Serum levels of bioactive IGF1 and physiological markers of ageing in healthy adults

OBJECTIVE

Senescent changes in body composition and muscle strength are accompanied by reduced production of GH and IGF1, but the causal relationship remains elusive. We speculate that serum bioactive IGF1, measured by the IGF1 kinase receptor activation assay, is closer related to human physiological ageing than total IGF1 measured by immunoassay.

DESIGN

We conducted a cross-sectional study in 150 adult males and females, between 20 and 70 years. After an overnight fasting, serum levels of bioactive IGF1, total IGF1 and IGF-binding protein 1 (IGFBP1) and IGFBP3 were assessed. Furthermore, body composition and muscle strength was measured.

RESULTS

Total IGF1 levels were higher in females (P=0.048). Bioactive IGF1 were identical in males and females (P=0.31), decreasing with age. Total IGF1 tended to decrease more with age compared with bioactive IGF1 (-1.48 vs -0.89 percent/year, P=0.052). Total body fat (TBF) was lower and BMI was higher in males (P<0.001 and P=0.005), and both increased with age. Knee extension and elbow flexion force were higher in males (P=0.001 and P=0.001), but decreased with age in both genders.  Total but not bioactive IGF1 was positively correlated to TBF, knee extension and muscle function in males. In multiple linear regression, only age predicted total IGF1, whereas age and IGFBP1 predicted bioactive IGF1.

CONCLUSIONS

Bioactive IGF1 tends to decrease to a lesser extent than total IGF1 with age and was not correlated with measures of body composition or muscle strength. Therefore, levels of circulating bioactive IGF1 does not appear to be a better biomarker of physiological ageing than total IGF1.

Circulating levels of pegvisomant and endogenous growth hormone during prolonged pegvisomant therapy in patients with acromegaly

OBJECTIVE

To investigate whether pegvisomant treatment in acromegaly induces gradual elevations in endogenous serum growth hormone (GH) levels and whether serum pegvisomant levels predict the therapeutic outcome.

PATIENTS AND METHODS

Seventeen patients (6 women), mean age 46·3 years (range: 23·2-76·2), were studied. For each patient, four hospital visits were identified including 'active disease' (no treatment) and last follow-up. At each visit, 12 blood samples were drawn during 3 h including an oral glucose tolerance test (OGTT). Eight patients received a somatostatin analogue in addition to pegvisomant on the last visit.

RESULTS

Median (range) pegvisomant doses (mg/day) were 10 (10-10), 15 (10-15) and 15 (10-15) at visits 2, 3 and 4, respectively, and the mean duration of pegvisomant treatment was 17·5 ± 3·2 (SEM) months. Serum IGF-I changed significantly during the treatment period with the highest level at baseline and lowest levels at visits 3 and 4. GH levels increased in a dose-dependent manner during pegvisomant treatment and decreased at visit 4. Changes in IGF-I levels correlated negatively with changes in serum pegvisomant levels between visits. Serum pegvisomant at each visit correlated with baseline growth hormone levels, whereas no associations between serum pegvisomant and either dose, gender, age or body weight were found.

CONCLUSIONS

(1) Serum GH levels increased initially, but remained stable during prolonged pegvisomant treatment in patients with acromegaly, (2) serum pegvisomant levels predicted the reduction in serum IGF-I during treatment and (3) the interindividual variation in serum pegvisomant levels seems not predicted by either age, gender or body composition.

Expression of vitamin D-metabolizing enzymes in human adipose tissue -- the effect of obesity and diet-induced weight loss

OBJECTIVE

Low vitamin D (VD) levels are common in obesity. We hypothesized that this may be due to metabolism of VD in adipose tissue (AT). Thus, we studied (1) whether the VD-metabolizing enzymes were expressed differently in AT of lean and obese individuals and in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), and (2) whether their expression was influenced by weight loss.

METHODS

Samples of SAT and VAT were analyzed for expression of the vitamin-D-25-hydroxylases CYP2R1, CYP2J2, CYP27A1 and CYP3A4, the 25-vitamin-D-1α-hydroxylase CYP27B1, the catabolic vitamin-D-24-hydroxylase CYP24A1, and the vitamin D receptor, using reverse transcriptase-PCR. Moreover, plasma 25-hydroxy-vitamin D (25OHD) level was measured and related to the expression of these enzymes. Samples of SAT and VAT from 20 lean women and 20 obese women, and samples of SAT from 17 obese subjects before and after a 10% weight loss were analyzed.

RESULTS

A plasma 25OHD level <50 nmol l(-1) was highly prevalent in both lean (45%) and obese (90%) women (P<0.01). Plasma 25OHD increased by 27% after weight loss in the obese individuals (P<0.05). Expression levels of the 25-hydroxylase CYP2J2 and the 1α-hydroxylase CYP27B1 were decreased by 71% (P<0.0001) and 49% (P<0.05), respectively, in SAT of the obese. CYP24A1 did not differ between lean and obese women, but the expression was increased by 79% (P<0.05) after weight loss.

CONCLUSION

Obesity is characterized by a decreased expression of the 25-hydroxylase CYP2J2 and the 1α-hydroxylase CYP27B1 in SAT, whereas the catabolic CYP24A1 does not differ between lean and obese women. However, the expression of CYP24A1 is increased after weight loss. Accordingly, AT has the capacity to metabolize VD locally, and this can be dynamically altered during obesity and weight loss.

Conventional and novel biomarkers of treatment outcome in patients with acromegaly: discordant results after somatostatin analog treatment compared with surgery

CONTEXT

Control of disease activity in acromegaly is critical, but the biochemical definitions remain controversial.

OBJECTIVE

To compare traditional and novel biomarkers and health status in patients with acromegaly treated with either surgery alone or somatostatin analog (SA).

DESIGN AND METHODS

Sixty-three patients in long-term remission based on normalized total IGF1 levels after surgery alone (n=36) or SA (n=27) were studied in a cross-sectional manner. The groups were comparable at diagnosis regarding demographic and biochemical variables. Each subject underwent 3 h of serum sampling including a 2-h oral glucose tolerance test (OGTT). Health status was measured by two questionnaires: EuroQoL and Acrostudy (Patient-assessed-Acromegaly symptom questionnaire (PASQ)).

RESULTS

Total and bioactive IGF1 (μg/l) levels were similar (total: 185 ± 10 (SA) versus 171 ± 8 (surgery) (P=0.28); bioactive: 1.9 ± 0.2 vs 1.9 ± 0.1 (P=0.70)). Suppression of total and free GH (μg/l) during OGTT was blunted in the SA group (total GH(nadir): 0.59 ± 0.08 (SA) versus 0.34 ± 0.06 (surgery) (P=0.01); free GH(nadir): 0.43 ± 0.06 vs 0.19 ± 0.04 (P<0.01)). The insulin response to OGTT was delayed, and the 2-h glucose level was elevated during SA treatment (P=0.02). Disease-specific health status was better in patients after surgery (P=0.02).

CONCLUSIONS

i) Despite similar and normalized IGF1 levels, SA treatment compared with surgery alone was associated with less suppressed GH levels and less symptom relief; ii) this discordance may be due to specific suppression of hepatic IGF1 production by SA; iii) we suggest that biochemical assessment during SA treatment should include both GH and IGF1.

Reduced cannabinoid receptor 1 protein in subcutaneous adipose tissue of obese

BACKGROUND

Cannabinoid 1 receptors are identified in various tissues involved in the internal metabolism including adipose tissue and the endocannabinoid system is claimed to be overactive in the obese state. To study the potential involvement of cannabinoid receptor 1 in the endocannabinoid system over-activity in adipose tissue in the obese state, we investigated the cannabinoid receptor 1 levels in adipose tissue from different fat depots in lean and obese humans.

MATERIALS AND METHODS

The adipose tissue samples were analysed by Western blot and by RT-PCR.

RESULTS

Both the gene expression and the protein of cannabinoid receptor 1 were lower in subcutaneous abdominal adipose tissue from obese subjects as compared with lean subjects (P < 0.01 and P = 0.058). Moreover, in lean subjects, the level of cannabinoid receptor 1 was significantly higher in subcutaneous adipose tissue compared with visceral adipose tissue (P < 0.05) for both gene expression and protein. The level of cannabinoid receptor 1 was similar between the two depots in obese subjects. The expression of cannabinoid receptor 1 was higher in subcutaneous gluteal adipose tissue as compared with subcutaneous abdominal adipose tissue (P < 0.05).

CONCLUSION

We found in lean subjects, a robust lower level of cannabinoid receptor 1 in visceral adipose tissue compared with subcutaneous adipose tissue (both RNA and protein levels), but similar levels of cannabinoid receptor 1 between the two depots in obese subjects. Our present findings do not indicate that cannabinoid receptor 1 is directly involved in the endocannabinoid system over-activity in adipose tissue in obesity.

Determination of free growth hormone

CONTEXT

Approximately 50% of circulating GH is bound to the high-affinity GH-binding protein (GHBP), which is known to affect the pharmacokinetics, bioactivity, and quantitative determination of GH. Nevertheless, the presence of GHBP is rarely taken into account in the clinical use of GH measurements.

OBJECTIVE

Our objective was to develop an assay for free GH in serum.

METHODS

We used ultrafiltration by centrifugation. Due to the small molecular difference between GH and GHBP, the size of GHBP and GHBP-GH complexes was increased by preincubation of serum with a monoclonal GHBP antibody (MAb 263).

