Basal, but not pulsatile, growth hormone secretion determines the ambient circulating levels of insulin-like growth factor-I

Trends of correlations between serum levels of growth hormone and insulin-like growth factor-I in general practice

Serum levels of growth hormone (GH) and insulin-like growth factor (IGF)-I are crucial in the diagnosis and management of GH-related diseases. However, these levels are affected by nutritional and metabolic status. To elucidate the correlations between GH and IGF-I in various conditions, a retrospective analysis was performed for adult patients in which GH levels were examined by general practitioners during the period from January 2019 to December 2021. Of 642 patients, 33 patients were diagnosed with acromegaly, 21 were diagnosed with GH deficiency (GHD), and 588 were diagnosed with non-GH-related diseases (NGRD). In contrast to the positive correlations found between the levels of GH and IGF-I in patients with acromegaly (R=0.50; P<0.001) and patients with GHD (R=0.39; P=0.08), a negative correlation was found in the NGRD group (R=-0.23; P<0.001). In that group, the results of multivariable analysis showed that GH levels were predominantly influenced by gender and body mass index (BMI), whereas IGF-I levels were modulated by albumin in addition to age and GH. Of note, in the NGRD group, there was an enhanced negative correlation between GH and IGF-I under conditions of BMI < 22 and albumin < 4.0 g/dL (R=-0.45; P<0.001), and the negative correlation between GH and IGF-I was reinforced by excluding patients with other pituitary diseases and patients taking oral steroids (R=-0.51; P<0.001 and R=-0.59; P<0.001, respectively). Collectively, the results indicate that attention should be given to the presence of a negative correlation between serum levels of GH and IGF-I, especially in lean and low-nutritious conditions.

Consensus on criteria for acromegaly diagnosis and remission

PURPOSE

The 14th Acromegaly Consensus Conference was convened to consider biochemical criteria for acromegaly diagnosis and evaluation of therapeutic efficacy.

METHODS

Fifty-six acromegaly experts from 16 countries reviewed and discussed current evidence focused on biochemical assays; criteria for diagnosis and the role of imaging, pathology, and clinical assessments; consequences of diagnostic delay; criteria for remission and recommendations for follow up; and the value of assessment and monitoring in defining disease progression, selecting appropriate treatments, and maximizing patient outcomes.

RESULTS

In a patient with typical acromegaly features, insulin-like growth factor (IGF)-I > 1.3 times the upper limit of normal for age confirms the diagnosis. Random growth hormone (GH) measured after overnight fasting may be useful for informing prognosis, but is not required for diagnosis. For patients with equivocal results, IGF-I measurements using the same validated assay can be repeated, and oral glucose tolerance testing might also be useful. Although biochemical remission is the primary assessment of treatment outcome, biochemical findings should be interpreted within the clinical context of acromegaly. Follow up assessments should consider biochemical evaluation of treatment effectiveness, imaging studies evaluating residual/recurrent adenoma mass, and clinical signs and symptoms of acromegaly, its complications, and comorbidities. Referral to a multidisciplinary pituitary center should be considered for patients with equivocal biochemical, pathology, or imaging findings at diagnosis, and for patients insufficiently responsive to standard treatment approaches.

CONCLUSION

Consensus recommendations highlight new understandings of disordered GH and IGF-I in patients with acromegaly and the importance of expert management for this rare disease.

Ethanol alters the relationship between IGF-1 and bone turnover in male macaques

Insulin-like growth factor 1 (IGF-1) influences bone turnover. Transient decreases in IGF-I levels and/or bioavailability may contribute to the detrimental effects of alcohol on bone. The goals of this non-human primate study were to i) evaluate the 20-h response of bone turnover markers to ethanol consumption and ii) assess how ethanol consumption influences the relationship between IGF-1 and these markers. Osteocalcin (bone formation), carboxyterminal cross-linking telopeptide of type 1 collagen (CTX, bone resorption), IGF-1, and IGF binding protein 1 (IGFBP-1) were measured in plasma from male rhesus macaques (N = 10, 8.4 ± 0.3 years) obtained at 12:00, 16:00, and 06:00 h during two phases: pre-ethanol (alcohol-naïve) and ethanol access. During the ethanol access phase, monkeys consumed 1.5 g/kg/day ethanol (4% w/v) beginning at 10:00 h. Osteocalcin and CTX were lower, and the ratio of osteocalcin to CTX was higher at each time point during ethanol access compared to the pre-ethanol phase. Pre-ethanol marker levels did not vary across time points, but markers varied during ethanol access. IGF-1 levels, but not IGFBP-1 levels, varied during the pre-ethanol phase. In contrast, IGF-1 levels were stable during ethanol access but IGFBP-1 levels varied. There were positive relationships between IGF-1 and turnover markers during the pre-ethanol phase, but not during ethanol access. In conclusion, chronic ethanol consumption reduces levels of bone turnover markers and blocks the normal positive relationship between IGF-1 and turnover markers and alters the normal relationship between IGF-1 and IGFBP-1. These findings support the hypothesis that chronic alcohol consumption leads to growth hormone/IGF-1 resistance.

Mean GH profile is more accurate than single fasting GH in the evaluation of acromegaly disease control during somatostatin receptor ligands therapy

PURPOSE

This study aims to compare the accuracy of mean GH profile (GHP) < 2.5 ng/ml and single fasting GH (SGH) < 1 ng/ml in the evaluation of disease control in acromegaly patients during somatostatin receptor ligands (SRLs) therapy.

METHODS

We retrospectively enrolled 100 acromegaly patients, 68 responder, and 32 partial responder to SRLs. Controlled disease has been defined as IGF-I levels within age-related normal limits, while partial response as pathological IGF-I values despite a reduction ≥ 50%. In all patients, GHP, SGH, IGF-I, and IGFBP-3 were evaluated.

RESULTS

Median GHP levels (1.2 ng/ml, IQR 0.5-2.3 ng/ml) were lower (p = 0.001) than SGH (1.9 ng/ml, IQR 1.0-3.6 ng/ml). Accuracy of GHP was 81%, whereas that of SGH was 55%, with a Kappa index of 0.520 and 0.237, respectively. In multivariable analysis GHP (p = 0.002) and IGFBP-3 (p = 0.004), but not SGH, were independently associated with normal IGF-I levels. At receiver-operator characteristic curve (ROC) analysis GHP cut-off sensitivity and specificity were 94.1% and 50.0%, respectively, while SGH sensitivity and specificity were 35.3% and 93.7%, respectively. Finally, in obese patients the GH cut-off level (both as SGH and GHP) associated to good disease control was significantly different with respect to not obese ones.

CONCLUSIONS

GHP associates with IGF-I (and therefore with appropriate control of disease) with higher accuracy than SGH. When GH evaluation is needed, the measurement of mean GHP should be preferred and use of BMI-related cut-offs is suggested.

