Vasoactive intestinal polypeptide (VIP) inhibits potassium-induced release of cholecystokinin (CCK) from rat caudato-putamen but not from cerebral cortex.

CCK release elicited by 40 mM potassium from slices of rat caudato-putamen (cp) was inhibited by VIP. The effect of VIP was maximal at 10(-7) M. VIP does not inhibit CCK release from cerebral cortex at either 10(-7) or 10(-6) M. VIP is known to elevate levels of cAMP in rat brain. VIP inhibition of CCK release appears to be independent of activation of adenylate cyclase because treatment of cp slices with forskolin (2 X 10(-6) to 10(-4) M) does not mimic the inhibitory action of VIP.