Measurement of endogenous release of cholecystokinin by radioimmunoassay

How to measure cholecystokinin in tissue, plasma and cerebrospinal fluid

This review examines a major problem for an old hormone. Hormones are defined by the ability to reach their targets via blood. Consequently, knowledge about a hormone requires measurement of its behaviour in blood. So far, however, it has proven exceptionally difficult to measure the classical gut hormone, cholecystokinin (CCK), in circulation. The review therefore describes the premises for reliable plasma CCK measurements as compared to the premises for measurement in tissue extracts and cerebrospinal fluid. The critical plasma premises comprise equimolar quantitation of the bioactive CCK peptides in circulation (CCK-83, -58, -33, -22 and -8) without interference from homologous gastrin peptides. The latter may appear nearly impossible, because the bioactive epitopes of CCK and gastrin are almost identical, and because the plasma concentrations of gastrin are more than tenfold above those of CCK. In comparison, measurement of CCK in tissue is considerably simpler, especially in extracts of the two main production sites, the brain and jejunoileal mucosa. For cerebrospinal fluid, degradation, low levels and shortage of material constitute major problems so that the molecular nature and biological/clinical relevance of CCK measurements in CSF still remain to be settled. The review finally enlists the reports on plasma CCK measurements published so far. A multitude of different immuno- and bioassays have been used with corresponding variation in the results. The theory for different types of assays in combination with general assay experience suggest that accurate CCK measurements require radioimmunoassay technology based on high-affinity antibodies. These antibodies have to be exquisitely specific for the 0-sulfated C-terminal heptapeptide amide of CCK without binding the similar gastrin epitope. Only few of such antibodies have been raised.

Modification of renal and tissue cation transport by cholecystokinin octapeptide in the rabbit

1. Reports that gastric sodium loads cause a greater natriuresis than those administered intravenously, suggest that a gastric or portal sodium monitor exists which releases a humoral natriuretic factor. To determine whether cholecystokinin octapeptide (CCK-8) had direct renal natriuretic effects (and was therefore a candidate for this gut-derived natriuretic factor) we compared the natriuretic response to CCK-8 infused intravenously with that infused directly into the renal artery of six conscious male rabbits. 2. CCK-8 produced a significant log dose-dependent decrease in the fractional excretions of calcium (P less than 0.05) and magnesium (P less than 0.005) and a log dose-dependent increase in fractional sodium excretion (P less than 0.025). The significant decreases in the fractional excretions of calcium and magnesium were accompanied by log dose-dependent falls in their plasma levels (calcium, P less than 0.05, and magnesium, P less than 0.005), indicating movement of calcium and magnesium to extravascular sites. Studies of tissue calcium and magnesium levels in response to CCK-8 infusion showed that calcium accumulated in kidney and skeletal muscle. 3. We conclude that CCK-8 has direct renal natriuretic effects at the tubular level and could be the gut-derived natriuretic factor. In addition to its effects on sodium excretion, CCK-8 causes renal retention and increased gut absorption of calcium and magnesium with movement of these ions to extravascular sites.

Effects of endogenous and exogenous secretin on plasma pancreatic polypeptide concentrations in dogs

The effects of exogenous and endogenous secretin with or without intravenous glucose infusion upon islet hormone secretion were studied in four conscious mongrel dogs fitted with a duodenal fistula. Intravenous infusion of secretin for 1 h at doses of 0.5 and 4 U/kg raised plasma secretin concentrations to physiological and pharmacological levels respectively, without affecting plasma insulin and pancreatic polypeptide concentrations. In contrast, bolus injections of secretin at high concentrations produced significant increases of plasma insulin at 0.5 U/kg and 4 U/kg and of pancreatic polypeptide at 4 U/kg. Plasma glucagon did not change during intravenous infusion of low dose secretin (0.5 U X kg-1 X h-1), but decreased during infusion of 4 U X kg-1 X h-1 or bolus injection of secretin (0.5 U/kg). Intravenous infusion of glucose together with secretin (0.5 U/kg and 4 U/kg) did not affect plasma insulin, glucagon, or pancreatic polypeptide levels significantly compared with the changes caused by glucose infusion alone. Intraduodenal instillation of HCl, which produced plasma secretin concentrations similar to those evoked by intravenous infusion of secretin (4 U X kg-1 X h-1), led to a rise in plasma pancreatic polypeptide. It is concluded that the stimulatory effects of secretin on insulin and pancreatic polypeptide and the inhibitory effect on glucagon are pharmacological, and that increase of plasma pancreatic polypeptide after intraduodenal infusion of HCl is not mediated by endogenous secretin.

