Somatostatin: physiology and clinical applications

Perioperative Drug Treatment in Pancreatic Surgery-A Systematic Review and Meta-Analysis

INTRODUCTION

Pancreatic resections for malignant or benign diseases are associated with major morbidity and changes in physiology. To reduce perioperative complications and enhance recovery, many types of perioperative medical management have been introduced. The aim of this study was to provide an evidence-based overview on the best perioperative drug treatment.

METHODS

The electronic bibliographic databases Medline, Embase, CENTRAL, and Web of Science were systematically searched for randomized controlled trials (RCT) evaluating perioperative drug treatments in pancreatic surgery. The investigated drugs were somatostatin analogues, steroids, pancreatic enzyme replacement therapy (PERT), prokinetic therapy, antidiabetic drugs, and proton pump inhibitors (PPI). Targeted outcomes in each drug category were meta-analyzed.

RESULTS

A total of 49 RCT were included. The analysis of somatostatin analogues showed a significantly lower incidence of postoperative pancreatic fistula (POPF) in the somatostatin group compared to the control group (OR 0.58, 95% CI: 0.45 to 0.74). The comparison of glucocorticoids versus placebo showed significantly less POPF in the glucocorticoid group (OR 0.22, 95% CI: 0.07 to 0.77). There was no significant difference in DGE when erythromycin was compared to placebo (OR 0.33, 95% CI: 0.08 to 1.30). The other investigated drug regimens could only be analyzed qualitatively.

CONCLUSION

This systematic review provides a comprehensive overview on perioperative drug treatment in pancreatic surgery. Some often-prescribed perioperative drug treatments lack high quality evidence and further research is needed.

The Influence of a Hyperglycemic Condition on the Population of Somatostatin Enteric Neurons in the Porcine Gastrointestinal Tract

Somatostatin (SOM) is the most common agent in the gastrointestinal (GI) tract that is involved in the regulation of several gastric functions, as well as in gastric disorders. Hyperglycemia, which develops as a consequence of improperly treated diabetes, can cause numerous disturbances in the appropriate functioning of the gastrointestinal tract. High glucose level is toxic to neurons. One of the lines of defense of neurons against this glucotoxicity are changes in their chemical coding. To better understood the role of SOM secreted by enteric neurons in neuronal response on elevated glucose level, pancreatic β cells were destroyed using streptozotocin. Due to the close similarity of the pig to humans, especially the GI tract, the current study used pigs as an animal model. The results revealed that the number of enteric neurons immunoreactive to SOM (SOM-IR) in a physiological state clearly depend on the part of the GI tract studied. In turn, experimentally induced diabetes caused changes in the number of SOM-IR neurons. The least visible changes were observed in the stomach, where an increase in SOM-IR neurons was observed, only in the submucosal plexus in the corpus. However, diabetes led to an increase in the population of myenteric and submucosal neurons immunoreactive to SOM in all segments of the small intestine. The opposite situation occurred in the descending colon, where a decrease in the number of SOM-IR neurons was visible. This study underlines the significant role of SOM expressed in enteric nervous system neurons during diabetes.

Somatostatin as an Active Substance in the Mammalian Enteric Nervous System

Somatostatin (SOM) is an active substance which most commonly occurs in endocrine cells, as well as in the central and peripheral nervous system. One of the parts of the nervous system where the presence of SOM has been confirmed is the enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract. It regulates most of the functions of the stomach and intestine and it is characterized by complex organization and a high degree of independence from the central nervous system. SOM has been described in the ENS of numerous mammal species and its main functions in the GI tract are connected with the inhibition of the intestinal motility and secretory activity. Moreover, SOM participates in sensory and pain stimuli conduction, modulation of the release of other neuronal factors, and regulation of blood flow in the intestinal vessels. This peptide is also involved in the pathological processes in the GI tract and is known as an anti-inflammatory agent. This paper, which focuses primarily on the distribution of SOM in the ENS and extrinsic intestinal innervation in various mammalian species, is a review of studies concerning this issue published from 1973 to the present.

Chromogranin A and other enteroendocrine markers in inflammatory bowel disease

Changes in the distribution and products of enteroendocrine cells may play a role in immune activation and regulation of gut inflammation. This review aims at critically evaluating the main enteroendocrine markers in inflammatory bowel diseases (IBD). A narrative review was performed by searching inflammatory bowel diseases and enteroendocrine biomarkers in PubMed. Relevant modifications of some enteroendocrine markers, such as Chromogranin A, and their correlation with disease activity have been reported in patients with inflammatory bowel diseases. Even if data about neuroendocrine markers are sometimes contrasting, they may be potentially useful for the diagnosis and clinical management of these patients.

