Species and tissue distribution of gholecystokinin/gastrin-like substances in some invertebrates

Twenty-six species of invertebrates representing eight phyla were surveyed for the presence of cholecystokinin/gastrin-like (CCK/gastrin-like) peptides by radioimmunoassay of various tissue extracts. This is the first report of the presence of CCK/gastrin-like peptides in representatives of the phylum Ectoprocta, the arthropodan classes Crustacea and Merostomata, and in the nervous systems of the gastropod mollusc Aplysia californica and the oligochaete annelid Lumbricus terrestris. It has been proposed that CCK/gastrin evolved in the invertebrates as a neural peptide and was subsequently exploited by the vertebrates as a regulatory peptide in both the nervous system and the gastrointestinal endocrine system. The present results indicate that some gastropod molluscs, a merostomatan arthropod, and an annelid have detectable CCK/gastrin in both nervous and gut tissue. However, extractable CCK/gastrin was found only in gut tissue and not in the central nervous system of a crustacean arthropod. The tissue origin of the extracted CCK/gastrin in Bugula (phylum Ectoprocta) was not determined. Final resolution of the question of the nervous versus gut endocrine cellular origin of CCK/gastrin in invertebrates awaits further investigation. CCK/gastrin-like peptides are widely distributed among the invertebrates, which thus provide a rich source of comparative material for study of these regulatory substances.     

Cholecystokinin peptides as local modulators of thyroidal calcitonin secretion in the dog?

Cholecystokinin (CCK) is a heterogeneous gut hormone which is also synthetized in extra-intestinal endocrine cells and neurons. In order to examine the possibility that CCK peptides are local modulators of calcitonin secretion, we have studied the structure-activity relationship on calcitonin secretion from perfused canine thyroid lobes as well as the presence and molecular nature of CCK in the thyroid. Peptides containing the intact COOH-terminal tetrapeptide amide of CCK (CCK-4, CCK-5, pentagastrin, CCK-8 and gastrin-17) all induced dose-dependent (0.1, 3 and 100 nmol/l) increases in calcitonin release (P less than 0.05, n = 4) with biphasic secretion during 6-min infusion periods. The deamidated tetrapeptide and the COOH-terminal tripeptide were without effect. Gel chromatography of neutral water and acid-ethanol extracts of thyroid tissue, monitored by sequence-specific CCK and gastrin radioimmunoassays, disclosed a variety of CCK and gastrin peptides of which a predominant form resembled small molecular forms like CCK-4 and CCK-5. The presence in the thyroid of small CCK-like peptides and the pronounced effect of such peptides on calcitonin secretion suggest that calcitonin secretion is modulated by local release of small CCK peptides. They could originate from intrathyroidal nerves or from sub-populations of C-cells.     

Pig brain contains cholecystokinin octapeptide and several cholecystokinin desoctapeptides.

A sequential method employing methanol extraction of the COOH-terminal fragment of cholecystokinin (CCK) from pig brain followed by HCl extraction of the more basic CCK peptides was used as the first step in purification of these peptides. Recovery was monitored with two different assays, one directed to the COOH terminus of CCK and the other to the NH2 terminus. The amino acid content and sequence were determined for each of five peptides after purification. The only peptide containing COOH-terminal immunoreactivity was CCK-octapeptide (CCK8). The other four peptides did not contain CCK8 and had lost one or two additional amino acids, perhaps as a consequence of the action of carboxypeptidases. These peptides were shown to be CCK33-desnonapeptide, CCK39-desnonapeptide and -desdecapeptide, and a large molecular weight precursor, CCK58-desnonapeptide, containing 19 amino acids (Ala-Val-Gln-Lys-Val-Asp-Gly-Glu-Ser-Arg-Ala-His-Leu-Gly-Ala-Leu-Leu-Ala-Arg) NH2-terminal to CCK39. The three NH2-terminal fragments of CCK58, CCK39, and CCK33 were about equally prominent. The brain, unlike the gut, appears to cleave CCK8 rapidly from a precursor peptide but to process the NH2-terminal portions of the molecule more slowly and incompletely.     

Distribution of cholecystokinin forms in intestinal secretory granule subtypes.

