Leptin receptor 5'untranslated regions in the rat: relative abundance, genomic organization and relation to putative response elements

Hypothalamic sensitivity to leptin has been suggested to be important for regulation of body fat mass. Mice heterozygous for a mutation in the leptin receptor (leptin-R) have an increased body fat mass suggesting that the abundance of leptin-R may be an important determinator of leptin sensitivity. Leptin-R cDNAs from several species contain alternative 5'untranslated regions (5'UTRs), suggesting that several distinct regulatory regions may exist. To investigate possible mechanisms by which leptin-R expression may be regulated, we searched for possible alternative 5'UTRs of the leptin-R in the rat and determined their location in relation to putative response elements. Four leptin-R 5'UTRs (exons 1A-1D), which diverged 23 bp upstream of the start codon, were identified by 5'Rapid Amplification of cDNA Ends (5'RACE) and sequencing. Exons 1B and 1C were present in 31 and 61%, respectively, of all leptin-R transcripts in the hypothalamus as determined by a ribonuclease protection assay. Analysis of the 5' flanking genomic sequences revealed an imperfect estrogen response element (ERE), two Spl-sites, three CCAAT-boxes and one octamer. Exons 1A and 1D corresponded to a putative second gene, encoding the OB-Receptor Gene Related Protein (OB-RGRP), which is transcribed from a promoter shared with the leptin-R. DNA sequencing revealed that the rat OB-RGRP had 98 and 97% homology with the mouse and human sequence, respectively. We report here that transcription of the rat leptin-R gene may generate transcripts with four alternative 5'UTRs. The presence of a putative ERE, close to the most frequently used transcriptional start sites of the leptin-R gene in the hypothalamus, provides a possible mechanism by which estrogen may exert its effects on food intake.

Growth hormone receptor interaction with Jak proteins differs between tissues

Janus kinases (Jak) play an important role in the initial steps of cytokine receptor signaling. The specificity of the four members of the Jak family (Jak1, Jak2, Jak3, and Tyk2) for different cytokine receptors is not fully understood. Recent studies have indicated that a specific cytokine receptor can activate several Jak and that this may differ between tissues. The growth hormone receptor (GHR) is believed to interact predominantly with Jak2, but studies on cell lines have shown that it may also induce phosphorylation of Jak1 and Jak3. Little is known about the interaction between the GHR and Jak in tissues. Our aim, therefore, was to elucidate which Jak interact with the GHR in two target tissues for GH, liver and adipose tissue. Western blot analysis showed that all four members of the Jak family are present in both rat liver and adipose tissue. However, coprecipitation using an anti-GHR antibody revealed that only Jak1 and Jak2 were associated with the GHR in these tissues. The relative amount of Jak1 and Jak2 that coprecipitated with the GHR differed markedly between tissues. In the liver, Jak2 dominated, and only a small amount of Jak1 was detected. In adipose tissue, at least one third of the coprecipitated Jak was Jak1. This is the first study to show that both Jak1 and Jak2 are associated with the GHR in rat tissues. The difference in the ratio between GHR-associated Jak1 and Jak2 in liver and adipose tissue may indicate that GHR signaling in different tissues could differ in terms of Jak specificity.

Partial genome scale analysis of gene expression in human adipose tissue using DNA array

OBJECTIVE

Large scale analysis of gene expression in adipose tissue provides a basis for the identification of novel candidate genes involved in the pathophysiology of obesity. Our goal was to explore gene expression in human adipose tissue at a partial genome scale using DNA array.

RESEARCH METHODS AND PROCEDURES

Labeled cDNA, derived from human adipose tissue poly(A+) RNA, was hybridized to a DNA array containing over 18,000 human expressed sequence-tagged (EST) clones. The results were analyzed by database searches.

RESULTS

Homology searches of the 300 EST clones with highest hybridization signals revealed that 145 contained DNA sequences identical to known genes and 79 could be linked to UniGene clusters. Of the 145 identified genes, 136 were nonredundant and subsequently characterized with respect to function and chromosomal localization by searching MEDLINE, UniGene, GeneMap, OMIM, SWISS-PROT, the Genome Database, and the Location Data Base. The identified genes were grouped according to their putative functions; cell/organism defense (9.6%), cell division (5.1%), cell signaling/communication (19.8%), cell structure/motility (12.5%), gene/ protein expression (16.9%), metabolism (16.2%), and unclassified (19.8%). Less than 50% of these genes have previously been reported to be expressed in adipose tissue. The chromosomal localization of 268 genes strongly expressed in adipose tissue showed that their relative abundance was significantly increased on chromosomes 11, 19, and 22 compared to the expected distribution of the same number of random genes.

DISCUSSION

Our study resulted in the identification of numerous genes previously not reported to be expressed in adipose tissue. These results suggest that DNA array is a powerful tool in the search for novel regulatory pathways within adipose tissue on a scale that is not possible using conventional methods.

Growth hormone isoforms in newborns and postpartum women

The neonatal and postpartum periods are characterized by alterations in pituitary GH secretion. We have investigated the proportion of circulating non-22kDa GH isoforms in newborns, in women within the early postpartum phase (just after the disappearance of placental GH from the maternal circulation) and in women during late postpartum (during the somatotroph recovery phase). We studied 10 newborns (7 males; 3 females; median postnatal age, 45h), who had been admitted because of polycythaemia, 10 women in the early postpartum phase (median, 48h after delivery; range, 42-54h), 18 women in the late postpartum phase (median, 10 weeks after delivery; range, 3-25 weeks) and 9 healthy non-pregnant women. The proportion of non-22kDa GH isoforms was determined by the 22kDa GH exclusion assay, which is based on immunomagnetic extraction of 22kDa GH from serum, and quantitation of non-22kDa GH isoforms using a polyclonal GH assay. In newborns, non-22kDa GH isoforms were measured in two arterial blood samples obtained with a 5-6h interval. In the other groups, serum samples were obtained 40min after an i.v. bolus administration of the GH secretagogue, GH releasing peptide-1 (GHRP-1). In newborns, the median proportion of non-22kDa GH isoforms was 10% (range, 7. 2-19.4%) and the values were similar in samples collected at different times. In early postpartum women, total GH levels after GHRP-1 were lower and the proportion of non-22kDa GH isoforms was higher compared with the values in non-pregnant and late-postpartum women. In late postpartum, there was a partial recovery of GH response to GHRP-1, as shown by an increment in total GH levels, which was associated with a decrease in the fraction of non-22kDa GH isoforms. In conclusion, we found that (i) the proportion of non-22kDa GH isoforms in the newborn is comparable to that in the adult (non-pregnant women), (ii) in early postpartum, the non-22kDa fraction is high within the small pool of readily releasable GH, (iii) in late postpartum, recovery of pituitary GH responsiveness is associated with a relative decrease in the release of non-22kDa GH isoforms.

A low serum leptin level at baseline and a large early decline in leptin predict a large 1-year weight reduction in energy-restricted obese humans

The difficulty in maintaining weight loss during obesity treatment may be caused by a counteracting neuroendocrine response. It has been proposed that leptin could be a regulator of this response. We examined the relations between leptin levels during an initial very low calorie diet, other simultaneous endocrine changes, and the 1-yr weight reduction. Sixty-nine obese (24 men and 45 women) were treated with very low calorie diet for 16 weeks, followed by a hypocaloric diet for 32 weeks. Serum levels of leptin, insulin, cortisol, and thyroid hormones were measured at weeks 0, 8, and 18. The relative weight reductions after 18 and 48 weeks were 20.1% and 14.4% in men and 15.4% and 11.8% in women. Low initial leptin levels and large declines in serum leptin were associated with a large 1-yr weight loss in both genders. Leptin levels (baseline or changes) were not independently associated with the changes in insulin, cortisol, or thyroid hormones. Our results may indicate that leptin by itself could be of minor importance for the neuroendocrine response to severe caloric restriction in humans.

Cyclical variations in the abundance of leptin receptors, but not in circulating leptin, correlate with NPY expression during the oestrous cycle

We have demonstrated previously that pharmacological doses of oestradiol decreased leptin receptor expression in the hypothalamus. We therefore analysed leptin receptor expression during the oestrous cycle in the rat, to establish if acute changes in oestradiol affect leptin receptor expression under physiological conditions. Radioactive in situ hybridization histochemistry was used to measure the gene expression under investigation. Total leptin receptor transcript levels were lowest in pro-oestrus in the choroid plexus, these changes correspond inversely with levels of circulating oestradiol in the rat 4-day oestrous cycle. In contrast full-length leptin receptor levels in both arcuate and ventromedial nuclei did not correspond to the levels of total leptin receptor in the same areas of the hypothalamus or serum levels of oestradiol. Full-length leptin receptor expression in the arcuate nucleus was negatively correlated with neuropeptide Y (NPY) expression (r = 0.447, p < 0. 05) in the same nucleus. Arcuate nucleus NPY expression did not correlate significantly with the expression of total leptin receptors in the arcuate nucleus (r = 0.080) or serum leptin levels (r = 0.251). Our results demonstrate that leptin receptor expression is regulated during the oestrous cycle. The unchanged serum leptin levels during the oestrous cycle together with the correlation between the expression of leptin-RL and NPY provide circumstantial evidence that regulation of leptin receptor abundance in the hypothalamus governs the biological actions of leptin.

