Growth hormone binding proteins and various forms of growth hormone: implications for measurements

Characterization of growth hormone disulfide-linked molecular isoforms during post-exercise release vs nocturnal pulsatile release reveals similar milieu composition

OBJECTIVE

To characterize the influence of mode (aerobic/resistance) and volume of exercise (moderate/high) on circulating GH immediately post-exercise as well as following the onset of sleep.

DESIGN

This study used repeated measures in which subjects randomly completed 5 separate conditions: control (no exercise), moderate volume resistance exercise (MR), high-volume resistance exercise (HR), moderate volume aerobic exercise (MA), and high volume aerobic exercise (HA).

METHODS

Subjects had two overnight stays on each of the 5 iterations. Serial blood draws began as soon as possible after the completion of the exercise session. Blood was obtained every 20 min for 24-h. GH was measured using a chemiluminescent immunoassay. Pooled samples representing post exercise (PE) and first nocturnal pulse (NP) were divided into two aliquots. One of these aliquots was chemically reduced by adding 10 mM glutathione (GSH) to break down disulfide-linked aggregates.

RESULTS

No differences were observed when pooling GH response at post-exercise (2.02 ± 0.21) and nocturnal pulse (2.63 ± 0.51; p = .32). Pairwise comparisons revealed main effect differences between controls (1.19 ± 0.29) and both MA (2.86 ± 0.31; p = .009) and HA (3.73 ± 0.71; p = .001). Both MA (p = .049) and HA (p = .035) responses were significantly larger than the MR stimulus (1.96 ± 0.28). With GSH reduction, controls significantly differed from MA (p = .018) and HA (p = .003) during PE, but only differed from HA (p = .003) during NP.

CONCLUSIONS

This study demonstrated similar GH responses to exercise and nocturnal pulse, indicating that mode and intensity of exercise does not proportionately affect GH dimeric isoform concentration.

Detection of doping with recombinant human growth hormone

Detection of doping with recombinant human growth hormone is one of the challenges for antidoping analysis. This review focuses on the most important relevant publications that provide insight into the laboratory measurement of human growth hormone (hGH), antibodies and standards, the isoform approach and the biomarker approach. The isoform approach monitors the changes of hGH molecular isoform composition in serum and was applied at the Olympic Games in Athens in 2004, Turin in 2006 and Beijing in 2008. The markers approach detects a formula score, which reflects the changes in concentration of IGF-1 and P-III-P. All these methodologies measure the concentrations of growth hormone and its isoforms for isoform approach, or the concentrations of IGF-1 and P-III-P. All factors that affect these measurements should be taken into account for the development of methods to detect doping with recombinant hGH.

Standardization of the IMMULITE systems growth hormone assay with the recombinant IS 98/574

BACKGROUND

The diagnosis of disorders of growth hormone (GH) secretion is based on the measurement of GH before and after dynamic stimulation or suppression tests. Over the years, specific cut-off values have been proposed without taking account of the considerable variation in results obtained using different methods for analysing GH. Recent publications have recommended the standardization of GH assays using IS 98/574, which is calibrated in mass and units (U). The IMMULITE range of GH assays have been recalibrated using this standard.

METHODS

We analysed 745 samples using the current and the restandardized GH assay kits. This series of samples contained 90 stimulation tests and seven suppression tests.

RESULTS

The data comparing the current and restandardized assays show a similar relationship for both basal and stimulated GH values for all IMMULITE platforms. There is a negative bias by the restandardized assay above approximately 20 microg/L. A conversion can be derived from this study which would mean that patient GH results expressed in milliunits per litre of IMMULITE in-house derived standard will be approximately three-fold of that expressed in micrograms per litre of IS 98/574.

CONCLUSION

Use of IS 98/574 offers standardized reporting in microgram per litre IS 98/574. This will permit compliance with the consensus recommendations and the development of a firm evidence base for defining decision-making GH values.

