Inhibition of gastrin and gastric-acid secretion by growth-hormone release-inhibiting hormone

Growth hormone-releasing factor (somatocrinin) stimulates epithelial cell proliferation in the rat digestive tract

The possible influence of growth hormone-releasing factor (GHRF) on epithelial cell proliferation in the digestive tract was investigated. Fasted young rats received five hourly subcutaneous injections of either GHRF or saline. They were killed 6, 12, or 18 h after the initial injection and 45 min after [3H]thymidine pulse labeling. At the time of death, blood was taken to determine circulating growth hormone and gastrin levels. After radioautography, DNA synthetic and mitotic activities were estimated in the fundic, antral, duodenal, jejunal, and colonic mucosae. Growth hormone-releasing factor significantly increased labeling indices 6, 12, and 18 h after the initial injection in fundic mucosa, and 6 and 18 h after injection in antral and duodenal mucosae. Furthermore, GHRF significantly increased mitotic indices at 12 h in fundic mucosa and at 12 and 18 h in jejunal mucosa. No effect was seen in the colon. At the three checkpoint times, circulating growth hormone showed no change, but plasma gastrin was increased in the rats treated with GHRF as compared with controls. However, whether the reported stimulatory effect of the GHRF on target cells is direct or indirect remains to be determined.

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.

The effect of SMS 201-995, a long-acting somatostatin analogue, on anterior pituitary function in healthy male volunteers

The endocrine effect of SMS 201-995, an octapeptide analogue of somatostatin, was assessed during a combined anterior pituitary function test. There was no effect on the extent of hypoglycaemia after intravenous insulin infusion or on the subsequent rate of recovery of plasma glucose. SMS 201-995 administration, however, resulted in a profound and selective suppression of the GH response to hypoglycaemia without affecting the ACTH or cortisol responses. There was also a marked reduction of TSH release in response to intravenous TRH; the prolactin response was unimpaired. The LH response to LHRH was blunted and the FSH response unaffected. SMS 201-995 does not significantly impair the counterregulatory mechanisms in response to hypoglycaemia, and, in particular, the hypothalamic-pituitary-adrenal axis remains intact.

Effect of intragastric pH, prostaglandins and prostaglandin synthesis inhibitors on the release of gastrin and somatostatin into the gastric lumen of anaesthetized rats

The object of the present work was to study the influence of antral pH, of aspirin and indomethacin, and of prostaglandins A2, E1 and E2 on the intragastric output of somatostatin and gastrin induced by electrical vagal stimulation (5 V, 2 ms, 2, 5 and 10 Hz). Experiments were performed on anaesthetized rats in which the stomach was perfused with a dextran solution (pH approximately 1.5 to approximately 6). To assess the effect of vagal stimulations on gastric acid secretion and on gastrin and somatostatin release, pH as well as somatostatin and gastrin levels was recorded in the perfusate effluent. During perfusion of the stomach with dextran solution, pH approximately 6, vagal stimulation at 10 Hz decreased perfusate pH to 1.3 and gastrin and somatostatin were released at a ratio of 2:1. Less gastrin and more somatostatin (ratio 0.1:1) was released by the same stimulation when the stomach was pre-perfused with acid solution (pH approximately 1.5), although also in these experiments the pH of the perfusate fell to 1.3. When vagal stimulations were performed after the rats had been pretreated with aspirin or indomethacin, more somatostatin than gastrin was detected in the perfusate independently of the perfusate pH. The vagally induced intraluminal release of somatostatin occurring in aspirin-treated animals was abolished by a low dose of atropine (0.05 mg kg-1) or by a simultaneous infusion of prostaglandin E1 (30 micrograms kg-1 h-1).

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.

Pharmacokinetics of SMS 201-995 in healthy subjects

The pharmacokinetics of a new somatostatin derivative, SMS 201-995, was investigated in a group of eight healthy subjects. SMS 201-995 was given intravenously in doses of 25 micrograms, 50 micrograms, 100 micrograms, and 200 micrograms and also subcutaneously in doses of 50 micrograms, 100 micrograms, 200 micrograms, and 400 micrograms in accordance with a randomized Latin-square design. Blood samples were taken up to 8 h. The tolerability of SMS 201-995 was very good. Routine blood chemistry variables remained normal. After intravenous administration of SMS 201-995 initial half-lives ranging from 9 +/- 2 min to 14 +/- 4 min and second half-lives of from 72 +/- 22 min to 98 +/- 37 min were calculated for the different doses. SMS 201-995 was rapidly absorbed after subcutaneous injection with a half-life ranging from 5.3 +/- 2.2 min to 11.7 +/- 7.6 min. The disposition half-life was from 88 +/- 20 min to 102 +/- 16 min for the different doses. Cp(tmax) and AUC (0 - infinity) increased dose-dependently after both routes of administration, pointing to linear pharmacokinetics for SMS 201-995. On the basis of its good tolerability, slow plasma clearance, and long action, SMS 201-995 represents a valuable tool for further clinical studies.

Somatostatin: historical aspects

Somatostatin, in essence an almost universal chalone, initially described as a 14 amino-acid-long peptide that inhibits growth hormone (GH) release, has been shown to be one of a family of related peptides, ubiquitous in distribution and versatile as a paracrine factor with a potentially important role in the regulation of gut, pancreatic, and nervous system function, in addition to its well-recognized influence on the pituitary secretion of GH and thyroid-stimulating hormone. With the development of new super agonists, it has become possible to manipulate the endocrine milieu, to modify gut, pancreatic, and pituitary function, and, in the case of several diseases such as acromegaly and intractable diarrhoea, to make a significant advance in therapy.

The role of somatostatin and a long-acting analogue, SMS 201-995, in acute bleeding due to peptic ulceration

During the past 10 years several drugs have been tested for their efficacy in controlling acute upper gastrointestinal (GI) bleeding. However, since the bleeding is self-limiting in 70-80% of cases, any drug tested in all cases of upper GI bleeding will have to perform extremely well to prove significantly better than placebo. Natural somatostatin has recently been investigated on the basis that it reduces gastric acid secretion and splanchnic blood flow. In severe cases of bleeding, an average success rate of 87% has been achieved, the highest ever reported for a drug in this indication. In unselected bleeders, however, somatostatin was no more effective than placebo. The long-acting somatostatin analogue, SMS 201-995, was investigated in the current studies and was found to be more potent than natural somatostatin in reducing gastric acid secretion and in reducing intestinal mucosal blood flow for a substantially longer period. A pilot study of SMS 201-995 in the treatment of severe acute upper GI bleeding resulted in cessation of bleeding, with no rebleeding during or within 24 h after the trial in 8 of 10 patients. No side effects were reported. The planning of a large controlled trial is described.

