Intraperitoneal injections of nanogram CCK-8 doses inhibit feeding in rats

The satiating effect of intraperitoneal injections of synthetic cholecystokinin octapeptide (CCK-8) was tested in non-deprived and 17 h-deprived male and female Sprague-Dawley rats that were maintained on pelleted diet and offered evaporated milk test meals. At the midpoint of the 12-h diurnal period, 40-160 ng/kg CCK-8 elicited a dose-related decrease in meal size. At midnight, CCK-8's threshold for inhibiting feeding was increased to 80-160 ng/kg in nondeprived and deprived rats, respectively. These doses are 25-50 times less than typically required to significantly decrease food intake after intraperitoneal injection. No CCK-8 dose stimulated nocturnal feeding and no consistent sex difference was observed in CCK-8's effect. Intraperitoneal injection of ng amounts of CCK-8 may mimic a paracrine action of endogenous gut cholecystokinin to signal satiety.