The growth hormone receptor associates with Jak1, Jak2 and Tyk2 in human liver

Studies in cell lines have shown that Jak2 is the primary tyrosine kinase involved in signal transduction by the growth hormone receptor (GHR). In addition, growth hormone (GH) stimulates tyrosine phosphorylation of Jak1 and Jak3 in certain cell lines, while the effect on Tyk2 has not been analysed. We have investigated the expression of Jak proteins in human liver and analysed their interactions with the GHR. Using Western blot analysis and immunohistochemistry, we demonstrate that Jak1, Jak2, Jak3 and Tyk2 are present in human liver. Immunoprecipitation by an antibody against the GHR (Mab 263) followed by immunoblotting with specific antibodies against Jak proteins showed that Jak1, Jak2 and Tyk2 were associated with the GHR in this tissue. We conclude that the GHR associates with Jak1, Jak2 and Tyk2 in human liver. Although experiments in vitro indicate that Jak2 mediates GH signalling, our results open the possibility that other Jak proteins may influence GHR signalling in human liver.

Scavenger receptor class B type I in the rat ovary: possible role in high density lipoprotein cholesterol uptake and in the recognition of apoptotic granulosa cells

Scavenger receptor class B type I (SR-BI) mediates the selective uptake of high density lipoprotein cholesterol. SR-BI is expressed at high levels in the ovary, indicating that it plays a role in the delivery of cholesterol as substrate for steroid hormone production. However, SR-BI also binds anionic phospholipids with high affinity and could therefore be involved in the recognition of apoptotic cells. In this study we have characterized the expression of SR-BI in rat ovarian follicles undergoing atresia. Atretic follicles with cells undergoing apoptosis were identified by in situ DNA end labeling, and SR-BI expression was determined by in situ hybridization and immunohistochemistry. SR-BI was expressed in thecal cells at all stages of follicular development, including atretic follicles, and in corpus luteum. Isolated apoptotic granulosa cells (but not viable granulosa cells) bound annexin V, indicating that they display anionic phospholipids on the cell surface. Transfection of COS-7 cells with an expression vector carrying the rat SR-BI complementary DNA resulted in increased binding to apoptotic granulosa cells (46 +/- 2% of the SR-BI-expressing cells bound at least one granulosa cell compared with 24 +/- 3% for the mock-transfected cells; P < 0.0001), whereas the binding to viable granulosa cells was unchanged. Apoptotic granulosa cells also bound to isolated thecal shells. We conclude that thecal cells of both nonatretic and atretic follicles express SR-BI. The location of SR-BI expression in the ovary supports a role of this receptor in the uptake of high density lipoprotein cholesterol. In addition, our data suggest that SR-BI mediates the recognition of apoptotic granulosa cells by the surrounding thecal cells and that it therefore may play a role in the remodeling of atretic follicles to secondary interstitial cells.

Discrepancy between serum leptin values and total body fat in response to the oral growth hormone secretagogue MK-677

OBJECTIVE

Growth hormone (GH) treatment decreases total body fat while this effect has not yet been documented for the oral GH secretagogue MK-677. In the present study, the effects of MK-677 treatment on serum levels of leptin, thyroid hormones and testosterone were determined.

DESIGN

This was a randomized, double-blind, and parallel study. Twenty-four healthy obese males, 19-49 years of age, with body mass index (BMI) > 30 kg/m2 and a waist:hip ratio > 0.95, were treated with MK-677 (25 mg/day; n = 12) or placebo (n = 12) for 8 weeks.

RESULTS

MK-677 treatment increased serum leptin levels and leptin/body fat ratio at 2 weeks of treatment (P < 0.05 vs. placebo) but no significant change was observed at 8 weeks. An increase in serum free 3, 5, 3'-triiodothyronine (free T3) was not detected until 8 weeks of MK-677 treatment (P < 0.05 vs. placebo). Peak serum thyroid stimulating hormone (TSH) concentration after MK-677 administration was similar to that after placebo administration at initiation of treatment and at 2 weeks. At 8 weeks of MK-677 treatment, mean peak serum TSH concentration was increased (P < 0.05 vs. placebo) although it remained within the normal range. Serum peak values of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were similar after MK-677 and placebo administration. MK-677 treatment reduced serum total testosterone (P < 0.05 vs. placebo) although total testosterone/sex hormone-binding globulin (SHBG) ratio (an index of free testosterone) was not changed.

CONCLUSION

Treatment with the oral GH secretagogue MK-677 transiently increased serum leptin levels and leptin/body fat ratio at 2 weeks of treatment, and increased serum free T3 after 8 weeks. These results indicate that MK-677 treatment is able to affect circulating factors of importance for adipose tissue mass and fuel metabolism.

Serum leptin concentration and insulin sensitivity in men with abdominal obesity

OBJECTIVE

We have examined the association between generalized adiposity, abdominal adiposity, insulin sensitivity, and serum levels of leptin in a cross-sectional study of abdominally obese men.

RESEARCH METHODS AND PROCEDURES

Thirty men, 48 to 66 years of age with a body mass index (BMI) of between 25 kg/m2 and 35 kg/m2 and a waist hip ratio of >0.95, were included in the study. Serum leptin concentration was measured using radioimmunoassay. Total body fat percentage was determined from total body potassium, abdominal adiposity was measured by computed tomography, and the glucose disposal rate (GDR) was measured during an euglycemic, hyperinsulinemic glucose clamp.

RESULTS

Significant correlations were found between serum leptin concentration and BMI, percentage body fat, abdominal subcutaneous adipose tissue, serum insulin, GDR, and 24-hour urinary-free cortisol. In a multiple regression analysis, it was shown that abdominal subcutaneous adipose tissue, GDR, and BMI explained 72% of the variability of serum leptin concentration. GDR demonstrated an independent inverse correlation with serum leptin concentration.

DISCUSSION

In abdominally obese men with insulin resistance, it was demonstrated that most of the individual variability in serum leptin concentration was explained by the amount of subcutaneous abdominal adipose tissue, insulin sensitivity, and BMI.

Human adipose tissue expresses angiotensinogen and enzymes required for its conversion to angiotensin II

Angiotensin II regulates blood pressure and may affect adipogenesis and adipocyte metabolism. Angiotensin II is produced by cleavage of angiotensinogen by renin and angiotensin-converting enzyme in the circulation. In addition, angiotensin II may be produced in various tissues by enzymes of the renin-angiotensin system (RAS) or the nonrenin-angiotensin system (NRAS). We have analyzed the expression of angiotensinogen and enzymes required for its conversion to angiotensin II in human adipose tissue. Northern blot demonstrated angiotensinogen expression in adipose tissue from nine obese subjects. Western blot revealed a distinct band of expected size of the angiotensinogen protein (61 kDa) in isolated adipocytes. RT-PCR, followed by Southern blot, demonstrated renin expression in human adipose tissue. Angiotensin-converting enzyme messenger RNA was detected by RT-PCR, and the identity of the PCR products was verified by restriction enzyme cleavage. Transcripts for cathepsin D and cathepsin G, components of the NRAS, were detected by RT-PCR, verified by restriction enzyme cleavage. We conclude that human adipose tissue expresses angiotensinogen and enzymes of RAS and NRAS. This opens the possibility that angiotensinogen-derived peptides, produced in adipose tissue itself, may affect adipogenesis and play a role in the pathogenesis of obesity.

Cloning of two novel growth hormone transcripts expressed in human placenta

Several isoforms of human GH (hGH) are produced by two related genes expressed in the pituitary (hGH-N) and in the placenta (hGH-V). These genes consist of five exons (denoted 1-5) separated by four introns (denoted A-D). In the present report, two new transcripts of the hGH-V gene are described. The coding region of the hGH-V gene was amplified by RT-PCR using placental complementary DNA as template. DNA sequencing of several clones revealed two novel transcripts. One had a 45-bp deletion caused by the use of an alternative splice acceptor site within exon 3, similar to that in the hGH-N gene, predicting a 20-kDa isoform of hGH-V. The other transcript was generated by the use of an alternative splice donor site causing a 4-bp deletion in the end of exon 4, predicting a 24-kDa protein with 219 amino acids, which we refer to as hGH-V3. The carboxy-terminal sequence of hGH-V3 differs from 22-kDa hGH-V and hGH-V2, the two previously reported transcripts of the hGH-V gene, and does not contain a predicted transmembrane domain as described for hGH-V2. Ligase chain reaction was then used to analyze the possible use of the same splicing pattern in transcripts derived from the other genes of the hGH-gene cluster. Alternatively spliced transcripts encoding the 20-kDa hGH isoform were detected from the hGH-N and hGH-V genes, but not from the human chorionic somatomammotropin-A/B genes. The alternative splicing generating hGH-V3 was only demonstrated in transcripts derived from the hGH-V gene. Using competitive RT-PCR, the expression of hGH-V3 was estimated to be 10% of the hGH-V messenger RNA in full-term normal placentas and in placentas from pathological pregnancies. The 20-kDa hGH-V was detected in two of four full-term normal placentas, whereas a weak signal was observed in one of the pathological placentas. We conclude that the hGH-V primary transcript undergoes alternative splicing pathways generating at least four different messenger RNAs, predicting the expression of different hGH isoforms, including two with a complete sequence divergence in the carboxy-terminus.