Brain peptides and the modulation of postoperative gastric ileus

Postoperative ileus (POI) develops after abdominal surgery irrespective of the site of surgery. When prolonged, POI can lead to longer hospitalization times and higher healthcare costs. Moreover, it is associated with complaints for the patient. In order to develop new strategies to treat this condition, a deeper understanding of the pathophysiology of the POI is necessary. This review will focus on brain peptides (ghrelin, nesfatin-1, somatostatin, corticotropin-releasing factor, thyrotropin-releasing hormone and calcitonin gene-related peptide) involved in the mediation of POI and the possible modulation of these pathways to shorten the time of POI. Lastly, the role of vagal signaling or chewing gum as potential treatment strategies of alleviating symptoms of POI is discussed.

Somatostatin in inflammatory bowel disease

Intestinal inflammation is controlled by various immunomodulating cells, interacting by molecular mediators. Neuropeptides, released by enteric nerve cells and neuroendocrine mucosa cells, are able to affect several aspects of the general and intestinal immune system, with both pro- as well as anti-inflammatory activities. In inflammatory bowel disease (IBD) there is both morphological as well as experimental evidence for involvement of neuropeptides in the pathogenesis. Somatostatin is the main inhibitory peptide in inflammatory processes, and its possible role in IBD is discussed.

Abdominal surgery inhibits circulating acyl ghrelin and ghrelin-O-acyltransferase levels in rats: role of the somatostatin receptor subtype 2

Clinical studies are evaluating the efficacy of synthetic ghrelin agonists in postoperative ileus management. However, the control of ghrelin secretion under conditions of postoperative gastric ileus is largely unknown. Peripheral somatostatin inhibits ghrelin secretion in animals and humans. We investigated the time course of ghrelin changes postsurgery in fasted rats and whether somatostatin receptor subtype 2 (sst(2)) signaling is involved. Abdominal surgery (laparotomy and 1-min cecal palpation) induced a rapid and long-lasting decrease in plasma acyl ghrelin levels as shown by the 64, 67, and 59% reduction at 0.5, 2, and 5 h postsurgery, respectively, compared with sham (anesthesia alone for 10 min, P < 0.05). Levels were partly recovered at 7 h and fully restored at 24 h. The percentage of acyl ghrelin reduction was significantly higher than that of desacyl ghrelin at 2 h postsurgery and not at any other time point. This was associated with a 48 and 23% decrease in gastric and plasma ghrelin-O-acyltransferase protein concentrations, respectively (P < 0.001). Ghrelin-positive cells in the oxyntic mucosa expressed sst(2a) receptor and the sst(2) agonist S-346-011 inhibited fasting acyl ghrelin levels by 64 and 77% at 0.5 and 2 h, respectively. The sst(2) antagonist S-406-028 prevented the abdominal surgery-induced decreased circulating acyl ghrelin but not the delayed gastric emptying assessed 0.5 h postinjection. These data show that activation of sst(2) receptor located on gastric X/A-like cells plays a key role in the rapid inhibition of circulating acyl ghrelin induced by abdominal surgery while not being primarily involved in the early phase of postoperative gastric ileus.

Somatostatin receptor subtypes mediate contractility on human colonic smooth muscle cells

This study demonstrates the expression of functional somatostatin receptor (sstr) subtypes in human circular and longitudinal colonic smooth muscle cells (SMC). Native somatostatin (SS) and sstr subtype-specific analogues were used to characterize the sstr subtypes present in both cell types by contraction/relaxation studies. Qualitative and quantitative mRNA analysis and immunohistochemistry of sstr subtypes were also carried out. sstr subtype 2 mRNA was expressed in circular SMC, and various levels of subtypes 1, 2 and 3 mRNA were expressed in longitudinal colonic SMC. Native SS and each subtype-specific analogue exerted a modest, but significant, contraction, although inhibition of carbachol-induced contraction (relaxation) was the main effect on SMC from both layers. CH-288, a sstr subtype 1-specific analogue, and octreotide, a sstr subtype 2-specific analogue, were the most effective relaxant analogues on longitudinal and circular SMC, respectively. sstr subtypes display a distinct expression pattern on human colonic SMC; on circular SMC, subtype 2 is the only sstr, whereas sstr subtypes 1, 2 and 3 are expressed on human SMC isolated from the longitudinal layer. The contractile effects of SS are mediated through sstr subtype 2 and sstr subtype 1 on circular and longitudinal human colonic SMC, respectively.