SnoRNA Snord116 (Pwcr1/MBII-85) deletion causes growth deficiency and hyperphagia in mice

Prader-Willi syndrome (PWS) is the leading genetic cause of obesity. After initial severe hypotonia, PWS children become hyperphagic and morbidly obese, if intake is not restricted. Short stature with abnormal growth hormone secretion, hypogonadism, cognitive impairment, anxiety and behavior problems are other features. PWS is caused by lack of expression of imprinted genes in a ∼4 mb region of chromosome band 15q11.2. Our previous translocation studies predicted a major role for the C/D box small nucleolar RNA cluster SNORD116 (PWCR1/HBII-85) in PWS. To test this hypothesis, we created a ∼150 kb deletion of the >40 copies of Snord116 (Pwcr1/MBII-85) in C57BL/6 mice. Snord116del mice with paternally derived deletion lack expression of this snoRNA. They have early-onset postnatal growth deficiency, but normal fertility and lifespan. While pituitary structure and somatotrophs are normal, liver Igf1 mRNA is decreased. In cognitive and behavior tests, Snord116del mice are deficient in motor learning and have increased anxiety. Around three months of age, they develop hyperphagia, but stay lean on regular and high-fat diet. On reduced caloric intake, Snord116del mice maintain their weight better than wild-type littermates, excluding increased energy requirement as a cause of hyperphagia. Normal compensatory feeding after fasting, and ability to maintain body temperature in the cold indicate normal energy homeostasis regulation. Metabolic chamber studies reveal that Snord116del mice maintain energy homeostasis by altered fuel usage. Prolonged mealtime and increased circulating ghrelin indicate a defect in meal termination mechanism. Snord116del mice, the first snoRNA deletion animal model, reveal a novel role for a non-coding RNA in growth and feeding regulation.

Abuse of growth hormone among young athletes

The underground abuse of growth hormone (GH) among young athletes presents a challenge to medical professionals. Health care professionals providing knowledgeable guidance regarding healthy ways to improve performance and appearance, as well as accurate information regarding substances' perceived benefits, risks, and unknown qualities, is invaluable to the young athlete. Further research focused on the profile and motivation of young people who use GH is essential to understanding and intervening better with those who use these substances.

Assessment of disease activity in acromegaly by means of a single blood sample: comparison of the 120th minute postglucose value with spontaneous GH secretion and with the IGF system

OBJECTIVE

It has been suggested that the threshold of 1 micro g/l of GH nadir after glucose load for definition of controlled acromegalic disease proposed in the 2000 consensus statement should be lowered to 0.30. We evaluated these two cut-off values in comparison with IGF-I, ALS and IGFBP-3 in a group of acromegalic patients. With the aim of simplifying the follow-up protocol in these patients we also tested if one single sample taken after glucose load could replace the nadir value.

DESIGN AND MEASUREMENTS

GH secretion was evaluated by oral glucose tolerance test (OGTT), and by studying spontaneous secretion (GH day curve) with sampling at hourly intervals from 08.00 to 18.00 h; from the day curve, mean (MGHDC) and minimum (TRGH) values were considered. IGF-I, ALS, and IGFBP-3 were measured in the basal state at the first testing. patients Fifty acromegalic patients (26-83 years, 31 females, 19 males) in various phases of disease activity. Forty-two patients had previously undergone pituitary surgery (10 also radiotherapy), 23 were treated with SMS analogues and three with dopamine agonist drugs.

RESULTS

The nadir GH value after glucose load correlated most significantly with the 120th-minute sample (R = 0.95). Comparison of the postglucose 120th minute at the two cut-off values with IGF-I, IGFBP-3 and ALS showed higher concordance of postglucose level at 0.3 with IGF-I, while concordance was similar for the two cut-off values with ALS and IGFBP-3. When the 120th minute postglucose GH value is lower than 1 micro g/l and IGF-I is within 2SD for age nearly all other parameters are normal. IGF-I correlated more with ALS (R = 0.78) than with IGFBP-3 (R = 0.50) and the latter was less concordant with GH secretion parameters than the previous two.

