β-arrestin expression in corticotroph tumor cells is modulated by glucocorticoids

Pituitary-directed medical treatment for Cushing's disease (CD) is currently represented by membrane receptor targeting drugs (somatostatin analogs and dopamine agonists). Somatostatin and dopamine receptors are regulated by β-arrestins, which have been shown to be differentially regulated by glucocorticoids in non-neuroendocrine cells. In this study we investigated the effects of glucocorticoids on β-arrestin expression in corticotroph tumor cells. First, AtT20 cells, a mouse model of CD, were exposed to dexamethasone (Dex) at different time points and β-arrestin expression was evaluated at mRNA and protein levels. Futhermore, β-arrestin mRNA expression was evaluated in 17 human corticotroph adenoma samples and correlated to patients' pre-operative cortisol levels. We observed that Dex treatment induced a time-dependent increase in β-arrestin 1 mRNA expression and a decrease in β-arrestin 2. The same modulation pattern was observed at protein level. Dex-mediated modulation of β-arrestins was abolished by co-treatment with mifepristone, and Dex withdrawal restored β-arrestin expression to basal levels after 72 h. The evaluation of β-arrestin mRNA in corticotroph adenomas from CD patients with variable disease activity showed a significant positive correlation between β-arrestin 1 mRNA and urinary cortisol levels. The effect of glucocorticoids on β-arrestin levels was confirmed by the analysis of two samples from a single patient, which underwent adenomectomy twice, with different pre-operative cortisol levels. In conclusion, glucocorticoids induce an inverse modulation of the two β-arrestin isofoms in corticotroph tumor cells. Since β-arrestins regulate membrane receptor functions, this finding may help to better understand the variable response to pituitary-targeting drugs in patients with Cushing's disease.

SAT-LB076 T2-Signal Intensity, SST Receptor Expression and First-Generation Somatostatin Analogues Efficacy Predict Hormone and Tumor Responses to Pasireotide in Acromegaly

Background: Previous studies indicate that PAS-LAR can achieve control of insulin-like growth factor I (IGF-I) levels and may reduce tumor size, however a subset of acromegaly patients responds poorly. T2-signal intensity, somatostatin receptor (SST) subtype 2 and 5 expression, and the response to first-generation somatostatin receptor ligands (SRLs) are recognized predictors of therapy response. Valid prediction of the response to PAS-LAR can alter treatment stratification. Aim: To analyze T2-signal intensity and SST receptor expression in relation to the hormone and tumor response during PAS-LAR treatment, and to determine to what extent this equals SRLs responsiveness. Methods: We included 45 patients initially receiving SRLs, followed by a combination therapy including pegvisomant, and finally treated with PAS-LAR. The hormone response to PAS-LAR was evaluated using IGF-I (x ULN) levels at 24 weeks. T2-weighted MRI signal intensity of the adenoma was visually assessed and quantified by region of interest measurement. A tumor volume change of ≥25% from baseline was considered significant. SST receptor expression in adenomas was evaluated in 13 out of 45 patients using a validated immunoreactivity score (IRS). The clinical characteristics and the hormone and tumor response to PAS-LAR were assessed using multivariable regressions. Results: Patients with the lowest percentage IGF-I (x ULN) reduction during SRLs also showed weak IGF-I (x ULN) control during PAS-LAR and, however, more significant tumor shrinkage (r=0.41, p=0.006; p=0.036). Lower IGF-I (x ULN) levels during PAS-LAR were associated with higher T2-signal intensity and less significant tumor shrinkage (ß=-0.29, p=0.045; ß=0.34, p=0.035). With regards to tumor response, adenoma volume at baseline was associated with higher random GH levels at diagnosis and greater absolute tumor shrinkage during PAS-LAR (ß=69, p=0.0018; ß=1.05, p=0.020). Significant tumor shrinkage was associated with female patients, higher IGF-I (x ULN) levels during PAS-LAR and borderline significant with non-hypointense adenomas at baseline (OR=6.35, 95% CI=1.42-36.4; OR=13.2, 95% CI=2.14-129.1; OR=5.97, 95% CI=0.91-65.5 respectively). Lower IGF-I (x ULN) levels after PAS-LAR correlated with higher (r=-0.68, p=0.011; r=-0.52, p=0.083), while significant tumor shrinkage correlated with lower SST₂ levels as well as SST₂/SST₅ ratio expression (p=0.040; p=0.024). Conclusions: Patients not responding to somatostatin analogs with particularly large adenomas, low SST₂ receptor expression and higher T2-signal intensity are more prone to show tumor shrinkage during PAS-LAR than patients with high SST₂ receptor expression and T2-hypointense adenomas. Surprisingly, tumor shrinkage is not accompanied by lower IGF-I (x ULN) levels, which are associated with a high SST₂ receptor expression and a higher T2-signal intensity. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

The IGF pathway is activated in insulinomas but downregulated in metastatic disease