Immunoreactivity of gastric ECL and A-like cells in fasted and fed rats and mice

The oxyntic mucosa of rat and mouse stomach harbors histamine-producing ECL cells and ghrelin-producing A-like cells. The ECL cells are known to be active when the circulating gastrin levels are elevated in response to food intake. The A-like cells are the main source of circulating ghrelin. In response to starvation, the circulating ghrelin is elevated as a hunger signal. The aim of the present work was to study the correlation between the immunoreactivities and cellular activities of the ECL cells and A-like cells. Rats were either fed or fasted for 48 h and mice for 24 h. Immunohistochemical examination with antiserum against chromogranin A-derived fragment pancreastatin revealed both the ECL cells and the A-like cells without a difference between fasted and fed animals. Histamine was limited to the ECL cells with no significant difference between fasted and fed animals. Histidine decarboxylase (HDC) immunoreactivity occurred predominately in the ECL cells of the fed, but not fasted, animals in which the HDC enzymatic activity in the oxyntic mucosa was higher than in fasted animals. Ghrelin immunoreactivity was increased in terms of intensity, but not cell density in fasted animals. Thus, the immunoreactivities of ECL cells and A-like cells might be affected by starvation.

Effects of Domperidone on Human Plasma Levels of Motilin, Somatostatin, Gastrin, Adrenocorticotropic Hormone and Cortisol

Domperidone, an upper gastrointestinal function regulatory medicine, has recently been evaluated for its clinical usefulness in the treatment of stress and depression. We examined the effects of domperidone on the plasma levels of motilin-immunoreactive substance (IS), somatostatin-IS, gastrin-IS, adrenocorticotropic hormone (ACTH)-IS, and cortisol under stress conditions by repetitive blood sampling. After a single oral administration of domperidone (30 mg), the plasma domperidone level was highest (58.6+/-6.4 ng/ml) in the sample taken 40 min after administration, after which the plasma level fell. Peak plasma motilin-IS levels (23.1+/-1.4 pg/ml) were achieved 40 min after administration of domperidone (p < 0.01 vs. placebo), and returned to baseline levels within a further 40 min. Plasma somatostatin-IS levels (13.0+/-1.2 pg/ml) increased 60 min after administration of domperidone (p < 0.01 vs. placebo). Plasma gastrin-IS levels did not change significantly. These results suggest that the pharmacological effects of domperidone on gastrointestinal functions are closely related to changes in motilin-IS and somatostatin-IS levels. Domperidone significantly suppressed increases in plasma ACTH-IS and cortisol levels compared with the response to a placebo. These modulatory effects might be beneficial in stress-related diseases and suggest that this medicine has clinical pharmacological activity.

Effect of Sho-hange-ka-bukuryo-to on Gastrointestinal Peptide Concentrations in the Plasma of Healthy Human Subjects

Sho-hange-ka-bukuryou-to, a traditional Chinese herbal (Kampo) medicine, has been used to treat hyperemesis of pregnancy, nausea and vomiting. Most traditional herbal medicines are prepared from several herbs. For example, Sho-hange-ka-bukuryo-to is prepared from three herbs: Pinelliae Tuber, Zingiberis Rhizoma and Hoelen. Thus, to determine the precise mechanism of the pharmacological effects of Chinese herbal medicines is too difficult. So we have elucidated the effect of some Chinese herbal medicines by examining the change of the plasma levels of brain-gut peptides. In this study, we investigated the effects of Sho-hange-ka-bukuryo-to on the plasma levels of gut-regulated peptides (gastrin, somatostatin, motilin and vasoactive intestinal peptide (VIP)) and gastrointestinal mucosa regulatory neuropeptides (calcitonin gene-related peptide (CGRP) and substance P) in healthy human subjects. A single oral administration of Sho-hange-ka-bukuryo-to caused significant increases in plasma somatostatin-, CGRP- and substance P-immunoreactive substance (IS) levels, compared with a placebo group. Transient elevation of gastrin-IS levels in the placebo group was inhibited by the administration of Sho-hange-ka-bukuryo-to, but the medicine showed no effects on plasma motilin- or VIP-IS levels. In conclusion, these results might indicate that the pharmacological action of Sho-hange-ka-bukuryo-to is closely related to changes in gastrin-, somatostatin-, CGRP- and substance P-IS levels in human plasma.

111In-labelled octreotide binding by the somatostatin receptor subtype 2 in neuroendocrine tumours

BACKGROUND

The aim of this study was to investigate the importance of somatostatin receptor subtype 2 (SSTR2) expression for 111In-labelled diethylenetriamine-pentaacetic acid (DTPA)-D-Phe1-octreotide binding and uptake of 111In in neuroendocrine tumours.

