Physiological plasma concentrations of cholecystokinin stimulate pancreatic enzyme secretion and gallbladder contraction in man

The present study was undertaken to determine whether infusion of cholecystokinin (CCK) to plasma concentrations comparable to those found after a meal stimulates pancreatic enzyme secretion and gallbladder contraction. Plasma CCK concentrations were measured by radioimmunoassay using antibody T204, which binds to all carboxyl-terminal CCK-peptides containing the sulfated tyrosine region. Ingestion of a standardized test meal in 7 normal subjects induced significant increases in plasma CCK from 2.0 +/- 0.2 pmol/l to levels between 4.6 +/- 0.6 and 7.3 +/- 1.0 pmol/l (p less than 0.05-p less than 0.0005). Infusion of 2.5 pmol/kg X h CCK 33 resulted in significant increases in plasma CCK from 2.0 +/- 0.2 to 3.9 +/- 0.3 pmol/l (p less than 0.0005). This infusion of CCK induced significant increases in trypsin secretion from 0.5 +/- 0.1 to 1.4 +/- 0.2 KU/15 min (p less than 0.005) and in bilirubin output from 1.6 +/- 0.7 to 30.3 +/- 8.0 mumol/15 min (p less than 0.05). It is concluded that physiological plasma concentrations of CCK stimulate pancreatic enzyme secretion and gallbladder contraction in man.     

The cholecystokinin receptor antagonist CR1409 increases plasma cholecystokinin in rats

This study was undertaken to determine whether plasma cholecystokinin (CCK) levels are affected by the administration of the CCK-receptor antagonist CR1409 to rats. Infusion of 0.19, 0.94 and 4.75 mg/kg.h CR1409 for 30 min each into 6 conscious rats increased (P less than 0.05) plasma CCK from 1.3 +/- 0.5 to 6.0 +/- 1.2, 5.4 +/- 1.2, and 5.4 +/- 1.0 pM, respectively. In a subsequent study infusion of stepwise increasing lower doses of 0.3, 1.5, 7.5, 37.5 and 187.5 micrograms/kg.h CR1409 for 30 min each into 6 other rats dose-dependently increased (P less than 0.05) plasma CCK from 1.4 +/- 0.3 to 3.1 +/- 0.6, 4.1 +/- 0.8, 5.4 +/- 1.0, 5.9 +/- 0.8 and 7.1 +/- 1.1 pM, while infusion of saline did not affect plasma CCK concentrations. We therefore conclude that the CCK-receptor antagonist CR1409 increases plasma CCK in the rat.     

Dose-related involvement of CCK in bombesin-induced pancreatic growth.

We examined the role of CCK in bombesin-induced pancreatic growth in rats using the CCK receptor antagonist L-364,718. Rats (155 +/- 1 g, 8-10 per group) received subcutaneous injections every 8 h for 5 days with bombesin (0.6, 1.7 and 5 nmol/kg) or bombesin in combination with L-364,718 (1 mg/kg). After 5 days the pancreas was removed and pancreatic weight, protein content, DNA, amylase and chymotrypsin contents were determined. Bombesin produced a significant increase (48-475%) of pancreatic weight, tissue contents of protein, DNA, amylase and chymotrypsinogen (F = 82, P less than 0.001). When a large dose of bombesin (5 nmol/kg) was combined with L-364,718 a significant inhibition (up to 70%) of all tissue parameters was observed (P less than 0.001). L-364,718 did not affect the growth response to a small dose of bombesin (0.6 nmol/kg). Plasma CCK levels 15 min after a single injection of bombesin (0.6, 1.7 and 5 nmol/kg) were significantly increased in response to the 5 nmol/kg dose (2.0 +/- 0.7 to 3.4 +/- 0.8 pM, F = 6.9, P less than 0.01). No increases of CCK plasma levels were found in response to the 0.6 and 1.7 nmol/kg doses of bombesin, corresponding to the lack of effects of L-364,718 on growth parameters at these doses. Measuring the time-course of CCK plasma levels after a single injection of 5 nmol/kg bombesin revealed an increase from basal values of 1.4 +/- 0.3 pM to maximal levels of 3.5 +/- 0.5 pM after 15 min (F = 7.1, P less than 0.001). Values returned to basal after 60 min. These results suggest that low doses of bombesin act directly at the acinar cell or through release of non-CCK growth factors whereas high doses of bombesin act in part through CCK release.     

