Inter-relations between growth hormone, insulin, insulin-like growth factor-I (IGF-I), IGF-binding protein-1 (IGFBP-1) and sex hormone-binding globulin in acromegaly

An updated view of hypothalamic-vascular-pituitary unit function and plasticity

The discoveries of novel functional adaptations of the hypothalamus and anterior pituitary gland for physiological regulation have transformed our understanding of their interaction. The activity of a small proportion of hypothalamic neurons can control complex hormonal signalling, which is disconnected from a simple stimulus and the subsequent hormone secretion relationship and is dependent on physiological status. The interrelationship of the terminals of hypothalamic neurons and pituitary cells with the vasculature has an important role in determining the pattern of neurohormone exposure. Cells in the pituitary gland form networks with distinct organizational motifs that are related to the duration and pattern of output, and modifications of these networks occur in different physiological states, can persist after cessation of demand and result in enhanced function. Consequently, the hypothalamus and pituitary can no longer be considered as having a simple stratified relationship: with the vasculature they form a tripartite system, which must function in concert for appropriate hypothalamic regulation of physiological processes, such as reproduction. An improved understanding of the mechanisms underlying these regulatory features has implications for current and future therapies that correct defects in hypothalamic-pituitary axes. In addition, recapitulating proper network organization will be an important challenge for regenerative stem cell treatment.

Novel insights in SHBG regulation and clinical implications

Sex hormone-binding globulin (SHBG) is produced and secreted by the liver into the bloodstream where it binds sex steroids and regulates their bioavailability. Traditionally, body mass index (BMI) was thought to be the major determinant of SHBG concentrations and hyperinsulinemia the main cause for low SHBG levels found in obesity. However, no mechanisms have ever been described. Emerging evidence now shows that liver fat content rather than BMI is a strong determinant of circulating SHBG. In this review we discuss evidence demonstrating that insulin might not regulate SHBG production, describe putative molecular mechanisms by which proinflammatory cytokines downregulate SHBG, and comment on recent findings suggesting dietary SHBG regulation. Finally, clinical implications of all of these findings and future perspectives are discussed.

Discordance between growth hormone and insulin-like growth factor-1 after pituitary surgery for acromegaly: a stepwise approach and management

INTRODUCTION

Follow-up management of patients with acromegaly after pituitary surgery is performed by conducting biochemical assays of growth hormone (GH) and insulin-like growth factor-1 (IGF1). Despite concordant results of these two tests in the majority of cases, there is increasing recognition of patients who show persistent or intermittent discordance between GH and IGF1 (normal GH and elevated IGF1 or vice versa).

METHOD

In this narrative review, the last three decades materials on the issue of discrepancy between GH and IGF1 were thoroughly assessed.

RESULTS

Various studies have obtained different discordance rates, ranging from 5.4 to 39.5%. At present, despite the use of current sensitive assays and more stringent criteria to define remission, the rate of discordance still remains high. A number of mechanisms have been proposed to explain the postoperative discordance of GH and IGF1 including; altered dynamics of the GH secretion after surgery, early postoperative hormone assay, inaccurate or less sensitive tests and laboratory errors, too high cut-off point for GH suppression in the GH assays, GH nadir values not adjusted to age, sex, and body mass index, the influence of concomitant medication, co-existing physiologic and pathologic conditions, and many other proposed reasons. Nevertheless, the underlying mechanisms are still far from clear, and the solution continues to evade complete elucidation. Similarly, the impacts of such a discrepancy over mortality and morbidity and the risk of biochemical and/or clinical recurrence are unclear.

CONCLUSION

As a challenging clinical problem, a stepwise evaluation and management of these patients appears to be more rational.

Pathophysiology of renal calcium handling in acromegaly: what lies behind hypercalciuria?

BACKGROUND

Hypercalciuria is frequent in patients with acromegaly, but it is unclear how GH/IGF-I regulate renal calcium handling. Elevated fasting plasma calcium levels despite increased glomerular filtration suggest enhanced renal calcium reabsorption.

OBJECTIVE

The aim of this study was to investigate the impact of acromegaly on phosphocalcium metabolism.

DESIGN AND SETTING

We conducted a prospective sequential study at a tertiary referral medical center and clinical investigation center (www.ClinicalTrials.gov Identifier: NCT00531908).

INTERVENTION

Sixteen consecutive patients (five females/11 males) with acromegaly received a single iv infusion of 25 mg of furosemide to induce an acute increase in calcium and magnesium delivery to distal tubular segments during a high-sodium diet with stable dietary calcium, magnesium, and phosphate intake.

MEASUREMENTS

Baseline plasma and urine electrolytes, plasma calciotropic hormones, and furosemide-induced changes in the fractional excretion and tubular reabsorption of Na, Ca, and Mg were measured before and 6 months (range, 1-12) after effective treatment of acromegaly.

RESULTS

Serum IGF-I concentrations normalized in all the patients after acromegaly treatment. Compared with controlled acromegaly, active acromegaly was associated with higher fasting plasma (P = 0.0002) and urinary calcium (P = 0.0003) levels, lower PTH levels (P = 0.0075), higher calcitriol levels (P = 0.0137), higher phosphatemia (P<0.0001) and tubular phosphate reabsorption (P = 0.0002), and a lower calciuric (P = 0.0327) but not magnesiuric response to furosemide related to higher baseline and postfurosemide tubular calcium (P = 0.0034 and P = 0.0081, respectively), but not magnesium reabsorption.

CONCLUSION

The IGF-I-mediated and PTH-independent increase in calcitriol synthesis in acromegaly is responsible for both absorptive hypercalciuria and increased fasting plasma calcium linked to enhanced distal tubular calcium reabsorption, as shown by the selectively diminished calciuric response to furosemide.

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

CONTEXT

Previous studies have shown that mean 24-h GH concentrations determine plasma IGF-I levels in patients with acromegaly. However, we have recently shown that continuous GH infusion, mimicking the interpulse GH levels, was significantly more effective than the pulsatile GH administration at increasing IGF-I concentrations.

OBJECTIVE

The aim of the study was to ascertain relative roles of total GH output (24-h mean), GH pulses, and interpulse GH level in determining plasma IGF-I concentrations.

DESIGN AND SETTING

We conducted a point-in-time observational inpatient study in the General Clinical Research Center at the University of Michigan.

PATIENTS OR OTHER PARTICIPANTS

Eighteen patients with acromegaly and 19 healthy control subjects participated in the study.

INTERVENTION(S)

We performed frequent (every 10 or 20 min) blood sampling over 24 h.

MAIN OUTCOME MEASURE(S)

Before data collection, we hypothesized that interpulse nadir levels of GH would correlate with IGF-I levels in normal and acromegalic subjects.

RESULTS

Mean and valley levels of GH correlated with serum IGF-I levels (r(2) = 0.44 and 0.48, respectively) in normal and acromegalic patients in a log-linear fashion. The strongest correlation, however, was observed between the log of nadir GH and IGF-I concentrations (r(2) = 0.77). GH pulse mass did not significantly correlate with IGF-I (r(2) = 0.001).

CONCLUSIONS

Plasma IGF-I concentrations correlated with mean 24-h GH concentrations. This relationship is dependent exclusively on the basal GH levels. GH pulses do not determine plasma IGF-I concentrations.

Diet-induced obesity is associated with hyperleptinemia, hyperinsulinemia, hepatic steatosis, and glomerulopathy in C57Bl/6J mice

Obesity and obesity-related illnesses are global epidemics impacting the health of adults and children. The purpose of the present work is to evaluate a genetically intact obese mouse model that more accurately reflects the impact of aging on diet-induced obesity and type 2 diabetes in humans. Male C57Bl/6J mice consumed either a control diet or one in which 60% kcal were due to lard beginning at 5-6 weeks of age. Body weight and fat measurements were obtained and necropsy performed at 15, 20, 30, and 40 weeks of age. Serum chemistry, histopathology, gene expression of the liver, and renal and hepatic function were also evaluated. In concert with significant increases in percent body fat and weight, mice fed the high-fat versus control diet had significantly increased levels of serum cholesterol. At ages 20 and 30 weeks, serum glucose was significantly higher in obese versus controls, while serum insulin levels were >/=4-fold higher in obese mice at ages 30 and 40 weeks. The effect of age exacerbated the effects of consuming a high-fat diet. In addition to being hyperinsulinemic and leptin resistant, older obese mice exhibited elevated hepatic PAI-1 and downregulation of GLUT4, G6PC, IGFBP-1, and leptin receptor mRNA in the liver, steatosis with subsequent inflammation, glomerular mesangial proliferation, elevated serum ALT, AST, and BUN, and increased numbers of pancreatic islets.