Somatostatin localization in tissues

The development of specific antibodies to somatostatin has enabled investigations on the distribution (radioimmunoassay) and precise tissue localization (immunocytochemistry) of somatostatin-immunoreactive (IR) material. Somatostatin immunoreactivity is broadly distributed both in the central nervous system and in many peripheral organs, including the gastrointestinal tract, pancreas, genitourinary system, heart, eye, thyroid, thymus, and skin. Somatostatin-IR cells display characteristic morphological features, including cytoplasmic elongations, which lend support to the postulated local or paracrine role for somatostatin. The intracytoplasmic electron-dense secretory granules in somatostatin-IR endocrine cells are characterized by their round shape, flocculent matrix, and closely apposed limiting membrane. Somatostatin-IR nerves are abundant in the gut and contain large, dense, P-type neurosecretory granules, which are distinct from those storing other peptidergic neurotransmitters. Somatostatin immunoreactivity is found frequently in neuroendocrine tumours, but the existence of the 'somatostatinoma syndrome' has recently been questioned.

Somatostatin: a metabolic regulator

Somatostatin, the hypothalamic release-inhibiting factor, has been found to stimulate gluconeogenesis in rat kidney cortical slices. Stimulation by somatostatin was linear and dose-dependent. Other bioactive peptides such as cholecystokinin, gastrointestinal peptide, secretin, neurotensin, vasoactive intestinal peptide, pancreatic polypeptide, beta endorphin and substance P did not affect the renal gluconeogenic activity. Somatostatin-induced gluconeogenesis was blocked by phentolamine (alpha adrenergic antagonist) and prazosin (alpha1 adrenergic antagonist) but not by propranolol (beta adrenergic antagonist) and yohimbine (alpha2 adrenergic antagonist) suggesting that the effect is via alpha1 adrenergic stimuli. Studies on the involvement of Ca2+ revealed that tissue depletion and omission of Ca2+ from the reaction mixture would abolish the stimulatory effect of somatostatin. Furthermore, somatostatin enhanced the uptake of 45calcium in renal cortical slices which could be blocked by lanthanum, an inhibitor of Ca2+ influx. It is proposed that the stimulatory effect of somatostatin on renal gluconeogenesis is mediated by alpha1 adrenergic receptors, or those which functionally resemble alpha1 receptors and that the increased influx of Ca2+ may be the causative factor for carrying out the stimulus.

Gastrointestinal somatostatin: distribution, secretion and physiological significance

Somatostatin-like immunoreactivity (SLI) has been found throughout the gastrointestinal tract in all species examined. In the stomach it is mainly present in endocrine-type D-cells whereas in the intestine there is also an extensive distribution in enteric neurones. In all regions of the gastrointestinal tract multiple forms of somatostatin exist. A precursor (prosomatostatin) has been partially sequenced, three forms with 20 (SS-20), 25 (SS-25) and 28 (SS-28) amino acids completely sequenced, and somatostatin-14 (SS-14) demonstrated by radioimmunoassay. Both SS-14 and SS-28 exert a wide range of actions on the gastrointestinal tract and there is strong supportive evidence for a role in the regulation of gastric acid and gastrin secretion, gastrointestinal motility and intestinal transport. Both in vivo and in vitro studies on the secretion of gastric SLI into the vasculature have shown that nutrients initiate the process but that subsequent events are regulated by a complex interplay between hormonal and neuronal pathways. GIP is one of the most potent hormonal secretagogues. In the stomach, acetylcholine, opioid peptides and substance P are probably involved in parasympathetic inhibitory pathways and gastrin releasing peptide in stimulatory pathways. The sympathetic nerves are also stimulatory. Regulation of secretion of intestinal SLI has not been so extensively studied. Although SLI is also found in the gastrointestinal lumen the significance is unclear. Despite these advances the exact route of delivery of somatostatin to its target organs is uncertain and paracrine, endocrine and neural pathways may all be involved.

Behavior of somatostatin-immunoreactive cells in the gastric mucosa before and after selective proximal vagotomy and pyloroplasty in treatment of gastric and duodenal ulcers

Antral somatostatin-immunoreactive cells (D cells) were counted pre- and postoperatively in 20 patients with duodenal ulcer and in 8 patients with gastric ulcer. Counts were obtained either over a 2-yr postoperative period (duodenal ulcer patients) at intervals of 0.5, 1, and 2 yr or over a greater than or equal to 4-yr postoperative period (gastric ulcer patients) at intervals of 1-2 yr. In patients with a normal population of gastrin-immunoreactive cells (G cells), the D cells were within the normal range (mean value 0.53% in duodenal ulcer patients and 0.67% in gastric ulcer patients). High G-cell values were accompanied by high D-cell values (e.g., in gastrin-cell hyperplasia) and low G-cell values were accompanied by low D-cell values. The G-cell to D-cell ratio was 8:1 and 6.6:1 in duodenal and gastric ulcer patients, respectively. After selective proximal vagotomy and pyloroplasty, the following observations were made: the relation of number of G cells to number of D cells remained unchanged; the postoperative rise in G-cell population was accompanied by a rise in D-cell population; hypertrophy of the D cells was apparent as was postoperative hyperplasia, with a postoperative increase in D-cell size. Morphologic coupling of the gastrin-somatostatin system in the antrum is assumed. This is constant in ulcer disease both before and after vagotomy.

Dual inhibitory actions of somatostatin on isolated gastric glands

The growth hormone release-inhibiting hormone or somatostatin is a potent inhibitor of gastric acid secretion. In the present paper these inhibiting properties were tested on isolated gastric glands from rabbit fundic mucosae, prepared as according to Berglindh & Obrink (1976). Parietal cell activity was measured as [14C]aminopyrine (AP) accumulation and O2-consumption. Glandular histamine release was determined after condensation with o-phthalaldehyde and measured fluorometrically. In the gastric glands there are two possible main processes that can be inhibited, namely (1) the release of histamine from some endocrine cells and (2) the activity of the parietal cell itself. It was found that somatostatin acted on both mechanisms. Basal histamine release was, however, not affected by somatostatin while the release induced by pentagastrin (Pg) at a concentration of 3 X 10(-9) M, or acetylcholine (10(-5) M) was dose-dependently (10(-12) to 10(-6) M) inhibited by this peptide. Maximal inhibition, which was about 70%, occurred at a dose of 10(-8) M somatostatin. Somatostatin also depressed parietal cell activity induced by histamine (10(-6) to 10(-4) M), isobutyl-methyl-xanthine (IMX, 10(-5) to 10(-4) M) or the combination of IMX (10(-5) M) and Pg (3 X 10(-9) M) Basal parietal cell activity was, however, unaffected. The IMX (10(-4) M) induced parietal cell activity in cimetidine-treated (10(-4) M) glands was also depressed by somatostatin, which indicates an action directly on the parietal cell not mediated via H2-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Is somatostatin a directly acting cholestatic hormone?

