Immunoreactive Secretin Research Articles

Patterns of acid-induced release endogenous immunoreactive secretin in children with cystic fibrosis and recurrent pain.

The release of endogenous secretin in response to acidic drinks has been examined in children with cystic fibrosis (CF), recurrent abdominal pain (RAP), and children with intermittent diarrhoea who were otherwise healthy. Plasma secretin was measured by radioimmunoassay. The healthy children and the children with cystic fibrosis responded with increases in plasma secretin concentrations. Significant increases were not seen in the children with RAP. It is concluded that children respond to ingested acid with increases in plasma secretin and that this response in intact in children with cystic fibrosis. The impaired response found in children with RAP requires further study but may be relevant to the pathogenesis of this condition.

The release of biologically active secretin-like immunoreactivity into duodenal lumen of dogs.

1. Immunoreactive secretin in the duodenal contents was determined in four conscious and four anaesthetized dogs in which hydrochloric acid (0.1 N) was infused into the duodenum at 2.2 ml./min. In the conscious dogs, immunoreactive secretin concentration in duodenal juice increased from 5-7 to 40-60 ng/ml. after infusion of HCl. In anaesthetized dogs, luminal immunoreactive secretin concentration increased from 2-3 to 12-16 ng/ml. after acid infusion. In both groups of dogs, a 20- to 30-fold increase in the total output of luminal immunoreactive secretin was observed. 2. Duodenal juice collected from anaesthetized dogs after diversion of both bile and exocrine pancreatic secretion was found to be the only source of luminal immunoreactive secretin. No immunoreactive secretin was found in either bile or pancreatic juice. 3. Gel filtration of the duodenal juice on a Sephadex G-50 column indicated that the immunoreactive secretin-like material in the duodenal juice possesses a molecular size similar to that of natural porcine secretin. 4. Immunoreactive secretin was partially purified from dog duodenal juice by chromatography on a SP-Sephadex column and found to be capable of stimulating pancreatic bicarbonate and water secretion in dogs.

Effect of sodium oleate on plasma secretin concentration and pancreatic secretion in dog

The effects of sodium oleate and triglyceride infused into the duodenum of dogs with chronic pancreatic fistulas on pancreatic secretion and plasma immunoreactive secretin were investigated. The responses were compared with those following intravenous secretin infusions. Oleate markedly increased pancreatic water and bicarbonate secretion in a dose-related fashion, and these increases were accompanied by a small, but significant rise in the level of circulating immunoreactive secretin. No change in pancreatic secretion or in plasma secretin level was observed by the administration of triglyceride. Comparison of the bicarbonate response after oleate infusion with that after secretin administration suggests that the pancreatic stimulatory effect of intraduodenal sodium oleate is mediated to a major extent by the release of endogenous secretin.

Secretin release from the isolated, vascularly perfused pig duodenum.

1. A method for the isolation and vascular perfusion of the porcine pancreas and duodenum was developed. 2. The oxygen consumption of the whole preparation was similar to that of the pancreas alone, and since the duodenal arteriovenous oxygen deficit was similar to that of the total preparation, it was concluded that the duodenum respired adequately. 3. The duodenum rapidly absorbed luminally administered radioactive glucose, and this absorption was strongly inhibited by ouabain and phloridzin. 4. The duodenum secreted secretin rapidly in response to hydrochloric acid, but did not respond to any other luminal stimuli, including lipids, proteins, carbohydrates and bile. Neither was secretin release stimulated by intra-arterially injected acetylcholine. 5. By gel permeation chromatography the release immunoreactive secretin behaved identically to pure natural secretin, indicating that the tissue form and the circulating form have identical molecular size. 6. It is concluded that this model offers an unique opportunity to study the endocrine secretion of the duodenum.

Identification, characterization, and distribution of secretin immunoreactivity in rat and pig brain.