Influence of growth hormone receptor d3 and full-length isoforms on biochemical treatment outcomes in acromegaly

CONTEXT

In acromegaly, a discrepancy between what are defined as "normal" levels of GH and IGF-I for every given patient is observed in up to 35% of subjects at diagnosis and during the follow-up.

OBJECTIVE

The aim of the study was to evaluate the impact of GH receptor (GHR) polymorphism on the biochemical assessment of the treatment of acromegaly and on prevalence of discordant levels of GH and IGF-I.

SETTING

The study was performed in an institutional referral center at a tertiary care hospital.

DESIGN, PATIENTS, AND METHODS

We studied prospectively and retrospectively 84 consecutive acromegalic patients with active disease after neurosurgery and treated them with somatostatin analogs. The GHR genotype (flfl, fld3, or d3d3) was determined from peripheral blood.

RESULTS

Lack of exon 3 of GH receptor (d3-GHR) was found in 40 of 84 patients (47.6%). After neurosurgery, 67 subjects (79.8%) of the study population, concordant active acromegalic patients, had high IGF-I and mean GH levels above 2 ng/ml, whereas the remaining 17 patients (20.2%, discordant active acromegalic patients) showed discordance between these two parameters (high IGF-I and GH levels < or = 2 ng/ml). Overall, 70.6% of discordant patients were carriers of the d3-GHR. After somatostatin analogs, discordant active acromegalic patients increased to 30.9%, 69.2% of whom were carriers of the d3-GHR. Logistic regression analysis demonstrated that d3-GHR carriers maintained the significant correlation with discordant GH and IGF-I values either after neurosurgery or after somatostatin analog treatment, independently of the effects of age, sex, duration of acromegaly, serum GH, and IGF- I values either at diagnosis of acromegaly or after neurosurgery.

CONCLUSION

The GHR polymorphism seems to have a relevant impact on the posttreatment biochemical assessment of acromegaly. Moreover, the d3-GHR isoform could be an independent predictor of GH and IGF-I discrepancy during the follow-up in acromegaly.

Growth Hormone (GH) Receptor Isoform in Acromegaly: Lower Concentrations of GH but Not Insulin-Like Growth Factor-1 in Patients with a Genomic Deletion of Exon 3 in the GH Receptor Gene

Background: A genomic deletion of exon 3 (d3-GHR) of the growth hormone (GH) receptor (GHR) has been linked to the effectiveness of GH therapy in children with GH deficiency. Carriers of the d3-GHR genotype had higher GH-induced growth rates than children homozygous for the full-length (fl)-GHR. The aim of this study was to test whether the relationship between GH and insulin-like growth factor-1 (IGF-1) concentrations is influenced by the GHR genotype in patients with acromegaly.

Methods: Study participants were 44 adult patients with established diagnosis of acromegaly. The genotype of the GHR was determined in leukocyte DNA from peripheral blood. Clinical and biochemical findings at the time of diagnosis of acromegaly were obtained from the medical records of the patients.

Results: fl-GHR homozygosity was found in 22 (50%) of patients, and 22 (50%) of patients had at least 1 d3 allele (d3-GHR). Demographic and clinical characteristics (age, height, weight, estimated duration of disease, and mean tumor size) of the 2 groups were comparable. Median (range) serum IGF-1 concentrations at the time of diagnosis were 670 (447–1443) μg/L in the fl-GHR group and 840 (342–1494) μg/L in the d3-GHR group (P = not significant). Basal GH concentrations were higher in the fl-GHR group [29.7 (3.8–159) μg/L] than in the d3-GHR group [8.4 (2.6–74 μg/L), P = 0.002], and so were mean (30.4 vs 6.1 μg/L, P = 0.005) and nadir (20.5 vs 5.1 μg/L, P = 0.003) GH concentrations during an oral glucose tolerance test.

Conclusions: The GHR fl/d3 genotype modulates the relationship between GH and IGF-1 concentrations in patients presenting with acromegaly.

Serum IGF-I levels in the diagnosis and monitoring of acromegaly

Insulin-Like Growth Factor-I (IGF-I) is a reliable marker of disease activity and growth hormone (GH) status in acromegaly, but its clinical utility has been hampered over the years by various issues including a lack of robust reference range data and variability in assay sensitivity and specificity. In acromegaly IGF-I correlates well with GH activity and nadir GH on oral glucose tolerance test (OGTT) and is the most sensitive and specific test in diagnosis, where serum IGF-I is persistently seen to be elevated to a range that is distinct from that in healthy individuals. However it should not be relied on exclusively for diagnosis or used as the sole indication of disease severity and GH burden. Successful medical or surgical treatment of acromegaly is usually associated with normalisation of serum IGF-I but there is discordance between GH and IGF-I in some patients. Patients with a normal IGF-I but an abnormal GH suppression to OGTT are at risk of relapse and therefore it should not be used alone to establish disease remission. In contrast to the diagnosis of acromegaly, there is also considerable overlap in serum IGF-I with normality after primary treatment of disease, even in the presence of persisting GH excess. Gender, age and prior radiotherapy alters the relationship between GH and IGF-I and reliance on one marker of disease activity such as IGF-I is particularly precarious in certain disease states. However an elevated serum IGF-I has been shown to be associated with excess mortality and normalising IGF-I normalises mortality making it a useful marker. The tightening up of the assays means that establishing absolute concentrations as well as standard deviation scores are essential to allow cross-study comparisons. This becomes especially important in the use of Pegvisomant, where IGF-I becomes the sole biochemical marker of disease activity.

Dynamic tests and basal values for defining active acromegaly

Acromegaly is a rare disease caused by excess secretion of growth hormone (GH), usually from a pituitary somatotrope adenoma. The prevalence of acromegaly is 38-40 cases/1,000,000 subjects, while the annual incidence is 3 new cases/1,000,000 subjects. The increase in morbidity and mortality associated with acromegaly is the result of GH and insulin-like growth factor (IGF)-I oversecretion and the direct mass effect of the pituitary tumor. Once the disease is clinically suspected, laboratory evaluation is mandatory to establish diagnosis. The standard method for the diagnosis of acromegaly has been the measuring of GH nadir (GHn) during an oral glucose tolerance test (OGTT) which in normal individuals is undetectable, while acromegalics failed to suppress GH levels. Determination of IGF-I levels is useful as they correlate with clinical features of acromegaly and with the 24-hour mean GH levels. According to the more recent consensus, a random GH <0.4 microg/l and IGF-I in the age- and gender-matched normal range exclude the diagnosis of acromegaly. If either of these levels are not achieved, an OGTT should be performed, and then GHn <1 microg/l during OGTT excludes acromegaly. The therapeutic goals for acromegaly include the relief of sings and symptoms, the control of the tumor mass, the correction of the biochemical markers to normal levels, and the reduction in morbidity and mortality to the expected rate for the normal population. According to the 2000 consensus criteria, biochemical control of acromegaly is achieved when circulating IGF-I is reduced to an age- and sex-adjusted normal range and GHn during OGTT is <1 microg/l. There is debate in the literature whether GHn or IGF-I levels are more reliable to evaluate treatment of acromegaly. It has been reported that 15% of acromegalics with GHn <1 microg/l after treatment demonstrate abnormal IGF-I levels, while 15% of patients with normal IGF-I fail to suppress GH levels <1 microg/l during the OGTT. Probably, GHn and IGF-I levels represent two different aspects of disease activity in acromegaly. While IGF-I evaluates the secretory function of the somatotropes, GHn provides evidence of the presence or absence of functional autonomy of these cells.