RESULTS

The ultrafiltration membrane almost completely retained all GHBP (>98.5%) and allowed free passage of unbound GH (>98.4%). Addition of increasing concentrations of GHBP reduced free GH dose dependently, and measured and calculated levels of free GH changed in parallel. During an insulin-tolerance test, free and total GH changed in parallel in all individuals (n = 11) and their peak values as well as area under the curve values were positively correlated (r = 0.89; P < 0.001 and r = 0.92; P < 0.001, respectively). Of note, the relative levels of free GH (calculated as the area under the curve of free to total GH) was inversely correlated with GHBP (r = -0.94; P < 0.001).

CONCLUSION

It is possible to measure free GH in human serum. Free GH correlated positively with total GH and inversely with GHBP. Measurement of free GH may be a helpful future tool in the management of GH disorders and in studies of GH-GHBP interrelationships.

11Beta-HSD type 1 expression in human adipose tissue: impact of gender, obesity, and fat localization

OBJECTIVE

Pre-receptor amplification of glucocorticoids is, in part, determined by the isoenzymes 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1 and type 2, interconverting inert cortisone and active cortisol. Increased tissue activity of cortisol may play a part in features of the metabolic syndrome. Our objective was to compare 11beta-HSD1 gene expression in different fat depots (visceral, subcutaneous abdominal, and subcutaneous gluteal) in lean and obese men and women.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study design was used for healthy patients undergoing minor abdominal surgery (lean men, 10), minor gynecological surgery (lean woman, 10), or gastric banding operations (obese men, 10; and obese women, 10). Gene expressions of 11beta-HSD1 in adipose tissue samples were determined by real-time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Lean women had lower 11beta-HSD1 gene expression in subcutaneous adipose tissue compared with men (62% lower, p < 0.01), whereas no significant difference was found between obese men and women. 11Beta-HSD1 mRNA in human adipose tissue was higher in obese subjects compared with lean subjects in both women and men and in both subcutaneous and visceral adipose tissue. No difference in mRNA expression of 11beta-HSD1 between visceral and subcutaneous adipose tissue or between subcutaneous adipose tissue from different depots was found.

CONCLUSIONS

11Beta-HSD1 in adipose tissue is increased in obesity in both women and men, and may contribute to the associated metabolic syndrome. As 11beta-HSD1 expression in lean women was found to be significantly lower than in lean males, the up-regulation associated with obesity may be relatively more devastating in women than in men, and may help explain the higher relative risk of cardiovascular disease in women suffering from the metabolic syndrome.

Assessment of hydration by means of bioelectrical impedance and arm muscle area during growth hormone (GH) replacement therapy: A prospective study of 130 GH-deficient patients

OBJECTIVE

Growth hormone (GH)-deficiency is associated with a reduced extracellular volume (ECV), whereas GH replacement may cause fluid retention. We have tested a simple method to assess hydration in GH-deficient patients (GHD) based on concomitant measurements of body resistance by bioelectrical impedance analysis (BIA), and arm muscle area (AMA).

DESIGN

We prospectively followed 130 patients (54 females, 76 males) with adult-onset GHD before and during 1-5 years GH replacement therapy.

METHODS

Concomitant measurements of body resistance and AMA were done on four occasions: before treatment, after one month and one year of treatment, and at the most recent visit. Based on normative data obtained in 142 women and 84 men an inverse relationship was documented between body resistance and AMA. Assuming that linear height and the concentration of electrolytes remain constant, body resistance at a given AMA will reflect specific hydration.

RESULTS

In the patients a gender-specific inverse correlation between body resistance and AMA existed, which was different from the control group and changed during GH replacement. A deviation between predicted (based on normative data) and measured body resistance at a given AMA was recorded in the patients before and during therapy compatible with relative dehydration in the untreated state followed by an increase in hydration during therapy.

CONCLUSIONS

Concomitant measurements of BIA and AMA in GHD patients may provide a non-invasive and simple means to estimate hydration before and during GH replacement.

Zinc-transporter genes in human visceral and subcutaneous adipocytes: lean versus obese

Zinc ions influence adipose tissue metabolism by regulating leptin secretion and by promoting free fatty acid release and glucose uptake. The mechanisms controlling zinc metabolism in adipose tissue are unknown. We therefore examined the gene-expression levels of a number of zinc-transporting proteins in adipose tissue, comparing subcutaneous fat with visceral fat from lean and obese humans. Both ZnT-proteins responsible for zinc transport from cytosol to extracellular compartments and intracellular vesicles and Zip-proteins responsible for zinc transport to the cytoplasm were expressed in all samples. This suggests that zinc metabolism in adipocytes is actively controlled by zinc-transporters. The expression levels were different in lean and obese subjects suggesting a role for these proteins in obesity. Furthermore, the expression levels were different from subcutaneous fat to intra-abdominal fat suggesting that the metabolic activity in adipocytes is to some extent dependent upon zinc and the activity of zinc-transporting proteins or vice versa.

Peripartum maternal and foetal ghrelin, growth hormones, IGFs and insulin interrelations

OBJECTIVE

Ghrelin may influence GH secretion and is associated with insulin sensitivity. In pregnancy, placental growth hormone (PGH) replaces GH. The aim of this study was to investigate the relationship between PGH and ghrelin and their relationship to insulin sensitivity in pregnancy.

DESIGN

Prospective, descriptive study.

PATIENTS

Thirty-seven singleton pregnant and six twin pregnant women

MEASUREMENTS

Maternal blood samples were drawn before and 2 days after elective caesarian section (CS). Serum total ghrelin, PGH, GH, GH-binding protein, insulin and IGF-I and IGF-II, and plasma glucose were determined. Insulin sensitivity indices (ISIs) were calculated. Cord blood samples were drawn at delivery for ghrelin determination.

RESULTS

Serum ghrelin only displayed a minimal, although statistically significant, decrease after CS. Prior to delivery serum PGH increased by 25% during fasting, and was undetectable the day after CS. Serum levels of GH were low until 48 h after CS. No significant correlations were detected between PGH or ghrelin and ISIs, although a trend was observed for ghrelin. Twin pregnancies had higher PGH levels than singletons; however, levels of IGFs were similar. In cord blood, ghrelin levels were higher in arterial than venous samples.

CONCLUSIONS

Maternal ghrelin levels were only minimally affected by parturition, suggesting that maternal ghrelin is not involved in the transition from PGH to GH secretion. The increased arterial ghrelin levels in the foetus suggest foetal ghrelin production. Serum PGH appears to be influenced by fasting. Finally, elevated PGH levels in twin pregnancies do not appear to affect maternal IGF levels.

Growth hormone (GH) substitution in GH-deficient patients inhibits 11beta-hydroxysteroid dehydrogenase type 1 messenger ribonucleic acid expression in adipose tissue

CONTEXT

Local tissue activity of glucocorticoids is in part determined by the isoenzymes 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1) and 11beta-HSD2, interconverting inert cortisone and active cortisol. Increased tissue activity of cortisol may play a central role in the features of GH deficiency and the metabolic syndrome.

OBJECTIVE

We investigated the effects of GH treatment on adipose tissue 11beta-HSD mRNA.

SUBJECTS AND METHODS

A randomized placebo-controlled double-blind study design was used. Twenty-three GH-deficient patients (16 males and seven females) were randomized to 4 months of GH treatment (2 IU/m2) (n = 11) or placebo treatment (n = 12). Adipose tissue biopsies and blood samples were obtained before and after treatment. Biopsies were obtained from the abdominal sc depot at the level of the umbilicus and do not necessarily reflect the metabolically more important visceral adipose tissue. Gene expressions were determined by real-time RT-PCR.

RESULTS

GH treatment decreased 11beta-HSD1 mRNA 66% [95% confidence interval (CI), 23-107%; P < 0.01] and increased 11beta-HSD2 mRNA 167% (95% CI, 33-297%; P < 0.05) in adipose tissue. Serum IGF-I and IGF-I mRNA increased in the GH-treated group by 187% (95% CI, 122-250%; P < 0.001) and 470% (95% CI, 88-846%; P < 0.01). The change in 11beta-HSD1 mRNA expression was negatively correlated with the change in serum IGF-I (R = -0.434; P < 0.05). In contrast, the change in 11beta-HSD2 mRNA expression was positively correlated with the change in serum IGF-I (R = 0.487; P < 0.05), and even stronger with the change in IGF-I mRNA expression (R = 0.798; P < 0.0001).

CONCLUSION

GH treatment is able to decrease 11beta-HSD1 mRNA and increase 11beta-HSD2 and accordingly may be able to reduce the amount of locally produced cortisol in adipose tissue.

Kinetics and secretion of placental growth hormone around parturition

OBJECTIVE

During pregnancy, placental growth hormone (PGH) is secreted into the maternal circulation, replacing pituitary GH. It is controversial whether PGH levels decline during vaginal birth. After placental expulsion, PGH is eliminated from the maternal blood. GH binding protein (GHBP) and body mass index (BMI) influence GH kinetics, but their impact on PGH kinetics is unknown. The present study was undertaken to define the kinetics of PGH during vaginal delivery and Caesarian section and to relate these kinetics to GHBP and BMI.

DESIGN

A short term, prospective cohort study.

METHODS

Twelve women had repeated blood samples drawn during vaginal delivery. From 26 women undergoing planned Caesarian delivery (CS) repeated blood samples were withdrawn before, during and after the CS, allowing PGH half-life determination.