Secretin immunoreactivity was detected in the central nervous system of the rat and pig with a highly specific radioimmunoassay. The secretin immunoreactivity in the rat and pig brain and duodenum extracts was fractionated by using a reverse-phase high-pressure liquid chromatographic system. The immunoreactive secretin from pig brain and duodenum coeluted precisely with synthetic porcine secretin. However, immunoreactive secretin extracted from rat brain and duodenum eluted slightly before porcine secretin. These data suggest a slight difference in the structure of rat and pig secretin. The detection of secretin in the brain lays the groundwork for studies to determine the role of the peptide in central nervous system function.

Immunocytological evidence of motilin- and secretin-containing cells in the human fetal gastro-entero-pancreatic system.

The ontogeny and distribution of immunoreactive motilin and secretin were studied in the gastro-entero-pancreatic (GEP) system of human fetuses, aged 5--24 weeks, using an indirect immunocytochemical method. Several controls to check for the specificity of the immunoperoxidase staining were performed. The first motilin- and secretin-containing cells were observed in the duodenal and jejunal mucosa in fetuses at a gestational age of 16 weeks. These immunoreactive cells were located in the glands of Lieberkühn and in the villi. No immunoreactive cells were present in the oxyntic and pyloric mucosa, ileum, colon and endocrine pancreas. These observations indicate that the motilin- and secretin-containing cells detected by our antisera appear (i) in the same organs of the fetus where they are also detectable in the adult, and (ii) after the completion of histogenesis of the gastro-entero-pancreatic (GEP) system.

Pancreatic exocrine secretion and immunoreactive secretin release after intraduodenal instillation of 1-phenyl-1-hydroxy-n-pentane and HCl in rats.

Portal plasma immunoreactive secretin (IRS) concentrations, pancreatic juice flow, and amylase output were simultaneously measured in response to intraduodenal infusion of 1-phenyl-1-hydroxy-n-pentane (PHP), as well as infusion of hydrochloric acid (HCl). These data were compared with those obtained from intravenous bolus injections of synthetic porcine secretin in anesthetized rats. The intraduodenal infusion of PHP or HCl at a rate of 2 ml/min for 2 min produced a dose-related increase in portal plasma secretin concentrations, pancreatic juice flow, and amylase output. However, the mechanism of secretin release by PHP seems to differ from that of HCl. The secretin response to 0.1 N HCl infused at a rate of 0.1 ml/min for 30 min was complete after 10 min, despite continued infusion, while PHP stimulated a secretin release which persisted for 10 min after cessation of infusion. The pH in the second portion of the duodenum, following PHP infusion, remained consistently greater than 6.3. PHP-stimulated pancreatic exocrine secretions were only partially suppressed by somatostatin, while secretin release was almost completely inhibited. However, intraduodenal PHP may stimulate the release of secretin along with other gastrointestinal hormones, and the endogenous release of these hormones may not be inhibited by somatostatin.

Effect of intraduodenal instillation of 1-phenyl-1-hydroxy-n-pentane on pancreatic exocrine secretions and immunoreactive secretion release in the rat.

Pancreatic juice flow and amylase output, and the concentrations of immunoreactive secretin in portal and peripheral blood were simultaneously determined in anesthetized rats in response to intraduodenal instillation of 1-phenyl-1-hydroxy-n-pentane (PHP), a phenyl carbinol derivative induced from one of the constituents of Curcuma. PHP stimulated both pancreatic juice flow and amylase output and increased portal and jugular plasma secretin levels in a dose-related fashion. During intraduodenal instillation of PHP the pH in the second portion of the duodenum remained consistently above 6.3. Infusion of cyclic somatostatin at a dose of 5 microgram/kg/h significantly suppressed the PHP-induced secretin release, though pancreatic flow rate and amylase output were only slightly and insignificantly suppressed. These observations suggest that PHP release secretin by an acid independent mechanism but also stimulates the exocrine pancreas by a mechanism independent of secretin.

Mucosal secretin of the duodenum in peptic ulcer disease.