Effect of the specific cholecystokinin-receptor antagonist loxiglumide on bombesin stimulated pancreatic enzyme secretion in man.

We have investigated the effects of the specific cholecystokinin (CCK) receptor antagonist loxiglumide on basal and bombesin stimulated pancreatic enzyme secretion, bilirubin output and plasma CCK release in six healthy subjects. The data were compared with those obtained in control experiments where saline was infused instead of loxiglumide. Basal amylase output (4.7 +/- 0.8 kU/45 min), trypsin output (2.9 +/- 0.8 kU/45 min) and bilirubin output (7.7 +/- 2.8 mmol/45 min) gradually declined during infusion of loxiglumide to values of 1.3 +/- 0.3 kU/45 min, 0.5 +/- 0.1 kU/45 min and 0.4 +/- 0.0 mmol/45 min, respectively, reaching statistical significance (P less than 0.05) in the 30 to 45-min period after the start of the loxiglumide infusion. In the control experiments saline infusion failed to influence basal amylase, trypsin and bilirubin output, while bombesin stimulated amylase output from 4.7 +/- 0.8 kU/45 min to 25.1 +/- 5.1 kU/45 min (P less than 0.05), trypsin output from 2.9 +/- 0.8 kU/45 min to 11.6 +/- 2.0 kU/45 min (P less than 0.05) and bilirubin output from 7.7 +/- 2.8 mmol/45 min to 68.0 +/- 16.0 mmol/45 min (P less than 0.05). Loxiglumide failed to significantly influence bombesin stimulated amylase output (36.7 +/- 9.0 kU/45 min) and trypsin output (8.3 +/- 2.9 kU/45 min), but almost abolished bilirubin output (9.7 +/- 3.6 mmol/45 min) (P less than 0.05). Basal plasma CCK (2.4 +/- 0.1 pM) was not significantly influenced by loxiglumide (2.4 +/- 0.2 pM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Determination of plasma cholecystokinin (CCK) concentrations by bioassay and radioimmunoassay in man. A critical evaluation.

The present investigation was designed to perform a direct comparison of a rat pancreatic acini bioassay system and a specific CCK radioimmunoassay (antiserum G-160) for the measurement of fasting and meal-stimulated plasma CCK in the presence and absence of the CCK receptor antagonist loxiglumide. The G-160 CCK antiserum is directed against the C-terminal O-sulfated tyrosine residue of the CCK molecule which is essential for full bioactivity of CCK peptides. For plasma extraction prior to bioassay measurement, hydrophobic reverse-phase chromatography on octadecylsilane cartridges was employed and resulted in simultaneous adsorption and elution of both CCK peptides and loxiglumide with recoveries of 87.5 +/- 9% and 75.0 +/- 5.9%, respectively. In the absence of loxiglumide, fasting and meal-stimulated values for CCK-like bioactivity and CCK-immunoreactivity (IR-CCK) were nearly identical (basal values: 1-2 pmol/l; meal-stimulated plateau levels: 4-6 pmol/l). After intravenous infusion of loxiglumide (30 mg/kg/h for 10 min, 10 mg/kg/h thereafter), resulting in plasma steady state levels of 200-300 mumol/l, meal-stimulated CCK-like bioactivity was undetectable, whereas IR-CCK levels were augmented 6.5-fold. In the bioassay system, standard samples containing 50 mumol/l loxiglumide produced complete inhibition of acinar lipase release in response to 50 pmol/l synthetic CCK-8. We conclude, that postprandial circulating non-CCK-like factors do not contribute significantly to the direct receptor-mediated stimulation of exocrine pancreatic secretion. The good agreement of CCK-like bioactivity and IR-CCK levels in the absence of loxiglumide confirms the sensitive and specific recognition of bioactive CCK peptides by the G-160 antiserum and suggests that this antibody exerts binding characteristics probably similar to a pancreatic acinar receptor.     