Previous experiments have demonstrated the cholestatic effects of somatostatin administration in several animal species. These effects were confirmed in the rat. Nine pairs of intact awake rats received intravenous sodium taurocholate (23 mg hr-1) to stabilize bile flow, and half were later given somatostatin at doses of 185 micrograms hr-1. After 1 hr of somatostatin the experimental group showed a significant decrease in bile flow compared to the control group. Cholestasis reversed when somatostatin infusion was stopped. An in situ isolated perfused rat liver technique was used to assess the direct effects of somatostatin on biliary flow. In 10 pairs of rat livers, after achieving stable bile flow, half of those perfused (the "experimentals") received continuous (370 micrograms hr-1) somatostatin infusion, while the controls received saline. The percentage change in bile flow from baseline in the somatostatin group was not significantly different from that in controls for any test period. Bile analysis revealed no significant differences between groups for cholesterol, phospholipid, or bile salt concentrations or outputs. These data suggest that somatostatin inhibits bile secretion by some mechanism other than direct inhibition of bile secretory mechanisms.

Somatostatin and intestinal calcium transport in the rat

In intact rats we studied the influence of low doses of intravenously (i.v.) administered somatostatin (SRIF) on the net absorption and the bidirectional fluxes (lumen-to-plasma, LP; plasma-to-lumen, PL) of calcium in the duodenum, jejunum, ileum and caecum. In the duodenum SRIF inhibited the LP-flux and the net absorption of Ca significantly at infusion rates of 0.75 and 1.0 microgram SRIF . kg-1 . h-1. The PL-flux was not altered by any of the SRIF doses administered. In the other gut segments studied (jejunum, ileum, caecum) neither the net absorption nor the bidirectional Ca fluxes were changed by i.v. SRIF. It is concluded that SRIF in the plasma levels achieved in this study has an influence on the duodenal calcium absorption (CaA) of the rat; questions regarding the mechanisms of this action as well as the physiological significance of our findings are as yet unresolved.

Effect of long acting somatostatin-analogue, SMS 201 995, on gut hormone secretion in normal subjects

SMS 201 995 is a new long acting analogue of somatostatin. We have investigated its effect on basal and meal stimulated secretion of gut hormones and have shown that after a single s.c. injection of 50 micrograms it lowers significantly the basal plasma levels of pancreatic polypeptide, secretin, motilin, pancreatic glucagon and insulin, it also effectively suppresses the postprandial release of pancreatic polypeptide, gastrin, secretin, gastric inhibitory peptide, pancreatic glucagon and insulin. Except for the usual brief discomfort of an injection, no symptoms or untoward effects were observed.

Gastrin and somatostatin in plasma and gastric biopsy specimens in pernicious anemia

Five patients with megaloblastic anemia due to deficiency of vitamin B12 and achlorhydria and six normal controls participated in the study. The patients with pernicious anemia (PA) had elevated plasma gastrin levels, as expected, and lower plasma somatostatin (SST) levels than the control patients. The amount of gastrin and SST in the antral mucosa did not differ in the two groups of patients. In the fundic mucosa, the patients with PA had increased tissue concentrations of both gastrin and SST as compared with the tissue concentrations in the controls. These findings of hormone tissue concentrations were correlated to the number of argyrophilic cells. Thus, in the antral mucosa the number of argyrophilic cells did not differ in patients with PA and in the controls. In the fundic mucosa, however, the number of argyrophilic cells was significantly elevated in patients with PA as compared with the controls.

Deficiency of immunoreactive somatostatin in the median eminence of Snell dwarf mice

Snell dwarf mice (dw/dw) are characterized by a genetically determined, congenital lack of pituitary GH, TSH and prolactin. Given that hypothalamic somatostatin is involved in the regulation of pituitary GH and TSH release, it was decided to investigate the content of immunoreactive somatostatin (IRS) in the median eminence of dw/dw and phenotypically normal mice of the same strain. The content of IRS in the pyloric antrum and pineal gland of these animals was also examined. The effects of ovariectomy and of hyperprolactinemia (induced by a pituitary graft under the kidney capsule) on the median eminence content of IRS were also studied in both normal and dwarf mice. Median eminence IRS content was significantly lower in the dw/dw (23.6 +/- 1.8 ng) than in normal mice (57.4 +/- 7.1 ng); no difference was found in the pyloric IRS content of dw/dw (16.9 +/- 1.6 ng/mg of protein) and normal animals (13.8 +/- 1.9 ng/mg of protein), nor in the pineal content of IRS (639.4 +/- 64.4 pg/gland in the dw/dw; 732 +/- 265 pg/gland in normals). Neither ovariectomy nor hyperprolactinemia were found to affect the IRS content in the tissues studied in normal or dwarf mice. Treatment of an additional group of 9 dwarf mice with L-thyroxine (L-T4 2 micrograms/48 h. s.c. for 2 weeks) significantly increased the animals weight (10.2 +/- 0.4 g versus 7.4 +/- 0.3 g) and produced maturation of facial features; however, it did not change the IRS content in any of the tissues studied. It is concluded that the content of IRS in the median eminence of mice with a congenital lack of GH, TSH and prolactin is significantly reduced and that this is unlikely to be related to the deficiency of thyroid hormones in these animals.

Vagal regulation of GRP, gastric somatostatin, and gastrin secretion in vitro

The effect of electrical stimulation of the vagus nerves on the release of immunoreactive gastrin-releasing peptide (GRP), gastrin, and somatostatin was investigated using the isolated perfused rat stomach. Electrical stimulation (10 Hz, 1 ms duration, 10 V) of the peripheral end of the subdiaphragmatic vagal trunks produced a significant increase in both GRP and gastrin but a decrease in somatostatin. The infusion of atropine sulfate at a concentration of 10(-5) M augmented GRP release and reversed the decrease in somatostatin release in response to vagal stimulation to an increase above basal levels. However, the gastrin response to vagal stimulation was not affected by atropine. The infusion of hexamethonium bromide at a concentration of 10(-4) M significantly suppressed GRP release but did not affect gastrin secretion in response to vagal stimulation. On the other hand, the somatostatin response to vagal stimulation was completely abolished by hexamethonium. These findings lead us to conclude that the intramural GRP neurons might play an important role in the regulation of gastrin as well as somatostatin secretion and that somatostatin secretion may be controlled not only by a cholinergic inhibitory neuron but also by a noncholinergic, e.g., peptidergic stimulatory neuron, both of which may be regulated through preganglionic vagal fibers via nicotinic receptors. In addition, because the infusion of 10(-7) M GRP suppressed the somatostatin secretion, we suggest that either GRP should be excluded from the list of candidates for the noncholinergic stimulatory neurotransmitter for somatostatin secretion or that there are different mechanisms of action for endogenous and exogenous GRP.