Mucosal secretin content of the duodenum was measured using bioptic specimen in healthy controls and patients of peptic ulcer. Immunoreactive secretin in the duodenal mucosa was found greater in healthy controls (7.73 +/- 2.71 ng/mg dry wt., mean +/- S.D.) than in gastric ulcer patients (5.76 +/- 3.51 ng/mg dry wt.) and duodenal ulcer patients (5.54 +/- 2.48 ng/mg dry wt.), but the difference was not significant. There was no significant relationship between mucosal secretin and acid output in these patients.

Secretin immunoreactivity in rat and pig brain

Secretin immunoreactivity in rat and pig brain has been identified and characterized utilizing a highly specific radioimmunoassay and fractionation on a high pressure liquid chromatographic system reverse phase column. One immunoreactive peak from each brain extract was observed. Secretin immunoreactivity from rat brain and duodenum coelute, but eluted slightly ahead of the immunoreactivity from pig brain and duodenum and from synthetic porcine secretin. Immunoreactive secretin is widely distributed in the thalamus, hypothalamus and olfactory bulb, cerebral cortex, midbrain, septum, striatum, hippocampus, medulla and pons. The highest concentrations occur in the pineal and the pituitary gland.

The influence of intraduodenal administration of pancreatic juice on the bile-induced pancreatic secretion and immunoreactive secretin release in man.

The exocrine pancreatic secretion of water, bicarbonate, amylase, and protein and the plasma levels of immunoreactive secretin (IRS) were studied after intraduodenal infusions of bile and pancreatic juice. Pancreatic secretion was obtained by endoscopic cannulation of the main pancreatic duct. Bile and pancreatic juice were infused into the duodenum through separate catheters attached to the outside of the duodenoscope. The unstimulated secretion was collected for 20 min. After intraduodenal stimulation of the pancreatic secretion with a nearly neutral solution of dried cattle bile, juice was collected for another 20-min period. Then, pure pancreatic juice was infused into the duodenum. It was shown that pancreatic juice reduced the flow rate and output of bicarbonate, amylase, and protein significantly (p less than 0.05). A significant reduction in plasma concentration of IRS (p less than 0.05) was also found. In the controls, i.e., when no pancreatic juice was instilled into the duodenum, a further increase in flow rate, bicarbonate secretion, and IRS was found. It is concluded that the exocrine pancreatic secretion and IRS release induced by intraduodenal administration of bile may be depressed by reinfusions of pancreatic juice. The corresponding effect on bicarbonate secretion and IRS release found in this study supports the view that secretin may play an important role in the exocrine pancreatic secretion induced by intraduodenal infusion of bile.

Exocrine pancreatic secretion and immunoreactive secretin release after repeated intraduodenal infusions of bile in man.

The exocrine pancreatic secretion of water, bicarbonate, amylase, trypsin, chymotrypsin, and lipase and the plasma concentration of immunoreactive secretin (IRS) were studied before and after repeated intraduodenal infusions of cattle bile in man. After endoscopic cannulation of the main pancreatic duct, juice was collected in 5-min samples for 20 min. A solution of 6 g dried cattle bile in 60 ml water was then infused into the duodenum through a separate catheter attached to the outside of the duodenoscope. Juice was collected for another 20 min. After this period a solution of 6 g dried cattle bile in 40 ml water was infused into the duodenum, and juice again collected for 20 min. Blood was frequently drawn from an arm vein for estimation of plasma concentration of secretin by radioimmunoassay. Both bile infusions caused significant rises in flow rate, bicarbonate concentration and output, and IRS (p less than 0.05). Enzyme concentrations decreased significantly after intraduodenal bile infusions (p less than 0.05). Outputs of enzymes rose significantly after the first bile infusion; however, a rise after the second bile infusion was found only for amylase. Further, a significant decrease in amylase and lipase concentration was found after the second bile infusion. The findings indicate that the increase in proteolytic enzyme and lipase secretion was due to a washout phenomenon. The increase in the plasma concentration of secretin after repeated bile infusions, with a corresponding effect on flow rate and bicarbonate secretion, indicates that secretin may be the main factor responsible for the exocrine pancreatic secretion caused by intraduodenal bile infusions.

