Circulating tachykinins (substance P, neurokinin A, neuropeptide K) and the carcinoid flush

What Is Carcinoid Syndrome? A Critical Appraisal of Its Proposed Mediators

Carcinoid syndrome (CS) is a debilitating disease that affects approximately 20% of patients with neuroendocrine neoplasms (NEN). Due to the increasing incidence and improved overall survival of patients with NEN over recent decades, patients are increasingly suffering from chronic and refractory CS symptoms. At present, symptom control is hampered by an incomplete understanding of the pathophysiology of this syndrome. This systematic review is the first to critically appraise the available evidence for the various hormonal mediators considered to play a causative role in CS. Overall, evidence for the putative mediators of CS was scarce and often of poor quality. Based on the available literature, data are only sufficient to agree on the role of serotonin as a mediator of CS-associated diarrhea and fibrosis. A direct role for tachykinins and an indirect role of catecholamines in the pathogenesis of CS is suggested by several studies. Currently, there is insufficient evidence to link histamine, bradykinin, kallikrein, prostaglandins, or motilin to CS. To summarize, available literature only sufficiently appoints serotonin and suggests a role for tachykinins and catecholamines as mediators of CS, with insufficient evidence for other putative mediators. Descriptions of CS should be revised to focus on these proven hormonal associations to be more accurate, and further research is needed into other potential mediators.

The roles of kisspeptin and neurokinin B in GnRH pulse generation in humans, and their potential clinical application

The delivery of gonadotropin-releasing hormone (GnRH) in a pulsatile mode to the gonadotropes has long been known to be essential for normal reproductive function. There have been numerous studies aimed at dissecting out the mechanisms underlying GnRH pulse generation. The discovery of kisspeptin as an upstream regulator of GnRH attracted the possibility that pulsatile kisspeptin governed the pulsatile secretion of GnRH. Subsequent studies have shown the importance of the neurokinin B (NKB) system in modulating kisspeptin secretion and this GnRH. A number of studies in laboratory rodents have supported this notion. By contrast, we present data from clinical studies in men and women, in a range of contexts, showing that continuous infusion of kisspeptin 10 at receptor-saturating levels gives rise to an increase in luteinizing hormone (LH) (GnRH) pulse frequency. This has been demonstrated in normal healthy and hypogonadal men, in normal women during the mid-cycle LH surge, in men and women with mutations in the genes encoding NKB or its receptor, neurokinin 3 receptor (NK3R), in women with polycystic ovary syndrome treated with NK3R antagonist, and in women treated with NK3R antagonist during the LH surge. These finds indicate that pulsatile secretion and action of kisspeptin on GnRH neurons is not required for the generation of LH (GnRH) pulses in humans. We also report that there is an absence of desensitization in humans exposed to continuous infusion of kisspeptin-10 at receptor-saturating concentrations over 22 h and briefly review GnRH, kisspeptin and NKB analogs and their clinical application.

Hypothalamic neurokinin signalling and its application in reproductive medicine

The discovery of the essential requirement for kisspeptin and subsequently neurokinin B signalling for human reproductive function has sparked renewed interest in the neuroendocrinology of reproduction. A key discovery has been a population of cells co-expressing both these neuropeptides and dynorphin in the hypothalamus, directly regulating gonadotropin hormone releasing hormone (GnRH) secretion and thus pituitary secretion of gonadotropins. These neurons also project to the vasomotor centre, and their overactivity in estrogen deficiency results in the common and debilitating hot flushes of the menopause. Several antagonists to the neurokinin 3 receptor, for which neurokinin B is the endogenous ligand, have been developed, and are entering clinical studies in human reproductive function and clinical trials. Even single doses can elicit marked declines in testosterone levels in men, and their use has elicited evidence of the regulation of ovarian follicle growth in women. The most advanced indication is the treatment of menopausal vasomotor symptoms, where these drugs show remarkable results in both the degree and speed of symptom control. A range of other reproductive indications are starting to be explored, notably in polycystic ovary syndrome, the most common endocrinopathy in women.