CONCLUSIONS

A sample taken at the 120th minute after glucose load, together with IGF-I and/or ALS evaluation can give sufficient information for a routine assessment of disease activity, both in the diagnosis and in the follow-up to treatment. If GH is lower than 1 micro g/l and IGF-I/ALS are normal, then the patient can be classified as 'nonactive' or 'controlled'; a pathological IGF-I and/or ALS value is a sign of disease activity irrespective of the GH values, while normal IGF-I/ALS with an elevated GH requires further assessment.

ELISA for Determination of Human Growth Hormone: Recognition of Helix 4 Epitopes

Human growth hormone (hGH) signal transduction initiates with a receptor dimerization in which one molecule binds to the receptor through sites 1 and 2. A sandwich enzyme-linked immunosorbent assay was developed for quantifying hGH molecules that present helix 4 from binding site 1. For this, horse anti-rhGH antibodies were eluted by an immunoaffinity column constituted by sepharose-rhGH. These antibodies were purified through a second column with synthetic peptide correspondent to hGH helix 4, immobilized to sepharose, and used as capture antibodies. Those that did not recognize synthetic peptide were used as a marker antibody. The working range was of 1.95 to 31.25 ng/mL of hGH. The intra-assay coefficient of variation (CV) was between 4.53% and 6.33%, while the interassay CV was between 6.00% and 8.27%. The recovery range was between 96.0% to 103.8%. There was no cross-reactivity with human prolactin. These features show that our assay is an efficient method for the determination of hGH.

Models of growth hormone and IGF-1 deficiency: applications to studies of aging processes and life-span determination

The remarkable progress in understanding the genetic basis of life-span determination in invertebrates indicates that impairments in the insulin-insulin-like growth factor 1 (IGF-1) signaling cascade increase longevity. Similarities among insulin and IGF-1-like signaling pathways in invertebrates and mammals raise the possibility that modifications of these pathways may extend life span in mammals. Investigators using Ames, Snell, and growth hormone receptor knockout models have concluded that decreased growth hormone and IGF-1 are responsible for increased life span. In this review, we critique the dwarf models and, based on multiple endocrine deficiencies and developmental anomalies, conclude that these models may not be sufficient to assess the consequences of growth hormone or IGF-1 deficiency on either biological aging or life span. We attempt to resolve some of these issues by presenting an alternative animal model of growth hormone-IGF-1 deficiency. Finally, we propose an integrated explanation of growth hormone and IGF-1's contribution to the aging phenotype and life-span determination.

Growth hormone pulsatility profile characteristics following acute heavy resistance exercise

This investigation examined the hypothesis that acute heavy resistance exercise (AHRE) would increase overnight concentrations of circulating human growth hormone (hGH). Ten men (22 +/- 1 yr, 177 +/- 2 cm, 79 +/- 3 kg, 11 +/- 1% body fat) underwent two overnight blood draws sampled every 10 min from 1700 to 0600: a control and an AHRE condition. The AHRE was conducted from 1500 to 1700 and was a high-volume, multiset exercise bout. Three different immunoassays measured hGH concentrations: the Nichols immunoradiometric assay (Nichols IRMA), National Institute of Diabetes and Digestive and Kidney Diseases radioimmunoassay (NIDDK RIA), and the Diagnostic Systems Laboratory immunofunctional assay (DSL IFA). The Pulsar peak detection system was used to evaluate the pulsatility profile characteristics of hGH. Maximum hGH was lower in the exercise (10.7 microg/l) vs. the control (15.4 microg/l) condition. Mean pulse amplitude was lower in the exercise vs. control condition when measured by the Nichols IRMA and the DSL IFA. A differential pattern of release was also observed after exercise in which hGH was lower in the first half of sleep but higher in the second half. We conclude that AHRE does influence the temporal pattern of overnight hGH pulsatility. Additionally, because of the unique molecular basis of the DSL IFA, this influence does have biological relevance because functionally intact molecules are affected.