Peptides and proteins destined to be released in response to stimuli are found in the regulated secretory pathway. Substances in this pathway are packaged into secretory granules, wherein they are often rendered osmotically inactive by complexing to an oppositely charged molecule. The complexing mechanism employed by members of the cholecystokinin (CCK) peptide family is unknown, but the heterogenous charges of CCK peptides makes it possible that different CCK peptides have different abilities to form intragranular complexes. If the number of osmotically active intragranular CCK peptides varies, corresponding variations in secretory granule density should result, and when intestinal CCK secretory granules were purified on isotonic density gradients, four granule peaks were observed. Granules containing greater proportions of short CCK forms tended to have the lowest buoyant densities, suggesting that they contain a greater number of osmotically active molecules than granules of lower density and that short or all intragranular CCK forms are osmotically active. CCK secretory granules also contained novel CCK forms; in addition to previously characterized forms, granules contained a CCK form that appears to be CCK-6 and a form that could arise from cleavage of CCK-58 at position 4, 10, or 12. Because intragranular enzymes are responsible for peptide posttranslational processing, the intragranular CCK forms observed in the present study are likely to be authentic CCK-processing products. Finally, CCK sorting in intestine apparently differs from that in a rat medullary thyroid carcinoma cell line, in which CCK-22 and CCK-33 are not found in the regulated secretory pathway.     

Comparative studies on the effects of cholecystokinins, caerulein, bombesin 6-14 nonapeptide, and physalaemin on gastric secretion in the ascidian Styela clava

The effects of cholecystokinins (CCK), caerulein, bombesin 6-14 nonapeptide (bombesin), and physalaemin on gastric secretion in Styela clava were measured using a perfusion technique. Varying concentrations of both CCK33 and CCK8 produced a significant dose-dependent response. Dose for dose, CCK33 was more potent than CCK8, while the assay was unable to show any discrimination between sulphated and nonsulphated forms of CCK8. The specific CCK inhibitor Bt2cGMP significantly reduced the response to both CCK33 and CCK8. Both caerulein and physalaemin were effective although with a considerably reduced response compared with CCK. Bombesin was the most potent of all secretagogues tested while glucagon was without effect on gastric secretion. It is suggested that the primitive prepancreatic zymogen cells in Styela possess a receptor or receptors with an ability to recognize those peptides which are also active on vertebrate pancreatic acinar cells. It is further suggested that while the results indicate a receptor system less sophisticated than that found in vertebrates, they also imply the presence of an endogenous polypeptide hormone or hormones with a sequence which might be expected to show similarities to more than one vertebrate gastrointestinal peptide.     

Receptors for cholecystokinin and gastrin]

Cholecystokinin (CCK) and gastrin belong to one family of gastrointestinal peptides that regulate a variety of functions in the gastrointestinal tract and in the central nervous system. On the basis of pharmacological, physiological and molecular studies, receptors for these peptides can be divided into at least two different types: CCKA- and CCKB-receptors. CCKA- and CCKB-receptors are both G-protein coupled receptors and are highly conserved between species. Molecular techniques have revealed a distinct species- and tissue-specific variation in receptor expression and pharmacology. In addition, previously unknown targets for CCK and gastrin such as the kidney were identified. This review discusses the physiological functions of the hormones CCK and gastrin and their receptors. The molecular structure of these receptors and the results of recent structure-function analysis are reviewed.     

Discovery of a cholecystokinin-gastrin-like signaling system in nematodes

Members of the cholecystokinin (CCK)/gastrin family of peptides, including the arthropod sulfakinins, and their cognate receptors, play an important role in the regulation of feeding behavior and energy homeostasis. Despite many efforts after the discovery of CCK/gastrin immunoreactivity in nematodes 23 yr ago, the identity of these nematode CCK/gastrin-related peptides has remained a mystery ever since. The Caenorhabditis elegans genome contains two genes with high identity to the mammalian CCK receptors and their invertebrate counterparts, the sulfakinin receptors. By using the potential C. elegans CCK receptors as a fishing hook, we have isolated and identified two CCK-like neuropeptides encoded by neuropeptide-like protein-12 (nlp-12) as the endogenous ligands of these receptors. The neuropeptide-like protein-12 peptides have a very limited neuronal expression pattern, seem to occur in vivo in the unsulfated form, and react specifically with a human CCK-8 antibody. Both receptors and ligands share a high degree of structural similarity with their vertebrate and arthropod counterparts, and also display similar biological activities with respect to digestive enzyme secretion and fat storage. Our data indicate that the gastrin-CCK signaling system was already well established before the divergence of protostomes and deuterostomes.     

