Amylase secretion by isolated pancreatic acini after chronic cholecystokinin treatment in vivo.

Rats were given subcutaneous injections of synthetic cholecystokinin octapeptide (CCK8, 5 micrograms/kg) in a depot carrier twice daily for 7-14 days. The pancreatic wet weight increased by 20.6 and 30.9% in the rats treated with CCK8 for 7 and 14 days, respectively. The increase in pancreatic weight was associated with an increase in the amount of protein per DNA, indicating hypertrophy of the acinar cells, and with an increase in the total amount of pancreatic DNA. Moreover, CCK administration also increased the amylase content per DNA. In acini prepared from CCK8-treated rats, responsiveness to CCK8 was increased when amylase release was expressed relative to DNA but was decreased when calculated as the percentage of the initial content in the acini. The dose-response curves for CCK8 were similarly shaped in both CCK8-treated and control rats, but they were shifted 3- to 10-fold toward higher concentrations of CCK8 after 7 and 14 days of CCK8 treatment. There were no major changes in the affinity and capacity of CCK receptors determined by studying the binding of radioiodinated CCK, suggesting that alterations in pancreatic amylase release were due to changes at a postreceptor loci. In support of this hypothesis, the secretory response to carbachol, known to act on a different receptor but by a common intracellular mechanism, was altered in a manner identical to the response to CCK8. Thus chronic stimulation with CCK sufficient to induce pancreatic hypertrophy does not greatly alter CCK receptors and induces only moderate postreceptor desensitization.