http://repub.eur.nl/res/aut/3312/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/33381/ 2011-07-01T00:00:00Z Context: GH is considered the main regulator of circulating IGF-I. Total (extractable) IGF-I is therefore routinely used for diagnosis of GH deficiency (GHD) and for monitoring treatment. Methods currently used for measurement of circulating total IGF-I may be hampered by interferences of IGF-binding proteins. Recently a kinase receptor activation assay was developed to determine IGF-I bioactivity in human serum. The principle of this assay is based on quantification of IGF-I receptor activation after stimulation with serum in vitro. Objective: The objective of the study was to investigate the diagnostic potential of IGF-I bioactivity in adults with GHD. Design: This was a single-center observational study. Study Participants: Ninety-four GH-untreated patients diagnosed with GHD by GH-provocative tests were included. Main Outcome Measures: IGF-I bioactivity (determined by the IGF-I kinase receptor activation assay) and total IGF-I (determined by immunoassay) were measured in fasting blood samples. Results: IGF-I bioactivity was more frequently below the normal range (<-2 SD) in untreated GH-deficient patients than total IGF-I levels (81.9 vs. 61.7%, respectively), especially in patients older than 40 years of age. IGF-I bioactivity decreased with the duration of GHD, whereas total IGF-I did not. With a decreasing number of additional pituitary deficits, total IGF-I levels more frequently remained within the normal range, whereas the percentage below the normal range was high for IGF-I bioactivity, independent of additional deficits. Conclusion: Determination of IGF-I bioactivity may offer advantages in the evaluation of adult GHD compared with total IGF-I as bioactivity better reflects GHD as defined by GH stimulation tests, especially in subjects older than 40 years of age. Copyright http://repub.eur.nl/res/pub/17896/ 2009-11-27T00:00:00Z Objective: To investigate the effects of unacylated ghrelin (UAG) and co-administration of acylated ghrelin (AG) and UAG in morbid obesity, a condition characterized by insulin resistance and low GH levels. Design and method: Eight morbidly obese non-diabetic subjects were treated with either UAG 200 μg, UAG 100 μg in combination with AG 100 μg (Comb) or placebo in three episodes of 4 consecutive days in a double-blind randomized crossover design. Study medication was administered as daily single i.v. bolus injections at 0900 h after an overnight fast. At 1000 h, a standardized meal was served. Glucose, insulin, GH, free fatty acids (FFA) and ghrelin were measured up to 4 h after administration. Results: Insulin concentrations significantly decreased after acute administration of Comb only, reaching a minimum at 20 min: 58.2 ± 3.9% of baseline versus 88.7 ± 7.2 and 92.7± 2.6% after administration of placebo and UAG respectively (P<0.01). After 1 h, insulin concentration had returned to baseline. Glucose concentrations did not change after Comb. However, UAG administration alone did not change glucose, insulin, FFA or GH levels. Conclusion: Co-administration of AG and UAG as a single i.v. bolus injection causes a significant decrease in insulin concentration in non-diabetic subjects suffering from morbid obesity. Since glucose concentration did not change in the first hour after Comb administration, our data suggest a strong improvement in insulin sensitivity. These findings warrant studies in which UAG with or without AG is administered for a longer period of time. Administration of a single bolus injection of UAG did not influence glucose and insulin metabolism. http://repub.eur.nl/res/pub/28834/ 2008-09-01T00:00:00Z Cushing's disease (CD) is a severe disorder characterized by chronic hypercortisolism due to an ACTH-secreting pituitary adenoma. Transsphenoidal adenomectomy is the treatment of choice in humans with CD, but recurrences occur frequently. Finding an effective and safe medical treatment for CD may improve long-term clinical outcome. The recent demonstration of expression of somatostatin receptor subtypes (mainly sst5) and dopamine receptor subtype 2 (D2) in human corticotroph adenomas offers the possibility for medical treatment of CD with novel somatostatin analogs and dopamine agonists. Investigation of the effects of these drugs is hampered by the low incidence of CD in humans. Interestingly, CD is a frequent disorder in dogs with striking clinical similarities with CD in humans. Therefore, we investigated the expression and functional role of D2and somatostatin receptors in corticotroph adenoma cells from 13 dogs with active CD