Role of pulsatile growth hormone (GH) secretion in the regulation of lipolysis in fasting humans

Background

The increase in growth hormone (GH) secretion during a prolonged fast stimulates lipolytic rate, thereby augmenting the mobilization of endogenous energy at a time when fuel availability is very low.

Study aim

To identify the specific component of GH secretory pattern responsible for the stimulation of lipolytic rate during fasting in humans.

Study protocol

We measured lipolytic rate (using stable isotope dilution technique) after an overnight fast in 15 young, healthy, non-obese subjects (11 men and 4 women), and again on four separate occasions after a 59 h fast. These four prolonged fasting trials differed only by the contents of an infusion solution provided throughout the 59 h fasting period. Subjects were infused either with normal saline (“Control”; n = 15) or with graded doses of a GH Releasing Hormone Receptor Antagonist (GHRHa):10 μg/kg/h (“High”; n = 15), 1 μg /kg/h (“Medium”; n = 8), or 0.5 μg /kg/h (“Low”; n = 6).

Results

As expected, the 59 h fast completely suppressed plasma insulin levels and markedly increased endogenous GH concentrations (12 h vs 59 h Fast; p = 0.0044). Administration of GHRHa induced dose-dependent reduction in GH concentrations in response to the 59 h fast (p < 0.05). We found a strong correlation between the rate of lipolysis and GH mean peak amplitude (R = 0.471; p = 0.0019), and total GH pulse area under the curve (AUC) (R = 0.49; p = 0.0015), but not the GH peak frequency (R = 0.044; p = 0.8) or interpulse GH concentrations (R = 0.25; p = 0.115).

Conclusion

During prolonged fasting (i.e., 2–3 days), when insulin secretion is abolished, the pulsatile component of GH secretion becomes a key metabolic regulator of the increase in lipolytic rate.

Early postoperative prediction of both disease remission and long-term disease control in acromegaly using the oral glucose tolerance test

PURPOSE

Transsphenoidal surgery (TSS) is the cornerstone of acromegaly treatment. Two biochemical parameters, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels, sometimes diverge postoperatively; however, it is important to maintain disease control without further treatment, regardless of whether these parameters converge. This study investigated whether remission and long-term disease control could be predicted using early postoperative GH and IGF-1 levels.

METHODS

We reviewed 36 consecutive surgically treated patients with acromegaly. IGF-1 levels and minimum GH levels during an oral glucose tolerance test (OGTT) were evaluated at 2 weeks, as well as at 3 months postoperatively. After comparison between the remission and nonremission groups, we analyzed whether early postoperative parameters could predict remission and long-term disease control.

RESULTS

Twenty-five patients (69.4%, Group A) achieved remission within 1 year postoperatively. Of the remaining patients (median follow-up period, 53 months), seven (19.5%, Group B) maintained normal IGF-1 levels without treatment, whereas four (11.1%, Group C) required additional treatment. GH levels <1.5 ng/mL measured on the morning after surgery and nadir GH levels <0.7 ng/mL during the OGTT conducted at 2 weeks postoperatively were predictive of remission, with the latter demonstrating 95.2% sensitivity and 100% specificity. All group C patients had nadir GH levels ≥0.7 ng/mL during the OGTT and IGF-1 levels ≥SD +3 at 2 weeks postoperatively.

CONCLUSION

Early postoperative nadir GH levels during the OGTT and IGF-1 levels at 2 weeks postoperatively demonstrated excellent predictive value for both endocrinological remission and the necessity for additional treatment.

Stimulation of endogenous pulsatile growth hormone secretion by activation of growth hormone secretagogue receptor reduces the fat accumulation and improves the insulin sensitivity in obese mice

Obese individuals often show low growth hormone (GH) secretion, which leads to reduced lipid mobilization and further fat accumulation. Pharmacological approaches to increase GH levels in obese individuals by GH injection or GH-releasing hormone receptor agonist showed promising effects on fat reduction. However, side effects on glucose metabolism and the heavy costs on making large peptides hindered their clinical application. Here, we tested whether stimulation of endogenous GH secretion by a synthetic GH secretagogue receptor (GHSR) agonist, hexarelin, improved the metabolism in a hyperphagic obese mouse model. Male melanocortin 4 receptor knockout mice (MC4RKO) were pair-fed and received continuous hexarelin (10.56 μg/day) or vehicle infusion by an osmotic pump for 3-4 weeks. Hexarelin treatment significantly increased the pulsatile GH secretion without detectable alteration on basal GH secretion in MC4RKO mice. The treated mice showed increased lipolysis and lipid oxidation in the adipose tissue, and reduced de novo lipogenesis in the liver, leading to reduced visceral fat mass, reduced triglyceride content in liver, and unchanged circulating free fatty acid levels. Importantly, hexarelin treatment improved the whole-body insulin sensitivity but did not alter glucose tolerance, insulin levels, or insulin-like growth factor 1 (IGF-1) levels. The metabolic effects of hexarelin were likely through the direct action of GH, as indicated by the increased expression level of genes involved in GH signaling pathways in visceral adipose tissues and liver. In conclusion, hexarelin treatment stimulated the pulsatile GH secretion and reduced the fat accumulation in visceral depots and liver in obese MC4RKO mice with improved insulin sensitivity without altered levels of insulin or IGF-1. It provides evidence for managing obesity by enhancing pulsatile GH secretion through activation of GHSR in the pituitary gland.

Rhythmic growth hormone secretion in physiological and pathological conditions: Lessons from rodent studies

Evolutionally conserved in all mammalians, the release of GH occurs in a rhythmic pattern, characterized by several dominant surges (pulsatile GH) with tonic low inter-pulse levels (tonic GH). Such pulsatile secretion pattern is essential for many physiological actions of GH on different tissues with defined gender dimorphism. Rhythmic release of pulsatile GH is tightly controlled by hypothalamic neurons as well as peripheral metabolic factors. Changes of GH pattern occur within a range of sophisticated physiological and pathological settings and significantly contribute to growth, ageing, survival and disease predispositions. Precise analysis of GH secretion pattern is vitally important for a comprehensive understanding of the function of GH and the components that regulate GH secretion pattern.

The GH Axis in Relation to Accepting an Early Macronutrient Deficit and Outcome of Critically Ill Patients

CONTEXT

Changes in the GH axis during critical illness resemble fasting in healthy adults and contribute to hypercatabolism, which potentially affects outcome. Accepting macronutrient deficits by withholding parenteral nutrition (PN) during the first week in the intensive care unit (ICU; late PN) reduced complications and accelerated recovery as compared with early use of PN (early PN).