Circulating GH isoforms and GH bioactivity in preterm neonates

Among the molecular variants of human GH, the monomeric 22-kD is the predominant isoform, whereas the 20-kD is the second most abundant isoform. Because little is known on the pattern of human GH isoforms in the early postnatal period, we evaluated serum levels of 22-kD GH by an immunofluorometric assay and of 20-kD GH by an ELISA using an anti-20-kD antibody, and measured GH bioactivity with the Nb2 cell bioassay in 19 preterm neonates (gestational age, 32 +/- 0.5 wk; mean +/- SEM) on the fourth and 15th days of life. As control subjects, we studied 19 full-term neonates (gestational age, 39 +/- 0.3 wk) on the fourth day of life and 20 healthy adults, aged 20 +/- 0.3 y. Four-day-old preterm neonates showed significantly higher serum values of 20-kD GH (0.99 - 0.14 ng/mL) than full-term neonates (0.33 +/- 0.07 ng/mL; p < 0.001) and adults (0.09 +/- 0.02; p < 0.0001). Likewise, 22-kD GH and GH levels by Nb2 cell bioassay were also significantly higher (p < 0.001) in preterm than in full-term neonates and young adults. A significant decrease (p < 0.01) in 20-kD, 22-kD, and Nb2-determined GH was observed in preterm neonates on the 15th day of life The percentage of the 20-kD isoform was similar in the preterm infants at the fourth and 15th day, in full-term-infants, and in adults (2.7%, 2.7%, 2.8%, and 3.16%, respectively). Our results indicate that 20-kD GH serum levels change throughout life as regards total amount, but not as regards percentage.

Comparison between four immunoassays for growth hormone (GH) measurement as guides to clinical decisions following GH provocative tests

OBJECTIVE

To compare four assays for the measurement of GH following provocative tests and to assess the projected clinical decisions, which would have been based on their respective results.

DESIGN

Multiple assays of serum samples obtained during provocative tests for GH response.

SUBJECTS

Forty-seven children with short stature, who underwent clinical evaluation and GH provocative tests.

METHODS

All samples were measured by the immunoassay Sorin-RIA (A), which is routinely used in our laboratory. Basal and peak samples were analyzed by three other immunoassays: Sorin-IRMA (B), DPC-RIA (C) and Wallac-DELFIA (D). Results were classified as low, partial and normal GH response, corresponding to <10, 10-17.9 and >18 microIU/ml peak serum GH levels.

RESULTS

High correlation was found between individual results by the four kits (r=0.92-0.94). However, the mean peak GH values were significantly different (p<0.0001). Further analysis using paired t-test has shown highly significant differences between the assays (p<0.0001) apart from assays A and B that were not significantly different. Clinical grouping by the four tests was profoundly different: by assay A, 14.9% were judged low response and 57.4% normal; by assay D, 36.2% were low and only 21.3% normal. Kappa statistics measurement demonstrated poor agreement between assays A and D and between B and D.

CONCLUSION

As the criteria for the diagnosis of GH deficiency and the indications for GH therapy are based on laboratory GH results, more must be done to ensure uniformity and comparability of the GH assays.

Immunofunctional vs immunoreactive growth hormone responses after resistance exercise in men and women

Immunoassays for growth hormone (GH) may yield variable concentrations for the same sample due to the molecular heterogeneity of growth hormone and epitope specificity of their antibodies. Strasburger et al. developed an "immunofunctional" assay that only detects those GH molecules possessing intact sites 1 and 2, which are necessary for inducing receptor dimerization and subsequent signal transduction. This study compared the immunoreactive (IR) vs immunofunctional (IF) GH concentrations before and after acute resistance exercise (i.e. six sets of 10 repetition maximum squats separated by 2 min rest periods) in 8 men and 6 women. IF concentrations were determined by an ELISA(DSL)and IR GH by a monoclonal IRMA(Nichols). Both men (M) and women (W) demonstrated similar increases for IR (M: 1.47 vs 25.0 ng/ml; W: 4.0 vs 25.4 ng/ml) and IF (M: 0.55 vs 11.66 ng/ml; W: 1.94 vs 10.41 ng/ml) GH following exercise. Post-exercise IF GH was significantly less than IR GH for both M and W. The ratio of IR/IF after exercise was approximately 2 and similar for both M and W. In summary, dynamic exercise elicited a similar rise in M and W for immunofunctionally active GH molecules, but the magnitude is lower than when detected with another conventional assay.