Short-term changes in serum leptin levels provide a strong metabolic marker for the growth response to growth hormone treatment in children. Swedish Study Group for Growth Hormone Treatment

The growth response to GH treatment varies between children. Besides regulating longitudinal growth, GH exerts important metabolic effects, including lipolysis. In this study we examined whether GH-induced changes in serum levels of the adipose tissue-derived hormone leptin can be used as a marker for the long term growth response to GH treatment in short prepubertal children. The study group consisted of 150 children (21 girls and 129 boys), who were 3-15 yr of age at the start of GH treatment and had a maximum GH secretory capacity ranging from very low to high. They were treated with GH (0.1 IU/kg x day) and followed for at least 1 yr. The first year mean increase in height SD score was 0.79 (SD, 0.34), with a broad range (0.08-2.27). Serum leptin concentrations were significantly reduced after 1, 3, and 12 months of GH treatment compared with levels at the start of treatment. The growth response correlated with the serum leptin concentration at the start of treatment (r = 0.49; P < 0.0001) and with the change in serum leptin concentration after both 1 month (r = -0.41; P < 0.01) and 3 months (r = -0.60; P < 0.0001) of treatment. When multiple stepwise regression analysis was applied to the auxological and biochemical variables that correlated (P < 0.10) with the first year growth response to GH treatment, the 3-month change in serum leptin concentration was the single most important variable for explaining the variance in individual growth responses. We conclude that leptin levels at the start of GH treatment as well as short term changes in leptin levels in response to GH treatment are valuable markers of the long term growth response.

Familial predisposition for obesity may modify the predictive value of serum leptin concentrations for long-term weight change in obese women

Leptin is believed to play a role in regulating food intake and body weight. The aim of this study was to examine the influence of parental history of obesity on the association between baseline serum leptin concentrations and subsequent 4-y weight changes. Changes in food intake were also considered in the analysis. Middle-aged, obese women with no obese parent (n = 25) or at least one obese parent (n = 24) were included in the analysis. At baseline, women with no parental history of obesity and women with a parental history of obesity did not differ in body mass index (in kg/m2: 41.2 and 40.2, respectively) or median leptin concentrations (40.8 and 38.8 microg/L, respectively). Four-year weight changes varied widely in both groups combined (from -30 to 24 kg). Stratified regression analysis, adjusted for age, weight, and height, revealed that high leptin concentrations predicted less weight gain (or more weight loss) in women with no obese parent (beta = -21.2, P = 0.0006) but played no significant role in predicting weight gain in women with at least one obese parent (beta = -3.8, P = 0.41). Adding changes in energy and fat intakes to the model reduced the association between leptin and weight change to nonsignificance in the women with no obese parent, indicating that the effect of leptin could be explained largely by dietary changes. In conclusion, serum leptin concentrations predict long-term weight change in obese women with no history of parental obesity, an association largely mediated by changes in food intake.

Growth hormone treatment prevents the decrease in insulin-like growth factor I gene expression in patients undergoing abdominal surgery

Acquired GH resistance together with reduced skeletal muscle mass are found in patients with increased protein catabolism due, for example, to sepsis, trauma, or major surgery. Both administration of glutamine-containing parenteral nutrition and GH treatment have been found to diminish this catabolism. The effects of GH are mediated in part by insulin-like growth factor I (IGF-I) that is produced in the liver and locally in GH target tissues. The aim of this study was to investigate the effect of GH treatment on expression of the IGF-I gene and GH receptor (GHR) gene in skeletal muscle after major surgery. A new quantitative RT-PCR-based assay was established to measure IGF-I gene expression. Metabolically healthy patients, without significant preoperative weight loss, who were undergoing elective abdominal surgery were included in the study. Five patients (one woman and four men) were treated with daily injections of GH (0.3 IU/kg.day) in addition to being given total parenteral nutrition including glutamine (0.28 g/kg.day). The control group consisted of eight patients (three women and five men), who were given glutamine-enriched total parenteral nutrition but no GH. A muscle biopsy was taken from the lateral portion of the quadriceps femoris muscle preoperatively (day 0) after induction of anesthesia. A second biopsy was taken under local anesthesia on postoperative day 3. Total ribonucleic acid (RNA) was extracted from the muscle biopsies, and IGF-I messenger RNA (mRNA) and GHR mRNA were measured by competitive quantitative RT-PCR assays. IGF-I mRNA and GHR mRNA levels were related to the expression of a housekeeping gene (cyclophilin). In the control group, IGF-I mRNA levels decreased from 1505 +/- 265 (mean +/- SEM) transcripts/cpm cyclophilin on day 0 to 828 +/- 172 on day 3 (P < 0.05). In contrast, IGF-I mRNA levels did not change in the GH-treated group (1188 +/- 400 transcripts/cpm cyclophilin on day 0 vs. 1089 +/- 342 transcripts/cpm cyclophilin on day 3). No statistically significant changes were seen in GHR expression. We conclude that administration of GH prevents the reduction in IGF-I gene expression in skeletal muscle after abdominal surgery.

Effects of growth hormone treatment on the leptin system and on energy expenditure in abdominally obese men

The present study has examined the short- and long-term effects of growth hormone (GH) treatment on the leptin system and energy expenditure. Thirty male individuals with abdominal obesity were randomised to GH or placebo treatment in a 9-month, double-blind study. The dose of GH was 9.5 microg/kg, administered subcutaneously every evening. Serum leptin concentrations were measured by a human leptin RIA. Total RNA was isolated from adipose tissue biopsies and leptin mRNA levels were determined by a semi-quantitative reverse transcriptase-PCR assay. Body composition was determined by potassium-40 and the basal metabolic rate (BMR) was measured by a computerised, ventilated, open-hood system. As compared with placebo, an overall decrease in serum leptin concentrations as assessed by the area under the curve (AUC) (P < 0.05) and an increase in BMR (AUC, P < 0.05) were observed during GH treatment. The overall GH-induced changes were due to marked changes in serum leptin concentrations and BMR after 6 weeks of treatment. After 9 months of GH treatment there was a significant reduction in body fat (BF) while serum leptin concentrations and BMR did not differ from baseline values. Leptin mRNA levels did not change over the study period. We speculate that long-term GH treatment induces a new energy balance steady state with decreased BF stores. The effects of GH on the leptin system is suggested to be of importance for the maintenance of a lower BF mass.

Growth hormone-binding protein levels over one year in healthy prepubertal children: intraindividual variation and correlation with height velocity

The role of GH-binding protein (GHBP) in growth regulation is still under debate. We investigated 29 prepubertal healthy children (13 girls/16 boys; mean age 9.3 y to study intraindividual variation in serum GHBP and to explore whether any such variation was related to changes in IGF-I, IGF-binding protein-3 (IGFBP-3) or urinary excretion of GH. The relationship between changes in GHBP concentrations, short-term height velocity, and changes in body composition was also studied. Blood samples were taken every month for 1 y, for measurements of GHBP, IGF-I, and IGFBP-3. The mean coefficient of variation in monthly GHBP concentrations in individual children was 18% (range, 6.7-33.0%). The values for each child were normalized by expressing the concentration as a ratio to the mean GHBP concentration. GHBP values were highest in January and lowest in August (22% difference). Maximal monthly changes in GHBP correlated with simultaneous changes in weight (rs = 0.38, p < 0.05) and IGF-I (rs = 0.38, p < 0.05). The mean GHBP concentration during the year correlated with height velocity (rs = 0.37, p < 0.05) and the mean serum concentration of IGF-I (rs = 0.42, p < 0.05) and IGFBP-3 (rs = 0.60, p < 0.001). We conclude that there is a significant monthly variation in GHBP concentrations in healthy prepubertal boys and girls, which is correlated to changes in weight and IGF-I. The mean GHBP concentration during the year is correlated with the mean serum concentrations of IGF-I, IGFBP-3, and with height velocity. Thus, the variation in GHBP concentrations appears to mirror GH sensitivity, because no parallel changes in urinary GH excretion were observed.

Differential expression and regulation of leptin receptor isoforms in the rat brain: effects of fasting and oestrogen

Leptin affects body weight and reproduction mainly via receptors in the central nervous system. Different isoforms of the leptin receptor (leptin-R) exist, including a long isoform (leptin-RL) with signalling capacity and short isoforms (leptin-RS) with unknown function. The aim of this study was to examine leptin-R gene expression in different regions of the brain under conditions with altered body weight, in the female rat, including ovariectomy (OVX), oestradiol (E2) treatment, fasting and a genetic model of obesity (Zucker fa/fa). Leptin-R gene expression was analysed by in situ hybridization using probes recognizing all receptor isoforms (leptin-R) or specifically leptin-RL. Transcripts recognized by the leptin-R probe were abundant in the choroid plexus (CP), arcuate nucleus (ARC), ventromedial nucleus (VMN), thalamus (TH) and piriform cortex (PC). Leptin-RL transcripts were detected in the ARC, VMN, TH and PC but not in the CP. Although no sex difference was observed, leptin-R gene expression was reduced by E2 administration and increased by OVX. Administration of E2 reduced leptin-RL gene expression in the ARC and VMN but did not alter the expression in the TH or PC. OVX had no effect on the expression of leptin-RL mRNA. Fasting also caused a differential regulation of leptin-R mRNAs, with an increase in abundance of leptin-RL transcripts in the TH despite a decrease in leptin-R in this area. Obese Zucker rats had a similar pattern of expression with an increased expression of leptin-RL transcripts in all brain areas analysed and a decrease in leptin-R gene expression. These results demonstrate a differential regulation of leptin-RL and leptin-RS which could provide a mechanism for regulating access to, and sensitivity of, discrete regions of the brain for circulating leptin. We suggest that fasting and E2 alter the balance between leptin-RL and leptin-RS and that this could increase tissue sensitivity to leptin.