The Challenges of Reliance on Insulin-Like Growth Factor I in Monitoring Disease Activity in Patients with Acromegaly

Serum insulin-like growth factor I (IGF-I) is an important marker of disease activity in patients with acromegaly, and epidemiological data indicate control of circulating IGF-I in patients with acromegaly restores life expectancy to normal. Improvements in the quality of, and access to, IGF-I assays has encouraged monitoring of acromegaly with IGF-I, although circulating growth hormone (GH) and IGF-I values provide different information, so ideally both should be monitored. However, the introduction of the GH receptor antagonist pegvisomant poses new challenges. Pegvisomant binds with high affinity to GH receptors, thereby blocking the action of GH at the tissue level and rendering the hormone biologically inactive. This leaves IGF-I as the principal marker of disease activity. It is conceptually possible to induce a state of functional GH deficiency (GHD) with pegvisomant with IGF-I values within the normal range. With the goal of minimizing the risk of over-treatment and GHD, we have provided preliminary guidance on the target range for IGF-I in patients receiving pegvisomant based on the gender- and decade-based percentile ranges for IGF-I of adult patients with untreated GHD enrolled in the Pfizer International Metabolic Database (KIMS).

[Usefulness of subcutaneous or long-acting octreotide as a predictive test and in the treatment of acromegaly]

We evaluated GH, IGF-1 and IGFBP-3 concentrations in ten acromegalic patients before and after treatment with subcutaneous octreotide (OCT-sc) and long-acting octreotide (OCT-LAR). We also evaluated the acute and short-period treatment (post 21 days) with octreotide as an index to test tolerance and responsiveness to both formulations. Patients were also evaluated after 6 months of treatment with each drug. Pre-treatment fasting GH (microg/l; IFMA), GH nadir during oGTT and IGF-1 (microg/l; IRMA) levels were 13.9+/-6.3; 11.4+/-6.3; 717+/-107, respectively. Fasting GH and IGF-1 were reduced after short treatment with OCT-sc or OCT-LAR (2.9+/-1.1 and 4.4+/-1.2; 491+/-80 and 512+/-80). All parameters were also reduced after a six-month period with OCT-sc or OCT-LAR (2.8+/-0.9 and 1.9+/-0.5; 1.6+/-0.4 and 1.6+/-0.5; 583+/-107 and 515+/-83), respectively. The efficacy of the two drugs was similar. IGFBP-3 was not a good parameter during follow-up of these patients. The acute test with OCT-sc was not a valuable index to predict tolerance, however, as well as the short-period test, it could predict the long-term GH responsiveness to OCT.

High levels of 150-kDa insulin-like growth factor binding protein three ternary complex in patients with acromegaly and the effect of pegvisomant-induced serum IGF-I normalization

OBJECTIVE

To assess the effect of pegvisomant-induced serum insulin-like growth factor 1 (IGF-1) normalization on IGF binding proteins 1, 2, 3 (IGFBP-1, IGFBP-2 and IGFBP-3), total, non-bound (45 kDa) and 150-kDa ternary complex-associated IGFBP-3, and in vivo IGFBP-3 proteolysis in patients with active acromegaly.

DESIGN

The above parameters were measured in 16 patients (median age 57 (range 27-78)) with active acromegaly (serum IGF-I at least 30% above the upper limit of an age-related reference range after washout) in a paired manner on samples obtained after washout and the first occurrence of serum IGF-I normalization during pegvisomant therapy (median dose 15 mg/day (10-40 mg)).

RESULTS

Total IGFBP-3 and 150-kDa ternary complex-associated IGFBP-3 were significantly elevated in patients at baseline compared to controls ((mean+/-SEM) 4345+/-194 vs. 3456+/-159 microg/L, P<0.01 and 3908+/-160 va. 3042+/-149 microg/L, P<0.01, respectively), but no significant difference in 45-kDa IGFBP-3 or in vivo IGFBP-3 proteolysis was observed. Serum IGF-I normalization (699+/-76 to 242+/-28 microg/L, P<0.0001) was associated with a fall in total IGFBP-3 (4345+/-194 to 3283+/-160 microg/L, P<0.001) due to a reduction in 150-kDa ternary complex-associated IGFBP-3 (3908+/-160 to 3008+/-140 microg/L, P<0.0001). 45 kDa IGFBP-3 and in vivo IGFBP-3 proteolysis were unaffected by GH receptor blockade (326+/-13 to 330+/-18 microg/L, P=0.86; 30+/-3.5 to 30+/-3.9%, P=0.75, respectively).

CONCLUSIONS

GH receptor blockade in patients with acromegaly lowers IGF-I and 150-kDa IGFBP-3 ternary complex formation. 50 kDa ternary complex formation (not in vivo IGFBP-3 proteolysis) is GH dependent and measurement of 150-kDa ternary complex-associated IGFBP-3 may provide useful information regarding treatment efficacy in patients with acromegaly.

Current concepts in the biochemical assessment of the patient with acromegaly

Biochemical assessment of a patient for acromegaly aims to definitively establish or exclude the presence of growth hormone excess. Whether applied to a newly recognized patient or to detect residual disease after therapy, this assessment is best accomplished by measurement of both the degree of GH suppression after oral glucose administration (OGTT) and levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). When measured properly and compared to a well-characterized, age-adjusted normative database, elevation of the serum IGF-I level is a sensitive and specific indicator for the presence of acromegaly or persistent disease after therapy. The diagnosis of acromegaly can be confirmed by documenting an elevated IGF-I level in combination with failure of GH to suppress after oral glucose to below 0.3 microg/l, when GH is measured with a highly sensitive and specific assay. Persistently, normal IGF-I levels along with a nadir GH <0.3 microg/l should exclude the diagnosis. In assessing disease status during or after treatment, normalization of IGF-I is an essential criterion for biochemical control. It is important to recognize that nadir GH levels are >0.3 microg/l in some healthy subjects, so this criterion alone is not diagnostic of acromegaly. Also, because of heterogeneity of clinically available GH assays, this GH criterion, which was developed with a research assay, may not be applicable to use with all other assays. A nadir GH cut off of 1 microg/l has been found to be reliable for use with some standard immunoassays. It is recommended that glucose-suppressed GH levels be interpreted in conjunction with those of IGF-I and with consideration of conditions other than acromegaly that can alter them. With greater assay standardization and the use of IGF-I levels along with new rigorous criteria for interpretation of GH suppression during a OGTT we can improve our identification of patients with acromegaly in earlier stages of the disease as well as better recognize residual disease during therapy.

Perturbations in adiponectin, leptin and resistin levels in acromegaly: lack of correlation with insulin resistance

BACKGROUND

Insulin resistance, impaired glucose tolerance and type 2 diabetes are common in acromegalic subjects. The mechanism underlying this insulin resistance is unclear.

DESIGN

We investigated the levels of the adipocytokines, resistin, adiponectin and leptin in a group of 18 acromegalic subjects and 18 control subjects matched for age, gender and body mass index.

RESULTS

Here we demonstrate for the first time significant elevation in adiponectin levels in acromegalic subjects compared to control subjects 12.5 +/- 1.2 vs. 8.97 +/- 1.1 mg/l, P = 0.029. The resistin levels were similar in acromegalic subjects and controls; 20.65 +/- 2.99 vs. 19.03 +/- 4.72 micro g/l. No evidence of a correlation between adiponectin and insulin resistance as calculated from HOMA-R was found. No correlation was observed either between adiponectin or resistin levels and GH levels, total IGF-I or free IGF-I levels. Leptin levels were significantly reduced in acromegalic subjects, 8.22 +/- 2.26 vs. 18.3 +/- 4.1 micro g/l, P = 0.004. In control subjects, significant correlations between leptin levels and HOMA-R and between resistin levels and HOMA-R were observed. These relationships were not apparent in acromegalic subjects.

CONCLUSION

From these data we conclude that changes in resistin and adiponectin levels are unlikely to account for the insulin resistance of acromegaly.

Growth hormone receptor antagonists: discovery, development, and use in patients with acromegaly

An understanding of the events that occur during GH receptor (GHR) signaling has facilitated the development of a GHR antagonist (pegvisomant) for use in humans. This molecule has been designed to compete with native GH for the GHR and to prevent its proper or functional dimerization-a process that is critical for GH signal transduction and IGF-I synthesis and secretion. Clinical trials in patients with acromegaly show GHR blockade to be an exciting new mode of therapy for this condition, and pegvisomant may have a therapeutic role in diseases, such as diabetes and malignancy, in which abnormalities of the GH/IGF-I axis have been observed. This review charts the discovery and development of GHR antagonists and details the experience gained in patients with acromegaly.