RESULTS

During vaginal delivery, median PGH values did not change before expulsion of the placenta, although individual fluctuations were seen. Clearance of PGH from the maternal circulation was best described by a two-compartment model. The initial half-life of serum PGH was (mean +/- s.d.) 5.8 +/- 2.4 min, and the late half-life was (median) 87.0 min (range: 25.1-679.6 min). The late half-life was correlated to the pre-gestational BMI (r = 0.39, P = 0.047), but not to the serum GHBP concentration.

CONCLUSIONS

Serum PGH did not decrease significantly during vaginal delivery. Elimination of PGH fitted a two-compartment model, with an estimated initial half-life of 5.8 min. The late phase serum half-life of PGH was related to BMI, suggesting a role for maternal fat mass in PGH metabolism.

GH-binding protein is related to bone mineral density in non-obese androgenized women

GH and IGF system components are important regulators of bone formation and at the same time pathogenetic factors in functional hyperandrogenism (FH) in lean females. We studied the relationships between bone mineral density (BMD) and serum concentrations of GH, GH-related parameters, androgens and estrogen, in 18 non-obese women of reproductive age with functional hyperandrogenism compared to a group of 10 healthy eumenorrheic age- and weight-matched women. In androgenized women, a significant positive correlation was found between BMD and GH-binding protein (GHBP), whereas BMD did not correlate to GH or other related parameters. It is suggested that higher tissue GH receptor responsiveness in non-obese androgenized women may contribute to their higher BMD.

Pain Perception after Subcutaneous Injections of Media Containing Different Buffers

Several hormones are administered by daily subcutaneous injections. Pain caused by subcutaneous injection is an unpleasant condition, which can limit patient compliance. The objective of the present study was to evaluate the perception of pain by subcutaneous injection of two different and commercially available solutions for dispensing recombinant human growth hormone. The solutions are characterised by pH, conservation, and buffer. Isotonic saline was used as reference solution. Fifty-four healthy volunteers (mean age (+/-S.E.M.): 35.5+/-1.1 years) were recruited to the double-blind, randomised study. All injections were performed pairwise (right and left thigh) in one day by the same experienced nurse. Perception of pain was evaluated by the volunteers immediately after injection and 2 min. after injection into the thigh of three formulations, which differed with respect to pH and buffers (histidine, citrate and saline, respectively). Significantly more participants (38/54) found than the citrate buffer caused more pain than the histidine buffer immediately after injection (P=0.002). Histidine buffer did not cause more pain than saline (P=0.996). After 2 min., there was no difference between the histidine and the citrate buffer (P=1.00), nor between the histidine buffer and saline (P=1.00). In summary, the solution-containing citrate as buffer caused more pain after subcutaneous injection than the solution with histidine as buffer. Considering patient compliance, it seems advisable to employ histidine-buffered solution rather than citrate-buffered solution for dispensing recombinant human growth hormone by daily subcutaneous injections.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

Sex steroids and the growth hormone/insulin-like growth factor-I axis in adults

In healthy adults insulin-like growth factor (IGF)-I levels do not differ between males and females, whereas spontaneous growth hormone (GH) secretion is approximately twofold higher in females. Untreated GH-deficient (GHD) women exhibit lower IGF-I levels compared with men and the increase in serum IGF-I during GH replacement is also significantly less. These data suggest a resistance to GH in women, which in healthy subjects is compensated for by increased GH secretion. Administration of oral oestrogen in healthy postmenopausal women suppresses hepatic IGF-I production and increases pituitary GH release, and oral oestrogen replacement in women with GHD lowers IGF-I concentrations and increases the amount of GH necessary to achieve IGF-I target levels during treatment. These data clearly suggest that hepatic suppression of IGF-I production by oestrogen subserves the gender difference in GH sensitivity, but it is also likely that sex steroids may interact with the GH/IGF axis at other levels. There is also circumstantial evidence to indicate that testosterone stimulates IGF-I production and it is speculated that a certain threshold level of androgens is essential to ensure hepatic IGF-I production. Whether these data should translate into earlier discontinuation of oestrogen replacement therapy in women with hypopituitarism merits consideration.

Serum insulin-like growth factor I levels in growth hormone-deficient adults: influence of sex steroids

Measurement of serum insulin-like growth factor I (IGF-I) concentrations remains the single most important tool in the evaluation of growth hormone (GH) replacement in GH-deficient adults, and the therapeutic goal is to maintain the level within the age-adjusted normal range. In healthy adults, IGF-I levels do not differ between males and females, whereas spontaneous GH secretion is approximately twofold higher in females. Untreated GH-deficient women exhibit lower IGF-I levels compared with men, and the increase in serum IGF-I during GH replacement is also significantly less. Put together, these data suggest resistance to GH in women, which in healthy individuals is compensated for by increased GH secretion. Administration of oral oestrogen in healthy post-menopausal women suppresses hepatic IGF-I production and increases pituitary GH release, and oral oestrogen replacement in women with GH deficiency lowers IGF-I concentrations and increases the amount of GH necessary to obtain IGF-I target levels during treatment. These data clearly suggest that hepatic suppression of IGF-I production by oestrogen subserves the gender difference in GH sensitivity, but it is also likely that sex steroids may interact with the GH/IGF axis at further levels. There is also circumstantial evidence to indicate that testosterone stimulates IGF-I production, and it is speculated that a certain threshold level of androgens is essential to ensure hepatic IGF-I production. Whether these data should translate into earlier discontinuation of oestrogen replacement therapy in adult women with hypopituitarism merits consideration.

Growth hormone binding protein and maternal body mass index in relation to placental growth hormone and insulin requirements during pregnancy in type 1 diabetic women

In pregnancy, the growth hormone axis is shifted from pituitary growth hormone (GH) to placental growth hormone (PGH). Their common binding protein, GH binding protein (GHBP), displays peak serum levels at mid-gestation in normal individuals. In the non-pregnant state, diabetes is known to be associated with elevated levels of GH and decreased levels of insulin-like growth factors (IGFs) and GHBP. Diabetes in pregnancy may therefore as well be associated with disturbances in the growth hormone axis. In the present study, we aimed at investigating the impact of GHBP and maternal body mass index (BMI) on levels of PGH, thereby enabling estimation of any association between free PGH and weight adjusted insulin requirements. In 51 type 1 diabetic women, blood samples were collected in gestational week 10+, 16+, 22+, 28+ and 34+, and analysed for their serum content of GHBP, PGH, and GH. Serum GHBP increased from the first weeks of pregnancy to median 2.07 nmol/l (range 1.17-4.26) in week 22+, then declined to median 1.29 nmol/l (range 0.77-2.35) in week 34+ (ANOVA P < 0.001). Serum PGH levels were highest in week 34+ at median 21.3 microg/l (range 5.1-165.4) (P < 0.001), whereas a steady decrease in GH values was observed throughout pregnancy to a median 0.17 microg/l (range 0-5.53). The fraction of calculated free PGH to total PGH increased from mid-gestation onwards to 55.2% (37.0-87.1) in week 34+ at a median level of free PGH of 10.4 microg/l (range 1.9-144.0) (P < 0.001). Similarly, the molar ratio of total PGH to GHBP increased to a maximum of 0.68 (0.12-6.62) in week 34+. As in normal pregnancies, the correlation between BMI and GHBP was lost in late pregnancy. The newborns birth weight z-score correlated with total PGH and derivatives here-of in week 34+. Neither total nor weight adjusted insulin requirements correlated to total PGH, calculated free PGH, nor GHBP. In conclusion, PGH and GHBP display a similar course during pregnancy in type 1 diabetic women as described in normal women. The well-known association between GHBP and BMI was lost in late pregnancy. Calculated levels of free PGH were positively associated to fetal growth, but not to maternal insulin requirements.

Ghrelin and its relationship to growth hormones during normal pregnancy

OBJECTIVE

Ghrelin and GH secretagogue receptors have been found in reproductive organs, including the placenta. The physiology of ghrelin in pregnancy has not been explored. In human pregnancy, pituitary GH is gradually replaced by placental GH (PGH). The present study was undertaken to examine serum ghrelin levels during normal pregnancy and to determine to what extent changes in ghrelin levels coincide with changes in serum levels of free and total GH and PGH. Design Prospective study with blood sampling from pregnant women in gestational weeks 8, 18, 26 and 36 and postpartum.

PATIENTS

Eleven nondiabetic pregnant women with singleton pregnancies.

MEASUREMENTS

Serum ghrelin was determined using an in-house radioimmunoassay. Serum PGH was determined in a solid-phase immunoradiometric assay, serum GH and insulin in a time-resolved immunofluorometric assay, and serum GHBP in an in-house immunofunctional assay.

RESULTS

Serum ghrelin levels peaked in week 18 (1.20 +/- 0.09 microg/l) and the lowest levels were observed in late third trimester (0.87 +/- 0.06 microg/l), corresponding to a mean decrease of 27.7% (P < 0.001) from peak levels. An increase was observed again postpartum. Serum GH diminished throughout pregnancy to low third-trimester values (0.12 +/- 0.03 microg/l; P < 0.001), and PGH increased to 25.7 +/- 2.86 microg/l (P < 0.001) in week 36. Neither total nor calculated free levels of growth hormones correlated to ghrelin levels, and no significant correlations were observed between ghrelin and maternal body mass index (BMI) or fasting insulin levels.

CONCLUSIONS

Serum ghrelin levels peak around mid-gestation in human pregnancy. Ghrelin levels during pregnancy are at their lowest in the third trimester at a time of increased body weight, development of insulin resistance and high serum levels of PGH. However, no associations were observed between ghrelin and the two growth hormones.