Clinical and molecular studies have implicated epidermal growth factor receptor (EGFR), insulin-like growth factor (IGF) and target of rapamycin (mTOR) signaling pathways in the regulation of pancreatic neuroendocrine tumor (PanNET) growth. Interpretation and comparison of these studies is complex due to clinical and molecular tumor heterogeneity. We therefore focused in this study on insulinomas, which we examined for mRNA and protein expression of EGFR, IGF and mTOR signaling pathway components by quantitative real-time PCR (n=48) and immunohistochemistry (n=86). Findings were compared with normal pancreatic islets and correlated with histopathological data and clinical outcome. Insulinomas showed low EGFR and high IGF2 expression. IGFBP2, IGFBP3 and IGFBP6 mRNA levels were 2-4 folds higher than in islets. High protein expression of IGF2, IGF1R and INSR (in 51-92% of the tumors) and low to moderate expression of mTORC1 pathway proteins p-PS6k and p-4EBP1 (7-28% of the tumors) were observed. Correlations were found between 1) ERK1 mRNA expression and that of numerous IGF pathway genes, 2) p-ERK and IGF1R protein expression and 3) decrease of IGF pathway components and both metastatic disease and shorter 10 years disease free survival. In conclusion, our observations suggest that high expression of IGF signaling pathway components is a hallmark of insulinomas, but does not necessarily lead to increased mTOR signaling. Reduced expression of IGF pathway components may be an adverse prognostic factor in insulinomas.

Potentials of interferon therapy in the treatment of pancreatic cancer

Pancreatic cancer is a highly aggressive malignancy with limited treatment options. To improve survival for patients with pancreatic cancer, research has focused on other treatment modalities like adding biological modulators such as type-I interferons (IFNs). Type I IFNs (ie, IFN-α/IFN-β) have antiproliferative, antiviral, and immunoregulatory activities. Furthermore, they are able to induce apoptosis, exert cell cycle blocking, and sensitize tumor cells for chemo- and radiotherapy. A few years ago in vitro, in vivo, and several clinical trials have been described regarding adjuvant IFN-α therapy in the treatment of pancreatic cancer. Some studies reported a remarkable increase in the 2- and 5-year survival. Unfortunately, the only randomized clinical trial did not show a significant increase in overall survival, although the increased median survival implicated that some patients in the experimental group benefited from the adjuvant IFN-α therapy. Furthermore, encouraging in vitro and in vivo data points to a possible role for adjuvant IFN therapy. However, up till now, the use of IFNs in the treatment of pancreatic cancer remains controversial. This review, therefore, aims to describe, based on the available data, whether there is a distinct role for IFN therapy in the treatment of pancreatic cancer.

Everolimus is an active agent in medullary thyroid cancer: a clinical and in vitro study

Everolimus, an mTOR inhibitor, which has been demonstrated to induce anti-tumour effects in different types of neuroendocrine tumours, has never been evaluated in patients with medullary thyroid cancer (MTC). The aim of this study was to evaluate the in vitro and in vivo effects of everolimus in combination with octreotide in MTC. Two patients with progressive metastatic MTC and high calcitonin levels were treated with everolimus 5–10 mg/day. Both patients were under treatment with octreotide LAR at the study entry. An in vitro study was also performed to assess everolimus effects on MTC cell lines (TT and MZ-CRC-1 cells). A tumour response was observed in both patients. Serum calcitonin decreased by 86% in patient 1 and by 42% in patient 2. In TT and MZ-CRC-1 cells, everolimus induced a significant dose-dependent inhibition in cell proliferation. This effect seems to be related to a cell cycle arrest in G₀/G₁ phase in both cell lines and to the induction of cellular senescence in TT cells. Everolimus in combination with octreotide may be active as anti-tumour therapy in patients with progressive metastatic MTC, suggesting to further evaluate this agent in MTC patients in a large prospective study.

Unsaturated fatty acids prevent desensitization of the human growth hormone secretagogue receptor by blocking its internalization

The composition of the plasma membrane affects the responsiveness of cells to metabolically important hormones such as insulin and vasoactive intestinal peptide. Ghrelin is a metabolically regulated hormone that activates the G protein-coupled receptor GH secretagogue receptor type 1a (GHSR) not only in the pituitary gland but also in peripheral tissues such as the pancreas, stomach, and T cells in the circulation. We have investigated the effects of lipids and altered plasma membrane composition on GHSR activation. Oligounsaturated fatty acids (OFAs) disrupt the structure of membranes and make them more fluid. Prolonged (96 h), but not acute, treatment of the GHSR cells with the 18C OFAs oleic and linoleic acid caused a significant increase in sensitivity of the receptor to ghrelin (EC(50) reduced by a factor of 2.4 and 2.9 at 60 and 120 microM OFAs, respectively). OFAs were found to block the inhibitory effects of ghrelin pretreatment on subsequent ghrelin responsiveness, suggesting that OFAs suppress desensitization of GHSR. Radioligand displacement studies did not show a significant shift in receptor binding after incubation with OFAs. However, it was found that OFA treatment suppressed GHSR internalization, likely explaining OFA-induced refractoriness to ligand-induced desensitization. The involvement of lipid rafts in this process was indicated by the altered responsiveness of GHSR under conditions that alter membrane cholesterol. In conclusion, our findings demonstrate the importance of membrane composition for GHSR activation and desensitization and indicate at least part of the mechanism through which OFAs and cholesterol could affect ghrelin's activity in vivo.

