Pancreatic somatostatinoma. Clinical features and physiological implications

The effects of somatostatin and selected analogs on lipid absorption in animals

Based upon the clinical finding that a Merck somatostatin-14 (S-14) analog induced steatorrhea in man, we sought to develop animal models to study the effects of S-14 and a series of synthetic analogs on absorption. Rats were trained to eat a diet (preweighed) containing 15% fat. Following the feeding period, the remaining diet was removed and the amount consumed recorded. This food conditioning of the rats was continued until the rats consumed approximately 15 g of the diet per day. Feces were collected and weighed prior to feeding periods. On test days, S-14 or analogs were administered sc to rats immediately prior to feeding. For each compound tested, fat absorption decreased in dose-dependent fashion. For example, S-14 at 0.5 mg/kg did not increase % of dietary fat in feces (% DFF). At 1.0 mg/kg, S-14 increased % DFF from 7.9 to 10.2 (p less than 0.01, pretest day vs test day), and at 10 mg/kg S-14, % DFF increased from 9.1 to 12.8 (p less than 0.001). For each analog, the subcutaneous dose required to decrease fat absorption in rats was several orders of magnitude higher than the intravenous dose required to inhibit insulin and glucagon. Moreover, the threshold for production of statistically significant increases in fecal fat differed among analogs when compared to their endocrine potencies. One analog administered in the model for 14 days was shown to produce consistent fat malabsorption throughout the entire test period; however, this lipid malabsorption was substantially more pronounced on the first three days of the treatment period. When the compound was not administered on day 15, the % DFF significantly decreased. In an attempt to develop a system more suitable for rapid screening, pancreatic secretagogues such as secretin or cholecystokinin, were administered intravenously to anesthetized rats whose duodena had been cannulated and perfused to enable collection of pancreatic secretions. Total amylase, lipase, and protein were determined in single animals in response to a secretagogue, both before and after iv pretreatment by S-14 or an analog. Pancreatic enzyme secretion in response to sequential secretagogue-stimulation was found to be reproducible for up to three injections and behaved in a dose-dependent fashion. In general, secretagogue-induced increases in amylase, lipase, and total protein were comparable. Pretreatment with the S-14 analogs substantially inhibited secretagogue-induced pancreatic exocrine secretion and was dose-dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin has an antiproliferative effect on concanavalin A-activated rat thymocytes

Somatostatin, a cyclic tetradecapeptide which is widely distributed in different tissues of the body, exerts an inhibitory effect on numerous cellular processes. It has been observed recently that somatostatin and its analogs were antimitogenic in several established cultured cell lines and in rat tumors. To determine whether this ubiquitous peptide had an antiproliferative effect on a primary culture of rat thymocytes, we observed its effect on the separation of the centrosome (a cell maker of the G1 to S traverse) and DNA synthesis of rat thymocytes activated by concanavalin A. Somatostatin inhibited both indices of proliferation in rat thymocytes at a concentration of 10(-8)M. This observation suggests that somatostatin, which has been localized in the thymus, may play a regulatory role in the growth and development of the cells found in the thymus gland, and may affect thymocyte function in disease states characterized by elevated circulating concentrations of somatostatin.

Production of immunoreactive-polypeptide hormones in cervical carcinoma

The levels of immunoreactive-polypeptide hormones were measured in tissue extracts of eight uterine cervical cancers by specific radioimmunoassays. In one case with argyrophil granules, high levels of somatostatin, pancreatic polypeptide, calcitonin, and vasoactive intestinal polypeptide (VIP) were found, ranging from 160 to 880 ng/g tissue. A second argyrophil cancer contained 310 ng/g tissue of somatostatin, and a third contained 1100 ng/g tissue of adrenocorticotropic hormone (ACTH) and 380 ng/g of beta-melanocyte-stimulating hormone (beta-MSH). In addition, of the five nonargyrophil cancers tested, four contained calcitonin, three had VIP, two had either somatostatin or glucagon, and one contained ACTH and beta-MSH; the measured levels of these hormones ranged from 1.4 to 2.3 ng/g tissue. Gel filtration on a Sephadex G-75 column showed that the immunoreactive-polypeptide hormones in the first case were chromatographically similar to the authentic or prehormones. These results indicate that ectopic production of multiple immunoreactive-polypeptide hormones is common not only in argyrophil cell carcinoma, but also in nonargyrophil cell carcinoma of the cervix.