OBJECTIVE

To investigate how late PN affects the GH axis in relation to its clinical outcome benefits.

DESIGN

Preplanned subanalysis of the Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients randomized controlled trial.

PARTICIPANTS

A total of 1128 patients for time-course study, 20 patients investigated for nocturnal GH pulsatility, and 600 patients investigated for muscle weakness, with early PN and late PN patients having comparable baseline characteristics.

INTERVENTION

Withholding PN during the first ICU week (late PN) vs early PN.

MAIN OUTCOME MEASURES

Changes in serum GH, IGF-I, IGF-binding protein (IGFBP) 3, and IGFBP1 concentrations from ICU admission to day 4 or last ICU day for patients with a shorter ICU stay (d4/LD) and association in multivariable analyses with likelihood of earlier live ICU discharge, risk of new infection, and muscle weakness.

RESULTS

Late PN attenuated a rise in serum GH and IGF-I (P < 0.0001), did not affect IGFBP3, and attenuated a decrease in IGFBP1 concentrations from admission to d4/LD (P < 0.0001) as compared with early PN. Late PN decreased nonpulsatile (P = 0.005), but not pulsatile, GH secretion. Adjusting the multivariable models for the observed GH axis alterations increased the independent benefit of late PN for all outcomes. GH axis alterations induced by late PN were independently associated with adverse outcomes (P ≤ 0.03).

CONCLUSION

Accepting macronutrient deficits early during critical illness further suppressed the GH axis, which statistically attenuated its clinical outcome benefits.

Is GH nadir during OGTT a reliable test for diagnosis of acromegaly in patients with abnormal glucose metabolism?

PURPOSE

The growth hormone (GH) nadir during oral glucose tolerance test (OGTT) is the gold standard diagnostic test for acromegaly. The utility of OGTT-GH suppression test in patients with abnormal glucose metabolism (AGM) has not been well established. In this study, we compared the GH nadir during OGTT in patients evaluated for acromegaly in the presence and absence of AGM.

METHODS

This is a retrospective cohort study of patients with acromegaly (G1, n = 40) and a group in whom acromegaly was not confirmed (G2, n = 53) who had OGTT-GH suppression test during 2000-2012, using a monoclonal GH immunoenzymatic assay. The patients were categorized as having normal glucose metabolism (NGM) or AGM. GH nadir during OGTT in each group were compared.

RESULTS

In G1 and G2, 17 and 19 patients had AGM, respectively. Among 17 patients with diabetes, median HbA1C was 7% (range 5.7-9.6%). All except one patient had HbA1C< 8%. There was no difference in the GH nadir in patients with or without AGM within G1 (p = 0.15) and G2 (p = 0.43). All G1 patients with AGM had GH nadir > 0.4 µg/L. Four G1 patients with NGM had GH nadir<0.4 µg/L. All G2 patients had GH nadir < 0.4 µg/L, except one with NGM and GH nadir of 0.4 µg/L.

CONCLUSION

Using highly sensitive GH assay, a GH nadir ≥ 0.4 µg/L during the OGTT-GH suppression test may be used for diagnosis of acromegaly in patients with AGM in the absence of poorly controlled diabetes.

Growth hormone-releasing hormone (GHRH) and its agonists inhibit hepatic and tumoral secretion of IGF-1

The role of hypothalamic growth hormone-releasing hormone (GHRH) in the release of growth hormone (GH) from the pituitary is well established. However, direct effects of GHRH and its agonistic analogs on extra-pituitary cells and tissues have not been completely elucidated. In the present study, we first demonstrated that human and rat hepatocytes express receptors for GHRH. We then showed that GHRH(1-29)NH 2 and GHRH agonist, MR-409, downregulated mRNA levels for IGF-1 in human cancer cell lines and inhibited IGF-1 secretion in vitro when these cancer lines were exposed to rhGH. Another GHRH agonist, MR-356, lowered serum IGF-l and inhibited tumor growth in nude mice bearing xenografted NCI-N87 human stomach cancers. GHRH(1-29)NH 2 and MR-409 also suppressed the expression of mRNA for IGF-1 and IGF-2 in rat and human hepatocytes, decreased the secretion of IGF-1 in vitro from rat hepatocytes stimulated with rhGH, and lowered serum IGF-l levels in hypophysectomized rats injected with rhGH. Vasoactive intestinal peptide had no effect on the release of IGF-1 from the hepatocytes. Treatment of C57BL/6 mice with MR-409 reduced serum levels of IGF-l from days 1 to 5. These results show that GHRH and its agonists can, by a direct action, inhibit the secretion of IGF-1 from the liver and from tumors. The inhibitory effect of GHRH appears to be mediated by the GHRH receptor (GHRH-R) and GH receptor (GHR), with the involvement of JAK2/STAT5 pathways. Further studies are required to investigate the possible physiopathological role of GHRH in the control of secretion of IGF-1.

Biochemical efficacy of long-acting lanreotide depot/Autogel in patients with acromegaly naïve to somatostatin-receptor ligands: analysis of three multicenter clinical trials

PURPOSE

In clinical research involving acromegalic patients naïve to somatostatin-receptor ligands (SRLs), 19 and 31% of those receiving the SRLs octreotide LAR and pasireotide LAR, respectively, achieved GH < 2.5 ng/mL + normalized IGF-1 concentrations. The proportions achieving control appeared higher in the post-surgery compared with the de-novo setting with pasireotide, but more similar with octreotide. Using pooled data from multicenter clinical trials, we examined the biochemical efficacy of lanreotide depot/Autogel in similar settings.

METHODS

Inclusion criteria: Ipsen-sponsored, 48-52-week trials in SRL-naïve acromegalic populations receiving lanreotide depot (60-120 mg); patients were included if de novo (no prior acromegaly treatment) or post-surgery (no medical treatment; radiotherapy allowed unless within previous 3 years). Efficacy endpoints included normalized IGF-1 levels and GH < 2.5 ng/mL + normalized IGF-1 at study end/last value available.

ANALYSES

all patients (analysis #1) and subset with baseline GH > 5 ng/mL (analysis #2).

RESULTS

Three studies were included. Analysis #1: normalized IGF-1 was achieved by 42% (71/171) of patients overall (post-surgery, 46% [21/46]; de-novo, 40% [50/125]); GH < 2.5 ng/mL + normalized IGF-1 was achieved by 35% (59/171) (39% [18/46] and 33% [41/125], respectively). Analysis #2: normalized IGF-1 levels, 39% (46/118) (post-surgery, 40% [10/25]; de-novo, 39% [36/93]); GH < 2.5 ng/mL + normalized IGF-1, 31% (36/118) (28% [7/25] and 31% [29/93], respectively).

