Stimulation Of Pancreatic Protein Secretion Research Articles

Administration of two antagonists of the cholecystokinin(B)/gastrin receptor does not totally inhibit the pancreatic response to a meal in the pig.

The role of the cholecystokinin B (CCK(B))/gastrin receptor in the pancreatic response to a standard meal was investigated in the pig. Twenty-four pigs were prepared surgically for the collection of the pancreatic juice and an intravenous perfusion. On experimental days, the pigs were perfused with one of two CCK(B)antagonists (L-365,260 or PD 135156) or the vehicle for 2 hours. We offered them a standard meal 30 minutes after the beginning of the perfusion. The pancreatic secretion was collected for 4 hours starting 30 minutes before the perfusion. Its volume was recorded, and the protein concentrations were assayed. Neither antagonist totally abolished the postprandial peak of the pancreatic protein. We suggest that the stimulation of pancreatic protein secretion by a meal is not mediated by CCK(B)/gastrin receptors. Because we previously showed that the CCK(A)receptor antagonist MK329 was no more able to abolish this response, CCK is probably not responsible for this response.

Reduced reactivity of pancreatic exocrine secretion in response to gastrointestinal hormone in WBN/Kob rats

We compared pancreatic exocrine secretion in 5-month-old WBN/Kob rats, a model of chronic pancreatitis, with that in Wistar rats of the same age in a conscious state. Basal pancreatic secretion and pancreatic wet weight in WBN/Kob rats were lower than the values for Wistar rats. There was no difference in plasma cholecystokinin (CCK) concentration between the two types of rats. When CCK-8 was intravenously administered, the stimulation of pancreatic protein secretion in WBN/Kob rats was weaker than that in Wistar rats. When bile and pancreatic juice were diverted from the duodenum, the resulting increase in the plasma CCK concentration was similar in both types of rats, but stimulation of the volume and protein output of pancreatic juice in WBN/Kob rats was weaker than that in Wistar rats. In addition, WBN/Kob rats exhibited little increase in pancreatic wet weight because of this diversion. When secretin was intravenously administered, the stimulation of fluid secretion in WBN/ Kob rats was also weaker than that in Wistar rats. The binding of CCK-8 to pancreatic membrane fractions in WBN/Kob rats was much weaker than that in Wistar rats. Histological findings in WBN/Kob rat pancreas showed proliferation of fibrous tissue and atrophy of acinar cells. In conclusion, pancreatic exocrine secretion in response to the gastrointestinal hormones, CCK and secretin, was lower in WBN/Kob rats than in Wistar rats. These findings suggest that the hyposecretion of pancreas in WBN/Kob rats is hyporeaction of pancreatic membrane to gastrointestinal hormones.

Soybean lectin stimulates pancreatic exocrine secretion via CCK-A receptors in rats.

Rats fed raw soy flour (RSF) show pancreatic growth due to excessive cholecystokinin (CCK) release. Soybean trypsin inhibitors are implicated, but rats fed soybean lectin also showed pancreatic growth. Therefore, we studied the effect of soybean lectin on pancreatic protein secretion in anesthetized rats. Intraduodenal administration of 30 mg of RSF stimulated a 1-h integrated rise in pancreatic protein output of 2.2 +/- 1.1 mg/h (mean +/- SE) in rats with bile pancreatic (BP) juice returned to the duodenum. Selective removal of the lectin by affinity to N-acetyl-D-galactosamineagarose abolished the response (-0.1 +/- 0.2 mg/h). Adding back the 84 micrograms of lectin restored the output of 2.2 +/- 0.9 mg/h. With BP juice returned to the duodenum, 84 micrograms of lectin required the added presence of protein and protease inhibitors to have this effect. However, when BP juice was not returned, 84 micrograms of lectin given alone produced a pancreatic response of 3.2 +/- 1.3 mg/h. Plasma CCK concentrations rose significantly from 6.6 +/- 1.9 to 14.3 +/- 2.9 pmol/l, and the pancreatic response was abolished by CCK-A receptor blockade (0.0 +/- 0.1 mg/h). We conclude that soybean lectin plays a major role in the acute stimulation of pancreatic protein secretion by RSF. The lectin releases CCK and the effect is mediated by CCK-A receptors.