Plasma Concentration of Secretin and Gastric Secretion following Intraduodenal Calcium Infusion in Man

The aim of the present study was to test whether the previously demonstrated release of immunoreactive plasma secretin following intraduodenal bile infusion could be mediated by the calcium content of the bile. The gastric acid secretion and the serum concentration of gastrin, ionized and total calcium, calcitonin, and parathyroid hormone were also measured. A total amount of 93 mg calcium was infused intraduodenally in eight healthy volunteers during constant gastric aspiration. No effect was seen on the concentration of immunoreactive plasma secretin or serum gastrin levels in peripheral blood. The total serum calcium concentration decreased slightly during the infusion and increased immediately thereafter. Ionized serum calcium increased throughout the experiment, the increase being significant only after the calcium infusion was stopped. No effects were observed on the serum concentrations of calcitonin and parathyroid hormone.

The effect of glucose on plasma immunoreactive secretin in normal man and after gastrectomy or pancreatectomy.

Oral intake of glucose increased the peripheral plasma immunoreactive secretin (IRS) concentration in patients after total pancreatectomy with duodenectomy (p < 0.05) and in patients after total gastrectomy (p < 0.01). In young healthy volunteers and in patients after partial gastrectomy, no effect on IRS was observed. Intravenous glucose reduced the IRS concentration in pancreatectomized patients (p < 0.05), whereas IRS was only reduced in young healthy volunteers when intravenous glucose was followed by oral glucose after an interval of 10 min (p < 0.025). The abnormal IRS release in pancreatectomized patients and in patients after total gastrectomy might be due to rapid intestinal passage and/or increased splanchnic blood flow induced by hypertonic glucose. A third possibility is that a glucose-induced increase in bile flow might release IRS.

The effect of atropine on secretin release and aspirated bicarbonate secretion after duodenal acidification in man.

The effect of duodenal instillation of hydrochloric acid on peripheral plasma immunoreactive secretin (IRS) concentration--without or with a constant intravenous infusion of atropine--was studied in eight healthy volunteers. Without atropine infusion, IRS increased from 1.2 +/- 0.3 pmol/l to a peak value of 17.1 +/- 4.4 pmol/l. The volume of duodenal aspirates increased from 0.74 +/- 0.12 ml/min to 5.03 +/- 0.46 ml/min, and the bicarbonate output from 7.6 +/- 1.7 mumol/min to 349 +/- 39 mumol/min. With atropine infusion (bolus of 500 micrograms + 750 micrograms/h of atropine sulphate), IRS increased from 1.4 +/- 0.3 pmol/l to 14.8 +/- 3.6 pmol/l. The volume of the duodenal aspirates increased from 0.71 +/- 0.08 ml/min to 2.76 +/- 0.37 ml/min and the bicarbonate output from 4.0 +/- 1.6 mumol/min to 142 +/- 33 mumol/min. The integrated IRS response to acidification was 18% lower during atropine infusion (p < 0.05). Both the aspirated flow rate from the duodenum and the bicarbonate output were markedly reduced by atropine infusion, 45% and 59%, respectively (p < 0.005).

Pure synthetic bile salts release immunoreactive secretin in man.

When 20 ml of 50 mmol/l pure synthetic bile salts (pH 6.5), of approximately the same composition as human bile, were infused into the duodenum of six healthy volunteers over 5 min during constant gastric aspiration, plasma immunoreactive secretin increased from 2.5 +/- 0.4 pmol/l to 3.6 +/- 0.5 pmol/l at 10 min (p < 0.025). Gastric acid secretion was not increased. No effect was seen when the same amount of physiological saline was infused under the same conditions in another group. It is concluded that bile salts in an amount and composition corresponding to that in the human gallbladder is able to release immunoreactive secretin from the human intestine.

Physiological doses of secretin do not stimulate acute insulin release.