Somatostatinoma of the cystic duct

An unusual tumor of the cystic duct in a 28-year-old woman is described. The patient presented with a painful distended gallbladder due to a small tumor occluding the cystic duct. Microscopically the tumor cells showed a nesting pattern suggestive of endocrine differentiation, but contained numerous lipid vacuoles and were argentaffin and argyrophil negative. Ultrastructurally, there were relatively few dense granules measuring 135 to 475 nm. Immunoperoxidase staining showed that the tumor cells contained somatostatin but did not contain immunoreactive ACTH, gastrin, calcitonin, glucagon, insulin, parathyroid hormone, or carcinoembryonic antigen. To the authors' knowledge, this is the first reported somatostatinoma occurring in the extrahepatic biliary tract.

Tumors of the diffuse endocrine system, histochemical and electron-optic aids, and pitfalls in diagnosis

Tumors of the Diffuse Endocrine System are a heterogeneous group of malignant neoplasms which have rather characteristic light microscopic and cytologic features. These are, however, not diagnostic and their identification with separation from non-neuroendocrine carcinomas require important adjunctive evaluations including histochemical analysis, immunocytochemical characterization and electron-optic identification of endocrine secretory products and paracrine effects in the cytoplasm of the neoplastic cells. The importance of proper classification cannot be over-emphasized because of the often considerable biologic and prognostic differences between neuroendocrine carcinomas and other types of carcinoma, notably metastatic carcinomas from the breast and the prostate. Furthermore, the separation of these lesions into two groups; a small cell type and those with large cells (carcinoid type) appears to have clinical significance in both diagnosis and response to therapy.

Growth hormone neuroregulation and the clinical relevance of somatostatin

The hypothalamus controls GH secretion from the anterior pituitary using two peptides; somatostatin inhibits GH, but physiologically the most important appears to GHRF, the structure of which has recently been discovered by two groups. This exciting development has not only given us further insight into the control of GH secretion, but also posed interesting questions as to the cause of the abnormal GH responses to various stimuli seen in patients with acromegaly. The other hypothalamic peptide controlling GH secretion, somatostatin has been the subject of intensive research in the last ten years. It is widely distributed and has important physiological actions including those involved in GH secretion and its action as a hypothalamic hormone. The secretion and synthesis of these two hypothalamic hormones is in turn modulated by a number of neurotransmitters, the most important of which appears to be dopamine. Knowledge gained in these studies has enabled the development of useful tools in the diagnosis of growth hormone deficiency as well as the only effective medical treatment for acromegaly. Much remains to be learnt of the physiology of growth hormone releasing factor and as a result further patients will benefit in the future.

Pancreatic somatostatinoma

The presence of cholelithiasis, steatorrhea, diabetes mellitus, and a pancreatic tumor initiated a diagnostic workup for somatostatinoma in a 43 year old black woman. The hypothesis of somatostatinoma was supported by a high level of plasma-like immunoreactivity and secretory granules resembling D-cell granules by electron microscopy. The patient has been euglycemic and well since complete resection of the tumor. This is the seventh reported case of somatostatinoma and the second to be benign.

Pancreatic somatostatinoma

A 66 year old woman was admitted for right hypochondriac pain and an abdominal tumor. A tumor of the pancreatic head with duodenal infiltration and liver metastases was found by laparotomy, and pancreaticoduodenectomy was performed. In addition, there was associated cholelithiasis and a goiter. Histopathologically, a tumor of the islets of Langerhans was suspected. The tumor tissue was positive by the Hellman-Hellerström silver impregnation method, and electron microscopy confirmed the presence of secretory granules similar to D cells. The tumor tissue contained a large quantity of somatostatin (1.3 micrograms/g). Finally, the diagnosis of somatostatin-producing tumor originating in the pancreas was made.