SOM230, A New Somatostatin Analogue, Is Highly Effective in the Therapy of Growth Hormone/Prolactin-Secreting Pituitary Adenomas

PURPOSE

We have previously shown that transgenic mice ubiquitously overexpressing the HMGA2 gene develop growth hormone/prolactin-secreting pituitary adenomas. This animal model has been used to evaluate the therapeutic efficacy of SOM230, a somatostatin analogue with high affinity for the somatostatin receptor subtypes 1, 2, 3, and 5, on the growth of the pituitary adenomas.

EXPERIMENTAL DESIGN

Four groups of 3- and 9-month-old HMGA2 transgenic mice were treated for 3 months with a continuous s.c. injection of two different dosages of SOM230 (5 or 50 microg/kg/h), one dose of octreotide, corresponding to that used in human therapy, and a placebo, respectively. The development of the tumor before and after therapy was monitored by magnetic resonance imaging of the pituitary region and evaluation of the serum prolactin levels.

RESULTS

The highest dose of SOM230 induced a drastic regression of the tumor, whereas octreotide was not able to induce any significant tumor regression, although tumor progression was significantly slowed down. No significant differences were observed between the animals treated with the lowest dose of SOM230 and those receiving placebo.

CONCLUSIONS

These results clearly support the efficacy of the SOM230 treatment in human pituitary adenomas secreting prolactin based on the dramatic tumor shrinkage and fall in prolactin levels. This beneficial effect could be of crucial clinical usefulness in patients bearing tumors resistant to dopaminergic drugs.

Acetylcholine regulates ghrelin secretion in humans

Ghrelin secretion has been reportedly increased by fasting and energy restriction but decreased by food intake, glucose, insulin, and somatostatin. However, its regulation is still far from clarified. The cholinergic system mediates some ghrelin actions, e.g. stimulation of gastric contractility and acid secretion and its orexigenic activity. To clarify whether ghrelin secretion undergoes cholinergic control in humans, we studied the effects of pirenzepine [PZ, 100 mg per os (by mouth)], a muscarinic antagonist, or pyridostigmine (PD, 120 mg per os), an indirect cholinergic agonist, on ghrelin, GH, insulin, and glucose levels in six normal subjects. PD increased (P < 0.05) GH (change in area under curves, mean +/- SEM, 790.9 +/- 229.3 microg(*)min/liter) but did not modify insulin and glucose levels. PZ did not significantly modify GH, insulin, and glucose levels. Circulating ghrelin levels were increased by PD (11290.5 +/- 6688.7 pg(*)min/ml; P < 0.05) and reduced by PZ (-23205.0 +/- 8959.5 pg(*)min/ml; P < 0.01). The PD-induced ghrelin peak did not precede that of GH. In conclusion, circulating ghrelin levels in humans are increased and reduced by cholinergic agonists and antagonists, respectively. Thus, ghrelin secretion is under cholinergic, namely muscarinic, control in humans. The variations in circulating ghrelin levels induced by PD and PZ are unlikely to mediate the cholinergic influence on GH secretion.

The endocrine response to acute ghrelin administration is blunted in patients with anorexia nervosa, a ghrelin hypersecretory state

OBJECTIVE

Ghrelin, a gastric-derived natural ligand of the GH secretagogue (GHS)-receptor (GHS-R), strongly stimulates GH secretion but also possesses other neuroendocrine actions, stimulates food intake and modulates the endocrine pancreas and energy homeostasis. Ghrelin secretion is negatively modulated by food intake. Similarly, glucose and also insulin probably exert an inhibitory effect on ghrelin secretion. Fasting ghrelin levels are reduced in obesity, elevated in anorexia nervosa and restored by weight recovery. The chronic elevation of circulating ghrelin levels in anorexia suggested the hypothesis of an alteration of the sensitivity to the orexigenic action of ghrelin in this condition. The aim of this study was to define the endocrine actions of ghrelin in patients with anorexia nervosa.

DESIGN

We enrolled nine women with anorexia nervosa of restricter type [AN; age (mean +/- SEM) 24.2 +/- 1.8 years; body mass index (BMI) 14.7 +/- 0.4 kg/m2] and seven normal young women in their early follicular phase as control group (NW; age 30.6 +/- 3.1 years; BMI 20.3 +/- 0.5 kg/m2).

MEASUREMENTS

In all the subjects we studied the GH, PRL, ACTH, cortisol, insulin and glucose responses to acute ghrelin administration (1.0 microg/kg as i.v. bolus). The GH response to GHRH (1.0 microg/kg as i.v. bolus) and basal ghrelin and IGF-I levels were also evaluated in all the subjects.

