Effect of low dose secretin and caerulein on pure pancreatic bicarbonate secretion and plasma secretin in man

In six healthy volunteers pure pancreatic juice was obtained by endoscopic cannulation of the main pancreatic duct. Following a 20-min basal period, secretin (0.03 CU/kg, h) was intravenously infused alone for 20 min and then with caerulein 15 ng/kg, h for further 20 min. From a basal level of 28 +/- 13 mu mol/5 min, secretin by itself significantly increased pancreatic bicarbonate to 182 +/- 24 mu mol/5 min. A further significant two-fold increase to 396 +/- 50 mu mol/5 min was observed during caerulein. The increment in plasma secretin of 2.1 +/- 0.3 pmol/l is comparable to the rise that may be observed post-prandially. It is concluded that secretin in combination with cholecystokinin may indeed play a physiological role in the regulation of duodenal pH.     

Effect of duodenal acidification on plasma secretin and pancreatic polypeptide in man (author's transl)

Plasma secretin and pancreatic polypeptide has been measured in 10 normal volunteers before and after intraduodenal acidification. Secretin rose rapidly from 1,4 +/- 0,44 to 11,2 +/- 1,24 pmol/l (+/- SEM). PP also rose significantly from 39,0 +/- 3,0 to 52.3 +/- 5,8 pmol (paired p less than 0.01) but much slower and to a lesser extent than seen after a meal. This supports the conclusion that acid plays no important role in control of postprandial PP release.     

Effect of secretin and jejunal acidification on gastric and pancreatic secretion in man

The inhibitory effect of intravenous secretin and intrajejunal acid infusion on basal and pentagastrin-induced gastric acid secretion as well as the stimulatory influence of both infusions on pancreatic flow rate and bicarbonate output were compared in two groups of healthy subjects.

Secretin strongly inhibited basal acid output and slightly decreased pentagastrin induced gastric secretion.

Intrajejunal acid infusion did not affect the gastric secretion but resulted in an increase in pancreatic volume flow and bicarbonate output reaching about 40% of the pancreatic response to secretin¹ infused intravenously in a dose of 2 units per kilogram per hour.

It is concluded that this provides evidence that secretin is a strong inhibitor of spontaneous gastric acid secretion and that acid in the jejunum causes the release of secretin in man.

     

Inhibition of secretin release and pancreatic bicarbonate secretion by somatostatin infusion in man.

Five healthy students were investigated on two different days with or without a constant infusion of somatostatin (500 microgram/h) into an arm vein a fluoroscopically placed Lagerl?f tube was used for the collection of gastric and duodenal juice. After 30-min basal period, 40 ml 100 mmol/l HCl was infused into the midpart of the duodenum over 5 min through a thin catheter attached to the tube. Plasma immunoreactive secretin was measured by radioimmunoassay employing 125I-labelled synthetic secretin, antibody against synthetic secretin, and standards prepared from pure natural porcine secretin. Secretin levels without somatostatin infusion were 4.6+/-0.7 pmol/l (mean+/-S.E.M.) basally and rose to a peak of 21.8+/-6.2 pmol/l after duodenal acidification (p less than 0.05) and with somatostatin infusion were 4.4+/-0.4 pmol/l basally and rose to a peak of 6.7+/-1.7 pmol/l (n.s.) after duodenal acidification. Pancreatic bicarbonate output increased from 8.0+/-2.5 mumol/min (mean+/-S.E.M.) to 283+/-44 mumol/min without somatostatin infusion (p less than 0.05) and from 6.7+/-2.1 mumol/min to 70+/-13 mumol/min somatostatin (p less than 0.05). This study shows that somatostatin (500 microgram/h can inhibit the release of secretin and the pancreatic bicarbonate secretion after duodenal acidification in man.     

Pancreatic secretion obtained by endoscopic cannulation of the main pancreatic duct and secretin release after duodenal acidification in man.

The main pancreatic duct was cannulated in 12 individuals with a teflon catheter by means of a side-viewing duodenscope. Six individuals received a duodenal infusion of 40 ml 100 mmol/l HCl over 5 min, while the other six served as controls for basal pancreatic secretion. Pancreatic juice was collected in 5-min samples, and blood was frequently drawn for radioimmunoassay of immunoreactive secretin (IRS). In the control group, during 20-min cannulation of the main pancreatic duct, no effect was seen on basal secretion of water, bicarbonate, or alpha-amylase--nor did the IRS levels change. After duodenal acidification there was a significant increase in IRS (p less than 0.02), reaching the highest level at 7 min. The mean flow rate, bicarbonate concentration, and bicarbonate output showed a significant increase as compared to the control group (p less than 0.02), the highest levels being reached in the third 5-min period after the start of the duodenal acidification. The alpha-amylase output was also significantly higher after acidification (p less than 0.02) than in the control group, but the mean alpha-amylase concentration decreased after acidification, reaching its nadir in the third 5-min sample (p less than 0.02). The present results demonstrate a basal and HCl-stimulated pancreatic secretion collected by endoscopic cannulation of the main pancreatic duct in man together with plasma IRS levels.     