Cardiac manifestations of gastrointestinal carcinoid tumor

Carcinoid tumors are rare, slow-growing tumors found primarily in the GI tract. Carcinoid syndrome develops when vasoactive substances (particularly serotonin) released by carcinoid tumors gain access to the systemic circulation. Carcinoid heart disease develops in patients with carcinoid syndrome and is commonly associated with the development of right-sided valve dysfunction and signs of symptoms of right heart failure. Timely surgical intervention provides relief from symptoms and may improve survival. Management of these patients should be undertaken in a specialized center by a multidisciplinary team with appropriate expertise.

Carcinoid heart disease

Carcinoid tumors are rare, indolent neuroendocrine tumors that are often associated with a syndrome characterized by episodic flushing, secretory diarrhea, bronchospasm, and hypotension-the carcinoid syndrome. Cardiac involvement occurs in one-half to two-thirds of patients with carcinoid syndrome and is associated with a worse clinical outcome. Carcinoid heart disease is characterized by endocardial plaque-like deposits found predominantly on right-sided heart valves, leading to the combination of valvular stenosis and regurgitation. Left-sided cardiac involvement can also occur in <10% of patients. Somatostatin analogs form the therapeutic cornerstone in the medical management of these patients. Cytotoxic chemotherapy has had only limited success in the treatment of metastatic carcinoid tumors. Hepatic resection or palliative cytoreduction may be of benefit in patients with limited hepatic disease. Hepatic artery embolization is usually applied if a patient is not eligible for surgical debulking. The development and progression of carcinoid heart disease are associated with an unfavorable outcome. In those patients having severe cardiac involvement and well-controlled systemic disease, valve replacement surgery has been found to be an effective treatment that can both relieve intractable symptoms and contribute to improved clinical outcomes.

New and emerging syndromes due to neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare, slow-growing neoplasms characterized by their ability to store and secrete different peptides and neuroamines. Some of these substances cause specific clinical syndromes whereas others are not associated with specific syndromes or symptom complexes. NETs usually have episodic expression that makes diagnosis difficult, erroneous, and often late. For these reasons a high index of suspicion is needed, and it is important to understand the pathophysiology of each tumor to decide which biochemical markers are more useful and when they should be used.

Treatment of gastric carcinoids

Gastric carcinoid tumors are uncommon, but their percentage among all gastric malignancies has increased to 1.8%. Although they are most often discovered incidentally during endoscopy, gastric carcinoids can present with abdominal pain, bleeding, or symptoms related to the secretion of bioactive substances, most commonly histamine. Gastric carcinoids originate from the foregut and are derived from histamine-containing enterochromaffin-like (ECL) cells. Type I gastric carcinoid, the most common, exhibits slow growth and benign behavior. It occurs within the setting of chronic atrophic gastritis with achlorhydria-induced hypergastrinemia. Gastrin acts directly on ECL cells to induce hyperplasia, dysplasia, and, eventually, neoplasia. Type II gastric carcinoid, the least common type, occurs in patients with gastrinoma-associated multiple endocrine neoplasia syndrome-type 1 (MEN-1). The overall survival is related more to the underlying MEN-1 syndrome than to the gastric carcinoid. Rodents readily develop gastric carcinoid tumors in response to hypergastrinemia. However, in humans, other factors in addition to hypergastrinemia, such as pernicious anemia or MEN-1, must be present, implying that a genetic predisposition is necessary for the development of these tumors. Type III or sporadic gastric carcinoids exhibit a more malignant behavior, with overall 5-year survival rates of less than 50% and normal serum gastrin concentrations. Treatment of all types of gastric carcinoids is predicated upon accurate classification and staging. Radiolabeled somatostatin analogues are superior to conventional radiologic imaging techniques in detecting both primary and metastatic lesions. Treatment of choice for localized disease is excision, either endoscopically or surgically. Antrectomy, by eliminating the trophic effect of gastrin, can be useful for select type I carcinoids. Long-acting somatostatin analogues are excellent palliative agents.