RESULTS

Basal morning ghrelin and GH levels in AN (643.6 +/- 21.3 ng/l and 10.4 +/- 0.5 microg/l, respectively) were higher (P < 0.05) than in NW (233.5 +/- 14.2 ng/l and 0.7 +/- 0.7 microg/l, respectively). However, IGF-I levels in AN (145.3 +/- 10.9 microg/l) were lower (P < 0.05) than in NW (325.4 +/- 12.6 microg/l). The GH response to GHRH in AN was higher (P < 0.05) than that in NW, but in AN the GH response to ghrelin was lower (P < 0.05) than that in NW. In AN and NW ghrelin also induced similar increases (P < 0.05) in PRL, ACTH and cortisol levels. Ghrelin administration was followed by significant increase in glucose levels in NW (P < 0.05) but not in AN.

CONCLUSIONS

This study demonstrates that anorexia nervosa, a clinical condition of ghrelin hypersecretion, shows a specific reduction in the GH response to ghrelin, despite the hyper-responsiveness to GHRH administration. The impaired GH response to ghrelin in anorexia nervosa agrees with previous evidence of blunted GH response to synthetic GH secretagogues and could reflect desensitization of the GHS receptor induced by the chronic elevation of ghrelin levels in this pathological state.

Standard light breakfast inhibits circulating ghrelin level to the same extent of oral glucose load in humans, despite different impact on glucose and insulin levels

Ghrelin levels are increased by fasting and energy restriction, decreased by food intake, glucose load and insulin but not by lipids and amino acids. Accordingly, ghrelin levels are elevated in anorexia and cachexia and reduced in obesity. Herein we compared the effects of a standardized light breakfast (SLB) on morning circulating ghrelin levels with those of oral glucose load (OGTT) in normal subjects. Specifically, 8 young adult volunteers [age (mean+/-SEM): 28.0+/-2.0 yr; body mass index (BMI): 22.4+/-0.6 kg/m2] underwent the following testing sessions: a) OGTT (100 g p.o. at 0 min, about 400 kcal); b) SLB (about 400 kcal, 45% carbohydrates, 13% proteins and 42% lipids at 0 min) on three different days; c) placebo (100 ml water p.o.). In all sessions, at baseline, blood samples were withdrawn twice at 5-min interval to characterize the inter- and intra-individual reproducibility of the variables assayed. After placebo and OGTT, blood samples were withdrawn every 15 min up to +120 min. After SLB, blood samples were taken at 60 min only. Ghrelin, insulin and glucose levels were assayed at each time point in all sessions. Similarly to insulin and glucose levels, at baseline, ghrelin showed remarkable intra-subject reproducibility both in the same sessions and among the different sessions. Placebo did not significantly modify ghrelin, insulin and glucose. OGTT increased (p<0.01) glucose (baseline vs peak: 80.0+/-3.6 vs 140.5+/-6.3 mg/dl) and insulin (20.2+/-6.2 vs 115.3+/-10.3 mU/l) levels. SLB increased (p<0.05) both insulin (16.3+/-1.8 vs 48.3+/-6.3 mU/l) and glucose (74.5+/-3.7 vs 82.9+/-3.1 mg/dl) levels. Notably both the insulin and glucose increases after OGTT were significantly higher (p<0.01) than that induced by SLB. After OGTT, ghrelin levels underwent a significant reduction (baseline vs nadir: 355.7+/-150.8 vs 243.3+/-98.8 pg/ml; p<0.05) reaching the nadir at time +60 min. Similarly, ghrelin levels 60 min after SLB (264.8+/-44.8 pg/ml) were significantly (p<0.01) lower than at baseline (341.4+/-54.9 pg/ml). No significant differences in the reduction of ghrelin levels after OGTT and SLB were observed. In conclusion, these findings show that light breakfast inhibits ghrelin secretion to the same extent of OGTT in adults despite lower variations in glucose and insulin levels.

Somatostatin receptor gene therapy combined with targeted therapy with radiolabeled octreotide: a new treatment for liver metastases

OBJECTIVE

To evaluate the effect of peptide receptor radionuclide therapy (PRRT) on somatostatin receptor (SSR)-transfected colon carcinoma cells in a rat liver metastases model.

SUMMARY BACKGROUND DATA

Previously the authors have shown highly effective therapy with PRRT of SSR-positive tumors. This treatment is SSR-mediated; successful treatment is seen only in SSR-positive tumors, with no effect in SSR-negative tumors. As many tumors lack this receptor, the idea arose to transfect SSR-negative tumor cells with an SSR gene to apply PRRT on these SSR-transfected tumor cells.

METHODS

CC531 colon carcinoma cells (SSR-negative) were transfected in vitro with an SSR (subtype 2) gene (CC2B). Liver metastases were produced after intraportal injection of these tumor cells in rats. On day 7, animals were treated with 185 or 370 MBq [177 Lu-DOTA0, Tyr3 ]octreotate. After 21 days rats were killed and liver metastases were counted.