Somatostatinoma syndrome. Clinical, morphological and metabolic features and therapeutic aspects

A case of somatostatinoma syndrome in a 30-year-old woman is presented. Basal levels of growth hormone and of pancreatic and gastric hormones were reduced and the response of growth hormone, insulin and C-peptide to stimuli such as arginine, glucose, glibenclamide and calcium was virtually abolished. Similarly, gastric acid secretion, pancreatic exocrine function and intestinal absorption were significantly reduced. On the other hand, basal and stimulated levels of adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH) were within the normal range. Plasma somatostatin-like immunoreactivity was increased to 600-2,000 pg/ml (normal: 88-140 pg/ml). Immunocytochemical studies demonstrated the presence of somatostatin immunoreactive material in the primary tumour in the head of the pancreas and in the liver metastases. In spite of two courses of chemotherapy with streptozotocin and 5-fluorouracil the patient died due to liver failure 5 months after the first admission to hospital.

Immunoreactive somatostatin and vasoactive intestinal polypeptide in adrenal pheochromocytoma. An immunochemical and ultrastructural study

An adrenal pheochromocytoma producing somatostatin (SRIF) and vasoactive intestinal polypeptide (VIP) in a 17-year-old boy is presented. High concentrations of immunoreactive (IR)-SRIF were found in plasma taken from the antecubital vein (31.0-33.0 pg/ml) and the inferior caval vein near the tumor (54.6 pg/ml), but after removal of the tumor the values became normal (11.0-15.2 pg/ml). In two portions of the resected tumor, considerable but different amounts of IR-SRIF (151.7 and 12.1 ng/g wet wt) and IR-VIP (13.0 and 5.5 ng/g wet wt) were demonstrated with size heterogeneities. Immunohistochemically, many IR-SRIF cells and a few IR-VIP cells were observed, but no cell reacting with both anti-SRIF and anti-VIP sera was found. Electronmicroscopically, many tumor cells had catecholamine-like granules (250-350 nm in diameter) while some others had VIP-like granules (110-140 nm in diameter). However, no granules resembling the SRIF granules seen in the pancreatic D cells were found. This seems to be the first report of an adrenal pheochromocytoma that produces SRIF and VIP simultaneously. It provides information on the histogenesis of hormone-producing neurogenic tumors.

Neurohormonal peptides in endocrine tumors of the pancreas, stomach, and upper small intestine: I. An immunohistochemical study of 27 cases

Preliminary observations have indicated the existence of characteristic spectra of gastroenteropancreatic (GEP) neurohormonal peptides in endocrine tumors arising in foregut, midgut, and hindgut derivatives. In order to further explore this feature of GEP endocrine neoplasms, islet cell tumors from 14 patients were studied, as were endocrine tumors of the stomach, duodenum, and upper jejunum from 6, 5, and 2 patients, respectively. All tumors were examined immunohistochemically with antisera raised against islet hormones [insulin, somatostatin, glucagon, pancreatic polypeptide (PP)], peptides of the gastrin family [gastrin, cholecystokinin (CCK)], peptides of the secretin family [secretin, vasoactive intestinal peptide (VIP)], and substance P, neurotensin, leu-enkephalin, beta-endorphin, motilin, calcitonin, and ACTH. In addition, an ultrastructural investigation was made. Whenever possible, the immunohistochemical observations were correlated with the clinical manifestations and with the results of radioimmunochemical determination of GEP neurohormones in the blood. The pattern of immunoreactive neurohormonal peptides and the clinical picture were those to be expected in endocrine tumors arising in foregut derivatives. Some principles are proposed for the classification of GEP endocrine tumors on the basis of their histopathologic growth pattern, their spectrum of neurohormonal peptides, and their clinical manifestations.

Endocrine tumors of the duodenum. Clinical characteristics and hormone content

Nineteen patients with primary duodenal carcinoid were analysed retrospectively, and eight of the tumors were immunocytochemically examined. One tumor contained somatostatin, two tumors gastrin, two tumors both these peptides, and one tumor contained serotonin. In two tumors no peptide or amine could be demonstrated. Eight patients had ulcer symptoms and nine had gallstone disease. Only four patients had metastatic spread in spite of long delay. Five-year survival was 75% in 12 operated patients. No patient died of the tumor per se. It is concluded that a simple excision seems justified when the tumor is smaller than 2 cm, while probably more extensive surgery is needed when the tumor is larger or when there is local spread. Modern techniques of histofluorescence and immunocytochemistry facilitating a more precise classification will probably result in a better understanding as to symptomatology, prognosis, and making possible better treatment in the heterogenous group of carcinoid tumors.