Test method: GH

The abuse of recombinant human growth hormone in sports is considered to be a widespread phenomenon, but until today all our knowledge thereof is based on rumor, anonymous surveys or accidental observations by customs officers. Although growth hormone (GH) is listed as a prohibited class E substance by the International Olympic Committee (IOC) no official test for the detection of GH abuse is implemented. Because of the high degree of identity in the amino acid sequence between recombinant and endogenous GH and because of the pulsatile nature of GH secretion, as well as inter-individual variations, it was believed to be undetectable. Recently, new proposals have been made to overcome this problem. On the basis of differential immunoassays it is possible to determine the relative content of GH isoforms in the circulation and thus to detect the application of recombinant GH. Furthermore, changes in GH dependent parameters after the administration of recombinant GH have been shown to be a possible indicator of GH abuse.

Transgenic models of growth hormone action

A growth-promoting principle of the pituitary gland was discovered in 1921, and bovine growth hormone (GH) was isolated in 1944. Since then, the structure of GH as it relates to its biological activities has been an exciting research topic. Equally fascinating is the relationship between GH structure and its metabolic activities. In attempts to define some of these activities, several investigators have used GH transgenic mice as models. In this review we summarize what is known about the molecular mechanisms of GH action. We then describe some of the GH transgenic models and point out potential targets for nutrition research.

Growth hormone bioactivity and immunoactivity in tall children

In subjects with constitutional tall stature, both low and high GH response to stimulation tests have been observed when measured by commercial kits. To investigate the reason for these conflicting results, we evaluated growth hormone (GH) secretion using different assays as well as GH-binding protein and insulin-like growth factor-I (IGF-I) concentrations in tall children. Serum samples were collected from 22 prepubertal constitutionally tall children, aged 2.87-13.25 years, during two pharmacological tests to evaluate serum GH levels measured by both immunofluorometric assay (IFMA) and the Nb2 cell bioassay. Serum IGF-I values were evaluated by RIA. Circulating low affinity (LA) and high affinity (HA) GH-binding proteins (GHBPs) were evaluated by FPLC gel filtration. Considering the highest serum GH levels as measured by IFMA, the 22 tall subjects were divided into two groups: group A including 16 children with blunted serum GH peak levels (5.78+/-0.68 ng/ml) and group B including 6 subjects with normal serum GH peak values (15.73+/-1.56 ng/ml). No differences were observed in serum GH peak levels as measured by the Nb2 cell bioassay between group A (14.77+/-1.54 ng/ml) and group B (16.03+/-1.96 ng/ml), and between both groups and 11 age-and sex-matched controls (12.25+/-1.19 ng/ml). In group A, the Nb2 cell bioassay/IFMA ratio of serum GH peak levels (0.29+/-0.08) was significantly higher (p<0.05) than in group B (0.07+/-0.01). No differences were found in serum LA-GHBP and HA-GHBP as well as in IGF-I concentrations between the 16 patients of group A and the 6 of group B. Likewise, no difference in auxological parameters was found between the two groups. The biological activity of GH evaluated using the Nb2 cell bioassay is similar in tall children with a low GH response as measured by IFMA in comparison with those with a normal GH response, and is in agreement with both the auxological data and serum IGF-I concentrations.

Physiological obstacles after xenotransplantation

The incompatibility of allografts is restricted to immunologic factors such as the MHC class I and class II antigens. Anatomic, physiological, and biochemical characteristics are identical. This is completely different in xenografts. The upright position of man is unique in nature. Gravity therefore exerts a different impact on the anatomic situation of organs such as lung, heart, liver, and kidney. More pronounced are differences on the humoral and enzymatic basis. Complex interactions existing in allografts are totally disturbed in xenogeneic situations. Up- and downregulation controlled by releasing factors on the one hand and inhibitors on the other must be species-specific. These actions of mainly proteases are both fast and in most cases depend on species-specific receptors. Examples are growth hormones which could stimulate the xenografts to unrestricted growth, as in pig hearts in the human patient. Enzymes not metabolized by the liver would constantly stimulate mechanisms to a level that is not compatible with life, and other reactions could be more expressed in the donor species than in man and thus disturb these interactions. Products like albumin are carriers for other molecules and need to be compatible for binding sites. Pig and human albumin have an amino acid identity of less than 65% erythropoetin (EPO) of less than 82%, and complement of less than 70%. All factors are obviously without specific function in the future recipient, the human patient. In contrast, pig complement would, as a foreign molecule, induce the alternative complement pathway in the human recipient, leading to unknown side effects. It is not sufficiently investigated whether under such physiological and anatomic differences a long-term survival of xenograft or recipient is possible--a chain is as strong as its weakest link.

