Monitoring recovery from iron deficiency using total hemoglobin mass.

INTRODUCTION: Using hemoglobin concentration ([Hb]) to diagnose borderline iron deficiency and monitor the progress of its treatment is difficult because of the confounding effects of plasma volume. Because hemoglobin mass (Hbmass) is not affected by plasma volume, it may be a more sensitive parameter. The aim of this study was to monitor Hbmass, iron storage, and maximal oxygen consumption (V˙O2max) during and after oral iron therapy in subjects with severe and moderate iron deficiency. METHODS: Three groups of female recreational athletes were monitored for at least 22 wk, as follows: 1) severe iron deficiency group (SID) (n = 8; ferritin, ≤12 ng·mL), 2) moderate iron deficiency group (MID) (n = 14; ferritin, ≤25 ng·mL), and 3) control group (n = 8; ferritin, >25 ng·mL). Hbmass and iron status were determined before, during, and up to 12 wk after at least 10 wk of oral iron supplementation. In total, five V˙O2max tests were performed before, during, and after the supplementation period. RESULTS: Hbmass increased markedly in the SID group (15.6% ± 11.0%, P < 0.001) and slightly in the MID group (2.2% ± 3.7%, P < 0.05) by the end of the supplementation period and remained at this level for the following 12 wk. [Hb] and Hbmass were similarly affected, but Hbmass was more closely related to mean corpuscular volume and mean corpuscular hemoglobin than [Hb]. The SID group incorporated 534 ± 127 mg of iron into ferritin and hemoglobin, whereas the MID group incorporated 282 ± 68 mg of iron. V˙O2max increased only in the SID group by 0.20 ± 0.18 L·min (P < 0.05) and was closely related to Hbmass (P < 0.01). CONCLUSIONS: Hbmass is a sensitive tool for monitoring recovery from iron deficiency anemia and assessing the effectiveness of iron supplementation in individuals with severe or moderate iron deficiency.

Effect of compression stockings on running performance in men runners.

The purpose of this study was to determine the effect of below-knee compression stockings on running performance in men runners. Using a within-group study design, 21 moderately trained athletes (39.3 +/- 10.9 years) without lower-leg abnormities were randomly assigned to perform a stepwise treadmill test up to a voluntary maximum with and without below-knee compressive stockings. The second treadmill test was completed within 10 days of recovery. Maximum running performance was determined by time under load (minutes), work (kJ), and aerobic capacity (ml.kg.min). Velocity (kmxh) and time under load were assessed at different metabolic thresholds using the Dickhuth et al. lactate threshold model. Time under load (36.44 vs. 35.03 minutes, effect size [ES]: 0.40) and total work (422 vs. 399 kJ, ES: 0.30) were significantly higher with compression stockings compared with running socks. However, only slight, nonsignificant differences were observed for VO2max (53.3 vs. 52.2 mlxkgxmin, ES: 0.18). Running performance at the anaerobic (minimum lactate + 1.5 mmolxL) threshold (14.11 vs. 13.90 kmxh, ES: 0.22) and aerobic (minimum lactate + 0.5 mmolxL) thresholds (13.02 vs. 12.74 kmxh, ES: 0.28) was significantly higher using compression stockings. Therefore, stockings with constant compression in the area of the calf muscle significantly improved running performance at different metabolic thresholds. However, the underlying mechanism was only partially explained by a slightly higher aerobic capacity.

Insulin-like growth factor I (IGF-I) in a growth-enhanced transgenic (GH-overexpressing) bony fish, the tilapia (Oreochromis niloticus): indication for a higher impact of autocrine/paracrine than of endocrine IGF-I.

