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Ontogeny of procholecystokinin maturation in rat duodenum, jejunum, and ileum
J F Rehfeld1, L Bardram, L Hilsted
1Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Denmark.
Insights
Procholecystokinin (proCCK) is expressed in fetal rat intestines, but its maturation into cholecystokinin (CCK) is delayed and varies across the small intestine after birth. This delayed processing suggests other factors regulate early pancreatic growth.
Area of Science:
- Gastroenterology
- Developmental Biology
- Molecular Endocrinology
Background:
- Procholecystokinin (proCCK) is a precursor peptide processed into various active forms of cholecystokinin (CCK).
- The expression and maturation of proCCK in the developing rat intestine are not fully understood.
- CCK plays crucial roles in digestion and potentially in regulating pancreatic development.
Purpose of the Study:
- To investigate the expression and processing of proCCK in the rat intestine during different developmental stages.
- To characterize the temporal and regional differences in CCK maturation.
- To explore the implications of delayed CCK maturation on pancreatic growth regulation.
Main Methods:
- Sequence-specific immunoassays were used to quantify proCCK and CCK levels.
- Enzymatic cleavage with processing-like enzymes was employed.
- Chromatographic techniques were utilized to analyze peptide processing and sulfation.
Main Results:
- Fetal proCCK levels were similar across the duodenum, jejunum, and ileum.
- Postnatal CCK maturation varied significantly between the duodenum, jejunum, and ileum.
- Duodenal proCCK fully matured to carboxyamidated CCK, while jejunoileal proCCK showed only partial maturation, with altered tyrosine-sulfation and N-terminal processing.
Conclusions:
- The CCK gene is expressed at the propeptide level in the fetal small intestine.
- Postpartum proCCK maturation is delayed and exhibits regional differences within the small intestine.
- The delayed maturation supports the hypothesis that CCK is not the primary regulator of pancreatic growth in fetal and neonatal life.
Abstract:
Expression and processing of procholecystokinin (proCCK) in rat intestine during development were examined using sequence-specific immunoassays, cleavage with processing-like enzymes, and chromatography. Fetal proCCK concentrations were similar in duodenum, jejunum, and ileum, but the maturation to CCK followed different courses: duodenal CCK increased from 14 pmol/g in the fetus to 86 pmol/g 4 days after birth and then declined to 17 pmol/g in the adult. In jejunum, CCK varied from 34 pmol/g in the fetus to 127 pmol/g at day 7, decreased to 54 pmol/g at day 21, and increased again to 93 pmol/g in the adult. Ileal CCK decreased from 20 pmol/g in the fetus to 10 pmol/g postnatally. Whereas duodenal proCCK after birth matured completely to carboxyamidated CCK, jejunoileal proCCK matured only partially. Chromatography showed an increase of tyrosine-sulfation and proteolytic processing of N-terminal sequences. At day 7 jejunal cholecystokinin octapeptide (CCK-8) constituted only a minute fraction of the carboxyamidated CCK, of which less than half was sulfated. However, in the adult jejunum, CCK-8 constituted a significant fraction, which was completely sulfated. It is concluded that the CCK gene is well expressed at propeptide level in the fetal small intestine. Postpartum maturation of proCCK, however, is late and differs in the three parts of the small intestine. The belated maturation supports the hypothesis that factors other than CCK regulate pancreatic growth in fetal and neonatal life.
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