Effect of antibodies to somatostatin on acid secretion and gastrin release by the isolated perfused rat stomach

The present studies were directed toward examining the effect of somatostatin on gastrin release and acid secretion by the isolated vascularly perfused rat stomach. Rat stomachs were perfused in situ with Krebs-Ringer bicarbonate buffer containing 10% ovine erythrocytes and gassed with 95% O2-5% CO2. Inclusion of pentagastrin in the perfusion buffer increased acid output from 2.2 +/- 0.4 microEq H+/h during control perfusion to 18.8 +/- 1.8 microEq H+/h (p less than 0.01). In order to determine the effect of somatostatin on acid secretion and gastrin release, specific antibodies to somatostatin were included in the perfusate. Inclusion of antibodies to somatostatin in the buffer without pentagastrin did not significantly enhance acid output; however, gastrin concentration in the portal venous effluent increased from 15.1 +/- 2.0 to 25.2 +/- 5.2 pg/ml at 45 min (p less than 0.05). When antibodies to somatostatin were perfused in the presence of pentagastrin, acid output increased by 32% to 24.9 +/- 1.2 microEq H+/h (p less than 0.05); however, no change in gastrin concentration over basal was detected in the portal effluent. Results of these studies indicate that the capacity of the isolated rat stomach to secrete acid permits direct assessment of factors involved in the regulation of acid secretion. Under the conditions of these experiments, gastric somatostatin inhibits basal gastrin release and directly inhibits pentagastrin-stimulated acid secretion without affecting gastrin release.

Vasoactive intestinal polypeptide-, somatostatin-, and calcitonin-producing adrenal pheochromocytoma associated with the watery diarrhea (WDHH) syndrome. First case report with immunohistochemical findings

A 30-year-old man presenting with watery diarrhea, hypokalemia, and hypochlorhydria (Verner-Morrison syndrome, WDHH syndrome) had raised plasma levels of vasoactive intestinal polypeptide (VIP), somatostatin (SRIF), calcitonin, and gastrin, as well as high urinary excretion of vanillylmandelic acid. A right adrenal pheochromocytoma was found and excised. The neoplastic cell population was immunohistochemically shown to contain VIP, SRIF, and calcitonin. Gross, histologic, and immunohistochemical evaluation of the pancreas revealed no abnormalities, whereas a marked hyperplasia of the gastrin-producing cells of the gastric antral mucosa was demonstrated. Postoperatively, the patient recovered from his symptoms and the plasma hormone levels returned to normal values. The clinical and histogenetic implications of this most unusual tumor of neural crest derivatives are discussed.

Cytoprotective effect of pentagastrin and epidermal growth factor on stress ulcer formation. Possible role of somatostatin

This study was designed to test the effects of pentagastrin and epidermal growth factor (EGF) on stress-induced ulceration and on the antral content of gastrin and somatostatin (SLI) in rats. Four groups of 14 to 15 rats had been prepared for 7 days by one of the following methods: saline injection (control); injection of pentagastrin (250 micrograms/kg, 3 times/day); injection of EGF (10 micrograms/kg, 3 times/day); or injection of EGF plus pentagastrin. At the end of the treatment period, half of each group of rats were sacrificed (nonstress group). There were no ulcers in the nonstress control groups of rats. Stress was applied by water immersion in the remaining half of the rats. The injections of pentagastrin and/or EGF resulted in substantial increase in antral content of SLI. After 20 hours of stress, the ulcer index was 40.5 +/- 3.3 in the controls, compared to 6.4 +/- 1.2 and 16.2 +/- 2.3 in rats that received pentagastrin or EGF, respectively. Injections of both pentagastrin and EGF resulted in an ulcer index of 26.2 +/- 2.0, which was significantly lower than that in controls, but higher than that in rats treated with either peptide alone. The stress resulted in significant decrease in antral SLI in all groups of rats, whereas SLI content in rats treated with pentagastrin and/or EGF remained significantly higher than that of controls. Antral content of gastrin did not differ significantly in the four groups tested. The ulcer index was inversely correlated with antral SLI content. We confirm and extend previous observations that pentagastrin and EGF prevent stress ulcer formation, and suggest that endogenous SLI may account, at least in part, for their antiulcer activity.

A prospective randomised controlled clinical trial comparing somatostatin and vasopressin in controlling acute variceal haemorrhage

Twenty two patients were entered into a randomised controlled clinical trial comparing the efficacy of somatostatin and vasopressin in controlling acute variceal haemorrhage. Somatostatin was significantly more successful in controlling acute variceal haemorrhage than vasopressin (p = 0.003). Furthermore, no complications were observed during treatment with somatostatin.

Non-surgical control of upper gastrointestinal bleeding

The non-surgical methods to control upper gastrointestinal bleeding include some recently developed endoscopic techniques (laser photocoagulation and electrocoagulation). Among drugs proposed to be effective in controlling upper gastrointestinal bleeding, somatostatin is considered particularly promising. The experience with these techniques and with somatostatin is reviewed.

Effect of exogenous somatostatin infusion on gastrointestinal blood flow and hormones in the conscious dog

The purpose of this study was to investigate the effects of intravenous somatostatin infusion on gastrointestinal blood flow and hormone release in conscious dogs. Gastric, duodenal, jejunal, and pancreatic blood flows, quantitated using radioactive microspheres, were significantly decreased during somatostatin infusion (200 and 500 ng/kg min), resulting in an overall 30% reduction in summed portal blood flow. Fasting blood levels of glucose fell an average of 10 mg/dl. Immunoreactive insulin, gastrin, glucagon, and pancreatic polypeptide were all profoundly suppressed by somatostatin infusion. Our studies provide one possible explanation for somatostatin's apparent effectiveness in the control of upper gastrointestinal hemorrhage.