Discontinuation of estrogen replacement therapy in GH-treated hypopituitary women alters androgen status and IGF-I

OBJECTIVE AND DESIGN

Compared with their male counterparts, healthy females secrete more growth hormone (GH) and those with GH-deficiency have lower insulin-like growth factor I (IGF-I) levels and are less responsive to GH substitution. To test whether this gender difference is related to sex hormones we measured androgen status and IGF-I related parameters in 38 hypopituitary women (mean (range) age 41.5 (20-58) years) during continued GH substitution as compared with a control group of 38 healthy women matched for age and menopausal status. Twenty six patients were studied twice: with estrogen replacement and after 28 days of estrogen discontinuation in a randomised design.

RESULTS

The patients were androgen deficient compared with controls (median, range), dehydroepiandrosterone sulphate (DHEAS): 185 (99-7800) nmol/l vs 4400 (820-13,000) nmol/l, P=or<0.001; androstenedione: 0.5 (0.1-7.1) nmol/l vs 4.3 (1.6-8.8) nmol/l, P=or<0.001; dihydrotestosterone (DHT): 0.13 (0.09-0.54) nmol/l vs 0.55 (0.09-0.89) nmol/l, P=or<0.001; testosterone: 0.28 (0.09-1.56) nmol/l vs 1.1 (0.71-2.24) nmol/l, (P=or<0.001); free testosterone: 0.004 (0.001-0.030) nmol/l vs 0.016 (0.001-0.030) nmol/l, P=or<0.001. The circulating levels of IGF-I, IGF-II, IGF-binding protein 1 (IGFBP-1), and IGFBP-3 did not differ between patients and controls. The subgroup of patients receiving hydrocortisone (HC) replacement (n=24) had significantly lower levels of androgens (suppressed by 80-100%) as well as IGF-I and IGFBP-3 as compared with the patients not receiving HC. IGF-I was correlated to free testosterone in patients (r=0.57, P=0.0005) as well as controls (r=0.43, P=0.008), and free testosterone was a significant positive predictor of IGF-I. Estrogen discontinuation induced an increase in IGF-I (167+/-15 vs 206+/-14 microg/l, P=0.005 and IGFBP-3 (3887+/-139 vs 4309+/-138 microg/l, P=0.0005). Estrogen discontinuation was associated with a significant increase in median (range) free testosterone (0.004 (0-0.02) vs 0.0065 (0-0.03) nmol/l, P=0.001) and a significant decrease in median (range) sex-hormone binding globulin (SHBG; 93 (11-278) vs 55.5 (20-142) nmol/l, P=0.001). DeltaIGF-I correlated with DeltaSHBG (r=-0.45 P=0.033) and DeltaIGFBP-3 (r=0.67 P=or<0.001). In a regression model DeltaE2, Deltatestosterone, DeltaSHBG and DeltaIGFBP-3 explained 93% of the variation in DeltaIGF-I.

CONCLUSIONS

Androgen levels are low in hypopituitary women and free testosterone correlates with IGF-I. Discontinuation of estrogen replacement in these patients induces elevations in IGF-I as well as free testosterone, and DeltaIGF-I correlated positively with Deltafree testosterone. These effects may contribute to the gender differences observed in the GH-IGF axis in healthy adults as well as in the responsiveness of hypopituitary patients to GH substitution.

Very short term dehydroepiandrosterone treatment in female adrenal failure: impact on carbohydrate, lipid and protein metabolism

OBJECTIVE

In female adrenal insufficiency, dehydroepiandrosterone (DHEA) secretion is impaired and circulating androgen levels are severely reduced. We wanted to analyse the acute effects of physiological DHEA substitution on substrate metabolism.

DESIGN

We studied nine females with adrenal insufficiency after 9 days of oral DHEA replacement (50 mg/day) in a double-blind, placebo-controlled crossover study.

METHODS

Whole body and regional substrate metabolism was assayed in the basal state and during a euglycemic hyperinsulinemic glucose clamp by means of isotope dilution techniques (glucose, phenylalanine, tyrosine), indirect calorimetry and in situ lipolysis (microdialysis technique).

RESULTS

DHEA treatment normalized the levels of all androgens. Basal and insulin-stimulated total energy expenditure and rates of protein, lipid and glucose oxidation were unaffected by DHEA. Whole body turnover of glucose and protein were also unaffected by DHEA. Forearm breakdown of protein was reduced by insulin to the same extent after placebo and DHEA. Insulin sensitivity as expressed by the glucose infusion rate during the euglycemic clamp was similar after placebo and DHEA. Finally, the interstitial release of glycerol in adipose tissue was not significantly influenced by DHEA.

CONCLUSIONS

Short-term oral DHEA replacement in women with adrenal insufficiency was not associated with measurable changes in total or regional substrate metabolism.

Gene expression of the GH receptor in subcutaneous and intraabdominal fat in healthy females: relationship to GH-binding protein

OBJECTIVE

Circulating GH-binding protein (GHBP) is produced by proteolytical cleavage of the extracellular part of the GH receptor (GHR) and is positively correlated to the amount of body fat. To test the hypothesis that adipose tissue may contribute to the production of circulating GHBP, we compared gene expression of two GHR isoforms in adipose tissue with serum GHBP concentrations in healthy females.

DESIGN

Twenty-two healthy females undergoing surgery for benign gynecological conditions were included in the study.

METHODS

During surgery, s.c. and intraabdominal fat biopsy samples were taken. Gene expression of the full-length GHR and a truncated GHR (GHRtr) was assessed by RT-PCR relative to the expression of beta-actin.

RESULTS

The full-length GHR was expressed to a much higher level than GHRtr in both tissues. The levels of both GHR and GHRtr mRNA were similar in intraabdominal and s.c. adipose tissues. Surprisingly, concentrations of circulating GHBP were negatively correlated to the levels of mRNA transcripts of both the full-length GHR and GHRtr in intraabdominal fat. Whole body resistance (as a measure of lean body mass) was positively correlated to mRNA levels for both GHRs in intraabdominal fat.

CONCLUSIONS

(i) The full-length GHR is expressed to a much higher level than GHRtr in s.c. as well as visceral abdominal fat; (ii) the observation of a significant correlation between GHR expression and GHBP levels further emphasizes the link between adipose tissue and GHBP; (iii) it remains, however, to be demonstrated whether circulating GHBP is produced to a significant degree by adipose tissue.

Dehydroepiandrosterone supplementation in women with adrenal failure: impact on twenty-four hour GH secretion and IGF-related parameters

OBJECTIVE

In women, GH secretion is strongly influenced by oestrogen status, whereas the role of androgens is unclear. We, therefore, examined GH secretory dynamics during low vs. normalized androgen levels in women with adrenal failure.

PATIENTS

Ten females with adrenal failure (AF), mean age of 42 years (range 22-54 years).

DESIGN

The effects of 8 days of oral dehydroepiandrosterone (DHEA; 50 mg/day) were studied in a double-blind placebo-controlled, cross-over design. A control group of healthy women was studied once without any treatment.

MEASUREMENTS

Before and after each treatment period, blood was sampled for measurement of androgens, IGF-I, IGFBP-3 and GHBP. A 24-h GH profile with measurements every 20 min was performed at the end of each period.

RESULTS

DHEA supplementation normalized the mean circulating levels of testosterone and androgen precursors. The secretory pattern of GH was unaltered during DHEA [placebo vs. DHEA; half-life 22.83 +/- 1.24 vs. 21.45 +/- 1.19 (min), P = 0.429; pulse frequency 9.9 +/- 0.7 vs. 10.5 +/- 0.5 (/24 h), P = 0.502; total production rate 62.27 +/- 13.44 vs. 52.61 +/- 7.06 (microg/l/day), P = 0.317]. Subgroup analysis, however, indicated that DHEA treatment increased GH secretion in patients not receiving oestrogen (n = 5), whereas the opposite was observed among patients receiving exogenous oestrogen derivatives (n = 5). Compared to the control group (CON), GH half-life was longer in AF (half-life CON: 16.48 +/- 0.91, P = 0.001). The additional features of GH secretion were similar. Unexpectedly, the levels of IGF-I, IGFBP-3 and GHBP were elevated in the patients as compared to controls, without significant effects of DHEA [AF vs. CON. IGF-I: 186 +/- 20 vs. 144 +/- 7 (microg/l), P = 0.04; IGFBP-3: 5196 +/- 224 vs. 3687 +/- 212 (microg/l), P = 0.001; GHBP: 2.27 +/- 0.25 vs. 1.41 +/- 0.13 (nmol/l), P = 0.002].

CONCLUSION

(1) Short-term DHEA administration in women with adrenal failure normalizes the circulating levels of androgens without uniformly affecting the GH-IGF axis; (2) The observation that exogenous oestradiol may mask a stimulatory effect of DHEA on GH secretion merits future investigation.