Evaluation of growth hormone bioactivity using the Nb2 cell bioassay in children with growth disorders

The Nb2 cell bioassay could be a useful tool for evaluating human growth hormone (hGH) bioactivity, but is not specific for hGH since it relies on the ability of the hormone to produce effects by cross-reacting with the lactogenic receptor on Nb2 cells. We studied the biological activity of both endogenous and exogenous hGH in short patients using the Nb2 bioassay after inhibiting the mitogenic effect of the other lactogenic hormone, that is human prolactin (hPRL), by adding a specific antibody against hPRL to each assay. The in vitro study showed a significant (p<0.0001) increase in Nb2 cell proliferation when increasing concentrations of highly purified hGH were added to the cell culture. A complete inhibition of Nb2 cell replication was observed after adding a specific antibody against hGH. The in vivo study showed a significantly (p<0.0001) lower hGH bioactivity (4.90+/-0.28 ng/ml) evaluated during stimulation tests in 9 children with total idiopathic GH deficiency, mean age 9.25+/-1.99 years, in comparison with that found in 11 short children with normal growth velocity, mean age 8.22+/-1.41 years (12.25+/-1.19 ng/ml). Likewise, serum GH levels measured by immunofluorometric assay IFMA in the same serum samples were significantly (p<0.001) lower in the 9 GH-deficient (1.97+/-0.37 ng/ml) than in the 11 short children (21.85+/-2.71 ng/ml). Moreover, we evaluated GH concentrations using both IFMA and the Nb2 cell bioassay in serum samples collected from another 11 idiopathic GH-deficient children, mean age 10.71+/-1.18 years, before and then, 6 and 24 hours following the 1 st injection of r-hGH (0.1 IU/kg sc). Serum GH values measured by both IFMA and Nb2 bioassay significantly (p<0.0001) increased 6 hours after r-hGH administration and decreased to reach basal levels after 24 hours. In conclusion, the Nb2 cell bioassay with minor modifications seems to provide a specific and sensitive assessment of hGH bioactivity.

Laboratory assessment of GH

The diagnosis of growth hormone (GH) deficiency is based primarily on clinical criteria. In paediatric endocrinology, auxological evaluation leads to the diagnosis, while in adult endocrinology evidence of severe pituitary disease is associated with GH deficiency. Final proof of the diagnosis, however, is sought by measurement of GH levels in serum after dynamic provocative testing of GH secretion. Although arbitrary cut-off levels exist, below which the maximum GH peak should be found in different provocative tests, these recommendations have to be considered vague in the light of the considerable heterogeneity between results from different commercially available GH assays. Factors influencing the results of GH measurement by immunoassay are the heterogeneity of molecular isoforms of circulating GH, assay design, standard matrix, choice of reference preparation for calibration and, to a considerable extent, the epitope specificity of the antibodies used. Ideally, GH should be measured by a true somatogenic bioassay. Such assays are too cumbersome for routine use, however, and in most instances are only suitable for investigation of purified GH preparations rather than quantification of GH levels in serum samples. Significant progress was made recently with the concept of immunofunctional measurement of GH levels, in which only GH molecules having both receptor interaction sites necessary for initiation of the signal transduction process in target cells are translated into an assay signal. Immunofunctionally measured GH levels are, therefore, closer to the results from bioassays than the determination of arbitrary immunoreactivity of GH isoforms with a given antibody or set of antibodies in conventional immunoassays. In the context of establishing a diagnosis of GH deficiency, it is mandatory that techniques for GH measurement are standardized more rigidly before recommendations on meaningful cut-off levels for different provocative tests are made.