The involvement of endogenous nitric oxide in vagal-cholinergic stimulation of exocrine and endocrine pancreas in dogs.

Previous studies showed that nitric oxide (NO), synthesized from L-arginine (L-arg) by NO synthase (NOS) in vascular epithelium and nerve terminals, affects exocrine pancreatic secretion, but its role in control of endocrine pancreas has not been studied. In this study, the role of NO in the control of pancreatic secretion in response to vagal-cholinergic stimulation and duodenal infusion of nutrients was determined in conscious dogs with chronic pancreatic fistulas. Sham feeding (SF), urecholine iv infusion, and duodenal perfusion with nutrients were used to stimulate the pancreatic protein secretion, and insulin and glucagon release in tests without and with iv infusion of NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, L-arg, a substrate of NOS, or their combination was used. SF, urecholine, and duodenal nutrient resulted in the stimulation of pancreatic protein secretion reaching, respectively, 50, 20, and 42% of cerulein maximum. Infusion of L-arg almost doubled the basal protein secretion and tended to increase the secretory response to SF and duodenal nutrient. After infusion of L-NNA, the pancreatic secretory responses to SF, urecholine, and duodenal nutrient were inhibited by about 70, 30, and 75%, respectively. When L-arg was combined with L-NNA, the reduction in pancreatic secretion by L-NNA was significantly attenuated. SF resulted in a significant rise in plasma insulin and glucagon, and this response was completely abolished by L-NNA infusion. Urecholine and duodenal nutrient also resulted in a marked increment in plasma insulin and glucagon, the insulin (but not glucagon) increment being abolished by the pretreatment with L-NNA and reversed by the addition of L-arg.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of CCK in the regulation of secretion and adaptation in the pig pancreas.

The effect of cholecystokinin (CCK) on the pancreas was investigated in the pig in two experiments. Fifteen pigs were fed a diet containing 17 or 48% protein with or without MK329 (4.5 mg per meal). MK329 enhanced the postprandial peak of plasma CCK during the first 30 min, but pancreas adaptation to high protein was not affected. Sixteen pigs were divided into two groups: 12 pigs were infused with CCK-8 + secretin for 1 h and four pigs received a standard meal. In both groups, pancreatic secretion tests were performed under infusion of the vehicle alone or with MK329. After CCK + secretin, MK329 (65-500 micrograms/kg/h) did not alter CCK plasma levels and reduced the early pancreatic protein response by about 30%. Enzyme outputs in pancreatic juice were modestly affected by MK329. After the meal, MK329 (500 micrograms/kg/h) doubled the postprandial peak of plasma CCK and lowered the pancreatic protein output by 35-40% for the first 30 min. We suggest that (a) pancreatic adaptation to high dietary protein is not mediated via CCK-A receptors and (b) the stimulation of pancreatic protein secretion by a meal or by exogenous CCK-8 is mediated partly by CCK-A receptors.

Integration of postprandial function in the proximal gastrointestinal tract. Role of CCK and sensory pathways.

Cholecystokinin (CCK) stimulates vagal afferent fiber discharge, both gastric and intestinal, which seems to result in reflex decrease in gastric motility, gastric acid secretion, and stimulation of pancreatic protein secretion. Endogenous release of CCK by fat or soybean trypsin inhibitor also alters function by way of a capsaicin-sensitive pathway. We suggest that CCK is released locally from the intestine and acts locally or systemically to stimulate vagal afferent fiber discharge to alter proximal gastrointestinal function (Fig. 14). In this way, in addition to its effect on food intake, CCK and the neural pathway integrate function in the proximal gastrointestinal tract, regulating the entry of food into the duodenum to ensure effective digestion and absorption.

Role of cholecystokinin in the inhibition of gastric acid secretion in dogs.