Studies on the mechanisms of somatostatin release after insulin induced hypoglycaemia in man

Insulin-induced hypoglycaemia, which stimulates gastric acid secretion, is associated with an increase in circulating somatostatin levels in man. In order to assess the mechanisms involved in this rise, six normal volunteers connected to a Biostator for continuous glucose monitoring were studied, on three separate occasions. On each occasion after basal blood sampling, 0.15 i.u./kg body weight of insulin was administered i.v. and further samples were obtained intermittently over 150 min. On one occasion, dextrose was infused by the Biostator to prevent hypoglycaemia, while on the other two, a constant infusion of either normal saline or the specific H2 antagonist cimetidine was administered. Insulin plus dextrose caused no significant changes in circulating somatostatin levels, whereas insulin plus saline was associated with a marked, sustained and significant rise in all subjects; insulin plus cimetidine also produced a rise but it was delayed; the area under the curve was significantly (P less than 0.05) greater with insulin plus saline than with insulin plus cimetidine. These results show that in man insulin itself does not stimulate somatostatin secretion directly, but indirectly via hypoglycaemia. Further, the inhibition of gastric acid secretion with cimetidine reduces somatostatin release during insulin-induced hypoglycaemia. This suggests that gastric acid may mediate somatostatin secretion associated with insulin-induced hypoglycaemia.

Somatostatin treatment of gastrointestinal fistulas: evidence for a rebound effect on withdrawal

Three patients with external fistulas from the gastrointestinal tract were treated with somatostatin, a peptide which inhibits pancreatic, gastric and intestinal secretion. Although somatostatin reduced fistula output in two patients and possibly prevented haemorrhage in one, it did not induce fistula closure in any; moreover on withdrawal of somatostatin one patient developed life threatening gastrointestinal haemorrhage and a transient fistula hypersecretion occurred in the others. This experience of somatostatin treatment was less favourable than that previously reported in other small series. Positive nitrogen balance was probably not maintained during treatment in the three patients reported here and in one patient in a previous study in whom somatostatin was ineffective; the peptide may only promote fistula closure in adequately nourished patients.

Response of circulating somatostatin, insulin, gastrin and GIP, to intraduodenal infusion of nutrients in normal man

We have studied the effect of direct infusion of nutrients into the duodenum of normal subjects on circulating plasma somatostatin, insulin, gastrin and gastric inhibitory polypeptide (GIP) levels. Six normal subjects were given on four separate occasions 150 ml of isotonic solutions containing 100 calories of carbohydrate, protein, or fat, and a control solution of saline, by infusion into the second part of the duodenum. Plasma somatostatin rose slightly after carbohydrate, mean basal 30 +/- 3 pg/ml, peak 46 +/- 16 pg/ml at 15 min; and more markedly after protein, peak 57 +/- 9 pg/ml at 30 min. However, fat was the most potent intraduodenal stimulus to plasma somatostatin release into circulation, peak 101 +/- 11 pg/ml at 30 min. The plasma insulin rise was greatest after carbohydrate, peak 68 +/- 10 i.u., but there was a significant rise after protein also, peak 34 +/- 6 i.u. Plasma gastrin rose significantly after protein only, peak 70 +/- 22 pg/ml. Plasma GIP rose markedly after carbohydrate, basal 506 +/- 50 pg/ml, peak 1480 +/- 120 pg/ml. Protein was also a potent stimulus of circulating plasma GIP release, peak 1200 +/- 190 pg/ml, while fat was the least potent, peak 730 +/- 190 pg/ml. Thus, calorie for calorie, fat is the most potent intraduodenal nutrient stimulus of circulating somatostatin. We postulate therefore that somatostatin may be an enterogastrone--a circulating hormone released by intraduodenal fat which inhibits gastric acid secretion. Fat is the least potent intraduodenal nutrient stimulus of circulating GIP release. This is evidence against the hypothesis that circulating GIP acts as an enterogastrone.

Role of circulating somatostatin in regulation of gastric acid secretion, gastrin release, and islet cell function. Studies in healthy subjects and duodenal ulcer patients

Studies were designed (a) to determine whether somatostatin is released into the circulation after meals in sufficient amounts to regulate gastric or pancreatic islet function in humans and (b) to investigate the possible role of somatostatin in the pathogenesis of duodenal ulcer disease. Mean plasma somatostatin-like immunoreactivity (SLI) increased from 6.2 +/- 1.5 pg/ml to a peak level of 13.8 +/- 1.3 pg/ml in eight healthy subjects after a 1,440-cal steak meal (P less than 0.005). When somatostatin-14 was infused intravenously, basal and food-stimulated gastric acid secretion and also basal and food-simulated plasma insulin and glucagon concentrations were reduced significantly at mean plasma SLI concentrations within the range seen after a meal. Thus, the amount of somatostatin reaching the systemic circulation after a steak meal was sufficient to inhibit gastric acid secretion and islet cell function. On the other hand, basal and food-stimulated plasma gastrin concentrations were reduced by intravenous somatostatin only at plasma SLI concentrations that were several-fold greater than post-prandial SLI concentrations. Although duodenal ulcer patients had significantly higher basal, food-stimulated, and peak pentagastrin-stimulated gastric acid secretion rates than healthy controls, duodenal ulcer patients and controls had nearly identical basal and food-stimulated SLI concentrations. Moreover, food-stimulated gastric acid secretion and gastrin release were inhibited by intravenous somatostatin to the same extent in ulcer patients and controls. These studies suggest that duodenal ulcer patients release normal amounts of somatostatin into the circulation and that target cells controlling acid secretion and gastrin release are normally sensitive to somatostatin in these patients.

A dual role of calcium in release of somatostatin from canine gastric antral mucosa

We have examined the factors regulating the mucosal release of somatostatin-like immuno-reactivity (SRIF-LI) from 1-cm2 sheets of isolated canine gastric antral mucosa mounted in a Ussing chamber. SRIF-LI was released predominantly into the luminal perfusate, was maximal at pH 2.5, 1,987 +/- 319 pg X ml-1 X h-1, and reached a nadir at pH 6.0 of 89 +/- 24 pg X ml-1 X h-1. Increasing extracellular Ca2+ to 10 mM stimulated the release of SRIF-LI at both high and low pH. The Ca2+ ionophore A23187 had no apparent effect at either pH 2.5 or 7.0. LaCl3 stimulated the release of SRIF-LI at pH 7.0 but not at pH 2.5. Ouabain and TMB-8 had no significant effect on the release of SRIF-LI. At pH 7.0, trifluoperazine (TFP) stimulated release of SRIF-LI (80 +/- 10 pg X ml-1 X h-1). EGTA stimulated release of SRIF-LI at pH 2.5 (1,134 +/- 137 pg X ml-1 X h-1) and at pH 7.0 (300 +/- 57 pg X ml-1 X h-1), which was reversed by replacement of Ca2+ (22 +/- 6 pg X ml-1 X h-1). Thus Ca2+ appears to exert a dual effect on the release of SRIF-LI: both an increase and depletion of extracellular Ca2+ release SRIF-LI.