RESULTS

Treatment with 370 MBq [177 Lu-DOTA0, Tyr3 ]octreotate showed a significant antitumor response in rats with CC2B liver metastases (SSR-positive) in comparison with controls. No significant antitumor effect was seen in PRRT-treated rats with CC531 liver metastases (SSR-negative). Also, a dose-dependent tumor response was seen in rats with CC2B liver metastases treated with 185 MBq [ 177Lu-DOTA0, Tyr3 ]octreotate compared with controls. In addition, rats with mixed liver metastases treated with 185 MBq [177 Lu-DOTA0, Tyr3 ]octreotate had significantly fewer metastases compared with controls.

CONCLUSIONS

The authors showed an impressive antitumor effect of SSR (subtype 2)-transfected colon carcinoma cells with PRRT in a rat liver metastasis model. Moreover, rats with mixed liver metastases had significantly fewer liver metastases compared with control rats, which may be due to a radiologic bystander effect of [177 Lu-DOTA0, Tyr3 ]octreotate. This phenomenon is beneficial in the concept of in vivo gene therapy.

Ghrelin secretion is inhibited by either somatostatin or cortistatin in humans

Ghrelin possesses endocrine and non-endocrine actions mediated by the GH Secretagogue (GHS)-Receptors (GHS-R). The regulation of ghrelin secretion is still largely unknown. Somatostatin (SRIF) modulates central and gastroenteropancreatic hormonal secretions and functions. SRIF actions are partially shared by cortistatin (CST), a natural SRIF analogue, that binds all SRIF receptors and also GHS-R. Herein, we studied the effects of SRIF-14 or CST-14 (2.0 micro g/kg/h i.v. over 120 min) and of placebo on ghrelin, GH, insulin, glucagon and glucose levels in 6 normal young men. Placebo unaffected GH, insulin, glucagon, glucose and ghrelin levels. SRIF and CST similarly inhibited (p < 0.05) spontaneous GH secretion of about 90%. After SRIF or CST withdrawal, GH levels recovered to baseline levels. Both SRIF and CST similarly inhibited (p<0.01) insulin secretion of about 45%. In both sessions, after SRIF or CST withdrawal, insulin overrode baseline levels. Both SRIF and CST similarly inhibited (p < 0.01) glucagon levels of about 40%. After SRIF or CST withdrawal, glucagon persisted lower (p < 0.05) than at baseline. Neither SRIF nor CST modified glucose levels. Both SRIF and CST similarly inhibited (p < 0.01) circulating ghrelin levels of about 55%. Ghrelin levels progressively decreased from time +15 min, reaching the nadir at 120 and 105 min for SRIF and CST, respectively. Even 30 min after SRIF or CST withdrawal, ghrelin levels persisted lower (p < 0.05) than those at baseline. In conclusion, this study first shows that SRIF and CST strongly inhibits ghrelin secretion that, differently from GH and insulin secretion, persists inhibited even after stopping the infusion of SRIF or CST.

Acute effect of pegvisomant on cardiovascular risk markers in healthy men: implications for the pathogenesis of atherosclerosis in GH deficiency

Cardiovascular risk is increased in GH deficiency (GHD). GHD adults are frequently abdominally obese and display features of the metabolic syndrome. Otherwise healthy abdominally obese subjects have low GH levels and show features of the metabolic syndrome as well. We investigated in healthy nonobese males the effect of the GH receptor antagonist pegvisomant in different metabolic conditions. This is a model for acute GHD without the alterations in body composition associated with GHD. We compared the effect of pegvisomant with that of placebo before and after 3 d of fasting. In addition, we investigated the effect of pegvisomant under normal, i.e. fed, conditions. Three days of fasting as well as pegvisomant alone decreased serum free IGF-I levels (1.0 +/- 0.15 vs. 0.31 +/- 0.05 ng/ml and 0.86 +/- 0.23 vs. 0.46 +/- 0.23 ng/ml, respectively). Fasting in combination with pegvisomant also decreased serum free IGF-I levels (1.0 +/- 0.15 vs. 0.31 +/- 0.07 ng/ml). Treatment with pegvisomant had no additional influence on the decline of free IGF-I induced by fasting. Pegvisomant alone had no influence on insulin sensitivity. The increase in insulin sensitivity induced by fasting was comparable to the increase in insulin sensitivity induced by fasting combined with pegvisomant. Among serum lipid concentrations, only serum triglycerides increased significantly as a result of pegvisomant alone (1.0 +/- 0.2 vs. 1.6 +/- 0.4 mmol/liter). The changes in lipid concentrations induced by fasting alone or pegvisomant were not different from those induced by pegvisomant alone. von Willebrand factor antigen levels declined significantly under the influence of pegvisomant alone (1.1 +/- 0.07 vs. 0.8 +/- 0.06 U/ml). In conclusion, in different metabolic conditions the GH receptor antagonist pegvisomant induces no significant acute changes in the major risk markers for cardiovascular disease. These data suggest that the secondary metabolic changes, e.g. abdominal obesity or inflammatory factors, that develop as a result of long-standing GHD are of primary importance in the pathogenesis of atherosclerosis in patients with GHD.