1. This study was designed to determine the involvement of cholecystokinin (CCK) in the gastric secretory responses to exogenous and endogenous secretagogues in conscious dogs with chronic gastric fistulae (GF), pancreatic fistulae (PF) and Heidenhain pouches (HP). 2. A meal of meat or intragastric application of peptone (300 mosM) increased secretion of HCl from the HP and pancreatic secretion of protein and plasma levels of gastrin, CCK and somatostatin. 3. The CCK receptor antagonist L-364,718 caused a further increase in the postprandial HCl secretion from the HP and in the plasma levels of gastrin and CCK but pancreatic output of protein and plasma concentration of somatostatin were significantly reduced. 4. Addition to intragastric peptone of 10% oleate or its acidification to pH 3.0 profoundly inhibited the HP secretion and gastrin release but significantly increased pancreatic secretion of protein and plasma levels of CCK and somatostatin. Administration of L-364,718 reversed the fall in the HP secretion and plasma gastrin while significantly attenuating pancreatic protein secretion and plasma somatostatin levels. 5. Intragastric administration of hyperosmolar (1200 mosM) peptone also inhibited HCl secretion from the HP but this was not affected by L-364,718. 6. Exogenous CCK and bombesin (but not gastrin) caused a small increase in HCl secretion from the HP and marked stimulation of pancreatic protein secretion accompanied by a significant rise in plasma levels of gastrin, CCK and somatostatin. Administration of L-364,718 resulted in a further increase in the HCl response of HP to bombesin and in plasma levels of gastrin and CCK but caused a reduction in plasma levels of somatostatin. 7. We conclude that CCK released by a meal of meat, intragastric peptone, oleate or acidified peptone and intravenous bombesin exerts tonic inhibitory influences on gastric acid secretion and that this effect is mediated, at least in part, by somatostatin.

Preparation and Characterization of a Fully Active Biotinylated Probe of Cholecystokinin

In this study we describe the synthesis and purification of biotinylated cholecystokinin-8 (Bio-CCK-8) and characterize its use as a probe for the pancreatic cholecystokinin receptor. CCK-8 (0.1 umoles) was reacted with either radiolabeled d-[8,9(-3)H]biotin succinimide ester (0.5 umoles) or N-hydroxysuccinimidyl-biotin in dimethylformamide and triethylamine, and purified by anion exchange chromatography. Concentrations of Bio-CCK-8 and CCK-8 needed for half-maximal inhibition of [125]I-CCK-8 binding to pancreatic membranes were the same (1.0 and 1.3 nM). Bio-CCK-8 retained full biological activity as determined by stimulation of pancreatic protein secretion from rats, and the biotin group bound to CCK-8 retained its high sensitivity for avidin.

Role of Cholecystokinin in Bombesin-Stimulated Pancreatic Enzyme Secretion in Conscious Rats

Since bombesin is a potent stimulus of cholecystokinin (CCK) secretion, it is assumed that the stimulatory effect of bombesin on pancreatic protein secretion is mediated by CCK. This study was undertaken to determine in the conscious rat with a cannulated pancreatic duct the role of CCK in the stimulation of pancreatic protein secretion by bombesin. Infusion of 18 pmol/kg/30 min of bombesin into rats stimulated pancreatic protein secretion from 6.7 +/- 1.1 to 9.9 +/- 0.4 mg/30 min (p less than 0.05). This stimulation of pancreatic protein secretion was accompanied by a significant increase in plasma CCK, measured by a specific and sensitive radioimmunoassay, from 3.2 +/- 0.2 to 4.7 +/- 0.2 pM (p less than 0.01). When a similar plasma CCK increment as during infusion of bombesin (1.5 +/- 0.2 pM) was achieved by infusion of 6 pmol/kg/30 min of exogenous CCK (1.6 +/- 0.3 pM), pancreatic protein secretion increased only from 6.9 +/- 0.7 to 7.6 +/- 0.7 mg/30 min (p less than 0.05). To achieve a pancreatic protein secretion similar to that during bombesin, large doses of exogenous CCK (24 pmol/kg/30 min) were needed, resulting in considerably higher plasma CCK concentrations of 10.9 +/- 0.7 pM. It is concluded that CCK is unlikely to play a significant role in the stimulation of pancreatic protein secretion by bombesin in the rat.