CONCLUSION

In these pooled analyses of SRL-naïve patients receiving lanreotide depot, 39-42% achieved IGF-1 control and 31-35% achieved GH and IGF-1 control. Control rates within post-surgery cohorts did not differ markedly from those in corresponding de-novo cohorts.

Silent somatotroph pituitary adenomas: an update

Silent growth hormone adenomas (SGHA) are a rare entity of non-functioning pituitary neuroendocrine tumors. Diagnosis is invariably made post-operatively of a tumor immunopositive for GH (and Pit-1 in selected cases) but without clinical acromegaly. Mainly young females are affected, and tumors are often uncovered by investigation for headaches or oligoamenorrhea. Integration of clinical, pathological and biochemical data is required for proper diagnosis. Beside normal IGF-1 levels, a third of SGHAs displays elevated GH levels and some will eventually progress to acromegaly. Almost two-thirds will be mixed GH-prolactin tumors and sparsely-granulated monohormonal GH tumors seems the more aggressive subtype. Recurrence and need for radiation is higher than other non-functioning tumors so close follow-up is warranted.

Twenty-four-hour growth hormone profiling in the assessment of acromegaly

OBJECTIVES AND BACKGROUND

Recent guidelines recommend insulin-like growth factor (IGF-1), random growth hormone (GH) and nadir GH on an oral glucose tolerance test (OGTT) for assessment of acromegaly. At this Regional Centre, the 24-hour GH profile has also been used.

DESIGN PATIENTS AND MEASUREMENTS

We evaluated 57 GH profiles from 34 patients from 2008 to 2012. Samples were drawn every 2 hour and matched with 0800 GH, nadir GH after OGTT and IGF-1.

RESULTS

Correlations between the mean 13-point profiles and mean 5-point profile, OGTT nadir and 0800 GH were as follows: r = .99, .99 and .90, respectively (P < .01 for all). The correlation between the mean 13-point profiles and IGF-1 was r = .32 P = .02.Of 5 patients with very high 0800 GH preoperatively (≥20 μg/L), mean 13-point GH reduced by 88%-99% postoperatively. IGF-1 did not normalize in these patients, and all required extra treatment. Preoperatively, all patients had concordant 0800 GH and IGF-1. Postoperatively, 6 patients had 0800 GH <1 μg/L and high IGF-1; only 2 of these had a 13-point mean >1 μg/L, but 5 required further treatment.

CONCLUSIONS

Growth hormone profiling is not necessary for assessing the majority of patients with acromegaly if there is confidence in the local IGF-1 assay. When undertaken, a 5-point profile is adequate. In patients with very high 0800 GH, 24-hour profiling was useful in demonstrating partial therapeutic success but did not alter management. Further work is needed to explore the possible role of GH profiling in stratifying patients with discordant IGF-1 and GH results.

"Micromegaly": an update on the prevalence of acromegaly with apparently normal GH secretion in the modern era

PURPOSE

Approximately 25 % of cases of clinically active acromegaly cases treated in our academic center between 1996 and 2000, were diagnosed in patients who had elevated plasma IGF-1 levels, but apparently "normal" 24-h mean plasma GH levels. The current study served to update the data for patients with acromegaly referred to our facility, after increasing awareness of this "normal" GH subpopulation throughout the medical community.

METHODS

A retrospective chart review was conducted on 157 patients with acromegaly who underwent resection of a confirmed somatotroph pituitary adenoma at the University of Michigan Health System between the dates of 1 Jan 2001 to 23 Sept 2015.

RESULTS

Overall prevalence of acromegalic patients with "normal" GH levels, defined as GH <4.7 ng/mL, was 31 %. Over time, the percentage of patients with "normal" GH at diagnosis did not decline: 26 % from 2001 to 2005, 19 % from 2006 to 2010, and 47 % from 2011 to 2015. Mean pituitary tumor size was 1.8 ± 0.1 cm for the group with elevated GH, and 1.2 ± 0.1 cm for the group with "normal" GH (p < 0.001). Percent microadenomas was higher in a group with "normal" GH as compared to those with elevated GH (48 vs. 12 %, p < 0.001), and tumors >2 cm in the maximal diameter were encountered more frequently in the group with elevated GH (43 vs. 14 %, p < 0.001).

CONCLUSIONS

Our data show that a substantial percentage of patients with clinical acromegaly have "normal" GH, and therefore strengthens the growing body of evidence which supports the leading role of IGF-1 levels in diagnostic evaluation. At the present time, questions about the natural course of "micromegaly" and treatment benefits compared to the subpopulation with elevated GH levels remain unanswered, but research continues to build on our understanding of the heterogeneous population of individuals.

The ongoing challenge of discrepant growth hormone and insulin-like growth factor I results in the evaluation of treated acromegalic patients: a systematic review and meta-analysis

OBJECTIVE

Growth hormone (GH) and insulin-like growth factor I (IGF-I) are the principal biomarkers used to assess disease activity in acromegaly, and any discrepancy between them renders interpretation of results inconclusive. Purpose of this study was to assess the frequency of this discrepancy and identify parameters that might affect its occurrence.

DESIGN

A systematic review of MEDLINE and Scopus was performed (1987-2013) followed by a meta-analysis to address the frequency of discrepant results between GH and IGF-I levels. Meta-regression and subgroup analyses were performed assessing the effects of the year of publication, the different types of GH testing and GH assays used, as well as the impact of treatment with somatostatin analogues (SSAs) on the occurrence of this discrepancy.

RESULTS

The analysis retrieved 39 eligible studies totalling 7071 patients. The pooled discordance rate between GH and IGF-I was 25·7% (95% CI: 22·3-29·4), and the predominant format was that of elevated IGF-I with normal GH levels (15·3%, 95% CI: 12·5-18·7). No significant correlation between the discordance rate and the year of publication was shown; whereas, the use of ultrasensitive GH assays resulted in higher discordance rates (30·7%, 95% CI: 25·9-35·9 vs 19·8%, 95% CI: 14·1-27·2, P = 0·04) as did treatment with SSAs (32·5%, 95% CI: 27·8-37·4) vs (21·6%, 95% CI: 17·8-25·6, P = 0·001).

CONCLUSIONS

Discrepancy between GH and IGF-I results is encountered in a quarter of treated patients with acromegaly, especially when using ultrasensitive GH assays or in patients receiving SSAs, a fact that the clinician should take into consideration when making clinical decisions.

DISCORDANCE BETWEEN GH AND IGF-1 LEVELS IN TURKISH ACROMEGALIC PATIENTS

OBJECTIVE

Discordance between insulin-like growth factor-1 (IGF-1) and growth hormone (GH) levels is an important problem in the follow-up of patients diagnosed with acromegaly. Our aims were to evaluate the discordance between IGF-1 and GH levels and compare the performance of different cut-off levels for the nadir in GH (GHn) in acromegalic patients.

