Modification of the cerebrovascular response to noradrenaline by bile duct ligation

The cerebrovascular response to norepinephrine: A scoping systematic review of the animal and human literature

Intravenous norepinephrine (NE) is utilized commonly in critical care for cardiovascular support. NE's impact on cerebrovasculature is unclear and may carry important implications during states of critical neurological illness. The aim of the study was to perform a scoping review of the literature on the cerebrovascular/cerebral blood flow (CBF) effects of NE. A search of MEDLINE, BIOSIS, EMBASE, Global Health, SCOPUS, and Cochrane Library from inception to December 2019 was performed. All manuscripts pertaining to the administration of NE, in which the impact on CBF/cerebral vasculature was recorded, were included. We identified 62 animal studies and 26 human studies. Overall, there was a trend to a direct vasoconstriction effect of NE on the cerebral vasculature, with conflicting studies having demonstrated both increases and decreases in regional CBF (rCBF) or global CBF. Healthy animals and those undergoing cardiopulmonary resuscitation demonstrated a dose-dependent increase in CBF with NE administration. However, animal models and human patients with acquired brain injury had varied responses in CBF to NE administration. The animal models indicate an increase in cerebral vasoconstriction with NE administration through the alpha receptors in vessels. Global and rCBF during the injection of NE displays a wide variation depending on treatment and model/patient.

A Gastric Neuroendocrine Carcinoma Expressing Somatostatin in a Bearded Dragon (Pogona Vitticeps)

A metastatic gastric neuroendocrine carcinoma in a 2.5-year-old inland bearded dragon ( Pogona vitticeps) with a chronic history of anorexia, weight loss, depression, and acute melena is described. Histologic examination of the gastric mass revealed a densely cellular tumor arranged in nests and occasional rosettes of hyperchromatic cells with oval to spindle-shaped nuclei and minimal cytoplasm; the tumor was supported by a moderate fibrovascular stroma. Similar cells invaded through the gastric mucosa, and there were multiple hepatic metastases. The neoplastic cells were weakly immunopositive for neuron-specific enolase and moderately positive for somatostatin but were negative for chromogranin AB and gastrin. Ultrastructural studies revealed scattered neurosecretory granules in the neoplastic cells, confirming the diagnosis of a neuroendocrine carcinoma.

Glucose homeostasis and the gastrointestinal tract: insights into the treatment of diabetes

The gastrointestinal tract is increasingly viewed as a critical organ in glucose metabolism because of its role in delivering glucose to the circulation and in secreting multiple glucoregulatory hormones that, in concert with insulin and glucagon, regulate glucose homeostasis. Under normal conditions, a complex interplay of these hormones acts to maintain plasma glucose within a narrow range despite large variations in the availability of glucose, particularly during transition from the fasting to fed state. In the fed state, the rate at which nutrients are passed from the stomach to the duodenum, termed gastric emptying rate, is a key determinant of postprandial glucose flux. In patients with diabetes, the regulation of glucose metabolism is disrupted resulting in fasting and postprandial hyperglycaemia. Elucidation of the role of the gastrointestinal tract, gut-derived glucoregulatory peptides and gastric emptying rate offers a new perspective on glucose homeostasis and the respective importance of these factors in the diabetes state. This review will highlight the importance of the gastrointestinal tract in playing a key role in glucose homeostasis, particularly in the postprandial period, and the role of established or new therapies that either leverage or modify gastrointestinal function to improve glycaemic state.

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.

The effect of octreotide on gastroduodenal blood flow measured by laser Doppler flowmetry in rabbits and man

OBJECTIVE

The somatostatin analogue, octreotide is valuable in the management of variceal bleeding, and it has been suggested that it may stop peptic ulcer hemorrhage by reducing gastroduodenal blood flow or increasing intragastric pH. The aim of this study was to determine the effect of intravenous octreotide infusion on gastroduodenal mucosal blood flow and gastric pH.

METHODS

Seven New Zealand white rabbits and five healthy human volunteers were used. Mucosal blood flow was measured using a laser Doppler flowmeter (LDF). The Doppler probe was positioned in the upper gastrointestinal tract of the seven rabbits and five human volunteers. Blood flow was measured before and after octreotide infusion.