Glucagonomas. Ultrastructure and immunocytochemistry

Pancreatic tumors harboring glucagon immunoreactive cells were found in four patients with diabetes mellitus. Alpha-cell (glucagon) granules were present in three tumors; pancreatic polypeptide (PP) immunoreactive cells were detected in two. In two patients the tumors were malignant and one of these had the glucagonoma syndrome; the other was a member of a family with MEN-type I syndrome. These cases illustrate three clinical subtypes of glucagonoma.

Duodenal somatostatinoma. Immunohistopathology and review of literature

A case of duodenal somatostatinoma is reported. The patient, a 54-year-old male, had complained of an epigastric pain due to gastric ulcer and a duodenal polyp was unexpectedly found at a gastrectomy. The polyp showed basically tubular adenocarcinoma, with negative argyrophil and argentaffin reactions. By an indirect immunofluorescent examination almost all of the tumor cells were revealed as somatostatin-immunoreactive. Big somatostatin was also positive. Radioimmunoassay of the tumor indicated 6400 pg of somatostatin-like immunoreactivity per milligram of wet tissue. This seems to be the second case of duodenal somatostatinoma, following the case reported by us previously.

Effects of some drugs and peptide hormones on the responsiveness of the rabbit isolated gall-bladder to cholecystokinin

1. The efficacies of some standard preparations of CCK were compared and the effects of some drugs and peptide hormones on the responsiveness of the rabbit isolated gall-bladder to cholecystokinin were studied with an established automatic method of estimating cholecystokinin. 2. Atropine, propranolol, phentolamine mesylate and lignocaine were shown to have no effect on the responsiveness of the rabbit isolated gall-bladder. 3. Glucagon, somatostatin, pentagastrin, pancreatic polypeptide, motilin and the Karolinska preparation of secretin had no effect on the preparation alone and caused only slight changes when given with cholecystokinin. 4. The Boots preparation of secretin exhibited a small cholecystokinin effect when given alone, but considerably inhibited cholecystokinin-induced contractions. 5. The desulphated C-terminal octapeptide of cholecystokinin also exhibited inhibitory effects.

Immunoreactive somatostatin in catecholamine-producing extra-adrenal paraganglioma

A patient with catecholamine-producing extra-adrenal paraganglioma was found to have a high concentration of immunoreactive somatostatin (IR-SRIF) in the peripheral blood plasma (47.0 pg/ml, normal; 13.3 +/- 5.3 pg/ml, mean +/- SD). After removal of the tumor, the plasma SRIF level fell within normal range (8.7 pg/ml). In the resected tumor, a considerable amount of IR-SRIF (71.0 ng/g wet weight)( was also detected and SRIF-positive tumor cells were demonstrated by the immunoperoxidase technique. Chromatographic analysis of an extract of the tumor showed the presence of two IR-SRIF components of large molecular size besides a component consistent with authentic tetradecapeptide SRIF (SRIF 14), and one of these had the same molecular size as octacosapeptide SRIF (SRIF 28). This seems to be the first report of a catecholamine-producing extra-adrenal paraganglioma that produces IR-SRIF with molecular heterogeneity.

Gastrointestinal/pancreatic hormone concentrations in the portal venous system of nine patients with organic hyperinsulinism

Percutaneous transhepatic sampling of blood in the portal venous system (TPVS) was used to; (1) localize hormone secreting tumors and help in differentiating tumors from diffuse disease (nesideoblastosis and hyperplasia with adenomata) in 9 patients with fasting hypoglycemia and hyperinsulinism, and (2) study the concentration an distribution of the immunoreactive peptides: insulin (IRI), gastrin (IG), glucagon (IRG), pancreatic polypeptide (hPP), and somatostatin (SRIF-LI), in the venous drainage of the uninvolved portion of the pancreas and GI tract. Localized elevations of IRI (64-920 microunits/ml) predicted tumor localization in 6 patients with single tumors that were not demonstrable angiographically. In one patient with nesideoblastosis and another with islet cell hyperplasia with adenoma, elevated IRI concentrations at multiple locations suggested a diffuse or multicentric process. Elevations of SRIF-LI in the same region as IRI elevations in one patient and of IRG in another patient suggested that these tumor produced two hormones. Some problems in the interpretation of portal venous insulin concentrations are discussed. The locations of maximum portal venous system plasma concentrations and portal-arterial gradients (mean +/- SE pg/ml) in five patients with small single insulinomas were: IG, gastrocolic trunk (126 +/- 27, 46 +/- 22); IRG, proximal splenic vein (130 +/- 30, 47 +/- 13) and gastrocolic trunk (131 +/- 23, 60 +/- 13); hPP, portal vein (164 +/- 48, 49 +/- 22); SRIF-LI, superior mesenteric vein (186 +/- 50, 57 +/- 20) and gastrocolic trunk (178 +/- 59, 55 +/- 21). It is concluded; (1) TPVS can be used successfully to localize single insulin-secreting tumors of the pancreas and to help distinguish them from diffuse disease but problems in such differentiation do occur, (2) circulating SRIF-LI and IRG are derived from both the pancreas and the gut, IG predominantly from the proximal gut and hPP from the head of the pancreas, and (3) The data provide new information for the interpretation of portal insulin concentrations in patients with organic hyperinsulinism and of hormone concentrations for localization of peptide-producing tumors of the pancreas other than insulinomas.