Release of radioimmunologic cholecystokinin in human subjects

After the development of reliable, highly sensitive, specific radioimmunologic methods for measuring physiologic CCK concentrations in human plasma, we have been able to study the importance of CCK in the postprandial activation of pancreatic enzyme secretion. In man, food causes a threefold increase in the basal plasma CCK concentration with a peak at about 60 minutes. The highest CCK concentrations are observed after intraduodenal fat infusion. Selective proximal vagotomy results in a significant increase in basal CCK concentrations in duodenal ulcer patients without altering the postprandial CCK output. After gastric resection (Billroth I or Billroth II) an initial greater postprandial CCK output is observed. In patients with chronic pancreatic insufficiency without enzyme substitution, basal plasma CCK concentrations and the early postprandial CCK output were elevated which indicated a feedback mechanism between pancreatic enzyme secretion and CCK release from the mucosa of the upper small intestine.

Radioimmunoassay of cholecystokinin in human tissue and plasma

A highly sensitive radioimmunoassay for cholecystokinin (CCK) without any cross-reactivity with gastrin is described. The antibody was raised in a rabbit by immunisation with 30% CCK and bound to all COOH-terminal CCK-peptides containing at least 14 amino acid residues. The affinity constant of the antibody was 59.4 X 10(10) l/mol. CCK 33 conjugated to [125I]hydroxyphenylpropionic acid-succinimide ester was used as label. The binding between label and antibody was inhibited by 50% (ID50) at a concentration of 2.8 pmol/l cholecystokinin 33. The detection limit of the assay was between 0.5 and 1.0 pmol/l plasma. Concentrations of CCK in aqueous acid extracts of human upper small intestine were 36.5 +/- 9.8 pmol/g and of human cerebral cortex 28.2 +/- 2.5 pmol/g tissue. Plasma samples were extracted in 96% ethanol prior to assay. No advantage was obtained by adding aprotinin to the tubes. When frozen at -20 degrees C plasma CCK was stable for at least 6 months. Basal plasma CCK concentrations in 30 normal subjects were very low, 0.9 +/- 0.1 pmol/l, range 0.5 to 3.1 pmol/l. Intraduodenal administration of fat induced significant increases in plasma CCK from 1.1 +/- 0.1 to 8.2 +/- 1.3 pmol/l (p = 0.01). Infusion of exogenous CCK, resulting in plasma CCK levels slightly lower than those measured during administration of fat, induced pancreatic enzyme secretion and gallbladder contraction. The reliability of this radioimmunoassay for measurements of CCK in human plasma was extensively evaluated.

Radioimmunoassay of cholecystokinin

A highly sensitive and specific radioimmunoassay for cholecystokinin (CCK) has been developed. Fully immunoreactive [125I]CCK33 was prepared by chloramine T-catalyzed iodination followed by purification by gel filtration and ion exchange chromatography. A high titer of antiserum was obtained by multiple immunizations of rabbits with 15% pure porcine CCK without conjugation. The antiserum was highly specific for CCK33 and CCK39, with 40% of the binding sites recognizing CCK8 at high affinity, but reacted weakly with gastrin. Plasma interference was eliminated by an XAD-2 resin column extraction technique with high recovery of CCK. The overall assay sensitivity was 3.3 pM with intra- and interassay coefficients of variation determined with a plasma of 11.2 pM at 9.6 and 20.8%, respectively. The assay was capable of detecting linear increments of both CCK33 and CCK8 added into plasma and intravenous infusion of CCK8 as low as 0.03 micrograms/kg/hr in dogs. The assay was validated by its ability to monitor increase of plasma CCK immunoreactivity after ingestion of a meat meal in both humans and dogs, as well as following intragastric infusion of liver extract meal and intraduodenal infusion of phenylalanine in dogs. When the CCK8 and gastrin binding sites of the antiserum were removed by immunoadsorption, the treated antiserum remained capable of measuring a postprandial change in plasma CCK concentration, indicating that CCK33-like immunoreactivity was present in the plasma.