To study the effect of physiological increments in plasma secretin concentrations on basal and glucose-stimulated insulin release, bolus iv glucose injections (5 g) were given to normal weight volunteers (less than 108% ideal BW) before, during, and 30 min after a secretin infusion at a rate of 0.125 U/kg.h, raising mean plasma immunoreactive secretin to 35.5 +/- 8.3 pg/ml. Acute insulin responses to glucose were unaffected during or after the secretin infusion. Furthermore, when plasma glucose was elevated to postprandial levels (128--165 mg/dl), a similar secretin infusion also failed to alter acute insulin responses. In addition, no changes in basal glucose or insulin levels were found when endogenous secretin concentrations were increased by intraduodenal acid infusion. Thus, increases in plasma secretin to concentrations seen in the postprandial state fail to alter acute insulin secretion. It is unlikely that secretin plays any role in the intestinal stimulation of insulin secretion.

Plasma secretin level and exocrine pancreatic secretion in response to intraduodenal infusion of 1-phenyl-1-hydroxy-n-pentane and HCl by using a new four lumen tube.

We have designed a four lumen tube which has enabled us to aspirate duodenal juice while infusing endogenous stimuli into the lower part of duodenum. Exocrine pancreatic secretion and plasma immunoreactive secretin (IRS) levels have been simultaneously observed in response to intraduodenal infusion of 1-phenyl-1-hydroxy-n-pentane (PHP) and 0.1 N HCl in normal subjects, patients with diabetes mellitus and patients with chronic pancreatitis by use of this tube. (1) Pancreatic flow rate and bicarbonate concentration were found to increase to twice those of basal levels and plasma IRS levels rose significantly after infusion of PHP or HCl in normal subjects. The same tendency was observed in patients with diabetes mellitus. (2) Exocrine pancreatic secretion did not change after infusion of PHP or HCl in patients with chronic pancreatitis. Pancreatic flow rate, bicarbonate concentration and amylase output were significantly low in patients with diabetes mellitus. (3) Pancreatic flow rate and bicarbonate concentration incresed to about twice those of basal levels after both PHP and HCl infusion. On the other hand, although pancreatic amylase output increased significantly after infusion of HCl as compared with basal secretion, it did not change after infusion of PHP. It appeared reasonable to conclude that PHP is a morespecific substance for releasing secretin than HCl.

Enkephalin inhibits the release and action of secretin on pancreatic secretion in the dog.

1. Pancreatic bicarbonate and protein secretion as well as immuno-reactive plasma secretin concentration in response to a meal, duodenal acidification and exogenous secretin or octapeptide of cholecystokinin (OP-CCK) have been measured following administration of methionine-enkephalin in chronic pancreatic fistula dogs. 2. Methionine-enkephalin inhibited pancreatic responses to both exogenous hormones (secretin and OP-CCK) and to endogenous hormones released from the gut by food or duodenal acidification. 3. Naloxone, a potent opiate receptor antagonist, partly prevents this methionine-enkephalin-induced inhibition of pancreatic secretion suggesting that this effect might be mediated by opiate receptors. 4. The inhibitory effect of methionine-enkephalin on pancreatic response to endogenous stimulants was more pronounced than that to exogenous hormones and was accompanied by a significant reduction in plasma immuno-reactive secretin concentration. 5. This study indicates that methionine-enkephalin inhibits pancreatic secretion, at least in part, by suppressing the release of the intestinal hormones stimulating the exocrine pancreas.

Immunoreactive secretin release following taurocholate perfusions of the cat duodenum.

Perfusion of the cat duodenum with sodium taurocholate (TC), 120 mmol/l, at pH 6.1 increased the plasma immunoreactive (IRS) concentration from 2.2 +/- 0.7 pmol/l to 29 +/- 6.1 pmol/l during the first 20 min. This was accompanied by an increased pancreatic secretion of fluid, while the chymotrypsin output showed a "wash-out' phenomenon. TC increased both the bile-acid-dependent and the bile-acid-independent bile secretion. In comparison, HCl, 150 mmol/l, increased IRS from 0.9 +/- 0.5 pmol/l to 41 +/- 15 pmol/l, producing an increase in the pancreatic fluid secretion. However, only a slight increase in the bile-acid-independent bile secretion was found, and the bile-acid-dependent secretion did not change. The effects of TC on the pancreatic secretion were produced at concentrations occurring in cat hepatic bile.