Selective effects of somatostatin-14, -25 and -28 on in vitro insulin and glucagon secretion

The widely occurring tetradecapeptide somatostatin (SRIF-14) has been variously implicated as a neurotransmitter, a neurohormone, a cybernin (local regulatory factor) and a hormone. In the first isolation of SRIF-14 from hypothalamic extracts and subsequent extracts of other tissues, peptides of higher molecular weight but with similar activity have been noted. Recently two such peptides have been characterized as the 28-amino acid SRIF-28 (from porcine gastro-intestinal tract and porcine and ovine hypothalamus and the 25-amino acid SRIF-25 (from ovine hypothalamus), each of which consists of an N-terminal extension of SRIF-14. We now report that SRIF-28 and SRIF-25 are more potent than SRIF-14 in the inhibition of insulin release, but that SRIF-14 preferentially inhibits glucagon release. This suggests that SRIF-28 and SRIF-25 are not mere biosynthetic precursors of SRIF-14 and that their differential release may be physiologically important.

Somatostatin and diabetes

Somatostatin, a tetradecapeptide originally isolated from the hypothalamus on the basis of its ability to inhibit the secretion of growth hormone, is now known to be widely distributed in various endocrine and gastrointestinal tissues and to have diverse actions, including inhibition of insulin and glucagon secretion. The location of somatostatin in pancreatic islet D cells suggests that it may act as a local regulator of insulin and glucagon secretion. Changes in islet D-cell function in experimentally-induced and spontaneous diabetes in animals suggest that the peptide may be involved in the pathogenesis of diabetes. Clinical studies with the peptide have provided insight into the physiologic roles of glucagon and growth hormone, and have indicated a potential therapeutic use for somatostatin in diabetes in man.

Effects of somatostatin on gastrointestinal hormone-induced glycogenolysis and gluconeogenesis in cultured liver cells

When isolated rat liver cells were incubated for 15 min in the presence of vasoactive intestinal peptide, gastric inhibitory polypeptide, secretin or glucagon at a concentration of 2.0 micrograms/ml, glycogenolysis was stimulated by 30%-67% above the control. Slight but significant increase on gluconeogenesis was also observed by the addition vasoactive intestinal peptide, gastric inhibitory polypeptide or secretin. Somatostatin inhibited both glycogenolysis and gluconeogenesis induced by these hormones, but the degrees of inhibition are clearly much higher in the hormone-induced gluconeogenesis than glycogenolysis, and no significant inhibition of glycogenolysis was observed in case of glucagon and VIP. These results suggest the possibility that the so-called enterohepatic axis may play a part of roles in the regulation of serum glucose levels through gastrointestinal hormones belonging to the secretin family, and that it may be further regulated by somatostatin through gluconeogenesis.

Isolation and structure of pro-somatostatin: a putative somatostatin precursor from pig hypothalamus

An octacosapeptide that we named pro-somatostatin has been isolated from acid extracts of porcine hypothalami and found to have the amino acid sequence Ser-Ala-Asn-Ser-Asn-Pro-Ala-Met-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys. This octacosapeptide possesses high somatotropin (growth hormone) and prolactin release-inhibiting activity in vitro. It also crossreacts strongly with antisera generated against the somatostatin tetradecapeptide. This octacosapeptide is most likely a precursor (pro-hormone) of somatostatin in the hypothalamus. The existence of still larger molecular size precursors of somatostatin was also observed.