Identification and measurement of molecular variants of cholecystokinin in duodenal mucosa and plasma. Diminished concentrations in patients with celiac disease

The amount and type of cholecystokinin (CCK) in duodenal extracts and plasma of celiac patients and normal subjects was studied by radioimmunoassay and gel filtration. In both groups there were similar patterns of molecular forms in extracts of duodenal biopsies, but concentrations in celiac disease were significantly depressed. In boiling water extracts of duodenal mucosa from both groups a factor with the properties of the COOH-terminal octapeptide of cholecystokinin predominated, but there were also significant amounts of a larger molecular weight form. In acid extracts of mucosa a factor with the properties of the 33 or 39 residue form was identified in amounts that were approximately 25% those of CCK8; there were also similar amounts of an acid-soluble form that had an apparent molecular weight higher than CCK39. Plasma immunoreactive cholecystokinin was studied after concentration by immunoaffinity adsorption and fractionation by gel filtration. In normal subjects fasting CCK-like immunoreactivity was less than 0.8 pmol/liter, and after a light breakfast increased to 2.0 +/- 0.7 (range 1.0 to 4.8) pmol/liter; CCK8-like activity accounted for all the increased immunoreactivity. In five of six celiac patients the concentrations of both fasting and postprandial CCK-like immunoreactivity in plasma were undetectable (less than 0.8 pmol/liter). We conclude that diminished production and release of CCK could account for the impaired pancreatic and gall bladder responses to intraluminal stimuli in celiac disease.

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.

Immunological blocking of exogenous and endogenous secretin in the dog

In mongrel dogs with chronic gastric and duodenal fistula the biological activity of secretin on exocrine pancreatic secretion could be blocked by preincubating the secretin injected with rabbit antisecretin antibody. In addition, the activity of endogenous secretin released by acid was markedly reduced by application of antibody. Since no such effect was observed after testmeal stimulation, secretin is most probably not released in a significant amount by the liquid meal used in this experiment.

Distribution of the gut hormones in the primate intestinal tract

Reliable and specific radioimmunoassays have been developed for the gut hormones secretin, gastrin, cholecystokinin, pancreatic glucagon, VIP, GIP, motilin, and enteroglucagon. Using these assays, the relative pattern of distribution of the gut hormones has been determined using the same bowel extracts for all measurements. VIP occurred in high concentration in all regions of the bowel, whereas secretin, GIP, motilin, and CCK were predominantly localised in the proximal small intestine. Pancreatic glucagon was almost exclusively confined to the pancreas. Like VIP, enteroglucagon also exhibited a wide pattern of distribution but was maximal in the ileum. The acid ethanol extraction method that was used was found to be unsuitable for gastrin. On gel chromatography of the extracts, motilin and VIP eluted as single molecular species in identical position to the pure porcine peptides. CCK, pancreatic glucagon, enteroglucagon and GIP were all multiform.