RESULTS

In the animal experiments, mucosal blood flow was decreased in a dose dependent manner in the gastric body (209.1-56.3 U) (p < 0.008), antrum (143.3-33.3 U) (p < 0.02) and duodenum (254-67.6 U) (p < 0.016) by doses of octreotide ranging from 10-50 microg/kg of body weight. In the human studies, mucosal blood flow was decreased in the gastric body (p < 0.016) and antrum (p < 0.009) after octreotide infusion (dose 1-1.5 microg/kg). Intragastric pH was significantly increased (p < 0.05). The change was not associated with systemic hemodynamic changes.

CONCLUSIONS

Gastroduodenal mucosal blood flow was reduced and intragastric pH increased by octreotide. This agent could be helpful in the management of gastroduodenal mucosal bleeding.

Rapid identification of subtype-selective agonists of the somatostatin receptor through combinatorial chemistry

Nonpeptide agonists of each of the five somatostatin receptors were identified in combinatorial libraries constructed on the basis of molecular modeling of known peptide agonists. In vitro experiments using these selective compounds demonstrated the role of the somatostatin subtype-2 receptor in inhibition of glucagon release from mouse pancreatic alpha cells and the somatostatin subtype-5 receptor as a mediator of insulin secretion from pancreatic beta cells. Both receptors regulated growth hormone release from the rat anterior pituitary gland. The availability of high-affinity, subtype-selective agonists for each of the somatostatin receptors provides a direct approach to defining their physiological functions.

Effects of lanreotide, a somatostatin analogue, on postprandial gastric functions and biliopancreatic secretions in humans

AIMS

Lanreotide is a novel synthetic somatostatin analogue. A long-acting formulation of lanreotide has been shown to be effective for the treatment of gastroentero-pancreatic hormone-producing tumours but effects on postprandial digestive and absorptive functions remain obscure. The aim of the present study was to evaluate the effects of intravenous lanreotide on gastric and biliopancreatic secretions in man as well as the absorption of nutrients and the duodeno-caecal transit time after ingestion of an homogenized meal (500 kcal, 55% carbohydrates, 15% proteins, 30% lipids).

METHODS

Eight healthy male volunteers were studied on two occasions within a 2 weeks interval, using a perfusion method. They received in single-blind and random order continuous i.v. infusion of either placebo or lanreotide (100 micrograms h-t after a bolus of 100 micrograms 15 min before the beginning of the study).

RESULTS

Lanreotide significantly decreased gastric acid secretion (90%) for the initial 3 h period. Gastric emptying was not significantly modified by lanreotide infusion. Compared with placebo, lanreotide almost completely abolished both bile salts and lipase responses to the meal. It largely increased the duodeno-caecal transit time and decreased significantly the duodenal absorption of carbohydrates and triglycerides.

CONCLUSIONS

Since lanreotide has powerful effects on gastrointestinal functions, it could be useful in the prevention or in the treatment of pancreatic and bowel fistulas as well as short bowel syndrome.

Identification of ligand binding determinants in the somatostatin receptor subtypes 1 and 2

The somatostatin (SRIF) receptors (SSTRs) 1 and 2 bind SRIF and SRIF 28 with high affinity, although a number of synthetic hexapeptide and octapeptide analogs of SRIF bind selectively to SSTR2. Extracellular loop three and its adjoining trans-membrane-spanning regions contain elements essential for the binding of such analogs to murine SSTR2. In particular, a stretch of amino acids from residues 294-297 (FDFV) in murine SSTR2 in trans-membrane domain seven can determine affinity for the SSTR2-selective analogs. Within this region, Phe294 has previously been predicted to be essential for the binding of octapeptides (Kaupmann, K., Bruns, C., Raulf, F., Weber, H., Mattes, H., and Lubbert, H. (1995) EMBO J. 14, 727-735) based on the observation that SSTR1 can bind the octapeptide SMS-201-995 with reasonable affinity after a Ser-to-Phe conversion in the analogous region of this receptor (SSTR1S305F). We find that SSTR1S305F has low affinity for a number of SSTR2-selective hexapeptides, suggesting that these analogs have different binding requirements than SMS-201-995. A correlation is seen between the ability of SSTR1S305F to bind hexapeptide analogs and the presence of a phenylalanine, but not tyrosine, at position two in these small cyclic molecules. Thus, a single hydroxyl group in hexapeptides can play a critical role in determining receptor binding to these receptor mutants. We also find that the second extracellular loop of SSTR1 is important for the selectivity of certain SRIF agonists for binding to SSTR1. Taken together, our data indicate that there are multiple elements in the somatostatin receptors that can determine the binding affinity and selectivity of peptide analogs.