Characterization and chromosomal localization of rat scavenger receptor class B type I, a high density lipoprotein receptor with a putative leucine zipper domain and peroxisomal targeting sequence

High density lipoprotein (HDL) participates in reverse cholesterol transport and in the delivery of cholesterol to steroid-producing tissues. Scavenger receptor class B type I (SR-BI) was recently shown to bind HDL and mediate internalization of its cholesterol content. We have cloned the rat homolog of this receptor, determined its chromosomal location, and examined its expression in rat tissues and in a model of follicular development, ovulation, and luteinization. The predicted protein contained two transmembrane domains, a leucine zipper motif, and a peroxisomal targeting sequence. The rat and human SR-BI genes were mapped to a region previously linked between rat and human chromosomes 12. SR-BI gene expression was detected in several rat tissues, with high levels in ovarian tissue, liver, and adrenal cortex, as determined by ribonuclease protection assay and in situ hybridization. A significant increase in SR-BI gene expression was detected in the late phase of corpus luteum formation, and transcripts were abundant in corpus luteum and in thecal cells at all stages of follicular development. In conclusion, the rat SR-BI complementary DNA predicted a protein with several conserved motifs, including a putative leucine zipper and a peroxisomal targeting sequence. The chromosomal locations of the rat and human SR-BI homologs suggest that this gene is a new member of a previously reported, conserved synteny group. SR-BI gene expression was high in steroid-producing tissues and in the liver, consistent with a role of this receptor in the uptake of HDL cholesterol.

Expression of functional leptin receptors in the human ovary

The size of body fat stores is known to influence fertility, indicating a link between adipose tissue and the reproductive system. Studies in mice have identified the adipocyte-derived hormone, leptin (Ob protein), as a possible mediator of this effect. The aim of this study was to investigate the possibility that leptin may have direct effects on the human ovary. To probe this hypothesis we first analyzed the expression of leptin receptors in the human ovary. Transcripts encoding both the long and short isoforms of the leptin receptor were present in human granulosa cells and thecal cells; however, the short isoforms were expressed at much higher levels. Immunoreactive leptin was present in follicular fluid at levels similar to those found in serum. ob gene expression, however, was undetectable in the ovary, as determined by reverse transcription-PCR, whereas it was easily detected in adipose tissue. To determine whether leptin could induce a biological response in ovarian cells, we examined the effect of leptin on estradiol production in cultured granulosa cells. Leptin (100 ng/mL) inhibited LH (0.1 ng/mL)-stimulated estradiol production. In contrast, leptin had no effect on estradiol production in the absence of LH. In conclusion, this study has demonstrated that the leptin receptor is expressed in the human ovary, that leptin is present in follicular fluid, and that leptin can induce a biological response in ovarian cells. These results suggest that leptin may have a direct effect on the human ovary.

Mechanisms of growth failure in non-growth-hormone deficient children of short stature

So far, the clinical evaluation of short children has focused on the measurement of immunoreactive growth hormone (GH) in the blood to determine if the growth retardation is due to GH deficiency. However, GH-dependent short stature may be caused by defects in either the secretion of bioactive GH or by the inability to respond to GH. Both GH secretion and GH responsiveness should, therefore, be evaluated when investigating the cause of short stature. Recent advances in molecular biology have generated new ways of studying different molecules involved in growth regulation, and new genetic defects have been identified in short children.

No evidence for involvement of the growth hormone/insulin-like growth factor-1 axis in psoriasis

We have examined whether alterations in the growth hormone/insulin-like growth factor-1 axis play a role in the pathogenesis of psoriasis. Serum, urine, full skin biopsies, and suction blister roofs were obtained from patients with psoriasis and from healthy controls. Serum concentrations of insulin-like growth factor-1 and insulin-like growth factor binding protein-3 were measured by radioimmunoassay. Growth hormone-binding protein was measured by ligand-mediated immunofunctional assay. Growth hormone concentration in urine was measured by an immunometric assay, and growth hormone receptor-gene expression was measured by RNase protection assay or by quantitative reverse transcriptase polymerase chain reaction in total RNA isolated from epidermal suction blister roofs. Serum concentrations of insulin-like growth factor-1 (249 +/- 12 micrograms per liter, mean +/- SEM, n = 42, and 277 +/- 21 micrograms per liter, n = 9, for psoriatic patients and controls, respectively), insulin-like growth factor binding protein-3 (3.1 +/- 0.08 mg per liter, n = 42, and 3.3 +/- 0.22 mg per liter, n = 9), growth hormone-binding protein (344 +/- 65 pmol per liter, n = 10, and 311 +/- 83 pmol per liter, n = 9), urinary growth hormone excretion during 24 h (12.8 +/- 2.7 microIU per 24 h, n = 12, and 12.3 +/- 1.6 microIU per 24 h, n = 9), and epidermal growth hormone receptor gene expression [32 +/- 12 x 10(3) mRNA transcripts per microgram total RNA (involved skin), n = 11, and 47 +/- 14 x 10(3) mRNA transcripts per microgram total RNA, n = 9] were similar in patients and controls. For insulin-like growth factor-1 and insulin-like growth factor binding protein-3 the values in psoriatic patients were also similar to those in larger control groups, n = 195 and n = 400, respectively. In addition, we found no evidence of local expression of growth hormone or prolactin in full skin punch biopsies from psoriatic involved skin by reverse transcriptase polymerase chain reaction. In conclusion, our results suggest that alterations in the growth hormone/ insulin-like growth factor-1 axis do not play a major role in the pathogenesis of psoriasis.

Serum leptin concentrations in relation to pubertal development

OBJECTIVES

The amount of adipose tissue influences pubertal development and fertility in girls. A candidate for mediating this is the hormone leptin, derived from adipocytes. This work was carried out to determine whether the leptin concentration in serum is regulated during pubertal development.

SUBJECTS AND METHODS

Serum concentrations of leptin were determined by radioimmunoassay in a sample of 252 healthy children representing all pubertal stages.

RESULTS

Serum leptin concentrations correlated directly with age (r = 0.53), body mass index (BMI) (r = 0.71), and weight for height SD score (r = 0.44) in girls and with BMI (r = 0.33) and weight for height SD score in boys (r = 0.36). Leptin concentrations increased with pubertal development in girls, resulting in significantly higher concentrations at pubertal stages 4 and 5 than at the prepubertal stage, whereas there was no change in the boys.

CONCLUSIONS

Serum leptin concentrations increased during pubertal development in the girls, but remained constant in the boys. Whether the increase in serum leptin concentrations in girls is of importance for, or a consequence of, pubertal development is still to be determined.

Serum leptin in short children born small for gestational age: relationship with the growth response to growth hormone treatment. The Swedish Study Group for Growth Hormone Treatment

The product of the obese (ob) gene, leptin, is an adipocyte-derived hormone that is involved in the regulation of appetite and body weight. This study was undertaken in order to describe the basal serum levels of leptin in prepubertal short children born small for gestational age (SGA) and their relationship with growth parameters, before and during growth hormone (GH) treatment. Eighty-nine prepubertal short children (66 boys, 23 girls; height standard deviation score (SDS), -5.4 to -2.0; age, 2.0 to 12.8 years) born SGA, 12 of whom (9 boys, 3 girls) had signs of Silver-Russell syndrome, were included in the study. Serum leptin concentrations were measured by radioimmunoassay. Leptin levels in the children born SGA were compared with those in a reference group of 109 prepubertal healthy children born at an appropriate size for gestational age (AGA). The mean (S.D.) change in height SDS was 0.11 (0.22) during the year before the start of GH therapy (0.1 IU/kg/day) and increased to 0.82 (0.44) during the first year (P < 0.001) and to 1.28 (0.59) during the 2-year period of GH therapy (P < 0.001). The children born SGA were significantly leaner than the reference group. An inverse correlation was found between leptin and chronological age in the SGA group (r = -0.31, P < 0.01). The mean serum level of leptin in the children born SGA who were older than 5.5 years of age was 2.8 micrograms/l which was significantly lower than the mean value of 3.7 micrograms/l found in the children born AGA of the same age range. The difference remained after adjustment of leptin levels for sex, age, body mass index (BMI) and weight-for-height SDS (WHSDSSDS). Leptin correlated with WHSDSSDS (r = 0.32, P < 0.001) and BMI (r = 0.36, P < 0.01) in the reference population, but not in the SGA group. No correlation was found between leptin and spontaneous 24-h GH secretion, insulin-like growth factor (IGF)-I or IGF-binding protein-3 levels, or with fasting insulin or cortisol levels. Leptin levels at the start of GH treatment were correlated with the growth response over both 1 year (r = 0.46, P < 0.001) and 2 years (r = 0.51, P < 0.001) of GH therapy. Using multiple regression analysis, models including leptin levels at the start of GH therapy could explain 51% of the variance in the growth response after 1 year and 44% after 2 years of GH treatment. In conclusion, serum leptin levels are reduced in short children born SGA and are inversely correlated with chronological age. Leptin concentrations correlate with the growth response to GH treatment and might be used as a marker for predicting the growth response to GH treatment.