Growth hormone increases vascular cell adhesion molecule 1 expression: in vivo and in vitro evidence

We investigated the impact of GH administration on endothelial adhesion molecules, vascular cell adhesion molecule-1 (VCAM-1) and E-selectin, in vivo and in vitro. Soluble VCAM-1, E-selectin, and C-reactive protein concentrations were measured before and after treatment in 25 healthy subjects and 25 adult GH-deficient (GHD) patients randomized to GH treatment or placebo. Furthermore, we studied the direct effect of GH and IGF-I and serum from GH-treated subjects on basal and TNF alpha-stimulated expression of VCAM-1 and E-selectin on cultured human umbilical vein endothelial cells. Baseline levels of VCAM-1, but not E-selectin, were significantly lower in GHD patients than in healthy subjects (362 +/- 15 microg/liter vs. 516 +/- 21 microg/liter, P < 0.001) and increased in GHD patients during GH treatment, compared with placebo [net difference between groups 151.8 microg/liter (95% confidence interval: 95.0-208.7 microg/liter); P < 0.0001]. In human umbilical vein endothelial cells, there was no direct stimulatory effect of either GH or IGF-I on the expression of VCAM-1 and E-selectin, but serum from GH-treated healthy subjects significantly increased the expression of VCAM-1 (P < 0.01). Our findings are compatible with the notion that GH may stimulate the expression of VCAM-1 indirectly through modulation of circulating factors. VCAM-1-mediated leukocyte extravasation is implicated in several illnesses including atherosclerosis and multiple-organ failure in sepsis, and we hypothesize that enhanced expression of VCAM-1 may contribute to the detrimental effects of GH in critically ill patients.

Evaluation of growth hormone stimulation tests in cured acromegalic patients

We have evaluated the GH peak response to insulin tolerance test (ITT) and to GHRH+arginine in 11 patients cured of acromegaly after treatment with surgery/radiotherapy and compared them to a control group matched for age and sex. GH peak response was significantly higher in the control group than in the patient group (11.21+/-6.98 vs. 4.46+/-6.90 ng/ml, p=0.010). Seven patients had a GH peak response of less than 3 ng/ml, compatible with the diagnosis of GH deficiency. Peak GH response after GHRH+arginine was significantly lower in the group of patients with GH peak of less than 3 ng/ml during ITT as compared to the group with GH peak of more than 3 ng/ml, and in all cases the diagnosis of GH deficiency was confirmed. Mean IGF-I level was not different between the patients and controls, as well as between patients with and without GH deficiency diagnosed by the stimulation tests.

CONCLUSION

The incidence of GHD diagnosed by stimulation tests is high in patients cured of acromegaly.

The gender differences in growth hormone-binding protein and leptin persist in 80-year-old men and women and is not caused by sex hormones

OBJECTIVE

Leptin and growth hormone-binding protein (GHBP) both show gender differences that might be explained by sex hormones. To study the potential relevance of oestradiol and testosterone, we have examined 80-year-old subjects in whom oestradiol is higher in men than in women. The interrelationships between leptin, insulin, GHBP and fat mass in this age group were also investigated.

DESIGN AND SUBJECTS

Ninety-four subjects (55 females and 39 males), all 80 years old, were investigated in a community-based study. None of the investigated subjects was being treated for diabetes mellitus and none of the women had oestrogen replacement.

METHODS

Levels of testosterone, oestradiol, SHBG, IGF-I, GHBP, glucose, insulin and leptin were analysed. Body composition was measured with bioimpedance analysis (BIA).

RESULTS

As in younger age groups, serum leptin, the ratio leptin/kilogram fat mass and serum GHBP were higher in the women (all, P< or =0.007), although serum oestradiol was higher in the men (P<0.001). There were no significant associations between sex hormones and leptin or GHBP either in women or in men (all, r<0.13, P>0.1). Leptin correlated to kilogram fat mass in both women (r=0.55, P<0.001) and men (r=0.47, P=0.003), but in contrast, there were no significant correlations between GHBP and fat mass and GHBP and IGF-I, either in women or in men (all, r<0.24, P>0.2). Insulin and leptin were significantly associated with GHBP, both in women (r=0.48, P<0.001 and r=0.43, P=0.001, respectively) and in men (r=0.40, P=0.01 and r=0.34, P=0.03, respectively).

CONCLUSIONS

Although the 80-year-old men had higher oestradiol levels than the women, the women had higher levels of leptin and GHBP. There were no correlations between sex hormones and leptin and GHBP, which indicates that the gender differences are not caused by sex hormones in old age. In contrast to studies in younger subjects, GHBP did not correlate to fat mass in the investigated 80-year-old men and women. In the older subjects investigated, as in younger subjects, GHBP was significantly correlated with leptin and insulin.

Biochemical definitions of disease activity in acromegaly

In acromegaly the therapeutic outcome is difficult to assess and depends on the biochemical method. We have ascertained disease activity in 70 acromegalic patients by means of a GH profile (8 hourly samples) and a single IGF-I measurement as compared to a healthy control group. As an estimate of the "stiffness" of the GH profile we calculated the SD/nadir(GH) from the GH profile. In the control group the following upper normal limits were obtained: IGF-I (microg/l) 217; mean GH (microg/l) 2.16; nadir GH (g/l) 0.3. Based on ROC plot analysis a value of 2.0 for the SD/nadir ratio was used as cut-off. This translated into the following surgical cure rates (%): IGF-I 47; mean GH 77; nadir GH 65; SD/nadir 30. Some of the patients post-surgery had elevated IGF-I levels despite "normal" GH levels. Abnormal SD/nadir versus normal IGF-I and vice versa were recorded in many patients post-surgery.

IN CONCLUSION

(1) cure rates of acromegaly depend strongly on the criteria being used and (2) estimates of GH secretion pattern may yield important information about GH status in acromegaly.

Impact of GHBP interference on estimates of GH and GH pharmacokinetics

OBJECTIVE

Circulating GH-binding protein (GHBP) may interfere with GH measurements in immunoassays by competing with the antibodies for ligands. The concentrations of circulating GHBP in humans are closely related to the amount of body fat, and subject to large interindividual differences.

SUBJECTS AND METHODS

To assess the influence of GHBP in a widely used commercial immunometric GH kit (DELFIA, Wallac, Finland) we systematically tested the effects of varying GHBP concentrations and assay incubation times on GH estimates over a broad range of GH concentrations. We subsequently investigated the impact of 24-h vs. 2-h incubation on estimates of GH pharmacokinetics obtained from two-step primed-constant infusions of GH in a group of 26 healthy nonobese men [mean age 37.3 years (range 22-55); body mass index (BMI) = 24.6 +/- 0.4 kg/m2].

RESULTS

GHBP at physiological concentrations of 0.2, 0.5, 1.0, 2.0 nm reduced the GH estimates by as much as 40% at low GH concentrations. By increasing the incubation time from the recommended 2 h to 24 h the interference from GHBP was almost completely eliminated. The increase in measured GH using 24-h vs. 2-h incubation showed a strong positive correlation to the subjects' GHBP levels (r = 0.66, P < 0.001). Consequently, the estimates of metabolic clearance rate (MCR) of GH at constant infusion rates of 1.5 micro g/kg/h and 3.0 micro g/kg/h were significantly reduced when using 24 h as opposed to 2 h incubation, and the changes were negatively correlated to the GHBP levels (r = -0.62, P < 0.001 and r =-0.54, P < 0.01, respectively). Furthermore, by reducing the interference of GHBP through 24-h incubation, the previously observed positive correlations between MCR and not only the subjects' GHBP levels but also with total body fat were reduced, while the positive correlation between baseline insulin concentrations and GH clearance was strengthened.

CONCLUSIONS

We conclude that differences in GHBP concentrations significantly influence GH measurements in this commercial immunoassay, and that interindividual differences in GHBP concentrations may interfere with the results in studies involving between-subject comparisons of GH concentrations and pharmacokinetics. We believe the extended incubation time allows for better 'extraction' of GH bound to serum GHBP, and that this effect should be investigated, and if relevant, be exploited in other GH immunoassays.

GH-IGF-I axis in non-obese women with functional hyperandrogenism

The study was conducted to assess the GH-IGF-I axis in non-obese women with functional hyperandrogenism (FH). Eighteen FH women aged 18-35 yr with a body weight within 20% of ideal body weight and 10 weight-matched controls were included in the study. Basal serum GH, GH-binding protein (GHBP), IGF-I, IGF-binding protein-3 (IGFBP-3) levels were determined as well as GH levels during GHRH stimulation. In addition, basal serum androgens [free T (FT), delta4 and DHEAS], insulin and glucose levels were determined. The group of non-obese patients with FH differed from controls in GHBP (1.21+/-0.37 vs 0.93+/-0.25 nmol/l; p<0.05) and androgen levels (FT: 8.0+/-3.2 vs 1.9+/-1.2 pmol/l, p<0.001; delta4: 10.5+/-3.2 vs 5.9+/-2.1 nmol/l, p<0.001; DHEAS: 9.3+/-3.0 vs 5.1+/-1.8 micromol/l, p<0.001). GH (r=0.365; p<0.05) and IGF-I (r=0.508, p<0.01) serum levels were significantly correlated to serum DHEAS levels in a combined group of patients and controls. Our results support the suggestion that the GH-IGF-I axis plays an important role in the evolution of hormonal and metabolic derangement in non-obese FH women.

Age dimorphism in the association between growth-hormone status and the respiratory quotient

OBJECTIVE

To investigate the impact of age on the association between the respiratory quotient (RQ) and growth-hormone (GH) secretion and to investigate the acute lipolytic response to an exogenous GH bolus.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study of 36 non-obese healthy subjects (18 women and 18 men) from two age groups was used: "younger" (mean age, 29.5 years; range, 27 to 34 years) and "older" (mean age, 50.8 years; range, 47 to 59 years). Endogenous GH secretion by means of deconvolution analysis of 24-hour serum GH concentrations was measured every 20 minutes. Resting RQ was measured after a 12-hour overnight fast. The lipolytic response to an intravenous exogenous GH bolus (200 microg) was assessed by measuring serum levels of free fatty acids as well as changes in RQ. Additional measurements included body composition (regional computed tomography scan and DXA) and physical fitness (VO(2)max).