Plasma secretin and pancreatic bicarbonate response to exogenous secretin in man.

The dose response of duodenal bicarbonate production during synthetic porcine secretin infusions was studied in six healthy volunteers and related to plasma secretin immunoreactivity. Secretin was infused in each individual at four different doses from 0-1 to 2-7 CU/kg/h, each infusion lasting for 60 minutes. Mean maximal bicarbonate secretion was 33 +/- 4 mEq/h. The secretin plasma level for half maximal bicarbonate response was estimated to be 22 pmol/l. As this level is reported to be achieved by intraduodenal acidification in man, it is concluded that secretin may well play a part in the control of duodenal pH.     

Physiological significance of secretin in the pancreatic bicarbonate secretion. II. Pancreatic bicarbonate response to a physiological increase in plasma secretin concentration.

The pancreatic response to physiological concentrations of secretin obtained after minute boluses of exogenous secretin was studied in 16 normal volunteers. Output of bicarbonate into the duodenum was measured by duodenal aspiration in 5 subjects and by endoscopic cannulation of the pancreatic duct in 11 subjects. Pure natural porcine secretin was injected intravenously in doses of 125, 250, and 500 fmol x kg-1 body weight (0.0013, 0.0027, and 0.0054 clinical units x kg-1). All three doses of secretin increased plasma secretin concentration, duodenal bicarbonate concentration, and duodenal bicarbonate output significantly. The bicarbonate output measured by the two techniques did not differ significantly. The increments in median plasma secretin concentration were 1.6, 3.0, and 6.4 pmol x 1(-1) after secretin, 125, 250 and 500 fmol x kg-1, and the corresponding 15-min bicarbonate output 283, 442, and 1435 micromol, respectively. The concentrations of secretin in plasma found after these doses of secretin are of the same order of magnitude as the secretin concentrations found during physiological conditions in man. It is concluded that the physiological concentrations or secretin influence pancreatic bicarbonate secretion.     

The effect of vasoactive intestinal peptide, secretin, and glucagon on human duodenal bicarbonate secretion

Duodenal luminal acidification increases duodenal mucosal bicarbonate production and also releases both secretin and vasoactive intestinal peptide (VIP). The effect of these two structurally similar peptides on human duodenal bicarbonate production has not been examined in humans. Our purpose was therefore to assess the effect of VIP and secretin and also glucagon, a homologous hormone, on human duodenal bicarbonate secretion. A 4-cm portion of either proximal or distal duodenum was isolated and perfused with iso-osmolar NaCl. Pure porcine VIP (200 and 400 pmol/kg-h intravenously) significantly increased proximal duodenal bicarbonate secretion. Although secretin (0.01 to 0.18 CU/kg-h intravenously) markedly increased pancreatic bicarbonate secretion, it failed to alter duodenal mucosal bicarbonate output in either the proximal or the distal duodenum. Glucagon (1 to 8 micrograms/kg-h intravenously) did not affect proximal duodenal mucosal bicarbonate output. It is concluded that VIP, but neither secretin nor glucagon, significantly stimulates human duodenal mucosal bicarbonate secretion.     

Effect of intraduodenal bile and Na- taurodeoxycholate on exocrine pancreatic secretion and on plasma levels of secretin, pancreatic polypeptide, and gastrin in man

The effect of intraduodenally administered cattle bile (CB) and Na-taurodeoxycholate (TDC) on basal pancreatic secretion and plasma levels of secretin, pancreatic polypeptide (PP), and gastrin were investigated on two separate days in 10 fasting volunteers. Doses of 2-6 g CB and 200-600 mg TDC were given intraduodenally at 65-min intervals. Volume, bicarbonate, lipase, trypsin, amylase, and bilirubin were measured in 10-min fractions of duodenal juice, and GI peptides determined by radioimmunoassay. CB and TDC enhanced significantly and dose-dependently volume, bicarbonate and enzyme secretion, and plasma secretin and PP levels. In contrast, plasma gastrin showed only a marginal increase. We conclude that the hydrokinetic effect of intraduodenal CB and TDC is at least partially mediated by secretin. Gastrin could be ruled out as a mediator of the ecbolic effect, whereas other GI peptides, primarily CCK, and/or neural mechanisms must be considered possible mediators. Both pathways may also play a role in the PP release observed.     

Effect of graded amounts of acid instilled into the duodenum on pancreatic bicarbonate secretion and plasma secretin in duodenal ulcer patients and normal subjects.