Partial amino acid sequence of a somatostatin receptor isolated from GH4C1 pituitary cells

A somatostatin receptor isolated from GH4C1 rat pituitary tumor-derived cells was cleaved with cyanogen bromide or cyanogen bromide+trypsin to obtain sequenceable fragments. Five unique amino acid sequences ranging from 6 to 27 amino acid residues were obtained. The sequence was identical to sequence recently reported for one of two somatostatin receptors cloned from human pancreas [Yamada et al., (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 251-255] except for a single valine to isoleucine substitution. This is the first report of amino acid sequence from a purified somatostatin receptor.

Subchronic treatment with metformin produces anorectic effect and reduces hyperinsulinemia in genetically obese zucker rats

The effect of subchronic metformin treatment on food intake, weight gain and plasma and tissue hormone levels was investigated in genetically obese male Zucker rats and in their lean controls. Metformin hydrochloride (320 mg/kg/day for 14 days in the drinking water) significantly reduced 24 hour food intake both after one and two weeks treatment in obese rats. In contrast, metformin had only a transient effect on food intake in lean animals. The reduced food intake was associated with body weight decrease, particularly in obese rats. Metformin markedly reduced also the hyperinsulinemia of the obese animals without altering their plasma glucose or pancreatic insulin content which may reflect an improved insulin sensitivity after metformin treatment. Metformin did not change plasma corticosterone levels or insulin and somatostatin concentrations in the pancreas. Metformin reduced pyloric region somatostatin content in lean rats. It is concluded that metformin has an anorectic effect and reduces body weight and hyperinsulinemia in genetically obese Zucker rat.

Effects of some gastrointestinal peptides on isolated human and rabbit gastric glands

The isolated gastric gland preparation, with aminopyrine accumulation as an index of the parietal cell response, has been used to study the effects of somatostatin (S-14), gastrin-releasing peptide (GRP), cholecystokinin (CCK-8), vasoactive intestinal peptide (VIP), and peptide YY (PYY) on the in vitro acid secretion in human and rabbit oxyntic mucosa. Somatostatin was able to inhibit the parietal cell response to histamine in both human and rabbit isolated gastric glands (maximal inhibition, 22% and 34%, respectively) but failed to inhibit the parietal cell response to db-cAMP. However, other peptides capable of inhibiting gastric acid secretion in vivo, such as CCK, VIP, and PYY, were unable to induce any inhibition of the parietal cell response to db-cAMP or histamine in the isolated gastric gland preparation irrespective of the species studied. GRP was not able to induce a parietal cell response, a finding that is in accord with the assumption that the stimulatory effect of GRP on gastric acid secretion in vivo is by releasing gastrin from antral G-cells.

Somatostatin in portal hypertension

The effect of somatostatin on portal pressure is mediated by splanchnic arterial vasoconstriction which induces a reduction in portal blood flow and pressure. One of the most important characteristics of somatostatin is that its splanchnic effect is not accompanied by major systemic hemodynamic effects. Somatostatin has been used in several controlled trials to test its potential in controlling acute variceal bleeding. The results remain controversial. Different findings in existing clinical trials may derive in part from distinct protocols for somatostatin administration. Published trials suggest that somatostatin may be as effective as vasopressin in the acute management of variceal bleeding. However, since the efficacy of vasopressin has been questioned, a comparison of two potentially ineffective drugs cannot establish definitively the efficacy of somatostatin in controlling variceal bleeding. The most significant finding of the two published studies has been the lower incidence of minor and major complications with somatostatin when compared to vasopressin. Newer trials in progress may shed new light into the potential use of somatostatin for the treatment of variceal bleeding.

Brain and CSF somatostatin concentrations in patients with psychiatric or neurological illness. An overview

Somatostatin was originally isolated as a 14-amino-acid peptide from the ovine hypothalamus. The peptide has a widespread regional distribution within the central and peripheral nervous systems, as well as in peripheral organs. Preservation of the chemical structure over a wide range of vertebral species indicates important functional roles of the peptide. Recent results about the role of somatostatin and related peptides in different psychiatric (depression, schizophrenia, Alzheimer's disease) and neurological (Huntington's disease, multiple sclerosis, Parkinson's disease) diseases, and the effects on the hypothalamic-pituitary-adrenal axis are summarized. Also, the influence of some psychotropic drugs (halo-peridol, carbamazepine) on somatostatin levels in cerebrospinal fluid is discussed.