A secretin releasing peptide exists in dog pancreatic juice

Canine pancreatic juice has been shown to stimulate exocrine pancreatic secretion in the dog. In the present study we investigated whether there is a secretin-releasing peptide in canine pancreatic juice. Pancreatic juice was collected from the dogs with Thomas gastric and duodenal cannulas while pancreatic secretion was stimulated by intravenous administration of secretin at 0.5 microg/kg/h and CCK-8 at 0.2 microg/kg/h, respectively. The pancreatic juice was separated into three different molecular weight (MW) fractions (Fr) by ultrafiltration (Fr 1; MW > 10,000, Fr 2; MW=10,000-4,000 and Fr 3; MW < 4,000), respectively. All the fractions were bioassayed in anesthetized rats. Fraction 3 dose-dependently and significantly stimulated pancreatic juice flow volume from 78.0% to 99.4% (p<0.05) and bicarbonate output from 128.9% to 202.1% (p<0.01), respectively. Plasma secretin concentration also increased from 1.2 +/- 0.5 pM to 5.0 +/- 0.8 pM and 6.0 +/- 1.0 pM (p<0.05). None of these fractions increased pancreatic protein secretion or plasma CCK level. The stimulatory effect of Fraction 3 on pancreatic secretion and the release of secretin was completely abolished by treatment with trypsin (1 mg/ml for 60 min at 37 degrees C) but not by heating (100 degrees C, 10 min). Intravenous injection of a rabbit anti-secretin serum, which rendered plasma secretin almost undetectable in rat plasma, also abolished Fr 3-stimulated pancreatic secretion of fluid and bicarbonate secretion. These observations suggest that a secretin-releasing peptide exists in the canine pancreatic juice. It is trypsin-sensitive and heat-resistant. This peptide may play a significant physiological role on the release of secretin and regulation of exocrine pancreatic secretion.     

Effect of pancreatic enzyme supplementation on postprandial plasma cholecystokinin secretion in patients with pancreatic insufficiency

To test the hypothesis, based on studies in healthy man and dog, that patients with impaired digestion due to severe pancreatic insufficiency have impaired postprandial cholecystokinin (CCK) secretion that can be improved by the addition of pancreatic enzymes, we have studied plasma CCK responses to a test meal with and without addition of pancreatic enzymes in 10 patients with pancreatic insufficiency and steatorrhea, in 8 patients with chronic pancreatitis without steatorrhea, and in 6 healthy subjects. The patients with steatorrhea had a significantly (P less than 0.001) lower integrated plasma CCK response to the meal (177 +/- 23 pM.150 min) than the healthy subjects (468 +/- 41 pM.150 min), while patients with chronic pancreatitis without steatorrhea had an intermediate integrated postprandial CCK secretion (327 +/- 101 pM.150 min). Addition of pancreatic enzymes to the meal significantly augmented the integrated CCK response in both the patients with steatorrhea to 483 +/- 72 pM.150 min (P less than 0.01) and in those without steatorrhea to 480 +/- 85 pM.150 min (P less than 0.05). These values were not significantly different from those in the healthy subjects (521 +/- 86 pM.150 min). Integrated CCK secretion in the three groups during bombesin infusion was similar (patients with steatorrhea 134 +/- 23 pM.20 min, patients without steatorrhea 131 +/- 33 pM.20 min, and healthy subjects 146 +/- 28 pM.20 min), indicating a normal capacity to secrete CCK in response to a humoral stimulus. These data are in agreement with the suggestions from previous studies that digestion of nutrients by pancreatic enzymes plays an important role in the regulation of plasma CCK secretion after feeding.     