Several lines of growth hormone (GH)-overexpressing fish have been produced and analysed for growth and fertility parameters. However, only few data are available on the growth-promoting hormone insulin-like growth factor I (IGF-I) that mediates most effects of GH, and these are contradictory. Using quantitative real-time RT-PCR, radioimmunoassay, in situ hybridization, immunohistochemistry, and radiochromatography we investigated IGF-I and IGF binding proteins (IGFBPs) in an adult (17 months old) transgenic (GH-overexpressing) tilapia (Oreochromis niloticus). The transgenics showed an around 1.5-fold increase in length and an approximately 2.3-fold higher weight than the non-transgenics. Using radioimmunoassay, the serum IGF-I levels were lower (6.22 +/- 0.75 ng/ml) in transgenic than in wild-type (15.01 +/- 1.49 ng/ml) individuals (P = 0.0012). Radioimmunoassayable IGF-I in transgenic liver was 4.2-times higher than in wild-type (16.0 +/- 2.21 vs. 3.83 +/- 0.71 ng/g, P = 0.0017). No hepatocytes in wild-type but numerous hepatocytes in transgenic liver contained IGF-I-immunoreactivity. RT-PCR revealed a 1.4-times higher IGF-I mRNA expression in the liver of the transgenics (10.51 +/- 0.82 vs. 7.3 +/- 0.49 pg/microg total RNA, P = 0.0032). In correspondence, in situ hybridization showed more IGF-I mRNA containing hepatocytes in the transgenics. A twofold elevated IGF-I mRNA expression was determined in the skeletal muscle of transgenics (0.33 +/- 0.02 vs. 0.16 +/- 0.01 pg/microg total RNA, P < 0.0001). Both liver and serum of transgenics showed increased IGF-I binding. The increased IGFBP content in the liver may lead to retention of IGF-I, and/or the release of IGF-I into the circulation may be slower resulting in accumulation of IGF-I in the hepatocytes. Our results indicate that the enhanced growth of the transgenics likely is due to enhanced autocrine/paracrine action of IGF-I in extrahepatic sites, as shown here for skeletal muscle.

Hypoglycemia due to paraneoplastic secretion of insulin-like growth factor-I in a patient with metastasizing large-cell carcinoma of the lung.

CONTEXT: Nonpancreatic tumors may cause recurrent hypoglycemia known as nonislet cell tumor hypoglycemia. It is due to overproduction and secretion by the tumor of incompletely processed IGF-II, termed big IGF-II. We recently identified a patient with recurrent hypoglycemia and low insulin, but without elevated big IGF-II. Multiple small lung nodules were detected by computed tomography scan. An undifferentiated large-cell carcinoma was diagnosed from an axillary lymph node metastasis. OBJECTIVE: The objective was to investigate whether the patient's hypoglycemia was due to excessive IGF-I production by the tumor. METHODS: Serum IGF- I and IGF-II, insulin, and GH were measured by RIA; the distribution of IGFs between IGF binding protein complexes in serum was analyzed after neutral gel filtration. Tissue IGF-I was identified by immunohistochemistry and in situ hybridization, and by RT-PCR after RNA extraction. RESULTS: Total and free serum IGF-I, but not total, free, and big IGF-II, was increased, and the IGF-I content of the two IGF binding protein complexes was elevated. Immunohistochemistry demonstrated IGF-I peptide in situ hybridization IGF-I mRNA in the lymph node metastasis. Combined GH/glucocorticoid treatment prevented hypoglycemia, but did not lower IGF-I. After chemotherapy with carboplatinum/etoposide, the lung nodules largely regressed, and serum IGF-I and the IGF-I content of the two binding protein complexes became normal. Hypoglycemia did not recur despite discontinuation of GH/glucocorticoid treatment. CONCLUSION: Our findings are compatible with a new form of tumor hypoglycemia caused by circulating tumor-derived IGF-I.

Effect of thyroxine replacement on serum IGF-I, IGFBP-3 and the acid-labile subunit in patients with hypothyroidism and hypopituitarism.