RESULTS

Resting RQ did not differ between the two age groups: 0.81 +/- 0.01 (young) vs. 0.82 +/- 0.01 (older; not significant). Several estimates of GH release correlated positively with RQ in the younger group, whereas a negative correlation was detected in the older subjects [GH production rate (microg/liter x kg) vs. RQ: r = 0.62, p < 0.01 (younger); r = -0.53; p = 0.02 (older)]. By regression analysis, 52% to 58% of the variation in RQ could be explained by GH status. After an exogenous GH bolus, the incremental response in nonesterified fatty acid was slightly higher in younger individuals (p = 0.09).

DISCUSSION

Resting RQ is significantly correlated with GH status. This association is positive in younger individuals and negative in older individuals. The lipolytic response to exogenous GH is moderately higher in younger compared with older individuals. GH status should be taken into account when investigating the residual variation in RQ.

A comparison of circulating and regional growth hormone-binding protein in cirrhosis

The growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis is disturbed in cirrhosis, with elevated basal GH and low IGF-I levels relating to liver function and prognosis. In plasma, GH is bound to a high-affinity GH-binding protein (GHBP), which has been found to be slightly reduced in cirrhosis, but with huge variations. GHBP is identical to the extracellular part of the hepatic GH receptor, but other tissues may contribute to the circulating GHBP levels. The aim was therefore to measure circulating and regional concentrations of GHBP in relationship to hepatic function and body composition in patients with cirrhosis (n = 38) and controls with normal liver function (n = 29). Blood samples from the hepatic, renal, and femoral veins and the femoral artery were collected simultaneously during a hemodynamic investigation. Plasma GHBP was directly measured by a specific and sensitive fluoroimmunoassay. Circulating GHBP levels were identical in the patients and controls (mean +/- SD) 1.03 +/- 0.56 nmol/L and 1.02 +/- 0.55 nmol/L, respectively (not significant). We found no significant hepatic, renal, or peripheral arteriovenous extractions or generations of GHBP, and it did not significantly correlate to liver function. In the controls, GHBP correlated significantly with body mass index (BMI) (r =.60, P <.005), whereas this relationship was not found in the patients with cirrhosis. In conclusion, high-affinity GHBP appears to be normal in patients with cirrhosis, with no significant hepatic generation or renal extraction and no association with the severity of the liver disease. Thus, our study supports the hypothesis that tissues other than the liver, despite its abundant GH receptors, may contribute to the circulating GHBP.

Growth hormone treatment in adults: is there a true gender difference?

The importance of growth hormone (GH) deficiency in adults became evident at the end of the 1980s, when the first clinical studies on GH replacement therapy in adults were published. Since then, accumulated experience has shown a great individual variability in the response to GH replacement, including a potential difference in responsiveness between genders. The aim of this paper is to review the data regarding the effects of gender differences on GH pharmacokinetics, pharmacodynamics, and efficacy of replacement. In addition, we start with a short review of the possible role of GH in sexual development and sexual life.

The growth hormone (GH)-insulin-like growth factor axis during testosterone replacement therapy in GH-treated hypopituitary males

Several studies suggest a direct effect of sex steroids on insulin-like growth factor-I (IGF-I) production. Oestrogen has been hypothesized directly to inhibit hepatic IGF-I production, but the role of androgens is not clarified. We aimed to investigate whether testosterone exerts a pituitary-independent effect on IGF-I and related parameters. Eight adult hypopituitary men (39.9 +/- 5.7 years) receiving growth hormone (GH) and testosterone replacement therapy (250 mg testosterone enantate every fourth week) participated in this prospective study. Frequent blood samples were drawn over a 5 week period in relation to two testosterone injections. Mean baseline IGF-I levels were 352 +/- 135 microg/L, and they remained unaltered during the study period (analysis of variance (ANOVA), P = 0.88). Free IGF-I levels did not change either (ANOVA, P = 0.35). Serum IGF binding protein-3 (IGFBP-3) and acid-labile subunit decreased (ANOVA, P = 0.04 and P = 0.02 respectively) but post hoc analysis did not reveal a particular difference between days. IGFBP-1 increased following testosterone administration (ANOVA, P = 0.05), whereas GH binding protein levels tended to decrease following testosterone administration (ANOVA, P = 0.08). Prostate-specific antigen tended slightly to increase after each testosterone injection (ANOVA, P = 0.08, post hoc, NS). We conclude that major changes in total IGF-I are not induced during conventional intramuscular testosterone replacement in GH-treated hypopituitary males, suggesting that testosterone effects on IGF-I are likely to be secondary to a stimulation of endogenous GH release.

Gene expression of a truncated and the full-length growth hormone (GH) receptor in subcutaneous fat and skeletal muscle in GH-deficient adults: impact of GH treatment

In humans at least two GH receptors are significantly expressed. One is the full-length receptor (GHR); the other is a truncated form (GHRtr), that lacks most of the intracellular domain. This receptor may inhibit the action of the full-length receptor. Circulating GH-binding protein (GHBP) is a proteolytically cleaved product from both of these receptors. The clinical relevance of the different receptor types is unknown. We examined the gene expression of GHR and GHRtr in human adipose tissue and skeletal muscle and the influence of GH treatment on this expression. Furthermore, we studied the relationship of circulating GHBP and body composition to GHR and GHRtr gene expression. Eleven adult GH-deficient patients were studied before and after 4 months of GH substitution therapy. Abdominal fat obtained by liposuction and femoral muscle biopsies were taken at baseline and after 4 months. Gene expression of GHR and GHRtr in adipose tissue and skeletal muscle was determined and expressed relative to the expression of beta-actin. Gene expression of GHR in abdominal sc adipose tissue was not altered, whereas the expression of GHRtr increased significantly. In skeletal muscle inverse changes were seen in the expression of messenger ribonucleic acid (mRNA) levels for the two GH receptor forms: expression of GHR increased significantly, whereas mRNA levels for GHRtr decreased. As expected, body composition changed with reduction of body fat mass after 4 months of GH treatment. Levels of circulating GHBP decreased significantly. We conclude that GH treatment in GH-deficient adults changes the expression of mRNA for GHR and GHRtr in adipose tissue and skeletal muscle. Whether these changes are responsible for the observed changes in body composition in response to GH treatment and the observed changes in levels of circulating GHBP, however, needs further elucidation.

The effect of 30 months of low-dose replacement therapy with recombinant human growth hormone (rhGH) on insulin and C-peptide kinetics, insulin secretion, insulin sensitivity, glucose effectiveness, and body composition in GH-deficient adults

The aim of the present study was to evaluate the long-term (30 months) metabolic effects of recombinant human GH (rhGH) given in a mean dose of 6.7 microg/kg x day (= 1.6 IU/day), in 11 patients with adult GH deficiency. Glucose metabolism was evaluated by an oral glucose tolerance test and an iv (frequently sampled iv glucose tolerance test) glucose tolerance test, and body composition was estimated by dual-energy x-ray absorptiometry. Treatment with rhGH induced persistent favorable changes in body composition, with a 10% increase in lean body mass (P < 0.001) and a 12% reduction of fat mass (P < 0.002); however, the glucose tolerance deteriorated significantly, and three patients developed impaired glucose tolerance. Fasting insulin level (P < 0.003) and the homeostasis model assessment insulin resistance score increased significantly, indicating a deterioration in insulin sensitivity; whereas the insulin sensitivity index, calculated from the frequently sampled iv glucose tolerance test, only decreased slightly. The clearance of C-peptide and insulin increased 100% and 60%, respectively, and the prehepatic insulin secretion was tripled during rhGH treatment; but related to the impairment in glucose tolerance, beta-cell response was still inappropriate. Our conclusion is that long-term rhGH-replacement therapy in GH deficiency adults induced a significant deterioration in glucose tolerance, profound changes in kinetics of C-peptide, and insulin and prehepatic insulin secretion, despite an increase in lean body mass and a reduction of fat mass. Therefore, rhGH treatment may precipitate diabetes in some patients already susceptible to the disorder.

Circulating levels of incretin hormones and amylin in the fasting state and after oral glucose in GH-deficient patients before and after GH replacement: a placebo-controlled study

OBJECTIVE

Hyperinsulinemia in association with GH excess is considered a compensatory response to insulin resistance, but the possibility of alternative insulinotropic mechanisms has not been investigated in vivo. It is also unknown how GH influences the secretion from pancreatic beta-cells of amylin, a peptide which regulates prandial glucose homeostasis and may be linked to development of beta-cell dysfunction. We therefore measured plasma concentrations of two gut insulinotropic hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulin-releasing peptide (GIP), and total as well as non-glycosylated amylin, in 24 GH-deficient adults before and after 4 months of GH replacement (daily evening injections of 2 IU GH/m).

DESIGN

Double-blind, placebo-controlled, parallel study.

METHODS

All participants underwent an oral glucose tolerance test (OGTT) at 0 and 4 months.

