# Sincalide (Kinevac): CCK-8 Cholecystokinin Research Profile
Sincalide — marketed as Kinevac and widely known by its pharmacological designation CCK-8 — is the FDA-approved synthetic C-terminal octapeptide of cholecystokinin (CCK). First approved in 1976, it remains the only regulatory-cleared CCK analog for parenteral administration, used diagnostically to stimulate gallbladder contraction, augment pancreatic secretion studies, and accelerate GI transit. In contemporary research settings, sincalide serves as an indispensable pharmacological tool for probing CCK receptor biology, gut-brain satiety signaling, and GI motility physiology.
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What Is Sincalide?
Cholecystokinin is a 33-amino acid peptide hormone first isolated from porcine intestinal mucosa in 1964 by Jorpes and Mutt. The biological activity of the full-length peptide resides in its C-terminal region, and the eight-amino-acid sequence that preserves full receptor-binding potency is designated CCK-8 — or, in its synthetic pharmaceutical form, sincalide.
Amino acid sequence: Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2
Molecular formula: C49H62N10O16S3
Molecular weight: 1,143.29 Da
CAS number: 25126-32-3
Brand name: Kinevac (Bracco Diagnostics)
The sulfated tyrosine at position 2 (Tyr(SO3H)) is critical for high-affinity receptor binding. Unsulfated CCK-8 retains roughly 1,000-fold lower potency at CCK1 receptors and has substantially altered pharmacology — an important consideration when interpreting research that uses sulfated versus unsulfated formulations. Sincalide (as Kinevac) is the sulfated, biologically active form.
Compared to full-length CCK-33 or CCK-58, the CCK-8 octapeptide produces a more rapid and reproducible pharmacodynamic response, making it the preferred research reagent for time-sensitive gallbladder kinetics and receptor pharmacology studies.
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Mechanism of Action
CCK1 and CCK2 Receptor Pharmacology
Two receptor subtypes mediate CCK signaling, distinguished by tissue expression and ligand selectivity:
| Receptor | Also known as | Primary location | Sincalide/CCK-8 affinity |
|---|---|---|---|
| CCK1R (CCK-A) | CCKA receptor | Gallbladder, pancreatic acini, vagal afferents, NTS, hypothalamus | Sub-nanomolar (high) |
| CCK2R (CCK-B) | CCKB/gastrin receptor | CNS (cortex, hippocampus, NTS), gastric parietal cells | Nanomolar (moderate) |
Sincalide acts primarily as a CCK1R agonist. Both receptors are Gq/11-coupled GPCRs; CCK1R activation triggers IP3-mediated calcium mobilization and diacylglycerol-dependent PKC activation, driving smooth muscle contraction and exocrine secretion.
Gallbladder and Biliary Effects
CCK1R activation on gallbladder smooth muscle produces coordinated contraction of the gallbladder fundus and body while simultaneously relaxing the sphincter of Oddi. The net effect is expulsion of concentrated bile into the duodenum. Following an intravenous bolus of 0.02 mcg/kg sincalide, maximal gallbladder contraction occurs within 5-15 minutes and typically reduces gallbladder radiographic size by at least 40% — the threshold considered diagnostically satisfactory (Kinevac prescribing information).
Pancreatic Exocrine Secretion
At physiological plasma concentrations, CCK acts primarily through a cholinergic relay rather than direct acinar cell stimulation. Studies using CCK-8 infusions at 10 ng/kg/h in healthy humans (producing plasma CCK levels equivalent to postprandial concentrations of approximately 6 pM) showed that atropine blocked 84% of trypsin output and 79% of lipase output, demonstrating a predominantly vagal-cholinergic mechanism (Soudah et al., PMID 1636705). At supraphysiological concentrations (40 ng/kg/h, plasma CCK ~18 pM), direct acinar receptor activation dominates and cholinergic blockade reduces enzyme output by only ~45%.
Satiety and Appetite Signaling
CCK-8 is one of the best-characterized peripheral satiety signals in vertebrate physiology. Postprandial CCK release from duodenal I-cells activates CCK1 receptors on vagal afferent terminals in the proximal intestinal wall; this signal is relayed via the vagus nerve to the nucleus tractus solitarius (NTS) and hypothalamus, suppressing food intake.
Research using CCK1R-selective antagonists (devazepide) confirmed that peripheral CCK1R activation mediates the satiety effect of exogenous CCK-8, while CCK2R antagonists (L-365,260) also reduce satiety when applied centrally — indicating both peripheral vagal and direct central mechanisms contribute (Reidelberger et al., PMID 14701717). Intracerebroventricular administration of CCK-8 at doses as low as 0.03 nmol/brain suppresses food intake within 20 minutes in rodents, demonstrating direct central activity.
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Research Applications
Gallbladder Function and Hepatobiliary Imaging
The primary clinical and research application of sincalide is cholecystokinin cholescintigraphy (CCK-HIDA scan). Sincalide infusion during 99mTc-iminodiacetic acid hepatobiliary scintigraphy enables quantification of the gallbladder ejection fraction (GBEF) — a functional parameter used to diagnose biliary dyskinesia, acalculous cholecystitis, and sphincter of Oddi dysfunction. Research protocols have established that slow IV infusion over 30-60 minutes produces more consistent gallbladder contraction and fewer side effects than rapid bolus injection (Tulchinsky et al., J Nucl Med Technology, 2019;47(3):210-218).
