Effects of short-time somatostatin infusion on the gastric and intestinal propulsion in humans

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.

Guidance on the management of diarrhoea during cancer chemotherapy

Diarrhoea induced by chemotherapy in cancer patients is common, causes notable morbidity and mortality, and is managed inconsistently. Previous management guidelines were based on poor evidence and neglect physiological causes of chemotherapy-induced diarrhoea. In the absence of level 1 evidence from randomised controlled trials, we developed practical guidance for clinicians based on a literature review by a multidisciplinary team of clinical oncologists, dietitians, gastroenterologists, medical oncologists, nurses, pharmacist, and a surgeon. Education of patients and their carers about the risks associated with, and management of, chemotherapy-induced diarrhoea is the foundation for optimum treatment of toxic effects. Adequate--and, if necessary, repeated--assessment, appropriate use of loperamide, and knowledge of fluid resuscitation requirements of affected patients is the second crucial step. Use of octreotide and seeking specialist advice early for patients who do not respond to treatment will reduce morbidity and mortality. In view of the burden of chemotherapy-induced diarrhoea, appropriate multidisciplinary research to assess meaningful endpoints is urgently required.

Effect of octreotide on enteric motor neurons in experimental acute necrotizing pancreatitis

Background/Aims

Amelioration of intestinal dysmotility and stasis during the early period of acute necrotizing pancreatitis (ANP) appears to be important to reduce the risks of secondary pancreatic infection. We aimed to characterize the association between the neuropathy of the enteric nervous system and gut dysfunction and to examine the effect of octreotide on motor innervation in the early stage of ANP.

Methodology/Principal Findings

The rats were randomly divided into eight groups: control+saline; control+octreotide; ANP+saline and ANP+octreotide (24 h, 48 h, 72 h). The spontaneous activity of ileal segments and the response to ACh, l-NNA were recorded. The alterations of myenteric neuronal nitric oxide synthase (nNOS), choline acetyltransferase (CHAT), PGP9.5 and somatostatin receptor 2 (SSTR₂) immunoreactive cells were evaluated by immunofluorescence and the protein expression of nNOS and CHAT were evaluated by western blot. We found the amplitude of spontaneous contractions at 48 h and the response to ACh at 24 h declined in the ANP+saline rats. A higher contractile response to both ACh and to l-NNA was observed in the ANP+octreotide group, compared with the ANP+saline rats at 24 h. A significant reduction in the nNOS and cholinergic neurons was observed in ANP+saline rats at the three time points. However, this reduction was greatly ameliorated in the presence of octreotide at 24 h and 48 h. The protein expression of CHAT neurons at 24 h and the nNOS neurons at 48 h in the ANP+octreotide rats was much higher than the ANP+saline rats.

Conclusion

The pathogenesis of ileus in the early stage of ANP may be related to the neuropathy of the enteric nervous system. Octreotide may reduce the severity of ileus by lessening the damage to enteric motor innervation.

Octreotide ameliorates intestinal dysmotility by interstitial cells of Cajal protection in a rat acute necrotizing pancreatitis model

OBJECTIVES

Intestinal motility is impaired in acute necrotizing pancreatitis (ANP). The aim of present study was to investigate the effects of octreotide on the small intestinal motor function during experimentally induced ANP.

METHODS

L-Ornithine was intraperitoneally injected to induce ANP. Octreotide was administrated subcutaneously every 8 hours. The small intestine migrating myoelectrical complexes and slow waves in vivo were recorded before and after (24, 48, and 72 hours) ANP induction. The morphological alterations of interstitial cells of Cajal (ICCs) in deep muscular plexus were evaluated by immunohistochemistry and Western blots.

RESULTS

Disturbed migrating myoelectrical complex cycle length and decreased dominant frequency of slow waves exacerbated gradually with time. The bolus applications of octreotide per 8 hours attenuated these functional abnormalities. The result of morphological study suggested that octreotide might ameliorate the damage of ICCs at 48 and 72 hours after ANP induction. Decreased expression of c-Kit protein at 72 hours was also attenuated by octreotide.

CONCLUSIONS

The pathogenesis of the ileus in ANP may be related to the sustained deficiencies in ICCs. Octreotide may ameliorate the severity of ileus by minimizing the injury of ICCs.

Octreotide acetate in prevention of chemoradiation-induced diarrhea in anorectal cancer: randomized RTOG trial 0315

BACKGROUND

In anorectal cancer patients, an acute side effect of chemoradiotherapy is gastrointestinal toxicity, which often impedes treatment delivery. Based on previous trials, octreotide acetate is widely recommended for the control of chemotherapy-induced diarrhea. However, the effectiveness of octreotide in preventing or controlling radiation- and chemoradiation-induced diarrhea is not known.

METHODS

A randomized, double-blinded, placebo-controlled trial was designed to determine the efficacy of long-acting octreotide acetate (LAO) in preventing the onset of acute diarrhea in patients undergoing chemoradiation therapy for rectal or anal cancer. Between 4 and 7 days before the start of radiation therapy, patients received a 30-mg dose of LAO (109 patients) or placebo (106 patients) via intramuscular injection. A second dose was given on day 22 (+/-3 days) of radiation treatment. A total of 215 patients were included in the final analysis. The primary endpoint was the incidence of grade 2-4 acute diarrhea; secondary endpoints included treatment compliance, medical resource utilization, patient-reported bowel function, and quality of life (QoL). Statistical tests were one- or two-sided, as specified.

RESULTS

After a median follow-up time of 9.64 months, incidence rates of grades 2-4 acute diarrhea were similar in both groups (49% placebo vs 44% LAO; P = .21). No statistically significant treatment differences in chemotherapy or radiation delivery, medical resource utilization, patient-reported bowel function, or QoL were observed.

CONCLUSION

In this study, the prophylactic use of LAO did not prevent the incidence or reduce the severity of diarrhea and had no notable impact on patient-reported bowel function or QoL.

Ecabet sodium raises plasma levels of calcitonin gene-related peptide and substance P in healthy humans

Ecabet sodium (ecabet), a cytoprotective drug, produces an increase in mucosal blood flow. One of the gastrointestinal motility regulatory factors has been assumed to be the induction of changes in the levels of peptides (gastrin, somatostatin and motilin) in plasma. On the other hand, recently, capsaicin-sensitive afferent nerves were shown to play an important role in gastric mucosal defensive mechanism. Capsaicin stimulates afferent nerves and enhances the release of calcitonin gene-related peptide (CGRP) and substance P in the stomach. We studied the effect of ecabet on human plasma gastrin-, somatostatin-, motilin-, CGRP- and substance P-like immunoreactive substance (IS) in healthy subjects. Ecabet sodium at a dose of 3.0 g, or placebo, was orally administered in five healthy males. The blood samples were taken before and at 20, 40, 60, 90, 120, 180 and 240 min after administration, subjected to extracting procedures, and submitted to a highly sensitive enzyme immunoassay system. Single administration of ecabet caused significant (P < 0.05) increases in plasma CGRP-, substance P- and somatostatin-IS concentration compared with placebo. Ecabet significantly decreased plasma gastrin-IS levels compared with placebo. In this study, we hypothesized that ecabet might stimulate capsaicin-sensitive afferent nerves indirectly and improve mucosal blood flow; this might be a key mechanism underlying its gastroprotective action.