Effects of fasting and pegvisomant on the GH-releasing hormone and GH-releasing peptide-6 stimulated growth hormone secretion

OBJECTIVE

Pegvisomant is a mutated GH molecule which prevents functional dimerization and subsequent activation of the growth hormone receptor. Pegvisomant and fasting both lead to GH resistance.

DESIGN AND PATIENTS

We performed a double-blind placebo-controlled cross-over study comparing the effects of pegvisomant and fasting on the GH-releasing hormone (GHRH)- and GH-releasing peptide-6 (GHRP-6)-stimulated GH-release before and after 3 days of fasting in 10 healthy lean male subjects. We also performed a single-arm open label study under nonfasting conditions in five of these subjects. On day 1, in random order, at 0800 h, a GHRP-6 or GHRH test was performed. At 1600 h, a GHRH (if the first test was a GHRP-6 test) or GHRP-6-test (if the first test was a GHRH test) was done. After the second test either pegvisomant (80 mg as a single subcutaneous injection) or placebo was administered. On day 4, GHRP-6 and GHRH tests were performed in the same order as on day 1. During the cross-over study, subjects fasted from 2400 h on day 1 until the end of the study.

MEASUREMENTS

During the GH stimulation tests, blood samples were drawn every 15 min from 15 to 120 min. GH was determined in all samples. Total insulin-like growth factor (IGF)-I and free IGF-I were determined from the samples at 0 min only.

RESULTS

Three days of fasting alone and pegvisomant alone as well as in combination increased GH concentrations, whereas a decrease in serum-free, but not total, IGF-I concentrations was observed. On day 4, fasting and pegvisomant, either alone or in combination, significantly increased GH concentrations after GHRH compared to baseline. Pegvisomant alone did not increase GH concentrations after GHRP-6 administration. Fasting alone increased GH levels after GHRP-6 administration. The combination of fasting and pegvisomant had a synergistic effect on GH release after GHRP-6.

CONCLUSION

These human in vivo data suggest that: (1) circulating free IGF-I, and not total IGF-I, is the major component in the negative feedback on GH secretion; (2) increased pituitary GHRH receptor expression plays a role in the mechanism whereby fasting leads to increased GH concentrations; (3) in vivo, GHRP-6 sensitivity seems to be regulated primarily by metabolic factors and not by changes in GH-IGF-I axis.

Magnetic resonance coronary angiography using navigator echo gated real-time slice following

Navigator echo gating allows for the elimination of breath-holding in MR imaging by providing a real-time monitor of respiratory position to gate image acquisition. In this study we examined the advantages and utility of real-time, navigator echo gated slice following technique in 2D magnetic resonance coronary angiography of patients with coronary artery disease. Thirteen patients with coronary artery disease were examined. MR images of the right coronary artery (RCA) were obtained parallel to the atrioventricular groove to image long sections of the RCA in a small number of slices. In-plane resolution was 0.7 x 0.9 mm and 2-6 signals were averaged to support this high spatial resolution. Targeted maximum intensity projection (MIP) images were generated from the slices to present the RCA in a single image. All patients had x-ray angiograms available for comparison with the MR images. Using the navigator echo gated real-time slice following technique, MRI successfully obtained images in 11 of 13 cases. The technique failed in two patients with irregular breathing patterns. The average length of the RCA seen in the 11 successful MR exams was 61 mm and the average length seen in the x-ray angiograms was 80 mm. Eight patients were determined to be without disease in the RCA by x-ray angiography, and all eight were correctly identified as normal on the MRI exam. In the three patients who had a successful MRI exam and were determined to have disease in the RCA by x-ray angiography, MRI identified the lesion in two cases. In the third case MRI indicated a discrete lesion and x-ray angiography indicated diffuse disease without a focal lesion. Navigator echo gating improves patient tolerance, provides aligned sections of coronaries over multiple slices, and allows for improved resolution through signal averaging. This preliminary patient study suggests that navigator echo gated magnetic resonance coronary angiography may play a role in evaluating coronary artery disease.

Two-dimensional coronary MR angiography without breath holding

PURPOSE

To determine whether breath holding can be eliminated in two-dimensional magnetic resonance (MR) imaging of the coronary arteries by using real-time respiratory gating.

MATERIALS AND METHODS

Thirty-one subjects (20 healthy volunteers, 11 patients) underwent MR imaging. In 13 subjects, a respiratory monitoring belt was used, and in 18 subjects, a navigator echo was used. MR imaging was performed with breath holding, respiratory gating, and respiratory gating with two signals acquired. Three reviewers conducted a blinded review of the images, and overall image quality was rated on a scale from 1 (poor) to 5 (excellent).

