RECIPROCAL INTERACTION OF 5-HYDROXYTRYPTAMINE AND CHOLECYSTOKININ IN THE CONTROL OF FEEDING PATTERNS IN RATS

1 The effect of the CCK(A) receptor antagonist, devazepide (100 mg kg- 1) on meal parameters during the initial phase of the dark period was studied in free-feeding rats by use of a procedure for continuously mo nitoring feeding patterns. 2 In a second experiment, the effect of dev azepide on the reduction in meal parameters induced by the 5-hydroxytr yptamine (5-HT) releaser and uptake inhibitor, (+)-fenfluramine (1.5 m g kg-1) in 4 h food-deprived rats was examined. 3 The hypophagic effec t of an intraperitoneal injection of cholecystokinin (CCK-8, 4 mug kg- 1) was studied in rats treated with the 5-HT receptor antagonist, mete rgoline (1 and 2 mg kg-1). 4 Devazepide increased the size of the firs t meal in free-feeding, but not in 4 h food-deprived rats and partiall y antagonized the effect of (+)-fenfluramine on the size and duration of the first meal. The reduction in eating rate induced by (+)-fenflur amine was not modified by devazepide. No changes in (+)-fenfluramine o r (+)-norfenfluramine levels were found in the brain of rats treated w ith devazepide. 5 The effect of CCK-8 on meal size was completely anta gonized by 2 mg kg-1 metergoline. A significant interaction was also f ound between 2 mg kg-1 metergoline and CCK-8 as regards their effect o n the inter-meal interval. 6 The results suggest a reciprocal interact ion between 5-HT and CCK-8 in enhancing the satiating effect of food i n rats.