Gastric acid secretion and drinking in the Atlantic cod (Gadus morhua) during acidic or hyperosmotic perfusion of the intestine

Cods were equipped with cannulae for drainage of the stomach and for separate perfusion of the stomach and intestine. Acidity, volume, and osmolality of the gastric outflow were measured. During perfusion of the intestine with a near-isosmotic saline (1 part sea-water, 2 parts distilled water, '33% SW') and the stomach with pure ('100%') SW, gastric acid output was high and volume output slightly above the infused volume. The osmolality of the gastric perfusate decreased during passage of the stomach. It was concluded that no drinking occurred, and that the decreased osmolality was due to dilution by gastric secretions and osmotically lost water. When substituting the isosmotic intestinal perfusion to a dehydrating perfusion (100% SW), gastric acid secretion was depressed but volume output was unaffected. Also perfusion of the intestine with acidified 33% SW depressed gastric acid secretion and in addition increased volume and osmolality of the gastric outflow. The results suggest that perfusion of the intestine depress the drinking reflex and that this depression is surmounted by intestinal acidification. Possible mediators of the intestinal feed-back mechanism for the inhibition of gastric acid secretion are discussed.

Pancreatic and gastric somatostatin release in response to intragastric and intraduodenal nutrients and HCl in the dog

The effects of the instillation of glucose, fat, casein hydrolysate, and HCl into the gastrointestinal tract upon plasma levels of somatostatin-like immunoreactivity (SLI) in the venous effluent of the pancreas, fundus and antrum of the stomach, and in the inferior vena cava (IVC) were determined in normal laparotomized dogs. Fasting SLI levels in the effluent plasma from these sites were significantly greater than IVC levels. The intragastric administration of glucose elicited a prompt and significant rise in SLI levels in pancreatic, fundic and antral venous plasma, and in IVC plasma; intraduodenal glucose elicited smaller increments. After intragastric fat, a smaller, more gradual increase in the pancreatic and fundic effluents was observed, whereas the rise in antral SLI was minute, and IVC SLI did not rise significantly. Intraduodenal fat elicited a prompt increase in the pancreatic and antral vein SLI levels, and a small but significant increase in fundic and IVC plasma which suggests faster release of enteric factors that influence SLI secretion in the pancreas and antrum. Intragastric casein hydrolysate elicited a prompt increase in SLI in both the pancreatic and fundic veins, the latter being marked, but the antral SLI response was small; IVC SLI rose significantly within 15 min. Intragastric HCl provoked a prompt and marked rise in pancreaticoduodenal and antral vein SLI but no increase in fundic vein SLI; IVC SLI levels rose significantly within 20 min. Intraduodenal HCl elicited an even more prompt and marked pancreatic SLI response, and SLI rose significantly in both the fundic and antral venous effluents; IVC SLI also rose more promptly. In dogs with a gastric fistula that prevented intraduodenal entry of HCl, intragastric HCl elicited only a very small and transient rise in pancreaticoduodenal vein SLI, markedly stimulated the antral SLI response, but completely suppressed fundic venous SLI levels. The results indicate that all three nutrients stimulate SLI release from the pancreas and stomach. The greater SLI response to intragastric, as opposed to intraduodenal, glucose suggests that unidentified local factors are of importance. The responses to the intraduodenal instillation of HCl and fat suggest a role of enteric hormones in the release of SLI from the pancreas and fundus and antrum of the stomach. Additionally, there is evidence of direct effects of HCl upon gastric SLI release.

Fasting serum cholecystokinin immunoreactivity in chronic relapsing pancreatitis

An increase in fasting cholecystokinin (CCK) levels has been reported in patients with pancreatic insufficiency, but the relationship of these findings to the clinical conditions has not been established. We, therefore, measured fasting serum CCK-like immunoreactivity in 70 patients with chronic relapsing pancreatitis (CRP) (38 non-surgically treated and 32 previously surgically treated) and in 44 healthy subjects. The radioimmunoassay detected three circulating forms of CCK. The mean value of the CCK levels in CRP (260.3 +/- 300.8 pg/ml) was significantly higher than that of the controls (56.6 +/- 61.7 pg/ml) (p less than 0.001), but in 39 (56.7%) of the 70 CRP cases the CCK was in the normal range. A smaller overlap with the controls was observed in the non-surgically than in the surgically treated patients (45 vs. 71.8%). In the 38 non-surgically treated CRP cases no relationship was observed between the CCK levels and each of the following parameters: age, length of history, presence or absence of pancreatic calcification, nutritional and alcoholic habits, and the results of exocrine function tests. The absence of the last-mentioned correlation is somewhat unexpected if the high CCK levels are due to the interruption of a feedback loop for CCK secretion. However, previous pancreatic surgical drainage and/or treatment with pancreatic enzymes, present in almost all these patients, could have an effect on CCK behaviour.