METHODS

111In activity concentrations in surgical biopsies from neuroendocrine tumours (midgut carcinoid and medullary thyroid carcinoma), breast carcinoma and blood were determined 1-8 days after intravenous injection of 111In-labelled DTPA-D-Phe1-octreotide (140-350 MBq). The ratio of 111In activity concentrations between tumour tissue and blood (T/B value) was calculated. The expression of SSTR2 messenger RNA (mRNA) in tumour biopsies was quantitated by ribonuclease protection assay and SSTR2 protein was localized by immunocytochemistry.

RESULTS

T/B values were highest for tumour biopsies from midgut carcinoids (mean 160 (range 4-1200); n = 65) followed by medullary thyroid carcinoma (mean 38 (range 2-350); n = 88) and breast carcinoma (mean 18 (range 4-41); n = 4). The expression of SSTR2 mRNA (relative to the NCI-H69 cell line) was highest in tumour biopsies from midgut carcinoids (mean 2.5 (range 0.83-6.0); n = 40) followed by medullary thyroid carcinoma (mean 1.3 (range 0.20-6.0); n = 7) and breast carcinoma (mean 0.66 (range 0.29-1.0); n = 9). In tumour biopsies SSTR2 protein was localized exclusively to tumour cells.

CONCLUSION

Midgut carcinoid tumours showed a much higher level of SSTR2 expression than medullary thyroid carcinoma in accordance with superior tumour imaging by octreotide scintigraphy. The high SSTR2 mRNA values and T/B values observed in midgut carcinoid tumours were positively correlated.

Hange-shashin-to raises levels of somatostatin, motilin, and gastrin in the plasma of healthy subjects

Hange-shashin-to has been used for chronic hypofunction of the gastrointestinal tract and to improve functional abnormalities of the upper and lower gastrointestinal system. To determine whether the pharmacological effects of Hange-shashin-to are due to gut-regulatory peptide levels, we developed a sensitive and specific double-antibody enzyme immunoassay (EIA) for detecting motilin and also examined the levels of somatostatin-, motilin-, gastrin-, and vasoactive intestinal peptide (VIP)-immunoreactive substances (IS) in plasma from healthy subjects. We developed a sensitive (3.5 pg, 1.4 pg/well) and specific (carboxy-terminal region) EIA for motilin. A single oral administration of Hange-shashin-to 6.0 g caused significant increases somatostatin-IS (20-60 min), motilin-IS (40 min), and gastrin-IS (40-90 min) levels in plasma compared with levels in a placebo group. Hange-shashin-to had no significant effect on VIP-IS levels after single administration. These changes in hormone levels (somatostatin, motilin, and gastrin) might relate to normalization of the upper and lower gastrointestinal system by Hange-shashin-to.

Rikkunshi-to raises levels of somatostatin and gastrin in human plasma

Rikkunshi-to, a traditional Chinese (Kampo) medicine, has been used to treat chronic hypofunctions of the gastrointestinal tract. The effects of Rikkunshi-to on the plasma levels of gut-regulated peptide (somatostatin, motilin, gastrin, and vasoactive intestinal peptide (VIP)) levels were studied in healthy subjects. A single oral administration of Rikkunshi-to caused significant increases in plasma somatostatin and gastrin levels at 60 to 240 min compared with a placebo group. On the other hand, this medicine showed no effects on motilin and VIP levels. In conclusion, these results might indicate that the pharmacological action of Rikkunshi-to is closely related to changes in somatostatin- and gastrin-immunoreactive substance levels.

Effects of Ninjin-to on levels of brain-gut peptides (motilin, vasoactive intestinal peptide, gastrin, and somatostatin) in human plasma

We examined the effects of Ninjin-to, a traditional Chinese (Kampo) medicine, on the levels of brain-gut peptides (motilin, vasoactive intestinal peptide (VIP), gastrin, and somatostatin) in plasma from healthy subjects. A single oral administration of Ninjin-to, at a dose of 6.0 g, caused significant increases in plasma motilin levels at 40 to 90 min and somatostatin levels at 20 to 90 min, compared with a placebo treated group. Transient elevations of gastrin levels in the placebo group were inhibited by administration of Ninjin-to, but the medicine did not alter the levels of VIP. In conclusion, these results suggest that pharmacological effects of Ninjin-to on gastrointestinal functions closely relate to changes of motilin, gastrin, and somatostatin-immunoreactive substance levels in human plasma.