Increased proportion of circulating non-22-kilodalton growth hormone isoforms in short children: a possible mechanism for growth failure

Current knowledge about the interaction between GH and its receptor suggests that the molecular heterogeneity of circulating GH may have important implications for growth. The aim of this study was to investigate the proportion of circulating non-22-kDa GH isoforms in prepubertal children with short stature (height less than -2 SD score) of different etiologies. We have also evaluated the relationships among the ratio of non-22-kDa GH isoforms, auxology, and spontaneous GH secretion. The study groups consisted of 17 girls with Turner's syndrome (TS), aged 3-13 yr, 25 children born small for gestational age (SGA) without postnatal catch-up growth, aged 3-13 yr; and 24 children with idiopathic short stature (ISS), aged 4-15 yr. The results were compared with those from 23 prepubertal healthy children of normal stature (height +/- 2 SD score), aged 4-13 yr. Serum non-22-kDa GH levels, expressed as a percentage of the total GH concentration, were determined by the 22-kDa GH exclusion assay, which is based on immunomagnetic extraction of monomeric and dimeric 22-kDa GH from serum and quantitation of non-22-kDa GH using a polyclonal antibody-based GH assay. All samples were selected from spontaneous GH peaks in 24-h GH profiles. The median proportion of non-22-kDa GH isoforms was increased in children born SGA (9.8%; P = 0.05) and girls with TS (9.9%; P = 0.01), but not in the group of children with ISS (8.9%), compared with that in normal children (8.1%). Individually, increased proportions of non-22-kDa GH isoforms, with values more than 2 SD above the mean for the normal group, were observed in 5 girls with TS, 5 children born SGA, and 4 children with ISS. In children born SGA, the proportion of non-22-kDa GH isoforms was directly correlated with different estimates of spontaneous GH secretion [mean 24-h GH concentration (r = 0.41; P = 0.04), area under the curve over baseline (r = 0.41; P = 0.04), and GH peak area (r = 0.61; P = 0.003)], whereas it was inversely correlated with height SD score (r = -0.42; P = 0.04). In conclusion, an increased proportion of circulating non-22-kDa GH isoforms was observed at spontaneous GH peaks in some non-GH-deficient short children. Our results suggest that the ratio of non-22-kDa GH isoforms in the circulation may have important implications for normal and abnormal growth.

Circulating non-22 kDa growth hormone isoforms in healthy children of normal stature: relation to height, body mass and pubertal development

The proportion of non-22 kDa GH isoforms was evaluated in 93 healthy children (48 boys aged 6.8-18.4 years and 45 girls aged 3.9-18.4 years) of normal stature (height +/- 2 s.d. score) at different stages of puberty. In addition, correlations among the proportion of non-22 kDa GH isoforms, auxology, spontaneous GH secretion and biochemical measurements were investigated. Serum non-22 kDa GH levels, expressed as percentage of total GH concentration in the samples, were determined by the 22 kDa GH exclusion assay, in which monomeric and dimeric 22 kDa GH are removed from serum and the non-22 kDa GH isoforms are quantitated using a polyclonal antibody GH assay. Samples were selected from spontaneous GH peaks in 24-h GH profiles. For boys, the median proportion of non-22 kDa GH isoforms was 8.5% (range 3.2-26.6%) and for girls it was 9.6% (1.8-17.4%), with no influence of age and no sex-related difference in prepubertal (boys, 7.2%; girls, 8.8%) or pubertal children (boys, 9.1%; girls, 9.9%). However, the median proportion of non-22 kDa GH isoforms was significantly higher in pubertal boys (9.1%) than in prepubertal boys (7.2%; P = 0.03). In pubertal boys, height S.D. scores (SDS) were inversely correlated to the proportion of non-22 kDa GH isoforms (r = -0.38; P = 0.02), especially at mid-puberty (r = -0.7; P = 0.01), indicating that the presence of increased amounts of circulating non-22 kDa GH isoforms was associated with less growth. In prepubertal children, positive correlations between non-22 kDa GH and weight SDS (r = 0.46; P = 0.03), weight-for-height SDS (r = 0.51; P = 0.01) and body mass index (r = 0.42; P = 0.04) were observed. No significant correlations were seen with spontaneous GH secretion or measurements of IGF-1, IGF-binding protein-3, insulin and leptin. These findings in normal children indicate that the proportion of circulating non-22 kDa GH isoforms may have physiologic significance for growth and metabolism in different stages of development, and emphasize the importance of evaluating the circulating ratio of 22 kDa and non-22 kDa GH in children with growth disorders.

Leptin levels are strongly correlated with those of GH-binding protein in prepubertal children

OBJECTIVE

Nutritional status is an important determinant of growth, and previous studies have indicated that this is due, at least in part, to an increased target-tissue sensitivity to GH. An attractive candidate for mediating this effect is leptin, a hormone secreted by the adipose tissue. The aim of this study was to investigate if there was a connection between GH-binding protein (GHBP) and leptin.

DESIGN AND METHODS

We investigated the relationship between serum levels of leptin and those of GHBP in 229 prepubertal children. These included 107 healthy children with normal GH secretion, 55 GH-deficient (GHD) children and 55 children born small for gestational age (SGA) sampled on one occasion for GHBP and leptin, and 12 healthy children followed longitudinally at monthly interval for 1 year.

RESULTS

In the healthy children and in those born SGA, the serum concentration of GHBP was positively correlated with that of leptin (r = 0.65, P < 0.001; r = 0.74, P < 0.001 respectively). There was no correlation between GHBP and leptin in the group of children with GHD (r = 0.27, not significant). This means that leptin alone explained 42% of the variation of GHBP in the healthy group and 55% in the SGA group. The correlation remained after adjustment for body mass index and age in the healthy children (r = 0.57, P < 0.0001, r2 = 0.33) and for children born SGA (r = 0.74, P < 0.0001, r2 = 0.55). There was a positive correlation between the intra-individual monthly changes in GHBP and changes in leptin respectively, in the 12 healthy children followed longitudinally, the mean of the correlation coefficients was 0.38 (median = 0.29; range 0.03 to 0.86; P < 0.05).

CONCLUSIONS

There was a highly significant correlation between serum levels of leptin and those of GHBP, except in children with GHD. The possibility that leptin could mediate the effects of body fat mass on GH sensitivity, therefore, merits further investigation.

Circulating non-22-kilodalton growth hormone isoforms in acromegalic men before and after transsphenoidal surgery

GH represents several molecular isoforms in addition to the main 22-kDa (22K) GH. There have been reports suggesting that circulating non-22K GH isoforms are increased in acromegaly, but the possible implications of such observations in the management of the disease have not been addressed. The aim of this study was to evaluate the proportion of circulating non-22K GH isoforms in acromegaly. In addition, the relationships between the amount of non-22K GH and tumor size, biochemical measurements, and body composition also were investigated. Samples with different GH levels were selected from 24-h GH profiles from 15 acromegalic men evaluated before and 1 yr after transsphenoidal surgery and from 13 healthy men. The serum non-22K GH levels, expressed as percentage of total GH concentration, were determined by the 22K GH exclusion assay, which is based on immunomagnetic extraction of 22K GH from serum and quantitation of non-22K GH using a polyclonal GH assay. The proportion of non-22K GH isoforms was fairly constant in different samples from the same patient, regardless of the GH level. However, a wide variation of values was observed among acromegalics, both before (14-51%) and after surgery (8-62%). The proportion of non-22K GH isoforms was increased in untreated patients, compared with controls (26.6 vs. 17.4%; P < 0.01), and the values correlated significantly to tumor size, mean 24-h GH concentration, serum PRL, and extracellular water. After surgery, patients not truly cured, with mean 24-h GH concentration of 1 microg/L or more, had an increased proportion of non-22K GH, compared with those with levels less than 1 microg/L (P < 0.01). In the former group, the median values were similar than those in untreated acromegalics (34 vs. 26.6%, respectively), whereas in the latter, they were comparable with those in the controls (15.2 vs. 17.4%, respectively). We conclude that acromegalics have an increased proportion of circulating non-22K GH isoforms. The values are fairly constant in different samples from an individual, regardless of GH level, but a large spectrum can be observed among patients. This variability suggests that different pituitary adenomas secrete GH isoforms in variable amounts. Our observation that a higher proportion of non-22K GH isoforms is present in patients not truly cured after surgery suggests that the evaluation of non-22K GH isoforms can be useful in the follow-up of acromegalic patients.