Gender and age influence the relationship between serum GH and IGF-I in patients with acromegaly

BACKGROUND

In patients with acromegaly serum IGF-I is increasingly used as a marker of disease activity. As a result, the relationship between serum GH and IGF-I is of profound interest. Healthy females secrete three times more GH than males but have broadly similar serum IGF-I levels, and women with GH deficiency require 30-50% more exogenous GH to maintain the same serum IGF-I as GH-deficient men. In a selected cohort of patients with active acromegaly, studied off medical therapy using a single fasting serum GH and IGF-I measurement, we have reported previously that, for a given GH level, women have significantly lower circulating IGF-I.

OBJECTIVE

To evaluate the influence of age and gender on the relationship between serum GH and IGF-I in an unselected cohort of patients with acromegaly independent of disease control and medical therapy.

METHODS

Sixty (34 male) unselected patients with acromegaly (median age 51 years (range 24-81 years) attending a colonoscopy screening programme were studied. Forty-five had previously received pituitary radiotherapy. Patients had varying degrees of disease control and received medical therapy where appropriate. Mean serum GH was calculated from an eight-point day profile (n = 45) and values obtained during a 75-g oral glucose tolerance test (n = 15). Serum IGF-I, IGFBP-3 and acid-labile subunit were measured and the dependency of these factors on covariates such as log10 mean serum GH, sex, age and prior radiotherapy was assessed using regression techniques.

RESULTS

The median calculated GH value was 4.7 mU/l (range 1-104). A significant linear association was observed between serum IGF-I and log10 mean serum GH for the cohort (R = 0.5, P < 0.0001). After simultaneous adjustment of the above covariates a significant difference in the relationship between mean serum GH and IGF-I was observed for males and females. On average, women had serum IGF-I levels 11.44 nmol/l lower than men with the same mean serum GH (P = 0.03, 95% CI 1.33-21.4 nmol/l). Age significantly influenced the relationship and for a given serum GH, IGF-I was estimated to fall by 0.37 nmol/l per year (P = 0.04, 95% CI 0.015-0.72).

CONCLUSIONS

In keeping with previous observations of relative GH resistance in normal and GH-deficient females we have observed lower serum IGF-I levels for equivalent mean serum GH levels in females patients with acromegaly. This gender-dependent difference is independent of disease activity and the use of concomitant medical therapy. Additionally, we have demonstrated that for a given serum GH level, age significantly influences IGF-I concentrations in patients with acromegaly. These data have important implications for the use of serum IGF-I and GH as markers of disease activity in acromegaly.

The IGF-system in healthy pre- and postmenopausal women: relations to demographic variables and sex-steroids

Plasma insulin-like growth factor (IGF)-I, free IGF-I and -II, IGF-binding protein (IGFBP)-1, -2, and -3 together with IGFBP-3 protease activity were measured in 114 postmenopausal and 39 premenopausal healthy women. For each parameter, the mathematical distribution was characterised, and the normal range for pre- and postmenopausal women described, together with correlations to demographic variables and sex-steroids (postmenopausal women). Postmenopausal women had lower levels of plasma IGF-I (P<0.001) and free IGF-I (P<0.001) compared to premenopausal women, while plasma IGFBP-2 (P<0.05) and immunoreactive IGFBP-3 (P<0.001) were higher in postmenopausal women. Free IGF-I (but none of the other parameters) was significantly lower in postmenopausal smokers compared to non-smokers (P<0.05).IGF-I and -II both correlated positively to height (r=0.203, P<0.05 and r=0.198, P<0.05, respectively), while IGF-II correlated positively to weight (r=0.250, P<0.01). Plasma IGF-I correlated positively to androstenedione (r=0.292, P<0.01) and dehydroepiandrosterone sulphate (DHEAS, r=0.202, P<0.05), while a significant positive correlation was observed between IGF-II on the one side and oestradiol (E(2), r=0.227), oestrone sulphate (E(1)S, r=0.238) and androstenedione (r=0.213) on the other side (P<0.05 for all). Our results support a relation between sex-steroids and IGF-I and -II in healthy postmenopausal women. The lower levels of total and free IGF-I in postmenopausal compared to premenopausal women indicate lower bioavailability of this growth factor in elderly females.

A cross-sectional study of IGF-I determinants in women

Evidence is accumulating that elevated circulating insulin-like growth factor I (IGF-I) is related to increased cancer risk. The identification of hormonal, reproductive and lifestyle characteristics influencing its synthesis and bioavailability is of particular interest. Data from 400 women, who served as controls in two case-control studies nested within the same prospective cohort study, were combined. IGF-I, IGF-binding proteins 1, 2 and 3 (IGFBP-1, -2, -3) and insulin were measured in serum samples from all subjects and cotinine in 186 samples. Age appears to be the most important determinant of total IGF-I levels in women. Anthropometric measures, such as body mass index (BMI) or waist-to-hip ratio (WHR) do not seem to influence total IGF-I concentrations in peripheral blood, but may modulate IGF-I bioavailability through insulin-dependent changes in IGFBP-1 and -2 concentrations. Age at menarche, phase of the menstrual cycle at blood draw, parity, menopause, past oral contraceptive or hormone replacement therapy use, and tobacco smoking do not appear to exert an independent effect on IGF-I and its binding proteins. There was some suggestion that regular physical activity may increase total IGF-I and that women with positive family history of breast cancer might have higher IGF-I levels than those without such diagnosis in their relatives.

Gender and age in the biochemical assessment of cure of acromegaly

The principal biochemical criteria for cure in acromegaly are normalization of both glucose-suppressed GH levels and IGF-I levels. As we have reported previously, measurement of GH by highly sensitive assay in conjunction with IGF-I levels has led to a re-appraisal of "normal" GH suppression criteria during an OGTT in subjects with acromegaly. In some patients with active acromegaly, glucose-suppressed GH levels as measured by highly sensitive assay are much lower than could previously be appreciated with less sensitive GH assays and some other patients in apparent remission have subtle abnormalities of GH suppression. A question to arise is whether gender differences in glucose-suppressed GH levels as found by others in young healthy subjects should be considered in our interpretation of OGTT criteria for cure in acromegaly. Therefore, we have evaluated parameters of GH secretion in a larger number of subjects from our cohort of postoperative patients with acromegaly and in healthy subjects in order to determine if gender or age associated differences in these parameters exist. Ninety-two subjects with acromegaly (49 men, 43 women) and 46 age-matched healthy subjects (26 men, 20 women) were evaluated with baseline GH and IGF-I levels and nadir GH levels after a 100 g. OGTT. GH was assayed by highly sensitive IRMA (DSL). Basal GH levels were higher in female than in male healthy subjects, but the fall in GH from baseline (% suppression) was also greater in females resulting in no significant difference in mean nadir GH levels in female vs. male healthy subjects (0.09 vs. 0.08 microg/L). In the subjects with acromegaly, there were no significant gender differences in basal, %GH suppression or nadir GH levels. Basal and nadir GH levels correlated significantly only in subjects with active disease (r=0.84, p<.0001). Similarly, IGF-I levels correlated significantly with basal (r=0.573, p=.0012), and nadir (r=.702, p<.0001) GH levels only in subjects with active disease. Gender differences in IGF-I levels were not apparent in any group of subjects. As expected, IGF-I levels declined with age in those groups of subjects with normal IGF-I levels. Nadir GH levels did not vary with age. In conclusion, we have not found significant gender or age-related differences in nadir GH levels and thus our data does not support separate OGTT criteria for cure in men and women with acromegaly.