Effect of somatostatin on lower esophageal sphincter characteristics in man

BACKGROUND

Somatostatin (SST) is known for its inhibitory effect on the gastrointestinal tract. Transient lower esophageal sphincter relaxations (TLESR), low or absent LES pressure (LESP) and swallow-induced LES relaxations are the most important reflux mechanisms.

METHODS

We have studied the effect of somatostatin on lower esophageal sphincter (LES) characteristics in man. Nine healthy volunteers participated in four experiments performed in random order and double-blind during continuous infusion of somatostatin (250 microg/h) or saline (control) under fasting and postprandial conditions. Esophageal motility was measured with sleeve manometry combined with pH metry.

RESULTS

Under fasting conditions LESP was not influenced by somatostatin. Ingestion of the carbohydrate meal significantly (P < 0.01) decreased LESP. During continuous somatostatin infusion the postprandial decrease in LESP did not occur; LESP was even significantly (P < 0.05) increased over basal levels. Somatostatin did not significantly influence TLESR frequency, neither under basal conditions, nor postprandially. The residual pressure during swallow-induced LES relaxation was significantly (P < 0.05) increased by somatostatin.

CONCLUSION

In humans somatostatin prevents postprandial reduction in LESP, does not affect TLESR, but inhibits swallow-induced LES relaxation.

Sjögren's syndrome: a possible pathogenetic mechanism involving somatostatin

Sjögren's syndrome is a chronic systemic disease that primarily affects the salivary and lacrimal glands. The pathogenesis of Sjögren's syndrome is unknown. We hypothesize that reduced somatostatin activity is an important factor in promoting immune dysregulation in patients affected by Sjögren's syndrome. Somatostatin is a multifunctional peptide with potent immunomodulatory properties. Its effects include reduced lymphocytic activity, reduced gastric and intestinal secretions, activation of the hypothalamic-pituitary axis, and anti-inflammatory action, all opposite to the general presentation in Sjögren's syndrome. We suggest that the activity of somatostatin is low in patients affected by this disease, and this contributes significantly to the pathology observed.

sst1 mRNA is the prominent somatostatin receptor mRNA in the rat gastrointestinal tract: reverse transcription polymerase chain reaction and in situ-hybridization study

The inhibitory peptide hormone somatostatin and its receptors (sst1-sst5) regulate many physiological functions in the gastrointestinal tract. In an attempt to correlate the various effects of somatostatin in gastrointestinal physiology to individual sst subtypes sst1-sst5, mRNAs have been localized by semiquantitative reverse transcription polymerase chain reaction amplification and in situ hybridization of sst1 and sst3 in the rat alimentary tract. sst1-sst4 mRNAs were found throughout the gastrointestinal tract, sst1 mRNA being more abundant than sst2 and much more abundant than sst3 and sst4 mRNAs. sst5 transcripts were at the detection threshold. sst1 and sst3 mRNAs are present in enterocytes and enteric neurons suggesting a role of these subtypes in the somatostatin-mediated inhibition of acetylcholine release from myenteric neurons and of secretomotor neuron activity in the submucous plexus. The presence of sst3 mRNA in smooth muscle cells points to an additional role of this receptor in regulating gut motility.

[111In-DPTA-D-Phe1]-octreotide scintigraphy in the management of patients with advanced renal cell carcinoma

Somatostatin receptor scintigraphy using the 111In-labelled somatostatin analogue octreotide (Octreoscan) was performed in 9 patients with metastatic renal cell carcinoma. In total 11 scintigraphies were performed. Positive tumor uptakes were observed in 9 patients. The results of the octreotide scans were correlated to diagnostic CT and/or X-ray images. Forty (59%) out of 68 known tumor localizations were visualized with the octreotide scan. A second scan following therapy was performed in two patients. These patients showed progressive disease despite treatment and also exhibited intensified uptakes at octreotide scintigraphy. One false positive lesion was observed in the 40 lesions visualized in scintigraphy. It was concluded that renal cell carcinoma expresses somatostatin receptors, as could be visualized with Octreoscan scintigraphy. The scintigraphic technique can be used as an instrument for in vivo characterization of the disease. The data could also form a basis for future investigations regarding the possible therapeutic effect of octreotide in the management of renal cell cancer.