Pancreatic Exocrine Function Testing
When combined with secretin, sincalide enables comprehensive assessment of pancreatic exocrine function. CCK-8 potentiates secretin-stimulated bicarbonate secretion at concentrations at or above 10.9 pmol/kg/h; below this threshold, CCK-8 does not significantly augment bicarbonate output when given alone. This synergism underlies the secretin-CCK test used in chronic pancreatitis research, where diminished enzyme output or bicarbonate concentration after combined stimulation indicates exocrine insufficiency. The secretin-sincalide protocol produces duodenal aspirates suitable for cytology, enzyme activity profiling, and composition analysis.
Satiety and Appetite Mechanistic Research
CCK-8 is routinely used in rodent and human feeding studies to dissect the central and peripheral components of satiety:
- •Peripheral CCK1R satiety: Intraperitoneal injections of 1-4 mcg/kg CCK-8 suppress meal size and duration in rats; this effect is blocked by subdiaphragmatic vagotomy, confirming vagal mediation.
- •Hybrid peptide research: A CCK-8/GLP-1 hybrid peptide demonstrated synergistic insulinotropic, glucose-lowering, and satiety effects in high-fat diet mice, pointing toward dual CCK1R/GLP-1R co-activation as a next-generation obesity target (Holt et al., PMID 25883113).
- •Neurotransmitter interactions: Co-administration of CCK-8 with serotonergic agents (fluoxetine) potentiates anorexigenic effects via 5-HT2C and beta2-adrenergic pathways, while opioid receptor activation blunts CCK-induced satiety.
GI Motility and Intestinal Transit
Sincalide accelerates transit of barium or radiolabeled meals through the small bowel by coordinating intestinal peristalsis. This reduces fluoroscopic exposure time during small bowel follow-through radiography. The underlying mechanism involves CCK1R-mediated stimulation of circular smooth muscle contraction in the jejunum and ileum, combined with pyloric sphincter contraction that coordinates gastric emptying with duodenal flow.
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Published Protocol Parameters
The following dosing ranges from research publications provide context for experimental design. These are reported doses from literature; laboratory protocols should be adapted by qualified researchers based on study-specific requirements.
| Application | Route | Published dose range | Notes |
|---|---|---|---|
| Gallbladder contraction (imaging) | IV bolus | 0.02 mcg/kg | Maximal contraction 5-15 min |
| Gallbladder (slow infusion protocol) | IV infusion | 0.01-0.02 mcg/kg over 30-60 min | Fewer side effects vs. bolus |
| Pancreatic enzyme secretion (physiological) | IV infusion | 10 ng/kg/h | Postprandial plasma CCK levels |
| Pancreatic enzyme secretion (supraphysiological) | IV infusion | 40 ng/kg/h | Direct acinar activation |
| Secretin potentiation threshold | IV infusion | 10.9 pmol/kg/h | Bicarbonate augmentation onset |
| Satiety (rodent) | IP injection | 1-4 mcg/kg | Meal-size suppression |
| Central CCK-8 satiety (rodent) | ICV | 0.03-0.3 nmol/brain | Food intake suppression within 20 min |
Use the peptide dose calculator to scale published protocols for target plasma concentrations.
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Stability and Storage
Formulation Chemistry
Kinevac is supplied as a sterile lyophilized white powder in 5 mL Type I glass vials, nominally containing 5 mcg sincalide with sodium chloride as bulking agent, and pH adjusted to 5.5-6.5. Vials are sealed under nitrogen headspace at less than 30% relative humidity. Reconstitution is performed with 5 mL sterile water for injection immediately before use.
The sulfated tyrosine renders CCK-8 susceptible to two main degradation pathways: (1) desulfation under acidic conditions, eliminating CCK1R binding affinity; and (2) methionine oxidation at positions 3 and 6 under extreme pH or in the presence of oxidizing agents. Maintaining slightly acidic pH (5.5-7.5) and oxygen-free headspace preserves both sulfation and methionine integrity.
Research-Grade Storage Guidelines
| Condition | Recommendation |
|---|---|
| Lyophilized, long-term | -80 degrees C desiccated; stable until expiry date |
| Lyophilized, short-term (under 3 weeks) | Below -18 degrees C with desiccant |
| Reconstituted (working solution) | 4 degrees C; use within 2-7 days |
| Long-term aqueous aliquots | Below -18 degrees C; add 0.1% BSA or HSA as carrier; avoid freeze-thaw cycles |
| Reconstitution vehicle | Sterile 18 MO-cm H2O at 0.5 mg/mL; dilute further in aqueous buffers |
Avoid reconstituting in DMSO or organic solvents — the hydrophilic nature of CCK-8 and the sensitivity of the sulfate group to organic solvents makes aqueous reconstitution mandatory.