Motilin response to a glucose load aberrant in smokers

Smoking is known to influence the blood glucose response to an oral glucose load, possibly by altering the gut motility. Because the peptide hormone motilin might be involved in the regulation of the gastric emptying pattern, we studied 12 heavy smokers and 9 non-smokers after an overnight fast and tobacco abstinence. After an oral glucose load non-smokers showed falling serum motilin levels, as expected, whereas the smokers had initially increasing values. We conclude that smoking affects the gastrointestinal tract, not only during acute nicotine exposure but also chronically.

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.

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.

Antramine (antral histamine) antagonizes somatostatin inhibition on endogenous gastrin-induced gastric secretion. A new hypothesis for the role of histamine in gastric secretion regulation

The effects of antramine, an antral histamine (AH), and of synthetic histamine (SH) on acid, pepsin, and gastrin responses to meals alone or in combination with somatostatin were studied in dogs equipped with a Heidenhain pouch. Food-induced acid secretion was potentiated by AH and only slightly increased by SH. Pepsin secretion was increased by AH and decreased by SH. Both AH and SH suppressed the inhibitory activity of somatostatin on food-induced secretion. AH potentiated gastrin response to feeding but decreased it when somatostatin was added to the meal. Since acid secretion was unrelated to gastrin response, it would appear that the secretory effects of AH involve a direct action on secreting cells, itself based on the suppression of somatostatin inhibition. Gastric secretion is probably related to gastrin efficacy on secreting cells, which would result from the antagonistic effects of somatostatin and AH. These data suggest an alternative hypothesis concerning the role of histamine in the control of gastric secretion.

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.

Gastric acid secretion results from antagonistic effects of antral histamine (Antramine) and somatostatin on gastrin

Gastric acid secretion, whole blood histamine concentration and serum gastrin were measured in dogs, equipped with Heidenhain pouch, in response to feeding alone and in combination with antral histamine (AH)--Antramine--or with somatostatin. Feeding stimulated acid secretion, histamine and gastrin responses in a dose-related manner. Addition of antramine to feeding resulted in a potentiated acid and gastrin responses while histamine response corresponded to sum of individual responses to antramine and to feeding. Somatostatin reduced markedly acid and histamine responses, while gastrin response was unchanged. Serum gastrin and whole blood histamine appear to be agonistic factors responsible together for acid secretion. Somatostatin suppresses histamine response and would inhibit gastrin activity on acid secreting cells by this mean. Somatostatin and histamine might act antagonistically on gastrin which would be their common substrate, and thus they could intervene in a regulation process of acid secretion. In regard to synthetic histamine, native antral histamine--antramine--appears to be a better candidate for a physiological histamine regulation of acid secretion.

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.

An inhibitor of cerebral uptake of noradrenaline in jaundiced blood plasma

The permeability of the blood-brain barrier to noradrenaline was estimated in rats with bile duct ligation by intracarotid injection of [14C]-L-noradrenaline, 3H2O, and [113mIn]ethylene diamine tetraacetate (EDTA) under pentobarbitone anaesthesia. Brain uptake of [14C]noradrenaline was expressed as a percentage of that of 3H2O (brain uptake index, BUI) and corrected for the "blood background" by the 113mIn. The BUI of noradrenaline (1.20 +/- 0.19) was not increased in jaundice (0.78 +/- 0.18). The capacity of oxygenated homogenates of rat brain to remove noradrenaline was measured. The presence of jaundiced plasma always caused a substantial suppression of noradrenaline removal. No effect of jaundice on specific radioactive assays for catechol-O-methyl transferase (COMT) or monoamine oxidase (MAO) could be demonstrated.

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.

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.

[Inhibition of glucose and leucin absorption by somatostatin in the dog (author's transl)]

Small bowel absorption of glucose and leucin was investigated under the influence of somatostatin (SST) using an isolated Thiry Vella loop in the unrestrained dog. SST infusion significantly reduced glucose and leucin absorption, inhibiting glucose absorption more than that of leucin.