OBJECTIVE: To describe the effect of T4 replacement in patients with primary and central hypothyroidism on components of the IGF binding protein complex: IGF-I, the acid-labile subunit (ALS) and IGFBP-3. PATIENTS AND METHODS: We determined IGF-I, ALS and IGFBP-3 (by 125I-IGF-II ligand blots and immunoblots) in serum of 19 patients with primary and 11 patients with central hypothyroidism. RESULTS: Mean (+/- SD) free T4 (fT4) increased from 4.4 +/- 2.4 pmol/l at baseline to 18.6 +/- 5.2 pmol/l following T4 therapy. In patients with primary hypothyroidism, IGF-I concentrations increased from 101 +/- 57 to 158 +/- 60 microg/l (P < 0.001) and ALS from 12.6 +/- 4.7 to 15.6 +/- 5.2 mg/l (P = 0.001). IGFBP-3 levels (in arbitrary units, AU), assessed by 125I-IGF-II ligand blot and by Western blot (the intensity of the 45/42-kDa doublet following T4 replacement defined as 1 AU) increased from 0.74 +/- 0.47 to 1 (P = 0.029) and from 0.76 +/- 0.42 to 1 (P = 0.018), respectively. In patients with hypopituitarism, IGF-I and ALS concentrations increased on T4 therapy from 49 +/- 23 to 97 +/- 36 microg/l (P < 0.001) and from 7.8 +/- 4.1 to 11.0 +/- 2.7 mg/l (P = 0.010), respectively. IGFBP-3 remained unchanged during T4 replacement. CONCLUSIONS: T4 replacement increases the serum levels of IGF-I and ALS in patients with primary as well as central hypothyroidism. IGFBP-3 levels increase in response to T4 replacement in patients with primary hypothyroidism but not in those with central hypothyroidism, suggesting that thyroid hormones increase IGF-I and ALS but not IGFBP-3 in patients with GH deficiency.

Pregnancy-induced changes in insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein 3 (IGFBP-3), and acid-labile subunit (ALS) in patients with growth hormone (GH) deficiency and excess.

BACKGROUND: Under most circumstances with altered growth hormone (GH) secretion, the changes of insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein 3 (IGFBP-3), and acid-labile subunit (ALS) are in parallel. The aim of the present study was to compare the effects of pregnancy in a hypopituitary patient with those of pregnancy in an acromegalic patient on IGF-I, IGFBP-3, and ALS. METHODS AND RESULTS: IGF-I and ALS were low before pregnancy in the hypopituitary patient under glucocorticoid and thyroxine treatment. Gonadotropin treatment allowed her to become pregnant; IGF-I and ALS levels rose in the second half of pregnancy and fell again after delivery. IGF-I concentrations were elevated in the patient with persistent acromegaly before and dropped into the normal range during the first half of pregnancy. In the second half of pregnancy and following delivery, IGF-I levels increased again. IGFBP-3 levels (as assessed by immunoblot analysis as well as by 125I-IGF II ligand blotting) decreased markedly during pregnancy in both patients, suggesting that the placenta rather than pituitary GH regulates IGFBP-3 proteolysis in human pregnancy. The increase of IGF-I (and ALS) during the second half of pregnancy in the individual with pituitary GH deficiency may be attributed to placental GH. The fall of IGF-I (and ALS) into the normal range in the acromegalic patient during the first trimester of pregnancy may be related to decreased production or decreased half-life of these proteins. CONCLUSION: Our data suggest that measures to continuously replace GH or to suppress GH secretion during pregnancy in patients with GH deficiency or excess, respectively, may not be warranted.

Changes in insulin sensitivity induced by short-term growth hormone (GH) and insulin-like growth factor I (IGF-I) treatment in GH-deficient adults are not associated with changes in adiponectin levels.

To test potential effects of altered insulin sensitivity on circulating adiponectin levels, we studied patients with GH deficiency (GHD) undergoing high dose GH and IGF-I treatment in a well-defined short-term setting. This design allowed to exclude confounding effects of GH and IGF-I treatment on body composition. Six patients (three women and three men) with acquired GHD were treated in a randomised cross-over trial with GH (subcutaneous injections of GH 0.03 IU/kg/daily) or IGF-I (continuous subcutaneous infusion of 5 microg/kg/h recombinant IGF-I) for 5 days. Median age of patients was 60 (range 25-72) years, BMI 24.7 (20.7-30.7) kg/m(2), and baseline IGF-I concentration 60 (30-83) microg/L. HOMA scores (to assess insulin sensitivity) at baseline were 0.8 (0.3-11.7) and adiponectin concentrations were 7.0 (2.5-14.8) mg/L. HOMA scores increased rapidly and significantly up to a maximum of 2.7-fold (from baseline) at day 5 of GH treatment and returned promptly to baseline when GH was stopped, while adiponectin serum levels remained within the baseline range throughout the study period. HOMA scores dropped to a nadir of 0.66 from baseline at day 2 of IGF-I treatment whereas adiponectin levels remained within the baseline range. These data suggest that changes in insulin sensitivity (induced by high dose and short-term GH and IGF-I treatment) in patients with GHD are not associated with changes in adiponectin levels.