Modulation of acetylcholine-induced secretion of gastric bombesin-like immunoreactivity by cholinergic and histamine H2-receptors, somatostatin and intragastric pH

Recently we have shown the release of bombesin-like immunoreactivity (BLI) from the isolated perfused rat stomach. In these experiments we have shown that BLI secretion is stimulated by acetylcholine. Gastric inhibitory peptide (GIP) exerts an inhibitory effect which is dependent on the intraluminal pH. The present study was designed to examine further the exact cholinergic mechanisms and to study the interaction between cholinergic and histaminergic mechanisms as well as the effect of the intraluminal pH. Acetylcholine elicited a dose-dependent increase in BLI and gastrin secretion (10(-6) M and 2 X 10(-6)M), whereas somatostatin release was suppressed at luminal pH 7. Blockade of muscarinic cholinergic receptors by atropine (10(-5)M) and nicotinic cholinergic receptors by hexamethonium (10(-5) M) abolished the effect of acetylcholine on all three peptides. Reduction of the intraluminal pH to 2 also abolished acetylcholine-induced stimulation of BLI and gastrin secretion and the inhibition of somatostatin secretion. Changes of intraluminal pH per se had no effect on the secretion of either peptide. Somatostatin (10(-7) M) reduced both BLI and gastrin secretion during stimulation with acetylcholine. The addition of the H2-receptor antagonist cimetidine (10(-5) M) abolished the effect of both doses of acetylcholine on BLI and somatostatin secretion and also the effect of the lower dose of acetylcholine (10(-6) M) on gastrin secretion during luminal pH 7. At luminal pH 2 cimetidine did not alter BLI and somatostatin secretion in response to acetylcholine, however, gastrin release was augmented in the presence of cimetidine. These data demonstrate that the effect of acetylcholine on BLI, gastrin, and somatostatin secretion is mediated by muscarinic and nicotinic cholinergic receptors and also by histamine H2-receptors. Somatostatin inhibits cholinergically induced BLI secretion. The cholinergic effects on BLI, somatostatin and gastrin secretion are abolished during an acidic intragastric pH. In this isolated perfused rat stomach model the inhibitory effect of intraluminal acid on gastrin secretion is, at least in part, mediated by H2-receptors. This suggests that the secretion of bombesin, a potential peptidergic neurotransmitter is modulated by neural, endocrine and local tissue factors and also by alterations of intragastric pH.

Beta-adrenergic regulation of cyclic adenosine 3',5' monophosphate accumulation in human gastric epithelial glands. Inhibitory effect of somatostatin

The action of catecholamines and somatostatin on cyclic adenosine 3',5' monophosphate (cyclic AMP) formation in human isolated gastric glands is reported. We show that: (1) there is a beta 2 receptor-mediated stimulation of cyclic AMP production in fundus. Catecholamines act with the order of potencies isoproterenol (ED50 = 50 nmol 1(-1) greater than epinephrine (ED50 = 0.1 mumol 1(-1] greater than norepinephrine (ED50 = 5 mumol 1(-1]. Their action is completely reversed by propranolol at doses 10(3) times lower than practolol, while unaffected by phentolamine; (2) isoproterenol and Vasoactive Intestinal Peptide (VIP) have additive effects on cyclic AMP in fundic glands whereas no additivity is observed between histamine and isoproterenol; this, together with the absence of catecholamine effect in antral glands, suggests that the beta 2 receptor is located on parietal cells; (3) somatostatin (1 mumol 1(-1] non-competitively inhibits the stimulation by catecholamines but does not affect VIP and histamine stimulations. These results suggest a physiological stimulatory effect of catecholamines on gastric acid secretion in man, through a beta 2 receptor coupled to the cyclic AMP system, regulated by somatostatin.

Influence of somatostatin on splanchnic haemodynamics in patients with liver cirrhosis

The influence of intravenous somatostatin infusion (7.6 micrograms/min) on systemic and splanchnic haemodynamics was examined in 10 patients with liver cirrhosis and portal hypertension. The hepatic vein catheter technique was employed and indocyanine green dye was injected to evaluate hepatic blood flow. Mean wedged hepatic venous pressure fell from 24.9 +/- 2.8 in the basal state to 21.4 +/- 3.2 mmHg (P less than 0.2) at 60 min of infusion and the mean arterial pressure decreased from 87 +/- 5 to 80 +/- 6 mmHg (P less than 0.05). The rate of indocyanine green dye disappearance decreased from 8.7 +/- 1.9 to 6.6 +/- 1.7%/min (P less than 0.001) during the infusion, indicating decreased hepatic blood flow. Arterial-hepatic venous oxygen differences rose from 69 +/- 11 to 78 +/- 11 ml/l. Blood glucose levels fell from 4.84 +/- 0.31 to 3.79 +/- 0.33 mmol/l at 60 min of infusion (P less than 0.005). It is concluded that a continuous infusion of somatostatin in patients with liver cirrhosis and portal hypertension causes a decreased hepatic blood flow with augmented hepatic oxygen extraction and a modest reduction in mean wedged hepatic venous pressure. In view of the magnitude of the observed haemodynamic changes the findings do not suggest an important role for somatostatin in the treatment of patients with bleeding oesophageal varices.

Analysis of food stimulation of gastrin release in dogs by a panel of inhibitors

The release of gastrin into the serum of five conscious gastric fistula dogs after a meat meal was monitored for 2 hours. Neither the rate of increase in serum gastrin nor the 2 hour cumulative integrated gastrin response was changed by administration of small doses of somatostatin tetradecapeptide (0.5 microgram/kg.hr IV for 2 hr), 16-16 dimethyl prostaglandin E2 (0.25 microgram/kg.hr IV for 2 hr or 1 microgram/kg intragastrically), or bethanechol (20 micrograms/kg.hr IV for 2 hr). Acidification of the food in the antrum to pH 1.2 to 1.4 eliminated serum gastrin release in response to food. In control studies, serum gastrin levels were not altered by IV administration of saline for 2 hr with no food or when a plate of food was held just out of the dogs' reach (teasing). Food-stimulated gastrin release was contrasted with that stimulated by bombesin under identical laboratory conditions [17]. In each case, antral acidification, somatostatin, prostaglandin E2 and bethanechol affected bombesin-stimulated gastrin release differently from that stimulated by food. We conclude that food and bombesin release gastrin by different pathways.