Growth hormone (GH)-binding protein in prepubertal short children born small for gestational age: effects of growth hormone treatment. Swedish Study Group for Growth Hormone Treatment

This study was undertaken to characterize the serum levels of GH-binding protein (GHBP) before and during GH treatment in prepubertal short children born small for gestational age (SGA) and their relationship with growth parameters. Sixty-seven prepubertal short children (49 boys and 18 girls; height SD score, -5.4 to -2.0; age, 2.0-12.8 yr) born SGA, 8 of whom (6 boys and 2 girls) had signs of Silver-Russell syndrome, participated in the study. Total GHBP was measured by a ligand-mediated immunofunctional assay. The mean (SD) change in height SD score during the year before the start of GH treatment (0.1 IU/kg.day) was 0.11 (0.20) SD score, and this value increased to a 0.84 (0.43) SD score during the first year (P < 0.001) and to a 1.27 (0.63) SD score during the 2-yr period of therapy (P < 0.001). The baseline GHBP values ranged from 49-392 pmol/L, and no relationships were found among sex, chronological age, and maximal GH response to an arginine-insulin tolerance test. A positive correlation between GHBP and body composition, expressed as weight for height SD score, was found in the whole group (r = 0.28; P < 0.05) and in boys (r = 0.44; P < 0.01). No relationship was found between GHBP and spontaneous 24-h GH secretion, in terms of either GH secretion rate or pulsatile pattern, whereas GHBP was positively correlated with insulin-like growth factor I (IGF-I) SD score (r = 0.28; P < 0.05) and IGF-binding protein-3 SD score (r = 0.39; P < 0.01). Using a multiple stepwise linear regression analysis, the model using the IGF-binding protein-3 SD score and the weight for height SD score at the start of GH therapy accounted for 33% of the variance in the baseline GHBP values. A mean increase of 27 (51)% in GHBP levels was found after 1 yr of therapy. However, a high degree of variability in the response of individuals to GH treatment in terms of GHBP levels was observed: in some children GHBP levels increased, whereas in others they decreased. In conclusion, GHBP levels in short prepubertal children born SGA were mostly within the normal range previously reported and correlated directly with body composition. An increase in GHBP levels was observed during GH treatment in some SGA children. No correlation was found between pretreatment GHBP levels and growth response to GH treatment.

Measurement of human growth hormone receptor messenger ribonucleic acid by a quantitative polymerase chain reaction-based assay: demonstration of reduced expression after elective surgery

Studies of GH receptor (GHR) gene expression in human tissues have been hampered by the limited amount of tissue available for analysis and the low sensitivity of conventional methods. We have developed a quantitative reverse transcriptase-PCR assay for measurement of GHR messenger ribonucleic acid levels in small human tissue biopsies. To compensate for sample to sample variation, an internal RNA standard, which differs from the wild-type GHR transcript by only a few nucleotides, was reverse transcribed and amplified together with the GHR transcripts. PCR was carried out using one biotinylated primer to permit the purification of single stranded PCR products on streptavidin-coated microtiter plates. The ratio between the wild-type and mutated transcripts was determined by two separate minisequence reactions in which a primer, annealed immediately 3' of a variable nucleotide, was extended by a single 3H-labeled nucleotide, complementary to either the wild-type or mutated sequence. The assay range was 0.125-8 x 10(5) transcripts/sample, the mean intraassay coefficient of variation was 8.7%, and the lower limit of detection was 0.125 x 10(5) transcripts/sample. GHR messenger ribonucleic acid levels were detectable in small amounts (10-100 ng) of total RNA extracted from adipose tissue, skeletal muscle, and liver. The GHR gene expression in liver was approximately 10-fold higher than that in skeletal muscle, whereas intermediate levels were found in adipose tissue. In nine patients undergoing elective abdominal surgery, GHR gene expression in skeletal muscle was reduced on day 3 after surgery compared to the baseline level. The decrease in GHR gene expression was accompanied by a decrease in skeletal muscle glutamine. This suggests that the postoperative protein catabolism may be caused at least partly by acquired GH insensitivity due to reduced expression of the GHR gene.

Obese (ob) gene defects are rare in human obesity

Our knowledge of the role of the recently cloned ob-protein (leptin) in the regulation of body fat stores is largely derived from experiments performed in mice. Different mouse models exhibit abnormalities in ob-gene expression, with extreme overexpression in mice which lack bioactive ob-protein, have nonfunctional ob-receptors or hypothalamic lesions, and undetectable expression in mice with suggested defects in regulatory elements. The aim of this study is to examine if defects, corresponding to those in mice, exist in human obesity. Adipose tissue was obtained from 94 adult obese subjects and from six children who had developed obesity after surgery in the hypothalamic region. Total RNA was isolated and ob-gene expression was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Northern blot. The coding region of the ob-gene was sequenced in both directions in the 94 obese adults. No mutations were detected in the coding region of the ob-gene and ob-gene expression was detectable in all subjects and none of the subjects had an extreme overexpression. There was no systematic increase in ob-expression in obese children with hypothalamic disease compared to their healthy brothers and sisters. These results show that severe abnormalities involving the ob-gene, analogous to those described in mouse models, are rare in human obesity. We therefore conclude that the cloning and subsequent analysis of the ob-gene has not provided information that can, by itself, explain the genetic component in the development of human obesity.

22-kD growth hormone exclusion assay: a new approach to measurement of non-22-kD growth hormone isoforms in human blood

Human growth hormone (GH) exists in a variety of isoforms. In the pituitary, the most abundant isoform is 22-kD GH (22 K GH), while other isoforms (non-22 K GH) are present in variable amounts. In human plasma, the GH heterogeneity contributes to the wide variability in GH levels measured by different immunoassays. The physiological role of the non-22 K GH isoforms is poorly understood, but they may represent a spectrum of agonists or antagonists of the GH receptor. It is possible that increased amounts of non-22 K GH isoforms in the circulation contribute to the growth failure observed in some short children and may be involved in the pathophysiology of acromegaly and other unrelated diseases. Currently, there is no method available to evaluate the ratio of non-22 K GH isoforms to total GH in large sets of serum samples. In this report, a novel assay procedure is described in which monomeric and dimeric isoforms of 22 K GH are removed from serum and non-22 K GH isoforms are quantitated. The 22 K GH exclusion assay (22 K GHEA) was established as a screening method to identify conditions in which the ratio of non-22 K GH isoforms to total GH in human blood is altered. A 22 K GH-specific monoclonal antibody (MCB) is used for binding to 22 K GH in serum. Magnetic beads coated with rat anti-mouse immunoglobulin G and a magnetic device are used to remove the 22K GH-MCB complexes from serum. The non-22 K GH isoforms are measured by a polyclonal antibody-based immunoradiometric assay (GH-IRMA). The assay procedure was optimized systematically by statistical experimental designs. In serum spiked with monomeric or dimeric 22 K GH, the 22 K GH extraction was efficient at GH levels up to 100 microg/l (range 96.3-100%). The intra- and interassay precision for non-22K GH levels of 3.9 microg/l were 2.6% and 8.7%, respectively, while for levels of 0.6 microg/l, which were very close to the detection limits of the assay, the coefficients were 17.0% and 21.6%, respectively. The percentage of non-22 K GH isoforms determined in serum samples from three different groups of subjects showed clearly distinctive values. The 22 K GHEA is a new method for evaluation of non-22 K GH isoforms in human blood under different physiological and pathophysiological conditions.

Recombinant human growth hormone (GH)-binding protein enhances the growth-promoting activity of human GH in the rat

To address the role of the GH-binding protein (GHBP) in GH physiology, two forms of recombinant human GHBP (rhGHBP) were given alone or in combination with rhGH to hypophysectomized rats or GH-deficient dwarf rats. Hypophysectomized rats were given daily sc injections of excipient, hGH, rhGHBP, or rhGH plus rhGHBP (produced in Escherichia coli) for 7 days. Injections of rhGH induced dose-related body weight gain and bone growth that were increased by the coadministration of rhGHBP with rhGH; rhGHBP alone had no effect. Serum insulin-like growth factor increased 24 h later when rhGH was given together with rhGHBP (P < 0.01), but not when rhGH was given alone. E. coli-derived rhGHBP also enhanced the bioactivity of coadministered rhGH in the GH-deficient dwarf rat. In contrast, the glycosylated rhGHBP, made in human A293 cells, inhibited the growth-promoting activity of coadministered rhGH. The opposite effects of these two forms of rhGHBP could be explained by clearance studies that showed radiolabeled rhGH bound to A293 cell-derived rhGHBP to be cleared more rapidly from the blood than free rhGH. Natural rabbit GHBP and E. coli-derived rhGHBP both prolonged the presence of rhGH in blood. It is proposed that by slowing the clearance of GH, GHBP increased the bioactivity of GH. In summary, codelivery of rhGHBP and rhGH caused a dose-dependent enhancement of the activity of rhGH in two rat models of GH deficiency. This suggests that endogenous circulating GHBP may increase the activity of blood-borne GH in a similar manner.