METHODS

The study included 63 acromegalic patients in a follow-up at a tertiary care university hospital facility. Levels of IGF-1, IGF binding protein-3 (IGFBP-3), and GH were investigated. The baseline GH and GHn levels were evaluated after an oral glucose tolerance test (cut-offs of 0.4 and 1 ng/mL, respectively). The discordance rates between GHn and IGF-1 levels, and IGF-1/IGFBP-3 ratios were determined.

RESULTS

We first adopted a GHn cut-off value of 1 ng/mL and found that 27 patients (42.9%) exhibited biochemical remission (BR) (IGF-1 <95^th percentile, GH <1), and 25 patients (39.7%) had no BR (NBR) (IGF-1 ≥95^th percentile, GH >1). Discordance in the presence of normal IGF-1 and nonsuppressed GH (DC1) occurred in 2 of 63 (3.2%) patients; discordance in the presence of high IGF-1 and suppressed GH (DC2) occurred in 9 of 63 (14.3%) patients. If the GHn cut-off value adopted was 0.4 ng/mL, the distributions were 17 of 63 (27.0%) patients in BR, 29 of 63 (46.0%) patients in NBR, 12 of 63 (19.0%) in DC1, and 5 of 63 (7.9%) patients in DC2. If only the baseline GH values were considered, the distributions were very similar to those with a GHn cut-off value of 0.4 ng/mL. The IGF-1/IGFBP-3 ratio was lowest in the BR group.

CONCLUSION

Adopting a GHn cut-off value of 0.4 ng/mL did not increase the test performance compared with baseline GH only. In contrast, in the follow-up of acromegalic patients, the IGF-1/IGFBP-3 ratio might be a useful measurement when discordance between IGF-1 and GH levels occurs. We propose that these values be considered in clinical practice.

ABBREVIATIONS

BR = biochemical remission DC1 = discordance group 1 DC2 = discordance group 2 DM = diabetes mellitus GH = growth hormone GHn = nadir in GH IGF-1 = insulin-like growth factor-1 IGFBP-3 = IGF binding protein-3 LAR = long-acting release NBR = not in biochemical remission OGTT = oral glucose tolerance test.

Sleep extension increases IGF-I concentrations before and during sleep deprivation in healthy young men

Sleep deprivation is known to suppress circulating trophic factors such as insulin-like growth factor (IGF)-I and brain-derived neurotrophic factor (BDNF). This experiment examined the effect of an intervention involving 6 nights of extended sleep before total sleep deprivation on this catabolic profile. In a randomized crossover design, 14 young men (age range: 26–37 years) were either in an extended (EXT; time in bed: 2100–0700 h) or habitual (HAB: 2230–0700 h) sleep condition, followed by 3 days in the laboratory with blood sampling at baseline (B), after 24 h of sleep deprivation (24h-SD), and after 1 night of recovery sleep (R). In the EXT condition compared with the HAB condition, free IGF-I levels were significantly higher at B, 24h-SD, and R (P < 0.001), and those of total IGF-I at B and 24h-SD (P < 0.05). EXT did not influence growth hormone, IGF binding protein 3, BDNF, insulin, and glucose levels. The only effect of 24 h of sleep deprivation was for insulin levels, which were significantly higher after R compared with B. In a healthy adult, additional sleep over 1 week increased blood concentrations of the anabolic factor IGF-I before and during 24 h of sleep deprivation and after the subsequent recovery night without effects on BDNF. With further research, these findings may prove to be important in guiding effective lifestyle modifications to limit physical or cognitive deficits associated with IGF-I decrease with age.

Effects of growth hormone-releasing hormone on visceral fat, metabolic, and cardiovascular indices in human studies

Increased visceral adipose tissue (VAT) is associated with reductions in endogenous GH secretion, possibly as a result of hyperinsulinemia, increased circulating free fatty acid, increased somatostatin tone, and reduced ghrelin. Reduced GH may, in turn, further exacerbate visceral fat accumulation because of decreased hormone-sensitive lipolysis in this depot. Data from multiple populations demonstrate that both reduced GH and increased VAT appear to contribute independently to dyslipidemia, increased systemic inflammation, and increased cardiovascular risk. The reductions in GH in states of visceral adiposity are characterized by reduced basal and pulsatile GH secretion with intact pulse frequency. Treatment with GH-releasing hormone (GHRH) provides a means to reverse these abnormalities, increasing endogenous basal and pulsatile GH secretion without altering pulse frequency. This review describes data from HIV-infected individuals and individuals with general obesity showing that treatment with GHRH significantly reduces visceral fat, ameliorates dyslipidemia, and reduces markers of cardiovascular risk. Further research is needed regarding the long-term efficacy and safety of this treatment modality.

Discordance of IGF-1 and GH stimulation testing for altered GH secretion in obesity

OBJECTIVE

To investigate the concordance/discordance of IGF-1 and peak stimulated GH in identifying subjects with reduced GH secretion and to determine the physiological significance of any discordance in obese subjects.

DESIGN, PATIENTS AND METHODS

95 obese and 43 normal weight men and women underwent measurement of IGF-1 and GH stimulation testing with GH releasing hormone (GHRH)-arginine. Reduced IGF-1 and GH secretion were defined using pre-determined cut-points. Cardiovascular disease risk was determined by measuring carotid intima-media thickness (cIMT). In a second study, IGF-1 was measured in 52 obese men and women who underwent GH stimulation testing and overnight frequent blood sampling. The association of IGF-1 and peak stimulated GH with parameters of endogenous GH secretion was assessed.

RESULTS

60% of obese subjects had normal IGF-1 and peak stimulated GH while 8.4% of obese subjects had reduced IGF-1 and GH secretion. Discordance rate for IGF-1 and peak GH was 31.6%. Subjects with both low IGF-1 and low peak GH had the highest cIMT, while subjects with both normal IGF-1 and peak GH had the lowest cIMT. Subjects with reduction in either IGF-1 or peak GH, had intermediate cIMT (P=0.02). IGF-1 and peak stimulated GH were associated with maximum and mean overnight serum GH and GH AUC as well as maximum peak mass and median pulse mass. Peak stimulated GH, but not IGF-1, was also associated with nadir overnight serum GH concentration and basal GH secretion.

CONCLUSION

Peak stimulated GH and IGF-1 demonstrate significant discordance in identification of subjects with reduced GH secretion in obesity. Subjects with reduction of either IGF-1 or peak GH had higher cIMT compared to subjects with both normal IGF-1 and peak GH. Subjects with reductions in both IGF-1 and peak GH had the highest cIMT. Peak GH, compared to IGF-1, has broader associations with various parameters of endogenous GH secretion which support its utility in identifying those with reduced GH secretion.