Inhibition of growth of pancreatic carcinomas in animal models by analogs of hypothalamic hormones

Using animal models of acinar and ductal pancreatic cancer, we investigated the effect of analogs of hypothalamic hormones on tumor growth. In Wistar/Lewis rats bearing the acinar pancreatic tumor DNCP-322, chronic administration of [L-5-Br-Trp8]somatostatin-14 significantly decreased tumor weights and volume. Somatostatin-28 and the cyclic hexapeptide analog of somatostatin cyclo(Pro-Phe-D-Trp-Lys-Thr-Phe) failed to influence the growth of this tumor. The agonistic analog of luteinizing hormone-releasing hormone [D-Trp6]LH-RH also significantly decreased tumor weight and volume in this model and reduced testosterone levels and the weights of the ventral prostate and tests. In Syrian hamsters bearing ductal type of pancreatic carcinoma, chronic administration of [L-5-Br-Trp8]somatostatin diminished tumor weights and volume. The percentage change in tumor volume was significantly decreased when compared to control animals. In one experiment, cyclic hexapeptide of somatostatin also inhibited growth of this tumor. [D-Trp6]LH-RH, given twice daily or injected in the form of microcapsules for constant controlled release, significantly decreased tumor weight and volume and suppressed serum testosterone levels. Hamsters castrated 4 days after transplantation of the pancreatic tumors showed a significant decrease in weight and volume of these tumors. This suggests that pancreatic cancers may, at least in part, be sex hormone sensitive. [D-Trp6]LH-RH may decrease the growth of pancreatic carcinomas by suppressing androgens. Somatostatin analogs reduce the growth of pancreatic ductal and acinar cancers, probably by inhibiting the release or stimulatory action of gastrointestinal hormones on tumor cells (or both). Inhibition of animal models of pancreatic tumors by chronic administration of somatostatin analogs and [D-Trp6]LH-RH suggests that these compounds should be considered for the development of a new hormonal therapy for cancer of the pancreas.

Inhibition of gastrin release by secretin is mediated by somatostatin in cultured rat antral mucosa

Somatostatin-containing cells have been shown to be in close anatomic proximity to gastrin-producing cells in rat antral mucosa. The present studies were directed to examine the effect of secretin on carbachol-stimulated gastrin release and to assess the potential role of somatostatin in mediating this effect. Rat antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h the culture medium was decanted and mucosal gastrin and somatostatin were extracted. Carbachol (2.5 X 10(-6) M) in the culture medium increased gastrin level in the medium from 14.1 +/- 2.5 to 26.9 +/- 3.0 ng/mg tissue protein (P less than 0.02), and decreased somatostatin-like immunoreactivity in the medium from 1.91 +/- 0.28 to 0.62 +/- 0.12 ng/mg (P less than 0.01) and extracted mucosal somatostatin-like immunoreactivity from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (P less than 0.001). Rat antral mucosa was then cultured in the presence of secretin to determine its effect on carbachol-stimulated gastrin release. Inclusion of secretin (10(-9)-10(-7) M) inhibited significantly carbachol-stimulated gastrin release into the medium, decreasing gastrin from 26.9 +/- 3.0 to 13.6 +/- 3.2 ng/mg (10(-9) M secretin) (P less than 0.05), to 11.9 +/- 1.7 ng/mg (10(-8) secretin) (P less than 0.02), and to 10.8 +/- 4.0 ng/mg (10(-7) M secretin) (P less than 0.02). Secretin (10(-7) and 10(-8) M) also increased concomitantly culture medium somatostatin concentration. To determine whether secretion inhibition of carbachol-stimulated gastrin release was mediated by somatostatin, antral mucosa was cultured with carbachol, secretin (10(-9)-10(-7) M), and antibodies to somatostatin. Inclusion of somatostatin antibodies in the culture medium abolished the capacity of secretin (10(-7) and 10(-8) M) to inhibit carbachol-stimulated gastrin release. Results of these studies indicate (a) that secretin inhibits carbachol-stimulated gastrin release and (b) that under the conditions of these experiments secretin inhibition of gastrin release is mediated, at least in part, locally through release of antral somatostatin.

A role for somatostatin in the control of hamster growth

Concentrations of somatostatin-like immunoreactivity (SRIF-LI) were measured in cerebral cortex, hippocampus, septum-POA, median eminence, gastric antrum, fundus and pancreas in adult female hamsters to determine whether changes in somatostatin could be related to increased growth hormone (GH) secretion and somatic growth that follow bilateral transections of hippocampus (n = 18; 17 controls). In addition, choline acetyltransferase (CAT) activity was measured in the four brain regions in hippocampectomized (n = 10) and control hamsters (n = 10) to gain insight into the relationship between these two neurotransmitters. Hippocampal transections induced: significant acceleration of somatic growth; increased serum GH concentrations; increased concentrations of SRIF-LI in septum-POA and gastric antrum; reduced concentrations of SRIF-LI in hippocampus and pancreas; and reduced CAT activity in the hippocampus. These results suggest that somatostatinergic and cholinergic projections to hippocampus via fornix suppress GH and somatic growth in adult hamsters and that reduced release of SRIF-LI in the gastric antrum may contribute to the acceleration of somatic growth through facilitated nutrient digestion and entry.

Growth hormone neuroregulation and the clinical relevance of somatostatin

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

Inhibition of gastrin release by secretin is mediated by somatostatin in cultured rat antral mucosa

Somatostatin-containing cells have been shown to be in close anatomic proximity to gastrin-producing cells in rat antral mucosa. The present studies were directed to examine the effect of secretin on carbachol-stimulated gastrin release and to assess the potential role of somatostatin in mediating this effect. Rat antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h the culture medium was decanted and mucosal gastrin and somatostatin were extracted. Carbachol (2.5 X 10(-6) M) in the culture medium increased gastrin level in the medium from 14.1 +/- 2.5 to 26.9 +/- 3.0 ng/mg tissue protein (P less than 0.02), and decreased somatostatin-like immunoreactivity in the medium from 1.91 +/- 0.28 to 0.62 +/- 0.12 ng/mg (P less than 0.01) and extracted mucosal somatostatin-like immunoreactivity from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (P less than 0.001). Rat antral mucosa was then cultured in the presence of secretin to determine its effect on carbachol-stimulated gastrin release. Inclusion of secretin (10(-9)-10(-7) M) inhibited significantly carbachol-stimulated gastrin release into the medium, decreasing gastrin from 26.9 +/- 3.0 to 13.6 +/- 3.2 ng/mg (10(-9) M secretin) (P less than 0.05), to 11.9 +/- 1.7 ng/mg (10(-8) secretin) (P less than 0.02), and to 10.8 +/- 4.0 ng/mg (10(-7) M secretin) (P less than 0.02). Secretin (10(-7) and 10(-8) M) also increased concomitantly culture medium somatostatin concentration. To determine whether secretion inhibition of carbachol-stimulated gastrin release was mediated by somatostatin, antral mucosa was cultured with carbachol, secretin (10(-9)-10(-7) M), and antibodies to somatostatin. Inclusion of somatostatin antibodies in the culture medium abolished the capacity of secretin (10(-7) and 10(-8) M) to inhibit carbachol-stimulated gastrin release. Results of these studies indicate (a) that secretin inhibits carbachol-stimulated gastrin release and (b) that under the conditions of these experiments secretin inhibition of gastrin release is mediated, at least in part, locally through release of antral somatostatin.