Long-term follow-up results of postoperative radiotherapy in 36 patients with acromegaly

In acromegaly, pituitary irradiation is a slow, but effective, intervention in decreasing GH concentration. Few studies addressing the outcome of radiotherapy have used the currently accepted strict criteria for remission in the analysis of data. These studies report a low percentage of remission after radiotherapy. Doubt has especially been raised as to whether radiotherapy is effective in normalizing serum insulin-like growth factor (IGF)-I concentration. We analyzed the long-term follow-up data of postoperatively administered radiotherapy in 36 patients with postoperative persistent acromegaly, using both the normalization of GH suppression during oral glucose loading (GTT) and the normalization of IGF-I concentration as criteria for remission. Before radiotherapy, mean suppressed GH was 9.8 +/- 1.9 mU/L (n = 31), and mean IGF-I concentration was 44.3 +/- 3.9 nmol/L, equivalent to + 4.76 +/- 0.78 age-related IGF-I SD score (n = 13). The median radiation dose was 40 Gray (range, 25-50 Gray). At 5, 10, and 15 yr follow-up, 18 out of 30 patients (60%), 23 out of 31 patients (74%), and 16 out of 19 patients (84%), respectively, achieved normal serum IGF-I concentration. At the last assessment of all patients, after a mean follow-up period of 139 +/- 12 months, 27 out of 36 (75%) patients had a normal IGF-I concentration without additional medication, whereas 5 patients still required treatment with octreotide. Remission, as judged by normalization of GH suppression during GTT, was documented in 65% of patients from 2-5 yr after radiotherapy (n = 34); in 69% of patients, up to 10 yr after radiotherapy (n = 29); and in 71% of patients, up to 15 yr post irradiation (n = 17). At the latest assessment, a mean of 125 +/- 11 months after radiotherapy, 71% of patients (n = 35) were in remission, as defined by normal suppression of serum GH during GTT. Remission, as judged by normalization of both GTT and IGF-I, was found in 40% of patients 3-5 yr after radiotherapy (n = 30); in 61% of patients, 6-10 yr after radiotherapy (n = 28); in 65%, after 11-15 yr after radiotherapy (n = 17); and in 63% of patients, at the end of the follow-up period (n = 35). Substitution of one or more pituitary hormone deficiencies was required in 11% of patients postoperatively; in 29%, 5 yr after radiotherapy; in 54%, 10 yr after radiotherapy; and in 58%, more than 15 yr after radiotherapy. Our findings support the use of radiotherapy as an effective intervention in the treatment of residual clinical activity of disease after surgery for acromegaly.

Clinical characteristics of acromegaly in Hong Kong

This study analyses the clinical characteristics of acromegalic patients in Hong Kong. All patients with acromegaly under follow up in Prince of Wales Hospital, Hong Kong between January 1984 and December 1992 were reviewed retrospectively. Detailed hospital notes were available for review in 28 out of 34. Of the 28 patients with full records available, 27 were Chinese and 1 was Nepalese. There were 8 (28.6%) males and 20 (71.4%) females. The mean age (+/- SD) at presentation was 51.2+/-16.8 years (range: 28 to 84 years) (male, 49.9+/-13.9 years [range: 28-66]; female, 51.7+/-18.1 years [range: 31-84]; p-value: NS). The commonest mode of presentation (n=22, 78.6%) was clinical suspicion by medical staff during consultation for other conditions, acromegaly being later confirmed. The estimated duration of symptoms, before diagnosis, was 14 years (range: 1 to 30 years). CT scan imaging of the pituitary gland showed that 12 patients (42.9%) had pituitary macro-adenomas (> or =1 cm), 3 (10.7%) had micro-adenomas (<1 cm), 6 (21.4%) had normal imaging, 1 (3.6%) had an empty sella and 6 (21.4%) had suspicious but inconclusive lesions in the pituitary gland. Surgery was offered as initial treatment to all patients. 4 to 6 weeks after surgery, if the maximal growth hormone response following glucose loading exceeded 10 microg/L, radiotherapy was offered. Of the 28 patients, 13 received surgery and radiotherapy, 2 surgery only, 4 radiotherapy only, 4 no treatment and 5 defaulted. At presentation, 50% had some abnormality of glucose tolerance. The mean early morning fasting baseline growth hormone was 52.8+/-37.0 microg/L (mean +/- SD, median: 48.1 microg/L) and the maximal growth hormone response during an extended oral glucose tolerance test was 63.2+/-34.9 microg/L (median: 61.3 microg/L). Forty five percents of patients had a maximal growth hormone response exceeding 60 microg/L. Of the 19 patients who underwent surgery and/or radiotherapy, 15 had their pituitary function reassessed 6 months after intervention. Their early morning fasting growth hormone and maximal growth hormone response in an extended oral glucose tolerance test were 21.3+/-25.8 and 35.4+/-37.5 microg/L, respectively. In conclusion, acromegaly in Hong Kong has an estimated annual incidence of 3.8 per million. There is a female preponderance, tendency to late presentation (>10 years) and low number of large tumors. Up to 80% were referred following observer suspicion.

Outpatient assessment of residual growth hormone secretion in treated acromegaly with overnight urinary growth hormone excretion, random serum growth hormone and insulin like growth factor-1

OBJECTIVE

To assess the outpatient investigations, overnight urinary growth hormone (uGH) excretion, random serum GH and insulin like growth factor 1 (IGF-1), and GH indices from the oral glucose tolerance test (OGTT) (fasting, nadir and mean GH), as measures of mean GH secretion in treated acromegaly, in comparison with a GH day series, which served as a gold standard.

DESIGN

Prospective cross-sectional study, with patients admitted to a metabolic ward for the following investigations: random GH, IGF-1, 6 point GH day series (day 1), 9 h timed overnight uGH excretion, OGTT with GH response (day 2). Agreements between the mean GH during the day series and the other outcome measures, and the diagnostic performance of the latter, for the presence or absence of active acromegaly (mean GH during day series > or = 5 or < 5 mU/l, respectively) were determined.

PATIENTS

26 patients with treated acromegaly (11 with inactive acromegaly off drug therapy).

MEASUREMENTS

Serum GH and uGH were measured by immunoradiometric assays and IGF-1 by radioimmunoassay.

RESULTS

Agreements with the mean GH during the day series were perfect for the nadir GH during the OGTT with a 2 mU/l cutoff (Cohen's kappa (kappa) = 1, P < 0.00001), almost perfect for the fasting and mean GH throughout the OGTT (both kappa = 0.92, P < 0.0001) and random GH (kappa = 0.85, P < 0.0001), and substantial for the nadir GH with a 5 mU/l cutoff (kappa = 0.77, P < 0.0001), IGF-1 (kappa = 0.62, P < 0.001) and overnight uGH excretion (kappa = 0.61, P = 0.002). Nadir GH with a 2 mU/l cutoff was completely accurate for diagnosing the presence or absence of active acromegaly (positive and negative predictive values (% +/- standard error percentage) 100 +/- 8% and 100 +/- 10%). None of the outpatient tests used alone was an adequate diagnostic test (positive and negative predictive values: overnight uGH excretion -86 +/- 10% and 75 +/- 13%; random GH -100 +/- 11% and 85 +/- 11%; IGF-1 -92 +/- 10% and 71 +/- 13%) and so combinations of tests were assessed. The best was overnight uGH excretion plus random GH (positive and negative predictive values 88 +/- 9% and 100 +/- 12%). Using all three outpatient investigations, the positive predictive value of three raised results was 100 +/- 13%.

CONCLUSIONS

In treated acromegaly, residual GH secretion can be reliably assessed with the OGTT, using standard diagnostic criteria. It can also be assessed on an outpatient basis with overnight uGH excretion and random GH, as direct measures, and IGF-1. If these are all normal, active acromegaly is excluded. Three raised results denote active acromegaly, and one or two raised results would need further investigation with a GH day series.

Serum free IGF-I, total IGF-I, IGFBP-1 and IGFBP-3 levels in an elderly population: relation to age and sex steroid levels

BACKGROUND

Most previous studies concerning the relationship between IGF-I and age used assays measuring total IGF-I. Although free IGF-I is considered of greater biological relevance, little is known about its relationship with sex steroids levels in elderly healthy subjects.

MEASUREMENTS

In a cross-sectional study of 218 healthy people (103 men, 115 women) aged 55-80 years we measured serum total and free IGF-I, IGFBP-1 and IGFBP3 levels and sex steroids. Free androgen index and free oestradiol index were used as an indicator for free oestradiol and free testosterone levels, respectively.

RESULTS

Free IGF-I levels did not decline with age in the whole study population. Free IGF-I levels even increased in individuals above 70 years of age in comparison to those aged between 55 and 70 years (mean +/- SE 0.106 +/- 0.007 nmol/l vs. 0.086 +/- 0.004 nmol/l, P = 0.009). Total IGF-I and IGFBP-3 decreased with age (r = -0.20, P = 0.005 and r = -0.24, P = 0.001, respectively). Total IGF-I levels were positively related with free oestrogen index in both sexes. Free IGF-I did not relate to free oestrogen or androgen index. In women only, free IGF-I was related positively with DHEAS while IGFBP-1 was inversely correlated with DHEAS.