Effects of pituitary adenylate cyclase activating polypeptide-27 (PACAP) and vasoactive intestinal polypeptide (VIP) on chloride in HT29 cells studied by X-ray microanalysis

The colon cancer cell line HT29 is a useful model to study intestinal chloride secretion. These cells have both cAMP-activated and calcium-activated chloride channels. Changes in elemental content of the cells after stimulation with agonists were determined by X-ray microanalysis in the scanning or scanning transmission electron microscope. Exposure of HT29 cells to pituitary adenylate cyclase activating polypeptide-27 (PACAP) caused a transient decrease in the cellular Cl and K concentrations, indicating (net) efflux of chloride. The effect of PACAP is inhibited by somatostatin, which is known to inhibit cAMP-activated as well as calcium-activated chloride secretion and by U-73122, an inhibitor of phospholipase C. Alloxan, an inhibitor of adenylate cyclase, did not significantly affect the PACAP-induced loss of chloride. The calcium-chelating agent EGTA inhibited the PACAP-induced loss of chloride, indicating the need for extracellular calcium ions. Also vasointestinal polypeptide (VIP) caused a decrease of the cellular chloride concentration in HT29 cells. VIP-induced loss of chloride could be inhibited by pre-treating the cells with somatostatin or UK14,304, an alpha-2 adrenergic agonist that has been shown previously to inhibit purinergically activated chloride efflux. Our results indicate that there is cross-talk between the cAMP- and the calcium-activated pathways for chloride secretion in HT29 cells.

Helicobacter pylori infection and the pathogenesis of duodenal ulceration

Helicobacter pylori is a gram-negative spiral bacterium confined to the habitat of gastric-type epithelium. H. pylori causes duodenal ulceration by a cumulative effect of antral predominant gastritis with increased acid secretion, consequent gastric metaplasia in the duodenum (a site of further colonization by H. pylori), duodenitis, reduced duodenal bicarbonate secretion, and mucosal damage. Bacterial factors influence outcome. Major determinants are the production of a vacuolating toxin and the presence of CagA, an immunodominant product of a nonconserved gene cagA, a marker for the cag pathogenicity island that encodes virulence genes involved in induction of epithelial chemokine responses. In ulcer patients the mucosal immune response is polarized to a T-helper-1 (Th1) cell-mediated response, which may contribute to mucosal damage. Eradication of H. pylori restores acid output to normal. Loss of both acid and bacteria halts gastroduodenitis and allows ulcer healing. Gastric metaplasia does not regress in the short term.

Plasma somatostatin-like immunoreactivity and somatostatin-28 levels in obese men

Somatostatin (SS) impairs nutrient absorption. It has been suggested that hyposomatostatinaemia may be involved in the pathogenesis of obesity. However, data on postprandial SS-like immunoreactivity (SLI) levels in obese subjects are controversial and the levels of SS-28, the main molecular form of circulating SLI in healthy subjects, have not been determined. To characterise the fasting and postprandial plasma pattern of SLI and SS-28 in obese men, we studied eight obese men (age 24-32 yr, BMI 33-42 kg/m2), with normal glucose tolerance test and normal gastric emptying of solids, and eight healthy men (age 24-39 yr, BMI 21-24 kg/m2). Blood samples were taken at regular intervals in fasting conditions and for 2 h after a standard solid-liquid meal (2.3 MJ). Plasma SLI and SS-28 were measured by RIA. Our results showed that fasting and postprandial plasma SLI and SS-28 levels were not significantly different in healthy and obese subjects. In conclusion SS-28 is the predominant form of circulating SLI in obese subjects. The normal pattern of fasting and postprandial plasma SLI and SS-28 levels in such subjects suggests that somatostatin does not have a pathogenetic role in obesity.

Cholecystokinin (CCK) regulates somatostatin secretion through both the CCK-A and CCK-B/gastrin receptors in sheep

1. Cholecystokinin (CCK) and gastrin both stimulate gastric somatostatin (SOM) secretion in vitro and thus have the potential to modulate their direct effects on the parietal cell. However, the relative potencies and the mechanisms of action of CCK and gastrin on SOM secretion in vivo have not been determined. 2. The objectives of the present study were to compare the in vivo potencies of the sulphated(s) and non-sulphated (ns) forms of gastrin heptadecapeptide (G-17) and CCK octapeptide (CCK-8) on SOM secretion, and to determine the nature of the receptors involved by repeating the studies in the presence of the CCK-A and CCK-B/gastrin receptor antagonists L-364,718 and L-365,260, respectively. All experiments were performed in the chronically cannulated sheep. 3. Dose-response experiments revealed the following potencies for SOM secretion: G-17s = CCK-8s > G-17 ns >> CCK-8ns. However, based on the plasma levels achieved and a higher metabolic clearance rate (MCR) for CCK, CCK-8s was the most potent. 4. Both the CCK-A and CCK-B/gastrin receptor antagonists suppressed CCK-8s-stimulated SOM output. In contrast, G-17s-stimulated SOM output was inhibited by only the CCK-B/gastrin receptor antagonist. 5. Both receptor antagonists increased basal plasma gastrin and CCK levels. 6. The predominant circulating SOM molecular form after both gastrin and CCK stimulation was SOM-14. 7. In conclusion, the sulphated forms of CCK and gastrin are more potent than the non-sulphated forms. Despite sharing a common biologically active carboxy terminus, CCK stimulates SOM secretion by both the CCK-A and CCK-B/gastrin receptors, while gastrin acts via the CCK-B/gastrin receptor alone. These findings explain in part why CCK is a net inhibitor of gastric acid secretion in vivo.