that underwent therapeutic hypophysectomy and normal anterior pituitary cells from five dogs. Quantitative RT-PCR and immunohistochemistry revealed that both in CD and normal anterior pituitary, sst2was the predominant receptor subtype expressed, whereas D2was modestly expressed and sst5was expressed only at very low levels. In primary cultures of canine adenomas (n = 7), the sst2-preferring agonist octreotide also showed the strongest ACTH-suppressive effects. In conclusion, canine corticotroph adenomas provide an interesting model to study CD, but differences in somatostatin and dopamine receptor expression between humans and dogs should be taken into account when using dogs with CD as a model to evaluate efficacy of novel somatostatin analogs and dopamine agonists for human CD. Copyright http://repub.eur.nl/res/pub/35143/ 2007-11-01T00:00:00Z Ghrelin is produced by the gastrointestinal tract, and its systemic concentrations are mainly regulated by nutritional factors. Our aim was to investigate: 1) endogenous portal and systemic acylated and unacylated ghrelin levels (AG and UAG, respectively); 2) whether an iv glucose tolerance test (IVGTT) modifies AG and UAG; and 3) whether the liver passage plays a role in regulating systemic AG and UAG. To elucidate this, we evaluated the effects of IVGTT or saline injection on endogenous portal and systemic concentrations of glucose, insulin, AG, and UAG in anesthetized fasting rats. Hepatic extraction of insulin, AG, and UAG and the ratio of AG to UAG were also measured. IVGTT suppressed both portal (P < 0.03) and peripheral (P < 0.05) UAG, whereas it only blunted prehepatic, but not peripheral, AG. During fasting, hepatic clearance of UAG was 11%, and it was decreased to 8% by IVGTT. AG was cleared by the liver by 38% but unaffected by glucose. The AG to UAG ratio was higher in the portal than the systemic circulation, both in the saline (P < 0.004) and IVGTT (P < 0.0005) rats. In conclusion, this study shows that: 1) the ratio of AG to UAG is very low in the portal vein and decreases further in the systemic circulation; 2) IVGTT in anesthetized fasting rats inhibits UAG, whereas it only blunts prehepatic, but not systemic, AG; and 3) hepatic clearance of AG is much higher than that of UAG. Thus, our results suggest that peripheral AG metabolic regulation and action are mainly confined within the gastrointestinal tract. Copyright http://repub.eur.nl/res/pub/10312/ 2004-01-01T00:00:00Z Treatment with the somatostatin receptor (sst) subtype 2 predominant analogs octreotide and lanreotide induces clinical and biochemical cure in approximately 65% of acromegalic patients. GH-secreting pituitary adenomas, which are not controlled, also express sst(5). We compared the acute effects of octreotide and SOM230, a new somatostatin analog with high affinity for sst(1,2,3,5) on hormone release in acromegalic patients. In a single-dose, proof-of-concept study, 100 microg octreotide and 100 and 250 microg SOM230 were given s.c. to 12 patients with active acromegaly. Doses of 100 and 250 microg SOM230 dose-dependently suppressed GH levels from 2-8 h after administration (-38 +/- 7.7 vs. -61 +/- 6.7%, respectively; P < 0.01). A comparable suppression of GH levels by octreotide and 250 microg SOM230 was observed in eight patients (-65 +/- 7 vs. -72 +/- 7%, respectively). In three patients, the acute GH-lowering effect of 250 microg SOM230 was significantly superior to that of octreotide (-70 +/- 2 vs. -17 +/- 15%, respectively; P < 0.01). In one patient, the GH-lowering effect of octreotide was better than that of SOM230. Tolerability for SOM230 was good. Glucose levels were initially slightly elevated after octreotide and SOM230, compared with control day, whereas insulin levels were only significantly suppressed by octreotide. We conclude that SOM230 is an effective GH-lowering drug in acromegalic patients with the potential to increase the number of patients controlled during long-term medical treatment. http://repub.eur.nl/res/pub/9931/ 2002-01-01T00:00:00Z Septic shock is the most severe clinical manifestation of meningococcal disease and is predominantly seen in children under 5 yr of age. Very limited research has been performed to elucidate the alterations of the GH/IGF-I axis in critically ill children. We evaluated the GH/IGF-I axis and the levels of IGF-binding proteins (IGFBPs), IGFBP-3 protease, glucose, insulin, and cytokines in 27 children with severe septic shock due to meningococcal sepsis during the first 3 d after admission. The median age was 22 months (range, 4-185 months). Eight patients died. Nonsurvivors had extremely high GH levels that