RESULTS

A 33% suppression of fasting GLP-1 concentrations was measured in the GH group at 4 months (P=0.02), whereas a non-significant increase occurred in the placebo group (P=0.08). Fasting levels of GIP and amylin did not change significantly after 4 months in either group. The incremental response in GLP-1 during the OGTT was significantly lower after GH treatment as compared with both baseline (P=0.02) and the response in the placebo group (P=0. 03). The stimulation of GIP secretion following OGTT was similar on all occasions. The OGTT-induced incremental response in non-glycosylated amylin was moderately elevated after GH treatment as compared with placebo (P=0.05). Plasma concentrations of glucose and insulin, both in the fasting state and after the OGTT, were higher after GH treatment, but the ratio between amylin and insulin remained unchanged.

CONCLUSIONS

GH-induced hyperinsulinemia is accompanied by proportionate elevations in amylin concentrations and a blunting of gut GLP-1 secretion. The mechanisms underlying the suppression of GLP-1 remain to be elucidated.

Serum levels of growth hormone binding protein in children with normal and precocious puberty: relation to age, gender, body composition and gonadal steroids

AIM

To study the regulation of GHBP serum levels by gonadal steroids in normal and precocious puberty.

STUDY PROTOCOL

We studied GHBP levels in relation to age, sex, pubertal maturation, body composition as well as to circulating IGF-I and gonadal steroid levels in 320 healthy children. Furthermore, we studied the regulation of circulating GHBP in 33 girls with central precocious puberty before and during gonadal suppression with GnRH agonist.

METHODS

GHBP was determined by a time-resolved fluoroimmunoassay (GHBP TR-FIA) based on a commercially available immunoassay for GH, the DELFIA GH assay.

RESULTS

In healthy children GHBP levels were significantly higher in normal girls compared with boys, and there was no significant increase in GHBP in puberty in both sexes. GHBP levels did not correlate with height (SDS), age, pubertal stage, IGF-I or testosterone/oestradiol levels in boys and girls, respectively. There were significant correlations between BMI and GHBP in boys and girls (R 2 = 0.14 and R 2 = 0.12, both P < 0.0001). Furthermore, GHBP correlated highly significantly with the percentage body fat, determined by BIA in 43 healthy girls (R 2 = 0. 40, P < 0.0001). GHBP levels were significantly higher in girls with central precocious puberty (CPP) (1.31 SDS (1.26), mean (SD)) compared to prepubertal controls (P < 0.0001), and above + 2 SD in 10 out of 33 patients. In girls with CPP, GHBP correlated inversely with oestradiol before treatment (R 2 = 0.26, P < 0.01) and there was a tendency towards a positive correlation with BMI (R 2 = 0.13, P = 0.078). By contrast, there were no signficant correlations between GHBP and IGF-I or height SDS. Gonadal suppression with GnRH agonist treatment caused a transient significant increase of 0.57 SD after 2 months of treatment (P < 0.001), but decreased to baseline levels hereafter.

CONCLUSION

We conclude that in children, as in adults, body fat is the primary determinant for the circulating level of GHBP, and that the difference in body fat is probably the main factor for the higher levels of serum GHBP in girls compared with boys, as well as for the negative influence of testosterone levels in boys and of oestrogen levels in girls. The elevation in GHBP levels observed in girls with central precocious puberty is probably due their higher body fat content.

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

OBJECTIVE

The regulation of IGF-I levels is complex and not only dependent on GH status, as the diagnostic sensitivity of serum IGF-I levels for GH deficiency (GHD) in adults is low. Other GH-related parameters have so far not proven to be of additional diagnostic value in GHD adults. In the present study we evaluated the impact of gender and androgen status on IGF-I levels and the diagnostic value of IGF-I and GH-related parameters in a population of adult hypopituitary patients and age- and gender-matched healthy subjects.

DESIGN

A cross-sectional study.

SUBJECTS

Fifty-nine GHD patients (40 males, mean age 39.3+/-1.7 (s.e.m.) years, and 19 females, mean age 41.9+/-2.6 years) and 69 healthy subjects (42 males, mean age 36. 7+/-1.5 years, and 27 females, mean age 38.9+/-2.1 years).

RESULTS

IGF-I levels were low in the GHD patients (91+/-7 vs 173+/-7 microgram/l, P<0.001), and lower in female patients than in male (68+/-10 vs 100+/-8 microgram/l, P=0.03). In the control group there was no gender-related difference in IGF-I levels (males: 178+/-8, females: 164+/-12 microgram/l, P=0.23). IGF-II and IGF-binding protein-3 (IGFBP-3) were also decreased in GHD without any gender-related differences. GH-binding protein (GHBP) levels were increased in the patient group. The diagnostic sensitivity (%) of IGF-I, IGF-I/GHBP, IGF-I/IGFBP-3, and of the combination of IGF-I plus IGF-II (both low or one normal and one low), was higher in female patients than in male (IGF-I: 57.8 vs 22.0, P<0.0001; IGF-I/GHBP: 84.2 vs 48.8, P=0. 002; IGF-I/IGFBP-3: 36.8 vs 7.3 P=0.001; IGF-I+IGF-II: 77.8 vs 52.6, P=0.01). Testosterone levels were reduced in the female patients compared with female controls (0.5+/-0.3 vs 2.1+/-0.2nmol/l, P<0.001). Forward regression analyses revealed that IGFBP-3 was a significant predictor of IGF-I levels in both patients and healthy subjects. In a combined analysis of both patients and controls, sex hormone-binding globulin (SHBG) level was the main contributor as an explanatory variable. Gender and prolactin also predicted IGF-I in patients, whereas SHBG and estradiol were significant predictors only in the control group.

CONCLUSION

(i) Levels of IGF-I, and of IGF-I/IGFBP-3 and IGF-I/GHBP ratios are lower in females compared with male adult GHD patients. (ii) IGF-I/GHBP has a high diagnostic sensitivity of adult GHD, in particular in women. (iii) We hypothesize that the gender difference in IGF-I levels among adult GHD patients are causally related to the very low androgen levels observed among females.

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

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

Regulation of uncoupling protein-2 and -3 by growth hormone in skeletal muscle and adipose tissue in growth hormone-deficient adults

The newly described uncoupling proteins, UCP2 and UCP3, may play a role in regulating energy expenditure (EE) in humans. GH deficiency (GHD) is associated with decreased lean body mass, increased adiposity, and reduced EE, which are reversed by GH treatment. In the present study we investigated whether GH treatment for 4 months influenced the expression of UCPs in skeletal muscle and adipose tissue in 22 GHD patients who were investigated before and after GH (n = 11) or placebo (n = 11) treatment. GH treatment increased the amount of lean body mass by 4.5% (P < 0.05) and decreased body fat mass by 12% (P < 0.05), whereas no changes in these parameters were observed after placebo treatment. The level of UCP3 messenger ribonucleic acid (mRNA) increased 3-fold (P < 0.005) in skeletal muscle and almost 2-fold (P < 0.05) in adipose tissue after GH treatment, with no changes observed after placebo treatment. Skeletal muscle UCP2 mRNA was slightly (25%), but significantly (P < 0.05), decreased, whereas the level of UCP2 mRNA in adipose tissue was unaffected after GH treatment. The T4 level was positively correlated with skeletal muscle UCP2 and UCP3 expression (r = 0.518; P < 0.05 and r = 0.463; P < 0.05, respectively). Furthermore, plasma free fatty acids were positively correlated with the expression of UCP2 (r = 0.573; P < 0.01) and UCP3 (r = 0.518; P < 0.05) in skeletal muscle. The marked increase in UCP3 expression after GH treatment indicates that the UCPs might play a role in the effects of GH on EE in GHD patients. Finally, the strong association between thyroid hormone and skeletal muscle UCP and the correlation between plasma free fatty acids and UCP expression in skeletal muscle indicate that these hormones/metabolites might influence UCP expression in humans as previously demonstrated in rodents.

Circulating levels of free insulin-like growth factors in obese subjects: the impact of type 2 diabetes

BACKGROUND

Obese subjects show major abnormalities in the growth hormone (GH)/insulin-like growth factor (IGF) system. Furthermore, they are prone to develop Type 2 diabetes, but the impact of diabetes plus obesity on the GH/IGF system remains unknown.

METHODS

We compared overnight fasting serum levels of free and total (extractable) IGF-I and -II, IGF-binding protein (IGFBP) -1, -2 and -3, and the high affinity GH-binding protein (GHBP) in matched groups of lean subjects (n=26) and obese subjects without (n=24) and with (n=29) Type 2 diabetes. Two groups (n=7) of healthy and Type 1 diabetic subjects were also studied.

RESULTS

Non-diabetic obese subjects had increased free IGF-I and -II, total IGF-II, IGFBP-3 and GHBP, reduced IGFBP-1 and -2 (p<0.05), but normal total IGF-I, when compared to lean subjects. In obese Type 2 diabetics free IGF-I was insignificantly reduced by 9% (p=0.3), when compared to non-diabetic obese subjects. However, the concentration was not significantly elevated when compared to that of lean controls (p=0.13). Also IGFBP-1 and total IGF-I were normal in obese Type 2 diabetics, whereas free and total IGF-II and IGFBP-3 remained elevated to a similar extent as in simple obesity (p<0.05). In contrast, GHBP was further increased and IGFBP-2 further reduced in obese Type 2 diabetics (p<0.05). In Type 1 diabetics total IGF-I and -II, and IGFBP-3 were normal. In contrast, free IGF-I and -II and GHBP were markedly reduced, whereas IGFBP-1 and -2 were increased (p<0.05).