Gastrin/CCK-like immunoreactivity in endocrine cells and nerves in the gastrointestinal tract of the cod, Gadus morhua, and the effect of peptides of the gastrin/CCK family on cod gastrointestinal smooth muscle

Immunohistochemistry shows the presence of one or several gastrin/cholecystokinin (CCK)-like peptides in the gastrointestinal tract of the Atlantic cod, Gadus morhua. Immunoreactive (IR) endocrine cells are present mainly in the lower part of the cardiac and in the pyloric stomach, with a concentration to the inner curvature, and in the proximal part of the intestine, especially in the area of the pyloric caeca, after which the population density of IR cells decreases anally. IR nerve fibers are found in the myenteric plexus and muscle layers of the stomach only. Radioimmunoassays, performed with two C-terminal specific gastrin/CCK antisera, confirm the immunohistochemical findings. The highest levels of IR material are found in the mucosa of the pyloric caeca, the proximal intestine, and the pyloric part of the stomach. The smooth muscle layers contain IR material in a decreasing gradient toward the rectum. The excitatory effect of gastrin/CCK-related peptides on gut smooth muscle is investigated in isolated strip preparations of the gut wall. Of the peptides tested, cerulein is the most potent, followed by CCK 8 and gastrin 17, while gastrin 5 is the least effective. Sulphated CCK 8 gives a higher amplitude of the response but in the same concentration range as nonsulphated CCK 8. It is concluded that one or several gastrin/CCK-like peptides are present in the gut of the cod and may be involved in the nervous and endocrine control of the cod gut motility.     

Quantitative comparison of the effects of cholecystokinin, secretin, and pentagastrin on gastrointestinal myoelectric activity in the conscious fasted dog.

The effects on gastrointestinal myoelectric activity of infused pentagastrin, cholecystokinin (CCK), and secretin at physiological doses were studied in live dogs with implanted serosal electrodes during 56 six-hour studies. Pentagastrin dose-dependently increased gastric and duodenal slow-wave frequencies; secretin and CCK did not. Pentagastrin and CCK diminished the incidence of fasting migrating myoelectric complexes (MMCs), but MMCs were abolished only in the proximal small intestine. Pentagastrin infusion was not reflected in an increased number of spikes, whereas CCK induced a dose-dependent increase in jejunal spike activity. Secretin dose-dependently decreased duodenal and jejunal spike incidence without a marked effect on MMC incidence. Analysis of patterns of spike activity showed significant dose-dependent changes with all three peptides. The different effects of pentagastrin and CCK on spike activity in these studies may have been a consequence of pentagastrin-stimulated gastric acid secretion. None of the three peptides produced a pattern of myoelectric activity which closely resembled that seen on feeding; since, unlike food, all three peptides had little or no effect on the distal small intestine, it seems unlikely that combinations of these peptides are responsible for the change induced by food. The failure of these peptides to abolish fasting patterns in the distal intestine suggests a possible mechanism for some types of post-vagotomy dysfunction.     

Synergistic impact of cholecystokinin and gastric inhibitory polypeptide on the regulation of insulin secretion

The modulation of insulin output from isolated perifused rat islets by the intestinal peptides cholecystokinin (CCK) and gastric inhibitory polypeptide (GIP) was assessed. In the presence of 7 mmol/L (126 mg/dL) glucose, but not 2.75 mmol/L (50 mg/dL) glucose, CCK (5 nmol/L) or GIP (50 ng/mL) alone evoke small insulin secretory responses. However, the combination of GIP (50 ng/mL) plus CCK (5 nmol/L) together with 7 mmol/L glucose results in a markedly amplified insulin secretory response. CCK (50 nmol/L) alone increases phosphoinositide (PI) hydrolysis in islets, an event reflected by an increase in 3H efflux from myo[2-3H]inositol prelabeled islets and parallel accumulations of labeled inositol phosphates. GIP (50 ng/mL) alone has no effect on PI hydrolysis. However, GIP reduces the quantitative impact of CCK on PI turnover, an effect attributable to the capacity of GIP to elevate islet cAMP levels. CCK has no significant effect on islet cAMP levels. The results support the concept that the synergistic action of these peptides on insulin output is mediated by their ability to generate separate beta cell second messenger molecules. Nutrient-regulated intestinal release of various peptides represents a remarkable control system to ensure the release of insulin from the beta cell in amounts commensurate with both the quantity and quality of nutrient intake.     