Somatostatin in neuroblastoma and ganglioneuroma

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. Somatostatin may inhibit neuroblastoma growth and induce apoptosis in vitro and was therefore investigated. Using a radioimmunoassay, we found that all ganglioneuromas contained high somatostatin concentrations (> 16 pmol/g), significantly higher than neuroblastomas (n = 117, median 2.8 pmol/g), healthy adrenals, Wilms' tumours, phaeochromocytomas and other neuroendocrine tumours (P < 0.001). Neuroblastomas contained more somatostatin than control tumours (P < 0.001-0.05). Neuroblastomas amplified for the MYCN oncogene contained less somatostatin than non-amplified tumours (1.2 pmol/g versus 4.0 pmol/g, respectively; P = 0.026). In a clinically unfavourable neuroblastoma subset (age > 12 months, stage 3 or 4) 16 children with high concentrations of somatostatin in primary tumours had a better prognosis than 23 with low somatostatin (46.7% versus 0% survival at 5 years, P < 0.005). Scintigraphy using 111In-pentetreotide identified tumours expressing high-affinity somatostatin receptors in vivo. However, no significant correlation was found between somatostatin receptor expression and peptide content in 15 tumours. Similarly, human SH-SY5Y neuroblastoma xenografts grown in nude rats showed low somatostatin concentrations, but were positive for somatostatin receptor scintigraphy. Treatment of these rats with the somatostatin analogue octreotide seemed to upregulate in vivo receptor expression of somatostatin and vasoactive intestinal peptide more effectively than 13-cis retinoic acid. In conclusion, somatostatin in neuroblastoma is associated with differentiation to benign ganglioneuromas in vivo and favourable outcome in advanced tumours. Furthermore, somatostatin receptor scintigraphy may identify tumours with high-affinity receptors in children that might benefit from targeted therapy using synthetic somatostatin analogues.

Biology of gut cholecystokinin and gastrin receptors

1. The stomach hormone gastrin and the intestinal hormone cholecystokinin (CCK) share a common C-terminal pentapeptide sequence but have different biological roles. Gastrin is the major stimulant of gastric acid secretion and has a growth stimulatory effect on the secretory part of the stomach. The physiological roles of CCK are the stimulation of pancreatic secretion and the contraction of the gall-bladder. 2. Several classes of receptors have been defined for peptides of the gastrin/CCK family. The CCKA receptor on pancreatic acini has a greater affinity for sulfated CCK than for gastrin, while the gastrin/CCKB receptor in gastric mucosa and brain has similar affinities for both gastrin and CCK. Potent and selective antagonists have been developed for both receptor classes. 3. The structures of the CCKA and gastrin/CCKB receptors have been deduced from the nucleotide sequences of cloned cDNA. The receptors, which both belong to the family with seven transmembrane segments, control secretion via similar signalling mechanisms. Occupation of either receptor leads to activation of phospholipase C, with resultant increases in intracellular levels of inositol triphosphate and Ca2+. Mitogenic signalling pathways are also being defined. 4. Recent studies have questioned the previous assumption that gastrin precursors are inactive. Glycine-extended gastrin17 has been shown to stimulate mitogenesis in some cell lines and may also have an autocrine role in the growth of colonic cancers. The receptors involved, which are clearly distinct in binding properties from the CCKA and gastrin/CCKB receptors, have not yet been cloned. Specific antagonists for the novel receptors will be required to define their function in further detail.

Stimulation of somatostatin secretion by 3-O-methylglucose in the perfused dog pancreas

CONCLUSION

3-O-methylglucose stimulates somatostatin secretion from the dog pancreas by a glucose-dependent and glucose-like effect. Therefore, it is possible that 3-O-methylglucose-stimulated somatostatin secretion is dependent on glucose metabolism.