CONCLUSIONS

Simple obesity was associated with marked changes in the GH/IGF system. Many of these abnormalities were unaffected by the concomitant presence of Type 2 diabetes (total IGF-I, free and total IGF-II and IGFBP-3). However, some changes became accentuated (GHBP and IGFBP-2), while others (free IGF-I and IGFBP-1) were no longer present. Notably, the impact of Type 1 diabetes on the GH/IGF system was clearly different from that of Type 2 diabetes.

Variety in growth hormone determinations due to use of different immunoassays and to the interference of growth hormone-binding protein

More than 30 years after their introduction, growth hormone (GH) immunoassays showed the poorest inter-laboratory agreement of the various hormone assays evaluated in 1998 by the UK National External Quality Assessment Scheme, in which different laboratories using different assays reported that analyses of identical samples differed two- to threefold in value. There is therefore an urgent requirement and desire within the scientific community, particularly within centres diagnosing and treating GH deficiency and acromegaly, to resolve this problem and to develop a GH assay(s) that measures solely all of the relevant components of circulating GH immunoreactivity. The main confounders in the estimation of GH levels (now that the use of GH standards other than that recommended by the World Health Organization has largely been eliminated) are GH heterogeneity, anti-GH antiserum binding site specificity and interference from circulating high-affinity GH-binding protein (GHBP). The effects of these factors are closely related. The present study investigates these factors, focussing on the influence of GHBP and antibody binding site specificity on various assays for GH. The findings lead the authors to suggest that a solution to the problem may be to develop a GH assay that measures specifically and solely all serum 22 kDa GH, as this is the major circulating fraction and carries the dominant GH bioactivity.

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

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

The effect of the deterioration of insulin sensitivity on beta-cell function in growth-hormone-deficient adults following 4-month growth hormone replacement therapy

The purpose of the present study was to evaluate the combined effect of GH treatment on body composition and glucose metabolism, with special focus on beta-cell function in adult GHD patients. In a double-blind placebo-controlled design, 24 GHD adults (18M/6F), were randomized to 4 months treatment with biosynthetic GH 2 IU/m2s.c. daily (n =13) or placebo (n =11). At inclusion and 4 months later an oral glucose tolerance test (OGTT), a frequently sampled intravenous glucose tolerance test (FSIGT) and dual-energy X-ray absorptiometry (DXA) whole-body scanning were performed. During the study period, body weight decreased 1.6 kg from 94.0 +/- 18.7 to 92.4 +/- 19.4 kg (mean +/- SD) (P<0.05) in the GH-treated group, but remained unchanged in the placebo group. Fat mass decreased from 32.4 +/- 9.6 to 28.1 +/- 10.5 kg (P<0.001), whereas lean body mass increased from 58.3 +/- 11.5 to 61.0 +/- 11.7 kg (P<0.01) in the GH-treated group. Treatment with GH for 4 months resulted in a significant increase in fasting blood glucose (before GH 5.0 +/- 0.3 and after 5.4 +/- 0.6 mmol/l, P<0.05), fasting plasma insulin (before GH 38.4 +/- 30.2 and after 55.3 +/- 34.7 pmol/l, P<0.02) and fasting proinsulin (before 8. 1 +/- 6.7 and after 14.6 +/- 16.1 pmol/l, P<0.05). The insulin sensitivity index SI, estimated by Bergmans Minimal Model, decreased significantly [before GH 1.1 +/- 0.7 and after 0.4 +/- 0.2 10(-4)(min x pmol/l), P<0.003]. The non-insulin-dependent glucose uptake (glucose effectiveness SG did not change (before GH 0.017 +/- 0.005 and after 0.015 +/- 0.006 min-1, NS). Insulin secretion was enhanced during GH therapy, but insufficiently to match the changes in SI, resulting in a higher blood glucose level during an OGTT. Blood glucose at 120 min was 5.5 and 6.3 mmol/l before and after GH treatment, respectively (P = 0.07). One patient developed impaired glucose tolerance. Short-term GH replacement therapy in a dose of about 2 IU/m2 daily in GHD adults induces a reduction in insulin sensitivity, despite favourable changes in body composition, and an inadequate enhancement of insulin secretion.

L-arginine-induced growth hormone secretion is not influenced by co-infusion of the nitric oxide synthase inhibitor N-monomethyl-L-arginine in healthy men

In animals, it has been demonstrated that nitric oxide (NO) is a potent neuroregulatory substance. By intravenous infusion, L-arginine is converted to NO and citrulline, but it is unknown whether NO is responsible for the GH stimulating effect of L-arginine in humans. We investigated whether intravenous infusion of the NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA) influenced L-arginine stimulated GH secretion. Ten healthy men, aged 28.6 +/- 1.9 (mean +/- SEM) years were examined twice. L-arginine was infused intravenously in a dose of 0.5 g/kg, max 35 g, from 0 to 30 min, accompanied by either: (1) L-NMMA from -5 to 0 min, in a dose of 3 mg/kg, max 250 mg, and in a dose of 3.5 mg/kg, max 250 mg from 0 to 60 min; or (2) a saline infusion. Heart rate increased (P = 0.032), and diastolic blood pressure decreased (P < 0.001) in the two situations. Plasma cGMP was unchanged and identical in the two situations (P = 0.679). Urine cGMP/creatinine ratio increased during both examinations (P = 0.041). Growth hormone secretion increased significantly during L-arginine infusion (P = < 0.001) without any effect of L-NMMA (P = 0.848). We did not find evidence that NO influences GH secretion. It remains to be tested, however, whether a higher dose of L-NMMA may influence L-arginine stimulated GH secretion.

Evidence supporting a direct suppressive effect of growth hormone on serum IGFBP-1 levels. Experimental studies in normal, obese and GH-deficient adults

It has occasionally been suggested that GH directly suppresses circulating IGFBP-1 levels, although it is generally believed that such an effect is secondary to a GH-induced increase in insulin levels. We present data from several experiments in which the effects of GH on IGFBP-1 could be studied more extensively. In normal subjects (n = 36), an i.v. GH bolus caused a small but significant decrease in plasma IGFBP-1 concentrations without changes in insulin [IGFBP-1 (microgram/l): 2.6 +/- 0.3 (GH) vs 3.2 +/- 0.4 (placebo), P < 0.05]. Conversely, a 28-h somatostatin infusion with and without GH administration during fasting in normal subjects yielded higher IGFBP-1 levels in the non-GH substituted study [50.5 +/- 5.3 (GH-suppression) vs 22.6 +/- 5.6 (GH-substitution), P < 0.01], comparable with an increased concentration of IGFBP-1 during fasting in GH-deficient patients without usual GH substitution [23.4 +/- 7.6 (GH pause) vs 14.1 +/- 4.9 (GH substitution), P < 0.01]. In both fasting studies insulin levels remained stable. During a hypocaloric diet, long-term GH treatment in obesity lead to a significant decline in IGFBP-1 level (2.3 +/- 0.6 vs 1.2 +/- 0.2, P < 0.01), while no changes were found in the placebo group. Again, insulin levels remained equally low in both studies. Finally, a significant rebound increase in IGFBP-1 level in response to insulin induced hypoglycemia was only observed among GH-deficient patients, but not in control subjects, the latter of whom responded to hypoglycemia with a significant increase in serum GH levels [23.2 +/- 7.2 (GHDA) vs 2.5 +/- 0.3 (controls), P < 0.01]. In conclusion, a suppressive effect of GH on IGFBP-1 appears to be unmasked in the presence of low or suppressed insulin levels, making GH a potential regulator of IGF-1 bioactivity in a hitherto unrecognized way.

Long-term effects of growth hormone (GH) on body fluid distribution in GH deficient adults: a four months double blind placebo controlled trial

OBJECTIVE

Short-term growth hormone (GH) treatment normalises body fluid distribution in adult GH deficient patients, but the impact of long-term treatment on body fluid homeostasis has hitherto not been thoroughly examined in placebo controlled trials. To investigate if the water retaining effect of GH persists for a longer time we examined the impact of 4 months GH treatment on extracellular volume (ECV) and plasma volume (PV) in GH deficient adults.

DESIGN

Twenty-four (18 male, 6 female) adult GH deficient patients aged 25-64 years were included and received either GH (n=11) or placebo (n=13) in a double blind parallel design.

METHODS

Before and at the end of each 4 month period ECV and PV were assessed directly using 82Br- and 125I-albumin respectively, and blood samples were obtained.

RESULTS

During GH treatment ECV increased significantly (before: 20.48+/-0.99 l, 4 months: 23.77+/-1.38 l (P<0.01)), but remained unchanged during placebo administration (before: 16.92+/-1.01 l, 4 months: 17.60+/-1.24 l (P=0.37)). The difference between the groups was significant (P<0.05). GH treatment also increased PV (before: 3.39+/-0.27 l. 4 months: 3.71+/-0.261 (P=0.01)), although an insignificant increase in the placebo treated patients (before: 2.81+/-0.18 l, 4 months: 2.89+/-0.20 l (P=0.37)) resulted in an insignificant treatment effect (P=0.07). Serum insulin-like growth factor-I increased significantly during GH treatment and was not affected by placebo treatment. Plasma renin (mIU/l) increased during GH administration (before: 14.73+/-2.16, 4 months: 26.00+/-6.22 (P=0.03)) and remained unchanged following placebo (before: 20.77+/-5.13, 4 months: 20.69+/-6.67 (P=0.99)) leaving no significant treatment effect (P=0.08).

CONCLUSION

The long-term impact of GH treatment on body fluid distribution in adult GH deficient patients involves expansion of ECV and probably also PV. These data substantiate the role of GH as a regulator of fluid homeostasis in adult GH deficiency.