Molecular forms of cholecystokinin in human plasma during infusion of bombesin

Bombesin is a tetradecapeptide with stimulatory actions on several gastrointestinal functions. Infusion of bombesin (60 pmol/kg. 20 min) into 7 normal subjects induced significant increases in plasma cholecystokinin (CCK) as measured with 2 sequence-specific radioimmunoassays. Employing antibody 1703, specific for carboxyl-terminal CCK-peptides containing at least 14 amino acid residues, plasma CCK concentrations rose from 0.8 +/- 0.2 pmol/l to 9.9 +/- 1.7 pmol/l (p less than 0.005), while using antibody T204, specific for the sulfated tyrosine region of CCK, plasma CCK levels increased from 2.9 +/- 0.5 pmol/l to 12.4 +/- 1.3 pmol/l (p less than 0.005). Plasma samples obtained from 3 subjects during bombesin infusion were fractionated by Sephadex column chromatography. Fractionation revealed 4 molecular forms of CCK: peak I eluted in the void volume and comprised 0-7% of CCK-like immunoreactivity, peak II eluted at 35% and comprised 8-41% of CCK-like immunoreactivity, peak III eluted at 50% and comprised 44-61% of CCK-like immunoreactivity, and peak IV eluted at 75% and comprised 15-27% of CCK-like immunoreactivity. Radioimmunoassay with a carboxyl-terminal CCK-antibody fully cross-reacting with gastrin did not reveal additional molecular forms of CCK. Since both the carboxyl-terminus and the sulfated tyrosine region are required for biological activity of CCK, it is likely that all these molecular forms of CCK possess biological activity.     

CCK and PYY do not participate in the delayed inhibition of pancreatic secretion, after stimulation by duodenal oleic acid infusion.

The role played by CCK in the stimulation of pancreatic secretion by duodenal infusion of oleic acid in conscious rats was studied using a potent and specific CCK receptor antagonist. CR-1409 did not alter basal secretion, which does not require CCK. The three doses of CR-1409 that were used (2, 4 and 8 mg/kg/h) suppressed the protein response to duodenal infusion of oleic acid and significantly enhanced the delayed inhibition normally observed in control rats (-81%, -87% and -88% vs. -51% of basal in controls). CR-1409 dose-dependently reduced the volume of pancreatic secretion after duodenal infusion of oleic acid (0.40 +/- 0.02, 0.36 +/- 0.02, 0.34 +/- 0.03 vs. 0.48 +/- 0.04 ml/30 min for 2, 4, 8 mg/kg/h and controls, respectively) and revealed a delayed inhibition of volume and a slight reduction of bicarbonate secretion. CCK appears to be directly responsible for the protein and also water response to duodenal infusion of oleic acid, and to be indirectly involved in bicarbonate stimulation. PYY antiserum significantly augmented protein output after duodenal infusion of oleic acid (10.75 +/- 1.40, 14.10 +/- 1.60 vs. 8.60 +/- 1.20 mg/30 min, 1 microliter, 2 microliters and controls), but failed to modify the delayed inhibition: PYY modulates the response to duodenal infusion of oleic acid and is not involved in the delayed inhibition, which was shown to be also present for volume, but which is normally masked by the action of CCK.     

Effects of cholecystokinin octapeptide on the pancreatic exocrine secretion in the pig