Glipizide does not affect absorption of glucose and xylose in diabetics without residual beta-cell function

We have previously demonstrated that oral glipizide suppresses the absorption of xylose in diabetics treated with diet alone. We suggested that glipizide might influence postprandial glucose levels by interfering with absorptive mechanisms. In the present study we have extended our observations to insulin-dependent diabetics (IDDM). Nine non-obese diabetics without residual beta-cell function and with normal respiratory sinus arrhythmia and Valsalva ratio were studied on two occasions. Their ordinary insulin treatment was discontinued 24 hours before the study and glucose control was maintained by i.v. insulin infusion. The experiments began at 8 a.m. after an overnight fast. Insulin was given as a continuous i.v. infusion of 0.01 U/kg/h at 8-11 a.m. and 0.005 U/kg/h at 11 a.m. -2 p.m. At 8 a.m. the patients ingested 25 g of xylose and 15 g of glucose in 300 ml of water. Glipizide (5 mg) or placebo were given 30 min prior to the glucose-xylose load in random order, each patient serving as his own control. Blood samples were taken every 60 min for analysis of glucose, xylose, C-peptide and glipizide. The rise in blood glucose in the control experiment was similar to that previously seen in non-insulin-dependent diabetics (NIDDM) given the same xylose-glucose load. Glipizide did not exert any effects on either blood C-peptide, glucose or xylose levels. We conclude that oral glipizide administered in a therapeutic dose does not reduce xylose absorption in IDDM, in contrast to its previously demonstrated effect in NIDDM.

Phase III, double-blind study of depot octreotide versus placebo in the prevention of acute diarrhea in patients receiving pelvic radiation therapy: results of North Central Cancer Treatment Group N00CA

PURPOSE

To assess the effectiveness of depot octreotide for the prevention of diarrhea during pelvic radiation therapy.

PATIENTS AND METHODS

Patients receiving pelvic radiation therapy (planned minimum dose, 45 Gy; 1.7 to 2.1 Gy daily) were eligible for the study. From May 10, 2002, through October 14, 2005, 125 patients were randomly allocated in a double-blind fashion to receive octreotide (100 microg, administered subcutaneously on day 1, followed by depot octreotide, 20 mg, administered intramuscularly on days 2 and 29; n = 62) or to receive a placebo (n = 63).

RESULTS

Grade 0, 1, 2, and 3 diarrhea were observed in 18%, 31%, 31%, and 21% of patients in the octreotide arm, respectively, and in 25%, 32%, 22%, and 21% of patients in the placebo arm, respectively (P = .64). Grade 0, 1, 2, and 3 abdominal cramps were observed in 32%, 45%, 21%, and 2% of patients receiving octreotide, respectively, and in 51%, 24%, 21%, and 5% of patients receiving the placebo, respectively (P = .053). Some patient-reported symptoms were worse in the octreotide group, including nocturnal bowel movements (70% v 45%; P = .004), clustering of bowel movements (90% v 69%; P = .004), and bleeding with bowel movements (57% v 35%; P = .01).

CONCLUSION

As administered in this study, octreotide did not decrease diarrhea during pelvic radiation therapy. Some gastrointestinal symptoms were worse in patients treated with octreotide. Octreotide is not indicated for prevention of diarrhea during pelvic radiation therapy.

[Clinicopharmacological study of gastrointestinal drugs from the viewpoint of postmarketing development]

Pharmaceutical development starts with the discovery of a new compound. Drugs become commercially available after non-clinical and clinical studies, but processes that take place after marketing are also important for pharmaceutical development. In recent years, use of the phrase "Ikuyaku" meaning postmarketing development has become more common. Sometimes, the proper usage, indications and harmful effects of a drug are discovered only after it becomes commercially available and is administered to many patients. Hence, pharmacists need to actively perform postmarketing studies to reveal the true nature of drugs. In the present clinicopharmacological study, we investigated the effects of histamine H(2) receptor antagonists (H(2)-RAs) on the plasma concentrations of gastrointestinal peptides from the viewpoint of postmarketing development. First we established an enzyme immunoassay for secretin, which is involved in gastrointestinal motility. Then we used this and existing peptide assays to investigate the above-mentioned issues. Ranitidine and nizatidine increased the plasma concentration of motilin. It is believed that the plasma concentration of Ach is elevated by ranitidine and nizatidine, which possesses an anti-AchE activity, and that the increased the plasma concentration of Ach facilitated release of motilin, elevating the plasma concentration of motilin. When compared to the placebo, lafutidine significantly increased the plasma concentration of CGRP (calcitonin gene-related peptide) and substance P. Furthermore, released CGRP stimulated CGRP1 receptors to facilitate secretion of somatostatin. Therefore, lafutidine appears to protect the gastric mucosa and regulate gastrointestinal motility. The same results were obtained with ranitidine and nizatidine. While H(2)-RAs have a common function in suppressing the secretion of gastric acid, they do not exhibit the same effects on factors related to recurrence of peptic ulcer, such as gastrointestinal motility and blood flow in the gastrointestinal mucosa. Hence, measuring the plasma concentration of gastrointestinal peptides can be used to estimate the effects of drugs on gastrointestinal motility. From the viewpoint of postmarketing development, we are in the process of establishing indicators for the proper usage of pharmaceutical drugs. Pharmacists need to closely follow and monitor adverse reactions. In order to further improve monitoring of drug therapy, it will be necessary to assess not only the blood concentrations of drugs, but also biological reactions to the drugs. Since the levels of peptides reflect the clinical efficacy of gastrointestinal drugs, measuring peptide levels appears to be useful for selecting appropriate drugs.