Management of endocrine disease: GH excess: diagnosis and medical therapy

Acromegaly is predominantly caused by a pituitary adenoma, which secretes an excess of GH resulting in increased IGF1 levels. Most of the GH assays used currently measure only the levels of the 22 kDa form of GH. In theory, the diagnostic sensitivity may be lower compared with the previous assays, which have used polyclonal antibodies. Many GH-secreting adenomas are plurihormonal and may co-secrete prolactin, TSH and α-subunit. Hyperprolactinaemia is found in 30-40% of patients with acromegaly, and hyperprolactinaemia may occasionally be diagnosed before acromegaly is apparent. Although trans-sphenoidal surgery of a GH-secreting adenoma remains the first treatment at most centres, the role of somatostatin analogues, octreotide long-acting repeatable and lanreotide Autogel as primary therapy is still the subject of some debate. Although the normalisation of GH and IGF1 levels is the main objective in all patients with acromegaly, GH and IGF1 levels may be discordant, especially during somatostatin analogue therapy. This discordance usually takes the form of high GH levels and an IGF1 level towards the upper limit of the normal range. Pasireotide, a new somatostatin analogue, may be more efficacious in some patients, but the drug has not yet been registered for acromegaly. Papers published on pasireotide have reported an increased risk of diabetes mellitus due to a reduction in insulin levels. Pegvisomant, the GH receptor antagonist, is indicated - alone or in combination with a somatostatin analogue - in most patients who fail to enter remission on a somatostatin analogue. Dopamine-D2-agonists may be effective as monotherapy in a few patients, but it may prove necessary to apply combination therapy involving a somatostatin analogue and/or pegvisomant.

[Biomarkers in endocrinology]

TSH assay is the best parameter of the thyroid function. For adults, the normal interval of TSH concentrations range from 0.4 to 4 mUI/L. At the first trimester of pregnancy, TSH levels must be <2.5 mUI/L. Normal TSH levels increase with aging and obesity. The biological diagnosis relies on the identification of excessive secretion of the metanephrines which are more sensitive and specific than those of catecholamines. The concentrations of the free plasmatic metanephrines reflect the ongoing production of tumor. Plasma methoxytyramine is a novel biomarker of metastatic pheochromocytomas and paragangliomas. Serum IGF1 is a reliable measure of integrated GH concentrations in patients with acromegaly. Accurate assessment of IGF1 concentrations requires age and sex-matched control values. IGF1 is a sensitive tool for the diagnosis of acromegaly and efficacy of therapies. Serum AMH assay is more sensitive, more specific and more reproducible that counting of ovarian follicles by ultrasound. AMH level above 5 ng/mL (35 pmol/L) could be chosen as one of the diagnostic criteria for the polycystic ovary syndrome. In early or "incipiens" ovarian failure, the decrease in serum AMH is far ahead of the increase in FSH. Thyroglobulin (TG) and calcitonin (CT) are the sensitive and specific markers of respectively well-differentiated thyroid cancers of follicular origin and of the medullary thyroid cancers. The same tumour marker assay should be used to monitor a given patient. Chromogranin A (CgA) is a highly efficient biomarker for diagnosis and follow-up of various endocrine tumours. Despite the lack of international standardisation, some CgA assays are reliable.

Sleep and insulin-like growth factors in the Cardiovascular Health Study

STUDY OBJECTIVES

Sleep and sleep disordered breathing (obstructive sleep apnea [OSA]) are known to affect the growth hormone/insulin-like growth factor (GH/IGF) axis. There are few relevant population studies in this area, particularly in the elderly. We conducted this study to investigate the relationship between sleep (architecture and OSA) and circulating IGF-I (insulin-like growth factor-1), IGFBP-1 (insulin-like growth factor binding protein-1), and IGFBP-3 (insulin-like growth factor binding protein-3) levels in an elderly population.

DESIGN SETTING

Cross-sectional analysis of participants from the year 9 visit of the Cardiovascular Health Study (CHS) who were enrolled in the Sleep Heart Health Study (SHHS).

PATIENTS OR PARTICIPANTS

1,233 elderly participants from the CHS and SHHS.

MEASUREMENTS AND RESULTS

The mean age of males (n = 526) and females (n = 697) was 77 years. The mean value of IGF-I (ng/mL) in males was 112.4 vs. 97.1 in females (p < 0.01). Mean IGFBP-1 and IGFBP-3 levels were higher in females than males (p < 0.01). As expected, slow wave sleep was better preserved in females compared to males (22% total sleep time vs. 9% total sleep time, p < 0.01). Furthermore, as expected, OSA (apneahypopnea index [AHI] ≥ 5/h) was more prevalent in males compared to females (60% vs. 46%, p < 0.01). Multivariable linear regression was used to determine the relationship between objective sleep parameters and circulating IGF-I, IGFBP-1, and IGFBP-3 levels, with adjustment for age, sex, race, BMI, diabetes, estrogen use, progestin use, and physical activity. We did not detect a significant association between slow wave sleep (SWS) (per 5 min) and IGF-I, IGFBP-1, and IGFBP-3 levels (ng/mL). We found no significant linear association between OSA (AHI ≥ 5/h) and IGF-I, IGFBP-1, and IGFBP-3 levels. Gender-stratification of the entire cohort did not alter these findings. Sensitivity analyses excluding diabetics revealed that moderate OSA (AHI ≥ 5 and < 15) is inversely associated with IGFBP-3 levels in women. Conclusions The relationship between SWS and GH/IGF system is not significant in the elderly. Furthermore, OSA does not appear to adversely influence the GH/IGF axis, as reported in younger individuals. Whether our study findings are due to diminished GH/IGF-I axis activity in elderly needs further investigation by replication in other large population based elderly cohorts.

Estrogen treatment for acromegaly

Estrogens have been used in patients with acromegaly since the 1930-1940s, suppressing plasma IGF-1 levels and improving clinical signs and symptoms of acromegaly. Estrogens antagonize GH function at the post-receptor level, inhibiting GH signaling, thus decreasing GH-induced hepatic IGF-1 synthesis. We report our experience with four female patients with active acromegaly, naïve to medical treatment or inadequately controlled by somatostatin receptor ligands (SRLs) or the GH-receptor antagonist. Adding estrogen treatment (contraceptive pills or transdermal estrogen patches) to their ongoing medical treatment, suppressed IGF-1 significantly in all patients, achieving hormonal remission in three of them. We review the available data on the use of estrogens and selective estrogen receptor modulators in acromegaly, and their mechanisms of action. Estrogens could be an alternative, inexpensive adjuvant treatment for females with active acromegaly, who are only partially responding to SRLs or to the GH-receptor antagonist.

Discordant growth hormone and IGF-1 levels post pituitary surgery in patients with acromegaly naïve to medical therapy and radiation: what to follow, GH or IGF-1 values?