A small dose of somatostatin inhibits the secretin stimulated secretion of bicarbonate, amylase, and chymotrypsin in man

The effects of a small dose of somatostatin (0.025 mg/h) on the pancreatic secretion of bicarbonate, amylase, and chymotrypsin during stepwise increasing doses of secretin was examined in six healthy volunteers. The secretion of bicarbonate, amylase, and chymotrypsin in response to secretin was significantly reduced by somatostatin. Both output and concentration of pancreatic enzymes were reduced, whereas the concentration of bicarbonate remained unchanged. The pattern of inhibition suggests that somatostatin is a competitive inhibitor of secretin in the stimulation of pancreatic secretion of bicarbonate, which supports the hypothesis of a direct effect of somatostatin on the exocrine secretory cells of the pancreas. The pattern of inhibition of amylase and chymotrypsin secretion is different and difficult to interpret from the present study, but somatostatin may inhibit also the secretin stimulated pancreatic secretion of enzymes completely, as the inhibitory effect seemed to decline when larger doses of secretin were applied.

Vasoactive intestinal polypeptide in vagally mediated pancreatic secretion of fluid and HCO3

The role of nerves that liberate vasoactive intestinal polypeptide (VIP) in the porcine pancrease as mediators of the atropine-resistant action of the vagus on flow and bicarbonate (HCO3) secretion was examined. Efferent electrical stimulation of the vagus in atropinized pigs produced a profuse flow of pancreatic juice with high HCO3 content concomitantly with a significant increase in pancreatic VIP output from 13 to 113 fmol/min. Intravenous administration of somatostatin (SRIF) during continuous electrical vagal stimulation caused a parallel suppression of the VIP release and the pancreatic fluid and HCO3 secretion to prestimulatory values. The SRIF-induced reduction in fluid and HCO3 secretion seemed to be mediated via an inhibition of the VIP release rather than through a direct effect on the exocrine cells, inasmuch as SRIF did not influence the VIP-provoked exocrine response from the in vitro isolated perfused porcine pancreas. The results support the view that VIP is transmitter in the vagally induced atropine-resistant water and HCO3 secretion from the porcine pancreas.

Somatostatin effects on lower esophageal sphincter function

The effect of somatostatin (GH-RIH) infusion (2 microgram/min) on lower esophageal sphincter pressure (LESP) responses to various stimuli was evaluated in adult male baboons. GH-RIH infusion did not affect basal LESP, but did cause a significant suppression of mean immunoreactive insulin (IRI) to 5.8% of basal values (P less than 0.05). Pentagastrin IV caused dose-related increases in LESP that were unaffected by GH-RIH. Abdominal compression caused a threefold rise in LESP (P less than 0.005) both without and with GH-RIH. However, atropine (20 microgram/kg iv bolus) completely blocked this cholinergic LES pressure response. Intragastric alkali as well as intragastric glycine caused significant increases in LESP (P less than 0.05). These LESP responses to alkali and to glycine were totally abolished by GH-RIH. In conclusion, GH-RIH infusion in the baboon does not affect basal LESP, LES smooth muscle response to exogenous stimulation, nor a cholinergically mediated LES response. GH-RIH does inhibit the response of LESP both to intragastric alkali and to glycine by the apparent suppression of a hormonally mediated mechanism.

Growth hormone release inhibitory hormone-like immunoreactivity in pancreas and gut in streptozotocin diabetes in the rat and response to insulin administration

In streptozotocin diabetes in the rat, growth hormone release-inhibitory hormone-like immunoreactivity (GHRIH-LI) content of pancreas, gastric antrum and colon was increased. Insulin therapy significantly lowered the increased pancreatic GHRIH-LI content but did not affect that of the gastric antrum and colon at the dosage used. The relevance of these findings in relation to pancreatic and gastrointestinal function in diabetes awaits clarification.