Release of bombesin-like immunoreactivity from the isolated perfused rat stomach

In the present study the release of bombesin-like immunoreactivity (BLI), somatostatin and gastrin was determined form the isolated perfused rat stomach. Gastric inhibitory polypeptide (GIP, 2 X 10(-9) M) had no effect on BLI while stimulating somatostatin and gastrin release. In these experiments the luminal pH of the stomach was kept at pH 7. Reduction of the luminal pH to 2 resulted in an inhibition of BLI secretion by GIP while gastrin release was abolished and somatostatin remained unaffected compared to luminal pH 7. Acetylcholine (10(-6) and 2 X 10(-6) M) elicited a dose-dependent stimulation of BLI secretion while gastrin was stimulated and somatostatin secretion suppressed independent of the administered dose. The present data demonstrate that release of bombesin-like immunoreactivity can be modulated by intestinal hormones and neurotransmitters and is integrated into the complex system of gastrointestinal neuroendocrine regulation.

Effects of prostaglandin E2 and D2 on gastric somatostatin and gastrin secretion

The effects of PGE2 and PGD2 on gastric somatostatin and gastrin releases were investigated using the isolated perfused rat stomach. In the presence of 5.5 mM glucose, the infusion of PGE2 elicited a significant augmentation in somatostatin release, but suppressed gastrin secretion from the perfusate. On the other hand, PGD2 did not affect somatostatin release, although the gastrin secretion decreased significantly, the same as after PGE2 infusion. These results suggest that PGE2 and PGD2 may be important in the regulation of gastric endocrine function, but that PGD2 does not affect gastric somatostatin secretion.

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

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

Differing postnatal development of the somatostatin- and luliberin- systems in the male and female rat

By means of light-microscopic immunohistochemistry the perikarya of the luliberin-(LRF-) and somatostatin systems of neonate rats were found to be in differing stages of development. At a time point when the LRF-producing neurons had obviously attained their final shape and size, the somatostatin-immunoreactive perikarya were still in a postnatal phase of maturation. Whereas the number of the latter perikarya increases with advancing age, the number of LRF-immunoreactive perikarya decreases significantly from postnatal day 7 onward. Both peptide-hormone systems do not project concomitantly and to the same extent to their principal neurohemal regions in the organum vasculosum laminae terminalis (OVLT) and the median eminence (ME). In all presently studied stages of development, despite considerable individual variations in one age group, among the components of the LRF-system the OVLT displays a more intense immunoreactivity than the ME. The somatostatin system, however, projects to the OVLT with a conspicuous temporal delay compared to the ME, and, furthermore, in the OVLT the pattern of immunoreactivity characteristic of adult rats is not yet attained at postnatal day 21. Evidence for differences in the immunoreactivity between male and female animals was restricted to the LRF-system. Finally, the results obtained on the stria terminalis speak in favour of the fact that the long-range extrahypothalamic projections of the somatostatin system also undergo postnatal maturation. In the stria terminalis, somatostatin-immunoreactive fibers can be demonstrated initially on postnatal day 7. They attain their full immunoreactivity on postnatal day 21. Furthermore, in the bed nucleus of the stria terminalis an intermittent cytoplasmic immunoreactivity is observed, which is limited to the animals of postnatal day 7 and disappears completely during the further course of development.

Inhibitory effect of intragastric glucose on gastric acid secretion and gastric emptying of liquids in man. Role of endogenous somatostatin, gastrin, and insulin

Intragastric glucose inhibits gastric acid secretion and gastric emptying in man. To determine if these effects are mediated by somatostatin--a known inhibitor of gastric acid production, gastrin secretion, and gastric motility--the plasma somatostatin-like immunoreactivity (SLI) levels were determined in healthy human subjects after an intragastric load of 30% glucose solution. These findings were compared with results after an instillation of distilled water. Following the glucose load, the intragastric acid concentration, the acid output, and the fractional gastric emptying rate declined significantly (P less than 0.01) before either the plasma glucose or plasma insulin levels had increased. Neither the gastrin nor SLI plasma concentrations changed after the water or glucose load. These findings suggest that the suppression of gastric acid secretion and inhibition of the rate of gastric emptying that occur with intragastric glucose are mediated by factors other than changes in the peripheral circulating levels of SLI, gastrin, insulin, or glucose.

Hormones and feed intake

During the several decades that hormones have been considered for roles in the control of feeding, certain ones have gained special attention, although the role assigned to any one hormone has varied from time to time. Three classes of hormones have been considered in this review: gastrointestinal, brain, and pancreatic. Of these classes, two have obtained the most compelling evidence for a physiological role in the control of feeding. CCK, an intestinal and brain hormone, appears to be involved in satiety. Glucagon of pancreatic origin appears also to play an important role in satiety. These hormones, when sequestered by a specific antibody, cause a delay in satiety and thus increase food intake. Insulin, another pancreatic hormone, has been considered for several roles in the control of feeding. Recently, attention has been given to the possibility that insulin of the CSF provides an integrated link between the metabolic state of the adipose tissue and the brain structures concerned with the control of feeding. Thus, insulin may be a primary hormone involved in the maintenance of energy balance or of body-weight. Finally, brain opiate peptides, e.g. dynorphin, are very likely involved in the transmission of information concerned with the interaction of feeding and maintenance of energy balance. Clearly, hormones play primary roles in the control of feeding behaviour and the regulation of energy balance, but much remains to be done to establish their specific actions or components of the associated physiological systems.

Influence of a continuous intragastric and intravenous infusion of somatostatin on stimulated gastric secretion

Our study demonstrated that somatostatin given i.v. in a dose of 250 micrograms/kg per hour significantly inhibited pentagastrin-stimulated gastric secretion, whereas continuous intragastric administration of somatostatin (up to 3 mg/h) failed to do so. We concluded, therefore, that luminally secreted somatostatin plays only a minor role in the regulation of gastric secretion.