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Research Considerations
Receptor Selectivity and Off-Target Pharmacology
Sincalide is highly selective for CCK1R over CCK2R (at least 100-fold selectivity at physiological concentrations). However, at supraphysiological doses, CCK2R activation may contribute to gastric acid secretion, anxiety-like behavior in rodents, and modulation of dopaminergic pathways. Researchers studying satiety or GI motility at high doses should consider CCK2R contributions when interpreting behavioral or secretory endpoints.
For studies requiring strict CCK1R selectivity, receptor-selective antagonists (devazepide for CCK1R, L-365,260 for CCK2R) serve as essential pharmacological controls. CCK1R-knockout and CCK2R-knockout mouse models are available for genetic validation.
Peptide vs. Small-Molecule CCK Agonists
Research comparing sincalide to small-molecule CCK1R agonists (e.g., SR146,131, GI181771X) has consistently shown that sincalide produces more complete gallbladder contraction and pancreatic enzyme secretion in human studies — a discrepancy attributed to differences in receptor activation kinetics and G-protein coupling efficacy. This makes sincalide the preferred reference agonist even when small-molecule agonists are the primary study compound.
Infusion Rate and Side Effects
A critical variable in sincalide research protocols is infusion rate. Rapid IV bolus frequently produces nausea, abdominal cramping, and transient hypotension due to simultaneous relaxation of vascular smooth muscle. Slow infusion over 30-60 minutes substantially reduces these effects without compromising gallbladder contraction endpoints, and is recommended for human volunteer studies.
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Supplier Selection for CCK-8 Research
For receptor pharmacology and in vitro studies requiring precise CCK1R activation, purity is the primary selection criterion. Contaminants from incomplete synthesis or degradation — particularly desulfated CCK-8, which shows altered receptor subtype selectivity — can confound receptor-specific experimental conclusions.
Minimum purity standards for research use:
| Application | Recommended purity | Key quality markers |
|---|---|---|
| In vitro receptor binding | 95%+ HPLC | Mass spec confirmation of sulfation |
| Cell-based functional assays | 98%+ HPLC | Endotoxin less than 1 EU/mg |
| In vivo rodent studies | 98%+ HPLC | Sterility tested; endotoxin less than 0.1 EU/mg |
| Human volunteer studies | GMP or Kinevac (Bracco) | FDA-approved product only |
When comparing suppliers for research-grade sincalide, request mass spectrometry data confirming the presence of the sulfate moiety on Tyr(SO3H). Desulfated peptide is significantly cheaper to synthesize but pharmacologically distinct from the active compound.
Use the peptide supplier comparison tool to evaluate current availability, purity certifications, and pricing across verified suppliers. For GI motility context, review the Motilin research profile and Secretin pharmacology profile. For satiety axis research, see the complete CCK research profile and the PYY appetite regulation profile.
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Key Citations
1. Kinevac (sincalide) prescribing information. Bracco Diagnostics Inc. FDA label, revised 2008.
2. Tulchinsky M et al. Sincalide: A Review of Clinical Utility, Proper Infusion Methodology, and Alternative Cholecystogogues. J Nucl Med Technology. 2019;47(3):210-218.
3. Soudah HC et al. Cholecystokinin at physiological levels evokes pancreatic enzyme secretion via a cholinergic pathway. Gastroenterology. 1992;102(3):1595-1601. PMID: 1636705.
4. Reidelberger RD et al. Abdominal vagal mediation of the satiety effects of CCK in rats. Am J Physiol Regul Integr Comp Physiol. 2004;286(6):R1005-R1012. PMID: 14701717.
5. Holt MK et al. A Novel CCK-8/GLP-1 Hybrid Peptide Exhibiting Prominent Insulinotropic, Glucose-Lowering, and Satiety Actions With Significant Therapeutic Potential in High-Fat-Fed Mice. Endocrinology. 2015;156(11):4092-4099. PMID: 25883113.
6. Meyer BM et al. Human pancreatic and biliary responses to physiological concentrations of cholecystokinin octapeptide. Gastroenterology. 1989;97(4):1163-1171. PMID: 4064569.
7. Crawley JN, Corwin RL. Cholecystokinin octapeptide analogues suppress food intake via central CCK-A receptors in mice. Peptides. 1994;15(3):429-433. PMID: 8214137.
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Research Use Only (RUO) Disclaimer
IMPORTANT: This article is provided for educational and scientific research purposes only. Sincalide (CCK-8) is an FDA-approved diagnostic agent (Kinevac, Bracco Diagnostics) indicated solely for use by or under the supervision of licensed physicians as a diagnostic imaging adjunct.
Research-grade sincalide peptides from commercial suppliers are sold strictly for Research Use Only (RUO) and are not approved for human administration outside of the clinical Kinevac product. These materials have not been evaluated for therapeutic safety or efficacy. They are not intended for use in humans, are not food or drug products, and must not be used as such. All research applications must comply with applicable institutional, ethical, and regulatory requirements.
This content does not constitute medical advice. Always consult qualified healthcare professionals and regulatory bodies before initiating any research involving human subjects or investigational compounds.