In conscious pigs, intravenous infusion of serial doses of cholecystokinin octapeptide (CCK8; 2.9-232.3 pmol.kg-1.min-1) upon a background of secretin resulted in a linear increase of plasma CCK-like immunoreactivity (CCK-LI) concentration and evoked a dose-related increase of pancreatic volume and bicarbonate and protein outputs. The threshold plasma CCK-LI concentration for significant pancreatic response was 103.8 +/- 10.2 pM using a CCK8 dose of 8.8 pmol.kg-1.min-1. The maximum pancreatic response was observed for a plasma CCK-LI level of 498.0 +/- 15.3 pM using 77.2 pmol CCK8.kg-1.min-1. In anesthetized pigs, the threshold plasma CCK-LI concentration for pancreatic response was 1500 pM (actual CCK8 dose of 60.3 pmol.kg-1.min-1). The physiological relevance of this finding was assessed by comparing the food-induced increase of pancreatic secretion with that of plasma CCK-LI. Food ingestion was followed by a sharp pancreatic response and by a progressive increase of plasma CCK-LI to a peak increment of about 15 pM. Gel chromatography of portal and peripheral plasma from fed animals revealed three major peaks in the volumes of CCK33/39 and CCK8, and in a volume intermediate between CCK33/39 and CCK8. An additional minor component eluted ahead of CCK33/39. CCK8, which is one of the CCK components released after food intake, appears to be a fairly weak pancreatic stimulant in pigs.     

Effect of atropine and somatostatin on bombesin-stimulated plasma gastrin,cholecystokinin and pancreatic polypeptide in man

Infusion of the neuropeptide bombesin stimulates the secretion of several gastrointestinal hormones by an unknown mechanism. We have investigated the effects of atropine (15 ng/kg as bolus followed by 2.5 ng/kg · 30 min) and somatostatin (125 μg as i.v. bolus followed by 62.5 μg/30 min) on the stimulation of 3 hormones (gastrin, cholecystokinin and pancreatic polypeptide) by 60 pmol/kg · 20 min bombesin in 6 healthy volunteers. Plasma samples for measurement of hormones by sensitive and specific radioimmunoassays were obtained at − 5, 0, 2.5, 5, 7.5, 10, 15, 20, 25 and 30 min. Bombesin induced significant increases in plasma gastrin (12 ± 2 to 34 ± 3 pM; P < 0.0005), cholecystokinin (1.2 ± 0.2 to 8.9 ± 0.7 pM; P < 0.0001) and pancreatic polypeptide (22 ± 4 to 72 ± 19 pM; P < 0.05). There were great differences between the effects of atropine and somatostatin on the hormonal responses to bombesin. Atropine slightly increased the response of gastrin by 19% and that of cholecystokinin by 15%, but strongly inhibited the bombesin-stimulated pancreatic polypeptide secretion by 97%. On the other hand, somatostatin inhibited the bombesin-induced secretion of gastrin by 48%, cholecystokinin by 82% and pancreatic polypeptide by 107%. These results point to considerable qualitative and quantitative differences in the stimulatory mechanisms of bombesin on the hormones studied.     

Effects of pancreatic polypeptide on the pancreatic exocrine secretion stimulated by secretin and cholecystokinin in the conscious pig

Fourteen castrated male Large White pigs, weighing 42.5 +/- 1.0 kg, were fitted with pancreatic and duodenal fistulae for pancreatic secretion studies. Moreover, catheters were placed in a carotid artery for blood sampling and in a jugular vein for peptide infusion. Pancreatic juice was automatically restituted to the animals and continuously sampled for analysis on experimental days. Following an 8-day recovery period, perfusion studies were performed after an overnight fast. After a 30-min basal period, sustained pancreatic flow and protein output were obtained and maintained throughout the assay with secretin (36 pmol/kg/h) and CCK-8 (600 pmol/kg/h) infusion. Then, 200, 400, 600, 800 or 1200 pmol/kg/h of porcine pancreatic polypeptide (PP) were infused for 60 min. Secretin + CCK infusion was continued for 1 h after PP infusion was stopped. Each dose of PP was given on a separate day. Neither pancreatic flow nor bicarbonate output were affected whatever the dose of infused PP. On the contrary, protein concentration and output decreased with the lowest dose of PP (200 pmol/kg/h) and the diminution was more pronounced with the other doses. With 600 pmol/kg/h as well as with 800 and 1200 pmol/kg/h of PP, pancreatic protein output fell to about 20% of values obtained with secretin + CCK. Plasma levels of PP were below or similar to postprandial values for 200, 400 and 600 pmol/kg/h and they were significantly larger with 800 and 1200 pmol/kg/h. Protein concentration and output returned to values obtained with secretin + CCK infusion after cessation of PP infusion. In conclusion, porcine PP given in physiological doses to the pig decreases pancreatic protein output whereas pancreatic flow remains unaffected.     