CONCLUSIONS

Free IGF-I levels do not decrease with age and are even higher in individuals above 70 years. There was no relationship between free IGF-I and free androgen or oestrogen index in either gender. We hypothesize that higher free IGF-I levels in older persons may be the consequence of selective survival in the cohort: subjects with high free IGF-I levels may live longer. The absence of a relationship between free IGF-I levels and free androgen and oestrogen indices suggests that there is no direct interaction between the biological activity of circulating IGF-I levels and sex hormone production in a healthy ageing population.

Effect of chronic treatment with octreotide nasal powder on serum levels of growth hormone, insulin-like growth factor I, insulin-like growth factor binding proteins 1 and 3 in acromegalic patients

Octreotide nasal powder is a delivery system of the somatostatin analogue developed to overcome the inconvenience of repeated subcutaneous administrations. Eight patients with clinically active acromegaly were treated for three months with octreotide nasal powder which was administered at the initial dosage of 0.125 mg tid, doubling the dosage up to 2 mg tid in order to obtain a mean GH value below 5 micrograms/l during 8 daytime hours. In 4 of these patients, treatment was prolonged till the sixth month. Blood samples were taken on days 15, 29, 43, 55, 90, 120, 150, 180 for GH, IGF-I, IGFBP-3, IGFBP-1 and insulin measurements. Before treatment, mean daytime GH and morning IGF-I serum levels were both increased but not correlated with each other. Serum IGFBP-3 levels were higher than normal and positively correlated with those of GH, IGF-I and insulin. Insulin levels were elevated and positively correlated with those of GH but not with those of IGF-I and IGFBP-1. Serum IGFBP-1 levels were in the low normal range and not correlated with any of the other parameters. Treatment with octreotide nasal powder induced in all patients a marked decrease of GH which lowered below 5 micrograms/l in 7/8 patients and IGF-I levels, which fell within the normal range in 1 patient. Serum IGFBP-3 and insulin concentrations decreased by 26% and 71%, respectively, and those of IGFBP-1 underwent an only transient increase in 5/8 patients. Opposite changes of insulin and IGFBP-1 levels, with a decrease of the former followed by an increase of the latter were noted during the 8 hours following an octreotide nasal insufflation. During chronic octreotide treatment, positive correlations were found between GH and IGF-I, GH and IGFBP-3, IGF-I and IGFBP-3, insulin and IGFBP-3 and insulin and IGF-I. An improvement of the clinical picture was registered in all patients after a few days of octreotide nasal powder administration. Treatment was well tolerated, with only mild side effects and no significant changes in the nasal mucosa, and the patients' compliance was excellent.

Nocturnal monitoring of growth hormone, insulin, C-peptide, and glucose in patients with acromegaly

Circulating growth hormone, insulin, C-peptide, and glucose levels were compared during the sleep state in adults with acromegaly and healthy control subjects. Growth hormone secretion was episodic in both groups, with the sleep-related growth hormone peak noticeably absent in the acromegalic subjects. The mean nocturnal plasma insulin concentration was greater in the acromegalics. There was no significant difference in the C-peptide between the two groups. Insulin and glucose levels did not show an early morning rise in either acromegalics or healthy subjects. The authors conclude that there is a marked difference in the circulating levels of growth hormone and insulin between the acromegalic and the healthy groups during the sleep state, and there is no sleep-related nocturnal growth hormone peak in the acromegalic subjects. The hyperinsulinism of patients with acromegaly cannot be attributed to excess secretion of insulin.

Clinical features and differential diagnosis of pituitary tumours with emphasis on acromegaly

Pituitary adenomas are frequently encountered, benign intracranial tumours. Clinically classified according to their capacity to produce and secrete hormones, pituitary tumours are diagnosed from the clinical manifestations and biochemical findings of specific pituitary hormone overproduction or of impaired pituitary function due to pressure on normal pituitary cells, the pituitary stalk or the hypothalamus. Additionally, the tumour may result in neurological manifestations due to its effect as an intracranial space-occupying lesion. Pituitary adenomas may present acutely with pituitary apoplexy after intrapituitary haemorrhage or infarction. The subsequent hypofunction of the pituitary with concomitant neurological sequelae of an expanding intracranial mass are often associated with excruciating headache, diplopia and visual field defects. Gradually developing neurological deficits or secondary endocrine failure over several years may precede the recognition of non-secretory tumours (30-40% of pituitary adenomas) as well as some of the hormone-producing adenomas, especially when they expand beyond the confines of the sella turcica. Asymptomatic masses occur in the pituitary in 5-27% of unselected autopsy series. About 10-20% of pituitaries imaged as part of a brain study contain lesions 'consistent with a pituitary adenoma', with about half being pituitary adenomas ('incidentalomas'). Many advocate screening such cases for a wide spectrum of pituitary function abnormalities. Clinical judgement should be utilized to determine the extent of the work-up and the frequency of follow-up. Acromegaly, a clinical syndrome caused by excess growth hormone secretion, accounts for one-sixth of resected pituitary tumours. This disorder leads to chronic progressive disability and a shortened life span, with approximately 50% of untreated acromegalic patients experiencing premature death. The prevalence of acromegaly has been estimated to range from 50 to 70 per million, with the age of diagnosis usually between the third and fifth decades. Conditions associated with acromegaly include glucose intolerance, diabetes mellitus, lipid abnormalities, cholelithiasis, goitre, and hyperthyroidism, respiratory complications, hypertension, cardiovascular disease, and calcium metabolism abnormalities. An association between acromegaly and cancer, especially of the colon, is now recognized. Epidemiological series have indicated that cancer of the colon, breast and other types of malignancy are a cause of death with increased frequency in acromegalics compared with expected rates. Hypopituitary symptoms secondary to the mass effect of macroadenomas in acromegalic patients are common. Among premenopausal women, menstrual irregularities and galactorrhoea have been reported in 40-70%, while more than half of the men complain of impotence and decreased libido.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessment of GH status in acromegaly using serum growth hormone, serum insulin-like growth factor-1 and urinary growth hormone excretion

OBJECTIVE

It is still not clear what is the most suitable method for monitoring progress of acromegaly. The aim of this study was to assess the relative merits of serum GH, serum IGF-I and urinary GH (uGH) excretion in the follow-up of acromegalic subjects.

SUBJECTS AND METHODS

Thirty-six acromegalic patients each had a GH day series performed consisting of five serum GH measurements, together with an estimate of serum IGF-I and uGH. The first sample taken for serum GH was fasting (basal) whilst the third (1430h) was arbitrarily chosen as a random value. uGH was measured from two overnight collections and the mean value used for subsequent data analysis.

MEASUREMENTS

Serum GH and IGF-I were measured by radioimmunoassay whilst uGH was estimated by an immunoradiometric assay using commercially available reagents.

RESULTS

There is a highly significant linear correlation between serum GH and IGF-I following log transformation of these two variables (r = 0.85; P < 0.0001). Analysis of the raw data shows that the relation is in fact curvilinear rendering IGF-I less useful as a surrogate for integrated GH secretion at high levels of serum GH. There is a strong linear correlation between both a singleton basal serum GH and uGH (r = 0.78; P < 0.001) and the mean of five measurements (day series) and uGH (r = 0.81; P < 0.0001). Both uGH and IGF-I are excellent predictors of those patients with persistent elevation of serum GH, identifying 95 and 96% respectively with serum GH > 5mU/l. We have identified a number of patients, however, with persistent elevation of IGF-I in the presence of serum GH < 5mU/l and normal uGH. Until the significance of these findings with respect to long-term outcome is known, serum GH should continue to be used in the follow-up of these patients. An alternative, which reflects integrated overnight GH secretion, is uGH which is convenient and easy to collect as an outpatient and correlates strongly with serum GH.

CONCLUSION

Acromegalic patients can be conveniently followed on an outpatient basis using a combination of uGH and serum IGF-I. Measurements of serum GH can be reserved for those with discrepant results.

Relations between sex hormones, sex hormone binding globulin, insulin-like growth factor-I and insulin-like growth factor binding protein-1 in post-menopausal breast cancer patients

OBJECTIVE

Oestrogens, androgens and anti-endocrine drugs such as tamoxifen and aminoglutethimide influence plasma insulin-like growth factor-I (IGF-I). IGF-I, in turn, has been found to stimulate the peripheral aromatase in vitro. The aim of this study was to examine relations between sex hormones, IGF-I and insulin-like growth factor binding protein-1 (IGFBP-1) in post-menopausal women with breast cancer.