Glucagonomas, VIPomas and somatostatinomas

The three new endocrine pancreatic tumour syndromes dealt with in this chapter--glucagonomas, VIPomas and somatostatinomas--are not common. Nonetheless, the patients are potentially curable by tumour resection and therefore wider knowledge of the clinical picture is of considerable importance. It is possible that there are still further, presently unrecognized, clinical syndromes waiting in the wings and studies are currently under way to try to ascertain the effects of elevated PP. Early tumour diagnosis depends firstly on clinical acumen but the easy availability of a reliable radioimmunoassay service is of considerable importance as this allows the physician to screen likely patients and so detect cases at an early stage. Tumour localization is still a major problem and requires expert radiological assistance. The dramatic effectiveness of the cytotoxic agent streptozotocin illustrates the great potential of chemotherapy and it may be expected that further drugs of this nature will be discovered, especially as it is now possible to establish isolated tumour strains for mass drug screening. These tumours have shown the effect of long continued peptide elevation and given valuable insight into the physiological role of the respective regulatory peptides.

Pancreatic somatostatinoma presenting with hypoglycaemia

A 33-year-old woman with a 2 month history of vague ill health was admitted to hospital in hypoglycaemic coma. Preoperative investigation suggested malignant insulinoma as the probable cause of illness, but immunohistological examination of the tumour showed it to consist mainly of somatostatin-containing cells but sparse insulin-secreting cells were also present. Plasma immunoreactive somatostatin levels were from fifty to 200 times the upper limit of normal and rose in response to arginine and fell during diazoxide infusion. The hypoglycaemia was unusually sensitive to the hyperglycaemic effects of diazoxide and chlorothiazide and, with 5-fluorouracil as the only specific anti-tumour agent, there has been clinical, biochemical and radiological evidence of tumour regression.

Molecular forms of somatostatin in normal subjects and in patients with pancreatic somatostatinoma

Two patients with somatostatin-secreting pancreatic tumours are described, one presenting with hypoglycaemia due to hyperinsulinism, and the other with Cushing's syndrome due to ectopic ACTH production. When plasma from these patients was subjected to gel chromatography under conditions designed to prevent somatostatin binding to larger proteins, a peak of monomeric immunoreactive somatostatin was observed as well as several large molecular weight forms. These larger forms of somatostatin could be dissociated into monomeric somatostatin by dithiothreitol. Similar studies on plasma obtained from normal subjects also showed heterogeneity of circulating somatostatin. Extracts of tumour tissue from both patients contained predominantly monomeric somatostatin, but only small amounts of high molecular weight somatostatin which differed from the profile seen in plasma. The site(s) of origin of the large molecualr weight forms of somatostatin seen in plasma and their relative biological activities remain to be established.

Isolation and characterization of immunoreactive somatostatin from fish pancreatic islets

Using a radioimmunoassay with labeled synthetic tetradecapeptide somatostatin, a large amount of immunoreactive somatostatin was found in the principal pancreatic islet of the channel catfish (Ictalurus punctata). The purpose of these experiments was to isolate and characterize the somatostatin-like material. Extracts of islets were chromatographed on a Bio-Gel P-30 column, and over 90% of the immunoreactive somatostatin migrated with proteins at least twice the size of synthetic tetradecapeptide somatostatin. This fraction was further purified by ion-exchange chromatography on carboxymethyl-cellulose and DEAE-cellulose columns. Two peptides were obtained with identical immunoreactivity, which was approximately 25% that of the synthetic somatostatin. Each peptide was judged to be >95% pure by thin-layer electrophoresis, polyacrylamide gel electrophoresis at pH 8.9, and highpressure liquid chromatography. Further criteria of purity included amino-terminal analysis of fraction IV yielding only aspartic acid. A total of 1.3 mg of fraction II, and 3.8 mg of fraction IV somatostatin-like peptides were obtained from 10 g of fresh frozen islets. Characterization of the two peptides revealed both peptides slightly more acidic than synthetic tetradecapeptide somatostatin. Fraction II had an isoelectric point of 8.0-8.3, and fraction IV 8.3-9.0. Molecular weight estimation by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis revealed similar mobility of both peptides, between pancreatic polypeptide (mol wt 4,500) and glucagon (mol wt 3,500). The mobility was not altered by reduction, and was approximately twice the size of synthetic tetradecapeptide somatostatin (mol wt 1,800). This confirmed that the peptides were single polypeptide chains and not aggregates, or somatostatin bound to larger proteins. Molecular weight determination by gel filtration chromatography on Bio-Gel P-6 in 8 M urea gave an estimated mol wt of 3,700. Amino acid analysis of the two immunoreactive somatostatins indicated that they were very similar in composition. Both pancreatic somatostatins (1 muM) had full biological activity relative to synthetic somatostatin measured as inhibition of growth hormone release from rat anterior pituitary cells.

