivation to 40% lowered serum GH, GHBP, IGF-I and IGFBP-3, and liver IGF-I mRNA. This was the only condition resulting in body weight loss (-15%) vs 39% gain in controls. Restriction to 60% calories had no impact on BP levels, slightly lowered IGF-I (-12%) in the face of a 95% inhibition of GH levels, while allowing a modest 9% body weight gain. Protein deprivation lowered serum GH, IGF-I and IGFBP-3, and liver IGF-I mRNA, while GHBP levels were normal. The reduced total IGF-I under these dietary conditions could not be explained by an increase in IGFBP-3 protease activity, or a decrease in the association of IGF-I with IGFBP-3 and the acid labile subunit.

Effect of oestrogen status on serum levels of growth hormone‐binding protein and insulin‐like growth factor‐I in non‐pregnant and pregnant women

Since there appears to be a relationship between circulating oestrogens and growth hormone, we have investigated the effect of the oestrogen status of adult women on serum levels of GHBP and IGF-I. The investigation was performed on serum samples of 14 spontaneously menstruating women, 10 women taking oral contraceptives containing 20-50 micrograms ethinyloestradiol, and 30 pregnant women at different stages of pregnancy. Serum levels of GHBP were measured by HPLC gel filtration and IGF-I levels were measured by RIA after acid-ethanol extraction. In the spontaneously menstruating women the mean +/- SD serum level of GHBP was 34.6 +/- 6.7% and of IGF-I 30 +/- 7 nmol/l. Serum GHBP levels were negatively (r = -0.67; P < 0.01) and IGF-I levels were positively related (r = 0.69; P < 0.01) to serum oestradiol concentrations. In the women taking oral contraceptives serum levels of GHBP were 47.0 +/- 7.4%. This was significantly (P < 0.001) higher than in spontaneously menstruating women. In contrast, IGF-I levels were not different from those obtained in spontaneously menstruating women. In the pregnant women, the mean +/- SD serum level of GHBP was not different from that observed in non-pregnant spontaneously menstruating women. Polynomial regression analysis, however, 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. Serum concentrations of IGF-I increased during the second half of pregnancy and were significantly (P < 0.005) elevated in the third trimester. In non-pregnant women the endogenous oestrogen status seems to modulate negatively GHBP levels and positively IGF-I levels, whereas oral oestrogen administration, in contrast, increases serum levels of GHBP without modification of IGF-I levels. During pregnancy serum GHBP levels increase slightly during the first half of pregnancy and decrease thereafter, whereas IGF-I concentrations increase during the second part of pregnancy. The oestrogen status of women has a complex effect on serum concentrations of GHBP and IGF-I and has therefore to be taken into account when evaluating serum levels of GHBP and IGF-I.

SERUM HALF-LIFE OF GROWTH HORMONE-BINDING PROTEIN (GH-BP) ASSESSED IN THE HUMAN NEWBORN

The serum half-life of the glycosylated GH-BP in the human is currently unknown. Circulating levels of the high affinity GH-BP are low in the neonatal period compared to adult life (Massa et al, Pediatr Res 1992). During an exchange transfusion (ET) for neonatal hyperbilirubinemia, the blood of the newborn is nearly completely replaced by adult donor blood. To evaluate the elimination rate of GH-BP we measured serum levels of GH-BP by HPLC gel filtration before and at different time intervals after an ET in 4 term neonates. Before the ET the mean±SE serum binding of 125I-hGH (GH-BP) was 6.7±1.2%. At the end of the ET, serum GH-BP was increased to 25.3±2.6% (P<0.005). Thereafter serum GH-BP decreased slowly and was 84 to 96 hours later still higher than before the ET. Analysis of the elimination curve by exponential stripping suggested an elimination according to a bi-exponential model : GH-BP(%) = 40 × e(5.1 x-03 ×time) + 64 x e(−2.5x-04 × time). The seruin half-life of the GH-BP complex was estimated to be 1.9 days. These data demonstrate : 1) that the GH-BP can be transfused, and 2) that the serum half-life of the GH-BP complex in neonates is in the order of magnitude of days. (This work was supported by a grant from the Belgian study Group of Pediatric Endocrinology).

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.