Development and validation of a specific radioimmunoassay for somatostatin in human plasma

Little is known about the factors controlling somatostatin secretion in man, and data are not available on the changes in circulating levels in various human physiological or pathophysiological states. This is mainly a consequence of the technical difficulties involved in measuring somatostatin in plasma. In the presence of plasma, binding of somatostatin tracer to antibody was consistently decreased by about 20%, and this could not be abolished by the addition of EDTA and aprotinin or by the use of specially prepared somatostatin-free plasma. Furthermore, in the presence of plasma, endogenous somatostatin does not dilute in parallel with synthetic cyclic somatostatin standard. We have, therefore, developed and validated a radioimmunoassay for somatostatin using prior extraction of the peptide onto leached silica glass. Tyrosine-II somatostatin was iodinated using lactoperoxidase and purified on ODS silica. This method is superior to iodination using chloramine-T with CMC cellulose purification, and gives a highly purified preparation with a shelf-life of at least eight weeks. Using this tracer and a specific antiserum, the limit of sensitivity of the assay was 10 pg/ml, with an intra-assay coefficient of variation of 12% (n = 16) and inter-assay coefficient of variation of 15% (n - 10). Parallelism has been demonstrated between standard synthetic cyclic somatostatin and all extracted plasma samples. The mean recovery of exogenous somatostatin from plasma was 78%. The fasting level of immunoreactive somatostatin at 0,900 hours in 40 normal subjects ranged from 17 to 81 pg/ml. Care is needed, however, when comparing these values with those obtained from other laboratories since standard preparations of somatostatin vary considerably in their immunopotency.

Effect of somatostatin on myoelectrical activity of small bowel

Somatostatin, a growth hormone-release inhibiting hormone, has been found to be a powerful inhibitor of gastric and pancreatic secretion as well as of hormone release in the digestive system. This study was undertaken to determine the influence of somatostatin on the myoelectrical activity pattern of the small bowel. Three conscious dogs were prepared with electrodes spaced 25 cm apart along the entire small intestine. Intravenous infusions of somatostatin were administered in various doses (0.6--5.0 microgram/kg.h) while spike activity and slow waves were recorded under fasting conditions, after a meat meal, or during intravenous infusion of gastrin, caerulein, or insulin. Somatostatin at a dose of 0.6 microgram/kg.h almost doubled the frequency of the interdigestive myoelectric complex. Somatostatin in fed dogs caused a dose-dependent decrease of the normal fed spike activity, and at higher doses it induced a pattern like that seen in fasting animals. The slow-wave frequency in both fasted and fed conditions was not changed significantly. We conclude that somatostatin given under basal conditions increases the frequency of the interdigestive complex and, when administered after feeding, converts the fed-type pattern to the fasted-type pattern. It may therefore play a promoting role in initiating the interdigestive myoelectric complex.

Plasma motilin levels in duodenal ulcer and effect of a truncal vagotomy and hypoglycaemia

The identical response of plasma motilin levels, in duodenal ulcer patients and healthy controls, to a test meal and insulin induced hypoglycaemia, fail to demonstrate any significant abnormalities in motilin release. The close correlation between blood glucose and motilin suggest a possible role of this new hormone in carbohydrate metabolism.

Somatostatin inhibits gastric motility in response to distention

Gastric motility and plasma gastrin concentration have been measured in 6 healthy volunteers before and after stepwise gastric distention. Distention was performed by filling a flaccid thin-walled bag, which was connected with a low pressure transducer for measuring intragastric pressure variations. Stepwise increase in gastric volume from 0-600 ml caused graded increases in gastric motility. No significant change was seen in the plasma gastrin level. When gastric distention was performed concomitantly with constant infusion of somatostatin (0.05 mg/h and 0.50 mg/h) in the same individuals on different days, motility was significantly reduced, without any changes in the plasma gastrin concentration. It is concluded that somatostatin, which probably plays a role in the gastro-intestinal tract, may have a physiological effect in the regulation of gastric motility too. This motility effect of somatostatin seems to be independent of any effect on the gastrin concentration.

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

The effect of short-time somatostatin infusion on gastric and intestinal propulsion of an oral glucose load was examined in healthy subjects by means of a multiple indicator dilution technique. The early gastric emptying rate was enhanced by somatostatin, indicating delayed gastric inhibition. After withdrawal of the somatostatin infusion, the late gastric emptying rate was decreased and the intestinal propagation rate markedly slowed. The effect of long-time somatostatin infusion has to be examined to analyse the nature of the events described.