A radioimmunoabsorbent assay for plasma somatostatin

A solid phase radioimmunoassay for determination of immunoreactive somatostatin (IRS) in plasma is described. Plasma samples obtained from 30 apparently healthy persons and from 5 anaesthetized pigs were extracted with acetone-petroleum ether. The antibodies (R 141 and R 101) were conjugated to cyanogenbromide activated microcrystalline cellulose. Tyr1-somatostatin was iodinated according to the lactoperoxidase method. After extraction the recovery of somatostatin varied between 80 and 118%. The sensitivity of the assay was 5--10 pg/ml and the intra- and interassay variation ranged between 8 and 20%. The mean (+/- S.D.) value of IRS in systemic blood in man was 77 (+/- 19) pg/ml. Intravenous administration of 10 micrograms/kg synthetic somatostatin to anaesthetized pigs was followed by a 20-fold increase in plasma IRS. The hypersomatostatinemia rapidly vanished with a half-life of 3.5 min. The level of IRS in cerebrospinal fluid was unchanged by intravenous somatostatin at this dose.

Somatostatinoma of the duodenum

An adenocarcinoma of the second portion of the duodenum in a 26-year-old male is presented. The patient was suffering from pain in the epigastrium. Immunofluorescent studies revealed that it consisted almost exclusively of cells with a distincly positive somatostatin-like immunoreactivity. Ultrastructurally, the cytoplasm of the tumor cells had numerous large round granules (about 400 micrometers) with variable electron density. Most of these cells closely resembled the D cells normally seen in the duodenum and the islets of the pancreas, although a few argyrophil cells could be demonstrated by light microscopy. Radioimmunoassay of extracts of the tumor revealed a large amount of somatostatin (2260 pg/mg); substance P and VIP were detected also. Somatostatinoma has been known to occur in the pancreas, but this seems to be the first somatostatinoma found in the intestine.

Pancreatic apudomas

Pancreatic apudomas are not common but are frequently curable. Thus, it is important for every clinician to be fully aware of the varied clinical syndromes that suggest their presence. The availability of specific radioimmunoassays has made confirmation of the diagnosis relatively simple. Advances in the techniques for staining the different cell types have led to the recognition that many of these tumors are mixed, and that the general term "pancreatic apudoma" is appropriate. Pancreatic endocrine tumors, as examples to "nature's experiments," have yielded considerable insight into the possible physiologic effects of the various peptides they produce. It is to be hoped that further study of tumors such as the somatostatinoma and PPoma may yield further information about these enigmatic compounds.

Somatostatinoma syndrome. Biochemical, morphologic and clinical features

Diabetes mellitus, steatorrhea, cholelithiasis and a tumor distorting the duodenum prompted a work-up for somatostatinoma in a 52-year-old man. The responses of pancreatic B-cells but not of A-cells to nutrient stimuli were inhibited, and growth-hormone release was suppressed, suggesting somatostatin resistance in some target tissues. Plasma somatostatin-like immunoreactivity ranged from 9000 to 13,000 pg per milliliter (normal: 88+/-8, mean +/- S.E.M.) and was distributed in four molecular forms, including free somatostatin. The primary tumor contained 5 microgram of somatostatin-like immunoreactivity per milligram of wet tissue, distributed in three of the molecular forms noted in plasma. Plasma calcitonin was also elevated (4650 pg per milliliter; normal: less than 120). Immunocytochemical studies showed that cells of the primary tumor contained somatostatin and calcitonin but no other peptide hormones. Only somatostatin was present in the metastases. Somatostatin was localized electron microscopically in all secretory granules, irrespective of size and shape, whereas calcitonin was present only within a single subpopulation of small granules in the same cells.