Effect of somatostatin on cholecystokinin-induced amylase release in rat pancreatic acini

The effect of somatostatin on cholecystokinin-induced amylase release was investigated in isolated rat pancreatic acini. Acini were isolated by enzymatic digestion and incubated in a HEPES buffered Ringer's solution with testing reagents for 30 minutes at 37°C. The activity of released amylase, cAMP, and inositol phosphate formation were measured. Intracellular calcium concentration ([Ca²⁺]_i) was also checked. Somatostatin 14 and octreotide, a somatostatin analog, inhibited CCK-stimulated amylase release in a concentration-dependent manner. The inhibitory effect of octreotide on CCK-induced amylase release was not shown when the acini were treated with 8-Br-cAMP, irrespective of the presence of IBMX. Forskolin potentiated CCK-induced amylase release and this effect was blocked by octreotide treatment; although CCK-8 (3 × 10^-11 M) failed to stimulate cAMP formation, octreotide significantly inhibited basal cAMP formation in the acini. The increase of [Ca²⁺]_i in response to CCK was inhibited by octreotide. However, CCK-induced inositol phosphate formation was not changed by 10^-9 M octreotide. Octreotide had no effect on CCK-stimulated tyrosine phosphorylation, and tyrosine phosphatase inhibitors (NaF and Na₂WO₄) did not influence the effect of octreotide on CCK-induced amylase release. From these results, we conclude that octreotide inhibits CCK-induced amylase release by inhibiting basal cAMP formation and decreasing the [Ca²⁺]_i stimulated by CCK.