APUD cells and the apudomas. A concept relevant to anaesthesia and endocrinology

A variety of cells found in the pituitary and pineal glands, sympathetic nervous system and adrenal glands, the gut, pancreas, thyroid (C-cells), chemoreceptors (type I-Cells), lungs (P-cells), skin (melanocytes) and the urogenital tract have a common origin from the neural crest. These cells are programmed for neuro-endocrine function and, as a group, can be regarded as one of the physiological control systems. They secrete a variety of amine and peptide hormones and have common cytochemical characteristics from which the term APUD cell is derived. Tumours of these cells are referred to as 'apudomas' and may synthesise not only their own hormones but also those which are normally produced by other APUD cells. The relevant physiological properties of some of the peptides which have been described relatively recently are discussed and the principal clinical syndromes produced by the APUDomas are described.

Extraction, gel filtration pattern, and receptor binding of porcine gastrointestinal glucagon-like immunoreactivity

Different techniques for the extraction and initial purification of porcine gastrointestinal glucagon-like immunoreactivity (GLI) were compared with reference to yield, and preservation of number and pattern of GLI components. The conventional acid-ethanol technique combined with ethanol-ether purification gave high yields and a reproducible pattern of components. Large amounts of tissue were more easily extracted using another technique, based on extraction by boiling, extraction and precipitation with acetone, and--if necessary--salting out. By means of the latter two techniques mucosal tissue from all of the porcine gastrointestinal tract was extracted and subjected to gel filtration. Glucagon-like peptides were searched for using: 1. a radioimmunoassay which quantifies gut type glucagon (GTG), as well as pancreatic type glucagon (PTG), 2. a radioimmunoassay highly specific for pancreatic type glucagon (PTG), and 3. a radioreceptor assay based on binding of glucagon to porcine liver cell membranes. The oesophageal, the fundic, and the antro-pyloric parts of the gastric mucosa contained very small amounts of GLI. The cardiac gland region contained small amounts of a peptide indistinguishable from "true" glucagon. The duodenal mucosa contained small amounts of "true" glucagon and may be a smaller, glucagon-like peptide. The mucosa of the small intestine contained large amounts of both high and low molecular weight GTG and, in addition, PTG of high molecular weight and "true" glucagon. The colon also contained these components with "true" glucagon in high concentrations. Only small GTG and "true" glucagon were receptor-active, the former with less than its immunometric potency.

Influence of somatostatin on carbohydrate disposal and absorption in diabetes mellitus

Infusion of somatostatin, an inhibitor of glucagon secretion, in insulin-dependent diabetics resulted in a 75-100% reduction in the blood-glucose rise after oral glucose administration, but did not improve intravenous glucose tolerance. Somatostatin reduced blood-xylose levels by 50-90% after ingestion of this pentose and delayed the peak increment in blood-xylose by 1-2 h. Similar effects on blood-xylose levels and a 30% reduction in splanchnic blood-flow were observed in normal subjects during infusion of somatostatin. Glucagon administration (3 ng per kg per min) or intraduodenal administration of xylose did not reverse somatostatin's effect on xylose tolerance. Somatostatin reduces postprandial hyperglycaemia in diabetes primarily by decreasing and/or delaying carbohydrate absorption rather than enhancing carbohydrate disposal. This effect may be mediated, in part, but a reduction in splanchnic blood-flow. These findings indicate that postprandial hyperglycaemia in diabetes is due primarily to insulin deficiency rather than glucagon excess.

Renal blood flow in obstructive jaundice: an experimental study in baboons

1. The distribution of intrarenal blood flow has been measured using the 133Xe-washout technique in thirteen baboons 2 weeks after ligation of the common bile duct. 2. In comparison with eight sham-operated baboons, there was a signifigant decrease in the percentage distribution of blood to the cortex, although the rate of flow was unchanged. These changes were accompanied by a significantly increased flow rate and percentage distribution of flow through the juxtameduallary circulation. 3. In a further five baboons treated in the same way, various doses of noradrenaline were infused into the renal artery. In these animals there was an enhanced pressor response to noradrenaline, and this effect was completely abolished by an alpha-adrenoreceptor blocking agent (phenoxybenzamine). The beta-adrenoceptor blocking drug (propranolol) had no such effect. 4. This enhanced response was not seen when noradrenaline was infused into three sham-operated baboons. 5. These observations suggest that the alterations in renal perfusion in obstructive jaundice may be due to an increase renovascular sensitivity to circulating catecholamines and an enhanced alpha-adrenoceptor activity.