The effect of hypophysectomy on pancreatic islet hormone and insulin-like growth factor I content and mRNA expression in rat.

The growth arrest after hypophysectomy in rats is mainly due to growth hormone (GH) deficiency because replacement of GH or insulin-like growth factor (IGF) I, the mediator of GH action, leads to resumption of growth despite the lack of other pituitary hormones. Hypophysectomized (hypox) rats have, therefore, often been used to study metabolic consequences of GH deficiency and its effects on tissues concerned with growth. The present study was undertaken to assess the effects of hypophysectomy on the serum and pancreatic levels of the three major islet hormones insulin, glucagon, and somatostatin, as well as on IGF-I. Immunohistochemistry (IHC), in situ hybridization (ISH), radioimmunoassays (RIA), and Northern blot analysis were used to localize and quantify the hormones in the pancreas at the peptide and mRNA levels. IHC showed slightly decreased insulin levels in the beta cells of hypox compared with normal, age-matched rats whereas glucagon in alpha cells and somatostatin in delta cells showed increase. IGF-I, which localized to alpha cells, showed decrease. ISH detected a slightly higher expression of insulin mRNA and markedly stronger signals for glucagon and somatostatin mRNA in the islets of hypox rats. Serum glucose concentrations did not differ between the two groups although serum insulin and C-peptide were lower and serum glucagon was higher in the hypox animals. These changes were accompanied by a more than tenfold drop in serum IGF-I. The pancreatic insulin content per gram of tissue was not significantly different in hypox and normal rats. Pancreatic glucagon and somatostatin per gram of tissue were higher in the hypox animals. The pancreatic IGF-I content of hypox rats was significantly reduced. Northern blot analysis gave a 2.6-, 4.5-, and 2.2-fold increase in pancreatic insulin, glucagon, and somatostatin mRNA levels, respectively, in hypox rats, and a 2.3-fold decrease in IGF-I mRNA levels. Our results show that the fall of serum IGF-I after hypophysectomy is accompanied by a decrease in pancreatic IGF-I peptide and mRNA but by partly discordant changes in the serum concentrations of insulin and glucagon and the islet peptide and/or mRNA content of the three major islet hormones. It appears that GH deficiency resulting in a "low IGF-I state" affects translational efficiency of these hormones as well as their secretory responses. The maintenance of normoglycemia in the presence of reduced insulin and elevated glucagon serum levels, both of which would be expected to raise blood glucose, may result mainly from the enhanced insulin sensitivity, possibly due to GH deficiency and the subsequent decrease in IGF-I production.

Effect of pituitary surgery in patients with acromegaly on adiponectin serum concentrations and alanine aminotransferase activity.

BACKGROUND: Thiazolidinediones increase adiponectin concentrations, improve insulin sensitivity and fatty liver disease (reflected by decreased alanine aminotransferase [ALT] activity) in type 2 diabetes. This study was performed to test the effect of neurosurgery in acromegaly (sharing at baseline insulin resistance but not increased visceral fat with type 2 diabetes) on insulin sensitivity, adiponectin concentrations and ALT activity. METHODS: Sixteen patients with acromegaly undergoing pituitary surgery (and 16 patients with type 2 diabetes treated with pioglitazone) were included. Insulin sensitivity, adiponectin concentrations and ALT activity were determined at baseline and after 4 months. RESULTS: Pituitary surgery in acromegalic patients increased adiponectin concentrations from mean (+/-S.D.) 9.3+/-3.8 to 10.2+/-4.4 mg/L (p<0.05). HOMA scores fell from 6.8+/-4 at baseline to 3.5+/-0.9 following neurosurgery (p<0.005) and ALT activity decreased from median (range) 21 (13-30) to 13 (10-42) U/L (p<0.05). In type 2 diabetics, pioglitazone treatment increased adiponectin concentrations; HOMA scores and ALT activity fell significantly. CONCLUSION: Pituitary surgery in patients with acromegaly led to a marked increase in insulin sensitivity and a slight increase in adiponectin serum concentrations, whereas ALT activity significantly decreased.