Effect of secretin on basal- and glucose-stimulated insulin secretion in man

Plasma immunoreactive secretin and insulin concentrations were measured in fasting normal humans after intraduodenal infusions of hydrochloric acid, isotonic or hypertonic glucose. The effect of intraduodenal acidification or intravenous bolus injections of secretin on plasma insulin concentrations during infusions of glucose was also examined. The intraduodenal glucose load did not cause an increase in plasma secretin concentrations. Secretin concentrations rose after acid both in the fasting state and during infusions of glucose. A concomitant rise in insulin levels was however only observed during infusions of glucose. Intravenous injection of secretin in a dose which mimicked the response to intraduodenal acidification was without effect on the glucose-stimulated insulin release, while a 30 times higher dose caused a highly significant augmentation of the insulin release. The insulin response pattern to this high dose of secretin differed completely from that observed after intraduodenal infusion of acid. It is concluded and confirmed that the stimulating effect of secretin on insulin secretion is pharmacological and that secretin plays no significant role in the entero-insular axis.

The effect of fat on secretin release

The effect of graded doses of intravenously infused secretin and intestinally perfused sodium oleate and HCl on pancreatic exocrine secretion and plasma secretin was determined in cats and dogs prepared with pancreatic fistulas. The pancreatic dose--response curves for bicarbonate following duodenal perfusion of oleate and HCl in cats were almost identical and paralleled the response to exogenous secretin. Although the bicarbonate response to oleate in dogs was less pronounced than the response to HCl or secretin, the bicarbonate output was observed to increase relative to protein output with increasing doses of the intestinally perfused fat. These observations suggested that secretin or a substance with secretin-like activity may be released from the intestine on contact with fat. The inability to detect changes in secretin immunoreactivity in both cats and dogs with increasing doses of oleate suggests that if secretin is released, it is in amounts undetectable by our radioimmunoassay or that some other unknown substance with secretin-like activity may be released.

Effects of intraduodenal acid on gallbladder net water absorption and motility in the cat

A recently described perfusion technique has been used in the study of gallbladder function during acid infusion into the duodenum in the anaesthetized cat. The method allows simultaneous measurements of the net water absorption, and thereby the concentrating function of the gallbladder, as well as the motility of the organ. Duodenal acidification, which is known to release several gastrointestinal hormones, was found to reduce the net water absorption and induce a contraction in the gallbladder. The results are discussed in relation to earlier studies of gallbladder function as influenced by gastrointestinal hormones.

The effects of glucagon, secretin, pancreozymin and pentagastrin on the hepatic arterial vascular bed of the dog

1 The sympathetically-innervated arterial vascular bed of the dog's liver was perfused from a femoral artery. Arterial blood flow and perfusion pressure were monitored continuously and the hepatic arterial vascular resistance (HAVR) calculated from these measurements. 2 Commercial preparations of secretin, pancroezymin, glucagon and pentagastrin were administered by intra-arterial (i.a.) injection and infusion. 3 Secretin and pancreozymin by injection caused dose-dependent hepatic arterial vasodilatation, and on a molar basis were both more potent than glucagon or pentagastrin. 4 Intra-arterial infusions of secretin and pancreozymin caused hepatic arterial vasodilatation at calculated blood concentrations close to those measured under physiological conditions by other investigators. The vasodilatation was of the same duration as that of the hormone infusions. 5 Pentagastrin by i.a. injection caused dose-dependent hepatic arterial vasodilatation; by i.a. infusion, vasodilatation occurred but there was marked 'escape' from the effects during the continued infusion. 6 As reported previously, glucagon by injection caused dose-dependent hepatic arterial vasodilatation of long duration; by infusion, glucagon caused vasodilatation that persisted after the cessation of the infusion. 7 Glucagon infused i.a. inhibited the vasoconstricter effects of i.a. noradrenaline, over the same range of infusions that caused hepatic arterial vasodilatation. 8 Secretin or pancreozymin did not antagonize the effects of noradrenaline on the hepatic arterial vascular bed at any doses used. 9 Pentagastrin did not antagonize the vasoconstrictor effect of noradrenaline whether hepatic arterial vasodilatation resulted from the pentagastrin infusion, or not. 10 These results are discussed with respect to the possible control of the hepatic arterial vascular bed by gastrointestinal hormones.