New criteria that define acromegaly remission are more stringent: normal (age/sex-adjusted) insulin-like growth factor type 1 (IGF-1), growth hormone (GH) random (GHr) <1 μg/L, and a GH nadir (GHn) during oral glucose tolerance test (OGTT) of <0.4 μg/L. Discordance between GH and IGF-1 values is often attributed to somatostatin receptor ligands (SRLs) or radiation. The purpose of this study was to evaluate rates of discordant IGF-1 and GH levels in patients with GH secreting adenomas (after pituitary surgery), who were naïve to any other treatment. We retrospectively analyzed data over a 5 year time period (2006-2010), in post-surgery acromegaly patients who had elevated IGF-1 but normal GH levels (per the new cure criteria). Symptoms of acromegaly were scored according to a 4-point scale. Fifty-four patients had post-operative GHr and IGF-1 measurements, 28 patients had GHn during OGTT, and 16 patients had 5-point 2-h GH day curve tests. Thirteen of 54 (24%) patients were found to have intermittent persistent discordant values; high IGF-1 and normal GH at final evaluation (77% of these patients were women). Patients had a median number of IGF-1 evaluations of 7.5 (range: 2-15) over a median of 22 months (range: 3-47 months). Mean elevated IGF-1 in the discordant population was 1.25 × upper limit of normal (ULN) ± 0.17 (range: 1.01-1.6 × ULN). Twelve of the 13 (92%) patients had macroadenomas; 10 of the 13 (69%) patients had mammosomatotroph, mixed lacto/somatotroph tumors or prolactin staining. No patient in the discordant population was on estrogen replacement therapy or had overt cardiac disease. When the relatively asymptomatic discordant population was compared with 35 patients from the concordant population (six were excluded because of preoperative medical treatment for acromegaly), no significant difference between age, gender distribution, body mass index (BMI), presence of diabetes mellitus (DM) or glucose intolerance and adrenal insufficiency between groups was noted. In our study of postoperative patients with acromegaly naïve to both SRLs and radiation, using new GH cut-off levels, 24% had intermittent or persistent discordant values. Our results highlight that relying on IGF-1 or GH measurements alone is not adequate for assessing disease control in surgically treated acromegaly patients. Management of such patients needs to be individualized and long-term studies evaluating morbidity and mortality incorporated into treatment decisions. Further studies with larger patient populations and longer follow-up are required to determine the long-term implications of discordant GH and IGF-1 value patterns.

The changing face of acromegaly--advances in diagnosis and treatment

Acromegaly is a chronic disease characterized by the presence of a pituitary growth hormone (GH)-producing tumour, excessive secretion of growth hormone, raised levels of insulin-like growth factor I (IGF-I) and characteristic clinical presentation of acral enlargement. Over the past two decades, major advances have occurred in the understanding of some aspects of acromegaly--such as the biology of pituitary tumours, the physiology, molecular mechanisms of GH secretion and IGF-I generation, and the pathogenesis of comorbidities. Moreover, new approaches to diagnosis and surveillance (both in terms of screening and follow-up) of acromegaly have led to increases in the number of patients diagnosed with active disease, many of whom would previously have been missed. The development of sensitive assays for detecting plasma GH and IGF-I levels, as well as the widespread use of MRI for visualization of small tumours, have been major contributing factors to these improvements. Treatment advances have resulted in improved cure rates and disease control through novel neurosurgical techniques and pharmacological approaches. This Review summarizes and discusses the changes in our understanding of the epidemiology, diagnosis, treatment, and follow-up of acromegaly and its comorbidities.

How useful are serum IGF-I measurements for managing GH replacement therapy in adults and children?

The optimal dosing of growth hormone (GH) therapy is challenging due to high inter-individual variability in subcutaneous GH absorption and sensitivity to the drug. Optimal dosing would maximize patient gains in height, body composition, and metabolic outcomes while minimizing GH adverse events. The pulsatile secretion of GH, however, does not allow direct assessment of circulating GH levels as a measure of response to GH therapy. Insulin-like growth factor (IGF-I), a key marker of GH activity, has been shown to be useful in monitoring and adjusting GH dose during treatment of GH deficiency (GHD). Traditionally, monitoring IGF-I levels in response to GH therapy has been recommended for assessment of treatment compliance and safety. More recently, GH treatment guidelines have stated that IGF-I levels should also be used to guide GH dosing. This review examines whether individualized GH dosing based on the IGF-I response to GH therapy provides a better method for determining the GH replacement needs of pediatric and adult patients compared with conventional GH dosing, and whether IGF-I-based dosing improves outcomes such as height and body composition, with reduced side effects. Because IGF-I measurement presents its own difficulties, the current state of IGF-I assays is also discussed. The reviewed studies show that the use of GH dose adjustments based on IGF-I responses to GH therapy successfully reduces adverse events in adults with GHD and results in greater positive height attainment in children, without increasing adverse events. Long-term outcome studies are needed, as are internationally accepted guidelines for IGF-I measurement.

Rapid suppression of growth hormone concentration by overeating: potential mediation by hyperinsulinemia

CONTEXT

The very low GH concentration in obesity is commonly attributed to high body fat mass; however, the influence of overeating on GH secretion is not clear.

OBJECTIVE

The aim of the study was to examine the effects of 2 wk of overeating on changes in GH secretion.

SETTING

Subjects were admitted to the hospital and stayed within the Michigan Clinical Research Unit throughout the entire 2-wk overeating period.

PARTICIPANTS

We studied seven healthy, nonobese men (body mass index, 24 ± 1 kg/m(2); age, 25 ± 1 yr).

INTERVENTION

Subjects ate standardized meals containing 70 kcal/kg fat free mass/d (∼4000 kcal/d) for 2 wk.

MAIN OUTCOME MEASURES

Twenty-four-hour plasma concentrations of GH (every 20 min) and insulin (every 2 h) were measured before overeating (baseline), on d 3, and after 2 wk of overeating.

RESULTS

Compared with baseline, average 24-h plasma GH concentration declined nearly 80% by d 3 of overeating (1.30 ± 0.18 vs. 0.36 ± 0.09 ng/ml; P = 0.01). This marked suppression of GH secretion occurred in the absence of an increase in body weight (77.0 ± 2.2 vs. 76.4 ± 2.4 kg). At the same time, average 24-h insulin concentration doubled (16.6 ± 2.1 vs. 31.7 ± 5.8 μU/ml; P = 0.009). After 2 wk, body weight significantly increased (79.0 ± 2.1 kg; P < 0.001), and body fat increased by more than 10% (P = 0.002). However, this did not induce a further suppression in plasma GH concentration (0.33 ± 0.08 ng/ml).