Clinical application of an enzyme immunoassay for cholecystokinin-like immunoreactive substance for determination of the human plasma levels: the effect of metoclopramide on gastrointestinal peptides and stress-related hormones

Metoclopramide, a prokinetic drug, is widely used to treat vomiting and nausea. Delayed gastric emptying and continual stress are considered important factors, among others, that induce nausea and vomiting. One gastrointestinal motility regulatory factor has been assumed to be the induction of changes in the levels of peptides such as gastrin, somatostatin, motilin, and cholecystokinin (CCK) in plasma. In contrast, adrenocorticotropic hormone (ACTH) and cortisol are used as indicators of stress. Here, we studied the effects of metoclopramide on human plasma gastrin-, somatostatin-, motilin-, and CCK-like immunoreactive substances (ISs) and ACTH-IS and cortisol under stress conditions using repetitive blood sampling in healthy subjects. Metoclopramide hydrochloride at a dose of 30 mg or placebo was orally administered to five healthy male volunteers. Blood samples were taken before and 20, 40, 60, 90, 120, 180, and 240 min after administration, subject to extracting procedures, and submitted to a highly sensitive enzyme immunoassay system. A single administration of metoclopramide caused significant increases in plasma somatostatin-IS levels compared with the placebo. Metoclopramide significantly decreased plasma gastrin- and suppressed ACTH-IS and cortisol levels compared with the placebo. We hypothesize that metoclopramide might have an accelerating gastric-emptying effect and a modulatory effect on the hypothalamo-pituitary-adrenal (HPA) axis and the autonomic nervous function. These effects might be beneficial in stress-related diseases, which suggest that this medicine has clinicopharmacological activities.

Effects of erythromycin on plasma gastrin, somatostatin, and motilin levels in healthy volunteers and postoperative cancer patients

Erythromycin, an antibiotic agent, is known to be a motilin receptor agonist. Motilin is a peptide hormone that regulates gastric motility. One of the gastrointestinal motility regulatory factors has been assumed to be the induction of changes in the levels of peptides (gastrin, somatostatin and motilin) in plasma. We have elucidated the effects of erythromycin by examining changes in the plasma levels of gastroinitestinal peptides. In this study, we investigated the effects of erythromycin on the plasma levels of gastrointestinal peptides (somatostatin, motilin, and gastrin) in healthy volunteers and patients with delayed gastric emptying (DGE). After a single oral administration, erythromycin caused a significant increase in plasma gastrin-like immunoreactive substance (IS) levels at 60 min. But the agent did not alter the levels of somatostatin- and motilin-IS. DGE is the most frequent postoperative complication after pylorus-preserving pancreatoduodenectomy. Molitin is assumed to be one important factor that influences DGE. We also examined the effects of erythromycin on the plasma motilin-IS levels of postoperative patients. The plasma motilin-IS levels were increased after 1 week of oral administration of erythromycin compared with preadministration. These results suggest that the pharmacologic effects of erythromycin in promoting gastric emptying are closely related to changes in plasma motilin-IS levels.

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.

Somatostatin receptors

In 1972, Brazeau et al. isolated somatostatin (somatotropin release-inhibiting factor, SRIF), a cyclic polypeptide with two biologically active isoforms (SRIF-14 and SRIF-28). This event prompted the successful quest for SRIF receptors. Then, nearly a quarter of a century later, it was announced that a neuropeptide, to be named cortistatin (CST), had been cloned, bearing strong resemblance to SRIF. Evidence of special CST receptors never emerged, however. CST rather competed with both SRIF isoforms for specific receptor binding. And binding to the known subtypes with affinities in the nanomolar range, it has therefore been acknowledged to be a third endogenous ligand at SRIF receptors. This review goes through mechanisms of signal transduction, pharmacology, and anatomical distribution of SRIF receptors. Structurally, SRIF receptors belong to the superfamily of G protein-coupled (GPC) receptors, sharing the characteristic seven-transmembrane-segment (STMS) topography. Years of intensive research have resulted in cloning of five receptor subtypes (sst(1)-sst(5)), one of which is represented by two splice variants (sst(2A) and sst(2B)). The individual subtypes, functionally coupled to the effectors of signal transduction, are differentially expressed throughout the mammalian organism, with corresponding differences in physiological impact. It is evident that receptor function, from a physiological point of view, cannot simply be reduced to the accumulated operations of individual receptors. Far from being isolated functional units, receptors co-operate. The total receptor apparatus of individual cell types is composed of different-ligand receptors (e.g. SRIF and non-SRIF receptors) and co-expressed receptor subtypes (e.g. sst(2) and sst(5) receptors) in characteristic proportions. In other words, levels of individual receptor subtypes are highly cell-specific and vary with the co-expression of different-ligand receptors. However, the question is how to quantify the relative contributions of individual receptor subtypes to the integration of transduced signals, ultimately the result of collective receptor activity. The generation of knock-out (KO) mice, intended as a means to define the contributions made by individual receptor subtypes, necessarily marks but an approximation. Furthermore, we must now take into account the stunning complexity of receptor co-operation indicated by the observation of receptor homo- and heterodimerisation, let alone oligomerisation. Theoretically, this phenomenon adds a novel series of functional megareceptors/super-receptors, with varied pharmacological profiles, to the catalogue of monomeric receptor subtypes isolated and cloned in the past. SRIF analogues include both peptides and non-peptides, receptor agonists and antagonists. Relatively long half lives, as compared to those of the endogenous ligands, have been paramount from the outset. Motivated by theoretical puzzles or the shortcomings of present-day diagnostics and therapy, investigators have also aimed to produce subtype-selective analogues. Several have become available.

Lafutidine changes levels of somatostatin, calcitonin gene-related peptide, and secretin in human plasma

We examined the effects of the histamine H2-receptor antagonist, lafutidine, on the levels of gastrointestinal peptides (somatostatin, calcitonin gene-related peptide (CGRP), gastrin, secretin, and motilin) in plasma from healthy subjects. After a single oral administration of lafutidine (10 mg), the plasma lafutidine level (186 +/- 13.4ng/ml) was highest in the 60-min sample after administration and then the plasma level fell. Lafutidine caused significant increase in plasma somatostatin levels at 20 to 120 min and in CGRP levels at 40 to 120 min, compared with a placebo group. The physiological release of plasma secretin was reduced by administration of lafutidine, but the medicine did not alter the level of gastrin or motilin. These results suggest that the pharmacological effects of lafutidine on regulation of gastrointestinal functions closely relate to changes of somatostatin-, CGRP- and secretin-immunoreactive substance levels in human plasma.

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.

Octreotide increases the proportions of arachidonic acid-rich phospholipids in gall-bladder bile

BACKGROUND AND AIMS

Octreotide treatment of acromegalic patients induces cholesterol gallstone formation, in part by impairing cholecystokinin release and gall-bladder contraction. However, there are few data on the effect of octreotide on biliary arachidonic acid-rich phospholipids or mucin glycoprotein, factors which also influence cholesterol gallstone formation.

METHODS

In acromegalic patients studied before and during 3 months of octreotide treatment, we measured mucin glycoprotein concentrations and the molecular species of phosphatidylcholine, and related the results to the cholesterol saturation and percentage of deoxycholic acid in gall-bladder bile.

RESULTS

The relative proportions of the major arachidonic acid-rich phosphatidylcholine species, PC 16:0-20:4 and PC 18:0-20:4, increased significantly during octreotide treatment. These changes were associated with a rise in the cholesterol saturation index and a non-significant twofold increase in mucin glycoprotein concentration. There were significant correlations between PC 16:0-20:4 and the cholesterol saturation index, percentage of vesicular cholesterol and percentage of deoxycholic acid in gall-bladder bile.

