Gastrointestinal somatostatin: extraction and radioimmunoassay in different species (original) (raw)
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Regulatory Peptides, 1999
In the absence of somatostatin antagonists, somatostatin antisera administered acutely or animals chronically immunized against somatostatin have been used to define the functions of somatostatin. However, the circulating immunoglobulins from immunized animals may contain substantial quantities of endogenous hormones. This has not been examined for somatostatin. We have measured the amount of free somatostatin bound to circulating immunoglobulins in somatostatin-immunized animals and the effect of this sequestering of the free peptide on somatostatin secretion and gastric somatostatin synthesis and storage. The average concentration of somatostatin bound to the antisera was 6.9 nmol / l, about 1000-fold higher than normal circulating levels. Compared to control animals, there was a doubling of somatostatin mRNA in the fundus and a 4-fold increase in fundic somatostatin peptide. Similar increases were seen in pancreas, but the antrum was not significantly affected providing further evidence of distinct regulatory mechanisms between the antrum and fundus. We suggest that withdrawal of active somatostatin activates a regulatory loop to increase fundic somatostatin biosynthesis and storage. The data support the concept that somatostatin autoregulates its own expression at both the RNA and peptide level.
CHARACTERIZATION OF SOMATOSTATIN BINDING SITES IN CYTOSOLIC FRACTION OF RAT INTESTINAL MUCOSA
Specific binding sites for somatostatin have been characterized in cytosolic fraction of rat intestinal mucosa by using 12s l-labelled TyrlLsomatostatin and a variety of physicochemical conditions. The binding depended on time, temperature and pH, and was reversible, saturable and specific. At apparent equilibrium, the specific binding of 125I-Tyrll-somatostatin was competitively inhibited by native somatostatin in the 1 nM-4 pM concentration range. Binding studies suggested the presence of two classes of binding sites: a class with high affinity (K d-0.07 ~tM) and low capacity (4.6 pmoi/mg protein) and a class with low affinity (K d = 1.05 pM) and high capacity (277 pmol/mg protein) at 25°C. Somatostatin exhibited competitive inhibition of tracer binding, while neuropeptides such as neurotensin, substance P, Leu-enkephalin, and vasoactive intestinal peptide were ineffective. The presence of somatostatin binding sites in cytosolic fraction of intestinal mucosa, together with the known occurrence of somatostatin in D-cells and nerve endings in the small intestine, strongly suggest that this peptide may be involved in the physiology and physiopathology of intestinal epithelium.
Evidence for the presence of somatostatin 28 in plasma
Diabetes, 1982
Somatostatin-like immunoreactivity (SLI) from dog and rat plasma eluted from Biogel P-6 columns as three distinct peaks. A large-molecular-weight peak was present in the void volume of the column, an intermediate-sized peak (SLI 28 ) coeluted with synthetic somatostatin 28 (S-28), and a small-molecular-weight peak (SLI 14 ) coeluted with SRIF. Material from the SLI 28 peak diluted in parallel to the S-28 standard in the radioimmunoassay and behaved identically to S-28 on high pressure liquid chromatography (HPLC). Levels of SLI 28 in the portal vein were consistently greater than the simultaneously measured peripheral levels (portal peripheral ratio 2.2 ± 0.2). Venous samples drawn from multiple sites suggested that SLI 28 is secreted by the duodenum and/or pancreas and the intestine. This data is consistent with the possibility that S-28 is a hormone distinct from SRIF. DIABETES 37: 474-477, May 1982.
Journal of Clinical Investigation, 1981
hepatic and renal metabolism of somatostatin-like immunoreactivity (SLI) was assessed simultaneously in an in vivo dog model. The hepatic extraction of this peptide was 29.4+±2.3% and was similar for endogenous and infused exogenous SLI. The renal extraction was 62.3±+5%. The renal clearance of SLI was significantly greater than that of inulin indicating that the peptide is handled by peritubular uptake from postglomerular blood in addition to glomerular filtration. In both organs SLI extraction was not saturable even at arterial concentrations in excess of 100 times physiological range. The overall metabolic clearance rate of SLI was 19.7±1.6 ml/kg per minute of which 32.7±4.6% was contributed by hepatic and 37±4.9% by renal uptake mechanisms. The plasma half disappearance time of exogenously infused SLI was 1.9±0.3 min. The studies indicate that in the dog, the liver and kidney are both major sites of SLI metabolism, together accounting for 70.0±8.7% of the metabolic clearance of the peptide.