An intestinal neuroendocrine tumour associated with paroxysmal ventricular tachycardia and melaena in a 10-year-old boxer

A 10-year-old female neutered boxer was presented with a five-week history of episodic collapse and melaena. Twenty-four-hour electrocardiograph (Holter) analysis revealed the collapsing episodes to coincide with episodes of paroxysmal ventricular tachycardia. Investigation of the dog's melaena revealed a gastric ulcer which was treated medically and an ileocaecal mass which was surgically excised. Histopathological examination of the mass was consistent with a neuroendocrine (carcinoid) tumour. The patient's recovery after surgery was unremarkable. At six-week follow-up, there had been no further episodes of melaena or collapse and repeat Holter analysis did not show any significant abnormalities. In this dog the gastric ulceration and paroxysmal ventricular tachycardia could be attributed to a paraneoplastic syndrome as a result of circulating vasoactive substances released by the tumour; this is supported by the evidence that all clinical signs resolved after surgical excision of the mass and the dog was clinically well 18 months after surgery.

Increased intestinal non-substance P tachykinin concentrations in malignant midgut carcinoid disease

BACKGROUND

Diarrhoea is an important feature of the carcinoid syndrome, and various agents which may be released from carcinoid tumours have been considered to contribute pathophysiologically. The aim of the present study was to determine luminal concentrations of possible chemical mediators in an uninvolved small intestinal segment using a two-balloon six-channel tube in nine patients with malignant midgut carcinoid disease.

METHODS

All patients were treated with interferon and/or octreotide to alleviate the most severe flush. Ion transport was measured during luminal perfusion and luminal perfusate concentrations of calcitonin gene-related peptide, neurotensin, prostaglandin E (PGE)2, neuropeptide Y, somatostatin, vasoactive intestinal polypeptide, substance P and other tachykinins (neurokinin A, neurokinin B, neuropeptide K, eledoisin) were determined by separate assays.

RESULTS

Carcinoid patients showed decreased absorption of Cl-, Na+, K+ and water and increased luminal content of non-substance P tachykinins to 424.5 fmol/cm per h, compared with 255.5 fmol/cm per h in control subjects. There were also increased luminal concentrations of PGE2, commonly claimed as a more general mediator of diarrhoea.

CONCLUSIONS

The observed increase in intestinal tachykinins may involve extended activity from tachykinin-containing intrinsic neurones in the enteric nervous system, contributing to enhanced intestinal motility and secretory diarrhoea in patients with carcinoid syndrome.

Immunostaining for vasostatin I distinguishes between ileal and lung carcinoids

Although chromogranin A (CgA) is a recognized marker of neuroendocrine tumours, little is known about the distribution of the CgA-derived peptides, vasostatin (VST) I or II, in these tumours. Rabbit polyclonal antiserum was raised to a fragment of VST I and used to immunostain sections (5 microns) of wax-embedded tumour tissue. Immunoreactivity (IR) was detected using swine anti-rabbit fluorescein secondary antibody and sections were viewed by fluorescence microscopy. Of 24 tumours from patients with lung carcinoids, one was weakly positive, while 23 of 26 ileal carcinoid tumours were immunoreactive. Metastatic deposits from patients with ileal carcinoids also tended to be immunoreactive (9/10). The difference in IR between lung and ileal carcinoid primary tumours did not appear to be related to the metastatic potential, since appendiceal tumours, which seldom metastasize, also tended to be immunoreactive (4/6) for VST I. The strongest IR was recorded in two patients with flushing as a result of ileal carcinoids; five other 'flushers' with ileal carcinoids were also immunopositive for VST I-like IR. By contrast, patients with flushing as a result of lung carcinoids were immunonegative for VST. In conclusion, VST I-like IR may assist in the identification of a secondary deposit from an unknown primary site.

Cardiovascular complications of malignant carcinoid disease

Carcinoid tumors are endocrinologic malignancies often associated with a characteristic syndrome-the malignant carcinoid syndrome. Cardiovascular manifestations of this rare illness result from unique pathophysiologic characteristics, are associated with poor prognosis, and are difficult to treat medically. The hemodynamic consequences of this disease present unique management problems perioperatively. New pharmacologic and surgical therapies for malignant carcinoids have improved quality of life for patients to the extent that carcinoid heart disease now has more impact on morbidity and mortality rates. Cardiologists may be called on to diagnose and treat this rare cardiac disease. We review, for consulting cardiologists, the pathophysiologic characteristics, cardiovascular manifestations, and management of this disease.