Cholecystokinin evokes secretion of oxytocin and vasopressin from rat neural lobe independent of external calcium.

Cholecystokinin (CCK) and its receptors are abundantly represented in the central nervous system. However, a specific role or mechanism of action for CCK in this context has not been established. CCK coexists with oxytocin in magnocellular neurons of the hypothalamic-neurohypophysial system, sharing common neurosecretory vesicles with oxytocin in the neural lobe of the pituitary. The neural lobe, which consists primarily of oxytocin- and vasopressin-containing axons and nerve terminals and their surrounding glia, provides a relatively simple model system allowing for the study of the regulation of neurosecretion at the nerve terminal level, free from the complex array of synaptic effects present throughout the rest of the central nervous system. In this paper, we demonstrate the presence of high-affinity CCK binding sites in the rat neural lobe and show that activation of these receptors by the sulfated octapeptide, CCK-8, and related peptides causes potent secretion of oxytocin and vasopressin from the isolated nerve terminals. The secretagogue action of CCK-8, which is blocked by a CCK receptor antagonist (L-364,718), is independent of electrical stimulation and extracellular calcium and is blocked by an inhibitor of protein kinase C. Thus, the action of CCK on the neural lobe provides an example of peptide ligand-induced neurosecretion apparently mediated by second messengers rather than depolarization-induced calcium influx.     

Cholecystokinin-Induced Gastroprotection: A Review of Current Protective Mechanisms

Cholecystokinin (CCK) is a member of a family of gastrointestinal peptides known to physiologically regulate pancreatic protein secretion, gallbladder contractility, and gut motility. In addition, CCK has been found to play important roles in endocrine and neural systems in the periphery as well as in the central nervous system. CCK has been proposed to play a role in satiety, anxiety, and intestinal transit in addition to its well-described effects in coordinating digestion of a meal. We and others have shown that exogenous and endogenous CCK prevent gastric injury from luminal irritants. These data suggest that the release of CCK may represent an important component of the intrinsic gastric mucosal defense system. This review focuses on the ability of CCK to render the stomach more resistant to injury from luminal insults and will summarize recent studies that examine the possible mechanisms involved.     

Molecular and functional characterization of cionin receptors in the ascidian, Ciona intestinalis: the evolutionary origin of the vertebrate cholecystokinin/gastrin family

Cholecystokinin (CCK) and gastrin are vertebrate brain-gut peptides featured by a sulfated tyrosine residue and a C-terminally amidated tetrapeptide consensus sequence. Cionin, identified in the ascidian, Ciona intestinalis, the closest species to vertebrates, harbors two sulfated tyrosines and the CCK/gastrin consensus tetrapeptide sequence. While a putative cionin receptor, cior, was cloned, the ligand-receptor relationship between cionin and CioR remains unidentified. Here, we identify two cionin receptors, CioR1 and CioR2, which are the aforementioned putative cionin receptor and its novel paralog respectively. Phylogenetic analysis revealed that CioRs are homologous to vertebrate CCK receptors (CCKRs) and diverged from a common ancestor in the Ciona-specific lineage. Cionin activates intracellular calcium mobilization in cultured cells expressing CioR1 or CioR2. Monosulfated and nonsulfated cionin exhibited less potent or no activity, indicating that CioRs possess pharmacological features similar to the vertebrate CCK-specific receptor CCK1R, rather than its subtype CCK2R, given that a sulfated tyrosine in CCK is required for binding to CCK1R, but not to CCK2R. Collectively, the present data reveal that CioRs share a common ancestor with vertebrate CCKRs and indicate that CCK and CCK1R form the ancestral ligand-receptor pair in the vertebrate CCK/gastrin system. Cionin is expressed in the neural complex, digestive organs, oral siphon and atrial siphons, whereas the expression of ciors was detected mainly in these tissues and the ovary. Furthermore, cioninergic neurons innervate both of the siphons. These results suggest that cionin is involved in the regulation of siphonal functions.     

