Centrally administered cholecystokinin suppresses feeding through a peripheral-type receptor mechanism

Agonists and antagonists selective for the brain-type [cholecystokinin (CCK)-B] and the peripheral-type (CCK-A) CCK receptor were used to localize the site(s) of action at which CCK inhibits food consumption. BC 264, a highly selective CCK-B receptor agonist, did not decrease consumption of a palatable meal when administered either i.p. or into the lateral ventricles of the brain, whereas CCK decreased feeding when administered i.p. at the same doses. CCK decreased feeding when administered i.v.t. at a high dose, 5 micrograms. L-364,718, an antagonist selective for the CCK-A receptor, blocked completely the action of centrally administered CCK, whereas L-365,260, a selective CCK-B receptor antagonist, had no effect on the ability of centrally administered CCK to inhibit feeding. To estimate the quantity of i.v.t. administered CCK which reached the periphery, a tracer of radiolabeled [3H]p-CCK8 ([3H]CCK octapeptide sulfate), combined with unlabeled pCCK8 (5 micrograms) was administered i.c.t. Thirty minutes after administration, intact radiolabeled pCCK8 was extracted from the plasma and measured in the blood in nanomolar concentrations, exceeding the amounts of CCK octapeptide sulfate reported previously to be present in the plasma after a meal. Intraventricularly administered CCK thus appears to reduce feeding in the rat through a mechanism involving a CCK-A receptor subtype in the periphery.