Interassay differences in growth hormone measurement in acromegaly

We measured plasma growth hormone concentrations by three different two-site immunometric assays (Pharmacia hGH RIA, IDS Gamma-BCT and Delfia 22 kDa hGH) to determine whether there are GH isoforms secreted by acromegalic patients that are under-recognized by some assays. There was a fairly good agreement between assays with the IDS Gamma-BCT and Delfia 22 kDa assays giving lower results than the Pharmacia IRMA. GH was measured on stored plasma samples from 24 patients with proven acromegaly. There was a consistent difference between the three assays of approximately 20% of the mean value for each patient.

Altered endogenous growth hormone secretory kinetics and diurnal GH-binding protein profiles in adults with chronic liver disease

OBJECTIVE

Increased serum GH concentrations and GH responses to a variety of stimuli have been reported in patients with chronic liver disease (CLD). We investigated the pulsatile pattern of endogenous GH release and GH-binding protein (GHBP) and insulin-like growth factor-I (IGF-I) diurnal profiles in adults with cirrhosis, in comparison with healthy, matched control subjects.

DESIGN

Case-control, cross-sectional.

PATIENTS

Seven patients with biopsy proven cirrhosis, and sex, age, height, weight and oestrogen status matched controls.

MEASUREMENTS

Serum immunoreactive GH concentrations in samples collected at 20-minute intervals for 24 hours were analysed using a multi-parameter deconvolution method to simultaneously resolve endogenous GH secretory and disappearance rates. Diurnal patterns of GHBP (specific immunoprecipitation method) and serum IGF-I (RIA after acid-ethanol extraction) were assessed.

RESULTS

The mean daily GH secretion rate in patients with CLD was increased (210 +/- 93 vs 100 +/- 55 mU/I/day; P = 0.025), and GH disappearance half-time was prolonged (43 +/- 10 vs 24 +/- 9 min; P = 0.006) compared to controls. Detectable GH secretory bursts were more frequent in patients with CLD (10 +/- 1 vs 6 +/- 3/day; P = 0.038), but of similar mean mass (21 +/- 10 vs 17 +/- 8 mU/I) compared to controls. In patients with CLD, mean serum GHBP was slightly lower (63 +/- 36 vs 71 +/- 14% pooled control; P > 0.1). Fasting serum IGF-I concentrations (after size-exclusion HPLC) were lower in the patients with CLD (13 +/- 5 vs 21 +/- 2 nmol/l; P < 0.0001). Multiple regression analysis showed that GH secretion rate was increased in patients with CLD with higher Child's classifications (R2 = 0.86; P = 0.002) and with lower serum IGF-I concentrations measured after HPLC (R2 = 0.11; P = 0.044).

CONCLUSIONS

Adults with chronic liver disease have (1) increased total daily GH secretion rates, which appear to be influenced by disease severity and diminished serum IGF-I-mediated negative feedback; (2) markedly impaired endogenous GH clearance, possibly reflecting changes in hepatic GH-receptor status; and (3) GHBP levels which do not correlate with GH kinetics or serum IGF-I concentrations.

Wide diversity in measurements of growth hormone after stimulation tests in short children are due to assay variability

A comparison of three commercially available assays for growth hormone (Pharmacia hGH RIA, IDS Gamma-BCT GH and Delfia 22 kDa hGH) were used to measure growth hormone (GH) secretion in 26 short children after pharmacological stimulation. The IDS Gamma-BCT assay was compared with Pharmacia assay in 15 provocative tests (13 children; n = 94). The Pharmacia assay showed a strong positive proportional bias and this was particularly marked at GH > 20 mU/L; the mean difference between the assays at GH < 10 mU/L was 12%. The IDS Gamma-BCT assay was also compared with the Delfia 22 kDa assay in 18 provocative tests (13 children; n = 100). Results from the IDS assay was higher throughout the range 0-90 mU/L with a mean difference of 11.4% in the range 10-90 mU/L; the mean difference between the assays at GH < 10 mU/L was -39%.