CONCLUSIONS

In acromegalic patients, octreotide increases the proportions of arachidonic acid-rich phospholipids, with associated rises in: (a) the cholesterol saturation index and percentage of vesicular cholesterol, and (b) the percentage of deoxycholic acid in gall-bladder bile-changes similar to those found in patients with cholesterol-rich gall-bladder stones.

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.

Dual effects of somatostatin analog octreotide on gastric emptying during and after intragastric fill

The effect of the somatostatin analog agonist octreotide (Oct) on gastric emptying of 12.5% glucose during and after intragastric fill was examined in nondeprived rats equipped with stainless steel gastric fistulas. The rate of intragastric infusion (1.0 ml/min) and the volumes delivered (6 or 12 ml) were within the ranges typically observed in rats normally ingesting the same stimulus. In experiment 1, a dose-related suppression of glucose emptying during 12-min infusions was obtained in response to Oct (0, 0.0014, 0.014, 0.14, and 1.4 nmol/kg sc) injected 60 min before the test. The highest dose tested yielded a 37% suppression of glucose solute emptying during fill. In experiment 2, the suppression of emptying during fill induced by Oct (1.4 nmol/kg) was reversed by 10 or 40 microgram/kg of the somatostatin antagonist cyclo(7-aminoheptanoyl-Phe-D-Trp-Lys-Thr[Bzl]). The antagonist did not by itself affect emptying. Experiment 3 showed that the suppression of emptying obtained with 0.14 and 1.4 nmol/kg Oct had disappeared when the gastric sample was withdrawn 36 min after the termination of 12-min glucose infusions. Experiment 4 showed that the Oct-induced reductions in emptying during 6- and 12-min infusions, in fact, were reversed within 6 min after infusion offset. The point of transition between suppressed and increased emptying did not depend on time from injection or from infusion onset but was linked to the offset of the intragastric infusion regardless of its duration. The present findings support the notion that separable mechanisms govern gastric emptying during vs. after gastric fill.

Somatostatin 2A receptor is expressed by enteric neurons, and by interstitial cells of Cajal and enterochromaffin-like cells of the gastrointestinal tract

Somatostatin exerts multiple effects by activating distinct G protein-coupled receptors. Here we report the cellular sites of expression of the somatostatin subtype 2A (sst2A) receptor in the rat enteric nervous system by using a C-terminus-specific, affinity-purified antiserum and immunohistochemistry. Antibody specificity was confirmed by the cell surface staining of human embryonic kidney 293 cells expressing the sst2A receptor, the lack of staining of cells expressing the somatostatin subtype 2B receptor, and the abolition of staining by preincubating the antiserum with the C-terminus peptide used for immunization, SSt2A(361-369). The SSt2A receptor antibody recognized a broad 80 kDa band on Western blots of membranes prepared from cells transfected with sst2A receptor cDNA; following receptor membrane deglycosylation, the antibody detected an additional 40 kDa band. In the enteric nervous system, the sst2A antibody primarily stained neurons of the myenteric and submucosal plexuses, and abundant fibers distributed to the muscle, mucosa, and vasculature. Immunoreactive staining was also observed in non-neuronal cells, including presumed interstitial cells of Cajal of the intestine and enterochromaffin-like cells of the stomach. Fibers expressing sst2A receptor immunoreactivity were often in close proximity to D cells of the gastric and intestinal mucosa. Colocalization of somatostatin and sst2A receptor immunoreactivities was not observed in endocrine cells nor in enteric neurons. Double-label immunohistochemistry revealed colocalization of sst2A and vasoactive intestinal peptide immunoreactivities in enteric neurons. The multiple types of cells expressing the sst2A receptor, including enteric neurons and non-neuronal structures, in addition to the relationship between somatostatin and sst2A receptor elements, provide evidence that the sst2A receptor mediates somatostatin effects in the gastrointestinal tract via neuronal and paracrine pathways.

Roles of gall bladder emptying and intestinal transit in the pathogenesis of octreotide induced gall bladder stones

BACKGROUND

Octreotide treatment of acromegalic patients increases the % deoxycholic acid conjugates and the cholesterol saturation of gall bladder bile, and induces gall stone formation.

AIMS

To study the roles of gall bladder emptying and intestinal transit in these phenomena.

METHODS AND PATIENTS

Gall bladder emptying and mouth to caecum transit was measured in (a) control subjects and acromegalic patients given saline or 50 micrograms of octreotide, and (b) acromegalic patients taking long term octreotide. In the second group, large bowel transit was also measured.

RESULTS

A single dose of octreotide inhibited meal stimulated gall bladder emptying, the ejection fraction falling from mean (SEM) 66.0 (2.3)% to 7.0 (5.3)% in controls (p < 0.001); from 72.5 (2.1) to 16.6 (5.1)% in untreated acromegalic patients (p < 0.001), and to 30.4 (9.5)% in acromegalic patients taking long term octreotide (p < 0.001 v untreated acromegalic group). Octreotide prolonged mouth to caecum transit time, from 112 (15) min to 237 (13) min in controls (p < 0.001), from 170 (13) min to 282 (11) min in untreated acromegalic patients (p < 0.001), and to 247 (10) min in acromegalic patients taking long term octreotide (p < 0.001 v untreated acromegalic patients). The mean large bowel transit in octreotide untreated compared with treated acromegalic patients remained unchanged (40 (6) h v 47 (6) h).

CONCLUSIONS

Prolongation of intestinal transit and impaired gall bladder emptying may contribute to lithogenic changes in bile composition and gall stone formation in patients receiving long term octreotide.

The effect of octreotide on human gastric compliance and sensory perception

Somatostatin or its analogue octreotide (OCT) has previously been shown to modulate gastric emptying, intestinal motor activity and visceral sensation. In the current study we sought to determine the effect of a single dose of OCT (1.25 micrograms kg-1 s.c.), which has previously been shown to have both motor and sensory effects, on proximal gastric compliance and on conscious perception of gastric distention. Gastric distention was performed in 13 healthy male volunteers, by either slow ramp distention (60 ml min-1) or by intermittent pressure steps (phasic distention; 4-20 mmHg) using an electronic distention device. Compliance curves (pressure-volume relationship), and thresholds for innocuous (fullness) and noxious sensations (discomfort, pain) were determined following vehicle or OCT injection. OCT consistently and significantly reduced the rate of the gastric accommodation reflex by 50%, resulting in a reduced compliance at distention pressures greater than 10 mmHg during phasic distention. In contrast, no effect was observed on the compliance curve obtained during ramp distention. OCT selectively increased the threshold for fullness during both ramp and phasic distention. During phasic distention, OCT decreased the volume thresholds for noxious (pain) sensations experienced at volumes greater than 300 ml, without affecting the corresponding pressure threshold. These findings suggest that at low distension volumes, OCT in the dosage used has a direct inhibitory effect on afferents mediating innocuous gastric sensations. The hyperalgesic effect observed during phasic distention may be secondary to OCT's inhibitory effect on the gastric accommodation reflex.