Cholecystokinin receptors and vagal nerves in control of food intake in rats

This study was designed to determine the specificity and physiological nature of short-term satiety effects of cholecystokinin (CCK) in rats with intact and transected vagal nerves. Rats with-the gastric fistulas, closed or open, were used for normal feeding or sham feeding of liquid meal offered for 30 min. CCK-8 (0.5-10 nmol/kg) injected intraperitoneally (ip) 15 min before feeding inhibited food intake dose dependently in both normal-fed and sham-fed rats at a minimal inhibitory dose of 1 nmol/kg. CCK-8 at the same doses caused a potent stimulation of pancreatic protein secretion, reaching maximum at a dose of approximately 0.5 nmol/kg. Pretreatment with a potent CCK receptor antagonist, L-364,718 (2.5 mg/kg ip), increased food intake during normal feeding (but not sham feeding) and almost completely blocked the satiety and pancreatic stimulatory effects of CCK. When feeding was preceded by intragastric administration of proteinase inhibitor (Foy-305, 200 mg/kg), food preload, or diversion of bile-pancreatic secretion to the exterior, there was a significant increase in the plasma level of CCK and an inhibition of food intake by about 36, 78, and 25%, respectively. Pretreatment with L-364,718 completely abolished this inhibition by Foy-305 and bile-pancreatic diversion and reduced that caused by food preload. Among other gut peptides given ip (10 nmol/kg) only bombesin reduced food intake, whereas gastrin, secretin, gastric inhibitory polypeptide (GIP), pancreatic polypeptide (PP), and peptide YY (PYY) were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulatory effect of hypercalcemia on pancreatic secretion is prevented by pretreatment with cholecystokinin and cholinergic agonists.

Recently, we demonstrated that hypercalcemia causes marked stimulation of feline exocrine pancreatic secretion, and that this effect is absent when a large dose of cholecystokinin (CCK) is infused prior to induction of hypercalcemia. To investigate this effect in more detail, anesthetized cats were given calcium i.v. after preadministration of CCK or urecholine (a cholinergic agonist) at specific doses, or of saline as a control. We found that the hypercalcemia-induced stimulation of pancreatic protein secretion was abolished after preadministration of CCK at large doses. After the prestimulus dose was decreased or the calcium dose was increased, however, the pancreatic secretory response to hypercalcemia was preserved. In contrast, the response to a submaximal dose of CCK was unchanged after prestimulation with a large dose of CCK. Similar results were obtained when urecholine instead of CCK was used as prestimulus. These findings indicate that loss of pancreatic responsiveness to hypercalcemia following prestimulation with CCK is dependent on doses of both prestimulus and calcium used, and that it is not specific for prestimulation with CCK but also inducible by cholinergic agonists. They further suggest that this phenomenon is not due to exhaustion of pancreatic secretory capacity, but may reflect decreased sensitivity to the hypercalcemic stimulus instead.

Modifications in pancreatic enzyme proportions following secretory stimulations.

The short-term influence of repeated secretory stimulations of the pancreas on pancreatic enzyme content was studied in the rat. The animals received 10 successive injections of either cholecystokinin-pancreozymin (CCK-PZ), secretin, CCK-PZ plus secretin, caerulein or pilocarpine. The pancreatic enzyme content was determined the next morning. CCK-PZ, with or without secretin, caerulein and pilocarpine had a similar influence increasing the chymotrypsinogen concentration in the pancreas twofold, while lipase and amylase concentrations increased by only 50 and 25%, respectively. Fasted and fed animals responded similarly. Secretin, a mostly ductal secretagogue, was without influence on the pancreatic enzyme composition. Thus, the mere stimulation of pancreatic protein secretion seems to result in a rapid change in enzyme composition in the pancreas.