were significant different compared with mean GH levels in survivors during a 6-h GH profile (131 vs. 7 mU/liter; P < 0.01). Significant differences were found between nonsurvivors and survivors for the levels of total IGF-I (2.6 vs. 5.6 nmol/liter), free IGF-I (0.003 vs. 0.012 nmol/liter), IGFBP-1 (44.3 vs. 8.9 nmol/liter), IGFBP-3 protease activity (61 vs. 32%), IL-6 (1200 vs. 50 ng/ml), and TNFalpha (34 vs. 5.3 pg/ml; P < 0.01). The pediatric risk of mortality score correlated significantly with levels of IGFBP-1, IGFBP-3 protease activity, IL-6, and TNFalpha (r = +0.45 to +0.69) and with levels of total IGF-I and free IGF-I (r = -0.44 and -0.55, respectively). Follow-up after 48 h in survivors showed an increased number of GH peaks, increased free IGF-I and IGFBP-3 levels, and lower IGFBP-1 levels compared with admission values. GH levels and IGFBP-1 levels were extremely elevated in nonsurvivors, whereas total and free IGF-I levels were markedly decreased and were accompanied by high levels of the cytokines IL-6 and TNFalpha. These values were different from those for the survivors. Based on these findings and literature data a hypothetical model was constructed summarizing our current knowledge and understanding of the various mechanisms. http://repub.eur.nl/res/pub/9165/ 1999-01-01T00:00:00Z Interferon-alpha (IFN alpha) may exert direct inhibitory effects on cell proliferation and on the production of different peptide hormones. We investigated the effect of IFN alpha on hormone production by 15 GH-secreting pituitary adenomas, 4 clinically nonfunctioning or gonadotroph pituitary adenomas, and 4 prolactinomas in vitro. In the GH-secreting pituitary adenoma cultures, a short term (72-h) incubation with IFN alpha (50-100 U/mL) significantly inhibited GH secretion in 3 of 7 cases and PRL secretion in 6 of 7 cultures. During prolonged incubation (14 days) with IFN alpha, GH and/or PRL secretion was significantly inhibited in 7 of 8 cultures (GH, 17-78% inhibition; PRL, 39-88% inhibition). In the clinically nonfunctioning or gonadotroph cultures, incubation with IFN alpha resulted in inhibition of the secretion of gonadotropins and/or alpha-subunit in all cases (27-62%), whereas in the prolactinoma cultures PRL secretion was inhibited by IFN alpha in all cases (37-76%). The effect of IFN alpha was additive to the inhibitory effects of the dopamine agonist bromocriptine (10 nmol/L) or the somatostatin analog octreotide (10 nmol/L). The inhibition of hormone secretion by IFN alpha was accompanied by inhibition of the intracellular hormone concentrations. The effect of IFN alpha was dose dependent, with an IC50 for inhibition of hormone secretion of 2.3 +/- 0.3 U/mL (n = 5), which is relatively low compared with the concentrations that are reached in patients treated with IFN alpha for various malignancies. In conclusion, the potent antihormonal effect of IFN alpha on cultured pituitary adenomas suggests that this drug might be of benefit in the treatment of selected patients with secreting pituitary adenomas. As treatment with IFN alpha is associated with considerable adverse reactions, studies with this drug should only be considered in inoperable, invasive aggressive, and dopamine agonist- and/or somatostatin analog-resistant functioning pituitary macroadenomas. http://repub.eur.nl/res/pub/8652/ 1997-01-01T00:00:00Z In the present study, we have investigated the role of estrogens in the regulation of somatostatin receptor subtype (sst) expression in 7315b PRL-secreting rat pituitary tumor cells in vitro and in vivo. sst were undetectable in freshly dispersed cells of the transplantable 7315b tumor. When 7315b cells were cultured in medium containing 10% FCS, the number of high affinity sst increased with prolonged culture time. However, when the medium was supplemented with 10% horse serum (HS) instead of FCS, no sst were detectable on 7315b cells even after three weeks of culturing. In contrast to HS, FCS contains high E2-levels (HS, 8 pM; FCS, 134 pM). The antiestrogen tamoxifen (0.5 microM) significantly inhibited the sst number to 50.5% of the value of untreated FCS-grown cells, suggesting that E2 stimulates sst expression in 7315b rat pituitary tumor cells. E2 (10 nM) induced a rapid increase in sst number in HS-grown 7315b cells. Octreotide (1 microM) significantly inhibited PRL release and the intracellular PRL concentration of 7315b cells that were cultured in medium supplemented with FCS or with HS + 10 nM E2 but not in HS alone. This indicates that the sst present on these cells are biologically active. RT-PCR analysis revealed that none of the five currently known sst subtypes were