DESIGN

To measure plasma sex steroids, sex hormone binding globulin (SHBG), IGF-I, IGFBP-1, insulin and urinary oestrogen metabolites in post-menopausal women with breast cancer not receiving any endocrine therapy.

PATIENTS

Thirty-two patients had fasting blood samples obtained between 0800 and 1000 h. A sub-group of 10 patients had 24-hour urine oestrogen metabolites determined.

MEASUREMENTS

Plasma steroids and proteins were measured by radioimmunoassays. Urinary oestrogens were measured by GC-MS.

RESULTS

SHBG correlated negatively with plasma androstenedione (P < 0.001), insulin (P < 0.001), IGF-I, height and plasma oestrone sulphate (P < 0.025 for all), but positively with plasma IGFBP-1 (P < 0.025). IGFBP-1 correlated negatively with IGF-I (P < 0.001) and the testosterone/SHBG ratio (P < 0.05). Neither IGF-I nor IGFBP-1 correlated with any of the plasma or urinary sex hormones or with the oestrone/androstenedione and oestradiol/testosterone ratios. Multivariate analysis revealed plasma SHBG to correlate positively with IGFBP-1 (P = 0.029) and negatively with insulin (P = 0.031). Plasma IGFBP-1 correlated negatively with IGF-I (P < 0.0001) but not with insulin.

CONCLUSION

Our results do not suggest any influence of plasma sex steroids in physiological concentrations on IGF-I or IGFBP-1 in post-menopausal breast cancer patients, nor do they indicate IGF-I at physiological concentrations influences the ratios between plasma oestrogens and their androgen precursors.

Determinants of clinical outcome and survival in acromegaly

OBJECTIVE

The extent to which treatment modifies the excess in morbidity and mortality in acromegaly remains uncertain. This study investigates the determinants of final outcome following therapy for acromegaly.

DESIGN

A retrospective analysis of patients treated at the Departments of Endocrinology and Neurosurgery, Auckland Hospital, New Zealand.

PATIENTS

One hundred and fifty-one patients (63 females and 88 males) with acromegaly or gigantism treated between the years 1964 and 1989. The mean duration of follow-up was 12 years (median 11 years).

MEASUREMENTS

Patients had their age, estimated duration of symptoms preceding diagnosis, serum GH at diagnosis, presence of diabetes mellitus, cardiovascular disease, hypertension and/or osteoarthritis at diagnosis and the last known serum GH documented. The final outcome at the time of study was graded under three classes: dead (n = 32), those with major complications (n = 47) and those with minor/no complications (n = 67).

RESULTS

The mean age at diagnosis of acromegaly was 41 years and the average estimated duration of symptoms prior to diagnosis was 7 years, with older patients showing longer duration of symptoms preceding diagnosis (P = 0.0002). Final outcome (dead, alive with major complications, alive and well) was significantly worse in those with older age at diagnosis (P = 0.008), longer duration of symptoms before diagnosis (P = 0.03) and higher GH at last follow-up (P = 0.0001). In multivariate analysis, survival was significantly influenced by the last known GH (P = 0.0001), presence of hypertension (P = 0.02) or cardiac disease (P = 0.03) at diagnosis, and duration of symptoms prior to diagnosis (P = 0.04). Survival in the acromegalic group, irrespective of treatment, was reduced by an average of 10 years compared with the non-acromegalic population.

CONCLUSIONS

Acromegaly has a significant adverse effect on well-being and survival. The predominant determinant of outcome is the final serum GH level following treatment.

Insulin-like growth factors (IGF)-I and -II and IGF binding protein-1, -2, and -3 in patients with acromegaly before and after adenomectomy

The interrelationship between insulin-like growth factors (IGFs) and their major binding proteins (IGFBPs) as a function of disease activity in acromegaly has not previously been prospectively evaluated. We studied basal and insulin-stimulated serum levels of IGF-I and -II and IGFBP-1, -2, and -3 in six acromegalic patients before and 2 months after successful adenomectomy compared with a group of sex- and age-matched healthy, untreated subjects. All were studied postabsorptively (11 AM) and at the end of a 2-hour euglycemic glucose clamp (0.4 mU insulin/kg x min). Serum IGF-I levels (mean +/- SE) were elevated in acromegaly but were normalized following therapy (basal state IGF-I [micrograms/L], 857 +/- 119 [active] v 255 +/- 65 [postoperative] v 190 +/- 20 [control]). Serum IGF-II levels did not change following therapy and were similar to those of the control group. IGF levels did not change during the clamp. Serum IGFBP-3 levels were elevated in active acromegaly, but were normalized after therapy (basal state IGFBP-3 [micrograms/L] 6,983 +/- 612 [active] v 3,939 +/- 504 [postop] v 3,358 +/- 125 [control]). The molar ratio of (IGF-I+IGF-II): IGFBP-3 was similar in all studies. Serum IGFBP-1 interacted significantly with time in all studies, exhibiting a gradual decrease in the basal state and ensued by further suppression during the clamp. Insulin and IGFBP-1 correlated inversely in the pooled data and in the acromegalic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

The impact of obesity, fat distribution, and energy restriction on insulin-like growth factor-1 (IGF-1), IGF-binding protein-3, insulin, and growth hormone

The aim of this study was to characterize the association between serum insulin-like growth factor-1 (IGF-1) and obesity, as well as fat distribution, before and during moderate energy restriction (1,200 kcal/d). In 51 females and nine males having a body mass index (BMI) between 27 and 39 kg/m2, relationships between serum IGF-1, IGF-binding protein-3 (IGFBP-3), insulin, growth hormone (GH), blood glucose, and anthropometric measurements of body fat were examined. The patients were studied before treatment and again after 8 and 16 weeks of dieting. Visceral adipose tissue (AT) was estimated by anthropometric computed tomography (CT)-calibrated equations. In females, IGF-1 was inversely associated with the abdominal sagittal diameter (SagD) and with the visceral AT (r = -.41, P = .006). No significant correlations were found between IGF-1 and BMI or other indices of adiposity. Weight loss caused a temporary increase in IGF-1 concentrations (P = .03) and continued decrements in blood glucose levels (P = .0004 at 16 weeks). A statistically significant inverse correlation between IGF-1 and blood glucose levels was present before (r = -.30, P = .02) and after 8 (r = -.37, P = .007) and 16 (r = .02, P = .02) weeks of dietary treatment. Both serum IGF-1 and insulin levels were positively correlated with serum IGFBP-3 levels (r = .34, P = .009 and r = .34, P = .008, respectively). We conclude that IGF-1 levels in obese females reflect the intraabdominal fat mass rather than obesity per se. IGF-1 and blood glucose levels are inversely correlated in obesity before and during energy restriction.

Long-term hormone replacement treatment in menopause: new choices, old apprehensions, recent findings

In recent years there has been an increase in the use of parenteral oestradiol as an alternative to the conventional oral preparations used in hormone replacement treatment (HRT) in menopause, such as conjugated equine oestrogens (CEE). The latter have been subject in the past to apprehensions, partly due to misunderstanding and oversimplification but also in relation to problems that have arisen during the history of HRT, for example the increase in endometrial cancer risk deriving from the use of non-progestogen-opposed treatment. However, confidence in long-term HRT comes from the epidemiological findings, which refer mainly to the use of oral CEE unopposed by progestogen: a reduced risk of osteoporotic fractures and of cardiovascular disease, and a very limited risk of breast cancer. Oral oestrogens produce marked hepatocellular effects. These effects are, on the whole, favourable from the point of view of cardiovascular risk. In addition, it cannot be excluded that some hepatocellular effects of oral oestrogen, for example increased sex hormone binding globulin levels and reduced circulating insulin-like growth factor I activity, offer protection to the breast. As progestogen supplementation is needed in non-hysterectomized women, priority should be given to preparations, such as progesterone or dydrogesterone, that feature good endometrial activity without opposing oestrogen hepatocellular effects.