Plasma secretin concentration in anaesthetized pigs after intraduodenal glucose, fat, aminoacids, or meals with various pH

The concentration of immunoreactive secretin in portal blood and the secretion from the exocrine pancreas were measured during intraduodenal infusion of isotonic or hypertonic saline, isotonic or hypertonic glucose, aminoacids, fat emulsion, or 0.1 mol X 1(-1) hydrochloric acid in 7 anaesthetized pigs. None of these substances, except hydrochloric acid, had any effect on plasma secretin concentration and pancreatic flow rate and bicarbonate output. Plasma secretin concentration rose significantly from 5.6 +/- 2.7 pmol X 1(-1) (mean +/- S.E.M.) to a peak value of 201.2 +/- 80.5 pmol X 1(-1) 15 min after infusion of hydrochloric acid. Pancreatic flow rate and bicarbonate output increased from 0.51 +/- 0.19 ml X h-1 (mean +/- S.E.M.) to 9.85 +/- 2.33 ml X h-1 and from 52 +/- 11 micronmol X h-1 to 1.004 +/- 290 micronmol X h-1, respectively. During intraduodenal introduction of meals with pH adjusted from 1.0 to 7.0 in 4 pigs amylase was secreted at all pH levels. However, only when pH of the meal was 1.0, resulting in an intraduodenal pH from 1.0 to 1.7 during the stimulation, was a significant increase in plasma secretin concentration and pancreatic flow rate observed from 5.5 +/- 2.8 pmol X 1(-1) (mean +/- S.E.M.) to 115.0 +/- 51.2 pmol X 1(-1) and from 0.20 +/- 0.08 ml X h-1 to 6.25 +/- 2.57 ml X h-1, respectively.

Plasma secretin concentration and pancreatic exocrine secretion after intravenous secretin or intraduodenal HC1 in anaesthetized pigs

The concentration of immunoreactive secretin in arterial blood and the exocrine pancreatic secretion were measured during intraportal infusion of secretin in doses of 0.03, 0.06, 0.1 and 3.0 clinical units kg-1 h-1, and during intraduodenal instillation of 50 ml 0.1 mol 1(-1) HC1. The lowest dose of exogenous secretin to significantly increase secretin concentration in blood was 0.03 clinical units kg-1 h-1, which was a subthreshold dose of exocrin pancreatic secretion. A linear relation was found between the dose secretin and the secretin concentrations measured. On the basis of secretin concentrations, release of secretin during instillation of HC1 was estimated to be 0.22 clinical units kg-1 h-1. Maximum pancreatic bicarbonate secretion was obtained with a dose of 1.0 clinical units kg-1 h-1, and the minimal effective dose was between 0.06 and 0.1 clinical units kg-1 h-1. On the basis of the flow rate of pancreatic juice and the pancreatic bicarbonate output, secretin during instillation of HC1 was estimated to be 0.3 clinical unit kg-1 h-1. It is concluded that the radioimmunoassay used has the sensitivity and accuracy necessary for measurements of secretin concentrations in plasma during physiological conditions.

Effect of sulfated and non-sulfated gastrin and octapeptide-cholecystokinin on cat gall bladder in vitro

This study demonstrates that for the isolated cat gall bladder a smaller molar dose of the sulfated form of OP-CCK and gastrin is required to produce contraction as compared to the respective non-sulfated forms. For OP the D50 for the sulfated form versus the non-sulfated form was 1.94. For gastrin it was 1.10.