Partial growth hormone insensitivity in childhood

There appears to be a continuum of GH-responsiveness, ranging from complete GH-resistance in Laron syndrome to normal GH-sensitivity. Partial GHI is suggested by findings at both ends of this spectrum; some patients with Laron-type dwarfism are less severely affected by their GHI than others (Savage et al, 1993; for a review, see Savage et al, 1995) and some short, non-GH-deficient, children have reduced responsiveness to GH. Among children with ISS, we have identified a subgroup where defects at the level of the GH receptor lead to a partial-GHI syndrome (Carlsson et al, 1994; Attie et al, 1995; Goddard et al, 1995). Partial-GHI may explain the growth failure in some children who do not meet the criteria for GHD. So far, the clinical evaluation of short children has been focused on the exclusion or demonstration of GHD. The diagnosis of GHD at present requires that stimulated or spontaneous GH concentrations should fail to reach a certain, arbitrarily determined level. This assumes that GH-sensitivity is equal in all subjects, with the exception of rare cases with Laron syndrome. The diagnosis of GHD is in itself controversial, and it has been suggested that GH testing should be supplemented by other measures such as auxological evaluation and measurement of other components of the GH/IGF-I axis (Rosenfeld et al, 1995). However, the fact that some short children have partial-GHI suggests that both GH secretion and GH responsiveness should be taken into consideration when investigating the cause of short stature (Figure 5). Many short children do not have GHD per se, but may be short due to inadequate GH stimulation because of reduced GH-sensitivity.

The rat extracellular superoxide dismutase dimer is converted to a tetramer by the exchange of a single amino acid

Extracellular superoxide dismutase (EC-SOD) is a secreted Cu and Zn-containing glycoprotein. While EC-SOD from most mammals is tetrameric and has a high affinity for heparin and heparan sulfate, rat EC-SOD has a low affinity for heparin, does not bind to heparan sulfate in vivo, and is apparently dimeric. To examine the molecular basis of the deviant physical properties of rat EC-SOD, the cDNAs of the rat and mouse EC-SODs were isolated and the deduced amino acid sequences were compared with that of human EC-SOD. Comparison of the sequences offered no obvious explanation of the differences. Analysis of a series of chimeric and point mutated EC-SODs showed that the N-terminal region contributes to the oligomeric state of the EC-SODs, and that a single amino acid, a valine (human amino acid position 24), is essential for the tetramerization. This residue is replaced by an aspartate in the rat. Rat EC-SOD carrying an Asp --> Val mutation is tetrameric and has a high heparin affinity, while mouse EC-SOD with a Val --> Asp mutation is dimeric and has lost its high heparin affinity. Thus, the rat EC-SOD dimer is converted to a tetramer by the exchange of a single amino acid. Furthermore, the cooperative action of four heparin-binding domains is necessary for high heparin affinity. These results also suggest that tetrameric EC-SODs are not symmetrical tetrahedrons, but composed of two interacting dimers, further supporting an evolutionary relationship with the dimeric cytosolic Cu and Zn-containing SODs.

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.

Mutations of the growth hormone receptor in children with idiopathic short stature. The Growth Hormone Insensitivity Study Group

BACKGROUND

Short stature in children who are not deficient in growth hormone (GH) is probably caused by a variety of defects. Some children with idiopathic short stature have low serum concentrations of GH-binding protein, which is derived from the GH receptor. The possibility that low serum concentrations of GH-binding protein might indicate partial insensitivity to GH led us to investigate possible defects in the gene for the GH receptor in children with idiopathic short stature and low serum concentrations of GH-binding protein.

METHODS

We studied 14 children with idiopathic short stature who were selected on the basis of normal GH secretion and low serum concentrations of GH-binding protein. Analysis of single-strand conformation polymorphisms and DNA sequencing were both used to identify mutations in the GH-receptor gene.

RESULTS

Mutations in the region of the GH-receptor gene that codes for the extracellular domain of the receptor were found in 4 of the 14 children, but in none of 24 normal subjects. One of the four children with mutations was a compound heterozygote, with one mutation that reduced the affinity of the receptor for GH and a second mutation that may affect a function other than ligand binding. The remaining three children had single mutations in one allele of the gene. One mutation introduced a premature termination codon, and two caused substitutions of single amino acids in a structurally conserved domain of the receptor.

CONCLUSIONS

Some children with idiopathic short stature may have partial insensitivity to GH due to mutations in the GH-receptor gene.

Growth responses to patterned GH delivery

We have investigated the effects of different patterns of administration of recombinant human growth hormone (rhGH) on weight gain, organ growth, serum GH binding protein (GHBP) and insulin-like growth factor-l (IGF-1) levels in a series of studies using hypophysectomized (Hx) or GH-deficient dwarf (dw/dw) rats. Animals were given rhGH either by subcutaneous (s.c.) injections (1 or 2 per day) or s.c. infusions and rhlGF-1 (2 mg/kg/day) by s.c. infusion. In Hx rats, all rhGH regimes increased body weight, tibial epiphyseal plate width, and organ weights in a dose-related manner. Dwarf rats showed a smaller growth response to rhGH than Hx rats, whereas rhGH induced greater elevations in serum GHBP in drarf rats. Growth responses depended on the pattern of rhGH administration (twice daily injections > continuous infusions > daily injections). The shape of the body growth curves also differed; rhGH injections increased weight gain linearly, whereas infusions gave an initial rapid weight gain which slowed with time (a curvilinear response). For both regimens, tibial epiphyseal plate width increased linearly with rhGH dose but infusions were 5-fold more potent than daily injections. Spleen and thymus weights were markedly increased by rhGH and were also affected by the pattern of GH exposure. At 5 mg rhGH/kg/day, thymus weights were 390±35 mg for injectionsvs. 613 ± 34 mg for infusions (P<0.001) compared with 248 ± 16 mg in vehicle-treated Hx controls. Infusions of rhlGF-1 also stimulated specific organ growth but caused less weight gain. RhlGF-1 additively increased the weight gain caused by rhGH injections but not by rhGH infusions. Circulating IGF-1 and GHBP levels were increased in a dose-dependent manner by rhGH infusion, whereas daily injections were ineffective. Thus, differential organ growth could be related to the higher serum IGF-1 concentrations induced by continuous rhGH administration. These studies show that whole body growth is best maintained by intermittent rhGH exposure, whereas, paradoxically, differential organ growth is most pronounced with continuous rhGH administration.

Acute and chronic effects of subcutaneous growth hormone (GH) injections on plasma levels of GH binding protein in short children

A ligand-mediated immunofunctional assay was used to measure levels of GH binding protein (GHBP) in plasma from children on GH treatment. Blood was drawn at the time of sc injection of GH and thereafter every 2 h for 16 or 24 h in the acute group. The samples were analyzed for GHBP and GH. To study changes in GHBP levels after onset of GH treatment, samples were taken at the start and after 10, 30, and 90 days of treatment (short-term group) and at the start and after 1 and 2 yr of treatment (long-term group). All children in the short-term and long-term groups were prepubertal throughout the study. For the study of short-term and long-term effects of GH treatment, the children were divided into two groups according to the maximal GH response (GHmax) in an arginine-insulin tolerance test and, if available, the maximum peak on 24-h secretion. Children with a GHmax below 20 mU/L(10 micrograms/L) were classified as GH deficient (GHD), and children with a GHmax above 20 mU/L were classified as children of short stature (SS). In the acute group, GH was injected either at 1800 h (n = 73) or at 1000 h (n = 12). In the group given GH at 1800 h there was a decrease in GHBP levels, with the lowest values occurring after 8-10 h, i.e. between 0200 and 0400 h. We have previously reported that there was no correlation between endogenous GH peaks and changes in GHBP levels, but there was a small but significant diurnal variation in GHBP levels (coefficient of variation of about 10%), with a nadir between 0000 and 0400 h. In the group given GH at 1000 h, GHBP levels decreased to a minimum at 10 h after injection (at 2000 h, P < 0.01), with a further decrease at 16 h after injection (P < 0.05), corresponding to the nadir seen in normal children. The mean GHBP levels fell to 71.2% of the baseline value after 90 days in children with GHD (P = 0.004), but was unchanged in children with SS (P = 0.92). In children with GHD, the GHBP levels were unchanged at 1 yr (100.5% +/- 10.7) and 2 yr (97.1% +/- 6.6) after start of treatment. In children with SS, there was no significant increase after 1 yr (125.6% +/- 10.9, P = 0.16) and 2 yr (120.3% +/- 6.4, P = 0.17).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for partial growth hormone insensitivity among patients with idiopathic short stature. The National Cooperative Growth Study

OBJECTIVE

To determine whether some patients with idiopathic short stature have partial resistance to growth hormone (GH). Patients with idiopathic short stature have decreased serum levels of the GH receptor-related GH-binding protein (GHBP), and low GHBP levels are associated with complete GH insensitivity (Laron) syndrome. We hypothesized that patients with idiopathic short stature and low GHBP levels may also have a degree of GH insensitivity.

DESIGN

Retrospective analysis of patients in a multicenter study.

SETTING

Ninety-six National Cooperative Growth Study centers in the United States and Canada.

SUBJECTS

Five hundred eleven patients with idiopathic short stature who were treated with GH. All patients had a baseline height standard deviation score of less than -2 and a maximum stimulated GH level greater than 10 micrograms/L. Of these, 101 (20%) had a baseline GHBP standard deviation score of -2 or less.

RESULTS

The patients with low GHBP levels, in comparison with those with normal GHBP levels, had a lower mean extracted standard deviation score for insulin-like growth factor I (-3.3 +/- 1.1 vs -2.5 +/- 1.4; p < 0.0001) but mean 12-hour GH values (2.8 +/- 1.1 vs 2.3 +/- 1.1 micrograms/L; p <0.0001). The differences between groups were statistically significant after control for age and weight-for-height standard deviation score. Among prepubertal patients, there was no significant difference between the low and normal GHBP groups in mean pretreatment or first-year growth rate (p = 0.74, 0.61 respectively) with comparable doses of GH.