Effects of growth hormone and IGF-I on glomerular ultrafiltration in growth hormone-deficient rats

In growth hormone deficient states glomerular filtration rate (GFR) and renal plasma flow rate (RPF) are both reduced. Studies were performed in growth hormone deficient rats to delineate the physiologic mechanisms by which growth hormone and IGF-I contribute to the regulation of glomerular function. Growth hormone deficient dw/dw rats received, for one week, subcutaneous infusions of vehicle, des(1-3)IGF-I or were injected i.m. with recombinant human growth hormone. Subsequent renal micropuncture and clearance studies revealed a low GFR and single nephron GFR (SNGFR) in vehicle treated growth hormone deficient animals. Glomerular function became normal with growth hormone or IGF-I treatment, respectively. Both treatments raised SNGFR by reducing arteriolar resistance and increasing the glomerular ultrafiltration coefficient. Furthermore, the two treatments also increased the glomerular tuft volume and the kidney weight which may contribute to the rise in SNGFR and GFR. It is concluded that, (1) in growth hormone deficiency glomerular function is reduced secondary to a high renal arteriolar resistance and a low ultrafiltration coefficient. Both result from a lack in IGF-I rather than the growth hormone deficiency state per se. (2) The growth hormone-IGF-I axis may contribute to the maintenance and physiologic regulation of GFR.

The regulation of insulin-like growth factor binding protein (IGFBP)-1 during prolonged fasting

OBJECTIVE

Insulin-like growth factor binding protein (IGFBP)-1 levels increase overnight, being inversely related to changes in insulin. With prolonged fasting IGFBP-1 levels increase further. In animal studies high IGFBP-1 levels increase plasma glucose levels possibly by regulating the insulin-like actions of 'bio-available' plasma IGF. Following prolonged fasting, there is an increase in insulin requirement. A proportion of this reversible insulin resistance may be due to inhibitory effects of high IGFBP-1 levels on IGF action. This study examined the regulation of IGFBP-1 in the presence of reversible insulin resistance.

SUBJECTS

Nine normal adult volunteers, seven female and two male (mean age 27.6 +/- SD 2.6 years, range 21.7-46.0 years) of normal body mass index were studied.

METHODS

Subjects fasted from 2200 h day 0 to 0900 h day 3 (59 hours), the fast being completed with a 75-g glucose meal. At least one week later, an 11-hour overnight fast was performed, followed by a repeat glucose meal. Blood samples were taken at regular intervals from 0900 h day 1 and for 5 hours during both glucose meal studies via an indwelling cannula.

MEASUREMENTS

Serum levels of IGFBP-1, insulin, GH, glucose, IGF-I and cortisol were measured at varying intervals during the fast and both glucose meal studies.

RESULTS

Following the initial 11-hour overnight fast IGFBP-1 levels rose from (mean +/- SEM) 32 +/- 5 micrograms/l to reach a maximum of 144 +/- 24 micrograms/l after 32 hours of fasting. IGFBP-1 levels then fluctuated, falling in the morning (93 +/- 8 micrograms/l) and then rising overnight (126 +/- 9 micrograms/l), but not regaining the initial peak levels. The increase of IGFBP-1 from overnight fasting levels was associated with a fall in plasma insulin from 5.7 +/- 0.7 to 2.2 +/- 0.2 mU/l. In comparison, 30 minutes after termination of the fast with the glucose meal, IGFBP-1 levels fell from 120 +/- 11 to 24 +/- 2 micrograms/l within 4 hours. After an overnight fast IGFBP-1 levels fell from 35 +/- 5 to 13 +/- 2 micrograms/l within 3 hours. There was glucose intolerance and increased insulin levels following the glucose meal preceded by the 59-hour fast when compared with the overnight fast. The fall of IGFBP-1 levels after the glucose meal was best expressed, taking into account subject variation, by the following regression equations: Glucose meal preceded by 11-hour fast: log [IGFBP-1] = 1.64-0.255 log [1 h previous insulin] (R2 0.51); Glucose meal preceded by 59-hour fast: log [IGFBP-1] = 1.41-0.265 log [1 h previous insulin] + 0.557 log [current glucose] (R2 0.82).

CONCLUSION

In man, insulin appears to regulate circulating IGFBP-1 levels in all circumstances, this regulation being unaffected by the resistance to insulin action induced by prolonged fasting. The high IGFBP-1 levels were statistically related to the higher glucose levels and may have directly contributed to the increased insulin requirement observed after prolonged fasting.

Elevated plasma insulin-like growth factor binding protein-1 levels in type 1 (insulin-dependent) diabetic patients with peripheral neuropathy

Previous studies have suggested that nerve regeneration may be defective in patients with diabetic polyneuropathy. Since insulin-like growth factor I (IGF-I) has been shown to stimulate nerve regeneration, and IGF binding protein-1 is acutely regulated by plasma insulin we have investigated the relationships between plasma IGF-I, IGFBP-1, glucose and insulin in Type 1 (insulin-dependent) diabetic patients with peripheral polyneuropathy. Plasma samples were taken at hourly intervals over an 11-h period (08.00-19.00 hours) in order to characterise secretory profiles for 15 Type 1 diabetic patients (eight neuropathic and seven non-neuropathic) and eight non-diabetic control subjects. In the non-diabetic subjects, mean plasma IGF-I levels were stable throughout the 11-h period with a range of 97 micrograms/l-169 micrograms/l. In contrast, mean plasma IGFBP-1 levels declined steadily from a high level of 1.99 micrograms/l at 08.00 hours to approximately one half (0.86 microgram/l) at 15.00 hours. Comparison of areas under the curves revealed significant negative correlations between IGFBP-1 and glucose (-0.88, p = 0.01), IGFBP-1 and insulin (-0.75, p = 0.016), and IGFBP-1 and IGF-I (-0.68, p = 0.03). A significant positive correlation was found between insulin and IGF-I (+0.89, p = 0.001). The diabetic patients had markedly elevated plasma IGFBP-1 levels (area under curve, p = 0.01) and lower plasma IGF-I levels (p = 0.033) even though these patients were hyperinsulinaemic throughout the study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin secretion and insulin-like growth factor-I levels in active and controlled acromegaly

OBJECTIVE

We examined the contributions of growth hormone (GH) and insulin-like growth factor-I (IGF-I) to insulin sensitivity and beta-cell function in acromegaly.

DESIGN

A cross-sectional study was used with continuous infusion of glucose with model assessment to determine insulin sensitivity and beta-cell function.

PATIENTS

Ten patients with active acromegaly, seven with controlled disease and 22 normal individuals were studied.

MEASUREMENTS

Glucose and insulin levels were measured fasting and at the end of the one-hour glucose infusion to calculate insulin sensitivity and beta-cell function. Random GH and IGF-I were recorded. Most patients had values of GH taken after a 100-g oral glucose tolerance test and K values from intravenous glucose tolerance tests. RESULTS Patients with active acromegaly had significantly decreased insulin sensitivity compared to the normal population (P less than 0.001), while those with controlled disease did not. There was a significant negative correlation between IGF-I and insulin sensitivity in those with active disease (P less than 0.05). Beta-cell function in both active and controlled patient groups was elevated compared to the normal population (P less than 0.05, P less than 0.01 respectively) and this was significantly related to IGF-I in the active group (P less than 0.05). GH levels did not correlate with fasting insulin, glucose, insulin sensitivity or beta-cell function in either group.

CONCLUSIONS

Patients with active acromegaly have decreased insulin sensitivity and increased beta-cell function that are significantly related to IGF-I but not GH levels. When the disease is controlled, beta-cell function remains elevated but insulin sensitivity improves.

Evaluation of a repeatable depot-bromocriptine preparation(Parlodel LAR) for the treatment of acromegaly

The effectiveness and side effects of a newly developed, repeatable depot-bromocriptine preparation, (Parlodel LAR, depot-bromocriptine), were studied in 7 acromegalic patients. A dose of 100 mg was injected at intervals of 28 days for 4 months, followed by 200 mg for 2 months. GH profiles (14 h) and an oral glucose load (oGTT) were performed prior to each injection. Depot-bromocriptine suppressed the mean serum profile GH concentration to less than 50% of the pretreatment value in 3 out of 7 patients (responders). Normalization of GH secretion was not achieved. During oGTT the mean serum GH concentration declined to 73%, 19% and 56% of the pretreatment value in the three responders (while on depot-bromocriptine 200 mg). IGF-I was reduced to 84% and 65% with 200 mg depot-bromocriptine in 2 GH responders only. No tumour shrinkage was observed in 3 patients with a visible tumor mass in NMR tomography. Side effects consisted of pronounced orthostatic dysregulation, nausea and vomiting on the day of injection in 3/7 patients. These results are comparable to the reported effectiveness and side effects of oral bromocriptine therapy. Depot-bromocriptine may be useful in selected responsive patients, particularly when compliance during oral therapy is a problem.