Pancreatic bicarbonate secretion and plasma secretin were measured in response to graded amounts of hydrochloric acid (0.94, 1.88, 3.75, and 7.5 mEq per 5 min) instilled directly into the duodenum in duodenal ulcer patients and in normal subjects. These graded amounts of acid produced graded increases in pancreatic bicarbonate in both groups. Mean bicarbonate secretion was significantly greater in the duodenal ulcer patients than in the normal subjects basally and after the lowest dose of hydrochloric acid. Mean (+/- SE) peak 30-min bicarbonate output (in milliequivalents) after duodenal acidification was 3.0 +/- 1.0 in the duodenal ulcer patients and 2.1 +/- 0.6 in the normal subjects (P less than 0.5). A significant (P less than 0.05) increase in plasma secretin occurred after duodenal acidification, but the increase in the duodenal ulcer and normal subjects was not significantly different (P less than 0.2). These results indicate that pancreatic bicarbonate secretion and increase in plasma secretin in response to graded amounts of duodenal acid are at least as great in patients with duodenal ulcer as in normal subjects.     

The unstimulated pancreatic secretion obtained by endoscopic cannulation, and the plasma secretin levels in man.

The technique of collecting juice from the main pancreatic duct by siphonage is described. The juice was collected in 5-min fractions under basal conditions for 20 min (32 subjects) and extended to 60 min (6 subjects). Flow rate and bicarbonate concentration were significantly higher during the first collected samples, whereas concentrations of amylase and protein rose during the first 20 min of the study. All variables remained nearly constant after this period. Immunoreactive secretin (IRS) in peripheral plasma was significantly higher immediately after cannulation of the main pancreatic duct, as compared to the pre-endoscopic level. When the catheter was left in the duct and pancreatic juice drained, the IRS stabilized at a level not significantly different from the pre-endoscopic level. Positive correlations were found between flow rate and plasma level of IRS and between flow rate and bicarbonate concentrations. A negative correlation was found between the flow rate and concentrations of amylase and protein. The higher flow rate, plasma level of IRS, and bicarbonate concentration at the beginning of the examination may be due to the presence of acid and/or bile in the duodenal contents shortly after the endoscope enters the duodenum. Later in the procedure the levels have stabilized, which indicates that little or no acid or bile is passing into the duodenum. It is also concluded that secretin may be one factor responsible for the basal pancreatic secretion in man.     

Action of secretin on pancreatic enzyme secretion in man. Studies on pure pancreatic juice

The action of pure, natural secretin on the pancreatic secretion of enzymes was investigated in six patients with external transduodenal drainage of the main pancreatic duct performed after biliary tract surgery. Secretin infused for five successive 50 minute periods at increasing doses of 0.03, 0.1, 0.3, 0.9 and 2.7 clinical units (CU)/kg/h, produce a dose dependent increase in protein and lipase output. A weak but significant (p less than 0.02) increase of enzyme output above the fasting level was already observed with the lowest dose. The maximal output of protein and lipase, observed with the highest dose of secretin infused, corresponded to about 50% of that induced by maximal doses of cerulein (100 ng/kg/h) plus secretin (1 CU/kg/h). As far as bicarbonate is concerned, the lowest dose of secretin (0.03 CU/kg/h) significantly (p less than 0.001) stimulated bicarbonate output. The dose of 0.9 CU/kg/h of secretin evoked a bicarbonate output of 526 +/- 49 micromol/min; trebling the dose of secretin did not significantly increase the output of bicarbonate above this value. Increasing doses of secretin induced a dose related increase in calcium output. There was a close parallel between calcium and protein outputs, suggesting that the increase in calcium output reflected primarily an increase in the enzyme-associated fraction of pancreatic juice calcium. It is concluded that secretin stimulates pancreatic enzyme secretion in man probably by a direct action on the acinar cells.     

Potentiation effect of cholecystokinin-octapeptide on pancreatic bicarbonate secretion stimulated by a physiologic dose of secretin in humans

We studied the potentiation effect of cholecystokinin-octapeptide and secretin on pancreatic secretion of bicarbonate and trypsin in humans. The pancreatic bicarbonate and trypsin outputs were determined by using a triple-lumen duodenal tube and indicator dilution technique while gastric juice was completely aspirated. When cholecystokinin-octapeptide in varied doses, 2.6, 5.3, 10.9, 26.3, 52.6, and 109.4 pmol . kg-1 . h-1, was added to i.v. infusion of secretin in a physiologic dose, 0.03 clinical units (CU) . kg-1 . h-1, the bicarbonate outputs were significantly greater than those achieved by secretin or cholecystokinin-octapeptide alone or the sum of the bicarbonate outputs produced by each hormone. The potentiation effect of cholecystokinin-octapeptide occurred at the dose of 10.9 pmol . kg-1 . h-1. No further further augmentation on the bicarbonate output occurred when the dose of cholecystokinin-octapeptide was increased in the dose range greater than 10.9 pmol . mg-1 . h-1. No potentiation on pancreatic secretion of trypsin was apparent when the two hormones were given simultaneously. Thus, cholecystokinin-octapeptide in a relatively small dose range potentiated the pancreatic bicarbonate secretion stimulated by a physiologic dose of secretin. The pancreatic enzyme secretion does not appear to be potentiated by two hormones.