Cholecystokinin does not stimulate prosomatostatin-derived peptides in man

In man, plasma cholecystokinin (CCK) and somatostatin-28 (S-28) levels increase after ingestion of a mixed meal. Both peptides originate from the gastrointestinal tract. In supra- and periphysiological doses, CCK stimulates the release of somatostatin-14 from in vitro pancreatic islets and gastric cells and increases circulating somatostatin-like immunoreactivity in dogs, leading to the conjecture that CCK regulates somatostatin-like immunoreactivity secretion. Nonetheless, whether CCK is responsible in part for the meal-induced rise in S-28 in man has not been established. Therefore, the present study was designed to determine if CCK, at both physiological and supraphysiological concentrations, increases the circulating levels of prosomatostatin (proS)-derived peptides in humans. On 3 separate days, five healthy men ate a mixed liquid meal or received iv infusions of CCK at rates of 18 or 38 pmol/kg.h. Plasma levels of pro-S-derived peptides, including pro-S, S-14, S-13, S-28, and CCK, were measured. Basal CCK levels averaged 0.9 +/- 0.1 pmol/L and increased after the meal to a peak level of 5.4 +/- 1.5 pmol/L and averaged 3.1 +/- 1.2 pmol/L over 90 min. The mean basal levels of pro-S, S-14, and S-13, measured collectively, was 6.1 +/- 0.4 pmol/L eq S14 and was unaltered by food intake. The S-28 level was 6.7 +/- 0.6 pmol/L and rose to a zenith of 13.1 +/- 3.3 pmol/L by 90 min. Infusion of CCK at 18 and 38 pmol/kg.h produced steady state plasma CCK levels of 4.1 +/- 1.1 and 9.9 +/- 1.5 pmol/L, respectively. Basal levels of pro-S-derived peptides were unaltered during the infusion of either the low or high dose of CCK. We conclude that CCK by itself is not a physiological signal to the release of pro-S-derived peptides in man.     

Differential expression of gastrin, cholecystokinin-A and cholecystokinin-B receptor mRNA in human pancreatic cancer cell lines.

BACKGROUND: It has been assumed that gastrin stimulates the growth of pancreatic cancer in an autocrine way through co-expression of gastrin and the cholecystokinin-B receptor (CCK-BR). However, pancreatic cancer cell lines established directly from patients have revealed a great heterogeneity in cell proliferation when exposed to CCK, gastrin and their receptor antagonists. The aim of this study was therefore to examine co-expression of CCK-A and CCK-B receptor (CCK-AR and CCK-BR), and gastrin mRNA as well as the secretion of CCK and gastrin peptides in these cell lines. METHODS: Fourteen cell lines were established from primary pancreatic cancers or their metastases. Total RNA was isolated from the cell lines and reverse-transcribed into single-stranded cDNA. A PCR technique based on Taq polymerase-antibody interaction and CCK-AR, CCK-BR and gastrin-specific primers, followed by Southern blot analysis, were the methods used. The incubation mediums were analysed for the presence of secreted CCK/proCCK and gastrin/progastrin peptides by specific radioimmunoassays (RIA). RESULTS: By means of nested Reverse-Transcribed Polymerase Chain Reaction (nested RT-PCR), combined with Southem blot analysis of the PCR amplified products, CCK-AR and gastrin mRNA co-expression was detected in cell lines LPC-6p and LPC-10m, whereas CCK-BR and gastrin mRNA could be detected in cell lines LPC-8p and LPC-12m. A low level of secreted CCK peptides was detected in cell line LPC-6p, which also expressed CCK-AR mRNA. In no other cases were CCK or gastrin peptides detected in the cell culture mediums. CONCLUSION: The lack of CCK-BR and gastrin mRNA co-expression, and not detectable levels of secreted CCK and gastrin in culture media, does not lend support to the hypothesis that concomitant gene-expression of CCK receptors and gastrin or CCK are essential to maintaining pancreatic cancer cell proliferation.     

An enteral therapy containing medium-chain triglycerides and hydrolyzed peptides reduces postprandial pain associated with chronic pancreatitis