BACKGROUND

Somatostatin secretion from the endocrine pancreas is stimulated by glucose, glyceraldehyde, and dihydroxyacetone but not affected by fructose, galactose, or ribose. Whether the nonmetabolizable glucose analog, 3-O-methylglucose affects somatostatin secretion is, however, not known.

METHOD

We therefore, examined whether the glucose analog affects somatostatin secretion in the perfused dog pancreas.

RESULTS

We found that when added to a medium containing 2.7 mM or 5.5 mM D-glucose, 3-O-methylglucose (10 mM) stimulated somatostatin secretion to the same extent as did an equivalent dose of D-glucose. The same stimulation was observed also with arginine at 2.5 mM in the perfusion medium. In contrast, 3-O-methylglucose did not stimulate somatostatin secretion in the absence of glucose in the perfusion medium. Mannoheptulose (5 mM), which inhibits glucose metabolism, completely blocked the secretion to both hexoses.

Effects of octreotide treatment on Graves' ophthalmopathy and circulating sICAM-1 levels

Efficacy of octreotide treatment for Graves' ophthalmopathy (GO) and the effects of this treatment on the serum levels of the circulating intercellular adhesion molecule-1 (sICAM-1) were evaluated. Ten patients with GO were treated with octreotide three daily SC injections of 100 micrograms, for 3 months. Octreotide treatment was initiated after restoration of euthyroidism with antithyroid drugs. All patients were treated with methimazole to maintain euthyroidism during the study. Sera were collected from all patients before and 3 months after initiation of the study, and from 20 age- and sex-matched healthy subjects for sICAM-1 measurement. sICAM-1 was measured by a sandwich ELISA method. Proptosis in all patients was evaluated by orbital CT scan before and 3 months after initiation of the study. Two of 10 patients did not respond to octreotide therapy, while the remaining eight patients showed regression or improvement after therapy. Octreotide therapy was particularly successful in patients with soft tissue involvement of GO (class II or III disease). Mean proptosis and ophthalmopathy index scores were significantly decreased after 3 months of octreotide therapy. Mean sICAM-1 levels were significantly higher in patients before octreotide therapy (470.5 +/- 52.6 ng/mL, p < 0.0001) when compared to normal subjects (186.5 +/- 53.3 ng/mL). Mean sICAM-1 levels were significantly decreased 3 months after octreotide therapy (from 478.7 +/- 52.6 to 415 +/- 42.8 ng/mL, p = 0.012) in the 8 patients who responded to therapy. In contrast, sICAM-1 levels remained unchanged or increased in two patients with poor response to octreotide therapy. Our results suggest that octreotide therapy could be a treatment modality in patients with GO. The mechanism by which octreotide acts on GO is not clear. The observed decrease in sICAM-1 levels during octreotide therapy suggests that octreotide may have immunomodulatory properties. Further investigation is needed to determine the optimal dose and duration of octreotide therapy.

Octreotide does not prevent bacterial translocation in an infant piglet model of intestinal ischemia-reperfusion

The process of bacterial translocation (BT) after ischemia/reperfusion (I/R) injury is reported to be mediated by local mucosal factors, the effects of pancreatic enzymes, epithelial disruption, and by dysfunctional intestinal motility. Octreotide (OCT), a somatostatin analog, has been postulated to protect against BT by influencing one or more of these factors. Twenty-two formula-fed piglets (weight, 3.5 +/- 0.5 kg; age, 20 +/- 5 days) were divided into four groups: control (no drug given; no I/R; n = 6), I/R (no drug given; n = 5), I/R plus low-dose OCT (LD OCT, 0.08 microgram/kg; n = 6), and I/R plus high-dose OCT (HD OCT, 8 micrograms/kg; n = 5). All experimental subjects had nonocclusive mesenteric ischemia induced by reversible pericardial tamponade with mesenteric flow decreased to 25 +/- 5% of baseline for 5 hours followed by 15 +/- 5 hours of reperfusion. Mesenteric lymph nodes (MLN), liver, spleen, blood, and peritoneum were harvested for blind microbial analysis. None of the animals in the control group experienced translocation to the tissues tested. All of the animals in the I/R group experienced BT to the MLN. The subjects in the LD OCT and HD OCT groups experienced BT to the MLN 66% and 80% of the time, respectively. Despite the reported clinical evidence that OCT can protect the intestinal mucosa from injury and increase the clearance of bacteria from the gastrointestinal tract, in this study in which variables other than I/R known to promote bacterial translocation were eliminated, OCT failed to modify or prevent the occurrence of translocation to the MLN after I/R injury.