Neurotensin elevates hepatic bile acid secretion in chickens by a mechanism requiring an intact enterohepatic circulation

Neurotensin (NT), given intravenously at 10-50 pmol/kg per min to anesthetized female chickens equipped with a bile duct fistula, dose-dependently elevated hepatic bile flow and bile acid output but only when the enterohepatic circulation was maintained by returning the bile to the intestinal lumen. Infusion of NT at 10 and 50 pmol/kg per min increased the average hepatic bile acid output over a 30-min period to 138 +/- 11 and 188 +/- 13% of control, respectively. During infusion of NT, plasma levels of immunoreactive NT (iNT) increased in time from the basal level (14 +/- 1.3 pM) to reach steady state at 30 min. There was a near linear relationship between the dose of NT infused and the increment in plasma iNT. In addition, infusion of NT at 40 pmol/kg min gave a plasma level of iNT (approximately/= 88 pM) which was within the range of those observed during duodenal perfusion with lipid (54-300 pM) and near to that measured in hepatic portal blood from fed animals (52 +/- 5 pM). Perfusion of duodenum with lipid released endogenous NT and increased the rate of hepatic bile flow. When NT antagonist SR48692 was given, bile flow rate decreased to the basal level. These results suggest that intestinal NT, released by lipid, may participate in the regulation of hepatic bile acid output by a mechanism requiring an intact enterohepatic circulation.     

The effect of atropine on bombesin and gastrin releasing peptide stimulated gastrin, pancreatic polypeptide and neurotensin release in man

The effects of 1-h infusions of bombesin and gastrin releasing peptide (GRP) at 50 pmol/kg per h and neurotensin at 100 pmol/kg per h on gastrin, pancreatic polypeptide (PP) and neurotensin release in man were determined following either saline or atropine infusion (20 micrograms/kg). Bombesin produced a rise in plasma neurotensin from 32 +/- 6 to 61 +/- 19 pmol/l and of PP from 26 +/- 8 to 36 +/- 7 pmol/l. There was a further rise of plasma PP to 50 +/- 13 pmol/l after cessation of the infusion. GRP had no significant effect on plasma neurotensin, but compared to bombesin, produced a significantly greater rise in plasma PP from 34 +/- 6 to 66 +/- 19 pmol/l during infusion. There was no post-infusional increase. At this dose, GRP was as effective as bombesin in releasing gastrin, although unlike bombesin its effect was enhanced by atropine. Neurotensin produced a rise in plasma PP from 17 +/- 4 to 38 +/- 8 pmol/l. Atropine blocked the release of PP during GRP and neurotensin infusion. Atropine had no effect on neurotensin or PP release during bombesin infusion, but did block the rise in plasma PP following bombesin infusion. We conclude that, in contrast to meal-stimulated neurotensin release, bombesin-stimulated neurotensin release is cholinergic independent. Despite structural homology, bombesin and GRP at the dose used are dissimilar in man in their actions and sensitivity to cholinergic blockade.     