CONCLUSION

Only a few days of overeating markedly suppressed GH secretion before any measurable weight gain and was accompanied by chronic hyperinsulinemia. Increased body weight and body fat by 2 wk of overeating did not further suppress GH secretion.

Effects of a growth hormone-releasing hormone analog on endogenous GH pulsatility and insulin sensitivity in healthy men

CONTEXT AND OBJECTIVE

Strategies to augment pulsatile GH may be beneficial in patients with excess visceral adiposity, in whom GH secretion is reduced. The objective of this study was to determine the effects of a novel GHRH (GHRH(1-44)) analog, tesamorelin, on endogenous GH pulsatility and insulin sensitivity in healthy men.

DESIGN, PARTICIPANTS, AND INTERVENTION

Thirteen males (mean age 45 ± 3 yr and body mass index 27.3 ± 1.2 kg/m(2)) received tesamorelin 2 mg sc once daily for 2 wk, with assessment made at baseline, after 2 wk of treatment, and after 2 wk of withdrawal.

OUTCOME MEASURES

The primary end point was change in mean overnight GH as determined by overnight frequent sampling. Secondary end points included insulin-stimulated glucose uptake as measured by euglycemic hyperinsulinemic clamp; IGF-I; and GH secretion parameters, including pulse area, pulse frequency, and basal secretion.

RESULTS

Tesamorelin treatment increased mean overnight GH (change +0.5 ± 0.1 μg/liter, P = 0.004), average log(10) GH peak area (change +0.4 ± 0.1 log(10) μg/liter, P = 0.001), and basal GH secretion (change +0.008 ± 0.003 μg/liter · min, P = 0.008). IGF-I increased by 181 ± 22 μg/liter (P < 0.0001). Neither fasting glucose (P = 0.93) nor insulin-stimulated glucose uptake (P = 0.61) was significantly affected by tesamorelin.

CONCLUSIONS

Once-daily short-term treatment with a GHRH(1-44) analog, tesamorelin, augments basal and pulsatile GH secretion. Moreover, although tesamorelin significantly increases IGF-I, peripheral insulin-stimulated glucose uptake appears to be preserved.

Limited utility of oral glucose tolerance test in biochemically active acromegaly

CONTEXT

Measurement of GH after oral glucose tolerance test (OGTT) is used for the diagnosis and surveillance of acromegaly. However, there are major discrepancies between glucose-suppressed GH and plasma IGF1 as indices of biochemical activity of acromegaly in patients with relatively mild GH oversecretion. This study was aimed to assess the performance of OGTT in patients with acromegaly and variable GH outputs.

METHODS

Forty adults with newly diagnosed, untreated acromegaly (15 with GH >4.3 μg/l and 25 with GH <4.3 μg/l) and elevated IGF1 levels were studied. All underwent Q10 min for 24 h sampling for GH followed by an OGTT.

RESULTS

Postglucose nadir GH (GHn) correlated significantly to 24 h GHn, mean 24 h GH, and baseline GH (P<0.001 for all comparisons). GHn correlated significantly to IGF1 z-scores for the 'low' GH group and for the entire group (P<0.0001 for both comparisons), but not for the 'high' GH group. None of the patients with mean GH >4.3 μg/l had GHn below 1 μg/l. In contrast, 13 out of 25 patients (52%) with GH <4.3 μg/l showed GHn lower than 1 μg/l, and 7 of them (28%) had GHn lower than 0.4 μg/l. These groups did not differ significantly either for average or for maximal GH suppression in OGTT.

CONCLUSIONS

Our data show that suppressibility of GH by glucose in acromegaly is a function of the degree of GH hypersecretion and that OGTT has only limited diagnostic value in patients with biochemically active acromegaly but only mildly increased GH output.

Gender, age, body mass index, and IGF-I individually and jointly determine distinct GH dynamics: analyses in one hundred healthy adults

BACKGROUND

GH secretion is quantifiable as mean, peak, and nadir GH concentrations; degree of irregularity (approximate entropy); and spikiness (brief staccato-like fluctuations).

HYPOTHESIS

Distinct GH dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, body mass index (BMI), and IGF-I concentrations.

LOCATION

The study took place at a clinical translational research unit.

SUBJECTS

Subjects included 100 healthy adults ages 20-77 yr (59 women and 41 men), BMI 18-42 kg/m(2), and IGF-I 9.2-38 nmol/liter.

MEASURES

Immunofluorometric GH assay was done on 10-min samples collected for 24 h.

RESULTS

Stepwise forward-selection multivariate regression analysis revealed that mean GH concentrations were simultaneously determined (overall r = 0.36; P < 0.001) by gender (higher in women, P < 0.001), BMI (negatively, P < 0.001), and IGF-I (positively, P < 0.001). Peak GH levels were influenced (r = 0.28) by both BMI (P < 0.001) and IGF-I (P = 0.001). Nadir GH values were jointly affected by gender (higher in women, P = 0.005) and BMI (negatively, P = 0.001). GH approximate entropy was triply defined (r = 0.29) by gender (greater irregularity in women, P < 0.001), age (P = 0.022), and BMI (P = 0.008) and dually (r = 0.25) by gender (P = 0.0001) and BMI (P = 0.017) if sex steroids were included. GH spikiness was determined (r = 0.29) by gender (higher in women, P = 0.0016) and BMI (positively, P = 0.0002).

CONCLUSION

In healthy adults, combinations of gender, age, BMI, and IGF-I specify distinct GH dynamics, thus requiring balanced representation of these variables in comparative GH studies.

Clinical laboratory indices in the treatment of acromegaly

Measurement of serum growth hormone (GH) and insulin-like growth factor-I (IGF-) is used to monitor the degree of improvement that occurs following treatment of patients with acromegaly. Improvement in GH assay sensitivity has led to changes in the definition of normal GH however many studies that assess the predictive value of GH were conducted in an era where assays were less sensitive. Other problems that have occurred with GH measurements include utilization of different standards and failure to prove commutability of commonly accepted standard. GH reference ranges vary in their quality and are not stratified for age, sex or body mass index. IGF-I measurements are associated with similar problems. They do not use a common standard that has been proven to be commutable and results can vary widely when the same specimens are assayed in different laboratories. Although age and sex stratified reference ranges exist, these do not always have adequate numbers of subjects and BMI adjusted ranges are not available. These problems have led to significant discordance in a significant number of patients wherein the IGF-I and GH values may yield a discrepant prediction of disease stabilization. In these cases in general the IGF-I values correlate better with the presence of persistent symptoms. Patients who fail to suppress GH to normal but have a normal IGF-I have to be monitored carefully for recurrence but usually do not require further therapy if they are asymptomatic. For the long term assessment of outcome and clinical disease activity measurement of both hormones is recommended.