Octreotide for treatment of postoperative alimentary tract fistulas

Eighteen patients with postoperative fistulas of the gastrointestinal tract were treated with the somatostatin analog octreotide between November 1989 and November 1992. Fourteen patients had enterocutaneous fistulas: seven from the duodenum and seven from the ileum. Another three patients had pancreatic fistulas, and one patient had a biliary fistula. Within 24 hours of octreotide treatment, a mean reduction of 52% in the intestinal fistulas' output, 40% in the pancreatic fistulas, and 30% in the biliary fistula was noted. In the intestinal fistulas group the closure rate was 72% after a mean of 11 days. Early closure (mean 6 days) was achieved in all three pancreatic fistulas. In the patient with the biliary fistula a 30% reduction was observed twice following the administration of octreotide, and an increase occurred when it was withheld. The reduction rate of the secretions in high-output intestinal fistulas (> 500 ml/day) was higher than in the low-output fistulas (63 +/- 8% versus 39 +/- 4%, p < 0.05). Fistula output and the initial response to octreotide treatment had no value in predicting spontaneous healing. In conclusion, octreotide is a valuable tool for the conservative treatment of fistulas of the digestive tract. It is especially valuable for management of high-output enteric fistulas and pancreatic fistulas.

Somatostatin levels during infancy, pregnancy, and lactation: a review

This paper reviews research on somatostatin (SS) levels during infancy, pregnancy, and lactation. Neonates have elevated levels of circulating SS, which reach a peak at the age of 3 months and then decrease gradually, but remain elevated during the first years of life. SS response to feeding is not well developed in newborns. Elevated levels are also found during pregnancy, especially during the late phases. Influence of sucking on maternal SS plasma levels is varied and could be related to vagal stimulation. pH levels, and basal SS levels. SS has been found in high concentrations in maternal milk. Milk-borne SS appears to be protected from proteolysis by milk components, but apparently SS is not absorbed in its intact form through the duodenal wall and its effects could be indirect. More research is needed to determine the regulating role of milk-borne SS and the contribution of SS to development.

The role of bile composition and physical chemistry in the pathogenesis of octreotide-associated gallbladder stones

BACKGROUND/AIMS

Treatment of acromegaly with octreotide inhibits cholecystokinin release and gallbladder contraction and induces gallbladder stones. However, little is known about the effects of octreotide on bile composition.

METHODS

Fresh gallbladder bile was obtained from three groups: (1) 11 nonacromegalic patients with cholesterol gallstones, (2) 6 acromegalic patients with octreotide-associated stones (treatment, 300-600 micrograms/day for 3-66 months), and (3) 8 acromogalic patients with no stones before octreotide treatment, 5 of whom were reexamined after 3-24 months of therapy.

RESULTS

Compared with stone-free acromegalic patients untreated with octreotide, bile from patients with cholesterol stones and from acromegalic patients with octreotide-associated stones had greater saturation indices (mean +/- SEM) (1.52 +/- 0.17 and 1.32 +/- 0.14 vs. 0.90 +/- 0.05, respectively; P < 0.01); more cholesterol in vesicles (61.2% +/- 4.5% and 67.7% +/- 7.2% vs. 37.7% +/- 3.5%; P < 0.009); more unstable vesicles (cholesterol/phospholipid ratios, 0.97 +/- 0.12 and 0.81 +/- 0.16 vs. 0.52 +/- 0.05; P < 0.02); more rapid nucleation (< 5 and < 5 days vs. > 18 days; P < 0.003); and more deoxycholic acid (22.8% +/- 2.4% and 23.6% +/- 4.8% vs. 13.9% +/- 1.4%; P < 0.05). In the paired studies, the saturation indices increased from 0.89 +/- 0.07 before octreotide treatment to 1.12 +/- 0.03 during octreotide treatment (P < 0.02), as did the percentage of deoxycholic acid from 13.3% +/- 2.1% to 24.9% +/- 2.7% (P < 0.03).

CONCLUSIONS

Acromegalic patients with octreotide-associated gallstones and stone-free acromegalic patients treated with octreotide have similar changes in bile composition to those in patients with "conventional" cholesterol gallstone disease.

Pharmacodynamic effects of Sandostatin in the gastrointestinal tract

Somatostatin (SST) is widely distributed throughout the human gastrointestinal system. There, it is found in neurons and fibers of both the submucosal and myenteric plexus and the pancreas, and also in the D cells of the stomach, gut, and pancreatic islets. Whereas in the intestinal nervous system, duodenum, and pancreas, somatostatin-14 (SST-14) appears to be the predominant molecular form, the endocrine-type D cells of the intestine primarily contain somatostatin-28 (SST-28). SST peptides may act very differently at different sites, as hormones, paracrine substances, or neurotransmitters. Because of this complexity of action, very little is known about the physiological effects of SST in the gastrointestinal tract. In contrast, the pharmacological actions of natural synthetic SST have been thoroughly studied and have given rise to many therapeutic applications. Octreotide, an analogue with a longer half-life and higher potency, has greatly facilitated the clinical application of SST. This review deals with the pharmacological effects of octreotide on different gastrointestinal functions. The SST analogue exerts a long-lasting inhibitory action on gastric acid, pancreatic enzyme, bicarbonate secretion, and on bile flow. It also inhibits stimulated intestinal secretion, ie, the release of neuropeptides from the gut and pancreas. It can also prolong orocecum transit time and prevent gallbladder contraction. It inhibits absorption of nutrients and exerts inhibitory effects on splanchnic hemodynamics. It is because of these actions that SST has attracted so much attention in the treatment of different gastrointestinal disorders.

Somatostatin analogues in diabetes mellitus

Growth hormone (GH) has long been considered to have importance in diabetes. With poor control in Type 1 diabetes GH levels are high and may aggravate poor metabolic control. Pharmacological suppression of GH release at this stage might reverse the metabolic changes, with the possible added benefit of lower plasma insulin concentrations. Diabetic patients with life-long GH deficiency rarely develop retinopathy, while pituitary ablation in patients with retinopathy often leads to improvement. Growth hormone release inhibiting factor, somatostatin, has a short plasma half-life, and multiple effects on the endocrine system and on the gastrointestinal tract, making it unsuitable for clinical use as a GH suppressant. Long-acting analogues have a long half-life, but remain non-specific in their effects. In Type 2 diabetes the analogue Octreotide suppresses insulin and glucagon release, leaving glucose levels either unchanged or somewhat elevated. Gastrointestinal side-effects have been common, but may diminish with long-term treatment. In Type 1 diabetes insulin requirement is decreased by Octreotide, but as in Type 2 diabetes GH suppression has been observed consistently only when the drug was given at bed-time. The decrease in insulin requirement may reflect suppression of glucagon release and/or gut effects. Amelioration of the 'dawn phenomenon' has not proved possible, and hypoglycaemia has proved a particular problem with Octreotide given subcutaneously at night. The lack of effective GH suppression (particularly in patients with proliferative retinopathy), lack of specificity, and the gut and hypoglycaemic side-effects, argue strongly against a clinical role for the current somatostatin analogues in diabetes mellitus.