present in freshly dispersed 7315b pituitary tumor cells. The expression of sst2- and sst3-messenger RNA (mRNA) was unequivocally correlated to the presence of E2 because these sst subtypes were detected only in cells that were cultured for 7 and 14 days in medium supplemented with FCS or with HS + 10 nM E2. sst1, sst4 and sst5 messenger RNA could not be detected. The 7315b tumor itself synthesizes and secretes huge amounts of PRL. The high PRL levels in tumor-bearing rats inhibit the ovarian E2-production. No detectable E2 levels could be measured in the serum of 7315b tumor-bearing rats. The sc administration of 20 micrograms/day E2-benzoate normalized the circulating E2 levels in 7315b tumor-bearing rats. Moreover, E2-treatment indeed induced sst expression in vivo as shown by ligand binding studies using membrane homogenates and [125I-Tyr3]-octreotide as radioligand and by autoradiography on tissue sections. In agreement with the in vitro studies, the expression of the sst2 subtype was established by RT-PCR analysis in 7315b tumors of E2-treated rats. However, in contrast to the in vitro studies, E2-treatment did not effectuate the expression of the sst3 subtype, suggesting that the in vitro stimulus of E2 is stronger. In conclusion: 1) sst2 and sst3 expression in the 7315b rat prolactinoma model is primarily dependent upon the presence of estrogens; 2) the antihormonal action of octreotide in 7315b tumor cells in vitro is mediated via the sst2 and/or sst3 subtypes; 3) the absence of sst expression in vivo can be explained by the hormonal environment of the 7315b tumor cells. The 7315b tumor cells in vivo may down regulate their own receptor status via their host, because of the ensuring hyperprolactinemia results in a hypo-estrogenic state. http://repub.eur.nl/res/pub/8716/ 1997-01-01T00:00:00Z The effects of somatostatin (SS-14 and/or SS-28) and of the three octapeptide SS-analogs that are available for clinical use (octreotide, BIM-23014 and RC-160) on hormone release by primary cultures of 15 clinically nonfunctioning pituitary adenomas (NFA), 7 prolactinomas, and 2 insulinomas were investigated. In the pituitary adenoma cultures, a comparison was made with the effects of the dopamine (DA) agonists bromocriptine and/or quinagolide. In 5 NFAs, 2 prolactinomas and 1 insulinoma somatostatin receptor (subtype) expression was determined by ligand binding studies and by in situ hybridization to detect sst1, sst2, and sst3 messenger RNAs (mRNAs). Four NFA cultures did not secrete detectable amounts of alpha-subunit, FSH, and/or LH. In the other cultures, hormone and/or subunit release was inhibited by DA-agonists (10 nM) in 9 of 11, by SS (10 nM) in 7 of 11, and by octapeptide SS-analogs (10 nM) in 3 of 10 cultures. In three NFA cultures, hormone release was sensitive to SS but not to SS-analogs. In all cultures, except for one, DA-agonists were the most effective in inhibiting hormone release. In the prolactinoma cultures, PRL release was inhibited by DA-agonists (10 nM) in 7 of 7, by SS in 4 of 4, and by octapeptide SS-analogs in 3 of 7 cultures. A dissociation between the effects of SS and SS-analogs was found in 3 cases. In the cultures sensitive to both bromocriptine and SS-28, bromocriptine was the most potent compound in 2 out of 4 cultures. In the 2 other cultures, both compounds were equally effective. In 2 insulinoma cultures, insulin release was inhibited by SS, and by octapeptide SS-analogs in only one. The presence or absence of an inhibitory effect by octreotide was in all cases in parallel with the presence or absence of the inhibitory effect by BIM-23014 and RC-160. Autoradiographic studies using [125I-Tyr0]SS28 showed specific binding in 4 of 5 NFAs, 1 of 2 prolactinomas, and 1 of 1 insulinoma. Specific [125I-Tyr3]octreotide binding was found in 2 of 5 NFAs, in 1 of 2 prolactinomas, and in the insulinoma. Two NFAs showed binding of SS28, but not of the sst2.5 specific ligand octreotide. The tumors showed variable sst1 and/or sst3 mRNA expression, whereas no sst2 expression was found. In conclusion, a dissociation between the inhibitory effects of SS on the one hand and of the octapeptide SS-analogs octreotide, BIM-23014 and RC-160 on the other hand, is observed in a small subgroup of NFAs, prolactinomas, and insulinomas, suggesting that novel sst subtype specific SS-analogs might be of benefit in the treatment of selected patients with somatostatin receptor positive secreting tumors not responding to octapeptide SS-analogs. However, in the majority of NFAs and prolactinomas, DA-agonists were equally or more effective than SS in the suppression of tumoral secretion products.