RESULTS

Respiratory gating with two signals acquired provided image quality superior to that with breath-hold imaging (3.7 vs 3.0, respectively; P < .05). Measurements of signal-to-noise ratio (14.5 for respiratory gating with two signals acquired and 11.9 for breath holding) supported the results of the image review. Navigator-echo gating provided better image quality than the monitoring belt (3.7 vs 3.1, respectively; P < .05).

CONCLUSION

Breath holding may be eliminated by gating image acquisition to a real-time monitor of respiratory position. Respiratory gating enables improved resolution by means of acquisition of multiple signals, provides aligned sections of coronary arteries, and improves patient tolerance.

A close correlation between the inhibitory effects of insulin-like growth factor-I and SMS 201-995 on growth hormone release by acromegalic pituitary tumours in vitro and in vivo

In the present study we compared the in-vitro effects of IGF-I and SMS 201-995 on GH release by cultured tumour cells obtained from seven acromegalic patients with the preoperative in-vivo GH dynamics, including the acute response to 50 micrograms SMS 201-995 subcutaneously. IGF-I and SMS 201-995 inhibited GH release during a 24 h incubation in four and five of the seven tumour cell preparations, respectively. The inhibitory effect of SMS 201-995 was greater than that exerted by IGF-I (P less than 0.01). There was a close correlation between the in-vitro inhibitory effects of IGF-I and SMS 201-995 (P less than 0.01). In addition, the acute inhibitory effect of 50 micrograms SMS 201-995 on circulating GH levels in vivo correlated with the inhibitory effects in vitro of both SMS 201-995 (P less than 0.01) and IGF-I (P less than 0.05). The inhibitory effects of IGF-I and SMS 201-995 on GH release in vitro were shown to be additive in two of four tumours. There was no relation between the in-vitro effects of IGF-I and/or SMS 201-995 and several in-vivo parameters, including fluctuations in GH levels, sleep-induced GH release, a paradoxical increase of GH in response to TRH, and the circulating IGF-I and PRL levels.

IN CONCLUSION

(1) there is a close correlation between the sensitivity of GH release by cultured human adenoma cells to IGF-I and SMS 201-995. (2) There is also a close correlation between the in-vivo inhibitory effect on GH release of SMS 201-995 and the in-vitro inhibitory effects of both SMS 201-995 and IGF-I. (3) A subgroup of acromegalic patients harbour pituitary tumours in which the qualitative regulation of hormone secretion is similar to that of normal GH secretion.

Studies on the conditions determining the inhibitory effect of somatostatin on adrenocorticotropin, prolactin and thyrotropin release by cultured rat pituitary cells

Somatostatin (SRIH) is a physiological inhibitor of growth hormone (GH) secretion, but its role in the regulation of adrenocorticotropic hormone (ACTH), prolactin (PRL) and thyroid-stimulating hormone (TSH) release is unclear. SRIH (1 pM to 1 microM) did not affect basal and corticotropin-releasing hormone (CRH)-stimulated ACTH release by normal rat pituitary cells cultured in medium with 10% fetal calf serum (FCS). In cells deprived of serum for 48 h, or preincubated with the glucocorticoid-receptor-blocking agent, RU 38486, CRH-stimulated ACTH release was significantly suppressed by 1 pM to 0.10 nM SRIH. Preincubation with 5 nM dexamethasone completely abolished this inhibitory effect of SRIH on ACTH release. PRL release by pituitary cells cultured in phenol red-free culture medium with 10% estrogen-stripped FCS showed a very low sensitivity to SRIH. Increasing concentrations of 10 and 50 pM and 1 nM estradiol made PRL release by these cells significantly less sensitive to 50 nM dopamine, whereas the sensitivity to SRIH increased to a similar extent. In all instances dopamine and SRIH together exerted additive inhibitory effects, the extent of which remained similar under all conditions. After a 2-hour incubation, thyrotropin-releasing hormone-stimulated TSH secretion was significantly suppressed by 100 nM and 1 microM SRIH only in cells cultured in medium with 10% hypothyroid serum, and not in cells cultured in medium with 10% FCS. Such a difference in the sensitivity of thyrotrophs to SRIH disappeared during longer incubation.