Gastrointestinal carcinoid tumors: current management strategies

BACKGROUND

Carcinoid or neuroendocrine tumors of the gastrointestinal tract, although characteristically indolent, are also quite heterogeneous both with respect to histologic and endocrine features and with respect to clinical presentation and behavior.

PURPOSE

This study was undertaken to review and summarize the current literature on classification controversies, site-specific carcinoid presentation and behavior, and diagnostic and management strategies for primary and advanced carcinoid tumors and the carcinoid syndrome.

RESULTS

For carcinoid tumors, oncologic results depend on the location of the primary tumor, extent of locoregional and metastatic disease, functioning status of the tumor, and the feasibility of complete surgical extirpation. Whereas favorable survival rates are typically observed for appendiceal and rectal primaries, less favorable rates are often observed for colonic and ileal tumors. A search for additional tumors is generally advised because multiple carcinoids and second neoplasms are not uncommon. Because of the indolent nature of the tumor and because these therapies have been shown to improve quality and quantity of life, otherwise fit patients with advanced carcinoid disease should be treated with aggressive medical and surgical therapies. Development of a malignant carcinoid syndrome indicates the presence of a functionally active carcinoid tumor and portends a poor prognosis.

CONCLUSION

Gastrointestinal carcinoids, although malignant, behave differently from other carcinomas. Results are highly variable and must be individualized according to the site of the primary tumor, extent of spread, and general condition of the patient. A prolongation of quality life can often be accomplished through aggressive medical and surgical therapies.

Gastroenteropancreatic effects of xenin in the dog

Xenin is a 25 amino acid peptide detected in the gastric mucosa of various mammals. It has since been found in low concentrations in other tissues. Xenin plasma concentrations increase after meals. The present study reports some gastroenteropancreatic effects of this peptide in the dog. Intravenous infusion of 64 pmol/kg min synthetic xenin significantly inhibited pentagastrin-stimulated gastric acid secretion and stimulated exocrine pancreatic secretion of volume and protein. Further, intravenous infusion of xenin in a dose of 1.0 pmol/kg min stimulated jejunal motility in the anaesthetized dog. An intravenous infusion of 32 pmol/kg min xenin raised plasma concentrations of pancreatic polypeptide, vasoactive intestinal polypeptide, insulin and glucagon. The present experiments therefore indicate manifold bioactive properties of intravenously infused xenin in the dog, with jejunal motility the most sensitive target. Conclusions as to the physiological role of xenin cannot be drawn from the present experiments. The release of other hormonal peptides indicates a complex action of xenin.

Carcinoid disease: review of the literature

Carcinoid syndrome is the product of a rare but fascinating malignant neoplasm. Carcinoid syndrome was described more than 100 years ago, and recent advances in diagnostic localization, elucidation of the mechanisms of oncogenesis, treatment options, and, consequently, patient prognosis have been made. Current modalities of treatment, possible therapeutic implications of new avenues of research, and current literature on the chemotherapeutic combinations used are reviewed.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.

Serotonin, catecholamines, and spontaneous midgut carcinoid flush: plasma studies from flushing and nonflushing sites

BACKGROUND/AIMS

Serotonin is the diagnostic hallmark of midgut carcinoids, but the pathophysiology of spontaneous flushing is unknown. The aim of this study was to assess to what extent serotonin and catecholamine blood levels are related in time with spontaneous midgut carcinoid flush.

METHODS

Using specific radioenzymatic assays, we measured prospectively before, during, and after spontaneous flushing platelet-poor plasma and whole blood serotonin and plasma catecholamines and their metabolites in 10 patients with primary midgut carcinoids. Blood was drawn simultaneously from a forearm vein and an external jugular vein draining the flushing area.

RESULTS

During flushing, plasma serotonin and norepinephrine levels increased (P < 0.001) over preflush levels at both sampling sites. Intraflush serotonin and norepinephrine were twice as high (P < 0.01) in external jugular (9.57 +/- 1.40 ng/mL and 857 +/- 33 pg/mL, respectively) than in antecubital plasma (4.59 +/- 0.73 ng/mL and 471 +/- 26 pg/mL). Preflush and postflush levels were similar at both venous sites.