Effect of the long-acting somatostatin analogue SMS 201-995 on small-intestinal interdigestive motility in the dog

The long-acting somatostatin analogue SMS 201-995, also called Sandostatin, is used in the treatment of acromegaly and peptide-secreting tumors. Little is known about its effect on gut motility, although such an effect might be expected considering the spectrum of activities of its parent molecule, somatostatin. We have studied the effect on the interdigestive motility of intravenous boluses of 0, 0.1, 0.5, 1.5, and 5.0 micrograms/kg of this analogue in 10 dogs with bipolar electrodes implanted along the entire small bowel. All doses induced, within 5 min of administration, premature phase-3 activity that was isolated to one segment, normally progressive, or simultaneous (stationary) in all channels. Only low doses induced isolated phase 3, whereas the frequency of the induction of stationary phase 3 increased with higher doses. In the next cycle of the migrating motor complex the duration of phase 1 was increased, although the duration of the whole cycle was not changed. This cycle ended with mostly ectopic phase-3 activity. During phase 2 of the following cycle ultra-rapid rushes of spiking activity progressing at a speed of 25 +/- 3 cm/sec in the upper jejunum were regularly observed. Although this pattern occurs very rarely under control conditions, it was present in 20%, 80%, and 100% of the experiments after doses of 0.5, 1.5, and 5.0 micrograms/kg, respectively. We conclude that gastrointestinal side effects observed during administration of SMS 201-995 might be related to these motility effects, which warrant further investigation. SMS 201-995 may be a tool to study the mechanism of the induction of ultra-rapid rushes and of stationary phase 3.

In vitro effects of the long-acting somatostatin analogue SMS 201-995 on electrolyte transport by the rabbit ileum

We have investigated the in vitro properties of SMS 201-995, a long-acting somatostatin analogue, on electrolyte transport in rabbit ileum. Similar to native somatostatin, serosal addition of this compound inhibits electrogenic anion secretion and stimulates neutral sodium and chloride absorption. Both compounds have similar maximal effects on ion transport; however, the ED50 of SMS 201-995 (2.4 X 10(-10) M) was 60 times less than that for somatostatin. In addition, unlike somatostatin, no inherent tachyphylaxis was observed in response to SMS 201-995. The antisecretory profile of SMS 201-995 was also compared with that of epinephrine. Unlike treatment with epinephrine, pretreatment of tissues with SMS 201-995 did not directly inhibit electrogenic anion secretion stimulated by vasoactive intestinal polypeptide, calcium ionophore A23187, and bethanechol. In contrast, this agent blocked vasoactive intestinal polypeptide and bethanechol inhibition of net sodium absorption. We conclude that SMS 201-995 has several unique in vitro properties that may explain its greater biologic activity compared with that of somatostatin. Its effects on secretagogue-stimulated electrogenic anion secretion and electroneutral NaCl absorption appear to differ.

Somatostatin may not be a hormonal messenger of fat-induced inhibition of gastric functions

The present study was designed to evaluate somatostatin as a hormonal inhibitor of gastric functions in humans. Seven healthy volunteers were investigated on 6 separate days. Peptone meal-stimulated gastric acid secretion was measured by intragastric titration for 2 h and gastric emptying was estimated with a dye-dilution technique. The effect of intravenous administration of somatostatin at 0, 12.5, 50, 100, and 200 pmol/kg.h was investigated and related to the effect of intragastric administration of 100 ml of vegetable oil. Plasma somatostatinlike immunoreactivity was elevated during intravenous administration of somatostatin at 100 and 200 pmol/kg.h, whereas no increase was detected in response to the oil. Somatostatin infusion at 100 and 200 pmol/kg.h significantly inhibited the acid secretion by 25% and 65%, and the oil reduced the acid output by 41%. Somatostatin at 100 and 200 pmol/kg.h significantly enhanced gastric emptying, whereas the oil inhibited gastric emptying. These observations suggest that somatostatin may not be an important hormonal messenger of fat-induced inhibition of acid secretion or gastric emptying.

Treatment of severe cryptosporidium-related diarrhea with octreotide in a patient with AIDS

Cryptosporidiosis commonly causes severe diarrhea in immunosuppressed patients. There currently are no antiparasitic drugs consistently effective for this infection. This case describes a 26-year-old hemophiliac patient with acquired immunodeficiency syndrome and cryptosporidiosis whose diarrhea improved with continuous intravenous administration of a long-acting somatostatin analog, octreotide. Somatostatin has a variety of inhibitory effects on gastrointestinal hormones as well as a possible nonspecific effect on gastrointestinal mucosal fluid and electrolyte secretion. The somatostatin analog should be considered for patients with secretory diarrhea refractory to other forms of therapy.

Successful treatment of idiopathic secretory diarrhea of infancy with the somatostatin analogue SMS 201-995

The somatostatin analogue SMS 201-995 has been reported to be effective in treating adult secretory diarrhea due to vasoactive intestinal polypeptidoma. We report the effectiveness of this drug in treating severe refractory secretory diarrhea of uncertain etiology in an infant. The patient developed diarrhea within the first few days of life, with mean stool output of 250 ml/kg.day (expected 10 ml/kg.day). Small bowel biopsy showed mild focal enteritis. Serum levels of known gastrointestinal secretagogues were normal. No tumor was detected. Diarrhea was not adequately controlled by various drug treatments. Addition of subcutaneous SMS 201-995 produced a significant sustained decrease in stool output to 80-100 ml/kg.day. During SMS 201-995 treatment, no metabolic, hormonal, or growth abnormalities were noted. SMS 201-995 was discontinued after 9 mo because of patient irritability. Stool output rose immediately to 173 ml/kg.day, and remained stable for 6 mo. It is concluded that SMS 201-995 was a safe and effective treatment in this single childhood case of severe idiopathic secretory diarrhea.