Insulin determination by specific and unspecific immunoassays in patients with insulinoma evaluated by the arterial stimulation and venous sampling test.

OBJECTIVE: The aim of this study was to compare insulin concentrations measured by a traditional radioimmunoassay (RIA) and a more specific enzyme-linked immunosorbent assay (ELISA) in blood samples obtained during the arterial stimulation and venous sampling (ASVS) test in patients with insulinoma. DESIGN: Prospective case series. METHODS: In 14 patients with an insulinoma undergoing an ASVS test, blood samples were obtained from the hepatic vein at baseline and 60 s after calcium injection into an artery supplying the tumour and a control artery (supplying pancreatic tissue without tumour). A selective arterial calcium stimulation was performed in five additional patients without evidence for an insulinoma. We measured insulin by a traditional RIA and a specific immunoassay. RESULTS: In patients with insulinoma, insulin concentrations increased between 2.3- and 24.2-fold (median 8.2-fold) when measured by RIA and between 7.3- and 59.4-fold (median 16) when measured by ELISA following calcium injection into the artery supplying the tumour. Following calcium injection into the control artery, insulin concentrations were 0.6 to 1.3 times (median 1.0) the baseline values by RIA and 0.5 to 2.5 times (median 1.1) the baseline values by ELISA. In patients without insulinoma, insulin concentrations increased following calcium stimulation between 0.7- and 2.1-fold (median 1.3-fold) when measured by RIA and between 0.6- and 4.7-fold (median 1.3-fold) when measured by ELISA. CONCLUSIONS: When insulin is measured by specific immunoassays, a higher cut-off (i.e. five- to sixfold increase) rather than the traditional criterion of a twofold increase should be used to localise an insulinoma during the ASVS test. The increase in insulin concentrations following calcium stimulation is significantly higher when insulin is measured by a specific assay compared with results obtained with traditional RIAs.

Up date on IGFBP-4: regulation of IGFBP-4 levels and functions, in vitro and in vivo.

Of the six known high affinity insulin-like growth factor binding-proteins (IGFBPs), IGFBP-4 appears to be unique in that it is the only IGFBP that functions mostly like a traditional binding protein. In this regard, none of the IGF independent effects that have been ascribed for other IGFBPs have been described for IGFBP-4. However, recent in vitro and in vivo studies, in particular the recent identification of pregnancy-associated plasma protein-A as a major IGFBP-4 protease, are consistent with the idea that IGFBP-4 is an extremely important component of IGF system in several tissues including gonads and bone. In this review, we have provided an update on IGFBP-4 research and we have summarized our current understanding of the regulation of levels and actions of IGFBP-4 and proteolytic fragments both in vitro and in vivo.

Assessment of hyperinsulinaemia at the termination of the prolonged fast.