CONCLUSIONS

Vein plasma serotonin and norepinephrine levels do increase during midgut carcinoid flush, especially in the flushing area. This may reflect a local release secondary to flush but also suggests a role for these bioamines in the pathogenesis of flushing.

Silent ischemia: a hypothetical mechanism

Ischemia of visceral organs, especially the heart, is often a painful and potentially life-threatening condition. However, in at least 75% of all cases myocardial ischemia may be "silent" (i.e., without pain or sensation). Yet, the mechanisms responsible for silent ischemia are not well understood. As such, many different theories have been advanced to explain silent ischemia; however, none have been able to adequately explain all of the experimental and clinical findings. This paper proposes a hypothetical mechanism that may help to understand mechanisms of silent ischemia.

Cutaneous markers of internal malignancy. II. Paraneoplastic dermatoses and environmental carcinogens

A variety of cutaneous disorders may reflect the presence of an internal disease. The ability to recognize those that may indicate an underlying malignancy is of particular importance. In part I of this series malignant involvement of the skin, either direct or metastatic, and the genodermatoses with malignant potential were reviewed. In this portion, we describe the paraneoplastic dermatoses as well as the cutaneous effects of some environmental carcinogens associated with internal malignancy. In addition, several uncommon and controversial associations between benign dermatoses and internal malignant disease will be discussed.

Calcitonin, as SMS 201-995, ameliorates the VIPoma syndrome

A 72-year-old woman was referred to our hospital for diarrhea, abdominal and back pain, weight loss, low serum potassium level. Pathological findings and high circulating Vasoactive Intestinal Peptide (VIP) levels allowed us to diagnose "VIPoma syndrome". The patient underwent a treatment with SMS 201-995 with improvement of symptomatology and reduction of circulating VIP levels. After a wash-out period the patient was treated with salmon calcitonin with a net improvement of diarrhea, normalization of potassium serum level and reduction of VIP level. The symptomatology recurred after calcitonin withdrawal. These data confirm the effectiveness of SMS 201-995 in the VIPoma syndrome and suggest that calcitonin may ameliorate symptomatology and reduce circulating VIP level in patients with VIPoma tumor.

Aspects on diagnosis and treatment of the foregut carcinoid syndrome

Eight patients with the foregut carcinoid syndrome (two gastric and six bronchial primary tumors) are reported. The patients presented with complex clinical symptoms including ectopic production of adrenocorticotrophic hormone and growth hormone-releasing factors. The most alarming symptoms were facial flush and edema, accompanied by severe bronchoconstriction, which easily was misinterpreted as asthmatic attacks. Conventional bronchodilatory drugs may be potentially dangerous in these patients, in whom combined blockade of histamine receptors and treatment with cortisone and octreotide are recommended. Owing to the patients' age and general condition individualized long-term therapy was instituted. Surgical therapy under optimal protection by drugs can be of substantial value also in patients with advanced disease. One patient with life-threatening hormonal symptoms underwent hyperthermic perfusion of the liver with cytotoxic drugs, resulting in good palliation.

Hormonal influences on morphology and neuropeptide gene expression in the infundibular nucleus of postmenopausal women

Neuronal hypertrophy occurs in a subpopulation of neurons in the infundibular nucleus of post-menopausal women. The hypertrophied neurons contain NKB, SP and estrogen receptor gene transcripts. Although associated with reproductive aging, post-menopausal neuronal hypertrophy is not a sign of central nervous system degeneration. Quite the opposite, because the hypertrophy is accompanied by marked increases in tachykinin gene expression, reflecting increased neuronal activity. We have proposed that infundibular neurons containing NKB, SP and estrogen receptor mRNAs participate in the hypothalamic circuitry regulating estrogen negative feedback on gonadotropin release in the human. In addition, there is evidence to suggest that the hypertrophied tachykinin neurons may be involved in the initiation of menopausal flushes. Because menopause affects a well characterized system, and has consistent and substantial changes in hormone levels, we have had the rare opportunity to correlate changes in hormone secretion with structural and neurochemical changes in the human hypothalamus. We suspect that future studies of the hypothalami of post-menopausal women will continue to be a fruitful avenue for investigating neuroendocrine regulation in the human.

