Although cholecystokinin (CCK) has been reported to stimulate pepsinogen secretion, this action has been poorly characterized. To assess the ability of CCK to regulate mammalian pepsinogen secretion, guinea pig fundic mucosa was incubated in Ussing chambers with CCK-8, carbamylcholine, and pentagastrin, and with cholinergic and CCK antagonists. CCK-8 stimulated pepsinogen secretion at 10(-10) M, with an ED50 of 10(-9) M and maximally (26-fold over basal) at 10(-8) M. Carbachol stimulated pepsinogen and acid secretion with an ED50 of 3 x 10(-7) M and maximally at 10(-6) M. Pentagastrin (10(-9) M-10(-6) M) did not affect acid or pepsinogen secretion, whereas gastrin-I (10(-6) M) stimulated acid secretion slightly but did not alter pepsinogen secretion. L364, 718 (10(-5) M), a specific CCK peripheral receptor antagonist, abolished all pepsigogic effects of 3 x 10(-9) M CCK-8 without altering basal acid or pepsinogen secretion or mucosal electric characteristics. L364,718-treated tissues unresponsive to CCK-8 nevertheless secreted pepsinogen and acid in response to 3 x 10(-7) M carbachol identically to control carbachol-treated preparations. Atropine (10(-5) M) blocked the response to 3 x 10(-7) M carbachol without inhibiting 10(-9) M CCK stimulation. These results support a specific receptor-mediated role for cholecystokinin in the physiologic regulation of guinea pig pepsinogen secretion.