Background/Aim: Pain in patients with chronic pancreatitis is difficult to manage. We examined if an enteral formulation containing medium-chain triglycerides (MCT) and hydrolyzed peptides would (1) minimally stimulate the exocrine pancreas by blunting cholecystokinin release and (2) decrease pain in patients with chronic pancreatitis. Methods: In the first part of the study, on separate days, 6 healthy controls consumed a standard enteral formulation, an enteral formulation containing MCT and hydrolyzed peptides, and a high-fat meal. Baseline and postprandial plasma cholecystokinin (CCK) concentrations were analyzed. Subsequently, 8 patients with chronic pancreatitis were enrolled and instructed to complete a visual analog pain assessment for a baseline period of 2 weeks followed by three cans per day of the enteral formulation containing MCT and hydrolyzed peptides for 10 weeks. Results: Mean CCK levels for our control subjects were 0.46 ± 0.29 pM at baseline, 10.75 ± 0.45 pM in response to the high-fat meal, and 7.9 ± 1.25 pM in response to the standard enteral formulation. Of note, CCK levels were 1.43 ±0.72 pM in response to the enteral supplement containing MCT and hydrolyzed peptides. In patients with chronic pancreatitis, the average improvement in pain scores from baseline to the conclusion of the study was 61.8% (p = 0.01). This corresponded to a clinical improvement in 6 of the 8 patients. Conclusions: A complete enteral supplement containing MCT and hydrolyzed peptides minimally increases plasma CCK levels. This therapy may be effective in reducing postprandial pain associated with chronic pancreatitis.     

On the biologically active structures of cholecystokinin, little gastrin, and enkephalin in the gastrointestinal system

The biologically active conformations of a series of four peptides [four cholecystokinin (CCK)-related peptides and enkephalin] in their interactions with gastrointestinal receptors have been deduced using conformational computational analysis. The two peptides that interact exclusively with peripheral-type CCK receptors are the heptapeptide COOH-terminal fragment from CCK (CCK-7) and the analogous sequence from cerulein (CER-7) in which threonine replaces the methionine proximal to the NH2 terminus. The two peptides that interact exclusively with the gastrin receptor in the stomach are the active COOH-terminal fragment of little gastrin and the COOH-terminal tetrapeptide sequence common to all of these peptides, CCK-4. We find that preferred conformations for the peripherally active peptides CCK-7 and CER-7 are principally beta-bends, whereas little gastrin and CCK-4 are fundamentally helical. In the class of lowest energy structures for both CCK-7 and CER-7, the aromatic rings of the tyrosine and phenylalanine lie close to one another whereas the tryptophan indole ring points in the opposite direction. This structure is superimposable on the structures of a set of rigid indolyl benzodiazepine derivatives that interact with complete specificity and high affinity with peripheral CCK receptors further suggesting that the computed beta-bends are the biologically active conformation. The biologically active conformation for CCK-4 and the little gastrin hexapeptide has also been deduced. By excluding conformations common to CCK-7 and CCK-4, which do not bond to each other's receptors, and then by selecting conformations in common to CCK-4 and the gastrin-related hexapeptide, which do bind to each other's receptors, we deduce that the biologically active conformation at the gastrin receptor is partly helical and one in which the indole of tryptophan and the aromatic ring of phenylalanine are close to one another while the methionine and aspartic acid side chains point in the opposite direction. These major differences in preferred structures between the common CCK-7/CER-7 peptides and the common CCK-4/little gastrin peptides explain the mutually exclusive activities of these two sets of peptides. We have observed that [Met]enkephalin strongly antagonizes the action of the naturally occurring peripherally active CCK-8 (CCK-7 with an NH2-terminal aspartic acid residue added). The computed lowest energy structures for this opiate peptide closely resemble key features of the computed CCK-7/CER-7 structure, further supporting the proposed structure.     

Non-sulphated cholecystokinin in human medullary thyroid carcinomas

The expression of gastrin/cholecystokinin (CCK) peptides and their precursors was examined in 16 medullary carcinomas of the human thyroid. Measurements with libraries of sequence-specific radioimmunoassays before and after enzymatic cleavage of extracts and chromatographic fractions showed that the carcinomas contained 1.7 pmol carboxyamidated CCK/g tissue (median; range 0.6-21.8 pmol/g), 0.9 pmol glycine-extended precursor/g (median; range less than 0.2-2.3 pmol/g) and 2.3 pmol further COOH-terminal-extended proCCK/g (median; range 0.9-6.2 pmol/g). Neither carboxyamidated gastrins nor any progastrins could be measured. Gel and reverse-phase chromatography revealed only small molecular forms, i.e. greater than 90% of the amidated immunoreactivity eluted like non-sulphated CCK-8 or CCK-7. The results show that human medullary thyroid carcinomas synthesize CCK peptides. The predominance of non-sulphated CCK is unusual. Taken together with earlier observations from dogs and pigs, our results raise the possibility that small non-sulphated CCK peptides modulate thyroid C-cell secretion in an autocrine manner.