APUDomas: acute complications and their medical management

APUDomas are rare tumours originating from a variety of endocrine cells localized in different organs. Acute complications from APUDomas usually result from the increased biosynthesis and release of bioactive amines or polypeptide hormones by the tumour. Less frequently, bleeding or compression by the tumour can occur requiring emergency surgery. Increased gastrin production by gastrinomas is the cause of ZES (peptic ulceration and diarrhoea) by gastrin effects on gastric acid secretion. Volume depletion, hypokalaemia, severe bleeding, duodenal perforation, oesophageal stricture and pyloric stenosis are the most dramatic complications. Treatment of these complications and their prevention has been facilitated by the availability of antagonists to H2 receptors and H(+)-K+ proton pump. These medications should control acid output in every patient with ZES. Frequent manifestations of carcinoid tumours, VIPomas and medullary thyroid carcinomas are flushing and diarrhoea. Octreotide, a long-acting somatostatin analogue, has markedly changed the management of these patients, their symptoms decreasing in severity or disappearing in most cases. Octreotide has also been used with success in the prevention and treatment of the carcinoid crisis, a dreaded complication of carcinoid tumours. A better understanding of the pathophysiology of APUDomas has enabled new treatment designs which have considerably ameliorated the quality of life of patients affected by these tumours; efforts must be continued to affect their life expectancy.

Pancreastatin-like immunoreactivity in human carcinoid disease

Pancreastatin-like immunoreactivity has been demonstrated in human carcinoid tumors by immunohistochemistry and radioimmunoassay, employing antisera raised to a synthetic C-terminal fragment of porcine pancreastatin. Immunohistochemistry revealed intense immunoreactivity in all tumors. By radioimmunoassay, high concentrations of pancreastatin-like immunoreactivity were measured in carcinoid tumors arising from the fore-gut (mean +/- S.D. and range: 369 +/- 955 and 9.4-3670 pmol g-1, respectively, n = 14), mid-gut (mean +/- S.D. and range: 1354 +/- 1538 and 337-3978 pmol g-1, respectively, n = 5) and in metastases associated with mid-gut tumors (mean +/- S.D. and range: 684 +/- 739 and 31-2255 pmol g-1, respectively, n = 7), compared to corresponding normal tissues (less than 1.4 pmol g-1). Individuals with hepatic metastases and carcinoid syndrome had elevated circulating levels of pancreastatin-like immunoreactivity (mean +/- S.D. and range: 770 +/- 1249 and 42-4120 pmol l-1; n = 12), significantly above the normal, fasting range (mean +/- S.D. and range: 14.9 +/- 7.5 and 4-37.5 pmol l-1, respectively, n = 42). However, patients with non-metastatic carcinoid tumors (n = 4), who had been clinically cured after primary tumor resection, had plasma levels within the normal range. Chromatographic analysis of extracts of primary lung and ileal tumors, hepatic metastases from ileal tumors and plasma from individuals with carcinoid syndrome revealed molecular heterogeneity of pancreastatin-like immunoreactivity.

Therapeutic strategies in the management of endocrine GEP tumours

The therapeutic principles in the management of endocrine gastroenteropancreatic (GEP) tumours include surgical extirpation of the primary tumour in the absence of metastases and medical control of symptoms in the preoperative phase. In the presence of metastases only palliative procedures are available. Tumour growth might be controlled by surgical procedures as debulking of tumour masses, medically by chemotherapy and more recently by new developments as a long-acting somatostatin analogue (SMS 201-995) and alpha-interferon. Their efficacy is currently evaluated in prospective studies. In contrast to inhibition of growth symptoms derived from excessive hormone production by GEP tumours can be well controlled. SMS 201-995 effectively prevents or at least improves flush and diarrhoea in the carcinoid syndrome, disabling diarrhoea in the Verner-Morrison syndrome and migratory erythema in the glucagonoma syndrome. SMS acts by inhibition of hormone release from the tumour and by a direct mechanism at the site of the target cell via SMS receptors present on tumour and target cells. For control of acid hypersecretion in gastrinoma patients omeprazole is superior to all former and present alternatives and replaced total gastrectomy completely. A similarly effective drug to prevent hypoglycaemia due to uncontrolled insulin release from insulinomas is not available since neither SMS nor diazoxide are effective in every insulinoma patient.

