Continuous infusion of cholecystokinin leads to down-regulation of the cholecystokinin-A receptor in the rat pancreas.
BACKGROUND
Infusion of sulphated cholecystokinin-8 (CCK-8S) in rats transiently increased the proliferation of pancreatic acinar cells, whereas the CCK-A receptor antagonist devazepide decreased such proliferation. This effect ceased after 3 days. CCK-8S or devazepide injected twice daily induced a persistent effect on the cell proliferation involving the major cells of the exocrine pancreas. The aim of this study was to examine the effect of continuous infusion of CCK-8S and devazepide on CCK-A receptor gene expression.


METHODS
Male Sprague-Dawley rats received subcutaneous continuous infusion of 5 microg/kg/h CCK-8S, 200 microg/kg/h devazepide, or 1% bovine serum albumin (BSA) by means of osmotic minipumps. The rats were killed after 4 days; I h before being killed they received 5-bromo-2-deoxyuridine (BrdU) intraperitoneally. Plasma was collected for analysis of CCK. The pancreas was dissected, and indirect immunofluorescence for BrdU and CCK-A receptor was performed. In situ hybridization to CCK-A receptor mRNA was performed for examination and semiquantification of receptor gene expression.


RESULTS
Continuous infusion of CCK-8S led to a sixfold increase in plasma CCK and a 40% increase in pancreatic weight. Devazepide did not affect the CCK level but decreased the pancreatic weight by 24% compared with BSA-infused rats. The BrdU labeling indicated that CCK-8S had no effect on cell proliferation. Immunofluorescence for the CCK-A receptor showed a decreased labeling intensity after CCK-8S infusion. The mean optical density of in situ hybridization labeling of the sections from CCK-8S-treated rats was decreased to 37% +/- 3% of that in controls. Devazepide did not affect the CCK-A receptor gene expression.


CONCLUSIONS
Continuous stimulation of the CCK-A receptor led to a downregulation of the receptor gene expression in pancreatic acinar cells and decreased labeling of the receptor at immunohistochemistry. The results suggest that down-regulation of the receptor is a protective mechanism against overstimulation.
Ohlsson
B
B
Dept of Surgery, University of Lund, Sweden,
Borg
K
K
Mulder
H
H
Rehfeld
J F
JF
Axelson
J
J
Sundler
F
F
D000818:Animals; D002417:Cattle; D002766:Cholecystokinin / Q000008:administration & dosage*; D020109:Devazepide / Q000494:pharmacology*; D015536:Down-Regulation; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007262:Infusions, Intravenous; D008297:Male; D023421:Models, Animal; D010179:Pancreas / Q000187:drug effects* / Q000378:metabolism*; D010446:Peptide Fragments / Q000008:administration & dosage*; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin / Q000187:drug effects / Q000378:metabolism*; D012016:Reference Values; D018709:Statistics, Nonparametric
D010446:Peptide Fragments; D043886:Receptor, Cholecystokinin A; D011949:Receptors, Cholecystokinin; C410885:cholecystokinin 8; D002766:Cholecystokinin; D020109:Devazepide