CONCLUSIONS

Patients with idiopathic short stature and low GHBP levels, compared with those with normal GHBP levels, had significantly lower standardized levels of insulin-like growth factor I, and higher mean 12-hour GH levels, which suggest partial GH insensitivity. There was no significant correlation of GHBP levels with the growth response to exogenous GH.

Mice lacking extracellular superoxide dismutase are more sensitive to hyperoxia

Extracellular superoxide dismutase (EC-SOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is a secreted Cu- and Zn-containing tetrameric glycoprotein, the bulk of which is bound to heparan sulfate proteoglycans in the interstitium of tissues. To test the function of EC-SOD in vivo, mice carrying a targeted disruption of the EC-SOD gene were generated. The EC-SOD null mutant mice develop normally and remain healthy until at least 14 months of age. No compensatory induction of other SOD isoenzymes or other antioxidant enzymes was observed. When stressed by exposure to > 99% oxygen, the EC-SOD null mutant mice display a considerable reduction in survival time compared to wild-type mice and an earlier onset of severe lung edema. These findings suggest that while under normal physiological conditions other antioxidant systems may substitute for the loss of EC-SOD; when the animal is stressed these systems are unable to provide adequate protection.

Expression of exon 3-retaining and exon 3-excluding isoforms of the human growth hormone-receptor is regulated in an interindividual, rather than a tissue-specific, manner

GH has multiple effects on growth and metabolism, and these functions are mediated through binding to specific cell surface receptors. The human GH receptor (GHR) exists in two known isoforms; in one form exon 3 is present (GHR3+), and in the other, exon 3 is absent (GHR3-). Recent reports have suggested that the expression of the two isoforms is tissue specific and/or developmentally regulated. We used a reverse transcription-polymerase chain reaction assay to study the expression pattern of the two isoforms in a variety of tissues from normal subjects and patients with acromegaly. In skeletal muscle from both normal subjects and patients with acromegaly, the GHR3+ transcript was expressed, either alone or together with the shorter (GHR3-) transcript. When multiple tissues from six subjects were tested, the expression of the two isoforms varied among subjects, whereas different tissues from the same subject showed the same expression pattern. These results indicate that the expression of the GHR isoforms is not tissue specific. Instead, the expression of the GHR isoforms appears to be specific for each individual, suggesting that it is under the control of factors that affect all tissues in the body.

Insulin-like growth factor-1 and growth hormone (GH) have distinct and overlapping anabolic effects in GH-deficient rats

The anabolic activity of recombinant human growth hormone (rhGH) and insulin-like growth factor 1 (rhlGF-1) given either alone or together were studied in two models of GH deficiency, hypophysectomized and GH-deficient dwarf rats. A range of rhGH doses (0.08 to 50 mg/kg/day, seven daily sc injections) were given either alone or together with one dose of rhIGF-l (2.4 mg/kg/day, sc infusion). When given alone, or co-administered with rhlGF-1, rhGH produced dose dependent increases in weight gain, bone growth and organ weights. Weight gain in response to rhGH given with rhlGF-1 was comparable to that obtained by a 25-fold higher dose of rhGH given alone. In both animal models absolute weights of the kidneys, liver, spleen and thymus were increased by rhlGF-1 while kidney and liver weight were increased by rhGH. In the hypophysectomized rat, spleen and thymus weights were increased by rhGH but the relative potency of the combination was a 1000-fold that of rhGH alone. The effects of rhlGF-1 and rhGH were additive indicating that the effects of GH or IGF-1 can be greatly increased by their co-administration.

Loss of the normal relationships between growth hormone, growth hormone-binding protein and insulin-like growth factor-I in adolescents with insulin-dependent diabetes mellitus

OBJECTIVE

It has been proposed that the dissociation between growth hormone secretion and insulin-like growth factor-I (IGF-I) concentrations in insulin-dependent diabetes mellitus arises because of partial resistance at the GH receptor. In order to explore this hypothesis further we have examined the relations between IGF-I, GH-binding protein (GHBP), and GH secretion in normal subjects and patients with diabetes during puberty.

DESIGN AND SUBJECTS

Blood samples for the estimation of IGF-I and GHBP levels were obtained from 104 patients with diabetes and 89 puberty matched controls. Thirty-four of the controls and 42 of the patients with diabetes also underwent an overnight GH secretory profile with measurements of GH every 15-20 minutes between 2000 and 0800 h.

RESULTS

In multivariate analysis using sex, puberty stage, and presence or absence of diabetes as dependent variables, diabetes was associated with increased GH levels (F = 23.04, P < 0.001), reduced IGF-I (F = 10.89, P < 0.001), and reduced GHBP levels (F = 31.36, P < 0.001). A negative relation between GH and GHBP levels (r = -0.44, P < 0.01) was found in normal subjects but this was absent in those with diabetes. Both GHBP and IGF-I levels in the diabetic subjects were correlated with total insulin dose (r = 0.4, P < 0.001, and r = 0.46, P < 0.001, respectively). Yet there was no direct correlation between GHBP and IGF-I concentrations. The variation in IGF-I levels was also related to glycosylated haemoglobin levels in the diabetics (r = -0.27, P = 0.01). In a stepwise multiple regression analysis insulin dose contributed 23%, HbA1 4.4% and C-peptide levels 3.7% to the variation in IGF-I levels.

CONCLUSIONS

In adolescents with insulin dependent diabetes mellitus, the elevated GH concentrations are associated with low circulating IGF-I and GHBP concentrations and the normal reciprocal relation between GHBP and GH is no longer evident. Although IGF-I and GHBP are both related to insulin dose, there is no direct correlation between these variables. This may indicate that GHBP reflects GH receptor numbers but not necessarily post receptor events, and the weak positive correlation between GH and IGF-I indicates that increased growth hormone secretion may compensate for reduced receptor numbers.

Reduced concentration of serum growth hormone-binding protein in children with idiopathic short stature. National Cooperative Growth Study

One possible explanation for the growth failure in children with idiopathic short stature (ISS) is reduced peripheral responsiveness to GH. In Laron syndrome, growth retardation is caused by GH resistance due to GH receptor (GH-R) defects, which are associated in most cases with absent or low serum concentrations of the GH-R-related GH-binding protein (GHBP). We tested the hypothesis that some children with ISS have reduced serum concentrations of GHBP and that this may reflect decreased sensitivity to GH. A ligand-mediated immunofunctional assay was used to measure biochemically active GHBP in serum from 1549 children, including 773 controls, 573 with ISS, 107 with GH deficiency (GHD), and 96 with Turner syndrome (TS). Ages ranged from 1-17 yr. Serum GHBP concentrations in children with GHD, ISS, and TS were converted to SD scores and compared to controls by analysis of variance. In male and female ISS subjects, approximately 90% had GHBP concentrations below the age- and sex-adjusted mean for controls, and 20% had GHBP concentrations below the normal range. The mean serum GHBP SD score was lower in both males and females with GHD (-0.6) or ISS (-1.2) than in controls (both P < 0.005). The mean for ISS males was significantly lower than that for GHD males (P < 0.0001). The mean GHBP SD score for girls with TS (-0.3) did not differ significantly from that of the control females. The decreased levels of serum GHBP in some children with idiopathic short stature suggest that these children could have a defect at the level of the GH-R.

Growth hormone-binding protein levels: studies of children with short stature

A high-affinity growth hormone-binding protein (GHBP) in serum is derived from the extracellular domain of the GH receptor. In an attempt to investigate the differences in GHBP levels in various conditions of poor growth, we measured GHBP levels by two methods--an Ultrogel chromatographic technique and a ligand-mediated immunofunctional assay (LIFA). The following three groups of children were studied: Turner's syndrome (n = 7), idiopathic and/or familial short stature ([ISS] n = 15), and organic or idiopathic hypopituitarism (n = 19). All groups were similar in age (Turner's syndrome, 10.1 +/- 0.9 years; ISS, 10.0 +/- 0.7; hypopituitarism, 11.5 +/- 1.0) and height SEM score (Turner's syndrome, -2.9 +/- 0.3; ISS, -3.0 +/- 0.4; hypopituitarism, -2.3 +/- 0.4). Their values were compared with those values of GHBP in healthy controls of similar age. Immunofunctional assay values for GHBP were as follows: Turner's syndrome, 235.4 +/- 26.0 pmol/L; ISS, 122.4 +/- 11.0; and hypopituitarism, 157.1 +/- 23.0. These results were significantly different in subjects with ISS and hypopituitarism as compared with a group of healthy controls between the ages of 9 and 12 years (N = 255; GHBP = 287.9 +/- 10.9 pMol/L; P < .001 compared with both ISS and hypopituitarism). Similar changes were found using Ultrogel chromatography. This difference in GHBP levels is still significant even when more stringent criteria are applied to define hypopituitarism (ie, peak GH responses to stimuli < 6.0 ng/mL, instead of < or = 10 ng/mL originally).(ABSTRACT TRUNCATED AT 250 WORDS)