CONCLUSIONS

(1) ACTH release by normal corticotrophs is only sensitive to SRIH in the absence of the physiological peripheral feedback regulation by glucocorticoids.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison between the effects of SMS 201-995, bromocriptine and a combination of both drugs on hormone release by the cultured pituitary tumour cells of acromegalic patients

The in-vivo reaction of the plasma GH concentration to the administration of the somatostatin analogue SMS 201-995, bromocriptine and their combination were compared with the in-vitro effects of both compounds and their combination on GH release and the GH tumour cell content of 9 acromegalic patients. Exposure of cultured GH-secreting pituitary tumour cells for 4-96 h to SMS 201-995 showed a variable, but in all instances during longer incubations statistically significant inhibition of GH release, which paralleled the sensitivity of GH secretion to the drug in vivo. This inhibitory effect on GH release was in two of the eight tumours accompanied by a decrease in the GH tumour cell content after 24-72 h of culture. These changes either reflect an inhibition of GH synthesis and/or an increase in intracellular breakdown (crinophagy) of GH and might be the basis for the tumour shrinkage which has been observed in about half of the acromegalic patients during long-term SMS 201-995 therapy. The inhibitory effects of bromocriptine on GH secretion were antagonized by haloperidol, while the inhibitory effect of SMS 201-995 was not affected by the dopamine receptor antagonist. This suggests that the effects of SMS 201-995 and bromocriptine are mediated via separate mechanisms involving different receptors. Additive but no potentiating inhibitory effects of both drugs on GH release were observed in a group of six patients in vivo and in three of six tumours in vitro.

The effects of bromocriptine, thyrotropin-releasing hormone, and gonadotropin-releasing hormone on hormone secretion by gonadotropin-secreting pituitary adenomas in vivo and in vitro

The characteristics and dynamics of hormone secretion in vivo and in vitro were investigated in six patients with gonadotropin-secreting pituitary adenomas. All six tumors secreted and contained FSH and different combinations of LH, beta-LH, and alpha-subunit. In addition, immunohistochemical examination of the pituitary tumor tissue showed staining with both LH and FSH in three and either LH or FSH in the other three tumors. TRH and GnRH stimulated hormone secretion in vivo and in vitro, and they also increased the hormone content of the cultured tumor cells. Bromocriptine significantly inhibited hormone release and reduced the hormone content of the tumor cells. In vivo, 2.5 mg bromocriptine significantly suppressed plasma hormone levels; the inhibiting effect on alpha-subunit concentrations was in general more marked than that on LH and FSH. We conclude that hormone release by gonadotropin-secreting pituitary adenomas can be stimulated by TRH and GnRH and inhibited by bromocriptine. Most of these tumors synthesize FSH, but there is a wide variation in the production of LH, beta-LH, and alpha-subunits. The sensitivity of hormone release to bromocriptine suggests that chronic therapy with this drug might have a beneficial effect on pituitary tumor size.

Differences in the interaction between dopamine and estradiol on prolactin release by cultured normal and tumorous human pituitary cells

We studied the interaction between dopamine and estradiol on PRL release by cultured normal and tumorous PRL-secreting cells prepared from human pituitaries. If pituitary glands were obtained within 3 h after sudden death of previously normal individuals, the viability of isolated pituitary cells prepared by dispersion with dispase was more than 75%. After 4 days of culture, dopamine (500 nM) inhibited PRL release by cells prepared from four normal pituitaries by 24 +/- 3% (+/- SEM). Pretreatment of the cells with 100 nM estradiol did not alter dopamine-mediated inhibition of PRL release. Estradiol alone increased basal PRL release and cell PRL content. Cultured PRL-secreting pituitary tumor cells, obtained by transsphenoidal operation from four patients, were similarly sensitive to dopamine. Estradiol stimulated tumor cell PRL release and content, but significantly diminished the inhibitory effect of dopamine. The estrogen receptor blocker tamoxifen did not alter PRL release, but it did reverse the estradiol-induced insensitivity of the prolactinoma cells to the dopamine agonist bromocriptine. In conclusion, these in vitro results indicate that estrogens do not antagonize the effect of dopamine on normal human PRL-secreting pituitary cells. In human pituitary tumor cells, however, estradiol decreased the sensitivity of PRL release to dopamine (agonists), and the estrogen action can be acutely reversed by tamoxifen.

Specific plasma cell accumulation in antigen-induced chronic inflammation in the guinea pig peritoneal cavity

Specificity of plasmacellular infiltration was studied using a guinea pig peritoneal inflammation model. Acute and chronic inflammations were induced by repeated injections of either of two non-crossreacting antigens (DNP-BSA and PPD). With an enzyme-immunohistochemical sandwich procedure allowing quantitation of DNP-BSA-specific plasma cells, specificity of plasmacellular infiltration could be demonstrated. DNP-BSA-specific antibody-forming cells were found not to enter inflammatory reactions elicited by PPD. Our data support the hypothesis that virtually all plasma cells in a chronic inflammatory exudate release antibodies specific for antigens that are locally available, and that such antigens are likely to play a central role in the perpetuation of chronicity.

The effectiveness of 3H-uridine and 3H-leucine for labeling of T and B cells of rats and mice

Using a technique for combined autoradiography and immunoperoxidase staining, we studied the incorporation of 3H-Uridine and 3H-Leucine into T and B lymphocytes of rats and mice. While in mouse both T and B cells were clearly labeled by incorporation of 3H-Uridine, a portion of rat T cells remained unlabeled. Furthermore, the majority of rat B cells was not labeled. In contrast, mouse T and B cells as well as rat T and B cells could be labeled with 3H-Leucine to a comparable degree.