BACKGROUND: Traditional criteria to diagnose hyperinsulinaemic hypoglycaemia are based on insulin measurements by unspecific insulin assays. This study was performed to test whether these traditional criteria can be applied when insulin is measured by specific immunoassays. METHODS: 29 consecutive patients undergoing a prolonged fast were included; 11 patients with insulinoma and 18 healthy individuals. We determined plasma glucose, insulin, C-peptide, proinsulin, and beta-hydroxybutyrate concentrations at the termination of the fast. Insulin was measured by an unspecific radioimmunoassay (RIA) and a specific enzyme-linked immunosorbent assay (ELISA). RESULTS: In 11 insulinoma patients, insulin concentrations at median plasma glucose concentration of 2.1 (range 1.3-2.5) mmol/l were 170 (76-340) pmol/l measured by RIA and 61 (11-156) pmol/l by ELISA. Insulin concentrations measured by RIA confirmed hyperinsulinaemia (i.e., >36 pmol/l, the proposed cut-off value for traditional insulin assays) in all insulinoma patients, whereas insulin concentrations measured by ELISA were <36 pmol/l in four patients. In three insulinoma patients, insulin concentrations measured by ELISA were <18 pmol/l, a proposed cut-off level to diagnose hyperinsulinaemia for specific insulin assays. CONCLUSION: When insulin concentrations are measured by specific immunoassays in patients evaluated for fasting hypoglycaemia, traditional reference values cannot be applied.

Localized insulin-like growth factor I delivery to enhance new bone formation.

Insulin-like growth factor I (IGF I) exerts an important role during skeletal growth and bone formation. Therefore, its localized delivery appears attractive for the treatment of bone defects. To prolong IGF I delivery, we entrapped the protein into biodegradable poly(lactide-co-glycolide) microspheres (PLGA MS) and evaluated the potential of this delivery system for new bone formation in two defect models of ovine long bones, i.e., a 8-mm methaphyseal drill hole and a 10-mm segmental tibia defect. Administration of 100 microg of IGF I in PLGA MS resulted in new bone formation within 3 weeks in the drill hole and bridging of the segmental defect within 8 weeks. The observed increase of 12% newly formed bone in the drill hole defect after 3 weeks was substantial, compared to the measured morphometric bone-to-total area ratio of 31% bone in normal cancellous bone. Bone regeneration was further explored by measuring gene expression of typical markers for local mediators and growth factors by real-time polymerase chain reaction. Inflammation was reduced in presence of IGF I and this in vivo observation was corroborated in vitro by quantifying gene expression of inflammatory proteins and by assessing the activation of the NF-kappaB pathway, playing an important role in the regulation of inflammation. Administration of the IGF I delivery system downregulated inflammatory marker gene expression at the site of bone injury, induced new bone formation and reduced bone resorption, and resulted in bridging of 10-mm segmental tibial defects within 8 weeks.

Pregnancy-associated plasma protein-A is involved in insulin-like growth factor binding protein-2 (IGFBP-2) proteolytic degradation in bovine and porcine preovulatory follicles: identification of cleavage site and characterization of IGFBP-2 degradation.

In mammalian ovaries, terminal follicular growth is accompanied by a decrease in levels of intrafollicular insulin-like growth factor binding protein-2 (IGFBP-2) and IGFBP-4. The decrease in IGFBP-4 is essentially due to an increase in proteolytic degradation by intrafollicular pregnancy-associated plasma protein-A (PAPP-A) in growing healthy follicles. In contrast, the decrease in IGFBP-2 is partly due to a decrease in mRNA expression by follicular cells and also to an increase in IGFBP-2 proteolytic degradation, as previously shown in ewes and sows. In the present work we show that bovine and porcine preovulatory follicular fluid contains a proteolytic activity that degrades IGFBP-2. Bovine and porcine preovulatory follicular fluids contain undetectable levels of native IGFBP-2 as assessed by Western ligand blotting in comparison with the corresponding serum. In contrast, much higher levels of 23- and 12-kDa proteolytic fragments were found by immunoblotting in bovine and porcine preovulatory follicular fluid than in the corresponding serum. Moreover, bovine and porcine preovulatory follicular fluids were able to induce proteolytic degradation of exogenous IGFBP-2, and this degradation was enhanced by insulin-like growth factors. Intrafollicular IGFBP-2 proteolytic activity was surprisingly immunoneutralized in both species by a polyclonal antibody raised against human PAPP-A. In addition, recombinant human PAPP-A (rhPAPP-A) was able to cleave IGFBP-2 between Gln165 and Met166 in vitro, generating 23- and 12-kDa proteolytic fragments. IGFBP-2 was shown to be less sensitive than IGFBP-4 to cleavage by rhPAPP-A in vitro. As in follicular fluid, cleavage of IGFBP-2 by rhPAPP-A was dose-dependently enhanced by IGFs and inhibited by a peptide derived from the heparin-binding domain of IGFBP-5 (P5). Finally, Biacore analysis showed that P5 peptide-induced inhibition of IGFBP-2 cleavage was due to a direct interaction of P5 with PAPP-A rather than with IGFBP-2. Overall, these data show that in bovine and porcine preovulatory follicles, PAPP-A is responsible for IGF-dependent IGFBP-2 degradation. During follicular growth, the increase in IGFBP-2 cleavage by PAPP-A, as well as the decrease in IGFBP-2 expression, are responsible for the decrease in intact IGFBP-2 levels and the increase in IGF bioavailability. In atretic follicles, the increase and decrease in IGFBP-2 and PAPP-A mRNA expression, respectively, as well as the inhibition of PAPP-A activity by heparin-binding domains present in IGFBP-5 or other proteins, might participate in higher IGFBP-2 levels and a decrease in IGF bioavailability.