Protein dynamics in whole body and in splanchnic and leg tissues in type I diabetic patients

To elucidate the mechanism of insulin's anticatabolic effect in humans, protein dynamics were evaluated in the whole-body, splanchnic, and leg tissues in six C-peptide-negative type I diabetic male patients in the insulin-deprived and insulin-treated states using two separate amino acid models (leucine and phenylalanine). L-(1-13C,15N)leucine, L-(ring-2H5)phenylalanine, and L-(ring-2H2) tyrosine were infused intravenously, and isotopic enrichments of [1-13C,15N]-leucine, (13C)leucine, (13C)ketoisocaproate, (2H5)phenylalanine, [2H4]tyrosine, (2H2)tyrosine, and 13CO2 were measured in arterial, hepatic vein, and femoral vein samples. Whole-body leucine flux, phenylalanine flux, and tyrosine flux were decreased (< 0.01) by insulin treatment, indicating an inhibition of protein breakdown. Moreover, insulin decreased (< 0.05) the rates of leucine oxidation and leucine transamination (P < 0.01), but the percent rate of ketoisocaproate oxidation was increased by insulin (P < 0.01). Insulin also reduced (< 0.01) whole-body protein synthesis estimated from both the leucine model (nonoxidative leucine disposal) and the phenylalanine model (disposal of phenylalanine not accounted by its conversion to tyrosine). Regional studies demonstrated that changes in whole body protein breakdown are accounted for by changes in both splanchnic and leg tissues. The changes in whole-body protein synthesis were not associated with changes in skeletal muscle (leg) protein synthesis but could be accounted for by the splanchnic region. We conclude that though insulin decreases whole-body protein breakdown in patients with type I diabetes by inhibition of protein breakdown in splanchnic and leg tissues, it selectively decreases protein synthesis in splanchnic tissues, which accounted for the observed decrease in whole-body protein synthesis. Insulin also augmented anabolism by decreasing leucine transamination.

Identification of growth hormone molecular variants in chicken serum

It has been described that pituitary growth hormone shows molecular and functional heterogeneity. In birds, size and charge variants of chicken growth hormone (cGH) have been shown in the chicken pituitary gland and in purified preparations of the hormone. Here we demonstrate the existence of cGH molecular isoforms in chicken serum, thus suggesting that they are secreted from the gland. The isolation of total cGH present in sera was performed by immunoaffinity chromatography employing a specific monoclonal antibody against cGH. Different analytical electrophoretic methods (SDS-polyacrylamide gel electrophoresis, isoelectric focusing, bidimensional polyacrylamide gel electrophoresis) followed by Western blot and immunostaining were employed to characterize the serum cGH isoforms, and compared to those present in a fresh pituitary extract. Several identical immunoreactive bands comigrated in both serum and the gland extract in the different systems (SDS-PAGE, MW 16, 22, 26, 29, 52, 62, 66 kDa; IEF, pIs 8.1, 7.5, 7.1, 6.8, 6.2), thus revealing a high correspondence of molecular isoforms of the hormone in the two tissues. Additionally, a glycosylated variant of chicken growth hormone (G-cGH) was also revealed in the serum after concanavalin A-Sepharose chromatography.

Diagnosis of growth hormone deficiency

Many ways of evaluating the physiological state of hGH secretion exist, some of which have been touched upon and none of which has as yet proven infallible. Apart from important clinical features like history, physical data and growth rate, the diagnosis of altered pituitary function is based on tests and their interpretation. The physician responsible has to be informed on their effectiveness and pitfalls. Results should be interpreted in relation to developmental age (bone age) rather than chronological age. Research is under way to try to facilitate the diagnosis of varying degrees of alterations of hGH secretion. Reliability in predicting the effect of therapy with hGH is the ultimate aim in order to prevent unnecessary cost and disappointment for the patients. With the help of doctors involved in child care, such as physicians at kindergarten or school, it should be possible to start the slow process of investigating growth disorders at an early age.