Regulatory Peptides, 2009
Extensive functional and morphological research has demonstrated the pivotal role of somatostatin (SOM) in the regulation of a wide variety of gastrointestinal activities. In addition to its profound inhibitory effects on gastrointestinal motility and exocrine and endocrine secretion processes along the entire gastrointestinal tract, SOM modulates several organ-specific activities. In contrast to these well-known SOM-dependent effects, knowledge on the SOM receptors (SSTR) involved in these effects is much less conclusive. Experimental data on the identities of the SSTRs, although species-and tissue-dependent, point towards the involvement of multiple receptor subtypes in the vast majority of gastrointestinal SOM-mediated effects. Recent evidence demonstrating the role of SOM in intestinal pathologies has extended the interest of gastrointestinal research in this peptide even further. More specifically, SOM is supposed to suppress intestinal inflammatory responses by interfering with the extensive bidirectional communication between mucosal mast cells and neurons. This way, SOM not only acts as a powerful inhibitor of the inflammatory cascade at the site of inflammation, but exerts a profound antinociceptive effect through the modulation of extrinsic afferent nerve fibres. The combination of these physiological and pathological activities opens up new opportunities to explore the potential of stable SOM analogues in the treatment of GI inflammatory pathologies.
Development and Validation of a Specific Radioimmunoassay for Somatostatin in Human Plasma
Annals of Clinical Biochemistry: International Journal of Laboratory Medicine, 1979
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-11 somatostatin was iodinated using lactoperoxidase and purified on ODS silica. This method is superior to iodination using chloramine-T with CMC cellulose ...
Contribution of the pancreas to circulating somatostatin-like immunoreactivity in the normal dog
Journal of Clinical Investigation, 1984
A~bstract. These studies were performed to assess the contribution of the pancreas to the somatostatinlike immunoreactivity (SLI) circulating in arterial and portal venous plasma. Basal SLI concentrations in arterial, pancreatic venous, and portal venous plasma were 95±9, 277±32, and 130±12 pg/mi, (+±SEM), respectively. Measurement of pancreatic and portal venous blood flow (5±1 vs. 365±46 ml/min) and hematocrit allowed calculation of net, base-line SLI output from the right lobe of the pancreas (521±104 pg/min) and from the gastrointestinal tract (8,088±1,487 pg/min), which suggested that the contribution of the pancreas to circulating SLI was minor when the D cells were not stimulated. To stimulate the secretion of SLI from both pancreatic and nonpancreatic sources, isoproterenol, a beta-adrenergic agonist, was infused intravenously for 1 h into six anesthetized dogs. Arterial SLI increased by 52±9 pg/ml; superior pancreatico-duodenal venous SLI increased by 380±95 pg/ml; portal venous SLI increased by 134±14 pg/ml. Pancreatic venous blood flow remained unchanged at 5±1 ml/min, but portal venous blood flow increased to 522±62 ml/min. SLI output from the right lobe of the pancreas increased by 684±227 pg/min and that from the gastrointestinal tract increased by 23,911±3,197 pg/ min, again suggesting that the pancreas was a minor source of circulating SLI even when the D cells were stimulated. We conclude that the measurement of arterial-venous SLI concentrations, in the absence of measurements of
Luminal gastric somatostatin-like immunoreactivity in response to various stimuli in man
Digestive Diseases and Sciences, 1986
This study investigates release of somatostatin-like immunoreactivity (SLI) into the gastric lumen of five healthy human subjects in response to pharmacological stimuli (pentagastrin and secretin) and physiolog!cal stimuli (sham feeding and intrajejuna! perfusion of elemental diet). Basal and poststimulation gastric juice aspirates were collected at 15-min intervals, extracted with acetone, and SLI determined by radioimmunoassay, with these results: (1) A considerable amount of SLI was secreted during the basal period. (2) Pentagastrin stimulated SLI release quickly and was associated with increased acid secretion. (3) Both secretin and sham feeding increased SLI only slightly. (4) During intrajejunal perfusion of the elemental diet, SLI increased significantly, was associated with decreased acid secretion~ and rapidly returned to basal level when elemental diet was replaced by saline. Basal levels of gastric luminal SLI thus showed distinct changes in response to each stimulus. Although the physiological action of luminal SLI remains to be studied, its levels may reflect gastric D-cell activities. Gastric D cells have been shown to have long processes, like neuronal processes, that come in contact with many effector cells. Other types of cells also appear to have contact with D cell processes on their terminals. Many D cell processes have contact with gastrin cells (G cells) in the antropyloric mucosa and with parietal cells in the oxyntic mucosa (1). Studie s have suggested that the activity of G cells and oxyntic cells of the stomach may be influenced by D cells via somatostatin. Somatostatin may be released into the interstitial Manuscript