The somatostatin analog octreotide inhibits GH-stimulated, but not IGF-I-stimulated, bone growth in hypophysectomized rats.

IGF-I mediates growth-promoting actions of GH. In the present study we investigated whether the somatostatin analog octreotide blunts the stimulatory effects of GH and/or IGF-I on bone growth in hypophysectomized rats infused for 6 d with vehicle, GH, or IGF-I. We found that octreotide significantly suppressed the GH-induced rise in liver IGF-I mRNA (-27%) and peptide (-32%) and the serum IGF-I level (-26%) and concomitantly inhibited GH-stimulated, but not IGF-I-stimulated, body weight gain (-31%), tibial epiphyseal width (-14%), and bone growth rate (-24%). Furthermore, octreotide significantly reduced the GH-induced increase in the number of IGF-I immunoreactive chondrocytes in all layers (except in the upper hypertrophic zone) of the tibial growth plate cartilage (P < 0.0001 for stem cell and proliferative zone; P < 0.0005 for lower hypertrophic zone). These findings demonstrate that octreotide does not interfere with IGF-I action, but does interfere with local GH-stimulated IGF-I production in the growth plate. Thus, besides inhibiting pituitary GH secretion, octreotide exerts inhibitory peripheral effects on GH-stimulated longitudinal bone growth.

IGF-I and GH stimulate Phex mRNA expression in lungs and bones and 1,25-dihydroxyvitamin D(3) production in hypophysectomized rats.

OBJECTIVE: X-linked hypophosphatemia, a renal phosphate (Pi)-wasting disorder with defective bone mineralization, is caused by mutations in the PHEX gene (a Pi-regulating gene with homology to endopeptidases on the X chromosome). We wondered whether changes in Phex and neprilysin (NEP) (another member of the family of zinc endopeptidases) mRNA expression could be observed in relation to vitamin D and Pi metabolism during GH- and IGF-I-stimulated growth of hypophysectomized rats. DESIGN: Animals were infused s.c. for 2 days with vehicle, 200 mU (67 microg) GH or 300 microg IGF-I/rat per 24 h. We determined serum osteocalcin and osteocalcin mRNA in bone, Phex mRNA in bone and lungs, serum 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) and serum Pi levels, and renal expression of 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase), of 25-hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) and of the Na-dependent Pi-cotransporter type I and II (Na(d)Pi-I and -II). RESULTS: As compared with vehicle-treated controls, body weight and tibial epiphyseal width significantly increased in GH- and IGF-I-treated animals. Serum osteocalcin and osteocalcin mRNA levels in bone, Phex mRNA in bone and lungs, serum 1,25-(OH)(2)D(3) and renal 1alpha-hydroxylase mRNA rose concomitantly, whereas expression of NEP in lungs was barely affected and renal 24-hydroxylase mRNA decreased. Na(d)Pi-I and -II gene expression in the kidney and serum Pi levels remained unchanged. CONCLUSIONS: Our findings suggest a coordinate regulation of Phex mRNA expression in lungs and bone and vitamin D metabolism during GH- and IGF-I-stimulated growth.