Feeding-suppressive mechanism of sulfated cholecystokinin (26–33) in chicks

The anorexigenic effect of cholecystokinin (CCK) is well documented in mammals, but documentation in neonatal chicks is limited. Thus, the present study investigated the mechanism underlying the anorexigenic effect of CCK in neonatal chicks. Intraperitoneal (IP) injection of sulfated CCK(26–33) (CCK8S) significantly decreased food intake in chicks at 60 and 300 nmol/kg. Non-sulfated CCK(26–33) (CCK8) also significantly decreased food intake, but its anorexigenic effect was observed only at the highest dose (300 nmol/kg) and short-lived. However, CCK(30–33) (CCK4) had no effect on food intake. Also, the intracerebroventricular (ICV) injection of CCK8S (0.2 and 1 nmol) significantly decreased food intake in chicks. Similar to IP administration, the anorexigenic effect of CCK8 was weak and CCK4 did not affect food intake. IP and ICV injections of CCK8S caused conditioned aversion and increased plasma corticosterone concentrations, suggesting that their anorexigenic effects might be related to stress and/or malaise. This might be true in ICV-injected CCK8S because co-injection of astressin, a corticotropin-releasing hormone receptor antagonist, tended to attenuate the effect of CCK8S. The present study revealed that N-terminal amino acids and the sulfation of Tyr are important for the anorexigenic effect of CCK8S after IP and ICV administered in chicks. Additionally, the effect of central CCK8S might be related to stress and/or malaise.