Cholecystokinin metabolism in man and dogs

We have developed a sensitive, specific and reproducible radioimmunoassay for cholecystokinin (CCK) with which basal levels of CCK of between 400-800 pg/ml have been measured in normal man, in patients with diabetes and with duodenal ulcer disease, and in normal dogs. After a meal, circulating levels of CCK rose to 1000-1200 pg/ml in human subjects. Release of CCK was more rapid in diabetic and duodenal ulcer patients than in normal subjects, but elevated postprandial levels persisted much longer in normal subjects. Patients with the Zollinger-Ellison syndrome had elevated values of cholecystokinin which rose after a meal. Lack of correlation between elevated basal levels of gastrin and CCK in patients with the Zollinger-Ellison syndrome suggest that the hypercholecystokininemia may be absolute. The disappearance half-time of exogenous CCK was about 21/2 minutes in normal subjects as well as in diabetic and duodenal ulcer patients. Studies in dogs demonstrated no uptake of basal levels of cholecystokinin by the kidney; on infusion of exogenous CCK-33, the kidney extracted 43% of the total CCK presented and 56% of the integrated CCK. We conclude that: 1) circulating basal and postprandial levels of CCK may be measured in a reproducible fashion; 2) postprandial release of CCK is more rapid in diabetic and duodenal ulcer patients than in normal man; 3) the disappearance half-time of exogenous CCK in man and dogs is about 21/2 minutes; 4) the kidney is a major site for uptake of CCK.

Hormonal control of gastrointestinal motility

The motor responses of the gastrointestinal tract to a meal are tuned to provide the optimal conditions for digestion and absorption of food. Hormones released from the mucosa of the intestinal tract play an important role in regulating and integrating the various motor events which occur. Complex feedbacks, both nervous and humoral, control the release of intestinal hormones and also modify their actions. Preliminary studies suggest that abnormalities in the secretion or action of various gastrointestinal hormones may play an important role in the production of motor disorders of the gastrointestinal tract.

Depletion of antral gastrin after food in rats

The results of these studies indicate that in fasting rats, there is an abrupt and prolonged rise in circulating gastrin after feeding. This increase in serum gastrin is accompanied by an early (five minutes) diminution in antral gastrin which is followed by slightly higher and more variable antral gastrin values. These findings suggest that feeding triggers the release of gastrin with early depletion of antral gastrin and that, subsequently, gastrin syhthesis and release interact cyclically to maintain antral and serum concentrations of gastrin. Antral, fundic, and duodenal gastrin values in rats are similar to those reported in dogs and cats. The jejunum of the rat contains little, if any, gastrin.

Radioimmunoassay of cholecystokinin-pancreozymin

A sensitive and specific radioimmunoassay for cholecystokinin-pancreozymin (CCK-PZ) has been developed, using rabbit antisera to crude porcine hormone. Highly purified porcine CCK-PZ, labelled with (131)I, and repurified by column chromatography on Sephadex G15, was used as tracer. Separation of free from antibody-bound labelled CCK-PZ was carried out using charcoal, ion-exchange resin, or a double antibody procedure. Non-specific interference with the assay system by serum factors was abolished (as judged by in-vitro and in-vivo recovery studies) by boiling and diluting the serum samples before assay. Ninety-nine per cent pure porcine CCK-PZ (standard), commercial CCK-PZ preparations, caerulein, the C-terminal 8- and 12-amino acid fragments of the CCK-PZ molecule, and endogenous human CCK-PZ all cross reacted in the assay system and showed parallel inhibition curves. No significant cross reaction was found with gastrin, secretin, glucagon, or insulin. The sensitivity of the assay is approximately 5 pg per ml of test solution, which proved adequate for measuring physiological levels of CCK-PZ in peripheral blood in man.The mean immunoreactive CCK-PZ concentration in 50 fasting normal subjects was 60.4 pg per ml. The distribution of individual values was skewed, however, so that the median was much lower (30 pg per ml). Older subjects had higher fasting levels of CCK-PZ than were found in young adults.