Effect of a long-acting somatostatin analogue (octreotide) on circulating tachykinins and the pentagastrin-induced carcinoid flush

Cutaneous flushing was provoked in seven patients with metastatic carcinoid tumours and the carcinoid syndrome by an intravenous injection of pentagastrin (0.6 micrograms.kg-1 body weight). The patients were studied before and 1 h after a subcutaneous injection of the long-acting somatostatin analogue octreotide 50 micrograms (Sandostatin). The severity of the carcinoid flush in all the patients was reduced by administration of the analogue. The rise in facial temperature was 1.3 (0.3) degree C before and 0.8 (0.2) degree C after octreotide. Six patients responded to pentagastrin with a rise in the circulating neurokinin A-like immunoreactivity (NKA-LI) and five patients with a rise in circulating substance P-like immunoreactivity (SP-LI). No cutaneous flushing or rise in tachykinin concentration was observed in healthy subjects (n = 6) after injection of pentagastrin. The rise in NKA-LI in the patients was decreased by 61 (14)% and the rise in SP-LI by 54 (13)% after octreotide. Although flushing still occurred, the tachykinin response in two patients was completely abolished. The data demonstrate that the release of tachykinins from carcinoid tumours during pentagastrin-induced flushing is subject to partial inhibition by octreotide. However, the occurrence of a flush in some patients in the absence of a detectable rise in circulating tachykinins indicates that the latter peptides cannot be the sole causative agent of the carcinoid flush.

Clinical features of carcinoid syndrome and the use of somatostatin analogue in its management

A review is given on the clinical features of carcinoid syndrome including symptomatology, diagnostics, biochemistry and treatment. We have reviewed the literature on current therapy of carcinoid patients with special emphasis on the use of the somatostatin analogue SMS 20-1995. In addition, we present data on the effects of SMS 201-995 on indices of a clinical, biochemical and tumor growth. Diarrhea is abolished or significantly reduced in 75% of patients, flushing improves in 100%, wheezing in 100% with a decrease in airways resistance, and in one patient myopathy has improved. Blood serotonin is notoriously resistant to intervention and urinary 5-HIAA will decrease in 75% of causes but subsequently rebounds in 38%. Tumors, in general, continue to grow, but this may be slowed or in rare cases tumor growth is arrested. In individual instances the tumor may even infarct, leading to spontaneous cure. Tumors secreting PP, ACTH and calcitonin may be particularly resistant to treatment, whereas VIP secreting tumors appear to be sensitive.

Therapeutic considerations for the malignant carcinoid syndrome

Symptomatology and pathophysiology of carcinoid syndrome are summarized and the therapeutic possibilities reviewed. It is underlined that severity of symptoms and effect of the disease on vital organ function should be considered in order to tailor treatment appropriately. In some patients with a mild syndrome, symptomatic treatment of diarrhea may be sufficient while more aggressive treatment with cytotoxic drugs, interferon, somatostatin analogue or hepatic artery occlusion may be indicated in patients with severe symptoms. Carcinoid crisis is a serious, life-threatening complication of carcinoid syndrome and in this condition somatostatin analogue seems to be an especially useful addition to the therapeutic arsenal.

Neuropeptide K suppresses feeding in the rat

We studied the effects of neuropeptide K (NPK), a 36 amino acid residue peptide of the tachykinin family, on latency to onset of feeding and cumulative 1 and 2 h food intake in three experimental paradigms. Intraperitoneal injection of NPK (1.25 and 3.14 nmol) to food-deprived rats delayed the onset of feeding and significantly decreased the cumulative food intake. Intraperitoneal injection of NPK (1.25 and 3.14 nmol) to water-deprived rats produced no effect on subsequent drinking behavior. Similarly, intraperitoneal injection of NPK (3.14 nmol) 15 min before onset of the dark phase (of the light-dark cycle) significantly delayed the occurrence of ingestive behavior and the cumulative food intake was markedly suppressed. Furthermore, administration of NPK intraperitoneally (0.5-3.14 nmol) 15 min before intraventricular (i.c.v.) injection of neuropeptide Y (NPY 0.47 nmol) to satiated rats significantly suppressed NPY-induced feeding and delayed the onset of ingestive behavior. However, when administered centrally prior to NPY injection, NPK delayed the onset of feeding response only. Collectively, these findings show that NPK can acutely and consistently suppress feeding behavior.