The effect of a long-acting somatostatin analogue (SMS 201-995) on intermediary metabolism and gut hormones after a test meal in normal subjects

SMS 201-995 is an octapeptide analogue of somatostatin. The effect of a single subcutaneous (s.c.) injection of 50 micrograms SMS 201-995 on post-prandial intermediary metabolism was investigated in normal subjects. In spite of a long-lasting post-prandial suppression of insulin secretion, there were no significant changes in the plasma concentration of alanine, glycerol, 3-OH-butyrate or lactate. However, SMS 201-995 impairs carbohydrate tolerance, probably due to inhibition of insulin secretion. Basal and post-prandial plasma concentrations of the gut regulatory peptides pancreatic glucagon, motilin, pancreatic polypeptide, gastric inhibitory polypeptide, enteroglucagon, gastrin and peptide YY were suppressed up to 5 hours after subcutaneous administration of a single dose of SMS 201-995.

Influence of centrally administered somatostatin and two related peptides on intestinal absorption of water and electrolytes in conscious dogs

The effects of intracerebroventricular (ICV) administration of somatostatin (SRIF) and two related peptides, anti SRIF and SMS 201-995, on jejunal fluxes of water, Na+ and K+ were investigated in dogs prepared with a Thiry-Vella (TV) loop. Intestinal transport in the TV loop and concomitant transit time were also measured during infusion (2 mg/min) of an isotonic electrolyte solution and phenol-red bolus injections. Basal net water absorption was reduced significantly (p less than 0.01) over periods of 2 to 5 hr and in a dose-related manner, with ICV administrations of SRIF (5 to 100 ng/kg); doses of SRIF, 5 to 25 times higher but administered IV, were inactive. Similar reductions in the net fluxes of water, Na+ and K+ were observed over 2 to 5 hr following ICV administration of a putative somatostatin antagonist and SMS 201-995 at doses of 100 ng/kg. Neither metoclopramide (1 mg/kg), phentolamine (0.1 mg/kg) nor methysergide (0.2 mg/kg) given IV were able to antagonize the effects of centrally administered SRIF (100 ng/kg) on intestinal fluxes. In contrast, the effects of SRIF were abolished completely by naloxone (0.2 mg/kg) but not methyl-naloxone (0.3 mg/kg) given systemically. It is concluded that somatostatin and the two related peptides act centrally to reduce jejunal absorption of water and electrolytes. The effects of SRIF appear to be related to opiate receptors, possible involving central nerve pathways which utilize opiate-like transmitters.

Effects of somatostatin analogue SMS 201-995 in non-insulin-dependent diabetes

The 24-h hormonal and metabolic profiles obtained in five non-insulin-dependent diabetics receiving twice daily s.c. injections of the long-acting somatostatin analogue SMS 201-995 (50 micrograms) have been compared with those obtained following placebo injection. Injections were given 30 min before breakfast and the evening meal. GH secretion was not suppressed by the analogue administered in this manner. Despite suppression of serum insulin levels following breakfast and the evening meal, blood glucose levels were similar during the two study periods with no evidence of worsening in diabetic control. Prolonged suppression of plasma glucagon levels was observed and the nocturnal elevation in serum TSH levels was abolished. Free T4 levels fell significantly following the analogue but total T3 levels were unaffected. Blood alanine levels were elevated throughout the study period following SMS 201-995 but changes in lactate, pyruvate, glycerol and 3-hydroxybutyrate were minor. All five subjects suffered gastrointestinal side-effects. SMS 201-995 (50 micrograms) given twice daily before meals does not cause a deterioration in metabolic control, does not suppress 24-h GH secretion and causes significant side-effects in patients with non-insulin-dependent diabetes mellitus.

Effects of somatostatin analogue SMS 201-995 in normal man

Long-acting somatostatin analogues may be of benefit in certain hypersecretory endocrine and gastrointestinal disorders. The 24 h hormonal and metabolic profiles of six normal male subjects receiving a twice daily subcutaneous injection of one such analogue SMS 201-995, 50 micrograms, has been compared to that obtained following placebo injection. Spontaneous daytime peaks of GH secretion were delayed until 1400 h following SMS 201-995 but nocturnal and total 24 h GH secretion were unaffected. The nocturnal rise in thyrotrophin was abolished by SMS 201-995 but thyroid function was unaffected. Insulin levels were suppressed following SMS 201-995 and the response to meals was inhibited. Glucose intolerance followed main meals. Glucagon levels were suppressed for up to 6 h. Circulating alanine levels were raised between 1200 h and 0600 h and there were intermittent elevations in lactate, pyruvate, glycerol and 3-hydroxybutyrate. Amino acid levels, including branched chain amino acids, were also increased. All six subjects suffered gastrointestinal side-effects. SMS 201-995, 50 micrograms, given twice daily shortly before meals does not suppress 24 h GH secretion, but demonstrates significant effects on metabolism and causes side effects in normal subjects.

Effects of a long-acting somatostatin analogue in patients with severe ileostomy diarrhoea

Proctocolectomy (PC) with small bowel resection may lead to profuse ileostomy diarrhoea which can be difficult to treat. The effect of a recently developed long acting somatostatin analogue (SMS 201-995) on ileostomy output was investigated in 5 patients who had undergone PC and ileal resection (median 120 cm) and who suffered severe diarrhoea (4-7 litres/24 h). Gastric emptying, transit of a standard meal through the small bowel and the amounts of nutrients excreted were simultaneously determined during double blind infusion of SMS (25 micrograms/h) and placebo (isotonic saline 125 ml/h). SMS 201-995 significantly reduced ileostomy output (P less than 0.05) and water excretion (P less than 0.05) and prolonged small bowel transit time (P less than 0.05). Whilst having little effect on gastric emptying, or on the excretion of glucose or nitrogen, fat excretion was significantly increased (P less than 0.05). In two patients subcutaneous administration of SMS 201-995 (50 micrograms b.d.) has maintained a reduced ileostomy output for 4 and 6 months respectively.

Physiological role of somatostatin in the digestive tract: gastric acid secretion, intestinal absorption, and motility

Somatostatin is found in both endocrine cells and nerve fibres of the gastrointestinal tract and has several inhibitory effects on the digestive tract. Somatostatin is a potent inhibitor of gastrin release; its secretion is regulated predominantly by the cholinergic pathway, which inhibits somatostatin and thus stimulates gastrin release. Gastric acid secretion is inhibited by both the paracrine and circulating peptide (hormonal) effects of somatostatin. Somatostatin secretion is a direct effect of acid on the somatostatin cell, since it is unaffected by the axonal blocker tetrodotoxin. Somatostatin antiserum eliminates the inhibitory effect of somatostatin and thus augments acid secretion. It therefore appears that somatostatin plays a physiological role in regulating gastric acid secretion, and it is possible that a lack of the inhibitory function of somatostatin is an aetiological factor in peptic ulcer disease. Postprandially, a rise in serum somatostatin concentration occurs which is twice as high with protein and fat as it is with carbohydrates. Several studies have shown that somatostatin inhibits nutrient absorption, indicating that somatostatin might be a physiological regulator in the homeostasis of ingested nutrients by modulating the intestinal absorption rate. Experiments have also demonstrated that somatostatin infusion inhibits intestinal motility; the interval between migrating myoelectric complexes is increased, and transit time is increased.