Effect of pancreatic polypeptide-antiserum on bombesin-stimulated pancreatic exocrine secretion in dogs

Bombesin is a potent stimulus of both pancreatic protein secretion and plasma pancreatic polypeptide (PP) release in dogs. Physiological plasma levels of PP have been shown to inhibit pancreatic exocrine secretion in dogs. We examined the question whether the concomitant release of PP exerts a suppressive action on the pancreatic exocrine response to bombesin in dogs by measuring pancreatic exocrine secretion with and without in vivo immunoneutralization of PP with a high affinity PP-antiserum. Bombesin was infused in a dose of 150 ng/kg·hr, resulting in a rise of plasma PP from 24±5 to 224±25 pM (p<0.01). Before this bombesin infusion, 7 ml of normal rabbit serum had been administered to the dogs (n=8). At a later stage, the study was repeated after administration of 7 ml of PP-antiserum to the same animals. The bombesin induced increase in pancreatic exocrine secretion during administration of PP-antiserum (flow rate 24±10 ml/hr, protein output 1.35±0.43 g/hr, and bicarbonate output 3.25±1.42 mmol/hr) was not significantly different from that during control rabbit serum (flow rate 21±7 ml/hr, protein output 1.26±0.38 g/hr, and bicarbonate output 3.18±1.10 mmol/hr). It is therefore concluded that the pancreatic exocrine response to bombesin is not affected by the concomitant secretion of PP.     

Inhibitory effect of pancreastatin on pancreatic exocrine secretion in the conscious rat

The effect of newly discovered pancreastatin on pancreatic secretion stimulated by a diversion of bile-pancreatic juice (BPJ) from the intestine was examined in the conscious rat. Exogenous pancreastatin infusion (20, 100 and 200 pmol/kg.h) inhibited pancreatic protein and fluid outputs during BPJ diversion in a dose-dependent manner. Pancreastatin did not affect plasma cholecystokinin (CCK) concentrations. Pancreastatin (100 pmol/kg.h) inhibited CCK-stimulated pancreatic secretion, but did not inhibit secretin-stimulated pancreatic secretion. Pancreastatin alone, however, did not affect basal pancreatic secretion. In contrast, pancreastatin (10(-10)-10(-7)M) did not suppress CCK-stimulated amylase release from isolated rat pancreatic acini. These results indicate that pancreastatin has an inhibitory action on exocrine function of the pancreas. This action may not be mediated by direct mechanisms and nor via an inhibition of CCK release. It is suggested that pancreastatin may play a role in the regulation of the intestinal phase of exocrine pancreatic secretion.     

Acid inhibition by intestinal nutrients mediated by CCK-A receptors but not plasma CCK

We examined the role of CCK-A receptors in acid inhibition by intestinal nutrients. Gastric acid and plasma CCK and gastrin levels were measured in rats with gastric and duodenal fistulas during intragastric 8% peptone and duodenal perfusion with saline, complete liquid diet (CLD; 20% carbohydrate, 6% fat, and 5% protein), and the individual components of CLD. Acid output was significantly inhibited (50-60%) by CLD, lipid, and dextrose. Plasma CCK was significantly increased by CLD (from 2.6 +/- 0.3 to 4.8 +/- 0.5 pM) and lipid (4.6 +/- 0.5 pM). CCK levels 50-fold higher (218 +/- 33 pM) were required to achieve similar acid inhibition by exogenous CCK-8 (10 nmol x kg(-1) x h(-1) iv). Intestinal soybean trypsin inhibitor elevated CCK (10.9 +/- 2.5 pM) without inhibiting acid secretion. The CCK-A antagonist MK-329 (1 mg/kg iv) reversed acid inhibition caused by CLD, lipid, and dextrose. Peptone-stimulated gastrin (21.7 +/- 1.9 pM) was significantly inhibited by CLD (14.5 +/- 3.6 pM), lipid (12.3 +/- 2.2 pM), and dextrose (11.9 +/- 1.5 pM). Lipid and carbohydrate inhibit acid secretion by activating CCK-A receptors but not by altering plasma CCK concentrations.     