Circulating bradykinin-like immunoreactivity and the pentagastrin-induced carcinoid flush

Bradykinin and structurally related peptides are potent vasodilators and a role for these kinins in the aetiology of the carcinoid flush has been proposed. Using an antiserum directed against the COOH-terminal region of bradykinin in radioimmunoassay, the concentrations of bradykinin-like immunoreactivity in extracts of peripheral blood were compared in patients with carcinoid syndrome (n = 11) and healthy subjects (n = 6). In the fasted state, the concentrations of bradykinin-like immunoreactivity in the patients (10 +/- 5 ng/l) were not significantly different from the concentrations in healthy subjects (6 +/- 3 ng/l). An intravenous injection of pentagastrin (0.6 micrograms/kg) provoked a flush of differing degrees of severity in all patients. In four patients, the flush was concurrent with large rises (277-, 26-, 11- and 10-fold over mean basal values) in bradykinin-like immunoreactivity that was resolved by high performance liquid chromatography into lysyl-bradykinin and bradykinin (approximate ratio 1:2). In two patients, small rises in immunoreactivity (2.4- and 1.7-fold) occurred after the flush and in the remaining five patients no rise in bradykinin-like immunoreactivity was measured. In the healthy subjects, the pentagastrin injection did not provoke a flush and no rises in bradykinin-like immunoreactivity were observed. The data support earlier results obtained using bioassays that the carcinoid flush in some patients is associated with the appearance in blood of bradykinin-related peptides. It has been shown, however, that these kinins cannot be the sole causative agent of the flush. It is suggested, therefore, that the aetiology of the flush is probably multi-factorial.

Neuropeptide K-(1-24)-peptide: storage and release by carcinoid tumors

An antiserum directed against the COOH-terminal region of neuropeptide K-(1-24)-peptide that shows only 0.5% reactivity with neuropeptide K has been used in radioimmunoassay to study the posttranslation processing of human beta-preprotachykinin. A primary midgut carcinoid tumor contained high concentration of substance P (2970 pmol/g), neurokinin A (3660 pmol/g) and neuropeptide K-(1-24)-peptide (3430 pmol/g) but only a very low concentration (less than 5 pmol/g) of intact neuropeptide K. Neuropeptide K-(1-24)-peptide was also detected in extracts of metastatic tumor tissue from four patients with midgut carcinoid tumors. The amino acid sequence of tumor neuropeptide K-(1-24)-peptide was identical to that predicted from the nucleotide sequence of a human beta-preprotachykinin cDNA. The fasting plasma concentration of neuropeptide K-(1-24)-peptide was elevated in a patient with the carcinoid syndrome (821 fmol/ml compared with less than 18 fmol/ml in healthy subjects) and rose approximately 2-fold after intravenous pentagastrin. The study has demonstrated that the Lys25-Arg26 bond in neuropeptide K (corresponding to Lys96-Arg97 in the precursor) is an important processing site in human beta-preprotachykinin.

Circulation of a fragment of haemoglobin alpha-chain during a pentagastrin-induced flush in patients with metastatic carcinoid tumours

Intravenous injection of pentagastrin (0.6 microgram/kg body wt) into two patients with metastatic carcinoid tumours evoked a severe carcinoid flush. Analysis by reverse-phase HPLC of acetone-extracts of peripheral blood taken from the patients during the flush indicated the presence of a peptide identified as the residues (1-33) fragment of the alpha-chain of haemoglobin. The peptide was not detected in blood taken from the patients immediately before stimulation of the flush or in the blood of healthy subjects after pentagastrin injection. The observation is interpreted as evidence that the pentagastrin-induce carcinoid flush is associated with the activation and possible release of a tumour protease that result in damage to erythrocytes.