Intestinal somatostatin function

Somatostatin is present throughout the intestine, both in D cells at the luminal surface and in neural elements. It inhibits the release or action of many gut hormones known to regulate gastro-intestinal function and undoubtedly has a wide range of actions. In the intestine, available information indicates that somatostatin may have an important regulatory role for water and electrolyte absorption and secretion. The peptide affects both the epithelial transport function and the intestinal motility function. The outcome associated with administration of somatostatin is inhibition of water and electrolyte secretion. Somatostatin has been shown to effectively reduce stool output in diarrheal syndromes associated with endocrine tumor and other conditions. Clinical application of somatostatin in diarrhea still awaits development of an orally active and/or gut-specific analog. Some preliminary results indicate that this may be possible in the future.

Structure-activity relationships of somatostatin analogs in the rabbit ileum and the rat colon

Somatostatin increases absorption of electrolytes and inhibits diarrhea in patients with endocrine tumors and short bowel syndrome. In an attempt to develop a gut-specific somatostatin analog, each amino acid in the somatostatin molecule was replaced with L-alanine, deleted, or substituted with its D-isomer. The potency of each analog to stimulate ion transport in the rabbit ileum was then determined using the modified Ussing chamber technique. The results were compared to the ability of each analog to inhibit the stimulated release of growth hormone from cultured rat anterior pituitary cells and to inhibit the arginine-stimulated release of insulin and glucagon in the rat in vivo. Analogs that showed gut selectivity were then tested for their ion transport properties in the rat colon.

RESULTS

(a) Substitution with L-alanine or deletion of the amino acid at position 6, 7, 8, or 9 and deletion of Threonine(10)-produced analogs with significantly reduced ion transport properties to <4% of somatostatin's action. The substitution also markedly reduced the ability of the compounds to inhibit the release of growth hormone, insulin, and glucagon. (b) Selectivity of intestinal ion transport was achieved by any one of the following alterations: L-alanine substitution at Phenylalanine(11), deletion of Phenylalanine(11), substitution with D-lysine at Lysine(4), or substitution with L-alanine at Lysine(4). These compounds had intestinal ion transport properties of 52, 34, 139, and 94%, respectively, while demonstrating little or no inhibition of growth hormone, insulin or glucagon release.

CONCLUSIONS

(a) Phenylalanine(6), Phenylalanine(7), Tryptophan(8), and Lysine(9) are required for the ion transport and other biologic actions of somatostatin, whereas Threonine(10) serves as an essential spacer. (b) Alteration at Phenylalanine(11) or Lysine(4) yields analogs that are selective for ion transport in the rabbit ileum and rat colon. These findings should be taken into consideration when developing a gut-specific somatostatin analog that can be useful in the treatment of diarrhea.

Somatostatin and the interdigestive migrating motor complex in man

The relationship between somatostatin and the interdigestive migrating motility complex (MMC) was determined in human volunteers. Motor activity was monitored manometrically by means of seven perfused catheters: four in the stomach, one in the duodenum, two in the jejunum. Blood samples were drawn every 10 min and radioimmunoassayed for motilin, pancreatic polypeptide and somatostatin. In four volunteers two activity fronts (AF) were recorded and somatostatin levels correlated to the manometric data. The start of an AF in the upper duodenum was accompanied by somatostatin peaks. Peak values, taken as the mean of the levels in the sample obtained after the start of an AF, the preceding sample and the next one, averaged 32 +/- 4 pM compared to 12 +/- 2 pM in the remaining period. In four volunteers somatostatin was infused in doses of 1.2, 2.4 and 4.8 pM/kg per min over three consecutive periods of 90 min, causing dose-dependent increments in plasma somatostatin levels of 7, 32 and 76 pM. In all volunteers and for all doses all gastric activity was completely inhibited. In the intestine phase 2 was abolished but phase 3 stimulated: during somatostatin infusion phase 3 occurred with an interval of 39 +/- 6 min. Motilin and PP levels were decreased. As the two lowest infusion doses caused increases in somatostatin levels that might be considered as physiological, somatostatin seems to have a physiological role in the regulation of the migrating motor complex. We propose that it facilitates the progressing of the activity front into the small intestine.

Effects of intravenous somatostatin and motilin on the blood glucose and hormonal response to oral glucose

Exogenous intravenous infusions of control saline, somatostatin, motilin and somatostatin and motilin together were compared in normal volunteers for their effects on the rise of blood glucose following 50 g oral glucose and for their effects on gastric emptying and plasma hormone concentrations. All regulatory peptide infusions increased the rate of gastric emptying by between 182% and 198% at 60 min post-ingestion. The glucose response during the oral glucose tolerance test was suppressed when somatostatin with or without motilin was infused but was increased during motilin. The somatostatin infusion reduced concentrations of motilin, insulin, gastric inhibitory polypeptide, gastrin and neurotensin whilst the motilin infusion was associated with an increased initial rise in insulin and gastric inhibitory polypeptide. The metabolic effects of the motilin infusion were overriden by the effects of somatostatin when both peptides were infused together; this suggests that somatostatin inhibits both the effects and secretion of motilin.

The effect of somatostatin and enkephalin on ion transport in the intestine

SRIF and enkephalin stimulate net Na and C1 absorption in the rabbit ileum and appear to do so primarily by stimulating the coupled influx of Na and C1 across the brush border membrane. The stimulatory effect of enkephalin on ion transport is blocked by verapamil and Ca-free solution, indirectly indicating that enkephalin may work as a Ca-channel blocker. The resultant lowering in cytosolic calcium level stimulates Na and C1 absorption. SRIF was able to block the effect of cyclic AMP-dependent and cyclic AMP-independent secretogogues in the rat colon without affecting cyclic AMP levels suggesting that it is inhibiting a distal step in the secretory pathway, probably involving a final common pathway. SRIF infusion blocked diarrhea in a patient with the carcinoid syndrome, indicating that it may be therapeutically useful in the treatment of secretory diarrheas. The antidiarrheal effect of opiates is probably due in part to their effect on electrolyte absorption, rather than an effect solely on intestinal motility.

Influence of somatostatin on gastric motility and meal absorption in rhesus monkeys, Macaca mulatta

The effects of somatostatin on gastric motility and nutrient absorption from a mixed meal were evaluated in conscious rhesus monkeys (M. mulatta). Continuous saline or somatostatin (0.8 microgram/kg X min) infusions were carried out prior to and for 2 hr following an intragastric infusion of a complete liquid diet trace-labeled with 3H-3-glucose and 3H-9, 10-triolein. Gastric motility was assessed from recordings of gastric pressure and from extraluminal strain gauges. Intravenous somatostatin did not alter gastric motility or the rate of absorption of the labeled glucose; lipid absorption, however, was markedly impaired.