Occurrence of VIP and peptide HM in human pancreas and their influence on pancreatic endocrine secretion in man

By immunohistochemistry it was found that VIP- and peptide HI/peptide HM (PHI/PHM)-like immunoreactivity occurred in autonomic neurons in the human pancreas. Antisera against both VIP and PHI/PHM reacted with neuronal cells in local ganglia and these ganglia also contained PHI/PHM- and VIP-immunoreactive fibre plexuses. VIP- and PHI/PHM-positive fibres were also seen close to the Langerhans' islets. In addition, PHI/PHM- but not VIP-like immunoreactivity was observed in the endocrine cells often located in the periphery of the islets. The nature of these PHI/PHM-positive cells remains to be established. I.v. infusion of VIP at constant rates of 300 and 900 pmol/kg X h for 30 min in 6 healthy volunteers resulted in plateau values of 102 +/- 26 and 291 +/- 25 pM, respectively. These levels of VIP which are above those found in the circulation under physiological conditions stimulated secretion of insulin, C-peptide and pancreatic glucagon dose-dependently. On the contrary prolonged (60 min) infusion of PHM in doses resulting in plasma levels up to 1340 +/- 405 pM had no effect on pancreatic hormone secretion. These findings suggest that VIP is a likely neurotransmitter in the control of endocrine pancreatic secretion while PHM has a less prominent role, if any.     

Involvement of peptide histidine isoleucine (PHI) in prolactin secretion induced by serotonin in rats

The possible role of hypothalamic peptide histidine isoleucine (PHI) in prolactin (PRL) secretion induced by serotoninergic mechanisms was investigated in male rats using a passive immunization technique. Intracerebroventricular injection of serotonin (5HT, 10 micrograms/rat) raised plasma PRL levels both in urethane-anesthetized rats and in conscious rats pretreated with normal rabbit serum (0.5 ml/rat, iv, 30 min before). Plasma PRL responses to 5HT were blunted in these animals when they were pretreated with rabbit antiserum specific for PHI (0.5 ml/rat, iv, 30 min before) (mean +/- SE peak plasma PRL: anesthetized rats 271.3 +/- 38.3 ng/ml vs 150.0 +/- 12.6 ng/ml, p less than 0.01, conscious rats 54.3 +/- 6.8 ng/ml vs 30.7 +/- 4.1 ng/ml, p less than 0.025). These results suggest that hypothalamic PHI is involved, at least in part, in PRL secretion induced by central serotoninergic stimulation in the rat.     

Immunoreactive cholecystokinin in human and rat plasma: correlation of pancreatic secretion in response to CCK

Immunoreactive cholecystokinin (CCK) levels in human and rat plasma are described using a radioimmunoassay specific for the biologically active sulfated end of CCK. This assay detected significant changes in plasma cholecystokinin levels during intrajejunal administration of amino acids and intravenous infusions of CCK-8 which were followed by increased pancreatic secretion. In humans, the concentration (pg/ml) of plasma cholecystokinin increased from 10.8 to 18.9 following intrajejunal amino acid instillation and from 15.4 to 31.1 during CCK infusion, while pancreatic trypsin secretion increased more than 15 fold. Ingestion of a test meal also caused a rapid and significant elevation (P less than 0.05) in both plasma CCK (14.5-21.7 pg/ml) and gastrin (50-160 pg/ml) levels. In the rat, an injection of 46 ng of CCK-8 produced a 300% increase in immunoreactive plasma CCK levels (2 min) and caused peak pancreatic protein secretion within 5 min; 4 fold lower doses (11.5 ng) elevated plasma CCK by 38% and pancreatic protein secretion to a small but significant extent. The ability of this assay to detect various forms of sulfated CCK in human plasma was also determined. Following gel chromatography on Sephadex G-50, at least three different immunoreactive peaks were found in plasma from fasted subjects and after intrajejunal amino acid stimulation. While the lower molecular weight CCK peptides (CCK-8 and CCK-12) were detected in plasma from both fasted and stimulated subjects, the larger form (CCK-33) was only present in measurable concentrations after amino acid infusion. The simultaneous measurement of increased plasma CCK levels and pancreatic secretion and the changes in the distribution of CCK peptides following amino acid infusion provides strong support that this assay detects physiologically relevant changes in biologically active CCK peptides.